Passionately Curious: Let There Be Light! And He Saw That It Was Weird.

Passionately Curious

Wait, what’s this? This strange science-y series that was going on last year is back? Well… not quite, just a one-shot for now! Still, there’s so much awesome stuff left to talk about! Take, for example, the weirdness that is light. Now, I’ve already gone into far too much detail on some of the stranger properties of light concerning special relativity and all that jazz, so today we’ve got some lighter fare. After all, there’s plenty of weirdness in the nature of light even in our everyday lives that you’ve probably never realized – and a great deal of it has to do with the notion of color.

You see, objects don’t actually ‘have’ colors – and neither does light itself (well… about 99% of the time1), though in a different way.

But, as usual, we’ll start at the beginning. What the hell is color, even? At least this bit is relatively straightforward: light, for our intended purposes, is a wave. Our eyes have different receptors that respond to different wavelengths or quantities of such light waves. If we’re hit by, say, a bunch of light waves in the 495–570 nm range, those trigger our ‘green’ receptors. These then tell our brain through terribly complicated neural pathways to display a mental image of a green thing.

So, in a sense, our eyes simply contain an organ that distinguishes between different wavelengths of light within a range that has proven to be pretty useful, and which we call the ‘visible range’ of wavelengths. One might then argue, from a philosophical perspective, that color does not even exist in the first place: after all, we are simply interpreting an incoming wave of light in a certain way. Colors (and really, any kind of vision at all) only truly exist within our heads – the universe itself is simply filled with all manner of waves of light just bouncing off of stuff.

But let’s entertain ourselves a little longer and not simply dismiss the notion of color on such philosophical arguments (or at the very least not these). For at least equally interesting as the idea that vision, and by extension color, only exists in our heads, is the fact that this means that the notion of a ‘color of light’ is terribly deceiving.

The stuff that we call ‘white light’ (produced, for example, by the sun, lightbulbs, or your supernova-bright led) is made up of all possible colors – as evidenced by the cover for Pink Floyd’s ‘The Dark Side of the Moon’, obviously. So how does this work? Well, the nuclear reactions inside the sun that produce our lovely white light are… rather messy. As a result the sun doesn’t actually emit one clean wavelength – instead, that ‘single ray’ of white light you observe contains billions and billions of different wavelengths. The prismdoesn’t so much ‘break’ the light, but rather it neatly sorts the light by wavelength, turning the jumbled, confused mess into a neat pile.

That is why, if you’ve ever looked real close at a digital screen (you could see it really well on old TVs) you can actually see that they’re all tiny little blobs (pixels) of red, green, and blue. After all, if our eyes can distill a giant mess of ranges of waves into a ‘single’ color, the screen can use this in a very clever way by combining relatively ‘pure’ sets of wavelengths into mixes pressed together tight enough that your eyes can’t resolve the individual pixels. The result gets interpreted by your brain as a mix of colors, cleverly dreamt up by the engineers who designed the thing.

And now, my dear readers, we get to the true reason why objects don’t ‘have’ a color.

Think about it for a moment: what is it that allows us to see anything at all? Light hitting our squishy little eyeballs. So then why can we see anything besides sources of light at all? Well, it seems the stuff we see must, in some capacity, reflect light from a source in order for us to see it. Whereas mirrors reflect light perfectly, conserving (usually) the exact wavelengths and whatnot that you fire at it, most surfaces in our daily life aren’t nice, smooth and shiny. Such ordinary, imperfect reflection is a terribly imprecise business: out of all the wavelengths in the light hitting an object, most are typically absorbed, and as a result transformed into tiny slivers of heat energy. The small selection of light that our particular object actually does reflect is tossed right back at us, and that is what we see. Your white shirt bounces off most colors within the visible spectrum and so does not absorb a whole lot of light – which is why it stays relatively cool. And anyone who’s ever touched dark pavement during the heat of summer knows that it gets pretty hot, which is because it’s been absorbing all those delicious solar rays, spitting back only very minimal bits of light here and there.

From a philosophical standpoint, you could therefore (rather naively) try to argue that in reality, an object has all colors except the one we actually see.

But this absorption versus reflection business is (as is the norm in these little articles) terribly complex and complicated. The very fine-grain texture of an object far too small for us to see might play a very important role in just which wavelengths are reflected back at us and which remain trapped in the structure. In addition, I mentioned red, blue and green already: those colors are important because we’ve only actually got receptors for those three colors. So what happens if we see, say, a lemon? Yellow, you might have noticed, is not in that list. Yellow, however, is on the opposite side of the spectrum from blue, so a lemon might be, in fact, a perfectly balanced composite mix of… red and green.

Mind = blown. Also, lemons.
That’s right.
Lemons ain’t yellow.
Deal with it.

And on that bombshell, I hope I’ve left you all more enlightened than confused. May you appreciate the light in your life, no matter what shape, form, or wavelength it takes, and remember: stay curious.

By Paul Hofma

Footnotes

1 The one exception? Lasers. Or, if you prefer, LASERs: Light Amplification by Stimulated Emission of Radiation. The Wikipedia article is rather technical, but if you want to know how it works the ‘Laser Physics’ section is at least somewhat readable.

2 A prism is the triangular, ‘Dark Side of the Moon’ piece of glass which turns your boring ol’ white light into disco fever! Want to know how exactly that magical magic works? As usual, Wikipedia is your friend.

Sources

https://en.wikipedia.org/wiki/Visible_spectrum

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