Yesterday there was a news conference at NASA about something called “dark energy.” What is this stuff? Well, strictly speaking it’s not matter. It’s a force. We’re all familiar with the force of gravity, which acts to hold things together, particularly at the atomic level. Across huge distances — and I’m talking big ones, like between galaxies and clusters of galaxies (what astronomers like to refer to as “cosmic” distances”), gravity is part of a complex dance that warps galaxies that pass too close and keeps members of a cluster more or less together. Important stuff, this gravity. We all know that the universe has been expanding since the Big Bang, about 13.7 billion years ago. Everybody just assumed that gravity would have some effect on this cosmic expansion, maybe even slow it down.
Such a gravitational braking force would affect light from distant objects, and people who study shifts in the wavelengths of light from very distant stellar explosions called Type Ia supernovae though that they’d see the slowing effect of gravity in the spectra (the minute details of the light) of the supernovae. Turns out they didn’t. In fact, what they DID find is that the expansion of the universe is speeding up! Something is accelerating the expansion and this speed-up started about 5 billion years ago — roughly about the time our Sun and planets were forming.
That “push apart” force is called “dark energy.” It’s a lousy name for a factor that Albert Einstein postulated way back in the early years of the 20th century. He couldn’t believe it existed and so he discarded it. In retrospect that doesn’t look like a good move on Einstein’s part, but hey — you have to admit it does seem a little strange to have something mysterious out there pushing the galaxies apart faster than gravity can hold them together.
Now, this dark energy doesn’t act on something as small as our planet or you and me — like gravity at cosmic scales, it acts across cosmic distances. So, I wouldn’t worry too much about the solar system flying apart or the Milky Way doing something brash like sending the Orion Arm on over to Andromeda for a friendly visit. It doesn’t work that way. The full extent of dark energy’s influence will echo across time for another 30 billion years or so, if it continues pushing at its presence pace.
It’s not really a big thing to worry about personally, but as part of the puzzle that is our universe — and while we understand much about the cosmos, we certainly don’t have a handle on all of it — it certainly does pose a tantalizing new piece for scientists to chew over as they push the limits of our telescopes back to the earliest epochs of history. Keep your ears open for more on this dark energy stuff — and don’t believe anybody who tells you it’s a fantastic new source of energy for perpetual-motion machine. That’s woo-woo territory…
A short programming note: I’d like to direct your attention to the link I added for Gemini Observatory over in my links column on the left. I’ve been doing some work with the fine folks there and I thought you might like to see some of the good astronomy they’ve been doing with their telescopes at Mauna Kea and Cerro Pachón in Chile. Give ’em a visit and see what’s new at Gemini!
