Book review: Time Regained!
Time Reborn: From the Crisis in Physics to the Future of the Universe
by Lee Smolin
reviewed by James Gleick
by Lee Smolin
reviewed by James Gleick
A pregnant moment in intellectual history occurs when H.G. Wells’s Time Traveller (“for so it will be convenient to speak of him”) gathers his friends around the drawing room fire to explain that everything they know about time is wrong. This after-dinner conversation marked something of a watershed, more telling than young Wells, who had never even published a book before The Time Machine, imagined just before the turn of the twentieth century.
What is time? Nothing but a fourth dimension, after length, breadth, and thickness. “Through a natural infirmity of the flesh,” the cheerful host explains, “we incline to overlook this fact.” The geometry taught in school needs revision. “Now, it is very remarkable that this is so extensively overlooked….There is no difference between Time and any of the three dimensions of Space except that our consciousness moves along it.”
Wells didn’t make this up. It was in the air, the kind of thing bruited by students in the debating society of the Royal College of Science. But no one had made the case as persuasively as he did in 1895, by way of trying to gin up a plausible plot device in a piece of fantastic storytelling. Albert Einstein was then just a boy at gymnasium. Not till 1908 did the German mathematician Hermann Minkowski announce his “radical” idea that space and time were a single entity: “Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality.”
So spacetime was born. In spacetime all events are baked together, a four-dimensional continuum. Past and future are no more privileged than left and right or up and down. The time dimension only looks special for the reason Wells mentioned: our consciousness is involved. We have a limited perspective. At any instant we see only a slice of the loaf, a puny three-dimensional cross-section of the whole. For the modern physicist, reality is the whole thing, past and future joined in a single history. The sensation of now is just that, a sensation, and different for everyone. Instead of one master clock, we have clocks in multitudes. And other paraphernalia, too: light cones and world lines and time-like curves and other methods for charting the paths of light and objects through this four-dimensional space. To say that the spacetime view of reality has empowered the physicists of the past century would be an understatement.
Philosophers like it, too. “I conclude that the problem of the reality and the determinateness of future events is now solved,” wrote Hilary Putnam in 1967.
Moreover, it is solved by physics and not by philosophy. We have learned that we live in a four-dimensional and not a three-dimensional world, and that space and time—or, better, space-like separations and time-like separations—are just two aspects of a single four-dimensional continuum….
“Indeed,” he added, “I do not believe that there are any longer any philosophicalproblems about Time.” Case closed.
Now comes a book from the theoretical physicist Lee Smolin aiming to convince us that time is real after all. He is frankly recanting the accepted doctrine—an apostate:
I used to believe in the essential unreality of time. Indeed, I went into physics because as an adolescent I yearned to exchange the time-bound, human world, which I saw as ugly and inhospitable, for a world of pure, timeless truth….
I no longer believe that time is unreal. In fact I have swung to the opposite view: Not only is time real, but nothing we know or experience gets closer to the heart of nature than the reality of time.
Smolin is a founder and faculty member of the Perimeter Institute for Theoretical Physics in Toronto, an authority on quantum gravity who has also written on elementary particle theory, cosmology, and the philosophy of science. He proposes to validate what we already know—those of us who wear wristwatches, cross the days off our calendars, mourn the past, pray for the future, feel in our bones the march of time or the flow of time. We unphilosophical naïfs, that is—known for short as the “man on the street.” Hilary Putnam again: “I think that if we attempted to set out the ‘man on the street’s’ view of the nature of time, we would find that the main principle…might be stated somewhat as follows: (1) All (and only) things that exist now are real.” Past things were real once but have ceased to exist. Future things don’t yet exist; they will become real only when the time comes.
This is the view that most physicists deny and the view that Smolin proposes to demonstrate in his book. For him the past is gone; the future is open: “The fact that it is always some moment in our perception, and that we experience that moment as one of a flow of moments, is not an illusion.” Timelessness, eternity, the four-dimensional space-time loaf—these are the illusions.
His argument from science and history is as provocative, original, and unsettling as any I’ve read in years. It turns upside-down the now standard view of Wells, Minkowski, and Einstein. It contravenes our intellectual inheritance from Newton and, for that matter, Plato, and it will ring false to many of Smolin’s contemporaries in theoretical physics.
We say that time passes, time goes by, and time flows. Those are metaphors. We also think of time as a medium in which we exist. If time is like a river, are we standing on the bank watching, or are we bobbing along? It might be better merely to say that things happen, things change, and time is our name for the reference frame in which we organize our sense that one thing comes before another.
That most authoritative of machines, the clock, has no purpose but to measure something, and that thing is time. In fact you can define time that way: time is what clocks measure. Unfortunately that’s a circular definition, if clocks are what measure time. (Smolin suggests, “For our purposes, a clock is any device that reads out a sequence of increasing numbers,” which is interesting, even if it isn’t in the dictionary.) Scientists devote considerable resources to quantifying time, going beyond our usual seconds and minutes. Humanity has a collective official time scale, established by a chorus of atomic clocks cooled to near absolute zero in vaults at the United States Naval Observatory in Washington, the Bureau International des Poids et Mesures near Paris, and elsewhere. Isaac Newton would be pleased. International Atomic Time appears to codify the notion of absolute time that he worked so effectively to establish. Newton’s view, handed down to us as if engraved on tablets of stone, was this:
Absolute, true, and mathematical time, in and of itself and of its own nature, without reference to anything external, flows uniformly….
The cosmic clock ticks invisibly and inexorably, everywhere the same. Absolute time is God’s time. This was Newton’s credo. He had no evidence for it, and his clocks were primitive compared to ours. He wrote:
It may be that there is no such thing as an equable motion, whereby time may be accurately measured. All motions may be accelerated and retarded, but the flowing of absolute time is not liable to any change.
He needed absolute time, as he needed absolute space, in order to define his terms and express his laws. Motion is nothing but the change in place over time; acceleration is the change in velocity over time. With a backdrop of absolute, true, and mathematical time, Newton could build an entire cosmology, a “System of the World.”
So Newton made time more real—reified it, as no one had done before. But he also made time into a useful abstraction, and in this way it began to fade away. When a scientist records a series of observations—the position of the moon, let’s say—the result is a table of numbers representing both space and time. A generation before Newton, René Descartes showed how to turn such tables into graphs, using different axes for different variables. Representing the orbit of the moon in Cartesian coordinates makes it a curve in space and time—the whole orbit becomes static, a mathematical object in a timeless configuration space. On such a graph time is frozen, and the history of a dynamical system is revealed for study at leisure.
The technique has had psychological side effects, Smolin suggests. It gives those who use it the idea that the experience of time passing is an illusion:
The method of freezing time has worked so well that most physicists are unaware that a trick has been played on their understanding of nature. This trick was a big step in the expulsion of time from the description of nature, because it invites us to wonder about the correlation between the real and the mathematical, the time-bound and the timeless.
This is his crucial dichotomy: the time-bound versus the timeless... read more