🚀 go-pugleaf

e5@gap.caltech.edu> brahm@cco.caltech.edu (David E. Brahm) writes:
>[I discussed the coordinate singularity at t=0 and Quantum Cosmology...]
>
>crb7q@kelvin.seas.Virginia.EDU (the ever-vigilant Cameron Randale Bass) says:
>> Simply saying that it is an inappropriate question of coordinates
>> seems to beg the question of 'beingness', since you clearly seem
>> to be saying that there is an initiating 'event'.
>
>To understand how quantum cosmology "explains" the universe, you must stop
>thinking in terms of sequential causation, i.e. that something (in t<0)
>"caused" the Big Bang (t=0), which subsequently evolved into the universe.
>There was no t<0.  Nevertheless, we can ask about (relative) quantum
>probabilities for universes, and show that ours is "likely."

     OK.  Tell me how to think of it.  

     You spoke of an initiating 'event'.  You say that there is no
     t<0.  I am fine with there being no t<0, but in what manner was
     the initiating 'event' set up?  What is a space-timeless background,
     and how does the initiating event come out of it?  What are the
     properties of a space-timeless background, and 'how' is it
     set up?

     Talk of relative quantum probabilities of universes is all fine and
     good, but it seems to be giving me no information.  What are 
     the bases of this assertion?

>> Um, like everyone else I enjoy getting 'something' out of 'nothing'.  So
>> explain to me how one does this, in even the most general terms...
>
>Feynman's way of understanding why a baseball goes from the pitcher to the
>catcher along a parabolic path is that it "actually" goes along all
>possible paths, with each path weighted by a phase (called the "action"),
>and that every physical measurement actually probes the sum of these
>weighted paths (the "Feynman path integral").  For the most part these
>phases cancel each other out, except for a small subset of paths where the
>phase is stationary, so effectively the path which extremizes the action
>dominates the sum.  The classical approximation is to consider only this
>path, and the extremization of the action is where classical equations of
>motion come from.

     Of course, I'm with you here.

>For the universe, one can consider a sum of "histories," which are 4D
>manifolds with metrics (modulo diffeomorphisms).  Hartle and Hawking
>proposed very simple boundary conditions, restrictions on the histories
>analogous to restricting the baseball to start at the pitcher and ending at
>the catcher: "This class consisted of curved spaces, without singularities,
>and which were of finite size, but which did not have boundaries or edges."
>This is called the "No Boundary" proposal.

     This has always seemed a bit mysterious to me, but why not ask the
     obvious question "Why restrict the class"?  Who does the restriction?
     God?  '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.

     See the trouble one gets into?  There will always be an assumption
     in such any theory that cannot be explained, and must be defined.
     You cannot get rid of God so easily; you can *never* show that
     a God does not exist.

>Thus the way we get "something out of nothing" is that we start with
>everything possible, all realizable universes, and show that our own
>dominates the path integral.

     *All* universes?  I hardly think that possible.  One makes assumptions.
     The theory is always vulnerable at those assumptions.

>I'll close with a quote from Hawking ("The Origin of the Universe") germane
>to our discussion:
>     "...So God would not have the freedom to choose the initial
>  conditions.  Of course, God would still be free to choose the laws
>  that the universe obeyed.  However, this may not be much of a choice.
>  There may only be a small number of laws, which are self-consistent,
>  and which lead to complicated beings, like ourselves, who can ask the
>  question: What is the nature of God.  Even if there is only one,
>  unique set of possible laws, it is only a set of equations.  What is
>  it that breathes fire into the equations, and makes a universe for
>  them to govern?  Is the ultimate unified theory so compelling that it
>  brings about its own existence?  Although Science may solve the
>  problem of how the universe began, it can not answer the question: why
>  does the universe bother to exist?  Maybe only God can answer that."

     He has not produced an acceptable theory that does what he
     implies.  The whole quotation smacks of hubris, and
     I wish that people like Hawking would leave God out of this.

     He seems to have lost the fact that all of his ruminations
     are based on *assumptions* that may well not be tenable.
     This said, he still seems to basically support the position I 
     have taken.

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