Jimmy Westlake: The dark side of the universe
March 22, 2011
Steamboat Springs — Did you know the universe has a dark side? You're probably more familiar with the bright side of the universe — the part we can actually see. But like an iceberg that shows only 10 percent of its mass above the water, the universe reveals only 4 percent of its total mass and energy in the form of visible matter that gives off light.
The visible stuff in the universe makes up the familiar planets, stars and galaxies that we see in space. The remaining 96 percent is invisible and its exact nature is unknown. Let me emphasize that last statement: We do not know what 96 percent of the universe is made of. If that seems a little weird, don't feel alone. Astronomers find it very weird, too, and they're looking at any and all possibilities, no matter how bizarre, to explain the dark 96 percent of the universe.
Ordinary matter, the stuff that you, I and the stars are made of, is called baryonic matter because it is made of baryons. The current Big Bang theory of the origin of the universe places constraints on the amount of baryonic matter that can exist. The bottom line is that there is way too much dark matter in the universe to be accounted for by dim baryonic things like planets, faint stars, black holes and gas between the stars. Dark matter has to be made of something other than the familiar forms of baryonic matter. It must be made of something much more exotic. What could it be?
Astronomers' favorite candidates are neutrinos and WIMPS. Neutrinos are ghost-like particles that are produced in huge numbers by ordinary stars like the sun. There are trillions of neutrinos passing through your body and the Earth each second. They interact so poorly with baryonic matter that they could pass clean through a wall of lead 30 light years thick like it wasn't even there. Each neutrino has the tiniest amount of mass, but they might be present in large enough numbers that their total mass could account for much of the dark matter in the universe.
WIMPS, or Weakly Interacting Massive Particles, are hypothetical — massive particles that so far have eluded detection. But, then, if they interact so very weakly with ordinary baryonic matter, it shouldn't be surprising that we haven't yet snagged one. They can zip right through any trap we set for them. If WIMPS do exist, they might exist in such large numbers that they also could account for much of the dark matter in the universe.
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Now it gets even weirder.
American astronomer Edwin Hubble discovered that the universe is expanding in all directions back in the 1920s. This led to the idea that the universe began with a colossal explosion of space at the beginning of time called the Big Bang. Astronomers always assumed that the combined gravity of all of the matter in the universe pulling on itself would slow down the expansion and maybe even grind it to a halt. Some even speculated that the universe might one day come crashing back down on itself, ending in a Big Crunch.
All that changed in 1998 when two different teams of astronomers, working independently, stumbled upon the same unbelievable discovery: the expansion of the universe is not slowing down as expected, but is accelerating and expanding faster and faster as time goes on. How can this be? It's as if some form of dark energy is pushing the contents of the universe apart and speeding up the expansion. What this dark energy is is anybody's guess, but it behaves like an antigravity force.
The best breakdown we can make today of the contents of the universe looks like this: 4 percent of the universe is made of ordinary atoms of baryonic matter; 21 percent is some form of exotic dark matter like neutrinos or WIMPS; and a whopping 75 percent is something that makes up the dark energy. It's a little bit humbling to realize that we don't know what 96 percent of the universe is made of.
Want to learn more about the dark side of the universe? The SKY Club, the student astronomy organization at Colorado Mountain College's Alpine Campus, hosts a free public program at 7 p.m. Wednesday in the library in Bristol Hall. I will present a special program entitled "The Dark Side of the Universe." Telescope observing will follow the indoor program. For more information, call me at 970-870-4537.
Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. He is an avid astronomer whose photographs and articles have been published all around the world. Check out Jimmy's website at http://www.jwestlake.com.