reply to post by jiggerj
You're still thinking of the Big Bang as the moving of matter. It's not. The "Bang" did nothing to cause matter to move. The energy of expansion
is not acting on matter to push it out, away, or any other direction.
The most promising physical analog of the cosmological constant (the thing expanding the universe in Einstein's field equations) is vacuum energy.
Vacuum energy is the potential energy released when the quantum vacuum collapses to a lower energy level. This energy has negative pressure, which
means it causes space
to stretch. It doesn't push objects away from each other...it causes the space
in between objects to stretch.
So, forget the expanding balloon. Cut a circle out of the balloon and lay it out flat (so you have a flat rubber circle), and put a bunch of dots on
it to represent matter. Now, you and a couple friends grab around the outside of the rubber circle and stretch it out. What happens? The dots all get
further apart, expanding away from each other. But, did you move the dots? No...you stretched the rubber. In the same way, nothing is causing the
matter in the universe to physically move further away from all other matter...the negative pressure of the cosmological constant is causing space
itself to stretch.
Of course, you may say, the circle of rubber still has a center. And that's true. If the universe is in any way bounded, then it does have a center.
But that doesn't mean everything is moving outward, toward the edges, away from that central point. The rubber is stretching and, in fact, that also
means that the space between the edge and the matter near the edge is expanding. So, objects near the edge are getting further away from the edge.
Objects near the center are getting further away from the center. And you can say that for any location... objects near Point X are getting further
away from Point X. The closer you get to Point X, the slower this action is; the further you get from Point X, the faster the actions is. The speed of
this expansion is proportional to the object's distance from Point X.
Objects at the center stay at the center. Objects near the center get further away from the center at a slow rate. Objects far from the center get
further away from the center at a fast rate.
Objects at the outer edge stay at the edge. Objects near the edge get further away from the edge at a slow rate. Objects far from the edge get further
away from the edge at a fast rate.
Yet we can still avoid a universe with a center by saying that the universe is infinite in size. An infinite space has no center. Plus, it makes more
logical sense. By saying that the universe has an edge, then we arrive at the "well, what's on the outside?" issue. An infinite space contains all
of our perceived reality and has no outside and no center. With this in mind, the rubber circle you and your friends were stretching earlier has to be
infinite in size, but it's the same principle.
Also, it should be pointed out that, although I'm getting you and your friends to expand the rubber circle by pulling it from the outside, the
negative pressure of the cosmological constant is actually a 'force' pushing outward on space from the inside. At every point in space, there is
this outward pressure pushing outward on the space surrounding it. This pushes every point in space away from every surrounding point in space, and,
consequently, every other point in space.
Your belief that the expansion is starting at a single point and pushing outward is essentially correct, The problem is, you're limiting it to a
single central point. This outward push is actually happening everywhere, not just at a single central point. And it isn't pushing on matter, it's
pushing on space.
In fact...the universe didn't even contain matter when it started expanding. Using vacuum energy as the cause, we have the following series of
1) the universe is infinite in size and completely empty (100% vacuum)
2) the vacuum is a quantum vacuum, capable of spontaneous energy collapse
3) the quantum vacuum spontaneously collapses to a lower energy level
4) a uniform amount of energy is released throughout the universe
5) this energy has negative pressure, pushing outward on the space around it
6) the universe experiences an initial period of rapid expansion (inflation)
7) the energy released by the vacuum collapse condenses as the universe cools
8) the condensing/cooling energy forms matter particles
Now, this is an overly simplified version, but it should help to get the gist.
In this scenario, when you and your friends are stretching the rubber circle, the circle initially has no dots on it. It's actually the energy of
your stretching that causes dots to appear on the circle.