
Quantum setback for warp drives - Anon84
http://www.technologyreview.com/blog/arxiv/23292/
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jerf
So, previously, if you applied an impossible amount of impossibly-stable
negative mass in an impossible configuration that was impossible to maintain
due to impossible-to-predict interactions with the interstellar medium and
goosed it in an impossible manner you might have been able to move faster than
light.

Now some guys have revealed that it's also impossible due to quantum effects.
Frankly, that's just one more "impossible" in a rich sea of impossible
assumptions to make this style of warp drive work.

As I like to say, once you accept one impossibility into your theory, the fact
that impossible results occur is not fundamentally interesting.

People who babble about how people thought that traveling faster than sound
was impossible and who are we to say this is actually impossible need to spend
more time with real relativity and not Star Trek "wishing is an acceptable
substitute for engineering" relativity. People who think that the Alcubierre
drive was ever actually possible betray a _profound_ misunderstanding of both
the drive and relativity, in their zeal to get to the results they want
instead of the reality they have. If FTL is possible, it won't be as a result
of QM or relativity. It might come from the eventual fusion, but a deeper
understanding of relativity shows that you're still facing a steep uphill
battle.

The thing that you come to understand if you actually understand relativity is
that it is not merely that FTL travel is "impossible" because c is some
"cosmic speed limit". c is not the cosmic speed limit. c is the number that
indicates the relationship between space and time in the Minkowsky metric. c
comes from the literal shape of the universe, which is not the Euclidean one
you think it is. Travelling "faster than c" is not merely breaking the 55mph
speed limit on your local road, it is fundamentally a undefined, gibberish
statement in relativity. Everything outside of your lightcone is profoundly
indistinguishable from anything else outside of your lightcone.

The deepest discussion of relativity I know of that is freely online:
<http://www.mathpages.com/rr/rrtoc.htm>

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grinich
I don't understand how Hawking radiation is significant. It's far less than
the cosmic background radiation everywhere in the universe. (This is why we
can't "see" black holes.)

~~~
jerf
This is something like standing on Pluto and saying you don't see what's so
bright about the sun. Why not come stand on the surface of the sun and then
make up your own mind?

Hawking radiation is not intrinsically weak. Hawking radiation _as generated
by a large blackhole_ is weak. Flashlights are not weak; flashlights as
powered by my nearly dead batteries are weak.

With a different spacetime configuration you can get arbitrarily strong
Hawking radiation, just like you can get arbitrarily strong light using more
power. Hawking radiation around a very small black hole tears it apart
relatively quickly.

The Universe does not seem to like playing games like this and it tends to
wipe out any structure that permits causality violation (as any FTL drive
would) in an unsurvivable blaze of either Hawking-radiation or in an explosion
of the vacuum energy (see Hawking's work on what would happen if you towed a
wormhole around enough at relativistic speeds to cause a causality violation).

And by "unsurvivable", I don't mean "probably fatal to life but we might be
able to engineer around it". I mean, "unsurvivable to the space-time structure
in question"; whatever mass or energy happens to get in the way is orders of
magnitude away from even affecting the outcome, let alone standing a chance of
survival.

~~~
grinich
Thanks for the great reply! I guess I'd only read about Hawking radiation with
respect to black holes, and never considered its implications on a larger
scale. Sounds like it has larger implications than I thought.

Were you citing a specific paper by Hawking (towing a wormhole)? I'd like to
read more.

~~~
thwarted
I haven't read the Hawking paper in question specifically, but the idea of
towing a worm hole around is that you move one end of a worm hole for some
period of time at relativistic speeds. Since as you approach c, time slows
down, so the stationary end of the worm hole is further in the future than the
one that was moved around. It's a pretty stock layman's example of how time
travel _could be_ possible and I'm sure Hawking has torn a, er, hole in it
some how.

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jimfl
If the bubble is unstable then it probably just needs constant modulation,
meaning the FTL ship is flown more like a helicopter than a rocket ship. That
makes it more maneuverable.

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DanielBMarkham
This just in: Quantum mechanics and relativity don't get along.

Film at 11

<<yawn>>

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geuis
Yeah let's get to the point where it's technically possible to build one. This
is exactly like preminent scientists in 1903 publishing papers about how
powered flight was impossible.

