Deep space Communication hypothetical question

[Panwasbipolar]

Not sure if this is the right part of the forum.

I suppose the question is a bit out of the ordinary but I need opinions.

Suppose a species did develop a way to travel far distances and approach near light speed.

Communication via radiowaves(or other forms) would be a bit archaic to use right?

I saw something on either the history channel or via hulu(can't remember where)
about communication techniques being possible via some type of particle that is nearly instant. Do any of you know anything about this? If so, what type of particles are they talking about? Is it being researched? I suppose if it was it'd be surrounded with government red tape, considering the possibilities if "anything" is using it.


Thanks

 

[Filip Larsen]

There is nothing in the set of natural laws and theories that science so far has consensus on that will allow general superluminal communication from point to point.

What you probably have heard about is what is called quantum entanglement [1], which (unfortunately for interstellar travelers) still does not allow for superluminal communication even if it does sound like it would when you hear the phenomenon explained as non-local interaction between entangled particles separated by an arbitrary distance, even light-years.


[1] http://en.wikipedia.org/wiki/Quantum_entanglement

 

[Panwasbipolar]

Thanks for your response.

 

[JoaoPais]

If the spin of one of two entangled particles was changed, the change would occur “instantaneously” in the other particle? Or the “entanglement” is broken?

 

[Filip Larsen]

I'm no expert, but I think it is so, that if one of the particles were to interact with some other particles that would allow the spin direction to be uniquely determined some way further down the road, then the entanglement is still there, now only involving more particles. However, if the spin direction is "lost" during the interaction with the other particles then the entanglement is broken.

 

[haael]

Communication between two individuals that move near the speed of light relative to each other would have little sense, since time slows significantly at this speed. The travellers would see each other effectively frozen - quite a boring conversation IMO.

 

[Panwasbipolar]

What I meant or was thinking didn't come out quite right. It's not so much about communication while traveling that fast, but the ability to communicate between points at enormous distances without the delay. I'm guessing some type of clock would need to be developed? Or am I missing something? Is time different between two galaxies?

 

[JoaoPais]

I'm no expert, but I think it is so, that if one of the particles were to interact with some other particles that would allow the spin direction to be uniquely determined some way further down the road, then the entanglement is still there, now only involving more particles. However, if the spin direction is "lost" during the interaction with the other particles then the entanglement is broken.

So, if I understand correctly, if we change the spin of one of the particles the entanglement is broken… ?

What I meant or was thinking didn't come out quite right. It's not so much about communication while traveling that fast, but the ability to communicate between points at enormous distances without the delay. I'm guessing some type of clock would need to be developed? Or am I missing something? Is time different between two galaxies?

Well, if the entanglement were to be maintained, we could create a communication line without the delay, it seems. If not, the faster we can go (for now =P) is the speed of light.

Is time different between two galaxies?

Well, were the problem is what’s “different”? because time is a completely subjective notion! We could create “clocks” that measure time in a different unit or so, then, time would be read differently. Otherwise, the time is the same here or in Andromeda. The real difference in time reading would be during the travel or if the other planet would be moving really fast relative to you.

 

[Filip Larsen]

So, if I understand correctly, if we change the spin of one of the particles the entanglement is broken… ?

I'm not quite sure what you mean by "we change". If we make a measurement on one of the particles that allows us to know its spin, then the particles no longer have their spin state entangled, but no one measuring the other particles would see any difference. Measurements at either particle alone will not reveal if the other particle has been measured yet or not. Only when comparing the result of the two measurements (which will require both results to "travel" alone a world line to a common point) will the 100% correlated states due to entanglement be clear.

Well, if the entanglement were to be maintained, we could create a communication line without the delay, it seems. If not, the faster we can go (for now =P) is the speed of light.

Think you have two misconceptions going here. First, entanglement doesn't mean that you can "force" one particle to be spin down and then have the other to magically pop up as spin up. Secondly, even if this wasn't so, you still can't reestablish the entanglement without having the particles to interact again, so there would be no "reuse" of the same pair.

So, in summary, you can't use an entangled particle pair as a kind of intergalactic morse-keys and you can't in fact use entanglement to send any information at all.

 

[Filip Larsen]

It's not so much about communication while traveling that fast, but the ability to communicate between points at enormous distances without the delay.

As mention before, it will not be possible to communicate without the delay. If you want to communicate with your friend in Adromeda, there is no faster way than to send him a message by light and then wait the two times 2.5 million years for the reply to come back (assuming here your friend is at rest relative to you).

One can speculate, that high communication delays more or less force any interstellar species to develop a structure of its civilization that can handle this, for instance by having long stability or great independence of each other, or both. It is also imaginable that a civilization that spread over significant distances could use some kind of continuous one-way broadcasts to allow remote colonies to stay "synchronize" with the delayed image of the core civilization. A colony placed, say, 400 light years from the core could then have its civilization (culture, politics, whatever) synchronized to the image of the core civilization, just delayed by 400 years.

I'm guessing some type of clock would need to be developed? Or am I missing something? Is time different between two galaxies?

Not sure why you think a clock is important. If you have a friend in Adromeda more or less at rest relative to you, then you would both see each others time go by at the same rate. If you had agreed with your friend that you will send messages to each other by pulsing a big laser in the right direction such that one symbol is transmitted each second, then you would both receive the message from the each other at this one symbol per second rate. If you wanted to, you and your friend could set up a procedure that would allow you to synchronize your clocks such that they show the same time. However, since it still take around 2.5 million years for each message to travel the distance, having synchronized clocks would mostly be for convenience when referring to local events and such. It would not have any special physical meaning.

 

[JoaoPais]

I'm not quite sure what you mean by "we change"(...)

So, in summary, you can't use an entangled particle pair as a kind of intergalactic morse-keys and you can't in fact use entanglement to send any information at all.

"We change" what i mean was exactly forcing the orientation of spin of one of the particles, but, you answered my question perfectly, so, after we measure the spin of one of the particles, we know what's the spin of the other, and that's it. We can't "use" them any longer as entangled particles. Too bad =P

Thanks for the answer!