General relativity and quantum mechanics take different approaches at looking at how the universe works. Many physicists feel that there must be a method that unites the two. One contender for such a universal theory is superstring theory, or string theory, for short. Let's take a brief overview of this complex perspective.
One string, no particles
Children in elementary school learn about the existence of protons, neutrons, and electrons, basic subatomic particles that create all matter as we know it. Scientists have studied how these particles move and interact with one another, but the process has raised a number of conflicts.
According to string theory, these subatomic particles do not exist. Instead, tiny pieces of vibrating string too small to be observed by today's instruments replace them. Each string may be closed in a loop, or open. Vibrations from the string correspond with each of the particles and determine the particles' size and mass.
How do strings replace point-like particles? On a subatomic level, there is a relationship between the frequency at which something vibrates and its energy. At the same time, as Einstein's famous equation E=mc2 tells us, there is a relationship between energy and mass. Therefore, a relationship exists between an object's vibrational frequency and its mass. Such a relationship is central to string theory.
Limiting the dimensions of the universe
Einstein's theory of relativity opened up the universe to a multitude of dimensions, because there was no limit on how it functioned. Relativity worked just as well in four dimensions as in forty. But string theory only works in ten or eleven dimensions. If scientists can find evidence supporting string theory, they will have limited the number of dimensions that could exist within the universe.
We only experience four dimensions. Where, then are the missing dimensions predicted by string theory? Scientists have theorized that they are curled up into a compact space. If the space is tiny, on the scale of the strings (on the order of 10-33 centimeters), then we would be unable to detect them.
On the other hand, the extra dimensions could conceivably be too large for us to measure; our four dimensions could be curled up exceedingly small inside of these larger dimensions.
Searching for evidence
In 1996, physicists Andrew Strominger, then at the Institute for Theoretical Physics in Santa Barbara, and Cumrun Vafa at Harvard, simulated a black hole with an excessive amount of disorder, or entropy. Such a black hole had been simulated two decades earlier by physicists Jacob Bekenstein and Stephen Hawking. At the time, no one could figure out why a black hole might harbor so much entropy.
The theoretical black hole created by Strominger and Vafa was not created like conventional black holes seen at the center of galaxies such as the Milky Way. Instead, they relied on string theory to simulate it, providing a link between the complex theory and the fundamental force of gravity that drives black holes. By basing its foundation on string theory instead of conventional particles, they lent more credibility to the potentially unifying theory.
Whether string theory is the "ultimate" theory — the theory of everything — is unknown. But it is a strong contender for explaining the inner workings of the universe.