BY DAN STOBER
Stanford Report,
August 23, 2010
Peter Sturrock, professor emeritus of
applied physics
Le
genre de nouvelle qui passe facilement inaperçue !
La théorie de la relativité a été développée par Albert Einstein
(Relativité restreinte puis Relativité générale) en raison de
certaines "incongruité expérimentale" (en particulier les suites
d'expériences telles celles de Michelson-Morley (1887) ou les
travaux de Maxell (électromagnétisme) et Lorentz) vis a vis de
certains présupposés sur le monde physique tel qu'envisagé par
Newton.
Bref, des résultats expérimentaux qui semblent douteux ou erratiques
peuvent finalement remettre en question les postulats qui fondent
des approches ou des théories scientifiques qui semblent pourtant
"fonctionner" dans un certain cadre, mais qui s'avèreront
incomplète, voire erronée. L'histoire de l'astronomie, entre
autres, peut être vue comme une suite d'erreurs expliquées ensuite
par un modèle plus complet.
Dans ce cas-ci, le postulat d'un taux de dégradation constant des
isotopes (Carbone 14, Radium, etc.) utilisés pour le radio datage
constitue le fondement de tout effort de chronologie et d'estimation
de l'âge de certains éléments physiques (terre, fossiles, géologie).
Des variations dans ces taux de dégradation expliqueraient des
anomalies déjà constatées, mais remettraient directement en question
le calendrier géologique et évolutionniste (évolution des espèces).
Pour l'Évolutionnisme, ce ne serait pas le premier grand coup porté
a des postulats de bases, puisque des la fin du XIXe siècle, deux
arguments principaux de Darwin (caractères acquis transmissibles par
reproduction et génération spontanée) furent réfutés complètement
par les travaux de Mendel (génétique moderne) et Pasteur (la vie
provient de la vie et de rien d'autre). La confiance en une
mécanique de mutation causée par des événements de pur hasard,
opérant sur des périodes de temps extrêmement grandes a permis de
maintenir la crédibilité de la théorie.
Mais si le temps s'avère plus court et que les chances de mutations
utiles et vraisemblables diminuent, ... les colonnes du temples sont
ébranlées !
B. F. pour LEQ
Voir aussi :
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When researchers found an unusual linkage between solar flares
and the inner life of radioactive elements on Earth, it touched off
a scientific detective investigation that could end up protecting
the lives of space-walking astronauts and maybe rewriting some of
the assumptions of physics.
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It's a mystery that presented itself unexpectedly: The radioactive
decay of some elements sitting quietly in laboratories on Earth
seemed to be influenced by activities inside the sun, 93 million
miles away.
Is this possible?
Researchers from Stanford and Purdue University believe it is. But
their explanation of how it happens opens the door to yet another
mystery.
There is even an outside chance that this unexpected effect is
brought about by a previously unknown particle emitted by the sun.
"That would be truly remarkable," said Peter Sturrock, Stanford
professor emeritus of applied physics and an expert on the inner
workings of the sun.
The story begins, in a sense, in classrooms around the world, where
students are taught that the rate of decay of a specific radioactive
material is a constant. This concept is relied upon, for example,
when anthropologists use carbon-14 to date ancient artifacts and
when doctors determine the proper dose of radioactivity to treat a
cancer patient.
Random numbers
But that assumption was challenged in an unexpected way by a
group of researchers from Purdue University who at the time were
more interested in random numbers than nuclear decay. (Scientists
use long strings of random numbers for a variety of calculations,
but they are difficult to produce, since the process used to produce
the numbers has an influence on the outcome.)
Ephraim Fischbach, a physics professor at Purdue, was looking into
the rate of radioactive decay of several isotopes as a possible
source of random numbers generated without any human input. (A lump
of radioactive cesium-137, for example, may decay at a steady rate
overall, but individual atoms within the lump will decay in an
unpredictable, random pattern. Thus the timing of the random ticks
of a Geiger counter placed near the cesium might be used to generate
random numbers.)
As the researchers pored through published data on specific
isotopes, they found disagreement in the measured decay rates – odd
for supposed physical constants.
Checking data collected at Brookhaven National Laboratory on Long
Island and the Federal Physical and Technical Institute in Germany,
they came across something even more surprising: long-term
observation of the decay rate of silicon-32 and radium-226 seemed to
show a small seasonal variation. The decay rate was ever so slightly
faster in winter than in summer.
Was this fluctuation real, or was it merely a glitch in the
equipment used to measure the decay, induced by the change of
seasons, with the accompanying changes in temperature and humidity?
"Everyone thought it must be due to experimental mistakes, because
we're all brought up to believe that decay rates are constant,"
Sturrock said.
The sun speaks
On Dec 13, 2006, the sun itself provided a crucial clue, when a
solar flare sent a stream of particles and radiation toward Earth.
Purdue nuclear engineer Jere Jenkins, while measuring the decay rate
of manganese-54, a short-lived isotope used in medical diagnostics,
noticed that the rate dropped slightly during the flare, a decrease
that started about a day and a half before the flare.
If this apparent relationship between flares and decay rates proves
true, it could lead to a method of predicting solar flares prior to
their occurrence, which could help prevent damage to satellites and
electric grids, as well as save the lives of astronauts in space.
The decay-rate aberrations that Jenkins noticed occurred during the
middle of the night in Indiana – meaning that something produced by
the sun had traveled all the way through the Earth to reach Jenkins'
detectors. What could the flare send forth that could have such an
effect?
Jenkins and Fischbach guessed that the culprits in this bit of decay-rate
mischief were probably solar neutrinos, the almost weightless
particles famous for flying at almost the speed of light through the
physical world – humans, rocks, oceans or planets – with virtually
no interaction with anything.
Then, in a series of papers published in Astroparticle Physics,
Nuclear Instruments and Methods in Physics Research and Space
Science Reviews, Jenkins, Fischbach and their colleagues showed that
the observed variations in decay rates were highly unlikely to have
come from environmental influences on the detection systems.
Reason for suspicion
Their findings strengthened the argument that the strange swings
in decay rates were caused by neutrinos from the sun. The swings
seemed to be in synch with the Earth's elliptical orbit, with the
decay rates oscillating as the Earth came closer to the sun (where
it would be exposed to more neutrinos) and then moving away.
So there was good reason to suspect the sun, but could it be proved?
Enter Peter Sturrock, Stanford professor emeritus of applied physics
and an expert on the inner workings of the sun. While on a visit to
the National Solar Observatory in Arizona, Sturrock was handed
copies of the scientific journal articles written by the Purdue
researchers.
Sturrock knew from long experience that the intensity of the barrage
of neutrinos the sun continuously sends racing toward Earth varies
on a regular basis as the sun itself revolves and shows a different
face, like a slower version of the revolving light on a police car.
His advice to Purdue: Look for evidence that the changes in
radioactive decay on Earth vary with the rotation of the sun. "That's
what I suggested. And that's what we have done."
A surprise
Going back to take another look at the decay data from the
Brookhaven lab, the researchers found a recurring pattern of 33 days.
It was a bit of a surprise, given that most solar observations show
a pattern of about 28 days – the rotation rate of the surface of the
sun.
The explanation? The core of the sun – where nuclear reactions
produce neutrinos – apparently spins more slowly than the surface we
see. "It may seem counter-intuitive, but it looks as if the core
rotates more slowly than the rest of the sun," Sturrock said.
All of the evidence points toward a conclusion that the sun is "communicating"
with radioactive isotopes on Earth, said Fischbach.
But there's one rather large question left unanswered. No one knows
how neutrinos could interact with radioactive materials to change
their rate of decay.
"It doesn't make sense according to conventional ideas," Fischbach
said. Jenkins whimsically added, "What we're suggesting is that
something that doesn't really interact with anything is changing
something that can't be changed."
"It's an effect that no one yet understands," agreed Sturrock. "Theorists
are starting to say, 'What's going on?' But that's what the evidence
points to. It's a challenge for the physicists and a challenge for
the solar people too."
If the mystery particle is not a neutrino, "It would have to be
something we don't know about, an unknown particle that is also
emitted by the sun and has this effect, and that would be even more
remarkable," Sturrock said.
Chantal Jolagh, a science-writing intern at the Stanford News
Service, contributed to this story.
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