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Our universe is made up not only of stuff you can see, touch, taste and hear, but also something more dangerous. Something called dark energy is slowly pushing the entire fabric of the universe apart.
The Mystery of the Universe
For most of us, tiny sparks of light flying across the dark sky turn thoughts to the flittering flashes of fireflies on carefree summer nights. But astronomers might be reminded of one of the strangest forces in the universe — dark energy — which arises from tiny particles that seem to pop in and out of existence throughout space.
"Dark Energy is the greatest mystery in all of astronomy and physics," says physicist Michio Kaku, and author of "Parallel Worlds." "It holds within it the destiny of the universe itself,"
Astronomers studying distant exploding stars — supernovas — discovered that the universe is not only expanding, but also that this expansion is actually speeding up. While we now live under a sky full of stars, if we're still around tens of billions of years from now, the sky will seem dark and empty.
"We're trying to figure out what the universe is made of, which is important if you want to know where the universe came from and where it's going to go," says University of Chicago theoretical physicist Sean Carroll. He explains that this expansion of space appears to be the work of dark energy.
It appears to have all begun with the Big Bang — the giant fireball that gave birth to our universe. The blast generated so much momentum that it's driven the expansion of the universe for more than 14 billion years, but gravity has been working against the outward thrust, drawing gas into a vast web of matter where galaxies and stars are born. Astronomers have long believed that all that matter in the universe, and all the gravity it exerts, should slow the expansion down. With enough gravity the expansion could stop completely and then the universe would implode.
Studying the brightness of supernovas, the researchers expected to confirm that the expansion of the universe is slowing, but instead they found that it seems to be speeding up.
"If you wait longer and longer, each galaxy will be moving away from you faster and faster. There's nothing that we know of that would make that happen except for dark energy," says Carroll.
Albert Einstein first introduced the idea of dark energy in 1916, calling it "the energy of nothing." Kaku says, "He called it his greatest blunder. However, today we know that Einstein's greatest blunder holds within it the destiny of the universe itself."
Now, cosmologists have estimated that as much as 70 percent of the universe is dark energy, with only five percent being ordinary matter and the remaining 25 percent being dark matter — matter particles that can't be detected by the radiation they emit, but are found by the gravitational effect they have on visible matter such as stars and galaxies.
A still image from an animation of the universe just beginning to expand after the Big Bang. image: NASA/Space Telescope Science Institute
The idea of dark energy is simple, if unusual: a tiny amount of energy that exists in every region of space, throughout the roughly 100 billion galaxies that are known to be scattered across the universe, and even in regions that are completely devoid of matter and radiation. But wherever it's found, it's pretty much the same, throughout space and time — it is a cosmological constant.
But how could something that's invisible and nearly undetectable have such a profound effect on the fate of our universe?
"There's a little bit of it in every cubic centimeter, and there's a lot of cubic centimeters in the universe, so if you count the whole universe, the dark energy wins," says Carroll.
If dark energy wins out, all life will be doomed to "the big freeze," when stars blink out and temperatures plummet. "Dark energy is like anti-gravity, instead of attracting the galaxies it's pushing the galaxies apart. As a consequence it's causing the entire universe to blow apart. In other words the universe is spinning out of control," Kaku explains. "The universe is like a careening car, out of control expanding to the point that temperatures will eventually hit absolute zero and all intelligent life will cease."
Nevertheless, Kaku believes civilization may yet have a chance.
"Perhaps billions, trillions of years from now advanced civilizations will be able to punch a hole in space, leave our dying, freezing universe, and escape to a younger universe. And perhaps, just perhaps, start all over again," says Kaku.
For now, while astronomers still have many questions, dark energy is keeping most of its secret to itself.
More detailed studies with NASA's Hubble space telescope and future missions such as NASA's "Constellation X" should provide astronomers with more answers about dark energy and the fate of our universe.
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