An important feature of quantum technology is entanglement (i.e., two or more particles are linked, so changes applied to one particle will be applied to the other entangled particles, no matter the distances or the materials between them).

According to Canadian futurist Sylvain Rochon, this allows for teleportation.

"In practicum, this technique, combined with very fine 3D printing technology and atomic scanning technologies, could lead to machines capable of copying 3D objects exactly atom for atom," Rochon explained. "Put your object in the device, and as it is scanned, an atomically exact duplicate is created from atomic [or] molecular feeds in a 3D printer."

So, assuming that the remote printer is placed on a planet other than Earth by 'conventional' means, does the above imply FTL space-travel?

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    $\begingroup$ This isn't 'travel' by any standard definition. This is FTL communication. You're only sending data, not actual things or people. You can use that data to MAKE things (or people), but nothing physical actually moves from one place to another. It's like the difference between a fax machine and a physical letter. $\endgroup$ Oct 10 '19 at 18:25
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    $\begingroup$ @MorrisTheCat There is no distinction between sending data and sending things. This is a fundamental property of physics and why we say things can't travel faster than light simply because signals can't. $\endgroup$
    – stix
    Oct 10 '19 at 18:28
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    $\begingroup$ Where is the Worldbuilding context to this question? Shouldn't this be in a different Stack Exchange site? $\endgroup$
    – overlord
    Oct 10 '19 at 18:55
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    $\begingroup$ @MorrisTheCat Lol no it's not; it's the fundamental underpinning of Lorentz covariance, which is perhaps one of the best experimentally supported theories in existence. $\endgroup$
    – stix
    Oct 10 '19 at 19:47
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    $\begingroup$ Ordinarily quantum teleportation requires the existence of a "classical channel" where information is transmitted in a normal classical way telling the experimenter at a different location what properties of their entangled particle(s) to measure. See for example the comment in this article, "Quantum teleportation does not transmit any faster-than-light causal influence, because you also need the classical channel — limited to light speed at best — to complete the process." $\endgroup$
    – Hypnosifl
    Oct 10 '19 at 22:03

Good luck 3D-printing anything alive.

Unless the printer is able to completely assemble the atoms before any kind of chemical interaction between atoms occurs... nothing living could be assembled successfully.

Even 3D-printing living beings without quantum entanglement would be unrealistic, let alone using it in the solution to faster-than-light travel.

Even without going into any specifics of quantum entanglement, the answer is still a resounding no.

  • $\begingroup$ If you have the technology for cryonics, you can beat the speed problem by printing at cryonic temperature, then thawing the resulting organism same as a regular corpsicle. $\endgroup$
    – Zeiss Ikon
    Oct 11 '19 at 11:19
  • $\begingroup$ @ZeissIkon Then you have an energy problem. If it is cold enough so that the atoms don't move or nearly don't move, that means you're at or close to absolute zero. If it's at absolute zero then nothing, not even the printer can move. If it's close to absolute zero, the printer might move so slow that it might not even be worth it. Not to mention, friction from the printer causes heat that might mess with the cryogenics. There are tons of variables at play here. It just doesn't seem like a system that can be utilized effectively. $\endgroup$
    – overlord
    Oct 11 '19 at 13:26

Short Answer: Insufficient Information Available To Provide Meaningful Answer

Previously, it has always been assumed that quantum entanglement can't be used to send information, which would mean no, you cannot use entanglement for FTL travel. The reason for this is that any situation which allows you to send any information faster than the speed of light can also be used as a time-machine under special relativity, and time-machines be scary.

Relativity and quantum mechanics are the two most tested, most successful models of reality ever created in the history of humanity.

They are also both wrong.

The problem is they don't agree. The two theories are completely incompatible with each other when it comes to the definition of what fundamental reality is. Relativity says spacetime must be smooth and continuous. Quantum mechanics says it can't be. Quantum mechanics says spacetime must be flat and unchanging, relativity says the presence of matter means that it cannot be and spacetime must curve. Relativity says nothing can move faster than the speed of light. Quantum mechanics says hold my beer.

Entanglement is what led Albert Einstein to finally disown his grandchild of Quantum Mechanics, because it implies that FTL communication might (big if) be possible. We have, for decades, assumed that Einstein was right and QM was wrong, and that entanglement cannot be used to transmit information faster than light, even if the process itself happens instantaneously. This debate was codified in the EPR Paradox. Every single experiment thus far shows that entanglement occurs instantaneously (i.e. faster than the speed of light), but so far no one has figured out a way to transmit information with it, and indeed, most scientists assume it is impossible because relativity says so.

So why all the heartburn about entanglement? Well as previously stated, any way to send information faster than light is equivalent to a time machine under relativity, and entanglement seems to do exactly this. So scientists continue to sweep the problem under the rug and say "but no information is transmitted," and experiments continue to say "well maybe there is," which scientists respond with "but that would mean a time machine is possible!"

Why is this a bad thing? Well, other than ideas about killing your own grandfather before you're born, it breaks a fundamental assumption about physics: locality.

Locality states that an object can only be influenced by its immediate surroundings (i.e. the surroundings that can be reached from it slower than light during any given time interval), and is the underpinning of our understanding of cause and effect in relativity. Without locality, it becomes impossible to measure cause and effect in relativity, and indeed, an effect could precede its cause without the tyranny of locality. This is because relativity says that space and time are the same thing, and you can trade one for the other, so long as the total amount of space and time doesn't change (space curvature). This is required to explain experiments which show that the speed of light is constant in all inertial reference frames. In other words, you and I will both measure the speed of light as 300,000 km/s, even if I'm traveling at 299,000 km/s and you're standing still.

The problem is quantum mechanics doesn't care. QM is a strong independent theory don't need no relativity, and seems to throw locality out the window with things like entanglement and quantum tunneling. Because QM treats space-time as flat and unchanging, it has no concerns about things exceeding the speed of light, and indeed, often requires things to happen faster than the speed of light.

But why can't we just take QM and plug it into relativity, like say let QM do it's thing on a bumpy spacetime? Well, when we do, the equations explode. Black holes form, the universe collapses, NaNs pop up everywhere. When QM and relativity are combined, they utterly and completely lose their ability to make predictions about the world. Do fairies pop up and move charges around with unicorns? Do angels dance on the heads of pins? Do Jesus and Buddha play basketball with planets? The short answer is yes, all of that and more, because the equations can no longer disprove that is what's going on.

Clearly this is absurd.

So then we have traditionally said "locality must hold" and swept QM's quirks under the rug by saying "but no information can actually be transmitted faster than light, even if QM does things that happen faster than light." We do this because experiments say relativity is absolutely correct, and relativity requires locality in order to be absolutely correct. However, experiments have also shown QM is absolutely correct, and QM doesn't require locality to be absolutely correct. This has never really been a problem since QM's experiments have rarely directly conflicted with anything relativity has said (i.e. said locality must not be correct), but because of better tests on QM, it's starting to look like locality might have to go.

This of course creates a huge problem, as the two best theories for understanding the universe are in direct conflict: relativity requires locality to exist, while quantum mechanics is starting to require that it does not exist.

What this means for physics is completely unknown. It has broad implications from questions like "What is time?" to "Do we have free will?"

For now though, in our almost religious fervor, we have put up a few bulwarks to protect locality. In QM these are known as no-go theorems. One no-go theorem is the no-teleportation theorem, which states that quantum states cannot be teleported instantaneously, and thus can't be sent over quantum entanglement. So no, you can't use entanglement to allow for FTL travel.

However, the justification for most of these no-go theorems is locality, so if that goes, the theorems must go as well, and experiments at this point are almost screaming at us to abandon locality, so ultimately, who knows?

In the end, we simply don't have enough information to say one way or the other, because it is at the edge of the frontier of physics. In order to truly put the question to rest, we have to have a grand unified theory, one that can explain all of the observed experiments of both relativity and quantum mechanics under the same framework.

Unfortunately, we've hit a wall with this. We've been attempting to unify relativity and QM for nearly 100 years, and it's been a series of abject failures. Without new experimental evidence about the world, we don't have any nuggets to point us in the right direction for how to solve the problem. We need an experiment that disproves, rather than proves, something about either QM or relativity, and that has not been forthcoming at all. Every experiment says "yes relativity is right" and "yes QM is right," but the math says "No! They can't both be right."

Ultimately, we may have to abandon locality in order to unify relativity and QM, and that means there may be some loopholes that allow us to go faster than light.

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    $\begingroup$ This post seems to contain a large number of misconceptions. First off, it conflates GR and SR-- the former is what has trouble integrating into quantum mechanics. But SR has been a part of QM for decades, in the form of quantum field theories. QFTs do not let information travel faster than light basically as a matter of principle--specifically, it is usually put forward as an axiom that space-like separated observables commute. Also, GR and QFT can be integrated into a single theory that reproduces both, the problem is just that renormalization starts breaking down at high energy scales... $\endgroup$ Oct 10 '19 at 20:00
  • $\begingroup$ (cont) So, they're not fundamentally incompatible, which makes sense cause they both describe the world very accurately in their respective domains. They're both simply low energy/gravitation limits of a more powerful theory that has yet to be fleshed out. And with respect to the quote "and experiments at this point are almost screaming at us to abandon locality", I say "which experiments?". Lorentz covariance has been tested and confirmed so many times that theories that break it are all on the far fringes of science. $\endgroup$ Oct 10 '19 at 20:09
  • $\begingroup$ @elduderino QFT has been criticized for lacking a rigorous mathematical foundation, and given that, by its very name, GR is more general than SR, it is almost certainly the more fundamental of the two, so unifying it into QFT doesn't really mean anything. If anything, it can be argued that QFT takes us farther from a grand unified theory, not closer. Feynman diagrams just sweep the problem of FTL communication under the rug; they don't explain why quantum mechanics can instantaneously occur without FTL. $\endgroup$
    – stix
    Oct 10 '19 at 20:15
  • $\begingroup$ @elduderino GR and QFT cannot be unified at low energies. What happens to the gravitational field of an electron in the dual slit experiment? Which experiments are screaming at us to abandon locality? Literally every QM experiment that has put a bullseye on Bell's Inequalities, which is oh, most of them? Everytime Bell's Inequalities are violated it always gets swept under the rug with "but muh information transfer!" We have ruled out loopholes for every single Bell inequality violation to the limits of experiment, but some still cling to locality like some tenet of faith. $\endgroup$
    – stix
    Oct 10 '19 at 20:29
  • $\begingroup$ (cont) As of 2015 we've closed all the loopholes on Bell (Hanson 2015), and we are already starting to show nonlocal effects in experiments with photons as of 2016 (Okamoto 2016). This is the entire point of my post, that GR says unequivocally, "things must be local" and QM says with similar confidence, "no they aren't." They absolutely can't both be correct. $\endgroup$
    – stix
    Oct 10 '19 at 20:33

This method of "teleportation" has been explored in science fiction for decades -- Fred Pohl and Jack Williamson had their tachyon transportation system, that made a copy of the subject at a distance (The Farthest Star, Wall Around a Star, etc.), and others have presents this for travel as "destroy the original as soon as the copy is confirmed okay" -- which raises the McCoy conundrum, more or less "After my atoms have been scattered across space and reassembled, am I still me?"

From a quantum standpoint, the problem with using entanglement for any sort of communication is either establishing entanglement of particles that are not together at the beginning, or getting the entangled particle(s) from point A to point B fast enough and without collapsing the wave function.

Then there's the issue of causality violation -- any method of trasmitting information (even as simple as "yes" or "no") faster than light raises the possibility of sending that same information back in time, allowing an effect to precede its cause in some local frame of reference. It seems very likely that the Universe doesn't like this.

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    $\begingroup$ The bigger problem with using entanglement for communication is that it's impossible for entanglement to transmit information. $\endgroup$
    – HDE 226868
    Oct 10 '19 at 18:47
  • $\begingroup$ @boardrider HDE's link is the only correct answer to your question, I think. $\endgroup$ Oct 10 '19 at 19:19
  • $\begingroup$ Theteleportation used in Frederik Pohl and Jack Williamson's The Saga of Cuckoo novels copies objects and people, via tachyons instead of quantum entanglement. The titles of the books are Farthest Star (1975) and Wall Around a Star (1983). Perhaps, you saw editions in another language. Causality violation upsets physicists. Chances are it doesn't worry the universe. It seems that with FTL travel time travel comes as a bonus. Good to see someone remembers the Pohl-Williamson Cuckoo novels. You are correct. The main problem is establishing & maintaining the quantum entanglement. $\endgroup$
    – a4android
    Oct 11 '19 at 4:29

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