Under the microscope: a theory of everything

Though gravity works to pull this paper toward the ground, it is easy to hold it at eye level because gravity is weak. (PHOTO CREDIT: MCT CAMPUS)

Though gravity works to pull this paper toward the ground, it is easy to hold it at eye level because gravity is weak. (PHOTO CREDIT: MCT CAMPUS)

Every other week, Mallory Locklear, a graduate student at Stony Brook University’s Department of Neurobiology and Behavior, will take a look at Stony Brook-related research and science news.

The field of physics has a problem. The general theory of relativity does a great job at describing gravity while the quantum field theory does an equally great job at describing electromagnetism and the forces that keep particles like protons and neutrons together.

However, these two theories are not interconnected. General relativity cannot describe the interactions between particles and quantum field theory cannot describe gravity—thus, the problem.

Beginning in the 1970s, physicists and mathematicians decided to explore the disconnect between the two theories and try to come up with a more unified theory—one that could describe all of the forces of the universe, not just a subset. As Stony Brook University professor and physicist Dr. Michael R. Douglas described, “They were driven by the beauty of the equations,” and it was through these equations that string theory was born.

Take an electron. Traditionally, an electron has been thought of as a zero-dimensional object, or a point, similar to the period at the end of this sentence. Conversely, string theory says that particles as we know them are not points, but instead are made up of one-dimensional strings.

These strings can be open or closed loops. They can vibrate in many different ways and in every dimension, of which string theory predicts there are ten. Different vibration patterns lead to different particles. One vibration pattern may result in an electron while another may result in a quark.

String theory has done quite well so far in explaining all of the forces of the universe. The theory has matured, and so have the mathematical equations it has produced. An equation describing the universe is considered successful if it is symmetrical. What that means is if the equation is taken apart and its components rearranged, it should still produce the same conclusion. If the rearrangement of an equation does not yield the same result, it is deemed unstable and not a good descriptor of the universe or its forces.

The equations that have stood up to the test of symmetry have predicted the existence of particles that help bridge the gap between general relativity and quantum field theory. For example, string theory predicts a particle called the graviton, thought to be a closed loop string that is responsible for the gravitational force.

Unlike really strong forces like electromagnetism and the force responsible for the interactions between protons and neutrons in the nucleus of an atom (which is actually called the strong nuclear force), gravity is quite weak. Yes, the very gravity keeps us planted on the surface of Earth and keeps Earth rotating around the sun.

But consider this: breaking apart the nucleus of an atom requires overcoming the strong nuclear force. This force is so strong that when it is broken, as it is in an atomic bomb, the energy released is so powerful it can destroy cities, as it did when an atomic bomb was dropped on Hiroshima during World War II.

Now consider gravity: A person reading this article in the newspaper is presumably holding it up at eye level. Gravity is working to pull the paper to the ground, but the person is overcoming the force of gravity with nothing but the muscles in their arms and hands. No explosions are occurring. No cities are being destroyed.

Gravity is weak.

String theory not only predicts the particle that constitutes gravity, it also helps describe why it is so weak.

Part of Douglas’s work has centered on the idea of membranes. It is thought that membranes permeate the universe and the open strings that are involved in the strong forces of the universe, like electromagnetism and the strong nuclear force, are connected to these membranes, keeping their strength focused.

Gravitons, on the other hand, are believed to be made of closed strings that do not attach to membranes. Because their force is not localized to the membranes, they are able to float away and disperse, reducing their strength.

The problem of gravity is only one of the issues that string theory has theoretically solved.  It has also tackled problems associated with black holes and the expansion of the universe, but string theory still has a ways to go.

Currently, the ability to test the predictions from string theory is very limited and some have said that this roadblock is impossible to overcome.

Douglas thinks otherwise.

The next phase of this theory will likely take a lot of hard work and fresh ideas. String theory has made enormous strides in the relatively short amount of time that it has been around, and it is thought by many to be the most promising of the so-called “theories of everything.”

In a few more years, who knows what exciting advances could be in store?

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