Can Physics Account for Our Whole Reality?

Mathematician turned philosopher Nancy Cartwright says no; reality is ultimately too complex for that

If only we could reduce the world to an equation, many think — preferably one that is solvable (unlike what happened in what happened in Restaurant at the End of the Universe), we would understand life better.

University of Durham philosopher Nancy Cartwright takes issue with that, arguing that the universe is “beautifully dappled, and requires a dappled science to explain it.” She is the author, most recently, of A Philosopher Looks at Science (Cambridge University Press, 2022). And she says,

 If physics is to have total dominion, she must not only help out with chemical bonding, signal transmission in neurons, the flow of petrol in a carburettor, and the like. She must be able in principle to entirely take over the disciplines that usually study these things, to explain and predict the rise in teenage pregnancies, the current level of inflation, the Protestant Reformation, and the fate of migrants crossing the channel. Plus, she must be able to get me off the hook for shouting at my daughter: after all, I was just obeying the laws of physics.

Nancy Cartwright, “Physics can’t deal with reality’s complexity” at IAI. News (October 17, 2022)

Now that she mentions it, pop psychology has featured many theories that tie together disparate phenomena like inflation, the Reformation, and shouting at loved ones. It’s comparatively easy to link very complex events to one another if we are allowed to choose any link we wish. Some might link Hurricane Ian with municipal elections in Vancouver and with high-starch diets in Texas. It takes creativity but many people have plenty of that.

Physics sets itself a harder goal: showing the numbers (serious numbers, not pop stats) and a rigorous theory behind them. That necessarily means leaving out a great deal, assuming that what is omitted is subsumed in the theory. But is it?

The idea of physics as queen of all that happens has powerful implications about just what the world we live in must be like. It must be a world made up entirely of the basic entities of physics—fundamental particles, curved space-time and the like — entities that have only the mathematical features that physics equations describe, features that often have no names of their own other than the names of the mathematical objects that are supposed to represent them, like the “quantum state vector” and the “metric tensor” of general relativity. The world has to be that way since these are the kinds of features that physics can rule.

Nancy Cartwright, “Physics can’t deal with reality’s complexity” at IAI. News (October 17, 2022)

She offers an alternative approach:

Instead of supposing that physics must be queen of all we survey, I recommend we construct our image of what an ultimate science might be like on the basis of what current science is like when it is most successful, from putting people on the moon to devising and carrying out a plan for the complete evacuation of the Royal Marsden Hospital (which took just 28 minutes when called into play by a gigantic fire, 2 January 2008)… This is a world in which irritability, generosity and social exclusion can affect what happens just as gravity and electromagnetic repulsion can.

Nancy Cartwright, “Physics can’t deal with reality’s complexity” at IAI. News (October 17, 2022)

As she says, that’s the world we actually live in, a world of many tiny, intersecting worlds where causes can include anything from fundamental physics to social psychology.

Physics, after all, doesn’t tell us about ethics: whether or not to stand up to the bully, whether we are our neighbors’ keepers, or whether it is worthwhile to gain the whole world at the loss of our souls.

Physics lies at the base of things, yes. But beyond a certain level of complexity, things can’t be reduced to their constituent parts without losing what they intrinsically are. Ice cream is not just its constituents. A birthday party is not just a cake and decorations. Our homes are not just their replacement value. Many complexities are simply irreducible. That’s why really simple philosophies along the lines of “It all comes down to… ” don’t really work out.

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