does 'seeing' constitute photon wave collapse?

[gib65]

When you look at the stars at night, you can see any one of them no matter where you are and no matter what time of night it is.

 

This is possible becomes photons are emitted from these stars and they travel as waves until they reach your eye and interact with your retina. Is this interaction an example of the way the wave form of a particle collapses and becomes more like a tiny point in space that interacts only with things local to it?

 

I have a follow up question, but let's start with this.

[GDG]

When you look at the stars at night, you can see any one of them no matter where you are and no matter what time of night it is.

 

This is possible becomes photons are emitted from these stars and they travel as waves until they reach your eye and interact with your retina. Is this interaction an example of the way the wave form of a particle collapses and becomes more like a tiny point in space that interacts only with things local to it?

 

I have a follow up question, but let's start with this.

 

I think you are confusing wave-particle duality with superposition of states. Both concepts derive from quantum mechanics. It is the superposition of states (i.e., a system with several possible states) that collapses into one state upon observation.

[gib65]

I think you are confusing wave-particle duality with superposition of states. Both concepts derive from quantum mechanics. It is the superposition of states (i.e., a system with several possible states) that collapses into one state upon observation.

 

But I thought there was no difference. I thought the wave nature of particles derives from their superposition. That is, the wave is made up of a superposition of the particle concentrated at the highest amplitude of the wave.

 

Is this wrong?

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It doesn't seem like this thread is progress too fast, so let me just cut to the chase:

 

If I'm right that light waves constitute photons in superposition states, and that in order for them to be intercepted by the human eye, it must interact with a molecule in the retina, thereby causing it to collapse (or be absorbed), then there must be billions upon billions of photons just in one's local vicinity. At least, this is the case when the photons in question come from distant stars. When I look up at the stars at night, I don't ever fail to see them - regardless of when it is or where I am - at least for the ones bright enough to see. This blows my mind when I think about the odds of a single photon being emitted by the star, traverse the great expanse of space between it and me, and happening to finally collapse upon interacting with a single molecule in my retina, a molecule out of trillions of others in interstellar space that it could have interacted with.

 

Now, these odds might not seem so striking if we consider that there are billions and billions (probably more like trillions and trillions) of photons being emitted by the star in question. With that many photons, the odds of one interacting with molecules in my retina are not that far off (are they?). It might not be that far off even when we consider that it isn't just a single photon interacting with my retinal molecule just once in momentary interval of time, but a whole stream of them constantly interacting with the same molecule such that I can see the star at any time in the night and at any angle I direct my eye and at any position on the Earth's surface. Add to that that there would have to be plenty of photons left over for billions of other human beings (and other animals) to see the same star.

 

But I would think that there would have to be a point at which the star becomes so distant that the odds of one of its photons hitting the eye would become noticeably deminished - such that seeing the star wasn't always guaranteed. It would have to be a point at which one would look up at the star and sometimes see it (if he were so lucky as to have the photon interact with his retina) but sometimes not (if he weren't so lucky). There would have to be a noticeable chance that while one person sees the star at one moment, another person right next to him wouldn't. Is this what would happen if the star were distant enough and the number of photons limited to a certain amount?

[Mokele]

There would have to be a noticeable chance that while one person sees the star at one moment, another person right next to him wouldn't. Is this what would happen if the star were distant enough and the number of photons limited to a certain amount?

 

Eh, yes and no. The retina doesn't simply detect photons like a CCD, nor does it actually transmit information directly to the brain without filters. In order for a rod to fire (you see stars with mostly rods, largely due to their superior sensitivity in low-light conditions), it has to be hit by a certain number of photons within a given space of time, and the closer those photons are to 498 nm, the more effect they'll have. Furthermore, multiple rods need to be stimulated in order to result in stimulation of the nerve associated with them.

 

If a star is emitting very few photons, chances are they would either fail to result in a nerve impulse, or be filtered out at the level of the ganglion or brain. There's a LOT of processing that goes into creating visual perception, and a lot of information gets thrown out in that processing, especially weak signals.

[gib65]

Right! Now that I think about it, what we'd probably see is the star becoming more and more faint. In fact, we do see this. The distant stars are the harder ones to make out. Am I right in thinking this is due to the concentration of photons becoming less and less?

[proton]

When you look at the stars at night, you can see any one of them no matter where you are and no matter what time of night it is.

 

This is possible becomes photons are emitted from these stars and they travel as waves until they reach your eye and interact with your retina. Is this interaction an example of the way the wave form of a particle collapses and becomes more like a tiny point in space that interacts only with things local to it?

 

I have a follow up question, but let's start with this.

I assume that you're more interested in the detection of photons and the collapse of the state rather than how the eye works so I'll refer to detection of photons in what follows. If you're wondering about the eye and how it detects photons please see http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.html

 

Yes. The wave-particle duality and the principle of superposition are closely tied. You can't address one without addressing the other.

 

The wave nature of light refers to the wave function that corresponds to the probability density corresponding to position measurements. If the wave function is that of a wave packet then it is the superposition of an infinite number of waves. When the photon is detected then its position is measured. This means that the wave function collapses into an eigenstate of position.

 

The further away from the source the detector is the smaller the amplitude of the wavefunction. This translates into a decrease in light intensity and thus a decrease in the probability of detecting a photon in a particular region of space.

 

Is that close to what you were looking for?