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The study of the large-scale structure, history, and future of the universe. Cosmology is about asking and answering questions about the "big picture" - the extent, origin, and fate of everything we know.

5
votes
1answer
Using the Kasner metric, given by $$ ds^2 = -dt^2 + \sum_{j=1}^D t^{2p_j}(dx^j) $$ it is possible to not only describe the cosmological expansion of some space directions (the ones with positive Kas …
asked Jun 12 '13 by Dilaton
5
votes
1answer
In his book "The Grand Design" on page 167-173 Stephen Hawking explains how one can get rid of the so called "time zero issue", meaning by this the very special initial state needed for inflation to w …
asked Feb 3 '12 by Dilaton
4
votes
1answer
, there is an idea that space is quantized. Would space expansion then be explained as the creation of new quanta in loop quantum cosmology? Or are there other different ideas, such as the quanta themselves changing properties? Do people actually working on this already have some interesting results? …
asked Dec 28 '11 by Dilaton
1
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explains in a very accessible way the formarly unsolved problems in cosmology and how thinking about them lead him to the idea of inflation. The many personal notes and experiences Alan Guth has included in …
answered Oct 25 '12 by Dilaton
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In addition to what John Rennie said, meaning by the number of dimensions the universe has the number of large dimensions, there are (yep somewhat wild) suggestions how the number of these could chang …
answered Nov 11 '12 by Dilaton
2
votes
1answer
If I understand this right the Ricci flow on a compact manifold given by $\partial g_{\mu \nu} = - 2R_{\mu \nu} + \frac{2}{n}\!R_{\alpha}^{\alpha} \,g_{\mu \nu}$ tends to expand negatively curved r …
asked Dec 11 '11 by Dilaton
1
vote
1answer
I recently got confused (and slightly annoyed by the lack of technical details) when reading a popular article (authored by Jonathan Feng and Mark Trodden) introducing the concept of super WIMPs. The …
asked Jun 23 '12 by Dilaton
5
votes
In string/M-theory, the multiverse corresponds to the number of different solutions to the dynamic equations. Each member of this multiverse is characterised by the specific way the space of the compa …
answered Dec 15 '12 by Dilaton
3
votes
1answer
Assuming a scenario of eternal inflation with a lot of "bubble universes" expanding, Lenny Susskind explains here that a potential signal of a collision of our universe with another bubble could be a …
asked Mar 3 '13 by Dilaton
12
votes
3answers
I`ve just stumbled about a sentence which says that high curvature of spacetime implies that any matter present is at high temperature. This somehow confuses me, so my probably dumb question(s) are: …
asked Mar 25 '12 by Dilaton
1
vote
0answers
I am just reading at the beginnin of this nice article, that axions could be responsible for spontaneously breaking of a symmetry in the early universe. Does anybody know which symmetry is alluded to …
asked Jul 3 '13 by Dilaton
4
votes
The inflating universe can for example be described by the FLRW metric $$ d\tau = dt^2-a(t)^2(dx^2 + dy^2 + dz^2)$$ The scale factor $a(t)$, which describes the expansion, is obtained from the appro …
answered Jan 6 '13 by Dilaton
2
votes
0answers
I've just reread chapter 11 of this book where it is explained among other things, that our four dimensional universe could be unstable concerning a decompactification transition, since potential ener …
asked Nov 11 '12 by Dilaton
1
vote
1answer
In this article discussing this and related papers, it is explained among other things, how the neighborhood of an observer's worldline can be approximated by a region of Minkowsky spacetime. If I u …
asked Apr 6 '13 by Dilaton
10
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7answers
what firewalls are used for in cosmology? What do they have to do with black holes and how are they related to complementarity? Edit to include followup questions From just reading the abstracts of …
asked Sep 22 '12 by Dilaton