美国国家公共电台 NPR Why Corned Beef Sandwiches — And The Rest Of The Universe — Exist（在线收听）

SCOTT SIMON, HOST:

When NPR science correspondent Joe Palca came to us and said he had a story about EDM, we thought (laughter) we could get down with that.

(SOUNDBITE OF SONG, "GRAPEVINE")

TIESTO: (Singing) My mind, my mind, my mind. My mind, my mind, my mind. My mind, my mind, my mind.

SIMON: Then Joe said the story is not about electronic dance music - much favored by BJ Leiderman, who writes our theme music - but instead the electric dipole moment of the neutron. We said, what is that? Joe said he'd explain.

JOE PALCA, BYLINE: When Indiana University physicist Chen-Yu Liu is asked why she's interested in the electric dipole moment of the neutron, she's ready with an answer.

CHEN-YU LIU: I say I'm trying to understand why we exist.

PALCA: In fact, she's trying to understand why everything exists - you, me, stars, galaxies, corned beef sandwiches, everything. Theories say the explanation may be hidden in the electric dipole moment of the neutron. It's not a moment as in a moment in time. It refers to the neutron being slightly more football shaped than perfectly spherical. You see, at the instant the universe came into existence billions of years ago, energy turned into matter.

Now, matter comes in two types - matter and antimatter. And when a particle of antimatter meets a particle of matter, they annihilate each other, and all that's left is light. So somehow, somewhere there had to be a slight imbalance, a bit more matter than antimatter, to make all the stuff in the universe. Theories predict the signal that explains that imbalance would be found if the neutron had a measurable electric dipole moment. But so far, no one has been able to measure one. Chen-Yu Liu says that maybe because it's small and hard to measure in neutrons.

LIU: To do measurement precisely, we need to be able to slow them down, confine them in space and watch them for a very long time.

PALCA: So basically you're trying to get the neutron to sit still while you study it.

LIU: Exactly.

PALCA: Liu is working on one way to slow down neutrons. At Oak Ridge National Lab in Tennessee, they're working on another.

VINCE CIANCIOLO: All right, so the main target is down there.

PALCA: We're at something called this Spallation Neutron Source at Oak Ridge. It's a cavernous room that throbs with energy. Vince Cianciolo is a physicist here. He says when you shoot a beam of protons at a target made of mercury, you get a spray of neutrons that can be diverted into multiple beamlines.

CIANCIOLO: This is the fundamental physics beamline - beamline 13 - and the dipole moment experiment will be mounted next on this beamline.

PALCA: To get the neutrons to slow down so you can study them, you need to build a special chamber where the neutrons can be chilled colder than 450 degrees below zero Fahrenheit. And that's just one of the challenges. Cianciolo points to a spot at the end of the beamline where the chamber will be installed.

CIANCIOLO: The support of this whole foundation has to be non-magnetic, so you can't use standard rebar. You have to use - we'll probably use fiberglass rebar.

PALCA: The construction here will take place over the next couple years. In the meantime, other pieces of the experiment are taking shape. At Caltech in Pasadena, physics grad student Marie Blatnik is working on that chamber that will ultimately go to Oak Ridge. It's a giant aluminum cylinder.

MARIE BLATNIK: We get to probe the smallest parts of the universe by making the world's largest machines. I mean, look at this thing (laughter). It's huge.

PALCA: Blatnik's adviser Brad Filippone says people have been trying for decades to find the neutron's electric dipole moment. He says the apparatus they're building here will take the search to the next level.

BRAD FILIPPONE: We believe we'll be able to increase the sensitivity by a factor of 100.

PALCA: But it's possible that even after this more sensitive search, physicists may still come up empty. Filippone says that's OK. Physicists will learn something.

FILIPPONE: Looking for the electric dipole moment is relatively easy to make the science case to other physicists. The question is, how much are you willing to spend?

PALCA: And convincing non-physicists the search is worth the money can be harder. Just ask physicist Leah Broussard at Oak Ridge.

LEAH BROUSSARD: My mom says, why are my tax dollars being wasted on this research?

PALCA: But Broussard has an answer for her mom.

BROUSSARD: Humans are explorers. We explore the unknown frontiers. I want to know how the universe came to be. Don't we all?

PALCA: I imagine so. Joe Palca, NPR News.