104,515 reputation
7143294
bio website motls.blogspot.com
location Czech Republic
age 40
visits member for 3 years, 9 months
seen 13 hours ago

Hi, I am a string theorist and a publicist.


Dec
28
revised Need some basic help with notation and the Christoffel symbols
added 316 characters in body
Dec
28
answered Need some basic help with notation and the Christoffel symbols
Dec
28
answered Do all planets rotate around the sun with the same acceleration?
Dec
27
revised How do we know the geodesic is a minimum?
added 137 characters in body
Dec
27
comment Spin angular momentum of a system of particles : Is there any energy associated with it?
Dear Rajesh, I don't think there's a contradiction. This answer quantifies exactly what I meant, turns it into equations. The comment that "it" only works for rigid bodies is true in the sense that only rigid bodies have their own "constant" value of the moment of inertia. For non-rigid systems of particles, you may define the value of $I$ for which the energy splits in this way but it's useless because $I$ may change arbitrarily, too.
Dec
27
answered how many times have the first photons lapped the universe?
Dec
27
revised How do we know the geodesic is a minimum?
added 488 characters in body
Dec
27
answered How do we know the geodesic is a minimum?
Dec
25
answered Physical interpretation of infinite total cross section
Dec
24
comment Spin angular momentum of a system of particles : Is there any energy associated with it?
It's still the same formula, just $I$ is time-dependent. It isn't as useful but the total energy may always be divided to the internal "rotational energy" above, and to the kinetic energy concentrated to the center of mass, $M_{total} V_{CM}^2/2$. That's an identity whether or not the pieces are rigid.
Dec
24
answered Spin angular momentum of a system of particles : Is there any energy associated with it?
Dec
24
answered Do a 1-dimensional conformal theory exist?
Dec
24
comment Where does the hidden supersymmetric sector of the MSSM come from?
Good, @Matt, will look at those as well.
Dec
23
awarded  Enlightened
Dec
23
awarded  Nice Answer
Dec
23
comment Is decoherence even possible in anti de Sitter space?
Thanks, @Ron. I still think that there are many confusions, however. AdS is a near-horizon geometry of a black hole geometry but AdS itself doesn't have any horizon. Also, the reversibility may require the system to be closed and finite, and AdS isn't one. More generally, I don't understand the logic of the original question because it mixes cosmology with local quantum prcesses, but that's not really your fault.
Dec
23
comment Gauge redundancies and global symmetries
4) whenever an action exists, a symmetry is really a transformation (rule) that keeps the action invariant, 5) keeping the Lagrangian invariant at each point means to have a symmetry that doesn't mix any points, a very "internal one", and e.g. diffeomorphisms and translations don't count, 6) non-Abelian symmetries are equally redundancies as U(1) gauge symmetries but U(1) gauge symmetries are easier to be gauge-fixed at the quantum level, e.g. no $bc$ ghosts are required because the functional determinants in gauge-fixing are constant etc.
Dec
23
comment Gauge redundancies and global symmetries
It's been answered before but 1) physical states have to be invariant under gauge symmetries, so all of them are singlets and there are no nontrivial representations, 2) this claim may be relaxed for gauge symmetry transformations that remain nontrivial even at infinity, so this "global part" of the gauge symmetries can admit nonzero charges and produce "global symmetries" out of the local one, 3) in general relativity one generally expects that all global symmetries arise from local symmetries in this way, so only local ones are fundamentally possible
Dec
23
comment Plausible explanations for 3 local space dimensions
Great to see you here, John! I hope you are, with smile and USD 500 in an envelope, celebrating the arrival of the Higgs to be discovered in Spring. My $500 is ready for you! ;-)
Dec
23
comment “gauge fixed world-sheet action”
good answer, +1. User: your first comment got invalidated because you wrote a quotation mark instead of a dollar in front of the first $T_{++}$ in it. So all maths and non-maths got exactly reverted afterwards. You still had time to edit it and fix it, a few minutes!