The Infinite Improbability Drive is a fictional faster-than-light drive in Douglas Adams' The Hitchhiker's Guide to the Galaxy series of books. The most prominent usage of the drive is in the starship Heart of Gold. It is based on a particular perception of quantum theory: a subatomic particle is most likely to be in a particular place, such as near the nucleus of an atom, but there is a fantastically small probability of it being found a long way away, for example close to a distant star. Thus, a body could travel from place to place without passing through the intervening space (or hyperspace, for that matter), if you had sufficient control of probability. In the movie, it is described like this:
:The Infinite Improbability Drive is a wonderful new method of crossing interstellar distances in a few seconds; without all that tedious mucking about in hyperspace. As the Improbability Drive reaches infinite improbability, it passes through every conceivable point in every conceivable universe almost simultaneously. In other words, you're never sure where you'll end up or even what species you'll be when you get there. It's therefore important to dress accordingly. The Infinite Improbability Drive was invented following research into finite improbability which was often used to break the ice at parties by making all the molecules in the hostess' undergarments leap one foot simultaneously to the left in accordance with the theory of indeterminacy. Many respectful physicists said they wouldn't go to stand for that sort of thing, partly because it was a debasement of science, but mostly because they didn't get invited to those sort of parties.

History

The Guide itself explains that generating finite levels of improbability using an electronic brain and a strong Brownian motion producer (say, a cup of hot tea) was very well understood, but that scientists lacked the means to create a drive that could produce the infinite improbability field required to allow a ship to travel anywhere instantaneously. It was generally concluded that such a drive was virtually impossible; the only use of improbability drives at the time was to break the ice at parties by making all the molecules in the hostess's undergarments leap one foot to the left simultaneously, in accordance with the theory of indeterminacy. Many other scientists decided that they wouldn't stand such a thing, partly because it was a debasement of science, but mostly because they didn't get invited to those sorts of parties.

Eventually, a student reasoned that the infinite improbability drive had to be a finite improbability to be a virtual impossibility. After working out exactly how improbable, he fed that value into the finite improbability generator, gave it a really hot cup of tea, and managed to generate the infinite improbability generator out of thin air. After winning the Galactic Institute's prize for extreme cleverness, he was later lynched by other scientists who had been trying to make the generator for years, who finally worked out that what they really couldn't stand was a smart-ass. In describing the invention of the drive, Douglas Adams exemplifies the principle of bootstrapping.


The Heart of Gold was the prototype ship for infinitely improbable travel. The principle is that as its drive reaches infinite improbability, the ship passes simultaneously through every point in the universe. It is then possible to decide at which point you actually want to be when improbability levels decrease.

It is the infinite improbability drive in The Hitchhiker's Guide to the Galaxy that saves Arthur Dent and Ford Prefect from certain death by asphyxiation in deep space after being thrown out of the Vogon ship.

An earlier attempt at using the improbability drive, Starship Titanic, was also mentioned. In theory, the infinite improbability drive would make it infinitely improbable that anything would go wrong. It was not successful, however, ending in Spontaneous Massive Existence Failure. This was due to the fact that, in these earlier times when the nature of improbability was less well understood, it wasn't appreciated that any event that is infinitely improbable will, by definition, occur almost immediately.

The infinite improbability drive has been superseded by the Bistromathic drive, based on the alternate math used by waiters in restaurants, which has the advantage of not having improbable side effects or improbable things going wrong. The Starship Bistromath is more maneuverable than the Heart of Gold, but it seems that the Heart of Gold is still the faster of the two.

Effects

Unfortunately, human beings are accustomed to travelling at normality (probability 1:1), and can be fairly distressed by events around them whilst the improbability drive is working: losing limbs, turning into sofas (in the movie), planets spontaneously becoming fruitcakes, nuclear missiles metamorphosing into sperm whales and bowls of petunias, and so forth. The starship Heart of Gold was somewhat insulated against this by having an improbability-proof drive room, allowing the pilots to remain more or less normal during the flight.

The most important side effects of infinite improbability travel were that hyperspace express routes became largely obsolete, and that the History department of the university of Maximegalon finally gave up trying to figure out the universe, as completely impossible things were increasingly commonplace.

Adams developed the notion of the improbability drive having greater causal (and narrative) effects in later books. For example: when Zaphod's grandfather discusses his great-great-great-great grandson's career-to-date he explains that he (Zaphod) cannot escape his destiny now the improbability field "controls you". This could be an early nod to the reverse-temporal abilities of the guide in the last book - although this may be good luck on DNA's part.

Improbability physics in other literature

The Infinite Improbability Drive is sometimes compared with a similar concept in the fiction of Stanisław Lem; specifically, the "improbability automatic" from Lem's story, "The Third Sally, or The Dragons of Probability". http://world.std.com/~mmcirvin/cyberiad.html

Improbability physics in the real world

Most scientists consider improbability physics to be completely ridiculous. However, a minority of scientists have pointed out that improbability physics is by its very definition, improbable, which implies that it is possible.

Trivia

In Star Trek: The Next Generation, there is a button marked "Infinite Improbability Drive" on the engineering console of the USS Enterprise-D bridge.

Category:Hitchhiker's Guide to the Galaxy
Category:Hitchhiker's Guide to the Galaxy technology
Category:Faster-than-light travel