On 7/31/2014 5:03 PM, LizR wrote:
On 1 August 2014 11:25, meekerdb <[email protected] 
<mailto:[email protected]>> wrote:

    On 7/31/2014 3:52 PM, LizR wrote:
    On 1 August 2014 09:05, meekerdb <[email protected]
    <mailto:[email protected]>> wrote:

        On 7/31/2014 11:27 AM, John Clark wrote:
        On Wed, Jul 30, 2014 at 7:57 PM, LizR <[email protected]
        <mailto:[email protected]>> wrote:

            > if space-time isn't an infinitely divisible continuum, it 
presumably has
            some sort of granularity,


        Our quantum theories may need work. Quantum theories of Physics insist 
that
        space is quantized just like everything else,

        I don't think that's true.  In fact all quantum field theories assume a
        continous spacetime.


    I would think that at the very least they assume a continuous Hilbert space.
    That too.  But the spacetime is a kind of background to the Hilbert space.  
The
    vectors in Hilbert space are square-integrable functions of positions or 
momenta in
    a continuous spacetime.  Of course it's impossible empirically to prove the
    spacetime is continuous; computationalist can just say they need more 
digits and
    hypothesize as many digits as they need.


Yes, it's awlays possible to claim a granularity smaller than our best measurements. How does this connect with QM and it being impossible to measure anything smaller than the Planck length? (Or does it?)

      Similarly the complex field for Hilbert space could be just the rational 
complex
    field; but that would imply a smallest non-zero probability which in turn 
would
    undermine unitarity, Everett, and time-reversibiity.


I can see that unitarity would be undermined, and hence Everett (I think), but how come time-reversibility?

It would mean that interference terms between different "worlds" could not become arbitrarily small. There would be a least quantum of probability and when something became more improbable than that, its probability would drop to zero. Then the time evolution couldn't be reversed.

Brent

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