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Gravity's quantum leaps detected
New Scientist ^ | 19:00 16 January 02 | Hazel Muir

Posted on 01/17/2002 4:06:29 PM PST by Ernest_at_the_Beach

Gravity's quantum leaps detected

 
19:00 16 January 02

Hazel Muir

 

Gravity's subtle influence in the quantum world has been directly observed for the first time.

On tiny scales, nature makes particles behave according to curiously rigid rules. For instance, negatively charged electrons trapped around a positive nucleus under the pull of the electromagnetic force cannot have any energy they want -they have to fall into a set of distinct energy levels.

In the same way, the pull of gravity should make particles fall into discrete energy levels. But because gravity is extremely weak on small scales, the effect has been impossible to spot. "To be able to measure it, you need to suppress interference from all the other fields," says Valery Nesvizhevsky of the Laue-Langevin Institute in Grenoble, France.

Now Nesvizhevsky and his colleagues have achieved the feat using a beam of neutrons. Neutrons were ideal because they're neutral, so they don't feel the electromagnetic force and can ignore its quantum rules.

Experts say it is a convincing result from an extremely tricky experiment. "The difficulty of this measurement should not be underestimated," says Thomas Bowles of Los Alamos National Laboratory in New Mexico. "In the quantum realm, the gravitational force is so weak that it is difficult to observe quantum effects."


Bouncing neutrons

Nesvizhevsky's team took a beam of ultracold neutrons with tiny energies, moving from left to right at less than eight metres per second. Under the force of gravity, the neutrons fell down onto a reflecting mirror and bounced off it before arriving at a detector.

The team could limit the energies of the neutrons arriving at the detector by placing an absorbing material at different heights above the mirror. The material mopped up all the neutrons that bounced too high.

Forgetting quantum mechanics, you would expect neutrons with any energy to arrive at the detector. But no neutrons appeared unless the neutron-mop was at least 15 micrometres above the mirror. This means the neutrons have to have a certain, minimum energy (equal to 1.41 x 10-12 electronvolts) in the Earth's gravitational field.


Step up

There were also hints that neutron transmission took little leaps at different, higher energies, corresponding to higher quantum levels. However, the team has still to confirm this.

Nesvizhevsky says the technology is exciting because it could test some other key ideas in physics - for instance, whether or not the neutron carries some minuscule amount of electric charge. "If it's there, it's very, very small," says Nesvizhevsky.

It could also put on trial the equivalence principle, a famous concept of Einstein's. It says that all particles, regardless of their mass or composition, should fall with the same acceleration in a uniform gravitational field.

Journal reference: Nature (vol 415, p 297)

 
19:00 16 January 02
 

 
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TOPICS: Extended News; Miscellaneous; News/Current Events
KEYWORDS: gravity; qm; quantummechanics; realscience
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1 posted on 01/17/2002 4:06:30 PM PST by Ernest_at_the_Beach
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To: RealScience
To find all articles tagged or indexed using RealScience

Click here: RealScience

2 posted on 01/17/2002 4:13:51 PM PST by Ernest_at_the_Beach
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To: Ernest_at_the_Beach
Schroder's cat alive or dead?

Nice to see some scientific headway!

3 posted on 01/17/2002 4:21:27 PM PST by Rain-maker
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To: Ernest_at_the_Beach
bump
4 posted on 01/17/2002 4:22:47 PM PST by Free the USA
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To: Rain-maker
Dead. And the glass is half empty.
5 posted on 01/17/2002 4:25:53 PM PST by A.J.Armitage
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To: A.J.Armitage
The glass is neither half-empty nor half-full. It's merely time for another round
6 posted on 01/17/2002 4:27:47 PM PST by muir_redwoods
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To: physicist
Any comments?
7 posted on 01/17/2002 4:34:50 PM PST by crypt2k
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To: crypt2k
Bump for later
8 posted on 01/17/2002 4:44:12 PM PST by America's Resolve
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To: crypt2k
I feel better having read it.
9 posted on 01/17/2002 4:46:17 PM PST by Eric in the Ozarks
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To: crypt2k
Any comments?

Yes, it sound like a nice piece of work. Even if nothing unexpected comes out of the results, it's an important experiment. It's a whole new tool in the kit.

Thanks for the ping!

10 posted on 01/17/2002 4:47:36 PM PST by Physicist
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To: muir_redwoods
Wrong again--the glass was over-engineered.
11 posted on 01/17/2002 4:50:23 PM PST by randog
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To: A.J.Armitage
All nine lives?
12 posted on 01/17/2002 4:51:36 PM PST by null and void
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Comment #13 Removed by Moderator

To: Ernest_at_the_Beach
Is gravity gaining gravitas?
14 posted on 01/17/2002 4:56:35 PM PST by Consort
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To: Ernest_at_the_Beach
analog does not exist.
15 posted on 01/17/2002 5:02:50 PM PST by sigSEGV
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To: Physicist; longshadow; radioastronomer; vaderetro; junior; thinkplease
Gravity bump.
16 posted on 01/17/2002 5:05:33 PM PST by PatrickHenry
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To: Ernest_at_the_Beach
To use an anachronistic vernacular term, this is a really heavy thread, dude.
17 posted on 01/17/2002 5:18:39 PM PST by snowfox
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To: snowfox
Maybe one of Einsein's theories will get a clever test!

Speaking of the equivalence theory.

I always thought the heavier stuff ought to fall faster!

18 posted on 01/17/2002 5:23:44 PM PST by Ernest_at_the_Beach
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To: Ernest_at_the_Beach
I always thought the heavier stuff ought to fall faster!

Well, at least it falls harder.

19 posted on 01/17/2002 5:31:33 PM PST by PatrickHenry
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Comment #20 Removed by Moderator


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