Chapter 18 of 'Einstein' - all chapters at

18. The Principia, by Isaac Newton lay on the corner of Einstein’s desk, behind the lamp. It was the heart of classical physics as practiced by all scientists as the 19th century morphed into the 20th, and virtually all laws in mechanics emanated from Newton’s theories. These theories, of course, were full of absolutes. Albert turned to the pages on the laws of motion. Like every other physicist, he knew them by heart. Nonetheless, as he had done that morning with Maxwell and Lorentz, he wanted to follow the logic of the theory. He wanted to put it together as Newton had, for the first time, trying to fathom the primordial thinking that went into the creation of these proofs and theories. He intended to explore the role time played in his laws of motion as he did so.

Einstein thought about the Law of Inertia: a body in motion would tend to stay in motion, and a body at rest would tend to stay at rest. If he were to consider the trolley in Bern’s central courtyard, an initial force would be required to move it forward. It would achieve a constant speed when all the forces acting on it were in balance. In a frictionless environment without any forces acting against its forward movement, it would move forward forever at a constant speed. Simple enough. However, the concept of speed was defined as movement in time. When one referred to “constant speed,” there was a reliance on constant, linear time. But what would happen if one assumed instead that the rate of passage of time depended on the environment? Might the passage of time speed up or slow down in an environment approaching the speed of light, where experimental evidence had shown problems with the adherence of Newton’s principles? The trolley in Bern’s central courtyard could not maintain a constant speed under these circumstances Albert thought. If time varied, the speed of any object would no longer be constant. The speed could increase or decrease without any external force acting on it. In other words, an object in motion would not necessarily stay in motion. Newton’s first law of motion would not work. “That’s exactly what would happen,” Albert mumbled under his breath. “With the Law of Inertia, that is. What about the Law of Acceleration? The Law of Acceleration stated that the force acting on an object was equal to the object's mass multiplied by its acceleration. What about an object in an environment that was changing? What if the entire environment within which this law was being applied was accelerating or decelerating? Would the law still hold?

Acceleration, velocity and speed were all functions of time. If the rate of passage of time varied according to the environment, then these measures were no longer reliable. The speed of the trolley might be ten feet per second, but if a second became a little longer in duration or a little shorter, then it would have a different speed. Albert nodded his head, but had a quizzical look on his face. These examples showed that in an environment approaching the speed of light, where the rate of passage of time might be altered, the concepts of speed, velocity and acceleration would no longer be measured in the same way. This concept, if true, would definitely cause complications for Newton’s second law of motion. Albert shook his head, as much to shake some sense into it as to express any displeasure with his thought process. As he moved through Newton’s laws of motion, the answer was probably yes, they were in jeopardy if time were not a constant, linear phenomenon. They would not work in the same way as Newton envisioned, because one of his most basic assumptions – the predictability of the rate of passage of time – would no longer apply. It was possible that a variation in time could explain the problems in mechanics that plagued scientists dealing with items traveling at great speeds. It was possible, but far from conclusive. I need experimental evidence about the nature of time, he thought. Don’t any of those experimental scientists know how important that is?

Scientists had addressed the absolute nature of light, but not the absolute nature of time. Lorentz and Fitzgerald had shown that the speed of light was unaffected by the velocity of its source, that the speed of light remained the same whether it's emitted by a stationary or moving source. This led some scientists, including Einstein, to believe that 186,000 miles per second might be an absolute limit. There were no experiments or mathematical proofs that did the same for time. While a small number of scientists believed that time could not hold up as an absolute, and that its absolute-ness would eventually be disproved by experimentation and mathematics, no one had proven anything yet. Not even close. On this evening in May 1905, Albert Einstein sighed and looked around for a cigar, or even the remnants of one. He did not need another one to smoke, but he wanted to chew on something as he went over this persistent and nagging problem. He rose from his desk and returned to the living room. It was quiet and mostly dark, Mileva having made sure everything was turned off and put away for the night. The only illumination came from the study, where Albert's lamp cast just enough light through the doorway for him to make out the different pieces of furniture. Albert sat down in his favorite stuffed chair. That stream of light coming from the study is composed of tiny packets of energy, he thought. It is traveling at 186,000 miles per second. And if its source were moving – despite the laws of mechanics developed by Newton, and in opposition to common sense – that light would still be traveling at 186,000 miles per second. He did not have a problem with this part, though he realized that other scientists, as well as philosophers and logicians, clearly did. To Einstein, it was now a fact to be absorbed, a factor to be considered within the context of a different way of looking at the natural world. The part that did cause a problem for him was his inability to get a sense of what the world would look like to someone traveling at the speed of light, someone who could jump on one of those tiny packets of light and ride it out. He had been pondering this particular problem since he was sixteen years old. But he felt no closer to answering the question now than he had been ten years ago, when as a teenager he was trying to come to grips with the nature of the world, especially as it was changing and being redefined by physicists, mathematicians, and yes, even philosophers. It was one of the issues that he and his colleagues considered when they created the Olympia Academy. For Einstein, he desperately wanted to understand better how everything fit together, even as the perspective of the scientific world was shifting and changing. He wanted to pursue the ultimate nature of things, the meaning of all the discoveries and new ideas of the late 19th and early 20th century, and it helped to discuss them with people of vision and knowledge in different fields. He had to do his own thinking, of course, and find order in the world from his own perspective, but there was also much to learn from the perspective of others. The Academy added insight and perspective to his inquiry in areas as ostensibly diverse as physics and philosophy, though Albert had come to believe that lines of inquiry in these two fields were not as diverse as it might appear.

But as deeply as they thought in the Olympic Academy, and as tirelessly as they discussed the nature of things, they never came up with any satisfactory answer to Albert’s nettlesome question of what the world would look like to someone traveling at the speed of light. Even for thinkers of vivid imaginations, it was impossible to imagine.

Albert sighed again and checked the ashtray on the small table for a cigar remnant. It was empty, a victim of Mileva's spot cleaning earlier in the evening. It was annoying not to be able to find a cigar when he wanted one, but now that he was sitting in the living room, he thought less about the cigar and more about the light that was emanating from his study.

He could not help himself and asked the familiar question again.

What would the world look like to someone traveling at the speed of light?

He still had no answer. He wondered, however, if it would be helpful to combine this familiar question with the unfamiliar one about time he had been considering that evening. What if he introduced the notion of non-linear time into his imaginary trip on a packet of light energy? Light would remain an absolute in this conceptual exercise, but time would not.

The juxtaposition of one against the other, light and time, preserving one as an absolute and the other as variable, might be revealing.

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