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-   -   Black holes, white holes, and time (http://www.physicsforums.com/showthread.php?t=315339)

ocman May20-09 05:07 PM

black holes, white holes, and time
 
Please forgive me if I am posting in the wrong place, and also if this has been discussed before.

Gravity is so strong in a black hole not even light can escape, Can the light be accelerated past c once inside of the event horizon? I know the universal answer that nothing can exceed c, but don't the laws of physics start to break down in a singularity? If (theoretically) the light did exceed c, it's my understanding that it could go back in time. Having read the discussions I understand that there is no point of reference for a photon, but some suggest that time for the photon doesn't exist, which leads me to wonder if the photons are accelerated past the speed of light they would then travel backward through time and return to their point of origin, and this return is seen by us as quasars(white holes?) and even the big bang(the biggest white hole ever?). The number one problem I have with this is the chicken and the egg.

I hope this is clear enough to illustrate my thoughts.

tiny-tim May20-09 06:35 PM

Welcome to PF!
 
Hi ocman! Welcome to PF! :smile:
Quote:

Quote by ocman (Post 2206661)
Can the light be accelerated past c once inside of the event horizon? I know the universal answer that nothing can exceed c, but don't the laws of physics start to break down in a singularity?

From a distance, light may seem to change speed (for example, light going very near the Sun)

But measured locally, light always has a speed of c.

(and, of course, the inside of an event horizon isn't a singularity the singularity is only at the exact centre :wink:)
Quote:

If (theoretically) the light did exceed c, it's my understanding that it could go back in time.
No, there's nothing in the maths that suggests that going faster than c would send anything backwards in time that's just a Star Trek thing. :wink:

Vorbis May20-09 07:04 PM

Re: black holes, white holes, and time
 
Hmm. I've always believed that traviling faster than c (which is impossible anyway) would send you back in time.

benk99nenm312 May20-09 07:35 PM

Re: black holes, white holes, and time
 
Vorbis is right. Tiny Tim, I'm sorry. :smile:

Take tachyons for example. They have imaginary relativistic mass. How? They exceed speed C. According to Einstein's formula,

E = mc^2
___(1- v^2/c^2)^ 1/2

Tachyons go backwards in time because they exceed speed c.

If I run fast, I age more slowly. If I run near the speed of light, I age extremely slowly. If I run at speed c (ignore the impossibilities) I will not age at all. If I outrun this, I start to get younger, or I age backwards in time.

But, it doesn't matter. If a photon would exceed speed C, it would attribute imaginary relativistic mass. This is most likely not possible.

tiny-tim May21-09 04:44 AM

Hi Vorbis! Hi benk99nenm312! :smile:

(try using the X2 tag just above the Reply box :wink:)
Quote:

Quote by benk99nenm312 (Post 2206794)
E = mc2
___√(1- v2/c2)

Tachyons go backwards in time because they exceed speed c.

If I run fast, I age more slowly. If I run near the speed of light, I age extremely slowly. If I run at speed c (ignore the impossibilities) I will not age at all. If I outrun this, I start to get younger, or I age backwards in time.

Nope time dilation is √(1- v2/c2), which of course -> zero as v -> c

but for v > c, √(1- v2/c2) is imaginary, not negative

as I said
Quote:

there's nothing in the maths that suggests that going faster than c would send anything backwards in time that's just a Star Trek thing.
:wink:

benk99nenm312 May21-09 06:57 AM

Re: black holes, white holes, and time
 
√(1- v2/c2) has two solutions, just like every other square root. It would be possible to get a negative solution.

As I stated, tachyons have some odd properties. One, they go backwards in time. Two, they accelerate when they lose energy. How would this exotic property be possible without going backwards in time?

tiny-tim May21-09 07:13 AM

Quote:

Quote by benk99nenm312 (Post 2207248)
√(1- v2/c2) has two solutions, just like every other square root. It would be possible to get a negative solution.

Yes so slower-than-light particles can travel either forward or backward in time.

But tachyons can't their time dilation is imaginary (and minus imaginary is still imaginary :wink:)
Quote:

As I stated, tachyons have some odd properties. One, they go backwards in time
No they don't

If we see a tachyon going from A to B, another observer may see it go from B to A that's all!
Quote:

Two, they accelerate when they lose energy. How would this exotic property be possible without going backwards in time?
Nooo energy = m0/√(1 - v2/c2), so either the energy of tachyons is also imaginary, or their rest-mass is.

benk99nenm312 May21-09 05:38 PM

Re: black holes, white holes, and time
 
[QUOTE=tiny-tim;2207256]No they don't

If we see a tachyon going from A to B, another observer may see it go from B to A that's all!QUOTE]

I see what you're on to. My definition of backwards in time is the observation, not necessarily whether it, the particle goes backwards in time. You are merely stating that the state of the particle, because it appears to travel backwards to an oberver, would appear to be negative but would really be positive due to the fact that it is imaginary.

The particle appears to an observer to backwards in time, even though it really doesn't. Are we in agreement now? :smile:

tiny-tim May21-09 05:50 PM

Hi benk99nenm312! :smile:
Quote:

Quote by benk99nenm312 (Post 2207911)
My definition of backwards in time is the observation, not necessarily whether it, the particle goes backwards in time.

Not following you we must observe things going forward in time, mustn't we? :confused:
Quote:

You are merely stating that the state of the particle, because it appears to travel backwards to an oberver, would appear to be negative but would really be positive due to the fact that it is imaginary.
Sorry, not following any of this :redface: and I'm definitely not saying it.
Quote:

The particle appears to an observer to backwards in time, even though it really doesn't. Are we in agreement now? :smile:
The tachyon appears to one observer to go, say, from the torch to the screen, but appears to another observer to go from the screen to the torch.

Both observers see it going forward in time (but the second observer thinks it looks weird :rolleyes:)

benk99nenm312 May21-09 06:39 PM

Re: black holes, white holes, and time
 
Quote:

Quote by tiny-tim (Post 2207924)
Hi benk99nenm312!
Both observers see it going forward in time (but the second observer thinks it looks weird.


Exactly. The second observer sees the process happen backwards, or reversed. That is what I was trying to say. But even so, from the particle's view, it is doing something sensible. If I were to throw an apple at a velocity of 1o meters per second, it continue forward. If I were to somehow give it energy.. enough to travel past the speed of light (somehow), it would gain velocity, and then, after it passes speed c, something happens. The apple, From its reference frame, would continue forward, accelerating as it does so. But I would start to see the apple slow down, and reverse its direction of motion. :biggrin:

It is that difference in apparent motion through space and time that I am trying to explain. Its prosseses are reverse from the observer's point of view. That is what I'm getting at. The apple itself never travels backwards in time, but we see its motion reversed. It, in a way, acts like an apple traveling backwards in time, because the motion in space is reversed. However, you are right when you say it is not actually going backwards in time.

I hope that clears it up. :smile:

tiny-tim May22-09 05:21 AM

Quote:

Quote by benk99nenm312 (Post 2207988)
If I were to somehow give it energy.. enough to travel past the speed of light (somehow), it would gain velocity, and then, after it passes speed c, something happens. The apple, From its reference frame, would continue forward, accelerating as it does so. But I would start to see the apple slow down, and reverse its direction of motion. :biggrin:

Nooo if you keep your velocity the same, you will simply see the apple go faster and faster (and faster than light) in the same direction

that's what speed is!

No observer will see anything reverse its direction of motion.

benk99nenm312 May22-09 07:02 AM

Re: black holes, white holes, and time
 
Quote:

Quote by tiny-tim (Post 2208528)
Nooo … if you keep your velocity the same, you will simply see the apple go faster and faster (and faster than light) in the same direction

that's what speed is!

No observer will see anything reverse its direction of motion.

But you have said it yourself.
"The tachyon appears to one observer to go, say, from the torch to the screen, but appears to another observer to go from the screen to the torch."

I'm getting confused. I need some decent sleep. :smile:

Also, now that I think of it, we couldn't see it pass the speed of light. Light wouldn't be able to keep up with it.

pegasus980 Aug12-09 05:13 AM

Re: black holes, white holes, and time
 
Quote:

Quote by benk99nenm312 (Post 2208592)
Also, now that I think of it, we couldn't see it pass the speed of light. Light wouldn't be able to keep up with it.

so there might be stuff travelling faster than the speed of light but we just can't detect it?

benk99nenm312 Aug12-09 08:13 AM

Re: black holes, white holes, and time
 
Quote:

Quote by pegasus980 (Post 2306024)
so there might be stuff travelling faster than the speed of light but we just can't detect it?

Not quite what I meant haha.

You wouldn't see it from behind, because light would have trouble catching up. Although, photons are still bouncing off the front face of the apple, at least, I think. In the last example, the front face is on the opposite side, so it would make it rather difficult to see I believe. This is a hazy subject for most haha, since it is speculative to begin with.


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