Dr. Michio Kaku, the originator of string theory Ted Thai/Time Life Pictures/ Getty Images

The Many-Worlds theory and the Copenhagen interpretation aren't the only competitors ­trying to explain the basic level of the universe. In fact, quantum mechanics isn't even the only field within physics searching for such an explanation. The theories that have emerged from the study of subatomic physics still remain theories. This has caused the field of study to be divided in much the same way as the world of psychology. Theories have adherents and critics, as do the psychological frameworks proposed by Carl Jung, Albert Ellis and Sigmund Freud.

Since their science was developed, physicists have been engaged in reverse engineering the universe -- they have studied what they could observe and worked backward toward smaller and smaller levels of the physical world. By doing this, physicists are attempting to reach the final and most basic level. It is this level, they hope, that will serve as the foundation for understanding everything else.



Following his famous Theory of Relativity, Albert Einstein spent the rest of his life looking for the one final level that would answer all physical questions. Physicists refer to this phantom theory as the Theory of Everything. Quantum physicists believe that they are on the trail of finding that final theory. But another field of physics believes that the quantum level is not the smallest level, so it therefore could not provide the Theory of Everything.

These physicists turn instead to a theoretical subquantum level called string theory for the answers to all of life. What's amazing is that through their theoretical investigation, these physicists, like Everett, have also concluded that there are parallel universes.

String theory was originated by the Japanese-American physicist Michio Kaku. His theory says that the essential building blocks of all matter as well as all of the physical forces in the universe -- like gravity -- exist on a subquantum level. These building blocks resemble tiny rubber bands -- or strings -- that make up quarks (quantum particles), and in turn electrons, and atoms, and cells and so on. Exactly what kind of matter is created by the strings and how that matter behaves depends on the vibration of these strings. It is in this manner that our entire universe is composed. And according to string theory, this composition takes place across 11 separate dimensions.

Like the Many-Worlds theory, string theory demonstrates that parallel universes exist. According to the theory, our own universe is like a bubble that exists alongside similar parallel universes. Unlike the Many-Worlds theory, string theory supposes that these universes can come into contact with one another. String theory says that gravity can flow between these parallel universes. When these universes interact, a Big Bang like the one that created our universe occurs.

While physicists have managed to create machines that can detect quantum matter, the subquantum strings are yet to be observed, which makes them -- and the theory on which they're built -- entirely theoretical. It has been discredited by some, although others believe it is correct.

So do parallel universes really exist? According to the Many-Worlds theory, we can't truly be certain, since we cannot be aware of them. The string theory has already been tested at least once -- with negative results. Dr. Kaku still believes parallel dimensions do exist, however [source: The Guardian].

Einstein didn't live long enough to see his quest for the Theory of Everything taken up by others. Then again, if Many-Worlds is correct, Einstein's still alive in a parallel universe. Perhaps in that universe, physicists have already found the Theory of Everything.

For more information on parallel universes, visit the links that follow.