# Naked Science Forum

## Non Life Sciences => Technology => Topic started by: Dmaier on 01/10/2009 11:15:17

Title: If you could travel faster than light, could you travel in time?
Post by: Dmaier on 01/10/2009 11:15:17
The closer to light speed you get the slower time becomes so if you went fast enough would you be able to go backwards in time?
Title: Re: If you could travel faster than light, could you travel in time?
Post by: Don_1 on 01/10/2009 12:30:21
No. You may be able to see the past, as we see the past when we look at the stars. But in the sense of a Dr Who type time travel, no.
Title: Re: If you could travel faster than light, could you travel in time?
Post by: wanhafizi on 04/10/2009 13:15:26
I don't know if one can go backward in time,

but, going fast will slow your time down
Title: Re: If you could travel faster than light, could you travel in time?
Post by: yor_on on 01/06/2018 06:56:26
Proper mass can't go that fast. The 'fastest thing' we know are 'massless photons' at 'c'. A immense black hole might from some observer far away make time 'stand still', like a rocket frozen over some event horizon as defined by that observer, although in reality all light should be red shifted into oblivion and so leave no trace of that rocket as it closes in to a 'stand still' from the point of view of that observer. But you won't find any serious person suggesting that the observer will 'see' the rocket travel 'backwards in time'.

Time is what makes change, and time has one arrow, not several. Time symmetry is like playing a movie backwards, but it's a theoretical construct. If you have a 'static universe' also called a block universe you might argue that time symmetry is not only a theoretical exercise, but for you to consider this you need the arrow we have.
Title: Re: If you could travel faster than light, could you travel in time?
Post by: ali.rafami on 12/06/2018 20:35:41
1. No, we cannot travel faster than light.  (By which I mean, the speed of light in a vacuum, 186,000 miles per second.  Light travels more slowly in a medium, including being completely stopped.)

2. I suppose anything is possible in a world as surreal as the one that gives us quantum mechanics and relativity.  But from the standpoint of relativity, traveling faster than light is not just impossible, it's meaningless.  The speed of light is really infinity.  As you go faster and faster, the world around you moves (relatively) slower and slower.  At the speed of light, you are moving infinitely fast, and you are already there.

Moving faster than that is literally meaningless.  You get infinities and imaginary numbers out of the equations.  Some might say it means time travel into the past, but that's more sci-fi speculation than physics.
It's not even possible to travel as fast as light, which would suffice, at least not for a massive object.  The difference between objects with (rest) mass and objects without (like light) is not yet completely understood, so it's conceivable that a loophole could be found to make you move as fast as light.  But with the physics we currently have and expect to see in the forseeable future (i.e. without a radical and unexpected change), even that is impossible.
Title: Re: If you could travel faster than light, could you travel in time?
Post by: Bill S on 16/06/2018 23:17:54
Quote from: Ali
Light travels more slowly in a medium, including being completely stopped.

It’s not quite as clear-cut as that. There’s a fair bit on the subject in various places on this Forum.  I’m not the best one to try to find it.

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The speed of light is really infinity.

Wouldn’t it require at least one equation involving infinity to establish that?

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At the speed of light, you are moving infinitely fast, and you are already there.

That would involve something progressing from finite to infinite speed.  How would it achieve that?

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Moving faster than that is literally meaningless.  You get infinities and imaginary numbers out of the equations.

Doesn’t this reasoning negate your assertion that “the speed of light is infinite”?

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…. with the physics we currently have and expect to see in the foreseeable future (i.e. without a radical and unexpected change), even that is impossible.

I’ll not argue with that.

Oh, what a tangled web we weave when first we struggle to perceive.  With apologies to Walter.
Title: Re: If you could travel faster than light, could you travel in time?
Post by: jeffreyH on 17/06/2018 15:46:52
@Bill S The infinity is in the gamma function when the magnitude of the velocity of a particle equals the speed of light. Time dilation becomes infinite and time stops for the object travelling at c. Since time stops in its frame of reference no local forces can operate to change the momentum of the object. It would require a collision with another object to cause this. Here we see where length contraction becomes absurd, since it too is infinite. If this was a physicality and not just a perception then the whole universe would be compressed into a singularity.

So the nearer the speed of light an object moves the more like a singularity the universe looks to the traveler. Of course this is not a physical reality. Note that I am NOT suggesting that any object with rest mass can reach the speed of light.
Title: Re: If you could travel faster than light, could you travel in time?
Post by: jeffreyH on 17/06/2018 16:02:52
For an object starting 'at infinity' and falling freely towards a black hole, the nearer it gets to the event horizon the more like a singularity the universe appears to be. Since the object is approaching the speed of light and its time dilation is approaching infinity. Is there a final velocity that falls well short of the speed of light?
Title: Re: If you could travel faster than light, could you travel in time?
Post by: Bill S on 17/06/2018 22:00:25
Quote from: Jeffrey
Time dilation becomes infinite and time stops for the object travelling at c.
Isn’t there still divided opinion about that in the scientific community?

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If this was a physicality and not just a perception then the whole universe would be compressed into a singularity.
So, is time stopping for an object travelling at c just a perception?

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Of course this is not a physical reality.

Is the “infinity in the gamma function” a physical reality?  Don’t say “define reality”, that’s a cop-out. :)
Title: Re: If you could travel faster than light, could you travel in time?
Post by: Bill S on 17/06/2018 22:05:07
Quote from: Jeffrey
For an object starting 'at infinity' and falling freely towards a black hole....

In what sense are you using "infinity" here?
Is your object infinitely far away; or is it just a large, but otherwise unspecified distance away?
Title: Re: If you could travel faster than light, could you travel in time?
Post by: Bill S on 07/10/2018 18:51:13
Jeffrey, it's unlike you to leave questions unanswered.
Title: Re: If you could travel faster than light, could you travel in time?
Post by: guest46746 on 11/11/2018 16:23:26
If you could travel in time, it is very likely nothing would be in the same place! lol
Title: Re: If you could travel faster than light, could you travel in time?
Post by: Audreyyy on 16/11/2018 07:40:45
I only know that if it’s really fast, the eyes can’t catch anything.
Title: Re: If you could travel faster than light, could you travel in time?
Post by: Paul25 on 19/03/2020 14:56:52
Technically you can only slow the rate of time