Looking past the woo in the article, would be great to see a lab result, even on miniature scale, that would do away with the exotic matter requirement. What do you think - possible?
Previously brought up here, there doesn’t seem to be much new on the topic as far as I can tell.
Well, the non-reliance on exotic matter is new, I think. If I understood the article correctly…
White’s version of the Alcubierre metric still requires a negative energy density, so it doesn’t do away with the requirement for exotic matter. Additionally, it’s not clear that these proposals work even with unobtanium, as it’s been argued that while these solutions exist in classical general relativity, once one takes quantum effects into account (as one must for a realistic description), the ‘warp bubbles’ won’t be stable.
I think you did, and the fascinating part is how that was accomplished:
You can reduce the energy required (that is, bring it closer to zero) in a number of ways. Personally, I’m fond of putting the whole thing in a TARDIS. But no matter how clever you get with the tricks, you still always need some.
And we’re so far from lab results, even preliminary ones, that one shouldn’t even bother worrying about that. If it’s possible at all (don’t bet on it), it’s going to take some major work from the theorists, first. The only “laboratory” that’s relevant is a computer.
Maybe I misread you, but the very part you quoted says that negative energy density—and thus, exotic matter—is still necessary. Any such bubble will require a region in which light rays defocus, which means a region of negative energy density. (In fact, IIRC, any scheme of FTL travel requires negative energy density.)
I think the idea is that the stress-energy operator of a quantum field in semiclassical gravity cannot be made to satisfy the same energy conditions as can be imposed on a classical stress-energy tensor in bog standard general relativity which allows for negative energy density without the field itself being exotic. That said the ‘Alcubierre drive’ is still highly implausible as an actual method of transportation for a lot of reasons.
The show stopper I see is time travel slash paradoxes. This is used as a common disproof : if the drive worked you could arrive before you left. I search Google looking for an alternate theory that would allow you to use this kind of engine, but not be able to go into the past. Or, at least not your past.
How does functioning as a time machine invalidate its purpose as a drive?
Because it would violate causality, which would make lot of people very angry and be widely regarded as a bad move.
I see no need to invalidate a star drive just because some people are pissy about exactly when you’ll arrive at your destination. People who want to stand around saying “It can’t be done because it can’t be done!” can go invent generation ships, or cryogenic suspension.
It’s not when you get there that is the problem, it’s when you get back. If you get back before you leave you can destroy your own ship before it takes off and a bunch of other weird stuff that could end up destroying the universe.
Then don’t come back right away. If you get someplace 4 light years away 4 years before you leave, pack 8 years worth of supplies and plan to set up a camp somewhere. There’s gotta be years and years worth of exploration to be done out there.
I hate when that happens.
This is the part I don’t understand.
Let’s say I leave Earth now. 00:00:00 on December 4, 2013.
I immediately (for some value of immediate) accelerate to 2c and fly out 2 light hours.
Now, the light waves generated by my travel have only traveled 1 light hour from Earth.
I bang a U and head back (still 2c), somewhere along the way, I pass the light waves generated by my outbound travel.
I get back to earth and it’s now 02:00:00 December 4, right? It still took time to go out and back, just not as much time as light would have taken to travel that far, but why does that matter? How did I go “back in time”?
Apparently it’s when you try to mix and match Alcubierre and relativistic effects, as I recall. At least, it works that way for wormholes.
From another thread on the subject (I only considered information transfer, but you can replace this with any mode of transmission you want; additionally, I’ve covered only the limiting case of instantaneous transmission, but basically the same story works for all speeds greater than c):
Personally I think our best bet at FTL travel is the current research thats showing some signs that the entire universe is actually a simulation:
We just need to figure out the equivalent of an SQL injection attack that lets us rewrite the position matrix for our desired object.