The Biggest Ideas in the Universe | 22. Cosmology 

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.

One of the greatest communicators and ambassador of physics and cosmology since Carl Sagan.

Sean..Your content will be counted as a treasure as this playlist matures ❤❤

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!

Sean you have been very very productive lately. I think that about 60% of my online listening is content of yours.

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

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.

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.

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".

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!)

I love this series! Half of what he says goes way over my head. The other half goes way, way over my head.

Thanks for taking the time to do this. I've really learned a lot.

Absolutely fantastic summary! Congratulations. Never stop giving these lectures.

"The Best Content" Amazing series going on Thank you so much Prof.Carroll

I love how Sean is just a bust floating in space. Like a Boltzmann Bust

How have I not found this channel until now?! Brilliant content, sir! 😊👍

As someone whose loved physics my entire life yet never pursued an education or career in that direction it’s greatly appreciated you take the time to educate us. Shows how passionate you are for this. Thank you.

I taught this man everything he knows, and now I can't even get him to send me an autographed-copy of _The_ _Biggest_ _Ideas_ _in_ _the_ _Universe._ Back during his "Swiss Patent Clerk" days, I remember when he used to believe that Noether's Theorem had something to do with disproving the luminiferous aether and that "cosmology" was the study and application of beauty treatment. He was an okay student, and I'm very proud of him. I want that book now!

The fact that you can put those equations into words and vise versa off the top of your head speaks to your understanding of the subject matter. Pretty impressive. Thanks for the insights and not talking down to us. I find the mathamatics essential to understanding physics.

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"

Thank you so much for this amazing series. Are you going to make videos about "String Theory" and/or "Loop Quantum Gravity"?

Thank you Dr Carroll for that summary of the history of the universe based on temperature scale! Such a fantastic & understandable framework to connect all the major events! And the impact of dark matter on the temperature perturbations! Also fantastic!

Another good lecture on cosmology is by prof. Leonard Susskind in stanford university

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.

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!!!! :) ).

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 RU-vid 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.

What an absolutely wonderful lecture. er, I mean Video.

I always knew that doing SOME exercise was infinitely more than none . Now I have mathematical proof . Thank you prof . Carroll . ♥️ from 🇨🇦

I miss this series, they were really good

I hope we all get theoretical physics degrees at the end of this series.

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.

Perfect for falling sleep at night! Thanks

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

This connection between dark matter and the scale deviations of the CMB.... a dynamite explanation. 1:46:38

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.

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.

22:02 I like to think that EVERY point is the "center" of the Universe. Under this perspective, the Big Bang happened everywhere. Also, under this perspective, each person can be said to be "The Center of the Universe."

What if Ariel knew more about Cosmology than we thought ?

Thank you very much for taking the time to produce these outstanding videos.

An excellent speaker and so so sharp. Your intelligence fascinates me sir.

The universe is amazing

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.

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 ?

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.

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.

Oh my. If studying stars is this messy, some galaxies must be Messier.

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.

1:56:10 - Thank you Professor! ^.^

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.

These videos sustain me.

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.

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.

Thank you for explaining the modified gravity theory, there are some dubious other you tubers

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

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?

Thanks Sean for the making of this videos!

When do sapiens drop the whole big bang idea? Redshift observed is just a gravitational distortion. Not only are light paths bent by gravity, frequency is stretched over time.

Fantastic stuff Sean...thank you!

16:45 Cat has a question.

My cat likes Astrology so I put him in a box. Now I don’t know what he thinks. Ah he got out !

I had been waiting for this video for a long time… Glad to see it. 😇

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?

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.

I love your stuff ~ pity about the multiverser..Everett Song

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?

Awesome. Love these lectures.

There is something really sexy about Sean Carroll.

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?

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).

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.

This was really a good video. Thank you so much.

1:20:00 I don't like the term "make fun of", and I don't see why anybody whose ever been on the receiving end of a bully would. I always replace it with "ridicule", to promote a more accurate connotation. But, in the case of _recombination_ , I would have to go with "make light of". (Note: That's a pun, if you don't realize)

FINALLY!!! Enough said.

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.

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.

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?

Amazing content. Much appreciated.

Won’t lie super complex but for a non physicist that never took physics this is pretty interesting.

Q: Does the mass of particles also vary with the temperature of the universe? 1:09:30

Finally getting around to listening your podcasts while I’m at work, love you talking about cosmology but hearing your input on politics and gender roles and other topics is amazing too. You’ve got a nice way of thinking, and a very nice way of conveying those thoughts. Much thanks to your wife for that, I hope y’all are staying happy and healthy. I do have a question, I know it won’t have a definite answer though. I’d just like to know your thoughts about time, like if you think it’s intrinsic to the state of being itself, as in the state of existing fundamentally requires a dimension of time, or if you think the universe had a real starting point within a larger Universe that contains a multiverse. Thank you for all the content ❤️

so wonderful! thank you again!!!!

Thank you Sean Carroll!!

As usually, thank you sir!

Awesome

What about the galaxies that are the leading galaxies ie. the ones furtherst away, they have no other galaxies on the one side from them?

Is there a time dilation or Lorentz contraction for objects at great distances, as there is for objects traveling at great difference of speed?

Wonderful! Thank you!!

How does it must be feeling being first human to know something so big like Hubble figured of big universe or of expanding universe

Your vlogs are fascinating.

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?

When Carroll speaks about "rapidly moving particles", in what rest frame is that measured? Relativity theory does away with the "fixed stars" of Newton.

DM is 5x matter, so why doesn’t it dominate the cmb spectrum and completely wipe out the matter contribution?

just amazing ❤️

8 min oleber's paradox, volumetrics nolocal nodal geodesics, brownian motion isnt Brownian motion, the convection zones in Suns to give their frequency of magnstroms... the rise and fall of the nile.

Semantics: U expands into existence? 45:25 pan clang sound (meal prepared?)

I've recently come to the conclusion that, altho the CMB is indeed a record of the time soon after the big bang whe the usiverse cooled to below plasma temperature, since then there has been so much star, galaxy and planetatry formation that the thermal signature of so much molecular chemistry that has also been red-shifted to microwave levels,;the fine-structure of the ripples in CMB are so washed out that there's nothing it can reliably say about cosmogenesis.

quibble: the concept of 'win' 58:34 requires a sort of observer/judge, who by virtue of the need for such a thing, throws off any meaningful understanding of the whole shooting match... (Didi: is there a cat in that box? Gogo: I don't know...shall we look?)

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.

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?

At around 54:00 the question is posed "could it be that some galaxies are made of matter and others are made of antimatter" and your answer was roughly "unlikely, as we should then be able to observe radiation from deep space where stray particles originating from a galaxy and an 'antigalaxy' collide". A follow up question I then have is: what about the possibility that these antimatter pockets might all be outside of the observable universe? Could it be that we are just deep enough inside a pocket of matter that we cannot observe the matter/antimatter interface?"