GUT stands for Grand Unification Theory. GUT drives have had many different incarnations and names, including vacuum energy engines, casimir drives, zero-point propulsion, and more. GUT drives of one form or another have appeared in a variety of science fiction sources, such as the novel The Songs of Distant Earth by Arthur C. Clarke, many "Xeelee" stories by Stephen Baxter, many "Known Space" stories by Larry Niven, and in driving the ships of the ancient, alien Vorlon and Shadow races in the Babylon 5 TV series.
The search for a Grand Unification Theory has been the holy grail of physics for nearly a century now, a single, eloquent series of equations that would tie together quantum physics and the theories of relativity. It would explain once and for all the origin and behavior of the four fundamental forces of nature (gravity, electrmagnetism, the strong nuclear force, and the weak nuclear force) as well as a number of loose quantum phenomena, most significantly virtual particles and zero-point energy. GUT is also assumed to be a precursor for some other speculative propulsion technologies, such as gravitic propulsion schemes and FTL drives, but those will be discussed in their own sections.
The real life physics that form the basis for the speculation about these propulsion schemes is very involved and not for the uninitiated. The summaries below are very simplified versions. See the "Related Information" section below for references that can much more fully explain the quantum physics involved.
GUT drives rest on the startling fact that a vacuum is not empty--it is actually seething with virtual particles and quantum fluctuations. The particles "borrow" energy from the vacuum via Heisenberg’s Uncertainty Principle and pop into existence in particle/antiparticle pairs. They survive for a few brief microseconds or less, and then annihilate each other again, returning the energy they "borrowed" to the fabric of spacetime. Because the energy is always returned, the net energy of a vacuum is zero, and thus to us appears empty.
The existence of this virtual particle soup and zero-point energy has been confirmed by experimental evidence, as the amount of attraction registered on two closely-suspended electrically charged metal plates, when all other factors were neutralized or accounted for. This force is called the Casimir Effect.
ZERO POINT ROCKETS
Tech Level: 21
GUT drives assume that a way can be found to take advantage of the virtual particle effect for propulsion. As the zero-point vacuum fluctuations are happening in every square centimeter of the universe, a ship that can tap into it would have an essentially endless supply of energy it can use for thrust. It is theorized that black holes can strip away one half of the particle/antiparticle pair before they annihilate and return to the vacuum, so it may be possible to use very powerful artificial gravity fields, or even a captured signularity, to do the same in a GUT drive. Another proposal was to use a supply of neutronium on board a ship to supply the gravitic fields necessary for zero-point energy acquisition.
The energy harnessed from the vacuum can be used in one of several ways. The charged vacuum-derived particles can be accelerated and expelled out a nozzle directly for thrust, very similar to a Beam-Core AntiMatter Rocket. Or, more simply, they can be used to superheat a reactive fluid such as hydrogen, which is in turn expelled for thrust. The particles, if antimatter, can also be used to catalyze fusion reactions.
As the zero-point rocket has an essentially endless supply of energy, it can theoretically accelerate to near lightspeed. How fast it can do so and how much thrust would be available to it would depend on how much energy the drive can liberate from the vacuum at any one time.
Tech Level: 23
Inertia drives are often referred to as reactionless thrusters. They’ve been seen in Larry Niven’s "Known Space" stories, and a reactionless engine was seen driving the Rama craft in the novel Rendezvous with Rama by Arthur C. Clarke.
Inertial drives reduce or eliminate inertia altogether on some or part of the spacecraft. The idea has been around for a number of decades now, but only with the discovery of quantum fluctuations in vacuum that they have come to be considered more than pure fantasy.
The quantum fluctuations are thought to cause minute planck-scale "ripples" in the fabric of space/time. It has been theorized that the cumulative effect of these ripples all over the volume of an object is what causes inertia, the resistance material objects exert to changes in their state of motion. Inertial drives neutralize or lessen these ripples over some or all of the craft.
If inertia is eliminated or reduced over the entire ship, the craft is accelerated by more mundane means. However, with no or little inertia, it takes far less fuel and engine power to move the vessel at a certain rate of acceleration than it would otherwise.
Inertia can also be eliminated over every part of the ship but the aft, whereupon the ship can use the quantum ripples to propel the ship forward. By shifting the inertial field over the ship’s mass, the vessel can maneuver. Exactly how fast a ship can move by using this method is a matter of some debate. One would think that the thrust provided would be very small, but with nearly all inertia eliminated over the rest of the ship it may be substantially more. Also, if a means exists to eliminate the quantum ripples over an area of space, a means to enhance that effect may also be developed, providing more potential thrusting power.
There’s also the question to what happens inside a ship when all the inertia is reduced or eliminated. Much of our mechanical technology depends certain values of inertia; changing inertia may have to necessitate a serious re-engineering of many systems to keep the ship viable and running. Reduction of inertia would also have disastrous effects on living organisms (what happens, for example, to your blood pumped by your heart if it suddenly loses its inertia and rips through your arteries at hundreds of miles an hour or more?) and unknown effect on electronics as we currently design them. Whether these effects could be mitigated by an inertia drive is unknown. It may be possible to reduce the quantum ripples affecting just the outer hull of the ship, but the ripples would still be affecting the interior volume of the ship, so the effectiveness of a such a technique would seem to be limited at best.
In Search Of Schroedinger’s Cat and Schroedinger’s Kittens by John Gribbin
On The Web:
Quantum Physics in General:
One fictional GUT drive explained in detail:http://www.orionsarm.com/ships/GUT_drive.html
Technical possibilities for a GUT drive:http://www.mancer.com/forums/viewthread.php?tid=8 http://www.geocities.com/qraal/exosolar03.html http://www.grc.nasa.gov/WWW/PAO/html/warp/ipspaper.htm
Links page to many scientific papers on zero point physics:http://home.earthlink.net/~projectspark/documents.html
More on Zero Point physics:http://www.intalek.com/Index/News/WarpDrive.htm http://www.guardian.co.uk/spacedocumentary/story/0,2763,418977,00.html
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