FTL communication

[Pawelk198604]

I just wonder when scientist develop FTL communication, i think it would be easier than FTL flight, like WARP drive.

The FTL communication would be good for space mission to Mars and other planets, i herd that radio communication with Mars is delayed 8-14 minutes, deepening on distance between planets.

[lajoswinkler]

There are superluminal phenomenons (even some quite banal ones), but none of them can transmit information. We simply don't have anything even close to it. As far as we're concerned with most groundbreaking physics today... we might never ever have superluminal communication.

[K^2]

There are superluminal phenomenons (even some quite banal ones), but none of them can transmit information. We simply don't have anything even close to it. As far as we're concerned with most groundbreaking physics today... we might never ever have superluminal communication.

There are definitely more options for FTL comms than FTL flight. So statistically, a bet on FTL communications is slightly more likely to eventually pay out. Not any time soon, though.

Keep in mind, most of the least-unlikely options are basically time machines with FTL comms being an obvious side effect. That does put it into perspective. For example, of Kerr interior solution was right, and fire wall hypothesis wrong, it should be possible to set up a quantum teleportation algorithm to pull information out of a black hole before it goes in. Yeah, it's gross violation of cosmic censor, among other things, but since it's a classical field theory conjecture, I don't see why it necessarily have to hold when we involve quantum fields.

Other methods have similarly absurd requirements. All in all, warp might still be our best option. And creating microscopic quantum warp bubbles for sending information might be more feasible than building warp ships. The down side is that we lack a lot more of the theory on how-to.

P.S. There are some purely stat-mech thoughts on doing local time reversals, some of which have been experimentally realized, but arrow of time is ridiculously persistent. There might be some quantum trick for pushing information through these against normal time flow, but even if it works, the time span would be measured in minutes, if not seconds. Not very useful for communications, but plenty useful for many other things.

[Las-pen]

http://www.cracked.com/blog/5-scientific-theories-head-explode/

Number 5: Quantum entanglement

[MeticulousMitch]

That Cracked article is appalling. Quantum entanglement cannot be used to transmit information at faster-than-light speeds.

http://www.projectrho.com/public_html/rocket/fasterlight.php

[cantab]

Keep in mind, most of the least-unlikely options are basically time machines with FTL comms being an obvious side effect.

If I understand right, this works both ways - any method of FTL communication necessarily implies the ability to communicate backwards in time.

If time travel of any sort ever is possible, its invention will be the most important event for humanity, ever. The possibilities make "bog-standard" FTL trivial in comparison.

[K^2]

That Cracked article is appalling. Quantum entanglement cannot be used to transmit information at faster-than-light speeds.

Exactly. There are theorems in QM to state as much. But entanglement might be an important element of a different scheme that would allow FTL, similar to how we use entanglement for teleportation.

If I understand right, this works both ways - any method of FTL communication necessarily implies the ability to communicate backwards in time.

It gets a little complicated with frames of reference, but ultimately, yes. FTL and time travel are equivalent.

[Helix935]

hmm whenever i try to think of FTL communication, i expect it to utilize miniature wormholes (like in the book Light Of Other Days which is a fantastic book) or tachyons as they travel faster than light

[rtxoff]

hmm whenever i try to think of FTL communication, i expect it to utilize miniature wormholes (like in the book Light Of Other Days which is a fantastic book) or tachyons as they travel faster than light

I am no expert but as far as i know tachyons are hypothetical particles, nobody has confirmed their existence and even if they exist there would probably be no way to interact with them due their imaginary mass.

[kidolvski]

Thachyons are supposedly faster than light but communicating with them brings some very weird paradoxes...

[rtxoff]

Thachyons are supposedly faster than light but communicating with them brings some very weird paradoxes...

It might just not be possible, you can't use something to communicate with that exists only in mathematics.

[Mazon Del]

No, but the mathematics can guide your physical experiments until you have something. Lots of people like to think of Engineers as magicians, others the pure math physicists. No, the real technomages of our world are the people that exist just to bridge the gap and take a purely mathematical formula and make a physical device out of it. A great example of this is the Time Crystal. The Time Crystal is a crystalline structure that has a dimension in time. Effectively the math says you should be able to create a crystal that has a lowest energetic state that involves motion. IE: You force it to stop moving, it will start moving later because that is more of a resting state than not moving. Sounds pretty impossible right? It's effectively an infinite energy source after all. Well, not quite. They are certain they can make it in the lab and sometime within the next 6 months or so is when they are supposed to complete the test rig. Right now the only methods we are aware of how to make a Time Crystal involve loads of equipment, and the TC only remains so while the equipment is on (needs to be supercooled, etc). So imagine we can make one molecule that never stops spinning. But to do that we have to dump hundreds of kilowatts constantly. In no fashion is this a net positive. Though admittedly their report states that if it works, then it "should" be possible to somehow design a TC that is room temperature stable and doesn't require additional equipment. Though they don't currently know how they might do that.

Note: TC's only work on the molecular scale as far as their math suggests.

[rtxoff]

Anyone can actually think of an situation where using FTL comms to control a mars rover could create some kind of time paradox? How fast must the signal be to control the rover with an lag of 1 sec.?

[ZetaX]

No, but the mathematics can guide your physical experiments until you have something. Lots of people like to think of Engineers as magicians, others the pure math physicists. No, the real technomages of our world are the people that exist just to bridge the gap and take a purely mathematical formula and make a physical device out of it. A great example of this is the Time Crystal. The Time Crystal is a crystalline structure that has a dimension in time. Effectively the math says you should be able to create a crystal that has a lowest energetic state that involves motion. IE: You force it to stop moving, it will start moving later because that is more of a resting state than not moving. Sounds pretty impossible right? It's effectively an infinite energy source after all. Well, not quite. They are certain they can make it in the lab and sometime within the next 6 months or so is when they are supposed to complete the test rig. Right now the only methods we are aware of how to make a Time Crystal involve loads of equipment, and the TC only remains so while the equipment is on (needs to be supercooled, etc). So imagine we can make one molecule that never stops spinning. But to do that we have to dump hundreds of kilowatts constantly. In no fashion is this a net positive. Though admittedly their report states that if it works, then it "should" be possible to somehow design a TC that is room temperature stable and doesn't require additional equipment. Though they don't currently know how they might do that.

Note: TC's only work on the molecular scale as far as their math suggests.

A time crystal is simply a crystalline structure (read: a repetitive pattern) in time (and normally also in space, then called a space-time crystal). This has no effect of magically starting moving again and thereby violating conservation laws. All it does (in theory; in praxis, you need energy to sustain the surroundings) is being a true perpetuum mobile by not wasting any energy; but it does not generate any, either.

[Mr Shifty]

Anyone can actually think of an situation where using FTL comms to control a mars rover could create some kind of time paradox? How fast must the signal be to control the rover with an lag of 1 sec.?

What introduces paradox is the possibility of a 3rd observer passing by at relativistic speeds who could observe the message arriving before it is sent and could, using the same FTL communication technique, send a message to Earth informing them ahead of time what message they're going to send to Mars.

[vger]

I am no expert but as far as i know tachyons are hypothetical particles, nobody has confirmed their existence and even if they exist there would probably be no way to interact with them due their imaginary mass.

If we can't interact with them then it's a pretty good assumption that their existence can't be confirmed.

[rtxoff]

What introduces paradox is the possibility of a 3rd observer passing by at relativistic speeds who could observe the message arriving before it is sent and could, using the same FTL communication technique, send a message to Earth informing them ahead of time what message they're going to send to Mars.

I fear it's not as easy as that.

[cantab]

It is.

Take any two events located in time and space such that a signal travelling at or below c could not leave one and arrive at the other, and there are potential observers that can see either one happening before the other.

Not that time travel necessarily creates paradoxes. A Universe with abdundant non-paradoxical time travel is perfectly reasonable.

[TheFlyingPigs]

I have no idea, I'm not a scientist, I'm a lemon

[Aethon]

I just wonder when scientist develop FTL communication, i think it would be easier than FTL flight, like WARP drive.

Pawelk. You're adorable, but I'm not sure this 'when' will ever happen and if it did, the energy budget to make super-luminal anything work would be enough to bankrupt any moderately sized civilization. The transfer of information through inscribed matter packets will almost always be more efficient, when delay beyond light transit time is acceptable.

As the USPS can tell you, driving a truck loaded with DVDs across town constitutes a very reliable channel with an extremely large bit rate. With todays' technology, S(canning) T(unneling) M(icroscope)s can place about 10¹⁵ bits per inch², using individual xenon atoms on a nickle surface. If we allow a 100 angstrom nickle buffer between layers we can achieve a bit density of 1.56x10²⁰ bits/cm^-3.

[rtxoff]

It is.

Take any two events located in time and space such that a signal travelling at or below c could not leave one and arrive at the other, and there are potential observers that can see either one happening before the other.

Not that time travel necessarily creates paradoxes. A Universe with abdundant non-paradoxical time travel is perfectly reasonable.

Despite talking about FTL comms is higly hypothetical i am pretty sure about following:

An FTL signal isn't traveling like an EM wave. FTL comms won't propagate like this and all you know about radio comms won't be valid for FTL comms. The possibility for an 3rd observer to catch the "signal" may not be there. If you wan't to find out how it might be done you will have to forget all you know about how it's done at the moment at lightspeed.

[N_las]

Despite talking about FTL comms is higly hypothetical i am pretty sure about following:

An FTL signal isn't traveling like an EM wave. FTL comms won't propagate like this and all you know about radio comms won't be valid for FTL comms. The possibility for an 3rd observer to catch the "signal" may not be there. If you wan't to find out how it might be done you will have to forget all you know about how it's done at the moment at lightspeed.

The 3rd observer doesn't have to "catch the signal". He can simply observe the mars rover. If the mars rover takes a turn left, he sends a FTL letter to earth saying that it went left. We at earth will receive the message what the rover did, before we send the "turn left" command to it.

If you don't think that creates a paradox, what about this? We put a bomb at the command center. The bomb will explode if the command center receives the FTL letter from the third observer, that contains the info that the rover turned left. If the command center issues only the command to turn right, then everything will be fine. We will get the future information that we will be turning right, and it matches our actual actions. But what if we send the command to turn left? The command center will explode before it even send the command. But if it didn't send the command, why did it explode?

Edited September 24, 2014 by N_las

[Mazon Del]

That was somewhat of a needlessly complex example that incidentally concludes that the FTL signal MUST operate in some fashion that involves going back in time due to relativistic effects.

Lets imagine for a moment that somehow we find a way to horribly abuse quantum entanglement for instant transmission. There is no time travel involved there. Yes the Earth base knows the rover turned left before they can see it, but that is effectively the same thing as seeing that a hammer hit the ground from a hundred feet away before hearing the bang when it hit.

Now again, my example here requires utilizing an effect that as far as we know right now cannot be used for this purpose. But the point is that an FTL message is not required by any means to actually involve time travel.

A more likely example, a spacecraft is in orbit around Mars. It gets the signal from the rover that it turned left, then the craft activates its warp drive to arrive at Earth a couple seconds later and then sends the message. Should we figure out how to make a warp drive in practice, this also ignores relativistic effects, so no FTL, no time travel.

[rtxoff]

Straight from Wikipedia:

[h=2]Birgit Dopfer's experiment[/h] Although such communication is prohibited in the thought experiment described above, some argue that superluminal communication could be achieved via quantum entanglement using other methods that don't rely on cloning a quantum system. One suggested method would use an ensemble of entangled particles to transmit information,^[4] similar to a type of quantum eraser experiments.^[5][6][7]

Birgit Dopfer, a student of Anton Zeilinger's, has performed an experiment which seems to make possible superluminal communication through an unexpected collective behaviour of two beams of entangled photons, one of which passes through a double-slit, utilising the creation of a distance interference pattern as bit 0 and the lack of a distance interference pattern as bit 1 (or vice versa), without any other classical channel.^[6][8] Since it is a collective and probabilistic phenomenon, no quantum information about the single particles is cloned and, accordingly, the no cloning theorem remains inviolate.^[9][10][11] Physicist John G. Cramer at the University of Washington is attempting to replicate Dopfer's experiment and demonstrate whether or not it can produce superluminal communication.^{[12][13][14][15]}

[N_las]

Lets imagine for a moment that somehow we find a way to horribly abuse quantum entanglement for instant transmission. There is no time travel involved there.

I think you missed an earlier point. If the response of the rover is instantaneous with the control decision from earth (from our point of view, both events happen at the same time), than it is necessarily possible for a 3rd observer in another reference frame to have the rover response happen BEFORE the control decision. Two events happening at the same time but at different positions are happening at different times from other observers. This 3rd observer could posses the same instantaneous communication device. Its FTL letter will arrive at the control station BEFORE the control decision.

We don't have to add a mysterious time-travel component to our FTL-communication for this paradox to work: Faster than light communication will enable time travel automatically.

A more likely example, a spacecraft is in orbit around Mars. It gets the signal from the rover that it turned left, then the craft activates its warp drive to arrive at Earth a couple seconds later and then sends the message. Should we figure out how to make a warp drive in practice, this also ignores relativistic effects, so no FTL, no time travel.

Imagine two alarm clocks, one on Earth and one on Mars. Lets assume Earth and Mars are stationary to each other, and they are seperated by 5 light-minutes. If we set up the clocks correctly, their alarm seems to go off at the same time (for a stationary observer at earth or mars). Of course, for people on earth the alarm signal from mars will only reach them five minutes later than the earth alarm signal, but because we know the distance and the speed of the alarm signal, we know they have gone off at the same time.

But thats only the case for a stationary observer on Earth or Mars. For a moving observer the situation may be different. From his perspective, the alarm clock at mars can go of an hour before the alarm clock on Earth. It all depends on his relative velocity to Mars.

So, from the perspective of the spacecraft around Mars, it can look like the rover response is happening an hour before the command deciscion on Earth (The velocity of the ship has to be right for that). So they have plenty of time to return with there FTL ship to earth, and tell them about the rover response, with the control decision on Earth still minutes into the future.

Edited September 24, 2014 by N_las