Billions of years ago the Big Bang sent everything flying apart. In theory, gravity should stop galaxies from moving apart and matter should eventually re-collapse on itself. Surprisingly, we have learnt that galaxies are actually moving apart with ever-increasing speed. Nothing in our current knowledge of physics can explain this, but theorists are developing a solution: dark energy. Roughly 70% of our universe is comprised of dark energy and yet very little is known about it. I will describe what we currently know about the nature of dark energy, how it affects other matter in the universe, and what plans we have for observing this mysterious force.