(November 10, 2014 at 4:10 pm)Pickup_shonuff Wrote: Ok..few more...for now...There speed toward each other has to be faster than the expansion of the space between them. No mind-blown answer on this one.
Considering the balloon analogy, how can galaxies collide if the space BETWEEN them is expanding?
Quote:Why is it that we don't actually experience the expansion of space? Is it because of the gravitational field? As in... it keep us "bounded" to this particular bodily composition, in terms of persons, planets, solar systems, galaxies, superclusters, etc.?It is too of a small scale for us to feel/see it. On the very large scale (supercluster level), all the small effects add up to something that we can observe.
Plus, the forces that keep us together (gravity for the big stuff and EM for the smaller stuff) are much stronger on the smaller scales. This might not be case in the far futher.
Quote:I understand Krauss to be arguing something to the effect that space must RESULT from fluctuations in the quantum gravitational field... but isn't this "quantum foam" itself an ultra-microscopic region of space? Doesn't he just mean that space can be inflated and produce matter from prior energy?
I think he believes similiar to me where you can create something from nothing as long you bring along its exact opposite. That would include space. What would be the exact opposite of space? No idea.
No prior energy required. The total energy of the visible universe has been measured to be very close to zero (note that we can't see all of the universe). It is believed that it is zero because that would produce a flat universe. The universe is observed to be flat.
It makes sense the total energy of the universe is 0 because gravity is negative energy. The way to visulize it, consider a ball sitting on the ground. It has zero potential energy. Now, you digged a hole that it can fall into. What is its potential energy? It's negative. Similiar with gravity, a flat spacetime is the ground, the curved spacetime gives you negative energy.
