BREAKING THE LAWS OF MODERN PHYSICS
Neutrinos travelling faster than light.
What is a neutrino?
Neutrinos are one of the fundamental particles which make up the universe. They are also one of the least understood.
Neutrinos are similar to the more familiar electron, with one crucial difference: neutrinos do not carry electric charge. Because neutrinos are electrically neutral, they are not affected by the electromagnetic forces which act on electrons. Neutrinos are affected only by a "weak" sub-atomic force of much shorter range than electromagnetism, and are therefore able to pass through great distances in matter without being affected by it. If neutrinos have mass, they also interact gravitationally with other massive particles, but gravity is by far the weakest of the four known forces.
Three types of neutrinos are known; there is strong evidence that no additional neutrinos exist, unless their properties are unexpectedly very different from the known types. Each type or "flavor" of neutrino is related to a charged particle (which gives the corresponding neutrino its name). Hence, the "electron neutrino" is associated with the electron, and two other neutrinos are associated with heavier versions of the electron called the muon and the tau (elementary particles are frequently labelled with Greek letters, to confuse the layman).
A Brief History of the Neutrino
Neutrino experiment replicates faster-than-light finding
The odds have shrunk that Einstein was wrong about a fundamental law of the Universe.
Scientists at the world's biggest physics lab said on Friday they have ruled out one possible error that could have distorted startling measurements appearing to show particles travelling faster than light.
Many physicists reacted with scepticism in September when measurements by French and Italian researchers seemed to show subatomic neutrino particles breaking what Einstein considered the ultimate speed barrier.
The European Organisation for Nuclear Research said more precise testing has confirmed the accuracy of one part of the experiment. "One key test was to repeat the measurement with very short beam pulses," said the Geneva-based organisation, known by its French acronym CERN.
The test allowed scientists to check if the starting time for the neutrinos was being measured correctly before they were fired 730 km from Geneva to a lab in Italy. The results matched those from the previous test, "ruling out one potential source of systematic error," said CERN.
Still, scientists stressed only independent measurements by labs elsewhere would allow them to declare the results a genuine finding. "A measurement so delicate and carrying a profound implication on physics requires an extraordinary level of scrutiny," said Fernando Ferroni, president of Italian Institute for Nuclear Physics. "The positive outcome of the test makes us more confident in the result, although a final word can only be said by analogous measurements performed elsewhere in the world."
According to Einstein's 1905 special theory of relativity, nothing is meant to be able to go faster than the speed of light — 299,792 km per second.
But the researchers said in September that their neutrinos travelled 60 nanoseconds faster, when the margin of error in their experiment allowed for just 10 nanoseconds.
Cross-checked
As the OPERA team involved in measuring the speed of neutrinos has already shown, the early arrival was cross-checked for six months and by measuring the speed of more than 15,000 neutrinos before the results were announced.
When a possible source of error concerning the longer duration (10.5 microseconds) of the proton pulses was raised, the OPERA team repeated the experiment by producing shorter-duration pulses. And the results were identical — neutrinos travelled 60 nanoseconds faster than light.
The latest confirmation brings them one step closer to shaking the very foundation of modern physics — Albert Einstein's 1905 Special theory of Relativity that states nothing can travel faster than light.
If the results announced two months ago shocked and stunned scientists all over the world, a sense of disbelief has set in after the team of scientists reconfirmed the results last Friday.
The experiment involved generating proton pulses and measuring the time taken for the neutrinos to travel 730 km from CERN, Europe's particle physics lab near Geneva to Gran Sasso National laboratory near L'Aquila, Italy. The 730 km distance between the two points has been measured with an error margin of just 20 cm.
A beam of light would take just 2.4 milliseconds to cover this distance. But in March 2011 scientists were shocked to discover that neutrinos travelled 60 nanoseconds (or 60 billionths of a second) faster than light.
This means that neutrinos were travelling at a speed of 299,798,454 metres per second, while the speed of light in a vacuum is slower at 299,792,458 metres per second.
It was not an isolated observation. In fact, scientists found more than 15,000 neutrinos arriving earlier than expected at the Gran Sasso Laboratory. They checked the accuracy of the data for six months before going public. Since the error margin was only 10 nanoseconds, neutrinos were indeed travelling faster than light.
But there was one factor that the team had overlooked. The proton pulses used for generating the neutrinos were of 10.5 microseconds duration and hence relatively longer. There was a possible room for error as it was difficult to tell whether the speed of individual neutrinos was compared with protons arriving at the beginning or end of the 10.5 microsecond-long pulse.
Hence the OPERA team repeated the experiment by reducing the duration of the pulse from 10.5 microseconds to just 3 nanoseconds — a 3,000-times reduction in pulse duration.
Results from 20 events produced from 3 nanosecond pulses showed that the neutrinos still arrived 60 nanoseconds earlier than light. This was the result that was announced a few days ago.
Other possible errors
There is one more possible error factor that has been raised — synchronising to within nanosecond accuracy the two clocks at both locations (in Geneva and L'Aquila, Italy) to time the neutrino's speed. The OPERA team had synchronised the clocks using GPS signals from a single satellite. The use of GPS in high-energy particle physics to synchronise the clocks at either end of the beam path may be one controversial issue as it has never been tried before.
According to an article in Nature, Carlo Contaldi of the Imperial College London has challenged the OPERA results as it has not taken into account one important aspect of the general theory of relativity — the difference in the force of gravity at the two locations affecting the rate at which the clocks tick.
Effect of gravity
Compared with Gran Sasso, the CERN site is further away from the centre of the earth and hence would experience slightly stronger gravitational pull. This would result in the clock at CERN running slightly slower than the one at Gran Sasso.
Dario Autiero of the Institute of Nuclear Physics in Lyons, France and physics co-ordinator for OPERA was quoted as saying in Nature that "Contaldi's challenge is a result of misunderstanding of how clocks were synchronised." The team is expected to soon explain the way the clocks were synchronised.
According to Nature, one more element that is generating more scrutiny is the "profile of the proton beam" that generates neutrinos as a "by-product of collision with a target."
Neutrinos travelling faster than light.
What is a neutrino?
Neutrinos are one of the fundamental particles which make up the universe. They are also one of the least understood.
Neutrinos are similar to the more familiar electron, with one crucial difference: neutrinos do not carry electric charge. Because neutrinos are electrically neutral, they are not affected by the electromagnetic forces which act on electrons. Neutrinos are affected only by a "weak" sub-atomic force of much shorter range than electromagnetism, and are therefore able to pass through great distances in matter without being affected by it. If neutrinos have mass, they also interact gravitationally with other massive particles, but gravity is by far the weakest of the four known forces.
Three types of neutrinos are known; there is strong evidence that no additional neutrinos exist, unless their properties are unexpectedly very different from the known types. Each type or "flavor" of neutrino is related to a charged particle (which gives the corresponding neutrino its name). Hence, the "electron neutrino" is associated with the electron, and two other neutrinos are associated with heavier versions of the electron called the muon and the tau (elementary particles are frequently labelled with Greek letters, to confuse the layman).
A Brief History of the Neutrino
1931 - A hypothetical particle is predicted by the theorist Wolfgang Pauli. Pauli based his prediction on the fact that energy and momentum did not appear to be conserved in certain radioactive decays. Pauli suggested that this missing energy might be carried off, unseen, by a neutral particle which was escaping detection. | ||
1934 - Enrico Fermi develops a comprehensive theory of radioactive decays, including Pauli's hypothetical particle, which Fermi coins the neutrino (Italian: "little neutral one"). With inclusion of the neutrino, Fermi's theory accurately explains many experimentally observed results. | ||
1959 - Discovery of a particle fitting the expected characteristics of the neutrino is announced by Clyde Cowan and Fred Reines (a founding member of Super-Kamiokande; UCI professor emeritus and recipient of the 1995 Nobel Prize in physics for his contribution to the discovery). This neutrino is later determined to be the partner of the electron. | ||
1962 - Experiments at Brookhaven National Laboratory and CERN, the European Laboratory for Nuclear Physics make a surprising discovery: neutrinos produced in association with muons do not behave the same as those produced in association with electrons. They have, in fact, discovered a second type of neutrino (the muon neutrino). | ||
1968 - The first experiment to detect (electron) neutrinos produced by the Sun's burning (using a liquid Chlorine target deep underground) reports that less than half the expected neutrinos are observed. This is the origin of the long-standing "solar neutrino problem." The possibility that the missing electron neutrinos may have transformed into another type (undetectable to this experiment) is soon suggested, but unreliability of the solar model on which the expected neutrino rates are based is initially considered a more likely explanation. | ||
1978 - The tau particle is discovered at SLAC, the Stanford Linear Accelerator Center. It is soon recognized to be a heavier version of the electron and muon, and its decay exhibits the same apparent imbalance of energy and momentum that led Pauli to predict the existence of the neutrino in 1931. The existence of a third neutrino associated with the tau is hence inferred, although this neutrino has yet to be directly observed. | ||
1985 - The IMB experiment, a large water detector searching for proton decay but which also detects neutrinos, notices that fewer muon-neutrino interactions than expected are observed. The anomaly is at first believed to be an artifact of detector inefficiencies. | ||
1985 - A Russian team reports measurement, for the first time, of a non-zero neutrino mass. The mass is extremely small (10,000 times less than the mass of the electron), but subsequent attempts to independently reproduce the measurement do not succeed. | ||
1987 - Kamiokande, another large water detector looking for proton decay, and IMB detect a simultaneous burst of neutrinos from Supernova 1987A. | ||
1988 - Kamiokande, another water detector looking for proton decay but better able to distinguish muon neutrino interactions from those of electron neutrino, reports that they observe only about 60% of the expected number of muon-neutrino interactions. | ||
1989 - The Frejus and NUSEX experiments, much smaller than either Kamiokande or IMB, and using iron rather than water as the neutrino target, report no deficit of muon-neutrino interactions. | ||
1989 - Experiments at CERN's Large Electron-Positron (LEP) accelerator determine that no additional neutrinos beyond the three already known can exist. | ||
1989 - Kamiokande becomes the second experiment to detect neutrinos from the Sun, and confirms the long-standing anomaly by finding only about 1/3 the expected rate. | ||
1990 - After an upgrade which improves the ability to identify muon-neutrino interactions, IMB confirms the deficit of muon neutrino interactions reported by Kamiokande. | ||
1994 - Kamiokande finds a deficit of high-energy muon-neutrino interactions. Muon-neutrinos travelling the greatest distances from the point of production to the detector exhibit the greatest depletion. | ||
1994 - The Kamiokande and IMB groups collaborate to test the ability of water detectors to distinguish muon- and electron-neutrino interactions, using a test beam at the KEK accelerator laboratory. The results confirm the validity of earlier measurements. The two groups will go on to form the nucleus of the Super-Kamiokande project. | ||
1996 - The Super-Kamiokande detector begins operation. | ||
1997 - The Soudan-II experiment becomes the first iron detector to observe the disappearance of muon neutrinos. The rate of disappearance agrees with that observed by Kamiokande and IMB. | ||
1997 - Super-Kamiokande reports a deficit of cosmic-ray muon neutrinos and solar electron neutrinos, at rates agreeing with measurements by earlier experiments. | ||
1998 - The Super-Kamiokande collaboration announces evidence of non-zero neutrino mass at the Neutrino '98 conference. | ||
Neutrino experiment replicates faster-than-light finding
The odds have shrunk that Einstein was wrong about a fundamental law of the Universe.
Scientists at the world's biggest physics lab said on Friday they have ruled out one possible error that could have distorted startling measurements appearing to show particles travelling faster than light.
Many physicists reacted with scepticism in September when measurements by French and Italian researchers seemed to show subatomic neutrino particles breaking what Einstein considered the ultimate speed barrier.
The European Organisation for Nuclear Research said more precise testing has confirmed the accuracy of one part of the experiment. "One key test was to repeat the measurement with very short beam pulses," said the Geneva-based organisation, known by its French acronym CERN.
The test allowed scientists to check if the starting time for the neutrinos was being measured correctly before they were fired 730 km from Geneva to a lab in Italy. The results matched those from the previous test, "ruling out one potential source of systematic error," said CERN.
Still, scientists stressed only independent measurements by labs elsewhere would allow them to declare the results a genuine finding. "A measurement so delicate and carrying a profound implication on physics requires an extraordinary level of scrutiny," said Fernando Ferroni, president of Italian Institute for Nuclear Physics. "The positive outcome of the test makes us more confident in the result, although a final word can only be said by analogous measurements performed elsewhere in the world."
According to Einstein's 1905 special theory of relativity, nothing is meant to be able to go faster than the speed of light — 299,792 km per second.
But the researchers said in September that their neutrinos travelled 60 nanoseconds faster, when the margin of error in their experiment allowed for just 10 nanoseconds.
Cross-checked
As the OPERA team involved in measuring the speed of neutrinos has already shown, the early arrival was cross-checked for six months and by measuring the speed of more than 15,000 neutrinos before the results were announced.
When a possible source of error concerning the longer duration (10.5 microseconds) of the proton pulses was raised, the OPERA team repeated the experiment by producing shorter-duration pulses. And the results were identical — neutrinos travelled 60 nanoseconds faster than light.
The latest confirmation brings them one step closer to shaking the very foundation of modern physics — Albert Einstein's 1905 Special theory of Relativity that states nothing can travel faster than light.
If the results announced two months ago shocked and stunned scientists all over the world, a sense of disbelief has set in after the team of scientists reconfirmed the results last Friday.
The experiment involved generating proton pulses and measuring the time taken for the neutrinos to travel 730 km from CERN, Europe's particle physics lab near Geneva to Gran Sasso National laboratory near L'Aquila, Italy. The 730 km distance between the two points has been measured with an error margin of just 20 cm.
A beam of light would take just 2.4 milliseconds to cover this distance. But in March 2011 scientists were shocked to discover that neutrinos travelled 60 nanoseconds (or 60 billionths of a second) faster than light.
This means that neutrinos were travelling at a speed of 299,798,454 metres per second, while the speed of light in a vacuum is slower at 299,792,458 metres per second.
It was not an isolated observation. In fact, scientists found more than 15,000 neutrinos arriving earlier than expected at the Gran Sasso Laboratory. They checked the accuracy of the data for six months before going public. Since the error margin was only 10 nanoseconds, neutrinos were indeed travelling faster than light.
But there was one factor that the team had overlooked. The proton pulses used for generating the neutrinos were of 10.5 microseconds duration and hence relatively longer. There was a possible room for error as it was difficult to tell whether the speed of individual neutrinos was compared with protons arriving at the beginning or end of the 10.5 microsecond-long pulse.
Hence the OPERA team repeated the experiment by reducing the duration of the pulse from 10.5 microseconds to just 3 nanoseconds — a 3,000-times reduction in pulse duration.
| The Gran Sasso National Laboratory of the Italian Institute of Nuclear Physics, located nearly a mile below the surface of the Gran Sasso mountain about 60 miles outside of Rome, detects tiny particles called neutrinos. |
Results from 20 events produced from 3 nanosecond pulses showed that the neutrinos still arrived 60 nanoseconds earlier than light. This was the result that was announced a few days ago.
Other possible errors
There is one more possible error factor that has been raised — synchronising to within nanosecond accuracy the two clocks at both locations (in Geneva and L'Aquila, Italy) to time the neutrino's speed. The OPERA team had synchronised the clocks using GPS signals from a single satellite. The use of GPS in high-energy particle physics to synchronise the clocks at either end of the beam path may be one controversial issue as it has never been tried before.
According to an article in Nature, Carlo Contaldi of the Imperial College London has challenged the OPERA results as it has not taken into account one important aspect of the general theory of relativity — the difference in the force of gravity at the two locations affecting the rate at which the clocks tick.
Effect of gravity
Compared with Gran Sasso, the CERN site is further away from the centre of the earth and hence would experience slightly stronger gravitational pull. This would result in the clock at CERN running slightly slower than the one at Gran Sasso.
Dario Autiero of the Institute of Nuclear Physics in Lyons, France and physics co-ordinator for OPERA was quoted as saying in Nature that "Contaldi's challenge is a result of misunderstanding of how clocks were synchronised." The team is expected to soon explain the way the clocks were synchronised.
According to Nature, one more element that is generating more scrutiny is the "profile of the proton beam" that generates neutrinos as a "by-product of collision with a target."
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