David Kestenbaum

David Kestenbaum is a correspondent for NPR, covering science, energy issues and, most recently, the global economy for NPR's multimedia project Planet Money. David has been a science correspondent for NPR since 1999. He came to journalism the usual way — by getting a Ph.D. in physics first.

In his years at NPR, David has covered science's discoveries and its darker side, including the Northeast blackout, the anthrax attacks and the collapse of the New Orleans levees. He has also reported on energy issues, particularly nuclear and climate change.

David has won awards from the American Association for the Advancement of Science, the American Physical Society and the Institute of Electrical and Electronics Engineers.

David worked briefly on the show This American Life, and set up a radio journalism program in Cambodia on a Fulbright fellowship. He also teaches a journalism class at Johns Hopkins University.

David holds a bachelor's of science degree in physics from Yale University and a doctorate in physics from Harvard University.

On the most recent episode of our show, we told you the story of two guys who think they've found a guaranteed way to buy low and sell high. Their secret strategy — buying and selling used textbooks.

Take a look at your signature the next time you buy something with a credit card. Maybe you spell out every letter. Maybe you just put a squiggly line. The other day, I drew a tree.

Signing is a very old ritual, according to Rabbi Pinchas Allouche. He's a scholar of the Talmud, a collection of Jewish texts that's over 1,000 years old.

The Talmud not only mentions signatures; it has rules for them. "A scribble is prohibited," Allouche says. The name has to be legible. "Just yesterday, when signing a Toys R Us receipt, I thought of the Talmud," he says.

Ikea, a company famous for keeping its costs down, recently announced that it would raise the average minimum wage for its retail workers to $10.76 an hour. Why would the company volunteer to pay its workers more?

"By taking better care of our coworkers," says Rob Olson, the acting president of Ikea U.S., "they will take better care of our customers, who will take better care of Ikea. We see it as a win-win-win opportunity."

The Stradivarius violin gets its name from master craftsman Antonio Stradivari. When he died in 1737, his secrets died with him: No one has ever been able to duplicate the sound of the violins or violas he made.

His instruments have taken on a mythical quality. Today they fetch millions of dollars at auctions; Sotheby's will soon auction off a viola that it expects to sell for $45 million.

When we talked to Katerina Margaritou two years ago, she was worried about how she would pay for her wedding dress. She was working for the government as a chemist, but hadn't received a paycheck in months.

Katerina was starting to lose faith in her country, starting to think she and her fiancee, Elias Tilligadas, would be better off leaving Greece.

President Obama has called for increasing the minimum wage, saying it will help some of the poorest Americans. Opponents argue that a higher minimum wage will lead employers to cut jobs.

Figuring out the effect of raising the minimum wage is tough. Ideally you'd like to compare one universe where the minimum was raised against an alternate universe where it remained fixed.

Ben Horowitz is a big-time venture capitalist. His firm invested in Facebook and Twitter. More recently, his firm invested some $50 million in startups related to bitcoin, the virtual currency that works like online cash. Ben thinks bitcoin is going to change the way people buy and sell stuff on the Internet.

We recently published a story about how used clothes that get donated in the U.S. often wind up for sale in markets in Africa. As part of the story, we published some photos of used T-shirts we found in a couple of markets in Kenya.

One shirt in particular caught our eye:

What would happen if Congress doesn't raise the debt ceiling and the U.S. defaults on its debt later this month? The broad economic implications are unpredictable, but a default could cause huge trouble for the global economy.

But whatever happens to the global economy, one thing is clear: People all over the world who have loaned the U.S. government money won't get paid on time.

The story of the birth of accounting begins with numbers. In the 1400s, much of Europe was still using Roman numerals, and finding it really hard to easily add or subtract. (Try adding MCVI to XCIV.)

But fortunately, Arabic numerals (1, 2, 3, 4, etc.) started catching on, and with those numbers, merchants in Venice developed a revolutionary system we now call "double-entry" bookkeeping. This is how it works: