Woody Allan once joked that he was thrown out of N.Y.U. his freshman year for cheating on his metaphysics final. He looked within the soul of the boy sitting next to him. I fear that we do not pay enough respect to the metaphysical assumptions that form the foundation of our contemporary world. Even the sciences are not immune to ignoring the fundamental questions.
One of the appealing aspects of physics and astrophysics is the strong ties to experiment and observation – even though many of the ideas are very abstract, a scientific theory must have testable implications. For instance, for centuries humans have speculated that there might be planets around other stars – however, these musing were outside the realm of science. Over the past decade, through careful observation and precise measurement, astrophysicists have been able to not only detect planets around other stars but also begin to find earth-sized planets in the habitable zones around their star. It is very likely that the next generation of instruments will be able to search for chemical evidence for life on some of these planets. What was once a question beyond the grasp of science - do planets capable of supporting life exist beyond the earth? - is now likely to be answerable by direct observation.
Physics and astrophysics seem to be at a high-water-mark right now. The standard model in particle physics, which provides our fundamental theory for the structure of matter and behavior of forces, has stood up to all tests for more than thirty years. The standard model’s prediction of the Higgs boson was confirmed by the Large Hadron Collider at CERN last year and its properties seem to be in agreement with expectations. Likewise in cosmology, the big bang theory has stood up to numerous experimental tests over the past forty years. The big bang provides the framework for our understanding of the early history of the universe (as far back to when the universe was microseconds old) and its subsequent evolution.
While successes abound for these theories, some physicist are beginning to look, not just for alternative theories, but at the fundamental assumptions (the metaphysics) that underlie them. Metaphysical questions are being addressed in books authored by distinguished scientists such as Lee Smolin’s Time Reborn. Questions like: What is time and space? Do the laws of physics change with time or are they eternal? What is dark matter and dark energy? And, why is our universe so fine-tuned for life?
What has caused these fundamental questions to arise now? Well, despite rousing successes, a number of troubling issues are vexing theoretical physicists. The inferred existence of dark matter and more recently dark energy now rest on strong observational footing. Dark matter explains the motion of galaxies. Dark energy provides the push for an acceleration of the expansion of the universe. Both are necessary for our understanding of the universe and neither is accounted for by the standard model for matter and energy. These mysterious, inferred but not directly observed, components of our universe combine to account for over 95% of the contents of our universe. The stuff that makes you and I and the earth, sun, and everything we see in the universe is relegated to the metaphoric “tip-of-the-iceberg”. The vast majority of the universe is unlike the matter we see around us, and to date, beyond our ability to detect.
Physics was in a similar situation before the turn of the last century. Newton’s laws of gravity and motion, the laws of thermodynamics, and Maxwell’s unification of electricity and magnetism were the underpinnings of the Industrial Revolution. Scientist lamented that all the “big discoveries” had been made. The triumphs of the existing theories led one to speculate that almost everything that was understandable was understood. But a few, at first seemingly minor issues, refused to be solved. Some examples of the unsolved questions were: How did the Sun generate energy over billions of years? Why did energy seem to radiate from its source in discreet amounts (quanta) and not continuously? And, why did light appear to travel at the same speed independent of the direction? These “loose ends” turned out to usher in entirely new branches of physics after 1900 – nuclear physics, quantum mechanics, and relativity were born from these and similar questions. All of these led to new ways of understanding space and time, the structure of matter, and the universe as a whole. Lengths and time intervals once thought immutable were found to depend on the observer’s relative motion. Energy and matter were related. The atom existed and consisted of even smaller particles. The universe itself was not infinitely old and though finite was much vaster in size than ever imagined.
Our metaphysics, whether consciously or unconsciously, influences the scientific questions we ask and the answers that we propose. How fundamentally different our descriptions of matter and the universe are today compared to a century ago! I suspect that another dramatic change is coming that will further alter our conception of time, space, matter, and the universe. If the history of science teaches us anything, it is to expect that our current theories are incomplete and that new ideas will shake the very foundation upon which those theories are built.