#science #physics #ideas The Biggest Ideas in the Universe | 4. Space

#science #physics #ideas The Biggest Ideas in the Universe | 4. Space 178,556 viewsApr 14, 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 #4, "Space." We talk about what is meant by three-dimensional space, why it might be three-dimensional, and why space exists at all. Why do we live in position space, rather than in momentum space, anyway? And what's so important about "locality"? 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://wallpapercave.com/w/Pr9hNhy #science #physics #ideas #universe #learning #cosmology #philosophy #math #space #locality #dimensions 435 Comments rongmaw lin Add a comment... Veroosh Tarot & Astrology Horoscope Veroosh Tarot & Astrology Horoscope 2 years ago I showed this to my dad and it turns out he's a fan too. His words, "he's a really great teacher." I agree. 32 Eric Eric 2 years ago Thanks Sean, for putting out these videos. We often take for granted how the internet grants us a wealth of knowledge at our fingertips, but it's like you're literally giving us a 1-on-1 lesson on these topics from the comfort of our homes. I find them incredibly interesting & informative. 146 vansdan vansdan 2 years ago These videos are exactly what I need. I could listen to you talking about science for hours, and you're granting me that ability; thank you! 71 Sandra sandra Sandra sandra 2 years ago Thank you dr Carroll, great lessons! High school made me hate physics, now I love it! Thank you for using your intelligence, your knowledge and skills to make the world a better place 13 Lunatic Cultist Lunatic Cultist 2 years ago I love how relaxed and friendly these are. Check out the phenomenal sound effects at 16:43. :) 34 Darren Evans Darren Evans 2 years ago Can I just say thanks for a great book (Something Deeply Hidden), a great podcast (Mindscape) and these great videos. You are single-handedly keeping me sane and entertained throughout this infuriating virus lockdown. 4 Nathan Moynihan Nathan Moynihan 2 years ago (edited) This is genuinely one of the biggest ideas in the universe: "Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space." - Douglas Adams 53 TheJonlamb12 TheJonlamb12 1 year ago I’m trying to “wrap” my head around thinking in four dimensions, but the idea seems to pass right by. Oh wait... Great video! Thanks for making this quarantine interesting. 7 Johnson Philip Johnson Philip 2 years ago Can we expect your next book: "The Biggest Ideas in the Universe". Much deserved one. 19 Wakeup Dog Wakeup Dog 1 year ago Sean, thank you SO MUCH for the free education. You are my favorite professor. We loved you on Joe Rogan as well. I wish you and your family the best! 2 soulremoval soulremoval 2 years ago so grateful the internet exists, letting people like Dr. Carroll and Dr. Greene give these amazing lessons. 26 Mikhail Barabanov Mikhail Barabanov 2 years ago Thanks for the video! Finally some understanding of how dimensions could be 'curled'. Could you(or somebody else) recommend some sort of introductory textbook with description of math behind such processes? 4 Benjamin Furstenwerth Benjamin Furstenwerth 2 years ago Thank you so much Sean, this series is amazing! Side note, your preferred interpretation of quantum physics solved the devs machine lol... One more episode to see if they screw it up :) 1 Mina Ghavimi Mina Ghavimi 1 year ago Thank you so much for taking the time to prepare these fantastic sessions to explain physics to the public. 2 Dan Stræte Lagergren Dan Stræte Lagergren 2 years ago (edited) You are making the lockdown bearable, and through this video series reaching people all over the world. Sean, keep spreading knowledge to the world! It’s your gift! Thanks from Norway! 5 ankles iii ankles iii 2 years ago Absolutely amazing, and so well communicated. 1 Rich156 Rich156 2 years ago Hello Sean Carroll, thank you for these videos! you and other physicists that post videos on youtube made me love to learn about physics. I used to hate physics in my school because we had a teacher who made it impossible to understand it for most of us, and back then with no internet, there was no one other to explain it. 1 Raed Shaiia Raed Shaiia 2 years ago (edited) Thank you very much for this fantastic series. I wish if you talk about theories that posit the existence of more than one time dimension :) Gully Foyle Gully Foyle 2 years ago That was great, a little more freewheeling, but fun and intriguing! Thank you Dr. Carroll. 1 PK PK 2 years ago Thank you Sean, these videos are gems! 2 Kieran Garland Kieran Garland 2 years ago I'd been meaning to bug you with a question about Lagrangians and Hamiltonians, and here you've beaten me to the asking of it. This is all really great, like a Theoretical Minimum for the layman. Thanks again. 4 Petr Stepanov Petr Stepanov 2 years ago Thank you Sean for these videos! I have a question or even an idea about why there are 3 dimensions: maybe the trick is that you need at least 3 spatial dimensions in order to ensure that conservation laws and least action principle are fulfilled at any time any two particles interact. As we know from solid state physics, when we start to reduce the number of directions the electron is free to move in the solid (from bulk "3D" to quantum well "2D" and then to quantum wire "1D" and to quantum dot "0D"), the energy spectrum becomes discontinuous and with it the number of possible outcomes of interaction with another electron is reduced. And it may cause a problem because if we would imagine two electrons interact in such a way that the final energy of one (or both) of them after the interaction falls in the "forbidden gap", then in would mean that the decay of an electron to some other particles would be possible, which no one has ever seen (or do I miss something?). Anyway, do you think there is any sense in such considerations? Another observation: as we know the electric and magnetic fields in the EM-wave are perpendicular to each other, so they already "occupy" 2 dimensions. The 3rd dimension is then needed for a photon to exist. No 3D - no light. Thank you again, please keep doing what you do. 1 Black Hermit Black Hermit 2 years ago Thanks for the free content Sean. You’re the man! raf raf 2 years ago This is so incredibly fun, thank you Sean. 8 Zemi Zemi 2 years ago (edited) Thanks for the great content, Sean. I've listened to all your The Great Courses lectures and I'm glad to continue here :) I'd have 2 questions about this talk: (1) You mentioned "a two-dimensional little sphere" (23:34). In what sense can a sphere be 2-dimensional? And then, just briefly after that, you don't talk about a sphere but a "tiny little circle" (24:12), seemingly referring to the same thing. (2) Why did you say that "phase space" is 6-dimensional (45:41)? Cannot it have some other number of dimensions as well? Thanks! sidg11 sidg11 2 years ago Question: Hello Sean, Thank you for the videos! When you talk about space you talk about it is as a thing or object rather than merely as the arena in which things reside. Is space a thing like matter is a thing? Does space have a sub-structure (like particles for matter)? Rollo Burgess Rollo Burgess 2 years ago Thanks very much for doing these, greatly enjoying watching whilst doing endless lockdown-related washing up! Slightly random question: 1. Quantum entanglement gives rise to EPR/Bell phenomena that look a lot like instantaneous action at a distance (with caveats re no info transmission etc.) 2. People have postulated that ultimate theories may involve additional spatial dimensions 'compactified' in various ways. Is it a meaningful conjecture to wonder if these two things could be related, i.e. could apparently nonlocal phenomena actually propagate via the hidden dimensions? If this makes sense could one devise some phenomenology and come up with an experiment? mokopa mokopa 2 years ago 15:09 Here's how I visualised it: It's easy to imagine that two strings in 3D space CANNOT pass through each other, but if you add the dimension of time, it's easy to imagine how one string passes first, and then the second string passes. Obviously they do not need to pass through each other because they are separated by time, that is, they are separated in the 4th dimension 2 Christopher Liggett Christopher Liggett 1 year ago Great series! I love that you bring up questions to which you don't have an answer, and even say "maybe one of you knows the answer". Great way to entice budding physicists to explore the ideas that interest them! Kieran Garland Kieran Garland 2 years ago I guess I do have a question after all. Do the concepts in what you've outlined so far roughly track with what a first year undergraduate would study (obviously in much more detail) at college? A corollary question: what are the big ideas/skills you would hope a first year student of physics might begin to master in their first year? Michael Jehlik Michael Jehlik 1 year ago Thanks a million Sean it's really great that you are teaching and sharing your ideas about physics on Youtube! You are such a great teacher! Your videos and presentation style are top notch. You teach advanced concepts in comfortable inspiring way that helps me postulate and want to dig in. Pericles Pericles 2 years ago You are a great teacher! Thank you! 1 Yannis Varoufakis Yannis Varoufakis 3 months ago I love watching your videos! In fact, I just ordered your book "Spacetime and Geometry: An Introduction to General Relativity". I anticipate it will be way over my head, since I am a layperson who even found this presentation challenging. But I will have it to inspire me to learn. Anyway, I still can't get past my lack of comprehension of the concept of space as having physical geometric properties. You mention Kant as believing in the a priori existence of space. How about Descartes, whom Einstein mentioned, and who expressed the view that space is nothing but the function of extension between bodies and thus there can be no space without bodies? How can "space" exist as an entity in and of itself apart from matter, since it is nothing but the distance of separation between bodies? If there is no matter in the universe, I cannot conceptually wrap my brain around the idea that space would still exists. Indeed, I can't imagine the existence of space even if there was only one object in the universe. As a thought experiment, I imagined that there was only one physical object in the universe, a billiard ball. Nothing else. No energy, no quantum fields, nothing at all. Just the eight ball. I can't imagine any way that it would be at all meaningful to ask what its position "in space" is. I would find it meaningless to ask whether it could move one foot to the left or right, since there would be no other object anywhere to define its position and therefore the existence of space outside of itself. It appears to me that the concept of curved space is a mathematical one to describe the motion of an object under gravitational influence, and not a physical one, just as a graph drawn on a blackboard with x, y and z coordinates is not a real place but merely a mathematical expression of some physical phenomenon. Moreover, while the idea is that an object in motion merely follows a curved path in space in the region of gravity, if the object were at rest, what would impart the motion to the object so it is drawn into that path? Christopher Christopher 2 years ago Sean, the production quality paired with your concise communication style makes this series an invaluable asset to the physics/cosmology community. We sincerely appreciate the time, effort, and thought you invest in these learning tools. All the best to you, Mr. Carroll. Boaz Rosenan Boaz Rosenan 1 year ago Thanks for this series. Although I know (some) physics, it's always good to reiterate on the basics. Regarding the claim that 2D space is not sufficient to do anything "interesting", Conways Game of Life is an example of something "interesting" (a Turing-complete computational model) that lives in 2D space + time. Furthermore, Rule 110 is an example for a cellular automaton that does something "interesting" (Turing complete) with 1D space + time. The extra 3rd dimension makes the computational models we can have in our universe much more efficient (e.g., the human brain), but overall, I don't think there is a fundamental difference. 1 Soul DFS Soul DFS 2 years ago I hope more people have your view on multiple dimensions, start to treat it as a fact, while moving above and beyond our current understanding. Bill Holland Bill Holland 1 year ago Lovely video! Two of the weirder aspects of 3D space and bounding surfaces that I’ve heard about: 1. The maximum information content of a volume of space is proportional to the area of its bounding surface, and 2. Logically our 3D space is equivalent to a holographic projection onto a 2D bounding surface. Maybe these things will come out in a future video? In any event, I’m hooked on these videos. Michael Ginever Michael Ginever 2 years ago So, a wonderful takeaway from this is that we live in 3 spacial dimensions, because how else would we tie our shoe laces. This really made me laugh while I was trying to get my head around the whole idea of a more than 3 dimensional space. I have always loved your voice. It's the way you inflect. Where does that come from? Is it a Californian thing? Perhaps a very regional thing? 1 fatma oylu fatma oylu 1 year ago You are an excellent tutor, thank you. 1 Julian Ngan Julian Ngan 1 year ago Sean made physics more accessible, appreciate that Galleo Boutique Galleo Boutique 1 year ago Love your talks & have much respect for what you guys do. Im a true physicist at heart. Thanks Sean, very interesting. Maciej M Maciej M 2 years ago Sean, you are one of the best educators on physics out there. I always hated physics and math but after seeing you on JRE I am now fascinated by it and want to know more. I'm in the middle of Susskind's Cosmic Landscape and im binging your podcast and the PBS Space-Time. Thanks for making me realize how awesome the universe is. Iulian Doroftei Iulian Doroftei 1 year ago I am a huge fan of Physics and you are my new hero! I have never watched something more engaging. What can I do to contribute to you continuing these lectures? Life has taken me to other endeavors but science will always be my number one reason to excitement and inspiration. One day soon, I will finance one of your projects, Sean! dAN-ABOLIC dAN-ABOLIC 2 years ago Thanks for your time and energy sir. These videos are great. 1 Veroosh Tarot & Astrology Horoscope Veroosh Tarot & Astrology Horoscope 2 years ago This is brain candy - just in the first five minutes you've explained several concepts in a totally unique way I have never heard them explained before. 10 Brendon Hammer Brendon Hammer 1 year ago (edited) I loved the cool way you made "dimensions" (literally the word) disappear, in a time reversed kinda way, from 19.25 to 19.45 min ;) Meanwhile, just such a great series. Thank you so much. bartk07 bartk07 2 years ago Dr. Carroll, great series! Can I ask about information vs entanglement? It is said that entanglement pass no information since it seems otherwise it would break locality. But isn't it a piece of information that spin of one particle is immidiately known as the other is measured? If Bob opened his box after the measurement by Alice but before information reaches him, could he deduct that Alice just made her measurement? And the second question: I know there is no universal "now" for everyone. But since entanglement seems to be somehow outside of the locality, what if we could theoretically conduct independent simultaneous measurement of both particles so we cannot say one of measurements determines the state of the other particle. Can it be possible in QM? Martin Polonski Martin Polonski 1 year ago You are the best! Thank you for the lectures! Cristiano Sarmento Cristiano Sarmento 2 years ago Sean makes an apparently dull and mundane topic such as space look incredibly interesting, mysterious and mathematically complex. You're a terrific communicator. Thanks for doing this PavaniGanga PavaniGanga 1 year ago (edited) Thank you! Only one physics course decades ago. It took me twelve hours, reduced playback speed, pausing the subtitles, multiple repetitions, and so much scratching my head, mulling my notes, and wrinkling my math-challenged brow. But I finally pulled through. I a 73 yo retired nurse was motivated, because you make the subject so interesting! (The other videos were much easier for me, but for some reason the Hamiltonian was tough.) Peter Packiam Peter Packiam 2 years ago Thanks, Sean for sharing your Precious Time & Services, most appreciated Cheers. 4 Ray Guthrie Ray Guthrie 1 year ago I'm enjoying your conversations on the biggest ideas in the universe. thank you for sharing your knowledge and invite to the common man such as me. Alex Cherfan Alex Cherfan 2 years ago Thanks again for this series Sean. I find these lectures extremely informative and interesting. I think you should grow the hair and beard out and just embrace the Jesus of quantum physics look. 10 Alpha Delta Alpha Delta 2 years ago Hey Dr. Carroll, there's something I've been wondering. What would happen if you doubled the speed of light? As everything morphs to keep it constant, would time pass twice as fast? Would we notice as the fundamental interactions between particles (virtual photons) speed up too? Hayden Hayden 2 years ago Q&A. For the spooky action at a distance. Does the entangled particle branch instantly or does the change spread out at the speed of light? 3 Fizikus Fizikus 2 years ago Hi and thanks. According to Big Bang, just do galaxies move away from each other? Or does space expand as spatial? AllThatJazzHiFi AllThatJazzHiFi 2 years ago extremely grateful for making complexity into simplicity. Leon Leon 1 year ago (edited) Very nice series Herr Carroll, keep it up and dont avoid too much mathematics, which is nice to really understand the idea behind the phenomena. Vielen Dank! Liebe Grüße, Leon pinball1970 pinball1970 1 year ago This is such a good series. I am writing up these notes into a book Gabriel Fernandes Steimbruch Gabriel Fernandes Steimbruch 1 year ago Great video Sean. I have a doubt though. You say that Alice and Bob's thought experiment doesn't brake relativity due to Alice not being able to tell Bob about it and all, so no information is actually transmited, but I don't get it since all Bob needs to do to know his particle's spin is measure it and when he does it he will also know Alice's. When Alice measures her particle's spin she now knows Bob's as well, she knows something about what's happening far away, and that's information being transmited right there. Nick B Nick B 2 years ago (edited) Read “the big picture” and it’s one of the most comprehensive theoretical physics books. I’ve read all of Brian green’s work as well as Susskind and Krauss. Sean is among the best physicists /public figures there is when it comes to understanding the laws of nature. So much fun to learn about this stuff. Wasp Venom Lemonade Wasp Venom Lemonade 2 years ago Doesnt the fact that we draw so many xy graphs denoting time along 1axis basically suggest that our calculations assume time as a 4th dimension? Why or why not? Thanks for your work, I adore you. :) Super Sleeper Super Sleeper 2 years ago The quality of content here and your podcasts are a massive contribution to science education. Thank you. May God bless you with a long and healthy life. It is a privilege to be alive in a time when access to this knowledge from such a deep knowing perspective is accessible. Dustin King Dustin King 2 years ago For complexity in 2D space, see the Game of Life, invented by John Conway (RIP). In this kind of space, there's reproduction (or at least production, in the form of glider guns and so forth), there are chaotic reactions, there are even Turing machines. 1 John John John John 2 years ago Good show Dr. Sean. Does a photon experience length contraction due to a speed of c? Theoretically its length could be infinitely contracted. Could time be slowed to zero in a black hole? Conversely theoretically in the total absence of gravity time could run at infinite speed, allowing for matter to exist in the form of standing waves. Cooldrums777 Cooldrums777 2 years ago Well I finally have an understanding of the Hamiltonian. I have read Wikipedia and a few other tutorials on this subject, but I never really understood them. Thank you for the excellent tutorial. Luke Murray-Smith Luke Murray-Smith 2 years ago (edited) Could different regions/dimensions become a parallel 3 dimensional space of our own separated by this shrinking/disappearing which seems like a form of size/interaction relativity? Also if so does this go with multi universe or multi our universe with regions potentially unreachable even if we could travel infinitely faster then light in our region. Bo Zo Bo Zo 2 years ago I really like this format. I was surprised though that there was no mention / explanation of time space in SR and GR. (Or maybe I Spaced it out.) I feel like I'm one clever diagram away from grokking GR. Thanks in advance lol. Austin Denny Austin Denny 1 year ago can you think of infinity as having dimensions? like how we talk about different kinds of infinity. an infinite plane is infinitely "larger" than an infinite line, and so on... zefSF zefSF 2 years ago (edited) Dear Sean Carroll, I really enjoy the knowledge you are sharing and I would like to thank you for making it so clear and accessible. I always have 2 recurrent interrogations about the scope of physics though: 1) does the physics describe our representation of the reality or does it describe the reality itself? If we are living in some kind of simulation, does the physics describe the rules of this simulation or is it grasping something more fundamental and absolute? Do we have a way to make the difference? 2) If we are inside a kind of shoe box (call it the observable universe), can we guess the shape and the color of this shoe box, or all its properties, from inside or are we fundamentally missing more dimensions to observe this shoe box entirely (from outside). I really wish you could address these questions someday. Thanks and good luck with the lockdown. Chris N. Chris N. 2 years ago Sean, have you taken a cursory look at Stephen Wolfram's new work and claims about finding a "path to a fundamental theory of physics"? It's making the rounds right now! 7 Mayfeld shot first Mayfeld shot first 2 years ago Although I love these vids, I think they are deeper and harder to follow than you initially advertised them. I don't mean that in a wrong way, they're full of information about subjects I thought knew more about than the average person. So for me, they're kind of lectures! Not something casual you can put on in the background. Jackson Trollinger Jackson Trollinger 2 years ago This is so great, I appreciate it a lot Vile Live Evil Vile Live Evil 2 years ago I am watching a version of you in two dimensions and it seems to be doing just fine ! 1 Boris Petrov Boris Petrov 2 years ago What is the definition of entropy? (you mentioned Max Tegmark) One I was told if a unit of material has zero entropy at absolute zero -- the amount of heat to bring it to a specific temperature entropy is that heat divided by temperature TheKelvinator11 TheKelvinator11 2 years ago Hey Sean, is it at all conceivable to have a spatial dimension where it is partially inaccessible? For example, a spatial dimension where I can move to the right but not to the left. I could remember what it was like to be to the left, but I could not observe it or access it in any way. Cat22 Cat22 2 years ago Can you do a talk about antimatter? I'd like to know all the properties that differ from a particle and its antimatter version. j n j n 2 years ago If curved spacetime is what we experience as gravity, and there are indeed tiny curled up dimensions, wouldn't they be detectable through their gravity? Such tightly wound dimensions would have very strong curvature, so you would say this should lead to a strong gravitational force. Paps Aebus Paps Aebus 2 years ago In the third part of your recent Book you mention that Space could be something that emerges from the quantum entanglement between degrees of freedom, maybe you could elaborate on what is actually meant by that a little more. Are individual degrees of freedom things that could be thought of as “Quantum of Space”? And also, is it even possible for them to decohere? 1 Mr. Starch Mr. Starch 2 years ago I feel like I understand time in a new way! Shoopaah Shoopaah 2 years ago I am doing an astrophysics PhD and I enjoy this very much 4 Steven Mathews Steven Mathews 2 years ago (edited) I could watch Dr. Carroll see if he could do things with the magic of technology all day as @ 16:02 but only if he's making the noises as he's drawing as @ 16:45 2 Edmundo de la Garza Edmundo de la Garza 2 years ago Thanks doc Carroll. Your matter-of-fact disposition is most inviting and whets my imagination for more; all the while smoothing the rough edges of uncertainty remaining from school. A Kumar A Kumar 2 years ago Thank you Sir for sharing great post. 4 andrei costache andrei costache 2 years ago (edited) Hi, Sean! Just a question: Starting from a 2-d space (surface of a baloon) expanding into a 3-d space, it’s appealing to think of our 3-d space expanding into a 4-d space... The 4-d space would allow a greater complexity and could behave quite differently from our 3-d space. Is there any piece of information (maths, observation, logic, etc.) which might prohibit such a 4-d space from existing? Vikram Cothur Vikram Cothur 2 years ago Question: Are there exceptions to locality ? Nicholas Reynolds Nicholas Reynolds 2 years ago (edited) A thought about life in 2d space. Couldn't there be a form that passes food like an esophagus, gradually contracting around and displacing it using 2 dimensional electric force and/or 1 dimensional magnetic? Thanks! dizy dizy 2 years ago Sean what you dont get is this is extremely important... you do these to educate and expand minds .... even if only 500 ppl watch these ... idk man I've spent years reading physics books ...what you are doing breaking it down and keeping it real ... is massive ... if I had these 20 years ago ... my life would be different... thank you is all I can say shmackydoo shmackydoo 1 year ago thank you for these videos. I am learning so much. Toni B* Toni B* 2 years ago Thankyou Professor Carroll, not just for the maths but for also being a decent person exactly when we need it. T.B from the U.K. LGB Gábor Lénárt LGB Gábor Lénárt 2 years ago 7:36 like the "2000 miles long man" (as he stated) in Leonard Susskind's lectures on GR :) OK, different context (there it was about explaining the tidal forces) but still it made me smile :) 2 Fergus Fergus 1 year ago Sean, these are great and welcome during the covid experience. At 8:44 you essentially talk about the energies of different wavelengths. This obviously has relevance to red and blue shifting of stars... moving away shifts the spectrum toward red. - Can you tell me if energy is conserved in the spectrum shifts cast off by celestial objects, since red-shifting must mean a loss of energy. - How much does relativistic space-time have to do with the conservation of such electromagnetic radiation. (I know Einstein wanted to find an eclipse to try to look at these curvatures) Thank you for your service! Jeremy McManus Jeremy McManus 2 years ago I could have sworn that the result of measuring one of two entangled particles was that the spins would be revealed to be opposite: measure one to be spin up, for example, and the other will be spin down. Here Sean tells us that both spin directions will be the same. Or have I misunderstood? michael convery michael convery 2 years ago (edited) You spoke of an asymmetry in phase space between position and momentum that is induced by position dependent interactions (like solid contact or Newtonian gravity). In what way does a momentum dependent force (like the Lorentz force) effect this asymmetry between position and momentum in phase space? P.S. Many thanks for your GR textbook. Love it! Ed Meko Ed Meko 1 year ago Sean, what you are trying to do here for all of us trying to learn about this Universe is really fantastic. Each episode gives me another small window into what is happening around me every day. Knowledge of the immense space in which I am swimming. Thank You so much. I also enjoy many of the episodes in Mindscape. Deepblue Seeds Deepblue Seeds 4 days ago I have a basic question that I never hear explained. whenever I see the model of the multiverse with the bubbles, what everyone asks is what’s between them? It’s not intergalactic space because they aren’t galaxies, so what is the space in between universes? It is not space right? And it is not just distance separating the universes which could be traveled like we could not just go forever and reach another bubble or even leave our bubble right? That model with the bubbles seems to portray this idea in a way that makes it seem like everything is just separated by distance and that is not the case right? Also the thought that the universe is expanding, then are the other ones all expanding closer and closer to each other too? Niloy Mondal Niloy Mondal 2 years ago How do things move in space? If an object has certain velocity, does it simply teleport itself to the next empty location in space at the plank scale? How to physicist explain Zeno's paradox? 3 marko alling marko alling 2 years ago Why Sean, how is it that the particles in our experiment become entangled, were they chosen at random from the entire universe, or created in an isolated system? 2 Wayne B Wayne B 2 years ago To sum up - space is the thing that enables stuff to bump into other stuff. So without space we wouldn't have to social distance! 1 Imaginose314159 Imaginose314159 7 months ago Is it possible there are more than one dimensions of time? And it increases with spatial dimensions. Maybe one per three, just wondering. Peter B Peter B 4 months ago Good video. Interesting topic and facts put over. Whilst I watch these videos for the physics, it was also interesting to hear about the psychology of time. And very funny at around 38 minutes, when David Eagleman measures time perception by throwing his subjects off buildings. (I know he is a good guy, and he has a good BBC series - and book - on the brain.) I am really loving The Biggest Ideas In The Universe episodes and am learning from them (I have been studying physics for some years). Mohammad Reza Mohammad Reza 1 year ago What does 'spooky action at a distance' (quantum entanglement) mean for space/locality? 1 Pavlos Papageorgiou Pavlos Papageorgiou 2 years ago Hi Sean, could you clarify how momentum is transferred by a field? I understand that the field can have momentum but where exactly? Is momentum diffused through space as some function of the field while in transit? Then how does it get "gathered up" to influence a particle in a local interaction? Is that the same question as how you get particles out of fields, or as the measurement problem? TheKoopaKing TheKoopaKing 2 years ago Is there a smallest unit of space? When cosmologists say space-time is expanding, does this mean that each individual packet of space is getting bigger, or that more space is being produced? Or is space truly continuous? E T Precision Machine E T Precision Machine 2 years ago Greetings Professor Carroll, I am so happy that you are so driven to teach, Though Science and The Scientific Method (should that be capitalized?) have been important in my life since I was a child I ended up being a Machinist. I am very good at what I do in large part because I use science to achieve the best results. Even though I like machining and all that's involved with complex metalworking, I still seek out a physics education that I missed. Folks like you really help. The math is fine, I struggle through some of it though because I'm an auto didact, and the concepts sometimes elude me. Your videos really help. Not just these latest however, but many previous videos of your lectures have also helped me to understand our universe. Thank you so much for spreading knowledge, you are making an important contribution to general human knowledge. Cheers, Eric Joel Virolainen Joel Virolainen 2 years ago (edited) The initial state was very uniform ... There was massive expansion amplifying the tiny quantum fluctuations ... the expansion slowed down ... the state is getting more uniform ... Gravity expands volumes that are too uniform ... 1) Is the big bang caused by gravity? 2) Does gravity cause the big rip? 3) Is the big rip the same as a big bang? Cepheid Cepheid 2 years ago This gets me excited to learn about classical mechanics soon! By the way I highly recommend anyone persueing a career that involves physics or engineering to get the textbook Mathematical Methods for Physics and Engineering by Riley, et al. It is well worth your time and has all the math you could possibly want. (Don't tell anyone but there's a PDF available online, but it was so usefull to me I eventually got the book) Devon Parsons Devon Parsons 1 year ago If you were to tie a knot in 4-space, but instead of strings you used 2d surfaces, would that knot be able to trivially come undone? DeltaXY DeltaXY 1 year ago This is a very, very good series. I certainly will spread the word. Antonin Besse Antonin Besse 1 year ago This series is brilliant. Full strop. mDecks Music Español mDecks Music Español 2 years ago At 47:16 you say that objects only interact when they are local in space. Don’t they have to also be local in time? Isn’t their relative velocity which is a consequence of the momentum also an interaction since time is relative depending on the point of view? Could you explain this? Thanks. Great videos by the way. Rodrigo Nader Rodrigo Nader 2 years ago Question: What do you mean by the size of a dimension? Isn't a dimension just a "direction" in which a being could travel? If imagining a universe like the "Super Mario World" game, the dimensions over there are only vertical and horizontal to me. Where do terms like "a tiny dimension" and "cylinder-shaped" dimension come in? Could you please elaborate on that? Shant Shahbazian Shant Shahbazian 2 years ago The questions of possibility of the emergence of complex entities in lower and higher dimensional spaces is tightly connected to the stability of atoms in these dimensions as well as the possibility of making chemical bonds between them. Without stable atoms and bonds in-between no complex creature, at least as far as is conceivable based on our experience in 3d space, may emerge. pizzacrusher pizzacrusher 2 years ago Fantastic, thank you so much! 1 Alton Moore Alton Moore 2 years ago These are really excellent videos. I still won't be converting to the many-worlds view, but the level of presentation is about right. The hair is looking good, hah! mike jones mike jones 2 years ago (edited) Maybe size is relative, like how big is the space between atoms relative to the space between stars? Still pretty huge id imagine, so relatively things are pretty big at small scales. And maybe the point at we cant see further is where those small dimensions begin that string theory talks about. Shane Strickland Shane Strickland 2 years ago This video was great as always. KJ Runia KJ Runia 2 years ago Anyone made a no-hair theorem joke yet? Thanks, Sean, for another lovely lecture! Carl Dehez Carl Dehez 1 year ago (edited) When Kant says space, time and causality are "a priori" concepts, these have little to do with physics but all the more with our cognitive abilities. We order and interpret reality automatically as we experience it. Visually, we order it in a 3-dimensional space. Even before we see something, we have this ability. Hence, space is an "a priori" concept. It is a condition of our understanding. Cinnabuns2009 Cinnabuns2009 2 years ago (edited) "you're allowed ONE miracle in your scientific theory" LOL! That is one of the best jokes I've ever heard in my life and Mr. Carroll played it off like it was thin air (after discrediting it of course)... curiouser and curiouser... Also, why haven't we moved on from string theory? Isn't that going nowhere? RedDoorYoga RedDoorYoga 2 years ago There actually are living things whose mouths are also used for excretion. See for instance the hammerhead worm. I can also imagine a system where the mouth closes when the anus opens and vice versa, thus always maintaining structural integrity.