David Kestenbaum

For more on what Bitcoin is and how it works, see our story "What Is Bitcoin?"

Gavin Andresen is chief scientist at the Bitcoin Foundation. I first talked with him about Bitcoin, the virtual currency, back in 2011. I checked back in with him this week, because so much has been going on with Bitcoin lately.

Robert Shiller was surprised when he got the call telling him he'd won the Nobel Memorial Prize in economics — surprised that he'd won (of course), but also surprised that he was sharing the award with Eugene Fama.

"He and I seem to have very different views," Shiller told me. "It's like we're different religions."

In particular, they have very different views about economic bubbles.

"The word 'bubble' drives me nuts, frankly," Fama told me.

For more of our reporting on this story, please see our work in The New York Times Magazine and on This American Life.

Earlier this week, I bought a Treasury bill.

Everybody calls Treasury bills T-bills, and they work like this: The government promises to pay holders of T-bills a specific amount on a specific day in the near future. For the T-bill I bought, the government promised to pay $1,000 on Oct. 31.

I bought the T-bill on Tuesday, before Congress had made the debt-ceiling deal, so it was unclear whether I would get paid back on time.

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.

Tuesday is a big day for Obamacare. The online marketplaces where people can shop for health insurance are supposed to open for business.

No one really knows who is going to sign up — not the Obama administration, not the insurance industry, not the president's critics. Yet the success of the law hangs on this question: Will the right mix of people sign up? In particular, will healthy people buy health insurance?

The government of Ecuador has abandoned a plan that would have kept part of the Amazonian rainforest off limits to oil drilling. The initiative was an unusual one: Ecuador was promising to keep the oil in the ground, but it wanted to be paid for doing so.

For more of our reporting on this story, please see our recent column in the New York Times Magazine, and the latest episode of This American Life.

For more of our reporting on this story, please see our recent column in the New York Times Magazine, and the latest episode of This American Life.

Why does anyone buy Bayer aspirin — or Tylenol, or Advil — when, almost always, there's a bottle of cheaper generic pills, with the same active ingredient, sitting right next to the brand-name pills?

Matthew Gentzkow, an economist at the University of Chicago's Booth school, recently tried to answer this question. Along with a few colleagues, Gentzkow set out to test a hypothesis: Maybe people buy the brand-name pills because they just don't know that the generic version is basically the same thing.

Climate change seems like this complicated problem with a million pieces. But Henry Jacoby, an economist at MIT's business school, says there's really just one thing you need to do to solve the problem: Tax carbon emissions.

"If you let the economists write the legislation," Jacoby says, "it could be quite simple." He says he could fit the whole bill on one page.

Basically, Jacoby would tax fossil fuels in proportion to the amount of carbon they release. That would make coal, oil and natural gas more expensive. That's it; that's the whole plan.

In many parts of the developing world, drinking a glass of water can be deadly — especially for young children, who can die of diarrheal diseases contracted from dirty water.

So getting clean water to people in the developing world has been a top priority for aid groups for a long time. But it's been a surprisingly hard problem to solve.

Over the past decade, some 39,000 people have come forward voluntarily to tell the IRS about offshore money they haven't been paying taxes on. This group provides a small window into the world of people who are hiding money in offshore havens. (It's a world we've been trying to learn more about, partly by setting up an offshore company in Belize.)