General Question

dookie's avatar

Can a human see a single photon?

Asked by dookie (61points) September 9th, 2008
11 responses
“Great Question” (3points)
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damien's avatar

Errrm, no. Photons are tiny. Really, really tiny.

Harp's avatar

The individual light receptors (rods) in the eye can respond to a single photon, but that reception won’t trigger a signal to the brain, so it can’t really be said that that photon is “seen”. For a signal to be sent, at least between five to nine photons must reach the rods within a time period of one hundred milliseconds. (source)

Harp (19174points)“Great Answer” (10points)
shilolo's avatar

This sounds a lot like a homework question. I suggest you look up rhodopsin (the protein) that senses photons, and go from there.

Les's avatar
Read about photons here. Photons are not really “things” like you’d call an atom or a molecule a thing. It is more of a concept of quantized energy. Mmm.. Planck.

Les (10005points)“Great Answer” (0points)
damien's avatar

Oh. I think I took that too literally.

sheepishly scoots out of the way

8lightminutesaway's avatar

well…. one of my physics teachers argued that you could. as a homework assignment, he had everyone go home find the darkest room possible, and to make sure no light was coming in and then wait until you see something. Not many people actually did it, but you were supposed to be able to see spots or small flashes of light after about 15 minutes when your were adjusted as much as they could. those spots/flashes he said were photons.

Knotmyday's avatar


Those flashes are called phosphenes. Your physics teacher needs to be spanked and sent to bed early.

Zaku's avatar

There are some juicy photons to see in many of the Star Trek movies. I recommend Star Trek II: The Wrath of Khan for good photon torpedo viewing.

Mamradpivo's avatar

No. We can see a general region where a single photon may or may not have existed immediately before we saw it. The mere act of looking for a photon changes its placement. At least, that’s according to my understanding of quantum physics.

Nullo's avatar

An old Psych professor once said that the cells lining your retina were thought to be sensitive enough to detect a single photon.
That said, you probably wouldn’t be able to get anything coherent out of it.

tigress3681's avatar

@Harp Your answer is right on the money, good job!

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