Faster than the speed of light?

Revered astrophysicists Carl Sagan and Stephen Hawking further piqued the public's fascination with talk of worm holes. And while Sagan remained reserved on the possibility of time travel, significantly he added that he believed it was still worth exploring. Astrophysicists concede that until the speed of light can be exceeded, time travel will remain an impossibility. But in September 2011 researchers working on the Opera experiment at CERN, Geneva, made an announcement that has the potential to turn the very foundation of physics on its head. For a period of months, teams at CERN and the underground Gran Sasso Laboratory of the Italian National Institute of Nuclear Physics had been observing more than 15,000 sub atomic particles called neutrinos. Neutrinos are produced by the decay of other particles such as neutrons in a radioactive nucleus. The main aim of the research was to observe neutrino oscillations - whereby the particles change 'flavour' as they travel. By measuring the oscillations, the masses of the neutrinos could then be determined. The researchers believed that an accurate measurement would give new insight into fundamental particle physics questions about how the mass of neutrinos and other particles arises. When the readings came back, the researchers discovered something astonishing. Results repeatedly indicated that the neutrinos had travelled at a velocity 20 parts per million faster than the speed of light. If these unexpected findings were proved to be correct, the implications could affect all aspects of cosmology, astrophysics and particle physics. The results were made public and the worldwide media immediately hypothesised potential applications for particles that could travel faster than light. Meanwhile, physicists across the globe demanded proof. Indeed, the Opera project leaders actively encouraged scrutiny from the broader particle physics community in a bid to fully assess the nature of the observation. The authors of the OPERA paper said: "We are not claiming things, we want just to be helped by the community in understanding our crazy result - because it is crazy." Within two weeks nearly 30 physicists had already published papers claiming faults with the findings. One such sceptic is Stephen Fairhurst, Royal Society University Research Fellow School of Physics & Astronomy Cardiff. "There is every chance that there is a less spectacular explanation of the results, and several papers offering alternatives have already been written," he said. "For example, one paper discusses the technical challenges of synchronising clocks to the required accuracy to make these measurements. Nevertheless, the discovery of faster than light travel would be truly remarkable." Neutrinos, invisible particles that rarely interact with matter, are the hardest of the sub atomic particles to study. Dario Auterio, Researcher at the Institut de Physique Nucleaire de Lyon, notes that such properties make tracking and detection extremely difficult. "Neutrinos do not have an electric charge and they interact very weakly with matter – so called 'weak interactions'. They are capable of passing the entire earth without interacting." And, while there are plenty of neutrinos available to research – approximately 400,000billion from the sun pass through the earth every second – until recently, it was not even known whether the particles have a very small mass, or no mass at all. If neutrinos do have a mass then they have the potential to make up part of 'dark matter' and, in theory, the universe could have sufficient gravity to stop expanding and start contracting. "Neutrinos have many interesting features in particle physics," continued Auterio. "At the beginning, we talked of neutrinos not having a mass. But, with the infiltration of the flux of neutrinos coming from the sun, people have been starting to think that they could have a mass and could change their nature during their travel path. They can transform themselves into three different types of neutrinos: electron neutrinos, muon neutrinos and tau neutrinos. The neutrinos are also linked to many aspects of cosmology, to the birth of the universe, they may be related to the symmetry between matter and anti matter and they're also the most common particles in the universe." To effectively track and detect the particles, the Opera Project researchers adopted a unique approach. High energy beam pointed towards Italy The Opera experiment was established in 2006 to analyse neutrino oscillations and to detect the appearance of tau neutrinos from the oscillation of muon neutrinos. A high energy beam of muon neutrinos was pointed from the Geneva based CERN accelerator complex (CNGS) towards Gran Sasso, 730km away. A beam of this kind is generated from collisions of accelerated protons with a graphite target, after focusing the particles produced in the desired direction. As products of the same 'parent' particle, muons and neutrinos continue to travel in the same direction. And because neutrinos rarely interact with matter, the particles were able to pass undisturbed, taking just 3ms to reach their destination. Auterio observed: "The interesting aspect of this measurement was the combination of techniques used in energy physics for neutrino detection. The high energy beam, which is sent to Gran Sasso, has a unique property to provide a very high rate of neutrino interactions that we can detect in our Opera detector. This is related to the fact that it is a high energy neutrino beam. "The other very interesting aspect was combining this with metrology techniques related to the measurement of space and time. These are commonly used in other fields but have never before been used in particle physics with this level of accuracy." The resulting interactions (tau leptons) were observed in 'bricks' of photographic emulsion films interleaved with lead plates – each one, effectively working as a photographic camera. Construction for the Opera experiment began in 2003 and it took five years to complete the apparatus which contains 150,000 of the bricks arranged into parallel walls, interspersed with plastic scintillator counters. A series of electronic detectors such as trackers and spectrometers were used to monitor the path of the neutrinos. To monitor the momentum and charge identification of penetrating particles, a magnetic spectrometer was used to track each target. As data was being taken, it was possible to tag neutrino interactions in real time and provide information on the exact location of the neutrinos on the bricks. Once these had been extracted from the wall, developed and scanned for evidence of tau decays, the researchers could detect all details of the neutrino events by measuring the elementary particles produced in the interaction of the neutrino with the brick. The Opera team discovered several particles that had left tracks in the brick at the point of interaction. According to the researchers, this indicated a tau neutrino interaction with a probability of about 98%. CERN's high energy accelerators and detectors were constructed specifically to analyse the foundations of the structure of matter. "We were very surprised because we conducted the analysis in a blind way," Auterio explained. "We were expecting negative results so were surprised to detect this anticipation of neutrinos with respect to what could be computed, assuming the light on the same travel path. The factor at which we measure it is equivalent to 60ns over a time of flight of 2.4ms – or if you want to express it in terms of distance, an anticipation of 20m over 730km." If the findings turn out to be correct, the research will have a spectacular impact on Einstein's theory of general relativity. "If particles can travel faster than the speed of light, this would force a major re-write of modern physics," said Fairhurst. "Einstein's special relativity does not permit faster than light travel. So, if it is observed, this would require a reformulation of relativity and every theory that is built upon it. At present, there is probably no theory that is capable of allowing faster than light travel and explaining everything else we have observed in the universe, from quantum physics on the smallest scales to astrophysics and cosmology on the largest." Time travel in the offing? So are we on the verge of witnessing the beginnings of time travel? If the Opera project data is proved to be correct, then it raises the question of whether materials can also be manipulated to exceed the speed of light. Fairhurst remains cautious. "One thing to point out is that it is very difficult to accelerate things close to the speed of light - it requires large experiments like CERN," he said. "In Einstein's relativity, to accelerate a particle to close to the speed of light requires a huge amount of energy. And the amount of energy required increases as you get closer to the speed of light so that it would actually require an infinite amount of energy to get to light speed." It may be a matter of weeks before it is established whether neutrinos can travel faster than light, but for now manipulation of time itself must remain the stuff of fiction.