Re: Cosmology

[David Bowman <David_Bowman@GEORGETOWNCOLLEGE.EDU>]

Regarding John Denker's comments:

> If you chalk up the presently-observed expansion pattern to a special
> initial condition, there's nothing non-Newtonian about it.

Well, actually the presently observed universe seems to have a nonzero
value of the cosmological constant.  This means that the strict
nonrelativistic Newtonian limit of GR with the CC turned on is not quite
Newton's theory of gravitation.  In Newton's theory if there are *only*
two massive particles separated by a distance R there is an attractive
force between them of the inverse square form (i.e. -G*M1*M2/R^2).  This
is not the case when the CC is turned on in a universe inhabited by only
two masses.  In the latter case the nonrelativistic limit of the
gravitational force on mass M1 when M2 is located at the spatial origin
is of the form:

-G*M1*M2/R^2 + M1*B*R

where B is a constant proportional to the CC.  This force has the usual
attractive behavior at short distances, but it is repulsive at
sufficiently large distances.  In fact, even when M2 = 0 and there is no
second particle at the spatial origin there is a repulsive force
pushing mass M1 away from that origin.  This effect is present no
matter *where* in space the origin is to be chosen in *any* supposedly
inertial frame.  In fact, such a situation may even be said to violate
Newton's 1st law *if* this isolated tendency of a free particle to
accelerate away from any origin is not associated with an explicit
gravitational 'force', but is a built in feature of the laws of nature.
But even if this effect is said to be a result of a gravitational
'force', the form of that force is not of the Newtonian form that
gravitational forces are supposed to take.  So I would claim that there
*is* something "non-Newtonian about it".

David Bowman
David_Bowman@georgetowncollege.edu