705 reputation
314
bio website
location Trieste, Italy
age 23
visits member for 1 year, 4 months
seen 3 hours ago

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


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?
Jan
14
revised Classical regime for Fermi-Dirac and Bose-Einstein gases
Improved the title
Jan
14
suggested suggested edit on Classical regime for Fermi-Dirac and Bose-Einstein gases
Jan
14
comment Classical regime for Fermi-Dirac and Bose-Einstein gases
Why do you expect an $\epsilon$-free asymptotic expression? I mean, you can express $\epsilon$ in terms of temperature and density, but to do so you absolutely need the partition function (I think).
Jan
4
awarded  Custodian
Jan
4
reviewed No Action Needed Oscillation of a rolling sphere in a bowl
Dec
31
awarded  Nice Answer
Dec
31
answered Why is a proton assumed to be always at the center while applying the Schrödinger equation?
Dec
28
accepted How can I integrate in $\mathrm{d}t$ the cube of the harmonic oscillator propagator?