Note: For at least a while, based upon discussion with folks at Patheos, I’ll be experimenting with a new approach to my blogging: Fewer posts, but longer. We’ll see how it works.
What follows here is inspired by and indebted to Chapter 5, “Spacetime is Quantum,” in Carlo Rovelli, Reality Is Not What It Seems: The Journey to Quantum Gravity, translated by Simon Carnell and Erica Segre (Penguin, 2017), 125-137:
Physics made enormous progress, almost literally unthinkable strides, in the twentieth century. Most of these strides can be grouped under two main headings: general relativity and quantum mechanics. From relativity — which is essentially a theory of gravity, and which sees the reality around us as a continuum that is warped or curved by the objects in it — flow such fields of inquiry as the study of black holes and gravitational waves, astrophysics, and cosmology. From quantum theory — which views reality as an assemblage of discrete, particular packets or “quanta” — we derive such things as atomic physics, nuclear physics, the study of elementary particles and of condensed matter, and a significant amount of cutting-edge technology. And each theory, general relativity and quantum mechanics, has passed test after confirming test. Both work extremely well
But there is a disturbing problem. It’s not only that quantum theory is probabilistic, something that Albert Einstein absolutely loathed. (“I, at any rate, am convinced that [God] does not throw dice,” he wrote in a 1926 letter to Max Born. [Jedenfalls bin ich überzeugt, daß der nicht würfelt.])
The more fundamental issue is that the view of reality provided by the two theories, when they’re taken together (or, better, when scientists attempt to take them together), is schizophrenic. They’re incompatible. As Rovelli, himself a prominent European theoretical physicist, puts it,
They cannot both be true, at least not in their present forms, because they appear to contradict each other. . . .
A university student attending lectures on general relativity in the morning, and others on quantum mechanics in the afternoon, might be forgiven for concluding that his professors are fools, or that they haven’t talked to each other for at least a century. In the morning, the world is a curved spacetime where everything is continuous; in the afternoon, the world is a flat one where discrete quanta of energy leap and interact. (125, italics in the original)
In most cases, the contradictions can be safely ignored. Microcosm and macrocosm are far enough apart that issues really don’t arise. In studying the lunar orbit, for example, the Moon is so large that tiny quantum issues needn’t be noticed. And atoms are too light to curve space significantly, so the overall curvature of spacetime described by general relativity plays no role worthy of attention.
But there are situations where both curvature of space and quantum granularity matter, and for these we do not yet have an established physical theory that works.
An example is the interior of black holes. Another is what happened to the universe during the Big Bang. In more general terms, we do not know how time and space behave at very small scale. In all these instances, today’s theories become confused and no longer tell us anything reasonable: quantum mechanics cannot deal with the curvature of spacetime, and general relativity cannot account for quanta. (126)
For a non-physicist such as I, who will never make any significant contribution in this life toward bridging the gap, one obvious lesson can be drawn from the present state of things: humility. For all of our successes and technological marvels, there are enormous and fundamental things that still elude us. There is so much that we don’t know!
Strikingly, though, Rovelli is not at all discouraged. In fact, he seems positively exuberant. He points out that “a band of theoretical physicists scattered across five continents is laboriously seeking to solve the problem” (127). He cites previous examples in the history of physics where massive contradictions have forced harmonizing breakthroughs. Newton’s discovery of universal gravitation, for instance, came as he reconciled Galileo’s description of terrestrial motion with Kepler’s laws of motion for the heavens. Maxwell and Faraday combined what was known about electricity with what was known about magnetism in order to formulate the equations of electromagnetism. But there seemed to be a conflict between Maxwell’s equations on electromagnetism and Newton’s mechanics; Einstein formulated special relativity to reconcile the two, and then, because his own special relativity had problems with Newton’s mechanics, he discovered general relativity through his attempt to resolve those problems.
Theoretical physicists are thus only too happy when they discover a conflict of this type: it is an extraordinary opportunity. (127)
I myself would note that many fields of modern science seem to work fruitfully on the boundaries or borders between previously distinct disciplines (e.g., geophysics, biochemistry, biophysics, astrophysics, perhaps paleobotany, and so forth).
Rovelli’s discussion in these pages is not merely scientific but historical and, to an important extent, biographical. He concentrates particularly on two significant physicists of earlier generations. John Archibald Wheeler (1911-2008) is one of the two; he is discussed in a chapter section called, simply, “John” (132-136). For what it’s worth, among those who have contributed to my Latter-day Saint Scholars Testify website is B. Kent Harrison, who earned his doctorate at Princeton University, studying under Wheeler and — with fellow students Masami Wakano and 2017 Nobel laureate Kip Thorne — co-authoring a 1965 book with him on Gravitation Theory and Gravitational Collapse:
The scientist who has most contributed to quantum gravity is John Wheeler, a legendary figure who has traversed the physics of the past century. A pupil of and contributor with Niels Bohr in Copenhagen; a collaborator with Einstein when Einstein moved to the United States; a teacher who can count among his students figures such as Richard Feynman . . . Wheeler was at the heart of the physics of the twentieth century. (133-134)
Before that, though, in a section simply called “Matvei” (128-131), Rovelli describes the contribution and the tragically short life of Matvei Bronstein (or Matvei Bronštejn; Матве́й Бронште́йн), and it is on him that I wish to concentrate here.
Matvei Bronstein wrote three books for children: Solar Matter (Солнечное вещество), X Rays (Лучи X), and Inventors of Radio (Изобретатели радио). But he wasn’t only a popularizer. He was a theoretical physicist who also authored works on astrophysics, semiconductors, quantum electrodynamics, and cosmology. Most directly relevant to Rovelli’s purposes, he was a pioneer in the field of quantum gravity.
Matvei was a younger friend of Lev Landau — the scientist who would go on to become the best theoretical physicist of the Soviet Union. Colleagues who knew them both would claim that, of the two, Matvei was the more brilliant. (128)
Here’s the problem that Bronstein intuited, as described by Carlo Rovelli:
Energy makes space curve. A lot of energy means that space will curve a great deal. A lot of energy in a small region results in curving space so much that it collapses into a black hole, like a collapsing star. But if a particle plummets into a black hole, I can no longer see it. (129, italics in the original)
Perhaps, here, science has discovered that space itself is discontinuous, “quantized,” particular, granular, and has done so applying general relativity at the microcosmic level.
Modern physicists talk about “Planck length,””the minimum size of a particle before it falls into its own black hole” (130), the smallest distance about which current experimentally corroborated models in physics can make any meaningful statement. At such small distances, the conventional laws of macro-physics no longer apply, and even relativistic physics requires special treatment. Rovelli contends that, in truth and justice, “Planck length” should be called “Bronštejn length,” since it was Matvei Bronstein who identified it.
In numerical terms, it is equivalent to approximately one millionth of a billionth of a billionth of a billionth of a centimetre (10-33 centimetres). So, that is to say . . . small.
It is at this extremely minute scale that quantum gravity manifests itself. To give an idea of the smallness of the scale we are discussing: if we enlarged a walnut shell until it had become as big as the whole observable universe, we would still not see the Planck length. Even after having been enormously magnified thus, it would still be a million times smaller than the actual walnut shell was before magnification. At this scale, space and time change their nature. They become something different; they become ‘quantum space and time’, and understanding what this means is the problem.
Matvei Bronštejn understands all of this in the 1930s and writes two short and illuminating articles in which he points out that quantum mechanics and general relativity, taken together, are incompatible with our customary idea of space as an infinitely divisible continuum. (131)
Unfortunately, like his friend Lev Landau, Matvei Bronstein was a naïve young idealist. He was really convinced that Communism would introduce a better world, without inequality and injustice. He believed — incorrectly, as we now plainly see — that Lenin was moving Russia toward that better world. When Stalin assumed power after Lenin’s death, however, both Matvei Bronstein and Lev Landau were disappointed and, eventually, horrified. Gently and cautiously, they dissented.
Landau suffered under Stalin, but survived. Matvei Bronstein was not so fortunate.
In August 1937, during Stalin’s “Great Purge,” Bronstein was arrested for disloyalty. In February 1938, he was convicted in a summary trial. Then, although his wife was told that he had been sentenced to ten years in a labor camp with no right of correspondence, he was executed later that same day. He was thirty-one years old.
Mattvei Bronstein’s unjust early death was a painful loss to science. Who can possibly know what contributions he might have made? (Gloriously, though, his books for children were eventually republished after his reputation had been rehabilitated by Stalin’s successors and Soviet censors in 1957.)
Moreover, his case should certainly be counted among the enormous damages visited upon the world by Marxism and Communism — indeed by socialism itself, which tends to lop off any and all heads that rise above the crowd or diverge from the mass, a tendency that Communism simply made more obvious and more violent. But it is also a specimen of the vast pain and injustice of this mortal world generally — and an illustration of the desirability, if not the reality, of a world beyond this one, in which oppression will be abolished, wrongs wil be righted, injustices will be recompensed, and there will be no obstacles to delighted learning and progress, and in which “God shall wipe away all tears from [our] eyes; and there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain: for the former things are passed away” (Revelation 21:4).