FTL Communication

[Overdog]

Originally Posted by Moontanman

No you misunderstand, the beam is already at the moon. According to the article you can move a shadow or a spot of light faster than the speed of light. If you moved the spot back and forth across the detector you could signal faster than light since the spot moves at the speed of it's source being moved back and forth. At it's source the speed could be just a few feet per second but the spot would be moving faster than light. Before I go any further with this, lets get some basics settled out. While I'm sure I am wrong in this lets see if I have the idea correct. If you had a small rod with a laser coming out of both ends and you caused it to turn in a circle at a few hundred RPS what would the beams look like if you could look down on them from a great distance? (lets assume you can see a laser beam) Would the beams be straight and true as a laser or would they spiral like the arms of a hurricane? If they would be straight then you could move the laser back and forth and at some point the beam would be moving faster than light but in sync with the source. Then you could turn a detector off and on with no time lag from the Earth to the detector. In essence you would signaling faster than light. Yes? No? Why? Why not?

The problem with that is if you move the laser beam while standing on earth, the laser light that is hitting the moon will not shift instantaneously, as the photons emitted from the laser since you moved it still have to travel all the way to the moon before any movement will be seen on the moon.

[Moontanman]

Originally Posted by Overdog

The problem with that is if you move the laser beam while standing on earth, the laser light that is hitting the moon will not shift instantaneously, as the photons emitted from the laser since you moved it still have to travel all the way to the moon before any movement will be seen on the moon.

Ok, so the rotating laser beams would form a spiral pattern? I see your point but it would indicate the laser wouldn't be a straight line if it was moved? It would be more like moving a water hose back and forth.....

[Overdog]

Exactly.

[Moontanman]

Originally Posted by Overdog

Exactly.

Oh well, hard science wins again, but if it is like moving a water hose back and forth then why does the dot move faster than light? when you move a water hose back and forth the end of the water stream doesn't move faster than end of the hose?

It's so hot here! it's just the first week in june and it's already a heat index of 110+

[Overdog]

Originally Posted by Moontanman

Oh well, hard science wins again, but if it is like moving a water hose back and forth then why does the dot move faster than light?

It is simply the apparent translational speed of the "dot" (which has no real existence), moving at right angles to the arriving photons across the face of the moon.

Originally Posted by Moontanman

when you move a water hose back and forth the end of the water stream doesn't move faster than end of the hose?

Yes, it does. You may swing the end of the hose in your hand 6 inches or so and easily cover six or more feet where it lands.

[Overdog]

Imagine you are at the center of a Dyson Sphere.

Dyson sphere - Wikipedia, the free encyclopedia

And the sphere is two light years in diameter. In the center of the sphere, holding a laser, you sweep the laser in a full circle. It takes you 6 seconds to perform the sweep.

It will take 1 year for the "Dot" (photons reflected from the inner surface of the sphere) to manifest itself, however, the "Dot" will now sweep across the full circumference of the sphere in 6 seconds, even though the circumference is 2pi * 1 light years.

[Moontanman]

Originally Posted by Overdog

Imagine you are at the center of a Dyson Sphere.

Dyson sphere - Wikipedia, the free encyclopedia

And the sphere is two light years in diameter. In the center of the sphere, holding a laser, you sweep the laser in a full circle. It takes you 6 seconds to perform the sweep.

It will take 1 year for the "Dot" (photons reflected from the inner surface of the sphere) to manifest itself, however, the "Dot" will now sweep across the full circumference of the sphere in 6 seconds, even though the circumference is 2pi * 1 light years.

Ok, you have me convinced ( didn't really think I had comeup with a FTL comm link) Can any one suggest how the universe would look as opposed to the way it does now if FTL communication was possible?

[Overdog]

Well, here's the problem. It appears that the limit of the speed of light is a fundamental property of the universe, and is intimately connected to other fundamental properties. In other words, the speed of light can't change without adjusting the value of some other property of the universe so the mathematics still works. This might sound like BS, but as far as reason is concerned, mathematics is the the best we've got, and if we have any hope of understanding the universe, the math has to work. So to answer your question "What would the universe look like if FTL communication were possible" we have to consider what the universe would look like if we changed some fundamental property of the universe.

Consider the expression that relates velocity with time.

velocity = distance/time

At one time, people belived that light was propagated through a substance called the ether, similar to the way waves on the surface of a pond are propagated through water.

According to the mathematics of this view, if you measured the speed of light if you were moving towards the light, you would measure the speed of light to be faster than if you measured it if you were moving away from the light.

But it turns out that no matter what speed we are moving towards the light or away from the light, we always measure the speed of light to be the same.

How is this possible?

It took the genius of Albert Einstien to explain it.

Einstien looked at the formula velocity = distance/time and said that TIME varies!

It was quite a revolutionary idea.

The math worked if you allowed time to be a variable. Then he went on to re-arrange our entire view of the universe by working out the implications of time being a variable.

This is what leads us to the believe that the speed if light is a constant, a fundamental property of the universe.

So what would the universe look like if we changed that fundamental property?

Well, for the math to still work, we would have to pick one or more other fundamental properties and adjust them such that the math still works (remember, the math has to work, or it's all hopeless).

So, now that we've gotten this far, I have to say that I am at a loss as to what the universe would look like if we changed one of its fundamental properties.

But even if we made a minor change somewhere so that say the the speed of light was twice what it is now, you would still be asking the same question in that universe as you are asking in this one.

Sorry, this is the best answer I can give.

[CraigD]

Originally Posted by Moontanman

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

Nimtz and Stahlhofen’s recent experiment in frustrated total internal reflection and quantum tunneling, discussed in this thread (one of the ones freeztar mentioned in post #2), appears to me to demonstrate a phenomena that could, in principle, be used to send a genuine information signal between to point is less time than a signal traveling at the speed of light. See this post for a earlier, lengthier explanation of why I think this.

In summary, this sort of FTL communication works by exploiting the probabilistic nature of quantum mechanics, the formalism that appears to best describe ultimate reality. Quantum mechanics predicts a very low probability of a particle, or ensemble of particles, being detected in volumes of space separated by a distance greater than the time between the measurements times the speed of light. Despite its tremendous predictive accuracy regarding macroscopic objects, relativity, with its absolute speed limit of the speed of light in vacuum, is a classical mechanical theory, in a very meaningful sense at odds with quantum mechanics, in a very statistically small number of cases.

In practical terms, Nimtz and Stahlhofen’s effect seems to have severe limitations. It requires a specially constructed light pathway (in the case of the published experiment, a pair of glass prisms), and looses a large percentage (multiplication) of its signal strength (number of photons) for each decrease in signal time (subtraction), so would require a lot of power to send a signal slightly faster than an electromagnetic signal without anything in it path. However, in principle, if used to communicate between 2 inertial frames with sufficiently large relative speed, such a device could in principle be used to pass a signal into its own past. We’re not talking about some sort of strange semantic trickery, such as superluminal group velocities or the “movement” of non-physical things such as the contact points of scissors – such a device could, in principle, be used to do such things as send horse race results back in time to give you infallible betting tips.

Assuming, based on the above principles and experimental evidence, that FTL signals, and thus signals into ones own past, are possible, suggests an answer to the question

Originally Posted by Moontanman

Can any one suggest how the universe would look as opposed to the way it does now if FTL communication was possible?

It would look exactly like it does now, because the laws of physics of our our universe do allow FTL and time communication. However, permitting it and having it be commonplace are very different things. If FTL communication can only occur as the result of tremendously difficult, artificial engineering, we may observe it no more than if it was prohibited in principle.

Consider something known to be, in principle, possible, but never observed:
We can, using particle accelerators and special coolers and particle traps, create antimatter. We could, in principle, manufacture sufficiently large amounts of it to blast planets into tiny piecess. Yet, we observe no planets being blasted into tiny pieces, because creating large amounts of antimatter is very difficult.

This suggests to me an additional (fourth?) Clarke-esque law:

A thing sufficiently difficult under a given civilization’s technology is indistinguishable from an impossible thing.

[Moontanman]

Originally Posted by Overdog

Well, here's the problem. It appears that the limit of the speed of light is a fundamental property of the universe, and is intimately connected to other fundamental properties. In other words, the speed of light can't change without adjusting the value of some other property of the universe so the mathematics still works. This might sound like BS, but as far as reason is concerned, mathematics is the the best we've got, and if we have any hope of understanding the universe, the math has to work. So to answer your question "What would the universe look like if FTL communication were possible" we have to consider what the universe would look like if we changed some fundamental property of the universe.

Consider the expression that relates velocity with time.

velocity = distance/time

At one time, people belived that light was propagated through a substance called the ether, similar to the way waves on the surface of a pond are propagated through water.

According to the mathematics of this view, if you measured the speed of light if you were moving towards the light, you would measure the speed of light to be faster than if you measured it if you were moving away from the light.

But it turns out that no matter what speed we are moving towards the light or away from the light, we always measure the speed of light to be the same.

How is this possible?

It took the genius of Albert Einstien to explain it.

Einstien looked at the formula velocity = distance/time and said that TIME varies!

It was quite a revolutionary idea.

The math worked if you allowed time to be a variable. Then he went on to re-arrange our entire view of the universe by working out the implications of time being a variable.

This is what leads us to the believe that the speed if light is a constant, a fundamental property of the universe.

So what would the universe look like if we changed that fundamental property?

Well, for the math to still work, we would have to pick one or more other fundamental properties and adjust them such that the math still works (remember, the math has to work, or it's all hopeless).

So, now that we've gotten this far, I have to say that I am at a loss as to what the universe would look like if we changed one of its fundamental properties.

But even if we made a minor change somewhere so that say the the speed of light was twice what it is now, you would still be asking the same question in that universe as you are asking in this one.

Sorry, this is the best answer I can give.

That is a very good answer, it explains a lot but I wonder how it can be shown (with math at least) that it's possible to travel faster than ligth if you travel in a bubble of your own space. Alcubierre drive - Wikipedia, the free encyclopedia How does this jive with causality violations? (since I seem to have people here that might actually know I can't resist asking)