Luboš Motl

68,068 reputation

566144

bio	website	motls.blogspot.com
	location	Czech Republic
	age	39
visits	member for	2 years, 4 months
	seen	16 hours ago
stats	profile views	24,248

Hi, I am a string theorist and a publicist.

	68,068 reputation	bio	website	motls.blogspot.com	visits	member for	2 years, 4 months
566144 badges		location	Czech Republic		seen	16 hours ago

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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.
Feb 19	revised	Is Mach's Principle Wrong? added 61 characters in body; added 148 characters in body
Feb 19	answered	Is Mach's Principle Wrong?
Feb 19	answered	Supersymmetry breaking and Goldstino
Feb 19	answered	Is the Woodward effect real?
Feb 19	revised	What does the fine structure constant describe? added 540 characters in body
Feb 19	answered	What does the fine structure constant describe?
Feb 18	answered	How does an altimeter work?
Feb 18	revised	What is the difference between a moment and a couple? edited tags
Feb 18	comment	Viscosity/Entropy ratio and unitary evolution in quantum gravity I wanted to say that in the effective macroscopic theories, the proposition that the "detailed microscopic degrees of freedom are lost" doesn't mean that they're lost in principle. It just means that by the very definition of the effective theory, these degrees of freedom are deliberately thrown away - denied - by the person who uses the effective theory. But this detailed information is needed to reverse the motion. When it's thrown away, the evolution is irreversible - and non-unitary. However, in principle, with all the knowledge, the evolution is unitary and reversible.