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Comment by maxerickson | Hacker News Reader

Time travel is entirely outside of our theory of physics.

If you want to insist on rules, you have to say that we can't do it, not argue about how it would work.

(I mean, it is entirely possible that the universe is a-causal in the presence of certain types of events that we do not yet understand)

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sorry to contradict you, but all the laws of physics are totally reversible, so in theory you could turn back physical time. The problem is that you need to do that for each atom, molecule from your body in order to reverse all the interactions. However it won't be time travel proper, except for the atoms/molecules in question.

So if I had specifically said 'the popular notion of time travel', would that have avoided this digression?

Because to me it looks like you were itching to contradict me.

(I'll totally own the fact that I might have made an imprecise overstatement or whatever, I'm lazy and this is just a message board, the context is clearly enough popping in and out of time, not magic level reversibility)

Well, point taken, indeed the popular notion of time travel is quite far fetched. However, at a basic level it is not outside the current scientific consensus. But things can change, we don't know a lot of what can, or can not be possible. And yes, this is a message board, we're here to contradict each other :))

I think it is lots of fun to pick at things, but I think it is more fun to pick at what someone is trying to say, rather than picking at how it was said.

(I'm being cranky here, I didn't get worked up over any of this or anything)

Physics is reversible only at microscopic level. The arrow of time is defined by statistical mechanics, and second law pretty much means that processes tend to go only in one direction.

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