# String Theory

March 13, 2021

Have you ever felt frustrated in a science class when one scientific theory or law would just lead to another and there never seemed to be an end? Unfortunately, that’s how science works, most of the time. Only most of the time? Actually, yes, there is a scientific theory described as possibly being the “theory of everything” or the “ultimate” or “final” theory. It is called “String Theory”.

String theory is given its grandiose descriptive terms because it attempts to describe all forces and matter in one mathematical picture. It is as popular as it is controversial, however, and although its math lines up, no one has succeeded in proving it in an experiment. How was it conceived? Let’s find out.

To understand the need for a theory like the string theory, we have to go back to the early 1900s. In the year 1905, physician and mathematician Albert Einstein published his “Theory of Relativity” in which the abstract concepts of gravity, energy, and mass were combined and explained. The infamous “E=mc^2” formula was published in this work, E being the energy, equal to mass (m) multiplied by the speed of light (c) squared. Einstein explained the relationship of the forces found within all mass, and he did so in one single formula. This was an astounding accomplishment, especially for the time period, but as Rohan Mandayam ‘23 puts it: “we all know Einstein was far ahead of his time.”

In the mid-1920s, familiar names such as Niels Bohr, Erwin Schrödinger, and Werner Heisenberg discovered the quantum realm, and with it, quantum mechanics: the theory in physics that describes the physical properties of nature at the atomic and subatomic levels. At these levels, physicists’ experiments discovered something peculiar. Each of their separate works contributed to finding out that Einstein’s theory of relativity explaining gravity didn’t hold up in the quantum realm. Suddenly, there was a discrepancy in the theory of relativity, and so, Einstein set out to fix it. He spent the last decade of his life trying to figure out a theory that would relate the two, similar to how he unified energy and mass in his theory of relativity. What was needed was a theory of unification, and Einstein was so invested in discovering this theory, that he was found in his deathbed still scribbling together his findings. Einstein was so ahead of his time that the issue he attempted to solve wouldn’t be picked up again for another decade. String theory itself dates back to 1968, 13 years after Einstein’s death.

But what is string theory? What does it entail? I’ve held back from explaining other concepts before, but this explanation is owed to you. Particle physics, a branch of physics that studies the particles that constitute matter and radiation, usually investigates the irreducibly smallest particles and the interactions necessary to explain their behavior. What string theory suggests is that the particles found on the lowest of levels are replaced by one-dimensional objects called strings. These strings move through space and interact with each other. Just like an ordinary particle, a string has a mass, a charge, and other properties that are determined by how the string vibrates. The strings differ from the particles because of a specific vibrational state of a string known as a graviton. This is why string theory is the theory of unification that Einstein spent the last decade of his life attempting to discover. String theory is a theory of quantum gravity, able to combine Einstein’s explanation of gravity in his theory of relativity with the discrepancies of that same theory found in the quantum realm. It is for that reason that string theory is a candidate for “theory of everything”, a theory that underlies all others, one that does not require or even allow for a deeper explanatory base.

Cauchy succinctly summarizes string theory in this way: “Physicists have a lot of confidence in Quantum Theory as it has proven to be correct many times and explains pretty much everything. General Relativity explains gravity on a macroscopic scale and it too has not been proven wrong. String theory tries to explain both at the same time. The math seems to work, so that is why there is hope it could be true.” But if nothing’s confirmed, is there a point in learning about this theory or should one wait for more evidence to come up? Ilana Princilus ’22 doesn’t think that “people should put their entire belief system into this theory as it has yet to succeed in experiments. For now, I think people should continue to learn about what theory seeks to accomplish and eventually, when there is more evidence, begin to develop a strong belief/disbelief in it.” Cauchy says that it’s “a good topic to ponder, but the speculative nature makes me think the time might be better spent on really cool things we know are true (at least for now).” The speculative nature Cauchy describes exactly explains the controversy of string theory, as it stands, more evidence through observation and experimentation would be required to confirm such a theory. Until then, it’s still fun to think how close we are to completing what Einstein started: unifying *everything* together.