Can the Universe Expand While Matter Converges Under Gravity?

[Glenn]

Hi,
I have read a bit about open, closed, and flat universes, Hubbles Constant, the accellerating universe, big bag, big cruch, etc...

Is it possible that the expansion rate (+ or -) of the universe might be independant of the expansion rate (+ or -) of the matter within it?

Is it possible that the universe might continute to expand while the matter within it might start to converge under the force of gravity?

Have these options been explored?

-Glenn

 

[HallsofIvy]

Before anyone could explore it you would have to define how you distinguish between "the expansion of the universe" and "the expansion of the matter in it".

 

[marcus]

Originally posted by Glenn


Is it possible that the universe might continute to expand while the matter within it might start to converge under the force of gravity?

local clumping is always a possibility

(you know about the Great Attractor in the hydra-centaurus direction, towards which the virgo cluster and its hangers-on are falling-----the speeds involved are on the ordr of 300 km/s or a THOUSANDTH of c)

however it is not hard to see that any particular local clumping can never involve more than a tiny fraction of the galaxies in the observable universe--just by a practical comparison of speeds

first of all, the great bulk of the observable is at redshift greater than 2----to take a random cutoff for calculation purposes (you probably know that a quasar has been observed with redshift 6.4 and the CMB has redshift 1100, so in the big picture 2 is a small redshift)

anything with cosmological redshift of 2 or more is in a part of space which is receding from us at a speed greater than c

(for an online calculator that gives the recessionspeeds for various redshifts, google "Siobahn Morgan" and find her astronomy course materials, the current Fall 2003 semester)

maybe largescale clumping is not a theoretical impossibility but the usual falling speeds (a thousandth) are just too tiny to
counteract the typical recession speeds (several times c)