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Saturday, September 5, 2015

Reading List: The Singular Universe and the Reality of Time

Unger, Roberto Mangabeira and Lee Smolin. The Singular Universe and the Reality of Time. Cambridge: Cambridge University Press, 2015. ISBN 978-1-107-07406-4.
In his 2013 book Time Reborn (June 2013), Lee Smolin argued that, despite its extraordinary effectiveness in understanding the behaviour of isolated systems, what he calls the “Newtonian paradigm” is inadequate to discuss cosmology: the history and evolution of the universe as a whole. In this book, Smolin and philosopher Roberto Mangabeira Unger expand upon that observation and present the case that the current crisis in cosmology, with its appeal to multiple universes and mathematical structures which are unobservable, even in principle, is a consequence of the philosophical, scientific, and mathematical tools we've been employing since the dawn of science attempting to be used outside their domain of applicability, and that we must think differently when speaking of the universe as a whole, which contains all of its own causes and obeys no laws outside itself. The authors do not present their own theories to replace those of present-day cosmology (although they discuss the merits of several proposals), but rather describe their work as a “proposal in natural philosophy” which might guide investigators searching for those new theories.

In brief, the Newtonian paradigm is that the evolution of physical systems is described by differential equations which, given a set of initial conditions, permit calculating the evolution of a system in the future. Since the laws of physics at the microscopic level are reversible, given complete knowledge of the state of a system at a given time, its past can equally be determined. Quantum mechanics modifies this only in that rather than calculating the position and momentum of particles (or other observables), we calculate the deterministic evolution of the wave function which gives the probability of observing them in specific states in the future.

This paradigm divides physics into two components: laws (differential equations) and initial conditions (specification of the initial state of the system being observed). The laws themselves, although they allow calculating the evolution of the system in time, are themselves timeless: they do not change and are unaffected by the interaction of objects. But if the laws are timeless and not subject to back-reaction by the objects whose interaction they govern, where did they come from and where do they exist? While conceding that these aren't matters which working scientists spend much time thinking about, in the context of cosmology they post serious philosophical problems. If the universe all that is and contains all of its own causes, there is no place for laws which are outside the universe, cannot be acted upon by objects within it, and have no apparent cause.

Further, because mathematics has been so effective in expressing the laws of physics we've deduced from experiments and observations, many scientists have come to believe that mathematics can be a guide to exploring physics and cosmology: that some mathematical objects we have explored are, in a sense, homologous to the universe, and that learning more about the mathematics can be a guide to discoveries about reality.

One of the most fundamental discoveries in cosmology, which has happened within the lifetimes of many readers of this book, including me, is that the universe has a history. When I was a child, some scientists (a majority, as I recall) believed the universe was infinite and eternal, and that observers at any time in the past or future would observe, at the largest scales, pretty much the same thing. Others argued for an origin at a finite time in the past, with the early universe having a temperature and density much greater than at present—this theory was mocked as the “big bang”. Discovery of the cosmic background radiation and objects in the distant universe which did not at all resemble those we see nearby decisively decided this dispute in favour of the big bang, and recent precision measurements have allowed determination of when it happened and how the universe evolved subsequently.

If the universe has a finite age, this makes the idea of timeless laws even more difficult to accept. If the universe is eternal, one can accept that the laws we observe have always been that way and always will be. But if the universe had an origin we can observe, how did the laws get baked into the universe? What happened before the origin we observe? If every event has a cause, what was the cause of the big bang?

The authors argue that in cosmology—a theory encompassing the entire universe—a global privileged time must govern all events. Time flows not from some absolute clock as envisioned by Newtonian physics or the elastic time of special and general relativity, but from causality: every event has one or more causes, and these causes are unique. Depending upon their position and state of motion, observers will disagree about the durations measured by their own clocks, and on the order in which things at different positions in space occurred (the relativity of simultaneity), but they will always observe a given event to have the same cause(s), which precede it. This relational notion of time, they argue, is primordial, and space may be emergent from it.

Given this absolute and privileged notion of time (which many physicists would dispute, although the authors argue does not conflict with relativity), that time is defined by the causality of events which cause change in the universe, and that there is a single universe with nothing outside it and which contains all of its own causes, then is it not plausible to conclude that the “laws” of physics which we observe are not timeless laws somehow outside the universe or grounded in a Platonic mathematics beyond the universe, but rather have their own causes, within the universe, and are subject to change: just as there is no “unmoved mover”, there is no timeless law? The authors, particularly Smolin, suggest that just as we infer laws from observing regularities in the behaviour of systems within the universe when performing experiments in various circumstances, these laws emerge as the universe develops “habits” as interactions happen over and over. In the present cooled-down state of the universe, it's very much set in its ways, and since everything has happened innumerable times we observe the laws to be unchanging. But closer to the big bang or at extreme events in the subsequent universe, those habits haven't been established and true novelty can occur. (Indeed, simply by synthesising a protein with a hundred amino acids at random, you're almost certain to have created a molecule which has never existed before in the observable universe, and it may be harder to crystallise the first time than subsequently. This appears to be the case. This is my observation, not the authors'.)

Further, not only may the laws change, but entirely new kinds of change may occur: change itself can change. For example, on Earth, change was initially governed entirely by the laws of physics and chemistry (with chemistry ultimately based upon physics). But with the emergence of life, change began to be driven by evolution which, while at the molecular level was ultimately based upon chemistry, created structures which equilibrium chemistry never could, and dramatically changed the physical environment of the planet. This was not just change, but a novel kind of change. If it happened here, in our own recent (in cosmological time) history, why should we assume other novel kinds of change did not emerge in the early universe, or will not continue to manifest themselves in the future?

This is a very difficult and somewhat odd book. It is written in two parts, each by one of the co-authors, largely independent of one another. There is a twenty page appendix in which the authors discuss their disagreements with one another, some of which are fundamental. I found Unger's part tedious, repetitive, and embodying all of things I dislike about academic philosophers. He has some important things to say, but I found that slogging through almost 350 pages of it was like watching somebody beat a moose to death with an aluminium baseball bat: I believe a good editor, or even a mediocre one, could have cut this to 50 pages without losing anything and making the argument more clearly than trying to dig it out of this blizzard of words. Lee Smolin is one of the most lucid communicators among present-day research scientists, and his part is clear, well-argued, and a delight to read; it's just that you have to slog through the swamp to get there.

While suggesting we may have been thinking about cosmology all wrong, this is not a book which suggests either an immediate theoretical or experimental programme to explore these new ideas. Instead, it intends to plant the seed that, apart from time and causality, everything may be emergent, and that when we think about the early universe we cannot rely upon the fixed framework of our cooled-down universe with its regularities. Some of this is obvious and non-controversial: before there were atoms, there was no periodic table of the elements. But was there a time before there was conservation of energy, or before locality?

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