Imagine if someone could come up with a theory for everything. A single, unifying theory that would explain anything: from erratic Baltimore weather to the basis of human emotion. This might seem improbable to some, but not to avid proponents of intelligent design.
However, in the realm of physics, research on such overarching theories, called Theories of Everything (TOE), is quite common. In fact, such theories are an area of research by Dr. Raman Sundrum, a professor at he Johns Hopkins physics department.
By combining theoretical physics and mathematics, TOEs attempt to explain the basis of molecular interactions in the universe. According to modern physicists, TOEs should attempt to explain the four fundamental interactions of nature: gravity, electromagnetism, weak nuclear force and strong nuclear force.
TOEs attempt to provide an overall theory that explains all physical phenomena.
A popular modern TOE is string theory. According to string theory, every particle in the universe is made up of infinite, vibrating strings rather than discrete points. In other words, if the fundamental particles that have been discovered, electrons, neutrinos, quarks, etc. were broken apart, we would find that tiny oscillating strings comprise these particles.
Albert Einstein was one of the earliest physicists who attempted to develop a TOE. According to Newtonian ideas, gravity was the force guiding the movement of matter in the universe. Einstein's general theory of relativity transforms the idea of space from the Newtonian definition.
In the Newtonian model, space is passive and the active force guiding particle movement is gravity. However, according to Einstein's general theory of relativity, space becomes a new dimension known as spacetime, through which matter and energy can move. Spacetime is four-dimensional, and Einstein's theory states that it curves around any mass or energy. In essence, this curving is what drives the motion of matter and energy through spacetime.
Stanford University's Gravity Probe Web site provides the following example: "The massive Sun curves spacetime around it, a curvature that reaches out to the edges of the solar system and beyond. The planets orbiting the Sun are not being pulled by the Sun; they are following the curved spacetime deformed by the Sun."
Sundrum indicates that the idea of curved spacetime makes it natural to discuss the existence of extra dimensions. If you imagine flat spacetime folding to form two dimensions around matter, it makes sense that extra dimensions exist. According to Sundrum, "If you think about a straight line, it makes sense that it is one dimensional, that is widely accepted. But, it has another dimension in that it is infinitely long, unlike a circle, which comes back upon itself."
The existence of extra dimensions is not intuitive to most people because, as Sundrum says, "they are as real as atoms. If you could miniaturize yourself, or if you had a very high-power microscope, you would be able to see them." These extra dimensions are believed to exist as microscopic circles that fold back on themselves.
Sundrum and Dr. Lisa Randall, a physics professor at Harvard University, used this idea of extra dimensions to solve what is known as the hierarchy problem of physics. Namely, there are fundamental constants of physics (speed of light, Newton's gravitational constant and Fermi constant for the weak nuclear interaction). However, Newton's constant and Fermi's constant are measured in units of area, unlike the speed of light, and they differ by a factor of 1030. This poses a problem because it has been shown that on the very microscopic level of quantum mechanics, particles tend to equalize these extremely different constants.
Sundrum and Randall investigated how it could be possible for particles to equate these two constants that differed at such high order of magnitude. According to the their model, the solution resided in Einstein's model of curved spacetime. If spacetime is curved, then the rules of geometry are altered in this warped dimension.
According to Sundrum, the difference in magnitude arises from the fact that the graviton (particle involved in mediating gravitational force) and the exposon (related to Fermi constant) live in very different areas. The radical difference in magnitude thus becomes a geometrical effect of the curved spacetime. The reason for the high difference in magnitude between Newton's constant and the Fermi constant is the fact that they are separate dimensions.
Sundrum explains this effect with an analogy. "It's like the old parable of the king who offered a poor subject who had pleased him with a gift of his choosing. The subject says, 'All I want is a chess board with rice. Just put one piece of rice on the first square and then double it on each subsequent square.' The irony of this story is that the amount of rice becomes immense at the end because of exponential doubling.
"This idea of exponential increase explains the order of magnitude difference between Newton's constant and the Fermi constant," he added. This difference also explains the weakness of the gravitational force compared to other natural forces.
The important aspect of Sundrum's and Randall's work is that they used the idea of extra dimensions inherent in theories of everything to elucidate an actual physical phenomenon. Sundrum says, "String theory has many, many possible manifestations and we are not sure which manifestation pertains to the world we live in," Sundrum added.
String theory has a lot of qualitative insight, but does not offer much quantitative insight. It puts forth the principles but everything else behind it remains to be derived. We took a specific quality of string theory and it motivated us to find a qualitative, new idea."
The theory proposed by him and Randall, has encouraged string theorists to go back and work the ideas they proposed into the model of string theory. Sundrum says, "Our construction was very in line with a lot of things inherent in string theory. The very fact that we did it gave the idea that you could study something like string theory, a theory of everything, in a very simple way."
