Sun in a Bottle - Charles Seife [17]
This baffled Thomson. The sun was emitting energy, and things that emit energy tend to cool down over time. So how can the sun stay so hot? Perhaps it was able to replenish its energy reserves by burning fuel—but what sort of fuel could it be using? It couldn’t be burning like a giant charcoal; burning is merely a chemical reaction, and no known chemical reaction could release the sorts of energy that the sun was radiating. No fire could generate that much heat. Could the sun be getting energy from another source—by gravity, perhaps? Meteors occasionally strike the sun, adding energy to the solar furnace, but there aren’t that many meteors around, and their energy is just a tiny drop in the tsunami of power coming from the sun. Thomson knew of no possible way to generate the quantity of energy that was escaping the sun every second, yet the first law of thermodynamics dictates that the energy has to come from somewhere.
It was clear to the physicist: no mechanism—chemical, gravitational, electrical, or whatever—existed that could generate the amount of energy the sun was emitting every moment. Since energy can’t be created out of nothing, the sun must be depleting its energy reserves at an enormous rate. And that meant that the sun must be slowly getting colder and colder. Unable to replenish its reserves through any means known to man, the sun, presumed to be a gigantic ball of hot liquid, must slowly be cooling down.
Once Thomson reached that conclusion, he wondered: If the sun is merely a huge molten sphere of liquid, where did it get its energy in the first place? The only answer he could think of was the energy due to gravitation. Imagine that the sun came from an enormous cloud of tiny rocks. Those rocks are attracted to one another by the force of gravity. Under their mutual attraction, they begin falling toward one another. As they fall inward toward the center of the cloud, they move ever faster. The cloud of rocks begins to collapse. The individual rocks speed inward quicker and quicker, because their gravitational energy is being converted into kinetic energy—the energy of their motion. As the fast-moving rocks stream toward the center of the cloud and collide, their kinetic energy gets converted into heat energy: the cloud heats up. Eventually, it gets so hot it glows.
Thomson calculated how hot such a protosun could have been. Then he calculated how long it would have taken to cool to its present temperature. Not long. The sun wasn’t more than a few tens of millions of years old, not long enough for the long, slow process of evolution Darwin proposed.
In fact, Darwin was deeply shaken by the calculations. He considered Thomson’s challenge to evolution “one of the gravest” that the theory had to face, and he could do little to counter it other than argue that scientists did not have a perfect understanding of the nature of the universe.
It was an impasse. The laws of physics seemed to say one thing, while the observations of biologists seemed to tell another.
Physicists would have to follow a tortuous path before they could resolve the contradiction—a path that led, first, to understanding the mystery of matter.
By the end of the nineteenth century, physicists and chemists had unraveled many of the mysteries of the universe. Isaac Newton had divined the physical laws that govern how objects move and how gravity works. James Clerk Maxwell had figured out the subtle interrelationships between electric and magnetic forces. Thermodynamicists had codified