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Warp Drive Might Be Less Impossible Than Previously Thought
runner_one writes "Harold 'Sonny' White of NASA's Johnson Space Center said Friday (Sept. 14) at the 100 Year Starship Symposium that warp drive might be easier to achieve than earlier thought. The first concept for a real-life warp drive was suggested in 1994 by Mexican physicist Miguel Alcubierre, however subsequent calculations found that such a device would require prohibitive amounts of energy, studies estimated the warp drive would require a minimum amount of energy about equal to the mass-energy of the planet Jupiter. But recent calculations showed that if the shape of the ring encircling the spacecraft was adjusted into more of a rounded donut, as opposed to a flat ring the warp drive could be powered by the energy of a mass as small as 500 kg. Furthermore, if the intensity of the space warps can be oscillated over time, the energy required is reduced even more."
Does this theory at all reduce the chance that when the Warp Drive ship arrives at its destination that it will emit a huge gamma ray burst? This planet destroying side effect would sure put a damper on any kind of arrival party for the warp drive ship.
Agreed.
Other important caveats not listed are things like, duration of field perturbation, and effective field size.
If it takes 500kg of raw mass energy equiv, to send something the size of a football on an ftl hop for 1 sec, it is still very very impractical.
If we are talking something the size of manhattan island being shot at FTL for over a year for 500kg mass energy, things are difficult, but interesting.
This still doesn't sole several other noteworthy problems with the alcubiere metric though. Things like hawking radiation snowplowing on the event shock of the warp field, nuking the ship and everything around it when the field drops as the ship leaves FTL.
(Basically, the spacetime bubble the ship occupies behaves the same as the event horizon of a black hole, as far as virtual particle interactions are concerned. The pocket tearing past at ftl speed forces the particle pairs to become real, robbing energy from the warp field, and plastering radioative exotics all over the shock front. When the bubble collapses, that radiation gets released.)
If they can pull it off, alcubierre's metric would only be useful for short jumps, not continual cruising, making it impractical for visiting very distant objects. It would also be an energy hungy monster.
As far as I understand it warp drive doesnt break the speed of light locally, so I recon no weird time reversal stuff can happen.
In Relativity, traveling faster than light relative to any reference frame, via any method, presents problems with causality. And the whole point of a Warp Drive is that someone will agree that you went faster than light, and thus went backward in time.
When I last read about the Alcubierre drive, one relevant point that was mentioned was that the inside of the warp field is causally separated from the outside, which solves the problems of causality while in transit, but raises the question of how one starts or ends the journey.
The ridiculous amount of energy required was another problem, more of a practical "how would you do that?" issue rather than a "how is it even possibly in theory?" question.
But the thing is -- it may actually be possible to do this in our universe. And the assumptions of constant c and General Principle of Relativity may also be correct. Which may mean that the assumption of causality isn't. What a universe that would be.
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But that's the point of how warp drive works - you bend space so that you don't travel faster than light.
You locally don't. The warp ship doesn't actually accelerate at all. This is how you get around the relativistic energy equation.
However, someone will observe you traveling faster than light, going from point A to point B faster than light would travel the same distance. If nobody sees you traveling faster than light, then how can you say you did so at all?
And the whole point of relativity is that the laws of physics have to hold everywhere. That observer, depending on their own velocity in space-time, potentially see you arrive at your destination before you left, violating causality according to them.
Given a few such warp ships, you could even arrange it so that that person would receive a message they had written and sent with you before they had actually written it. And then causality is broken for everyone.
But hey, maybe it's not a causal universe! I await their experiments.
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If going 99.9999% C, it would take you an outrageous amount of (outside) time to flick the switch. The universe could end before then!
Still, assuming you did indeed flick the switch, it would be the same as with sound propogation. An ambulance travelling at 99% speed of sound with sirens blaring will emit a higher frequency sound, until after it passes, and then the tone will be dialated the other way.
The light won't move faster. Instead, the frequency will be insanely high. Your infrared emitting tungsten filament bulb will be emitting gamma ray photons.
If you are going 100% speed of light, you will *never* succeed in toggling the switch.
Here is where the whole FTL thing becomes unnecessary:
If you are taveling 50% of C, the degree of seperation between internal and external clocks will be sufficient that even though it takes you 400 years to reach that star 200 light years away, a considerably shorter time will be recorded by the ship's onboard clock.
The closer to C you travel, the less "time" you experience. So, FTL is not necessary. The crew will be alive and well, and feel only a few months have passed on their 400 year journey. Everyone they left back home will be dead and buried, but for them, only a few months will have passed.
If all you care about is *your* lifetime, FTL is not needed to explore the universe.
We have seen this effect, just not in regular solid matter; we can see it in certain configurations of regular matter, such as the Casimir effect. So it's not *real* exotic matter, but it does show that negative energy is technically an observable thing. How exactly we can make use of that to do the necessary space-folding is still unknown. It's an incredibly hard, potentially impossible engineering problem, but impossible engineering problems have a tendency to become trivial given enough time and motivation.
Exotic matter, by definition, requires violations of the known laws of physics.
That's a very peculiar definition of exotic mater you have there. Elsewhere, "exotic matter" generally refers to matter of a type neither observed nor predicted by current theory. No violation of known physics is implied. It is just that we haven't seen any and there is no particular reason to believe that it exists.
The particular flavor of exotic matter needed for the warp drive is "negative" matter. Negative matter has negative energy. Unlike antimatter where antimatter + matter = lots of energy, negative matter + matter = nothing.
'Last I heard, running the usual math through with negative matter results in some situations that don't make a lot of sense. They aren't necessarily wrong or forbidden, we just don't know what they mean. Math is like that sometimes.
"No, nothing can go faster than the speed of light because it will violate causality. Which is more or less forbidden by the entirety of physics."
Incorrect. There is nothing we know of that actually works to prevent the violation of causality. There are a number of ways it can theoretically be done.
See Tipler, "Rotating Cylinders and the Possibility of Global Causality Violation".
All rhetoric (like the post at that link) aside, all we really have about it is guesses. The fact that we have never observed anything, so far, that would violate causality says absolutely nothing about the possibility. Further, it is not necessarily true that limited instances of causality violation would render the entirety of physics invalid, any more than relativistic situations render Newton "invalid". They are "special cases". That is all.