Earlier this month I posted about Quantum Reality (2020), Jim Baggott’s recent book about quantum realism. Now I’ve finished another book with a very similar focus, Einstein’s Unfinished Revolution: The Search for What Lies Beyond the Quantum (2019), by Lee Smolin.
One difference between the books is that Smolin is a working theorist, so he offers his own realist theory. As with his theory of cosmic selection via black holes (see his 1997 book, The Life of the Cosmos), I’m not terribly persuaded by his theory of “nads” (named after Leibniz’s monads). I do appreciate that Smolin himself sees the theory as a bit of a wild guess.
There were also some apparent errors that raised my eyebrows.
That said, I have high regard for Smolin’s openness, honesty, and humbleness. And he is (generally) a clear and readable author. While I may not always agree with his views, I have a lot of respect for his thinking and approach.
As is usually the case, the Preface provides an overview of the territory the book explores. In it, I highlighted 12 different bits of text that caught my eye, and rather than try to explain them, I’ll let Smolin speak for himself, starting with the opening sentences:
We human beings have always had a problem with the boundary between reality and fantasy. To explain the world to ourselves we make up stories and then, because we are good storytellers, we get infatuated by them and confuse our representations of the world with the world itself.
Which appeals to me both as someone fascinated by storytelling and as someone dismayed by the, to me inexplicable, current popular fantasies of science. One reason I appreciate Smolin and Baggott is that they share this dismay.
Quantum mechanics (QM), depending on where one denotes its beginning, is either well over or very nearly 100 years old, yet it remains one of the greatest puzzles in science. Since the early days there has been a schism between two views: realism and anti-realism. Smolin defines the divide with two fundamental questions:
First off, does the natural world exist independently of our minds? More precisely, does matter have a stable set of properties in and of itself, without regard to our perceptions and knowledge? Second, can those properties be comprehended and described by us? Can we understand enough about the laws of nature to explain the history of our universe and predict its future?
As he goes on to say, answering yes to both makes one a realist. Einstein was a realist; Smolin is a realist; Baggott is a realist; I am, too. On the other hand, Niels Bohr was a staunch anti-realist before quantum mechanics and imposed that view on the Copenhagen interpretation which become the dominant view because his institute was the place for the study of quantum mechanics.
But, as Smolin points out:
If it is true that quantum mechanics requires that we give up realism, then, if you are a realist, you must believe that quantum mechanics is false. It may be temporarily successful, but it cannot be the fully correct description of nature at an atomic scale.
Smolin isn’t pulling his punches in calling QM “false” — the polite term typically used is “incomplete” (which Einstein suggested at least as far back as the famous EPR paper from 1935). But Smolin isn’t wrong. If a theory is incomplete and claims to be complete (which many see QM as doing), then it is false.
The thing is, we know QM cannot be a complete theory of reality because it is in serious conflict with our other greatest theory of reality, Einstein’s general relativity (GR). Neither entirely describe the world we’ve discovered through experiment. As an aside, one thing motivating Einstein’s realist view is that GR is a realist theory. He was convinced QM should be as well.
It might be tempting to see the debate between realism and anti-realism as a pointless metaphysical question that doesn’t matter, but as Smolin writes:
THIS ALL MATTERS because science is under attack in the early twenty-first century. Science is under attack, and with it the belief in a real world in which facts are either true or false. Quite literally, parts of our society appear to be losing their grip on the boundary between reality and fantasy.
As just one example of the danger, proponents of intelligent design theories have pointed out the hypocrisy of condemning their view as unscientific while simultaneously taking various multiverse theories as serious science. They’re not entirely wrong. The notion of “post-empirical” science is an abomination. As Smolin mentions, there are even humanist academics “who should know better” who see science as purely a social and relative construct.
I’ve said many times in the past years that society seems to be sliding back into a dark age thinking that, in the name of social and political agendas, disdains and discards reason, intellect, and expertise. As Smolin says:
One danger of anti-realism is to the practice of physics itself. Anti-realism lowers our ambition for a totally clear understanding of nature, and hence weakens our standards as to what constitutes an understanding of a physical system.
So, realism matters. Science, which is at root the belief the real world exists before us, outside of us, and after us, is — or should be — a deep and abiding commitment to realism.
Smolin begins with the notion that in quantum mechanics we can only ever know half the information about a system. This is the Heisenberg Uncertainty Principle. It’s usually expressed in terms of position and momentum, but there are other pairs of properties that are also mutually exclusive. We can never know both of the pair to arbitrary precision. In fact, if we know one of them exactly, then we know nothing about the other.
The book is intended for the average intelligent reader, so he avoids the math and sets up an interesting analogy involving a party in which everyone has both a political identity (left or right) as well as a pet-lover identity (dogs or cats). The political and pet-lover identities are meant as a mutually exclusive pair.
We imagine that we know everyone at the party is politically left (perhaps we asked them when they came in the door). We then ask everyone whether they prefer cats or dogs and find a 50/50 mix between them. We put all the cat lovers in the living room and all the dog lovers in the kitchen.
But in knowing the pet-lover identity, we’ve lost our knowledge of their political identity. If we go through the living room and ask the cat-lovers their political identity, we find a 50/50 mix between left and right. We find the same thing with the dog-lovers in the kitchen.
While this seems preposterous in our classical world — political identity doesn’t change just because we know pet-lover identity — this is indeed how quantum mechanics works. Classically we can (in theory) know all there is to know about a system, but with quantum systems, we can only ever know half of a system’s properties.
Part 1 of the book is An Orthodoxy of the Unreal. In it, Smolin explores several essential (and generally non-controversial) principles of quantum mechanics, the first of which, discussed above, is:
We can only know half of what we would need to know if we wanted to completely control, or precisely predict, the future.
The next one is:
Any system quantum mechanics applies to must be a subsystem of a larger system.
This is because QM refers only to physically quantities, which we measure with instruments, and these are outside the quantum system. Quantum mechanics is about what is observed.
This in contrast to what John Bell called be-ables — real properties of a system. (I confess I long thought it was a nonsense word Bell made up that was pronounced “beebles”. It makes a lot more sense with the hyphen!)
The next principle is:
Given the quantum state of an isolated system at one time, there is a law that will predict the precise quantum state of that system at any other time. This law is called Rule 1. It is also sometimes called the Schrödinger equation. The principle that there is such a law is called unitarity.
Smolin later states Rule 2, which involves measurement of a quantum system. As far as we know, this is probabilistic and follows the Born rule. Further, a measurement changes the quantum system. (As, for example, when we sorted cat-lovers and dog-lovers and changed that everyone until then had a left political identity.)
As an aside, this is backwards from the original formulation by John Von Neumann, who broke QM into Process 2, the fully deterministic, time-reversible, unitary evolution of the wavefunction, and Process 1, the apparently random “collapse” of the wavefunction into a measured state. (I’ve always found von Neumann’s order strange, so I don’t blame Smolin for reversing it.)
Another principle is:
Any two quantum states may be superposed together to define a third quantum state. This is done by adding together the waves that correspond to the two states. This corresponds to a physical process that forgets the property that distinguished the two.
Cats are either dead or alive, not a superposition of both. I’ve long thought superposition (along with interference and entanglement) are the three key mysteries of QM. All three represent behaviors we never experience in the classical world.
The last principle Smolin lists is:
The probability of finding the particle at a particular location in space is proportional to the square of the height of the corresponding wave at that point.
Which is the Born rule. The only time we can be sure of a measurement result is when we measure the same property in quick succession. For example, a photon that passes through a polarizing filter is guaranteed to pass a similar filter immediately after it.
He devotes two chapters to deBroglie’s theory from 1927 (which soared like the proverbial lead balloon given the hold the Copenhagen interpretation had on the thinking of the time) and to David Bohm’s reviving it decades later. Some still work on it today, but Smolin points out its ontological extravagance. The pilot wave, which is taken to be real, never goes away, so the world is filled with ghosts of pilot waves past.
Neither Baggott nor Smolin think much of the MWI. Both refer to it as “magical realism” (so do I). Smolin devotes two chapters, Magical Realism and Critical Realism, to his objections. While he respects the physicists and philosophers devoting their energies to it, he rejects it as a viable theory. He lists what he sees as major problems with it:
The first problem with Everett’s formulation is that he suggested that the branching happens when a measurement is made. But this makes measurements appear to be special,
Which has always been the problem with QM. Measurement seems, in most interpretations, to have a special status (the von Neumann-Wigner interpretation ties it to human consciousness, which is about as special as it gets).
A second problem is that if the branching is to replace Rule 2, then it must be irreversible, to reproduce the basic fact that we observers experience every experiment to have a definite outcome.
And strike three:
A third big problem with giving up Rule 2 has to do with probabilities—or rather, their absence.
He talks about the many pages Everett devoted (in the middle sections of his famous paper) to trying to solve this:
But it turns out something was concealed in his derivation. Like many erroneous proofs, the argument assumed what was to be proved.
Which means I don’t need to try working through those pages of Everett’s math. I’ve always found it impenetrable but also always wanted to understand it. Now I can just skip it.
Yet another problem with Everett’s original formulation of the Many Worlds Interpretation was that splitting the quantum state into branches is ambiguous.
Which is what’s known as the preferred basis problem.
All this in the first of the two chapters. The second chapter digs more deeply — and critically — into these issues. Near the end of the second chapter, he makes a point (with regard to all the copies of worlds):
This sounds more like science fiction than science, but it does seem a straightforward consequence of Everett’s hypothesis. Since this is science and not faith, we don’t have the option of taking a “liberal” interpretation of Everett in which we choose to believe certain aspects, such as the existence of a wave function of the universe, while ignoring others.
I’ve begun to wonder if the anti-realist stance, with roots in post-WWI, post-modernism and deconstruction, and our now steady diet of science fiction and comic books, hasn’t corrupted the views of too many thinkers in academia and science. And, as Smolin pointed out in his Preface, given our current political and social rat’s nest, this kind of thinking is dangerous.
It seems to me that the Many Worlds Interpretation offers a profound challenge to our moral thinking because it erases the distinction between the possible and the actual. […] 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?
Perhaps now you see why I’ve been so critical of the MWI. (It’s nice to know I’m not alone in that view.)
This has gotten long, so I won’t get much into Part 3, Beyond the Quantum, which explores Smolin’s theory of events and relations. (I wouldn’t want to spoil the ending.) Suffice to say it descends from Leibniz’s relational view. Its most peculiar aspect is how it transcends locality. Events similar to other events anywhere in the universe are linked, so measurement probabilities are due to an aggregate of all similar measurements.
My question was about unprecedented events, and Smolin writes:
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. This could be and, I hope, will be a question for experimental physics.
Well, okay, then. Question answered. As I said, I’m not terribly persuaded.
I mentioned some apparent errors. When discussing tests of Bell’s inequality (or “restriction” as Smolin terms it), he uses “atoms” where I’m pretty sure he means “particles” — I am not familiar with any tests involving whole atoms.
Even weirder was his description of Schrödinger’s Cat, which he says had its ears wired to a transformer that electrocuted it if the Geiger counter detected a particle. Every account I’ve seen involves a vial of poison gas.
In discussing quantum computing he refers to “Peter Shore” — it’s Peter Shor. (There is a British politician named Peter Shore, whose Wiki page mentions, “Not to be confused with the theoretical computer scientist Peter Shor…”)
In the same section, he also, I believe, misattributes to David Deutsch a seminal paper describing a quantum mechanical “Turing Machine” by Paul Benioff in 1980. It led to quantum computing.
Stay accurate, my friends! Go forth and spread beauty and light.