On Tue, Aug 13, 2013 at 05:26:41PM -0700, Pierz wrote:
> I need clarification of the significance of quantum theory to determining 
> the *past*. I remember having read or heard that the past itself is subject 
> to quantum uncertainty. Something like the idea that the past is determined 
> only to to the extent that it is forced to be so by the state of the 
> present, if that makes sense. In other words, there may be more than one 
> history that could lead to the current state of the world. Let's say it 
> might have been one way or another and then we make a measurement which 
> resolves this question, we are 'forcing' the past to be one way or another. 
> In MWI, that would be saying my 'track' through the multiverse is ambiguous 
> in both directions, both into the future and 'behind me' so to speak. I'm 
> unclear on this and what it precisely means. I seem to recall that it was 
> critical in calculations Hawking made about the early universe - at a 
> certain point these uncertainties became critical and it meant that it was 
> no longer possible to say that the universe had definitely been one way or 
> another. Can someone clarify this for me?
> 

This idea of the past not being determinate until such a time as a
measurement in the present forces the issue is fundamental to my
interpretation of QM. It is also related to the Quantum Eraser. Saibal
Mitra has written some stuff on this too - maybe he'd like to comment?

On the other hand, I don't think this view is particularly
mainstream. Even many worlds people tend to think that the multiverse
has decohered in the past, and that there is a matter of fact which
branch we are in, even if we're ignorant of that fact.

I can't comment on Hawking's work, unfortunately, as I'm not aware of that.

Cheers
-- 

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Prof Russell Standish                  Phone 0425 253119 (mobile)
Principal, High Performance Coders
Visiting Professor of Mathematics      hpco...@hpcoders.com.au
University of New South Wales          http://www.hpcoders.com.au
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