Luboš Motl

67,764 reputation

466141

bio	website	motls.blogspot.com
	location	Czech Republic
	age	39
visits	member for	2 years, 4 months
	seen	22 hours ago
stats	profile views	24,166

Hi, I am a string theorist and a publicist.

	67,764 reputation	bio	website	motls.blogspot.com	visits	member for	2 years, 4 months
466141 badges		location	Czech Republic		seen	22 hours ago

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Feb 21	answered	Do extra-dimensional theories like ADD or Randall-Sundrum require string theory to be true?
Feb 20	revised	What is the physical meaning of enhanced gauge symmetries in string compactifications? added 337 characters in body
Feb 20	revised	What is the physical meaning of enhanced gauge symmetries in string compactifications? added 778 characters in body
Feb 20	revised	What is the physical meaning of enhanced gauge symmetries in string compactifications? added 696 characters in body
Feb 20	comment	What is the physical meaning of enhanced gauge symmetries in string compactifications? Sorry, I gave you -1 because I don't believe that your condensed-matter story may be equivalent to the stringy enhanced symmetries. If you convince me otherwise and edit your comment, I will change my vote. The stringy enhanced symmetries depend on fundamental string winding modes. You don't have them in your CMT models so you can't really get new, non-Abelian massless gauge bosons in this way, I think.
Feb 20	answered	What is the physical meaning of enhanced gauge symmetries in string compactifications?
Feb 20	answered	If we are willing to accept tachyonic string modes, are there valid projections other than the GSO projections?
Feb 20	comment	Wavefunction collapse in relativity Nice answer, @Marek, +1. Dear @sb1, your uneasy feeling is pretty clearly coming from the fact that you are imagining that the wave function is a classical wave. It's not. It's just an ensemble of complex numbers that may be used to predict the probabilities of any outcomes - any combination of outcomes of the entangled subsystems. The "collapse" is only a simplification of our bookkeeping - instead of the full probabilities $P(A=A_i,B=B_j)$, we may use the conditional probabilities with $A=A_m$ once it's known that tne $m$th result of $A$ was measured. The collapse only occurs in our heads.
Feb 20	revised	If : V(Phi) : is nonlocal in space, does that mean interacting quantum field theory is nonlocal? added 2439 characters in body; added 395 characters in body
Feb 20	revised	If : V(Phi) : is nonlocal in space, does that mean interacting quantum field theory is nonlocal? deleted 1772 characters in body
Feb 20	answered	If : V(Phi) : is nonlocal in space, does that mean interacting quantum field theory is nonlocal?
Feb 20	asked	Dual conformal symmetry and spin networks in ABJM
Feb 20	comment	Is Mach's Principle Wrong? @Deepak, the variation of Mach's principle you wrote, "Local physical laws are determined by the large-scale structure of the universe," is in no way equivalent to the equivalence principle. Quite on the contrary, the equivalence principle says that the local physical laws in a freely falling frame are completely unaffected by any distant objects - GR is a method to impose locality in a manifest way. Your (or your quote from Wikipedia) version of Mach's principle has undoubtedly been shown invalid, too. In GR, the large structure is determined by local physics and local sources, not vice versa
Feb 20	comment	Is Mach's Principle Wrong? Dear @Moshe, I would respectfully disagree. In fundamental physics, the ultimate question is always whether XY is right or wrong, not whether it is useful - which is left to managers and perhaps engineers. The observation that Mach's principle is no longer "useful" doesn't mean that we can't answer the question whether it's right or wrong. Yes, we can.
Feb 20	comment	Is the Woodward effect real? See my answer under the very same question Gordon reasked here: physics.stackexchange.com/questions/5483/…
Feb 20	comment	Is Mach's Principle Wrong? John, Einstein had thought that Mach's Principle was the way to go because it (also) made the universality encoded in the equivalence principle manifest. The equivalence principle says that all objects will be influenced equally - the same acceleration - by the whatever agent is causing gravity. Mach's principle satisfies the criterion "totally" - it removes any field-like agent. Well, it's going "too far" in this sense. Of course that Einstein was struggling for years to make Mach's principle compatible with the speed limit $c$ - and GR is what eventually came out of it.
Feb 20	comment	Is Mach's Principle Wrong? Dear @Gordon, arXiv is representative of the whole literature. Still, you should make at least some post-publication quality tests. If a paper claims a discovery of a new fundamental thing and it has less than 50 citations after many years, it's probably wrong, and you need to rely on other people's knowledge, well, then this paper is probably wrong.
Feb 19	revised	Would it be worthwhile to work out a manifestly supersymmetric superspace formalism for 16 and 32 real SUSY generators? added 97 characters in body
Feb 19	answered	Would it be worthwhile to work out a manifestly supersymmetric superspace formalism for 16 and 32 real SUSY generators?
Feb 19	comment	Is Mach's Principle Wrong? Dear Gordon, there are no serious physicists who want to test Mach's principle in 2011. Such things were being solved by Einstein in 1911.