Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Multifaceted on 10/09/2020 00:23:22
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Forgive me if my reasoning is based on flawed logic and information. I am no physics expert.
As I understand it when light strikes an object the energy of the photons is absorbed by the atoms that make up the object. An atom's electrons can only orbit its nucleus at one level or another, nothing in between. When the atom absorbs the photon, the electrons jump up another level before going back down again. When this happens a new photon is emitted by the atom, it's energy dictated by the level the electron fell. Once this photon enters the eye we perceive it as a color prepending on how much energy it has. This is the photoelectric effect.
In other words, when I turn on the light in my living room, the light hits my walls and is absorbed by the atoms in the purple paint. They tune the light to their own frequency, in a sense dye the light, and eject it out into the world. This is how we not only see in colour but see at all.
Atoms that emit photons at very specific levels and only a finite number of levels, like cars have a finite number of gears and are either in one or another.
From this line of reasoning, I suspect that means there are a finite number of possible colors. That the spectrum we can see is quantized and not continuous. If light depends on the atoms in the physical matter to give them colour and atoms can only emit photons at a fixed set of discrete frequencies based on what element they are, then it would follow there are a fixed, finite number of colors, of shades that could possibly exist in the universe.
Is this true? Is every photon that comes off an object the same? Does this apply to monitor too? Is every colour we see part of a fixed pallet? Something predetermined and unchangeable? Like a cheap art program where you can only select from a list of pre-programmed colours? Is mixing paints, mixing atoms of various elements together make it continuous or is it still quantized and finite? It is said that colour is a wavelength and a wavelength can be any length and there can be an infinite number of differences between 2 points if you make the integer small enough. So there can hypothetically be any wavelength, any colour, any shade within the visible spectrum. But how can wavelengths be infinitely variable if they depend on atoms that can only emit wavelengths of certain colours? Yes I know that photons come from other places as well as atoms, but I'm talking about their colourization, once it leaves an object.
I write this because I have always been a very creative person and this idea is very upsetting to me. I have discussed this sort of thing with others but some of them were not very sympathetic or And if it's a vast but finite number of colours it would still upset me. Without going into how human perception works, could you answer my question? This is very important to me so please, if you answer, make the argument intelligent and open-minded. I know that scientists sometimes talk about unproven things as if they are proven. I've never been able to pick up on that so if your answer is based on something that's still theoretical, please let me know because I tend to take things literally and think in absolutes. Someone talks about a theory like it's a truth and I can't help but assume it's already been proven beyond a doubt.
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There is a finite number of quite narrow atomic transitions in the visible region, but most of the colors around us are reflected by molecules whose electron orbitals are distorted by heat and the presence of other molecules, so in principle you can generate a photon of any energy with a bit of chemistry and physics.
What you perceive, however, isn't entirely determined by the photons that enter your eye, but by the way the brain interprets them. A TV screen can only emit three colors, red, green and blue, but the brightness ratio of these at any point is infinitely variable, producing the sensation of a continuous spectrum. Same with paint.
I know that scientists sometimes talk about unproven things as if they are proven.
That's a priest, politician or philosopher, not a scientist. Scientific knowledge is the residue of predictive hypotheses that have not been disproven.
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Just to add to Alan’s excellent answer.
In other words, when I turn on the light in my living room, the light hits my walls and is absorbed by the atoms in the purple paint. They tune the light to their own frequency, in a sense dye the light, and eject it out into the world. This is how we not only see in colour but see at all.
What actually happens is that white light - a mixture of a large range of frequencies (colours) hits the wall and only colour of purple is reflected (or rather the mix of frequencies that make up the colour we see). However, what we perceive as white light is very variable, in the morning it has more blue and in the evening more red and this affects our perception and comparison of colours. Add to this the fact that the colour sensors in the eye are more sensitive to red, green and blue (which is why those colours were chosen for the colour tv screen) and you can begin to see that the colours we perceive are not the full range of frequencies available. Also, the colours we see are heavily influenced by colours around them and by the brightness of the light.
So, overall there are a lot of factors affect the colours we see, and at the end of the day what you see is what you get.
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An atom's electrons can only orbit its nucleus at one level or another, nothing in between.
This "line spectrum" applies to separated atoms in a low-pressure gas, such as you may find in a "neon" light.
- As the pressure increases, and the atoms in the gas get closer together, these narrow lines broaden into a range of energies
- Additional effects come into play in solids and liquids, further broadening these narrow lines
The other major source of light is from a hot object, such as you will find in the filament of an "incandescent" light, or the surface of the Sun.
- This "black body" radiation emits light of all possible energy levels
- The mix of energy levels is determined by the temperature of the hot surface
- And may be modified by filters (eg the Earth's atmosphere reduces the amount of ultraviolet light energy that reaches the ground)
You can also get mixtures of black-body radiation and line spectra, such as in the Sun
- line spectra come in two flavors: emission spectra=bright lines and absorption spectra=dark lines.
See: https://en.wikipedia.org/wiki/Emission_spectrum
https://en.wikipedia.org/wiki/Black-body_radiation