In the 1920s, Einstein’s general theory of relativity provided the best explanation of how our universe began. According to Einstein’s theory, the universe was born approximately 10 to 20 billion years ago in a gigantic explosion called the Big Bang. All the matter in the universe, including the stars, galaxies, and planets, was originally concentrated in one superdense ball, which exploded violently, creating our current expanding universe. This theory explains the observed fact that all the stars and galaxies are currently moving away from the earth (propelled by the force of the Big Bang).
However, there were many gaps in Einstein’s theory. Why did the universe explode? What happened before the Big Bang? Theologians as well as scientists have for years realized the incompletenessof the Big Bang theory, because it fails to explain the origin and nature of the Big Bang itself.
Incredibly, the superstring theory predicts what happened before the Big Bang. According to superstrings, the universe originally existed in ten dimensions, not the four dimensions (three space dimensions and one time dimension) of today. However, because the universe was unstable in ten dimensions, it cracked into two pieces, with a small, four-dimensional universe peeling off from the rest of the universe. By analogy, imagine a soap bubble that is vibrating slowly. If the vibrations become strong enough, the soap bubble becomes unstable and fissions into two or more smaller soap bubbles. Imagine that the original soap bubble represents the ten-dimensional universe, and that one of the smaller soap bubbles represents our universe.
If this theory is true, it means that our universe actually has a sister universe that coexists with our universe. It also means that the original fissioning of our universe was so violent that it created the explosion that we know as the Big Bang. The superstring theory, therefore, explains the Big Bang as a by-product of a much more violent transition, the cracking of the ten-dimensional universe into two pieces.
You do not have to worry, however, that one day as you are walking down the street you will fall into another other-dimensional universe as if in a science fiction novel. According to the superstring theory, the other multidimensional universe has shrunk to such an incredibly small size (about 100 billion billion times smaller than the nucleus of an atom) that it can never be reached by humans. Thus, it becomes an academic question what higher dimensions look like. In this sense, the prospect of traveling between higher dimensions was possible only at the origin of the universe, when the universe was ten-dimensional and interdimensional travel was physically possible.
In addition to multidimensional spaces, science fiction writers sometimes spice up their novels with talk of dark matter, a mysterious form of matter with properties unlike any found in the universe.
Dark matter was predicted in the past, but wherever scientiststrained their telescopes and instruments in the heavens, they found only the hundred or so familiar chemical elements existing on the earth. Even stars in the farthest reaches of the universe are made of ordinary hydrogen, helium, oxygen, carbon, et cetera. On one hand, this was reassuring; we knew that wherever we traveled in outer space, our rocket ships would encounter only the chemical elements found on the earth. On the other hand, it was a bit disappointing knowing that there would be no surprises in outer space.
The superstring theory might possibly change that, for the process of fissioning from a ten-dimensional universe down to smaller universes probably created a new form of matter. This dark matter has weight, like all matter, but is invisible (hence the name). Dark matter is also tasteless and has no smell. Even our most sensitive instruments cannot detect its presence. If you could hold this dark matter in your hand, it would feel heavy, but it would otherwise be undetectable. In fact, the only way to detect dark matter is by its weight: it has no other known interaction with other forms of matter.
Dark matter also may help to explain one of the puzzles of cosmology. If there is sufficient matter in the universe, then the gravitational attraction of the galaxies should slow down its expansion and even possibly reverse it, causing the universe to collapse. However, there is conflicting data as to whether there is enough matter in the universe to cause this reversal and eventual collapse. Astronomers who have tried to calculate the total amount of matter in the visible universe find that there is simply not enough matter in stars and galaxies to cause the universe to collapse. However, other calculations (based on calculating the red shifts and luminosities of stars) indicate that the universe might collapse. This is called the missing mass problem.
If the superstring theory is correct, then it may explain why astronomers fail to see this form of matter in their telescopes and instruments. Moreover, if the theory of dark matter is correct, dark matter may pervade the universe. (Indeed, there may be more dark matter than ordinary matter.) In this regard, the superstring theory not only clarifies what happened before the Big Bang but predicts what may happen at the death of the universe.