Re: Doomsday Example

Robin Hanson (
Mon, 24 Aug 1998 13:37:03 -0700

Today the Fall Semester started here, and so the Philosophy library finally opened, allowing me to read the Dieks vs. Leslie exchange in the '92 Philosophical Quarterly. They discuss the same issue Nick and I are discussing now: does it make sense to think I could have been a rock?

Leslie writes: "First: Dieks would be very obviously wrong if he had just said that more observers meant more opportunities of being an observer rather than, say, being an unconscious collection of atoms, ... things which do not actually observe anything and which therefore must be left out of any calculations about what observers could be expected to observe."

I think I fundamentally disagree with Leslie here. The universe doesn't know whether we exist, and doesn't care. If we're going to create a state space and prior describing possible universes, we should do so in a way that is faithful to our best understanding of the physics of universes, and neutral relative to whether some set of atoms is organized so as to create an "observer."

We ordinarily want to talk about what would happen if I died or if humans had never evolved. And it seems to me the natural neutral physics-oriented way to do is to talk about what would otherwise happen to the material that now makes me up. It seems natural to me to talk about this as saying "I could have been a rock," though Nick thinks this misuses the word "I". Maybe so, but since the basic notion I'm trying to speak of makes sense, there aught to be some similar words I could use to describe it. Let my "I" stand for that.

Doomsday argument folks also seem to want talk about the possibility that I might have been some other human at some other place in space-time. This seems sorta metaphysical on first blush, but not wanting to be a prude about such things, I've said O.K., I can do this if I imagine that instead of being made of the material I am, I could have been made of other material, perhaps arranged differently.

If I could have a rock, and if Nick could have been a rock, then it seems we have to accept the possibility that we could have both been rocks. If we now add in the possibility that I could have been Nick and he me, it seems there are two ways we could be rocks. I could be my rock and he could be his rock, or we could switch. Nick complains this looks metaphysical, but it seems no more so to me that saying I could have been Nick and he me.

Of course there are complexities related to the fact that the material that makes up me changes with time, but I don't see these as essentially changing the situation.

Robin Hanson RWJF Health Policy Scholar, Sch. of Public Health 510-643-1884 140 Warren Hall, UC Berkeley, CA 94720-7360 FAX: 510-643-8614