Einstein's Unfinished Revolution: The Search for What Lies Beyond the Quantum

by Lee Smolin

A hard lesson to learn is that our sensations are partly caused by reality, but are fully constructed by our brains to present the world to us in just the form we need to make our way in nature. Beyond those sensations, nature hovers, fundamentally mysterious and just at the edge of what we can know.

In my view, there is little reason for conflict between most religions and science. Many religions accept—and even celebrate—science as the way to knowledge about the natural world. Beyond that, there is mystery enough in the existence and meaning of the world, which both science and religion can inspire us to discuss, but neither can resolve.

The simplest notion is that probability is a measure of our credence or belief that something will happen. When we say there is a 50 percent chance of heads on the next coin toss, that is not a statement about the coin; it is a description of our belief about the result of tossing the coin. These are called Bayesian probabilities. When we say the Bayesian probability for rain tomorrow is 0 percent, that is just a way of saying we believe it will not rain, and when we say that probability is 100 percent, that says we are sure it will. Probabilities between them, such as 20 percent, 50 percent, or 70 percent, refer to the strength of our belief that it will rain. In particular, when we say something has a 50 percent probability of happening, we are really confessing we have no idea whether it will happen.

A second kind of probability comes into play when we keep records of the relevant events. If we toss a large number of coins and keep records of how often they come up heads, we can define the proportion of heads in that sequence of tosses to be a probability. These are called frequency probabilities. Batting averages and other sports statistics are frequency probabilities. They give the proportion of the times that a batter got on base after he was at bat.

Thus, on its own terms, in which it cannot address what is true, but can only offer advice about how best to place bets, Deutsch’s argument implies that it is no more rational for observers inside an Everettian world to believe in Everett than it is for them to believe in Bohr or de Broglie, Bohm or any other interpretation. So, in the best case, even assuming that Everett is right, observers in an Everettian world cannot muster any evidence to believe Everett’s hypotheses over the alternative hypotheses.

The existence of all these copies of ourselves would then seem to me to present a moral and ethical quandary. If no matter what choices I make in life, there will be a version of me that will take the opposite choice, then why does it matter what I choose? There will be a branch in the multiverse for every option I might have chosen. There are branches in which I become as evil as Stalin and Hitler and there are branches where I am loved as a successor to Gandhi. I might as well be selfish and make the choices that benefit me. Irrespective of what I choose, the kind and generous choice will be made by an infinite number of copies living in an infinite number of other branches.

It from bit symbolizes the idea that every item of the physical world has at bottom—at a very deep bottom, in most instances—an immaterial source and explanation; that what we call reality arises in the last analysis from the posing of yes-no questions and the registering of equipment-evoked responses; in short, that all things physical are information-theoretic in origin and this is a participatory universe.

The lesson I draw from these theories is that to extend quantum mechanics to a theory of the whole universe, we have to choose between space and time. Only one can be fundamental. If we insist on being realists about space—as Barbour and Gomes do—then time and causation are illusions, emergent only at the level of a coarse approximation to the true timeless description. Or we can choose to be realists about time and causation. Then, like Rovelli, we have to believe that space is an illusion.

It is worth noting that the idea of unifying space and time into a single entity called spacetime was not part of Einstein’s original conception of relativity. The idea of spacetime was introduced two years later by his teacher Hermann Minkowski as a model which exemplified Einstein’s principles.

five closely related principles: The principle of background independence The principle that space and time are relational The principle of causal completeness The principle of reciprocity The principle of the identity of indiscernibles

Leibniz called the principle of sufficient reason. This states that every time we identify some aspect of the universe which seemingly might be different, we will discover, on further examination, a rational reason why it is so and not otherwise. For example, given present knowledge, it seems that space might have more or less than three dimensions. (By this I mean the three large dimensions that we see around us; this doesn’t count hypothetical tiny, “rolled-up” dimensions perceivable only on a subatomic scale.) This is because all our current theories, including general relativity and quantum mechanics, would also make sense in a world with a different number of spatial dimensions. Leibniz’s principle of sufficient reason advises us that this must be because our current theories are incomplete. We must seek to complete our theories, and one sign of success will be when we find out why the number of large spatial dimensions is three.* Leibniz believed we could uncover a rational explanation for every apparent choice God might seem to have made in the creation of the universe. He spoke of the state in which this understanding would be achieved as one of having “sufficient reason.” His principle of sufficient reason states that the universe can be completely understood.

A scientist who aspires to be rational must be a relationalist.

a lesson from a survey of approaches to quantum foundations, which is that space and time cannot both be fundamental. Only one can be present at the deepest level of understanding; the other must be emergent and contingent.

A physical system, when faced with a choice of outcomes of a measurement, will pick a random outcome from the collection of similar systems in the past. This law of precedents guarantees that most of the time, the present will resemble the past, in that the probabilities for the various possible outcomes of the same experiment will be unchanged. If this is right, the appearance that atoms are governed by unchanging laws is an illusion created by the fact that the universe is old enough and big enough that there is ample precedent for most situations an atom will find itself in. But what if there are no precedents? What if we prepare a quantum state which has never so far existed in the history of the universe? If we make a measurement of it, how will we determine its outcome, if there are no past similar instances to refer to? I don’t know the answer to this question.

Symmetries are properties of fixed backgrounds, and the occurrence of a symmetry in a theory is a clear sign that that theory is background dependent. A symmetry is an operation that translates or rotates the system we are studying, with respect to the background, which is left unchanged. Symmetries characterize a system that has been isolated from a larger universe, and arise from what is ignored in that isolation.

An important consequence is that the laws of nature, rather than being timeless, evolve in time. This reverses the belief, common among physicists, that time is not present in the most fundamental laws, but rather emerges from those laws. Instead, we argue that time, in the sense of the present moment and its passage, is fundamental, while the laws are emergent and subject to change.

Marina Cortês insisted that the laws at the most fundamental level must be irreversible, in two senses. First, the laws are not the same if you reverse the direction of time. If you take a video of a lawful process, you do not get another lawful process by playing it backward. This directly contradicts a widely held belief that the laws of nature are unchanged if you reverse the direction of time.

Here is a one-sentence summary of this theory: the universe consists of nothing but views of itself, each from an event in its history, and the laws act to make these views as diverse as possible. From here the story unfolds very much like that of the real ensemble theory. Similar views interact with each other, as a result of the mandate to evolve in the direction of ever more diversity. This leads to the emergence of space and of locality in that space. Nonlocality also emerges as interactions which are distant in the emergent space but nearby in terms of similarity of views. Finally, as in the real ensemble formulation, quantum mechanics arises from these nonlocal interactions as an approximate description of the dynamics of views. The causal theory of views is then a route to a completion of quantum mechanics. It is a realist completion, because it is a theory of beables, which are the views themselves. Most important, it demonstrates that a single fundamental theory can be at the same time a completion of quantum mechanics and an atomic model of spacetime. It can explain the emergence of both locality and nonlocality, of both spacetime and quantum mechanics. This theory is still only part of the story, and there is still much to learn about it, but it is a way the world might be.

There is no more reasonable bet than that our current knowledge is incomplete. In every era of the past our knowledge was incomplete; why should our period be any different? Certainly the puzzles we face are at least as formidable as any in the past. But almost no one bets this way. This puzzles me.

A friend once told me that the academic world was modeled on monasteries, which were designed to perpetuate old knowledge while resisting the new. Even after decades in the system I am amazed at how the fine mechanics of this work. There is no arguing with the logic of academic fame, which rewards every scientific success with distractions that make it harder to do more science, while imposing enormous disincentives to putting aside polishing your legacy to take on new challenges. The academic world is very well suited to support what Thomas Kuhn called normal science. That is great until it becomes long past due to complete a revolution.

To my knowledge, few have stumbled on a major discovery by accident; most true breakthroughs were found after years and years of hard, unrewarding work. Feynman said to discover something new you have to take the time to make every mistake possible along the way. And he surely knew.