# Can black holes be used for time travel?

1. Jan 4, 2004

### lan418

As ridiclous and far-fetched as it may seem, say if one is able to get past the event horizon, hypothetically. Do you believe a hole in space is a bridge between several other dimensions where you are able to go back through time?

2. Jan 5, 2004

### Orion1

Space-Time...

Q: Do you believe a hole in space is a bridge between several other dimensions where you are able to go back through time?

Your reference is to a WormHole.

Reverse-Time Travel results in a new Space-Time Coordinate, i.e. another dimension.
$$C(X, Y, Z, \Delta T_0) -> C(X, Y, Z, T_0 - T_1)$$

However, read the provided reference material and arrive at your own conclusions.

Reference:
http://www.geocities.com/zcphysicsms/chap12.htm#BM12_2

Last edited: Jan 5, 2004
3. Jan 5, 2004

### kleinma

way i see it.. if time travel was possible (into the past) we would all be gone due to some paradox that would undo the universe...

as far as time travel into the future, suspended animation seems to be the only likely posibility, which while not instant, it would seem so to the one traveling

4. Jan 5, 2004

### lan418

I believe that it is possible to mess with time concerning those wormholes. My opinion is: We aren't the only universe that is present. Other parallel universes may coexist with ours, the only difference is time.

5. Jan 6, 2004

### kleinma

and Jet Lee lives in each one right?

6. Jan 6, 2004

### Loren Booda

Look up to the stars for light illuminating events billions of years in the past.

Our spacetime horizons are necessarily defined as limits that disallow our relative travel into the past, or observation of such travel by massive bodies. The horizon demarcates superluminal from other velocities, and restricts our physics to |v|<c.

7. Jan 6, 2004

### lan418

Oh, he lives in more than just two of these...

8. Jan 6, 2004

### Orion1

Cerenkov...

Physics is not necessarily restricted to $$|v| < c$$.

For example, in the Cerenkov Effect the particle's wave velocity exceeds the medium luminal velocity $$|u| > v(w)$$.

The cerenkov particle is observable from the luminous 'shock wave' emitted from the transluminous particle. Therefore physical observational restrictions are not necessarily restricted to subluminal velocities.

It is possible to describe space-time as a medium conductor for 'vacuum' luminous velocity. Transluminous velocities in such a medium is only possible if the physics allows this, for example the existence of a Wormhole or Blackhole.

It can be suggested that a particle transcending a Wormhole vortex or Black Hole event horizon also emits cerenkov radiation.

Cerenkov Shock Wave:
$$|u| > v(w)$$
$$\sin \Theta = \frac{ u}{v(w)}$$

Reference:
http://teachers.web.cern.ch/teachers/archiv/HST2002/Bubblech/mbitu/cerenkov_effect.htm

Last edited: Jan 6, 2004
9. Jan 7, 2004

### Loren Booda

[correction]... and restricts our physics with massive bodies to |v|<c.

10. Jan 7, 2004

Staff Emeritus
11. Jan 7, 2004

### Orion1

Einstein's neighbor at Princeton, Kurt Gödel, perhaps the greatest mathematical logician of the past 500 years, found a new solution to Einstein's own equations which allowed for time travel.

The 'river of time' now had whirlpools in which time could wrap itself into a circle. Gödel's solution was quite ingenious: It postulated a universe filled with time that flowed like a rotating fluid. Anyone walking along the direction of rotation would find oneself back at the starting point, but backwards in time!

in 1963, Roy Kerr, a New Zealand mathematician, found a solution of Einstein's equations for a rotating black hole, which had bizarre properties. The black hole would not collapse to a point (as previously thought) but into a spinning ring (of neutrons). The ring would be circulating so rapidly that centrifugal force would keep the ring from collapsing under gravity.

Anyone walking through the ring would not die, but could pass through the ring into an alternate universe.

In the quantum theory, we can have multiple states of any object. For example, an electron can exist simultaneously in different orbits (a fact which is responsible for giving us the laws of chemistry). Similarly, Schrödinger's famous cat can exist simultaneously in two possible states: dead and alive. So by going back in time and altering the past, we merely create a parallel universe. So we are changing someone ELSE's past by saving, for example, Abraham Lincoln from being assassinated at the Ford Theater, but our Lincoln is still dead. In this way, the river of time forks into two separate rivers.

Because of the enormous amount of work done by theoretical physicists within the last five years or so, Hawking has since changed his mind, and now believes that time travel is possible (although not necessarily practical).

Wheeler has argued that because there is no such thing as time in the singularity, when BKL tidal gravity forces peak, space gives way to "Quantum foam"

The previously provided references by Loren, Adjoint are not in respect to trans-event horizon luminous velocity physics for WormHoles and Black Holes, but rather for accretion disk flux.

If transluminous physics were impossible then the cerenkov effect u > v(w) would violate Lorentz Invariance, and as a result, the cerenkov effect would be theoretically impossible.

Loren is correct that cosmic obsevations are limited by |v| < c, however physics and Superstring Theories are not necessarily limited by |v| < c, but rather by |u| > v(w).

Proof that space-time fabric is a medium for luminous velocity is from the curved space-time effects on photon vectors resulting in the 'lensing effect'.

Space-Time medium luminous velocity
B, p are not constant or new constant for |v| < c
$$v(w) = \sqrt{ \frac{ B}{p}}$$

Universal Vacuum:
B, p are constant for |v| = c
$$v(w) = \sqrt{ \frac{ B}{p}} = \frac{1}{ \sqrt{ \mu_o \epsilon_o}} = c$$

Space-Time Fabric Medium:
$$B = \frac{ 1}{ \epsilon_o}$$
$$p = \mu_o$$

B, p are not constant or new constant for |v| > c
$$v(w) = \sqrt{ \frac{ B}{p}} \geq c$$

v(w) - Space-Time medium luminous velocity.
B - Space-Time Bulk Modulus.
p - Space-Time fabric density.

Reference:
http://www.pbs.org/wnet/hawking/mysteries/html/kaku1-1.html
http://dnausers.d-n-a.net/dnetGOjg/Black/Holes.htm

12. Jan 8, 2004

### Labguy

Quote from above(Partial):
"If transluminous physics were impossible then the cerenkov effect u > v(w) would violate Lorentz Invariance, and as a result, the cerenkov effect would be theoretically impossible."

I really don't know exactly the point being made regarding the original "time travel" post, but can't agree with the "transluminous" V being possible with the Cerenkov effect used as an example. The charged particles travelling in a non-vacuum, transparent medium (water in this case) create a phase angle of the light cone emitting the Cerenkov photons, usually violet, and the charged particle is in effect travelling, by time, a longer path than the apparent straight line. It has been shown that Cerenkov radiation and Synchotron radiation are essentially the same animal from the same/similar process. See: http://www.hep.princeton.edu/~mcdonald/accel/bates86.pdf for a fair bit on that. "Phase angle" of the cone depending on the refractive index of the particular medium.

Also, we, the observer, see the charged particle travelling at V > c in that medium, but that is our observation and in a TIME measured and perceived by us. To the charged particle itself, its time is such that it is not exceeding c. The Cerenkov effect is possible, and observed but the Lorentz Invariance is not being violated. Cerenkov radiation is commonly seen in the "Gamma Ray Cascades"(electromagnetic showers) in the Earth's atmosphere as seen at: http://www.shef.ac.uk/physics/teaching/phy320/topic8.html

One university(Leeds) explanes, in a crumpled paper I have a copy of, that for the speedy particles:

"The result of this is that there is an intense time dilation, where by the particles experience time slower than we do. This is exactly the same as the proverbial "twins paradox". In the twins paradox two people, twins, are separated one remains on Earth while the other experiences travel at speeds approaching c. After a given length of time as measured by the Earth bound twin, the two people are reunited. However, the length of time the twin moving with velocity tending towards c is always less than the earth bound twin. We can calculate this using the Lorentz Fitzgerald contraction. The one we are interested in is time:
T=To/sqrt(1-(v2/c2))"

So, I guess I'm of the opinion that the Cerenkov "effect" is just that, an apparent but not an actual superluminal event.

Last edited: Jan 8, 2004
13. Jan 9, 2004

### Orion1

Cerenkov Relativity...

Cerenkov Lorentz Invariance:

$$v(w) = \frac{ c}{ n} < c_v$$

n - index of refraction, n = 1.333 (H2O)

$$\cos \Theta = \frac{ c}{ n v} = \frac{ v(w)}{u}$$

$$\Theta$$ - Cerenkov angle

$$T' = \frac{ T_0}{ \sqrt{ 1 - ( \frac{ v}{ c})^2}}$$

Lorentz Invariance Violation: u > v(w)
$$T' = \frac{ T_0}{ \sqrt{ 1 - ( \frac{ u}{ v(w)})^2}}$$

Lorentz Invariance Conservation: v(w) < u < c
$$d' > d_0$$
$$v'T' > v_0 T_0$$

$$u = \frac{ v(w)}{ \cos \Theta}$$

$$T' = \frac{ T_0}{ \sqrt{ 1 - ( \frac{ v(w)}{ c \cos \Theta})^2}}$$

14. Jan 9, 2004

### Labguy

Re: Cerenkov Relativity...

Neat math! What does it mean as a reply to a "time travel" question?

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