How to Build a Time Machine

frank249 writes "The September issue of Scientific American has an article discussing the possibility of time travel. They say that it wouldn't be easy, but it might be possible. It could be a while until we can expand worm holes and tow them to a neutron star but didn't someone say that if it is possible it will happen. If it is impossible it will just take a little longer."

Comments

It's simple, really.

[TrumpetPower!]

Time travel isn't possible, except for the everyday kind that your wristwatch measures.

If time travel were possible, somebody (human, alien, whatever) from the future (perhaps billions of years into the future, or maybe just next week) would have traveled into the past already.

So, let's consider what can happen. Somebody will travel back in time to before the initial discovery in order to beat the ``original'' researcher to the punch. Now, we've got a cascade of ``inventions'' of the time machine racing backwards through time. Life and time-travel technology reach the earliest time after the Big Bang that the two are sustainable and both are prolifically spread throughout the infant universe. Clearly, that hasn't happened.

Don't think that some sort of morality would prevent this from happening, either. Time travel is an incredibly powerful weapon; consider what a knife to the throat of the infant Hitler would have done to history, and how many people would leap at the chance, consequences be damned. All it would take is one person to do so...at any time in the next many billion years.

The instant time travel becomes possible, the only possible method for self-preservation is to race to the beginning. After all, how do you know that some far-distant alien race with souls of pure evil won't do the same just out of spite?

There's a wonderful quote, and I wish I could remember who said it. ``Time is Nature's way of keeping everything from happening all at once.'' The obvious corollary is that, if you can break time, then everything will happen all at once.

Some people try to get around this in a few different ways. For one, there's the many-universes ilk: each act of time travel creates a whole new universe. In such a case, all of those universes would be on the same headlong rush to take time travel as early as possible. Besides, think of the incredible amount of energy and information needed to duplicate the universe--but I digress.

Others try to justify it by saying that it requires huge energy sources or otherwise make it hard. To this I say, ``so''? All you're talking about is a hard engineering project that'll take a lot of time. And--guess what? Even if it takes ten thousand years to build and the energy output of several stars, the payoff is worth it. Again, the alternative is to let somebody else do it...and invite certain disaster.

I take the mere fact that I'm typing this note as all the proof that I need that time travel is pure fantasy.

Cheers,

b&

Re:It's simple, really.

[Dr. Manhattan]

If time travel were possible, somebody... would have traveled into the past already.

As has been noted, GR time machines can't go back any further than when they were assembled. So you can't goi back any further than the first one.

...consider what a knife to the throat of the infant Hitler would have done to history...

It's impossible to know. History is chaotic. Consider a simple thing, like weather. That's chaotic, with a lambda on the order of a few days. You appear, kill baby Hitler, disappear. A few days later, it's raining instead of sunny.

All the weather, subsequently, is different. That affects when people make love; even a small difference in position and timing changes which sperm reaches the egg. The next generation consists of completely different individuals from the one in "our" history. Madonna and Nelson Mandela are never born.

If you can change the past, then you must, and you can't predict how you will change it.

I cover all this and more in my time travel page.