The Impossibility of Why

So I think we’ve all been rather busy here. Hence the lack of posts. I’m going to try to keep this one short but sweet. A lot of people think that physics tells us why things happen. Why is the sky blue? Why does the earth orbit the sun? Why does copper transmit electricity so well? These all seem like perfectly reasonable questions to ask. Questions that we, as physicists can answer. Yet, I entitled this post the impossibility of why. In general, questions about why are not good questions for physicists More accurately we answer questions about how. Or what. What phenomena causes use to see the sky as blue? What forces cause the earth to orbit the sun? How does copper transmit electricity so well? In general, we can’t answer a question of why. A friend once asked me (at the end of a talk I gave, nonetheless) ‘why can’t two electrons be in the same quantum state, while two bosons can?’. That’s an example of a question that we as physicists can’t answer. We have no idea about why that is. The best answer we can give is ‘I don’t know. However, experiment tells us that’s what happens.’ In general, physics cannot be built in a vacuum. We cannot sit down and write down the laws of nature. Not without looking at nature. That is the difference between physics and mathematics. Mathematicians can construct arbitrary logical systems. Anything with a given set of logical axioms that is consistent can be a valid system of mathematics. Of course, only a few are useful systems. This allows mathematicians to generate exceedingly interesting playgrounds for the mind. Physics is meaningless without experiment. We have to test our theories against the world as we know it. We can no more explain why F = ma or the Pauli exclusion principle is the way of the world than we can answer why the universe exists. We can (at least we hope) tell you how the world works, what to expect, cause and effect. But why we found this particular set of rules and not another, different but consistent system, is something we can’t, and usually don’t try to answer. In many ways, I think this reduces much of the perceived conflict between religion and science. As long as one doesn’t read God’s (or gods, depending on your religion) word literally, religion is an attempt to explain why. Physics is an attempt to explain how. There’s no inherent conflict in that. At least, that’s my thinking.

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By Jesse