(From article in Scientific American)
According to previous theories, there were three alternatives: (a) Expansion of the universe is decelerating rapidly; this will make it collapse back onto itself in a “Big Crunch”. (b) The expansion of the universe is decelerating slowly, which will cause the universe to expand forever, but asymptotically to a limited size. (c) The expansion of the universe is decelerating at a rate which is “just right” to make the expansion stop at some point. This means that the universe is “flat”. [Why?]
However, recent observations lead to the conclusion that the expansion of the universe is not decelerating at all, but accelerating. (This conclusion follows from the observation of distant supernovae Ia.) This would mean that the universe is a hyperbolic space-time, which would make it older than we thought. This would remove the contradiction between the ages of the oldest stars and the age of the universe. (Some stars seemed to be older than the universe, which is impossible.)
But why would the expansion of the universe accelerate? Here there are two possibilities:
- Either intergalactic space is not empty, but is filled with virtual particles popping in and out of existence from the vacuum field. This would be linked to a fifth force (“quintessence”?) linked to anti-gravity, which is repulsive rather than attractive.
- Or the inflation of the very early universe, a theory which explains many other features very well, did not happen after the Big Bang. However, it may have happened before the Big Bang, which would imply the presence of many “bubble” universes.
The “missing matter” in the universe has been a puzzle for some time. It now seems that there are four types of matter:
| (a) | Visible (stars, galaxies) contributes | 1% to the total. |
| (b) | Dark baryonic (brown dwarfs, MACHOs) | 5% “ “ “ |
| (c) | Dark non-baryonic (axions, neutrinos) (WIMPS) | 30% “ “ “ |
| (d) | Cosmological (virtual particles) | 60% |
| Total | 96% |
But the cosmological, although it is known as “the cosmological constant”, may not be constant.
Before the Big Bang, our universe was stuck in a false minimum, but tunnelled its way out of it to reach the true minimum. The break-out of the false minimum represents the Big Bang. [Or the inflation?]
We might well live in an infinite universe in finite space.