The Biggest Ideas in the Universe | Q&A 22 - Cosmology 

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.

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.

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.

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.

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!

*High quality content here. Keep em coming Sean*

Absolutely amazing! My mind is blown to pieces!

find the best content here. Thanks Prof. Sean

This two-hour lecture by Professor Carroll is simply superb. Thank you!

It is good that I can time travel within this video. Thanks Sean!

You are genius sir

As usual: the best!

A real pleasure to watch. SC makes a difficult subject fascinating to learn about. Great sense of humour, beautifully presented with just the right balance of basic ‘stuff’ and depth. Such a positive contribution to on line education. Thank you.

You’re a legend! Keep em coming.

Sean, Thanks for another video!

Thank you so much for this content

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.

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

The Universe is so cool and even cooling more!

For me this is the first time these topics get apparantly correctly explained.......

Thanx Mr Carroll 🙂👍

I feel blessed

“Stephen Hawking, God, or the Wave Function of the Universe” is maybe my favourite thing you have said.

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.

My yellow submarine thesis went Nowhere! Very Good!

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.

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.

Last time I've been this early Electroweak was still a force!

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.

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?

Ty Sean

Yay! Haircut! :-)

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!

Thanks

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.

Hi! And thanks for you immense work. Can we explore the Hard Problem in science here? 👩🏽‍🚀🙈🙉

You need a better example than the metal disk resting on the elastic membrane. The static friction provides a limiting value greater than zero for a tensioned membrane, although obviously very small, as you said. The vacuole is perhaps better, but this starts to appear like the entanglement phenomenon, not readily explicable in words. Thanks for these excellent discussions and elucidating presentations.

1:26:41 - This advice will prove highly appropriate, I claim. ^.^

One request, could you put the chapter number and such, before the series title, RU-vid truncates it, and that makes it hard to find what one is looking for. Thanks.

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. .

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.

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.

Sean, please invite Gisin to talk about INTUITIONISTIC MATH and physics on your podcat.

can you do a talk about chantal's paradox one day?

Black Hole: expention regulator! I love it. 👩🏽‍🚀🙈🙉

I put up with you - what a pleasure

The Moon is moving out therefore our gravity well is flattening to more shallow shape, thus Brooklyn is expanding.

Is there a model where expansion is a volume (the universe) filling a void (space)?

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.

So would the many world's still be branching if there were no humans? Would the branching happen in a static Universe?

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.

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.

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).

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.

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.

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.

Don't worry, we're all friends by now...

Hypothetical question of Einstein, if Space = 0, and the Universe = 1, what, if any, would be the tensile strength of Space/Time?

Cant find the list of videos with titles.. 48 videos and all with the same cover and intro, could not find specific one by the title..

👏🏽👏🏽👏🏽

Anything beyond our viewable Universe doesn't exist until viewed or measured ?

Don't mess up with the equations Sean, or we'll be forced to beat the crap out of you lol!

Is the universe electrically charged?

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.

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.

The Brooklyn Bridge might still be there, but the Hudson is likely to expand owing to global warming and rising sea levels !

if the hubble's constant changes then why we call it as a constant

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.

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?

Idk what cosmetology has to do with space but ok

Cool! I’m expanding but not bcz of the universe ;-) Thanks for awesome lectures. Love these.

I was confused over the Cephid variables.I listen out of interest and am not a science graduate.

Problems with a WordPress-driven site? Well I never!

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... 😜

"When i was in your age"..? 🤔😄😄

My favorite on so far. BTW: You haven't been 67 yet......

16:50 "one quadrillionth of a plank time"? Um, I thought the plank time was the smallest there is.

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.

Seriously Sean? "When I was your age..." Kids these days, sheesh. : )

Who spotted Friedmann Equation in the video? 🤭🤭

GeneRelativity

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

the north star........

I wonder how many homeschoolers will come here for hair and cuticle lessons xD

God or Stephen Hawking.. They are one! 😂😂

... Stephen hawking or God... Lol