All The Myriad Ways

You merely get a new future.

True, the next version of you will not make the trip. You've eliminated his motive. Thus on the next cycle the damyankees will win the Civil War, Hitler will lead Germany into WWII, and so forth. But you've merely introduced a double cycle. There is no paradox.

Further, your time machine need be nothing more than an EXTREMELY durable time capsule.

OBJECTIONS: Three. First, some people don't believe in cyclic time. (I don't.) Second, locating the proper era is a nontrivial problem when you've got the whole lifetime of the universe to search in. You'd be lucky to find any section of human history. Third, removing your time capsule from the reaction of the Big Bang could change the final configuration of matter, giving an entirely different history.

DEFENSE OF TIME TRAVEL #II: Known as the theory of multiple time tracks.

Let there be a myriad of realities, of universes. For every decision made by any form of life, let it be made both ways; or in all possible wars if there are more then two choices. Let universes be created with every choice.

Then conservation of matter and energy holds only for the universe of universes. One can move time machines from one universe to another.

You've got to admit it's flamboyant!

You still can't visit the past. But you can find a universe where things happened more slowly; where Napoleon is about to fight Waterloo, or Nero is about to ascend the throne. Or, instead of changing the past, you need only seek out the universe where the past you want is the one that happened. The universe you want unquestionably exists. (Though you may search a long, weary time before you find it.)

Ersatz time travel becomes a special case of sidewise-in-time travel, travel between multiple time tracks.

The what-if story has fascinated many writers. Even 0. Henry wrote at least one. From our viewpoint, sidewise-in-time travel solves conservation laws, Grandfather Paradox, everything.

I hate sidewise-in-time travel stories.

Let me show you why.

First, they're too easy to write. You don't need a brain to write alternate-world stories. You need a good history text.

In the second place…did you ever sweat over a decision? Think about one that really gave you trouble, because you knew that what you did would affect you for the rest of your life. Now imagine that for every way you could have jumped, one of you in one universe did jump that way.

Now don't you feel silly? Sweating over something so trivial, when you were going to take all the choices anyway. And if you think that's silly, consider that one of you still can't decide...

In the third place, probability doesn't support the theory of alternate time tracks.

There are six ways a die can fall, right? Which makes thirty-six ways that two dice can fall, including six ways to get a seven. Each way the dice can fall determines one universe. Then the chance of your ending in each of the thirty-six universes is one in thirty-six, right?

Then it doesn't matter if the dice are loaded. One chance in thirty-six, exactly, is the odds for each way the dice can fall. One chance in six, exactly, of getting a seven.

Experience, however, shows that it does matter if the dice are loaded.

DEFENSE OF TIME TRAVEL #III: The idea of reversing the flow of time isn't nearly as silly as it sounds. I quote from an article in the October 1969 issue of Scientific American, "EXPERIMENTS IN TIME REVERSAL," by Oliver E. Overseth.

"All of us vividly recognise the way time flows; we take considerable comfort, for example, in our confidence that the carefully arranged marriage of gin and vermouth is not going to be suddenly annulled in our glass, leaving us with two layers of warm liquid and a lump of ice. It is a curious fact, however, that the laws that provide the basis for our understanding of fundamental physical processes (and presumably biological processes as well) do not favor one direction of time's arrow over another. They would represent the world just as well if time were flowing backward instead of forward and martinis were coming apart rather than being created."

Is the universe really invarient under time reversal? Many physicists think not. Overseth and his partner Roth spent almost two years looking for a case in subatomic physics in which invarience under time reversal is not preserved.

They knew exactly what they were looking for. They were watching (via some very indirect instruments) the decay of a lambda particle into a proton plus a pi meson. The anomaly would have been a nonzero value for the beta component of the spin of the proton.

The point is that they failed to find what they were looking for. There have been many such experiments in recent years, and none have been successful. At the subatomic level, one cannot tell whether time is running backward or forward.

Could a determined man reach the past by reversing himself in time and waiting for last year to happen again?

Present theory says that he would reverse both the spin and the charge of every subatomic particle in his body. The charge reversal converts the whole mass to antimatter. BOOM!

Less dramatically, there is conservation of mass/energy. Reverse the direction of travel in time of a human body, and to any physicist it would look like two people have vanished.

Clearly this is illegal. We can't do it that way.

We might more successfully reverse a man's viewpoint: send his mind backward in time. If there is really no difference between past and future, except in attitude, then it should be possible.

But the traveler risks his memory healing to a tabula rasa, a blank slate. When he reaches his target date he might not remember what to do about it.

For there is still entropy: the tendency to disorder in the universe, and the most obvious effect of moving "forward" in time. Entropy is not obvious where few reactions are involved, as in the motion of the planets, or as when a lambda parlicle breaks down. But the mushroom cloud left by a hydrogen bomb is difficult to return to its metal case. That's entropy.

Any specialist in geriatric medicine knows about entropy.

Let's try something less ambitious.

Suppose we found a clump of particles already moving backward in time. (Exactly what Roth and Overseth and their brethren might find in their experiments, if time-reversal turns out to be valid. Though most expect to find just the opposite.) Now we write messages on that clump. Simple messages. "Blue Ben in the sixth, 4/4/72."

But from our viewpoint, we start by finding a message and end by erasing it! And if it went wrong…We find a message: "Blue Ben in the sixth, 4/4/72." We bet on him, and he loses. Now what? Can we unwrite a different message? Or just refuse to erase it at all?

But if it did work, we could make a fortune. And it violates no known physical laws! Practically.

Meanwhile, Roth and Overseth and a number of others are all convinced that there must be exceptions to the symmetry of time. If they find just one, it's all over.

DEFENSE OF TIME TRAVEL #IV: The oldest of all, going back to Greek times. Philosophers call it fatalism or determinism. A fatalist believes that everything that happens is predetermined to the end of time; that any attempt to change the predetermined future is fated, is a part of the predetermined future itself.