The Significance Of Speeding Neutrinos

As you likely already know, there has recently been a furore over the behaviour of an infamous lepton. Some measurements of these sub-atomic particles that have been taken in Italy that suggest that c, the speed of light, may not be the absolute speed limit for matter in our universe. These measurements are those of neutrinos apparently travelling at speeds in excess of c. The problem with this is that it goes against all of our current theories relating to this area of science, namely those of Einstein's special relativity. Einstein engaged in many thought experiments and was especially fascinated by light. He came up with the paradox of holding a mirror in front of your face and travelling faster than the speed of light, such that the image of your face disappeared from the mirror. He resolved this paradox, writing four sensational papers about it and citing no external sources. His conclusion was that we were thinking about space-time wrongly. Another thought experiment, similar to Einstein's, proposes the following scenario. Someone carries a torch on board a train. When the train leaves from the station and is travelling at speed, this person gets up from their seat and shines their torch down the length of the train, in the same direction as the train is travelling. To them, the beam of light travels at the speed of light, but to an observer who is outside of the train, would the beam appear to travel at the speed of light plus the speed of the train, therefore breaking the speed of light? Einstein's theories resolve this problem. Einstein remained convinced that the speed of light was a constant and that to get around problems, such as those previously mentioned, it was time that wasn't a constant. This means that rather than the observer seeing light travelling faster than c, time on board the train would be slower than outside of it and so they would see it travelling the distance that the beam apparently covered (taking into account the beam's movement and the train's movement), but to them, it would seem to have taken longer to cover the distance than the person shining the torch would have perceived. From this, you should be able to see that the faster you travel (relative to something else), the more time slows down (relative to that something else). There is proof of this concept. For example, G.P.S.s have to take it into account because the satellites involved in calculating the positions on Earth are travelling at around 14,000km/h, and at these relative speeds, the time dilation effect comes into play, resulting in the atomic clocks on board satellites being 7µs (7E-6s) slower than those on the ground per day of orbit. However, the satellites are also orbiting Earth at a height of 20,000km, therefore the curvature of space-time at the satellite will be larger than it is on the ground, due to time travelling faster when closer to a massive object. Due to this effect, the atomic clocks on satellites ought to be faster than those on Earth by 45µs per day. The combination of these two relativistic effects results in atomic clocks on satellites being faster than those on the ground by 38µs per day (45-7=38). This is the same as thirty-eight millionths of a second, which may sound small, but it is more than a thousand times larger than the degree of precision that is required for G.P.S. to work properly: 20-30ns (1ns=E-6s). Therefore, if these effects weren't taken into account, a position reading from a G.P.S. would be false in two minutes; errors in global positioning would accumulate at a rate of 10km per day, rapidly making the system useless. This hasn't happened because the engineers who designed the G.P.S. system took these effects into account to make sure that it would work once deployed, reducing the rate at which the on board atomic clocks "ticked". Neutrinos are essential for the nuclear reactions that formed the elements. They were predicted by Wolfgang Pauli, who thought that it would be impossible to ever find them because of how inert they are. The first time neutrinos were detected was during Project Poltergeist in a nuclear reactor where they are emitted in vast numbers. Something important to note is that neutrinos are extraordinarily aberrant particles; if you asked a physicist to put money on which particle was going break the speed of light (before these measurements were announce), he would almost certainly bet on the neutrino. The project in Italy is a fascinating one: it is taking place in the heart of a mountain, the purpose of which is to eliminate false readings of neutrinos from external sources such as cosmic rays. The mountain reduces the background neutrino (ve) count to 1vem^-3h^-1. The project is called OPERA and its purpose is to study neutrinos in their three different forms (ve, vµ, v?). This is carried out by having neutrinos produced at CERN, near Geneva, fired through the Earth to OPERA in Italy: a distance of 730km. The neutrinos are emitted from CERN at a rate of E9 (one-billion) a day. Around thirty of these are detected each day at OPERA. The measurement, which this article is trying to focus on, gave the speed at which the arriving neutrinos had travelled at as being 0.0005% faster than c. This went against all current thought and the OPERA operators, knowing this, set about trying to find out where they had gone wrong. They factored in changes in distances between CERN and OPERA, due to tectonic movement, as well as going through their calculations with a fine-toothed comb. In a most sage fashion, they only allowed themselves to publish the result when they were all out of ideas as to how they might have gotten the measurement wrong. In addition to this, the result was published more for the purpose of gaining the assistance of other scientists, so that they would help find the mistake in the OPERA measurement. To give you an idea of just how precise this measurement is, the distance between CERN and OPERA was calculated to ±20cm of the true value, and when this, in addition to all of the other margins of error, was considered, the possible deviation from the true value of how long the neutrinos were taking to arrive at OPERA was calculated to be ±10ns. This makes the OPERA measurement incredibly precise - precise enough for operators to be unable to account for the 60ns, which the neutrinos were early by, with lack of precision of the reading. The problem with things being able to travel faster than the speed of light is that it challenges the whole idea of cause and effect. This is because an absolute speed limit, c, results in time only being able to pass in one direction. Without this, jokes like "The barman said, 'We don't serve neutrinos here.' A neutrino walked into a bar." become less funny and more a concerning reality. Measurements of the speeds of neutrinos have been takes before. At Fermilab, they were able to account for the fact that the neutrinos seemed to be travelling faster than the speed of light with a lack of precision in their experiment. More interestingly, however, a supernova in the Tarantula Galaxy, which took place 100,000 years ago, produced vast amounts of light and a huge number of neutrinos. The light from this only reached us more recently and as one would expect, the neutrinos arrived just after the light did. This is compared with the four years that would have passed after the arrival of the neutrinos, before the light arrived, if the measurement at OPERA is accurate. The following are ways in which the measurement at OPERA may be inaccurate or resolvable: First, particles travelling faster than the speed of light have already been theorised mathematically. Without the possibility of matter travelling faster than c, there are problems with the moments just following the Big Bang that cannot be resolved. Second, String Theory requires about six more invisible dimensions, in addition to the four of space and time that we experience. This can explain the faster-than-light reading because in String Theory, the neutrinos could, unlike light, leave the membrane of our universe, travel through the bulk for a bit and then re-enter the membrane of our universe again at a point further ahead of where light from the same source would be, all the while travelling at a speed less than c, but arriving at the destination before light would. I appreciate that the terms "membrane" and "bulk" are unfamiliar here and that this explanation is insufficient as a whole, but String Theory isn't something to be explained in passing. Third, in response to the difference in the apparent speeds of the neutrinos from CERN and those from the Tarantula Galaxy, some physicists have suggested that this may be due to the fact that the neutrinos from CERN are created in extremely violent reactions, possibly giving them abilities that those created in supernovae don't have, such as the ability to travel trans-bulk (an example of a String Theory-related explanation). Fourth, certainly one physicist has suggested that there may be an error in the calculation of the measurement at OPERA in that the operators may have assumed that the pattern that the incident neutrinos formed in their detector was the same as the pattern of the beam of neutrinos produced at CERN. This may not necessarily be true, and assumptions concerning it could lead to errors in the resulting readings. In conclusion, all we can do is wait and think.