Faster than the Speed of Light
Joao Magueijo at Cafe Scientifique, Live Theatre, 15th March 2004
Review by Caspar Hewett

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This event was the contribution of the now well-established Café Scientifique to Newcastle Science Festival 2004 and a great opening to the week it was. The speaker Joao Magueijo, is a Reader in Theoretical Physics at Imperial College, London and author of Faster Than the Speed of Light: The Story of a Scientific Speculation. He opened by explaining how Einstein’s theory of relativity is the foundation of every other theory in modern physics and that the assumption that the speed of light is constant is the foundation of that theory. Thus a constant speed of light is embedded in all of modern physics and to propose a varying speed of light (VSL) is worse than swearing! It is like proposing a language without vowels.

For Magueijo relativity is not really difficult to grasp and a constant speed of light is the start point. To help to visualise this he invited the audience to imagine driving alongside a car made of light. Since the speed of light is constant it does not matter what you do in terms of accelerating or decelerating the light car will still have the same relative speed to you. This counter-intuitive notion led Einstein to propose that speed and time must be variable - in particular that time advances at different rates for objects moving relative to each other. The speed of light, c, thus is a speed limit - it is not possible to go faster than it. This is quite annoying - especially from the point of view of space travel. Although it is very fast compared to the speed at which we do things, c is slow compared to the size of the Universe - there is a disparity of scale especially considering the length of human life.

Those proposing a VSL have been described as the punk rockers of physics, but the notion is not without precedent. Einstein himself proposed a VSL theory in 1911, but abandoned it. Like any assumption in science the constant c is not dogma - all theories are open to revision in the light of experimental or observational evidence.

So, why propose a VSL? According to Magueijo a number of problems in physics led to the VSL theory - primarily in the area of cosmology. In 1930 Edwin Hubble discovered that the Universe is expanding. This means that space is literally being created between the galaxies. Hubble was observing the creation of distance. Reading time backwards this suggested that the Universe was increasingly small the further back in time we go, and led to the conclusion that everything started from a point - The Big Bang. Magueijo drew attention to the horizon problem this gives rise to - at any time the Universe has a finite age and thus there is only a finite time for information to travel through it and things can only travel a finite distance. This means that we can only see to the horizon of the Universe and cannot be affected by anything beyond this. The closer in time (and space) we are to the Big Bang the smaller that finite distance is. If we allow for c to be higher earlier in the Universe then information could travel faster. Magueijo claimed he had a hangover when he first considered this - it must have been some headache!

Magueijo drew attention to Dirac’s complaint in 1968 that there was too much speculation in cosmology. It seemed to Dirac that cosmologists were making any assumptions they fancied, especially in the light of the possibility that the laws of physics may be varying with cosmological time. For Magueijo the fact that we live in an expanding Universe means that it makes sense to question the static nature of the laws of physics. However, as a scientist he believes that it is a matter for experiment to decide whether any theory is right or wrong.

The second part of the story is related to the ongoing search for a Grand Unified Theory (GUT) for the laws of physics. The theory of relativity is 100 years old next year and it was Einstein’s great dream to find a GUT. However there has been a 100% failure rate so far. The fact that this has still not been solved is another reason to abandon constant c. In his theory of general relativity Einstein showed that gravity is a property of space-time - the presence of matter warps space-time and it is this distortion that we experience as gravity. The other fundamental forces are electro- magnetism and the strong and weak nuclear forces, all of which are characterised by quantum effects. For a GUT gravity needs to be quantized, but this would mean that time could not be continuous. This gives rise to the notion of a granular property of space - As Magueijo puts it ‘Planck space’ is pot holed. Thus we have to ask what kind of object would fall through holes in space. In relativity length, like time, is not absolute - there is the theory of length contraction which, according to Magueijo needs to switch off at some point if a GUT is to be achieved.

Following his engaging introduction the audience were invited to quiz Magueijo on the VSL theory. A number of people asked about the experimental support for a VSL and what type of experiment could be designed to support or disprove the theory. Magueijo gave a variety of answers. First he pointed to the existence of ultra high energy cosmic rays. These particles have been detected passing through the earth and represent a contradiction with relativity. Relativity predicts that there should be a limit to the energy level possible for cosmic rays and the theory has thus been shown to be wrong. Further evidence comes from astronomical observation - astronomers look into the past when they look into space and have been measuring and observing quasars. Reconstructing the speed of light in the past it seems that it was slightly higher 7 or 8 billion years ago than it is now. This work has not been repeated and thus cannot be taken as irrefutable yet. Another experiment Magueijo suggested to test the VSL hypothesis is to try to measure how much cvaries from year to year. If c varies over the history of the Universe then we would expect a very small variation in the course of a year. Magueijo pointed to the way atomic clocks are becoming ridiculously accurate and suggested that, if they keep improving, we should be able to measure whether c varies year to year quite soon.

Magueijo was scathing about string theory, describing it as ‘like intellectual masturbation.’ He doesn’t like string theory for sociological reasons, his main objection being that it is completely disconnected from experiment, making it hard, or impossible, to confirm or disprove. He conceded that it may be possible to consider a VSL theory and string theory together, but considered the notion a strange one. In contrast, when asked whether there is any mileage left in the ether hypothesis Magueijo thought that perhaps there is! The idea of the ether originates with the discovery of the wave properties of light. The hypothesis was that, if light is a wave, then it must travel in a medium - the ether. If it existed the ether would be a preferred frame of reference for the speed of light - an idea which does not fit in with relativity theory, but if there is a VSL the situation may be different. However, this must be tempered with the recognition that there is strong experimental evidence against such a preferred frame of reference, for example in the Michelson-Morley experiment which was central in Einstein originally formulating the constant c hypothesis. Michelson and Morley showed that different observers measure light at the same speed - Magueijo was clear that if the VSL theory is correct the results of such experiments must still hold at the appropriate scale in this part of the Universe at this time - if not there is no justification for adopting such a theory since the experimental evidence is clear and repeatable.

Expressed with humour and great clarity Magueijo managed to get across some very complex notions to a non-expert audience. It was clear from the questions from the floor that there were a number of physicists in the audience, but also a good cross-section of the general public. The high level of intelligence shown by the audience and expected by the speaker is what I have come to expect of Café Scientifique and is what science festivals should be all about. More please!

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