I always thought of him as more like a five-year old.
I am not someone who thinks “What the bleep do we know”.
We clearly understand a lot about the universe and what we know is not going to be jettisoned, only added to.
But in the context of talking about extraterrestrial species, who may be millions or even billions of years ahead of us technologically, I would be very reluctant to declare X Y Z impossible.
Only if something very clearly is logically contrary to the properties of the universe, like, say, perpetual motion.
But this is not one of those situations. This is more like “Humans will never fly; our shoulders are not strong enough” i.e. declaring something impossible just because the speaker cannot think of a way to achieve it.
Travelling faster than light does cause some very severe logical problems, since the speed of light is linked very closely with causality. If you travel faster than light, in some frames of reference you are travelling back in time.
I wouldn’t be surprised if the universe has some kind of chronological protection system in place, similar to the one which prevents perpetual motion. Such a system would forbid FTL travel, and keep the universe nice and consistent.
Yes, of course the Voyager probes are invisible, and have been for a very long time. If they weren’t actively making their presence known, we’d have no chance whatsoever of detecting them, even knowing exactly where we expect them to be.
There have been asteroids hundreds of meters across which have passed closer to us than the Moon, and which we’ve only detected once they had already passed. And those are things that aren’t even making any effort to go unseen. I know that different technologies advance at different rates, but do you seriously think that aliens who can cross interstellar space haven’t figured out the arcane secrets of black paint?
The middle ground between true and false is “unproven”. Occam’s Razor treats “false” and “unproven” as the same, but Occam’s Razor is neither true, nor false - it is convenient.
Un-falsifiable theories like “aliens might be able to travel faster than light and hide themselves well enough that no serious person believes in them” are also unproven. Therefore, science can and should do nothing with the theory - if it can’t be falsified, it is not a fit subject for scientific investigation. The scientists have better things to do with their time. Get back to us when you have evidence.
As far as we know, nothing can go faster than light. The best theory is the simplest one that explains all the known facts. If and when someone shows something that has been accelerated past the speed of light, we will adjust our theory. Until, we use the theory that works.
Regards,
Shodan
I was replying to a point about whether a ship could be undetectable, not about FTL.
But, since you brought it up, yeah my personal suspicion is that an advanced race thousands or millions of years ahead of us will traverse space in a very different way from rockets, and their tech may look at first glance to us as though it breaks laws of physics.
But it won’t.
Because I also think our understanding of physics is correct (just not complete), so if they do use some exotic method to do roundtrips in a time which should be impossible in a given frame of reference, then perhaps it does also include time travel? Maybe that’s part of why we don’t see them?
All just WAG of course.
Oh, that’s because they don’t want to be seen.
But for some reason they wanted to be seen a few thousand years ago. Even posed with their 1950’s space helmets on for laughs. But they’ve never left behind a single artifact.
We’re talking about them evading detection after they’ve entered our atmosphere. Black paint ain’t gonna cut it.
Oh? So what do you call the Great Pyramid? Or are you a person with no music in your soul who sees it as just a pile of rocks assembled by people not entirely out of the Stone Age, with a large population with time on their hands? I mean, they wore KILTS, for God’s sake! You cannot get more primitive than that.
Harumph!
ETA: Episode 1 of Stargate SG-1 is on YouTube.
Unless they are traveling through space in ways we literally can’t picture or even imagine they are going to leave a signature. Understand, if they CAN travel at large fractions of the speed of light through normal space they ARE literally light years ahead of us…we have no way to move large masses through real space (or any other kind) today, and can barely imagine ways we MIGHT be able to do something like 5-10% light speed if we squint hard. But regardless, given the way the universe works, moving a large space craft through real space at, oh, say 90% the speed of light is going to leave a big signature…not only will it be putting out ungodly amounts of energy but it’s going to be hot, as at those speeds even interstellar gas and dust are going to glow as it impacts the ship or the ships magic energy shield or whatever. Now, if they are billions of years in advance of us (something I frankly doubt, but what the hell) maybe they can magically jump between world using wormholes, but, sadly, wormholes that you create are ALSO going to leave a big freaking signature. This isn’t ‘humans will never fly; our shoulders are not strong enough’, it’s ‘well, we know we can fly these bi-plane thingies, and we can kind of sort of see how we could fly at speeds greater than the speed of sound in the atmosphere, but doesn’t seem likely we’ll have the materials to fly at 100 times the speed of sound without melting the aircraft’. Maybe, someday, we will…but probably not, not unless we find some fundamental error in our understanding of physics. As far as our current understanding goes, there is no way to propel a craft that has a large mass without a hell of a lot of energy…which is going to leave a pretty big footprint in the sky saying ‘something evil this way comes!’.
Not to mention running into macroscopic objects, even very small ones. In another thread I did a quick calculation of what would happen if a craft traveling at .99999c hits a golf ball at that relative velocity. It would be quite a bang! Specifically, it would release about 1.3 x 10[sup]18[/sup] Joules of energy, equivalent to a 310.7 megaton nuclear explosion. The collision would briefly be brighter than the sun, blazing with X-rays and gamma rays, and would trigger nuclear fusion. It would be the most impressive fireworks ever!
I guess the lesson for interstellar travelers is to slow way down and strictly observe speed limits when approaching stellar planetary systems! 
I dunno about you all, but when I travel between solar systems I use wormholes and hyperspace travel like a normal person. High-speed collisions just aren’t an issue - I emerge back into normal space at a dead stop relative to the nearest massive object.
Of course I still don’t have proper cloaking technology - that wasn’t included in the basic package. And the disguise tech that came standard sucks - after the first time I used it it broke and now my ship’s stuck looking like an old british police box for some random reason.
Just a bit of clarification, please: I understand what happens when you travel slower than the speed of light, pretty much. The same goes for when you travel faster than the speed of light, pretty much.
But when you are traveling from STL to FTL in most cases you are going to be traveling AT the speed of light for a brief period of time, and I was wondering what happens at that point.
IANAP, and you’ll undoubtedly get a much better answer than mine, but FTL particles (i.e.- tachyons) are purely theoretical and I believe the current best guess is that they do not and cannot exist (if we could detect and exploit the characteristics of tachyons, we could communicate with the past, and one might note that we’re not getting a lot of communication from the future at the moment).
But the theory, such as it is, is that tachyons can only asymptotically approach c from above, just as ordinary matter can asymptotically approach it from below. In either case, and certainly in a real sense for ordinary matter, the physics at the actual speed of light is undefined because it involves infinite energy and infinite mass and zero time.
There is, however, an interesting analog with general relativity when objects fall into a black hole. According to the time dilation observed from an outside reference frame, an object approaching the event horizon will never fall in; i.e.- it will take an infinite amount of time to complete the crossing. But according to the reference frame of the infalling object, it crosses the event horizon in ordinary time according to its indicated velocity, and indeed objects do this all the time, causing the event horizon to grow symmetrically. There are a number of ways to try to explain this intuitively, some of them fascinatingly creative, but really the bottom line is that our intuition just doesn’t work in these circumstances.
Are you talking to me? Per pretty much all the authoritative documentation on the subject, FTL travel is done by exiting the universe entirely and reentering it at a different point. You don’t actually go faster than the speed of light at any point; you take a shortcut.
And by “authoritative documentation” I of course mean fiction. About the only exception to this rule that leaps to mind is Star Trek, where things appear to be a bit more complicated, but I’m still not sure the ship itself experiences relativistic speeds.
It’s worth noting, in all seriousness, that the biggest problems with FTL travel are the violations of simultaneity that occur when an object arrives at a distance faster than the propagation of causality allowed by special relativity. Taking a shortcut through a wormhole doesn’t prevent those violations.
Myself, I think a possibility for FTL (like) travel would be something like the Alcubierre drive. Basically, you are compressing space time in front of the craft while stretching it out behind. What that does is let you travel (relative to a space frame outside of the one you are in) apparently faster than light, even though the space craft itself isn’t actually moving that fast (or at all). It’s space that’s expanding and contracting. And we know that space itself can expand faster than the speed of light.
However, if some advanced civilization can actually build one (assuming it’s even possible), it’s, again, not going to be exactly stealthy. I don’t recall exactly what energy levels we are talking about, but it’s vast…like the suns output vast. Not something you are going to use to sneak up on folks to be able to steal their cows or do some serious anal probing on them.
Yeah - I’ve yet to be convinced that that’s a real violation of causality. It looks like time travel to the observer - a person watching my starting point through a telescope will see me still at my starting point when I arrive next to them, but that’s just because I outran light. When I read arguments about how instantaneous signals can violate causality it always just seems like it looks like a causality violation from a specific inertial frame, but it isn’t really one and you can’t use it to go back in time and shake your own hand.
But even if we suppose that tesseract travel is time-travel - so what? So I ‘violated’ causality. What’s the consequence? Time cops come and arrest me?
I think physicists bearing pitchforks would come to arrest you! 
A very powerful concept that helps one understand causality in the context of special relativity is the concept of the light cone.