Can the Universe Expand While Matter Converges Under Gravity?

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SUMMARY

The discussion centers on the possibility of the universe expanding while matter within it converges under gravitational forces. Key concepts include local clumping, the Great Attractor, and the implications of redshift, particularly noting that observable galaxies at redshift greater than 2 are receding at speeds exceeding the speed of light. Participants highlight that while local clumping may occur, it represents only a minuscule fraction of the universe, given the overwhelming recession speeds. The conversation emphasizes the need to differentiate between the expansion of the universe and the behavior of matter within it.

PREREQUISITES
  • Understanding of cosmological concepts such as open, closed, and flat universes
  • Familiarity with Hubble's Constant and its implications for cosmic expansion
  • Knowledge of redshift and its significance in astronomy
  • Awareness of gravitational effects on cosmic structures, including local clumping
NEXT STEPS
  • Research the implications of the Great Attractor on cosmic structure formation
  • Explore the concept of redshift and its calculation using tools like Siobhan Morgan's online calculator
  • Study the dynamics of local clumping in the context of cosmic expansion
  • Investigate the relationship between gravitational forces and the expansion of the universe
USEFUL FOR

Astronomers, astrophysicists, and cosmologists interested in the dynamics of cosmic expansion and the interplay between gravity and matter distribution in the universe.

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 independent 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
 
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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".
 
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)
 

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