On Monday, July 8, 2002, at 03:40  PM, Hal Finney wrote:
> Future uncertainty is familiar to us, but one of the things that the
> many universe model introduces is past uncertainty.  There is a sense
> in which the past is not unique and determined.  My mental state is
> consistent with many macroscopically distinct pasts.

I'm not convinced that this is so. Sure, there are many views of past 
events, of history, faulty memories, changing memories, etc.

However, the "single past" model is quite well-supported by science and 
a kind of "convergence" of knowledge:

-- we may not have complete knowledge of the past, but experience points 
to the fact that the more different observers learn about the past, the 
more they will (if they are honest) agree on what that past was.

-- archaeology is a good example: more and more bits and pieces add 
together to "converge" to a unitary past, not to multiple, diverse pasts

-- this is analogous with measurements in QM: honest observers will 
report the same measurement

> My brain and my mind hold only a certain amount of information.
> Vastly more information than that has existed in my past light cone, the
> history of the universe which has led up to me.  My brain is therefore
> very probably consistent with a great many past histories, each of which
> will lead to a brain, a mind and a mental state which is 
> indistinguishable
> from that which I am now experiencing.  From my first-person 
> perspective,
> the past is indeterminate in much the same way as the future is, 
> although
> to a lesser degree.

I agree that many possible causal pasts lead up to what you are. The 
placement of grains of sand on a beach in Greece is not going to 
significant affect who you are right now, so this is just one of a vast 
multitude of possible causal pasts which will not affect your currrent 
mental state.

But this does not mean these possible pasts have equal "actuality." For 
example, two different observers may have carefully photographed the 
patch of beach where the possible variations occurred. The more accurate 
their observations or photographs are, the more closely they will agree 
on what that past was (again, assuming honest observers).

Nothing in science points to the "many actual pasts" possibility, even 
though I acknowlege your point that "many _possible_ pasts" would lead 
to a indistinguishable equal mental state for you or me.

In other words, science points to a single actual past. There is, so 
far, no evidence for multiple actual paths.

(And in the consistent histories picture, we should not be surprised. We 
find ourselves in whichever universe we are in, and we will see one 
actual trajectory through space-time.)

--Tim May
(.sig for Everything list background)
Corralitos, CA. Born in 1951. Retired from Intel in 1986.
Current main interest: category and topos theory, math, quantum reality, 
Background: physics, Intel, crypto, Cypherpunks

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