Brilliant Blunders: From Darwin to Einstein - Colossal Mistakes by Great Scientists That Changed Our Understanding of Life and the Universe by Mario Livio

that Kelvin produced—roughly one hundred million years—was broadly consistent with an earlier estimate he had made of the age of the Sun. This was significant, since even some of Kelvin’s contemporaries realized that the strength of his argument about the age of the Earth derived at least part of its credibility from his solar calculation. Kelvin’s basic premise in the paper “On the Age of the Sun’s Heat,” and in a few similar later papers, was not very different from his central thesis in his analysis of the age of the Earth. The key assumption was that the only source of energy that the Sun had at its disposal was the mechanical gravitational energy. This was supposed to be supplied either by the falling-in of meteors, as Kelvin originally thought, but later rejected, or, as Kelvin proposed later and forcefully reiterated in 1887, by the Sun continually contracting, and dissipating its gravitational energy in the form of heat. Since, however, the energy supply was clearly not infinite, and the Sun was unceasingly losing energy by radiation, Kelvin concluded justifiably that the Sun could not remain unchanged indefinitely. To calculate its age, he borrowed elements from theories for the formation of the solar system proposed by the French physicist Pierre-Simon Laplace and the German philosopher Immanuel Kant. He then supplemented those with important insights on the Sun’s potential contraction gained from the work of his contemporary German physicist Hermann von Helmholtz. Weaving all of these ingredients into one coherent picture,Kelvin was able to obtain a rough estimate of the Sun’s age. The last paragraph in Kelvin’s paper reflected his acknowledgement of the many uncertainties involved:
     
It seems, therefore, on the whole most probable that the sun has not illuminated the earth for onehundred million years, and almost certain that he has not done so for five hundred million years. As for the future, we may say, with equal certainty, that inhabitants of the earth can not continue to enjoy the light and heat essential to their life for many million years longer unless sources now unknown to us are prepared in the great storehouse of creation.
     
    As I shall describe in the next chapter (and explain in detail in chapter 8), the last sentence proved to be truly farseeing.
    The fact that the calculated ages of the Sun and the Earth turned out to be comparable—even though the estimates were determined independently—made Kelvin’s calculation more compelling, since there was every reason to suspect that the entire solar system had formed around the same time. Still, quite a few British geologists remained unconvinced. It almost seemed as though, for some of them, it was more convenient to explain everything not by the laws of physics but rather by what the American geologist Thomas Chamberlin cynically termed in 1899 “reckless drafts on the bank of time.” The best illustration of the skeptical attitude toward Kelvin’s findings is a fascinating exchange Kelvin had in 1867 with the Scottish geologist Andrew Ramsay. The occasion was a lecture by the geologist Archibald Geikie on the geological history of Scotland.Kelvin later described the conversation he had with Ramsay immediately following the talk, noting that almost every word of it remained “stamped on my mind”:
     
I asked Ramsay how long a time he allowed for that history. He answered that he could suggest no limit to it. I said, “You don’t suppose geological history has run through 1,000,000,000 [one billion] years?” “Certainly I do!” “10,000,000,000 [ten billion] years?” “Yes!” “The sun is a finite body. You can tell how many tons it is. Do you think it has been shining for a million million years?” “I am as incapable of estimating and understanding the reasons which you physicists have for limiting geological time as you are incapable of understanding the geological reasonsfor our unlimited estimates.” I