Why Can't We See Air?

 Why Can't We See Air?

We can feel air's its usual presence when we move through it, a comfortable presence when walking across a gentle breeze in the spring. So, why can't we see the air?

To answer the question, we must first talk about how we can see things.

For us to see an object, we need light. After the light has hit an object, some of the colors will be absorbed by it, and other colors will be reflected by it. Those colors that are reflected by the object travel to your eyeball and are interpreted by your brain. What this means is that if you see a red firetruck, then that object has reflected red light into your eyes, but it has absorbed all of the other colors of light that have hit it.

So, why is air invisible?

Since our eyes can only see within a very narrow range on the color spectrum, anything that we are able to see must be reflecting light that fits within that range. For air, it turns out that the colors that are able to be reflected do not lie in that visible range. (Air molecules are sparsely distributed, so light passing through the air has a small (but non-zero) chance of interacting with air molecules along its trajectory. However, if there's a lot of air (imagine a 50-mile stretch), lots of these improbable interactions add up, and the effect of the air molecules becomes visible). If humans were capable of seeing those particular reflections, our field of vision would be constantly disrupted by the air in front of us. Every day would be like living in the middle of a giant cloud; small changes in color would be noticeable, but you wouldn’t be able to see clearly because the cloud is in the way.

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