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.