— Why does heat distort what I see?
In: Physics
When light crosses between two materials it gets bent. This is how prisms work, or maybe you’re familiar with [the light deflection between water and air?](https://media.sciencephoto.com/c0/30/81/62/c0308162-800px-wm.jpg)
Anyway, air’s density changes a lot with temperature. Hot air and cold air have very different densities and therefore bend light differently. In fact they’re so different that it’s like hot air and cooler air are two different materials, so you end up seeing light bending and distorting as it crosses temperature-changes in air, just like what happens when light goes from air to water etc.
Add to that that the hot air above direct heat sources like open flames, BBQs, and hot asphalt tends to get all swirly as hot air rises and causes turbulence. So you don’t just have one hot-cold air boundary, you have hundreds of hot-cold-hot gradients and they’re all moving and changing, each one of them bending the light a bit as it passes through. So overall it makes the whole area look all shimmery as the light gets bent and re-bent by all the temperature changes on the way through.
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