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seen Mar 14 at 14:18

Feb
25
answered Is it valid to apply Einstein's Relativity to scenarios involving expansion of space?
Feb
25
revised Intuition as to why the orientation (of a 3D object) is not a conserved quantity?
deleted 12 characters in body
Feb
25
comment Intuition as to why the orientation (of a 3D object) is not a conserved quantity?
@DonHatch: see edit
Feb
25
revised Intuition as to why the orientation (of a 3D object) is not a conserved quantity?
describe algorithm
Feb
25
answered Intuition as to why the orientation (of a 3D object) is not a conserved quantity?
Feb
19
awarded  Taxonomist
Feb
16
comment Why does it take a projectile as long to get to its apex as it does to hit the ground?
@DavidHammen: I'm slightly ashamed to admit it, but I actually did have to draw some pictures to convince myself that this is valid reasoning ;)
Feb
15
comment Why does it take a projectile as long to get to its apex as it does to hit the ground?
note to self: verify that ascent and descent actually do not take the same amount of time once you add drag...
Feb
15
revised Why does it take a projectile as long to get to its apex as it does to hit the ground?
added 18 characters in body
Feb
15
answered Why does it take a projectile as long to get to its apex as it does to hit the ground?
Feb
15
comment Does a symmetry necessarily leave the action invariant?
if we want to apply Noether's theorem, the infinitesimal transformation needs to leave the action invariant (up to a divergence term)
Feb
11
awarded  Nice Answer
Feb
8
comment It's established that universal energy is not constant. But is the net change positive or negative?
in some sense, the total energy of a homogeneous isotropic universe is well-defined: FLRW spacetime comes with a privileged set of observers, making Pirani's expression for energy well-defined; that energy is trivially 0 in any finite volume as the density vanishes identically, yielding a vanishing total energy as limit
Feb
8
comment Why does heat added to a system at a lower temperature cause higher entropy increase?
$\frac QT = \Delta S = \Delta(k \ln\Omega) \approx k \frac 1\Omega \Delta\Omega \Rightarrow \Delta\Omega\approx \Omega \frac Q{kT}$, ie transferring heat into a system opens up a new number of microstates $\Delta\Omega$ proportional to the number of existing ones and the number of degrees of freedom we can excite given by heat $Q$ divided by average energy per degree of freedom $kT$; cf physics.stackexchange.com/questions/33372/…
Feb
5
comment Gravity: Is there curved space besides curved spacetime?
@AlfredCentauri: but I am, and I suspect Moonraker does so as well
Feb
5
comment Gravity: Is there curved space besides curved spacetime?
@AlfredCentauri: I'm talking about general spacetimes. How would you define spatial geometry in a Schwarzschild spacetime? Aribtrary non-homogeneous, non-insotropic spacetimes? Preferred spatial slicings may exist on a case-by-case basis, but in general, I do not believe there's such a thing as spatial geometry
Feb
5
revised Gravity: Is there curved space besides curved spacetime?
added 68 characters in body
Feb
5
comment Gravity: Is there curved space besides curved spacetime?
@AlfredCentauri: in GR, there isn't really such a thing as spatial geometry - a more appropriate way to think about it is as the matter distribution being layered
Feb
5
answered Gravity: Is there curved space besides curved spacetime?
Feb
4
revised “Reality” of EM waves vs. wavefunction of individual photons - why not treat the wave function as equally “Real”?
added 9 characters in body