Reputation
7,041
Next privilege 10,000 Rep.
Access moderator tools
Badges
22 55
Newest
 Nice Answer
Impact
~60k people reached

  • 0 posts edited
  • 0 helpful flags
  • 132 votes cast
Sep
7
comment Is there any relationship between Gravity and Electromagnetism?
@DImension10, thanks for the feedback. I just went through that entry again and expanded a bit more here and there. For instance the Examples-section now has a new subsection "Cascades of KK-reductions from holographic boundaries" ncatlab.org/nlab/show/… .
Sep
4
comment Is there any relationship between Gravity and Electromagnetism?
ncatlab.org/nlab/show/Kaluza-Klein+mechanism
Sep
2
comment Calabi-Yau manifolds and compactification of extra dimensions in M-theory
See on the nLab at ncatlab.org/nlab/show/M-theory+on+G2-manifolds
Sep
2
awarded  Announcer
Sep
1
comment What are the details of the renormalization of Chern-Simons theory?
Not sure what you mean. (Out of date?? And of course there is Chern-Simons in the book, see the explicit links above.) But let's leave it at that. Maybe somebody else has what you are after.
Sep
1
comment What are the details of the renormalization of Chern-Simons theory?
John, maybe renormalization as such is not for beginners? I think Costello's account is about the best that there is. A beginner might take it as incentive to study and learn more and eventually cease to be a beginner and become an expert.
Aug
31
answered Why quantum mechanics?
Aug
30
answered Why one-dimensional strings, but not higher-dimensional shells/membranes?
Aug
30
comment Why one-dimensional strings, but not higher-dimensional shells/membranes?
More commented references on membrane/M2-brane physics are here: ncatlab.org/nlab/show/M2-brane
Aug
29
revised What are the details of the renormalization of Chern-Simons theory?
added 196 characters in body
Aug
29
answered What are the details of the renormalization of Chern-Simons theory?
Aug
28
awarded  Nice Question
Aug
28
comment What is Mathematical formulation of entropic Gravitational force?
...is another question. And an ill-defined one, to my mind.
Aug
28
comment What is Mathematical formulation of entropic Gravitational force?
@Guest: what these replies are trying to say is that this idea is very vague and hence has no mathematical formulation. I wish it had a physical formulation. The best there is maybe is Ted Jacobson's derivation of the Einstein's equations from the assumption that horizon areas are proportonal to entropy and application of thermodynamic laws to this. See here: ncatlab.org/nlab/show/Bekenstein-Hawking+entropy#Jacobson95 This is a solid argument which, after one accepts the assumptions, should be mathematically rigorous. But if from that it follows that "gravity is an entropic force" is...
Aug
28
comment Is it possible all matter in the universe emerges from nothing?
+1 for trying to make people think more formally and phrase questions and answers more carefully, hence more scientifically.
Aug
27
comment Why does string theory have such a huge landscape?
I have now added a corresponding item to the nLab String Theory FAQ: ncatlab.org/nlab/show/…
Aug
27
revised Why does string theory have such a huge landscape?
added pointer to new FAQ entry
Aug
27
comment Why does string theory have such a huge landscape?
... is 10 per cycle, and 500 times a choice of 10, hence 10^500 choices. As you see, this number is hand-waving incarnate and the only information it carries is this: look, while there are finitely many of choices of internal flux, due to a charge quantization condition, on a typical Calabi-Yau there are still quite a few such choices.
Aug
27
comment Why does string theory have such a huge landscape?
...akin to the Dirac charge quantization condition which makes anything finite in this game at all. Moreover, the higher these integral periods are, the more they contribute to some potential energy. Some other constraints say that this energy cannot be too big. So as a rule of thumb on says that one has a choice between 10 different values for each such flux field on each cycle. Similarly, as a rule of thumb, one says that a generic Calabi-Yau has 500 nontrivial cylces, give or take a few hundred. The conclusion of this thumb-counting is that the number of choices for the flux fields is...
Aug
27
comment Why does string theory have such a huge landscape?
No, that number 10^500 which has become so famous in public discussion plays no specific role. It is just a generic example of the following counting: 1. IF one assumes that 10 spacetime is compactified on a Calabi-Yau (which one used to be interested in (only) because this makes the effective 4d thory N=1 supersymmetric) and 2. IF one considers type II "flux vacua", then the highr form fields of string theory (the higher electromagnetic fields, if you wish) are quantized/constrained to have integral periods over the cycles of the compact Calabi-Yau. It is this quantization condition, akin...