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out from a flashlight. According to common sense, if we run fast enough we could in principle catch up with the front of the beam of light as it advances forward. Common sense might even suggest that we could jog alongside the front of the beam if we managed to run at the speed of light. But if we are to follow Maxwell’s equations to the letter, then no matter how fast we run, the beam still recedes away from us at a speed of 299,792,458 meters per second. If it did not, the speed of light would be different for the person running compared to the person holding the flashlight, contradicting Michelson and Morley’s experimental results and our assertion that the speed of light is a constant of nature, always the same number, irrespective of the motion of the source or the observer. We seem to have talked ourselves into a ridiculous position. Surely common sense would advise us to reject, or at least modify or reinterpret Maxwell’s equations: Perhaps they are only approximately correct. Now, that doesn’t sound like an unreasonable proposition, since the motion of any realistic experimental apparatus would cause only a tiny variation in the 300 million meters per second that appears in Maxwell’s equations. So tiny indeed that perhaps it would have remained undetected in Faraday’s experiments. The alternative is to accept the validity of Maxwell’s equations and the bizarre proposition that we can never catch up with a beam of light. Not only is that idea an outrage to our common sense, but the next chapter will reveal that it also implies that we should reject the very notion of absolute time.

Breaking our attachment to absolute time is just as difficult to grasp today as it was to the nineteenth-century scientists. We have a strong intuition in favor of absolute space and time that is very hard to break, but we should be clear that intuition is all it is. Moreover, Newton’s laws embrace these notions wholeheartedly and, even to this day, those laws underpin the work of many engineers. Back in the nineteenth century, Newton’s laws seemed untouchable. While Faraday was laying bare the workings of electricity and magnetism at the Royal Institution, Isambard Kingdom Brunel was driving the Great Western Railway from London to Bristol. Brunel’s iconic Clifton Suspension Bridge was completed in 1864, the same year that Maxwell achieved his magnificent synthesis of Faraday’s work and uncovered the secret of light. The Brooklyn Bridge opened eight years later, and by 1889 the Eiffel Tower had risen above the Paris skyline. All of the magnificent achievements of the age of steam were designed and built using the concepts laid down by Newton. Newtonian mechanics was clearly far from being abstract mathematical musing. The symbols of its success were rising across the face of the globe in an ever-expanding celebration of humanity’s mastery of the laws of nature. Imagine the consternation in the minds of the late nineteenth-century scientists when they were faced with Maxwell’s equations and their implicit attack on the very foundations of the Newtonian worldview. Surely there could be only one winner. Surely Newton and the notion of absolute time would reign victorious.

Nevertheless, the twentieth century dawned with the problem of the constant speed of light still casting dark clouds: Maxwell and Newton could not both be right. It took until 1905 and the work of a hitherto unknown physicist named Albert Einstein for it to be finally demonstrated that nature sides with Maxwell.

3

Special Relativity

In Chapter 1 we succeeded in establishing that the very intuitive Aristotelian view of space and time was laden with excess baggage. That is to say, we showed that there is simply no need to view space as the fixed, immutable, and absolute structure in which things happen. We also saw how Galileo appreciated the irrelevance of holding on to the notion of absolute space, while firmly maintaining the idea of a universal time. In the last chapter, we took a detour into the nineteenth-century physics of Faraday and Maxwell, where