Time postulates:

No, I was arguing that while the future may be multi-worlded, everything we know about science (evidence, archaeology, measurements, ...) points to a _single_ past.

The laws of physics, including the laws of quantum mechanics, are symmetric with respect to the arrow of time, with occasional and rare exceptions that are only apparent at high magnification. if quantum mechanical ambiguity exists about the future, then it also exists about the past.

For example, a single past world line for me, for you, for Hal, for Chaucer, for Einstein.

Now we may not know what this world line is very accurately, but as we look at more closely, e.g., by examining the photographs someone may have taken, or their diaries, or whatever, the more we home in on what that world line was. We never look closely and see two or three or N different histories, we just see a higher fidelity view of what we must assume is the One True Past.

As you measure the past by examining the record of it, you of course collapse wavefunctions, and produce eigenstates of what you are measuring. It is not necessary to assume the One True Past existed prior to those measurments being made, simply because no measurements contradict.

I don't doubt that Hal gets the sense that many potential Hals could have resulted in the current Hal...an interesting notion. But everything does in fact point to a One True Past which various measurements get closer and closer to, and which no measurements contradict.

This, of course, is the "hidden variable theory," in which we have a One True Past, (and One True Future) as well, which evolves deterministically, based in part on degrees of freedom which are by definition unobservable by any experiment. If this is true, we have no free will, and Stephen Wolfram's suspicion that the universe contains only pseudorandomness produced by complex deterministic mechanisms at a small scale holds true. Still, Nature abhors overcomplexification, and plain old quantum mechanics works just fine for predicting the results of experiments.

This is what I meant by "convergence." Homing in, getting closer, sharpening the image, filling in the details.

As for "tacitly assuming some kind of communication between observers," I am _explicitly_ saying that observers get together and compare notes...and they find no contradictions, if they are honest observers.

Nowhere does this imply that what was observed always existed in its observed state prior to the measurement being made. -- Eric Michael Cordian 0+ O:.T:.O:. Mathematical Munitions Division "Do What Thou Wilt Shall Be The Whole Of The Law"