Sunday, July 27, 2008

“I have realized that the past and future are real illusions, that they exist in the present, which is what there is and all there is.” - Alan Watts

Clearly, the present never is changed by mischievous time-travellers: people don't suddenly fade into the ether because a rerun of events has prevented their births - that much is obvious.

So either time travel is not possible, or something is actually acting to prevent any backward movement from changing the present.

For most of us, the former option might seem most likely, but Einstein's general theory of relativity leads some physicists to suspect the latter.

According to Einstein, space-time can curve back on itself, theoretically allowing travellers to double back and meet younger versions of themselves.

And now a team of physicists from the US and Austria says this situation can only be the case if there are physical constraints acting to protect the present from changes in the past.

Quantum behaviour is governed by probabilities. Before something has actually been observed, there are a number of possibilities regarding its state. But once its state has been measured those possibilities shrink to one - uncertainty is eliminated.

So, if you know the present, you cannot change it. If, for example, you know your father is alive today, the laws of the quantum universe state that there is no possibility of him being killed in the past.[...]

"You wouldn't be able to kill him because the very fact that he is alive today is going to conspire against you so that you'll never end up taking that path leads you to killing him."

image: xkcd

3 comments:

pual said...

great post, definitely a good read, haha and i love the image, thats why i think math is so appealing; cuz it is so pure

Jay said...

Look I'm no physicist but this theory seems incredibly tenuous.

"people don't suddenly fade into the ether because a rerun of events has prevented their births - that much is obvious."

That's like the Back to the Future school of thought on time travel; of course that wouldn't happen, but isn't it conceivable that if past events were altered, we would just cease to be, as though dying instantaneously, while a new reality took our place? I couldn't of course watch somebody "fade away," because if they never existed in the first place, I wouldn't be hanging out with them. I'd be elsewhere, or would never have been born either.

Or, if you really could get away with neatly removing a single person from the universe, without affecting anything else, I would just be sitting on the bus, and the person across from me would stop being there, and I wouldn't have a memory of him having been there at all.

I thought quantum physicists had already solved this problem with the multiverse theory? And hasn't it also been addressed in a Simpsons Halloween Special?

katie t. said...

Yeah, it seems like we wouldn't be able to tell if the past was changed, the present could be the way it is because it HAS been changed--there's no way to know! And if you went back in time and changed something, it wouldn't change the present (like poof and someone disappears), it would change from that point in the past onwards. This article was kind of weird