Feeblea

Feeblea, a patient hooded watcher, opens a dark wooden box with a faint glow inside.

The Physics

In 1909 a young G. I. Taylor photographed the shadow of a needle with light so dim that, in modern terms, rarely more than one photon was in the box at a time (Proc. Camb. Phil. Soc. 15, 114). His longest exposure ran about 2000 hours, roughly three months. The diffraction fringes were just as sharp as with bright light.

t_exposure ≈ 2000 h

• t_exposure: exposure time of the faintest photograph

It is often called the first single-photon interference experiment.

Honest caveat: Taylor did not detect single photons and was testing a different idea; a classical wave also explains his result. Truly single-photon interference came in the 1980s.

On the sticker

Feeblea leans over an open wooden box with a faint warm light inside. Printed text: FEEBLEA with the line ~2000 h. Pixel-art kiss-cut vinyl sticker, white, in 2″, 3″, 4″ and 6″ sizes.