Does Dark Energy Exist?
his image of the Type 1a supernova remnant 0509-67.5 was made using data from NASA’s Hubble Space Telescope and Chandra X-ray Observatory. Analyses of Type 1a supernovae's motion through space has led astronomers to conclude that the universe’s expansion is accelerating, driven by a mysterious force called dark energy.

Credit: NASA, ESA, and B. Schaefer and A. Pagnotta (Louisiana State University, Baton Rouge); NASA, ESA, CXC, SAO, the Hubble Heritage Team (STScI/AURA), J. Hughes (Rutgers University)

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 SpacemanWe Don’t Planet, and COSI Science Now. Sutter contributed this article'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]