God Awful Things

I’m just about sure everyone have seen this classified ad before, but if not.. here it is in all its glory.

I could link to some really interesting time travelers famous on the internet but I haven’t the time before leaving work, but if you’ve never read up on time travelers on the internet, it is highly entertaining.

Instead, I link you to Discover Magazine: Rules for Time Travelers

It is, of course, a interesting read.. and here are my personal favorites.

Traveling to the future?

1. Traveling into the future is easy.

We travel into the future all the time, at a fixed rate: one second per second. Stick around, you’ll be in the future soon enough. You can even get there faster than usual, by decreasing the amount of time you experience elapsing with respect to the rest of the world — either by low-tech ways like freezing yourself, or by taking advantage of the laws of special relativity and zipping around near the speed of light. (Remember we’re talking about what is possible according to the laws of physics here, not what is plausible or technologically feasible.) It’s coming back that’s hard.

This is in regards to the difficulty of traveling back in time.

From your own personal, subjective point of view, you always more forward in time — more technically, you move on a timelike curvethrough spacetime. But the large-scale curvature of spacetime caused by gravity could, conceivably, cause timelike curves to loop back on themselves — that is to say, become closed timelike curves — such that anyone traveling on such a path would meet themselves in the past.

Oh this is good..

What people want to do with time machines is to go into the past and change it. You can’t. The past already happened, and it can’t un-happen.

Of course, my whole arguments with Spolans is what if it can un-happen.. blow your mind much?

But thankfully, wrapped up in a way this stuff can happen..

9. Unless you go to a parallel universe.

Parallel universes — the kind we contemplate in the many-worlds interpretation of quantum mechanics (MWI) — provide potential loopholes for some of the above rules. According to the MWI, there exist different “branches” of the wave function of the universe, distinguished by different observed outcomes for the measurement of quantum events. In the celebrated Schrödinger’s catthought experiment, there is a “universe” where the cat is alive, and one where it is dead. Some imaginative (but respectable) physicists, especially David Deutsch, have speculated that we could combine this idea with the possibility of closed timelike curves to contemplate travel into the past of a different universe. If time travel is unlikely, this idea is (unlikely)², but it’s not inherently paradoxical.

If you could travel to the past in a different branch of the wave function, then we are allowed to contemplate changing that past in a self-consistent way, because it’s no longer really “your” past. So almost all cinematic invocations of time travel — where they are constantly mucking about, changing the past in crucial ways — would have to appeal to something along these lines to make any sense. But even if you can change what you thought was the past, all of the rules of continuity and sensibility still apply — no flashing lights, no disappearing, no sudden changes in the future, no re-writing of your memories, etc.