Some scientists go way beyond asking about other forms of life, though. Certain scientists have theorized that there may be another universe out there right alongside ours. Some believe there could be an infinite number of such universes, which they call parallel universes.

Could this be true? Could there be another version of you out there somewhere who exists in your future or your past? Those who think about parallel universes believe our universe may be just a branch on a tree of universes that all exist simultaneously — only in different states of time with different pasts and different futures.

It sounds like the stuff of science fiction novels and movies, doesn't it? There have certainly been enough of those over the years to twist the minds of readers and viewers everywhere. But is the idea of a parallel universe just make-believe?

The idea of parallel universes dates back to 1954, when Hugh Everett III, a Princeton University student, developed the bold idea that parallel universes — exactly like and related to our universe — exist. These parallel universes branch off from ours, and our universe branches off from others.

In parallel universes, the world wars might have different outcomes. Species, such as dinosaurs, might have lived in certain parallel universes. Indeed, humans themselves might have become extinct in certain parallel universes!

Does this sound a bit far-fetched to you? Why would a young scientist propose such a radical idea? Everett's Many-Worlds Theory, as it came to be known, was his attempt to answer some unanswered questions raised by the results of experiments performed in the growing field of quantum physics.

Quantum physics is the study of the quantum level, which is the smallest level scientists have detected so far. Quantum matter, which exists on the subatomic level, appears to behave erratically at times, which has led scientists to believe there are other scientific laws at work that we don't yet know about.

For example, scientists studying quantum matter soon realized that quantum particles, such as photons, seem to take different forms arbitrarily. Scientists who observed photons noticed that sometimes they acted like particles and at other times they acted like waves. That's like you being a solid human being one minute and a gas the next! Scientists call this phenomenon the Heisenberg Uncertainty Principle.

Physicist Werner Heisenberg theorized that we affect the behavior of quantum matter simply by observing it. Another physicist, Neils Bohr, agreed. He believed that quantum particles exist in all possible states at once. When we observe them, we affect their behavior, forcing them to choose one state at that moment in time.

Everett's Many-Worlds Theory is an alternative to Bohr's view of quantum matter. According to Everett, observing quantum matter causes an actual split in the universe rather than a choice of one state over another. The universe literally duplicates, splitting into multiple parallel universes for each possible state of the quantum matter.

The Many-Worlds Theory has some implications that disturb some scientists. For example, if you've ever encountered a situation in which one possible outcome was death, then by Everett's theory there exists a parallel universe out there in which you died! Many people also dislike Everett's theory because it conflicts with our basic understanding of the concept of time.

Everett's theory was considered far-fetched for many years, but recently scientists have become interested in it again, due to the fact that some scientists conducted thought experiments that seemed to show that Everett's theory is theoretically possible.

Interestingly, Everett's theory is not the only alternative theory that attempts to explain quantum mechanics. Another theory, known as String Theory, claims that there exist particles even smaller than quantum matter. String Theory also claims that parallel universes can exist.

So who knows? Maybe there are parallel universes out there! Maybe you'll grow up to study quantum physics one day and answer all of these questions the world wants to know!