From black holes to black history

Alan Boyle Science editor • Profile • E-mail

Astrophysicist Neil deGrasse Tyson — director of New York’s Hayden Planetarium, host of “Nova ScienceNow” on public television and author of the newly published book “Death by Black Hole (and Other Cosmic Quandaries)” — may well be one of the world’s best-known black scientists.

But don’t invite him to speak at a Black History Month celebration. Tyson is likely to turn you down.

It’s not that the 48-year-old Bronx native has anything against the idea of celebrating notable blacks in American history every February. It’s just that race doesn’t play any part in his line of work — and that’s why he deflects speaking requests that are specifically tied to the monthlong event.

“If the only time you think of me as a scientist is during Black History Month, then I must not be doing my job as a scientist,” he told MSNBC.com. “All I tell them is, invite me some other month and I’ll be happy to give a talk.”

Tyson is more eager to talk about his scientific duties, which include doing research on the scientific frontier; exposing the public to scientific issues through his books, lectures and TV gigs; and speaking out on scientific policy matters great and small:

• Years ago, he changed the displays at the Hayden Planetarium to take Pluto out of the lineup of the solar system’s major planet — a decision that sparked an outcry from legions of schoolchildren but was backed up by a controversial vote last year by the International Astronomical Union.
• He helped shape NASA’s new vision for space exploration in the wake of the 2003 Columbia tragedy, as a member of the President’s Commission on the Moon, Mars and Beyond.
• In addition to his planetarium post, he serves as chairman of the board for the Planetary Society, a nonprofit space advocacy group. In that role, he fills the shoes of the late astronomer Carl Sagan — a telegenic scientist to whom Tyson is often compared.

In a wide-ranging interview with MSNBC.com, Tyson started out by discussing “Death by Black Hole,” a collection of essays drawn from his long-running column in Natural History magazine. But he branched out to discuss how Hollywood and the news media get science wrong, what frustrates him about his role as celebrity astronomer, and yes, his perspective on being a scientist who also happens to be black. Here's an edited version of the Q&A:

MSNBC: How did you select the title “Death by Black Hole”?

Tyson: Well, the title selects itself. If you had an essay called “Death by Black Hole,” wouldn’t you call the book “Death by Black Hole”? And the subtitle is, of course, “... and Other Cosmic Quandaries.” The essays are chosen primarily for their discussion of things that can go wrong in the universe — either in the actual universe, or things that can go astray in our understanding of the universe.

So let’s start with how to die by black hole. Perhaps the most intriguing aspect of the scenario derives from the simple fact that if you take a feet-first dive to a black hole, at all times the force of gravity at your feet will be greater than the force of gravity at your head — because your feet are closer to the black hole than your head is.

By the way, that’s true even if you’re just standing on Earth. Earth’s gravity is stronger at your feet than it is at your head. But you don’t notice this because all that matters to you is the difference in that strength of gravity. And when you’re standing on Earth, it’s so small as to go unnoticed.

Q: Right, because it’s proportional to the difference in the distance to the center of the earth.

A: Exactly. You’re not very tall compared with the radius of the earth where you’re standing, so that radius shows up to be minuscule. But as you descend toward a black hole, the gravity just keeps growing and growing and growing. And the difference in gravity between your head and feet keeps growing and growing and growing.

So this is fine and well and good, until you compare the difference in force in gravity between your head and feet and the ability of the molecules of your body to hold your flesh together. Now, people who are in good shape can stretch. Your body has some flexibility to it. So initially you might just feel good: “Oh, this is a nice stretch!” But then the stretch becomes unrelenting. There will come a point when the force of gravity exceeds the forces of the molecules in your flesh that keep them together. And at that moment you snap into two pieces, top and bottom.

As you continue to descend, each of those two pieces snaps into two pieces. And you go from one to two to four to eight to 16 to 32, and it just continues. Meanwhile, as if that’s not bad enough, the fabric of space-time narrows as you approach the center of the black hole. So you’re becoming funneled, extruded, like toothpaste through a tube. You’re being stretched and squeezed simultaneously.

There’s a word for this. We call it spaghettification. You will reach the center of the black hole as this stream of atoms, having been stretched and extruded through the fabric of space-time. Of course, this would be the envy of the Spanish Inquisition, which had those machines to stretch people on the rack.

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