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location Trieste, Italy
age 24
visits member for 1 year, 6 months
seen Nov 17 at 19:10

I'm a second-year student of the Theoretical physics master's course at the University of Trieste.


Sep
24
awarded  Autobiographer
Sep
16
accepted Who developed the phase space path integral?
Sep
9
comment Who developed the phase space path integral?
Moreover, the only thing that should change with different orderings of an hamiltonian in the path integral is the prescription on how to discretize the action (i.e., the Weyl ordering gives the midpoint prescription; normal ordering gives a different prescription plus some extra terms)
Sep
9
comment Who developed the phase space path integral?
Sakita assumes the standard form for the Hamiltonian only to obtain the configuration space path integral, not in the derivation of the phase space one.
Sep
9
comment Who developed the phase space path integral?
The most concise one is in "Quantum Theory of Many Variable Systems and Fields", by B. Sakita, Chapter 1. A good reference is also Zinn-Justin's "Path Integrals in Quantum Mechanics", Chapter 10.
Sep
9
comment Who developed the phase space path integral?
As far as I know, the second equation is a little more general than the first; you can derive it in an independent way in a sort of simple calculation. The first formula for propagators is valid only if the hamiltonian has the form $H = \frac{p^2}{2} + V(q)$, and is obtained from the phase space path integral by performing the gaussian integrations in $\mathrm{d}p$. In the derivation of the phase space path integral, however, one never postulates a specific form of the Hamiltonian.
Sep
9
revised Who developed the phase space path integral?
added informations
Sep
9
asked Who developed the phase space path integral?
Jul
9
comment Why does time stop in black holes?
"So as observer gets closer and closer to a black hole time passes more slowly"; in which sense? It's true that external observers will see someone freefalling into a Schwarzschild black hole asymptotically approaching the event horizon, but for the observer in freefall, the event horizon is just as any other point in spacetime and is reached in a finite amount of time.
Jul
2
awarded  Curious
Jun
27
comment Linearity of the time evolution operator for the reduced density matrix of an entangled state
Thank you for your answer. I get that if the system is factorized the evolution is $\rho_S(t) = e^{-itH_S} \rho_S e^{itH_s}$ (this is what I meant when in the question I've written "it can be easily proven that if the initial state is not entangled, the operator $\Gamma_t$ is linear"). What I don't understand is why you say that "the time evolution "mixes" between the two spaces, and you can't get a linear evolution"; can't the mixing between the two spaces behave in a linear way in $\mathcal{H}_S$? In general this won't be the case. But is what I'm saying impossible, in principle?
Jun
27
asked Linearity of the time evolution operator for the reduced density matrix of an entangled state
Jun
26
comment If there is no gravity, does that mean there's no mass as well?
Sloppy reasoning; you can have structures (e.g. Hydrogenic systems) without gravity. Is not "only gravity" that pulls with infinite range, but also electromagnetism.
May
16
comment Which experiment gave scientists reason to believe nuclear fission/fusion produced energy?
more info on en.wikipedia.org/wiki/Nuclear_binding_energy
May
16
comment Which experiment gave scientists reason to believe nuclear fission/fusion produced energy?
One might think that the mass of helium-4 is the mass of 2 protons added to the mass of 2 neutrons, so approximately 4 times the mass of hydrogen. However, if you measure it, it is slightly less (there is a so-called "mass defect"). The mass defect is there because in the mass of helium-4 you have to take into account also of the binding energy between the nucleons, aside of their mass.
May
5
awarded  Yearling
Mar
12
answered What does library number 539 mean in physics books?
Feb
27
revised Wicks Theorem and Gaussian Integrals
Added an explanatory footnote
Feb
27
answered Wicks Theorem and Gaussian Integrals
Jan
30
answered If one is travelling at a significant fraction of $c$, will the length of the trip be shortened?