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Desert Diary
Physics/Lord Kelvin


Many people are disturbed by the lack of absoluteness of scientific thought. Unlike the race track gambler who knows beyond doubt that Sofarbehind is going to win the next one, the scientist prefers to talk about greater or lesser confidence in a scientific explanation.

But why, when theories have huge amounts of evidence, are scientists hesitant about claiming them as facts? One reason is that there always could be something unknown that will upset the apple cart. For example, in the nineteenth century, Lord Kelvin estimated the age of the earth as 25 million years by calculating how long a molten earth at 2000° Celsius would take to cool to its present temperature. Furthermore, he determined that heating of the sun by gravitational contraction would take the same amount of time—thus two independent estimates agreed, even if geologists and paleontologists didn't. Despite the elegance of his calculations, there were two things nobody knew at the time: namely, that radioactive substances in the earth generate heat and that the sun isn't heated by gravitational contraction, but by nuclear fusion.
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Listen to the Audio (mp3 format) as recorded by KTEP, Public Radio for the Southwest.


Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.

Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.