# Time Travel. Is it possible?

## Main Question or Discussion Point

Time Travel. Is it possible?

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so far i've learnt in my special relativity class that you can only slow time down if you travel (which is very difficult) close to the speed of light (within 0.1c and 0.9c)

Time travel is only possible if you travel faster than the speed of light in which case you have contradictions like

lets say your spaceship travelled in a straight line at speed 0.9c and then accelerates to 1.2c then you will actually see the past i.e., you will pass the light that your spaceship radiated from itself. So you can see the past. You may not see time pass backwards if yo were on the ship, but if you stood still watching this ship, you would actually see things go backward.

i could be flawed in this thinking though!

Time travel is possible!

Time is not a Universal quantity.

space and time are two dimentions that are relative to another. If you travel at fast speeds, you will be bending the space, therefore you will strech the time dimention. and as it streches, the length that was to be 1 sec, would be at a diffrent rate ( a lot slower that 1 sec) 1 sec for you would be more than 1 sec for others.

Imagine SpaceTime as AirPresure.

As a airplane passes through the air, the wings are going through the air, due to its shape the air that passes through tht top part has to travel a longer distance, the longer the distance the lower the presure. because the bottom of the wing has more pressure it allows the airplane to lift off.

SpaceTime work in similar yet diffrent way.

GONE2UCF said:
Time Travel. Is it possible?
I bet 1...(how many 0 u want)\$ that it's not possible!

blue

stunner5000pt said:
so far i've learnt in my special relativity class that you can only slow time down if you travel (which is very difficult) close to the speed of light (within 0.1c and 0.9c)
This is not correct. Any differential in spatial motion will result in temporal differences. What you have learned is that significantly and easily measurable differences require large enough variances such as you described.

Time travel is only possible if you travel faster than the speed of light in which case you have contradictions like
I disagree. If there is a differential in spatial motion, then two objects have a temporal differential. The object with the greater spatial motion moves more slowly through time. It therefore moves into the future of the other object.

lets say your spaceship travelled in a straight line at speed 0.9c and then accelerates to 1.2c
Not possible.

stunner5000pt said:
lets say your spaceship travelled in a straight line at speed 0.9c and then accelerates to 1.2c
With all due respect, you're taking a relativity class and are talking about accelerating to faster than c? At any rate, even hypothetical FTL speeds don't translate into translate into time reversing. Just undefined equations, or imaginary numbers.

Gonzolo
Travel to the future is possible and happens all the time for particles, but it would require unheard of amounts of energy to produce the effect for a human. But in principle, you only have to travel extremely fast in any direction and come back. When you have come back, if your watch has advanced a minute, the place's clocks will have advanced 2 minute, 3 hrs, or 60 years, depending at how fast you were going. this is elementary special relativity.

Travel to the past belongs to advanced relativity, has never been observed, involves paradoxes, unverified hypothesis, is highly questionable, and in order to remain sane, I personnally keep away from those who seriously believe in it.

Gonzolo said:
Travel to the future is possible and happens all the time for particles, but it would require unheard of amounts of energy to produce the effect for a human. But in principle, you only have to travel extremely fast in any direction and come back.
Let me rephrase what you said:

Travel to the future is possible and happens all the time. We are always moving into our future. We can also move into the future of people around us, for example. All we have to do is to move with respect to the earth around us.

Prometheus said:
Let me rephrase what you said:

Travel to the future is possible and happens all the time. We are always moving into our future. We can also move into the future of people around us, for example. All we have to do is to move with respect to the earth around us.
That make a lot of sense to me

blue

Gonzolo
Not to me. I am not sure what is implied. I reinstate what I said word for word, adding what's in [] in an attempt to be clearer :

Travel to the future is possible and happens all the time for particles, but it would require unheard of amounts of energy to produce the effect [on a common timescale] for a human. But in principle, you only have to travel extremely fast in any direction and come back. When you have come back, if your watch has advanced a minute, the place's clocks will have advanced 2 minute, 3 hrs, or 60 years, depending at how fast you were going. this is elementary special relativity.

Gonzolo said:
Not to me. I am not sure what is implied.
Repeating what you said makes no more sense to me than before.

I reinstate what I said word for word, adding what's in [] in an attempt to be clearer :
I still disagree with it. Why not expand your thinking, to see a wider scope of possibilities? Rather than repeat what you said, why not address what I wrote, as I did for what you wrote? You do not need to agree with me, but repeating something that I challenged will not make the point more surely.

Gonzolo said:
But in principle, you only have to travel extremely fast in any direction and come back.
Ok this makes sense, some austronauts have been through this effect.

Prometheus said:
Let me rephrase what you said:

Travel to the future is possible and happens all the time. We are always moving into our future. We can also move into the future of people around us, for example. All we have to do is to move with respect to the earth around us.
What do u mean "move with respect to the earth around us"?

Doesnt that mean just travel very fast in any direction?

Fredrik
Staff Emeritus
Gold Member
PIT2 said:
Ok this makes sense, some austronauts have been through this effect.
No astrononaut has ever moved at velocities that are close close to the speed of light. I don't think they've ever moved faster than a few km/s, and the speed of light is 300000 km/s.

PIT2 said:
What do u mean "move with respect to the earth around us"?

Doesnt that mean just travel very fast in any direction?
What he said means move at any speed in any direction. Actually you don't have to move at all. As you're sitting on your chair reading this, you're "moving" forward in time. In a second you'll be in the future...

...and now you're there.

Fredrik said:
No astrononaut has ever moved at velocities that are close close to the speed of light. I don't think they've ever moved faster than a few km/s, and the speed of light is 300000 km/s.
Ok maybe im mistaken, but ive read that one guy spent 9 months in space (in a spacestation travelling some 18.000km per hour around earth if i remember correctly) and it took him a few seconds into the future(compared to ppl on earth).

What he said means move at any speed in any direction. Actually you don't have to move at all. As you're sitting on your chair reading this, you're "moving" forward in time. In a second you'll be in the future...

...and now you're there.
Yeah thats obvious, but when people refer to time travel, they usually mean travelling faster or slower through time than they already do. But ur quite right, this whole world is one big mess of time travelling creatures!

PIT2 said:
What do u mean "move with respect to the earth around us"?

Doesnt that mean just travel very fast in any direction?
Not really. The difference is the word fast. If we move at all with respect to the earth, then there is a time differential with respect to the earth and all things that are stationary with respect to the earth. There is also a time differential with all things that are moving with respect to the earth at a rate different than ours.

The use of the word "fast" is irrelevant, in my opinion, and its use suggests that perhaps there is an implication that reflects a misunderstanding.

Fredrik said:
What he said means move at any speed in any direction. Actually you don't have to move at all. As you're sitting on your chair reading this, you're "moving" forward in time. In a second you'll be in the future...

...and now you're there.
Excellent. The difference is that with a differential in spatial motion, it is possible to move into the future at a different rate than another person, and therefore to "move into his future", so to speak.

No astrononaut has ever moved at velocities that are close close to the speed of light.
If you define the speed of light in purely spatial terms, as you do, then I agree. However, if we define the speed of light in spatial-temporal terms, then everyone always moves at the exact same speed, the only possible speed, the speed of light.

jcsd