Eric
Reputation
592
Next privilege 1,000 Rep.
Create new tags
Badges
5 14
Newest
Impact
~10k people reached

• 0 helpful flags
• 14 votes cast

# 11 Comments

 Oct 22 comment What does “the ${\bf N}$ of a group” mean? Maybe you meant $so(3)$ instead of $SO(3)$. The Lie group $SO(3)$ has irreps of only odd dimension but it's Lie algebra $so(3) = su(2)$ has irreps of every dimension. Aug 29 comment Is 3+1 spacetime as privileged as is claimed? I think that the uncertainty principle is a pretty strong assumption to start with if you're trying to justify three spatial dimensions. Feb 21 comment Has every possible interaction between elementary particles been observed? I guess I am mostly interested in examples that fall within the energies that accelerators are currently able to test (including things beyond the SM, but I was under the impression we don't have the energy to test any of those things yet). Feb 21 comment Has every possible interaction between elementary particles been observed? Thanks for these answers! The wikipedia article says that models that predict proton decay say the half life is around 10^36 years. Considering this is so much longer than the age of the universe, how likely is it that this could be observed? And I'm guessing this 10^36 years is the average half-life of a proton, is it possible that some protons could have already decayed? Is it theoretically possible to speed up this decay by say elevating its energy or something? Dec 14 comment What is known about the topological structure of spacetime? Very interesting! Thanks for this answer. Dec 13 comment Electromagnetic Field as a Connection in a Vector Bundle Well, if you're working on a vector bundle then the connection forms are really only defined relative to a local frame. If you patch them together to get something global then it doesn't take values in any nice bundle. However, the curvature form is a global two form with values in the adjoint rep. But if you go from a vector bundle to its associated principal bundle, then the connection form is a global 1 form on the principal bundle with values in the Lie algebra (not ad rep) and the curvature form is a 2 form on the principal bundle with values in the Lie algebra. Dec 12 comment Electromagnetic Field as a Connection in a Vector Bundle Just to nitpick: a connection is specified by a one-form with values in the Lie algebra (not the adjoint bundle); but this is a one-form on the associated principal bundle. you only get a form description on the base manifold locally. You might be confused with the curvature which can be seen as a form on the base manifold with values in the adjoint bundle. Dec 10 comment What is known about the topological structure of spacetime? Oh ok, so that would still be a geometric thing: scaling a cylinder doesn't change any topology. Dec 10 comment What is known about the topological structure of spacetime? Thanks for the answer. I do not see why EFEs cannot contain topological data since you need a global solution to them (you can solve it locally but they need to patch together to form a global metric). For example, if the EFEs implied something like positive scalar curvature then that would really limit the topology (being positive at a point is local, being positive everywhere is global). The adding of topological invariants looks very interesting-- I'll have to read more into it. Dec 10 comment What is known about the topological structure of spacetime? What do you mean by scale of the topology? But Einstein's equations need to be solved globally so couldn't they put some restrictions on the topology? For example if Einstein's equations implied positive scalar curvature, then that would limit the possible manifolds. Also, With there not being any classification of even simply connected 4-manifolds, it seems likely there are nontrivial ones which wouldn't have the "wrap around" property of light rays. Nov 3 comment Lie theory, Representations and particle physics you may want to check out this question: math.stackexchange.com/q/622