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Can a Human See a Single Photon? (1996)

math.ucr.edu

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Re: Can a Human See a Single Photon? (1996)

#91

Post by yamtaddle »

phailhaus wrote: post #51
mensetmanusman wrote: post #38

Earlier quoted context omitted.

Would be fun to see if it’s possible to set up the experiment as a double slit. Would humans sense an interference pattern? Is the back of an eye a sufficient observer? :)

Yep! Any interaction counts. If something interacts with a photon, and that interaction can only happen if it goes through one of the two slits (i.e., it tells you "which way" the photon went), then the interference pattern will disappear.

What escapes my understanding with the whole "interaction is observation" thing is that I don't get how anything could ever not be interacting with a whole lot of other stuff. Gravity and EM fields are everywhere. Even if photons are somehow immune to that (which, they're not, because gravity can re-direct photons) it's my understanding that we can see the same interference patterns with particle streams of ordinary matter, and I can't for the life of me figure out how those could ever not be interacting with basically everything remotely nearby, including the entire test apparatus.

Re: Can a Human See a Single Photon? (1996)

#93

Post by devindotcom »

Sharlin wrote: post #71
notfish wrote: post #65

This fun fact gets even more fun when you consider that a human radiates a nonzero amount of visible light via blackbody radiation - on the order of a photon/minute - which means that in theory, with some luck, in an otherwise cold and completely dark room, two humans might be able to notice each other through vision alone. You can check my math here if you want to convince yourself: https://www.spectralcalc.com/blac…

A bit more than just “some” luck needed for one of those photons to be emitted straight into the other person’s pupil! The angular diameter of a human pupil (~5 mm) at a distance of ~2 m is about 0.2 degrees, taking the small angle approximation. So the area of the pupil is maybe 0.04 square degrees, or around one millionth of a full solid angle (~41,000 square degrees). Assuming a spherical isotropically radiating h…

>Assuming a spherical isotropically radiating human

...in a vacuum, of course!

Re: Can a Human See a Single Photon? (1996)

#94

Post by phailhaus »

yamtaddle wrote: post #91
phailhaus wrote: post #51

Earlier quoted context omitted.

Yep! Any interaction counts. If something interacts with a photon, and that interaction can only happen if it goes through one of the two slits (i.e., it tells you "which way" the photon went), then the interference pattern will disappear.

What escapes my understanding with the whole "interaction is observation" thing is that I don't get how anything could ever not be interacting with a whole lot of other stuff. Gravity and EM fields are everywhere. Even if photons are somehow immune to that (which, they're not, because gravity can re-direct photons) it's my understanding that we can see the same interference patterns with particle streams of ordinary…

> Gravity and EM fields are everywhere.

And now you understand why "quantum gravity" is such a big question in physics right now! We don't understand it all. I actually don't know anything about how EM fields affect superposition, perhaps someone else can chime in.

Re: Can a Human See a Single Photon? (1996)

#95

Post by ASalazarMX »

devindotcom wrote: post #93
Sharlin wrote: post #71

Earlier quoted context omitted.

A bit more than just “some” luck needed for one of those photons to be emitted straight into the other person’s pupil! The angular diameter of a human pupil (~5 mm) at a distance of ~2 m is about 0.2 degrees, taking the small angle approximation. So the area of the pupil is maybe 0.04 square degrees, or around one millionth of a full solid angle (~41,000 square degrees). Assuming a spherical isotropically radiating h…

>Assuming a spherical isotropically radiating human ...in a vacuum, of course!

In a perfectly dark room, isolated from cosmic rays, at zero Kelvin.

Re: Can a Human See a Single Photon? (1996)

#96

Post by ask_b123 »

Sharlin wrote: post #71
notfish wrote: post #65

This fun fact gets even more fun when you consider that a human radiates a nonzero amount of visible light via blackbody radiation - on the order of a photon/minute - which means that in theory, with some luck, in an otherwise cold and completely dark room, two humans might be able to notice each other through vision alone. You can check my math here if you want to convince yourself: https://www.spectralcalc.com/blac…

A bit more than just “some” luck needed for one of those photons to be emitted straight into the other person’s pupil! The angular diameter of a human pupil (~5 mm) at a distance of ~2 m is about 0.2 degrees, taking the small angle approximation. So the area of the pupil is maybe 0.04 square degrees, or around one millionth of a full solid angle (~41,000 square degrees). Assuming a spherical isotropically radiating h…

Do we have to account for blink rate?

Re: Can a Human See a Single Photon? (1996)

#97

Post by ASalazarMX »

de6u99er wrote: post #84
Sharlin wrote: post #71

Earlier quoted context omitted.

A bit more than just “some” luck needed for one of those photons to be emitted straight into the other person’s pupil! The angular diameter of a human pupil (~5 mm) at a distance of ~2 m is about 0.2 degrees, taking the small angle approximation. So the area of the pupil is maybe 0.04 square degrees, or around one millionth of a full solid angle (~41,000 square degrees). Assuming a spherical isotropically radiating h…

What if the room was made out of perfect mirrors?

It's still more likely to be reabsorbed by other part of the body than the other's retinas. Wonder if anyone will dare to do the math.

Re: Can a Human See a Single Photon? (1996)

#98

Post by sbaiddn »

ilyt wrote: post #7
sbaiddn wrote: post #4

Question in the title -> No. TL/DR: No, we cant. The retina itself can respond to a single photon, but we are not retinas. Instead, the eye filters out this low light sensitivity lest we go crazy with the resulting visual noise at night.

So that would be yes but our noise filter in brain doesn't let us see it

You are not a retina. You cant see photons.

Re: Can a Human See a Single Photon? (1996)

#99

Post by thesimonlee »

eternauta3k wrote: post #90
notfish wrote: post #65

This fun fact gets even more fun when you consider that a human radiates a nonzero amount of visible light via blackbody radiation - on the order of a photon/minute - which means that in theory, with some luck, in an otherwise cold and completely dark room, two humans might be able to notice each other through vision alone. You can check my math here if you want to convince yourself: https://www.spectralcalc.com/blac…

Does an infrared photon have enough energy to stimulate a rod?

Definitely. 20 years ago when homes were not littered with LEDs all over, I would wake in the night to total blackness. I could still find my way around the house just able to see based on what is I suppose a noise floor of ambient temperature. Go into the kitchen & behold the stove top emitting 'bright' white light, from I suppose a temperature of around 30degC /90F.

Obviously everything is a blackbody, but those photons surely can't be 'single' visible ones.

Re: Can a Human See a Single Photon? (1996)

#100

Post by kulahan »

phailhaus wrote: post #94
yamtaddle wrote: post #91

Earlier quoted context omitted.

What escapes my understanding with the whole "interaction is observation" thing is that I don't get how anything could ever not be interacting with a whole lot of other stuff. Gravity and EM fields are everywhere. Even if photons are somehow immune to that (which, they're not, because gravity can re-direct photons) it's my understanding that we can see the same interference patterns with particle streams of ordinary…

> Gravity and EM fields are everywhere. And now you understand why "quantum gravity" is such a big question in physics right now! We don't understand it all. I actually don't know anything about how EM fields affect superposition, perhaps someone else can chime in.

The feeling of asking a question and realizing you've reached the edge of human understanding is very fun
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