#science #physics #ideas The Biggest Ideas in the Universe | 22. Cosmology

#science #physics #ideas The Biggest Ideas in the Universe | 22. Cosmology 286,487 viewsAug 18, 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 #22, " Cosmology." Perhaps more a field of study than an "idea," but it is made possible by an extremely powerful idea: that our universe is uniform and simple enough to be understandable. We go through the expansion of space, the thermal history of what makes up the universe, and a bit about dark matter and the cosmic microwave background. 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/playlist?list... Blog posts for the series: http://www.preposterousuniverse.com/b... Background image: https://www.spacetelescope.org/images... #science #physics #ideas #universe #learning #cosmology #philosophy 402 Comments rongmaw lin Add a comment... Kaptain 1964 Kaptain 1964 1 year ago Sean Carroll’s gently spoken manner plus his ability to explain this material is just the most wonderful way for us in the public to gain some insight into the beauty and wonder that is our universe. These videos are simply a gift to all. 7 Christian Godin Christian Godin 1 year ago I am really impressed by your clear and professional presentation. I have the impression that I understand GR much more than e.g yesterday. Thank you very much indeed. 5 Kanabell Hitoshi Kanabell Hitoshi 1 year ago How have I not found this channel until now?! Brilliant content, sir! 😊👍 6 Linda Hope Linda Hope 1 year ago Thanks Sean. I learn a little more every time I listen to your podcasts/lectures. Thanks for taking the time to educate and inform us. And thanks for referring to Schrödinger’s cat as awake or asleep. As a cat lover, that is so much easier to think about for me. 2 Descartesdom77 Descartesdom77 1 year ago (edited) Dropping a like at 1sec into the video, I was waiting for this topic. One of my favorite fields in all of science. And I know Dr Carroll will do it justice, having owned and read his fantastic book, " Spacetime and Geometry: An Introduction to General Relativity". 3 valrossen valrossen 1 year ago Amazing episode! So satisfying when all the subjects from all the other videos come together and creates something new (knowledge), but still familiar (our universe!) 2 muzakgeek muzakgeek 1 year ago I read Sean's books. I listen to Sean's podcasts. I watch Sean's videos. I spend a lot of time with Sean... and I love it. 83 Delbert Winters Delbert Winters 1 year ago I appreciate Sean Carroll so much, I’m happy Joe Rogan had him on and introduced me to one of my favorite teachers. (Even though I’ve never taken an actual class, I learn so much from his videos) KAĞAN NASUHBEYOĞLU KAĞAN NASUHBEYOĞLU 1 year ago "The Best Content" Amazing series going on Thank you so much Prof.Carroll 4 chrertoffis chrertoffis 1 year ago "We're made of star stuff. We are a way for the cosmos to know itself" - Carl Sagan "Our universe is the ultimate spherical cow" - Sean Carroll 86 Ali Farah Ali Farah 1 year ago Thank you so much for this amazing series. Are you going to make videos about "String Theory" and/or "Loop Quantum Gravity"? 4 Paul C. Paul C. 1 year ago (edited) Many thanks again Professor Sean. I didn't get to see this until the Wed morning, but it was well worth waiting for, as always. And one of my personal favourite topics too. As an amateur astronomer, who happens to find himself living in a Universe, and wondering about that, I reckon that makes me an amateur Cosmologist as well !! Thank you. 1 Gilbert ENGLER Gilbert ENGLER 1 year ago Absolutely fantastic summary! Congratulations. Never stop giving these lectures. 1 John DiVincenzo John DiVincenzo 1 year ago (edited) Prof. Carroll, Thanks so much for making this series! I have a question and was wondering if folks in this field see any practical information to be gathered by looking at the CMB profile over time. If the maps we have represent a 2D projection of the inside of a sphere, then it would seem that every year we ought to be able to see 1 light year deeper into the boundary of recombination. However not sure what resolution span or depth is required to pick out any 3D variations of interest and if that is any function of d-rho (e.g., if ~10^11 light year circumference and 10^5 resolution that might suggest features to be noticed are 1M light years wide/deep). If it took ~1M years to notice any relevant T fluctuation in depth, then that doesn't seem practically useful. So is there any interest in plotting the T fluctuations visible over time? Thanks for any feedback or if you can touch on in the Q&A video. h3 rotor h3 rotor 1 year ago Thank you very much for taking the time to produce these outstanding videos. Mimidhof Mimidhof 1 year ago (edited) Great content, made to be understood... thank you so much to share your love about the Universe and life. Gonzo Batano Gonzo Batano 1 year ago It's just amazing how knowledgeable Sean Carroll is and how well he presents complex stuff in an understandable way. I Z I Z 1 year ago I have a question about time. The duration / time from the begining of the Universe, isn't that a universal constant which started with time zero and is the same everywhere in the universe. And then the relativistic time is like small "branches" of the universal time, depending on gravitational or motion local conditions. Is it reasonable to believe that we can use this "universal time" as a reference and then we can then measure all the relative times, relative to this "unique time, since the universe came to existence"? Moshe Callen Moshe Callen 1 year ago Yeah, as a physics undergrad in the early 1990's, I was a complete dark matter skeptic. When I did a Master's in physics in the early 2000's, I accepted a non-zero cosmological constant but thought surely dark matter was not the explanation. Now I've gone back and am doing a doctorate in physics, and yeah, the only question is what the dark matter actually is. Ruppinstein Ruppinstein 1 year ago Sean..Your content will be counted as a treasure as this playlist matures ❤❤ 78 Whatitis Whatitis 1 year ago I think Seans most impressive understanding to me is his stuff on the direction of time its a concept that i find very seductive yet ive never been able to wrap my mind around. Its in part though not wholly based on the fact that im not well versed at thermodynamics. David Gray David Gray 1 year ago Has this question been addressed by any cosmologists? If things falling into black holes seem to freeze to us at the event horizon due to relativity, how are we able to detect gravitational waves, which can be the product of black holes colliding? Jainal Abdin Jainal Abdin 1 year ago Question for Q&A: Regarding the Cosmic Microwave Background radiation, can you get cosmic background gravitational waves from the Big Bang that are even older than the CMB? As old as the Big Bang itself, and from this, get more insight of the early universe, dark matter and dark energy? Naimul Haq Naimul Haq 1 year ago For someone who knows cosmology, I am surprised he didn't mention the most crucial part 'negative cosmological constant', which besides phases of matter, brings a variety of properties to the cosmos. Bill Holland Bill Holland 1 year ago Another fantastic video! Thanks, Professor Carroll. (Sad to think we are getting close to Video 24 and the end.) The idea that the expansion of the Universe does not conserve energy, that it is time asymmetric, is surprising. Where is the energy coming from? (I guess it’s the vacuum energy magically driving the expansion and creating more space between everything.) Theoretically, could we tether two huge masses light years apart and harvest free energy? Graham Lawton Graham Lawton 5 months ago Doc, great video and I loved the humor and irony…….. cosmology is easy and cosmologists only need a short attention span. However, the video is 1h 59 min long! Looking forward to finishing the series - thanks for all the good stuff. The Man Behind the Ads The Man Behind the Ads 1 year ago One of the greatest communicators and ambassador of physics and cosmology since Carl Sagan. Hawthorne Hill Nature Preserve Hawthorne Hill Nature Preserve 1 year ago Sean Carroll is a superhero! Sir, you are the professor I wish I had and the professor I am so honored to have access to and could listen to you forever. What a mind and educator. Even when I don’t completely follow all the complexities, I find I learn something each time I listen. Your passion is infectious! Mark Calvo Mark Calvo 1 year ago I am very grateful that you've taken the time (significant amount) to do all these and answer questions is very commendable to say the least. I wish I had an opportunity to meet and learn from, no, exchange ideas with you. I sent you a invite on Linkedin. Nick B Nick B 1 year ago Fantastic stuff Sean...thank you! 1 David Hand David Hand 8 months ago I just watched a video by Sabine that reviews several credible lines of evidence that the cosmological principle does not hold - at least not at the scales that have been widely used to evaluate the expansion of the universe. She claims that there is no conflict between our measurements of the expansion rate within a significantly under-dense region and a universe with no dark energy. At some scales, the particulars of the forces of nature form more or less uniform structures within their hierarchy. I.e. at molecular scales, there are only molecular structures, at nuclear scales there are only nuclear structures. The hierarchy itself is delineated by the equilibria between forces as distance changes. Once we reach the scale at which gravity dominates, though, there don't appear to be any additional equilibria to cross; gravity is the weakest force by far but the most persistent over long distances. It's therefore very difficult to imagine how features could form at greater scales from a more or less uniform state at the big bang. If it's truly the case that we live in a significantly sparse region of the universe, then we may have to accept that some of our premises beyond the cosmological principle are faulty. mobilemarshall mobilemarshall 1 year ago I thought one of the modern measurements of the cosmological constant found that the curvature is lumpy. Different areas were found to have slight variations in the expansion rate. pizzacrusher pizzacrusher 1 year ago This one may be my favorite one yet!!! I actually feel like I understood everything he was saying. (As he said, cosmology is for simple minded people with short attention spans, hahaha!!!! :) ). 5 ProfessorBeautiful ProfessorBeautiful 1 year ago This connection between dark matter and the scale deviations of the CMB.... a dynamite explanation. 1:46:38 2 John P John P 1 year ago Sean.. I promise to mention you when I receive the Nobel price for my work on the Inflationary theory. I plan to start working on it as soon as I retire from my current job in a few years. Thanks for another inspiring lecture. Ryan Cole Ryan Cole 1 year ago Q: Does the mass of particles also vary with the temperature of the universe? 1:09:30 1 Aslamic Adika Futra Aslamic Adika Futra 1 year ago Thanks Sean for the making of this videos! Infinitum Neo Infinitum Neo 1 year ago This is a truly great series because of so many interesting topics. Are Axions a possible source of dark matter in the early universe? Bert Rich Bert Rich 1 year ago (edited) Fantastic! i like your calm way of of presenting. I hope you dont mind if i also use this particular video for meditation :-) (and i've also started studying maths and physics, it's a huge pleasure to be able to at least somewhat follow videos like this.) Bill Vanderburgh Bill Vanderburgh 1 year ago Really well done. Thanks! Elliot Eckel Elliot Eckel 1 year ago (edited) Given the idea around 47:20 (..." Voila! A conversion from electrons to photons.") can I ask I about EW / GUT / ToE unification? I'm interested in what it takes to hold onto a magic co-moving box of space with a helpful scale factor in which I can happily sustain an equilibrium of different particles in the zoo: When I think about rewinding the universe to hotter moments such as above 80 GeV, would we expect to see real (non-virtual) W & Z bosons being created, and perhaps also see 'rapid' conversions between fermion flavors? If we could hold our magic box at this temperature, could we see weak neutral current flowing and a highly-probable weak (non-kinetic) scattering of neutrinos, and see some semblance of equilibrium between fermions and the massive vector bosons? When the U gets above ~125 GeV at the Higgs Mass, would many particles then decouple from the Higgs field and four massless bosons (W1, W2, W3, and B) whiz about with relative ease compared to the previous magic box with massive real W & Z bosons? (If I understand, they would exchange the EW force between particles with the unified EW charge, rather than merely pair-creating to create an equilibrium.) In this environment, would the Higgs itself still be massive; and, at T = ~125 GeV, would we expect to see similar equilibrium diagrams where photons can converge to produce a Higgs just as rapidly as the Higgs decays into any of its decay products? For a GUT at ~10^16 GeV, would we expect to see a similar 'rapidly produced' equilibrium of X bosons and leptoquarks whizzing about happily in an environment hot enough to pair-create them outpacing the pair annihilation or decay? (Is this also where people refer to the epoch of baryogenesis, given the matter-favored decay products over antimatter?) To complete the picture, should we imagine gravitons and the numerous X bosons unifying above ~10^19 GeV, some 10^-43 seconds or less after the big bang? By this principle would there have been an equilibrium of gravitons and all else saying "hello!" to each other at the quantum scale (given quantum gravity paints a tangibly similar picture to this train of thought)? Thanks for all the great videos! 1 L. Ron Gardner L. Ron Gardner 1 year ago AMAZING STUFF!!! I just found a multiverse in my bowl of quinoa. Will miracles never cease, including the miracle that miracles don't violate the law of cause and effect, and that people take seriously Sean Carroll's cosmological crappola. Vldmr Vldmr 1 year ago Amazing content. Much appreciated. 1 dabrownone dabrownone 1 year ago The simplest analogy for explaining expansion of the universe is to focus on the scale factor. Picture a map with a scale, say 1 inch to 1 mile. Then over time, say the scale is now 1 inch to 10 miles. Thats expansion. The map is the same shape, but everything is farther away Boris Petrov Boris Petrov 1 year ago A question: -- Is Einstein's cosmological constant == (same) as "dark energy" -- Why has over time the term "dark energy" replaced the original term "cosmological constant" -- Are the two terms identical or not -- and why Many thanks in advance 2 Narf Whals Narf Whals 1 year ago (edited) How exactly does expansion act on massive particles? If it stretches their wavelength, how does it know to stop at their rest-mass? Or do they keep themselves together by their own gravity at that point? Edgar A. Leon Edgar A. Leon 1 year ago Great and yes inspiring. You mentioned that you give a 50% percent to inflation (and I agree a lot). Can you give also your opinion about which could be the better contenders to explain dark matter and dark energy? By the way, today Mark Trodden gave a lecture online titled "What could Dark Energy be?" ...but actually it was almost totally about massive gravity and Galileons.. so again dynamical Dark Energy. Thank you again! FractalMachine FractalMachine 1 year ago (edited) it's an interesting thought, that there are people alive today, who have been born before we knew (even scientists) that there are other galaxies in the universe. 1 Reginald Carey Reginald Carey 1 year ago Question: if neutrinos have mass, why don’t we see them at all energy levels? Gravity must slow them down. Rick Harold Rick Harold 1 year ago Awesome. Love these lectures. 1 Kanwar Physics Discussion Singh Kanwar Physics Discussion Singh 1 year ago Sir i like your way of explaining things, which no doubt shows your vast knowledge towards physics. But i have one question which you may consider as philosophical one also. "Every time when we human give solution to one question then from that solution other question takes birth and this process is being continues since human try to satisfy his intuition. Do you think in this way we ever could reach to ultimate answer.?" Regards Sir artistphilb artistphilb 1 year ago Maybe I'm missing something? but when we look at the most distant galaxies with large red shifts we are also looking back in time, so how do we know that space is expanding and causing the redshift rather than that things were moving apart faster in the early stages of the universe? Michael McConnell Michael McConnell 1 year ago Dr. Carroll- first of all, thank you again and again for this series. not only has it satisfied my curiosity on a level no science communicator has been able to, its helped keep me, and I'm sure so many others, sane during this ....interesting time. maybe I missed it, but aside from recombination happening at BB+380,000 years I was wondering if you could mention the times in relation to the distinct events in thermal history. how soon after the big bang did nucleosynthesis occur, for instance? thank you again. gkelly34 gkelly34 2 months ago I wonder if you can detect gravitational waves beyond/further back in time from the CMB. And will they be able to help you figure out what caused the perturbations? George Tauchen George Tauchen 1 year ago Brilliant, very lucid and balanced exposition. 1 Lindsay Forbes Lindsay Forbes 1 year ago Brilliant! The skill of the teacher has to be inversely proportional to the ability of the audience. I think I understood acoustic oscillations for the first time and where that CMB graph came from. What a privilege to have access to this great communicator. Making it simple is not easy. Many thanks 14 PugetSoundFlyer PSF PugetSoundFlyer PSF 1 year ago I love this series! Half of what he says goes way over my head. The other half goes way, way over my head. 1 Sam Barta Sam Barta 1 year ago Question for people who have read 'something deeply hidden', is it worth the read if i have already watched almost every one of Seans lectures on QM and spacetime emergence? Imaginose314159 Imaginose314159 1 year ago The examples you spoke of about the Universe expanding are used to show how things further away are moving away faster, which was helpful at least for me. A. Rodimtsev A. Rodimtsev 1 year ago This was really a good video. Thank you so much. 1 Isaac Ziskin Isaac Ziskin 1 year ago Kinda sad you don't teach more classes at Caltech. Your presentation is SO clear. I gotta take a GR and cosmology graduate level class with you online! Please!! Miodrag Prokic Miodrag Prokic 1 year ago (edited) Effectively, the same problematic related to understanding natural forces (including gravitation), structure of our universe, motions and interactions among elementary and other particles is part of generalized “matter-waves and wave-particle duality theory”. See much more here (download PDF book): http://mastersonics.com/documents/revision_of_the_particle-wave_dualism.pdf Sebastian Dierks Sebastian Dierks 1 year ago (edited) At the end of the video, you drew a graph of a(t) with its three phases. Could you quantify that graph? I'm asking because I was wondering whether the velocity of expansion was ever slower than c. I have problems envisioning looking at the sky at far distances when the expansion was slower than c such that photons can catch up with the expansion. For example, imagine a universe expanding with a constant velocity slower than c since the big bang. How would that picture about that backwards light cone would look like at 1:23:00, especially if the universe was not infinitely big? Alasdair Whyte Alasdair Whyte 1 year ago (edited) Hi Sean, are we not surrounded by the microwave back ground radiation which must(?) mean we live inside a sphere of some sort? never mind, it's just an horizon 😊 Giskard Reventlov Giskard Reventlov 1 year ago (edited) A few questions. 1) Given the scale equations at 43:00, - For matter and radiation, H ~ 1/t - For vacuum, H ~ constant Can astronomical measurements see far enough in distance and time to observe H ~ 1/t? 2) Can you give a phenomenological explanation for the different scale equations (43:00) of the matter, radiation and vacuum domains of the expansion in terms of gravitation (the gravitational force being attractive), etc? 3) Vacuum energy is a quantum concept. Is it correct to say that quantum gravity is not needed for understanding the rate of expansion (except in the beginning of the universe), because the length scales of interest are much longer than the Planck distance? Thank you for these videos. They are interesting, informative and clear. Narayan Mohanram Narayan Mohanram 1 year ago Thanks professor. You talk about the observable universe and assessing a finite size on it. However you talk about infinite universe when you talk about a flat/negatively curved universe. You also mention that "we know how much stuff is in the universe". You also talk about "scaling infinite numbers - and the result being infinite". All these statements seems to be in conflict with each other (to a rookie - such as myself). Stephen Bryant Stephen Bryant 1 year ago I had a major in the humanities, but took a Cosmology course in college. In retrospect, I value that one over any other and still have my notes, decades later. I know a lot has changed in the intervening decades, and have somewhat kept up with the field. I’m looking forward to this lecture with special interest. Michael Cornish Michael Cornish 1 year ago Class, loved this video great discussion of dark matter. Sebastian Dierks Sebastian Dierks 1 year ago At 43:25, do you use an initial condition when solving the Friedman equation to find that the universe starts expanding at all? So do you have to put that (the big bang) in, possibly even give the initial velocity a certain value? I mean I could imagine that otherwise, for a radiation and matter dominated universe, the expansion doesn't start at all because gravity keeps everything together. If you don't put that in as an initial condition, wouldn't the Friedman equation (and thus GR) predict the big bang, or make it inevitable, if expansion starts no matter what? Abhishek Singh Abhishek Singh 1 year ago How does it must be feeling being first human to know something so big like Hubble figured of big universe or of expanding universe Bennett Yankowitz Bennett Yankowitz 1 year ago I have a question: I believe that you said that energy is not conserved when we look at the entire universe, because of dark energy, and in fact energy is increasing as the universe expands. I have been watching Alan Guth's MIT Open Course lectures on cosmology, and he says that the increase due to expansion is offset by negative energy in the form of increased gravitation in the expanding space, and that the two balance out to preserve conservation of energy. Am I misunderstanding something here? Rajeev Gangal Rajeev Gangal 1 year ago This uniformity on large scale somehow still seems inconceivable. It's just that the universe is so big that patterns and clusters disappear when visualised as the mo of galaxies and stars is so high. What about lanaekea ? Does that not show evidence of large scale structure, also the great wall... Which means it cannot be isomorphic at particular scales Jan Bastrup Jan Bastrup 1 year ago Is there a coloration between how much the universe expands and how much matter and spacetime black holes consumes? Could black holes be the reason why space is expanding? Since the biggest black holes are in the centers of galaxies and they are fundamentally the rulers of those galaxies. Meaning the galaxies follow the path of the black hole, like our solar system follows our sun. Crab-Dog Jones Crab-Dog Jones 1 year ago Thanks for taking the time to do this. I've really learned a lot. 20 Sebastian Dierks Sebastian Dierks 1 year ago (edited) At 43:25, does dark matter just behave like matter or radiation, depending on its velocity? Or is there a new relation between a and t for it? Elto Desukane Elto Desukane 1 year ago 18:30 When we say space is getting bigger, space is expanding, would it be equivalent to say matter is contracting? (we do observe that the ratio "distance between galaxies"/"galaxy size" is increasing) Om3ga Om3ga 1 year ago Prof. Sean Carroll isn't there going to be any video on Relativity? By the way, love your videos 4 4.669 4.669 1 year ago It's like your shirt is becoming one with the deep field 😂 I'm so glad I found this channel! The way you explain the Universe is very mind opening, and I really enjoy your lectures on time. NoMad NoMad 1 year ago Really great content. Thank you very much for your quality time and ideas. 1 Patrick McHargue Patrick McHargue 1 year ago Related to cosmology, do you have any thoughts on redshift quantization, AKA redshift periodicity? Is it real, and what might explain it? Sebastian Dierks Sebastian Dierks 1 year ago (edited) Can you tell something about the (far) future of the universe? At around 43:25, you explain how a(t) goes in a matter, radiation and vacuum energy dominated universe. I guess you could just take the derivatives a dot and a dot dot (aka the velocity and acceleration of the scale factor) and see that in a universe with matter or radiation, the expansion slows down and you get a heat death and in a vacuum energy universe you get exponential growth leading to a big rip right? So how do you get a big crunch from the equations? Or periodic/cyclic universes? Do you need curvature not equal to zero for that? As I understood, these solutions for a(t) were for a case where the curvature is 0. Also, as the universe is measured to accelerate today, not decelerate, is it true that it's therefore vacuum energy dominated now and therefore going to rip in the far future? Reginald Carey Reginald Carey 1 year ago Based on what you said just before 50:00, black holes must produce matter (from hydrogen on up through the heaviest elements) in a region where light gains enough energy to interact and produce that matter and fling it into the space surrounding the black hole. Some of this matter must obtain escape velocity. Crucially, a black hole must be a matter factory. Lighter or more energetic elements are more likely to obtain escape velocity. This should correspond to the relative abundance of elements in a galaxy and may be related to the mass and spin of the black hole. Super massive black holes may create their own galaxies! It also says that we are more likely to find life at our radial distance or further if star formation corresponds to density. Galaxies grow to a certain size based on the black hole mass and spin. A black hole massive enough to produce matter in this fashion must grow by the mass generated in this energy density region. Either gravity wins and this region eventually falls inside the event horizon or the black hole is in a run away positive feedback loop constantly increasing in mass. SCOTT REDDEN SCOTT REDDEN 1 year ago An excellent speaker and so so sharp. Your intelligence fascinates me sir. daapdary daapdary 1 year ago (edited) At 44:55, Sean writes: log(eˣ) = x From the context, the log's base is e (not 10) so it means: logₑ(eˣ) = x or ln(eˣ) = x Apparently, physicists assume log is a natural logarithm (base e). However, engineers, calculators, and general convention all assume that log is a common logarithm (base 10). That's a problem, isn't it? :-) Decades ago, I was taught that log has base 10 and ln has base e. The international standard ISO 80000-2 (section 12 "Exponential and logarithmic functions") describes this notation: logₐ x : log to the base a of argument x. ln x = logₑ x (natural logarithm). lg x = log₁₀ x (decimal logarithm). lb x = log₂ x (binary logarithm). log x is used when the base does not need to be specified. log x shall not be used in place of ln x, lg x, lb x, or logₑ x, log₁₀ x, log₂ x. I recently adopted this standard a few weeks ago, which makes me the first person ever to do it! :-) 1 John Długosz John Długosz 1 year ago opening: I think it's not a matter of "must be right", but rather ask, "above what scale does the universe become uniform?" and also compare that with the size of the universe (much much greater). Shytam Shytam 1 year ago Wonderful! Thank you!! 1 Saint Burnsy Saint Burnsy 1 year ago (edited) 24:15 Could it be that the Universe is a finite, but very very very large sphere- that just appears to be flat? Not unlike how we perceive the surface of the spherical Earth to be flat? But then, how might we be able to distinguish between this and a truly flat Universe? Christian O. Holz Christian O. Holz 1 year ago The exact math is a bit beyond me, but your accompanying narration does provide a nice overview and context to the underlying connections and principles ManWhoUsesComputer ManWhoUsesComputer 1 year ago @ 49:20 (https://youtu.be/tZQadPmTd84?t=2959), Sean mentions that when two photons join to form an electron / positron pair, the pair is relativistic (moving close to the speed of light). I have a question: how is momentum conserved here, where photons (massless particles) create fast moving, massive anti/particles -> it seems momentum would increase. Is it that positrons have negative momentum? Thanks. Sebastian Dierks Sebastian Dierks 1 year ago When you explain the thermal history of the universe, except of only giving temperature, could you also translate that to lifetimes of the universe? You only mentioned 380,000 years for the CMB. I guess you mentioned T~1/a and a~t^(1/2) for a radiation dominated universe in the beginning, so in principle I could figure it out if I had the proportionality constant. Reginald Carey Reginald Carey 1 year ago The photons of the early universe are gone. The only thing left is the weakly interacting neutrinos with non-zero mass. As the universe expands, they have fewer opportunities to interact with anything other than the curvature of ST which they are curving. There should be high density regions of neutrinos. ProfessorBeautiful ProfessorBeautiful 1 year ago (edited) "We're gonna predict it, we're gonna get it wrong, and we're gonna fix it". 1:31:05 Classic! 1 Waaridh Borpujari Waaridh Borpujari 1 year ago (edited) I had been waiting for this video for a long time… Glad to see it. 😇 Elto Desukane Elto Desukane 1 year ago 1:56:40 Should not the yellow inflation curve be steeper than the regular curve (since the scale factor grows much faster during inflation)? spin_glass spin_glass 1 year ago I’m just waiting for a new series of lectures, Seannnnnnn 1 Saint Burnsy Saint Burnsy 1 year ago (edited) I fell asleep listening to this and dreamed that my former First Sergeant was actually my high school PE teacher, and that he happened to be very well-versed in cosmology for some reason 14 lower case t lower case t 1 year ago 21:00 I've heard you say a couple of times already that you don't like the balloon analogy, because space does not expand "into something". But, if you're living on the 2-dimesional surface of the balloon, it does not expand into another area either as the balloon grows. If you compare the radius of the balloon to our distance in time from the big bang (so you could call the entire thing "arearadius" or "areatime", just as we speak of "spacetime", the area is growing as the radius increases, just as our space grows as time progresses. I think that is a valid analogy, and by taking away one space dimension we get a three-dimensional "areatime" that we can at least comprehend with brains that are hardwired for imagining 3-dimensional constructs. I like that analogy especially for pointing out how little sense it makes to ask what was "before the big bang": In a balloon-like areatime this would be equivalent to asking, what's "inside the center" Travis Fitzwater Travis Fitzwater 11 months ago Why does taking the square root of a number occur so frequently in so many relativistic, cosmological, and physics equations. It seems like the square root is some sort of magical thing like Pi or something. Ben Jones Ben Jones 8 months ago they should measure how rapidly 2 galaxies 10 ly distant from us and 10 ly distant from each other are separating to pin down the hubble constant Ryan Pescott Ryan Pescott 1 year ago Could someone please tell me the software he's using to write with that pen? Looks like a very efficient way to do my college work Joel Dobbs Joel Dobbs 1 month ago I left this on in the background while I was painting and now I have a strange urge to walk naked into my back yard and stare into the star strewn depths of an incomprehensibly vast and ancient universe, stare in breathless wonder and know with utter certainty that cosmology is so far beyond my ability to comprehend that I might as well be throwing twinkies into the sky to see if anything up there is close enough to poke with a stick. Ah well, plenty of content on Youtube that will make me feel like a genius after watching it for ten minutes, plenty plenty. Actually I very much enjoyed the video and I will likely watch it again with my entire brain engaged. Beena Plumber Beena Plumber 1 year ago 22:00 - "There is no center." Aren't we off-center from the CMB? Relative to the CMB, aren't we moving slowly toward Leo? (I've read that and heard that from a couple sources now.) That tells me there is a center identified with the big bang, and we're not there, not even from our own inertial frame. 1 Don Wortzman Don Wortzman 1 year ago Another Quantum Interpretation Imagine a simple square maze made-up of many rows where the entrance is at the corner of the first row. Humans walk down the row and when they come to the end, there is an opening to the next row, and so on, until they come to the end where there is a door to the outside. However, the walls of the maze are made of a mesh, where small insects can pass thru unencumbered. The insects can negotiate the entire maze by going a length d. Humans will have to travel d^2 a much longer trip to get outside. Also, the insects have access to a wider region. However, if the insects want food or water, that only humans possess, they may need to ride with the humans for a while going the long way with them. The universe follows a similar paradigm, but the rows are much closer, and in addition, it performs this feat in all 3-dimensions, rows, columns, and sheets. Hence particles are small objects and can appear as spread-out waves because they can easily distribute thru the partitions. They can interact with other particles wave-like but must reveal their true small particle nature when interacting with large objects, which shunts their ability to spread thru the separation. Consequently, a single photon is wavelike up until, for example, it actually hits the screen in the double-slit experiment, or the electron is wavelike up until it enters a vapor chamber. Also, a cat, a flask, or a hammer are never in a superposition of states. The walls are so thin that even a most superficial sensitive interaction with a large object turns it into a small object for at least an instant, but might enable it to start anew as wave-like when it escapes the grasp of the large object. It is the hidden structure of the universe that explains and describes these and other of nature's “tricks.” Don Wortzman wortzman@gmail.com protoword protoword 1 year ago As usually, thank you sir! 1 schel sullivan schel sullivan 1 year ago Sean you have been very very productive lately. I think that about 60% of my online listening is content of yours. 34 Adam Jacob Rogers Adam Jacob Rogers 1 year ago I find it very appropriate and appreciate that Prof. Sean can manipulate math models and equations to back up his topics and lectures. I love Neal Degrass Tyson as a speaker, representing the cosmos and being a great science communicator and advocate but he never busts out any math to back up his lectures which for me, is not as impressive as Prof. Sean's grasp of and display of the math that underpins and proves most or all of his videos topics and shows way more how and why we have the knowledge we have gained as a whole. And why the universe is the way it is. Bravo Sir. 1 Valdagast Valdagast 1 year ago The length of an episode (in seconds) is given by kx+m, where is 161, x is the episode number and m is 2579 (least squares method). 1 susmarcon susmarcon 1 year ago I am reminded of a little Einsteinian anecdote I once read, that went something like this: Assistant: “Doctor Einstein, I notice your examination paper has the exact same questions as last years test. Einstein: Yes that is true. But the answers have changed. Fairies and goblins might exist. God and dark matter might exist. I believe Steven Hawking at one time thought that an event horizon might exist. But electricity, magnetism and gravity do exist. Occam's Razor is the principle that, "non sunt multiplicanda entia praeter necessitatem" [i.e., "don't multiply the agents in a theory beyond what's necessary."] If two competing theories explain a single phenomenon, and they both generally reach the same conclusion, and they are both equally persuasive and convincing, and they both explain the problem or situation satisfactorily, the logician should always pick the less complex one. The one with the fewer number of moving parts, so to speak, is most likely to be correct. “Space News from the Electric Universe” provides the counterweight to a variety of views held by the mainstream. The E.U. maintain that electricity is in fact the primal force in the universe. Their view allows many of these questions to be resolved through the known mechanisms of plasma physics and electricity. Happy hunting. Darren Hill Darren Hill 1 year ago If farther objects are moving away from us faster, and farther objects are further back in time, doesn't that mean the expansion is slowing the closer you get to present time? I had that thought one day, and I can't seem to wrap my head around why it's wrong. ET Stalker ET Stalker 1 year ago (edited) Professor Carroll. You said maybe someone watching this will figure it out and if they do don't forget where they learned it. I have not forgot and I will not forget. So you have to honor the request that you made. 1 pizzacrusher pizzacrusher 1 year ago so wonderful! thank you again!!!! 1 alan silverman alan silverman 1 year ago Those who question the use of the term "recombination" aren't trying to be cute; they're legitimately confused because their introduction to the topic is by way of "the era of recombination" and so if there's an era of recombination it stands to reason that there must have been an earlier era where the original combining took place... Henley Cheung Henley Cheung 1 year ago fantastic ideas, thanks Giskard Reventlov Giskard Reventlov 1 year ago When you state that the universe is expanding, do you mean that the scale and geometry (metric tensors) are expanding? - If any two points in space are moving apart, does it mean that objects are getting bigger and less dense? For example, are our bodies expanding, even by a very minuscule (unmeasurable) amount? Or is the physics at the local scale affected by the matter we see and not by the increasing scale of space? - Is "chemistry" changing? In other words, in principle, are the interactions (the model parameters) at the energy scale of 1 - 10eV changing or is the available energy to make chemical reactions just changing because the university is cooling? Django Cyclebrazil Django Cyclebrazil 1 year ago gravitaional waves: are they quantised like EM waves, or somehow analogue? Ian Cartwright Ian Cartwright 1 year ago The assumption that the universe is uniform, isn't this more of an assumption of uniformity over time given our observations represent a cross section of how things look over a very wide period of time? Does this also imply further assumptions about other properties and constants remaining, er, constant over that large window of time? Not explaining this well, but it seems we assume a lot about how the universe is 'now' based on many observations of points in the past. It's there enough 'stuff' that is 'nearby' aka 'recent' to mean this is a reasonable thing to do? David Campos David Campos 1 year ago 21:11 There is a chance that the Universe is expanding into dark matter, since there's so much of it. 1 Amir# Amir# 1 year ago Another good lecture on cosmology is by prof. Leonard Susskind in stanford university 11 joeflosion joeflosion 1 year ago 16:45 Sean Carroll is a cat guy confirmed. Damn do I hope to bump into you at a Flyers or Phillies or Sixers, hell even a Wildcats basketball game one day. I'd say God Bless, but since I know your deal, I'll just say I hope you have a great day Sean. Thank you for teaching me so much over the last few years. You've made a bigger impact in my life than you can ever imagine. 1 Nicholas Wallingford Nicholas Wallingford 1 year ago Leavitt wasn't using parallax to measure distances to Cepheid variables. She was cataloging stars in the Large Magellanic Cloud, and observed the relationship in the Cepheid variables there. Since all the stars in the Large Magellanic Cloud are all roughly the same distance away, she observed the relationship between period and APPARENT luminosity. James Morrris James Morrris 5 months ago Hubble gives me hope in humanity he started out a lawyer and became a scientist Chakradhar Mahapatra Chakradhar Mahapatra 1 year ago How natural is our universe? (A universe which is natural means that its laws are inevitable and predictable. An unnatural universe is one which is based on a peculiar permutation of the laws of nature, among the almost limitless possible permutations, which enables conditions in the universe to be conducive for life to arise and exist. A universe that is natural is knowable, at least theoretically. An unnatural universe is not knowable, since its laws are fine-tuned and do not make any logical sense). speculawyer speculawyer 1 year ago Can Einsteinian GR be reconciled with the standard model graviton? Jason Lee Jason Lee 1 year ago Thank you Sean Carroll!! David Hand David Hand 1 year ago Is it accurate to say that the motion of the expansion is not due to any force or acceleration? It doesn't make sense to get a reading on a perfect accelerometer, yet there is clearly a d2/dx2 x. Objective_Truth Objective_Truth 1 year ago (edited) Vacuum has energy, therefore our expanding universe is creating infinite amount of energy. Why? Because, if our universe is not embedded in a larger space and is expanding all by itself then it is creating infinite volume of vacuum for a long long time, perhaps a google years or longer. Does this sound right ? 2 Mark Calvo Mark Calvo 1 year ago Sean, At about 47.25 minutes you state that 2 photons colliding turns into an electron and positron. Is this fact? I think not. When two laser pointer beams or sunlight cross paths, nothing happens. No matter-antimatter annihilations occur to produce to new photons. I think your chart should show that when a neutrino and antineutrino collide they result in a conversion to electron and positron, and vice versa in reverse (photon absorb or release on collision). America Lost America Lost 1 year ago How can we say the universe is the same everywhere, when what's outside our visible horizons may be five times as big or a trillion billion...? Or infinite? J M Leaf J M Leaf 1 year ago (edited) Did not Hubble do something along the lines of the individual who took the picture of an eclipse proving an Einstein Theory? Hubble used a hypothesis developed by Henrietta Leavitt's period luminosity relation work. Did Einstein's photographer win a Nobel Prize? Big Bang? I thought LeMatre came earlier. Farooque Parvez Farooque Parvez 10 months ago wonderful ideas are sprinkling at us from such a great mind of our time........ I Z I Z 1 year ago (edited) I have a question of light. Let's think of the following experiment. A flash light in a closed room with walls made of mirrors. When the flashlight is turned off why don't photons continue to bounce around. Where do they go? Do they lose their energy, and disappear, what do they change to? This is by comparison to the light from the stars which travels so long from the moment they were emitted. Stumpy Mason Stumpy Mason 1 year ago I hope we all get theoretical physics degrees at the end of this series. 52 ROHIT ROHAN ROHIT ROHAN 1 year ago just amazing ❤️ 1 #science #physics #ideas The Biggest Ideas in the Universe | Q&A 22 - Cosmology 40,038 viewsAug 23, 2020 801 DISLIKE SHARE DOWNLOAD CLIP SAVE 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 #22, " Cosmology." We talk mostly about how the Friedmann equation works, and what the Big Bang really means. 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/playlist?list... Blog posts for the series: http://www.preposterousuniverse.com/b... Background image: https://www.spacetelescope.org/images... #science #physics #ideas #universe #learning #cosmology #philosophy 104 Comments rongmaw lin Add a comment... Boris Petrov Boris Petrov 1 year ago One can be only humbled by watching Sean Carroll so far 44 lectures (60-70 hours all together). His smooth and elegant delivery of complex concepts, including historical details and credits to past contributors, his personal "stands" on controversies, clear delineation of facts versus mere hypotheses --- all delivered with high scientific integrity -- are truly unparalleled. I learned a lot from this lectures, Sean's books and "Mindscape" interviews -- including just how little I know about theoretical physics. An immense pleasure so far and even greater gratitude and many thanks for your efforts. 18 Jim Donegan Jim Donegan 1 year ago Fantastic explanations. I think this is my fave video yet, having followed them all. I now realise that I have not understood universal expansion properly until now. Looking forward to whatever is next! 4 NightwindArcher NightwindArcher 1 year ago (edited) Wow, just wow. I love your work. You make everything so accessible. I am a prospective physics graduate student and I have been reading two of your books "Spacetime and Geometry" your GR textbook, and I've also been reading your popular book "Something deeply hidden". Love your content. 3 Quahntasy - Animating Universe Quahntasy - Animating Universe 1 year ago High quality content here. Keep em coming Sean 17 Paul C. Paul C. 1 year ago Thanks again Professor Sean, for providing something really worth watching on a Sunday evening. . . . Hope we’re not keeping you from church, ha, ha !! . . . BTW, if I could mention this again, what are your opinion(s) please, of Roger Penrose’s objections to Inflationary Cosmology ? Thanks. and best wishes from West Wales. 3 Jeremi Wieczorek Jeremi Wieczorek 1 year ago As always great lecture, thank you. I'm wandering if that magnetic dipol nature could be compared in a distant way to what happens when you separate two quarks away and doing so you apply enough energy to actually create new pairs out of gluon bond? Alan Myers Alan Myers 8 months ago This two-hour lecture by Professor Carroll is simply superb. Thank you! Hamoud Alwardy Hamoud Alwardy 1 year ago It is good that I can time travel within this video. Thanks Sean! Balazs Pandi Balazs Pandi 1 year ago Absolutely amazing! My mind is blown to pieces! Josh Hickman Josh Hickman 1 year ago I mean, inflation does sort of explain why entropy was small, in that the low-entropy state was extremely simple to describe. It's not entirely clear we will ever get any meaningful grip on questions like "why is there something as opposed to nothing?" but descriptively simple beginnings have something to recommend them. Elliot Williams Elliot Williams 1 year ago You’re a legend! Keep em coming. Rodrigo Castro Cordero Rodrigo Castro Cordero 1 year ago My Hypothesis: Vibrations that produce EM waves also produce Gravity Waves (perturbations). Photons released (EM waves) also produce a local gravity field (energy is equivalent to mass). Photon's gravity and the Gravity Waves "attract", hence the photons stick to the GW and travel with it (photons are glued to the GW and travel with it). It isn't the speed of light that is a universal or fundamental constant, it is the speed of GW that carries light. Light doesn't have the stature that GW has…If during inflation GW traveled faster then light traveled faster, Lorentz factor accommodates to speed of GW. John Długosz John Długosz 1 year ago Conservation of Energy: It appears to me that the rescaling of the universe is a conservative effect. That is, if you were to go back to the previous scale (e.g. reign in a section of the universe and make it scaled smaller) then the value of E would be restored to what it was when it was previously that scale. This means you can describe the scale factor has having a type of potential energy, that balances things. If the universe is open and does not re-collapse, then this never happens, but that doesn't change the principle. Is there a reason why we don't simply call it a form of potential energy? In GR all forms of energy, including potential (i.e. energy storage) affect the energy tensor. Here we're saying that a potential (source/sink to which E can be transferred) is outside the total E that affects curvature. In order to be excused from Noether's Theorem, we have to say that it's a change to the laws of the universe, rather than a change to the conditions within the universe. It is contradictory to say it's a change to the laws of the universe while writing equations that explain it: it's a law to *something*, and if that something is not "the universe" then we're just arguing semantics. by writing dE/dt = f(matter,spacetime) you are agreeing that E is dependent on the configuration (integrate both sides). This is what we ordinarily call "potential energy". We must say that the stress-energy tensor of GR simply does not include this form of energy, or is balanced by another term (involving the scaling factor) on the other side. Eugenius Bear Eugenius Bear 1 year ago (edited) So the CMB stems from the 2nd order kinetic energy density driving the accelerated expansion of a spherical universe. As the universe keeps expanding, this second order energy density per unit volume decreases. As the CMB drives toward zero, the accelerated expansion of the universe declines as well. Eventually the universe expands at a uniform rate. Andre Goran Andre Goran 1 year ago My explanation when I correct the statement "The universe came into existence" goes like this: For someone to come into the house, the house must first be present and devoid of that person. If a house is built around me, I acquire the property of being in it, but I never came into it. The universe similarly is in existence, but never came into it. Stay Primal Stay Primal 1 year ago (edited) Sean, one day, a new star will shine in the cat eye's nebula, and that new star will be Ariel, watching you Sean. PS : More seriously, thx you very much professor. 10 Isaac Ziskin Isaac Ziskin 1 year ago Prof Carroll, what are your thoughts on Prof Penrose's Conformal Cyclic Cosmology? I've been thinking about it a lot for the past few months and it seems like a beautiful solution to the smoothness of the CMB question without the need to introduce an inflaton field. Hannes Stärk Hannes Stärk 1 year ago (edited) Not really related but it is what I thought about and this is probably a good place to ask: Is there any argument against the possibility that space is quantized (maybe with the planck length) and that time is quantized? Thanks for any answers. Georg Wrede Georg Wrede 1 year ago (edited) Sorry to comment the wrong video, but earlier you talked about momentum and used Silly Putty in an example of inelastic collision. There is hardly any household substance that is /less/ appropriate for the purpose. I think you meant regular modelling clay. (Silly putty collides elastically, but turns to liquid when not stressed.) Thank you for an excellent series! Eugenius Bear Eugenius Bear 1 year ago (edited) Time itself is likely a derivative property of the universe that is governed by, for lack of a better term, the vacuum pressure of space. The vacuum pressure of space is what governs the flow of energy from field element to field element. Time is continuous at a level which we cannot sense, measure or "know", but becomes discrete and therefore "knowable" at the Plank scale where we can sense the transfer of energy from one field element to another. alan silverman alan silverman 1 year ago (edited) On the question about conservation of energy - the energy of the matter in the box is NOT constant...it's kinetic energy is decreasing with time as the expansion of the universe proceeds... Also, raisins and pennies are solid - galaxies are not. David Jordan David Jordan 1 year ago 57.21 "I'm not showing you what that equation is, it's a mess." I am a muscian , I like to listen to you while practicing. I like comedy but I don't don't like comedians in general. I don't know beans about equations. I think that was one of the greatest set ups for a punch line EVER! Almost an hour! I think you are hilarious. I am hoping that someone collects and edits your"inflation rants". Absolutely the best bit on inflation since Victor Borge. I hope there is some way he gets to hear it. He would have a great come back I am sure. Thanks so much for taking the time to make these things Chirality452 Chirality452 1 year ago I don't really see the problem with the idea that the entropy of the early universe was much lower than at present. Isn't this just a natural consequence of the Second Law of thermodynamics? Om3ga Om3ga 1 year ago find the best content here. Thanks Prof. Sean 3 David Hand David Hand 1 year ago To me, it would be a whole lot weirder if the initial state of the universe had all kinds of asymmetries and inhomogeneities. So why is everyone trying to tell me that there needs to be some sort of explanation for the homogeneity of the CMB? I don't get why it would be any other way. What would be the cause of the lumps you want to see? It makes no sense. Henrik Scheel Henrik Scheel 1 year ago You said that one knows the total amount of mass in the universe. So if the universe is inifinite it must be rather dense as we get further and further away. LV75RDM LV75RDM 1 year ago Is there a model where expansion is a volume (the universe) filling a void (space)? David Socha David Socha 1 year ago Hi! And thanks for you immense work. Can we explore the Hard Problem in science here? 👩🏽‍🚀🙈🙉 Cliff Hudson Cliff Hudson 1 year ago The easy conversational tone of these videos is probably the most profoundly useful piece of educational presentation I've ever had the pleasure of participating in. 3 apper cumstock apper cumstock 1 year ago For me this is the first time these topics get apparantly correctly explained....... Agustin Carvajal Agustin Carvajal 1 year ago Thank you so much for this content Eugenius Bear Eugenius Bear 1 year ago Shouldn't the most fundamental question in Physics be "Why is the speed of light limited?" I think it's the gateway to unlocking unification. Objective_Truth Objective_Truth 1 year ago Certain cosmology asserts that black hole will start new universe.. Given that only a tiny fraction of matter in our universe is captured by any black hole, does this cosmology assumes that the succeeding universes will get smaller and smaller until there is not enough matter left for next black hole formation? I wonder what was in the mind of those cosmologists. 1 Eugenius Bear Eugenius Bear 1 year ago If baryonic matter is itself comprised of animated or energetic dark matter, it wouldn't be capable of locally or "relatively" sensing the other dark matter that surrounds it. Its not until you view it at an aggregate level, far away from the observer (i.e. at the cosmological scale), that you can sense the composite effect of dark matter carrying energy that does not manifest itself as baryonic matter. . Jerry Elizondo Jerry Elizondo 1 year ago 58:50 "When I was your age" ... Sorry professor, you have never, ever been my age. When you get to be my age, I'll probably be dead. Anyway, thank you for your effort on educating us on the important things in the Universe. Rhonda Goodloe Rhonda Goodloe 1 year ago Sean, Thanks for another video! Rick Harold Rick Harold 1 year ago Cool! I’m expanding but not bcz of the universe ;-) Thanks for awesome lectures. Love these. LV75RDM LV75RDM 1 year ago Hypothetical question of Einstein, if Space = 0, and the Universe = 1, what, if any, would be the tensile strength of Space/Time? Taira Kirkland Taira Kirkland 1 year ago “Stephen Hawking, God, or the Wave Function of the Universe” is maybe my favourite thing you have said. 1 Gilbert ENGLER Gilbert ENGLER 1 year ago As usual: the best! 1 PrimatoFortunato PrimatoFortunato 1 year ago (edited) It’s funny how the q&a is just a way to use half as many natural numbers. They give rise to many more questions than were ever posed!! 😂 What do you mean the curvature of an infinite universe was infinitely small? Ahahahah, no wonder Lovecraft came up with understanding the ultimate truth as a way to lunacy in the 1920s Ginkgo Biloba Ginkgo Biloba 10 months ago The Universe is so cool and even cooling more! David David 1 year ago (edited) Sean, please invite Gisin to talk about INTUITIONISTIC MATH and physics on your podcat. Rust in Peace Rust in Peace 1 year ago Why would the early Universe have low entropy moving from a singularity, and a Blackhole be high entropy, moving forward in time, in the direction to the Blackholes singularity. Is it to do with the direction of time, even though time is considered to be emergent. Harry Nicholas Harry Nicholas 9 months ago can you do a talk about chantal's paradox one day? Ron Brideau Ron Brideau 1 year ago The Moon is moving out therefore our gravity well is flattening to more shallow shape, thus Brooklyn is expanding. 4.669 4.669 1 year ago So would the many world's still be branching if there were no humans? Would the branching happen in a static Universe? Henry J. Henry J. 1 year ago Why does the "size" of a black hole vary with mass? Why doesn't it simply shrink to a point? What's inside (matter wise). dollarsing dollarsing 1 year ago (edited) 16:50 "one quadrillionth of a plank time"? Um, I thought the plank time was the smallest there is. 1 Bat Daddy Mac Bat Daddy Mac 3 months ago Dark matter is a type of fabric that can be nothing and everything when met with dark energy the byproduct is gravity. Dark energy met with dark matters byproduct is time. Eugenius Bear Eugenius Bear 1 year ago (edited) Dr. Carroll, The Michelson Morley conclusions are built on two underlying assumptions which need to be re-examined. 1) That light is a discrete entity, distinct from the luminiferous aether which resists its motion. 2) the luminiferous aether is a static, UNIFORM field that extends throughout the universe in all directions. If light is not a discrete entity, apart from the aether, rather it is an energetic wave form that passes through the aether AND if aether is actually more fluid and is capable of having regional rotation that surrounds, for example, the experimental apparatus...well, then the null result from the experiment still makes sense. If we can get some respect for the aether, we can explain the rapid expansion of the universe and the relative uniformity of the CMB. We can also explain why light is both a wave and a particle and why the mass of that particle appears to be zero...but that is a separate issue. Battery9876 Battery9876 1 year ago Don't mess up with the equations Sean, or we'll be forced to beat the crap out of you lol! David Socha David Socha 1 year ago Black Hole: expention regulator! I love it. 👩🏽‍🚀🙈🙉 Tony D'Arcy Tony D'Arcy 1 year ago The Brooklyn Bridge might still be there, but the Hudson is likely to expand owing to global warming and rising sea levels ! Kevin Hanley Kevin Hanley 1 year ago Is the universe electrically charged? David Hand David Hand 1 year ago It's funny that we ask why the energy should be the same at two points in the horizon problem. I would ask why two things should be different. There is more information in an asymmetric universe than a perfectly uniform one. It's a higher entropy. More information needs more explanation. This has always seemed backwards to me. 2 Richard Sullivan Richard Sullivan 1 year ago Seriously Sean? "When I was your age..." Kids these days, sheesh. : ) CorwynGC CorwynGC 1 year ago One request, could you put the chapter number and such, before the series title, Youtube truncates it, and that makes it hard to find what one is looking for. Thanks. Mr. Aspy Mr. Aspy 1 year ago I wonder how many homeschoolers will come here for hair and cuticle lessons xD Tim M Tim M 1 year ago Anything beyond our viewable Universe doesn't exist until viewed or measured ? Robert Molldius Robert Molldius 1 year ago Thanx Mr Carroll 🙂👍 bluesmokerH1 bluesmokerH1 1 year ago My yellow submarine thesis went Nowhere! Very Good! MC Squared MC Squared 1 year ago (edited) If GR doesn't explain the Big Bang, why do you believe it can explain the fate of the Universe? If QM needs to be integrated with gravity, GR needs to be integrated with QM... This is preposterous... 😜 John Gruntfest John Gruntfest 1 year ago I put up with you - what a pleasure rink rink 1 year ago I feel blessed 1 Om Om 1 year ago You are genius sir 3 NWN NWN 1 year ago Problems with a WordPress-driven site? Well I never! Abhinav Srivastava Abhinav Srivastava 1 year ago if the hubble's constant changes then why we call it as a constant Robert Molldius Robert Molldius 1 year ago God or Stephen Hawking.. They are one! 😂😂 Alfred Zharoff Alfred Zharoff 1 year ago Last time I've been this early Electroweak was still a force! 5 Jurassic Fart Jurassic Fart 1 year ago Idk what cosmetology has to do with space but ok 1 Luan Babuza Luan Babuza 1 year ago 👏🏽👏🏽👏🏽 2 Jack CF Jack CF 1 year ago My favorite on so far. BTW: You haven't been 67 yet...... 1 Deep Recce Deep Recce 1 year ago Who spotted Friedmann Equation in the video? 🤭🤭 Mike Petersen Mike Petersen 1 year ago Yay! Haircut! :-) Milos Marinkovic Milos Marinkovic 1 year ago Don't worry, we're all friends by now... 1 Robert Molldius Robert Molldius 1 year ago "When i was in your age"..? 🤔😄😄 2 Youssef Youssef 1 year ago Thanks Patrick TAYLOR Patrick TAYLOR 1 year ago GeneRelativity Diego Valdes Diego Valdes 1 year ago ... Stephen hawking or God... Lol Christian Chapman Christian Chapman 1 year ago Ty Sean Madmacs FPV Madmacs FPV 1 year ago the north star........ Mark Callaghan Mark Callaghan 1 year ago Lawrence Krauss is misleading us ? 3