Point 19 seems to conflate quantum fields with imaginary mass and superluminal particles. As far as I know, tachyonic quantum fields and tachyonic 'particles' are unrelated except for an unfortunate naming convention (historically, tachyonic fields were thought to result in tachyonic particles; the name was kept around even after the mistake had been realized).<p>Note that tachyonic particles are not very particle-like at all, so I prefer the name 'tachyonic interaction':<p>Tachyons cannot be properly localized, there's a critical frame where they have no energy, their 'life-time' is space-like, both endpoints of the interaction may have the same (intrinsic) type (absorption-absorption, emission-emission), to name just some of the peculiar properties.<p>Recami argues (imo convincingly) that you cannot use such tachyons to violate causality.<p>Point 13 is also somewhat questionable, but this is more of a matter of semantics. While each of the galaxies are at rest (or in free fall, if you prefer), they are not at rest relative to one another according to parallel transport along the light ray (otherwise, there would be no red-shift). This is imo the correct way to handle relative velocities in a general-relativistic setting; the fact that their comoving distance is constant doesn't mean they are at rest in any physically meaningful way, but one can at least argue this point both ways.
> But multiverses are entirely out of keeping with the Ockham's Razor approach to doing science, and constitute more of a popular interpretation of quantum mechanics than a serious physical theory.<p>The multiverse is not a theory - it's a logical consequence of a simple theory. This claim is logically akin to claiming that the universe is identical to the observable universe, because to propose that matter exists outside of direct observation is a violation of Ockam's Razor.
One way would be to fire an entangled photon down both ends of fibre optic cable in the middle. On the sending end you could observe/ ignore it, and on reviving end you'd observe it.<p>We'd have to develop cables capable of preserving the entangled state of light particles, and a beam splitter that's more reliable. You could improve the bandwidth considerably by measuring the polarisation of the particle, even more if you could somehow encapsulate the entangled photon for a given period of time.
A thought I've had about this is that perhaps the speed limit within a universe (299,792,458 m/s in ours) is relative to a constant at its Big Bang moment such as total energy contained or maximum rate of expansion of space-time. If the smallest particles of our universe are smaller universes and our universe is a tiny particle within a larger universe, then the speed limit within each could be different.<p>This theory would allow FTL travel in a larger universe relative to the speed limit of our universe, but not FTL communication. FTL travel within one universe may be the escape velocity required to enter the next larger universe outside of the origin universe's boundary. But a transmission, originally traveling FTL, sent into a smaller universe may be slowed by its speed limit (similar to light propagating through a non-vacuum medium). In a universe expanding like ours, the transmission would never reach the destination.
The consensus interpretation is that FTL is not possible in normal space, since the speed of something is just another way of looking at how "fast" it travels through time - FTL becomes impossible by definition.<p>However, there is reason to assume a lot of things may be going on that are not strictly speaking taking place in normal flat space.<p>The article mentions the expansion of the universe as an example, and that's actually a good point to start. By virtue of the universe expanding, the distance between points grows faster than the speed of light as long as those points are sufficiently far apart. This becomes more interesting when you realize that new space in between these points is being created. Sure, the galaxies traveling on this expanding medium are not actually speeding apart powered by classical movement, but they are nevertheless changing position relative to one another in an interesting way.<p>In fact, what we're interested in when we talk about FTL is not classical movement at all - what we want is to change positions instead. There are places in nature where we know this is happening right now, for example we do know space can "flow" faster than the speed of light on the far side of event horizons.<p>So if we abandon the idea that we need to accelerate towards a destination, FTL becomes a broader idea of manipulating spacetime in order to be somewhere in less time than if we had actually flown there at the speed of light. There exist proposals for propulsion systems that go in this direction, for example the "warp drive" ideas that cheat by simply shortening the amount of space a vessel has to travel through. Some of these concepts seem to work in theory, for some definition of <i>work</i>.<p>The trouble with all these ideas is they need impractical amounts of energy. Which is wasteful, since we only need to bend spacetime for a short while and then return it to its original state behind us, something that works analogous to a catalyst would be much better.<p>At the most fundamental level though, what we are missing is a way of hacking spacetime. Huge masses and energies are how nature bends it, but ideally we would need some other way of manipulating the fabric of existence directly. This is the reason why drive systems in science fiction all have some kind of yet-unknown mystery substance critical to their function. Given how little we actually know about the basic fabric of the universe, ways of doing these manipulations may well exist. They might not. We most likely won't find out for centuries, if ever.<p>Until then, we must answer the question so that yes, FTL is most likely possible in theory, but it's not even remotely within our grasp right now. It might never work in practice.<p>Another observation worth considering: cosmic travel times seem utterly problematic right now because we individually live for extremely short periods of time. Spending a few thousand years in transit is much less worrisome if you're, say, an autonomous machine carrying an AI through the galaxy.
re: point 18: It is quite possible to get around this paradox, if you have absolute time. Absolute time means you can't send a message back in absolute time, which means you can't get 'causal loops'.
> Is Faster-Than-Light Travel or Communication Possible?<p>No.<p>Pretty simple stuff. No, it is not.<p>No matter how many sci fi movies tell you other wise. It is not.<p>Every experiment that comes out saying different is either lying/incompetent or the news reporting on it is lying/incompetent.<p>Just because you want it to be true does not make it either true or possible.