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Fermi Problem Friday: How much energy do you save by having a white roof?

This Friday, in honor of my new facebook friend Steven Chu, I'd like to examine his "White Roofs" campaign through a Fermi problem.

Steven Chu has said that we could all save energy simply by painting our roofs white. The idea is the same one behind why I don't wear a black shirt on a sunny day (and white after Labor Day). Black objects absorb light, and with it, heat, while white objects reflect it. So if you're trying to keep your house cool in the summer, it makes sense to have a roof that reflects sunlight instead of absorbing it. Here's the schpiel:



But how much energy do you save, really?

The Fermi Problem:



The solar flux at Earth's atmosphere is about 1360 watts per square meter. About 0.3 of this is reflected back into space, while the rest is absorbed by the earth. Given the square footage of your roof, how much energy (assumed as heat) would a black roof absorb? How much energy would a white roof absorb?

Now, you could give Secretary Chu the benefit…

Add Steven Chu on facebook

I've long gotten over the novelty of being able to "add" famous physicists like Isaac Newton, Richard Feynman, and James Clerk Maxwell as friends on Facebook. Fans have their choice of several online impersonators, of varying degrees of convincingness, for each scientific luminary. But in between hanging out with astronauts and watching Toy Box videos, I somehow missed the fact that Secretary of Energy Steven Chu has joined facebook.

Chu must be our most popular and recognizable Secretaries of Energy yet. I mean, can anyone even name a former secretary off the top of their heads? Maybe it's because Chu radiates that ineffable rock star aura known as Geek. He's smart, he bicycles, and he's the first Secretary of Energy who's actually a scientist. And not just your test-tube-shuffling, garden-variety boffin; Chu has a Nobel Prize. (And he's still publishing.)


But part of me raises an eyebrow at such a public figure using such a casual medium to speak to …

Your comments on jerks and traffic jams

Yesterday's post generated a lot of great conversation, so I thought I'd respond to some of the interesting points brought up in the comments section. First, are platoons (chains of several cars that are traveling close together) really that bad?
Anonymous said...
The thing about these "platoons" is that when you're driving that close you're not just watching the car in front of you but the car in front of him. You actually end up monitoring a couple of cars ahead. So if you see something happening to the car 2,3 or 4 cars ahead you start easying off and you have more time to brake when the mud really hits the fan. Strangely enough, Dr. Appert-Rolland told me that the specific expressway she was looking at rarely had accidents, though that wasn't the focus of her study. With such long platoons, it seems like rear-end collisions would happen pretty frequently, so maybe there's something to the above comment. I'd be interested to know why accidents d…

Jerks actually reduce the risk of traffic jams

The next time someone cuts you off on your morning commute, don't be so quick to call the driver a jerk; you may have a reason to say thanks. According to the latest physics research, rule-breakers—drivers passing you on the wrong side or changing lanes too close to the intersection—actually help smooth the flow of traffic for the rest of us.
"The interesting finding is that if most of the people are law-abiding, and you have a certain amount of people who are breaking the rule, then you are actually getting the minimum chance of a [traffic] jam," said Petter Minnhagen, a physicist at Sweden's Umea University and an author of the paper published in the journal Physical Review E.
Physicists at the school uncovered this phenomenon while constructing a computer model of how a crowd of people move across a confined space, such as a pedestrian-only street. They divided the space into squares, like a chessboard, and randomly placed pedestrians in some of the squares. Li…

Physicists at TED Global Conference

The hallowed halls of Oxford University have been echoing with even more good ideas than usual lately. Last week the venerable institution hosted the 2009 TED Global Conference. A sort of variety show for the mind, the conference featured talks by innovators, thinkers, musicians, artists, architects, scientists, and even British Prime Minister Gordon Brown (warning before you click: his talk is about pretty tough stuff, and includes photos from war zones in the first few minutes.)
If you haven't heard of TED, go right to the website. There you can find videos of talks by anyone from famed primatologist Jane Goodall to engaging string theorist Brian Greene, and former UN director Louise Fresco to aspiring millennium man Ray Kurzweil. The brainchild of WIRED editor-in-chief Chris Anderson, TED stands for Technology, Entertainment, and Design. It's like a mini-YouTube for the most daring, unusual, thought-provoking ideas (and thinkers) out there. Think of it like the Harvard clas…

Fermi Problem Friday

Hurry back guys! Time to head to Pluto.

We recently celebrated the 40th anniversary of the Apollo 11 moon landing, we're airing a special edition of Fermi Problem Friday in honor of Buzz, Neil, and Mike (you know, Michael Collins, the guy who drew the short straw and had to stay in lunar orbit).

Here is the problem:

It took the Apollo 11 crew four days to reach the moon, blasting off from the Kennedy Space Center on July 16, 1969 and arriving at the moon on July 20. What planet would they be closest to today, about 40 years later, if they'd decided to skip the moon and head out into the solar system?
Extra credit: How many Swedish Fish would it take to form a ring around Saturn that the astronauts could see as they flew by, if they made it that far?

Share the problem with friends, try it out on your blind date tonight, and remember, all you need is your common sense, intuition, and a vague idea of how fast our intrepid crew was traveling.

Electricity From Salty Water

The Mississipi delta, where the freshwater river pours into the salty Gulf of Mexico, would be an enormous source of energy if we could tap it.
A device that gleans usable energy from the mixing of salty and fresh waters has been developed by University of Milan-Bicocca physicist Doriano Brogioli. If scaled up, the technology could potentially power coastal homes, though some scientists caution that such an idea might not be realistic.

Extracting clean, fresh water from salty water requires energy. The reverse process—mixing fresh water and salty water—releases energy. Physicists began exploring the idea of extracting energy from mixing fresh and salty waters, a process known as salination, in the 1970s. They found that the energy released by the world’s freshwater rivers as they flowed into salty oceans was comparable to "each river in the world ending at its mouth in a waterfall 225 meters [739 feet] high," according to a 1974 …

Space fever!

July is the month for space nuts. We're in the midst of a wonderful hullaballoo surrounding the 40th anniversary of Apollo 11, giving the younger generation a taste of the original excitement. The Guardian, the New York Times, and almost every other major newspaper is providing tons of Apollo 11 anniversary coverage, although my favorite piece of media so far is a stunning collection of high-resolution photos from the mission, thanks to the Boston Globe's amazing photo essay collection, The Big Picture. There's something timeless about these gigantic photos; one of my favorites is the close-up shot of Neil Armstrong from an earlier mission, where he had to pilot Gemini VIII through the atmosphere and dock it to a vehicle in orbit. He looks wonderfully lost in thought, almost melancholy; my romantic brain thinks it's the expression only a man who's seen earth from space could wear.
But enough reminiscing. In July space nuts are spoiled for choice, because we've a…

NASA followers gather for tweetup

With the Smithsonian (@ReliveApollo11) tweeting the 40th anniversary of the Apollo11 mission and current space shuttle mission commander Mark Polansky (@Astro_127) tweeting the crew's work on the International Space Station, no space nut these days can operate without a twitter account. Today NASA took the experiment one step further and held a tweetup. Part of the growing twitter lexicon this term refers to a real-life meetup for tweople (people on twitter, I'm led to believe). Usually this means a dozen or so people in a bar, but in the case of NASA followers, which broke 100,000 today, the auditorium at NASA headquarters did the trick today. A lucky 150 or so people flew in from as far away as Arizona, Vancouver, and even (wow!) Spain, crowded in, turned on their iPhones and laptops, and were treated to a good two hours with the crew of the STS-125 shuttle mission to make repairs to rejuvenate the Hubble space telescope.

We've come a long way since the first TV transmiss…

Where were you when we landed on the moon?

I think I'll always regret not being alive during the moon landing, forty years ago today. If the Beatles form Exhibit A in the case for me being born in the wrong decade, Apollo 11 is exhibit B. I can't remember it, so what I remember is my dad describing the moon landing as a near-psychedelic experience, forever bound to the bad classic rock song he happened to be listening to at the same time. Figures. It was 1969, and he was 21 years old, living in his parents' basement in Queens, which was lined with those slender, acid-yellow paperbacks that formed the Old and New Testaments of his childhood: Heinlein, Kornbluth, Verne, Asimov.
"I was jumping up and down in that basement cave with all the science fiction books that I'd grown up with, and it was actually happening," he recalls.
A ghostly Neil Armstrong stepping off a ladder 240,000 thousand miles away flickered on the old black-and-white, while WBAI FM simulcast Lothar and the Hand People's "Walk…

Crazy (in a good way)

After a month of cramming for finals and living off raw ramen noodles, there's nothing more appealing to a college student at the end of May than a long summer doing nothing, punctuated, if you're feeling really ambitious, by an occasional camping trip or jaunt to the beach.Unless you're Laurie Stephey or Brad Dinardo. In that case you might feel more up to nine weeks of performing cutting-edge scientific research.

Laurie and Brad are two of this summer's Society of Physics Students interns, a group of motivated, physics-lovin' college students who spend nine weeks every summer working on projects ranging from from locating ice under the Martian soil to developing fun hands-on science curriculum. The interns worked at NASA Goddard Space Flight Center, the University of Maryland's Materials Research Science and Engineering Center, the American Institute of Physics, and the American Physical Society. Laurie and Brad worked at the National Institutes of Standards a…

'Invisible' Building Design Could Reduce Earthquake Damage

Engineers have been developing earthquake-resistant buildings for years, but a group of physicists now believe it's possible to make an entire building effectively disappear from an earthquake's destructive path, avoiding serious damage. Inspired by the recent development of novel materials that precisely control the flow of light waves around objects, they've shown that the same ideas can work whether the waves make up light, sound or earthquakes.

Earthquakes are some of the most destructive forces in nature. The waves they produce ripple across the earth's surface, much as water waves travel across the ocean. The waves from earthquakes crumple buildings, bridges, and other structures, causing millions of dollars in damage and often death. Despite efforts to understand earthquakes and reinforce buildings against them, damage from the shaking ground is nearly impossible to avoid. But that may not be the case for long, say a team of physicists in France and the United Ki…

"Sixty Symbols"

Whether ยต, h, and l make perfect sense or are (literally) Greek to you, don't miss "Sixty Symbols", the latest in science video yumminess from the hilarious, kooky, and frequently brilliant media team at the University of Nottingham. Now that they've completed their quest to capture the essence of every element in the periodic table in a five minute video, they've decided to take on the mysterious and meaningful language of scientific symbols.


Each video is an intimate desk-side chat with a scientist, taking on concepts ranging from the fundamental, such as vectors, to the erudite, such as chaos theory's Feigenbaum constant. The style is a cocktail of home video and scientific portrait. I love that director Brady Haran keeps them short and sweet and gets interesting angles on even drier-sounding symbols like "magnetic susceptibility" (the above video features levitating beer!) Think of the series as a meandering, nonlinear journey through the world…

USA! USA! USA!

Hey there sports fans there's an international showdown going on that you might not even know about! Right now some of the brightest high school physics minds in the United States are down in Mexico matching wits against some of the brightest high school physics minds of the rest of the world. It’s the annual International Physics Olympiad! Go team go!

Ok, I got that out of my system, but the IPHO, being held this year in Merida Mexico, really is an incredible event. Each year over 65 teams representing countries from around the world vie for the gold. Instead of incredible feats of strength the participants must perform incredible feats of intellect. Through three physics problems and a lab held over the course of eight days from July 12th to the 19th, the teams will duke it out to see who goes home with the gold!

I had the privilege of meeting some of the team members and coaches in May when they were training at the University of Maryland. I was really blown away when I met them;…

Manhattan's grid is a modern-day Stonehenge

{creator and copyright holderManicMaurice, image available on Flickr}

Yesterday evening, the citizens of New York City enjoyed an awesome spectacle of the sun setting exactly in line with the east-west streets of the Manhattan grid. Known as Manhattanhenge, a term coined by Hayden Planetarium's director, Neil deGrasse Tyson, the phenomenon is just like what you see at Stonehenge at the summer and winter solstices. But in New York City, the special days are May 30 and July 12. This is due to the fact that the grid, made up of streets running east to west and avenues running north-south, isn't exactly in line with the compass. It's offset 28.9 degrees east from geographic north.
As Tyson suggests, I can just imagine the archaeologists of the future trying to piece together why Manhattan's streets are aligned just the way they are. What's so important about 28.9 degrees? Were May 30 and July 12 the holy days of this lost civilization?
To save archaeologists the trouble, …

The numbers are in: people like science

Yesterday the Pew Research Center for the People and the Press released an extensive study exploring how the public feels about scientists and how scientists feels about the public. (It occurs to me that the way I phrased that makes it sound like they recently went through a bad breakup.) Here are the results, in a nutshell: Public: "Oh look, scientists! Hey, I'm a big fan. I mean, thanks for the internet and medication and stuff." Scientists: "Um, you're welcome?" Public: "But you know what, to be honest, I don't really understand you very well." Scientists: "Maybe you're short-selling yourself." Public: "No, seriously. Ask me a question." Scientists: "Okay. Let's see...hey, here's an easy one. Which are smaller, atoms or electrons?" Public: "Um..." Scientists: "Sigh...Well, I suppose it's not your fault, considering the abysmal state of science education and science media in this country.&…

Putting old particle physics experiments out to pasture

Somewhere in the quintessentially Californian golden hills above Stanford University, a giant physics experiment is quietly rotting. "In" is the operative word here; the behemoth sits in a three-story-deep, concrete-lined hole in the ground, sheltered in a warehouse-sized structure in one of the more deserted reaches of SLAC National Accelerator Laboratory's sprawling campus. Cars and trucks still park in the lot outside, bearing scientists, construction workers, and engineers to the lab's current big project, accessible via two entrances nearby. But this particular piece of physics junk is closed for business.A hulking steel beast seemingly overgrown with wires, this detector, known as Mark II, was once a microscope that could peer into the most fundamental building blocks of our universe. And it's only a small piece of the much larger experiment that made it happen. Although you can't see them, the two halves of a 2.2-km circular tunnel come together here.…