If you try to think through what’s going on in the famous double slit experiments, the wave / particle duality is the mental puzzle that’s made its way into the scientifically curious parts of pop culture. Now, just think of light as a particle. This is supposed to be the easy part–we can deal with light as a particle or light as a wave but balk at it being both. So, imagine light as a particle with two slits before it. Odds are, you have an image in your mind. I certainly do, as I write this. In this mental image, what is it we are imagining illuminates light?

A mental image is, I think, a simulation of visual experience. During our ordinary visual experiences, it is obvious that there is an observer. Although we don’t usually think about it, if we know a little about vision we recall that the visual experience relies on light being emitted in over here, bouncing off of or being absorbed by objects, ending up in our retinas, and so on. In mental images, this is less obvious. As a simulation of an experience that has these features, a mental image implies a mental observer, mental light, and mental retinas, but the image seems to simply appear, floating freely and unencumbered, on the mental stage. We can put our implied mental retina on stage as a new character if we like, but this is an unconvincing sock puppet. The implied mental retina is part of the stage, not a character on it.

In our ordinary uses of visualization, there’s no obvious utility in trying to keep track of the stage on which mental images appear, although it can be an entertaining mental exercise in its own right. If we watch our imagined particle of light speeding towards a slit, though, we should probably pause to consider what an absurd and self-contradictory image this is. If we cast visualization as a tool rather than a stage, this is like trying to use a hammer as a hose. We should be a little surprised if it works at all, rather than puzzled when it works poorly.

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I don’t know if this line of thinking leads to any insight into physics. I doubt it does. It might be useful as a prompt to consider the relationship between our representations and the phenomena represented. We should not assume that the two are compatible, and it is not obvious what outcome we should expect when they aren’t. What kind of relationship between representation and reality should we expect when the mental representation of a phenomenon is in direct conflict with what we know of the phenomenon? Does our understanding break down completely? How much of it breaks down? Does our awareness of the representation’s deficiencies allow us to correct for them?