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Scientists Seek To Take The Measure of Antimatter



Up next, another installment in the continuing quest to understand antimatter, that stuff that's supposed to be the opposite of matter. It's supposed to have been created during the Big Bang in equal amounts as normal matter, but for some reason, it's all disappeared. No one knows why - yeah, that stuff or actually that anti-stuff.

Well, when we last left our story just under two years ago, we talked with Jeffrey Hangst at CERN where researchers reported that they had been able to catch and trap antimatter particles, antihydrogen, keeping these particles confined in a trap for a 1,000 seconds, over 16 minutes. That's an eternity in the world of particle physics.

Having trapped the antimatter for a quantum eternity, scientists begin to study what they had in the bottle. And one of their questions they wanted to answer was, is antimatter so anti, what happens when you drop it? Will it fall up instead of down just like in the bizarro world? Well, here with me now to give an update on the project is Dr. Hangst. He's with us again. He's one of the authors on the paper published this week in the journal Nature Communications. It takes a first look to try to measure the gravitational mass of the particles. Welcome back to the program, Dr. Hangst.

JEFFREY HANGST: Thank you. It's always a pleasure to be with you.

FLATOW: Did you really try to drop and see if it drops - it goes up instead of down?

HANGST: Absolutely. First, you have to hold on to it, which we've talked about earlier. So we hold this antihydrogen in a kind of a magnetic bottle. We can't allow it to touch the walls or touch any matter. So we've got it there. And in the course of our normal experiments, we release it intentionally. That's how we actually know that we had it. So we have all these data where we've released this antihydrogen atoms, and we have a detector that looks at where they annihilate when they hit the wall of our apparatus. So it actually measures the vertical position of where the atoms annihilate. So we went back and looked through all our data and said can we see any evidence of gravity in these measurements?

FLATOW: And you found?

HANGST: We found that we have a good technique for doing this now, which is to us a kind of a minor revolution that you can do this at all. So far, we don't have the sensitivity to say that they obey the normal law of gravity or that they look like they want to go up when you release them. But we know now that we can do these experiments and with improvement, we can actually make a determination as to whether they fall up or down.

FLATOW: Will someone do the experiment?

HANGST: Absolutely. The thing is, right now, CERN in general is shutdown. There's a period for making a maintenance and intervention improvement on the Large Hadron Collider, the LHC, which is the main business of CERN. So for the next year and a half, CERN is shut down. As soon as we can start to get some antimatter beam from CERN again, we'll continue to investigate this. But it's - we know how to get from point A to point B now.

This - what's interesting about this article is that we demonstrated that you can do this. And we know how to improve it so that in the coming years, we can actually make this determination.

FLATOW: If you were a betting man - and I'm not saying that you are - would you suppose that it does fall up?

HANGST: I'm paid not to bet, Ira.


HANGST: That's - we got to be very clear about this, OK? No metaphysics for me. I'm an experimentalist. I believe what I can measure. And until then, the jury is out.

FLATOW: Yeah. But the - I'll bet you the theoretical particle physicists would bet on this.

HANGST: Actually, I was quite surprised. One of the interesting things about publishing this result is that people contact us and say, actually, I have a theory, you know, a legitimate theory that's been published in reviewed articles that says that antimatter will fall up, that it must fall up. So one of the sort of side benefits of publishing this measurement, even though it's a bit premature in terms of making a real determination, is that these guys contact us and say, oh, yeah, I'm really interested in that. And I have a theory that says that it will go up. So it's within reach. That's what's so exciting about this.

FLATOW: I should give you some of the theories that we get over our...


HANGST: Oh, no. I think we are - we're on the same list, my friend.


HANGST: I get those all the time.

FLATOW: Only if Al Einstein was still around to talk about...

HANGST: Yeah, exactly.

FLATOW: Well, the last time we spoke to you, I just published this paper about holding the antihydrogen in a trap for thousandths of a second.

HANGST: That's right.

FLATOW: Have you gone passed any of that time?

HANGST: Actually, OK, yeah. We did one result that you've missed in the meantime. And that was to make actually the first measurement on an atom of antimatter, and that was kind of a nice thing. The way you trap antihydrogen is that it's a little bit magnetic. You can think of it as kind of a little compass needle that points along the magnetic field that we use to trap it. It has spin in atomic language, so what we do is shine some microwaves on that atom and flip the spin, turn it around. And when you do that, it jumps out of the trap, OK? So the compass needle pointing one way, it wants to be trapped. If you use the microwaves and flip it, then it goes out and you can detect that.

So that's actually the first ever quantum interaction with an antimatter atom. We did that - so we published that last year in, I think, March or April. So that was also, you know, our main goal in all of this is to study the structure of antihydrogen and compare it to hydrogen. So that was a big milestone for us to actually make a measurement on, you know, a number, a quantum number associated with an antimatter atom. So we've had a couple of good years.

FLATOW: Yeah. Does anybody still have any better idea of where all the antimatter went?

HANGST: No. There's no sort of smoking gun theory about that. So our philosophy is anytime you can get your hands on some antimatter, you should take a really careful look. And the best way to do that is with atomic physics techniques to look at the spectrum of antihydrogen. What kind of light does it like to absorb and emit? Is that the same color of light that hydrogen absorbs and emits?

So also in the meantime, we've built a new machine we call ALPHA-2, which is improved and upgraded, that will allow us to actually shine laser light on trapped antihydrogen. So when we come back online in 2014, we have a brand-new machine. We'll have some lasers to shine on it, and it's a really very exciting time for us.

FLATOW: Can you keep it trapped for longer than 16 minutes?

HANGST: You know, it's not really worth looking because it's long enough. We showed with the microwave experiment that that was long enough. I have to tell you, it's an incredibly boring experiment to do. You know, you trap your antihydrogen. You wait for 16 minutes and you release it. You know, go have a coffee or something while you're - it just doesn't tell you anything more that we really need to know right now.

FLATOW: Well, you know, that's not what happened in the movie.

HANGST: No, no, I understand.


HANGST: But you're talking to the real deal now, Ira. This is not about - there's no science fiction here.

FLATOW: When you have an antihydrogen and a hydrogen bumping into each other, they get annihilated, right?

HANGST: That's right.

FLATOW: But what happens if an antihydrogen bumps into something bigger - let's say a carbon atom?

HANGST: Yeah, well, in fact, what our(ph) antihydrogen atoms bump into when we release them is gold. The inside of our apparatus is gold-plated, so they're actually hitting gold nuclei. So what happens is the antiquarks in the antiproton finds some quarks in a gold nucleus and annihilate with those. The amount of energy released is about the same, right? You're annihilating the rest mass of the antiproton on the same rest mass of the quarks that make up the nucleus.

FLATOW: So does the gold get changed any way from...

HANGST: Not in any way that you would measure macroscopically, right, but - because we're talking about, we trap one atom at a time, right? So there's no macroscopic effect that you would be able to measure. But for us, that's a microscopically violent event, right? There's a lot of energy released, and we're pretty good at detecting that so we can actually see the energy release when you lose one atom of antihydrogen. By the way, you couldn't do that with hydrogen. If hydrogen hits the wall, nothing happens, right? So this is one way that antimatter is actually fun to work with.

FLATOW: When you shoot that radiation at it to flip it around, does it self-annihilate against the wall? Is that what happens?

HANGST: Yeah, what happens is the - it's trapped because of that little magnetic compass needle, if you will, always pointing in the right direction. If you flip it, it gets shoved out and then it annihilates, and you can see that. Or when you try to throw it away, it's not there anymore. That's another way to look at that measurement.

FLATOW: Last time when you were here, I asked you a question. I want to see if you remember what it was.


FLATOW: Do you remember that question about any practical applications? And what did you say? Do you remember what you said?

HANGST: Yeah, I said practical applications are science fiction, that we just can't make enough antimatter to be useful. It would take longer than the age of the universe to accumulate macroscopic amounts of antimatter to make a weapon or a rocket fuel or something like that. So this is really pure research, right? We're looking at, you know, one or few atoms at a time. There's 10 to the 24th atoms in a macroscopic amount of hydrogen or antihydrogen, so we're just nowhere near there. But it's still a lot of fun.

FLATOW: Yeah. So the answer to the question of a practical application is still absolutely no.

HANGST: Yeah, nothing has changed there and...

FLATOW: That's good to hear.

HANGST: Yeah, you feel safer that way, actually.

FLATOW: Yeah. We like to hear knowledge for the sake of knowledge.

HANGST: Now, if you found some antimatter, you know, if someone found some antimatter out in the universe, that would be another interesting story.

FLATOW: Well, if we hear about it, we'll let you know.

HANGST: Yeah, call me up, man.


FLATOW: OK. All right. Thank you, Jeffrey.

HANGST: My pleasure.

FLATOW: Have a good weekend.

HANGST: You too.

FLATOW: Jeffrey Hangst is the spokesman for the ALPHA Collaboration at CERN. He's also professor of physics at Aarhus University in Denmark. Transcript provided by NPR, Copyright NPR.