Monday, November 30, 2009

Causal Loop

And now, with no fanfare or reintroduction, The Odds Are One resumes its original charter of blogging about Odds-Are-One-y things. For at least this one post. Maybe.

I read about a thought experiment with pool tables and time travel in an article in Slate a couple of months ago (several other interesting ideas about the current thinking on time travel in there as well--for instance, they've pretty much dismissed the idea of multiple futures branching off which we here at the Odds Are One had figured out years ago, and they seem to think that time travel requires an entry and an exit portal--kind of like a tunnel--such that people from the future can't come back to tell us about the invention of time travel until somebody invents a time machine for them to come back in. So that explains why we don't see those time travelers from the future wandering around. I guess). The idea behind this experiment seems to me to throw a wrench in our thinking about free will, which is always fun to contemplate.

Imagine a pool table with a little time-traveling tunnel on it. You shoot ball into one end of the tunnel, and it goes back in time one second and comes out the other end. So you see your pool ball roll out of the far end of the tunnel a second before you shoot it into the near end (if I had this setup I'd probably sit there for a while trying to fool the tunnel into making the pool ball roll out without actually rolling it in in the first place. That'd be awesome. Except that it wouldn't work, but whatever). Then you'd realize that if you lined up the two ends of the tunnel, you could make your shot interfere with itself: you could make it so that the ball would come out from the future right as your shot was going towards the entrance to the tunnel, knocking it out of the way so that it didn't enter the that it would never have gone back in time in the first place. You'll have created a physical paradox: if the ball goes in the tunnel, it would knock itself out of the way and never go into the tunnel. But if it doesn't go into the tunnel, then it wouldn't be there to knock itself out of the way, so it would roll into the tunnel. And so on.

Some people spent a lot of time thinking about this and figured out that what would happen is that you would always knock your ball askew such that it went into the tunnel at a different angle than you planned, making it come out of the tunnel in the past at a different angle than you planned, making it glance off its future self at a different angle than you planned, etc. etc. They further noted that this is a sort of simplified model of the Going-Back-In-Time-And-Killing-Your-Own-Grandfather paradox: the implication being that no matter how hard you tried to do it, you would fail. You'd go back in time and try and kill your Grandfather and someone would stop you, or it'd turn out your Grandmother had already conceived, or you'd kill somebody you thought was your Grandfather but it turned out there was a family scandal that you'd never heard about and that guy wasn't really your Grandfather. No matter what you did, the fact would remain that you had already been born, and you therefore couldn't prevent yourself from being born.

In this thought experiment there are clear limits on the exercise of your free will. Do what you like, but you will not kill your biological grandfather before your mother or father is conceived because it didn't happen that way. The same is true of the pool-table experiment: if you've got, say, a five minute tunnel loop set up, and you see a pool ball roll out of the from-the-future end of the tunnel, you now know that in five minutes you (or someone) is going to have to roll the ball into the other end of the tunnel, and no matter what you do in the intervening five minutes, that has to happen (I don't know about you, but that would creep me the hell out. Imagining a psychotic murderer entering the billiard room, killing me (with the lead pipe), and then becoming curious about what the tunnels on the pool table do and rolling a ball in, I'd stand there in a cold sweat looking over my shoulder for five minutes and then roll the ball into the tunnel). Anyway, two questions:
  1. can you construct a similar experiment that demonstrates such limits on the nature of free will that doesn't require time travel (I suspect, but can't yet prove, that you can)?
  2. can free will instead be salvaged by an advanced understanding of cause-and-effect? The Odds are One sides with the Buddhists on this (there's no such thing as cause-and-effect) but lacks a better model to explain pool balls from the future or, really, anything else.