Why does an infalling object cross the event horizon in finite proper time?

[Antenna Guy]

Again, in thermodynamics it is really isolated systems you should be talking about if you want to discuss the second law, not closed ones. ... Anyway, as I said, there is no violation of the second law as long as you say that a black hole's entropy is defined by the area of its event horizon, since when matter or energy falls in the event horizon grows by an amount enough to offset any decrease in entropy in the region outside the event horizon.

Are you sure that's what you want to say?

Regards,

Bill

 

[JesseM]

Again, in thermodynamics it is really isolated systems you should be talking about if you want to discuss the second law, not closed ones. ... Anyway, as I said, there is no violation of the second law as long as you say that a black hole's entropy is defined by the area of its event horizon, since when matter or energy falls in the event horizon grows by an amount enough to offset any decrease in entropy in the region outside the event horizon.

Are you sure that's what you want to say?

Yes. Weren't we discussing a larger isolated system that contains both a black hole and some matter/energy outside it? That's what you seemed to be talking about in the second paragraph of post #22 (which begins 'Now consider an arbitrarily larger closed system that contains a random distribution of bodies of mass - including a black hole'), and that's what I was responding to. So, for the larger system to qualify as "isolated" it must be true that no matter/energy is crossing the boundary of the larger system (say, a giant box containing a black hole and some other stuff), but matter/energy can certainly cross the event horizon.

 

[Antenna Guy]

Yes.

Consider how the entropy of a black hole changes within the context of the first bold.

Is a black hole an "isolated system"?

Regards,

Bill

 

[MeJennifer]

Is a black hole an "isolated system"?

No, it is not.

 

[JesseM]

Consider how the entropy of a black hole changes within the context of the first bold.

Is a black hole an "isolated system"?

On its own? Not if any matter/energy crosses the event horizon, by definition.