Physicists
at
Italy’s Gran Sasso neutrino detector, named “OPERA”, made a shocking
announcement last week: their regular deliveries of Swiss neutrinos
arrived too soon — — a 16th of a millionth of a second before Einstein
said was possible.
If correct, this would invalidate several hallowed theories of physics
and would conflict with previous experiments that confirm Einstein.
The scientific world is aghast. Can their measurements be correct? Will
this revolutionize physics, or end up as merely a fanciful Italian
opera?
Since I’ve done neutrino experiments, I was eager to understand what
all the fuss was about. I found and read the original scientific paper
containing all the juicy details not reported in the popular press.
Here is what I found.
Like all neutrino experiments, OPERA is a lavish production. Nearly 300
physicists from 50 institutions and a dozen countries have contributed.
The detecting target weighs 625 tons and is located inside the largest
mountain in the Apennines, Mt. Gran Sasso, about 80 miles from Rome. A
picturesque image of Gran Sasso is shown below.
A
six-mile
long tunnel was bored
through the mountain for a freeway and to provide a place for OPERA,
below nearly one mile of solid rock, thus shielding it from cosmic rays.
The source of neutrinos for OPERA is an older proton accelerator at
CERN, the major European physics lab located 430 miles away near
Geneva, Switzerland. There, over a mile of tunnels were dug for the
apparatus that produces a high-energy beam of neutrinos aimed precisely
at OPERA. The neutrinos hardly notice passing through hundreds of miles
of bedrock. Over 30 months, 100 billion, billion protons at CERN
produced 16,000 detected neutrinos at Gran Sasso. An artist’s sketch of
the neutrino source at CERN is shown below.
In 1905, Einstein declared that nothing can travel through space faster
than c, the speed of light in empty space, which is 671 million mph in
American units, or as I like to say, one foot per nanosecond (a
nanosecond, “ns”, is one billionth of a second). Since 1905, tens of
thousands of experiments have tested Einstein's statement to
extraordinary precision. While a few claimed to prove Albert wrong, no
such claim held up under scrutiny. Einstein’s theories have been
confirmed to the limits of our best instruments, in some cases one part
in a billion, billion (18 decimal digits). In addition, our theories
predict a variety of absurdities if anything really can go faster than
c.
When shocking claims are made, physicists (like everyone else) demand
compelling proof. We are less than impressed when extraordinary claims
are based on complex, convoluted arguments or data that must be
extensively “massaged.”
Speed is generally easy to determine—one divides the distance traveled
by the transit time. Ideally, to prove that something traveled faster
than c, we would observe that thing move across a precisely measured
distance in a precisely measured time. That is NOT what we have here.
This experiment measured where and when neutrinos arrived, but did not
directly observe where and when any one of these neutrinos was
produced. Additionally, measuring the distance and transit times is
complicated by the fact that both the source and detector are deep
below ground. The OPERA physicists made great efforts to overcome these
limitations, and have seemingly done a professional job. But the
measurements contain a lot of “black boxes” and data massaging, which
present opportunities for error.
One might think that with hundreds of physicists involved no mistake
should go unnoticed. But as someone with similar experiences, I can
imagine a lot of chaos with hundreds of strong egos, from scores of
universities and a dozen countries, speaking a multitude of languages.
Is there any one person who understands everything and can ensure all
the pieces fit together as they should?
OPERA was not designed to measure neutrino speeds, but to study how
certain neutrinos evolve during their journey from the Alps to the
Apennines. When the group first attempted to measure neutrinos’ speed,
their initial result was that the neutrinos arrived 1049 ns too
soon—their flight time from CERN to Gran Sasso was 1049 ns less than
the time light would take to make the same trip, making the neutrinos’
speed 1.001 c.
Over several years, they carefully re-measured their distances and
re-calibrated their clocks. They then made six “corrections” to their
first result: three corrections added a total of 1386 ns to the transit
time, while the other three corrections subtracted a total of 398 ns.
Overall, the result decreased by a factor of 16. Fifteen “black boxes”
and a GPS satellite are used to synchronize clocks at the two sites;
one box has a delay of 41,000 ns. Even a minor misunderstanding of any
of these devices could drastically alter the result.
Below is a plot of OPERA’s measured location—clearly evident are the
gradual tectonic plate drift and a sudden shift of 3 inches during an
earthquake in 2009.
After making all these corrections,
OPERA’s final result is that neutrinos arrive from CERN 61 ns before
light would arrive, with an estimated precision of ±10 ns. This makes
their speed 1.000,025 c ±3 in the last digit.
An earlier
measurement by several groups, comparing the arrival times of neutrinos
and light from supernova SN1987a, concluded that the speed of those
neutrinos equaled c to two parts in a billion. That result is 1000
times more precise than OPERA's, but a lower energy.
Considering the
intricacy of the problem and the importance of the result, the jury
will likely remain out on OPERA until other groups perform similar
experiments.
Best Regards,
Robert
Sept 26th, 2011
* * * * * * * * *
* * * * * * * * * * * * * * * * * * * * * * * * * * *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Never too young or
too old
to wonder: Why?
Dr Robert
Piccioni,
Author of "Everyone's
Guide to Atoms, Einstein, and the Universe"
and " Can Life Be
Merely An Accident?"
|
