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.
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.
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!
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.
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"
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.
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.
Denis Goddard Lol, I laughed at this. jsk, he explained in an earlier video in the Biggest Ideas in the Universe series. The last 2 Big Ideas were recorded before he got it formalized(cut).
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.
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.
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.
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!
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 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)
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!
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
Inverse proportional would mean that teacher that has great knowledge of the subject and with a high pedagogical aptitude is unable to pass knowledge to a highly gifted student, but a teacher with low skills would be successful in bringing the same student to a high level of understanding the subject. But that is not quite right is it? The relation between teacher skill and student ability, in regards of successfully passing the knowledge can only be direct linear.
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 UA-cam 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.
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".
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
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.
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.
Ha. A Carl Sagan vid clip popped up on my youtube algorithm earlier today. Last night I watched a Freeman Dyson video & a Richard Feynman interview a couple days ago. I'm glad other people enjoying these as much as I am. Lol😹
Universe? Uni-verse? Hardly! It’s a novel at least; an epic, Opera, Trilogy, or Film series. And uni? Only one? Certainly multi is more likely, or at least a duet? So there is no universe, it’s a multopera! A Deutrilogy? A novel Multepic? C’mon, folks! Think outside the bun!
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.
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.
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
Yeah Lenny is Amazing so is Sean; though Seans lecture here is less mathematical and for a wider audience. Heres one that while has math doesn't use too much technical stuff ua-cam.com/video/saf-1OZrVh4/v-deo.html theres 3 parts to it.
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!!!! :) ).
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).
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.
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.
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."
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! :-)
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.
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.
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.)
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.
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?
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.
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.
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
overlaps---> gaps and symmetries, eqn to predict symmetry breaking outcome, even for spontaneous symm breaking, outcome can already be know, like kicking an acorn, or a [ine cone, and knowing which way each vertex will point before even kicking it. like called cards and dice, translated into book words, translated into heard convos in public domain while flipping pages in a boiok synched.
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?
Good point. The fine structure constant is independent of the scale of space (it does not reduce when the scale increases). Is that correct? H ~ 2 x 10^-18 m/s at 1 meter.
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.
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 ?
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).
As someone here said Susskinds Lectures on relativity are really good. Ive watched all of em multiple times. The ones on cosmology too. In this channel theres some stuff ua-cam.com/video/saf-1OZrVh4/v-deo.html And Sean has a real good introductory to advanced book thats used in many universities to introduce the subject. Also recomend PBS spacetime. you need many sources to learn relativity. Its not easy subject.
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.
Physicists are lame anyway, they are practically mathematicians. No real urge to understand, and make sense of the fundamental stuff in this world. All they want is to calculate.
@@nafnist ? What exactly do You mean by "understand" ? And what group of people (if any) do You think are in pursuit of "understanding and making sense of the fundamental stuff in this world" ? Best regard.
nafnist There is no way to deeply understand the universe without the calculations. The quantification of the universe and its concepts is the only way to break through the biased lens of human perception and get a real glimpse at objective reality. I have a feeling you simply can’t handle the math and so you lash out against it altogether, like a child throwing a tantrum. Nice.
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
The "cosmological constant" is a factor in the equation, put in before there was any physics for it to correspond to. "Dark Energy" is the physics that was discovered in 1995, and it uses a non-zero value of the C.C. to describe its effects. It's like, "what's the difference between momentum in the lab and the symbol rho in the formula?" Another thing, Sean gave only the modern writing of Lambda. I believe Einstein's original C.C. was written on the other side of the equation. That is, do you interpret it as a fudge factor in the curvature of spacetime, or something _in_ spacetime that contributes to the total energy of a region? If you look at the Wikipedia page, you'll see that D.E. being the C.C. is just one possibility.
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.
@@wavydaveyparker I mean, it will give you an average value, but it doesn't fit the curve perfectly. The actual curve looks more like an x^3 curve when you look at it - up, saddlepoint and then continues up. But I don't know how to tell Excel to calculate that. :o) Also: This is for ordinary episodes, not Q&A episodes.
@@wavydaveyparker No, you put in the episode number for _x_, and out pops the episode length. Actually, I managed to get a polynomial. t(s) = 1,81x^3-65,15x^2+808,31x+1124,4, where t (s) is episode length in seconds and x is episode number.
22:20 ish, and forgive my ignorance here, but I understand that you are making the relativity point here, but if we were to be looking at the universe in its entirety, doesn't there by definition HAVE to be a center if everything is expanding at a constant rate as a whole. I may be missing something here, would love to be informed on this. Thanks for these videos, this series has been AMAZING!
Not every geometry needs to have a center, expansion or not. For example, there is no center point on the surface on a sphere, nor in a flat torus. Since the expansion is not an acceleration through space, there is no way to locally detect is as motion. If you were to define the universe in a more Newtonian way, then you might end up using a static background grid of space to plot out motion of galaxies and find an apparent center, but that grid is not physically real. You could just define a center into existence wherever you like just by choosing that grid. If you are taking into account that the space itself is expanding, and that the expansion looks the same no matter where you start looking, that apparent center goes away.
If you know the most basic cosmology 2d spacetime model youd not ask this question. You draw an x t coordinate axis. the x=constant lines are worldlines of galaxies (wlg )if you draw a t=0 vector it points between two of these (wlg) and the length of this vector is a(t) as t changes the distance changes equally between any two wlg that started at same distance and theres no spatial center to this. If you have an infinite forest of trees wheres the center. Nowhere. Wheres the center of an infinite plane Nowhere the is none or evrywhere every point can be center.
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.
I love how Sean is just a bust floating in space. Like a Boltzmann Bust
Two years later and I still love coming back onto these. ❤
We can come back 5 years or 10 years and still be amazed.
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.
It's just amazing how knowledgeable Sean Carroll is and how well he presents complex stuff in an understandable way.
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!
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.
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"
good point
i like the balloon analogy also. flatland but not flat
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.
He’s awesome, his books are something special....
Isn't it weird to have a friend who knows nothing about you? lol
You’re not alone ;)
@@Psnym Wouldn't it be "he's not alone"?
Jeff Bass *we’re* not alone!
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.
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.
Sean..Your content will be counted as a treasure as this playlist matures ❤❤
Sean: Cosmological Principle... homogeneous and isotopic...
Me: DUDE! Did you finally get a haircut?!
Denis Goddard Lol, I laughed at this. jsk, he explained in an earlier video in the Biggest Ideas in the Universe series. The last 2 Big Ideas were recorded before he got it formalized(cut).
@@adhdasian1896 renormalized
@@Psnym The Cosmological constant is a well known fixture of the Universe.
Fascinating,Sean keep it coming.
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.
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.
I love this series! Half of what he says goes way over my head. The other half goes way, way over my head.
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.
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!
Absolutely fantastic summary! Congratulations. Never stop giving these lectures.
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 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)
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!
Hmm, perhaps the limit as ego goes to infinity sets the boundary condition for book transmission?
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
Excellent comment
Making it simple is not easy......
Copyright that
Or as Steve Jobs puts it: Simplicity is the ultimate sophistication 😉
Inverse proportional would mean that teacher that has great knowledge of the subject and with a high pedagogical aptitude is unable to pass knowledge to a highly gifted student, but a teacher with low skills would be successful in bringing the same student to a high level of understanding the subject.
But that is not quite right is it?
The relation between teacher skill and student ability, in regards of successfully passing the knowledge can only be direct linear.
"The Best Content"
Amazing series going on
Thank you so much Prof.Carroll
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 UA-cam 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.
How have I not found this channel until now?! Brilliant content, sir! 😊👍
Sean you have been very very productive lately. I think that about 60% of my online listening is content of yours.
Exciting!!!
Prove it.
Same for me.
sundial is only possible on a flat earth. They have lied to us.
And 40% is pornhub
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".
Thanks for taking the time to do this. I've really learned a lot.
nice hippo
yeah. it looks like a really really good hippo
Sean Carroll, the Bob Ross of science
Brilliant, very lucid and balanced exposition.
The universe must be energy, because it doesn’t matter
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
Made up. It didn't even sound cool either...
@@josephhall5681 hello there little troll, aren't you cute...
Lol.
Well Sean Carrol does have quite the soothing voice.
I fall asleep listening to these every night for a month Atleast lok
I always knew that doing SOME exercise was infinitely more than none . Now I have mathematical proof . Thank you prof . Carroll . ♥️ from 🇨🇦
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.
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.
wonderful ideas are sprinkling at us from such a great mind of our time........
Thank you so much for this amazing series. Are you going to make videos about "String Theory" and/or "Loop Quantum Gravity"?
"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
LOL!
Ha. A Carl Sagan vid clip popped up on my youtube algorithm earlier today. Last night I watched a Freeman Dyson video & a Richard Feynman interview a couple days ago. I'm glad other people enjoying these as much as I am. Lol😹
Universe? Uni-verse? Hardly! It’s a novel at least; an epic, Opera, Trilogy, or Film series. And uni? Only one? Certainly multi is more likely, or at least a duet? So there is no universe, it’s a multopera! A Deutrilogy? A novel Multepic?
C’mon, folks! Think outside the bun!
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.
What an absolutely wonderful lecture. er, I mean Video.
"Lecture in disguise"
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.
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
Another good lecture on cosmology is by prof. Leonard Susskind in stanford university
Yeah Lenny is Amazing so is Sean; though Seans lecture here is less mathematical and for a wider audience. Heres one that while has math
doesn't use too much technical stuff ua-cam.com/video/saf-1OZrVh4/v-deo.html theres 3 parts to it.
An excellent speaker and so so sharp. Your intelligence fascinates me sir.
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!!!! :) ).
Thank you very much for taking the time to produce these outstanding videos.
0:49 My new favourite phrase is "the universe is the ultimate spherical cow."
I’m just waiting for a new series of lectures, Seannnnnnn
Perfect for falling sleep at night! Thanks
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).
I don’t love analogies in general myself but I challenge anyone to show me the direct center of a loaf of bread.😂❤
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.
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.
This connection between dark matter and the scale deviations of the CMB.... a dynamite explanation. 1:46:38
Thanks Sean for the making of this videos!
"We're gonna predict it, we're gonna get it wrong, and we're gonna fix it". 1:31:05 Classic!
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."
I miss this series, they were really good
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! :-)
Hubble gives me hope in humanity he started out a lawyer and became a scientist
This is a truly great series because of so many interesting topics. Are Axions a possible source of dark matter in the early universe?
Oh my. If studying stars is this messy, some galaxies must be Messier.
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.
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.
This was really a good video. Thank you so much.
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.)
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.
I had been waiting for this video for a long time… Glad to see it. 😇
yeah man i love good precise explanation that dont skimp on the math
Fantastic stuff Sean...thank you!
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.
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?
yes for sure we will be able to do this
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.
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.
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
overlaps---> gaps and symmetries, eqn to predict symmetry breaking outcome, even for spontaneous symm breaking, outcome can already be know, like kicking an acorn, or a [ine cone, and knowing which way each vertex will point before even kicking it. like called cards and dice, translated into book words, translated into heard convos in public domain while flipping pages in a boiok synched.
Amazing content. Much appreciated.
Yeah man i love cosmology and math
Awesome. Love these lectures.
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?
Good point. The fine structure constant is independent of the scale of space (it does not reduce when the scale increases). Is that correct?
H ~ 2 x 10^-18 m/s at 1 meter.
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.
excelllent video, matter is what we and the stars are!
Thank you Sean Carroll!!
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 ?
Dont know what to tell you cuz as I understand it from something I read energy conservation can be violated in general relativity
I love your stuff ~ pity about the multiverser..Everett Song
What if Ariel knew more about Cosmology than we thought ?
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).
Prof. Sean Carroll isn't there going to be any video on Relativity? By the way, love your videos
Look up the Gravity episode. Lots of stuff about general relativity there.
As someone here said Susskinds Lectures on relativity are really good. Ive watched all of em multiple times. The ones on cosmology too. In this channel theres some stuff ua-cam.com/video/saf-1OZrVh4/v-deo.html
And Sean has a real good introductory to advanced book thats used in many universities to introduce the subject. Also recomend PBS spacetime. you need many sources to learn relativity. Its not easy subject.
Your vlogs are fascinating.
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.
1:56:10 - Thank you Professor! ^.^
Carroll's Theorem: All parallelograms tilt to the right.
That way they look like Tennessee.
@@beenaplumber8379 uuhb bb ubbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbububybbbbbbbbbybubbbbbbbbnbnbbbbbnbnrnnnnnnnnnn
@@beenaplumber8379 uuhb bb ubbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbububybbbbbbbbbybubbbbbbbbnbnbbbbbnbnrnnnnnnnnnn
Both you and they are right
I hope we all get theoretical physics degrees at the end of this series.
Only if you do the associated mathematics.
Physicists are lame anyway, they are practically mathematicians.
No real urge to understand, and make sense of the fundamental stuff in this world.
All they want is to calculate.
@@nafnist ?
What exactly do You mean by "understand" ?
And what group of people (if any) do You think are in pursuit of "understanding and making sense of the fundamental stuff in this world" ?
Best regard.
@@mrdr9534 Shut up and calculate
nafnist There is no way to deeply understand the universe without the calculations. The quantification of the universe and its concepts is the only way to break through the biased lens of human perception and get a real glimpse at objective reality. I have a feeling you simply can’t handle the math and so you lash out against it altogether, like a child throwing a tantrum. Nice.
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
The "cosmological constant" is a factor in the equation, put in before there was any physics for it to correspond to. "Dark Energy" is the physics that was discovered in 1995, and it uses a non-zero value of the C.C. to describe its effects.
It's like, "what's the difference between momentum in the lab and the symbol rho in the formula?"
Another thing, Sean gave only the modern writing of Lambda. I believe Einstein's original C.C. was written on the other side of the equation. That is, do you interpret it as a fudge factor in the curvature of spacetime, or something _in_ spacetime that contributes to the total energy of a region?
If you look at the Wikipedia page, you'll see that D.E. being the C.C. is just one possibility.
Wonderful! Thank you!!
Sean Carroll is not a salesman. Respect. Hate my salesman job
Although he does love a good sales pitch.
Thank you for explaining the modified gravity theory, there are some dubious other you tubers
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.
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).
@@wavydaveyparker I mean, it will give you an average value, but it doesn't fit the curve perfectly. The actual curve looks more like an x^3 curve when you look at it - up, saddlepoint and then continues up. But I don't know how to tell Excel to calculate that. :o)
Also: This is for ordinary episodes, not Q&A episodes.
@@wavydaveyparker No, you put in the episode number for _x_, and out pops the episode length.
Actually, I managed to get a polynomial. t(s) = 1,81x^3-65,15x^2+808,31x+1124,4, where t (s) is episode length in seconds and x is episode number.
so wonderful! thank you again!!!!
Class, loved this video great discussion of dark matter.
22:20 ish, and forgive my ignorance here, but I understand that you are making the relativity point here, but if we were to be looking at the universe in its entirety, doesn't there by definition HAVE to be a center if everything is expanding at a constant rate as a whole. I may be missing something here, would love to be informed on this. Thanks for these videos, this series has been AMAZING!
Not every geometry needs to have a center, expansion or not. For example, there is no center point on the surface on a sphere, nor in a flat torus. Since the expansion is not an acceleration through space, there is no way to locally detect is as motion. If you were to define the universe in a more Newtonian way, then you might end up using a static background grid of space to plot out motion of galaxies and find an apparent center, but that grid is not physically real. You could just define a center into existence wherever you like just by choosing that grid. If you are taking into account that the space itself is expanding, and that the expansion looks the same no matter where you start looking, that apparent center goes away.
Ben Marolt thank you!
If you know the most basic cosmology 2d spacetime model youd not ask this question. You draw an x t coordinate axis. the x=constant lines are worldlines of galaxies (wlg )if you draw a t=0 vector it points between two of these (wlg) and the length of this vector is a(t) as t changes the distance changes equally between any two wlg that started at same distance and theres no spatial center to this. If you have an infinite forest of trees wheres the center. Nowhere. Wheres the center of an infinite plane Nowhere the is none or evrywhere every point can be center.