Alcubierre Drive Direction: How Does Craft Move?

[Davephaelon]

I was watching an excellent presentation of the theory of the Alcubierre warp given by Miguel Alcubierre himself at the 2017 Starship Congress (link below). At the 43:55 mark Alcubierre explains that the negative energy is located around the circumference of the craft in a toroid. I always thought that it was located at the rear of the craft where spacetime is expanded, so this was a surprise. But that made me wonder how does the craft decide which way to move, since at first glance the configuration seemed to be perfectly symmetrical forward and back. I did, however, notice that in the diagram on the screen, (at 43:55), the side profile view of the negative energy region looks to be slightly forward of center, as defined by the x-y coordinate grid. So maybe that's the answer.

 

[jerromyjon]

At 47:45, he goes into the "horizon" problem, saying you can't put the negative energy in front of the ship from inside the ship. The diagram shows the negative energy expanding spacetime in the front and the spacetime contracting behind the ship, from undisclosed reasoning. How that configuration arises, after like you said he states the negative energy is needed symmetrically around the ships sides, is beyond me. My laymen's two cents seems to think the actual motion of the ship through space is amplified by the warp bubble, and again the unsolved horizon problem means you'd have to have an exterior preexisting warp field to travel through since there is no known way to project that warp field from the ship utilizing it.

 

[Davephaelon]

jerromyjon, Thanks for the response. I'm pretty sure the horizon problem only occurs if the ship is superluminal, but will have to check up on that. I'm tempted to write to Harold "Sonny" White about this issue of the spacetime expanding behind the ship, even though the negative energy material is located around the circumference of the ship. I'm also wondering if this single toroidal region of negative material is also responsible for the contraction of space forward of the ship, which admittedly doesn't make sense to me as a layperson, as such material is only supposed to expand spacetime. I suspect I need to really knuckle down and understand the metric equations for this warp system before I can appreciate how it actually works.

 

[Davephaelon]

Some time ago, probably several years, I had printed out Dr. Harold White's "Warp Field Mechanics 101" paper. I finally found it, and to my delight he addresses exactly the problem of which direction the craft starts to move in from a stationary start. The argument in the paper is somewhat technical, but the gist of it is if the craft already has a direction of motion from a conventional rocket engine, then it will select that direction when the warp field is turned on.

 

[DrStupid]

The argument in the paper is somewhat technical, but the gist of it is if the craft already has a direction of motion from a conventional rocket engine, then it will select that direction when the warp field is turned on.

But the initial motion is frame-dependent and in the rest frame of the ship there is no motion at all.