eli5: If the human eye can only see 10 million colors, how do we know there are 18 decillion colors in the universe in total.
In: Biology
I have no idea where you got your 18×10^33 number from. A “color” is just a language convention for a certain part of the light spectrum. Since EM spectrum is continuous, you can have an arbitrary number of colors fit within it. In English, light between 570 and 590nm is called “yellow”. There’s no reason we can’t break that up and say “570-580” is “yellow” and “580-590” is “murgle”. Some color names like “pink” or “brown” don’t exist on the light spectrum; they only exist when our eyes react to two or more different wavelengths and our brains combine those signals and attribute a name to them. And given that our eyes are limited to only a part of the EM spectrum, we know there are wavelengths outside that some other animals can perceive, or whose effects we can empirically prove, so we have given them names as well like “ultra violet” (btw, people with cataract surgeries often can perceive far into the violet spectrum, beyond normal eyes). So it’s pretty arbitrary, and you can attribute any number to your color count, as long as you have the words for it, as it’s more of a language than physics/biology question. Heck, there are languages who only recognize three or four colors in total. Japanese to this day isn’t clear on green-blue split, and there are languages that have different words (and thus consider them separate colors) for what English would call dark and light blue. Irish makes a distinction between what in English is “green” and Hungarian has two terms for “red” (and no, they are not light and dark red). And there are languages with three terms only – light, dark and red.
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