I’m not even kidding with that headline. This BuzzFeed post, which has been shared nearly 28 million times in 18 hours, is the apotheosis of viral content. It’s visual, not textual, it’s simple enough for a four-year-old to understand, and there’s a mystery at the heart of it guaranteed to spark ferocious debate among everyone who views it. Weirdly enough, it reminds me a little of why the Rathergate memos broke big online back in the day. That was the first time I can remember that a major political story revolved around evidence that the viewer could examine for himself right on his screen as the story unfolded in real time. You didn’t need to follow links and sit through long ideological arguments to participate in the debate. You were a co-investigator, able to judge with your own eyes how similar a modern Word document was to memos purportedly written on a typewriter 30 years earlier. The dress uproar has a whiff of that. Is it blue and black or white and gold? Are there other photos in different lighting? Will the mystery be solved? Because the central question is so simple, everyone who views the image forms an opinion instantly and is completely wedded to that opinion. No wonder Neetzan Zimmerman, a guy who knows something about viral content, called it the “viral singularity.”

At one point last night, BuzzFeed was hosting more than 670,000 users simultaneously, a population greater than Washington D.C.’s. Recognizing that they had unwittingly won the traffic equivalent of Powerball, the writing staff bought a bunch more tickets by publishing no fewer than seven follow-up posts. (Follow the links at the bottom here.) CNN.com rushed out a video about the dress photo at 3:14 a.m. ET this morning to buy some traffic-lottery tickets of its own. The paper of record was up bright and early with a story about how the photo had “melted the Internet.” Surely the august Wall Street Journal would pass, right? No — they’ve got a story up too. Of the two dozen major papers I follow on RSS, I’m reasonably sure that every one of them has at least a small item about this. That’s what kind of pageview gold rush we’re talking about here. Celebrities chimed in too:

So did quasi-celebrities. Note the number of retweets on this one:

Politicians? Of course:

I’m not even the first HA blogger today to tackle this topic:

All this — for a fairly easily explained optical illusion.

Light enters the eye through the lens—different wavelengths corresponding to different colors. The light hits the retina in the back of the eye where pigments fire up neural connections to the visual cortex, the part of the brain that processes those signals into an image. Critically, though, that first burst of light is made of whatever wavelengths are illuminating the world, reflecting off whatever you’re looking at. Without you having to worry about it, your brain figures out what color light is bouncing off the thing your eyes are looking at, and essentially subtracts that color from the “real” color of the object. “Our visual system is supposed to throw away information about the illuminant and extract information about the actual reflectance,” says Jay Neitz, a neuroscientist at the University of Washington. “But I’ve studied individual differences in color vision for 30 years, and this is one of the biggest individual differences I’ve ever seen.” (Neitz sees white-and-gold.)

Usually that system works just fine. This image, though, hits some kind of perceptual boundary. That might be because of how people are wired. Human beings evolved to see in daylight, but daylight changes color. That chromatic axis varies from the pinkish red of dawn, up through the blue-white of noontime, and then back down to reddish twilight. “What’s happening here is your visual system is looking at this thing, and you’re trying to discount the chromatic bias of the daylight axis,” says Bevil Conway, a neuroscientist who studies color and vision at Wellesley College. “So people either discount the blue side, in which case they end up seeing white and gold, or discount the gold side, in which case they end up with blue and black.” (Conway sees blue and orange, somehow.)

It all comes down to the ambient light. If you perceive the background lighting as more bluish, your brain will assume that the bluish color on the dress is actually blue light hitting a white fabric and will adjust for that. If you perceive the background lighting as more gold, you’ll see the fabric as a darker blue that appears faded because of the color of the light. I thought the dress looked blue and black from the word go and that it wasn’t a close call, but to my amazement, plenty of commenters chipped in on our Headlines thread this morning to say, “nope, looks white and gold.” Good lord. You people probably think “gif” is pronounced with a hard “G” and that “Die Hard” is a Christmas movie too. Never again will I doubt American decline.

In lieu of an exit question, here’s my attempt to achieve the smartest of all global Smart Takes about the dress: It’s really a metaphor for religion, no? The atheist looks at life and sees gloomy deep blues and black. The believer looks at it and sees lovely golds and white. “What am I missing?” the atheist wonders. “Why can’t I see what they see?” Some us are just wired differently, my friends. Wired, that is, to see … the truth.