Black Holes: Falling in and Looking out?

[FGLC Nate]

I think we're all familliar with the old "What if you fell into a black hole?" Event horizons, time dilation (I think is the right term), and spagettification. There is however one thing these thought experiments never seem to cover that I'm really curious about.

As I understand this scenario, once you cross the event horizon all of eternity has passed on the outside universe. Or rather, time is passing infinitely quickly outside. Correct?

So what do you see if you look back out through the event horizon?

Does space junk randomly appear as it is sucked past the event horizon and thus brought closer to your timeframe of referance? Is it just junk or the entire contents of the galaxy or even the universe?

Or, would you look out and see the end of the universe (whatever that may be)?

Or, would you be blinded by an eterneties worth of starlight from all the visible stars light suddenly being released from it's prison on the edge of this frozen star?

 

[PAllen]

I think we're all familliar with the old "What if you fell into a black hole?" Event horizons, time dilation (I think is the right term), and spagettification. There is however one thing these thought experiments never seem to cover that I'm really curious about.

As I understand this scenario, once you cross the event horizon all of eternity has passed on the outside universe. Or rather, time is passing infinitely quickly outside. Correct?

Not correct. If you are watching a distant clock as you fall through the horizon and head for the singularity, you see that clock continuing to advance normally. Further, you will see it registering a short amount of time from when you crossed the horizon until you reach the singularity.

So what do you see if you look back out through the event horizon?

Does space junk randomly appear as it is sucked past the event horizon and thus brought closer to your timeframe of referance? Is it just junk or the entire contents of the galaxy or even the universe?

You can see other objects that fell through the horizon shortly after you did. But not for long - you reach the singularity quite quickly (your time), even though the distant observer never sees anything cross the horizon.

Or, would you look out and see the end of the universe (whatever that may be)?

Or, would you be blinded by an eterneties worth of starlight from all the visible stars light suddenly being released from it's prison on the edge of this frozen star?

 

[Chronos]

An observer free falling into a black hole would see external clocks slowing. The infalling photons stuggle to catch up with the infalling observer as that observer approaches light speed.

 

[PAllen]

An observer free falling into a black hole would see external clocks slowing. The infalling photons stuggle to catch up with the infalling observer as that observer approaches light speed.

Ah, that is even further away from the claim that the infalling observer sees time go infinitely fast outside. All I had figured out is that the proper time on a distant clock world line between the point whose photon reaches the infaller at the horizon, and the point on this clock world line whose photon reaches the infaller at the singularity - is finite and short. I never bothered to investigate the rate of this clock compared the infaller's as seen by the infaller. Thanks for the clarification.

 

[Passionflower]

So what do you see if you look back out through the event horizon?

Does space junk randomly appear as it is sucked past the event horizon and thus brought closer to your timeframe of referance? Is it just junk or the entire contents of the galaxy or even the universe?

Or, would you look out and see the end of the universe (whatever that may be)?

Or, would you be blinded by an eterneties worth of starlight from all the visible stars light suddenly being released from it's prison on the edge of this frozen star?

When you are free falling at escape velocity then exactly at the event horizon you will measure twice the emitted frequency of a beacon far removed.

 

[George Jones]

When you are free falling at escape velocity then exactly at the event horizon you will measure twice the emitted frequency of a beacon far removed.

Half the frequency.

 

[Passionflower]

Half the frequency.

Oops, you are correct, the measured frequencies are red shifted so it is half not double the frequency.

Thanks for correcting me!

 

[PatrickPowers]

I think we're all familliar with the old "What if you fell into a black hole?" Event horizons, time dilation (I think is the right term), and spagettification. There is however one thing these thought experiments never seem to cover that I'm really curious about.

As I understand this scenario, once you cross the event horizon all of eternity has passed on the outside universe. Or rather, time is passing infinitely quickly outside. Correct?

So what do you see if you look back out through the event horizon?

Does space junk randomly appear as it is sucked past the event horizon and thus brought closer to your timeframe of referance? Is it just junk or the entire contents of the galaxy or even the universe?

Or, would you look out and see the end of the universe (whatever that may be)?

Or, would you be blinded by an eterneties worth of starlight from all the visible stars light suddenly being released from it's prison on the edge of this frozen star?

There is a professor at University of Colorado who has put a great deal of effort into animated videos of the interiors of black holes. I heartily recommend his web site, which has some of the best explanations of relativity anywhere. In short, it is very complicated. He says much of the energy goes backward in time, which is has got to be the weirdest physics thing ever.

 

[George Jones]

There is a professor at University of Colorado who has put a great deal of effort into animated videos of the interiors of black holes.

Andrew Hamilton

I heartily recommend his web site, which has some of the best explanations of relativity anywhere.

His site has spectacular animations and some good explanations, but it also has some explanations that are not so good. For example,

Inside the Schwarzschild radius, proper radial distances and proper times appear to become imaginary (that is, the square root of a negative number).

from

http://casa.colorado.edu/~ajsh/schwp.html#redshift

is wrong.

In short, it is very complicated. He says much of the energy goes backward in time, which is has got to be the weirdest physics thing ever.

Can you give a specific reference for this?

 

[PatrickPowers]

Andrew Hamilton


His site has spectacular animations and some good explanations, but it also has some explanations that are not so good. For example,


from

http://casa.colorado.edu/~ajsh/schwp.html#redshift

is wrong.


Can you give a specific reference for this?

[/PLAIN]
http://casa.colorado.edu/~ajsh/phys5770_08/bh.pdf[/URL]

"The Black Hole in the Reissner-Nordstr¨om geometry is bounded at its inner edge by not one
but two inner horizons. The two distinct horizons play a crucial role in the mass inflation
instability described in §3.13.9 below.
The inner horizons can be called ingoing and outgoing. Persons freely falling in the Black
Hole region are all moving inward in coordinate radius r, but they may be moving either
forward or backward in Reissner-Nordstr¨om coordinate time t. The conserved energy along
a geodesic is positive if the time coordinate t is increasing, negative if the time coordinate t
is decreasing. Persons with positive energy are ingoing, while persons with negative energy
are outgoing. Both ingoing and outgoing persons fall inward, to smaller radii, but ingoing
persons think that the inward direction is towards the Wormhole, while outgoing persons
think that the inward direction is in the opposite direction, towards the Parallel Wormhole.
Ingoing persons fall through the ingoing inner horizon, while outgoing persons fall through
the outgoing inner horizon."

 

[George Jones]

Thanks. When I get some time, I will take a detailed look at this. Also, to be fair, I should explain why I think that the passage which I quoted is wrong.

I'm not sure when I will get the required time. Papers at which I have to look are accumulating on my desk at such a rate that a black hole threatens to form.