What life wants: Dead matter has no goals of its own, yet life is constantly striving. That makes it a deep puzzle for physics
The separation between sciences is crumbling. Nature doesn’t recognise disciplinary borders, and as we deepen our understanding, we see more of what these traditionally distinct branches of science have in common. There remain, however, curious hold-outs.
Physics deals with the basic properties of matter and energy and how they interact. Chemistry asks how atoms get together to form more complex molecules and what effect this has on the resulting substances. What both have in common is that they study inanimate matter.
Biology, on the other hand, studies living organisms. And here we encounter the central obstacle to seeing all of natural science as one big coherent whole. Inanimate matter seems to obey the laws of nature without exception and down to the last letter. Living things, by contrast, appear to have a will of their own. They are best understood — perhaps even best defined — by what might be called purposiveness. They try to do things, and while they cannot violate the laws of nature, they certainly can exploit them in order to realise their goals. You can’t say the same for inanimate matter.
It is hardly surprising, then, that the links between physics and chemistry should be much better established than the links between either of these fields and biology. Very few scientists would deny that the laws of quantum physics (our most accurate fundamental laws of nature at present) also fully explain the laws of chemistry. Yes, it might be difficult to calculate all the intricate details of certain complex reactions using physics alone, but most scientists agree that chemistry does nevertheless follow in its entirety from quantum theory. Biology seems like a different matter, though. Some parts of biology look detached from chemistry, let alone reducible to quantum physics.