928 reputation
212
bio website
location
age
visits member for 2 years, 4 months
seen Jul 9 at 14:51

May
18
revised Where do I start with Non-Euclidean Geometry?
added 236 characters in body
May
18
answered Where do I start with Non-Euclidean Geometry?
May
18
comment Is anti-matter matter going backwards in time?
@RonMaimon Do you know of a good source, where the analytic structure of the amplitudes is discussed?
May
16
comment Why not using Lagrangian, instead of Hamiltonian, in non relativistic QM?
@RonMaimon There is a path integral formulation of the Hamiltonian formalism. It is equivalent to the usual formulation for theories quadratic in the momenta.
May
14
awarded  Citizen Patrol
May
12
revised How does the string worldsheet affect the space-time in which they live?
added 152 characters in body
May
12
answered How does the string worldsheet affect the space-time in which they live?
May
6
awarded  Commentator
May
6
comment Why does work equal force times distance?
@RonMaimon: Well, ok but what is Force? Mathematically it is a one form, you tell me what direction you want to move in and I tell you what force you are experiencing. In standard physics courses forces are of course drawn as vectors, but if you think about it, the direction of the force and the magnitude are really separate. What actually happens is: You or something else decides on a direction and then you get back the magnitude of force in that direction. One forms are naturally integrated along paths.
May
6
revised Is the converse of Noether's first theorem true: Every conservation law has a symmetry?
added 3 characters in body
May
6
comment Is the converse of Noether's first theorem true: Every conservation law has a symmetry?
This answer is wrong or at least imprecise. One should never accept arguments from authority.
May
6
answered Is the converse of Noether's first theorem true: Every conservation law has a symmetry?
May
6
revised Why does work equal force times distance?
added 1 characters in body
May
6
comment Why does work equal force times distance?
So the answer to why force and distance is: You want to keep track of the change in potential energy. Infitesimally that change is determined by definition by $\vec F \cdot d\vec r$, now as you move along a path, you have to sum up (or integrate) those small contributions to get the total change in potential energy. Only in very simple circumstances the end result will literally be simply force times distance.
May
6
comment Why does work equal force times distance?
Well, I am not sure what you mean by $dV$. Indeed in standard mathematical notation, $dV = \partial_x V dx + \partial_y V dy + \partial_z V dz$ and physicists like to write this as $dV = \vec F \cdot d \vec r$. In words: The infinitesimal change in potential energy is the Force times the infinitesimal change in position. If you like that is the definition of a force. That definition might not be compatible with what you learned in your physics course. But it is the right definition for conservative forces. Non conservative forces like friction are a bit trickier.
May
5
awarded  Critic
May
5
comment Feynman diagrams in effective theories
Bjorn Wesen: There is, look for example at chapters 2 and 3 of Cvitanovics Field Theory notes: chaosbook.org/FieldTheory/pdf.html
May
5
revised Why does work equal force times distance?
added 184 characters in body
May
5
answered Why does work equal force times distance?
Apr
29
comment Poincare Symmetry in QFT
To clarify: I am perfectly happy to accept that since space is almost flat, we can approximately neglect curvature. Similiarly how one can demonstrate that GR gives back Newtonian gravity in suitable limit. But in all other cases I know how to argue that these effects can be neglected, whereas in QFT some of the standard constructions seem to depend on the global structure of spacetime. This belief might be completely misguided, but I do want to understand why.