The red barns that dot the American countryside are, more often than not, painted red. They're not red because they would otherwise be too hard to see--they're big buildings. They're not red to be fashionable. They're red because red paint is historically the cheapest. And the next logical question--if you haven't dozed off thinking about barns and red paint--is why red is the cheapest. And that question, as answered by Google's Yonatan Zunger in a Google+ post and picked up by BoingBoing, is actually fascinating. Red paint is cheap because of billions of years of nuclear fusion.

Photo credit: Flickr user swainboat via Creative Commons.

Heavy, right? Zunger titled his post "How the price of paint is set in the hearts of dying stars," but before he arrives at his explanation, he offers a crash course in how colors work and how we create paints. Nuclear fusion comes into play when he gets into the root of how and why pigments are formed. But at the high level, we have to start with paints; paints are formed by the combination of a pigment, typically formed from a mineral, and a binding agent, like an oil or acrylic, that makes the liquid stick to something when it dries.

Zunger first posed this question: what makes a good, cheap pigment? "To be a good pigment, first and foremost, something has to have a nice, bright color," he wrote. "The way pigments produce color is that light shines on them, and they absorb some, but not all, of the colors of light. (Remember that white light is a mixture of many colors of light) For example, red ochre, a.k.a. hematite, a.k.a. anhydrous iron oxide (Fe2O3), absorbs yellow, green and blue light, so the light that reflects off of it is reddish-orange. (This happens to be the pigment that’s used in barn paint, so we’re going to come back to it.) Light is absorbed when a photon (a particle of light) strikes an electron in the pigment and is absorbed, transferring its energy to the electron. But quantum mechanics tells us that an electron can’t absorb just any amount of energy: the particular energies (and therefore colors) that it can absorb depend on the layout of the electrons in the material, which in turn depends on its chemistry."

Photo credit: Flickr user hiddenson via Creative Commons.

His explanation of quantum mechanics gets more involved at this point, but here's the most important part: the rotational speed of an atom's outermost electrons affect its ability to become a pigment. There are fixed increments of this property, called angular momentum, and this shows up in the periodic table in different blocks of elements. The only one we really care about is the "d" block, which is the big section in the middle. The "d" electrons produce an amount of energy that corresponds with visual light. These elements, then, tend to make for excellent pigments.

Now we get to the good stuff: Why red pigments are cheap.

It takes a very special baseball pitcher to throw a 100 mile per hour fastball. 90 miles per hour? That's a breeze. 95? A whole bunch of them can do that. But when you top 100 miles per hour, the list thins out. Experts estimate that baseball legend Nolan Ryan threw the fastest pitch of all time--108 miles per hour--in 1974. There's a reason Ryan and fellow blazing-fast-fastball pitcher Randy Johnson own the top two spots on the all-time strikeout leaderboard: It's really tough to track, much less hit, something moving at 100 miles per hour.

Photo credit: Flickr user sidehike via Creative Commons.

There's science to back that up. There’s a 100 millisecond delay between the moment your eyes see an object and the moment your brain registers it," writes Surprising Science. "As a result, when a batter sees a fastball flying by at 100 mph, it’s already moved an additional 12.5 feet by the time his or her brain has actually registered its location."

Some researchers at Berkeley decided to find out. They put subjects through an fMRI to figure out which parts of the brain are responsible for predictive vision. A summary of the study's results says "Findings suggest that the middle temporal region of the visual cortex known as V5 is computing where moving objects are most likely to end up."

The researchers used the test below, which uses a moving background to trick the brain into thinking a stationary object is sliding around.

Here's what's happening when you watch that video:

Fourteen billion years ago, when one tiny, dense point became an unfathomable explosion creating all the matter in the universe, no one was around to witness the spectacle. We may not have first hand accounts of just how hot the blast or just how fast the matter traveled, but that also doesn’t mean that our knowledge of the universe’s early years are blank pages. There is a record of what happened, and from it, you can make music—the big bang’s original sound track, in fact.

In 2003, the mother of an 11-year old contacted John Cramer, a physicist at the University of Washington, with a question about the big bang. She was helping her son on a school project, and she wondered if anyone had been able to record what the explosion sounded like. The answer, of course, was no, but he kept returning to the question.

Image credit: Flickr user altemark via Creative Commons.

Cramer was a frequent contributor to the magazine, Analog Science Fiction & Fact, and just two years earlier he had written enthusiastically about how recent research projects looking at the cosmic wave background allowed scientists to hear “the sound of a Big Bang from a distance of 14 billion light years!” Cramer’s linguistic flourish actually meant that the data gathered could be used to understand what the big bang sounded like over a period of hundreds of thousands of years as the universe rapidly expanded. But scientists hadn’t actually heard the sound with their ears. Cramer had access to enough information. Why not recreate the sound?

Staging a revival of a very, very old explosion took Cramer just 16 lines to program, and an one hour on a Saturday morning. He constructed the sound in the software Mathematica, which gives users the option to render mathematical functions as sound. For all his interest in the subject, Cramer explains now ten years later, “I didn’t know what I was going to get.”

Photo credit: Seattle P-I file

The sound (embedded below), compressed to cover the first 760,000 years of the universe’s life, shoots up and then drops into a chest-vibrating hum that sounds like an airplane landing mixed with the static of the television. What came out of the speakers shocked more than just the physicist. Cramer’s two Shetland Sheepdogs came running into the room to inspect what in the world was going on. It was something bigger.

In the next few days, Bertrand Piccard will leave San Francisco on an airplane headed to New York. That's a long flight--five hours or so, on your typical 747--but he won't arrive until sometime in June or July. The plane Piccard is flying, dubbed Solar Impulse, only travels at about 50 miles per hour. It's also entirely solar powered, which will make the cross-country flight a historic milestone. Piccard and his partner André Borschberg have spent the better part of a decade designing Solar Impulse and preparing for solar-powered flights. And here's the most amazing part: This isn't even the most interesting thing about Bertrand Piccard.

Smithsonian Mag has a great story about Solar Impulse's impending flight, and it briefly touches on Piccard's history. In 1999, Piccard circumnavigated the globe in a gas-powered balloon. His father, Jacques Piccard, was one of the two men who first descended to the bottom of the Marianas Trench in 1960. They were the only men to reach the deepest point in the Ocean until James Cameron in 2012.

Photo Credit: SolarImpulse.com

Piccard's grandfather Auguste Piccard was also a balloon explorer and invented the bathyscape, used in undersea exploration. He designed the Trieste, which his son used to explore the Marianas Trench. And if the family wasn't acclaimed enough already, Auguste's twin brother Jean Felix Piccard invented high altitude unmanned balloons. Auguste served as the inspiration for Professor Cuthbert Calculus from Tintin, and he and Jean Felix had their family name adapted into Star Trek: The Next Generation character Jean-Luc Picard by George Roddenberry.

Bertrand Piccard clearly has a legacy to live up to, and his solar flight from California to New York is hopefully only a lead-up to a solar-powered circumnavigation of the globe. Solar Impulse won't be able to make that flight, however. Despite its 12,000 solar cells and 900 pounds of batteries, Solar Impulse couldn't sustain a pilot for the flight across the oceans, which will take 3-5 days to fly over at less than 50 miles per hour. Piccard plans to add a larger cockpit and weather-proof electronics to Impulse's successor. The new plane will also be bigger and lighter, with a more advanced carbon fiber frame and more efficient batteries. Solar Impulse already has a wingspan of 69 yards.

The plane should have what it takes to make it across the continental United States. In 2010, Borschberg piloted the plane for 26 hours straight, proving that the energy it stored during the day could keep it flying through the night. In a few years, Solar Impulse may prove something else: That planes can fly around the entire world without burning an ounce of fuel.

Check out Popular Science's feature on Bertrand Piccard and Solar Impulse for more photos and technical information on the aircraft, and the Solar Impulse website for some awesome photos and videos of the plane.

The ripples in carnival mirrors prepare us for what we're about to see when we look into them. Where the surface of the mirror bulges out or contracts inwards, so too does our image, stretching out our reflections into bloated torsos and oddly shrunken heads. No matter how you pose in front of a funhouse mirror, you're going to look weird and misshapen. By contrast, the San Francisco Exploratorium's giant curved mirror isn't so predictable--you can't tell how its metallic surface will distort your image. As a result it's one of the museum's most fun and striking exhibits.

The mirror's metallic surface is so massive and reflective that it fills your entire peripheral vision from a few feet away, drawing the eye inwards and making it difficult to focus on the mirror's edge. But it also produces an effect that you've probably never seen in another mirror: From the right perspective, reflections leap out of the mirror like 3D projections. It's far better than watching a 3D movie. Yeah, you lose the transforming robots and projectiles shooting out of a screen, but you gain a feeling of tangibility that no movie screen can produce.

"I think that one of the reasons that's a little surprising to us is that when we use mirrors or lenses we often project the images onto a two dimensional surface," said Thomas Humphrey, Ph.D, who introduced us to the exhibit. I talked to Humphrey about the mirror after his presentation, expecting a detailed physics lesson, and ended up getting a more experiential overview of how our eyes interact with the gigantic reflective surface. He continued:

"When you use a camera and a lens you project it into a [two dimensional] sensor array...or if you go to a non-3D movie, you project it onto a 2D screen. Your plasma screen at home is a 2D screen. So all the images we see, they're really, geometrically, two dimensional. And we use other features of the image--like one thing is in front of something else, that blocks it, obscures it--[to] tell us that one is in front. But this [mirror] shows us something that you pretty rarely see. It shows you that mirrors actually make 3D images, and when we put a screen up, we're just taking part of that 3D image, one slice of that 3D image, and showing it on the screen. The thing that's most common is that a mirror makes a 3D image, but we never see that because we're always slicing screens in there to see part of it. We're not allowing ourselves to see the whole thing. But actually what lenses and mirrors do fundamentally is make 3D images."

The 3D images this mirror produces happen to be upside down--but only sometimes. Just watch the video below.

Hydrophobic nano-coatings like Liquipel have the potential to be the Next Big Thing for electronics. We were impressed with Liquipel at CES 2013. Who wouldn't want a smartphone impervious to the threats of rain and an accidental drop in the ocean (or a toilet)? While Liquipel is focused on electronics, there are other companies selling waterproof nanocoatings for other purposes. Like--just for example--ketchup resistance.

Ars Technica took up the challenge of testing out a nanocoating called Ultra-Ever Dry by exposing it to a battery of tests. They applied the coating to a toilet bowl, sheet of glass, concrete driveway, clothing, and, of course, a slip-and-slide. Their experiments revealed some surprising results. In some cases, the Ultra-Ever Dry worked just as well as it appears to in this commercial, which parades waterproof object after waterproof object across the screen.

But Ars' tests also showed that the coating, which requires a two layer application process, isn't as transparent or safe as it first appears. "The Ultra-Ever Dry coatings in their liquid state are based on xylene (bottom coat) and acetone (top coat) and emit powerful amounts of fumes," writes Ars' Lee Hutchinson. The Ultra-Ever Dry coating itself is not transparent; it leaves a whitish haze on things when applied...Applying the coatings to anything inside a house or apartment is absolutely out of the question. Even outdoors, coming anywhere near the stuff requires nitrile gloves and a P100-rated respirator fitted with organic vapor filters."

Hutchinson does note that better equipment, like an air compressor, could apply the coating more evenly, producing less cloudy results. But it's still not a perfectly transparent solution. For some purposes, that's okay, and each of the video tests Ars shot are interesting. Make sure to check out the slip-and-slide video, which answers an important question: Which wins out, hydrophobia or the rough, textured surface of the Ultra-Every Dry coating?

"The Mechanics of the Pull-Up (and Why Women Can Absolutely Do Them)" is a Scientific America story that delves into the physics behind that most awkward of elementary school P.E. exercises. The parenthetical in the title seems like a "duh" statement at first--of course women can do pull-ups!--but it's actually a response to a study that claimed the exact opposite.

"Last year, in an article titled “Why Women Can’t Do Pull-Ups,” Tara Parker-Pope at the Well blog commented on a study which found that after training regular women three days a week for three months, almost none of the women could complete a pull-up," writes Scientific American's Kyle Hill. "She then generalized the study out to all women, citing grade school fitness tests to keep would-be pull-uppers on the ground...So, the only thing that the study really says is that these women needed more than three months of training to do a pull-up."

Photo Credit: USMC Flickr via Creative Commons

Hill discounts the argument that women have trouble with pull-ups due to lower centers of gravity. That's not a problem, he writes. Being able to do a pull-up comes down to mass and arm length. Bodybuilders with hugely developed arms may not be able to do pull-ups because that mass is working against you. And the longer your arms are, the harder it is to lift your body:

"Take two people of the same mass, say 100 kilograms. If one person has to contract half a meter of arm to complete a pull-up, he or she is exerting 490 Joules of energy. If the other person, quite a lanky individual, has to pull through one full meter, he or she exerts 981 Joules of energy—the same amount released by a quarter gram of TNT. With just a moderate variability in arm length among us, pull-ups become harder or easier."

Women are at a disadvantage when performing pull-ups, but the task is hardly impossible. Hill writes that men do, naturally, have more muscles in their bodies, but women can make up the difference with proper training. Long-armed men and women alike, though, may be out of luck.

We picture black holes as giant, unmoving nothings in space, their gravitational force so crushing that everything nearby is sucked in. It's true that black holes absorb all sorts of matter, but it's not true that they do it as totally motionless voids. In fact, a recent study from NASA and the European Space Agency found that a black hole at the center of a nearby galaxy rotates as it sucks in everything around it. And it rotates at an estimated 670 million miles per hour.

That's nearly the speed of light--light travels at the speed of 671 million miles per hour, and scientists believe nothing can go faster. But black holes, apparently, can get close. NASA's NuSTAR telescope, launched in 2012, and the ESA's XMM-Newton were used together to study the black hole 60 million light years away in galaxy NGC 1365.

A NASA press release from Wednesday explains how the telescopes were able to determine that the black hole was rotating:

" 'We can trace matter as it swirls into a black hole using X-rays emitted from regions very close to the black hole,' said the coauthor of a new study and NuSTAR principal investigator Fiona Harrison of the California Institute of Technology in Pasadena. 'The radiation we see is warped and distorted by the motions of particles and the black hole's incredibly strong gravity.' "

Both telescopes were crucial in the study. XMMM-Newton was designed to detect low-energy x-rays, while the NuSTAR was designed to detect high-energy x-rays. Using only one telescope, scientists weren't sure that they could get accurate readings through clouds of dust obscuring the black hole. But with two, they could detect more x-rays and determine that the black hole was warping them with its gravitational force.

Once they could detect that warping and discount cloud interference, they could measure it:

Taken a certain way, "Brown researchers build robotic bat wing" is a horrifying headline. Does...does that mean science has created a cyborg bat? Half machine, half screeching terror of the night? That's the most intimidating image this side of Batman. Thankfully, that's not quite what the headline means. Brown University researchers have indeed developed a robot bat wing, but not to surgically attach to a one-winged bat. Their aim is to better understand the (organic) machinations of the real thing.

The wing, modeled after a fruit bat, flaps in a wind tunnel while attached to a force transducer. That transducer then measures the aerodynamic force produced by the wing. The study also measures how much power the mechanical wing's three servo motors produce while moving the wing's seven joints. All that information adds up to create a picture of just how much energy it takes to flap a fruit bat's wing.

The researchers built a mechanical bat wing because there was no way to force bats to cooperate into flapping at a certain pace or strength. With an accurate model, they can study each dynamic of the wing separately. The Brown researchers discovered, for example, that bats fold their wings backwards during an upstroke to decrease negative lift.

How did the researchers create this accurate reproduction of a bat's wing, anyway? No surprise here: they used a 3D printer. A 3D printer created the mechanical wing's plastic "bones," while a silicone elastomer took the place of stretchy skin. Impressive as the wing's seven joints are, it's actually far simpler than a real bat's wing, which has 25 joints. But simplifying the design makes the bat's wing easier to study without sacrificing the basics of its functionality. The researchers did find, however, that some mechanical flaws could be overcome with organic-like modifications.

"During testing, for example, the tongue and groove joint used for the robot’s elbow broke repeatedly," writes the Brown University News. "The forces on the wing would spread open the groove, and eventually break it open. [Grad student] Bahlman eventually wrapped steel cable around the joint to keep it intact, similar to the way ligaments hold joints together in real animals...The wing membrane provided more lessons. It often tore at the leading edge, prompting Bahlman to reinforce that spot with elastic threads. The fix ended up looking a lot like the tendon and muscle that reinforce leading edges in bats, underscoring how important those structures are."

Cyborg bats may not be too far off, after all.

Ping pong guns are usually built from hard, colorful plastic, cast in candy colors that fit right in with the rest of the toys sold alongside them at drugstores and dollar marts. They're fragile. A good one might be able to propel a ping pong ball 10 feet a few dozen times--inevitably, the spring action punching the balls out of the barrel will break. Such is the life of the ping pong pop guns I grew up with, which makes me wish I'd known a mad scientist like Perdue University's Mark French--French and two of his mechanical engineering grad students built a ping pong gun that fires at about 900 miles per hour, aka more than Mach 1.

We're talking ping pong balls as fast as Russian MiG fighter jets. Fast enough to blow a hole straight through a paddle. On second thought, it's probably a good thing the pop guns I had as a kid didn't fire this fast.

French isn't actually the first to create a supercharged ping pong launcher. His gun builds on an existing concept that fired the lightweight balls at about 700 feet per second, or less than 500 mph. It's an incredibly simple design: the ping pong ball sits in a PVC tube which is sealed with duct tape on each end. When a nozzle is added to the tube and the air is sucked out, it creates a vacuum. And once there's a vacuum, popping the tape on one end will send a huge wave of air into the tube, blowing the tape out on the other end and shooting the ball down the barrel with "an initial acceleration of about 5000g," according to French.

His does it better. The professor made a great video that explains how these designs work; his gun actually takes inspiration from the nozzles in rocket engines, which are designed to create supersonic flow. Basically, French fills a container with pressurized air until it breaks its duct tape seal. That pressurized air is pushed through the nozzle into the ball's vacuum chamber, and we have lift-off. And boy, does that thing fly.

Mach 1.23, or about 930 miles per hour, is the ball's top speed so far. It's fast enough to blow through two empty soda cans and put a dent in a third. Perdue says not to try this at home--the scientist's equivalent of "you'll shoot your eye out"--but there's a real appeal to causing destruction with something that weighs a tenth of an ounce, or less than 3 grams.

The term "absolute zero" conveys a crystal clear idea: This is the coldest it gets. Ain't gettin' no colder. Except, well, science just figured out how to reach temperatures lower than absolute zero, or 0 Kelvin. Negative temperatures, here we come.

Live Science writes "To comprehend the negative temperatures scientists have now devised, one might think of temperature as existing on a scale that is actually a loop, not linear. Positive temperatures make up one part of the loop, while negative temperatures make up the other part. When temperatures go either below zero or above infinity on the positive region of this scale, they end up in negative territory."

Photo Credit: Flickr user kuyman via Creative Commons.

So, in a way, atoms with negative temperature are actually infinitely hot, and thus warmer than 0 Kelvin. If that just elicited a "huh" from you, Live Science explains:

"As one might expect, objects with negative temperatures behave in very odd ways. For instance, energy typically flows from objects with a higher positive temperature to ones with a lower positive temperature — that is, hotter objects heat up cooler objects, and colder objects cool down hotter ones, until they reach a common temperature. However, energy will always flow from objects with negative temperature to ones with positive temperatures. In this sense, objects with negative temperatures are always hotter than ones with positive temperatures.

"Another odd consequence of negative temperatures has to do with entropy, which is a measure of how disorderly a system is. When objects with positive temperature release energy, they increase the entropy of things around them, making them behave more chaotically. However, when objects with negative temperatures release energy, they can actually absorb entropy."

Image Credit: LMU/MPQ Munich

German scientists encountered negative temperatures by placing about 100,000 atoms in a vacuum to control the environment and then lowering their temperature to a few nanokelvin, just a handful of billionths above absolute zero. Using lasers and magnets, they were able to rigidly control the movement and potential energy of each atom, arranging them in a unique optical lattice. The result was a gas in which atoms attracted one another more than repelling one another, which runs counter to how a gas (which naturally expands) typically acts.

Now that science has laughed in the face of absolute zero's limits, what can we do with their achievement? In addition to telling us all sorts of interesting things about matter, negative temperatures could theoretically improve the technology of the combustion engine to more than 100 percent efficiency. If an engine draws energy from heat, negative temperatures could help them draw energy from cold atoms, too. Because cold atoms with negative temperatures are actually infinitely hot. Way to go, science.