Tuesday, February 11, 2014 5:50:53 AM
It's nice to throw around theories about this but let`s be honest we haven`t the faintest clue. And making ascertations right now about what will happen quadrillions of years in the future at "THIS" time is pretty pointless. When we finally figure out how to harnass the power of a star we should probably look into this. (Hopefully if it doesn`t take us trillions of years.)=p
Tuesday, February 11, 2014 4:45:02 AM
...This is a bit of an oversimplification, and it also has to do with dark energy, since the density of dark energy never changes, but the density of matter does, and the forces influenced by each.
Tuesday, February 11, 2014 4:43:19 AM
@Fred: Ok I'll try. Newtonian gravity, F = GmM/r2 as taught in high school, is always attractive.
Newtonian gravity is approximately correct, but breaks down for extremely large scale systems such as the observable universe, and very dense systems such as neutron stars. If you observe the orbit of Mercury with incredible precision, over a few centuries the position of Mercury will shift very slightly in comparison with what Newtonian gravity predicts. One can account for this discrepancy, and understand systems such as neutron stars and the large scale universe with Einstein`s General Relativity. You would need a good understanding of General Relativity and its equations to see how it predicts expanding universe, gravity, etc.
But to answer your question, gravity is not just one force but a combination of forces. Within the solar system the attractive force is stronger, but in deep space matter isn`t dense enough to overcome the repulsive force.
Tuesday, February 11, 2014 4:40:48 AM
A more appropriate title might have been, "Three currently-debated models disregarding several others that do not have the same degree of acceptance in popular literature."
Too many assumptions and not enough evidence to justify thinking of this as a scientific subject. It is a matter of philosophical discussion. When physicists delve into philosophical debate they should remember to take off their physicist hats and put on their philosopher hats (so people will not get confused) and use the tools of philosophers in their discussion. It's okay for physicists to be philosophers also, but to offer yourself as one without the necessary set of skills and tools is like a butcher pretending to be doctor without the training.