4 ms·

Can they reach the center? And how long would that take? I ask because time will slow down for them as they accelerate towards the center.

XorNot 3y ago
Your first question is the problem: they must always be moving towards the center - which implies they must be getting closer to it. Because if they can never actually reach the center, then in 4D spacetime they're no longer moving towards it - they'd be traveling parallel with it. Which would imply that singularity isn't a singularity - i.e. the "hole" it makes would in fact be highly curved spacetime in one dimension, but completely flat in another (i.e. it would be a cylinder). Which creates a hole lot of weird infinities in the system: i.e. a black hole becomes a finite bounded volume on the outside, but contains an infinite amount of space on the inside (since no matter how much you distort spacetime, the molecules of whatever falls in can just pull themselves together more tightly provided the distortion doesn't happen too quickly).
SpaceManNabs 3y ago
Time doesnt slow down for them. They reach the center in their time as normal. We never see them reach the center. You can use kruskal coordinates and other tools to understand this.
- wholinator2 3y ago
  Right, time doesn't slow down for them, but it would appear so for an outside observer. So would the "experience" of a particle sent in to be that it circles closer and closer for some time on the order of years and at some point when it is arbitrarily close to the center it just pops out some billion or trillion years later once the black hole has evaporated? Assuming it isn't destroyed and somehow can experience it's own time.
  - SpaceManNabs 3y ago
    It would be more than a few trillion years I think, but that is the thinking unless you are a certain contentious Berkeley astrophysicist. The particle does see itself “reach” the black hole though. And so would an outside observer if they had infinite time. The black hole dissipating sure would make some of the experience odd. I would need to revisit my notes to make a claim about that, but discontinuities like that arent uncommon.

XorNot 3y ago

Your first question is the problem: they must always be moving towards the center - which implies they must be getting closer to it. Because if they can never actually reach the center, then in 4D spacetime they're no longer moving towards it - they'd be traveling parallel with it. Which would imply that singularity isn't a singularity - i.e. the "hole" it makes would in fact be highly curved spacetime in one dimension, but completely flat in another (i.e. it would be a cylinder). Which creates a hole lot of weird infinities in the system: i.e. a black hole becomes a finite bounded volume on the outside, but contains an infinite amount of space on the inside (since no matter how much you distort spacetime, the molecules of whatever falls in can just pull themselves together more tightly provided the distortion doesn't happen too quickly).

SpaceManNabs 3y ago

Time doesnt slow down for them. They reach the center in their time as normal. We never see them reach the center. You can use kruskal coordinates and other tools to understand this.

wholinator2 3y ago
Right, time doesn't slow down for them, but it would appear so for an outside observer. So would the "experience" of a particle sent in to be that it circles closer and closer for some time on the order of years and at some point when it is arbitrarily close to the center it just pops out some billion or trillion years later once the black hole has evaporated? Assuming it isn't destroyed and somehow can experience it's own time.
- SpaceManNabs 3y ago
  It would be more than a few trillion years I think, but that is the thinking unless you are a certain contentious Berkeley astrophysicist. The particle does see itself “reach” the black hole though. And so would an outside observer if they had infinite time. The black hole dissipating sure would make some of the experience odd. I would need to revisit my notes to make a claim about that, but discontinuities like that arent uncommon.