String theory has been the darling of the theoretical physics community for decades. It has reigned as the dominant theory in prestigious US research institutions since the 1980s. Elegant books, TV shows, and grandiose TED talks have hyped it to the public. Brilliant theoretical physicists tell us that this theory is the best answer to the hardest problem that their field has ever attacked.
All that is fine, but here's the unequivocal truth: string theory has failed as a scientific theory.
What do you do when you can't succeed when playing by the rules? You can go home or you can try to change the them. And that's precisely what string theory is now doing. In case my experimentalist bias is shining too clearly, let's restate this as a (somewhat) balanced question:
Is it time to change our notions of what science is to accommodate a single spectacularly difficult problem and the decades of struggle by those theories attempting to tackle it?
Remarkably, this exact question has been hearing open debate among proponents of string theory. String theorists met jointly with academic philosophers at a conference last month to talk about what we require of a theory for it to be held as correct. Do we need to test it experimentally? Or, are the qualities of beauty, consistency, mathematical interest, and greater funding proof enough?
It is a debate on which of two philosophies science ought to follow: empiricism or rationalism. The choice, to this physicist, is stingingly clear.
Science has been for its entire history fantastically successful precisely because it requires experimental tests to verify and confirm its claims. That criterion can be defined simply: empiricism. Ideas are not true simply because of their logic or conceptual beauty but because they are observed by human senses -- or the extension thereof by cameras, telescopes, spectroscopes, thermometers, and so forth -- and verified. Empiricism is not necessarily the best system of philosophy for all endeavors. Moral human beings accept many ideas and laws that are not learned from observation but instead found within (or without) and supported by the heart.
A different type of philosophical system describes the new guidelines that string theorists lust for: rationalism.
Rationalism derives truth via the process of deductive logic. Rationalism is the system of the mathematician. Theorems are logically correct because they can be built logically from a dictionary of axioms followed by deductions. Mathematics, however, need not be true in the external universe that we live in and perceive. Mathematics need only make logical sense in the minds of mathematicians. That's not a dismissal: mathematical tools are fantastically useful not only in physics but in engineering, medicine, accounting and a host of other human endeavors.
The history of science is littered with theories that sounded rationally simple and logically brilliant but turned out to be utterly false empirically. Meat does not spontaneously grow maggots. The Universe does not revolve around the earth. The bumps on the human skull do not reveal the intelligence of the brain residing within. Light does not travel through a luminiferous aether. The failure of these theories was not found through rationalist logic but through careful experiment upon nature itself.
The fire igniting critics of string theory is not personal animus or professional jealousy. It's the idea that a single theory has become so entrenched and popular in its field that its failures cannot be addressed truthfully. Now, physicists ask that the rules be bent or changed just to accommodate it. To loosen the principles of our fantastically successful scientific method just to allow for one passing theoretical fad to continue would be a disaster.