On 1/8/2014 4:11 PM, LizR wrote:
On 9 January 2014 07:58, John Clark <johnkcl...@gmail.com <mailto:johnkcl...@gmail.com>> wrote:


    On Tue, Jan 7, 2014 at 2:59 PM, Jesse Mazer <laserma...@gmail.com
    <mailto:laserma...@gmail.com>> wrote:

        > Well, most physicists already agrees physics is time-symmetric


    I think you would have enormous difficulty finding one single physicist on 
the face
    of the earth who says time is symmetrical.... well OK,... maybe a physicist 
who just
    hag a stroke. You could find many that think Quantum Mechanics states time 
is
    symmetrical, or almost symmetrical.   So much the worse for Quantum 
Mechanics.


The equations of Newtonian dynamics are time-symmetric, similarly for relativity (both SR and GR - even gravitational collapse is reversible according to the equations) - and quantum mechanics is, too. The only thing in the entirety f physics that isn't based on time symmetric equations is thermodynamics, which most physicists agree is an emergent phenomenon, due to a special initial arrangement of the components of the universe coupled with the likelihood that they will come to occupy more probable states over time..

The second law of thermodynamics is based on the argument that a system in a low entropy (i.e. improbable) state will head towards a high entropy (i.e. more probable) state through the statistical result of random movements, because there are by definition far more probable states than improbable ones. This assumes the dynamical interactions involved are time-symmetric, since otherwise there would be no need for this argument - the universe would head that way for some other reason, due to some built-in time asymmetry. Since there is no such known time asymmetry, thermodynamics relies on a statistical argument and an improbable initial state. This was all explained by Boltzmann about 140 years ago.

Look up Schulman's "special state" theory of QM. He uses the time symmetry and a requirement that there be no "grotesque" states (superposition of macroscopic systems) to explain the appearance of randomness in QM.

Brent

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