Photon Wave Nature: Exploring Vision in Quantum Terms

[durant35]

I red that photon has wave properties so it can go through both slits simultaneously in the double slit experimen.
What about photons that hit our eyes and construct our vision? How do we know which path they traveled and what they reflected, or to say it better how would you describe the propagation of light with respect to our eyes in quantum terms? Thanks in advance.

 

[Orodruin]

Images in your eyes are not created from single photons.

 

[durant35]

So wave of light with billions of photons can be said to connect my eyes with the object I am perceiving?

 

[bhobba]

So wave of light with billions of photons can be said to connect my eyes with the object I am perceiving?

You need to be more precise with what, in this context, you mean by connect.

Generally photons are reflected, absorbed and emitted by objects, and as they impinge on the eyes our brain decodes that as an object.

Thanks
Bill

 

[durant35]

By that I mean a photon has a wave nature which makes it travel in all possible directions at once. So how can we know what do indvidual photons represent if they may pick up information from more than one thing, and how do we know that the light that strikes our eyes directly connects us with the object since an individual photon has wave nature and travels many paths?

 

[Nugatory]

By that I mean a photon has a wave nature which makes it travel in all possible directions at once. So how can we know what do indvidual photons represent if they may pick up information from more than one thing, and how do we know that the light that strikes our eyes directly connects us with the object since an individual photon has wave nature and travels many paths?

Photons aren't what you think they are. They don't travel in the sense that you're using the word; I can use a wave equation to calculate the probability of finding a photon at a given position if I look there but that doesn't mean they "have a wave nature"; and although I calculate probabilities on all paths that doesn't mean the photon actually takes all paths.

To understand light and vision, you need a different model. Ordinary classical no-QM electrodynamics says that light is electromagnetic radiation, traveling waves in the electrical and magnetic fields in a given region of space. Some of these light waves are reflected from (or emitted by) the object that you're looking at; these ordinary boring classical no-QM waves enter your eyes and strike your retina. Only then do photons come into the picture: when electromagnetic radiation interacts with matter (in this case, your eyes) it always delivers its energy in discrete unit at a single point. Whenever a bit of energy is delivered to a particular spot we say "a photon hit there", and the probability of a photon hitting at a given point is proportional to the intensity of the electromagnetic radiation at that point.

 

[durant35]

Photons aren't what you think they are. They don't travel in the sense that you're using the word; I can use a wave equation to calculate the probability of finding a photon at a given position if I look there but that doesn't mean they "have a wave nature"; and although I calculate probabilities on all paths that doesn't mean the photon actually takes all paths.

To understand light and vision, you need a different model. Ordinary classical no-QM electrodynamics says that light is electromagnetic radiation, traveling waves in the electrical and magnetic fields in a given region of space. Some of these light waves are reflected from (or emitted by) the object that you're looking at; these ordinary boring classical no-QM waves enter your eyes and strike your retina. Only then do photons come into the picture: when electromagnetic radiation interacts with matter (in this case, your eyes) it always delivers its energy in discrete unit at a single point. Whenever a bit of energy is delivered to a particular spot we say "a photon hit there", and the probability of a photon hitting at a given point is proportional to the intensity of the electromagnetic radiation at that point.

Thanks for the effort but it seems way too complex for me to understand. I may shorten my question, considering that photons distribute as probability waves how can I know that the light that represents the object and hits my eyes really represents the object since photons can be found anywhere. In SR the light reflects of the object and hits my eyes in a deterministic way, what's different here and how do we know that light actually represents what we see if it is based on probability

 

[Orodruin]

We know it because the classical limit of quantum electrodynamics gives you back classical electrodynamics. You are back to the classical description.

 

[durant35]

We know it because the classical limit of quantum electrodynamics gives you back classical electrodynamics. You are back to the classical description.

Ok, thanks. So what are the conditions? Macroscopic objects and much light reflected from them?

 

[Nugatory]

Thanks for the effort but it seems way too complex for me to understand.

Then you can further simplify it: Just stop reading at the point where I said "Only then do photons come into the picture...". You've confused yourself because you're trying to explain what's going on in terms of photons.

The only reason to ever introduce photons into any discussion of light is because you want to understand some uniquely quantum effects; otherwise you're just making an easy problem difficult. There aren't any uniquely quantum effects in the question you're asking in this thread, so no need to think in terms of photons at all.

 

[durant35]

Thank you Nugatory for the clarification and your patience.

 

[durant35]

So at any instant we can desribe the behavior and propagation of the light with classical electrodynamics, time isn't a factor here? No matter how low we go on the timescale light will still behave classicaly?

 

[blue_leaf77]

No matter how low we go on the timescale light will still behave classicaly?

At least, our well-established Maxwell's equations is mathematically valid for all time (for light which behaves classically). I don't think there are theories or observations that discriminate the applicability of Maxwell's equations for different times relative to the instant when the light was produced.

 

[A. Neumaier]

No matter how low we go on the timescale light will still behave classically?

Ordinary light or laser light, yes. Only specially prepared light in nonclassical states will behave differently. It requires already quite some skill to create such nonclassical light.