One of the last aspects of "Enterprise," the most recent Star Trek spinoff, to be finalized during its creation was the time period: it was either going to be in the 22nd century or the 28th. As one can learn from episodes of other Star Trek series, these two time periods have vastly different technological capabilities. (They eventually settled on the nearer date, for those who haven't seen it, who are probably the majority--the show has had barely mediocre success thus far.) The 28th century would have been an intriguing choice, because, by Star Trek chronology, time travel is as fully developed then as is space travel in the 24th century. This would have allowed missions to penetrate through time as frequently and nonchalantly as the current shows speed across interstellar distances. Unfortunately, Star Trek has a dismal record keeping its rules of time travel straight, if it ever had any.

But it makes for entertaining speculation. Instead of searching out the fastest possible drives, they would probably instead have the most efficient, most reliable drives possible, because any drive hooked up to a time machine is an infinite-speed drive. As soon as the captain pointed and said, "Engage" melodramatically, the ship would then already be at the destination. Alternatively, if the plan was to rendezvous with an alien ship without timedrive, they could set the time-travel part of the drive in a way that would allow them to arrive at the meeting point at the exact same instant the other ship did, with as much or as little time as they like occurring in between for them. Likewise, computation attached to a time machine would also become infinite-speed, and therefore effectively infinite-capacity as well, although that would not be usable. Food could be grown instantaneously. Weapons could age a person to death just as quickly. Work could take as long as it needs and still be done before deadline.

When time is actually reversed, however, things get trickier. StarFleet Command could send an order instructing the crew to go save the universe from an anomaly in another quadrant, but the crew might instead take a relaxing month-long vacation on Riza, then go save the universe. Any need to hurry, or at least not dawdle, is thrown out the window, and a whole lot of plot vitality with it. For that matter, the admiral back at StarFleet could go home and take a nap, confident that the universe is being saved, before he even bothered to send the order--he can send it later and it will still arrive on time because of those marvelous machines. Talk about the ultimate license for procrastination. Technology would reach its limits extraordinarily quickly, as companies' R&D facilities would send advanced products back in time; but temporal competition would probably be limited to existing companies, because of the Prior Order thing found three paragraphs below. War would become insanely complicated, and almost impossible between two time-traveling societies, once Prior Orders would proliferate--every action taken could be foiled by arriving a little earlier with a bigger gun, and the winner would be whoever declared war first. Maybe we'd finally be free of politician's lies, as we could look ahead and catch the ones who would.

Star Trek, of course, is notorious for fixing the laws of physics to be whatever they need to be for each episode. As a result, the writers conveniently ignore all effects of paradox that should foil them. They've bungled paradox in both directions: characters see the future and then change the actions that led to it, and characters go to the past to change actions. In the first, what was it that viewer actually saw? In the latter, the condition they changed then never existed, meaning there was no reason to change that condition.

A friend and I came up with a set of solutions and rules for time travel possibilities. They make assumptions that cannot be tested, naturally, which opens the doors to disagreements and different ways of looking at the various parts. What ideas have you come up with?

The biggest assumption, made for convenience, is that paradoxes won't be allowed to happen. This leaves room for only two ways of changing the past that we could think of. First, it seems totally legal to change a condition in the past provided that the specific orders for changing that specific event were given *before* the condition is to be changed. To use the traditional kill-Hitler example, Hitler could only be killed *after* the orders were given to kill him. Otherwise, the orders would never have been given. The second manner that seems acceptable is for the past to be unintentionally changed. While any condition one specifically goes back to eliminate will also eliminate the reason for going back, conditions one *did not intend* to change would not violate that logic. So, if you went back in time to assassinate Hitler, but accidentally shot Mussolini instead, that would probably succeed in changing the timeline. Both of these, of course, have the constraint that actions in the past can't stop the time-traveler or time machine from having existed. If Star Trek were held to those rules, any mission to alter the past timeline would be doomed to failure. Merely observing the past would be fine, as would be rescuing lost objects and people such as the Holy Grail and Amelia Earhart.

In the other direction, the future has its own challenges. Observing the future means you can change it, and if you did, the future you observed would not occur, and you couldn't have seen it in the first place. Jumping into the future and not coming back is allowed, no holds barred. Jumping into the future and coming back holds a "maybe," providing your actions between now and then don't nullify what you will have done.

gab"Probably wrong, but still interesting"by