Symmetry is vital to the workings of our world from particles to wheels (Image: Sophie Chivet / Agence VU/Camera Press)
Discovering symmetry's unsung heroine is all part of a very wild ride through Dave Goldberg's book The Universe in the Rearview Mirror
"IF WE'RE trying to understand all that there is, we're going to have to dig a little bit deeper," says astrophysicist Dave Goldberg, laying out his ambition for this book. This ambition is nothing less than to illuminate the basis of modern physics and, arguably, the fulcrum of our knowledge of the world ? the idea of symmetry.
Symmetry is more than the aesthetic balance in colonnades and butterfly wings. In the much more general, physics sense, it can apply to time, space, electrical charge, spin, and even more abstruse properties of matter.
Loosely, symmetry means that when you change one thing, other things remain unchanged and still behave the same way. Rotate a square by 90 degrees, and it looks the same. A circle is more symmetrical, because it can be rotated by any angle and look the same. As well as rotation, symmetries include reflection, translation (shifting everything along in one direction) and translation in time (resetting the clocks). As Goldberg explains, symmetry is not just the reason why wheels work, but also why E = mc2, why atoms exist, and why the floor holds you up.
Emmy Noether's theorem may be the most profound idea in science (Image: Science Photo Library)
Symmetry's central position in modern physics stems from a stunning insight by a German mathematician called Emmy Noether. The daughter of Max Noether, a mathematics professor at the University of Erlangen, she chose to stay in the family business despite the resistance to women in the field. Working unpaid for much of her career, Noether surpassed her eminent father when, in 1915, she proved that every symmetry in nature leads to a conserved quantity.
Her work was inspired in part by Einstein's newly published general theory of relativity, an extension of his special theory.
It may sound obscure, but Noether's theorem is possibly the most profound idea in science. It tells us that because physics remains unchanged if you move a bit to the left or right, total momentum in the universe must remain unchanged. Because physics is the same today as it was yesterday, there is a conserved thing called energy. The idea of a link between time and energy is still startling today. And that is only the beginning. After Noether's work, fundamental physics became a search for symmetries.
Unsurprisingly, she was not always well treated by the mathematics establishment. Goldberg tells us how she found an ally in the mathematician David Hilbert, who recalled how "tradition, prejudice, external considerations, weighted the balance against her scientific merits and scientific greatness, by that time denied by no one".
When Noether was first denied a Privatdozent (a title conferring the right to lecture), Hilbert made a rousing but futile defence of her. "I do not see that the sex of the candidate is an argument against her admission," he said. "After all, we are a university, not a bathhouse."
Although Noether is well known among mathematicians today, having established much of the basis of modern algebra, she deserves wider fame. Goldberg is a cheerleader, considering her the star of his story. Even so, I was disappointed by how briefly she appears, and wanted more on how she proved her theorem.
But Goldberg is a restless author and there is much to cover. And so we are off, discovering more of nature's strange and subtle symmetries. We learn how particle replacement symmetry and the quirks of quantum spin combine to nail together the periodic table ? and how physicists Chen Ning Yang and Robert Mills extended Noether's work to show that symmetries generate all the particles and forces in the universe.
We also discover that symmetries can break in interesting ways. Broken symmetries today hide the underlying simplicity of unified quantum fields, which would have been evident to a physicist lurking in the very hot early universe. The main object of fundamental physics is to reconstruct these ancient symmetries from our cooler perspective.
One slightly broken symmetry allowed matter to triumph over its evil twin, antimatter, in the early universe. Matter sprang from a hot bath of gamma radiation: our genesis is "much like [that of] The Incredible Hulk," says Goldberg. Clearly it helps to be on top of your comic books and speculative fiction, as Goldberg packs in sci-fi, superheroes and fantasy references.
On the whole, this tendency doesn't warrant the apologies that Goldberg makes, although the allusions sometimes seem forced. He describes, for example, how it is possible to detect neutrinos by "building giant detectors underground ? oddly reminiscent of the Dwarrowdelf in Middle Earth".Continue reading page |1 |2
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