The cosmic clock of Newton (or God), marking time absolutely, everywhere the same, did not survive. Einstein shattered it. He did this by refusing to take it for granted and asking a simple question: Is it possible to say that two distant events occur at the same time? Is that even meaningful? Suppose you assert that lightning has struck a railway embankment at points A and B, distant from each other, and that the lightning flashes were simultaneous. Can you—a physicist with the most excellent equipment—establish that for sure?
You cannot. It turns out that a physicist riding on the train will disagree with a physicist standing at the station. Every observer has a reference frame, and each reference frame includes its own clock. Simultaneity is not meaningful. Now is relative. As Smolin puts it, “the clocks can be funky—that is, they can run at different rates in different places, and each can speed up and slow down.” We don’t have to like that. Every experiment confirms it.
Put another way, events in our universe can be connected, such that one is the cause of the other; or they can be close enough in time and far enough apart that they cannot be connected and no one can even say which came first. The distinction between past and future begins to decay. No observer has access to the now of any other observer. Everything that reaches our senses comes from the past.
Thus space and time are wedded. One cannot be measured—cannot be defined, can barely be talked about—independent of the other. Spacetime, having begun as a convenient technique of visualization, becomes indispensable. Time is frozen into the four-dimensional block. Motion gives way to geometry.
H.G. Wells said the only difference between time and space is that “our consciousness moves along it,” and likewise a half-century later the mathematician, physicist, and philosopher Hermann Weyl explained that the universe doesn’t “happen”—it “simply is”:
Only to the gaze of my consciousness, crawling upward along the world line of my body, does a section of the world come to life as a fleeting image in space which continuously changes in time.
Three weeks before his death, in 1955, Einstein wrote, “People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion.” Yet Einstein was not altogether sanguine. He could not explain away our sense of time passing, our awareness of the present moment. “The problem of the Now worried him seriously,” recalled Rudolf Carnap.
He explained that the experience of the Now means something special for man, something essentially different from the past and the future, but that this important difference does not and cannot occur within physics.
Carnap, a philosopher of the Vienna Circle, suggesting leaving this sort of problem to the psychologists. Not Smolin: he thinks we should embrace Einstein’s discontent:
Everything we experience, every thought, impression, action, intention, is part of a moment. The world is presented to us as a series of moments. We have no choice about this. No choice about which moment we inhabit now, no choice about whether to go forward or back in time. No choice to jump ahead. No choice about the rate of flow of the moments. In this way, time is completely unlike space. One might object by saying that all events also take place in a particular location. But we have a choice about where we move in space. This is not a small distinction; it shapes the whole of our experience.
Still, he knows that intuition is not an argument. For most of history, human experience made it clear that up and down are special directions, everywhere the same—down being where things fall and up being the home of sun and stars—and that did turn out to be an illusion. If you are in outer space, there is no up or down—those concepts are meaningful only relative to the surface of the earth or some other planet. Our senses tell us all sorts of lies.
In an empty universe, would time exist?
No, it would not. Time is the measure of change; if nothing changes, time has no meaning.
Would space exist, in the absence of any matter or energy? Newton would have said yes: space would be empty.
For Smolin, the key to salvaging time turns out to be eliminating space. Whereas time is a fundamental property of nature, space, he believes, is an emergent property. It is like temperature: apparent, measurable, but actually a consequence of something deeper and invisible—in the case of temperature, the microscopic motion of ensembles of molecules. Temperature is an average of their energy. It is always an approximation, and therefore, in a way, an illusion. So it is with space for Smolin: “Space, at the quantum-mechanical level, is not fundamental at all but emergent from a deeper order”—an order, as we will see, of connections, relationships. He also believes that quantum mechanics itself, with all its puzzles and paradoxes (“cats that are both alive and dead, an infinitude of simultaneously existing universes”), will turn out to be an approximation of a deeper theory.
For space, the deeper reality is a network of relationships. Things are related to other things; they are connected, and it is the relationships that define space rather than the other way around. This is a venerable notion: Smolin traces the idea of a relational world back to Newton’s great rival, Gottfried Wilhelm Leibniz: “Space is nothing else, but That Order or Relation; and is nothing at all without Bodies, but the Possibility of placing them.” Nothing useful came of that, while Newton’s contrary view—that space exists independently of the objects it contains—made a revolution in the ability of science to predict and control the world. But the relational theory has some enduring appeal; some scientists and philosophers such as Smolin have been trying to revive it.
Nowadays, the Internet—like the telegraph a century before—is commonly said to “annihilate” space. It does this by making neighbors of the most distant nodes in a network that transcends physical dimension. Instead of six degrees of separation, we have billions of degrees of connectedness. As Smolin puts it:
We live in a world in which technology has trumped the limitations inherent in living in a low-dimensional space…. From a cell-phone perspective, we live in 2.5-billion-dimensional space, in which very nearly all our fellow humans are our nearest neighbors.
The Internet, of course, has done the same thing. The space separating us has been dissolved by a network of connections.
So maybe it’s easier now for us to see how things really are. This is what Smolin believes: that time is fundamental but space an illusion; “that the real relationships that form the world are a dynamical network”; and that the network itself, along with everything on it, can and must evolve over time.
We know that time runs one way, despite the apparent reversibility of most physical laws. The relational view supports the idea of the universe as a one-way street, growing ever more structured and complex in apparent contradiction to the second law of thermodynamics, which states that all isolated systems become more uniform over time. The second law has led physicists for more than a century to suggest that the fate of the universe is the cosmic equilibrium of “heat death,” a uniform state of maximum entropy and perfect disorder, but that’s not the universe we see. Instead it seems that the universe gets persistently more interesting. Smolin argues that the second law of thermodynamics applies to any isolated system within the universe but not to the universe taken as a whole; that, in a universe where time is real and fundamental, it is natural for complexity to evolve and for systems to become more organized.
By declaring space to be secondary, he makes a mathematical trade that avoids contradicting general relativity: relative size for relative time. If size and location are relative, then time doesn’t need to be. He arrives at a notion of “preferred global time” that extends throughout the universe and defines a boundary between past and future. It imagines a “family” of observers, spread throughout the universe, and a preferred state of rest, an abstract standard against which motion can be measured. Even if “now” need not be the same to different observers, it retains its meaning for the cosmos.
Time Reborn means to present a program for further study. Smolin maintains a fairly puritanical view of what science should and should not do. He doesn’t like the current fashion in “multiverses”—other universes lurking in extra dimensions or branching off infinitely from our own. Science for him needs to be testable, and no one can falsify a hypothesis about a universe held to be inaccessible to ours. For that matter, any theory about the entire cosmos has a weakness. The success of science over the centuries has come in giving rules and language for describing finite, isolated systems. We can make copies of those; we can repeat experiments many times. But when we talk about the whole universe, we have just the one, and we can’t make it start over. So Smolin sees little scope for science in the family of cosmic questions beginning with “Why…”:
Why is there something rather than nothing? I can’t imagine anything that would serve as an answer to this question, let alone an answer supported by evidence. Even religion fails here….
Better not to think of science as a quest for timeless truths. Science, he writes, creates “effective theories.” These are models—incomplete by definition. They are effective in limited domains, and they are approximate. That doesn’t have to be a failing. Science can construct better and better theories, approaching the truth with closer approximations. But a perfect model of the universe would have to be the size of the universe. We humans are finite creatures, with little brains.
It may seem that Smolin himself is taking on one of the grandest cosmic questions of all. He does try to restrain himself, though, to hypotheses that make testable, falsifiable predictions about the universe we can observe. The scientific case he makes is intricate, involving methods from loop quantum gravity (one of several approaches to combining quantum theory and the theory of relativity). He depicts the geometry of space as a graph with nodes and edges. He has reserved some detail for online appendices at www.timere born.com and plans to publish a more rigorous formulation in collaboration with the Brazilian philosopher Roberto Mangabeira Unger.
“The world remains, always, a bundle of processes evolving in time,” says Smolin.
Logic and mathematics capture aspects of nature, but never the whole of nature. There are aspects of the real universe that will never be representable in mathematics. One of them is that in the real world it is always some particular moment.
In a coda he ruminates briefly on the problem of consciousness—“the really hard problem.” He doesn’t propose any answers, but I’m glad to see physicists, mathematicians, and computer scientists continuing to wrestle with it, rather than leaving it to neurologists. Whatever consciousness will turn out to be, it’s not a moving flashlight illuminating successive slices of the four-dimensional spacetime continuum. It is a dynamical system, occurring in time, evolving in time, able to absorb bits of information from the past and process them, able also to create anticipation for the future.