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What is the inertia or velocity of a vehicle upon exiting or shutting down an Alcubierre bubble? Would the vehicle maintain the velocity it had in the bubble?

I'm not sure I asked the question in a meaningful way so I'll try another question that targets what I'm after. If a vehicle was traveling in one of these bubbles how hard would it be to come to a full stop?

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    $\begingroup$ The Alcubierre drive is a physical fantasy. As in any other fantasy, you can make everything just the way you wish. If you want the ship to stop (in any coordinate system of your choice), it will stop. If you want the science officer of the ship to have pointy ears and no sense of humor, you can make him a Vulcan. $\endgroup$ – CuriousOne Aug 20 '14 at 3:55
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    $\begingroup$ Realize that you are asking for details regarding a physically impossible device. If you allow for the existence of a warp bubble, you may as well import anything else you desire from science fiction to help alter its properties. $\endgroup$ – user10851 Aug 20 '14 at 3:58
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    $\begingroup$ @CuriousOne By this argumentation you would disqualify e.g. the Kerr metric from any kind of discussion because with it's CTCs it is "physically impossible" or "a physical fantasy". We dearly discuss vast speculations such as spin foams and 26 dimensions, but every time a different sign of mass is mentioned, we denounce it as science fiction? To avoid an argument about physicality, you can consider this a mathematical play on Einstein equations. The constraints are Einstein equations and say an arbitrary manipulation with the sources including "exotic matter". $\endgroup$ – Void Aug 20 '14 at 9:31
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    $\begingroup$ @Void: The GR field equation isn't a constraint; you can plug any spacetime geometry into it and get a stress-energy tensor out. That's what Alcubierre did. The result doesn't obey any laws of physics. The exotic matter doesn't come from anywhere, it just appears spontaneously from the vacuum, goes where it needs to go with nothing directing it there, then vanishes. See also this answer. $\endgroup$ – benrg Aug 20 '14 at 9:43
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    $\begingroup$ @benrg That is a valid point, the constraints still leave too much freedom. I guess the answer then would be that we can only posit some "plausible" scenario (or find out there is no such thing). But I do not agree with just laughing away this question without properly explaining these considerations. $\endgroup$ – Void Aug 20 '14 at 10:14
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All the treatments of the Alcubierre drive I've seen have not dealt with the acceleration and deceleration. The nearest I've seen is the paper The Alcubierre Warp Drive: On the Matter of Matter, but this is mainly interested in the interactions of matter with the drive and it doesn't deal with the mechanism of acceleration.

You'd have to specify how the acceleration was achieved. For example it might be achieved by gradually bringing the exotic matter from infinity, or if you were using some sort of field generator as proposed by Harold White by ramping up the field. In either case there's probably no analytic solution to the equation of motion so you'd have to do it numerically.

There is probably a way to ramp up the drive that produces no inertial forces on the occupants. They would feel no force as the ship accelerates then decelerates, and with the drive off their original velocity would be unchanged. However I must emphasise that in the absence of any proper treatment of the problem no definitive statement can be made.

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  • $\begingroup$ Looking around the web I couldn't find anything dealing with stopping and starting such a thing. You have confirmed that no such material exists discussing the matter. Seems if you're going to come up with some theoretical way of going really fast there should be some discussion of what happens when you try and stop. $\endgroup$ – Michael Gantz Aug 20 '14 at 10:45
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    $\begingroup$ @MichaelGantz: I suspect that the reason no-one has put in the effort to publish such an analysis is because no-one takes the Alcubierre drive seriously enough to make it worth the (considerable) effort involved. This sort of physics is good fun, but there is little chance it corresponds to anything in the real universe. $\endgroup$ – John Rennie Aug 20 '14 at 10:47
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Because of the way that an Alcubierre drive alters space to get a ship to exceed $c$, unwarping that space (in order to stop/travel at sublight speeds) would undo the fancy compression/expansion of space that allows the ship to travel above $c$. In short, the act of destroying the "warp bubble" would bring the ship's velocity down below $c$. The ship would then travel at some high fraction of $c$ until it stopped, jumped back to warp, etc.

As to how long/hard it would take to stop, the quickest and easiest way would probably be to reverse the direction of the warp bubble. This would stop it rather quickly (no numbers, as I doubt anyone has ever calculated anything exact), probably within a few "bubble-lengths". The rapid "deceleration" would likely wreak havoc on the occupants of the craft though.

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