🚀 go-pugleaf

In article <1dkugvINNgpn@gap.caltech.edu> brahm@cco.caltech.edu (David E. Brahm) writes:
>[My description of quantum cosmology as a Feynman sum over histories...]
>> There was no t<0.  Nevertheless, we can ask about (relative) quantum
>> probabilities for universes, and show that ours is "likely."
>
>Proving that even aero engineers waste their weekends on UseNet,
>crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) wrote,
>>     OK.  Tell me how to think of it.  
>
>Well, Dale, that's what my last post was supposed to do.  Of all the
>possible 4D manifolds (satisfying some constraints), ours is the one that
>dominates the path integral.

     (Proving that not all aero engineers can sleep when they're supposed to.)

     But why 4D manifolds?  Why path integrals?  You were disproving
     the existence of God, remember.  Assuming such speculations true,
     why do the restrictions exist.  Did God, in his infinite wisdom,
     read Feynman and Hibbs before setting up the manifolds and allowing
     the 'histories' to evolve.   Did He decide that that would
     be a good way to go? 

     This seems like as good an ultimate 'explanation' as any.

>>     I am fine with there being no t<0, but in what manner was
>>     the initiating 'event' set up?
>
>'Set up' sounds to me like you're still asking about 'beforehand'.  I am
>probably guilty of using misleading terminology when I first spoke of our
>universe as an "event" in a "spacetime-less background"; I should have said
>a "history" in a "Feynman sum", but at the time I hadn't defined those
>terms.  By "event" I did not mean the Big Bang event, i.e. (t=x=0).

     Ok.  How is a 'space-timeless background' set up?

>>     Talk of relative quantum probabilities of universes is all fine and
>>     good, but it seems to be giving me no information.
>
>Hawking claims that the 'no boundary' proposal makes some predictions, e.g.
>that there are no true singularities; and that density fluctuations all
>started in the ground state and then were inflated, leading to a Zel'dovich
>spectrum which is consistent with COBE results.

     I thought he had already assumed that there were no true singularities
     in the basic 4D manifolds?

     And you're starting to sound like something is banging again with
     'density fluctuations all started in the ground state'.  Where did
     the ground state come from?  What do the manifolds look like before
     the density fluctuations.  Is or is this not a good question and why?

>>     ...'Without singularities' seems to be an odd a priori restriction
>>     coming from Hawking.  It also seems to be odd in that you mention
>>     the 'coordinate singularity at t=0' earlier.
>
>At the moment I think this is an ad-hoc assumption.  Without it I don't
>think anyone knows how to make any predictions.  Please note that the
>coordinate singularity at t=0 is not a (physical) singularity, though.

     How does one finesse away the apparent physical singularities in
     a) classical GR b) all this banging stuff?  Why is t=0 not a physical
     singularity since there appears to be no spacetime at t=0?  How can
     we possibly discuss t=0 and still have 'boundaryless' manifolds?
     Please describe the physical nature of the manifolds about t=0.

>>     See the trouble one gets into?  There will always be an assumption
>>     in such any theory that cannot be explained, and must be defined.
>
>A sweeping statement I would like to see proven.  The fact that quantum
>cosmology is not (yet) a complete and convincing theory does not show that
>such a theory is impossible; at least some people have the guts to try.

     How does one create a theory without an assumption?  At a minimum,
     you've assumed that the universe operates by a set of rules.  This
     single assumption seems to be devoid of physical content, though
     very necessary.  

     And you're missing the point, this began with an assertion that
     such things provided proof that God did not exist.  I certainly do not 
     wish to deny the ultimate utility of such musings.  I have every 
     confidence that will work itself out eventually.  These musings do, 
     however, have absolutely nothing to do with disproving the concept of 
     'God'.

>So, yeah, the field is still in its infancy, and may all turn out to be
>garbage; that's how science goes.  I find it interesting mostly in that it
>attempts to bring science to bear on those "deep" questions of existence
>once thought to be purely the realm of religion.  Whether it will do so
>successfully remains to be seen.  And now you know everything I know about
>quantum cosmology, and more.

     But you've gotten no closer to 'proving' anything of the sort.
     At some point, one can ask why, and you'll have to shrug your
     head and say 'dunno'.   You cannot get around making assumptions,
     the nature of which denies logical 'proof'.  At that point someone
     can always stick their head in and go 'there's God in them thar
     hills'.

     Also, the fact that certain people are apparently unaware of
     basic assumptions made in *all* physical theories is a bit shocking.

     I ask you to ponder an axiomless mathematics.  I hear greek letters
     crashing to the ground all around me.

                               dale bass

-- 
C. R. Bass                                          crb7q@virginia.edu        
Department of Mechanical, 
     Aerospace and Nuclear Engineering
University of Virginia                              (804) 924-7926