Astounding discovery: Faster-than-light particle

Re: Astounding discovery: Faster-than-light particle

Postby kostmayer » Wed Oct 19, 2011 7:33 pm

Via TechnologyReview.Com

Faster-than-Light Neutrino Puzzle Claimed Solved by Special Relativity

The relativistic motion of clocks on board GPS satellites exactly accounts for the superluminal effect, says physicist.

It's now been three weeks since the extraordinary news that neutrinos travelling between France and Italy had been clocked moving faster than light. The experiment, known as OPERA, found that the particles produced at CERN near Geneva arrived at the Gran Sasso Laboratory in Italy some 60 nanoseconds earlier than the speed of light allows.

The result has sent a ripple of excitement through the physics community. Since then, more than 80 papers have appeared on the arXiv attempting to debunk or explain the effect. It's fair to say, however, that the general feeling is that the OPERA team must have overlooked something.

Today, Ronald van Elburg at the University of Groningen in the Netherlands makes a convincing argument that he has found the error.

First, let's review the experiment, which is simple in concept: a measurement of distance and time.

The distance is straightforward. The location of neutrino production at CERN is fairly easy to measure using GPS. The position of the Gran Sasso Laboratory is harder to pin down because it sits under a kilometre-high mountain. Nevertheless, the OPERA team says it has nailed the distance of 730 km to within 20 cm or so.

The time of neutrino flight is harder to measure. The OPERA team says it can accurately gauge the instant when the neutrinos are created and the instant they are detected using clocks at each end.

But the tricky part is keeping the clocks at either end exactly synchronised. The team does this using GPS satellites, which each broadcast a highly accurate time signal from orbit some 20,000km overhead. That introduces a number of extra complications which the team has to take into account, such as the time of travel of the GPS signals to the ground.

But van Elburg says there is one effect that the OPERA team seems to have overlooked: the relativistic motion of the GPS clocks.

It's easy to think that the motion of the satellites is irrelevant. After all, the radio waves carrying the time signal must travel at the speed of light, regardless of the satellites' speed.

But there is an additional subtlety. Although the speed of light is does not depend on the the frame of reference, the time of flight does. In this case, there are two frames of reference: the experiment on the ground and the clocks in orbit. If these are moving relative to each other, then this needs to be factored in.

So what is the satellites' motion with respect to the OPERA experiment? These probes orbit from West to East in a plane inclined at 55 degrees to the equator. Significantly, that's roughly in line with the neutrino flight path. Their relative motion is then easy to calculate.

So from the point of view of a clock on board a GPS satellite, the positions of the neutrino source and detector are changing. "From the perspective of the clock, the detector is moving towards the source and consequently the distance travelled by the particles as observed from the clock is shorter," says van Elburg.

By this he means shorter than the distance measured in the reference frame on the ground.

The OPERA team overlooks this because it thinks of the clocks as on the ground not in orbit.

How big is this effect? Van Elburg calculates that it should cause the neutrinos to arrive 32 nanoseconds early. But this must be doubled because the same error occurs at each end of the experiment. So the total correction is 64 nanoseconds, almost exactly what the OPERA team observes.

That's impressive but it's not to say the problem is done and dusted. Peer review is an essential part of the scientific process and this argument must hold its own under scrutiny from the community at large and the OPERA team in particular.

If it stands up, this episode will be laden with irony. Far from breaking Einstein's theory of relatively, the faster-than-light measurement will turn out to be another confirmation of it.


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Re: Astounding discovery: Faster-than-light particle

Postby Mikey » Wed Oct 19, 2011 8:23 pm

Oops. :lol:
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Re: Astounding discovery: Faster-than-light particle

Postby IanKennedy » Thu Oct 20, 2011 9:42 pm

Why the hell are they relying on GPS to keep time. Sure the system has some pretty impressive clocks, but the signal is not exactly reliably readable. Surly a couple of atomic clocks would be better.
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Re: Astounding discovery: Faster-than-light particle

Postby Mikey » Thu Oct 20, 2011 11:24 pm

Maybe someone warned them against just using their Mickey Mouse wristwatches.
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Re: Astounding discovery: Faster-than-light particle

Postby IanKennedy » Sun Oct 23, 2011 6:53 pm

Mikey wrote:Maybe someone warned them against just using their Mickey Mouse wristwatches.

I'm not away that Disney has ever issued a Mickey Mouse atomic clock. If you can point me to one then I'd love to order it. It would be very cool. :)
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Re: Astounding discovery: Faster-than-light particle

Postby Mikey » Mon Oct 24, 2011 12:28 pm

That was actually contextually addressed to the researchers use of fallible timekeeping, not toward the atomic clocks you mentioned. 's OK, though.

And remember - Disney unleashed Britney Spears on the world, I wouldn't be surprised no matter what else they came up with.
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Re: Astounding discovery: Faster-than-light particle

Postby Captain Picard's Hair » Fri Nov 18, 2011 8:32 pm

The story continues:

http://news.cnet.com/8301-30685_3-57327499-264/reclocked-cern-neutrinos-still-break-the-speed-limit/

"After many months of studies and cross-checks we have not found any instrumental effect that could explain the result of the measurement," said Antonio Ereditato of the University of Bern and spokesman for the OPERA experiment that produced the paper. "While OPERA researchers will continue their studies, we are also looking forward to independent measurements to fully assess the nature of this observation."


This short article makes no specific mention of the atomic clock timing issue noted previously, though one would guess the scientists must have discounted that after all. Or, they've put buffoons in charge of global physics research. :mrgreen:
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Re: Astounding discovery: Faster-than-light particle

Postby Thorin » Mon Dec 26, 2011 3:17 pm

Atomic clocks are used in GPS. They are still subject to the effects of relativity, inaccuracies in position/velocity, disturbances in the atmosphere (changing refractive index, electric fields...). Just because at near absolute zero in ideal circumstances they are accurate to one part in a hundred trillion, doesn't mean they always are.
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Re: Astounding discovery: Faster-than-light particle

Postby Captain Seafort » Tue Dec 27, 2011 4:36 pm

Welcome back Thorin. Again. :P So, as the resident expect, what do you reckon's gone pear-shaped (assuming that's the case)?
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Re: Astounding discovery: Faster-than-light particle

Postby Thorin » Wed Dec 28, 2011 12:36 am

Thanks... Again.

I'm really not sure - I'd be shocked if it were to do with the GPS time stamping. Indeed, the prime example quoted to budding young physicists about the importance of relativity in our day to day lives is to do with GPS. Something like if relativity were not taken into account, our sat navs would be off by a mile or two!

Honestly, I'd love it if these measurements were confirmed, and the neutrinos were travelling faster than the speed of light. The chance?

...Round about nil.
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Re: Astounding discovery: Faster-than-light particle

Postby Captain Picard's Hair » Wed Feb 22, 2012 8:50 pm

Update: it may have to do with the atomic clock... sort of.

http://arstechnica.com/science/news/2012/02/faster-than-light-neutrino-result-apparently-a-mistake-due-to-loose-cable.ars

This is a single report and unconfirmed, but if true... :doh:
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Re: Astounding discovery: Faster-than-light particle

Postby Mikey » Wed Feb 22, 2012 9:02 pm

The noise you're hearing is the ghost of Einstein saying, "OK, what else ya got?"
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Re: Astounding discovery: Faster-than-light particle

Postby colmquinn » Sun Feb 26, 2012 4:10 am

The media report I read stated that there was one solution that would make the measurement slower than peceived & hence fall in line with expectations but also the opposite - if the connection was true then the difference was even more than currently calculated and the 60 nano seconds was an underestimation. Again it all depends on the wiring used. (I don't have a dirct quote to link to the story but it was the guardian onlilne version I was reading).

Peersonally I fall in the camp of Einstein was right but I'd love a new mystery :-)
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