Why Does E=mc2_ - Brian Cox [74]
equations just appear when we “ask” the master equation how the particles with electric charge interact with each other. And of course, the whole structure rests firmly on Einstein’s special theory of relativity. In fact, the part of the Standard Model that explains how light and matter interact is called quantum electrodynamics. The “quantum” reminds us that Maxwell’s equations had to be modified by the quantum theory. The modifications are usually very tiny and lead to subtle effects that were first explored in the middle of the twentieth century by Richard Feynman and others. As we have seen, the master equation also contains the physics of the strong and weak forces. The properties of these three forces of nature are specified in all of their details, which means that the rules of the game are laid out with mathematical precision and without ambiguity or redundancy. So, apart from gravity, we seem to have something approaching a grand unified theory. It is certainly the case that no one has ever found any evidence anywhere in any experiment or through any observation of the cosmos that there is a fifth force at work in the universe. Most everyday phenomena can be explained pretty thoroughly using the laws of electromagnetism and gravity. The weak force keeps the sun burning but otherwise is not much experienced on Earth in everyday life, and the strong force keeps atomic nuclei intact but extends barely outside of the nucleus, so its immense strength does not reach out into our macroscopic world. The illusion that such solid things as tables and chairs are actually solid is provided by the electromagnetic force. In reality, matter is mainly empty space. Imagine zooming in on an atom so that the nucleus is the size of a pea. The electrons might be grains of sand whizzing around at high speeds a kilometer or so away—the rest is emptiness. The “grain of sand” analogy is stretching the point a little, for we should remember that they act rather more like waves than grains of sand, but the point here is to emphasize the relative size of the atom compared to the size of the nucleus at its core. Solidity arises when we try to push the cloud of electrons whizzing around the nucleus through the cloud of a neighboring atom. Since the electrons are electrically charged, the clouds repel and prevent the atoms from passing through each other, even though they are largely empty space. A big clue to the emptiness of matter comes when we look through a glass window. Although it feels solid, light has no trouble passing through, allowing us to see the outside world. In a sense, the real surprise is why a block of wood is opaque rather than transparent!
It is certainly impressive that we can shoehorn so much physics into one equation. It speaks volumes for Wigner’s “unreasonable effectiveness of mathematics.” Why should the natural world not be far more complex? Why do we have a right to condense so much physics into one equation like that? Why should we not need to catalog everything in huge databases and encyclopedias? Nobody really knows why nature allows itself to be summarized in this way, and it is certainly true that this apparent underlying elegance and simplicity is one of the reasons why many physicists do what they do. While reminding ourselves that nature may not continue to submit itself to this wonderful simplification, we can at least for the moment marvel at the underlying beauty we have discovered.
Having said all that, we are still not done. We haven’t yet mentioned the crowning glory of the Standard Model. Not only does it include within it the electromagnetic, strong, and weak interactions, but it also unifies two of them. Electromagnetic phenomena and weak interaction phenomena at first sight appear to have nothing to do with each other. Electromagnetism is the archetypal real-world phenomenon for which we all have an intuitive feel, and the weak force remains buried in a murky sub-nuclear world. Yet remarkably the Standard Model tells us that they are in fact different manifestations of the same thing. Look