Perry, Kelvin, and the age of the sun
Department of Mathematics and Department of Physics, Tulane University, 70118
New Orleans, USA
Received in final form: 2 November 2012
Published online: 6 December 2012
Lord Kelvin argued that the Sun had to be between 20 and 100 million years old, based on the assumption that the Sun’s energy source was gravitational contraction. As everyone now knows, the Sun’s actual power source is the thermonuclear fusion of hydrogen into helium. But Kelvin’s number is based on a physical assumption for which he could give no justification: the Sun’s density is approximately constant. Had Kelvin assumed instead that the Sun had a small core near a black hole radius – an assumption allowed by the knowledge of physicists at the end of the nineteenth century – he would have obtained an age for the Sun as long as 10 trillion years, completely consistent with the long time scale required for evolution. Conversely, had Kelvin accepted the geologists’ time scale, he would have been forced to acknowledge the existence of very dense objects, making it easier for twentieth century astronomers to accept the existence of black holes and neutron stars.
© EDP Sciences, Springer-Verlag 2012