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# Theory of Relativity and Time Travel

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I'm fascinated by the Theory of Relativity and have tried hard to understand it but it still leaves me confused. I'm not sure I understand the literal meaning behind going back in time. I'm hoping you guys could shed some light on this for me.

My questions don't exactly revolve around the ideas that are portrayed in movies such as a person getting into a machine to travel back in time. I've seen many people say that you couldn't travel back further than the date a time travel machine was made but I'm trying to stay away from that concept. I'm more interested in what exactly it means to go back in time based on the Theory of Relativity.

The way I understand it is as follows. Please let me know if I have something wrong.
1. The faster you are moving, the slower time is going. (Clocks move slower)
2. To completely stop time, you would have to travel exactly at the speed of light. (Clock Stops)
3. If you travel faster than the speed of light, you are now going back in time. How does the Theory of Relativity and the idea of "Time Travel" work?

My questions based on the list above are -

Q. If you are moving fast enough to slow down time, does that literally mean that you age slower?

Q. People are living close to 100 years old on earth. If I was moving fast enough, could I live to be 200, 300, 400, etc.?

Q. Does time feel the same? In other words, if somehow there was a way to set up an experiment where a person lived on earth in specific conditions for 1,000 days. Then that same person was able to live in a replicated environment with the exact same conditions but at a much higher velocity for 1,000 days, would it feel as though the 1,000 days went by quicker when moving at a faster speed?

Q. Take the same experiment above but for this question, lets say there are two people - Person 1 lives on earth in specific conditions for 1,000 days. Person 2 somehow has a plane with the exact same conditions that will circle around the earth for 1,000 days without refueling and at a much higher velocity. After each person has finished their 1,000 days, they are to report back to their facility. Would person 2 physically report and walk back into their facility while person 1 still has days left to go before their 1,000 days are finished?

Q. If I was able to move at the speed of light, it is said that it would stop time. Lets say an experiment was set up as follows - I stand still at the starting line and watched a normal ticking clock. As soon as the clock struck 1:00, I would immediately start running around the block 1,000,000 times at the speed of light. Somehow, I am able to stop on a dime right where I started. When I did stop, would the clock still be at 1:00?

Q. Would it matter how many times I ran around the block? If I ran an infinite number of times around the block, would the clock still be at 1:00 regardless of when I stopped? In other words, is there a certain amount of laps to where the clock would eventually move?

Q. If the above question is correct as in the clock would still be at 1:00, would that essentially mean that if I was a builder of some sort, lets say furniture - I could stand right in front of you, build a new chair at the speed of light and to you, it would almost appear as though the chair magically appeared?

Q. On the idea of being able to physically go back in time as shown in the movies. It doesn't sound as though a time machine is really necessary as far as it being some kind of portal that you enter and leave. A real time machine sounds more like a vehicle that is able to carry you at a speed faster than the speed of light. Lets say I had a vehicle that would move faster than the speed of light and I circled the earth long enough to go back to when I was 15 years old. The means my physical body sat inside a vehicle, left earth on a plane and re landed 15 years in the past. I then drove back to the home I lived in at that time. Would there now be two of me?

Q. If the above question is not true as in there would not be two of me - would I just re land on earth as a 15 year old? If so, when I drove back to the home I lived in at that time, would it be as though I'm just walking back in the house as the same 15 year old I was then? Would it just eliminate the memory of traveling back in time and the memories I gained from 16 years old on? I mean somehow I had to remember how to land the plane.

Those are a few questions I don't really see being talked about much and a couple of them I can't fathom how they would be possible. I appreciate you guys for taking the time to read the post. I apologize for it being a bit long but hopefully this can spark an interesting discussion that can focus on some of the, what I think are, the most interesting details about this topic that are kind of left vague in most published articles. I'm looking forward to hearing your thoughts.

Thanks

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Just now, Mx449 said:

The way I understand it is as follows. Please let me know if I have something wrong.

1. The faster you are moving, the slower time is going. (Clocks move slower)
2. To completely stop time, you would have to travel exactly at the speed of light. (Clock Stops)
3. If you travel faster than the speed of light, you are now going back in time. How does the Theory of Relativity and the idea of "Time Travel" work?

My questions based on the list above are -

Q. If you are moving fast enough to slow down time, does that literally mean that you age slower?

Q. People are living close to 100 years old on earth. If I was moving fast enough, could I live to be 200, 300, 400, etc.?

Q. Does time feel the same? In other words, if somehow there was a way to set up an experiment where a person lived on earth in specific conditions for 1,000 days. Then that same person was able to live in a replicated environment with the exact same conditions but at a much higher velocity for 1,000 days, would it feel as though the 1,000 days went by quicker when moving at a faster speed?

Q. Take the same experiment above but for this question, lets say there are two people - Person 1 lives on earth in specific conditions for 1,000 days. Person 2 somehow has a plane with the exact same conditions that will circle around the earth for 1,000 days without refueling and at a much higher velocity. After each person has finished their 1,000 days, they are to report back to their facility. Would person 2 physically report and walk back into their facility while person 1 still has days left to go before their 1,000 days are finished?

Q. If I was able to move at the speed of light, it is said that it would stop time. Lets say an experiment was set up as follows - I stand still at the starting line and watched a normal ticking clock. As soon as the clock struck 1:00, I would immediately start running around the block 1,000,000 times at the speed of light. Somehow, I am able to stop on a dime right where I started. When I did stop, would the clock still be at 1:00?

Q. Would it matter how many times I ran around the block? If I ran an infinite number of times around the block, would the clock still be at 1:00 regardless of when I stopped? In other words, is there a certain amount of laps to where the clock would eventually move?

Q. If the above question is correct as in the clock would still be at 1:00, would that essentially mean that if I was a builder of some sort, lets say furniture - I could stand right in front of you, build a new chair at the speed of light and to you, it would almost appear as though the chair magically appeared?

Q. On the idea of being able to physically go back in time as shown in the movies. It doesn't sound as though a time machine is really necessary as far as it being some kind of portal that you enter and leave. A real time machine sounds more like a vehicle that is able to carry you at a speed faster than the speed of light. Lets say I had a vehicle that would move faster than the speed of light and I circled the earth long enough to go back to when I was 15 years old. The means my physical body sat inside a vehicle, left earth on a plane and re landed 15 years in the past. I then drove back to the home I lived in at that time. Would there now be two of me?

Q. If the above question is not true as in there would not be two of me - would I just re land on earth as a 15 year old? If so, when I drove back to the home I lived in at that time, would it be as though I'm just walking back in the house as the same 15 year old I was then? Would it just eliminate the memory of traveling back in time and the memories I gained from 16 years old on? I mean somehow I had to remember how to land the plane.

Those are a few questions I don't really see being talked about much and a couple of them I can't fathom how they would be possible. I appreciate you guys for taking the time to read the post. I apologize for it being a bit long but hopefully this can spark an interesting discussion that can focus on some of the, what I think are, the most interesting details about this topic that are kind of left vague in most published articles. I'm looking forward to hearing your thoughts.

Thanks

From your perspective time runs at the same rate for you regardless of how fast you are travelling.

It is other people travelling slower or faster than you which you see as having an altered flow rate of time. Those travelling slower than you have a faster flow rate of time. Those travelling faster than you have a slower flow rate of time.

Time travel is thought impossible because not all of the known forces have time symmetry meaning you cannot get back to the same position by reversing the flow of time. That leaves the only means for time travel being if the universe isn't stationary but moving faster than 0m/s.

We currently have the technology to create a `stasis chamber` allowing a person sat inside to experience a day passing inside for years outside. Electro-magnetic fields also cause time dilation so a chamber with walls made from electro-magnets charged to trillions upon trillions of volts would work.

Unfortunately you would need to be a billionaire to afford the electricity bill.

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1 hour ago, Mx449 said:

The way I understand it is as follows. Please let me know if I have something wrong.
1. The faster you are moving, the slower time is going. (Clocks move slower)
2. To completely stop time, you would have to travel exactly at the speed of light. (Clock Stops)
3. If you travel faster than the speed of light, you are now going back in time. How does the Theory of Relativity and the idea of "Time Travel" work?

Time is experienced different from an observers point of view, not for the one who is involved in the time distortion. If you travel half the speed of light for a year (your clock and calendar helps you keep track of time), you will experience it as a year. No more, no less. But when you return to your starting point, much more than a year has passed for everybody else (the observers).
Traveling at the speed of light or higher is only possible in thought experiments, because matter turns into energy at that speed. It loses it's solidity. And speeds above is a violation of natures laws. You can't do it.

1 hour ago, Mx449 said:

Q. If you are moving fast enough to slow down time, does that literally mean that you age slower?

Not from your own POV, but for everybody else, yes.

1 hour ago, Mx449 said:

Q. People are living close to 100 years old on earth. If I was moving fast enough, could I live to be 200, 300, 400, etc.?

Again, only from the perspective of those who observe you. You would not experience living longer yourself.

1 hour ago, Mx449 said:

Q. Does time feel the same?

Yes. Always. Time feels the same no matter if you time travel or not.
Imagine you travel 1 hour into the future, and the journey takes 10 seconds. Your friend watches you do it.
You count to ten, and an hour has passed. You did not feel any difference. But your friend will tell you an amazing story afterwards!
He'll tell you, that you almost froze, moving extremely slow, and that it took you 10 minutes to say "one", 10 minutes to say "two", a.s.o...

1 hour ago, Mx449 said:

When I did stop, would the clock still be at 1:00?

Yes, and maybe a few Planck time units, if you had a clock that could count those.

1 hour ago, Mx449 said:

Q. On the idea of being able to physically go back in time as shown in the movies.

Sorry, that is a violation of causality, one of the laws of relativity. You can't reverse entropy.

Hope the above answers are satisfying. If not, you are welcome to ask again.

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10 hours ago, Mx449 said:

Q. People are living close to 100 years old on earth. If I was moving fast enough, could I live to be 200, 300, 400, etc.?

Not from your frame of reference.

10 hours ago, Mx449 said:

Q. Does time feel the same? In other words, if somehow there was a way to set up an experiment where a person lived on earth in specific conditions for 1,000 days. Then that same person was able to live in a replicated environment with the exact same conditions but at a much higher velocity for 1,000 days, would it feel as though the 1,000 days went by quicker when moving at a faster speed?

Assuming the days are fixed time periods, you'd both experience 1,000 days.  However the time comparisons will be different.  During this experiment you'd be away longer from earth than 1,000 days.

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Small edit to my above post: It would take 6 minutes to say "one" a.s.o., not 10.

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22 hours ago, Mx449 said:

Q. If you are moving fast enough to slow down time, does that literally mean that you age slower?

Only relative to someone not travelling at these speeds. This is meant by "relativity" - it is that time is only measured a certain way relative to other reference points. There is no "ultimate" time.

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Q. People are living close to 100 years old on earth. If I was moving fast enough, could I live to be 200, 300, 400, etc.?

No, because your perception of time doesn't change, the measure of time only changes relative to another measurement of time in a different frame of reference. You could be travelling at a million miles and hour, and a clone at 10 miles an hour, and you'd both experience time in the same way, and live to the same age. But they would reach 100 before you did. Its worth remembering that both these experiences are "correct" - that is, one isn't "sped up" or "slowed down" compared to everything else happening in the universe - they only are compared to each other.

Quote

Q. Does time feel the same? In other words, if somehow there was a way to set up an experiment where a person lived on earth in specific conditions for 1,000 days. Then that same person was able to live in a replicated environment with the exact same conditions but at a much higher velocity for 1,000 days, would it feel as though the 1,000 days went by quicker when moving at a faster speed?

Time would feel exactly the same, because for you, time would be the same.

Quote

Q. Take the same experiment above but for this question, lets say there are two people - Person 1 lives on earth in specific conditions for 1,000 days. Person 2 somehow has a plane with the exact same conditions that will circle around the earth for 1,000 days without refueling and at a much higher velocity. After each person has finished their 1,000 days, they are to report back to their facility. Would person 2 physically report and walk back into their facility while person 1 still has days left to go before their 1,000 days are finished?

If person 2 was orbiting the earth at relativistic speeds (i.e. a good percentage of the speed of light) and measured the 1000 days on a clock on board the ship (rather than by the rotation of the earth), then they would arrive back after the 1000 days had completed for person 1. I think.

Quote

Q. If I was able to move at the speed of light, it is said that it would stop time. Lets say an experiment was set up as follows - I stand still at the starting line and watched a normal ticking clock. As soon as the clock struck 1:00, I would immediately start running around the block 1,000,000 times at the speed of light. Somehow, I am able to stop on a dime right where I started. When I did stop, would the clock still be at 1:00?

If you traveled at 1,000,000 times the speed of light, you'd hypothetically arrive before you left, but this is a moot point as its physically impossible. If you traveled at the speed of light, it would depend if you were carrying the clock with you. If you weren't, then no - as it takes time for light to travel a given distance. If you also had a clock with you, then yes, hypothetically they'd be out of sync - the one on the wall would say 1:01 (for arguments sake) while the one you took with you would be 1:00, as time wouldn't have passed for you.

Quote

Q. Would it matter how many times I ran around the block? If I ran an infinite number of times around the block, would the clock still be at 1:00 regardless of when I stopped? In other words, is there a certain amount of laps to where the clock would eventually move?

If you're carrying the clock (i.e if the clock is moving at the speed of light), then it doesn't matter how many times you run around the block - if you are travelling at the speed of light, time would stop for you. You would also need infinite energy to get up to that speed and take on infinite mass, but these are mere details.

Quote

Q. If the above question is correct as in the clock would still be at 1:00, would that essentially mean that if I was a builder of some sort, lets say furniture - I could stand right in front of you, build a new chair at the speed of light and to you, it would almost appear as though the chair magically appeared?

Errr. I guess so, but it would be impossible to do, as you'd take on infinite mass and would need more energy than exists in the universe to make the chair.

Quote

Q. On the idea of being able to physically go back in time as shown in the movies. It doesn't sound as though a time machine is really necessary as far as it being some kind of portal that you enter and leave. A real time machine sounds more like a vehicle that is able to carry you at a speed faster than the speed of light. Lets say I had a vehicle that would move faster than the speed of light and I circled the earth long enough to go back to when I was 15 years old. The means my physical body sat inside a vehicle, left earth on a plane and re landed 15 years in the past. I then drove back to the home I lived in at that time. Would there now be two of me?

This is all fine and dandy, but it is physically impossible to travel at the speed of light if you have mass, and travelling faster than the speed of light is likewise impossible, mass or no mass.

Quote

Q. If the above question is not true as in there would not be two of me - would I just re land on earth as a 15 year old? If so, when I drove back to the home I lived in at that time, would it be as though I'm just walking back in the house as the same 15 year old I was then? Would it just eliminate the memory of traveling back in time and the memories I gained from 16 years old on? I mean somehow I had to remember how to land the plane.

From a purely mathematical point of view, i think there would be two of you, yes. But as I said, this is impossible to actually achieve.

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My knowledge of this is very poor but I do believe I read a piece on space travel.

I am sure you will correct me if and where I am wrong.

It went like this if you were travelling to Alpha Centauri at a speed that allowed you to complete the journey in 20 years on board the ship you would only experience a few years pass.

I guess this fits into the relativity where the journey only takes 20 years if its observed from Earth.

Is that correct?

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Thank you all for the replies. Makes a lot more sense now

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There seems to be a misconception about traveling at speed and time.

The simple way to remember this rule is that no frame of reference is any better than another or that no frame of reference is preferred.

If we were on Earth and we saw a spaceship fly by a relativistic speeds we'd notice that the clock on that spaceship is running slower than our clocks. Let's turn this around. If we are on the spaceship we can view it as if the Earth is moving by at relativistic speeds and the clocks on the Earth are moving slower than the ones on the spaceship.

Each observer notices the same effect on the other frame of reference.

The same is true about shortening in the direction of travel. The classic case is the pole vaulter. They are running towards a barn with doors at each end of the barn. An observer at the barn sees that the pole vault pole is say 1/2 its normal length. The runner sees that the barn is 1/2 its normal length.

Each observer notices the same effect on the other frame of reference.

So here is the problem of the pole vaulter. If the doors slam down and open up at the same time as the pole vaulter is inside of the barn, a 20 foot pole fits inside of a 20 foot barn because someone at the barn sees a 10 foot pole fitting inside of the 20 foot barn.  The pole vaulter sees his 20 foot pole going into a 10 foot barn. Why doesn't the doors closing down hit the pole? Because the doors close and open at different times, not together from the perspective of the running pole vaulter.

Here we have the same effects, but the times that events happen can be different for observers in different frames of reference.

What about the twins, one on the Earth and one on a spaceship. Everyone knows that the one on the spaceship will be younger when the twins are reunited. True. The reason is not that the spaceship traveled fast, at relativistic speeds, but that they were accelerated twice. Once to reach relativistic speeds and one to slow down from relativistic speeds. It is during those times that the spaceship twin undergoes events not experienced by the Earthbound twin.  This same effect can  be detected by taking an atomic clock and raising it from the surface of the Earth. It goes to a place where gravity is lower and therefore the clock runs faster. Time slows down as gravity increases.

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