with all the recent talk about faster-than-light particles, we thought it timely to bring you selected excerpts from physicist Ben Still’s Neutrino Blog looking at how such speeds might be possible, what that means for physics and how we might have seen this all once before. illustration by Sister Arrow
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The neutrinos released in supernova deaths of stars, such as SN1987a, a far less energetic than the neutrino beam used by the OPERA experiment. In fact, the energy of neutrinos fired from CERN to the OPERA detector in Gran Sasso, Italy, are of the order 1000 times as energetic as those seen from SN1987a.
Einstein’s theory of relativity assumes that nothing can travel faster than the speed of light, this property is known as Lorentz invariance. It is hard coded into the mathematics and it is the ratio of the squares of the mass and energy that determines how close to the speed of light a particle can travel. The smaller the ratio m2/E2 the closer to the speed of light a particle gets.
The extremely small mass of the neutrino, means that it requires very little energy to travel at amazingly fast speeds. At an energy of 10 of MeV, neutrinos are traveling at 99.999999999998% the speed of light. The difference in speed when we raise the energy of the neutrino to 10GeV is a tiny 0.00000000001998%. If 10MeV (roughly that from SN1987a) and 10GeV (roughly the energy of OPERA) neutrinos were in a race all the way from the large Magellanic cloud, where SN1987a died spectacularly, then the 10GeV neutrinos would arrive just one tenth (0.1) of a second before the 10MeV energy neutrinos. Although the OPERA energy neutrinos would be faster, note that because of Lorentz invariance they would not travel faster than light.
The only way in which this can explain faster than light neutrinos would be if a new physics, beyond our current understanding, ‘switches on’ at high previously unexplored energies. ‘Switches on’ is a phrase that theorists like. New physics may exist at scales of energy over the horizon of our previous experiences as it is in these lands that theories lie. The GeV energies used by the OPERA is indeed a new frontier in our understanding of the neutrino.
The forerunner of theories which allow the neutrino to travel faster than light is that of quantum gravity. Here the neutrinos interact differently than light does with the backdrop of the Universe; the foamy space-time upon which Nature in played out. This difference in interaction, effectively sees particles of light – photons – and neutrinos traveling through different subsets of extra dimensions.
I would not claim any great knowledge in quantum gravity, but I understand that as yet there is no evidence for extra dimensions or the quantum space-time foam talked of. If the OPERA results do withstand the rigorous tests and scrutiny they will most certainly be under then it may be the first hint of quantum gravity. Only time, repeat results, and a lot of hard work will tell.
The Kamiokande-II experiment was used to detect neutrinos in a massive tank of 3000 tonnes of ultra pure water – usually around six of the trillions upon trillions of neutrinos that passed through it every day. Imagine their surprise then, when asked by optical astronomers to check their data on 23rd February 1987, in seeing a spike of 12 neutrinos in just 12.4 seconds! With so many neutrinos seen in such a short space of time there must have been a huge intensity of neutrinos passing through the Earth – far greater than that from the Sun and atmosphere combined.
Intensity of neutrinos equates to intensity of energy, as it is the neutrinos that take energy away from the supernova. The intensity of neutrinos and energy was calculated and found to agree well with theoretical models. In these models the energy taken away from supernova accounts for 99% of the total energy emitted. The energy released in forming a neutron star comes primarily from essentially the difference in mass between the normal core and the new neutron star. This is a value that is well constrained. So I argue that if the intensity of neutrinos see just hours before SN1987a accounts for 99% of the theoretically modeled energy released, then there could not have been neutrinos missed 4.14 ±1 years previous.
Of the three neutrino observatories that saw antineutrinos from SN1987a, only the IMB and Baksan detectors were active in 1983, both of which started operation in 1982. Kamiokande in Japan was the largest of the three but did not begin operation until the second quarter of 1983. As far as I am aware there was no neutrino spike such as that seen in 1987 – after this detection of a supernova in neutrinos was made all historical data was scrutinised and nothing appears in publication.
The neutrinos seen by these detectors were electron antineutrinos. The reason for this is that the likelihood for electron antineutrinos to interact with the normal stuff around us is far far higher because they have the possibility to interact by inverse beta decay p + anti-νe → n + e+. One could then make the argument that perhaps the other types of neutrino traveled faster than light and then we missed them four years previous because we did not see them.
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Ben Still is a research associate at Queen Mary, University of London and works on the Tokai to Kamioka (T2K) neutrino oscillation experiment based in Japan. You can find out more about his research at benstill.com
Sister Arrow is an artist and illustrator working with drawing, painting and animation. Her inspirations include nature, metaphysics, sci-fi, primitive life, caves and Japan. A selection of her recent work is currently on show at Beach London.