Since my last post, a couple of months back, about the Faster Than Light (FTL) neutrinos, there has been quite a lot of activity in the world of particle physics. New papers have been published by both the supporters and the detractors of FTL neutrinos. It is high time I got back to this topic.
Though I have already discussed the story in my previous post, I will summarize the result once again. Physicists at CERN, working at the OPERA experiment, observed that neutrinos took 60ns lesser than what it would take light to travel from the source (Geneva, Switzerland) to the detector (Gran Sasso, Italy). This observation was made using the state of the art GPS technology. The result was also well outside the standard error of measurement. This took the team by surprise as it has been shown convincingly by Einstein's theory of relativity that nothing can travel faster than the speed of light. Unable to explain the anomaly, the team published their results, waiting for the theorists to interpret them.
The result caused a huge uproar within the physics community. Very few scientists were excited about the result while most of them expressed their doubts. Many physicists openly attacked the result with Dr. Jim Al-Khalili, a physicist at the University of Surrey, going to the extent of vowing to eat his boxer shorts on live television if the result holds up. Every detractor of the result had a different reason to believe why FTL neutrinos cannot exist. Some of the reasons were scientific while others were based on their faith in Einstein. In this post I will be discussing some of the strongest arguments against the result.
1. By far the strongest argument opposing the idea of FTL neutrinos came from theorists Andrew Cohen and Sheldon Glashow (winner of the Nobel prize in Physics for his contributions to the standard model of particle physics). They published a paper within a week of publication of the OPERA result. Their calculations showed that if neutrinos travel faster than light, all the high energy neutrinos produced at the source would decay by the time they reached the detector at Gran Sasso. But the OPERA team did not observe any such effects. This boosted the confidence of the detractors.
2. Another strong argument came from an experimental result. Astronomers, in 1987, observed that the neutrinos from the supernova explosion SN 1987A reached Earth a few hours after the light from the supernova reached us. If neutrinos travel faster than the speed of light by the amount measured by the OPERA team, the neutrinos should have reached Earth years before the light from the supernova reached us.
3. Apart from the above arguments, the detractors also proposed a number of reasons that could lead to a small experimental error in such a sensitive experiment performed by the OPERA team. One of the most common criticism of the result was that the OPERA team did not know when exactly the neutrinos left the source at Geneva. The neutrinos were generated in pulses and if the pulse was too long, it could have led to errors in measurement of speed of the neutrinos.
4. Another proposed reason was that light travels slower within the Earth's atmosphere than it does in vacuum. Since the time and distance measurement in the experiment depends on signals received from GPS satellites, if the correction accounting for the slower speed of light within Earth's atmosphere wasn't made, then it could result in errors in the measurement of both distance and time which was shown to be equal to the anomaly observed in the OPERA result.
5. There were a few other lesser known reasons proposed to explain the anomaly. One of them was that continental drift occurs continuously on Earth's crust which could have altered the distance measured between the source and the detector. Another proposed reason was that Moon distorts Earth's crust by a tiny amount which could have also altered the distance between Geneva and Gran Sasso.
The OPERA team has not addressed any of the above issues except for the neutrino pulse uncertainty problem. Earlier this month the team published another paper describing an experiment performed with shorter pulses. They once again observed the anomalous result. This experiment strengthened the team's claim and it also silenced their critics.
But the excitement was short-lived for the OPERA team. Another group of physicists at CERN, the ICARUS team, published a paper which convincingly showed that the high energy neutrinos did not decay as they traveled from the source to the detector. This result supports Cohen and Glashow's calculations. Though this result has boosted the confidence the detractors, neither side has dealt the final blow yet to seal the argument.
My take on FTL neutrinos is that the measurements of time and distance in this experiment could go wrong in a number of ways - some of them have been discussed above. Without accounting for all these errors, I believe that there is no reason for the theorists to get involved in trying to interpret the results.
I believe that there are two basic experiments that can be performed to make this result more credible. The first experiment is to use a technique different from the GPS method to measure time and distance. If the new method also gives the same result then it would add some credibility to FTL neutrinos. The second one is to get a different team to repeat the experiment and then compare the results from the two teams. Currently the physicists at MINOS are trying to repeat the experiment. Their result should be available in a year or two.
Once all the errors have been eliminated, if the result still holds up, then this is definitely the most interesting result in physics since the observation of the accelerating universe in 1998 and this result will definitely shake the foundation of both Einstein's Relativity and Quantum Mechanics.
Though I have already discussed the story in my previous post, I will summarize the result once again. Physicists at CERN, working at the OPERA experiment, observed that neutrinos took 60ns lesser than what it would take light to travel from the source (Geneva, Switzerland) to the detector (Gran Sasso, Italy). This observation was made using the state of the art GPS technology. The result was also well outside the standard error of measurement. This took the team by surprise as it has been shown convincingly by Einstein's theory of relativity that nothing can travel faster than the speed of light. Unable to explain the anomaly, the team published their results, waiting for the theorists to interpret them.
The result caused a huge uproar within the physics community. Very few scientists were excited about the result while most of them expressed their doubts. Many physicists openly attacked the result with Dr. Jim Al-Khalili, a physicist at the University of Surrey, going to the extent of vowing to eat his boxer shorts on live television if the result holds up. Every detractor of the result had a different reason to believe why FTL neutrinos cannot exist. Some of the reasons were scientific while others were based on their faith in Einstein. In this post I will be discussing some of the strongest arguments against the result.
1. By far the strongest argument opposing the idea of FTL neutrinos came from theorists Andrew Cohen and Sheldon Glashow (winner of the Nobel prize in Physics for his contributions to the standard model of particle physics). They published a paper within a week of publication of the OPERA result. Their calculations showed that if neutrinos travel faster than light, all the high energy neutrinos produced at the source would decay by the time they reached the detector at Gran Sasso. But the OPERA team did not observe any such effects. This boosted the confidence of the detractors.
2. Another strong argument came from an experimental result. Astronomers, in 1987, observed that the neutrinos from the supernova explosion SN 1987A reached Earth a few hours after the light from the supernova reached us. If neutrinos travel faster than the speed of light by the amount measured by the OPERA team, the neutrinos should have reached Earth years before the light from the supernova reached us.
3. Apart from the above arguments, the detractors also proposed a number of reasons that could lead to a small experimental error in such a sensitive experiment performed by the OPERA team. One of the most common criticism of the result was that the OPERA team did not know when exactly the neutrinos left the source at Geneva. The neutrinos were generated in pulses and if the pulse was too long, it could have led to errors in measurement of speed of the neutrinos.
4. Another proposed reason was that light travels slower within the Earth's atmosphere than it does in vacuum. Since the time and distance measurement in the experiment depends on signals received from GPS satellites, if the correction accounting for the slower speed of light within Earth's atmosphere wasn't made, then it could result in errors in the measurement of both distance and time which was shown to be equal to the anomaly observed in the OPERA result.
5. There were a few other lesser known reasons proposed to explain the anomaly. One of them was that continental drift occurs continuously on Earth's crust which could have altered the distance measured between the source and the detector. Another proposed reason was that Moon distorts Earth's crust by a tiny amount which could have also altered the distance between Geneva and Gran Sasso.
The OPERA team has not addressed any of the above issues except for the neutrino pulse uncertainty problem. Earlier this month the team published another paper describing an experiment performed with shorter pulses. They once again observed the anomalous result. This experiment strengthened the team's claim and it also silenced their critics.
But the excitement was short-lived for the OPERA team. Another group of physicists at CERN, the ICARUS team, published a paper which convincingly showed that the high energy neutrinos did not decay as they traveled from the source to the detector. This result supports Cohen and Glashow's calculations. Though this result has boosted the confidence the detractors, neither side has dealt the final blow yet to seal the argument.
My take on FTL neutrinos is that the measurements of time and distance in this experiment could go wrong in a number of ways - some of them have been discussed above. Without accounting for all these errors, I believe that there is no reason for the theorists to get involved in trying to interpret the results.
I believe that there are two basic experiments that can be performed to make this result more credible. The first experiment is to use a technique different from the GPS method to measure time and distance. If the new method also gives the same result then it would add some credibility to FTL neutrinos. The second one is to get a different team to repeat the experiment and then compare the results from the two teams. Currently the physicists at MINOS are trying to repeat the experiment. Their result should be available in a year or two.
Once all the errors have been eliminated, if the result still holds up, then this is definitely the most interesting result in physics since the observation of the accelerating universe in 1998 and this result will definitely shake the foundation of both Einstein's Relativity and Quantum Mechanics.
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