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solariha
2006-Aug-27, 06:11 AM
A- How do we measure
1. The size of the universe
2. The total normal matter that was produced by the big bang
B- How do we predict that the universe will form stars for another 70 billion years and not 56 billion years if we assume that 20% of the total mass was used up for star formation in the first 14 billion years

Wolverine
2006-Aug-27, 01:58 PM
Moved from Universe Today Story Comments to Questions & Answers.

antoniseb
2006-Aug-27, 02:03 PM
1. We can measure the size of the observable universe. We have models that can extend observation to give the size of the whole universe, but there is room for doubt.

2. Same answer as 1. above. Mass is one measure of size of the universe.

3. As to 70 vs. 56... we don't have it that precisely. You can expect that the Hydrogen consumption will dwindle, rather than keep getting used at a constant rate. The actual number might be a trillion years, depending on that the cutoff is between saying there is some left, and there's not enough to count.

Blob
2006-Aug-29, 03:00 AM
Hum,
The total normal matter that was produced by the big bang can be gauged by counting the number of background photons from just after the bigbang (CPT violation (http://www.pparc.ac.uk/ps/bbs/bbs_antimatter.asp)).
The mass left over from the matter/antimatter cancellation can be judged by the small amounts of Lithium-7 and deuterium produced during the early universes nucleosynthesis phase.

http://www.bautforum.com/showthread.php?t=45858

Another method may be to calculate the amount of stars and gas in a typical galaxy, and count the number of galaxies in a small patch of sky and extrapolate the total mass of the observable universe.