SALT LAKE CITY — One can only shed a little light on dark matter and dark energy: even scientists have no idea what they are; they only know what they do.

In a nutshell, dark energy seems to be the fuel that’s powering the expansion of the universe. But beyond that, scientists know absolutely nothing else about it.

Dark energy likely does other things too, but since it’s such a newly discovered phenomenon, scientists don’t yet know what those other things might be, writes researcher Brian Schmidt.

Schmidt, an astronomer at the Australian National University in Canberra, discovered dark energy in 1997 while he was observing the far edges of the universe. He expected to see that the expansion of the universe at that distance would be slowing down. Instead he saw that it was accelerating.

Schmidt, who won a share of the 2011 Nobel Prize in physics for his discovery, thought the universe’s expansion would be slowing down at its edges because it was farther from the center of the Big Bang and gravity had had longer to work.

The universe is full of matter, which is all gravitationally attracted to other matter. With all that matter being attracted to each other, theoretically, the expansion of the universe should be slowing down and eventually reach a point that it stops expanding and maybe even collapses, Schmidt writes.

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Utah dark energy study hints at the end of the universe

Will it die with a bang or a whimper? Will the universe eventually collapse into a "Big Crunch," a fateful inverse of the "Big Bang"? Or will it expand forever until it leaves a void that is dark, lonely and astonishingly vast?

But this isn’t happening.

An early explanation for why the expansion of the universe was accelerating at its distant edges was that matter was being diluted as it spread, and since that matter's gravitational pull would be diluted too, the expansion wouldn't be slowed as much by gravity. But this was soon proved not to be the case, says Pearl Sandick, professor of physics and astronomy at the University of Utah, who specializes in dark matter and dark energy.

Not only was the universe's growth not slowing down at its edges, it was accelerating at a higher rate, as if it were being fueled by something, a concept supported by observation and mathematical models. Scientists began referring to this mysterious "something" as dark energy, and the name stuck. The "fuel" could just have easily have been named Energy X, or Mystery Space Energy.

Even after it had been given a name, the existence of this new concept only led to more questions. Whatever dark energy is, shouldn’t it too get diluted as the universe expands? And as a result, shouldn’t the expansion of the universe slow down? Maybe not.

Einstein theorized that dark energy is the very property and product of space, so that as the universe expands it actually creates more dark energy, which then continues to fuel the expansion of the universe. (Geez, is there anything that Einstein didn't think of?)

Sandick's take on this mysterious material is that we know more what dark energy does, rather than what it is.

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If you are a total geek/nerd like the author, then you'll know that the universe of the Lord of the Rings was created by ancient gods and demigods performing music together in harmony.

Observing how dark energy works is similar to watching leaves blow on a tree. Once one discovers the leaves don't move of their own accord, one can theorize they move because another force is acting on them. Even though no one can see the wind, everyone can observe its effects.

With this discovery, suddenly, astronomers and theoretical physicists were surprised to find they have the same problem explaining dark energy as believers have explaining God. A believer can’t point to God as proof; he can only point to various phenomena that seem to indicate God is acting on them. Now scientists, unable to point to dark energy, can only point to certain phenomena and mathematical models and say, “These are caused by dark energy.”

Basically, in a plot right out of “The Hitchhiker’s Guide to the Galaxy,” science had discovered the answer, without knowing what the question was. So now theoretical physicists and astronomers have the rare but delicious task of knowing what something does and reverse-engineering it until they figure out what it is. And what to a scientist could be more intriguing than that?

In future years, after scientists have figured out what dark energy is, they will also investigate what else it might be doing, or what it might be harnessed to do. If it can power the expansion of the universe, what else can it power?

Even though theorists can’t tell us now what dark energy is, they can tell us how much of it there is, due to its observable signatures — about 68 percent of the universe is made up of the mystery material.

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What happens to a galaxy when it gets older? Much like the rest of us, it gets a little fat around the belly. That's what University of Utah astronomers have been studying by looking far into the universe's past in order to see the future of many galaxies.

They also know that dark matter makes up roughly 27 percent of the universe. Everything else — all observable matter such as stars, planets, asteroids, comets — makes up less than 5 percent of the universe.

So what is the difference between dark energy and dark matter? Like dark energy, scientists know more about what dark matter is not than what it is. “We can’t be certain yet whether or not (dark matter and dark energy) are related,” says Sandick, “but they are two fairly different phenomena.”

A big reason scientists can “observe” dark matter is that it behaves like visible matter, Sandick says. Dark matter is a gravitating substance that helped structures clump together and form in the early universe.

So even though dark matter isn’t itself observable, its gravitational effects on other matter are observable. When scientists see matter clumping and gravitating together with greater attraction than it should have, they can deduce than dark matter is present and contributing to the gravitational influence.

Dark matter is not made of the same components as visible matter, or normal matter, which is made up of baryons. The most common theory is that dark matter is formed from more exotic particles like axions or WIMPs (weakly interacting massive particles).

If you have a science subject you'd like Steven Law to explore in a future article send him your idea at curious_things@hotmail.com.

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