Coming of Age in the Milky Way (50 page)
Read Coming of Age in the Milky Way Online
Authors: Timothy Ferris
Tags: #Science, #Philosophy, #Space and time, #Cosmology, #Science - History, #Astronomy, #Metaphysics, #History
Nonetheless, hope continued to run high that there is a fundamentally beautiful, symmetrical principle to nature that has generated the particles and forces, and that it can perhaps be glimpsed by the human mind. “Maybe it isn’t true,” Weinberg allowed. “Maybe nature is fundamentally ugly, chaotic and complicated. But if it’s like that, then I want out.”
37
Which brings us back to the other Greek definition of symmetry—“due proportion.” To the Greeks, symmetry consisted, not simply of invariance, but of an aesthetically pleasing
kind
of invariance. This implies that there is a higher order of perfection, a more perfect world, that we glimpse through the windows proffered by symmetry and by which the elegance of any symmetry theory can be gauged. Supersymmetry portrays this ultimate perfection as a hyperdimensional universe, of which our poor imperfect universe is but a paltry shadow. It implies that physicists—in identifying, say, the weak and electromagnetic forces as having arisen from the breaking of the more symmetrical electroweak force, or in finding concealed symmetries cowering in the cramped nuclear precincts where the strong force does its work—are in effect piecing together the shattered potsherds of that perfect world. Indeed, the theory indicates that there may be countless more such debris, in the form of supersymmetric particles that have as yet remained undetected because they interact only weakly or not at all with the particles we are made of and have come to know.
Where, then, is the hyperdimensional universe of perfect symmetry to be found? Certainly not here and now; the world we live in is fraught with broken symmetries, and knows but four dimensions. The answer comes from cosmology, which tells us that the supersymmetric universe, if it existed, belonged to the past. The implication is that the universe began in a state of symmetrical perfection, from which it evolved into the less symmetrical universe we live in. If so, the search for perfect symmetry amounts to a search for the secret of the origin of the universe, and the attention of its acolytes may with good reason turn, like the faces of flowers at dawn, toward the white light of cosmic genesis.
*
Dirac meant, of course, not that one should ignore the empirical results altogether, but that a beautiful theory need not be abandoned just because it fails an initial test. He had in mind Erwin Schrödinger’s reluctance to publish his estimable equations of wave mechanics merely because they conflicted with experimental data. “It is most important to have a
beautiful
theory,” Dirac told the science writer Horace Freeland Judson. “And if the observations don’t support it, don’t be too distressed, but wait a bit and see if some error in the observations doesn’t show up.”
5
*
The ratio is approximate because the numbers generated by the Fibonacci series are “irrational”—i.e., the ratio upon which they converge cannot be expressed exactly in terms of a fraction. The Pythagoreans discovered irrational numbers, and are said to have been so unsettled by them that they prescribed the death penalty to any of their sect who revealed their existence to the untutored multitudes. Hippasus was banished for defying the ban. He drowned at sea, a fate that the Pythagoreans ascribed to divine retribution.
*
Richard Feynman, Gell-Mann’s chief competitor for the title of World’s Smartest Man but a stranger to pretension, once encountered Gell-Mann in the hall outside their offices at Caltech and asked him where he had been on a recent trip; “Moon-
TRW-ALGH!”
Gell-Mann responded, in a French accent so thick that he sounded as if he were strangling. Feynman—who, like Gell-Mann, was born in New York City—had no idea what he was talking about. “Don’t you think,” he asked Gell-Mann, when at length he had ascertained that Gell-Mann was saying “Montreal,” “that the purpose of language is communication?”
*
Quantum interactions customarily are depicted as taking place not in the conventional space that makes up the theater for macroscopic events, but in an assessment complex space described in part by the quantum wave functions. Quarks, for instance, are for convenience depicted as existing in a three-dimensional “color” space described by quantum chromodynamics—color is a quantum number that plays a role in the strong force analogous to that of the charge in electrodynamics—while electrons normally occupy a one-dimensional space the two directions of which represent positive and negative electrical charge.
*
Connections between the weak and electromagnetic interactions had been noted before; Fermi in 1933 formulated the first model of the weak force by analogy with electromagnetism. But a great many such threads weave their way through the history of physics, and this book is not the place to attempt to trace more than a few of them.
*
Compare, for instance, the value of
g
, the gyromagnetic ratio of the electron, as predicted by the theory of quantum electrodynamics and as tested experimentally:
Theory: £ = 1.00115965241
Experiment: £ = 1.00115965238, ± 0.00000000026
*
Electrons, since they also carry an electrical charge, can also be employed; the resulting explosions are cleaner and therefore easier to study, but as electrons are less massive than protons they collide less violently, and so electron accelerators yield weaker collisions relative to their energy consumption.
†
After Ernest Walton, an Irish physicist, and John Cockroft, the English physicist who on one fine day in 1932 could be seen stopping strangers on the streets of Cambridge and exclaiming, “We have split the atom! We have split the atom!”
*
Since antiprotons have opposite electrical charge, the same sequence of magnetic pulses that kept protons moving clockwise around the ring would keep the antiprotons moving counterclockwise. A somewhat more exotic way of looking at the situation, proposed by Feynman years earlier, was to say that antimatter particles move in reverse time.
T
HE
A
XIS
OF
H
ISTORY
Every present state of a simple substance is naturally a consequence of its preceding state, in such a way that its present is big with its future.
—Leibniz
He who has seen present things has seen all, both everything which has taken place from all eternity and everything which will be for time without end; for all things are of one kin and of one form.
—Marcus Aurelius
T
he late twentieth century may be remembered in the history of science as the time when particle physics, the study of the smallest structures in nature, joined forces with cosmology, the study of the universe as a whole. Together these two disciplines were to sketch the outlines of cosmic history, investigating the ancestry of natural structures across an enormous range of scale, from the nuclei of atoms to clusters of galaxies.
It was a shotgun wedding between two very different disciplines. Cosmologists tend to be loners, their gaze fixed on the far
horizons of space and time and their data tenderly garnered from trickles of ancient starlight; none will ever touch a star. Particle physicists, in contrast, are relatively gregarious—they have to be; not even an Einstein knows enough physics to do it all by himself—and
physical:
They are by tradition hands-on students of the here and now, inclined to bend things and blow up things and take things apart.
*
Physicists work hard and fast, haunted by the legend that they are unlikely to have many useful new ideas after the age of forty, while cosmologists are more often end-game players, devotees of the long view, who can expect to still be doing productive research when their hair turns white. If physicists are the foxes that Archilochus said know many things, cosmologists are more akin to the hedgehogs, who know one big thing.
Yet by the late 1970s, particle physicists were venturing to cosmology seminars to bone up on galaxies and quasars, while cosmologists were hiring on at CERN and Fermilab to do high-energy physics at underground installations blind to the stars. By 1985, Murray Gell-Mann could declare that “elementary particle physics and the study of the very early universe, the two most fundamental branches of natural science, have, essentially, merged.”
1
Their meeting ground was the big bang. As we saw in the
previous chapter
, the physicists identified symmetries in nature that today are broken but which would have been intact in a high-energy environment. From the cosmologists came word that the universe was once embroiled in just such a high-energy state, during the initial stages of the big bang. Put the two together, and a picture emerges of a more or less perfectly symmetrical universe that fractured its symmetries as it expanded and cooled, creating the particles of matter and energy that we find around us today and stamping them with evidence of their genealogy. Steven Weinberg, a champion of the new alliance, described the electroweak unified theory in terms of its connection with the early universe:
The thing that’s so special about the electroweak theory is that the [force-carrying] particles form a tightly knit family, with
four members: There’s the W
+
, the oppositely charged W
−
, the neutral Z, and the fourth member is our old friend the photon, the carrier of electromagnetism. These are siblings of each other, tightly related by a principle of symmetry that says that they’re really all the same thing—but that the symmetry is broken. The symmetry is there, in the underlying equations of the theory, but it’s not evident in the particles themselves. That’s why the W and the Z are so much heavier than the photon.But there was a time, in the very early universe, when the temperature was above a few hundred times the mass of the proton, when the symmetry hadn’t yet been broken, and the weak and electromagnetic forces were all not only mathematically the same, but
actually
the same. A physicist living then, which is hard to imagine, would have seen no real distinction between the forces produced by the exchange of these four particles—the Ws, the Z, and the photon.
2
Similarly, if less distinctly, the emerging supersymmetry theories suggested that all
four
forces may have been linked, by a symmetry that evidenced itself in the even higher energy levels that characterized the universe even earlier in the big bang.
The introduction of an axis of historical time into cosmology and particle physics benefited both camps. The physicists provided the cosmologists with a wide range of tools useful in trying to piece together how the early universe developed: Evidently the big bang was not the impenetrable wall of fire that Hoyle had scoffed at, but an arena of high-energy events that might very possibly be comprehensible in terms of relativistic quantum field theory. Cosmology, for its part, lent a tincture of historical reality to the unified theories. Though no conceivable accelerator could attain the titanic energies invoked by the grand unified and supersymmetry theories, these exotic ideas still might be tested, by investigating whether the particle constituency of the present-day universe accords with the sort of early history the theories imply. As Gell-Mann put it, “The elementary particles apparently provide the key to some of the fundamental mysteries in early cosmology…. and cosmology, it turns out, provides a sort of testing ground for some of the ideas of elementary particle physics.”
3
Viewed from this new, historical perspective, the proliferation of particle types that had been so discouraging to the physicists
(prompting Fermi to muse that he should have been a botanist) began to look less like a burden than a boon. Once it became clear that every particle has arisen from a process of cosmic evolution, about which it can testify, one could regard the variety of particles as evidence of the richness of cosmic history. Physicists no longer needed to feel unhappy about the diversity of the particle world, any more than archaeologists would be disappointed if, say, while excavating the ruins of ancient Herculaneum they unearthed the foundations of an even older city beneath it. Instead, they could consider that nature is complicated and imperfect because it has a past—that, as the American physicist Thomas Gold remarked, things are as they are because they were as they were.
Indeed, one could discern signs of a direct relationship linking the size, binding energy, and age of nature’s fundamental structures. A molecule is larger and easier to break apart than an atom; the same is true of an atom relative to an atomic nucleus, and of a nucleus relative to the quarks that comprise it. Cosmology suggests that this relationship results from the course of cosmic history—that the quarks were bound together first, in the extremely high energy of the early big bang, and that as the universe expanded and cooled the protons and neutrons made of quarks adhered to one another to form the nuclei of atoms, which thereafter attracted electrons to set up shop as complete atoms, which in turn linked up to form molecules.
If so, the more closely we examine nature the further we are peering back in time. Look at something familiar—the back of your hand, let us say—and imagine that you can turn up the magnification to any desired power. At a relatively low magnification you will discern individual cells in the skin, each looming as large and complex as a city, its boundaries delineated by the cell wall. Increase the magnification and you will see, within the cell, a tangle of meandering ribosomes and undulating mitochondria, spherical ly-sosomes and starburst centrioles—whole neighborhoods full of complex apparatus devoted to the respiratory, sanitary, and energy-producing functions that maintain the cell. Here, already, we encounter ample evidence of history: Though this particular cell is only a few years old, its architecture dates back more than a billion years, to the time when eucaryotic cells like this one first evolved on Earth.