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Hi, I am a string theorist and a publicist.


Aug
28
comment is there an operator which measures the mass of particles?
The rest mass is fixed because it's a law of physics. For all states that are allowed in Nature, the rest mass of an electron is always 511 keV. So the mass $m$ is an operator on the Hilbert space that is proportional to the unit operator/matrix. We say that it is a $c$-number, a classical number. The equally big value is the only eigenvalue of the operator. Every state of the Hilbert space is an eigenstate of this operator with the same eigenvalue. Almost just like $\pi$, is a fixed parameter of the laws of physics, not a dynamical variable.
Aug
28
comment Do apparent event horizons have Hawking radiation?
Yes, it's directional. The "apparent source" at infinity has no preferred direction but we're observing it from a direction. Yes, it's from behind. Because of the equivalence principle, one may see that the direction is the same in the black hole case or Unruh case. The direction where the "source" sits is the side on which the stomach presses the interior of your belly. That's true for a black hole above which you try to keep your distance, so it must be true for any acceleration. The source is a distant point from which you accelerate away.
Aug
27
comment Suntan: UV absorption vs daytime
Good for reminding me about this question, Rick, I missed anderstood's comment before - even though I was interested about this question every summer including this one. ;-) The drop in the morning and afternoon seems almost linear - I sort of expected it to be more brutal, exponential, like exp(-t) in the evening, because of the exponentially decreasing transmission through the absorbing layer, but it apparently ain't so.
Aug
27
awarded  Nice Question
Aug
26
comment How does work function transform in Einstein's special theory of relativity?
Plain and old special relativity holds anywhere and everywhere and always (at least if GR is not needed - if the gravity is weak or otherwise easily incorporated). The laws have the simple form in all reference frames. Just the laws describing the properties of materials, including ionization, are simpler in the rest frame of the material. But in each frame, you may simply say that the law is "whatever you get by Lorentz-transforming the laws in the rest frame into our frame".
Aug
25
revised Why speaker beeps when a cellphone is kept near it?
added 177 characters in body
Aug
25
revised Why speaker beeps when a cellphone is kept near it?
added 476 characters in body
Aug
25
answered Why speaker beeps when a cellphone is kept near it?
Aug
25
comment How does work function transform in Einstein's special theory of relativity?
In the movie frame, the metal is moving, and the minimum energy of the photon to knock off an electron is then obviously different, so that the condition is equivalent in all frames. The minimum energy to knock off an electron is normally specified in the metal's rest frame.
Aug
24
awarded  Enlightened
Aug
24
answered Why do electrical storms cause metal objects to vibrate?
Aug
24
answered Does deceleration (or negative acceleration) feel like acceleration?
Aug
23
awarded  Enlightened
Aug
23
awarded  Guru
Aug
23
answered Do physicists have idea about medium that would be required to perceive other dimensions?
Aug
23
revised Matter to energy conversion
added 360 characters in body
Aug
23
answered Matter to energy conversion
Aug
21
comment A classical universe from a quantum one?
Our Universe never becomes exactly classical. Clas. ph. holds approximately only. The history we believe going back to the Big Bang is a retroactive interpretation of the results of measurements we have (or a given observer has) made. It allows us to be "almost" sure about the value of many quantities (quantitative or qualitative descriptions of the events in the distant past) because those values or assumed facts are very likely to evolve to the future outcomes we have actually observed. But if we can't determine these answers about the past, then they are as undetermined as everything in QM.
Aug
21
answered Eigenspaces of angular momentum operator and its square (Casimir operator)
Aug
21
comment Can pure-bosonic string theories exist in curved spacetime?
Interesting question. For some examples of non-SUSY AdS/CFT examples that rely on the validity of the BF bound, try e.g. arxiv.org/abs/hep-th/0105047 - a problem is that the paper is in "SUGRA" only. The critical dimensions aren't imposed in general and the CFTs are only described rather vaguely by some operators and properties.