This Week's Discoveries

Archimedes' Death Ray

Die, Romans, die

In 212 BC, the Romans besieged the Sicilian city of Syracuse, home to one of the greatest mathematicians who ever lived: Archimedes. Now, old Archimedes wasn't just a numbers guy. He used his mathematical powers to invent things. He was pretty handy with pulleys and levers, for example, allegedly saying, "Give me a place to stand and I will move the world!"

So, if you were Archimedes facing Roman legions, what would you do? That's right. You'd invent a death ray. Old histories of the era tell the tale: "At last in an incredible manner he burned up the whole Roman fleet. For by tilting a kind of mirror toward the sun he concentrated the sun's beam upon it; and owing to the thickness and smoothness of the mirror he ignited the air from this beam and kindled a great flame, the whole of which he directed upon the ships that lay at anchor in the path of the fire, until he consumed them all."

For centuries, historians have debated whether it really happened. Recently, a TV show called MythBusters even tried to recreate the ray, failed, and called it an "urban legend." But students at MIT weren't convinced. This month, they built their own death ray, using only sunlight, 127 mirrored tiles, and their MIT brainpower. Once the sun came out from behind a cloud, it took less than 10 minutes for the students' death ray to make a Roman ship (well, a foot-thick, red-oak facsimile) burst into flames.

No one knows if Archimedes did make a death ray like MIT's. But it looks like he could have. Either way, it didn't save him or Syracuse. Eventually, the Romans took the city. According to ancient historians like Valerius Maximus, the Roman general was so impressed with Archimedes' war machines that he ordered that his life be spared. But when a pillaging soldier broke into his house and asked him who he was, Archimedes was too absorbed in drawing mathematical diagrams on the floor to answer. Protecting the diagram with his hands, he said only, "I beg you, do not disturb this!" and was killed.

See how MIT students made their death ray

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Quantum Dots Could Light Up Your Life

This way to the future

Few inventions have changed the world like the light bulb. But time and technology have a way of replacing even the brightest ideas. In fact, light emitting diodes (LEDs) have been doing more of the world's lighting work in recent years--not only in electronic devices, but in architectural lights, traffic lights, flashlights, and more.

LEDs have some serious advantages over incandescent bulbs. They're sturdier, they produce twice as much light watt for watt, and they last 50 times as long. One problem: while LEDs are great for making colored light, they're not so good at making the bright white light we like to live and work by. Until now, that is--thanks to an accidental discovery by Michael Bowers, graduate student at Vanderbilt University.

Bowers was cooking up a batch of quantum dots--tiny crystals a thousand times thinner than a human hair. And not just any quantum dots, but "magic-sized cadmium selenide nanocrystals," which contain just 33 or 34 pairs of atoms. The dots were intended for a coworker's research project, but when Bowers shined a laser on them he got a surprise all his own. They gave off "a beautiful white glow."

Energized quantum dots normally give off colored light. As soon as Bowers saw the white light, he knew he was on to something. So he and another student mixed the quantum dots into polyurethane and coated a blue LED light bulb with quantum-dot goop. Result? An LED that gives off a warm, sunny light. Someday, instead of flipping on the lights, we might just energize the magic-sized dots.

Run down the top 10 accidental discoveries of modern times

Michael Himick and Steve Sampson
October 28, 2005