Einstein's theory of relativity and time travel

[Amateur-God]

Hey so from my understanding of Einsteins theory of relativity the closer you travel to the speed of light the slower time is for you, is that right? if it is right does that give to reason that there could be a critical speed past the speed of light for which time for the object traveling at that speed stops all together let's call it C^T and if so then a speed past C^T at which time starts to reverse? let's call that speed x(C^T)

 

[Ibix]

Hey so from my understanding of Einsteins theory of relativity the closer you travel to the speed of light the slower time is for you, is that right?

Not quite. Time is always normal for you; other people's clocks tick slowly. There is a thing called differential aging where you travel out and back and end up younger than someone who stayed at home, but this is closer to taking a shortcut through spacetime than being because "time is slow for you".

Any travel at speeds exceeding c allows you to construct circumstances in which you arrive before you leave, according to vanilla special relativity. Google for the tachyonic anti telephone. However, special relativity makes it impossible to accelerate to the speed of light, let alone exceed it.

 

[willem2]

If you go close to the speed of light other people will think that time goes slower for you, and you will appear to move slower to them. Your own time always will appear normal to yourself.
The theory of relativity predicts that as you approach the speed of light this effect will become larger and larger.
Moving at or past the speed of light is not possible, so there's no point in asking what happens .

 

[Amateur-God]

If you go close to the speed of light other people will think that time goes slower for you, and you will appear to move slower to them. Your own time always will appear normal to yourself.
The theory of relativity predicts that as you approach the speed of light this effect will become larger and larger.
Moving at or past the speed of light is not possible, so there's no point in asking what happens .

but aren't they're subatomic particles which travel faster than the speed of light?

 

[king vitamin]

but aren't they're subatomic particles which travel faster than the speed of light?

No, there aren't.

 

[Nugatory]

but aren't they're subatomic particles which travel faster than the speed of light?

No.

 

[willem2]

but aren't they're subatomic particles which travel faster than the speed of light?

You mean those?
https://en.wikipedia.org/wiki/Tachyon
Seems to be no evidence they exit.. If they exist you could communicate back in time will give lots of problems with causality, such as sending a message to not send the message.

 

[Amateur-God]

No, there aren't.

No.

That's not what this article says:

"Since Einstein, physicists have found that certain entities can reach superluminal (that means "faster-than-light") speeds and still follow the cosmic rules laid down by special relativity. While these do not disprove Einstein's theory, they give us insight into the peculiar behavior of light and the quantum realm."

Source:
https://www.sciencealert.com/these-4-cosmic-phenomena-travel-faster-than-the-speed-of-light

 

[Janus]

Hey so from my understanding of Einsteins theory of relativity the closer you travel to the speed of light the slower time is for you, is that right? if it is right does that give to reason that there could be a critical speed past the speed of light for which time for the object traveling at that speed stops all together let's call it C^T and if so then a speed past C^T at which time starts to reverse? let's call that speed x(C^T)

As already pointed out, Only someone you are moving relative to would say that time is passing slower for you as you approach the speed of light relative to them. This is called time dilation.
So, the next question would be: What would they say happens to your clock if you were to exceed the speed of light relative to them? To answer this, we can look at the equation for time dilation:
[tex]T = frac{t}{sqrt{1-\frac{v^2}{c^2}}}[tex]
Here c is the speed of light and v is the relative speed.
t is time as measured by our "moving clock" and T is time measured by our observer. As v gets larger, the part under the square-root gets smaller and T grows compared to t. Thus if t were 1 sec measured by the moving clock, Our observer would measure a longer time T pass on his own clock during this same period. So for example if v= 0.866c, Then in the time it takes for our observer to measure 1 sec tick off on the moving clock, 2 sec would have ticked off on his own clock.

Thus as v gets closer and closer to c, the lower half of the fraction on the right side of the equation approaches 0. if v=c then you get T=t/0.
But division by 0 is undefined. It has no answer. If we try to make c > v, you end up with a negative number under the square-root. Which has no real answer either. It is an "imaginary number"*. So at greater than c velocities, you would see an "imaginary" tick rate for the moving clock. What this really boils down to is that greater than c velocities are in a kind of "no man's land" that cannot be reached.

While in this case it leads to an unsolvable problem, Unlike division by 0, which is strictly verboten, Imaginary numbers can be useful in math and physics at times.)

 

[Ibix]

That's not what this article says:"Since Einstein, physicists have found that certain entities can reach superluminal (that means "faster-than-light") speeds and still follow the cosmic rules laid down by special relativity. While these do not disprove Einstein's theory, they give us insight into the peculiar behavior of light and the quantum realm."Source:

https://www.sciencealert.com/these-4-cosmic-phenomena-travel-faster-than-the-speed-of-light

None of that is traveling faster than light. Quantum entanglement does not permit faster than light communication (Kaku's explanation is extremely over-simplified) Cerenkov radiation occurs when particles travel faster than light in a medium - it's the speed of light in vacuum that's impossible to beat. Wormholes - if they exist - are simply shortcuts. And all massless particles travel at the speed of light, but do not exceed it.

 

[phinds]

@Amateur-God you are relying on pop-sci descriptions of physics. This will cause you no end of confusion and misunderstandings.

 

[Nugatory]

Source:
https://www.sciencealert.com/these-4-cosmic-phenomena-travel-faster-than-the-speed-of-light

Pop-sci articles like that one are not acceptable references under the Physics Forums rules. We have this rule because so many of them are inaccurate/misleading/oversimplified, and this one is unusually bad.

If you are at all serious about understanding relativity, you will find spending some quality time with a correct explanation of the theory to be very rewarding. Taylor and Wheeler's "Spacetime Physics" has been a favorite of mine.

 

[Flatland]

but aren't they're subatomic particles which travel faster than the speed of light?

Where are you getting all these nonsense info from?