Neutrinos. These tiny particles have created quite a ripple in the Physics community of late with reports of them traveling faster than light. The speed of light is held to be the maximum possible speed attainable and hence anything travelling faster than light is bound to create a stir.
So what are these neutrinos? Neutrinos are the lightest elementary particles known to man. They have surprised scientists time and again and prompted scientists to rethink their understanding of the universe. The existence of neutrinos was first predicted by Nobel laureate Austrian physicist Wolfgang Pauli as early as in 1930 in order to explain the mechanism of Beta decay ( a well known Radioactive process). It was only in 1956 that neutrinos were reported to have been experimentally observed. In 1965, neutrinos produced in the Earth’s atmosphere due to interaction with particles coming from outer space, were first observed in the Kolar Gold Mines in India.
Neutrinos are neutral particles that interact with other particles through what is known as a weak interaction, which as the name suggests is very weak. Hence, they rarely interact with other particles and are very difficult to detect. Neutrinos are produced in stars, in nuclear reactors, in other radioactive processes and also in the atmosphere of the earth through nuclear interactions. It is estimated that over 50 trillion electron neutrinos from the sun are passing through the human body every second!
Neutrinos are of three types and have very small mass. In fact, for a long time it was believed that neutrinos were massless. However, in 1998 at the Super Kamiokande experiment in Japan, it was observed that neutrinos of different types can change from one kind to another and that they do have mass, although very small. This discovery changed physicists’ understanding of the fundamental particles that form the universe since according to the Standard Model of Particle Physics, which was believed to explain the different particles in the universe and their interactions, neutrinos should have been massless. Now, another discovery regarding the speed of neutrinos might force scientists to rethink the basic laws of Physics.
Since Einstein introduced his Special Theory of Relativity in 1905, one of the fundamental principles in physics is that the speed of light is constant and that nothing can be accelerated to a speed that is greater than that of light. Einstein’s revolutionary theory of Special Relativity, which is the basis of the famous equation E = mc2, changed some of the basic concepts of physics that were in place since the times of Galileo and Newton. For example, say two trains are moving in opposite directions at certain speeds. If an observer is sitting in one of the trains, he will observe the other train to be approaching much faster than the speed of the train with respect to the ground. According to the pre-Einstein understanding of motion, one would say that the speed of the approaching second train as viewed by the person sitting in the first train would simply be the sum of the speeds of the two trains. However, according to Einstein’s Special Theory of Relativity, this is not so and the speed of the second train recorded by the observer would be slightly different from simply the sum of the speeds of the two trains. At ordinary speeds, this difference would be negligible, but when we approach the speed of light i.e. approximately 300 thousand kilometers per second, the difference becomes significant. According to Special Relativity, the equations become such that no matter what the speed of the observer is, the speed of light appears to be the same. So the speed of light is constant, and another idea to come out of this theory is that nothing can be accelerated to a speed beyond the speed of light.
Since 1905, the Special Theory of Relativity has stood the test of time and has been able to explain various experimental results including the famous Michelson-Morley experiment. Now, if neutrinos do travel faster than the speed of light, then the basic idea of Einstein’s Special Theory of Relativity is challenged.
On 23rd September 2011, the OPERA (Oscillation Project with Emulsion Racking Apparatus) experiment located at Gran Sasso in Italy announced to the world that they had observed neutrinos that were traveling with a speed that was more than the speed of light.
A beam of neutrinos generated at CERN (European Organisation for Nuclear Research) located near Geneva, Switzerland, is sent through the Earth (note that neutrinos hardly interact and hence can pass through parts of the Earth) to Gran Sasso in Italy where they are detected using a complex detector arrangement by the OPERA experiment. The particle accelerator at CERN that is associated with the LHC (Large Hadron Collider) experiment is used to generate the neutrino beam. The distance from CERN to the OPERA site is around 720 km and the actual distance is measured to an accuracy of 20cm using methods of geodesy and with the help of GPS. Synchronised clocks at CERN and OPERA were used to measure the time of travel of the neutrinos and the timing measurement is being made with an accuracy of around 1 nano-second (1 part in a billion parts of a second). After a complicated but precise detection of neutrinos, measurement of the travel time and the distance of travel, according to the OPERA experiment, neutrinos were found to reach OPERA from CERN 60.7 nanoseconds before light would cover the same distance. That is,neutrinos found to be travelling at around 7.4 kilometers per second faster than the speed of light.
The OPERA experiment was not designed with the specific purpose of measuring the speed of neutrinos. The main goal of the experiment is to observe the “neutrino oscillations” or the changing of neutrinos from one type to another. Measuring the speed of neutrinos is just a part of the experiment. The way the OPERA experiment put it was that after taking into account all factors, neutrinos were found to be covering the distance between CERN and OPERA in a time shorter than light would take to cover the same distance. Lacking any other explanation, the conclusion to be drawn is that neutrinos were travelling at a speed that was faster than the speed of light.
This measurement can potentially have a massive impact on physics as a whole. If neutrinos do indeed travel faster than light then there needs to be a theoretical explanation for this phenomenon. Perhaps the Special Theory of Relativity needs to be scrapped, though some scientists feel that some modifications to that theory may be able to accommodate neutrinos that travel with super-luminal speeds. Time - travel, space exploration and a few other fantastic concepts were limited by the theoretical bound on the maximum speed that a object can travel with, the speed of light. If the speed of light is no longer an upper limit then many of these concepts considered impossible become merely improbable. Mind you, this does not mean the large distance space travel or time travel is just around the corner. Most scientists remain sceptical of the measurements by OPERA; let the results be confirmed first.
OPERA invited external scrutiny of their experimental methods and results and also suggested that other independent verifications of their discovery be made. OPERA came up with another verification of their result using shorter beams of neutrinos to overcome some of the doubts some external scientists had expressed.
In February, 2012, OPERA came out with a statement explaining that while checking their experimental apparatus thoroughly for sources of error, they have identified two possible sources of error - a faulty or loose connection of the fibre optic cable to the GPS system that was used for time synchronisation and a machine error that might affect the time recorded for each measurement. These errors are very small in absolute terms (less than a few hundred nan-seconds), but due to the precision required in the experiment, they might become significant in explaining the discrepancy of their measurement with the theoretical expectation that the speed of neutrino should be less than that of light. The scientists at OPERA are not sure of whether or not these effects had affected their initial measurements significantly and another period of data taking in May 2012 is expected to determine the accuracy of their previous measurement.
There have been other measurements of the speed of neutrinos but none dealing with the kind of neutrinos being detected by OPERA and with the same accuracy. In one measurement associated with a Supernova, neutrinos were found to be traveling at speeds slower than the speed of light, however the energies of those neutrinos were much lower than that of the neutrinos being detected at OPERA and a comparison can not be made as the difference in speeds might be attributed to the difference in energies.
Currently there are facilities in the USA and Japan where the OPERA result may be verified, but that will take time. The facility in the USA - MINOS had also reported that they had observed the speed of neutrinos to be greater than the speed of light, however the uncertainty quoted in their measurements were much higher than that at OPERA. Until independent confirmations of OPERA’s discovery are made, most physicists continue to be sceptical about whether neutrinos can travel faster than light. INO (India-based Neutrino Observatory) is also coming up near the border of Kerala and Tamil Nadu on the South of India that aims to study neutrinos. Perhaps in another few years measurements of the speed of neutrinos might be made in India in order to confirm or contradict the OPERA results.
With so many experiments trying to confirm OPERA’s measurements, and OPERA themselves re-checking their own measurements, we should be able to ascertain whether the OPERA measurements can be attributed to some experimental errors or that neutrinos do indeed travel with speeds faster than the speed of light very soon.
So what are these neutrinos? Neutrinos are the lightest elementary particles known to man. They have surprised scientists time and again and prompted scientists to rethink their understanding of the universe. The existence of neutrinos was first predicted by Nobel laureate Austrian physicist Wolfgang Pauli as early as in 1930 in order to explain the mechanism of Beta decay ( a well known Radioactive process). It was only in 1956 that neutrinos were reported to have been experimentally observed. In 1965, neutrinos produced in the Earth’s atmosphere due to interaction with particles coming from outer space, were first observed in the Kolar Gold Mines in India.
Neutrinos are neutral particles that interact with other particles through what is known as a weak interaction, which as the name suggests is very weak. Hence, they rarely interact with other particles and are very difficult to detect. Neutrinos are produced in stars, in nuclear reactors, in other radioactive processes and also in the atmosphere of the earth through nuclear interactions. It is estimated that over 50 trillion electron neutrinos from the sun are passing through the human body every second!
Neutrinos are of three types and have very small mass. In fact, for a long time it was believed that neutrinos were massless. However, in 1998 at the Super Kamiokande experiment in Japan, it was observed that neutrinos of different types can change from one kind to another and that they do have mass, although very small. This discovery changed physicists’ understanding of the fundamental particles that form the universe since according to the Standard Model of Particle Physics, which was believed to explain the different particles in the universe and their interactions, neutrinos should have been massless. Now, another discovery regarding the speed of neutrinos might force scientists to rethink the basic laws of Physics.
Since Einstein introduced his Special Theory of Relativity in 1905, one of the fundamental principles in physics is that the speed of light is constant and that nothing can be accelerated to a speed that is greater than that of light. Einstein’s revolutionary theory of Special Relativity, which is the basis of the famous equation E = mc2, changed some of the basic concepts of physics that were in place since the times of Galileo and Newton. For example, say two trains are moving in opposite directions at certain speeds. If an observer is sitting in one of the trains, he will observe the other train to be approaching much faster than the speed of the train with respect to the ground. According to the pre-Einstein understanding of motion, one would say that the speed of the approaching second train as viewed by the person sitting in the first train would simply be the sum of the speeds of the two trains. However, according to Einstein’s Special Theory of Relativity, this is not so and the speed of the second train recorded by the observer would be slightly different from simply the sum of the speeds of the two trains. At ordinary speeds, this difference would be negligible, but when we approach the speed of light i.e. approximately 300 thousand kilometers per second, the difference becomes significant. According to Special Relativity, the equations become such that no matter what the speed of the observer is, the speed of light appears to be the same. So the speed of light is constant, and another idea to come out of this theory is that nothing can be accelerated to a speed beyond the speed of light.
Since 1905, the Special Theory of Relativity has stood the test of time and has been able to explain various experimental results including the famous Michelson-Morley experiment. Now, if neutrinos do travel faster than the speed of light, then the basic idea of Einstein’s Special Theory of Relativity is challenged.
On 23rd September 2011, the OPERA (Oscillation Project with Emulsion Racking Apparatus) experiment located at Gran Sasso in Italy announced to the world that they had observed neutrinos that were traveling with a speed that was more than the speed of light.
A beam of neutrinos generated at CERN (European Organisation for Nuclear Research) located near Geneva, Switzerland, is sent through the Earth (note that neutrinos hardly interact and hence can pass through parts of the Earth) to Gran Sasso in Italy where they are detected using a complex detector arrangement by the OPERA experiment. The particle accelerator at CERN that is associated with the LHC (Large Hadron Collider) experiment is used to generate the neutrino beam. The distance from CERN to the OPERA site is around 720 km and the actual distance is measured to an accuracy of 20cm using methods of geodesy and with the help of GPS. Synchronised clocks at CERN and OPERA were used to measure the time of travel of the neutrinos and the timing measurement is being made with an accuracy of around 1 nano-second (1 part in a billion parts of a second). After a complicated but precise detection of neutrinos, measurement of the travel time and the distance of travel, according to the OPERA experiment, neutrinos were found to reach OPERA from CERN 60.7 nanoseconds before light would cover the same distance. That is,neutrinos found to be travelling at around 7.4 kilometers per second faster than the speed of light.
The OPERA experiment was not designed with the specific purpose of measuring the speed of neutrinos. The main goal of the experiment is to observe the “neutrino oscillations” or the changing of neutrinos from one type to another. Measuring the speed of neutrinos is just a part of the experiment. The way the OPERA experiment put it was that after taking into account all factors, neutrinos were found to be covering the distance between CERN and OPERA in a time shorter than light would take to cover the same distance. Lacking any other explanation, the conclusion to be drawn is that neutrinos were travelling at a speed that was faster than the speed of light.
This measurement can potentially have a massive impact on physics as a whole. If neutrinos do indeed travel faster than light then there needs to be a theoretical explanation for this phenomenon. Perhaps the Special Theory of Relativity needs to be scrapped, though some scientists feel that some modifications to that theory may be able to accommodate neutrinos that travel with super-luminal speeds. Time - travel, space exploration and a few other fantastic concepts were limited by the theoretical bound on the maximum speed that a object can travel with, the speed of light. If the speed of light is no longer an upper limit then many of these concepts considered impossible become merely improbable. Mind you, this does not mean the large distance space travel or time travel is just around the corner. Most scientists remain sceptical of the measurements by OPERA; let the results be confirmed first.
OPERA invited external scrutiny of their experimental methods and results and also suggested that other independent verifications of their discovery be made. OPERA came up with another verification of their result using shorter beams of neutrinos to overcome some of the doubts some external scientists had expressed.
In February, 2012, OPERA came out with a statement explaining that while checking their experimental apparatus thoroughly for sources of error, they have identified two possible sources of error - a faulty or loose connection of the fibre optic cable to the GPS system that was used for time synchronisation and a machine error that might affect the time recorded for each measurement. These errors are very small in absolute terms (less than a few hundred nan-seconds), but due to the precision required in the experiment, they might become significant in explaining the discrepancy of their measurement with the theoretical expectation that the speed of neutrino should be less than that of light. The scientists at OPERA are not sure of whether or not these effects had affected their initial measurements significantly and another period of data taking in May 2012 is expected to determine the accuracy of their previous measurement.
There have been other measurements of the speed of neutrinos but none dealing with the kind of neutrinos being detected by OPERA and with the same accuracy. In one measurement associated with a Supernova, neutrinos were found to be traveling at speeds slower than the speed of light, however the energies of those neutrinos were much lower than that of the neutrinos being detected at OPERA and a comparison can not be made as the difference in speeds might be attributed to the difference in energies.
Currently there are facilities in the USA and Japan where the OPERA result may be verified, but that will take time. The facility in the USA - MINOS had also reported that they had observed the speed of neutrinos to be greater than the speed of light, however the uncertainty quoted in their measurements were much higher than that at OPERA. Until independent confirmations of OPERA’s discovery are made, most physicists continue to be sceptical about whether neutrinos can travel faster than light. INO (India-based Neutrino Observatory) is also coming up near the border of Kerala and Tamil Nadu on the South of India that aims to study neutrinos. Perhaps in another few years measurements of the speed of neutrinos might be made in India in order to confirm or contradict the OPERA results.
With so many experiments trying to confirm OPERA’s measurements, and OPERA themselves re-checking their own measurements, we should be able to ascertain whether the OPERA measurements can be attributed to some experimental errors or that neutrinos do indeed travel with speeds faster than the speed of light very soon.
No comments:
Post a Comment