# New Warp Drive Drive Design

Brave New Warp Fields

The Alcubierre geometry has a number of problems associated with it, this impart inspired Broeck to consider a microscopic warp bubble. Recently there have been some proposed modifications to the Alcubierre geometry, among the two discussed is a warp drive with null curvature and one which allows superluminality.

Warp Drive with Zero Expansion

One of the characteristics of a warp drive is the fact that it bends space and time to allow for faster than light travel. However recently a researcher proposed a warp drive, that well doesn’t warp (J. Natario Warp Drive with Zero Expansion Class. [Class. Quant. Grav 19 (2002) ] gr-qc/0110086). Now how can that be you ask? Well I don’t know either if someone figures it out please email me (an accurate model, not something ad hoc), now I can go into further detail in the matter to explain the scientific problems. The general idea which the author neglects to mention to the reader is to have a spaceship catch a warp drive wave.

Much like a sail boat catches the wind, in principle to Moon can be thought as catching the gravitational wind of the earth (for analogy purpose only), but the Moon still has a field which distorts space and time, so even ordinary gravitation has a positive expansion. Thus what the author proposed was a warp drive which was not connected to a spaceship (or flat region of the field), and that’s the problem with the paper. This is because the Natario paper is based on a Newtonian approximation of general relativity (figure A above), where only a cross section of gravitation is approximated. This is find for calculating orbits (such as the “hockey puck” orbiting the sphere in figure A), if there are other gravitational bodies present the x in the middle of the yellow sphere moves outward. Now the problem with this is that gravitational waves (purple region of figure B, this is also the reason for the title “Warp Drive with Zero Expansion”) don’t exist in this picture, and these play a crucial role for warp drives (not considering this means you can only consider the motion of a warp bubble through space and not its internal dynamics [remember its a cross-section]).

Now of course it might be possible to save the idea by extending and electromagnetic field of very high density from the ship to the warped region to act as a go between. The problem the author does not even consider the possibility just the magic carpet ride that an observer would see, if the thing worked.

 One of topics covered in the the Natario work is the so called horizon problem, where a warp drive moving at the speed of light begins to form an impenetrable barrier.  The way the paper is written one would suspect that this is a new affect, that is not the case, in fact Alcubierre was aware of this when he wrote his famous 1994 paper (Class.Quant.Grav. 11 (1994), L73-77).  The horizon forms in a manner similar to a sonic boom (the dark region of the figure to the left), cutting of the superluminal portion of a warp drive from the subluminal part.

Now that most of the work is done in the Newtonian approximation of general relativity, it can be “easily” updated to include more complicated geometries which use general relativity, such as the Alcubierre Warp Drive.  The Natraio work in short shows that the Alcubierre Warp Drive will not work in the Faster Than Light case, however again this was all ready known, the Alcubierre Warp Drive was created to show the premise was valid, it was not an exact solution for FTL traavel.  So really what the Natario paper shows is all ready known problems of the warp drive and describes them technically rather than generally.  However the author has stated that captain Picard [from the Star Trek series] may say something along the lines of  “Make it No,” for warp drives.  However in New Scientist magazine Michael Pffenning stated that the photon behavior Natario may not be very accurate and may be a glitch in the Natario work (“The truth about warp drive.” New Scientist Vol 173 (2002) page 9) involving the horizon issue.

Time Travel

You must be thinking I thought all Warp Drives travel Faster Than Light, well that is not the case!  Warp Drives have the potential to achieve speeds greater than that of light, but it doesn’t mean that this is always the case.  The problem of superluminal (faster than light) warp drives is that they run into the same problem an astronaught would it that person was unlucky enough to fall into a black hole.  There’s a big communication after the astronaught falls into an event horizon Mission Control will never hear the last radio call, “Houston We’ve got a Problem.”  To communicate to the outside world the radio signal must travel at superluminal speeds, the problem with a warp drive is that faster than light speeds don’t occur for the spaceship, but space.

Since part of the warp drive is actually traveling faster than light if you told the warp filed to turn off it would never get the signal, you’re simply trapped in a runaway spaceship.  Now luckily there is away around this that colleagues of mine discovered (F. Loup, et al. A Superluminal Warp Drive spacetime gr-qc/0202021), if you change the path of light by increasing the surface area of space you can change the cut off point of the signal.  Thus by modifying the geometry to a maximum surface area you are capable of traveling at greater speeds with the ability to still turn of your engines.  Now of course this just mathematical trick, just what is needed to cause such a geometry is still an unknown in the equations.