Wednesday, July 9, 2008
Wednesday Math, Vol. 31: The trouble with string theory
Wolfgang Pauli, a 20th Century theoretical physicist, had a favorite derogatory statement about poorly constructed ideas in physics: "That is not even wrong." This meant either that there were too many mistakes in an idea to make it worth salvaging, or that it was not testable, with no way to prove if the idea was right or wrong with an experiment. Peter Woit has chosen the title Not Even Wrong to discuss his view of string theory, the popular ideas in theoretical physics about how unseen dimensions might be the best way to explain how the world works, and to reconcile the contradictory views of the design of the universe that are the underlying assumptions in the two great leaps forward in 20th Century physics, general relativity and quantum mechanics.
We like to think we live in a three dimensional world, but Einstein famously put forward that the universe has four dimensions, the fourth being time, to go along with the other three physical dimensions, which we call height, width and depth. The fourth dimension is obviously very different from the first three, and the math behind Einstein's spacetime reflects that difference. Physical objects, from particles to people to planets, have some latitude in how they can move up/down, left/right and front/back, but all of us are being carried forward in time together at seemingly the same rate. Einstein said that some things could travel faster in time than others, and he proposed experiments that could test this hypothesis. The experiments aren't easy, and some show that certain details of relativity may have been misstated, but the basics ideas of relativity have been proven true over the last 100 years. Einstein's original concept and the refinements that have been added, which together are called the standard model, are the best idea we have of the way the universe works. My favorite teacher Stu Smith calls the standard model the greatest work of art of the 20th Century.
The trouble starts, at least in Peter Woit's view, with a mathematician named Kalusa. Kalusa sent a letter to Einstein with a lot of fancy math that postulated that if the universe were actually five dimensional instead of four dimensional, the force of gravity and the electromagnetic forces could actually be shown to be manifestations of the same principle, which in physics talk means they can be unified. Unifying all the forces of nature, gravity, electromagnetic and two sub-atomic forces called strong and weak, was Einstein's great goal, and the unfinished work of the last fifty years of his life. He told friends about the Kalusa paper, and the idea was very intriguing. Unlike Einstein and his fourth dimension of time, Kalusa had no idea what this fifth dimension might be and did not even speculate. It was really a mathematical exercise more than a physical one, because there was no way to test its validity, unlike Einstein's relativity which can be tested.
String theory can be simply stated that if five dimensions are cool, eight or ten or even more could be even cooler! It hopes that all the forces can be shown to be manifestations of a single force and the seeming contradictions in relativity and quantum mechanics are not contradictory at all in the full n dimensional universe, but just puzzling evidence that those of us with only enough senses to comprehend what we call spacetime can perceive.
While the two ideas have very different sets of enthusiasts, string theory and intelligent design share a troubling and fatal flaw. Neither is testable, which is to say neither fulfills the first rule of science. String theory is a hopeful attempt at synthesis between relativity and quantum mechanics, while intelligent design is a hodgepodge collection of complaints by people whose world view cannot bear the idea that modern biology actually understands the working of the world better than the creation myths put forward by some pig ignorant dirt farmers from five to seven thousand years ago. Without some way to test the ideas put forward, both of these ideas would have to be put in the category Pauli called "not even wrong".