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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.
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.
Dec
29
comment Can one of Newton's Laws of motion be derived from other Newton's Laws of motion?
@Timaeus Here in the real world we need only consider accelerations. Realistic equations of motion are always first or second-order.
Dec
23
comment What are the relative limitations of the Schrödinger, Pauli, and Dirac Equations?
Both the Dirac equation and the Klein-Gordon equation fail to make much sense if you attempt to use them as single-particle wave equations. They both require the "correct" interpretation, which is in the context of quantum field theory. When you mix relativity and QM you're inevitably led to many-particle systems, where particles can be created and destroyed.
Dec
12
comment What's the Cause of Quantum Entanglement?
@Sofia Just so you know, you said "the-function" instead of "wave-function."
Dec
5
comment Can Schwarzschild black holes evaporate?
The Schwarzschild metric is static by definition. If the metric changes over time then it's not the Schwarzschild metric. Simple as that.
Dec
5
comment Find time-parametrization given path and speed of a particle
Hint: the speed is the magnitude of $r'(t)$.
Dec
1
comment The virtual particles are only a fictive tool in equations? DO they exist or DON'T? And if they exist, why do we call them VIRTUAL?
@PeterShor I see what you're saying, that anything we interact with must be a bit off-shell, but I think you're carrying the interpretation of Feynman graphs too far. They are just approximation tools. Particles aren't "really" in momentum eigenstates either. If I was going to describe what's "really" going on I wouldn't use perturbation theory or virtual particles to begin with.
Dec
1
comment The virtual particles are only a fictive tool in equations? DO they exist or DON'T? And if they exist, why do we call them VIRTUAL?
@PeterShor An external line doesn't necessitate observation, as you seem to imply. That's just bad logic. External lines correspond to particles which can be observed, but they don't need to be.
Dec
1
comment The virtual particles are only a fictive tool in equations? DO they exist or DON'T? And if they exist, why do we call them VIRTUAL?
@PeterShor It seems like you're going out of your way to make it sound absurd. Virtual particles are internal lines by definition. Internal lines are not observed by definition. Therefore, virtual particles are not observed by definition. It's not complicated, and it's not circular. Also notice that I never said, "particles are virtual because they're not observed." That simply does not follow from the logic.
Dec
1
comment The virtual particles are only a fictive tool in equations? DO they exist or DON'T? And if they exist, why do we call them VIRTUAL?
@PeterShor How is it a tautology to say something is true by definition?
Nov
30
comment Schwarzschild Radius vs Gravitational Pull? Error in Model?
Newtonian gravity is a weak-field static limit approximation of General Relativity. That means it works well when the gravitational field is relatively small and everything is moving slowly compared to light. When you want to consider extreme objects like black holes, Newtonian gravity will simply fail to be accurate in their vicinity. You need to do full-fledged GR to get the correct predictions.
Nov
28
comment Why do we use functional integration in QFT?
@AlexNelson But the path integral doesn't say that "$x^0$ is the $t$-coordinate." You integrate over four-volume $\sqrt{-g} d^4 x$, which is a coordinate-invariant object.
Nov
25
comment On which basis we think there is something more than just super dense matter in black holes?
Peter should also be aware the Schwarzschild coordinate $r$ does not actually correspond to "distance from the center." The distance between two values of $r$ is determined by an integral over the line element.
Nov
25
comment Gravity at event horizon
Except the quantity you've defined as "g" is not particularly meaningful. It does not correspond to any type of measurable acceleration. The proper acceleration required to hover near the event horizon asymptotically approaches infinity as $r \to 2GM/c^2$.
Nov
24
comment Gravitational Time Dilation Formula?
@Hypnosifl Indeed. I'll edit my post accordingly.