Questions about light (split from does light actually travel)

[Kramer]

 

The photoelectric effect shows that light travels in packets on energy called quanta. Light has been shown to knock electrons off metal. There is no doubt that light travels.
------ Leaving aside the cause for fun and mocking about this thread, I think that there are some important question for debate:

The concept of “movement” for a lay man is created by everyday experience of material “things” that change place …
In the case of sun-light “the things “ are a torrent particles (photons) that flow like a not interrupted flow of water from a hose.
Now when we see the flow of water, we don’t see the molecules of water, and in the example of sun-light, the torrent of photons is a not interrupted flow of light.
This ‘not interruption’ create the false idea of absence of movement.
For me the important questions are:
--- What is a quanta as a thing?
--- What cause it’s movement?
--- Why move in linear movement?
--- Knocks electrons of metal or transform itself in electrons? The mechanism of “knocking”?
--- In what consists the difference between gamma photons, from those of microwave photons. What cause the difference? What is difference from other bosons?
etc.

[swansont]

For me the important questions are:

--- What is a quanta as a thing?

--- What cause it’s movement?

--- Why move in linear movement?

--- Knocks electrons of metal or transform itself in electrons? The mechanism of “knocking”?

--- In what consists the difference between gamma photons, from those of microwave photons. What cause the difference? What is difference from other bosons?

etc.

 

Quanta means a discrete units.

 

Movement that's not linear requires some sort of force, since it represents an acceleration.

 

Knocks electrons out. Energy and momentum are conserved.

 

The difference is in the energy and the source. Gammas are generally high energy and come from nuclear interactions, though a more relaxed definition is just high energy. The difference is how they are created.

[Enthalpy]

The photoelectric effect is properly explained by light being absorbed in quanta. Whether it travels in quanta is a distinct question.

 

Light propagates as a wave. In vacuum and with a beam broad enough, this resembles a straight path.

 

In a semiconductor, we observe directly that electrons are knocked away from the valence band, so they're not created. That's consistent with more general rules that charge is conserved, and then an electron+positron pair would need 1022keV, far more than visible light brings.

[JoeLight]

I have a question about photons and haven't been able to research an answer. If I'm standing by the road and I'm looking at a yellow line on the road for instance, I know that photons are being emitted by the yellow paint and travel as wave form in primarily the yellow spectrum to my retina where they then become photon particles again and my brain processes the chemical reaction in my eye and allows me to see the line. My question is why do we see the origin of the photons rather than where they currently are. How does my brain know that the photons came from a specific distance rather than just being bombarded with color from a direction. It makes sense to me why we would know the direction the light is coming from but the distance part confuses me. How does the brain allow you to see the photon as it was 10 feet away and not as it is at my eye. Is it a characteristic of the photon. Is the photon itself just a form of data being interpreted by the brain?

[Strange]

... to my retina where they then become photon particles again

 

Just a detail. They never stop being particles. And they never stop being waves. They are always photons with wavey-particley behaviour.

 

 

My question is why do we see the origin of the photons rather than where they currently are. How does my brain know that the photons came from a specific distance rather than just being bombarded with color from a direction.

 

Because the brain makes up what you see from a lot of information including how your eyes are aligned (and possibly how the lenses are focussed). If you look at something a long way away, the lines of sight of each eye are nearly parallel. If you look at something close, the eyes turn towards each other.

 

From this the brain interprets the fuzzy blobs of light on your retina to create the complex 3D world you see around you.

Edited August 5, 2014 by Strange

[swansont]

I have a question about photons and haven't been able to research an answer. If I'm standing by the road and I'm looking at a yellow line on the road for instance, I know that photons are being emitted by the yellow paint and travel as wave form in primarily the yellow spectrum to my retina where they then become photon particles again and my brain processes the chemical reaction in my eye and allows me to see the line. My question is why do we see the origin of the photons rather than where they currently are. How does my brain know that the photons came from a specific distance rather than just being bombarded with color from a direction. It makes sense to me why we would know the direction the light is coming from but the distance part confuses me. How does the brain allow you to see the photon as it was 10 feet away and not as it is at my eye. Is it a characteristic of the photon. Is the photon itself just a form of data being interpreted by the brain?

 

A technical nit: light is not emitted from the yellow paint, it is reflected.

 

You can judge distance because we have stereoscopic vision, not because of photon properties.

 

As Strange has explained, there is focusing of the light into an image happening in your eye and processing by the brain that are crucial to the whole process of seeing.