Just a few minutes before I wrote this blog entry, NASA concluded a press conference to announce further evidence for dark energy — the mysterious whatever-it-is that is causing cosmic expansion to accelerate.

A team of astronomers using the Hubble Space Telescope has found a couple dozen additional Type Ia supernovae, explosions of white-dwarf stars that have relatively similar characteristics. Scientists use these extremely luminous events to look backward in time to map the universe's expansion history. The new supernovae were seen so far back in time that astronomers could map how fast the universe was expanding in it is youth.

There are a lot of things out there in the universe that the human mind has a difficult time grasping. Based on conversations with many amateur astronomers and S&T readers, dark energy is probably near the top of the confusion scale. I get the sense that many astronomy aficionados don't really understand it (the same could be said for many scientists!), and are by no means convinced that it actually exists.

But anyone interested in how the universe works should give the current cosmological paradigm a fair hearing. For example, the results announced today are exactly what astronomers expected, and to be honest, they didn't really tell us anything that scientists didn't already know, or what S&T hasn't covered in recent issues (such as Anthony Aguirre's cover story in the December 2006 issue). But they add one more link in the solid chain of impressive evidence built up over the past few decades that the universe experienced an explosive growth spurt in its youth, then began decelerating due to the gravitational attraction of matter, and is now in a second (and perhaps permanent) epoch of accelerated expansion because there is an unidentified energy source, called dark energy, that is acting like an antigravity force.

This standard cosmological model is extremely well supported by high-quality observations from many independent techniques: mapping the hot and cold spots in the cosmic microwave background, seeing how galaxies cluster together on large scales, observing the X-ray properties of galaxy clusters at different distances, and observing Type Ia supernovae. All of these results are consistent with one another and they tell a consistent and compelling story. The theory behind them continually makes accurate predictions of future observations. That's the hallmark of a mature science, and it's this self-consistency that explains why the overwhelming majority of cosmologists embrace this picture.

This is not necessarily the universe that scientists wanted to uncover, and I don't get the impression it's what the public wanted either. But science has taught us over and over again that the universe is under no obligation to conform to human expectations or desires. Heck, I would prefer not to have shared a common ancestor with a gorilla, but the evidence is overwhelming that I do, so I accept it and marvel at nature's ingenuity and creative force operating over enormous timescales. The universe is what it is, and it's science's job to figure it out, whether we like the results or not.


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