Yet more questions about light

Magical Realist

Magical Realist

Valued Senior Member
If photons have no mass, how can they have energy. Is not the energy of moving objects converted from their mass?

How do light waves carry information to our brains about the physical world? Are our eyes capable, at the quantum level, of processing the data imprinted in light into facts about our physical world? Or does this all happen later on inside the brain? Might differences in the lightwaves hitting our eyes be interpreted by our brains as motion, much like how a movie is but a running light projection of successive photographic frames?
 
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Magical Realist said:
If photons have no mass, how can they have energy. Is not the energy of moving objects converted from their mass?

How do light waves carry information to our brains about the physical world? Are our eyes capable, at the quantum level, of processing the data imprinted in light into facts about our physical world? Or does this all happen later on inside the brain?
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Yes, but that’s kinetic energy. There are many other kinds of energy too. Radiation energy is one of them. Consider: water waves carry energy but, even though water has mass, no mass travels in the direction of the wave. Radiation consists of waves in the electric and magnetic fields.

The retina of the eye absorbs photons in special cells that are thereby stimulated to produce an electrochemical signal - a nerve impulse that corresponds to the optical image that the lens forms on the retinal surface. The optic nerve (which is really an extension of the brain) and the brain itself interpret this as facts about - or at least impressions of - the physical world.
 
When light hits the retina, is it wave or a particle? It seems that to see color, it would have to be a waveform since color is the wavelength of light. But to produce electricity (the photoelectric effect) it would have to be particles that can knock loose those electrons from the atoms of those cells. So which is it? Both? Perhaps it flips back and forth depending on what we are consciously seeing?
 
Magical Realist said:
When light hits the retina, is it wave or a particle? It seems that to see color, it would have to be a waveform since color is the wavelength of light. But to produce electricity (the photoelectric effect) it would have to be particles that can knock loose those electrons from the atoms of those cells. So which is it? Both? Perhaps it flips back and forth depending on what we are consciously seeing?
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The light interacts with proteins, opsins. Off the top of my head but this will all be in wiki.

Wave particle duality is kind of an outdated concept with the physics guys I have spoken to.
 
Magical Realist said:
When light hits the retina, is it wave or a particle? It seems that to see color, it would have to be a waveform since color is the wavelength of light. But to produce electricity (the photoelectric effect) it would have to be particles that can knock loose those electrons from the atoms of those cells. So which is it? Both? Perhaps it flips back and forth depending on what we are consciously seeing?
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It’s not really either/or. For a molecule to absorb a photon, the photon must have the energy that corresponds to the energy difference between two allowed quantum states of the molecule. With visible light, this involves promoting an electron in the molecule from one orbital to another one of higher energy. A photon has a wavelength. The shorter the wavelength the higher the energy of the photon. Different types of molecules have different energy gaps between orbitals. So they each absorb at different wavelengths. So they respond to different colours of light. The cones in the retina of the eye make use of this principle to give us colour vision. The excitation of these molecules is converted to a nerve impulse. Don’t ask me for the details of how this happens though. I would have to read that up.
 
I was reading online in a physics blog just now that light does not actually carry information. I find that ridiculous. Nearly all the information we receive about our environment is transmitted thru light. And it does not even require a brain to extract that information. A simple transparent lens is sufficient to bend the rays of light and you can project a perfect image of a scene on a white surface that shows us what information was contained in the light. The image is even moving and updated like a movie. Someone can enter the room behind the lens and you will see them moving in the image on the screen. In a sense all the light that is hitting our eyes is projecting a little live movie thru the lens of our eyes onto the retina. How can light do this? How can the information of everything it has reflected off of be retained in the waves dispersing in space and then reproduced as a perfect 2d image of that "remembered" scene by being magnified thru a mere transparent lens?
 
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Magical Realist said:
I was reading online just now that light does not actually carry information. I find that ridiculous. Nearly all the information we receive about our environment is transmitted thru light. And it does not even require a brain to extract that information. A simple transparent lens is sufficient to bend the rays of light and you can project a perfect image of a scene on a white surface that shows us what information was contained in the light. The image is even moving and updated like a movie. Someone can enter the room behind the lens and you will see them moving in the image on the screen. In a sense all the light that is hitting our eyes is projecting a little movie thru the lens of our eyes onto the retina. How can light do this? How can the information of everything it has reflected off of be retained in the waves dispersing in space and then manifested as a perfect 2d image of that "remembered" scene by being magnified thru a mere transparent lens?
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You don’t even need a lens to form an image. Have you never made a pinhole camera? Look it up: it’s quite easy to do. https://en.wikipedia.org/wiki/Pinhole_camera
 
Pinball1970 said:
Light is not just physics, it is physical properties like wave length and intensity of light PLUS a biological system to detect and interpret it.
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I'd have thought light is physics. Surely it is the perception of light (possibly including the perception of colour) by an organism that requires the biological system, isn't it?
 
Pinball1970 said:
The light interacts with proteins, opsins. Off the top of my head but this will all be in wiki.

Wave particle duality is kind of an outdated concept with the physics guys I have spoken to.
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Is that right, though? I'd certainly agree physicists don't need either pure particle or pure wave models for quantum entities, because quantum mechanics provides a single model that yields both wavelike and particle-like results as appropriate.

But when explaining QM to people that have not studied it, I think it is still customarily explained in terms of both wave and particle ideas. In chemistry, we implicitly use particle or wave pictures all the time, switching between the two without even thinking about it. For instance, an "orbital", which is a QM state, is a essentially a standing wave pattern (a spherical harmonic if it is an atomic orbital) which we mentally "populate" with electrons (particles).

But perhaps you have in mind the distinction between the use QM operators and Dirac's bracket notation, i.e. Heisenberg's matrix mechanics, rather than the - in some ways more primitive - wave mechanics of Schrödinger.
 
exchemist said:
I'd have thought light is physics. Surely it is the perception of light (possibly including the perception of colour) by an organism that requires the biological system, isn't it?
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Yes I should have said colour or perception of light.
What is not usually understood is that colour is dynamic, it is not a "thing" like an apple.

Designers and techs always seem a little surprised when I tell them that colour does not exist until I turn on the light box.
 
exchemist said:
Is that right, though? I'd certainly agree physicists don't need either pure particle or pure wave models for quantum entities, because quantum mechanics provides a single model that yields both wavelike and particle-like results as appropriate.

But when explaining QM to people that have not studied it, I think it is still customarily explained in terms of both wave and particle ideas. In chemistry, we implicitly use particle or wave pictures all the time, switching between the two without even thinking about it. For instance, an "orbital", which is a QM state, is a essentially a standing wave pattern (a spherical harmonic if it is an atomic orbital) which we mentally "populate" with electrons (particles).

But perhaps you have in mind the distinction between the use QM operators and Dirac's bracket notation, i.e. Heisenberg's matrix mechanics, rather than the - in some ways more primitive - wave mechanics of Schrödinger.
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I do not want to misquote them so I'll check and feedback.
 
exchemist said:
Is that right, though? I'd certainly agree physicists don't need either pure particle or pure wave models for quantum entities, because quantum mechanics provides a single model that yields both wavelike and particle-like results as appropriate.

But when explaining QM to people that have not studied it, I think it is still customarily explained in terms of both wave and particle ideas. In chemistry, we implicitly use particle or wave pictures all the time, switching between the two without even thinking about it. For instance, an "orbital", which is a QM state, is a essentially a standing wave pattern (a spherical harmonic if it is an atomic orbital) which we mentally "populate" with electrons (particles).

But perhaps you have in mind the distinction between the use QM operators and Dirac's bracket notation, i.e. Heisenberg's matrix mechanics, rather than the - in some ways more primitive - wave mechanics of Schrödinger.
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This crops up a lot in discussions and here is an example.

https://www.physicsforums.com/threa...-it-a-wave-and-when-is-it-a-particle.1011377/
 
Pinball1970 said:
This crops up a lot in discussions and here is an example.

https://www.physicsforums.com/threa...-it-a-wave-and-when-is-it-a-particle.1011377/
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OK but that’s just saying what I too have been saying: QM dispenses with the need to force nature into either a pure wave or a pure particle model.

QM is QM, basically and the resort to waves and particles is just a way for us to visualise what happens, in terms of familiar (macroscopic) concepts. Which in practice we do a lot, at least in chemistry, given that chemical systems are far too complicated to be modelled at all readily in QM mathematics.
 
Pinball1970 said:
Yes I should have said colour or perception of light.
What is not usually understood is that colour is dynamic, it is not a "thing" like an apple.

Designers and techs always seem a little surprised when I tell them that colour does not exist until I turn on the light box.
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Sure, colour is a sensation rather than a property in physics.
 
Sure, colour is a sensation rather than a property in physics.
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Yes! I was thinking about this last night and about what happens to the information carried by light once it strikes our retina. Now its not like the retina "sees" the little movie projected on it. The retina is blind. It is instead stimulated by the photons to produce electrical impulses. So we go from the medium of light to the medium of electricity. After that point it is a matter of changes in electrical potential and synaptic firings. It's the same for the other 4 senses as well. Everything becomes encoded into electrical impulses and becomes sensations. And that's where the mystery happens--how color somehow emerges out of all those firings as an experienced sensation and gets spatialized as if it were a physical property adhering to the lighted objects outside the body.

Here is a beautiful synopsis about how color is created. It is all so clear and logical until the nerve impulses reach the brain. And then they just say "and so a perception is created". That's the limit of what can be presently understood. It is also Chalmer's Hard Problem of Consciousness in a nutshell: how can we go from physical processes like light and electrical impulses to the experience of colors? A huge gap exists between the two. Try as we will we will never find colors in the brain. Yet they are being constantly perceived nonetheless.

https://petapixel.com/2021/09/16/this-is-how-the-human-brain-processes-color/
 
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Magical Realist said:
Yes! I was thinking about this last night and about what happens to the information carried by light once it strikes our retina. Now its not like the retina "sees" the little movie projected on it. The retina is blind. It is instead stimulated by the photons to produce electrical impulses. So we go from the medium of light to the medium of electricity. After that point it is a matter of changes in electrical potential and synaptic firings. It's the same for the other 4 senses as well. Everything becomes encoded into electrical impulses and becomes sensations. And that's where the mystery happens--how color somehow emerges out of all those firings as an experienced sensation and gets spatialized as if it were a physical property adhering to the lighted objects outside the body.

Here is a beautiful synopsis about how color is created. It is all so clear and logical until the nerve impulses reach the brain. And then they just say "and so a perception is created". That's the limit of what can be presently understood. It is also Chalmer's Hard Problem of Consciousness in a nutshell: how can we go from physical processes like light and electrical impulses to the experience of colors? A huge gap exists between the two. Try as we will we will never find colors in the brain. Yet they are being constantly perceived nonetheless.

https://petapixel.com/2021/09/16/this-is-how-the-human-brain-processes-color/
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There is only a huge gap if you are prisoner of Cartesian dualism. Set that aside and there is no reason why the electrical patterns cannot themselves be the sensation we experience.

The "hard problem of consciousness" is imaginary, in my view. I'm with Massimo Pigliucci on that: https://philosophynow.org/issues/99/What_Hard_Problem
 
From above article:

"A category mistake occurs when you try to apply a conceptual category to a given problem or object, when in fact that conceptual category simply does not belong to the problem or object at hand. For instance, if I were to ask you about the color of triangles, you could be caught off guard and imagine that I have some brilliant, perhaps mystical, insight into the nature of triangles that somehow makes the category ‘color’ relevant to their description as geometrical figures. But of course this would be a mistake (on my part as well as on yours): triangles are characterized by angles, dimensions, and the ratios among their sides, but definitely not by colors."
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I'm familiar with the category mistake argument against Cartesian dualism and the hard problem. The philosopher Gilbert Ryle proposed it originally, arguing that expecting physical or empirical processes to exhibit properties that are essentially mental or phenomenal in nature is to confuse the two. He uses the example of someone giving you a tour of the university-- the science bldg, the english bldg., the dormitories, the cafeteria, and so forth--and then you asking at the end, "But where is the university?" The mistake here is in confusing an example of the category of collective entities with an example of the category of individual discrete entities. Is that what is happening with the hard problem? Pigluicci continues:

Of course an explanation isn’t the same as an experience, but that’s because the two are completely independent categories, like colors and triangles. It is obvious that I cannot experience what it is like to be you, but I can potentially have a complete explanation of how and why it is possible to be you. To ask for that explanation to also somehow encompass the experience itself is both incoherent, and an illegitimate use of the word ‘explanation’.
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That does make initial sense to me. But with an explanation of consciousness , of experience itself, we seem to have entered new territory. In this case we are trying to explain how the experience arises--as in the perception of color or any other qualia--from physical explanations. The explanation is expected to show how it is that the brain can have phenomenal experiences at all. It's a question not of confusing experience with explanation, but of how a categorical difference between the explanatory and the experiential comes about at all. IOW, if scientific explanations are by definition only accounts of physical third person events, and experiences are by definition only phenomenal first person events, how do we bridge that gap?
 
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