Paul Sutter is an astrophysicist at The Ohio State University and the chief scientist at COSI Science Center . Sutter is also host of Ask a Spaceman , We Don’t Planet , and COSI Science Now . Sutter contributed this article to Space.com’s Expert Voices: Op-Ed & Insights .
Newsflash: the universe is expanding . We’ve known that since the pioneering and tireless work of Edwin Hubble about a century ago, and it’s kind of a big deal. But before I talk about dark energy and why that’s an even bigger deal, I need to clarify what we mean by the word “expanding.”
The actual observation that you can do in the comfort of your own home (provided you have access to a sufficiently large telescope and a spectrograph) is that galaxies appear to be receding from our own Milky Way. On average, of course: galaxies aren’t simple creatures, and some, like our a-little-too-close-for-comfort neighbor Andromeda, are moving toward us. [The Universe: Big Bang to Now in 10 Easy Steps]
This recession is seen in the redshifting of light from those galaxies. The fingerprint frequencies of certain elements are shifted down to lower frequencies, exactly like they are for the Doppler effect. But to explain the cosmological observations as a simple Doppler shift requires a few head-scratching conclusions: 1) We are at the center of the universe; 2) Galaxies have preposterous mechanisms that propel them through space; and 3) The universe conspires to make galaxies twice as far away from us move exactly twice as fast.
That seems like a bit of a stretch, so astronomers long ago reached a much more simple conclusion, one powered by the newfangled general theory of relativity : the space itself between galaxies is expanding, and galaxies are just along for the ride.
Edwin Hubble established the expansion of the…