(Orignally written a few years ago as sort of an op-ed after an interesting meeting on fundamental physics in the gorgeous resort town of Lake Bled in Slovenia, “Time and Matter 2007.”)
As the sun sets over the Julian Alps, as evening embraces the Assumption of Mary Pilgrimage Church in the middle of Lake Bled in Slovenia and church bells herald day’s end, we come to the conclusion of Time & Matter 2007, an unusually diverse gathering of physicists and philosophers, assembled here to bring their different perspectives to bear on the deep, unsolved problems of contemporary physics.
In the one hundred years since the quantum and relativity revolutions, advances in fundamental physics have completely transformed our understanding of nature. Powerful particle accelerators allow us to probe the structure of the tiniest subatomic particles, while orbiting observatories let us look out to the edge of the universe and back in time to its beginnings. No century produced an expansion of physical knowledge such as we saw in the twentieth century.
But where do we stand now? Modern physics is built on two foundations. Einstein’s theory of general relativity explains gravitation and the large-scale structure of the universe. Quantum mechanics–the work of Einstein, Max Planck, Niels Bohr, Werner Heisenberg, Erwin Schrödinger, and others–is the framework for explaining the other three fundamental forces–electromagnetism, and the strong and weak nuclear forces. With quantum field theory and the so-called “standard model” of particle physics–the quark model–quantum mechanics explains the microstructure of the universe. Part of what’s remarkable about twentieth-century physics is that each of these theories has been confirmed with extraordinary precision. One could be forgiven for thinking that we are on the verge of achieving a complete and final understanding of nature.
And yet the presentations and conversations here at Lake Bled have been dominated by talk of theoretical analyses and experimental tests that could very well refute every one of these theories. Tests of what are known as Einstein-Podolsky-Rosen correlations in neutral kaon decay could refute quantum mechanics. The still unresolved black-hole information loss paradox could point to a fundamental contradiction between quantum mechanics and general relativity. When CERN’s large hadron collider begins operation in 2008 the standard model might be refuted if the Higgs boson is not detected. More than one talk at Time & Matter 2007 used the acronyms, “BSM” and “NP” for “beyond the standard model” and “new physics.”
But more than anything else, the question looming over the meeting–in conversation at the opening reception and in talks on the closing day–are the problems of dark matter and dark energy. Within just the past ten years, observation has shown that the universe is populated with a strange form of matter, “dark matter,” that interacts gravitationally with ordinary, “baryonic” matter but is otherwise invisible, so far, to our current physics. Other observations have shown that the expansion of the universe is accelerating in a way seemingly explainable only if it is filled with a still stranger stuff, “dark energy,” that is completely invisible to current physics. Moreover, we now think that 96% of the universe consists of this strange new stuff. According to our best estimates, 22% of the universe is dark matter, and 74% is dark energy. That means that only 4% of the universe is made up of the kind of stuff–baryonic matter–that is explained by all of the revolutionary, new, physical knowledge that we accumulated in the twentieth century. That’s right. After all that hard work, our current best physics explains, at most, 4% of what’s in the universe.
There is irony in the fact that it was the very physics whose dramatic shortcomings are now revealed that made possible the discovery of those limitations. And physicists are to be admired for the fact that, proud as they are of what they’ve done, they turn right around and subject it all to tough, critical examination. No dogma here, just the patient, steady, self-critical effort to know more. But perhaps most important is the lesson of that 4% figure. The discovery of dark matter and dark energy provide the clearest proof known to me of the basic insight of Socrates, that wisdom lies in knowing what it is that we don’t know, that intellectual humility is the mark of true wisdom.
These are very exciting times in physics.
August 31, 2007