Nobel Prize: Our Expanding Universe

This year, the Nobel Prize for Physics went to three American scientists for their discovery in 1998 that the universe is not only expanding, but expanding at an accelerating speed.

The winners, Saul Perlmutter, Brian Schmidt and Adam Riess were studying and observing distant supernovae far from earth, much older than our sun. Expecting to find evidence to help confirm the theory that the universe's expansion was slowing down due to gravity, they actually found the rate at which the universe is expanding is increasing.

The Nobel laureates and another group working on a very similar project in Australia also discovered that there appears to be massive amounts of "dark energy" in the universe, holding galaxies together.

Many scientists theorize that dark energy is what is driving the acceleration of the universe. Dark energy has never been directly observed, measured or tested, yet it appears to account for 72 percent of the mass-energy of the universe.

If dark energy really is driving the acceleration of the universe, then it is highly possible the universe will end with the Big Rip. In tens of billions of years, dark energy may drive everything apart at the atomic level, effectively ending the universe. But many scientists refute that scenario.

Dark energy is a very new idea, and it's true nature is unknown. It has also been suggested dark energy may simply be an illusion that could be caused by several things.

Much about dark energy is not known, so it is still possible the universe will one day slow down and begin to recede. If the universe recedes, gravity will pull everything together, in a phase called the Big Crunch. The Big Crunch phase may end with another Big Bang, suggesting a never-ending universe.