It's beginning to look like it is near the middle of this range at about 12 billion years. We cannot pinpoint the age accurately right now because we do not have enough independent, high accuracy 'clocks' that we can use.
You tell your friends to meet you somewhere at exactly 11:45 AM, but some come at 11:30 and others come at 12:05. How can this be? You told them a very precise time! Alternately, if someone watching this activity were asked "What time did they decide to meet? He would have looked at the range of arrivals between 11:30 and 12:05 and come up with an answer something like "I estimate 11:40 with an uncertainty of 15 minutes".
The US Democrats, Republicans and the Congressional Budget Office all agreed in the early 1990's that the US budget was running a deficit of between 150 and 250 billion dollars, but despite the fact that the annual budget was 1.6 trillion dollars, they could not agree on exactly how many dollars this deficit actually amounted to, to within 50 billion dollars of each other. How can this be? Aren't there a fixed number of dollars in the annual budget, and a fixed number of tax dollars collected? Why is there an uncertainty in the deficit by as much as 50/150 = 33 percent?
To determine the age of the universe, astronomers have been trying to develop several different kinds of 'clocks' that can be compared with one another. They use the expansion rate of the universe, and the age of the oldest stars very commonly. But as we know, there is still an uncertainty in how fast the universe is expanding depending on whether you believe Alan Sandage's 'supernova' standard candles of Wendy Freedman's 'Cepheid variables' in determining how far away galaxies are. The range is between 8 and 15 billion years depending on whether the expansion factor is closer to 50 or 100 kilometers/sec/megaparsecs. As for the oldest stars, theoretical evolution models depend on many input parameters including the 'metalicity' of the stars and their current color and luminosity. The latter depends on distance, which can again introduce errors. The range of ages for the oldest globular cluster 'clocks' in the Milky Way is 9 - 14 billion years.
It is hoped that as the distance standards become more precise, the ages will also converge to a common number, and that the current uncertainty of 12 +/- 3 billion years ( a 25 percent uncertainty) will be reduced to perhaps 10 percent. Unless someone comes up with a better 'clock' we may have to live with an uncertainty of a billion years or so. No big deal.
Copyright 1997 Dr. Sten Odenwald
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