The scientific case for time being an illusion is formidable. That is why the consequences of adopting the view that time is real are revolutionary.
The core of the physicists’ case against time relies on the way we understand what a law of physics is. According to this dominant view, everything that happens in the universe is determined by a law, which dictates precisely how the future evolves out of the present. The law is absolute and, once present conditions are specified, there is no freedom or uncertainty in how the future will evolve.
As Thomasina, the precocious heroine of Tom Stoppard’s play Arcadia, explains to her tutor: “If you could stop every atom in its position and direction, and if your mind could comprehend all the actions thus suspended, then if you were really, really good at algebra you could write the formula for all the future; and although nobody can be so clever as to do it, the formula must exist just as if one could.”
I used to believe that my job as a theoretical physicist was to find that formula; I now see my faith in its existence as more mysticism than science.
Were he writing lines for a modern character, Stoppard would have had Thomasina say that the universe is like a computer. The laws of physics are the program. When you give it an input — the present positions of all the elementary particles in the universe — the computer runs for an appropriate amount of time and gives you the output, which is all the positions of the elementary particles at some future time. Within this view of nature, nothing happens except the rearrangement of particles according to timeless laws, so according to these laws the future is already completely determined by the present, as the present was by the past.
This view diminishes time in several ways.1 There can be no surprises, no truly novel phenomena, because all that happens is rearrangement of the atoms. The properties of the atoms themselves are timeless, as are the laws controlling them; neither ever changes. Any feature of the world at a future time can be computed from the configuration of the present. That is, the passage of time can be replaced by a computation, which means that the future is logically a consequence of the present.
Einstein’s theories of relativity make even stronger arguments that time is inessential to a fundamental description of the world, as I’ll discuss in chapter 6. Relativity strongly suggests that the whole history of the world is a timeless unity; present, past, and future have no meaning apart from human subjectivity. Time is just another dimension of space, and the sense we have of experiencing moments passing is an illusion behind which is a timeless reality.
These assertions may seem horrifying to anyone whose worldview includes a place for free will or human agency. This is not an argument I will engage in here; my case for the reality of time rests purely on science. My job will be to explain why the usual arguments for a predetermined future are wrong scientifically.
In Part I, I will present the case from science for believing that time is an illusion. In Part II, I will demolish those arguments and show why time must be taken to be real if fundamental physics and cosmology are to overcome the crises they currently face.
To frame the argument of Part I, I trace the development of the concepts of time used in physics, from Aristotle and Ptolemy through Galileo, Newton, Einstein, and on to our contemporary quantum cosmologists, and show how our concept of time was diminished, step by step, as physics progressed. Telling the story this way also allows me to gently introduce the material the lay reader needs for an understanding of the argument. Indeed, key points can be introduced by ordinary examples of balls falling and planets orbiting. Part II tells a more contemporary story, since the argument that time must be reinserted into the core of science arose as a result of recent developments.
My argument starts with a simple observation: The success of scientific theories from Newton through the present day is based on their use of a particular framework of explanation invented by Newton. This framework views nature as consisting of nothing but particles with timeless properties, whose motions and interactions are determined by timeless laws. The properties of the particles, such as their masses and electric charges, never change, and neither do the laws that act on them. This framework is ideally suited to describe small parts of the universe, but it falls apart when we attempt to apply it to the universe as a whole.
All the major theories of physics are about parts of the universe — a radio, a ball in flight, a biological cell, the Earth, a galaxy. When we describe a part of the universe, we leave ourselves and our measuring tools outside the system. We leave out our role in selecting or preparing the system we study. We leave out the references that serve to establish where the system is. Most crucially for our concern with the nature of time, we leave out the clocks by which we measure change in the system.
The attempt to extend physics to cosmology brings new challenges that require fresh thinking. A cosmological theory cannot leave anything out. To be complete, it must take into account everything in the universe, including ourselves as observers. It must account for our measuring instruments and clocks. When we do cosmology, we confront a novel circumstance: It is impossible to get outside the system we’re studying when that system is the entire universe.
Moreover, a cosmological theory must do without two important aspects of the methodology of science. A basic rule of science is that an experiment must be done many times to be sure of the result. But we cannot do this with the universe as a whole — the universe only happens once. Nor can we prepare the system in different ways and study the consequences. These are very real handicaps, which make it much harder to do science at the level of the universe as a whole.
Nonetheless, we want to extend physics to a science of cosmology. Our first instinct is to take the theories that worked so well when applied to small parts of the universe and scale them up describe the universe as a whole. As I’ll show in chapters 8 and 9, this cannot work. The Newtonian framework of timeless laws acting on particles with timeless properties is unsuited to the task of describing the entire universe.
Indeed, as I will show in detail, the very features that make these kinds of theories so successful when applied to small parts of the universe cause them to fail when we attempt to apply them to the universe as a whole.
I realize that this assertion goes counter to the practice and hopes of many colleagues, but I ask only that the reader pay close attention to the case I make for it in Part II. There I will show in general, and illustrate by specific example, that when we attempt to scale up our standard theories to a cosmological theory, we are rewarded with dilemmas, paradoxes, and unanswerable questions. Among these are the failure of any standard theory to account for the choices made in the early universe — choices of initial conditions and choices of the laws of nature themselves.
Some of the literature of contemporary cosmology consists of the efforts of very smart people to wrestle with these dilemmas, paradoxes, and unanswerable questions. The notion that our universe is part of a vast or infinite multiverse is popular — and understandably so, because it is based