From: alex@csn.org (ALEX MATTHEWS)
Subject: Re: "Modeling" the Expanding Universe?
Summary: Definitions, definitions!
Organization: University of Colorado, Boulder
Date: Thu, 28 Jan 1993 21:07:13 GMT

In article <C1KnCo.5rH@well.sf.ca.us> metares@well.sf.ca.us (Tom Van Flandern) writes:
>
>schumach@convex.com (Richard A. Schumacher) writes:
>
>> If one adds two test particles to the universe, the general expansion
>> does NOT by itself cause the test particles to move apart.  Subsequent
>> movement of the test particles depends on their mutual gravity and the
>> gravitational or electromagnetic forces imposed on them by other
>> matter/energy in the usual, non-cosmological ways.
>
>     If the matter density is uniform, then the pair of test particles
>increases its mutual separation due to the appearance of new space between
>them, although both stay put in space.  

No.  You are saying that the test particles are somehow forced apart 
by "new space".  Either you are proposing a new entity you call "space"
that acts on matter via some unstated force, or we are not defining "space"
the same way.  I suspect it is the latter.  Here are some definitions
that may be useful in continuing this discussion:

SPACE: Nothingness, vacuum, absence of matter and energy; has no 
       intrinsic measure; can only be visualized and manipulated
       by the imposition of an artificial coordinate system, as can
       be defined with matter in an inertial reference frame. 

COORDINATE SYSTEM:  A way of measuring a measurable physical system. 
       A change of coordinates does not change the physical system;
       the physical system will exist with or without the coordinate
       system.  One cannot influence another.

UNIVERSE:  The space around us and the energy and matter it contains.

INTERGALACTIC MEDIUM (IGM):  The matter and energy that exists in
       space, between galaxies.

Space, as I define it, cannot be considered a physical system because
it is infinite, isotropic, homogeneous (there's only one of it) and
collisionless.  In other words, you can't see, hear, taste, touch,
or smell it.  It is self-similar, so two different coordinate systems
will paradoxically yield the same measure.  Space has no scale.

I and others have been referring to the Big Bang as an expansion of
the universe, with the assumption that an expansion is only defined
for a measurable physical system; properly, we should only talk about
the expansion of the matter(energy) distribution of the universe.  The 
concept of space should be decoupled from the concepts of matter and energy.
To illustrate this, consider two pens side-by-side on my desk--if I
move them apart, have I created space between them?  No, I have 
merely increased their separation, as measured using rulers defined
by matter or energy.  I did not disturb space because
space is aphysical.

Similarly, if I leave the pens alone, does the motion of cars on the
street outside increase or decrease the space between the pens?  Again,
no; only now, the separation between pens is constant, according to the
same ruler.

What if I change my definition of space to allow a coordinate
system, or ruler, to be placed in it, and let the ruler expand or
contract with time?  Then, suddenly, I would be able to see matter
streaming about unintuitively, but only because I've thrown out the 
idea of an inertial reference frame.  Matter would be moving because of 
a pseudoforce, not a real force.  Cosmologists have reference
frames like this which they use to separate out bulk motions,
but they make no assumptions about them being tied to space; they
are all tied to matter.  The most familiar one is the comoving 
coordinate system, which expands by definition at the same rate 
as the Hubble flow.

Tom, if you have definitions different than these please state them.
As I have defined space, we can only discuss it from a metaphysical
standpoint.  If you think there should be a physical component to
space, then we all can talk physics.  And the first thing we'd ask
you for is some evidence that this "physical space" exists--some 
measurement of its properties, for example.  I understand that you
are trying to use RAA to disprove the Big Bang and GR: "The big bang
theory says that space expands, but the solar system doesn't expand,
therefore not big bang."  The weak link in your argument is your 
definition of space.  As I and others define space, the behavior of 
the solar system is entirely consistent with the big bang and GR.
-- 
- Alex Matthews  (new address: alexm.csn.org)

  "A typical Grand Prix race.  High noon.  Tension mounts.  Throttles clench."
                        Patricia Zonker, _Murdercycles_
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