The Physics of the Present

What happens when you see something? Say, for the sake of argument, this sentence you are now reading. Dismissing the whole business of how the brain processes visual stimuli, let’s set our focus on the travel time of the information you receive. And to simplify matters even further, let’s also ignore how atoms absorb and reemit light, taking only into account the classical propagation of photons (or the basic units of all light).

We can then agree that photons of light are bouncing around the room you’re currently at. Either because a window is open or a lamp is on (or maybe a combination of both). And in their bouncing they happen to hit things, such as the surface of the device you’re using right now to read.

Some of this prancing light then gets absorbed, while some is reflected outwardly in many directions. After all, electronic gadgets absorb and emit light in different ways that remain encoded in the reflected light. A fraction of this reflected light then travels from the device to your eyes, and thanks to the brain’s wondrous ability to decode sensory information, you are able to read these words.

All this seems to be immediate, right? You might even go so far as to assert, “I’m reading this sentence right now.’’

But, are you really?

Believe it or not, you’re not.

Allow me to explain.

Since light travels at a finite speed, it takes time for it to bounce from your gadget to your eyes. If you are looking at your device at a distance of 30 cm from your eyes, for example, the travel time of light from said gadget to your eyes is about one nanosecond (or one billionth of a second). As a result, when you see a word, you are seeing it as it appeared some time in the past. And this same process repeats itself for every object you observe and every person you talk to.

For instance, take a look at the objects around you. The light bouncing from each one of them takes a different time to get to your eyes. The brain then has the task of integrating these different sources of visual information. And it is so good at doing this that it fools you into thinking that you are looking at everything “at once”, in spite of the different distances said objects have from you.

In reality though, there is a contrast. Although one that we can’t distinguish, since the differences in light’s arrival time are much smaller than what our eyes can discern and our…