Philisophical question.

[BigRob]

I personally like the alternate reality theory, but I could susbscribe to any of them really. The butterfly thory would make sense if no alternate realities could exist, but time-travel would be spectacularly dangerous in that kind of world.

 

Anyone care to go ape-hunting in Africa 2000000 BCE?

[Echon]

Time travel will never be possible due to the simple reason that time does not exist. Time is an abstract concept invented by humans to make it easier to relate to the changes that happen in the present. There is no past or future, only a constantly changing present.

 

-Echon

[Guest Guest]

It's a philisophical question, not a scientific one.

[Galactygon]

Your feet stretching to an infinite distance from your head would pose a significantly more immediate problem.

 

Relative to what? An observer standing outside? Both time and space would be distorted in a black hole, but only relative to everything else outside the universe.

 

The fact that you'd be crushed if you standed on a neutron star comes is because the surface crushes you, not the gravity. There is no solid object in a black hole, so you wouldn't get crushed.

 

-Galactygon

[CamDawg]

You understand tidal forces, do you not?

[Galactygon]

I do. It might sound a bit odd for many people who have accepted various other sub-theories revolving around the black hole and the theory of relativity.

 

-Galactygon

[CamDawg]

The point is that you'd never cross the event horizon--my apologies, I did not initially realize you were referring to inside the event horizon. You'd still have the problem of crossing the Cauchy horizon, where all the light (read:energy) that is ever going to fall into the black hole would catch up with you at once.

[Andyr]

Yeah, black holes are one of the theories of possibility. But it is thought that perhaps the hole might close after use, or crush you in the process, or something.

 

I believe you would never reach the center of a black hole beacause time would slow down infinetly as gravity would become infinite. Einstein's Theory of Relativity claims as gravity increases, time slows down.

 

You would just float forever going infinitely nearer and nearer to the center, but you would never make it.

 

-Galactygon

<{POST_SNAPBACK}>

 

I believe this is not quite correct... To an outside observer you would appear to 'freeze' on the event horizon but in actual fact you would pass into the singularity.

 

Cam: The people that think it might be possible suggest it happening on very massive black holes, in which such tidal stretching forces are less extreme (i.e. the difference in force on your head and feet would not be as great). Though, yeh, I dunno what would actually happen.

[CamDawg]

I believe this is not quite correct... To an outside observer you would appear to 'freeze' on the event horizon but in actual fact you would pass into the singularity.

 

Cam: The people that think it might be possible suggest it happening on very massive black holes, in which such tidal stretching forces are less extreme (i.e. the difference in force on your head and feet would not be as great). Though, yeh, I dunno what would actually happen.

It's not so much as you freeze as you would take an infinite time to reach the event horizon--semantics, I know. Whether you then proceed directly to the singularity at the center or do as Galc suggests is still under debate, and given how much we can observe inside an event horizon, not likely to be determined any time soon. You're absolutely correct though--I had learned that the tidal forces become infinite at the event horizon and I must recant it as it is not strictly true, particularly in the case of supermassive black holes.

 

There's an even more interesting theory concerning the idea of "rivers" of matter (!) that can penetrate both the event horizon and the Cauchy horizon with minimal molestaton under very specific circumsances. AFAIK there's been no observations to support it--not that there really could be--and it sounds as practical as the "stable wormhole" time travel machine, but there you go.

 

Poor Loké. Your philosophical question has been entirely hijacked by the geeks and I apologize.

[Andyr]

What's the Cauchy horizon? I do not think I am familiar with it...

[Guest Guest]

Well, to add to what I believe, an object never reaching the center (or, event horizon) relative to an outside observer means that time (or space, rather) would infinitely speed up relative to the object nearing the center.

 

Now, the mystery lies that no one knows what might happen when you see everything sped up infinetly. Perhaps the universe might end with a big crunch, or (most likely) not.

 

That's why I have thoughts you would never reach the destination. I'd be delighted to be proved wrong.

 

-Galactygon

[CamDawg]

What's the Cauchy horizon? I do not think I am familiar with it...

I'd need a better understanding of it myself to adequately explain it. The Cauchy horizon lies inside the event horizon and appears to be the boundary at which causality breaks down. I've seen it described as a chronological or causality horizon as well. One paper suggested that just as the event horizon reverses space and time, so does the Cauchy horizon. At any rate, beyond the Cauchy horizon the mathematics suggest that you could indeed meet yourself by going into orbit around the singularity. This has led to the standard physicist response when faced with a breakdown: a) something will make it not possible, b) you've entered another universe by passing the Cauchy horizon, c) the singularity must be the Cauchy horizon or d) we've gotten it wrong and it must not exist.

 

The practical issue to which I referred, though, was touched upon by Galc. Yes, you would see the history of the universe from inside a black hole--or at least, whatever light would enter the black hole during its lifetime. The problem is that the rate at which you'd see it accelerates asymptotically, so that you would see the majority of light in the last moments. To top it off it would also be radically blueshifted, meaning you would be irradiated with a ridiculous (that's a scientific term ) amount of x and gamma rays.

 

This is assuming that a) Cauchy horizons exist and b) I understand them correctly.

 

Aren't you working with some astrophysicists at Uni? I'd love to hear one of them explain it and what sort of acceptance, if any, it has within the astro/physics community.

 

That's why I have thoughts you would never reach the destination. I'd be delighted to be proved wrong.

 

-Galactygon

I think physicists everywhere would be delighted to see anything on this matter proven at all.

[Andyr]

Cam: Thanks. I wasn't familiar with that name for it, but do know vaguely what you mean.

 

And no, I'm not currently working with astrophysicists. If I get accepted to one of the PhDs I'm applying for, though, I will be...