When reading this SE Q&A: Would visible light still be in a separate classification if we saw "colors" in a different wavelength? I started to wonder if we evolved to see the visible slice of the EM spectrum precisely because that's what most matter emits and reflects, more so than the rest of the spectrum; perhaps at least at our everyday temperatures. If this were not the case, it seems there would be no reason why most animals evolved to perceive the same slice of the EM spectrum. I understand that some matter emits, and some animals perceive, slightly below and above visible frequencies. My own guess at an answer would be yes. And the speculative reason would be that existing atoms have electrons in a limited range of energy levels and thus emit a limited range of frequencies when excited. One reason I ask is because answers to the linked question say that there is nothing special about visible light, but I suspect there is. Edit: I understand there is nothing qualitatively different or intrinsically special about visible light. Rather I'm wondering if there is something special about the relationship between matter and visible light.

  • $\begingroup$ Your thinking is incorrect. At room temperature, most everyday objects emit maximum electromagnetic radiation in the infrared range not the visible range. Note that the Sun at $5000$K radiates most of its light in the visible spectrum. $\endgroup$ – Sam Feb 9 at 20:19
  • $\begingroup$ @sam Hmmm. Then is this infrared EM largely of the same frequencies, so that we couldn't tell the difference between different materials if we could see it? $\endgroup$ – Tom B. Feb 9 at 20:25

It may be because visible light is the shortest wavelengths not significantly absorbed by air. This corresponds to the brightest light emitted by the sun.

Here is the transmittance of the atmosphere.

enter image description here

By contrast, this is the absorption spectrum of water. In 10 feet of water, red objects appear black. I would expect many fish not to see red.

enter image description here

Image 1 is from https://en.wikipedia.org/wiki/Infrared_window, which attributes it to the public domain.

Image 2 is a screenshot taken from https://en.wikipedia.org/wiki/Sunlight, which attributes it to Nick84 - File:Solar_spectrum_ita.svg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=24648395

Image 3 is from https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_water, which attributes it to the Wikimedia Commons.

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  • $\begingroup$ The last part is highly important because the basics of vision evolved in the early Cambrian, before critters crawled out of the ocean. Visible light is the only portion of the electromagnetic spectrum that transmits through water for any reasonable distance. The extinction rate in water in the ultraviolet and above is rather fierce, and similarly in the red and below. $\endgroup$ – David Hammen Feb 9 at 21:08
  • $\begingroup$ @DavidHammen - I believe vision has evolved independently many times. E.G. Insect compound eyes are nothing like our own. Octopus eyes look a lot like ours, and yet evolved independently. $\endgroup$ – mmesser314 Feb 9 at 22:11
  • $\begingroup$ Human eyes are very clearly derived from fish eyes, insect eyes from arthropod eyes. Eyes of several different types developed during the evolutionary arms war of the early Cambrian. This occurred well before any critter crawled onto land or flew into the sky. The ability to see developed under water. There have been some evolutionary refinements that were made after critters left the oceans, but those are small. $\endgroup$ – David Hammen Feb 9 at 22:56
  • $\begingroup$ @DavidHammen - Cool! I did not know that. $\endgroup$ – mmesser314 Feb 9 at 23:12

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