The Atheist's Guide to Reality_ Enjoying Life Without Illusions - Alex Rosenberg [26]
This is a very stringent demand. It goes far beyond the requirement that biology be compatible with physics, not disagree with it. Scientists have long demanded consistency with well-established physics as a requirement on all other theories in science. In fact, the nineteenth-century critics of Darwin’s theory were eager to adopt the standard of consistency with physics as a way to blow the theory of evolution out of the water. One of these opponents was Lord Kelvin, of second law fame. Soon after the publication of On the Origin of Species, Kelvin argued that the Darwinian theory of natural selection had to be false. Darwin estimated that at least 300 million years had been required for natural selection to provide the level of adaptation we see around us. (He was off by three orders of magnitude—1,000 percent.) But Kelvin thought that he could prove that the sun was no more than 20 million years old. Given the amount of energy it generated and the best theory of heat production available at the time (Kelvin’s own theory), the upper limit on the sun’s age was 40 million years. So there could not have been enough time for natural selection to provide adaptations by the process of natural selection.
Of course, Kelvin didn’t have the slightest idea what the real source of the sun’s energy is. It was only after World War II that Hans Bethe won the Nobel Prize in Physics for figuring out that the sun is a very long-lasting hydrogen-fusion-driven explosion. But in 1870, Kelvin’s objection had to be taken pretty seriously. Explanations of adaptation must be compatible with the correct physical theory, and in 1870, Kelvin’s was the best-informed guess about the physics of solar energy. Darwin himself owned up to being very worried about this problem, since he accepted the constraint of consistency with physics as a requirement on any theory of adaptation.
Kelvin was wrong about the age of the sun (and therefore wrong about Darwin). He was, of course, right about the second law of thermodynamics. Since the nineteenth century, Kelvin’s discoveries about the nature of heat, as reflected in the first and second laws of thermodynamics, have become established physics. Any explanation of adaptation had better not fall afoul of them.
But as noted, scientism requires more than just logical compatibility. If the physical facts fix all the facts, then the emergence and persistence of adaptations had better result from the laws of physics alone. In fact, they had better be the result of the operation of thermodynamics. Otherwise we will have to admit that there is more going on in the universe than what physics tells us there is. Some physicists may be okay with this, but scientism has to reject it. We need an explanation of adaptation that makes it the consequence of purely physical processes. We need to show that the process Darwin discovered starts with zero adaptations and builds them all as a result of the laws of physics alone. Otherwise we will find ourselves on a slippery slope. If we have to add a separate and independent Darwinian theory to physics for completeness’s sake, who’s to say completeness won’t require us to add Sigmund Freud’s, or Karl Marx’s, or, for that matter, Jacques Derrida’s theory to physics. Worst of all, what if completing the picture requires the theism of the Abrahamic religions—Judaism, Christianity, and Islam?
We have to satisfy ourselves not just that Darwin’s theory is true, but that physics is enough to make it true. And we need to show that when it comes to explaining adaptation, the causal closure of physics makes Darwinism the only game in town.
Although Darwinian biologists have not noticed, their theory also needs the causal closure of physics. It’s not enough to show that Darwinian theory gets it mostly right