NEWS:
26 September 2011 9 (Wired Magazine)
Neutrinos and the Speed of Light — A Primer on the CERN Study
Cross section of the CNGS experiment through the Earth. (Image: CERN)
Recently, a group of physicists have been working to measure the neutrinos generated from a particle accelerator at CERN. This group discovered neutrinos arriving faster than would have been expected and they appear to be traveling faster than the speed of light itself, but they draw no definitive conclusions. This has been widely reported as being the end of Relativity, but this is not the case at all.
Let’s take a look at what is going on in the experiment and what was reported in the journal article.
First, it might help the reader to gain an understanding of the neutrino. Neutrinos are interesting little neutral particles that have almost zero mass. Due to their nature, they can pass through matter without being absorbed.
There are three known types of neutrinos: the electron neutrino, the muon neutrino, and the tau neutrino.
The experiment in the journal article is referred to as CERN neutrinos to Gran Sasso, or CNGS. The CNGS team is searching for a phenomenon known as neutrino oscillation where muon neutrinos may change into tau neutrinos. A secondary goal of the experiment is to measure neutrino velocity to a great accuracy.
In the experiment, neutrinos are generated at theSuper Proton Synchrotron(SPS) particle accelerator at the CERN LHC complex in Geneva and further accelerated down a 1 km beam line toward the Gran Sasso National Laboratory in Italy. At Gran Sasso, a detector instrument called OPERA measures the neutrinos. The distance from CERN to Gran Sasso is 732 km straight through the Earth, traveling up to 11.4 km below the Earth’s surface.
Remember, neutrinos don’t interact with matter so the Earth is invisible to the tiny particles.The distance between the two systems is known to within 20 cm.
Time is also measured with extreme precision utilizing GPS timing signals and a cesium atomic clock. The GPS used in timing also allows the team to track any small movements in the Earth itself. This even allowed consideration of the effect of the L’Aquila Earthquake that moved the OPERA detector 7 cm.
Due to the nature of the experiment, the time is not calculated with a simple, stopwatch style, start to finish measurement. It instead relies on measurements and comparisons of probability distribution functions at the source and the detector. In other words, there is a lot of math involved.
In addition to understanding the timing and position variations in the experiment, the physicists also took into account many other variables, such as day versus night and seasonal changes. The sensitivity of this experiment is roughly an order of magnitude better than previous experiments.
The speed of neutrinos is measured and compared to the speed of light by subtracting the expected time for light to travel the distance from the time for the neutrinos to travel the same distance. One would normally expect this to be zero for neutrinos traveling at the speed of light or negative for any value below the speed of light.
The case presented in the article shows a positive value of 60.7 nanoseconds with statistical and systematic errors providing not nearly enough potential difference to account for the positive value. This value has six-sigma significance. This is, obviously, a stunning finding.
The final paragraph is what appears to be overlooked all too often in the reporting on this finding:
Despite the large significance of the measurement reported here and the stability of the analysis, the potential great impact of the results motivates the continuation of our studies in order to investigate possible still unknown systematic effects that could explain the observed anomaly. We deliberately do not attempt any theoretical or phenomenological interpretation of the results.
This is an important paragraph. This is the group of physicists, together, stating that they don’t know how they came to a result that shows neutrinos apparently exceeding the speed of light.
- They are not drawing any conclusions in this article and are simply providing the finding and the methods used to obtain the finding.
- They are trying to find where there could be errors in their measurements.
- They do not claim that the neutrinos are actually exceeding the speed of light, only that the measurements to date show something unexpected.
- They are reaching out to the high-energy physics community to improve the experiment and data analysis.
- They are not looking to fundamentally change physics but to ensure that they are producing sound data.
We may find that nothing comes of this. We may find that there is an effect known in physics that accounts for the difference. We may find that neutrinos are capable of moving slightly faster than the speed of light. It is simply too early to make definitive, wide-reaching conclusions.
The conclusion that can be drawn from this article is that a group of experimenters found an unexpected result using some of the most amazing and precise instruments and techniques ever created. No matter what is found to be the actual cause of this 60.7 nanosecond variation, the conclusion you can draw is that it is an amazing time in history where such measurements can be made and an exciting time to be a practitioner or admirer of science.
Imagine the findings that will be made by the next couple generations of scientists who are sitting in elementary classrooms right now and just learning that a rainbow is the spectrum of sunlight.
Einstein wouldn’t be disappointed by these findings; he would be intrigued and proud to see the legacy of great science continuing forward.
Brian is a NASA engineer by day and a GeekDad contributor by night. Opinions shared are my own and do not necessarily reflect the opinion of NASA.
23 September 2011 Last updated at 13:03 ET
Speed-of-light results
under scrutiny at Cern
By Jason Palmer Science and technology reporter, BBC News
Enormous underground detectors are needed to catch neutrinos, that are so elusive
as to be dubbed "ghost particles"
A meeting at Cern, the world's largest physics lab, has addressed results that
suggest subatomic particles have gone faster than the speed of light.
contains any mistakes.
If it does not, one of the pillars of modern science will come tumbling down.
Antonio Ereditato added "words of caution" to his Cern presentation because of the
"potentially great impact on physics" of the result.
The speed of light is widely held to be the
Universe's ultimate speed limit, and much of
modern physics - as laid out in part by
Albert Einstein in his theory of special relativity -
depends on the idea that nothing can exceed it.
“We want to be helped by the community in
understanding our crazy result - because it is crazy”
Thousands of experiments have been undertaken
to measure it ever more precisely, and no result
has ever spotted a particle breaking the limit.
"We tried to find all possible explanations for this,"
"We wanted to find a mistake - trivial mistakes, more complicated mistakes, or nasty effects - and we
didn't.
"When you don't find anything, then you say
'well, now I'm forced to go out and ask the community to scrutinise this'."
Friday's meeting was designed to begin this process, with hopes that other scientists
will find inconsistencies in the measurements and, hopefully, repeat the experiment
elsewhere.
"Despite the large [statistical] significance of this measurement that you have seen
and the stability of the analysis, since it has a potentially great impact on physics,
this motivates the continuation of our studies in order to find still-unknown systematic
effects," Dr Ereditato told the meeting.
"We look forward to independent measurement from other experiments."
Neutrinos come in a number of types, and have recently been seen to switch
spontaneously from one type to another.
The Cern team prepares a beam of just one type, muon neutrinos, and sends them
through the Earth to an underground laboratory at Gran Sasso in Italy to see how
many show up as a different type, tau neutrinos.
In the course of doing the experiments, the researchers noticed that the particles
showed up 60 billionths of a second earlier than they would have done if they had
travelled at the speed of light.
This is a tiny fractional change - just 20 parts in a million - but one that occurs
consistently.
The team measured the travel times of neutrino bunches some 16,000 times, and
have reached a level of statistical significance that in scientific circles would count
as a formal discovery.
But the group understands that what are known as "systematic errors" could easily
make an erroneous result look like a breaking of the ultimate speed limit.
That has motivated them to publish their measurements.
"My dream would be that another, independent experiment finds the same thing -
then I would be relieved," Dr Ereditato told BBC News.
But for now, he explained, "we are not claiming things, we want just to be helped
by the community in understanding our crazy result - because it is crazy".
Related Stories
Sep 23, 10:34 AM EDT
Physicists wary of junking light speed limit yet
By FRANK JORDANS
Associated Press GENEVA (AP) --
Physicists on the team that measured particles traveling faster than
light said Friday they were as surprised as their skeptics about the
results, which appear to violate the laws of nature as we know them.
Hundreds of scientists packed an auditorium at one of the world's
foremost laboratories on the Swiss-French border to hear how a
subatomic particle, the neutrino, was found to have outrun light
and confounded the theories of Albert Einstein.
"To our great surprise we found an anomaly," said Antonio Ereditato,
who participated in the experiment and speaks on behalf of the team.
An anomaly is a mild way of putting it.
Going faster than light is something that is just not supposed to
happen, according to Einstein's 1905 special theory of relativity.
The speed of light - 186,282 miles per second
(299,792 kilometers per second) - has long been considered a
cosmic speed limit.
The team - a collaboration between France's National Institute for
Nuclear and Particle Physics Research and Italy's Gran Sasso
National Laboratory - fired a neutrino beam 454 miles (730 kilometers) underground from Geneva to Italy.
They found it traveled 60 nanoseconds faster than light. That's
sixty billionth of a second, a time no human brain could register.
"You could say it's peanuts, but it's not. It's something that we
can measure rather accurately with a small uncertainty,"
Ereditato told The Associated Press.
If the experiment is independently repeated ( my emphasis - K.K. )-
most likely by teams in the United States or Japan - then it would
require a fundamental rethink of modern physics.
"Everybody knows that the speed limit is c, the speed of light. And if
you find some matter particle such as the neutrino going faster than
light, this is something which immediately shocks everybody,
including us," said Ereditato, a researcher at the University of Bern,
Switzerland.
Physicists not involved in the experiment have been understandably
skeptical.
Alvaro De Rujula, a theoretical physicist at CERN, the European
Organization for Nuclear Research outside Geneva from where the
neutron beam was fired, said he blamed the readings on a so-far
undetected human error.
If not, and it's a big if, the door would be opened to some wild
possibilities.The average person, said De Rujula, "could, in principle,
travel to the past and kill their mother before they were born.
"But Ereditato and his team are wary of letting such science fiction
story lines keep them up at night.
"We will continue our studies and we will wait patiently for the
confirmation," he told the AP. "Everybody is free to do what they want:
to think, to claim, to dream."
He added: "I'm not going to tell you my dreams."
