# A proof against time travel

#### MathematicalPhysicist

Gold Member
what proof will do in order to wrap it up?
do we need a mathematical proof or experimental proof (although i dont know how could do it, perhaps with a thought experiment which the results are known)?

for the question of thought experiment could the time paradoxes do it for a proof that time travel is impossible?

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#### Fuego

i don't think its possible to disprove timetravel (yet), even on a macroscopic level.

you are trying to prove a negative which is hard to do.

i don't think it can be disproved with mathematics due to Godel's incompleteness theorem.

the various time travel paradoxes are only paradoxes if you believe things will have a 'free will' when they go back in time.

#### jcsd

Gold Member
There's not solid proof that (bacwrads) time-travel is impossible, infact in GR there are certain situations where it does occur, though no-one has yet found a physically realistic way.

#### Sikz

There's not solid proof that (bacwrads) time-travel is impossible, infact in GR there are certain situations where it does occur, though no-one has yet found a physically realistic way.
There are? What are they?

#### jcsd

Gold Member
Well one involves a rotating universe (a Godel universe) and the other infintely long cylinders (Van Stokum cylinders)

#### MathematicalPhysicist

Gold Member
would you care to explain about the latter?

#### jcsd

Gold Member
Orbits around infintely long cyclinders can lead to temporally closed loops in GR.

Staff Emeritus
Gold Member
Dearly Missed
The cylinders have to be rotating and massive. IIRC the circumference had to be moving at above 1/3 the speed of light. James Tipler had a piece of this solution too. If I am not mistaken there are CTCs (closed timelike curves) in the neighborhood of a Kerr (spinning) black hole also.

All of these solutions depend on a massive spinning object. The idea is that the combination of high curvature due to strong gravity and weird coordinates due to spin will cause the light cones to tip over so that the past cone of one point overlaps the future cone of a nearby one, enabling a timelike path that goes into the past and returns.

Proof against time travel? Forward time travel happens whenever two bodies have differing velocities relative to each other, and has been measured and recorded with atomic clocks on airplanes. The only limiting factor to how far forwards in time you can travel is how fast you can go..

Secondly, isn't backwards time travel (FOR SMALL INTERVALS OF TIME) not only possible, but an essential part of Feynmans QED theory?

So NO, their will never be proof against it, only proof for it!

J

#### jpritch

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#### hey.like

The proof should right first

If the question is wrong or no value, no mean to proof by some times.
specialy in a future study direction, I think it is no mean.

#### VBPhysics

feynmann did argue the possibility of time travel (for the subatomic world anyway). In a simplified sense, He argued the existence of positrons as electrons floating backwards in time with the photons given off in e+ e- interactions as the U-turn in time triggers. The one really interesting extrapelation from this idea is that there could be only one electron in the universe.

"A proof against time travel"

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