The rare breed of comic book lovers/physics nerds will no doubt roll their eyes at me for this, but yesterday I was thinking about Superman's X-ray vision (like you do…) and realized the whole thing was a sham. It is a fictional comic, you'll say, but I guess I did get my hopes up a bit because "X-ray vision" sounds like it took inspiration from real science, as much as a comic book glazed in delicious fictional syrup can. But it skips over one important detail: if Superman hoped to see anything with X-ray vision he'd have to EMIT X-rays as well as be able to see them. We cannot see things with our lowly human eyes unless they are illuminated by a source of visible light; most often the sun (or the glow of a computer screen if you're living in a writers cave like me). The sun does not emit X-rays, so superman would have to have another source. Underwear detector BUSTED.
This goes for the 1950's X-ray Glasses as well. I know these were meant as some sort of party gag, but they equally dropped the physics ball. X-rays pass through clothing but they also pass right through flesh. Did men in the 50's find skeletal structures attractive? More importantly, who's idea was it to turn X-rays into a vehicle for SUPER CREEPINESS? These things turn a guy from clean cut to creeptacular faster than you can say "This packaging is really degrading to women."
It's true though, that the Superman pic above suggests superman DID, in fact, strike his subjects with self-generated X-rays. But I didn't automatically assume this because such vision would also leave behind a suspicious trail of tumors and hair loss. If superman were real. Which he's not. I do know this.
When Superman debuted in 1938, the public was generally familiar with X-rays (discovered around 1875) and understood that these invisible beams could pass through materials that visible light could not. They have a high enough frequency that they interact with matter, and interact they do. X-rays are a form of ionizing radiation (thanks Lee for the recent post) and as they pass through your flesh they release electrons that careen through your body and damage cells. The X-rays are only stopped by the density of your bones. So I guess if I were searching for a fictional means of looking through walls, X-rays would be a good first pick. You couldn't use radiowaves, which are another form of light, because they are so large they don't really collide with the atoms in most materials, and instead pass right through them harmlessly. There's infrared light, but that frequency doesn't penetrate much more than visible light.
But that was in 1938. Since Superman's entrance into the world, we've really jumped ahead in our understanding and manipulation of light. And if Superman had been created sometime after the year 2000 I guarantee he would have teravision instead. What's teravision? I'm so glad you asked. Because I really do want to help Superman get a useful and scientifically accurate super power. I really do. So lets explore, shall we?
Terahertz refers to light with frequencies lower than visible light (and much lower than X-rays) somewhere around the microwave range. It's a magical portion of the EM spectrum that when finely tuned can pass through clothing, cardboard, wood, plastic and ceramics, but not metal or skin. BUT HOW?!
Think, for a moment, about the sort of things that block visible light: clothing, skin, bricks. Now, consider things that do not: glass, water, air. Density has a lot to do with this fact. Even in the clearest water, you cannot see as far as you can through air because the water is ultimately denser. But the glass in greenhouses tinted glass (lets say green) absorbs all visible light except green light frequencies, which it reflects and sends back out (which is why we see it) pass through it like clear glass. So there's more at work than just density. The atomic structure of a material makes it possible to absorb some frequencies of light and not others. Terahertz radiation passes through clothing and not skin because this specific range of radiation is absorbed by water, which of course makes up a good portion of your body. How convenient. By finely tuning the frequency, scientists can even determine the water density of tissue.
Scientists have only figured out how to generate these very specific frequencies in the past decade, so they're only just now becoming available for a wide array of applications. And as you can see from the almost-not-safe-for-work-image below, it is already rolling into an airport near you.
Thanks to a mad rush of technology, terahertz radiation is now available in compact, wholesale scanners that have many potential applications like, for example, making sure folks getting on planes aren't hiding plastic guns in their pants. The scanners are so good that they reveal what those fictional x-ray specs always wanted to: the curves, crevices and potential weapons beneath your clothes. While a politically correct pat-down can take a precious five minutes, a terahertz scanner can swing over a randomly selected traveler in less than thirty seconds. And the TSA reports that many people prefer being looked at naked by a stranger than touched by one. Did I mention terahertz do all this without the health threats of X-rays? Seems almost too good to be true.
It probably is. Last year the TSA decided to adopt the machines, (which have a variety of names: "Fully Body Scans" "Whole Body Imaging" or "submillimeter imaging") in a handful of airports. But of course they had to put in place regulations to make sure the images weren't abused. The people who look at the images are in another room far away from the passengers. They cannot bring any recording devices into the room, the computers cannot save, print or send data, and the person's face is blurred on the screen. But really, somewhere, something is going to slip. Patrick J Kiger just wrote an awesome post on this topic over at his "Is This A Good Idea?" blog at Discovery.
The agency is juggling the decision to place them in more airports or not, while Congressman Jason Chaffetz, representing the third district of Utah, introduced legislation to have them outlawed. In regard to this issue he has maybe my favorite quote of the year on his website:
"No body needs to see my wife and kids naked to secure an airplane." -Congressman Jason Chaffetz.
You have a point, Chaffetz, but remember that just like every other safety precaution in the airport, there are some people who we may want to see naked…er…search in order to secure the plane for your wife and children.
So while uses for security are probably the hottest issues being discussed right now, there are medical applications for terahertz technology as well. For example, because the light can pass through the top layer of your skin, doctors think they can use it to detect skin cancer, or even breast cancer. Apparently about 85% of cancers lie in the skin, but are too small to detect. So you know, Superman could help cure cancer and not cause it.
He would of course be on his own in figuring out how to generate and detect terahertz radiation using only his eyes. I don't think we're on the way to compact, glasses-sized devices of that kind. But you know, there's only so much I can do for the guy.