I didn’t want to start this in the purple/violet thread.
So what if some one could see off the end of what we consider the visible spectrum? I don’t see that it is physically impossible, we just haven’t developed that way.
What color would it be? Would it be some new color that we cannot even imagine or describe because it is not in our present realm?
Dennis
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Probably. There are many animals that can see a wider spectrum than us, and/or are tetrachromats.
If they have anything like the conscious experience of colour that we do then they would likely see a fourth primary colour, and orders of magnitude more total shades than we can see.
Alas, the conscious experience of colour is something we don’t have great understanding of at this time. Perhaps right now the colours you see are vastly different to mine? Perhaps there’s a limit to the total distinct shades that brains as we know them can perceive, so even if you enhanced the human eye, all you’d see is a “redistribution” of the palette you’re familiar with. We don’t know (although that latter point at least should be testable eventually).
I should also add, that there are some people capable of seeing UV.
UV light is just blocked by the cornea, so if you remove it, it can be seen.
However, it just appears as white light to us because it activates all of our colour cones. It’s not the same thing as having a fourth colour cone sensitive to UV.
How would you describe the color red to a color-blind person?
Basically, we cannot imagine how colors we cannot see would be perceived. It is likely that if we could perceive ultraviolet with a separate receptor, it would be a color as different from those we can see as red is from green.
Most vertebrates are tetrachromats that can perceive a greater range of colors than we can. We are unusual among mammals in being tricromats. Most mammals have only two kinds of color receptors.
Color is not a property in physics. Or, rather, it’s a manifestation of a property in physics, but the actual physical property is infinitely more complex, with what we think of as color being only a vast oversimplification of it, and there are a multitude of other possible simplifications of it. We see in only a three-dimensional color space, but the actual physical color space is infinite-dimensional, and so there are an infinite number of possible choices for those three dimensions. Another species’ evolution might (almost certainly would) have made other choices: What we think of as “color” is a manifestation of the way our eyes (and brain and everything in between) work.
Thus, if we ponder our eyes working in some other way, then our perception of color would necessarily be different. Different how? Well, you tell me. We could have another color receptor, and see in a four-dimensional color space instead of three. We could still have three, but arranged differently. We could have the same three arranged the same way, and just perceive the new wavelength ranges as being indistinguishable from colors we already know. Once you open the doors of “what if our eyes were different?”, there’s very little limit to the ways in which they could be different.
Nothing would be able to see too far into the UV or IR … the atmosphere tends to be opaque if we drift from the visible light spectrum. The Earth itself would start shining in the IR.
Here’s a bloke who reckons he can see UV after cataract surgery; he makes a good case. In general things seem just a bit brighter in sunlight, which may not be that much of an advantage.
Not only that, but your eyeball starts shining in the IR, and you wouldn’t be able to see through it.
But there’s still some near-IR and near-UV we could see if our eyes were constructed somewhat differently.
If we achieve IR and UV vision simply by extending the wavelength range of the 3 cones (i.e. the “blue” cones will also see UV, and the “red” cones will also see IR), and the rods, then we’d still have the same set of colors, but some things would change color. I believe most flowers are bright in UV, so they’d look more bluish.
It’s worth reminding, here, that IR and UV are each a far broader band than the entire visible range combined. It’s misleading to say things like “we can’t see in IR because our eyes themselves shine in IR”, because you could easily double the spectral range of human vision without getting close to the point where body heat interferes.
Kind of amazing that our atmosphere is transparent in exactly the same wavelengths of light our G2 star produces it’s maximum energy. Although I don’t think any other star class would inhibit life developing, it may well inhibit any advanced life like humans.
Octarine, of course! 
Not related to infrared/ultraviolet vision, but there probably are some human women with tetrachromatic vision. Some scientists think that up to 12% of women have tetrachromacy. They walk among us, for the most part unaware that they see more colors than normal people. And of course they can’t describe the extra colors that they see, any more than you can explain what red looks like to someone with protanopia.
–Mark
From the wiki:
It doesn’t seem that functional tetrachromacy is very common, and the improvement in colour gamut is still largely unknown.
Of course I’m not saying there’s anything special about visible light and/or the primary colours we’re familiar with.
Just that it’s still disputed whether women with a fourth pigment have significantly greater colour resolution than regular trichromats.
Mostly, it would add shading to colors we can already see, they way a color photo taken at sunset adds in a lot of red to the real colors. The pure UV and IR colors would just be given names, and defined by pointing to things that color and saying “that color”, the same way we do with red, yellow and blue as a means of defining that they look like.
I think the world would look somewhat like it does now but with an overly of what a hear-sensitive image would look like:
https://i.kinja-img.com/gawker-media/image/upload/ubocuz4bjoseoiocciqp.jpg
Those are both fairly broad ranges, so it’s not surprising that there’d be some overlap.
And of course, where that overlap is is what our eyes evolved to detect, so that’s not a coincidence at all (though I gather you already grasped that part).
We can’t see UV because our lens filters out this light. It protects our eyes from UV damage, and animals that do see into this range tend to be less long lived.
Infrared sensing animals tend to be cold blooded. If we could detect it the signal would me masked by the noise from our own bodies. Any method would have to overcome these weaknesses (eye stalks?)
UV and infrared are not of a different substance to visible light. People with cataract surgery can detect into the UV range somewhat with existing S cones but the EM spectrum extends far.
Warm or hot, passionate, angry, violent.
I think that approach is about the best you can do with language and colors.
You only make those connections because you know that fire, other hot things, and blood are red. They would be completely meaningless to a blind person.
Yes. I could see the flashes of the laser during my LASIK surgery. They use a 193 nm excimer laser, and it appeared as mostly white, with a bit of a blue tinge. They peel off a good part of the cornea and of course the laser is quite bright to start with, so a bit of UV makes it through.