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Shaw
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SR implies that mass can't reach c, but mass does reach a black hole's event horizon. How is this reconciled with SR?
Shaw said:SR implies that mass can't reach c, but mass does reach a black hole's event horizon. How is this reconciled with SR?
Shaw said:I know that GR sits on top of SR, so to speak, when it comes to gravitation, so I expected there would be a reason for it not to be taken literally.
Shaw said:If we just consider SR, acceleration to the event horizon implies acceleration to the speed of light
Shaw said:you've explained that it's the event horizon itself that's moving at the speed of light, so SR calculations don't apply here
Shaw said:I've reached a mathematically provable conclusion from all my previous posts, and I will present it shortly.
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Shaw said:If we just consider SR, acceleration to the event horizon implies acceleration to the speed of light, but you've explained that it's the event horizon itself that's moving at the speed of light, so SR calculations don't apply here, therefore it can't be taken" literally."
PeterDonis said:It does no such thing. First of all, in SR there is no such thing as an "event horizon", because spacetime is flat. The best we can do in SR is to consider analogues of the black hole event horizon, which can share some of its properties, but not all.
Second, if we consider the closest analogue, a Rindler horizon, a free-falling observer who appears, to a Rindler observer, to be "accelerating towards the horizon" is not accelerating "to the speed of light"--again, the horizon is moving at the speed of light, not the inertial observer.
Incorrect; in the SR analogue of the black hole horizon, the horizon is indeed moving at the speed of light and the inertial observer is not. See above.
nitsuj said:I'd suspect an accelerometer would measure zero for "stuff" crossing the EH
nitsuj said:(distant observer)
nitsuj said:there is no "force" acting on the object, in turn is not subject to the restrictions of acceleration approaching c
nitsuj said:idealizing a constant (infinite/ gravitational potential
nitsuj said:what is the max "rate" for gravity or is there even one?
nitsuj said:I suppose that is asking if the metric can flip spacetime to timespace
nitsuj said:my post were questions...not sure your intent here but it wasn't to answer
Shaw said:SR implies that mass can't reach c, but mass does reach a black hole's event horizon. How is this reconciled with SR?
thedaybefore said:the rest energy of an object/particle recduces when the object goes deeper into a gravity well
PeterDonis said:Not as measured locally; only as "measured" (using gravitational red shift) by an observer far outside the gravity well. Locally, the object's rest mass is unchanged.
Also, this reasoning applies to an object that is static in the gravitational field; but there are no such objects at or inside the horizon. So this isn't relevant to the OP's question anyway.
thedaybefore said:As the object aproaches the event horizon, more and more of its enrgy will be shifted from internal energy to momentum/kinetic energy.
thedaybefore said:Talking about what happens when an object aproaches an event horizon doesn't make sense unless you talk about it from some observer's perspective.
PeterDonis said:Not sure why you put this in.
PeterDonis said:Relative to a particular viewpoint, things can be interpreted this way, yes. Although even there I would question interpreting what is happening as "transferring" energy from internal (rest) energy to kinetic energy. A static observer at a given finite altitude, measuring the free-falling object passing it, will not measure its total energy to be the "reduced" amount; he will measure it to be the object's full rest energy plus the kinetic energy it has accumulated while falling. The "reduced" amount of energy is an amount calculated by a distant observer by taking into account the gravitational redshift from the finite altitude to infinity.
The object itself counts as an "observer's perspective". And measurements made in the object's local inertial frame will show its rest mass to be unchanged.
thedaybefore said:If you are measuring the object from a local inertial frame, then the object will have no velocity
thedaybefore said:Unless, you mean that a local inertial frame is a co-moving frame outside the gravity well (an infintly far location with a g00 value of 1).
thedaybefore said:By that definition of a local inertial frame, the rest enrgy of the object goes to zero as it aproaches the event horizon.
The mass velocity at a black hole event horizon refers to the speed at which matter or objects are pulled towards a black hole's event horizon, the point of no return where the gravitational pull becomes too strong for anything, including light, to escape.
The mass velocity at a black hole event horizon is calculated using the formula v = √(2GM/r), where v is the velocity, G is the gravitational constant, M is the mass of the black hole, and r is the distance from the center of the black hole to the event horizon.
No, anything that crosses the event horizon is pulled towards the singularity at the center of the black hole with a velocity greater than the speed of light, making escape impossible.
As an object approaches the event horizon, time dilation occurs, meaning time appears to slow down for an observer outside the black hole. As the object reaches the event horizon, time appears to stop completely.
No, the mass velocity at a black hole event horizon varies depending on the mass and size of the black hole. Smaller black holes have a higher mass velocity at their event horizons compared to larger black holes.