Re: FTL without warp drive...time dilation?
They're also all things for which there is no observable evidence...
Not true, because science doesn't work that way. Since everything follows the same laws of physics, you can extrapolate the way the laws would apply in an exotic context by observing how they apply in known contexts. General Relativity has been consistently verified by every single experiment we've ever thrown at it. Its equations work reliably and consistently. And the predictions of warp drives, wormholes, and the like are derived, not from different, untested equations, but from the very
same equations that have been tested extensively -- just with different terms plugged into those equations.
This is what so many laypeople don't understand about science. They assume you can't know anything about what hasn't been directly observed, but the whole point of theory -- the reason it's such a powerful tool -- is that it allows you to
predict things beyond what you've observed. If you can understand the fundamental rules that underlie your observations, then you can figure out how those same rules would apply in a new situation. No, you can't be absolutely certain of how they'd play out in an untested situation because there might be factors you're unaware of, but you can make a prediction that's consistent with everything you do know and that has a good probability of being right. And just about every prediction of General Relativity that's ever been experimentally tested has turned out to be correct.
Note that Einstein's original idea of wormholes was realized to be impossible, though the mathematics took a generation to work out; are you willing to take a bet that the current crop of Fantastic Further Relativistic Notions will survive to, say, 2050 intact?
Actually more recent work has lent
more credence to the possibility of wormholes and warp drives, not less. Theorists have devised potential workarounds to the negative-energy problem and the infinite-energy problem, which were once considered to be insoluble.
Anyway, you're redefining the question. Of course we can't predict future discoveries, but that's not what you said before. You said, specifically, that
relativity could not "form a coherent explanation" of an entity moving faster than light. In fact, most of the theories we have about faster-than-light propulsion come
directly from General Relativity. So relativity absolutely can provide an explanation for how we
expect objects would behave if they could travel superluminally. No, that doesn't mean we can be sure the explanation is absolutely true, but that's irrelevant, because science never claims absolute certainty. It only makes predictions. And the point is that relativity can and does predict the behavior of FTL entities in quite precise mathematical detail.
We can make some suppositions about things that would probably follow, but we are talking about something which is, in detail, beyond the bounds of our knowledge. If you want to make up effects, that's fine and dandy and probably fun, but it also means you can make up whatever side effects you want.
All you're doing is betraying a fundamental misunderstanding of how science works. Deriving predictions from a theory is not "making up effects" -- it's
doing mathematics. It's developing equations that explain and codify our observations and make testable predictions. You don't "make up" the results of an equation in new conditions -- you just plug in the numbers and do the calculations. For instance, if you know the equation d = (1/2)at^2 for an object falling under gravity, then you can calculate how long it would take an object to fall from a given height on any planet or moon with any strength of gravity. You wouldn't need to go there and measure it, you wouldn't have to "make up" a result, because it's
math and math is consistent and predictable. The only things you make up are the initial conditions, the variables you plug into the equation -- e.g. dropping something from a height of ten kilometers onto a planet with a surface gravity of 8 gees. The
results of the computation arise inexorably from the math. And that lets you reliably predict what would happen in conditions you've never actually experienced, even conditions that can't physically exist.
And again, that's what we're talking about here -- not whether FTL travel is actually possible, but just whether relativistic theory can predict how it would happen if it did occur. And the answer is, yes, it can, and it does. Most of our FTL theories come directly from relativistic equations.