# Alcubierre drive and inertia.

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?

• 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. – CuriousOne Aug 20 '14 at 3:55
• 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. – user10851 Aug 20 '14 at 3:58
• @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". – Void Aug 20 '14 at 9:31
• @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. – benrg Aug 20 '14 at 9:43
• @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. – Void Aug 20 '14 at 10:14

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.