FTL Communication

[Moontanman]

Maybe I should have specified meaningful communication? Does anyone want to tackle the other parts of the post as well?

[modest]

Originally Posted by Moontanman

Maybe I should have specified meaningful communication? Does anyone want to tackle the other parts of the post as well?

Originally Posted by Moontanman

What would our universe look like if FTLC was possible? What would be different? What would be the same?

According to relativity time is fundamentally linked to the universal constant of c - the speed of light. If anything (including information) were to travel faster than light it would travel back in time. This creates a lot of paradoxes.

Let's say we sent some information FTL to the rover on mars and it sent it instantly back to us. From our reference this information will arrive before we sent it. This opens a whole ugly can of worms which I won't describe because it drives me bonkers, but it's all here.

Originally Posted by Moontanman

Are there any theoretical ways to communicate faster than light in our universe?

GR wormholes are a popular possibility. If you've ever seen Stargate they make it look pretty easy. I'm afraid both the physics and practical aspects are not so easily overcome - but the possibility persists.

-modest

[Moontanman]

Originally Posted by modest

According to relativity time is fundamentally linked to the universal constant of c - the speed of light. If anything (including information) were to travel faster than light it would travel back in time. This creates a lot of paradoxes.

Let's say we sent some information FTL to the rover on mars and it sent it instantly back to us. From our reference this information will arrive before we sent it. This opens a whole ugly can of worms which I won't describe because it drives me bonkers, but it's all here.



GR wormholes are a popular possibility. If you've ever seen Stargate they make it look pretty easy. I'm afraid both the physics and practical aspects are not so easily overcome - but the possibility persists.

-modest

Ok, I went "here" as specified in your post and found nothing about communication faster than light resulting in the signal going back in time. Why would it, lets say a signal that takes one second to go to mars and one second to come back, not arrive two seconds after you sent it? Is the limit for communication due to the speed of light being as fast we know something can travel or is it because of a fundamental property of the universe that says information cannot travel faster than light? What about tachyons? they might not have been detected yet but if I have read correctly they are possible, if so then could they be used to send information faster than light? Or does the universe forbid information traveling faster light no matter what

[freeztar]

Originally Posted by Moontanman

Ok, I went "here" as specified in your post and found nothing about communication faster than light resulting in the signal going back in time. Why would it, lets say a signal that takes one second to go to mars and one second to come back, not arrive two seconds after you sent it?

No, because to get there in one second it would have to be travelling *way* FTL.

Here's some more info on that subject:

Speed of light - Wikipedia, the free encyclopedia

Is the limit for communication due to the speed of light being as fast we know something can travel or is it because of a fundamental property of the universe that says information cannot travel faster than light? What about tachyons? they might not have been detected yet but if I have read correctly they are possible, if so then could they be used to send information faster than light? Or does the universe forbid information traveling faster light no matter what

I found this a very helpful read on the subject. (same link as above, just further down)

Speed of light - Wikipedia, the free encyclopedia

It seems as if the universe forbids information traveling FTL.

Even if tachyons were conventional, localisable particles, they would still preserve the basic tenets of causality in special relativity and not allow transmission of information faster than light[3].

Tachyon - Wikipedia, the free encyclopedia

[modest]

Originally Posted by Moontanman

Ok, I went "here" as specified in your post and found nothing about communication faster than light resulting in the signal going back in time.

That may not have been the best link, better link below.

Originally Posted by Moontanman

Why would it, lets say a signal that takes one second to go to mars and one second to come back, not arrive two seconds after you sent it?

I'm drawing up a spacetime diagram and I think you're right. We would see mars' future and mars would see ours but a signal would not return before it left. It couldn't get to its own past lightcone. Ok, I'm doing an awful job with this.

There are paradoxes associated with FTL. This link shows a better example than my rover mishap:

Why FTL implies time travel (tachyon pistols)

In essence, a person shoots a tachyon bullet that kills someone else. He is however killed by a tachyon bullet himself before he can fire the shot that killed the other person. Neither person fires a shot, yet they both die from the bullet the other fired. It's a paradox - an FTL paradox. Difficult to describe, but the link does a good job - I'd really suggest you read it.

Originally Posted by Moontanman

Is the limit for communication due to the speed of light being as fast we know something can travel or is it because of a fundamental property of the universe that says information cannot travel faster than light?

According to relativity it isn't just light that travels at c but simultaneity. In essence, "now" travels at the speed of light. The constant c is fundamental to the universe. It shows up in a lot of physics equations - it's certainly much more than the speed of light.

Originally Posted by Moontanman

What about tachyons? they might not have been detected yet but if I have read correctly they are possible, if so then could they be used to send information faster than light? Or does the universe forbid information traveling faster light no matter what

I wouldn't say we know the universe forbids it. We do know that no particle we have ever observed (either with mass or massless) can exceed the speed of light.

-modest

[InfiniteNow]

If I may suggest, the primary confusion seems to be "how the distance" traversed gets measured. IIRC, things don't travel faster than light, they just travel different paths.

I think...

[freeztar]

Originally Posted by InfiniteNow

If I may suggest, the primary confusion seems to be "how the distance" traversed gets measured. IIRC, things don't travel faster than light, they just travel different paths.

I think...

I like the analogy given in the wiki link I posted above.

Originally Posted by wiki

Another example can be seen when watching ocean waves washing up on shore. With a narrow enough angle between the wave and the shoreline, the breakers travel along the waves' length much faster than the waves' movement inland.

Speed of light - Wikipedia, the free encyclopedia

[Overdog]

One consequence of the light-cones I've always been fascinated with is the idea that from the moment of the big bang (if that's what happened) our view of of the universe has been constrained to just the parts of the universe where the light cones from those parts have intersected with our light cone. In otherwords, there may be parts of the universe that we can never detect, or have knowledge of...parts of the universe who's light-cone never intersects with ours.

[Moontanman]

Originally Posted by freeztar

No, because to get there in one second it would have to be travelling *way* FTL.

Here's some more info on that subject:

Speed of light - Wikipedia, the free encyclopedia



I found this a very helpful read on the subject. (same link as above, just further down)

Speed of light - Wikipedia, the free encyclopedia

It seems as if the universe forbids information traveling FTL.


Tachyon - Wikipedia, the free encyclopedia

I went to the site you recommended and it specifically said that if faster than light travel was possible then communication faster than light would be possible so that would indicate the the problem is with the speed limit not causality. If you assume that getting a signal before you sent it is nonsensical then if you found a way to transmit information faster than light it wouldn't nesesarrily result in time travel of the signal. It also said the time travel of the signal could occur in "some" reference frames, this indicates to me that some would not.

[freeztar]

Originally Posted by Overdog

One consequence of the light-cones I've always been fascinated with is the idea that from the moment of the big bang (if that's what happened) our view of of the universe has been constrained to just the parts of the universe where the light cones from those parts have intersected with our light cone. In otherwords, there may be parts of the universe that we can never detect, or have knowledge of...parts of the universe who's light-cone never intersects with ours.

Indeed.

We had a discussion about this a little while back, but I can't remember which thread.

The basic premise was that in this scenario:

G_A...................G_B.....................G_C

Galaxy B was within the light cones of both Galaxy A and C, but Galaxy A could not see Galaxy C and vice versa.