Our gothic universe
||It's a dark, dark, universe out there…positively gothic. Ninety five percent of the universe is governed by dark matter and energy of which we know only a small amount.
This might shock you: All the stuff you've ever seen makes up a paltry five percent of the universe. And scientists don't have a definitive theory to describe the remaining 95 percent. We think that 95 percent is made of two mysterious substances - dark matter (23 percent) and dark energy (72 percent). Today's column focuses on the latter.
In 1998 and 1999, two collaborations were measuring how the expansion of the universe was changing. They expected to see that the expansion was slowing, based on this simple fact - gravity attracts. Throw a ball up and it slows and then falls back down. If you had Superman's arm, you could throw the ball hard enough for it to escape the Earth's gravity. But even in that case, the ball would slow down as it flew into space.
The expectation was the same with the expansion of the universe. Early in the history of the universe, the expansion was faster and gravity should have slowed it down in the intervening eons. Scientists were then shocked to find that the expansion of the universe wasn't slowing down. It was speeding up! Something was overcoming the force of ordinary gravity. What could that be?
Einstein added a cosmological constant to his equations of general relativity. The formulas said the universe should be expanding or contracting, and the new constant protected against a Big Crunch. When Edwin Hubble discovered in the 1920s that the universe was expanding, Einstein abandoned the cosmological constant and called it his biggest blunder.
With the observation of the speeding expansion of the universe, the cosmological constant was revisited. The idea is that the universe has an energy field throughout it with constant density. Cosmologist Michael Turner coined the term "Dark Energy" to describe this energy field.
Click here to read the expanded column on Dark Energy and current research into this phenomenon.
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