[haloboy100]

Dragon, I missed zero in your post. Of course I was speaking about entanglement when I mentioned that you cannot have data transferred faster than light. The reason, as I stated previously, is that this "teleported data" is not readable and confirmable until you get external sublight confirmation that indeed the data is read correctly. It is more complex than this, but rest assured, the light barrier is still king. This effect cannot produce the Mass Effect communication device.

Can you define "correctly?" You either receive the data or you don't - isn't the order or interpretation of the data handled by the design aspect of such a device?
I mean...for a human being to receive data, you just need to have a sublight emission happening at the point of reception for this teleported data.

Or, whatever. Maybe this really is just way over my head. 

[Mongoose]

Basically, if you have a pair of particles that are entangled, their quantum states are tied to each other.  This means that, if you conduct a measurement on one and observe a certain state value, the other particle will always take on the corresponding opposite state value.  The crazy part is that this effect happens faster than the speed of light could have conveyed information between the two particles...in fact, it's (theoretically at least) an instantaneous process.

Now on the surface, this seems like we could use this phenomenon in order to send faster-than-light messages, but here's the catch: there's no way to actually deliver useful information with it.  Let's say that a person at point A measures the first particle, and then a person at point B measures the second and observes the opposite value.  From the perspective of the person at point B, they have no idea whether what they saw was the result of the corresponding measurement at point A, or if their own measurement was first and collapsed the particle's wavefunction down to that state.  There's absolutely no way to tell the difference, other than the person at point A sending a message saying when they observed their particle and what they saw.  And since that message would be, at the very fastest, bound to the speed of light, information can't possibly travel any faster using this method.

Hopefully that makes things a bit clearer, though when you're dealing with quantum stuff, there's only so clear you can really get.

[Dragon]

Note, this is currently an area of heavy research. That's why I said it "might" allow for FTL transmissions. At this point, there are a number of theories, some of which could allow such transfer. Answering that question with certainty could probably net you a Nobel Prize. The results are still inconclusive, that's precisely why this field is so interesting. That there's no way to actually transfer information through quantum entanglement at this time does not mean one wouldn't be found. The conservative viewpoint is that it's impossible, but there are others that permit it.

[AdmiralRalwood]

Quantum entanglement would be much more useful for encryption than data transmission.

Well, and quantum computing, obviously.

[666maslo666]

Note, this is currently an area of heavy research. That's why I said it "might" allow for FTL transmissions.

It is also an area that was studied for a long time (80 years or so?), is understood quite well with no evidence of a FTL transmission and FTL violates basic laws of physics. I wouldnt hold my breath.

[Rheyah]

Yeah, the whole Alcubierre drive thing is pretty dumb. Gravity and presumably any change to the curvature of space can only propagate at the speed of light. So you can't use it to speed up the trip to anywhere you haven't been. Portals maybe, warp drives no.

IMO the NASA guy who's trying to make an Alcubierre drive should be defunded immediately.

The expansion and contraction properties of space time are not subject to relativistic effects.  Relativity is a property of particles propagating through space.  It is not a property of space time itself.  Thus through expansion it was possible for information to exceed the speed of light relative to an outside observer if the universe itself is expanding faster than light.

The main problem with the Alcubierre metric (which is a solution of general relativity, by the way - it is not something invented for the fun of it) is the fact it requires a negative energy density to function and generates yottawatts of radiation at the front of the bubble.

[The E]

Note, this is currently an area of heavy research. That's why I said it "might" allow for FTL transmissions. At this point, there are a number of theories, some of which could allow such transfer. Answering that question with certainty could probably net you a Nobel Prize. The results are still inconclusive, that's precisely why this field is so interesting. That there's no way to actually transfer information through quantum entanglement at this time does not mean one wouldn't be found. The conservative viewpoint is that it's impossible, but there are others that permit it.

No, it's actually pretty conclusively not possible.

[haloboy100]

Note, this is currently an area of heavy research. That's why I said it "might" allow for FTL transmissions. At this point, there are a number of theories, some of which could allow such transfer. Answering that question with certainty could probably net you a Nobel Prize. The results are still inconclusive, that's precisely why this field is so interesting. That there's no way to actually transfer information through quantum entanglement at this time does not mean one wouldn't be found. The conservative viewpoint is that it's impossible, but there are others that permit it.

No, it's actually pretty conclusively not possible.

I don't think "pretty conclusively" means "disproven beyond any reasonable doubt".

Maybe splitting hairs here, but hey. Science.

[S-99]

Well, even if they did get light to interact with itself to form structures, that doesn't mean those structures would, as such, interact as physical objects. They're still made of light, and would only interact with matter like any light would - give it enough intensity and it'll burn through, but it won't really knock things around like a physical blade would.

Apart from the fact that it's, you know, confined to the really cold matter that makes it slow down enough to form said "structures" in the first place - I suppose you could knock someone around with a super cold piece of equipment, but I believe the light would be the least important factor in the damage caused.

Well, they did say the photons slowed down, bounced off of other molecules, and formed with other slowed down photons to form molecules. That i think is very telling of what happened. That's why i said earlier, screw lightsabers, let's think about teleporters and replicators. This is what i think this actually applies to.

It's easy to directly convert matter to energy; campfires. It's another thing to do the opposite. Now one thing tells me if you slowed down photons to the point that they are behaving like matter, to the point that these slowed down photons have formed molecules with other slowed down photons. It gets me thinking that an energy to matter conversion actually happened. Which is why i was thinking replicators and transporters (transporters in the area of conversion of energy back to matter, not the teleportation part).

Maybe they didn't speak literal enough, but i thought the article did. These slowed down photons were no longer particles of light.

This gets into another great area of the universe. This means that light travels faster and slower in certain areas of the universe. Or that at once, light travelled slowly, then faster, perhaps kept the same speed, or perhaps light slowed down (science has yet to find this out later wth more discovery). Either way, we learn much from slowing down particles and the big bang perhaps.

The catalyst being simple, an outburst of energy in 0k.

[Luis Dias]

Note, this is currently an area of heavy research. That's why I said it "might" allow for FTL transmissions. At this point, there are a number of theories, some of which could allow such transfer. Answering that question with certainty could probably net you a Nobel Prize. The results are still inconclusive, that's precisely why this field is so interesting. That there's no way to actually transfer information through quantum entanglement at this time does not mean one wouldn't be found. The conservative viewpoint is that it's impossible, but there are others that permit it.

No, it's actually pretty conclusively not possible.

I don't think "pretty conclusively" means "disproven beyond any reasonable doubt".

Maybe splitting hairs here, but hey. Science.

It actually means "disproven beyond any unreasonable doubt". To allow FTL transmissions is the same as allowing FTL travel, which would all violate Lorentz symmetries (basically allowing not only FTL travel, but also time travel, and thus allowing impossible paradoxes of the father-son category). All the romantic research involving Lorentz violations have failed miserably so far (and predictably).

[Herra Tohtori]

It all depends on how you define "FTL".

Quantum entanglement cannot be used to transmit information because even if you have an entangled pair of particles, you can't actually measure a particle's state without changing it, and when you change one particle's state, the other particle's state also changes and you get this back and forth effect of measurement affecting the particle's state and if you try to measure it in both ends you just end up with a continuous noise of measurements on both ends changing the particle's state.

Basically, quantum entanglement is only useful if you have, like, two quantum entangled encryption keys which you then use to encrypt and decrypt messages. But if you want to compare the quantum states of the entangled particles, you need independent communication anyway to do that...


However, there's no causality problems associated with most of the "more realistic" FTL schemes.

If information goes from A to B in shorter time than t=s/c, it just means that the distance s that the information used was actually shorter than you thought. That's all.



By the way, even if it turns out Alcubierre Drive doesn't work for FTL - don't you think it would have some applications in subluminal space travel regardless?

Not needing propellant would be reasonably useful. We could also extract infinite energy from Newton's grave.

[Luis Dias]

However, there's no causality problems associated with most of the "more realistic" FTL schemes.

If information goes from A to B in shorter time than t=s/c, it just means that the distance s that the information used was actually shorter than you thought. That's all.

But then it means there was no FTL travel / communication at all, obviously.

By the way, even if it turns out Alcubierre Drive doesn't work for FTL - don't you think it would have some applications in subluminal space travel regardless?

Not needing propellant would be reasonably useful. We could also extract infinite energy from Newton's grave.

That's quite a different discussion that I'm sure engineers will discuss when they try to make it work... but I think it's quite useful to tell them what *not* to expect coming out of it, lest they have wrong expectations.

[Herra Tohtori]

But then it means there was no FTL travel / communication at all, obviously.

That's why I said it depends on the definition of FTL.

I think there's pretty good consensus that it isn't possible to exceed speed of light in any local reference frame - so we have to figure out a way around that obstacle, not through it.

And sometimes the route around is shorter than through.


But, for practical purposes, if Alcubierre drive allows traveling from A to B faster than distance between A to B seems to be I would call it FTL travel and be done with it.

By the way, even if it turns out Alcubierre Drive doesn't work for FTL - don't you think it would have some applications in subluminal space travel regardless?

Not needing propellant would be reasonably useful. We could also extract infinite energy from Newton's grave.

That's quite a different discussion that I'm sure engineers will discuss when they try to make it work... but I think it's quite useful to tell them what *not* to expect coming out of it, lest they have wrong expectations.

Yeah, well, the problem with uncharted territory is you don't know what's behind the next hill until you get an overhead satellite pass to give you a picture.

We have some theory-based guesses on what to expect. In theory, Alcubierre drive would for example create a hefty bit of radiation and I have really no idea how it would affect the surrounding space-time (ie. how well would the warp bubble be contained).

Practical problem currently is we have no idea how to actually make negative energy (or negative pressure) aside from Casimir effect which isn't really a demonstration of negative energy IMHO, but rather lower vacuum energy density between plates than outside of them. It's only "negative" if you fix zero point energy level to vacuum; this may not be the case. Even though the recent reduction in estimated energy requirement made it slightly more feasible, there are still several hurdles of "we have no idea if this is possible, much less how to actually do it" left.

[Luis Dias]

But, for practical purposes, if Alcubierre drive allows traveling from A to B faster than distance between A to B seems to be I would call it FTL travel and be done with it.

You didn't understand the criticism against the AD.

You can well create (theoretically) a drive that shortens the distance between A and B. What you (and many others!) are missing is that the process of "shortening up" the distance between A and B is through gravitational waves... which travel at light speed! See the problem? You can't get around this.

Perhaps something like creating "lanes" would eventually be possible. Really far fetched and not at all what is being discussed when speaking about ADs, since they depend on the idea of not only shortening AB but also lengthening AB in the "back" of the drive. Since this process cannot happen faster than the waves making the lane, you are still travelling slower than light.

Yeah, well, the problem with uncharted territory is you don't know what's behind the next hill until you get an overhead satellite pass to give you a picture.

But we do have a lot of pictures. They are all quite pessimistic in this notion. You are of course free to dream, but never should be under the illusion that current physics are giving you hints for your optimisms, for they are clearly not.

[jr2]

With the quantum entangled particles, why not just have one pair dedicated to communications from A to B, and another pair for B to A? Then have them constantly transmitting on a frequency, and being measured at the other end at the same frequency. Obviously, measuring changes the value, but you know that and this simply invert the values read. The only problem would be if the transmitting and measuring processes got out of sync, but then you could just try flipping all the values read to their inverse past the point where the data became unreadable, and keep it inverted until the next out of sync. Obviously you'd want parity checks, yes? So you would know if the data stream became unsyncronized.

Now, what am I missing? I'm sure that can't be the answer, someone would have tried it already.

[Luis Dias]

Well, when you eventually cancel all the fuzzinesses and ambiguities you are left where you began: with an unuseful device for FTL comms. The maths become hard really fast and I'm no expert on this at all, so I refer to Lubos Motl in the Physics Stack Exchange fora:

There is no experiment in which genuine information could be sent faster than light and there is no contradiction between this fact and quantum mechanics – as built by the Copenhagen school. Quite on the contrary, the proper, Copenhagen-like interpretation of quantum mechanics is needed for a description of known experiments that is compatible with special relativity and its most general consequences, locality and causality.

You would have to describe your experiment in detail if you wanted the interference and its disappearance to be discussed seriously.

However, quite generally, if there are entangled pairs produced, a single particle from this pair won't contribute to an interference pattern by itself. (A typical example is an entangled electron-photon pair where the electron participates in a double-slit experiment and the photon is used to "look" at the electron. The photon gets entangled with the electron but the electron's own interference pattern disappears.) The interference pattern may only be glimpsed if one compares some appropriate measured properties of both particles in the entangled pair. But that's only possible much later, when these results of measurements are communicated to a single place, and because the comparison occurs much later, it can't be used to transmit any information faster than light.

[FlamingCobra]

I thought this thread was about lightsabers. Boy was I wrong! It's about FTL travel!

[The E]

With the quantum entangled particles, why not just have one pair dedicated to communications from A to B, and another pair for B to A? Then have them constantly transmitting on a frequency, and being measured at the other end at the same frequency. Obviously, measuring changes the value, but you know that and this simply invert the values read. The only problem would be if the transmitting and measuring processes got out of sync, but then you could just try flipping all the values read to their inverse past the point where the data became unreadable, and keep it inverted until the next out of sync. Obviously you'd want parity checks, yes? So you would know if the data stream became unsyncronized.

Now, what am I missing? I'm sure that can't be the answer, someone would have tried it already.

This would rely on absolutely precise synchronization between the two readers, which is pretty much impossible to guarantee (especially if one or both of them are in motion). Also, your parity checking would need to be done via normal, known secure methods, thus invalidating any supposed speed advantage.

[Luis Dias]

That precise sync is also inherently impossible due to the uncertainty principle. QED.

[The E]

Here's my attempt at explaining why it doesn't work:

1. You cannot measure the state of an entangled particle without altering said state.
2. When you measure the particle, there is no way for you to tell whether or not it has been altered by a measurement the other person took, or whether it's due to some other interaction.
3. As such, you would need confirmation that an alteration has happened (and what exactly that alteration was!) delivered through traditional means, which are of course not FTL.