Hi Cougar

Thanks for the inquiry. The debate about expanding galaxies was “closed” by W. de Sitter in his 1931 article in the Bulletin of the Astronomical Institute of the Netherlands Volume number 6. Once one allows galaxies to expand, where do you then stop the expansion? Do solar systems expand? Since atoms are mostly space, do atoms also expand? If solar systems expand, then how can they maintain their stability? When the age of the universe was 1/2 of what it is now, the distance between points would be 1/2, if one assumes a constant rate of expansion. if the earth were twice as far from the sun, the centrifugal force would be reduced in half, but the gravitational force would be reduced by a quarter, solar systems would fly apart. Since solar systems and galaxies have been stable structures for billions of years, they “can not expand”. The popular argument is that they are gravitationally bound, so they resist the expansion of space. (Note the proposed theory maintains the necessary stability is maintained by requiring the velocity of objects be reduced by the expansion.)

This is not a closed topic of discussion though. There are a number of articles/theories that allow galaxies to expand, or not expand, mostly in an effort to explain the spiral structure of spiral galaxies. A check of recent published articles will give a more current review on the topic.( http://adsabs.harvard.edu/abstract_service.html use galaxies and expand as title search words).


Thanks

Snowflake