Posted on 01/17/2002 4:06:29 PM PST by Ernest_at_the_Beach
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Gravity's quantum leaps detected |
| 19:00 16 January 02 |
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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."
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.
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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But after looking over that thread from a year ago, I see it's just a pointless exchange of unpleasantries, not worth remembering.
As indicated below, I specifically stipulated, in my SECOND reply to you in the thread in question, the discrete nature of the quantum world, and indicated that I was referring to phenomenon in the larger world:
53 Posted on 01/04/2001 06:06:17 PST by longshadow
To: NebullisIt is made of particles.
And those particles, do they move in discrete instantaneous JUMPS, or do they move CONTINOUSLY?
And more to the point, does the phenomona of "our world" act in instantaneous jumps, or does it act smoothly and continously? Quantum mechanics excluded; we already know and acknowledge that.
But after looking over that thread from a year ago, I see it's just a pointless exchange of unpleasantries, not worth remembering.
Well, if you ignored my stipulation noted above, I guess it was a rather pointless exchange. As for the "unpleasantries," the record indicates that they began with your gratuitous assertion HERE:
99 Posted on 01/04/2001 12:34:36 PST by Nebullis
To: longshadowYou don't know math.
to which I replied in kind HERE:
100 Posted on 01/04/2001 12:37:14 PST by longshadow
To: NebullisYou don't know math.
In addition to being a fool, you are now also a liar.
In any case, thanks for the "discrete reminder"....
You're welcome.
The "observatories" each consist of two 6' diameter stainless steel vacuum "beam tunnels", each 2.5 miles long and about 6 ft. in diameter, at right angles to each other.
The difference in gravitational waves in the interferometer is expected to be several orders of magnitude smaller than a human hair.
How much is this costing the taxpayers?
Looking at the web site for the NSF, it appears that spending so far is about $400 million. That's from the NSF. It is virtually impossible to find out if other government agencies are sharing the cost.
Your tax dollars at work.
Actually, it isn't working. Someone that I know very well was just down in LA several weeks ago, helping to apply a band-aid that they hope will work. Seems that the laser is subject to interference from 60 Hz and computer fans.
As a matter of fact I was not a big fan of the SSC. From my understanding there were several problems, among them:
1. The cost was going through the roof and "promised" foreign financial cooperation was not forthcoming.
2. The SSC was basically duplicating the work being done by CERN in Europe.
By the way, I was working on superconductors when I retired in 1991 - among other things.
Nobody has ever built a large-scale device (particularly a first-of-its-kind device) that didn't have bugs that needed to be worked out. In my experience as an experimentalist, 98% of experimental physics consists of working out problems like that. I see no cause for hand-wringing.
You know how that game is played. Congress is handed a schedule: this is what we're going to do, and this is how much it will cost each year. Then congress says, great, we'll give you this smaller amount. That stretches the project out and raises its cost. Congress cuts it again the next year, which raises the cost still more. This continues until congress says, look at the cost! We didn't agree to that! And they kill it.
and "promised" foreign financial cooperation was not forthcoming.
Again, that was a politically created problem having nothing to do with the machine or the physics. Japan, for example, was looking for a little cooperation from the U.S. for a project of its own (TRISTAN II/BELLE). They thought it was all worked out, one hand washing the other. Then we stiffed them and went our own way (PEP II/Babar). There are other examples, but the upshot is that our government was so uncooperative that we couldn't expect any cooperation in return.
2. The SSC was basically duplicating the work being done by CERN in Europe.
That's simply flat-out wrong. Perhaps you're thinking of the Isabelle project that was cancelled a decade or so before the SSC.
No, I'm talking about CERN's Large Electron-Positron Collider (LEP) and its Large Hadron Collider (LHC).
In 1988 I was at KEK (Kou Enerugi Butsurigaku Kenkyuujou, the National Laboratory for High Energy Physics in Japan) when Carlo Rubbia (then director of CERN) came to pitch the LHC. Of course, people were concerned that there was too much overlap with the SSC. Rubbia explained that there was very little overlap, because the LHC could not do a "minimum bias" program. This was because each interaction region would produce 5 kilowatts of pi-mesons. The packed hall gasped en masse. Everybody instantly recognized that track reconstruction was impossible in such a high-rate environment. The LHC was designed to measure one signature (the 4-muon decay of the Higgs, which would have been tough at the SSC) and to do it well.
After the SSC fell, of course, the LHC was the only game in town, and the impossible became the absolutely necessary. People started to devise ways of doing track reconstruction under such conditions. We'll see how well the schemes work (they have to work, so they will) in maybe 2008, 16 years after what should have been the completion date of the SSC.
The speed of light. It falls right out of Maxwells equations.
That's the way it goes with weapons systems.
Only with highways do they not take the final step and cancel them, they just finish them at higher cost and well after the capacity is needed.
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