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This year we've covered debates on everything from health care to gun control. And we're going to add one more to the list today, black holes. There are regions of space so dense that nothing, not even light, can escape. There's a long-standing view about what happens when things fall into these holes. But new research suggests that that may be wrong. NPR'S Geoff Brumfiel reports on what could be called this year's most massive argument.

GEOFF BRUMFIEL, BYLINE: All right. Let's say you're falling into a black hole.

LEONARD SUSSKIND: How big is a black hole?

BRUMFIEL: Stanford researcher Leonard Susskind. I guess size matters. Big, big. Let's make it...

SUSSKIND: All right. Really, really big.


SUSSKIND: A black hole a billion masses of the sun, like in the center of some galaxies.

BRUMFIEL: So you're falling into this huge black hole. According to the traditional version of things, at first you're not going to notice much of anything. But the black hole's gravity is getting stronger and stronger. And eventually you pass a point, a point of no return.

SUSSKIND: It's kind of like you're rowing on Niagara Falls and you pass the point where you can't row fast enough to escape the current. Well, you're doomed at that point. But passing the point of no return, you wouldn't even notice it.

BRUMFIEL: But now you can't get out. And gravity from the black hole is starting to pull on your feet more than your head. Joe Polchinski is a physicist at the University of California at Santa Barbara.

JOE POLCHINSKI: The gravity wants to sort of stretch you in one direction and squeeze you in another.

BRUMFIEL: There's a technical term for this stretching.

POLCHINSKI: It's called spaghettification.

BRUMFIEL: And as the black hole spaghettifies you, it's going to hurt.

POLCHINSKI: It'd be kind of medieval. It would be like something on "Game of Thrones."

BRUMFIEL: The old theory says that's the end of you and the story. But Polchinski's got a new version of things, a version that is so radical, it set the field of black hole physics aflame.

POLCHINSKI: So our hypothesis is that the inside of a black hole, it may not be there at all.

BRUMFIEL: Wait, so black holes don't have an inside?

POLCHINSKI: Well, the final outcome of the story may be something more interesting still, but that's where things stand now.

BRUMFIEL: Right. Do holes have to have insides? This is starting to get deep. But if you're struggling, don't worry. Leonard Susskind, that whiz from Stanford is having trouble with it, too. He thinks it sounds crazy, but he can't put his finger on why.

SUSSKIND: Nobody quite knows exactly what's wrong with their argument and that's what makes this so important and interesting.

BRUMFIEL: You see, Susskind says this no inside idea tries to solve a really big problem with black holes. There's this rule in physics. In the simplest terms, it's this: Stuff just can't disappear from the universe. This rule is really fundamental.

SUSSKIND: Everything is built on it. If it were violated, everything falls apart.

BRUMFIEL: For a long time, people thought that when you fall into a black hole your spaghettified remains would always be in there somewhere, but for decades, there's been a problem. Back in the '70s, the famous physicist Stephen Hawking clearly showed black holes evaporate. Very slowly, they vanish. And that breaks the fundamental rule because your spaghettified remains vanish, too.

SUSSKIND: The black hole evaporates, they're gone.

BRUMFIEL: Why don't you think Hawking was sort of bothered by this?

SUSSKIND: I don't know. I'm not a psychiatrist and I can't psychoanalyze him.

BRUMFIEL: But it did bother Joe Polchinski. He reanalyzed Hawking's equations.

POLCHINSKI: What we did is we took Hawking's original argument and very carefully ran it backwards.

BRUMFIEL: And Polchinski and his colleagues found one way to keep things from vanishing when they fall inside a black hole. They got rid of the inside. Instead the point of no return becomes kind of a cosmic manhole cover with nothing behind it.

POLCHINSKI: Probably that's the end - we're not sure, but probably that's the end of space itself. There's no inside at all.

BRUMFIEL: So in Polchinski's version, when you fall into a black hole, Leonard Susskind says you don't disappear. You smack into the end of the universe.

SUSSKIND: You've just come to the end of space and there's nothing beyond it. Terminated.

BRUMFIEL: So you're just gently falling in and then all of a sudden...

SUSSKIND: And then you're gone.

BRUMFIEL: It sounds very like "Looney Tunes," you know. Like, you're just...

SUSSKIND: Yeah, right. Right, right. You can imagine a cartoon where he just goes zip, he's gone. That's got to be wrong.

BRUMFIEL: In fact, even Joe Polchinski still feels instinctively like black holes should have insides, but nobody's got a better theory and as crazy as it sounds, this is progress. In the year ahead, Susskind hopes someone can find a flaw in Joe Polchinski's argument, just the way Polchinski found a flaw in Stephen Hawking's argument. But it will be awhile before we understand black holes inside and out. Geoff Brumfiel, NPR News.

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