Re: Quantum Computers

Dan Fabulich (
Thu, 26 Aug 1999 01:10:15 -0400 (EDT)

On Wed, 25 Aug 1999 wrote:

> Then doesn't this bring me back to my original question. The photon
> that passes through gate A in Universe 1 and gate B in Universe 2 goes
> on to be absorbed by particles X and Y respectively, and unless and
> until we devise a measurement that allows us to precisely trace its
> "actual" trajectory, we never know for sure which universe we're in.
> Right? And since this sort of subatomic interaction takes place
> googols of times a second, universes are being created googols of
> times a second. And because measurement of these phenomena takes place
> on only a laughably small fraction of the total, alternate universes
> collapse only rarely.
> And if I'm still following a valid logical chain, what particular set
> of events causes us to perceive *this* particular universe over all
> the others, or is it just chance?

Try imagining a split just ABOUT to happen. During this split, one split version of you will go on to exist in "Universe A," while the other split version of you will go on to exist in "Universe B." From this past perspective, it obviously doesn't make sense to ask "Why will I perceive A and not B?" because, in point of fact, you (that is, the unsplit you) will perceive both (once you split). Why X? Not X.

The reason your question is harder to think about after the split is because when a split version of you thinks about the other split version of you, the other split version necessarily seems a little less real. This is not a fact about physics; this is a fact about psychology and the way we use language.

Suppose the A version of you is thinking about the B version of you. When the A version says "I," it means the A version and ONLY the A version; not the B version. The B version is different from the A version; since we are very used to the idea that "I" refers to only one thing and not two different things, it's quite natural to think, right or wrong, that after the split, you are not the same person as the other version of you in the other branch. Since you seem very, very real to yourself, anything that is not you (in this case, version B) seems slightly less certain; slightly less real. [Or, in the case of an abstract theory like MWI, perhaps far, far less certain/real indeed.]

Now we return to your question, "why do I perceive A and not B?" I'd argue that this is because it's very natural for one to think of a person on one side of the branch as different from the person on the other side of the branch. The other version of you is perceiving B, but since that version isn't "you," "you" aren't perceiving B. That is why "you" perceive A and not B. If you were to call both splits in both branches "you," which comes quite naturally BEFORE the split, since before the split both versions DO seem more like yourself, the question would seem pretty meaningless.

(You know, sometimes I wonder if I'm in John Clark's killfile.)