The looking glass and its trickery
A recent New York Times article had a curious revelation about perception, citing research by Professor Marco Bertamini and colleagues at the University of Liverpool. Whereas most people assume that the reflection of their face in a mirror is the same size as their face, and will remain the same size even when they step back, that’s not the case at all.
In fact, if you circle the outline of your face on the mirror with a marker, it turns out to be exactly half the size of your actual face. Step back and the outline will remain half the size of your face. But the reflection of something else moving in the room will indeed grow or shrink in our view.
No matter how close or far you are from the mirror, it’s always halfway between you and your reflection. That’s why it’s half your size.
The Times quotes the university’s Rebecca Lawson as suggesting you imagine an identical twin — six feet tall, like you — standing in the room with you, on the other side of a movable partition.
“How tall would a window in the partition have to be to allow you to see all six feet of your twin? The window needs to allow light from the top of your twin’s head and from the bottom of your twin’s feet to reach you, Dr Lawson said.
“These two light sources start six feet apart and converge at your eye. If the partition is close to your twin, the upper and lower light points have just begun to converge, so the opening has to be nearly six feet tall to allow you a full-body view.
“If the partition is close to you, the light has nearly finished converging, so the window can be quite small. If the partition were halfway between you and your twin, the aperture would have to be — three feet tall.
“Optically, a mirror is similar,” Dr Lawson said, “except that instead of lighting coming from your twin directly through a window, you see yourself in the mirror with light from your head and your feet being reflected off the mirror into your eye.’”
