Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Cosmology



Regarding Bob Zannelli's comment & questions:

<< 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. >>

Dave This is hard idea to understand. The cosmological constant produces a
repulsive force IAW F=A*R*M*C^2 where A is the cosmological constant (As you
basically say) . However assuming that there is only one mass in our Universe
is what sense is R a meaningful term? With nothing else in the Universe to be
distant from what can R possible mean?

The concept of a universe with only 1 (gravitating) mass is not
necessarily supposed to be taken *so* literally as to suppose that no
other particles can exist. Such a situation certainly would cause
problems for the measurement of R (or anything else) since such a
universe has no room for any observers or their measuring equipment.
Rather, the idea is that there is only one object that *matters* for the
phenomenon being described (i.e. acceleration away from the origin) in
that all the other objects (used in observing and defining the inertial
coordinate system) have so little mass that they don't exert any
significant gravitational force on the one body of interest, and that
any Newtonian gravitational forces that that body exerts back on the
other (negligible mass) particles/observer/apparatus etc. are
appropriately cancelled by appropriate *non*gravitational (in the
Newtonian sense) forces so that any origin labeled by the location of
such an (asymptotically low mass) object/particle can be considered as
labeling the origin of an (Newtonian) inertial coordinate system. Since
we *do* admit observers and their apparatus as long as they don't exert
any significant gravitational influence on the body of interest, and that
any possible influence that that body exerts on them is appropriately
cancelled out by other nongravitational effects, there is no *in
principle* problem with the gedanken scenario I mentioned in my post.

Admittedly, there probably *would* be real (likely insurmountable)
technical problems with trying to implement the situation in the *real
world*.

David Bowman
David_Bowman@georgetowncollege.edu