#science #physics #ideas The Biggest Ideas in the Universe | 6. Spacetime

#science #physics #ideas The Biggest Ideas in the Universe | 6. Spacetime 285,689 viewsApr 28, 2020 Sean Carroll 154K subscribers The Biggest Ideas in the Universe is a series of videos where I talk informally about some of the fundamental concepts that help us understand our natural world. Exceedingly casual, not overly polished, and meant for absolutely everybody. This is Idea #6, "Spacetime." Which, naturally, is about the major idea underlying special relativity -- that both space and time are different parts of one unified, four-dimensional spacetime. Learn the real reason why two twins age differently if one stays home and the other zips out near the speed of light. My web page: http://www.preposterousuniverse.com/ My YouTube channel: https://www.youtube.com/c/seancarroll Mindscape podcast: http://www.preposterousuniverse.com/p... The Biggest Ideas playlist: https://www.youtube.com/watch?v=HI09k... Blog posts for the series: http://www.preposterousuniverse.com/b... Background image: https://www.amazon.com/Spacetime-Geom... #science #physics #ideas #universe #learning #cosmology #philosophy #math #spacetime #relativity 526 Comments rongmaw lin Add a comment... Descartesdom77 Descartesdom77 2 years ago Even as someone who is educated on these subjects, I found this lecture very enjoyable and informative. You really have a gift for teaching. 58 PK PK 2 years ago Sean you continue to create marvellously educational and inspirational content, thank you! 16 Sandy McDonald Sandy McDonald 2 years ago Thank you for doing these Professor Carroll, such an interesting series of lectures. I look forward to each and every one! 9 Andrew Stoehr Andrew Stoehr 1 year ago It is ridiculous how perfect this entire series is. Thank you for giving the masses enough credit to teach us spacetime from the top down. 1 Lorio Myoreo Lorio Myoreo 2 years ago I enjoy all of your efforts and I have learned so much from you, quite painlessly too, I might add ! Thank you Professor. 10 william wolfe william wolfe 2 years ago Love these videos -- the format is perfect -- the writing/drawing/grayboard sketches forces Sean to slow down, and pace the presentation -- love it! 4 ankles iii ankles iii 2 years ago (edited) Good god, this is amazing Sean. Thanks for teaching a Texan with a ged about the true structure of spacetime. 32 qclod qclod 2 years ago Thank you so much for these! I just won your new book in a giveaway (thank you Matt Ingebretson!!) and I'm extra excited to have these lectures to keep me thoughtful while waiting for it to arrive. 3 Spenser Jordan Spenser Jordan 2 years ago Thank you Sean for sharing your knowledge of physics with us. reda abakhti reda abakhti 1 year ago thank you so much please continue with this that course was priceless the top down point of view that you exposed was extremely convenient for me because I needed a tidy framework to organize what I knew and understood about relativity and this is just on point 1 Sebastian Clarke Sebastian Clarke 2 years ago Thank you very much for another amazing video Professor Sean! Taking dark energy into account, how long until the light from the furthest visible galaxies reaches us at our "future visibility limit" of 61 billion light years? How old will the light be from those galaxies? pizzacrusher pizzacrusher 2 years ago These are so excellent! Thank you very much for doing this!!!! I wish everyone was as generous with their knowledge & expertise. Thanks again! 2 Gulsher Singh Gulsher Singh 1 year ago Sean Carroll I cannot thank you enough for doing this. Going through the motion of knowing more and understanding less which is exciting. 2 Climbing Snufkin Climbing Snufkin 2 years ago I love the way you explain all these ideas. Thanks for the awesome videos! I have a short question regarding spacetime and time dilation. If I fall into a black hole with my back first, eyes facing outwards to the universe. Would I as I pass the event horizon see the whole future of the universe in a blink of an eye due to time dilation? If not, what would happen? Or if the above don't work. If I had an engine on my back which could stop me extremely close to the event horizon and stay there would I then see the whole future of the universe thanks to time dilation? I need to know for my bucket list :) Ken Lee Ken Lee 2 years ago Sir, you are one of the best lecturers I have seen. Thank you. 4 BreakItDown BreakItDown 2 years ago I love Sean Carroll - he's one of those people who were just born to teach / impart knowledge. 3 Nathan Adolph Nathan Adolph 1 year ago Thank you. This was the best explanation of special mechanics I can recall. I really appreciate your effort. Jukka Pursiainen Jukka Pursiainen 2 years ago Thank you very much! This makes me think about if there is a connection between rates of time elapsing and entropy change and how causality is linked with the elapsing of time. Is there more or less "action" in a place in the universe depending on the "flow rate" of time. As you see I am a layman. mdiem mdiem 2 years ago These and Brian Greene's Equation of the Day have been a great way to review all the physics I haven't seen since university many years ago. Thanks to all the scientists and mathematicians keeping us sharp with these lessons! 13 hdrflow hdrflow 2 years ago Question: how do VSL theories differ in how they address the limit? Awesome series btw :) Scott Arbeit Scott Arbeit 2 years ago Question: are there any theories that include multiple dimensions of time? or; is there a useful reason that we might consider multiple dimensions of time? Thanks for the whole series! 4 Nae _Folk Nae _Folk 2 years ago Thank You. This is just such a gift to us during the covid-19 debacle we're navigating through. 👏✌🤯💓 68 G Wills G Wills 2 years ago Thank you Sean! Honestly, I think your top-down approach is more intuitive. 11 Sed Na Sed Na 2 years ago (edited) Thank you, that was really interesting. I have 2 questions : 1. About light cone : does it mean that everything we can possibly detect is contain within that light cone ? I read that gravitational waves are another way of getting information about the universe, so I wonder if there are some ways to get past this cone . 2. About the big bang : when we say that it happened 13,8 billion years ago, in what sense is it true ? It's an event which concerns our universe as a whole (it's "absolute") , and our local observation of time of this event can't be extended to the entire universe (it's "relative"), so I am a little confused. 1 Sepheryn Sepheryn 2 years ago Thanks for these great videos, Professor Carroll. 1 Tanio Diaz Santos Tanio Diaz Santos 2 years ago (edited) Really great videos. Thanks. It would be nice if in your Q&A could talk about the special case of photons and how they "see" the Universe and (not) experience time (also maybe in the context of their interaction with other particles, e.g. in the photo-electric effect, when they "appear/disappear") Thompson Schwabbel Thompson Schwabbel 1 year ago I went from having a rough idea to a profound insight into such an abstract concept in 1h? That's absolutely amazing. Thanks a lot good sir! Yamil Martinez Yamil Martinez 1 year ago I appreciate the time taken to explain in precise detail its awesome Javi Kroonenburg Javi Kroonenburg 2 years ago This is absolutely great, the way you explain these physical concepts/idea's is just soooo good and understandable! Thanks for doing this! uptown3636 uptown3636 2 years ago I love that this series exists. If only the other people I'm with in lockdown watched it too, I would be able to have conversations with people about topics more interesting than the weather and tiger king. 3 aman neelappa aman neelappa 2 years ago Hi Sean. Thanks for the videos. Is there a reason why spacetime has this special structure where the relationship between space-like and time-like dimensions is regulated by the constant c? Does big bang cosmology, or perhaps string theory, have anything to say about it. Does, or could the expansion of the universe have any impact on this structure? Lelouch Lamperouge Lelouch Lamperouge 11 months ago Watching a legend’s lecture! This is the blessing of science & technology— you can watch the best of the bests from anywhere at anytime. 💟 2 mDecks Music mDecks Music 2 years ago Best lesson I’ve ever had in special relativity! What an amazing job! Thanks for all your work!! 8 Matthias Wolf Matthias Wolf 2 years ago Thanks for this great lesson, but i am still struggling with a question regarding the Twin Paradox: what if space is positively curved and the universe is closed? The one twin starts the journey with the rocketship and is travelling just in a 'straight' line all across the universe. As space is positively curved and closed he would just arrive at where he started his journey. How could it be that only the twin who is travelling is aging more slowly? Arent Both, the twin in the rocketship and the twin staying at earth, in an inertial reference frame? From the persective of each of the twins, the other is in motion and time should tick slower compared to the 'stationary' twin. I am confused 1 Peter Nový Peter Nový 1 year ago Thank you Sean for this. I have question: and it is related to perceived procesies in time - it is change. It can be distance, chemical or mechanical characteristic or death of living thing. This means that space-time is not only elated to distance traveled by light but to changes generally. Which is not included in formula about general relativity.. :) Michael Li Michael Li 1 year ago Great video very educating! I have a question that if space=V*time, then you said light speed is the limit. But what if something travel faster than light? Will this equation cause more space to be created if speed exceed light speed and does that mean something could reach other space dimension if it travel faster than light? Thank you! 1 M-Class Designs M-Class Designs 4 weeks ago I love this series. Even though I don't understand everything and I forget most of it, I keep coming back and listening again. I suspect I will keep doing so for the rest of my life. 🤣🤣🤣 Ane Håkansson Ane Håkansson 2 years ago It's always refreshing to see new approaches to the subject. Very nice and keep on the good job. stat a87c stat a87c 1 year ago (edited) Just found u did this whole series and digging in now. Thanks so much for doing this man. Youre a legend for putting this out there for free. Tommy Heron Tommy Heron 1 year ago You never fail to help me understand. Thanks Sean. Konsam Tambradhwaja Konsam Tambradhwaja 1 year ago For the excellent videos ,I enjoyed the time spent on this videos during Covid-19/ Lockdown .Thank you so much Prof.Sean ! Ezio Wayne Ezio Wayne 1 year ago I love these videos! Love the candid vibe! Thank you so much! bestape bestape 2 years ago Thank you for this! 14:05 to 18:13 and 37:05 to 46:12 are my favorite parts. "A feature of the Universe which is surprising to you, that's not what qualifies as a paradox.... Energy and momentum are tied together. ENERGY IS THE TIME COMPONENT OF MOMENTUM." :o) Cloud Room Beacon Place Cloud Room Beacon Place 2 years ago Thanks, Professor. Well done and interesting. Enjoyed all 6 teflontelefon teflontelefon 1 year ago This is one of the best explanations that I have come across so far. Dean Batha Dean Batha 2 years ago Loving these videos. May our light cones continue to intersect. 3 blueckaym blueckaym 1 year ago Brilliant lecture! I want to ask a question that another SpaceTime, Gravity video popped. If you have space-time diagram expressing the distance from Earth - ie having the "vertical" coordinate (away from Earth) being the Space X (Hey I just realized why Musk called his company so! :)), and the "horizontal" is the Time T coordinate; And if we pick a tall object (like a squirrel, ie anything that has tallness, which is basically anything no matter how tiny) at some distance above the Earth surface, we know that Time slows down closer to the Earth as the Gravity is stronger. So this means that the feet of the squirrel will age slower than its head. Or you can express this by saying there's a Time dilation gradient relative to the Earth below. And if you have picked stationary (in Space) squirrel it's head will "move" faster thru Time than its feet. So far so good - that Time-coordinate stretch of the squirrel isn't a Space stretch so the squirrel is mostly fine. So my question is: Is it possible in ANY way that (as we can't stop Time obviously) this "movement" in Time curves in a way that translates to a movement thru Space too? So is this quote "In a space-time diagram, a rotation is a change in speed... also known as an acceleration." correct? And if so, WHY? Corey Morgan Corey Morgan 2 years ago (edited) Question: Since there is no elapsed time for light, how does it wave? I've been puzzling about this ever since Susskind mentioned it in one of his lectures. My guess is that it is the EM wavefield in space-time that is doing the "waving" and not the particle? I realize that a particle is the field. Still confused though. Thank you in advance. Stoffel Lombard Stoffel Lombard 1 year ago Thanks for a great video. My question is about whether space-time is taken as a physical concept or as a measurement framework. In GR Einstein seems to define space-time as resulting from what one measures with a ruler and a clock; how is it defined in e.g. QFT? In GR it seems that space-time is dependent on the energy-momentum structure in space-time, so it is sort of implicitly solved. Are the fields in space-time the source of space-time? Personally it seems to me more satisfactory to think of space-time as a non-physical framework we use to order our perceptions and measurements, somewhat like a 3d spreadsheet. 1 ph ph 2 years ago Sean is very pleasant and interesting to listen to. Thankful greetings to Sean for having these lectures! 1 Vinay G R Vinay G R 2 years ago Hi Sean, It was very interesting to be revealed that energy is the missing element of the 4-d tuple that also includes momentum along the three spacial dimensions. Can you please explain if there's more to this grouping? Is this one of the implications of mass-energy equivalence when momentum is also taken into account? Cepheid Cepheid 2 years ago I remember during my intro PHYS class my prof mentioned stress-energy tensors during our solids and fluids chapter. Needless to say the entire class breathed a sigh of relief when he said tensors wouldn't be on the exam. Anuran Kar Gupta Anuran Kar Gupta 2 years ago Could you describe in greater detail, what happens to objects and their observed times when they travel at different speeds? Vitaliy Khudenko Vitaliy Khudenko 2 years ago I enjoyed the time spent on this. Thank you! artyom Diogtev artyom Diogtev 2 years ago This is the first part I’m rewinding back over and over at certain moments to get the idea and I love it 😎 Jim's Mind Jim's Mind 2 years ago This really helped me visualise the speed of light being the "speed limit" of the universe as a result of it's geometry. My question would be, is the speed of light always invariant? Are there any situations where it varies, and what would the consequences of that be? Thanks for these videos, I really enjoy them! Nic holas Nic holas 2 years ago Just finished reading “Something Deeply Hidden” and have started “From Eternity to Here”. The videos and podcasts definitely makes it easier to understand Jeff Mott Jeff Mott 2 years ago Thanks Sean, as a non-physicist I had never understood why the speed of light appears in so many equations - it just seemed weird that light was somehow so important in the fabric of the universe. Now that I understand that it is just a conversion factor and that it would be true even if light didn't exist it now makes so much more sense! Greg Ewing Greg Ewing 7 months ago It's kind of confusing that when we measure less time we call it "dilation", but when we measure less space we call it "contraction". Go Away Go Away 2 years ago I always wonder what it'd be like to be a photon. If length contracts as you approach c, and photons travel at c, then how big would a photon think itself to be from its own frame of reference? Infinitely large? Is that the flip side of considering how a photon experiences zero time for its entire existence? If I were a photon, would I ever even feel like I existed at all? 1 The RF Noob The RF Noob 1 year ago Thanks Prof. Carroll, this lecture was amazing. I am very grateful. While watching, I think I grasped why the doppler effect in radios occur (in ham radio, it happens when you communication with satellites in low orbits). And indeed in the wiki page https://en.wikipedia.org/wiki/Doppler_effect it says it's related to relativity! WOW! Before it was just a mysterious thing, now it (kinda) makes sense thinking in terms of the CONES in space time, and radio waves moving at the edge of the cone. I will have to think more about it. But if you happen to do a generic Q&A, perhaps you can mention/explain it? THANKS!!!!!! 1 HappoApina HappoApina 1 year ago The little sound effect the rocket made when the flames came out was quite adorable :P Thanks for this series Sean! B Tr B Tr 1 year ago Sean makes me feel like a cal tech grad rather than a failure in high school physics. Rama Bommaraju Rama Bommaraju 1 month ago great teacher you are! I am going to listen to this a few times more to comprehend as you want us to unòrsominòre. unòrsominòre. 2 years ago Thanks for these fantastic videos Sean! Big up. Btw: Minkowski was lituanian, not german ;) Doug G Doug G 1 year ago We really appreciate you taking time to do this. hbofbyu1 hbofbyu1 1 year ago If time slows down (from our perspective) of an object closer to a gravitational field, then why are we able to see 2 black holes collide? Wouldn't we see them getting closer so slowly but never colliding? Or if they did it would happen in slow motion? olrik666 mortimer olrik666 mortimer 1 year ago That was excellent, as were all the others talks I saw. Thank you. Rahul Singh Rahul Singh 9 months ago Sir please start a series on general relativity.. I read your book on general relativity .. I really appreciate it . How cool it'll be if you explain the stuffs ☺️☺️☺️☺️ Todd Desiato Todd Desiato 2 years ago Awesome presentation Prof. Carroll. I'm very impressed with these casual videos you are doing. Question: Your last written statement, "General Relativity: Spacetime is dynamical, responding to matter / energy. => Gravity". Since we cannot measure space, time or space-time without physical tools made of matter / energy. Wouldn't it be equally true to say, "Matter is dynamical, responding to other matter /energy nearby => Gravity". The point being, we can't observe empty space-time, we can only observe its effects on the observable matter / energy it contains. John Till John Till 1 year ago Well done! I’m interested in the app and equipment you use to present your content. Gautam C Gautam C 1 year ago Besides the normal course explanations...these discussions are very helpful in clearing many points which are confusing at a glance during the formal courses....Thanks a lot Prof. Carroll Gilbert ENGLER Gilbert ENGLER 2 years ago (edited) Thanks prof Carrol, Finally I better understand some aspects of special relativity which was for me still rather vage and a bit confusing. Many thanks! Allow me to ask a question a bit out of context. If gravity is a pure consequence of the nature and curvation of spacetime and not, as often said “a real force”, why do physicists want to unify gravity with the 3 other forces? Is it correct that gravity just seems to act like a force since the path of an object in a gravitational field undergoes a linear acceleration as a consequence of the shape of spacetime? Thanks a lot. 2 Steve Seamans Steve Seamans 1 year ago Love all your explanations. I’m a big fan. I think it’s interesting Light cones look like hourglasses. Very fitting somehow. Leonard Belfroy Hertog van Cydonia ♔ Leonard Belfroy Hertog van Cydonia ♔ 2 years ago Speed of light is not constant; it depends on gravitional field density. 1 Mrhollowdadon Mrhollowdadon 1 year ago Sean you’re a gift to humanity. You have an incredible gift of taking big ideas (pun intended) and making them comprehensible to laypersons like myself. Thank you. Barefoot Barefoot 2 years ago (edited) Good episode. I like the top-down approach. I actually wonder what would happen if we were to experimentally take a group of children and explicitly raise and school them from birth using this top-down approach, truly freeing them from Newtonian ideas so they get a genuine intuition about Relativity and no longer need to draw the x and t axes to make sense of the world. Children are remarkably adaptable and their neuroplasticity can accomplish absolutely astonishing things (like bootstrapping a language, which also serves as the brain's operating system in a sense, with no reference point from which to begin). I've often been bothered by a certain tendency in science education, especially advanced topics like GR and QM: the instructors seem to have an attitude of, "I experienced this from a place of classical intuition and it was very confusing, mystifying, and jaw-dropping, and I want you to have that same experience." So I often wonder what would happen if the entire educational framework was reversed and instead of "I want you to learn like I did because it's fun and nostalgic to watch your face screw up in confusion like mine did," we genuinely did our very best to teach the way the world really is in the most approachable, intuitive way with a top-down approach like this (only even more extreme). I'm not saying instructors who enjoy that nostalgia are bad people or anything; I've done the exact same thing many times myself! "Ooh, look at this crazy thing, like the delayed choice quantum eraser, doesn't it just totally blow your mind?" And I grin as I watch their minds explode like mine did when I first learned about it. Yet I'm also perfectly aware of a paradigm in which that experiment makes perfect sense, which puts across a feeling more like, "Oh, well of course that's what happens. Why would it be any other way?" But that one isn't as fun to teach. Not until I've watched someone's brain melt first; then I get to hand them the better paradigm and "rescue" them from their confusion, which is also great fun. Only sometimes it doesn't work, and their confusion just makes them unable to understand, and they walk away from trying. Ted Bates Ted Bates 1 year ago (edited) The defining of terms like spacetime help me to order these things in my mind. I still have a ways to go but I think I can grasp it better given the terminology. Thank you. It's been 4 1/2 decades since I studied physics and calculus. And for me it's not easy stuff. Now let's figure out the GUT. frodo0111 frodo0111 2 years ago OMG. Thank you so much. FRAMING! I was asking questions about time and space (and concerned about my framing) and you pointed out that when asking questions about Einsteinian physics we can be confused by thinking in a Newtonian framework. (Note to self - try not to do that in future.) Thanks :P Wolfgang Himmelsbach Wolfgang Himmelsbach 2 years ago (edited) Excellent video, I liked your „top down“ approach very much! Thank you! 2 bob smith bob smith 1 year ago (edited) Professor Carrol. Thank you so much for explaing things in a clear manner. I have a question that is naive.. If the energy of × is quantum, is the speed of lights energy up to 10 out of 10 on the quantum scale? As in light has reached the maximum charge? I wonder because how can red and blue light shift occur? No doubt you have covered this subject many times. (Got a link?) I am very interested in your top down approach to teaching. At school learning was difficult as it seemed to have no practical applications.. Maths was extremely tedious, and I think its the teacher not the student that trail blazes your enthusiasm. As a fan boy I have bought your book Something Deeply Hidden and was hooked.🤓 A Kumar A Kumar 2 years ago This is the one I have been waiting for, space time, a dazzling feat of the human mind, I hope I understand it better, its a difficult topic for a layperson. 31 Shoopaah Shoopaah 2 years ago Very very good quantitative discussion of big ideas in physics. Very impressed. Well it is Sean Carroll... Alex Agotsch Alex Agotsch 2 years ago This is such a cool series. Thank you for the excellent brain massage. Shibly Ahmed Shibly Ahmed 2 years ago I think Physicists would have been in a far better position if they had given a completely different name to SpaceTime. 5 Steve DeHaven Steve DeHaven 1 year ago (edited) I watched this a second time because I thought I had missed something, but I didn't find it. Finishing around the 24:04 point, you offered Tau^2 = t^2 MINUS x^2 as your answer to why the "twin paradox" happens, and I follow that math, but what I don't see is Minkowski's justification for changing Pythagoras' PLUS to a MINUS. What did I miss? Saleem Raza Saleem Raza 1 year ago I put a question in comments on the previous video about time and got the answer for it in this video ! Isn't Sean amazing in how he anticipates "possible questions" Slartibartfast Slartibartfast 2 years ago (edited) This is so well explained that I am actually slightly ahead of your explanation in places. The way in which you explain things allows me to actually understand some of this for once. I think this is a fantastically well explained video. I just wonder about the limit on the speed of light -> given that as you reach the speed of light times slows down. Could it be said that you cannot travel faster than the speed of light because quite simply there is not longer any time available in which to accelerate given that in effect time has stopped at that point? E Wolfe E Wolfe 1 year ago I think it is possible to invert some of the logic of special relativity by moving "c" from a velocity through space into "c" as a volume of space. Several of Einstein's thought experiments have always bothered me in that they don't reduce to all possible frames of reference; i.e. that experiment with the lightbulb in the center of a moving room (elevator) where an observer inside the room sees light as striking the floor and ceiling simultaneously and an observer outside the room (detecting the motion of the room) sees light as hitting the floor and ceiling sequentially. Special relativity does a brilliant job at creating a logic between the two observers such that simultaneous and sequential can be equalized between the two observers. But what about from the frame of reference of the photon? Does the photon observe itself striking the floor and ceiling sequentially or simultaneously? It has to be one or the other, right? Unless a set of photons exists in two frames of reference, it cannot observe BOTH sequential and simultaneous impact of floor and ceiling. This is my problem with SR; it creates a relativity between observers; not necessarily a relativity between observer and photon. There is a way to make simultaneous and sequential the same; there is a single frame of reference in which photons can do both. It involves playing around with the size of space as a frame of reference. Modern physics assumes that spatial frames of reference are identical in volume, but if they aren't, we can say that a photon exists in zero space and that our observation of a photon travelling through space comes from our spatial frame of reference (which would be c, a volume measured and observed as a velocity from our frame of reference). The light clicks on, a photon travels zero distance through zero spatial volume and strikes the floor and ceiling simultaneously. The observer inside the moving room has a different spatial frame of reference and observes simultaneous impact after the photons travel at c velocity across the distance that he observes between the lightbulb and floor/ceiling. The observer outside the room, having his own unique frame of reference given that he observes the floor moving towards the photons and the ceiling moving away, measures sequential impact of floor and ceiling. This connects the frames of reference between observer, observer AND photon. It allows for sequential, simultaneous, and both at the same time; which appears to be what the logic of SR states must be happening. Jerry Hampton Jerry Hampton 1 year ago Great lecture Sean. However, at 39:46 there appears to be an error. Shouldn't the horizontal line you've drawn actually be vertical? Jaeghead Jaeghead 2 years ago (edited) There is also another way to see that it isn't about the acceleration: The Fermilab channel on youtube did a video about this topic some (space-)time ago where they introduced a second spaceship flying towards the observer on earth. The two spaceships exchange their times while passing each other (without stopping) and the second spaceship arrives on earth with a shorter time than the observer on earth measured, even though none of the three observers ever accelerated. 12 EarlWallaceNYC EarlWallaceNYC 1 year ago Once again..Great insights into topics I thought I know well. But as Prof. Carroll said about himself..: "I am the authority figure, trust me". :-) Amit Khambekar Amit Khambekar 2 years ago Please can you tell more about impact of our movement through space due to movement of the Earth, the Sun and the Milky way, and expansion of space itself.....if all these were not moving, would we have experience different time altogether? Stewart Hayne Stewart Hayne 1 year ago (edited) QUESTION: in an earlier episode you described moving from the very low entropy Big Bang to a higher entropy state now. Can you explain this? It seems to me that the primordial stew of particles immediate post Big Bang is high entropy, higher than organized stars and planets. Like evenly distributed gas in a box versus the gas being clumped together in parts of the box. Help! PaxAnimi PaxAnimi 2 years ago Imagine Sean Carrol and Jim Al Khalili together in a scientific online school. The laymen applaud! 12 Stu Bonham Stu Bonham 2 years ago Please write a book based on this series. I would love it to have a little more maths than the videos though (but don't go all Road to Reality on us ;-) ). Highly enjoyable series thanks for making these Carol Haynes Carol Haynes 1 year ago (edited) I studied relativity a very long time ago at university (and revisiting now like an old half remembered friend). Have to say I am really enjoying this series of videos (thank you) but I think the spacetime diagram in lightyears-years units/cones was really helpful in understanding why perceived time is different to the from frame time. For future reference I think that would be good place to start teaching the difference between Euclidean space and space time. The earlier part of the video had me very confused because it was really hard to see t and tau are different because in frame assuming m and s units they really aren't very different. It is a really difficult concept to grasp without understanding the speed limit and light cones first. Assalmi Hassan Assalmi Hassan 2 years ago Dear Prof Carroll, please can the quantum vacuum fluctuation exist inside black holes (at singularity) ?? Thank you sir :) 1 Harpoika Harpoika 2 years ago Hey Mr Carroll. Multiverse is true because particle small enough to be in a quantum state is an universe in it self. When you use calculus in Feynman diagrams, you connect relativity and quantum mechanics. 1 TaliwhakerRotmg TaliwhakerRotmg 1 year ago Energy is the time equivalent of momentum... Absolutely mind blowing if true! Ryan Kelly Ryan Kelly 2 years ago Hey Sean, cool vids. So if light moves at a constant speed, and presumably the polarization angle of circularly polarized photons with +\hbar angular momentum rotates at a constant speed, could you measure the distance of a path by counting the number of times the polarization angle of a photon moving along this path rotates? Lyleman Lyleman 2 years ago Total layman here but the choice of the speed of light being used to satisfy things like x=t seems to be an arbitrary convenience. It seems like a good choice because it is real and invariant but I am still left unsatisfied with the idea that we can simply introduce it to allow equations mixing units to be allowed. Love the videos! Steen Eugen Poulsen Steen Eugen Poulsen 2 years ago "You have a twin, two twins that's what makes them twins." - Sean Carrol 28 April 2020. 74 Vlad Mihai Vlad Mihai 2 years ago Sean Carroll, ladies and gentlemen! A legend! #physics #theoryofrelativity #Einstein What is Relativity? | Sean Carroll on Einstein's View of Time and Space Wondrium 428K subscribers According to Einstein's special theory of relativity, there is no such thing as a moment in time spread throughout the universe. Instead, time is one of four dimensions in spacetime. Learn how this "relative" view of time is usefully diagramed with light cones, representing the past and future. From the series: Mysteries of Modern Physics: Time https://www.wondrium.com/youtube/myst... 0:00 Understanding Cosmology, Gravity, and Relativity 1:00 Taking a Four-Dimensional Viewpoint of Relativity 2:15 Moving Into a Space-Time View of Reality 3:40 Differences Between a Newtonian and Einsteinian View of the Universe 4:45 The Notion of Simultaneity 5:55 Einstein’s Clocks, Poincaré’s Maps by Peter Galison 6:05 Recurrence Theorem 8:00 Einstein's Clock Patents 8:45 Constructing the Present Moment 10:40 Why Space-Time Is Relative 14:00 What is a Muon? 15:00 Carl Anderson Discovers Muons 15:50 Why Do the Muons Reach Us Before Decaying? 18:30 Einstein's Notion of Time as Personal 20:30 What Are Light Cones? 24:20 Time Dilation and Length Contraction 27:00 How Einstein Conceptualizes Space-Time 28:00 Newtonian Rule for Time Travel 28:45 Implications of Relativity ------------------------------------------- The Great Courses is the global leader in lifelong learning and our video-on-demand service The Great Courses Plus gives you unlimited, uninterrupted access to a world of learning anytime and anywhere you want it. 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Chukwu Igwe Chukwu Igwe 1 year ago I like how Sean Carroll explains these complex ideas in a way that is well within reach of the minds of non-physicists. Well done sir. 46 dennis galvin dennis galvin 1 month ago (edited) "There's no such thing as one moment spread through out the universe that everyone can agree on" [Sean Carrol] Interestingly the word moment despite being defined as "..a brief period of time" is in fact a brief period of an event because moment comes from momentum which is tantamount to events. Meaning that periods \ duration are of events not time. So events have duration that are measured by time as space has distance that's measured by the metric system or imperial units. What we perceive as the passing of time is just the passing of events. 3 Nicholas Garcia Nicholas Garcia 9 months ago I always thought Sean Carroll was one of the best science communicators. Great to see him in his element like this 17 J man J J man J 2 months ago Great job explaining complicated material! I find it interesting that our modern model of (space-) time, with its forward and backward looking light cones, looks so similar to one of our oldest timekeeping devices, an hourglass 1 Ahmed Rafea Ahmed Rafea 9 months ago It is always a joy to watch and listen to professor Carroll. Complicated concepts are clearly explained and visualized. Thanks for this very informative lecture. 5 Binu Varghese Binu Varghese 11 months ago Really very helpful to understand time... his explanation is very precise and even a layman can also understand the concept and importance of relativity and time 2 Sujit Kumar Dash Sujit Kumar Dash 1 year ago That was really a great lecture to watch. I got my own CONE out of intuition. LOL. Joke aside, To grasp such an idea of spacetime isn't easy as you might think ,but Mr. Carroll nailed it. Thank you sir. 3 gotatochigs314 gotatochigs314 1 year ago It's interesting to think from the muon's perspective, where the earth is moving towards it at close to the speed of light. The earth still reaches it before it decays though, since the earth experienced less than 2 microseconds of time along the way. 3 Alexander Koryagin Alexander Koryagin 1 year ago Excellent lecture, thank you! 4 Wondrium Eric Pham Eric Pham 1 year ago (edited) In multi body problems each axis has it's own time function depending on its acceleration therefore spacetime are bending and changing in multi body problem is mind boggling. Meaning our time is not known by another outside of our body and so are the other bodies. Just like the same harddrive memory could be used by many clients on same physical drive but the time of CPU and access time are different could get different data because of accessing method just like existence is different 2 Live īnfra Live īnfra 1 year ago (edited) Absolutely wonderful lecture , thankyou great courses plus for bringing these insightful sessions available to everyone 🙏 . 13 Wondrium karlwashere123 karlwashere123 1 year ago Sean always crushes a good lecture 1 Dan Breeden Dan Breeden 1 year ago I'm very thankful for his teaching he presents his information very clearly 2 Wondrium Nah Bohdi Nah Bohdi 1 year ago He's one of the few people I disagree with in fundamental physics but still listen to for general discussion. 11 Dmitry N Dmitry N 1 year ago Thanks for the great explanation! And for the undeniable proof that the past exists - the tie :) 5 Wondrium Luca Luca 1 year ago prof. Carroll is phenomenal 3 Wondrium harold floyd harold floyd 9 months ago (edited) Did Newton really have all that hair? I am skeptical. Love the “running back” analogy…the profound insight of relativity for me (that took me years to comprehend) is that C is the only constant, it’s space and time that are mutable, light speed never varies ever. 1 Randall Grubbs Randall Grubbs 3 days ago Time is: A measure of change in the entire existing universe, caused by the motion of matter/energy/fabric of space expansion in relation to itself. Because time is an emerging property of change/motion, time is relative to speed. If ALL change in the existing universe were to stop completely, there would be NO time. And in order to go back in time, you would have to REVERSE ALL CHANGE/MOTION in the existing universe to a previous position, which is impossible because it would require all (mass/energy in the existing universe) +1. Which, by definition, rules out traveling back in time. The Alpha Nigga The Alpha Nigga 6 months ago It must be nice being Einstein, he's given credit for things that he didn't come up with i.e Light cone idea, the spacetime-diagram as a whole, those are Minkowski's ideas. PoolBeast TV PoolBeast TV 1 year ago Amazing lecture This man has a wonderful voice 13 Wondrium Zack 120 Zack 120 11 months ago 12:37 - they came back with 'different reading' of time is because they were affected by different forces by each going through different path/speed/trajectory, while the TIME remains the same everywhere which is an abstract thing that nothing can change it, i.e. it is absolute. So the Newtonian theory seems to make sense. 1 Gotta Grab Gotta Grab 3 months ago I never knew there was a thing called "time".. so HUGE TY for telling me about it!! Shoaib Nature Shoaib Nature 1 year ago Thanks. I appreciate the time and effort to put all these information. 14 Wondrium AL AL 1 year ago Maybe gravity exist only because we do. That'd make gravity very difficult to understand. The biggest problem with the theories about gravity is how far across space gravity, weak as it is, reaches out. It seems it's more likely that something, like warped spacetime, is what reaches out so far from objects, and when another object comes in contact with this their path is altered towards said object. WindUp Doll WindUp Doll 9 months ago "Like sands through the hour glass, so are the days of are lives" What are the chances that Newton and Einstein were both wrong? Its a simple probabilty equation with just a few theoretical factors. Bur the chances are as close to 100 percent as you can get. Marek Samsel Marek Samsel 5 months ago So many of these kind of. Vids yet this one, actually explains things in the most wonderful way, I'm impressed and grateful SunRoad SunRoad 11 months ago "Time taken in stocking energy to build an energy system, adding to it the time taken building the system will always be longer than the entire useful lifetime of the system." No system will ever outlast the Energy system that brought it to existence, regardless of its speed. Therefore, Time is universal. (A proposal, 2017). NEW - KNOWLEDGE NEW - KNOWLEDGE 1 year ago How did he do it ? He looks so much younger. We, the people, believe he knows of, and has practised, time travel. Either that, or this one really old video. 24 Roberto Escobar Roberto Escobar 3 months ago Simply wonderful. 2 Ryusei Iijima Ryusei Iijima 10 months ago this video or channel this is my first watch,this is a fantastic and brilliant video thankyou for great lecture sire Wondrium Mathew Anderson Mathew Anderson 1 year ago (edited) The 'clocks on spaceships' reference as a test idea, but then it was sad that relativity shows us that you can't measure time throughout the universe as one single moment that everyone agrees on. Key words here are "everyone agrees on" I feel. We should also hold to the importance of the idea that we can still identify a single 'moment in time', at least in principle. Say you freeze all of spacetime and look at it as a whole from a god's eye point of view. That's your single moment in time. Sure, the clocks of those spaceships and their viewpoints with each other will be different from their starting location, but that's just their rate of cause and effect (their time) changing. You can still justifiably state that picture as "a single moment in time", which if everyone could also look back and view, could all then agree upon that picture as well. Please correct me if I'm somehow wrong on this idea. 2 Joseph Collins Joseph Collins 7 months ago I wish I had words to express how much I want to understand all of this. Why can't it be explained? You are the very best I have seen. I like the way you present (OMG, can I say that now?) and pace what you say. I am rather intelligent in everything else! WTF? Help!!! Neti - Neti ( नेति नेति ) Neti - Neti ( नेति नेति ) 8 months ago So, the speed of light measured by a person seating in front of a measuring machine that seats in Transilvania, Europe, Earth, that travels through a Galaxy in Universe that has its place in the infinite is not relative? Venkat Babu Venkat Babu 1 year ago (edited) Relativity is the time differential of light to create mass. Everything moves at the speed of light except when slowed down. Colby Nye Colby Nye 1 year ago Fantastic lecture! 3 Wondrium yadan huub yadan huub 1 year ago (edited) I tried my best to compress the words and sentences ,and ignore things in between the thoughts and let the intelligence of the reader fill these gaps so we don't need to mention things twice. We need to distinguish between matter/energy level (where humans live ) and subatomic level where everything happening .The classic physics in matter/energy level cannot be applied on subatomic level, our observation is a reflection to what is happening on subatomic level including time ,for example, what we experience it as heat is actually atoms vibrating on subatomic level, and what we see it shinning is actually photons created and ejected from an object undergoing transformation on subatomic level. The whole universe works on subatomic level, The universe does not see sun ,earth , planets , trees and buildings. It sees concentration of particles that form these objects, and with particles it deals, any term in physics associated with matter/energy is meaningless or does not exist on quantum level including (mass,force,time,energy,...etc) so in this case any physical laws that include these terms does not apply on quantum level. We need to find the aspects that play role and the physical laws that govern them on inertia scale ,and they are thousands if not millions, the mathematical equations are few kilometers long,you call uber to correct something at the other side of it. We can understand quantum physic better if we use the term (behavior of particles of the universe) , there are nothing such as particles, there are only particles of the universe and the universe forces particles to behave on a certain way in certain conditions and one of these behaviors is gravity, gravity is behavior of particles, dark matter is behavior of particles , Why Oxygen is a gas and iron is solid metal is behavior of particles , Why photons penetrate glass and reflected on other media is behaviors of particles ,any chemical process or reaction is behavior of particles. Why some elements mix with each other and some not is behaviours of particles, Movement in space is behavior of particles, the electrical charge (- and +) are behavior of particles (so they are not properties of particles),double slit experiment is behavior of particles, the Gyroscope is behavior of particles, the speed of light is behavior of particles, and ALL fundamental forces humans know are actually behavior of particles ,particles change their behavior accordingly with the circumstances surrounding them The existence of black holes is still to be investigated ,but for the moment let's assume there is black hole in the center of each galaxy, the galactical behavior is totally different than the behavior of mass on smaller scale like planets orbiting stars and solar systems which controlled by what we know as gravity ,on galactical scale it is totally different (no matter if they are close or far from the center of the galaxy) , where the stars far from the center of the galaxy orbit faster than the stars close to the center of the galaxy ,The only explanation for this is that the behavior of particles is a function of distance (or space) let's take 2 magnets north and south and put them close to each other ,their particles will change behavior and pull each other and if we move them away from each other their particles behavior start to change, and the attraction force starts to weaken so space in fact change the behaviors of particles, the same applies for matter that circle the galaxy ,the space is much greater of matter in galaxies than space between the mass on solar systems ,that is why particles on galactical level behave differently. This was explained by scientists by the effect of dark matter So for all what mentioned above the origin of the universe was not the big bang but when particles started to get their properties and behaviors and atoms started to bond together and take shape to form matter and its companion energy ,the universe was different to what we see now ,The properties and behaviours of particle are ever changing ,and continue to do so for ever. Entropy is a good example for this. The issue with big bang theory is that it turned many aspects of the universe to constants, and we know very well that nothing in the universe is constant everything is changing all the time (including properties and behaviors of particles ) and everything is moving in space, and nothing is stand still. We have expansion of the universe and we have a big bang ,we just need to fill the gap between them and we have a theory of creation. The behaviors of particles in your body is reacting to ,the particles surrounding them ,the particles of the planet you are on, the particles of the solar system your planet in, the particles of galaxy your solar system part of, and particles of all galaxies in the universe, particles have multy behaviors at the same time. So if we remove all galaxies in the universe ,and only remain you and the most distance galaxy then the particles of your body will behave according with this galaxy. The change in properties and behaviors of particles over de course of time was not equal or at the same rate everywhere in the universe, some regions didn't develop matter yet or developed to different properties We can say that vacuum is existence, or part of existence ,and what applies on everything exists in the universe applies also on vacuum, but humans observe vacuum from their perspective in matter/energy level , if we want to know and identify vacuum from perspective of quantum level then it will be something totally different ,if we say vacuum is absence of particles (and I mean everything we call particle, even fundamental particles) then still vacuum is influenced by the same aspects of the universe that influent all particles and give particles their properties and behaviors, so vacuum in a way or another does carry the properties and behavior by the influence of the aspects of the universe and because vacuum fill the gap between particles (at least what we know till now) then vacuum play major role in "communication" between the aspects of the universe and particle. was the early universe only vacuum ,then particles started to emerge? Humans are limited to their senses and brain ability and accuracy of their equipment's so there are lot of aspects in the universe human cannot interact with for example multi dimensions so it will take some time to know what vacuum consist of and its behaviors and properties So any thing happening around us could be and must be explained on behavior of particles on subatomic level,the big masses matter on any size are eventually composite of particles..and the behaviour of their particles gives the big masses their behaviors and actions in space It is certain that all particles have no mass,mass only starts to build when atoms start to bond and make matter ,so anything more that 2 atoms have mass..mass is something associated with matter/energy level ,it is nonsens that some think that the mass of big bodies is the summation of the masses of its particles , Where are the boundaries?,when we are going to apply the quantum physics rules and when we are going to apply classical physics,explanning this is very long task ,but there is one principle here is that the formation of atoms from Hydrogen till atoms of heavy element all subject to quantum level and mainly ruled by behaviours of particles any thing comes after is subject for matter/energy level still we need to take into account that the bonds between atoms of the same elment,or the bonds between atoms of different elements are directly concidered as behaviours of particles,if we understand this it will lead us to know how all elements and anything matter or energy formed and have its own charastaristices and properties and their transformation froma stat to another and from sort element to another by fusion ,decay ,radiation or what ever process . Are life and biological realm a product or a consequence of behaviour of particles on subatomic level ,the answer is yes,The ingredients in humans body or any living body even small tiny single cell creatures are all made from the same elements that every thing in the universe is made off,the difference is that they have life,or what we call it life. So what kind and what percentage of each element available on a planet that have the right environment to support life would create what kind of biological world..? So it was not a spark. We see this very clear on differences between plants ,animals,humans and the biological world as a whole on each continent on earth it self,and it is an example how behaviours of particles follow a certain path when it goes higher in complexity level.So it was not spark. Neil Libertine Neil Libertine 8 months ago Suppose a coach moving with relative speed to ground and there is lights at both ends. Time is synchronised for both observers in coach and at ground at the instance of light flashes from both ends of coach, also both observers are equidistant from both ends of coach at the instance of events. Now according to theory of relativity whose that version which is accepted by academician, observer in coach measures time taken by light on instance of flash from both ends is equal and there is no time difference for two events separated by distance, so events are simultaneous in coach. For observer on ground, according to above discussed theory speed of light is invariant to motion of coach and travels with same speed from both ends for instance of light flash at both ends of coach to observer on ground. Thus time taken by light from both ends is also equal for ground observer and both events are simultaneous. So two events are simultaneous as observed by two observers in relative motion according to theory of relativity as per accepted interpretation of theory. So in above mentioned example treated with special relativity, now discuss in terms of classical relativity. To those who didn't know about classical relativity, it was replaced by theory of relativity. Other than difference in scale conversion for relative measurement from theory of relativity, major difference is it had no special provison for speed of light as it possess no special quality for laws of mechanics when speaking about motion. For observer in coach sees time taken by light from both ends of coach is same because there is no relative speed for source and observer in coach. Therefore events are simultaneous for observer in coach. For observer on ground there is relative speed of source to observer, so speed of light must be relative. Suppose speed of light at rest is c and coach is moving with speed v to rest then from classical relativity, speed of light from moving source to rest is, c + v sin□, where □ is angle between perpendicular to motion of frame v and c, and angle measured positive if in direction of v otherwise negative. So speed of light from rear end is, c + v sin□, and speed of light from front end is, c - v sin□. As speed of light from rear end is more than speed of light in absolute frame, c, similarly speed of light from front end is less than c. Therefore time taken by light from rear end is less and hence event of light from rear end happened before from light flash at front end. So two events are not simultaneous for ground observer. Therefore two events simultaneous in inertial frame is non-simultaneous in relative motion according to classical relativity. Mitch Raemsch Mitch Raemsch 3 months ago Move and it looks like other things do.. but Einstein left out it is always an opposite appearance. Begin to move and you see other thing appear to... but backwards. Look at the sky turning opposite the Earth. There is real motion that creates an opposite appearance. In history this was seen as retrograde motion. Neil Libertine Neil Libertine 6 months ago So how would length of an object is measure. By placing it against standard scale, its one end is marked on scale then other end. The difference in value of two ends is length. One thing is assumed here that an object is at rest with scale which is also called as coordinate or frame. Now if an object have some speed against the scale or frame then does its length could be measured accurately. No, because it's not possible to mark both ends at same time and if object and scale have relative speed then one of end either contract or expand the measured length of object. This is relative measurement and when object is at rest with scale is proper or absolute measurement. Now relativists says that both measurement are correct and more than that if either object or scale is moving then relative measurement is giving actual description of object's physical quantity. So whether length contract or expand that relative measurement define physical state of object as by relativists. Further than that, in most conditions there is no frame moving with light speed and some events happening in it. Observation of planet is not relative because observer with scale like clock and angular scale is on earth. In case of far objects it's not possible to directly measure object so light is used. But relativists says that speed of light is constant whether source or observer have relative speed or not. First thing, general science laws doesnt allow it, second it require that light should have special quality which it has not so. In classical relativity that replaced by theory of relativity which we know now, has no problem with measurement of distant objects because its absolute and relative measurements are same so no problem. All problems start with insistence of relativists that speed of light is constant so they change fundamental quantities like length, time, mass. Suppose some children are playing in ground which is stationary. Now if an observer moving with quarter of light speed measure length of ground as per theory of relativity, found that length of ground is small as compared to what is told. Another observer with half light speed measure length of ground and found that length is contracted and also differ from first observer, then who is right, observer at rest with ground or moving observers. Does measurement of moving observers that differ from rest one, in any way affect or give actual representation, no. Same thing is with time, moving observers says children are slow. Does clock of moving observer change the movement of children on ground, no. Question is why they are doing so inspite of evidences against their theories. Reason is that constancy of speed of light is required for their model of universe, if that is changed then their model collapse. Kyles monster madness Kyles monster madness 3 months ago Man it’s amazing listening to you guys Wondrium Neil Libertine Neil Libertine 6 months ago What more observational anomaly than theory in relativistic gravitational theory is that inspite of big bang, orbits of planets are stable, atleast for many thousand years, also no detection of angular separation of stars. So meaning of stable orbits is that diagonal elements of mass-energy tensor are zero, because there is no expansion of orbits in radial direction. So i think there would no independent or orthogonal space-time coordinates, Theory could improve if they consider space and time coordinates differently. Time is part of space-time but not interfere length of coordinates of space. Thus space have 3 dimensions constituting volume and time is indicator of motion like orbit is clockwise or not and thus time in forward or backward direction. So space become a dimension and time another dimension of 2 dimensional space-time having volume. Other problem is that differential geometry or topology is construct based on idea or model which have flaws like length of curve is given in term of speed, so more curvature has less speed, but this is not as observed because distant orbits have same speed as nearer one, that is why different time period. It should be as, space is elongated and time is dilated so speed remain same, which is observable as distant orbits have bigger orbit and longer period. Relativistic gravitation was developed because in newtonian model not account for how everything starts from origin. It only account for stable orbit where orbital motion account for entropy or force in action. So what was before newtonian model could explain by relativistic gravity where diagonal energy have some value and cease at stability, it is transitory model. Karlos Jeffers Karlos Jeffers 1 year ago Can I go back in time and learn this fascinating science in school....when I should’ve been learning it? 9 Luke .Haidautu Luke .Haidautu 1 year ago (edited) I understand Sean's words, grammatically, but it's hard for me to understand the concepts that he's talking about. 4 Matteo Ricchetti Matteo Ricchetti 13 days ago Inside an atomic clock an oscillator emits about 4GHz photon that reaches a Cesium atom, which absorbs and emits about 4G photon times per second. If I place a second atomic clock near a mass the Cesium atom emits 4G - a small value of photons per second. The mass influences what? The frequency of the photon of the oscillator? The oscillation frequency of Cesium? How ? By lengthening the space between the oscillator and the atom? Neil Libertine Neil Libertine 6 months ago Q. What is gravity. A. Gravity is phenomenon of objects falling down to ground with force and it seems that intensity of force or energy decreases with square of distance. This is observed on earth only that objects are pulled down but by inference we generalized it to whole planetary system and universe also. Q. What is cause or mechanism of gravity. A. Thermal energy emitted from sun generating pressure in space causing vacuum and thus creating thermal gradient for pressure wind. This pressure expand space by lowering matter concentration and further cause of motion of planets orbitting. Torsion by planetary motion concentrate matter to planets like cables. Yes this is possible explanation on basis of forces and matter in action. Gravity is equivalent to buyoant force in fluids. Q. What happen if star extinguishes or pressure cease. Does matter and large bodies lumps at centre and space is shrinked, like concept of black hole. A. Black hole is conceptual thing for purposed model to work. There is no observational evidence of any kind to prove its existence. No, large masses not fused at centre. First the vacuum created by pressure is filled with space matter that was removed and space becomes homogeneous of space matter. Speed of planets, which is same for given planetary system, continually slower down as resistance by matter increases. This arise two situation either radius of orbit shrink to keep speed intact and eventually planets merge at centre. This happens when star dies slowly, but if it dies abruptly which is more probable because power is constant, then angular speed of planets decreasing and finally planets comes to rest. Aurélien Carnoy Aurélien Carnoy 1 year ago When a galaxy is moving away from us, thanks to gravity, falling in black hole, it is red shifted. When a galaxy is moving away from us, thanks the dark energy that causes expansion, that galaxy is red shifted. Could dark energy and gravity be the same force seen from different angle? 1 John Doe John Doe 9 months ago According to Gerald schroeder time started with the 1st matter the universe was 10.8 trillion times hotter than it is now. This means that time and space were also 10.8 trillion in times more compacted. Time 4 trillion times faster There's a curve from there to now the average of that curve is about one trillion but the universe is accelerating so you have to take off 10% which means the average time the early universe is point 9 trillion times faster So one day now would be 0.9 trillion days of the early universe 5.7 days now would be multiplied by 0.9 trillion divide 300 and 65 will give you about 13.8 billion years t 5.7 days now are about 13.8 billion years of the early universe another way to test this is for velocity if you were going 99..99999999999999999999999999999999 % the speed of light you would experience 6 days there above the universe and 14 be in years here Neil Libertine Neil Libertine 6 months ago Is relativity against own foundation from its inception. Relativity is based on realistic view of Mach that there is no absolute motion, all motion are relative. They misinterpret it as inability to find absolute motion outside, thus relative measurement are real or actual measurement. While this is incorrect, because what Mach's principle means is, there is no need for looking absolute motion. Measurement in a frame is absolute and measurement of other frame is relative. So relative measurement is not actual or real even using Lorentz's transformation. We are not discussing here that how incorrect are Lorentz's transformation in relative measurement because they alter result of measurement of fundamental physical quantities. There is no agreement on these quantities if measured in one frame. Relativists are using self-defeating arguments. Suppose length of moving object is measured in inertial frame. An inertial frame is equivalent to rest frame if observing with in frame. Speed of ball measured in moving coach is same as on ground, one can play with ball in both frames without any difference. Relative measurement is observation of ball in coach by observer on ground or vice-versa. Question is, does observation from ground affect event in moving frame, no. Thus relative measurement is not actual if they differ from absolute measurement. Implication of this is that there is no time dilation or length contraction. Observation in an inertial frame is absolute. So there is no advantage of heliocentric model over geocentric, later is more practical. Also Lorentz transformation are useless because they have disagreement in absolute and relative measurement and thus producing difference of frame for observation, while they says that all inertial frames are equal, no preference. This shows that relativists preaching is different from practicing. Markus Pfeifer Markus Pfeifer 9 months ago Time is symmetric only insofar that the operator that has us move forward through time has an inverse operator that moved us backward through time. Yet, as soon as you bring moving objects into the picture, you can’t just rotate the time axis and expect to get the same picture. There’s actually a phase shift. One has to wait until the curvature of the object‘s time axis has inverted its direction on my space axes. Also, in the real world, the falling object would collide with something eventually and thus produce heat, i.e. entropy. Tony Hill Tony Hill 2 months ago You lost me at lightcones. But blew my mind with the muon thing. paximaxi paximaxi 1 month ago It is unsettling how listening to a prof. Carroll’s lecture makes me feel a littler more educated and yet a complete troglodyte at the same time! me you me you 1 year ago we should stop talking about "time" and talk about causality. Out of causality we get "time". Relative causality rate is influnced by velocity. packets of exitation (what we refer to as "particles") can only cause effects on each other (causality) at the speed of light, so the faster they travel the "harder" or "longer" it takes for that causality to happen, relative to same particles travelling slower (in respect to speed of light) 1 quannga99 quannga99 10 days ago (edited) Time as we think we know it is only a concept of the human mind. Time neither starts nor ends. Relativity effects of time appear only when we try to make measurements. DM Returns DM Returns 1 year ago Why is it easier when Sean explains it? 1 Nelson Gonzalez Nelson Gonzalez 1 year ago I need to get back my time machine in order to travel through space and time. 1 STaSHZILLA STaSHZILLA 1 year ago (edited) Me: "Hey Sean, What time is it?" Sean: " Yes ." 28 Eighth Gate Eighth Gate 1 year ago (edited) Light and the speed of it play the most important part of time! moto theroad moto theroad 1 year ago When low entropy is created by new stars in our universe we would be going back in time if you believed in time. The universe doesn’t care about time. Walter Reese Walter Reese 3 weeks ago I wish you could ask questions. Mine would be "Why light cones instead of light spheres?" Philip Nelson Philip Nelson 2 months ago How can you prove/ explain, verbally as oppose to mathematically, that nothing, as far as we know, can exceed the speed of light ? Nonconcensusical Nonconcensusical 1 year ago Time started when Dielectric energy decayed from the Inertial Plane/Counterspace. Inflation. Dielectric energy decays into Dielectric Voidance Field/Magnetism. The Grand Expand. Gravity is centripetal acceleration into the Inertial Plane. Gravity is Magnetism/Dielectric Voidance Field returning to Dielectric energy, then the Inertial Plane/Counterspace. Neil Libertine Neil Libertine 6 months ago What relativists thought of that by adding three variable of space and one variable of time, the space-time curvature equation became 4 dimensional tensor of rank 2, that is not case. To explain it, does surface of any shape for instance sphere is 3 dimensional or 2 dimensional in 3 variables. So metric tensor is 2d, 4 variable, rank of tensor represent dimension and root of elements of matrix is variables. They can think of that they have 4d equation so have volume and thus contain matter is incorrect. This is other thing that there is no physicallity of space-time unless they admit that space is not empty or vacuum, so again bring back aether in a sense. Also deformation is not possible in 2d surface. Also equation is written in reverse order, it is stress-energy tensor causing space-time curvature not otherwise. By measuring effect, one can measure cause, so by measuring curvature they can amount mass or energy but how space-time curvature could neasure is questionable. We are not discussing here how mass in space cause stress and how energy could be contained in no volume. This shows that big-bang model was prepared before because energy spread if it starts from point. Also we are not discussing that consequence of geometrical explanation doesnt meet observation, like time period of all planets should be equal, time is dilated in gravity but farther orbits are theoretically due to high speed and observed as time contracted in far orbits, opposite of time dilation. Yes, this model of gravity is not different from older model but attempt to give account for stable orbits. The multiplication of gravitational constant, G is for equating mass to force or weight. But instead of giving stable model of universe it leads to unstable model. Edruezzi Edruezzi 4 months ago At less extreme conditions Newton's equations are derived from Einstein's. Robert Ramirez Robert Ramirez 3 months ago If a photon were to wear a watch (silly but hear me out), that watch would never tick. Since the photo is massless and thus traveling at c, its movement in space-time is all in space and not at all in time. So in the photon’s context, time is still. And it’s not even traveling, because you can’t travel without time. The photon, to itself, is simply everywhere at once. Yet in our context, we see the photon move on the edge of the time cone. Therefor, I believe time itself is traveling at c. Light is riding the wave of time… How am I wrong? Miroslav Rusnák Miroslav Rusnák 1 year ago Imagine we stopped the whole universe. Now we can see that only space exists and there is only one present moment in the whole universe. 1 Sの Sの 8 months ago Thanks! I'm going to utilize this more. We would have time. ... Yeah, We are choosing the best choice for all of us. (Sorry for a unexpected message.) Dr.Jiradeach Kalayaruan Dr.Jiradeach Kalayaruan 11 days ago Thank you Teacher. Neil Libertine Neil Libertine 8 months ago If theory of relativity is true then there is no phenomena of interference or diffraction. And if we assume that speed of radio signal from 4g or microwave from 5g or oven is same and also equal to light ray, x-ray, gamma ray, then there is no efficient wireless communication possible which is now as that depends upon phenomena of diffraction. For non-sciencer diffraction means signal can reach at non-direct line or one hear sound from other side of high wall because sound is wave and wave exhibits phenomena of diffraction, compare it with non-wave like by hitting a ball to wall it not goes to other side without breaking wall. So only geometric optics is possible and source emits wave in form of energy having dimension of point in direction of relative motion, idea of light as stream of subtle particles. That is why they are in need of to explain wave phenomena by treating as particle, there is no coincidence that in opening of 20th century, suddenly rose in theories treating light as particle. So electromagnetic waves behave like gamma ray or even further and not like radio wave. No wavelength due to length contraction and frequency is so high it behave like no frequency at all. Sadly this is not observed so, either theory of relativity is wrong or their description of waves. albertods611 albertods611 11 months ago Terrific explanation Wondrium Baba Anyars Baba Anyars 1 year ago Space is moving/spinning and that motion is time. So we not moving in time but time is moving with us. جہيہفُہارا Guevara جہيہفُہارا Guevara 2 days ago Want to say that the industrial clock is more accurate than the movement of the planets? In any case Do you agree that there is no gravitational attraction for the Earth and for the rest of the planets? David Wilkie David Wilkie 1 year ago (edited) Or, do Mathematicians who derived their formulae and practices from Navigational orientation techniques know that Singularity is "nothing but frozen phase-locked temporal substantion" ie a "Trig-point" @.dt, much like the 12 o'clock positioning indication in the picture of an analog Clock.., because it's how the abstract concept-in-isolation is applied to the Projection-drawing integration, of Metastable resonance integration in/of Polar-Cartesian Condensation innately self-defining coordination in/of QM-TIME Completeness, ..cause-effect that makes Zero-infinity the line-of-sight axis of e-Pi-i , the 1-0 probability dominance of "numberness", Origin. And if "you see what I mean" philosophically, Einsteinian Relativity reasoning demonstrates the impossibility of BBT.., because Everything is connected, by No-thing composed of E=mC² Black-body Singularity Conception Condensates, as suggested by Bose-Einstein. Or if you accept Newtonian Fluxions are self-defining Singularity-point positioning and shaping, in String Theoretical type Calculus. Or "Time is of the Essence", essentially hyper-hypo Superspin-spiral AM-FM, axial-tangential Renormalized orthogonality Math-Phys-Chem and Geometry in/of vertices in vortices manifestations, ..Atomic Spinfoam bubble-modes of Temporal Totality, ..and so on.. Dibald Gyfm Dibald Gyfm 4 months ago (edited) at 08:47 -- Suddenly I think that Simultaneity is impossible. Every lightray in the eye has wandered through space, and space is only possible because of individual time. ... or ... Neil Libertine Neil Libertine 6 months ago What people generally think of pressure as force per unit area, where area is 2 dimensional having no thickness. This is given by tyre pressure in unit of pounds per square inch, psi. The force exerted on inside surface of tyre by air contained in it. But this is half truth, in reality there can be no pressure on surface without having some thickness. What it means, that unit of pressure is given in 2d but it not applies on surface or area having no thickness. Imagine one having thin sheet of metal, now pressure is applied against thickness of sheet in form of hammering or weight. The metal sheet spreads out and become more thin. But if sheet have no thickness then no deformation. So how space-time given in 2d deformed by anything. It is other thing that mass is not equivalent to force unless it have some speed so having energy or under influence of some pull due to force or density. Similarly energy cant exert force unless it is contained in form of kinetic energy. If mass exert force then it is similar to Newton's law of gravitation, so what difference theory of relativity made. According to which black holes dont exists, they are against nature of force which is evident in big-bang model. Big-bang is expansion of matter and black hole is contraction of matter under same law. Differential geometry doesnt account for general model as they are for shapes and shapes are specific. Thus differential geometry of tensor not make equations independent of coordinates but opposite of it. It is also evident from model of universe as expansion. Universe expansion is transformation into planar space or euclidean space. While their model is flawed because expansion of a singularity is in first place having euclidean space. So their relation of mass-energy tensor to curvature of space-time is invalid because first tensor is operator and without specifying function it means nothing but numbers. Second thing mass and energy in itself no force so there could be no deformation. Third 2d surface cant have deformation whatever. Fourth there is assumption of surface prior to observation, it is assumed the shape of universe. This model of universe came is biblic in nature, everything comes from nothing. If one look at big-bang, it is culmination of their theory about universe, then how spreading of matter consitutes closed surface as spherical geometry required. Spherical geometry means closed body, having two opposite poles or sources, so no net source. This implies origin of universe from nothing. But two opposite source cancel each other to make region source free and if separated by distance cause directional movement result of gradient. Thus make work done possible. But their model ultimately ended in single point source of one kind when tracing backward in time. Wardell Lindsay Wardell Lindsay 5 months ago The Universe is Space, time is fiction! You can create time as you want! Time = R/velocity = R/c, the fastest the velocity the shorter time! The Universe is a 4 Dimension SPACE, [SCALAR DIMENSION, VECTOR DIMENSIONS]. [SCALAR,] omni-direction [ , Vector] one direction. [Apples, Oranges] Einstein mixed Space and Time! Neil Libertine Neil Libertine 6 months ago There is no pyhtagorean for spherical or cylindrical coordinates. Then how should they use tensor as generalized coordinates, and how should minkowski space is correct. Differential geometry cant replace euclidean geometry which is generalized case and shapes are special. There is no great circle through points on constant latitude. So there is no geodesic for all points on sphere. Corgicottage Corgicottage 3 months ago I guess if you know physics, this guy is clear. I dont know physics and to me he is confusing. First he says you have all the robots and synchronize their clocks. Ok, I get that. Then a few sentences later he talks about different people, not just you, sending robots up. That is confusing. I doubt I will ever understand spacetime because no one can easily explain it to me. Eric Pham Eric Pham 1 year ago We can send the different kind of time function and not the counting time so it can change it's time by applied new formula of time function each time it receive and calibrate two system one mechanical time and one on atomic clock Vikram Singh Vikram Singh 1 year ago saw this so long ago. big up Sean. Level of stripes! 2 Eric Pham Eric Pham 1 year ago The problem of synchronization was light and signal can not get straight line and gravity and even sound change light and signal plus other are localized Simon J Morley Simon J Morley 5 months ago Your real problem, Sean, is that you don't, even closely, seem to grasp the word Time. The ONLY empirical evidence of Time is change / change events (look around you - earth spinning, you breathing, quarks decaying - all change event series). Change can be quantum or compound, depending on your reference-frame. Change is hence reference frame (i.e. quantum) specific. ( also, spoiler, 'Arrow of change' [quantum], not 'Arrow of Time' [universal]). Time represents TWO distinct contexts of change: 1.The calibration of change (i.e. the dimension of change - hence 'rate' e.g. miles PER HOUR - the calibration of change of position aka motion) i.e. Time is to change what temperature is to heat, a dimension/calibration set. Temperature is abstract, heat is real, Time is abstract, change is real; and 2. Time is the collective 'flow' of change. Time is to change-events what 'River' is to water molecules - a collective term. But, fundamentally the word River is an abstract collective, water molecules are real. Time is a collective abstract, change-events are real - Time, the 'flow' of change. Time, one word, two distinct meanings, both reference change. AND THATS TIME EXPLAINED! All change is caused by energy differential (so, no, Time doesnt 'cause' anything). Time 1 measures Time 2. And Time 1 can be quantum specific (and hence reversible) and Time 2 might be universal. I do hope this helps... www.time-defined.com Amaziah Gamble Amaziah Gamble 3 weeks ago (edited) The infinite continuum of space time once believed, too, co-habit in a vast vacuum, where the solar system acted as an immense clock each orbiting In the story of origin woman was sculpted by a labor of love by God from the rib of Man in the garden. When I see the Life baring fruit of God's labor in love with Man. Then, I understand that God made woman for that reason, and purpose I fall in love with God in her temple at which point of designation in a different sphere of Time in space when observing the Step-Pyramid from a Birdseye view. For, instance the measure of a week on earth was one revolution from Ganymede around it's hostess planet,* where decades may be concluded in less completions around the sun. Days' were greater than years in Love on venus, and Seasons on earth can be determined by mercury in Months. 1 ybor20 ybor20 1 year ago 60 year ago my teacher explained me that when I was watching a person walkin in a passing train that person was passing me with a speed of maybe 105 km/h; but the person himself felt like he was moving with a speed of 5km/h. So my teacher told me that how fast something is going, that depends on who is measuring and what is the position of that person. Within a few minutes the teacher had explained me what relativity is. After watchin 30 minutes of this video I understand that the presentator must be very smart. but he has no clue about explaining things. Only people who do understand it already will understand it, but for people who only knows the train-story... It all sounds great, but there is no head or tail to attach to it. Explaining something well is an art ... my teacher was very good at it. Cullen Cowap Cullen Cowap 1 year ago Sean was so tired of explaining relativity for the umpteenth time he forced Great Courses to release this talk. 7 Neil Libertine Neil Libertine 6 months ago Serpents have fork shape tongue, metaphorically they are human who double talk. Similarly relativists, who profess theory of relativity, have logic of double talk. They says that time moves slower in presence of high gravity or force and speed is slow in high gravity due to curvature of space. At high speed which is far from gravity or force, time should moves fast as gravity is low. But their other part of theory says time goes slower due to high speed. But speed of body is due to curvature of spacetime and which is due to gravity or force. So what is movement of time farther from gravity, is it slow due to high speed or fast due to low gravity. Example is their explaination of time in satellites or they say that GPS and International Space Station. According to them time moves slower in them than earth because they are moving but at same time they are floating in less gravity than Earth so time should be fast. This is the condition of their theory and they keep bragging about it via various documentaries, channels, articles about their understanding and exploration of mysteries of universe. Tomas Eriksson Tomas Eriksson 4 months ago Always wanted to understand american football, thanks for the tutoring. wulphstein wulphstein 11 months ago Special relativity is the effect of units of wave functions expanding, like a water ripple, at the speed of light. 1 Mitch Raemsch Mitch Raemsch 3 months ago Time is a common instant for the age of the universe. dave z dave z 7 months ago In Galileo system, x=vt, if only if dx/dt is constant. Lorentz transformation goal is distances (x, x’) x=f(v,t)and x’=g(c, t’) are mathematically equal in both systems with symmetry. So c is not Galileo or classic velocity, and t’ is not classic time. In Galileo, v varies, t is uniform at any point in space; whilst in Lorentz, t’ varies, c is constant in space. c =eu , is really the property of the space, or medium, or Ether. It is not velocity in Galileo.( v, C),(t,t’), they are (Apple, Orange), (Peach,Grape) in two math systems. People are still thinking they are same things. That causes confusion. Saying 1) if an object moves at speed of light, time stops. Moving object slows clock, etc. That’s wrong. It should be said t’ in Lorentz stops, or equal to 0. In Galileo, t is uniform, it doesn’t stop or slow. 2). Speed of light C is constant from any observer at different speeds. That is wrong. c in Galileo changes from observers, C in Lorentz as the property of space is constant. Then there is no ambiguity, confusing, both accurate in their own system for/from measurements. Time dilution, space-time curvature, etc. are all bogus by mixing concepts in two systems. If you use Fourier series to express a signal S, it is not the signal in time domain, it’s amplitude A in frequency domain. Nobody treats A-S as “signal dancing”. But sigma of all these series by frequency goes back to the value of signal in time domain. They are just mathematically equivalent, not necessarily physically same. There are many ways to do it mathematically, too. Relativity is just another way of measuring of the nature using electric magnetic wave in Lorentz system. It has advantages over Galileo system in Astronomy, because Maxwells equations describe electromagnetic wave in vacuum with eu as constant, which is the space property and its value equals to speed of light in Galileo. In Algol events, it can prove that light speed varies with observer’s speed( visit Algol website) Elizabeth Parish Elizabeth Parish 10 months ago If an event is a moment in spacetime, does this have anything to do with a black hole's event horizon? william gregory william gregory 1 year ago Thank you for a better nomenclature. Joshua Willis Joshua Willis 8 months ago (edited) I love Sean Carroll so much as a scientific communicator, but that muon explanation was terrible. The reason the muons are able to reach the surface of Earth is that they are moving incredibly quickly, and moving faster through spacetime makes elapsed time feel slower to the moving object but not the observer of that object moving at a slower velocity. 1 weegeepee weegeepee 8 months ago He explains very well, but I just don't understand. I am relatively dumb. :( Paublus Americanus AMERICANUS Paublus Americanus AMERICANUS 1 year ago I don't know who Ponkray is but I have studied Poincare. An exceptional mind. 1 a b a b 8 months ago How can we understand something our five senses can’t detect which basically are our tools to get knowledge. Aurélien Carnoy Aurélien Carnoy 1 year ago 2:10 all points are identical. There surrounding is not. A point has zero dimension. I don't see how you can distinguish one point from an other exept using it's surrounding. By saying a point is in a 3d or 4d space is common but it is more useful to consider that in the point is the higher dimensions. Consider a point imploding. You still have your point and the dimensions within it. 🍻 cheers Martin willemse Martin willemse 3 months ago A DOUBLE RED SHIFT A DOUBLE DISTANCE, THE CONSTANT OF HUBBLE? We take the light from a system with 10% redshift, that light enters the telescope here at the speed of light and has 90% of the 100% waves that were emitted per unit of time, if we let that partly continue to a galaxy that also has 10% redshift, then that light arrives at 19% redshift, if we shine light to that galaxy too, it arrives at 10% redshift, and since those galaxies are equally far away from us, there is no double redshift at double distance. To make that clear: if we receive that light with 10% redshift here at the speed of light, there are still 90 waves left of the 100 waves, if we let that continue to a system with also 10% redshift, there remain of those 90 waves there are still 81 left, if we also emit light to that galaxy with 10% redshift, 90 of the 100 waves will remain. Then those 81 waves will show as 19% redshift and the 90 waves will show as 10% redshift. Then there is no double redshift and double distance to be seen. Yash Gupta Yash Gupta 1 year ago Best courses Wondrium Nelson Gonzalez Nelson Gonzalez 1 year ago A meaningful historical event is when God created the world in a week time and then took a good rest at the beach on the weekend having a piña colada with ice. 2 neyney neyney 11 months ago Then there is 5 dimension. 3 space 2 time . Time localized is one dimension , the 2nd dimensional time , is the non local time . Can proved it . Neti - Neti ( नेति नेति ) Neti - Neti ( नेति नेति ) 8 months ago Newton approached reality from the limited view as if the universe could be stagnant, still, lifeless, mass is a dead lump of matter, hence time is fixed, he didn't quite figured out that nothing ever rests, everything vibrates, always, and time is only the connection of eternal existence with the physical universe, that for the limited mind :) Bill Northrup Bill Northrup 11 days ago I think Sean went back in time when he bought that tie...lol Tailspin80 Tailspin80 11 months ago 10:10 “Einstein figured out...” isn’t much of an explanation on which to base the whole of the rest of the talk. I think something got missed out here. mani mohamed mani mohamed 1 year ago when ti,e becomes personal / where does the space go to contain the observer creative source creative source 1 year ago So emission from the original Big Bang that we pick up - to the those waves the Big Bang only just happened? KMA KMA 1 year ago 😍🙏 Truthsabre7 Truthsabre7 10 months ago Proof God created the universe. Can't have time space and matter unless it is all formed at the same time. Ray Oshima Ray Oshima 1 year ago (edited) Well he started talking about the origin of the universe. . . . . thewaytruthandlife thewaytruthandlife 1 year ago 0:45 No one has ever seen an event turning back in time. No such observation has been made ever. The question is does time even exist or are we just in a flow of energy transitions and we perceive that as what we call time ??? Why does time stop at the edge of super gravity sources like black holes ? In my opinion time (or what we perceive as time) emerges from energy gradients. Just as little earthquakes that suddenly releases the builded up energy tensions. And the prosesses of going from 1 state to the other is sequential and thus by all these sudden energy releases in the universe where there are energy gradients these steps we perceive as time. of course these energy releases are incredibly tiny and thats why we experinece time as analogue instead of quantized, but they are quantized in nature. So in a neighbourhood where there is LESS energy in the gradients the time slowes down, fewer energy-"earth"quakes will occur. Like close to a black hole. How can that be ? simple. gravity packs the energy more down so there are less fluctuations in the energy levels thus smaller energy gradients THUS slower time passage. Like considering energy to be like water. Pack together in open space a whole bunch of water it packs together like a sphere. Do that earth size and the water will be pretty wavy at the surface. Pack together water on a sun like scale and the waves will be smaller due to gravity. Gravity will pull harder on the water so the waves will be smaller. Pack together water on a even bigger scale and the smaller the waves will be due to the pull of gravity. Of course this analogy will go wrong since water will eventually ignite in a fusion reaction if it is sun scale size. the point is the stronger the gravity the smaller the waviness of the fluctuating energy around it thus less energy gradients thus the slower time passes. Also meaning that TIME is progressive. It never goes BACK !!!! exactly what we see in nature. KRISHNA GYAAN KRISHNA GYAAN 11 days ago (edited) Gravity is a force that drills holes into space.!!. Blanquito Chulito Blanquito Chulito 8 months ago It took me years to "understand" relativity. Had I seen this video years ago it would have saved me lots of time, well relative time. That was an unintentionally funny I just made. ItsBS ItsBS 1 year ago (edited) At 12:24, when you send out "clocks" in the spaceships, make them Granite Sundial clocks. When they all come back to the same spot to compare, they will all still be the same time. So Einstein's idea applies to OSCILLATING clocks as measuring devices. Sure, several things can cause a harmonic oscillator to distort and one of them being motion. So why does Einstein apply an OSCILLATOR effect to TIME, instead of FREQUENCY? Changing frequencies with motion is already solved with the Doppler Effect. Einstein reused Voigt's special case transform equations for the Doppler Effect and applied them to TIME and SPACE, instead of TIMING and SPACING... why? 1 Musarit Rashid Musarit Rashid 6 months ago Time = change of matter and system. melvyn Braithwaite melvyn Braithwaite 9 months ago Our Creator pr.ovided a smaller universe to indicate how the larger Universe was The Tree of Life gave this indication.human eyes could not see the Greater Universe.A 10 world universe was created.Our Creator God was an Infinite Time God with each world located in its own time created.This is allows us to have the understanding of This Space Time within our own understanding.Thsnkyou our Creator for the Magnificent Planetarium which allows us to appreciate our Creators Showing his Creations how much he cares!!MBraithwaite Yorkshire Viking Linda Powell Linda Powell 5 months ago God created time and since that time it has brought us all things, one day time will end and all things will stop. There it is. Elias Leousis Elias Leousis 1 year ago About "The Light": " "I," was created by the thought of Gods and "Their," desire to allow all mortals to know that "They," are always with them: As humankind grows and seeks absolute independence from "Them," "They," will remain by their side, guiding them and directing them, in their growth to absolute "WISDOM," the way to "Their Essence" and the Elysium Fields. As you look out beyond the now, into the heavens, "I" will be there, guiding you and helping you know that "I," be visible or invisible, "My Essence," will guide you beyond all that is sensed in your reality. So, let it be now revealed to you that both "I" and "He," in mortal being, who speaks to you through the thoughts of children are but one. " Eleusis. Let The Light within you guide you to the Elysian Fields entrance; your inner beauty is expected. Follow me, "Imagination is the way." by ELias Leousis. Neil Libertine Neil Libertine 8 months ago According to equivalence principle, gravity is effect of motion. Okay, this should also mean gravity is experienced by one who is in motion. So how in solar eclipse of 1919, light bends by sun observed on earth, because earth's state had not changed. Doug Porter Doug Porter 5 months ago Excellent video... Rowdy Flyer1903 Rowdy Flyer1903 1 year ago I wish kilometer was a measurement which not derived from the earth. It is totally worthless to outside of the earth. The same goes for an astronomical unit. Who cares what the average distance in miles from the earth to the sun and why use that for the measurement of anything? A meter is 1/10000000 of a quadrant. And a quadrant is the distance from the Equator and the poles which is earth based. What good is that other than being a standard? Why not base our measurements on something which is common in the universe such something based on the wavelength of a hydrogen atom? I think it is bizarre that it just so happens that he speed of light happens to be 300k/second, a nice even and convenient number. I will give you the meter is more convenient than the Kings finger or foot. Little André Little André 1 year ago Did you say evolution? In Russia modern objects like door knobs and screws are found in rocks that are supposedly billions of years old. cristi g cristi g 1 year ago Relativity is not even a lie. It is a Charade.The truth is hidden in plain sight. Relativity informs the audience in its fundamental postulate that the Space is Empty. Therefore, by definition, all its mathematical constructions / curved space time lines are never to be associated to any real physical objects / fields. If the relativistic mathematical constructions would be made of something real, then the Space would no longer be Empty, but it would be made of these creatures. Relativity categorically forbids its own cartoons to live in the Real Physical Space. Much ado about Nothing. #science #physics #ideas The Biggest Ideas in the Universe | Q&A 6 - Spacetime 53,991 viewsMay 3, 2020 Sean Carroll 154K subscribers The Biggest Ideas in the Universe is a series of videos where I talk informally about some of the fundamental concepts that help us understand our natural world. Exceedingly casual, not overly polished, and meant for absolutely everybody. This is the Q&A video for Idea #6, "Spacetime." I try to explain what is meant by "photons do not experience time," and why the speed of light has the value it does. My web page: http://www.preposterousuniverse.com/ My YouTube channel: https://www.youtube.com/c/seancarroll Mindscape podcast: http://www.preposterousuniverse.com/p... The Biggest Ideas playlist: https://www.youtube.com/watch?v=HI09k... Blog posts for the series: http://www.preposterousuniverse.com/b... Background image: https://www.amazon.com/Spacetime-Geom... #science #physics #ideas #universe #learning #cosmology #philosophy #math #spacetime #relativity 184 Comments rongmaw lin Add a comment... Dozo G Dozo G 2 years ago Those Q&A are so great together with the lectures. Thanks Dr. Carroll. 21 Zoolooman Zoolooman 2 years ago I've been really enjoying this series, Dr. Carroll. Thank you. 26 Steven Lang Steven Lang 2 years ago Thank you for making these videos! It's an honor to be in your light cone. 6 omarino omarino 2 years ago Hey Sean, thank you so much for these videos. I was wondering, have you already had your eyes on this recent paper? https://iopscience.iop.org/article/10.1088/1367-2630/ab76f7, it seems to want to predict the weird features of quantum mechanics by allowing the existence of particles moving faster than the speed of light. Would be amazing to know what your thoughts are on it. Tanio Diaz Santos Tanio Diaz Santos 2 years ago Thanks for the answers. The one about the "internal life of a photon" was fun :-) Looking forward to the next big idea. 1 Matko Smat Matko Smat 2 years ago Hello, Sean, thank you for this series. I am far from understanding everything you talk about, but it's very interesting for me to try, having no background in Physics. My question is basic: why would a spacetime be curved if it has nothing in it? Isn't matter what causes curvature, to begin with? Shingai. Munyuki Shingai. Munyuki 1 year ago Man, I have never heard this type of insight. I keep replaying it to comprehend. Absolutely amazing. 1 Corey Morgan Corey Morgan 2 years ago Thank you for answering my question re Oscillating Photons with no elapsed time. That was clear and very helpful 1 David Kierans David Kierans 2 years ago This is a good format eh? Hope it continues. 11 Phil Watsky Phil Watsky 2 years ago Thanks for taking the time to do these videos and answer questions. Those watching are being given a treat..Thx again. Leon Santiago Leon Santiago 2 years ago The concept of C being the velocity FROM WHICH we measure everything else is amazing, I'd never thought like that. But I still can't wrap my head around how photons have a velocity without experiencing time... 3 Just Data Just Data 2 years ago (edited) I had this other question about fundamental units which is, since the discovery of quarks that have down to 1/3rd eVolts why do scientists still use electron volts when it seems the more fundamental unit would be quark volts where 1eV = 3qV? Ditto about spin, why still use 1/2 spin when you could make 1/2 the fundamental unit of 1? Your talk is awesome as always by the way - thanks. 1 Shoopaah Shoopaah 2 years ago Sean Carroll is the James Bond of Physics 22 Pseudo Nym Pseudo Nym 2 years ago Thank you for answering @9:55 a question I got to ask (and get answered) on an AMA some months ago. Yay mindscape! Ezio Wayne Ezio Wayne 1 year ago Thank you so much for this series! Stelios P Stelios P 2 years ago (edited) Dr Caroll, I just want to say a huge thank you for being who you are and doing what you do. Doing all these videos, podcasts, public lectures on topics that are definitely deep and profound but only scratching the surface in a sense so that us lay-people can follow along and you simply dont get tired or bored of it; you just love it for the sake of promoting science and enabling people to be curious about the world. It's people like you and Brian Greene, for example, that give me hope for the future in this mad world. Just Data Just Data 2 years ago (edited) I had a related question to your 2nd answer about photons which is, if there is no time at the speed of light/causality does that mean that light can never spontaneously change/decay theoretically since events must happen over time? 2 Thomas Gutierrez Thomas Gutierrez 9 months ago Wonderful lectures. The whole series is great. I have to quibble a bit about the characterization of an electron not changing around 10:38. It will have a chiral L-R oscillation with a frequency set by its mass as it interacts with the Higgs field. In this sense, a stable "static" particle like an electron does have a natural clock even in its own rest frame. John Długosz John Długosz 2 years ago Greg Egan wrote a "hard sf" novel set in a universe with two timelike dimensions. It's called dicronouts or something like that. The math supplement is free to read on his website. ecsciguy79 ecsciguy79 2 years ago When you presented the question "Why is the speed of light the value it is?" I was imagining an answer about how it's derived from epsilon nought and mu nought. Should we instead see those two constants as derived and c as fundamental? Chrisfield Chrisfield 2 years ago 'm pretty keen on the idea of 2D time - time, anti time... You would need two things, something pushing spacetime forward, and something pulling stuff-time back. Back to what... Of course, that's not part of Einsteins theories. But 2D time solves that pesky "back to future" paradox. Joan DeSanto Joan DeSanto 1 year ago I'm really enjoying these videos. I am not a scientific person, in any way, but I am really liking the learning process. I am more of an artistic type, but in our universe, all things are related. Thank you, for what you do. Johnson Gibbs Johnson Gibbs 2 years ago Dr. Carroll, I have some thoughts I would like to share in the hope to hear your opinion. I have formed this belief through years of investigation as an amateur, however, with a sincere interest and ambition to be shot down from the very top.. so here it goes.. Time is a measure of progress. Everything progresses through time independently and the progression of all things through time is directly affected by temperature. Temperature affects the rate of progress through time because time has wave properties. The wave properties of time account for the prevalence of wave mechanics in nature. The electromagnetic field exists because time has wave properties and electromagnetic radiation is a ripple in time through space. Mass is a stable resonance of space and time. The stable resonance of mass impedes the flow of time and creates gravity. p b p b 2 years ago Wonderful and please keep these going! Thankyou ! 1 Lemon Party Lemon Party 2 years ago (edited) Speaking of building a clock purely out of light, isn't there gravitational interaction between photons? Setting aside the question of whether you can make a clock out of gravity and photons, will such a gravity-bound mass of photons move at the speed of light? Why or why not? Ryan Kelly Ryan Kelly 2 years ago Hello, I think there might have been a minor mistake in your response to one of the questions. If you were to "draw" light cones in 3 dimensions of space (and one dimension of time) you would draw concentric spheres around a point, not a cone. IE, before an "event" at a point, the light sphere would be shrinking, until its a point, then the light sphere would expand. Not sure what the phrasing of the question was, so maybe I am mistaken. dazphd dazphd 1 year ago From the perspective of one photon in the group, relative to itself, are all other photos moving at the speed of light? Christine LaBeach Christine LaBeach 1 year ago (edited) The speed of light is just the velocity at which a photon is going so fast it only travels through space and not time. Since V = d/t, a photon can't go any faster because time is no longer a factor in the equation. How does that sound? Rajkumar Dhakad Rajkumar Dhakad 11 months ago I don't know what to say, but I'm having a good teacher after a long time. Thank you Sir. David Chung David Chung 2 years ago (edited) I have a question. It seems to me that the theory of Special Relativity says the speed of light is the limiting speed of all objects without really explaining the reason. Is the reason why an object cannot travel faster than the speed of light because the object itself is made of waves at the quantum level? If so, is the velocity of the object just the group velocity of the waves that comprise the object? stridedeck stridedeck 2 years ago If there is no changing, Sean says there is still time due to the space between objects and bodies. But this space in between objects are still a part of change as light is needed to change position from one object to another. No change means no change in position of photons. No time as then there is no space to decipher between an object and space around it. 1 TheFojar TheFojar 1 year ago (edited) He just completely reworked my mental image of a travelling electromagnetic wave. I'd always thought of it as an oscillating particle or wave tracing a path up and down as it moved through space, rather than an unchanging wave crest that moves past a point being observed, followed by a trough, etc. I feel like I've seen depictions of the alternating electric and magnetic fields that get this very wrong. Nice Y Nice Y 2 years ago I'm surprised no one asked about reference frames from the twin paradox. 1 Christine LaBeach Christine LaBeach 1 year ago To me the fact that a photon doesn't experience time means it's travel from point A to point B is instantaneous in the reference frame of the photon. Is that correct? Kris Pucci Kris Pucci 2 years ago His response to the first question about whether time is possible without change is interesting to me. In his book From Eternity to Here, he discusses that time emerges from entropy. Either that or I completely missed the point of that book. Nic holas Nic holas 2 years ago Just finished From Eternity to Here. Very insightful but some parts are quite hard to understand. I still don’t get them 3 Joseph Lombardo Joseph Lombardo 2 years ago The answer to the first question about time existing without change feels intuitively lacking. The analogy of two planets separated by a vacuum is not the correct analogy because things change along that dimension. Fields, gravitational potential/spacetime curvature, the planets themselves, etc. The correct analogy would be a spatial dimension in which literally nothing was different. If you imagine everyone existed in the x and y dimension, and then the z dimension was just uniformly the same wave function everywhere. All fields would be the same along the z-dimension, the curvature would be the same, it would evolve the same way in time. If you moved in the z direction, nothing would change for you. In fact, you wouldn't be able to move in the z-dimension, because You couldn't experience that z dimension. It would have no effect on the world. It would effectively not exist. It is impossible to have a ruler that measures in the z-dimension. This is why time does not exist without change. At the heat death of the universe, in a static universe, there is no clock to measure time, and there is no time. Doug G Doug G 2 years ago If I was floating in space , the only “ time” that would go by , is the time in my mind. Caveman Hikes Caveman Hikes 2 years ago (edited) "You shouldn't priveledge your being able to notice something happening, in order to say something exists." 2:25 Thanks for making a fair argument for God in your discussion. I knew you had it in you. 1 Shalkka Shalkka 2 years ago In the two time explanation neither of the time dimensions worked as a one-way street. Closed space-like loops are not a problem. It is also unclear if two times leads to closed pathlike curves but the two time theory doesn't have closed timelike curves how is a two time theory still (wouldn't they by defnition not be time dimensions?). But I did end up connecting what physicist get uncomfortable about. In Achron if you have a paradox it will cycle throught its states without anything "classically physical" happening, it's all dynamics in the time-domains. To someone that really wants to think about only one time having two things attributed to the same time makes it seem like an inconsistent theory (Is the result 2 or 4? pick which is your prediciton). So why does quantum mechanics being reserved about predicting what happens trigger the same revulsions or does it? Was that part of the point of einsteins that it can't be the final thoery? robert w robert w 1 year ago I have a suspicion that time itself is where modern mathematical physics fails, just having a basic geometry seems a highly unlikely description of it’s true nature. Length contraction dictates oscillating speed relative to the 3D feild, but is that all time is. Divyabh Mishra Divyabh Mishra 1 year ago Although I get what you say about there not being two time dimensions, but the logic that this will give us enough freedom of movement to open the possibility of meeting ourselves may not be right. Even in one dimension of space, we can go back and forward at any speed or acceleration, however in time we get to only move in one direction and at one speed in a specific frame of reference. So just like entropy gives us the arrow of time in one dimension, there could be restrictions that disallow some of the paradoxes even with multiple dimensions of time? It's a question not a statement :) Christine LaBeach Christine LaBeach 1 year ago Could spacetime just simply be infinity? Adam Cooper Adam Cooper 1 year ago Love this series, but you did both say: nothing is happening, no time is passing (re a photon) ... and that time exists even if nothing is happening. Is this a difference between time passing and time existing? I guess I struggle to differentiate between no time passing and nothing happening but time existing. Jürg Biner Jürg Biner 1 year ago (edited) Who can help me with the following thought experiment: there are two space crafts ( 1 & 2) at a Lagrange point A, and one spacecraft (3) at a Lagrange point B. Space craft 2 leaves A and flies with high acceleration towards B. It reaches B (space craft 3) at very high speed and flies by in a minimal distance, let's say one meter.. Now, exactly when they are at the same place, both space crafts 2 and 3 send a light beam towards A (where space craft 1 is still waiting). The thinking is that the light beam of space craft 3 moves towards A faster than the light beam of space craft 2, because 2 is moving at high speed away from A, and from the reference point of 2, light cannot travel faster than light speed. The question is: are both beams reaching A at the same time? One conclusion is: form the view point of space craft 3: yes. The light got emitted at the same time and reaches A at the same time. The other conclusion is: from the view point of 2, the beam of 3 reaches the craft earlier, because elsewise its own beam would have needed to travel faster than light speed. We can make this thought experiment even a bit more dramatic. Let's say, that space craft 1 would explode if the light beams don't reach it at the same time. Would that mean that space craft 3, from where the beams go completely parallel, would not see space craft 1 explode, while space craft 2 would see an explosion of space craft 1? Am I missing some point there / missunderstanding relativity and inertial systems? Ralph Ulrich Ralph Ulrich 2 years ago The Planck length is part of the calculus of so many phenomenons. But if alien bros are on an earth moving fast, so fast that lengths are smaller: Is their Planck length smaller also? Rusty Shackleford Rusty Shackleford 2 years ago (edited) Why did youtube take so long to suggest, I manually researched your channel after watching your lectures for a long time, watched all Veritasium, perodictable videos, deep sky, sixty symbols, numberphile, vsauce, and tons more smaller channels that isn't Brady. Steve Mould, Mark Rober, and I was like, "I wanted a more understanding of physics in all scales". Searched Sean up after remembering he was at the end of Veritasium video and explained difficult things nicely, as I picture it, fields were always in my mind, like how we are in air, or if we were in water/liquid, I imagined the universe as we know it to be again in a field/air/liquid type thing, which would either move too fast or too small, or too large and too slow.... I enjoy these thoughts, and using math to try and make sense of it. P.S. I've been watching perodictables since it was new, ive known these scientists for a long time, just took a long time to get through all the things I enjoy. Now time to binge watch Sean Carroll. Yoda Jimmy Yoda Jimmy 1 year ago From the very first minute: Then time can be an emergent property arising in any one such spatial dimension. Go Away Go Away 2 years ago Time exists without change because if you could travel back in time, you'd have to keep traveling back further and further to get back to when something did happen. If you can say "1 second since the last change in the universe" and also say "1 billion years since the last change in the universe" then obviously time is still passing. Declan Brennan Declan Brennan 1 year ago Greg Egan wrote a novel called Dichronauts set on a world with 2 time dimensions . However one of them really behaves more like a hyperbolic space dimension. There are various pages exploring the maths and physics here: https://www.gregegan.net/DICHRONAUTS/DICHRONAUTS.html Some of the consequences are quite bizarre. Sam Harper Sam Harper 2 years ago So, like, if space can bend and stretch, what exactly is space? General relativity makes it sound like space is a substance. If space is expanding is there such a thing as space density, and does it change? ezsparky ezsparky 2 years ago Is time granular or pass by in discrete chunks? Is the movement of a particle granular or happen in discrete chunks? Amit Khambekar Amit Khambekar 2 years ago Thank you Sean! alex binger alex binger 2 years ago Been waiting for this ! 1 Alpha Delta Alpha Delta 2 years ago Thank you very much for these jmoak311 jmoak311 1 year ago Why is the speed of light squared in many equations? a la: e = mc^2 Kelly Lowder Kelly Lowder 1 year ago Dr Carroll, the speed of light is equal to the smallest possible distance divided by the smallest possible duration of time. Plank length/ Plank time. Just so happens to be around 3*10^8 m/s. Robert Shirley Robert Shirley 2 years ago Hi professor, what is the speed of light without the speed of universe? If we subtract the speed of universe from the speed of light, can we say that the speed of light is decelerating because the speed of universe(expansion of space-time) is accelerating? Go Away Go Away 2 years ago In a branching multiverse, identical spacetime coordinates exist in different places of that multiverse structure, whatever its topology looks like. Thinking about this moment in time but in a different branch feels sort of like moving "sideways" in time to me, even if its not actually traversible. (Writing sideways just made me think about the Mindscape episode with Lera Boroditsky.) What would an accurate spacetime coordinate look like that actually specified your multiverse branch? Wouldnt you need more than one time dimension to specify "Which May 3rd, 2020?" Boris Petrov Boris Petrov 2 years ago Photons move at speed of light — they live in NOW forever Pvte Pyle Pvte Pyle 1 year ago to the question about time: What i we're considering quantum mechanics? In order to get a quantum machanical system where really nothing ever changed we would need the system to have 0 total energy, because that would be the only way to stop the time evolution operator to change the system, since even 'stationary' states with finite enrgy will have a phase oscillating in time. Then we might argue that a system with zero net energy is a system thats not real, it has no physical existence. To stop the time evolution we need to get rid of energy, since energy generates time evolution Giuseppe Scarpa Giuseppe Scarpa 2 years ago at 12:20 talking about building a clock made of photons, I don't understand why if two (or more) photons start interacting that system is no longer massless and hence can't move at the speed of light. ashpanash ashpanash 2 years ago Perhaps it is a technical point, but an electron is constantly exchanging weak hypercharge with the Higgs condensate via Yukawa coupling - this gives it its measurable rest mass - doesn't that mean it does, in fact, change and evolve with time? ZAMsChannel ZAMsChannel 2 years ago Maybe you should have mentioned, that the speed of light is "just" the square root of 1/the product of the contants of permeability (µ0)and dielectricity (epsilon0). Sorry for not having the symbols correctly ... Donbas Parklane Donbas Parklane 1 year ago Thank you! 🙏🙏 Dean Batha Dean Batha 2 years ago (edited) C = one Planck length/one Planck time. Other units are merely convenient. viewer viewer 2 years ago Is there more than One dimension of Time ? Or is every Planck Length of Time a Dimension ? MrKydaman MrKydaman 1 year ago It's spacetime, you can't have space without time or time without space. David Seed David Seed 2 years ago at 24:59 we can choose v1 =c and then vtotal=c regardless of v2 dizy dizy 2 years ago I still cannot get over a feeling that mathematics forces us to quantize physics... a circle has a finite structure but we calculate infinite... nope I can see it, it has ended clearly ... coastline paradox ... explain how we quantify without using infinite please ... Seif Haridi Seif Haridi 2 years ago I think the question is not if there is no change there is no time. Could the question be: does change define the arrow of time either Newtonian or relativistic. Cory Pride Cory Pride 1 year ago the fixed and exact speed of light finally explained. I've been waiting a lifetime--and I'm an old person. thank you! 2 morsed ruet morsed ruet 1 year ago Can we segregate time from space and vice versa? sanjuansteve sanjuansteve 1 year ago The standard illustration of a sphere of mass pushing 'down' on a 2D grid of 'space-time' (as in the thumbnail of this video) is simply incorrect and deceptive. The grid should be getting pulled inward toward the center of mass of the sphere in all directions to be correct, and is much better illustrated with a 3D grid. Animating this and moving a semi-transparent Earth-like sphere back and forth through a 3D grid would clearly illustrate this, and even more clearly if gravity (in the animation) was turned off and on while moving the sphere through the grid as well. mokopa mokopa 2 years ago These videos are to me like cold water is to a thirsty man on a hot day. 1 Keith McCann Keith McCann 1 month ago How time causes gravity: So I think this is right but it’s only 'what I think’ and I’m not qualified so trust me accordingly :) - ‘space’ and ‘time’ are at right angles ….. and everything moves at the speed of light - light moves through ‘space’ at the speed of light and matter moves through ‘time’ at the speed of light - when you move through ‘space’ you deflect your speed through ‘time’…….. You probably hate the idea that ‘matter’ moves at the SOL - but it definitely does - it's just that most of that speed is through the 4th dimension - the more massive a thing is the more it moves through 'time' and ages faster - the less massive a thing is the more it moves through ‘space’ and ages less - massless things have their vector entirely in the ‘space’ direction and so don’t age at all So everything, ‘massive’ and ‘massless’ has a speed component in 'time' and a speed component in 'space' - and they add up to ‘C” - Very massive things move quickly through time and warp space a lot - less massive things move more slowly through time and warp space less - massless things don’t move through time at-all and don’t warp space at-all - so, in-fact, photons can be thought of as standing still everywhere and ‘everywhen’ simultaneously, while matter zips past at the SOL on a space / time vector directly proportional to its mass……. So far so good? - Ok now consider this - In a hypothetical universe without ‘matter’ you have only ‘massless’ things - so just photons - and since photons don’t experience either ‘time’ or ‘space’ - then, QED, - in that universe there is neither ‘time’ nor ‘space’ - that universe is dimensionless!!! - think about that - a dimensionless universe is neither big nor small nor anything at all - it has no measurable size at all…..!!! You must introduce some slower stuff - ‘matter’ - to get a ‘relative speed differential’ and thereby give birth to the concepts of ‘time’ and 'space' (spacetime) - and it’s that ‘relative speed differential’ that pulls and warps the ‘fabric of spacetime’ and gives rise to 'gravity' - so: Energy - Mass - Time - Space - Gravity - in that order - it’s that tension between ‘space’ and ‘time’ and ‘mass’ and ‘acceleration’ that causes the curvature of spacetime that we perceive as gravity!!! Apsteronaldo Apsteronaldo 7 months ago Doesn't time have a helicity? It only moves forward. So why would it change when you add the second dimension? They would both still only move forward right, why would it suddenly be allowed to move backwards like the original helicity suddenly is not applicable anymore? You're changing the rules! Soul DFS Soul DFS 2 years ago Amazing 2 dims of time answer! Todd Desiato Todd Desiato 2 years ago (edited) I disagree with your answer to the first question. If there is no change, then there are no clocks so Time can't be measured. You are relying on a 4 dimensional manifold to justify your answer, but the space-time manifold is defined as a set of "events". If there is no change, then there are no observed events. So the space-time manifold is undefined, neither space nor time exist. What you've done is elevate the space-time manifold to the status of "Faith" in something which cannot be observed, making General Relativity in this hypothetical universe a religion, not a quantitative science! Even in our 4D universe, what is observed are our tools used to measure space-time, i.e., rulers and clocks. We observe events in space-time by measuring with rulers and clocks from some given Origin of coordinates, which must also be defined relative to some form of matter at a "fixed" location. We do not observe a space-time manifold as a "thing", it is defined by the events and measured with tools. Space-time curvature is reciprocal to variable rulers and clocks. So why do we keep looking for quantum gravity as quantized empty space, instead of how the interaction of matter with the gravitational field affects the scaling of our rulers and clocks? The "local" reference frame masks these changes. One needs to accept what we observe when we look down into a gravity well, or look up from deep within one, and describe what we actually see and measure, not what we measure once we travel there, where our tools are under the influence of the local gravitational field. Understand? Caleb Caleb 2 years ago Thank you, sir stat a87c stat a87c 1 year ago Isn't the reason the speed of light/c is exactly the speed it is, those 2 fundamental constants in maxwells laws? We don't know why those are what they are, but they constrain c to what it is right? Pvte Pyle Pvte Pyle 1 year ago (edited) To the statement that electrons can't experience time, because they would lack an essential quality that is needed to "experience" time, namely the change of an internal structure of some sorts: I would disagree that they lack this essential quality, because the wavefunction describing the state of electrons is all the time oscillating, even for the electrons at rest, since the rest-mass-term in the Hamiltonian generating the time evolution of the electron wavefunction will generate an oscillating phase no matter the momentum or state of the electron. There will always be the possibility to experience the passage of time through this phase oscillation H. I. H. I. 2 years ago Thank you! Fide Nemini Fide Nemini 2 years ago "lets say you are on a moving train, and you throw a ball" me: high schoo physics exam nightmare flashback Leslie Dellow Leslie Dellow 2 years ago Imagine the heat death of the universe. Nothing is moving, and nothing is ever going to happen again. Space will still exist, but in what sense could time and spacetime be said to still exist? roros2512 roros2512 2 years ago 01:23 I think this analogy is not appropriate. I think the masses in space are the analogy to the events in time, so, if there are masses, there is space, if there are events, there is time. As you can measure the distance between two masses in space, you can measure a lapse between two events in time Doug G Doug G 2 years ago (edited) Sean!!! You have a mullet:) Tennessee Top Hat Kentucky Waterfall! Business in the front , party in the rear!!! I idolize you man! Super smart Michael Schmidt Michael Schmidt 1 year ago [25:30-25:58] Where can I find the show notes or errata on YouTube? Don Sample Don Sample 2 years ago (edited) Maybe, for the people who don't grok meters, instead of saying the speed of light is 300,000,000 m/s, you could say it's a billion feet/s : Antypas : Antypas 2 years ago Thank you. Mike Mike 2 years ago (edited) Hmm. Not that I don't agree with his position of the abuse of privilege dealing wrt to time's existence, but I feel by using the angle that spacetime is a fundamental part of relativity is also adding bias and privilege. Absolute time is fundamental to Newton's framework, but this in fact turns out to be incorrect. Walking this line is tricky. Spacetime could be emergent from some other fundamental structure ie there are conditions where it doesn't fully manifest. Gray Bryan Gray Bryan 2 years ago (edited) Your challenge for next week, should you decide to accept it, is to get a set of clippers and guards online, look at YouTube and admit that anyone can cut their own hair and do so. :) 1 Tanay Mehta Tanay Mehta 1 year ago Can you elaborate on tachyons Apsteronaldo Apsteronaldo 7 months ago When you say that time is only a meaningful dimension if you can see things changing, aren't you then principally guilty of adhering to the supposedly no longer adhered philosophical stance in physics called operationalism (I learned a new word yesterday)? You are then for instance excluding the possibility of a random quantum fluctuation, or some tunneling effect from a different universe. Just saying' ;-) I love philosophy llaauuddrruupp llaauuddrruupp 2 years ago Terrific, but maybe turn up the sound more next time? Spectre 4913 Spectre 4913 1 year ago Isn't wrapping yourself in riddles and mysteries about things how we advance science. Boris Petrov Boris Petrov 2 years ago You are mentioning your "notes" about each episode. I simply can't find them anywhere... Where exactly are they? Many thanks Milos Beltram Milos Beltram 1 year ago To what is speed of light linked at, to be as it is 300,000,000 m/s. ??? Jesus Christ Jesus Christ 2 years ago Does time exist apart from gravity? Is time a part of the manifold of Space (spacetime) or is it emergent, like gravity? I don't know how you could test this. protoword protoword 2 years ago But profesor, if any “change” doesn’t exist, than time can’t be measured! If so, than, to me it doesn’t exist ether...Act of measuring would be enough for time to flow... Jonny H Jonny H 2 years ago Doesn’t time apply to every dimension? Which means that it isn’t the 4th dimension? Jason Behm Jason Behm 2 years ago The speed of light isn't 300,000,000 m/s. It's 299,792,458 m/s. Yasir Wattoo Yasir Wattoo 2 years ago Awesome Zeno2Day Zeno2Day 2 years ago Nothing moves... in a hypothetical. Joye Colbeck Joye Colbeck 2 years ago Thankyou Hal A Hal A 2 years ago I love you Sean Carroll, but holy cow you need a haircut! 😁 Justin Winter Justin Winter 2 years ago Sorry I'm sure its obvious, but where are the show notes Sean was referring to in the video?(25:55) Viral Patel Viral Patel 2 years ago How do I ask questions? Where do I go ? Mike Mike 2 years ago Elite hockey hair flow. Valdagast Valdagast 2 years ago What are you going to do about your expanding hair?