Expert: Jayendra Upadhye - 2/18/2005

Question
The big bang theory tells us that the universe began as a singularity that has been expanding ever since. ie From any point is space, 'all' objects should appear to be moving away.  How is it possible then for GALAXIES to collide?

I can see how novae and supernovae could toss material in all directions and overcome expansion, but I cannot understand how whole galaxies could 'buck' the current.

Answer
Garry!
You seem to have overlooked gravity!
Secondly, new light on the big bang especially by the COBE project has suggested that there was a "lumpiness" or anisotropy associated with the bang.
These lumps, became seeds around which huge clouds of elementary premordial hydrogen collapsed, to form galaxies.

Over time as of now, the LARGE SCALE STRUCTURE of the universe shows a "spongiform" nature. Huge voids enclosed in filament like bridges of galaxies, rather like the network of neurons in a brain.

Gravity often causes the galaxies to collide. Elliptical galaxies emerge after spiral galaxies undergo many collisions. This is seen from the large populations of old er red stars in elliptical galaxies.

The neighbour of the milky way, m31 or the andromeda galaxy is headed our way too, and it will be a great free for all when m31, its two satellites, and the milky way with it magellanic clouds, collide in the distant future.

The whole milky way andromeda and others..known as the local group is speeding towards the virgo super cluster of galaxies at 300 km/sec and will reach there in 10s of billions of years!
Hope that sets things in perspective.

Ofcourse, we can never catch up with those centers of attraction that are receding faster due to the cosmological expansion, than we approach them at conventional speeds!
Jayen