Exceeding FTL (and breaking causality) is basically a sci fi trope at this point with about as much credibility as psychics. To have at least some credibility you need one of: a testable hypothesis, or an unexplained phenomenon. Right now we have neither. At best, we have some equations, that work below light speed, where we can extrapolate past light speed and see how the math works. The problem is: none of these equations are testable as they all contain infinities or other asymptotic features that prevent passing light speed itself. So, if there’s no viable math to get from sublight to FTL, and there’s no unexplained phenomena, then what we’re left with is nothing.
Even quantum entanglement, which is a darling of sci fi whenever they need a plot device (hello Le Guin and the ansible), has categorically been shown to obey causality and the light speed limit in every lab test.
At some point it’s like asking for negative mass, antigravity, or other things that the math would allow. Except our universe doesn’t.
Obviously if we were to exceed light speed we would turn into lizards and mate with each other and have lizard babies. I thought this was common knowledge.
in scifi there seems to be several types of ftl: one is typical warp like drive of trek, and star wars, and hyperdrives which is similar to transwarp/slipstream/xindi vortex travel, which is interdimensional travel so not technically violating light speed. and the least common one is interdimensional teleportation, BSG reimanging uses this tech, although they dint bother trying to explain it with technobabble at all, because of the showrunners allergy to trek-speak. STD, and a single episode arc of tng a group of terrorists were using interdimensional transporters.
trek also had other forms of ftl, but those are very rare, and its pretty much similar to the last 2.
Basically, physics says that nothing, not even information can actually travel faster than the speed of light. It’s a universal limit that shows up when you do the math on relativity. This concept is called “causality”.
Because of this, FTL communication is probably impossible. Quantum entanglement seems like it could provide a loophole, but it doesn’t actually work that way. To actually use quantum entanglement for communication, it actually needs a confirmation message, which would have to be delivered by a different means (every quantum message needs a non-quantum confirmation). That confirmation would be bound by the speed of light, thus preserving causality.
This is a very very rough description based on my memory, so some details may be a little off, but it should cover the gist. This article goes into more detail:
Edit: After reading, the answer is more that attempting to impart information onto the entangled particles to send a message necessarily breaks the entanglement and thus does not transmit the information to the other side. Entangling the particles makes their states related to each other, but only at the time of entanglement, and anything that changes either particle (including measuring it) will break the entanglement going forward.
Yup. You just summed up the start of the conversation I had with ChatGPT to figure out exactly what we were talking about Here and why the fact that even if we can’t directly send coherent information, if it appears that a change in particle A directly causes a change in particle B, and it appears that that causation happened Instantaneously, we can’t ever prove it or measure it or know it for certain, because the proving measuring and knowing would have to have occurred at instantaneously themselves in order to actually be proof at all. The even more fascinating part I wound up with is discovering the Holographic Principle, as discovered by Beckenstein and later expanded on and proven by Stephen Hawking, that says that all information in the 3-D world is actually encoded into a 2-D framework. That one blew my mind and I’m gonna be thinking about that for a while.
The holographic principle is fascinating, though a quick nitpick: I’m pretty sure we’ve only proven it for contracting spacetimes (as opposed to our expanding one), but a lot of people imagine it does apply to ours as well (I certainly suspect it does)
If you change one of the particles it just breaks the entanglement. If you measure one, then you instantly know the state the other will have when measured, but the result of your measurement - and therefore the other one also - is random. The only way to correlate the two measurements of the two particles is to send the results (at C or slower) to the same place and compare them. Otherwise each just looks like a random result.
Could you to the sub-C measurement test enough times to show that it just empirically works, and then use it on that basis? Or are you saying that the sub-C measurement would prove that it doesn’t work (and it produces random noise)?
I read it. Doesn’t mention FTL, because that’s not a possibility for actually transmitting info.
Edit: I think the way these quantum encryption systems work is that basically the photons (and I assume it’s polarization being measured) become the encryption key to a message that is sent conventionally.
Like the sender generates a bunch of entangled photons, sends the paired ones to the recipient, measures their photons and uses the results to encrypt the message, the receiver measures theirs and gets the same results, the sender sends the encrypted message over email or whatever, and the recipient has the same key because of entanglement.
Meanwhile an eavesdropper measuring the photons would mess them up for the recipient so the message wouldn’t decrypt.
I’m familiar with quantum entanglement. It doesn’t work because you have no way of affecting which state you’ll measure, and thus what state the other particle will be in.
No they didn’t, they sent a conventional signal that was encrypted with an entangled particle. Nothing was sent ftl, this is like if I had two boxes that I know have the same thing in them, an encryption key, and traveled across the world, and sent you a message, you have the other box, the information in that box didn’t go ftl you just opened it later.
The FTL is the sci-fi component that is the subject of the thread, the quantum entanglement communication part is the real world piece they actually got working.
It will never be possible to use this for ftl communications. This is like saying in 100 years we will use very long steel rods to communicate ftl by pushing on them. The problem is fundamental.
That’s not the part you were trying to say couldn’t be done. ;) You were trying to argue that quantum entanglement couldn’t be used to communicate, clearly it can.
The FTL bit is the science fiction premise of the thread. ;)
That is indeed that bit I was saying couldn’t be done. Entanglement alone can’t be used to communicate; a signal has to be sent conventionally over the distance.
The FTL bit is physically impossible, so it’s not really “achievable in a reasonable time-frame”
I’m familiar with quantum entanglement. It doesn’t work because you have no way of affecting which state you’ll measure, and thus what state the other particle will be in.
FTL communication using quantum entangled particles.
https://www.esa.int/Enabling_Support/Preparing_for_the_Future/Discovery_and_Preparation/ESA_takes_steps_toward_quantum_communications
Not FTL though. Slower than light, causality preserving version? Sure.
Huh?
Exceeding FTL (and breaking causality) is basically a sci fi trope at this point with about as much credibility as psychics. To have at least some credibility you need one of: a testable hypothesis, or an unexplained phenomenon. Right now we have neither. At best, we have some equations, that work below light speed, where we can extrapolate past light speed and see how the math works. The problem is: none of these equations are testable as they all contain infinities or other asymptotic features that prevent passing light speed itself. So, if there’s no viable math to get from sublight to FTL, and there’s no unexplained phenomena, then what we’re left with is nothing.
Even quantum entanglement, which is a darling of sci fi whenever they need a plot device (hello Le Guin and the ansible), has categorically been shown to obey causality and the light speed limit in every lab test.
At some point it’s like asking for negative mass, antigravity, or other things that the math would allow. Except our universe doesn’t.
I’ve got a wormhole to sell you ;)
Obviously if we were to exceed light speed we would turn into lizards and mate with each other and have lizard babies. I thought this was common knowledge.
in scifi there seems to be several types of ftl: one is typical warp like drive of trek, and star wars, and hyperdrives which is similar to transwarp/slipstream/xindi vortex travel, which is interdimensional travel so not technically violating light speed. and the least common one is interdimensional teleportation, BSG reimanging uses this tech, although they dint bother trying to explain it with technobabble at all, because of the showrunners allergy to trek-speak. STD, and a single episode arc of tng a group of terrorists were using interdimensional transporters.
trek also had other forms of ftl, but those are very rare, and its pretty much similar to the last 2.
And every one of those are as grounded in reality as sci fi’s agelong obsession telepaths, telekinesis, or mutants with powers.
There is a class of modern sci fi authors are all coming to terms with this.
I’d recommend checking out stories like Neptune’s Brood – sci fi which takes on interstellar economics in slower than light scenarios.
Basically, physics says that nothing, not even information can actually travel faster than the speed of light. It’s a universal limit that shows up when you do the math on relativity. This concept is called “causality”.
Because of this, FTL communication is probably impossible. Quantum entanglement seems like it could provide a loophole, but it doesn’t actually work that way. To actually use quantum entanglement for communication, it actually needs a confirmation message, which would have to be delivered by a different means (every quantum message needs a non-quantum confirmation). That confirmation would be bound by the speed of light, thus preserving causality.
This is a very very rough description based on my memory, so some details may be a little off, but it should cover the gist. This article goes into more detail:
https://bigthink.com/starts-with-a-bang/quantum-entanglement-faster-than-light/
Edit: After reading, the answer is more that attempting to impart information onto the entangled particles to send a message necessarily breaks the entanglement and thus does not transmit the information to the other side. Entangling the particles makes their states related to each other, but only at the time of entanglement, and anything that changes either particle (including measuring it) will break the entanglement going forward.
Yup. You just summed up the start of the conversation I had with ChatGPT to figure out exactly what we were talking about Here and why the fact that even if we can’t directly send coherent information, if it appears that a change in particle A directly causes a change in particle B, and it appears that that causation happened Instantaneously, we can’t ever prove it or measure it or know it for certain, because the proving measuring and knowing would have to have occurred at instantaneously themselves in order to actually be proof at all. The even more fascinating part I wound up with is discovering the Holographic Principle, as discovered by Beckenstein and later expanded on and proven by Stephen Hawking, that says that all information in the 3-D world is actually encoded into a 2-D framework. That one blew my mind and I’m gonna be thinking about that for a while.
The holographic principle is fascinating, though a quick nitpick: I’m pretty sure we’ve only proven it for contracting spacetimes (as opposed to our expanding one), but a lot of people imagine it does apply to ours as well (I certainly suspect it does)
I followed this branch of the rabbit hole. Goddamn you for bringing another contradiction into play in my brain!
Not possible; entanglement collapse can’t be used to send information
The idea is this:
2 particles are quantum entangled. Whatever happens to one instantly happens to the other regardless of distance.
So you establish a state that means “0” and a state that means “1” and you can send binary.
At a minimum, you have quantum Morse code.
If you change one of the particles it just breaks the entanglement. If you measure one, then you instantly know the state the other will have when measured, but the result of your measurement - and therefore the other one also - is random. The only way to correlate the two measurements of the two particles is to send the results (at C or slower) to the same place and compare them. Otherwise each just looks like a random result.
(I know nothing about this)
Could you to the sub-C measurement test enough times to show that it just empirically works, and then use it on that basis? Or are you saying that the sub-C measurement would prove that it doesn’t work (and it produces random noise)?
I’m not sure what you mean by ‘use it on that basis’. Yes, entanglement has been proven to work, but it can’t be used to communicate FTL.
Read the link posted. They already did it. In 2007. At a distance of 144km.
I read it. Doesn’t mention FTL, because that’s not a possibility for actually transmitting info.
Edit: I think the way these quantum encryption systems work is that basically the photons (and I assume it’s polarization being measured) become the encryption key to a message that is sent conventionally.
Like the sender generates a bunch of entangled photons, sends the paired ones to the recipient, measures their photons and uses the results to encrypt the message, the receiver measures theirs and gets the same results, the sender sends the encrypted message over email or whatever, and the recipient has the same key because of entanglement.
Meanwhile an eavesdropper measuring the photons would mess them up for the recipient so the message wouldn’t decrypt.
I’m familiar with quantum entanglement. It doesn’t work because you have no way of affecting which state you’ll measure, and thus what state the other particle will be in.
Read the link posted. They already did it. In 2007. At a distance of 144km.
No they didn’t, they sent a conventional signal that was encrypted with an entangled particle. Nothing was sent ftl, this is like if I had two boxes that I know have the same thing in them, an encryption key, and traveled across the world, and sent you a message, you have the other box, the information in that box didn’t go ftl you just opened it later.
there is no path to ftl communication here.
have a basic video on the topic: https://www.youtube.com/watch?v=9oBiS_Yb9Ac
The FTL is the sci-fi component that is the subject of the thread, the quantum entanglement communication part is the real world piece they actually got working.
It will never be possible to use this for ftl communications. This is like saying in 100 years we will use very long steel rods to communicate ftl by pushing on them. The problem is fundamental.
That wasn’t FTL
That’s not the part you were trying to say couldn’t be done. ;) You were trying to argue that quantum entanglement couldn’t be used to communicate, clearly it can.
The FTL bit is the science fiction premise of the thread. ;)
That is indeed that bit I was saying couldn’t be done. Entanglement alone can’t be used to communicate; a signal has to be sent conventionally over the distance.
The FTL bit is physically impossible, so it’s not really “achievable in a reasonable time-frame”
This you?
That’s exactly the part they DID get working.