FTL Communication

[Moontanman]

Is faster than light communication totally forbidden in our universe? What would our universe look like if FTLC was possible? What would be different? What would be the same? Are there any theoretical ways to communicate faster than light in our universe?

[freeztar]

Some conversation on this subject occurred last year.

 

http://hypography.com/forums/news-brief/12558-we-have-broken-speed-light.html

http://hypography.com/forums/physics-mathematics/1937-can-something-move-faster-than-light.html

http://hypography.com/forums/physics-mathematics/12750-ftl-signaling-via-frustrated-total-internal.html

 

Your questions are interesting, but I don't understand how it is an alternative theory. It's more like philosophy.

 

It's always good to think about these things in any case.

[Overdog]

My understanding of Einsteins theory is that the transmission of information faster than light is not possible. That is different from saying that an event which exceeds the speed of light is not possible.

 

That said, I (and probably a lot of others) would very much like to believe that Einstein is wrong in this respect. But you have to admit, the man's theory has substantial staying power. People have been attacking it for a long time....

 

If there is the possibility of communication faster than light, then it is by some mechanism completely unknown to us, even worse, as far as I know we don't even have any reasons to suspect Einstein might be wrong about this.

[modest]

That is different from saying that an event which exceeds the speed of light is not possible.

 

This is a really insightful point. I assume you're referring to quantum entanglement and I agree there seems to be a rather important distinction. Entangled pairs do seem to communicate faster than light, but causality is preserved because the rest of the universe can't use this process for communication. Fascinating really.

 

-modest

[sanctus]

This is a really insightful point. I assume you're referring to quantum entanglement and I agree there seems to be a rather important distinction. Entangled pairs do seem to communicate faster than light, but causality is preserved because the rest of the universe can't use this process for communication. Fascinating really.

 

-modest

 

Just wanted to bring up this example too. But Modest, in my understanding entangled pairs do not SEEM to comunicate faster than light but how theory explains this phenomena so far it DOES comunicate faster than light.

[modest]

Just wanted to bring up this example too. But Modest, in my understanding entangled pairs do not SEEM to comunicate faster than light but how theory explains this phenomena so far it DOES comunicate faster than light.

 

I agree. I was concerned someone would throw a local, hidden variable interpretation at me. But, I do think entanglement is by far the best theory, and according to that theory entangled pairs must and absolutely do communicate faster than light.

 

-modest

[Overdog]

Yes, quantum entanglement was what I was referring to. It is definitely fascinating (spooky). But I wonder if it reallly is information that is exchanged between entangeled pairs, and not something else even spookier.

[sanctus]

If it were information we would have FTL comunication...

[Jay-qu]

I dont see what is so different about entanglement from usual experience.

 

Take this example: put two rocks in a bag, one white one black, remove one rock but dont look at it, jump in your trusty spaceship and fly an appreciable distance away, then look at the rock in your hand. Now you instantly 'gained' information about the rock you left behind on Earth, you have inferred its colour from the one you are holding.

[Overdog]

I dont see what is so different about entanglement from usual experience.

 

Take this example: put two rocks in a bag, one white one black, remove one rock but dont look at it, jump in your trusty spaceship and fly an appreciable distance away, then look at the rock in your hand. Now you instantly 'gained' information about the rock you left behind on Earth, you have inferred its colour from the one you are holding.

 

But isn't it a little stranger than that? My understanding (which may be flawed) is that it is more like having two coins in a box, and taking one of the coins (in your trusty space ship, of course) to another location and placing it on the table you observe that it is heads...and because of entanglement, you know that the coin you left in the box is showing tails...?

[Moontanman]

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

[modest]

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

 

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.

 

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]

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]

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]

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.

 

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.

 

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.

 

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]

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.

 

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