Crossing an event horizon

[Umbran]

If it's any consolation, Einstein would have probably agreed with you. He didn't believe that singularities were possible, and even wrote a paper attempting to prove this. I don't know if he ever changed his mind about this before his death

Not publicly, he didn't. But he died in 1955, before many of the major bits of work on them were completed. The very term "black hole" is post-Einstein.

but there were a lot of aspects of quantum physics, including black holes, that he really didn't like.

Yes, well, the existence of black holes owes more to Einstein's own General Relativity than to quantum mechanics. In essence, all QM does is fail to provide forces sufficient to prevent gravitational collapse. The singularity that Einstein didn't like is in his own equations of General Relativity, not in QM.

 

[Mustrum_Ridcully]

I was confused for a moment about this notion that an object cannot cross an event horizion. It absolutely can do that. What doesn't happen is that we actually observe this happening. All signals informing us of the events are slowed down and delayed so much we will never see them.

 

[Umbran]

I was confused for a moment about this notion that an object cannot cross an event horizion. It absolutely can do that. What doesn't happen is that we actually observe this happening. All signals informing us of the events are slowed down and delayed so much we will never see them.

It isn't just the signals are delayed. The actual event is delayed. As far as the universe far away from the hole is concerned, the clocks down near the event horizon tick so slowly that things never get around to crossing.

As I noted up thread, (as far as classical physics goes) if you could attach a rope to someone, and push them in, let them sit down there for 1000 years of our time (or whatever arbitrary length of time you wish), and haul them back up. They will have aged less than the rest of the universe you know. If you can haul them back up, they obviously didn't cross the event horizon yet.

 

[jonesy]

If only we had a supply of indestructible immortals to throw at black holes. They could hold hands and form a chain into it.

Richard Gott calculated that it only takes a tenth of a second for your avarage human to go from 'I don't feel too good' to 'shredded to atoms' when he closes with a black hole, regardless of how big the black hole in question is.

If you drop someone into a black hole with the mass of the Sun it would take, from his perspective, 2 months to fall all the way in.

The interesting part is that that 2 months would, from our perspective, be so long that it's hard to know whether the universe would have enough time left for that to actually happen.

So it's not about whether it's possible, it's about whether there's enough time for it.

Obviously the matter that a star had before it became a black hole did enter the event horizon. The event itself was matter crushing itself into a tiny space.

 

[Umbran]

Richard Gott calculated that it only takes a tenth of a second for your avarage human to go from 'I don't feel too good' to 'shredded to atoms' when he closes with a black hole, regardless of how big the black hole in question is.

Supermassive black holes don't have strong tidal effects near their event horizons - they don't shred you as you approach. Once you are across the horizon, that's another matter.

Obviously the matter that a star had before it became a black hole did enter the event horizon. The event itself was matter crushing itself into a tiny space.

Technically, no - the event horizon doesn't exist before the collapse. It only forms once sufficient mass is crushed into a small enough space. You could imagine the object falling in on itself, it's normal surface shrinking down, light coming off it red-shifting as it goes, until it is then shrouded in a cloak of blackness.

 

[jonesy]

Supermassive black holes don't have strong tidal effects near their event horizons - they don't shred you as you approach. Once you are across the horizon, that's another matter.

For supermassives the killlzone is inside the event horizon, yes. But if you could get there the same effect would apply. As far as gravity affecting you is concerned, you'd be fine all the way up to the crush and then you'd go pop.

Technically, no - the event horizon doesn't exist before the collapse. It only forms once sufficient mass is crushed into a small enough space. You could imagine the object falling in on itself, it's normal surface shrinking down, light coming off it red-shifting as it goes, until it is then shrouded in a cloak of blackness.

Does that mean that when a black hole is formed all of the matter that the star has instantly becomes the singularity? There won't be any, umm, leftovers to briefly hover above it?

 

[Umbran]

For supermassives the killlzone is inside the event horizon, yes. But if you could get there the same effect would apply. As far as gravity affecting you is concerned, you'd be fine all the way up to the crush and then you'd go pop.

So long at the thing is not rotating, yes. Rotating black holes, if they exist and follow the math, may provide an out, a way to avoid the singularity. But then we start talking about time-travel, and things get very messy.

There won't be any, umm, leftovers to briefly hover above it?

Briefly, from whose point of view? Anything left outside the event horizon will be subject to the same time dilation effects as someone dropped in after the hole forms. From out point of view far from the hole, the hovering may be anything but brief.

 

[Shag]

I'm gunna leave this thread because an M-theory war might break out and I don't want any trouble!

 

[jonesy]

I'm gunna leave this thread because an M-theory war might break out and I don't want any trouble!

"I had retired to the Martian Empire when the man and the dog walked into my bar and ordered JP5 with a twist. They looked a mysterious duality. He winked and drew a laser. I dodged and the wall behind me burned to a hole. Which was interesting. It would be called the first day of the M-Theory Wars and everyone wanted me dead. So began my quest to defeat.. the Murky Rangers."

 

[GameDaddy]

I was confused for a moment about this notion that an object cannot cross an event horizion. It absolutely can do that. What doesn't happen is that we actually observe this happening. All signals informing us of the events are slowed down and delayed so much we will never see them.

I'm not certain about this, just yet. If someone crossed the event horizon eons ago, we should be able to observe that.

Matter of fact, we should be able to see it all the time, especially with the older black holes, if only that background radiation generated by the accretion disk, and all the rest of the junk that manages an orbit that won't bring it across the event horizon, wasn't obstructing our view.

We should be able to see into the past clearly enough, we certainly do in all other regards...