# Relativistic Effects of a Black Hole

1. Jul 11, 2013

### m_robertson

So, I was thinking about this the other day. If we watch material approaching near the event horizon of a black hole get scattered all over the place, then would the opposite be seen for an observer falling into a black hole? Instead of us seeing them scattered all over the place, would they see the universe around them get scattered all over the place instead? Because if for the observer falling into the black hole they notice no significant changes in space-time, then surely according to relativity it must the the universe which changes instead?

I remember the debate that the thermodynamic properties of a black hole, such as, heat, entropy and electromagnetic radiation, do not reflect the real contents of the black hole, so if the observer was able to make measurements of the universe around them, how would it look from their perspective and what kind of measurements would they make? Would the universe appear hotter, with higher entropy and stronger electromagnetic radiation instead?

2. Jul 11, 2013

### Simon Bridge

What do you mean by "scattered all over the place"?

Note - infalling light gains energy.
Don't forget time dilation etc.

3. Jul 11, 2013

### m_robertson

One argument says an object passes through the event horizon, the other argument says it is destroyed at the event horizon, if both are true then there must be equal and opposite relativistic effects (assuming a person within a black hole could observe and measure the outside world), which is what I'm enquiring about.

4. Jul 12, 2013

### Simon Bridge

5. Jul 12, 2013

### m_robertson

See: Black Hole Complementarity

Last edited by a moderator: Sep 25, 2014
6. Jul 12, 2013

### Simon Bridge

The question was designed to guide you ... what is it about the presentation in the video that suggests that things are both destroyed at the event horizon and also pass through it?

7. Jul 13, 2013

### Simon Bridge

Hmmm no?
I think you have misunderstood what the video is about.

Recall - everything in relativity depends on the observer.
Alice approaching the event horizon passes through - presumably seeing a curtain glowing with Hawking radiation, and Bob, a long way away, sees the thermalized radiation that is sent back. Only one thing happens in each reference frame. Can you find a frame in which both things must happen, bearing in mind that no observer is omniscient?

8. Jul 14, 2013

### timmdeeg

Hmmm, what means "a curtain glowing with Hawking radiation"?
I think a freely falling observer will see the Hawking radiation blue-shifted. And besides that he will see nothing special while passing through the event horizon.

9. Jul 18, 2013

### Simon Bridge

10. Jul 19, 2013

### timmdeeg

Thanks, I wonder how serious the firewall conjecture is considered.

http://en.wikipedia.org/wiki/Firewall_(physics [Broken])

Last edited by a moderator: May 6, 2017
11. Jul 19, 2013

### Simon Bridge

How would you go about finding out?
Have you tried doing a literature review?

12. Jul 20, 2013

### Chronos

The firewall conjecture is interesting, even attractive at some level. But, I think it ultimately fails. Applying a naïve form of complementarity, it might appear the external universe is time accelerated and blue shifted toward infinity for an infalling observer crossing the event horizon. This is untrue. Actually the exterior universe is red shifted asymptotically towards z=2. See http://www.phys.vt.edu/~jhs/faq/blackholes.html#q11 for a thumbnail discussion.

13. Jul 20, 2013

### timmdeeg

Thanks for these hints and the very interesting link. I will be in the mountains for a while and might come back to this.

14. Jul 20, 2013

### Chronos

Black holes are not very intuitive. That explains why so many related papers are still being published.

15. Jul 20, 2013

### Haelfix

The black hole firewall argument(s) is taken very seriously by most experts, and at this time, no resolution to the paradox exists.

The general 'feeling' is that it probably is untrue, and that complementarity holds at some level, but the details are still very much a work in progress.

16. Jul 22, 2013

### m_robertson

Sorry for the late reply. Both things don't happen in the same frame, they happen in two separate frames of reference but according to relativity both accounts are true.

The question I'm asking is, if Alice passes through the event horizon unharmed, then what relativistic effects does she, or would she hypothetically speaking, observe in the universe around her as she passes through the event horizon? If we measure the event horizon and find heat content as well as other forms of radiation (which according to most views of science we would do), then we could assume that she hit the firewall and was destroyed at the event horizon. But if Alice actually passes through the event horizon unharmed then she must observe at least some relativistic phenomenon around her as she passes through the event horizon. She appears to have hit the firewall in our frame of reference, but in her frame of reference nothing special happens, so to her would it appear as if we hit a firewall instead? Or perhaps an "icewall?"

Last edited: Jul 22, 2013
17. Jul 23, 2013

### Simon Bridge

That question is explicitly answered in the video in the context of the apparent paradox.

I also gave you a link that discusses what sort of effects she will experience.
To her, the Schwarzschild radius is no different from any other spot in space as far as general travel is concerned. Presumably she will be able to detect the hawking radiation from around there as she approaches it (someone correct me). What sort of effects did you have in mind?

Relativistic effects are not normally observed directly - they become apparent only when you have to compare two reference frames. i.e. the only time the twins paradox is important is when the twins meet to compare notes. In that case, they both agree about which twin is the younger, but disagree about how this happened. If the twins never communicated, they'd go on "seeing" the other as the younger one... and the "paradox" is unresolved from the POV of a hypothetical omniscient observer who can "see" both situations "at the same time".

In this example, Alice and Bob can never meet - not even in principle.
The point the speaker in the video is trying to make is that the conflict is only apparent from the POV of someone omniscient.

This is work in progress mind you - all the vid is saying in the end is that it is a little early to abandon the picture held since the 40's (?)

18. Aug 4, 2013

### SriLanka

Can you explain that for me.

19. Aug 5, 2013

### Simon Bridge

20. Aug 8, 2013