How old is the Universe?
In relatively modern times opinions have differed but the estimate is rising steadily.
1650: James Ussher (1581-1656), Archbishop of Armagh
and Primate of All Ireland, painstakingly correlated Middle Eastern
and Mediterranean histories and Holy writ, arriving at the date
of creation: Sunday 23 October 4004 B.C. This date was included
in a 1701 authorized version of the Bible, used for 200 years
in English editions of the Bible, and came to be considered by
Christians to be as authoritative as the Bible itself. Based
on this, the earth and the universe would have been 6000 years
old in 1997. (Remembering, of course, that there was no year
"zero". We must be precise about these matters.)
For two centuries thereafter one sees little scientific discussion
of the age of the universe, partly because of lack of evidence
and theory. But people were pondering the question of the age
of the earth, and of course, the universe is very likely older
than the earth.
In around 1700 Benoit de Maillet (1656-1738) estimated the earth to be 2 billion years old, based on studies of the decline of sea levels.
A little later Buffon (1707-88) calculated the time of cooling of earth from its molten state. He estimated the age of the earth to be 75,000 years.
1800's: Charles Lyell estimated an age of 80 million years for the Cenozoic period alone, based on evolution of marine mollusks.
1897: William Thomson (1824-1907) used improved knowledge of heat conduction and radiation to estimate the earth's age by calculating the time it took to cool from an initial hot molten state. Conclusion: between 20 and 400 million years. Geologists and biologists knew from their field evidence that the earth's age must be considerably greater than that.
In about 1900 meteorite bombardment became recognized as an additional source of thermal energy during earth's history, a consideration which hadn't been taken into account in earlier cooling calculations. This suggested a longer cooling time.
In 1896, Antoine Becquerel (1852-1908) discovered radioactivity, forcing further upwards revision of the calculations of earth cooling, since radioactive decay is an additional source of thermal energy within the earth.
1901: John Joly (1857-1933) calculated the rate of delivery of salt from rivers to oceans, determining the earth's age to be 90 to 100 million years.
1905-1907: Rutherford and Boltwood measured the age of rocks and minerals by measuring radioactive decay. Ages of 500 million years to 1.64 billion years were obtained. Subsequent work found rock samples as old as 4.3 billion years. Because of convection, that lifts and buries crustal material, none of the oldest rocks survive to be dated, so the earth's age is surely greater than that of the particular rocks dated. At the same time some meteorites were determined to be 4.6 billion years old.
1929: Edwin Hubble (1889-1953) interpreted the red shift of distant galaxies as being due to the general expansion of the universe.
The rate of this expansion is called the Hubble constant, and if the universe were expanding uniformly since its beginning, would tell us how old the universe is. Extrapolating backward would bring the galaxies together about 2 billion years ago, using Hubble's original figures.
Geologists were unhappy with this figure, insisting that the earth must be at least 3 billion years old.
1947: George Gamow (1904-68) used Hubble's original data on luminosity of Cepheid variables to conclude that the universe's "expansion must have started about two or three billion years ago." In a footnote he says "More recent information leads to an estimate of somewhat longer time periods."
1952: Bart Jan Bok (1906-83) estimated that galactic clusters must be between 1 and 10 billion years old and that the age of our own galaxy must be between 2 and 5 billion years, based on the distribution of energy amongst the stars. Geologists at this time still concluded that the earth was at least 5 billion years old. Hubble's data was found to be in error. After correcting this error, the estimated age of the calculated universe was increased to 5 billion years. Still, the astronomers and geologists didn't seem to be paying attention to each other, and comparison of these estimates suggests that the earth is approximately as old as the universe.
1999: Astronomers working for NASA announced that the universe is about 12 billion years old, based on revised estimates of Hubble's constant using supernova as standard candles. If everything is expanding at an accelerating rate, as a growing number of people believe, that makes the universe about 13.5 billion years old...
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| The figure shows the best estimates at large in the western tradition with dates. The editor sees no reason to suppose that the state of enlightened bliss is about to be reached any time soon. Watch this space. |