Warped Passages - Lisa Randall [33]
The conflict between the two scientific approaches is interesting because it reflects two very different ways of doing science. This division is the latest incarnation of a long debate in science. Do you follow the Platonic approach, which tries to gain insights from more fundamental truth, or the Aristotelian approach, rooted in empirical observations? Do you take the top-down or the bottom-up route?
The choice could also be phrased as “Old Einstein vs. Young Einstein.” As a young man, Einstein rooted his work in experiments and physical reality. Even his so-called thought experiments were grounded in physical situations. Einstein changed his approach after learning the value of mathematics when he developed general relativity. He found that mathematical advances were crucial to completing his theory, which led him to use more theoretical methods later in his career. Looking to Einstein won’t resolve the issue, however. Despite his successful application of mathematics to general relativity, his later mathematical search for a unified theory never reached fruition.
As Einstein’s research demonstrated, there are different types of scientific truth and different ways of finding them. One is based in observations; this is how we learned about quasars and pulsars, for example. The other is based on abstract principles and logic: for example, Karl Schwarzschild first derived black holes as a mathematical consequence of general relativity. Ultimately, we would like these to converge—black holes have now been deduced from both the mathematical description of observations and from pure theory—but in the first phases of investigation, the advances we make based on the two types of truth are rarely the same. And in the case of string theory, the principles and equations are not nearly so well laid out as are those of general relativity, making deriving its consequences that much harder.
When string theory first rose to prominence, it sharply divided the particle physics world. I was a graduate student in the mid-1980s when the “string revolution” first split the world of particle physics asunder. At that time, one community of physicists decided to devote themselves wholeheartedly to the ethereal, mathematical realm of string theory.
String theory’s basic premise is that strings—not particles—are the most fundamental objects of nature. The particles we observe in the world around us are mere consequences of strings: they arise from the different vibrational modes of an oscillating string, much as different musical notes arise from a vibrating violin string. String theory gained favor because physicists were looking for a theory that consistently includes quantum mechanics and general relativity and that can make predictions down to the tiniest conceivable distance scales. To many people, string theory looked like the most promising candidate.
However, another group of physicists decided to stay in touch with the relatively low-energy world that experiments could explore. I was at Harvard, and the particle physicists there—which included the excellent model builders Howard Georgi and Sheldon Glashow, along with many talented postdoctoral fellows and students, were among the stalwarts who continued with the model building approach.
Early on, the battles between the merits of the two opposing view-points—string theory and model building—were fierce, with each side claiming better footing on the road to truth. Model builders thought that string theorists were in