The 60-second Philosopher by Andrew Pessin

Author:Andrew Pessin
Language: eng
Format: epub
Publisher: Oneworld Publications

RELATED CHAPTERS: 8, 22, 41, 50

33

I CAN’T SEE FOR MILES AND MILES

Indeed you cannot. Not even for kilometers and kilometers, or meters and meters, or feet, or inches. In fact you cannot literally see any distance at all.

Imagine you have your eye on Jessie at the office. It certainly seems that you can see how far away she is from you—ten meters and counting, as Jessie sees you staring and begins to retreat. But all you can “see,” strictly speaking, is whatever is available on your retina, the membrane in the back of your eye—which provides the only way for visual information to get inside your brain. The distance between you and Jessie is measured by a straight line from Jessie to your eyeball, namely the line that each light ray travels from her to your eye. And here’s the problem: your eye only receives the “end” point of that line. You only receive the light when it hits your retina and your retina simply cannot know how far that light has traveled. So you cannot “see” how far away she is.

Yet Jessie is now fifteen meters away from you and picking up speed.

It gets worse. Again, you see things only by means of the image they cast on your retina. But now the very same retinal image can be cast by objects at almost any distances. For example, you see the moon because it casts an image of a certain size and shape on your retina. But that very same image would be cast there by a very tiny round object very close to your eye, a medium sized object at some distance away, or a great big object such as the moon at a great distance. The retinal image itself therefore carries no information about how far away its object is. And so you simply cannot “see” distance.

Yet there is Jessie now twenty meters away from you frantically dialing the police on a cell phone. How do you know this, if not by seeing it?

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