here are some theoretical questions about time travel?

Question

well i know that the future is undetermind so travel to the future would be impossible, but if a person could travel backward in time, how would the expansion of the universe affect time travel, would the person traveling back in time become more dence on a molecular level the farther back he goes, because doesn't the expansion of the universe cause the mass of the universe to expand with it, would time travel to the past be like being in a black hole.

Answer 1

No, because as the universe expands, the gravitational force on a single point by all parts of the universe gets weaker due to the increasing distance between bodies. So there is no ongoing force that would make a single body less dense. Of course it would be like entering a black hole if you went back to the first few moments of the universe.

Answer 2

Yes, as "minuteblue" pointed out, time travel to the future has been achieved, but going back to the past can prove impossible. Here is why:

Let me begin by pointing out an experiment that was conducted by the government, In which they secured two synchronized atomic clocks. They placed one in a rocket and sent it in to orbit around the earth, at a very high rate of speed. The second clock was left here on earth. When the rocket returned to earth, the time on the clocks were compared one with the other. The clock from the rocket was found to have slowed down. This experiment physically proved that Einstein's Theory of Relativity was indeed true. http://www.btinternet.com/~j.doyle/SR/sr4/sr4.htm

The Theory states that time among other things are relative to the observer: Time can shrink, time can expand depending on your position in space relative to the object in question. So if you left earth, and orbited it at a high rate of speed, you would be younger then you would have been had you not taken the journey. Given enough speed, upon return your Friends would be old and Gray; making it possible to travel to the future. However using speed to get back to your time will prove very difficult if not impposible, you will be stuck in the future. http://www.pbs.org/wgbh/nova/time/through.html

Let me give you an idea of what I think might happen if you could travel back into time. since your presence in the past effects the future, you could and probably would wipe yourself out of existence.

as for the expanding universes effects on a time traveler, Yea you just might find yourself a little more dense, unless you yourself expanded a little on the time trip.

Answer 3

Actually, traveling into the future is far more plausible than traveling into the past at the moment.

Astronauts, when they are in space, orbit the Earth, causing them to be in a constant stat of acceleration. Upon returning to Earth, according to the theory of special relativity, they have aged less than those on Earth.

Sergei Avdeyev, who was in space for over 700 days, is an example of this. Due to the constant acceleration, speed he was going, and time he spent in ths state, he is 1/50 of a second younger than he'd otherwise be.

From another point of view, he traveled into the future by 1/50 of a second.

But to answer your questions, you may find this site very helpful:
http://curious.astro.cornell.edu/question.php?number=274

Answer 4

now if the universe's expansion were cause the rest of mass to expand with it then we would have no knowledge of such behavior because our reference point would be changing with it. therefore blackhole theore would not happen. also if we were to travel threw time our matter would not be effected by the time change. there some people who believe that since not even light can escape a black hole that there would be an absence of time with it. since time can really only be measured using light or movement.

Answer 5

I would say you are thinking of 2 different things. The universe is expanding, not the size of the objects inside it. They just get farther apart.