Physics is Ultimately Subjective

N.B. A basic and perhaps obvious point that nonetheless I think people get confused about. Despite the somewhat provocative title, my goal is not to say anything new to the average Less Wrong reader, only to emphasize a point and try to explain it so that it can be clearly seen.

Summary: Physics, by which I mean models of how reality works at the most fundamental level, is a subjective endeavor. Physics seems to be objective, but that’s because there’s high intersubjective consensus about which models best explain and predict reality. Rounding this off to objective causes confusion, and the point generalizes for all seemingly objective things.

Art, and in particular modern art, is highly subjective. Some people are impressed by the artistry of paint splatters, blank canvases, and signed toilets, while others roll their eyes. People like different things and only sometimes agree, so we generally accept that art is subjective.

Assessing a work of art looks sort of like this:

A person sees some art and they subjectively judge it good or bad.

Physics, by contrast, seems totally objective. The world is how it is, and our models of it are good or bad insofar as they accurately and precisely describe the world. Whether or not you like general relativity, for example, has no bearing on whether it’s a good theory. All that matters is how well general relativity explains and predicts what we observe.

The picture for physics might look like this:

Physics theories describe reality and are objectively good or bad.

But both of these pictures are wrong! The first leaves out the detail that art has to exist in reality—it’s not art first, but atoms first, and it only becomes art when it’s observed by someone who thinks of it as art. The second leaves out that theories of physics don’t exist on their own, they exist in our heads. To suppose otherwise is to suppose the existence of a paradoxical view from nowhere. So really both pictures are the same picture:

Judgments are mediated by agents.

What does this mean for art and physics? Art is just as it was. The picture only makes it clearer that art doesn’t exist independently: it exists within someone’s experience of the world. For physics, though, it’s a bigger deal. Physics feels like it’s objective, and physical theories seem like they should be good or bad regardless of who does the assessing. And our experience matches this: people disagree about what art is good, but almost everyone agrees about what physics is good. What gives?

The difference is that art has low intersubjective consensus and physics has high. But that’s just a fancy way of saying people strongly agree about physics and only weakly agree about art. Why is that the case?

We ultimately assess art by checking to see if we like it. The whole point of art is to make things we like looking at. We assess physics by checking to see if our theories match our observations. That’s the point of physics: to model reality. So they behave differently, because even though in both cases each person independently runs their own evaluative function for art and physics, the art functions are loosely constrained while the physics functions are highly constrained.

At this point you might be frustrated that I’ve given a convoluted explanation of what we really mean—rather than what philosophers literally mean—when we say that something’s objective. And fair, in everyday use you can get away with saying that physics is objective even though that’s not literally true. But sometimes the details matter, and even if they don’t, it’s still good epistemic practice to be precise whenever possible to avoid injecting confusion into your thinking.

But I know some of you will still write that physics, and other seemingly objective things, are objective rather than have high intersubjective agreement. Why? For one, “objective” is shorter. For another, there are people who deny intersubjective consensus, not on grounds of specific evidence, but because they deny the value of evidence all together. That is, there’s people who believe in invisible dragons and they are, in a real sense, the enemies of good epistemology. It’s tempting to line up against them, reverse their stupidity, and claim physics, and much else, can be objectively known.

But just because something seems like a good idea if we go up one or more simulacrum levels doesn’t mean it’s right. Subjectivity gets a bad rap because of its connotations, not because of what the concept actually points to. As bounded agents embedded in the world, we can do nothing other than deal with the world subjectively with our knowledge mediated by our experiences. Any sense of objectivity we have comes from intersubjective agreement that gives us confidence that it’s not just our observations that support a belief but everyone’s observations.

It’s worth remembering that what looks to be objective is actually the result of intersubjective agreement, and that agreement comes from the aggregation of many individual, subjective assessments and not from reality itself…except insofar as we see subjective evidence to suggest a persistent world that exists independent of our experiences.