Krauss - The physics of Star Trek

The Physics of Star Trek

The Most Bang for Your Buck

Nothing Unreal Exists. Kir-kin-tha's First Law of Metaphysics (Star Trek IV: The Voyage Home,)

If you are driving west on Interstate 88 out of Chicago, by the time you are 30 miles out of town, near Aurora, the hectic urban sprawl gives way to the gentle Midwestern prairie, which stretches forward and flat as far as you can see. Located slightly north of the interstate at this point is a ring of land marked by what looks like a circular moat. Inside the property, you may see buffalo grazing and many species of ducks and geese in a series of ponds.

Twenty feet below the surface, it is a far cry from the calm pastoral atmosphere above ground. Four hundred thousand times a second, an intense beam of antiprotons strikes a beam of protons head on, producing a shower of hundreds or thousands of secondary particles: electrons, positrons, pions, and more.

This is the Fermi National Accelerator Laboratory, or Fermilab for short. It contains the world's highest-energy particle accelerator. But more germane for our purposes is the fact that it is also the world's largest repository of antiprotons. Here, antimatter is not the stuff of science fiction. It is the bread and butter of the thousands of research scientists who use the Fermilab facilities.

It is in this sense that Fermilab and the U.S.S. Enterprise bear a certain kinship. Antimatter is crucial to the functioning of a starship: it powers the warp drive. As I mentioned earlier, there is no more efficient way to power a propulsion system (though the warp drive is not, in fact, based on rocket propulsion). Antimatter and matter, when they come into contact, can completely annihilate and produce pure radiation, which travels out at the speed of light.

Obviously, great pains must be taken to make sure that antimatter is contained whenever it is stored in bulk. When antimatter containment systems fail aboard starships, as when the Enterprise's system failed after its collision with the Bozeman, or when the containment system aboard the Yamato failed due to the Iconian computer weapon, total destruction inevitably follows soon afterward. In fact, antimatter containment would be so fundamental to starship operation that it is hard to understand why Federation Lieutenant Commander Deanna Troi was ignorant of the implications of containment loss when she temporarily took over command of the Enterprise in the Next Generation episode Disaster, after the ship collided with two quantum filaments. The fact that she was formally trained only as a psychologist should have been no excuse!

The antimatter containment system aboard starships is plausible, and in fact uses the same principle that allows Fermilab to store antiprotons for long periods. Antiprotons and antielectrons (called positrons) are electrically charged particles. In the presence of a magnetic field, charged particles will move in circular orbits. Thus, if the particles are accelerated in electric fields, and then a magnetic field of appropriate strength is applied, the antiparticles will travel in circles of prescribed sizes. In this way, for example, they can travel around inside a doughnut-shaped container without ever touching the walls. This principle is also used in so-called Tokomak devices to contain the high-temperature plasmas in studies of controlled nuclear fusion.

The Antiproton Source for the Fermilab collider contains a large ring of magnets. Once antiprotons are produced, in medium-energy collisions, they are steered into this ring, where they can be stored until they are needed for the highest-energy collisions, which take place in the Tevatronthe Fermilab high-energy collider. The Teva-tron is a much larger ring, about four miles in circumference. Protons are injected into the ring and accelerated in one direction, and antiprotons are accelerated in the other. If the magnetic field is carefully adjusted, these two beams of particles can be kept apart throughout most of the tunnel. At specified points, however, the two beams converge and the collisions are studied.

Besides containment, another problem faces us immediately if we want to use a matter-antimatter drive: where to get the antimatter. As far as we can tell, the universe is made mostly of matter, not antimatter. We can confirm that this is the case by examining the content of high-energy cosmic rays, many of which originate well outside our own galaxy. Some antiparticles should be created during the collisions of high-energy cosmic rays with matter, and if one explores the cosmic-ray signatures over wide energy ranges, the antimatter signal is completely consistent with this phenomenon alone; there is no evidence of a primordial antimatter component.

Another possible sign of antimatter in the universe would be the annihilation signature of antiparticle-particle collisions. Wherever the two coexist, one would expect to see the characteristic radiation emitted during the annihilation process. Indeed, this is exactly how the Enterprise searched for the Crystalline Entity after it had destroyed a new Federation outpost. Apparently the Entity left behind a trace antiproton trail. By looking for the annihilation radiation, the Enterprise trailed the Entity and overtook it before it could attack another planet.

While the Star Trek writers got this idea right, they got the details wrong. Dr. Marr and Data search for a sharp gamma radiation spike at 10 keVa reference to 10 kilo-electron volts, which is a unit of energy of radiation. Unfortunately, this is the wrong scale of energy for the annihilation of protons and antiprotons, and in fact corresponds to no known annihilation signal. The lightest known particle with mass is the electron. If electrons and positrons annihilate, they produce a sharp spike of gamma radiation at 511 keV, corresponding to the mass of the electron. Protons and antiprotons would produce a sharp spike at an energy corresponding to the rest energy of the proton, or about 1 GeV (Giga-electron volt)roughly a hundred thousand times the energy searched for by Marr and Data. (Incidentally, 10 keV is in the X-ray band of radiation, not the gamma-ray band, which generally corresponds to radiation in excess of about 100 keV, but this is perhaps too fine a detail to complain about.)

In any case, astronomers and physicists have looked for diffuse background signals near 511 keV and in the GeV range as signals of substantial matter-antimatter conflagrations but have not found such signals. This and the cosmic-ray investigations indicate that even if substantial distributions of antimatter were to exist in the universe, they would not be interspersed with ordinary matter.

As most of us are far more comfortable with matter than antimatter, it may seem quite natural that the universe should be made of the former and not the latter. However, there is nothing natural at all about this. In fact, the origin of the excess of matter over antimatter is one of the most interesting unsolved problems in physics today, and is a subject of intense research at the present time. This excess is very relevant to our existence, and thus to Star Trek's, so it seems appropriate to pause to review the problem here.

When quantum mechanics was first developed, it was applied successfully to atomic physics phenomena; in particular, the behavior of electrons in atoms was wonderfully accounted for. However, it was clear that one of the limitations of this testing ground was that such electrons have velocities that are generally much smaller than the speed of light. How to accommodate the effects of special relativity with quantum mechanics remained an unsolved problem for almost two decades. Part of the reason for the delay was that unlike special relativity, which is quite straightforward in application, quantum mechanics required not just a whole new world view but a vast array of new mathematical techniques. The best young minds in physics were fully occupied in the first three decades of this century with exploring this remarkable new picture of the universe.