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 Dec 26 reviewed Approve A question on energy levels of molecular orbitals Dec 24 comment What exactly does the Kretschmann scalar implies and how does it work? When you test whether or not a singularity is removable, you're basically just testing whether or not scalars make any sense there. The easiest way to do this is probably with the volume element. Or, more simply, the metric determinant. If det(g) is zero or infinite then volumes don't make sense, so the singularity is not removable. Dec 23 comment What exactly does the Kretschmann scalar implies and how does it work? Wouldn't it be easier to determine if a metric has a removable singularity by whether or not the volume element $\sqrt{det(g_{\mu \nu})} d^4 x$ makes sense? If it blows up or becomes zero at the singularity in question then it is not removable. Dec 23 comment Black hole and relativity They would appear to asymptotically slow down as they approached the event horizon, and the light coming from them would be asymptotically red-shifted until they were no longer visible. Note that this isn't what 'actually' happens to the person who's falling, as they would experience nothing unusual when they approached and passed the event horizon (besides some potentially very strong tidal forces if the BH is small enough). This is just what would appear to happen due to the BH's effect on light. Nov 12 reviewed Approve Computing covariance matrix of two mode state? Oct 28 reviewed Approve Confusion about gravity Oct 14 awarded Necromancer Sep 27 comment $\hbar \rightarrow 0$ in quantum mechanics @UnlimitedDreamer We do the same sort of thing when we take $c \to \infty$ to get from relativistic equations to Newtonian equations. $c$ has a definite value, but by pretending it is infinite our equations become Newtonian. In the same way, when we pretend Planck's constant is zero our equations go from quantum to classical. Edit: Just realized this is an old question. Not sure why it popped up in my recent questions page. Sep 8 reviewed Approve Do solar systems typically spin in the same direction as their galaxy? Sep 8 awarded Custodian Sep 8 reviewed Approve Do solar systems typically spin in the same direction as their galaxy? Jul 2 awarded Enlightened Jul 2 awarded Nice Answer Mar 22 comment Why does the electric field escape a black hole? A field isn't a 'thing' that can be sucked into a BH. A field is a mathematical object that has value(s) at every point in space. There is no reason to ad hoc assume that the EM field outside of a BH is zero. Feb 10 awarded Yearling Jan 22 comment Does potential energy always equal kinetic energy? @StanShunpike $T=V$ under special circumstances. What's important is that $T+V=constant$ over time. There may be some points on a particle's path where $T=V$, but it certainly won't be true everywhere. Jan 22 comment Does potential energy always equal kinetic energy? But $T \neq V$ in general. However $dT/dt = -dV/dt$ in general. Jan 22 comment Confusion about what the Euler-Lagrange equation says I'm not sure I understand what you're asking. Given a Lagrangian, the E-L equations tell you what the equations of motion are. Dec 30 comment Can one of Newton's Laws of motion be derived from other Newton's Laws of motion? @Timaeus x(t)=t^3 does not have a(t)=0. It has a(t)=x''(t)=6t. The only moment where a=0 is at t=0. It is implicit in my answer (and I have now explicitly said it) that I'm setting a(t)=0 for all t, not just at a single instant. a(t)=0 does in fact imply v(t)=const. Dec 30 comment Can one of Newton's Laws of motion be derived from other Newton's Laws of motion? @Timaeus Why the strawman? I clearly never said "a=0 at a single instant is enough to tell you v=const." When I say "set F=0" I'm implicitly doing this for all time, and that is indeed enough to tell you that v=const. You're arguing against a strange strawman that I clearly never stated nor implied in any way.