Quantum Setback For Warp Drives 627
KentuckyFC writes "Warp drives were generally considered impossible by mainstream scientists until 1994 when the physicist Michael Alcubierre worked out how to build a faster-than-light drive using the principles of general relativity. His thinking was that while relativity prevents faster-than-light travel relative to the fabric of spacetime, it places no restriction on the speed at which regions of spacetime may move relative to each other. So a small bubble of spacetime containing a spacecraft could travel faster than the speed of light, at least in principle. But one unanswered question was what happens to the bubble when quantum mechanics is taken into account. Now, a team of physicists have worked it out, and it's bad news: the bubble becomes unstable at superluminal speeds, making warp drives impossible (probably)."
Longer lifetimes is the answer (Score:5, Interesting)
The SCI-FI buff in me holds out hope that physics will uncover a trick to FTL, but...
It doesn't really matter if we cannot travel faster than the speed of light so long as we can live long enough to get there.
Who cares if it takes 50 years to fly to Alpha Centauri if we can engineer ourselves to live for a thousand!
Causality (Score:5, Interesting)
Faster-than-light travel always causes causality paradoxes [orionsarm.com], so a priori, FTL drives are impossible unless special relativity is wrong. (That's is a bit like saying that perpetual motion machines are impossible unless thermodynamics is wrong.) The proposed mechanism behind the FTL drive doesn't matter -- it'll still cause a time paradox.
Just like we know any proposed perpetual motion machine must have a flaw, any proposed FTL drive must also have a flaw. They belong to the same class of impossible device, and deserve the same degree of consideration.
Re:Causality (Score:5, Interesting)
IIRC Einstein said they GR and SR may be proven wrong, but that the laws of entropy will never be broken (ie entropy is always getting bigger). I would aggree with this. ie FTL is less sci fi than "vacuum energy" or anti inertia drives.
But if I were a betting man, I would bet on light speed as the ultimate speed limit of the universe.
Quantum mechancs+General relativity incompatible? (Score:4, Interesting)
I thought we knew that combining these two theories resulted in answers we know to be nonsense. So the implication is one or both of them are wrong in some way. So I'm a little confused why we should trust results based on the combination of two theories that don't work together.
Granted I'm just a laymen, but does anyone else want to comment about the intersection of these two theories?
Re:Causality (Score:4, Interesting)
I'm not sure perpetual motion is, strictly speaking, impossible.
Thermodynamics doesn't seem to preclude 100% efficiency, allowing motion in perpituity. Some real-universe examples:
Light on the fringes of the universe will continue travelling forever (unless we assume something new to stop it).
The electron on an atom that never falls into a star, black hole, or the like will forever circle the nucleus.
Heck: the atom itself will never stop moving.
Nor, best as we can tell, will the universe. It will be in motion perpetually (I suppose unless it all disintegrates into Hawking radiation, but then *that* will be in motion.
There are two problems with perpetual motion machines. One is the false math that you can derive infinate energy from one. That's not true at all. You could derive exactly the energy put into one.
The second is 100% effeciency, which is required for perpetual motion to obey thermodynamics, is not possible in what we would likely call "a machine"
Re:Paper was submitted 1. April (Score:2, Interesting)
Not saying it's necessarily a hoax, as the math seems valid at a casual glance (although IANA theoretical physicist), but they misspelled "a priori".
Re:Proof! (Score:5, Interesting)
The problem is that in order to have a region of spacetime moving in relation to the outside universe, space has to expand behind it and contract in front, which demands negative and positive gravity in those regions. You need a large negative mass held in place in front of you, and a large positive mass behind. (We'll leave aside the problem that nobody has demonstrated the existence of negative mass, I personally don't believe it could exist precisely because it would enable FTL, but that's seperate to this point.) What you have to achieve is to have the centre of gravitation of the two masses at the centre of the edges of distortion. It means inevitably that half of the negative mass you are using has to stick out of the bubble ahead of you into normal unwarped space, and so that in order to keep generating the field ahead of you, it has to travel faster than light in its local frame. That is strictly not allowed.
We already have faster-than-light communication! (Score:2, Interesting)
Sorry, but we already have faster-than-light communication trough quantum entanglement. The change in state happens instantly, without any delay, no matter what the distance is.
Of course in praxis, you would first have to fly a large mass of entangled matter to the other place at sub-light speed. But when it's there, you could communicate at FTL speeds, until the matter is used up.
I think with moving matter, you are basically correct. But even thermodynamics is just a theory of how things work. It can always happen that we find an exception to it. Pretty much all our scientific knowledge got refined more and more over the time, showing us how there are exceptions here and there (eg. superconductivity).
So it may be pretty unlikely, that searching for FTL drives will bring some results. But it is not per-se wrong or impossible.
Special relativity just has to hat so be a little tiny bit wrong.
Please stop acting as if theories were absolute unchangable laws. They may look, or be very close to that, but they never are exactly that.
(So I agree with you for 99.99999%. But not 100%! And say that there is a very important difference there.: )
Re:Quantum mechancs+General relativity incompatibl (Score:2, Interesting)
The only "somewhat" reliable theory we have so far that should work when both quantum and relativist thresholds are reached is the superstring theory (or it's advanced counter part or M-branes). Unfortunately nobody can tell if that theory is right or not since we don't have the means to measure any of the results that are predicted by that theory and are not in conformity with the general relativity or quantum physic.
Maybe with the LHC that with be possible, but that may not be the case. The maximum energy that LHC will be able to handle will in principle not be enough to put some of those principles in practice. BUT, perhaps we can observe a sub-"product" of superstring (M-brane) theory, the unfolding of extra spacial dimensions (6 or 11) and in that case, that should give us a pretty good idea that M-branes are the way to go.
Still, even if we don't see any of that with LHC, it doesn't mean the theory is wrong until we build a powerful enough particle accelerator that finally confirms or dismisses M-branes theory.
Re:Quantum mechancs+General relativity incompatibl (Score:4, Interesting)
First of all it's worth remembering that quantum mechanics and relativity are not 100% incompatible. In fact "relativistic quantum mechanics" has been around for a long time. Quantum theory was greatly advanced when relativistic effects were included.
But you're right that we have good reason to believe that something is wrong with either quantum mechanics or relativity (or both), since they give contradictory predictions in a certain number of extreme cases. (Quantum gravity is not yet solved...)
However we also have ample evidence that quantum mechanics and relativity are incredibly accurate and predictive theories in a vast range of circumstances. We have every reason to believe that the correct "Theory of Everything" will reduce to conventional quantum mechanics and conventional relativity in the appropriate limits. And thus we have every reason to continue using those theories to make predictions all over the place.
Now a warp bubble is one of those extreme situations where the two theories might be expected to give contradictory results, in which case only the hypothetical theory-of-everything would give the correct answers. But it is certainly still useful to ask what our current theories would predict for these extreme situations. It helps us better understand the theories. And, again, we have reasons to believe that many of the things our current theories predict (even in extreme situations) will be right. Absent the theory-of-everything, quantum mechanics + relativity will give us the "best guess" about how such objects would behave
Re:Mod parent up (Score:5, Interesting)
Yeah but you need a massive amount of fuel to accelerate to C and then slow down again. About 40,000 times the size of the shuttle's boosters.
Perhaps this is why, despite our best efforts, no other civilization has contacted us. It's simply too hard to bridge the huuuuge gap between the stars.
Yes, if I was going to build a universe with all sorts of playthings in it, I'd probably separate the experiments with enough spacetime that when the odd experiment blows up it doesn't really affect any others around it.
Not that I think that the universe was actually designed, but if it was, that would be how I would do it.
Michael
3 laws (Score:3, Interesting)
Arthur C. Clarke formulated the following three "laws" of prediction:
1. When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
2. The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
3. Any sufficiently advanced technology is indistinguishable from magic.
(http://en.wikipedia.org/wiki/Clarke%27s_three_laws)
I assume then, a statement about superluminal travel being impossible, is actually good news.
Re:Longer lifetimes is the answer (Score:3, Interesting)
Actually it sounds crazy but it is not.
I was part of a proposal to NASA to build a massive (150 meter diameter) GEO based telescope. When you do the math, it works out to be far cheaper and much less fuel to mine the moon for all the raw titanium and fuel you need, manufacture the parts and then robotically assemble them in orbit, than it would to launch from earth all the pre-manufactured component parts.
It's the fuel spent escaping earths gravity that kills you.
Re:Longer lifetimes is the answer (Score:5, Interesting)
No, it's time dilation and space contraction. If you're traveling at 0.9c relative to earth, your gamma is something like .44. So if you travel one light year, an observer on earth will see you go one light year in about 1.1 years. But from your perspective, you will have traveled only about .44 light years, and it would take something like .48 years. If you travel fast enough, you can reach even distant stars in very short times from your perspective. But you won't get a nice, tidy Galactic Federation, because people on earth will be getting very old very fast. That's the real problem with relativity. It's not that you can't get somewhere fast. Tell me where you want to go and how fast you want to get there, and we can calculate how fast you need to go (relative to the earth) to make it in that time, and it will be less than c.
In other words, we could (in theory) colonize all of the habitable planets in the galaxy in a fairly short time. But the colonies would all basically be cut off from each other. Even sending a radio message to another colony would take prohibitively long. And forget about "rescue" or "supply" ships.
I Still Prefer Option 2 (Score:2, Interesting)
The idea for traveling large distances within the universe which involves folding space/time into a higher dimension seems both more efficient and generally better understood today. As was noted above, working with something like superluminous velocities is going to inevitably require analysis involving two of our most powerful models of physics, relativity and quantum mechanics, which at this point still don't play well with each other (at least not in every circumstance).
However, it seems like the general trend towards the theory of everything research continues to lean to higher dimensions as an accurate model. That being said, ideas that have been expressed that involve folding and or dropping out of the space/time continuum and reentering at a different location/configuration in the universe seems like it might still be a more viable option for traveling large distances.
Still though, superluminous speed does seem like it would be cool...
1 G isn't magic (Score:3, Interesting)
Sustaining 1G for several years isn't magic. It's just advanced technology.
James Powell, the co-inventor of super-conducting maglev, described a mechanism to build a 1G rocket to travel to the stars. His basic idea was to use Mercury as a solar collector to manufacture a few tons of anti-matter. When you react the anti-matter, you get both power and ejectable mass moving at very high speed. A sci-fi author, Charles Pelligrino, wrote up the idea in the appendix to his book, Flying to Valhalla [amazon.com].
The Orion designers were thinking that once they got the first version working to ferry between the planets, they could build a star ship that would get to Alpha Centauri for $100 Billion in 1960 dollars. The cost was so far out of reach, the idea was almost forgotten.
The point is, you don't need magic to travel at 1G, you need resources.
Re:We already have faster-than-light communication (Score:3, Interesting)
You can only roll the dice once. After that they are no longer entangled.
So Joe carries 1000 particles, which have twins back home, to Joe's Space TV/VCR Repair Center, which is out near Betelgeuse. I want to send him a message: "Pound pastrami, can kraut, six bagels--bring home for Emma."
I "roll" particles to encode a 1 and leave 'em alone for 0. Sez I:
01010000 01101111 01110101 01101110 01100100 00100000 01110000 01100001 01110011 01110100 01110010 01100001 01101101 01101001 00101100 00100000 01100011 01100001 01101110 00100000 01101011 01110010 01100001 01110101 01110100 00101100 00100000 01110011 01101001 01111000 00100000 01100010 01100001 01100111 01100101 01101100 01110011 00101101 00101101 01100010 01110010 01101001 01101110 01100111 00100000 01101000 01101111 01101101 01100101 00100000 01100110 01101111 01110010 00100000 01000101 01101101 01101101 01100001 00101110
Re:Hiesenberg says.... (Score:3, Interesting)
Re:We already have faster-than-light communication (Score:3, Interesting)
Ask Franz Embacher and his team from the university of Vienna. They do exactly what I described and transferred information over half the city. [primidi.com] I think he can control which number shows up.