What with Harold White’s new design for an Alcubierre Drive, it looks like a warp drive may become eventually possible. But it begs a few questions:
It involves expansion and contraction of space, fine, I can see how you can accelerate a bubble of space time faster than light. But, wouldn’t it then take years for the spaceship to escape the warp bubble once it got to its destination? And receive communications?
If not, then how do you prevent or explain the “apparent” FTL travel of light/information using the bubble? What in practical terms is preventing causality issues or creating a time travel device with it?
Is there a difference between a portion of space-time compressed by a warp drive, and one compressed by gravity/acceleration?
The idea is pretty…but anything that gets around the FTL barrier is going to lead to problems, including (potentially) global causality violation.
This doesn’t prove, in itself, that such things can’t happen. MAYBE there are ways to produce a “warp field” that actually compresses space so much that, by travelling through it, you go FTL with respect to the nearby stars. Unlikely…but maybe.
Maybe wormholes can be produced. Maybe a spaceship can be translated into another universe entirely, where different physical laws apply. Maybe. How can anyone prove otherwise?
But if any of these things happen, and produce working FTL travel, then causality paradoxes cannot be too far behind.
I’m voting in favor of “earth-shattering kaboom” as one of the probable outcomes of early experiments, and hope that we conduct such experiments someplace far away. Pluto, for example.
I wouldn’t get too excited. The Alcubierre Drive isn’t just some machine that we can’t construct using standard industrial processes, or even something like a space elevator that can’t be made with current materials, but could be made with some materials we could reasonably imagine having. To make such a drive, you need a lot of “exotic matter” of a type that we don’t have a theoretical reason to believe exists.
So “it looks like a warp drive may become eventually possible” may be an overstatement.
The causality violations of FTL travel are the result of different observers being in different reference frames and therefore having different metrics for time and space. However, since traveling by Alcubierre Drive doesn’t involve *moving *per se, a traveler and a stationary observer will not observe time dilation, or Lorentz contraction or other relativistic effects.
For example, we don’t observe time dilation when we look at the most distant galaxies, even though they’re “moving” away from us as a substantial fraction of the speed of light.
Agreed that FTL via “teleportation” (wormhole, whatever) doesn’t involve Lorentz effects. But it would open the way to causality violation, simply by the creation of two space-time events, causally linked (the same spaceship, the same astronauts) one outside of the light-cone of the other. Another person entirely, travelling in the usual way, at a very high (but less than c) speed could perceive these two events in reverse of their own internal causal order.
Tom Swift, so to speak, could perceive “Old Alcubierre” as living in an earlier time-frame than “Young Alcubierre.”
re your last note…I’m not totally sure, but I think I disagree. I think that we do perceive time dilation when observing very distant, fast-moving galaxies. That their “speed” is due to expansion of space, and not ordinary travel, isn’t relevant. But I will defer to those who know better.
I mean I’m thrilled that the advanced propulsion laboratory is getting press but this isn’t anything to be excited about. It’s a massive, tentative “let’s go poke over there and see if there’s something to find” expedition. It’s the kind of thing you’d want to see at NASA but I’m not holding my breath for 1 year trips to Neptune anytime soon.
Special Relativity states that anything that can be used to make an FTL drive, regardless of how it works, can also be used to make a time machine, and vice-versa (and here, I use both the terms “FTL drive” and “time machine” in the sense that a science fiction fan would expect). What SR does not say is whether either of those things is possible, just that if either is, they both are. Maybe, for all Einstein can tell us, we just might be in a universe where time travel is doable. And if it’s not doable, it’s because of some other law of physics beyond the scope of relativity.
You forgot “Warp drives do work, and our understanding of space/time/etc. is just fine”. There is nothing in our understanding of relativity which is violated by warp drives. There does appear to be something in our understanding of the properties of matter which is violated by warp drives, but that’s a separate issue.
“Possible” doesn’t mean “practical”. There could very well be a specific configuration of black holes, damned souls, and immersion blenders that reliably pumps matter into the distant past at the rate of three neutrino masses per century. That doesn’t mean that even in all of human history, anyone will ever be able to send someone into the past to inscribe instructions on how to make a time machine into a platinum tablet and bury it under Stonehenge.
And then there is theorectically doable and practically doable.
Sure, if collide 40 galactic mass black holes just right we will create the required wormhole.
Pan Galactic Construction Council: “Ughh, I don’t think we can afford that”
And that whole if time travel or warp space travel is practical why aren’t we awash in space or time travelers? Because space is big and time and space is even bigger and we present humans are sampling a very tiny fraction of it.
Not so sure about that. If TT is possible and on-going then there would be visitors from an unimaginably far off future. With enough time almost anything is possible. If a culture has the curiosity to pursue building a Time machine it seems logical that they would eventually explore everywhere. If that culture is earth-based I’m sure we would have gotten around to seeing our earlier selves by now.
I agree with your central point, and maybe I agree with you period, but it depends what you mean by this closing sentence.
The perception people have is that scientists frequently claim to know something and are then proven wrong. That Relativistic physics showed Newtonian physics to be wrong, which was then in turn shown to be wrong by Quantum Mechanics.
So…what the bleep do we know?
But if the laws of motion and relativity are wrong, why do we use them for real-world applications millions of times every day?
Actual instances of theories going through the scientific method: making accurate, surprising predictions, verified independently many times elsewhere, and then later being shown to be outright wrong are pretty rare.
I’m not saying FTL will be impossible forever and ever, I’m just saying a jettisoning of what we know is unlikely.
