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Debate Over Color of the Universe Raises Some Red Flags

April 01, 2002|K.C. Cole

There's been a certain amount of snickering in astronomy circles lately over the "color of the universe" brouhaha. In case you missed it, in January, astronomers from Johns Hopkins University announced that the universe was turquoise. In February, they found a bug in their code, and now they say it's closer to beige ("cosmic latte" is the current favored name).

"Why just the color?" one astronomer cracked. "Why not its texture? How does it feel?"

Is it sticky or smooth? Sad or gay? If it's on the green side, does that mean it's jealous of some other universe? If it's red, is it blushing? If it's beige, is it bored?

There's a serious reason to study the color of the galaxies: Spectral lines in the light from stars reveal the mix of ingredients that make them up.

What raised eyebrows was the fact that the astronomers figured out the color of the universe only as it would seem to human eyes--an awfully anthropocentric way to look at things: Me, me, me. The universe would look quite different to a snake or a cat or a bee or a bat.

Focusing on visible light, in fact, means throwing away 99% of the electromagnetic spectrum. Astronomy depends on a wide array of telescopes that look at all of the light, from gamma rays to microwaves.

And if you took all the wavelengths into account, the galaxies would radiate in the infrared. Even that light would be swamped by the microwave glow left over from the big bang.

Of course, most of the matter in the universe doesn't give off light at all. So the true color of the universe has to take into account the 90% of matter that is "dark" or, more accurately, transparent. That would make the universe the color of clear glass.

And cosmologists are becoming convinced that most of the universe isn't even made of matter, but some mysterious "dark energy" that pushes galaxies apart, behaving like a kind of anti-gravity. Color it repulsive.

In truth, the Johns Hopkins astronomers hit on something far more subtle and interesting than the color question, which they attached to a larger paper admittedly for "a bit of fun," as one of them put it.

"One moral of this story is we should have paid more attention to the 'color science' aspect," this astronomer said.

In fact, how we see color is a complex and controversial question: "The history of the investigation of colour vision is remarkable for its acrimony," writes Richard L. Gregory in his classic book "Eye and Brain."

"The problems have aroused more passion than passion itself."

Color vision is completely counterintuitive. In the first place, the human visual system evolved to do more with less (rather unlike our economic system). In fact, it's been known for nearly 200 years that we see the entire panorama of possible color with just three kinds of receptors, those for red, green, and violet.

Colors like yellow are mixtures--in this case of red and green. The sensation of "yellow" is something like H2O, a mixture that is nonetheless pure--and with properties entirely different from the ingredients that make it up. So if you shine a red light and a green light on a white wall, the place where they overlap is yellow. Add violet to this mix, and colors immediately bleach into white. No matter how many times I've played this trick, it still astonishes me. (Definitely try this at home.)

Still, the wavelength of light is only part of the story. Seminal experiments by Edwin Land showed that it takes only two narrow bands of light to reproduce nearly the entire visible spectrum in the brain. The color we see depends on everything from general surroundings to expectation, from edges to illumination, physiology and psychology alike.

As Gregory concludes: "Any simple account of colour vision is doomed to failure."

The trickiest color of all is white, and it got the Johns Hopkins astronomers in trouble. There's no exact formula for "white"; the brain constantly recalibrates white depending on context.

Normally, what we see as "white" is just the whitest thing around. If you take a white piece of paper into a room illuminated only in red, for example, the paper still looks white. The brain keeps colors constant under different lighting conditions; otherwise, the world would be a kaleidoscopic blur.

Unknown to the Hopkins' astronomers, the freeware program they used to calculate the color of the universe set a "white point" for a reddish environment. This made the color of the galaxies appear, on average, turquoise.

As the universe ages, there will be fewer young, hot, blue stars, and more older, cooler, reddish ones, pushing the universe further into the red. Eventually, the stars themselves will collapse into black holes.

Only then will the universe finally find itself in the black.

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