Which Came First, Quantum Mechanics or String Theory?

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The extra-dimensional nature of string theory can be represented with a Calabi–Yau manifold such as this. By vchal/Shutterstock

If theoretical physicists had their own version of the age-old question about the chicken and the egg, they might instead ask: What came first, quantum mechanics or string theory?

String theory, in its broadest sense, was first envisioned as one possible way of trying to unify the world of physics, to bridge the theoretical chasm that exists between our understanding of the very smallest of things, quantum mechanics, and our understanding of how things work on the grandest of scales, general relativity. It postulates that the universe is fundamentally composed of tiny objects called strings, rather than the point-like particles of conventional particle physics.

However, because string theory is so convoluted, and since the principles of quantum mechanics are so well tested, quantum theory has typically been used to try to validate string theory, rather than the other way around. But this could soon change, if two USC researchers have anything to say about it, reports USC News. They have proposed a link between string theory and quantum mechanics that could open the door to using string theory as the basis of all physics. (In other words, if they're right, string theory would come first.)

"This could solve the mystery of where quantum mechanics comes from," said Itzhak Bars, lead author of the paper.

In their paper, Bars and grad student Dmitry Rychkov reformulate a version of string theory — called M-theory — into clearer language. Most importantly, however, the two researchers show that a set of fundamental quantum mechanical principles known as "commutation rules" can be derived from the geometry of strings joining and splitting.

"Our argument can be presented in bare bones in a hugely simplified mathematical structure," explained Bars. "The essential ingredient is the assumption that all matter is made up of strings and that the only possible interaction is joining/splitting as specified in their version of string field theory."

Deriving the commutation rules from string theory would be a monumental step forward; it's these rules that essentially predict uncertainty in the position and momentum of every point in the universe. This accomplishment, if it holds true, could not only help to explain some of the mysteries at the heart of quantum mechanics, but it could establish string theory as the basis of all physics.

In other words, this could make string theory a leading candidate to be a theory of everything.

"The commutation rules don’t have an explanation from a more fundamental perspective, but have been experimentally verified down to the smallest distances probed by the most powerful accelerators. Clearly the rules are correct, but they beg for an explanation of their origins in some physical phenomena that are even deeper," Bars said.