Comments on: CERN Lectures on Cosmology and Particle Physics

By: Phillip Helbig

Phillip Helbig — Wed, 02 Nov 2011 17:54:55 +0000

@27: No, it is not limited to this interval. In fact, one can sometimes travel around such a universe and return to one’s starting position (but only if a) it doesn’t recollapse first and b) it doesn’t expand too quickly). As the old joke goes, if you look hard enough, you can see the back of your head. If you look even harder, you can see Uranus.

By: ZLN

ZLN — Wed, 02 Nov 2011 00:58:26 +0000

Suppose we do the naive integral for the vacuum energy, but pick a k_max such that I get the 1e-3 eV, what is the value of that k_max?

By: HK

HK — Thu, 20 Oct 2011 20:44:49 +0000

@Jensen (20) – Sean recorded a series of lectures called Dark Matter, Dark Energy: The Dark Side of the Universe for the Teaching Company (which is actually how I first learned about him). As the title suggests, the focus is certainly around the dark stuff, but the lectures also cover a lot of the general cosmology topics that he’s referencing and explaining in these CERN videos. I have zero formal training in physics, astrophysics, or cosmology (just a healthy interest and some math background), and was able to follow along quite easily with maybe a little bit of rewinding necessary. The lectures are aimed at a popular audience, so not as many specific ‘industry’ references or examples that were in the CERN lectures, and may be something to look into given your comments…

Cheers,
HK

By: Shantanu

Shantanu — Mon, 17 Oct 2011 12:08:48 +0000

Sean ,what do you think of this paper on Dirac-Milne universe?
http://arxiv.org/abs/1110.3054

By: James

James — Mon, 17 Oct 2011 10:01:32 +0000

Hi Sean, great lectures as ever.

Can I ask a question about global topology?

We describe an FRW universe with positive spatial curvature as “closed”, as it has the metric of a three-sphere, but I want to know what this actually means. We derive the three-sphere metric by changing coordinates from r to χ, where χ = Sin(r). Is χ not limited to the interval [0,π/2), since beyond that we are simply reproducing the same r? In which case, is the universe not really one “hemi-threesphere” and not closed in the same way as a full sphere is?

You state in your book that the “only possible global structure is the complete three-sphere”, but you don’t go into why.

The book, btw, is excellent (I particularly enjoy the time you spent at the beginning going into diff. geometry etc, although I still don’t quite get the link, other than notational, between differential forms and integral measures, such that we can integrate p-forms as if they were ordinary integrals).

By: Baby Bones

Baby Bones — Mon, 17 Oct 2011 06:31:56 +0000

Thanks Sean. I watched the first lecture and it was very informative for me since it harkened back to an astrophysics class I took in my fourth year of university.

By: An Introduction to Cosmology by Sean Carroll | CourseKeeper.com

An Introduction to Cosmology by Sean Carroll | CourseKeeper.com — Mon, 17 Oct 2011 05:01:24 +0000

[...] and the Early Universe, and Inflation and Beyond. The lectures (all nicely packaged together at Cosmic Variance) will appear in the Physics Section of our collection of Free Courses Online. You may also want to [...]

By: Phil

Phil — Mon, 17 Oct 2011 04:15:20 +0000

I haven’t watched the lectures yet, but I sure hope you mentioned that Catholic priest, Monsignor Georges Henri Joseph Édouard Lemaître, was the first to propose the Big Bang theory origin of the universe, and preceded Hubble in deriving Hubble’s Law in 1927.

By: Yair

Yair — Sun, 16 Oct 2011 21:33:21 +0000

Wow. The breadth, The Clarity, The Perspective.
Many thanks for bringing the lectures to our attention.

By: Phil h

Phil h — Sun, 16 Oct 2011 12:18:02 +0000

I think there’s an error on the 5th lecture in terms of the history of science. You claim inflation was created to solve the horizon and flatness problem. Yet in Alan Guth’s book “The Inflationary Universe” he claims that inflation was actually motivated by the monopole problem. It was only afterwards that it was realised that it solves other cosmological problems.

By: FmsRse12

FmsRse12 — Sat, 15 Oct 2011 21:03:03 +0000

I have always wondered why we can’t explain galaxy rotation curve as a result of “screening” phenomenon of some sort with some characteristic screening distance……then maybe it’s possible for stars to move at constant speed over large distances from the center of galaxy …..or galaxy wouldn’t hold together if we do this???

By: Jens

Jens — Fri, 14 Oct 2011 21:46:03 +0000

I can honestly say that 15 minutes into your talks I was lost. You spouted in-the-know jargon like a con-artist!

Sean, I have an M.S degree in electronics. I love science and everything we are discovering. But I often don’t understand what you say, as much as I want to. Have you ever thought about “dumbing down” your lectures or your posts? At least to the degree that us slobs not versed in the gargon could still be enlightened?

By: Heb je even tijd voor Sean Carroll?

Heb je even tijd voor Sean Carroll? — Fri, 14 Oct 2011 18:54:04 +0000

[...] Cosmic Variance. Deel deze blog:EmailPrintFacebookShareStumbleUponRedditDigg Gerelateerde Astroblog:Heb je ook [...]

By: CERN Lectures on Cosmology and Particle Physics | Undertow851

CERN Lectures on Cosmology and Particle Physics | Undertow851 — Fri, 14 Oct 2011 17:58:06 +0000

[...] Source: Cosmic Variance [...]

By: Jimbo

Jimbo — Fri, 14 Oct 2011 16:51:26 +0000

Sean,
Wonderful lex ! I am taking a course in the early universe & these are an immense help. Best of all is that the vids forego factors O(1), concentrating on concepts, but the TASI lex fill in those details. Primo.

By: Sean

Sean — Fri, 14 Oct 2011 15:45:19 +0000

I don’t know. You might leave a comment on the YouTube page.

By: Shantanu

Shantanu — Fri, 14 Oct 2011 13:38:47 +0000

Sean , are all CERN lectures on youtube? CERN has a great collection of videos, but its very hard to search for them.
shantanu

By: Paul Stankus

Paul Stankus — Fri, 14 Oct 2011 03:04:24 +0000

Is there room here for friendly competition? Though I’m not nearly at Sean’s level as an expert I delivered a 5-lecture series on intro cosmology for physicists in 2007, which was pretty well received. The video is publicly available, though in an obscure location. Interestingly, completely unknown to me someone picked up one of the segments, edited it down a bit and re-posed it on YouTube. It’s ten minutes long, taken from the section on “Why Brooklyn Is Not Expanding,” pivoting off from a classic bit in an old Woody Allen movie. The reposted segment is here: http://www.youtube.com/watch?v=hLhl2MSQ1R0

If the public demands it, I can link to the whole series, or maybe even get them up on the ‘Tube. ** End of self-promotional announcement **

By: Charlie

Charlie — Thu, 13 Oct 2011 19:56:54 +0000

Thanks! That’s a satisfyingly small number. I can see that the difference between a mm and the universe isn’t much to a number like that.

By: Sean

Sean — Thu, 13 Oct 2011 19:17:25 +0000

Charlie-- the rate of a fluctuation that would take you from our current vacuum "1" to some inflationary state "2" is essentially exp(S₂-S₁), where "exp" means exponential and S_i is the entropy of vacuum state i. In fact the entropy of the inflationary state is so much tinier than the entropy of ours that this is basically equal to exp(-S₁). The entropy of our current state is approximately S₁ = 10¹²⁰, so the rate is about exp(-10¹²⁰). If you play around a bit you can convince yourself that the units don't really matter -- per Planck volume per Planck time is basically the same as per Hubble volume per Hubble time on these scales.