View Full Version : How fast is everything slowing down?

Cheap Astronomy
2008-Nov-18, 02:00 PM
I understand that there was initially cosmic inflation which was apparently a wildly exponential acceleration rate. That all seem to settle down to a more sedentary acceleration after the first few moments of the big bang.

But we still say the universe is expanding - and now we say it's expanding at an accelerating rate. So what's sequence of events here? After inflation, did the universe's acceleration slow right down and now is speeding up again - or is the universe's expansion just accelerating at a steadily slower rate now than it was earlier?

2008-Nov-18, 02:21 PM
"When astronomers succeed in observing supernovae with redshifts and distances much larger than those of the supernovae with redshifts between 0.4 and 0.7, the Hubble diagram for the universe actually reverts toward the original line describing a cosmos with no acceleration produced by a cosmological contant. This reversion occurs because as we look farther out in space, we look further back in time, to eras when the cosmological constant had produced a cumulative effect much smaller than at the present time or at times 'only' 4 to 7 billion years ago. We can effectively recapture the Hubble diagram for a universe without a cosmological constant by looking so far back in time that we observe epochs when the cosmological constant had produced negligible results." -- Goldsmith

2008-Nov-18, 03:35 PM
So what's sequence of events here?

NASA Wilson Microwave Anisotropy Probe (WMAP): Timeline of the Universe (http://map.gsfc.nasa.gov/media/060915/index.html)

http://map.gsfc.nasa.gov/media/060915/060915_320.jpg (http://map.gsfc.nasa.gov/media/060915/index.html)

More recently, the expansion has begun to speed up again as the repulsive effects of dark energy have come to dominate the expansion of the universe.