Dark Matter, Dark Energy: The Dark Side of the Universe

Everything we can see with our eyes and with powerful instruments-everything we think of as atom-based matter-is only 5 percent of what we know exists. The rest of the contents of the cosmos is invisible to our current methods of detection-but something out there is holding galaxies and galaxy clusters together, and something else is causing space itself to fly apart. These invisible components are dark matter and dark energy, the most eagerly studied subjects in astronomy and particle physics today.