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visits member for 1 year, 8 months
seen Jul 23 '13 at 10:51

String theory grad student.


Aug
8
comment Ghosts in Pauli Villars Regularization
I think your propagator is missing a $-i$ (from $e^{iS}$), no?
Aug
8
revised What is the fundamental differences between bound and entangled states
edited body
Aug
8
answered What is the fundamental differences between bound and entangled states
Aug
7
answered Relating angular and linear kinematics
Aug
7
comment How do I find work done by friction over a curve represented by a polynomial?
@user1220376 The normal force you wrote down is for a body that is at rest. When a body moves on a curve the normal force is different because there is acceleration in the normal direction (as you get in circular motion). Beyond that, see Qmechanic's answer below.
Aug
6
awarded  Citizen Patrol
Aug
6
comment “Time” by epistemic subdivision of a closed system
Okay, thanks for letting me know.
Aug
6
comment Derivation of the enhancement of U(1)$_L$ x U(1)$_R$ to SU(2)$_L$ x SU(2)$_R$ at the self-dual radius
Yes, Polchinski section 8.3 (volume 1).
Aug
5
answered Why are there two ways to solve for energy of a spring?
Aug
5
comment “Time” by epistemic subdivision of a closed system
I'm sorry but I don't think this is a question in physics.
Aug
5
comment Does String theory say that spacetime is not fundamental but should be considered an emergent phenomenon?
@RonMaimon As for AdS/CFT, I think that just by matching the symmetries it is clear that only one dimension is emergent in the CFT description. The non-commutativity you are referring to happens for example with D-brane coordinates but not with bulk coordinates, so I don't see how it changes the answer.
Aug
5
comment Does String theory say that spacetime is not fundamental but should be considered an emergent phenomenon?
@RonMaimon I agree that the nature of spacetime in string theory is not as simple as it appears in the worldsheet action, because of what you say. But the question was whether spacetime is emergent. In the usual (i.e. modern, textbook) treatment that everyone uses today, spacetime points are there from the start as fundamental variables, and therefore I think that spacetime is clearly not emergent.
Aug
5
comment Does String theory say that spacetime is not fundamental but should be considered an emergent phenomenon?
@NickKidman in the usual formulation, where you start e.g. with the Nambu-Goto action, you also have a spacetime metric as part of the string background.
Aug
4
revised First Postulate of Special Relativity: What does it mean?
added 2 characters in body
Aug
4
answered Does String theory say that spacetime is not fundamental but should be considered an emergent phenomenon?
Aug
4
answered First Postulate of Special Relativity: What does it mean?
Aug
4
comment Relativity - time dilation
On more general grounds, as someone on earth you cannot gain a speed advantage by doing a calculation on a moving ship (e.g. a ship orbiting the earth). In our frame a moving computer will always take longer to complete the calculation than one staying on earth. This is even without accounting for the time it takes to transmit the result back to earth.
Aug
4
comment Relativity - time dilation
You have to be careful about simultaneity, which is not a frame-independent concept. In your original question, you defined simultaneous events in the frame of observer A (whether you intended to or not). As long as you stick with a frame you're fine. But now you launch the second chip in one frame, and want to discuss what it looks like in the first chip's frame, so you have to be careful. For example, in the first chip's frame the new launch does not happen when he is $10^{-6}$ months old, but after that! You have to work it out carefully.
Aug
4
awarded  Commentator
Aug
4
comment How is $\frac{dQ}{T}$ measure of randomness of system?
A microscopic description (like statistical mechanics) considers the underlying degrees of freedom, and should explain how the observed 'macroscopic' phenomena emerge from the detailed model. If you derive the ideal gas law by postulating tiny atoms bouncing around -- that is a microscopic description. Of course a microscopic model at one level may become phenomenological once you go to more detailed observations, so this distinction depends on one's point of view. People who study optics would not call particle physicists 'phenomenologists' -- but strings theorists would.