Dark Energy

Question: Can you help me understand dark energy?

Answer:

I can try - but that's a tough one!

Edwin Hubble discovered around 1930 that Galaxies are moving away from each other. The further apart they are, the faster their relative velocity - implying that the Universe itself is expanding. This expansion is believed to have started with the Big Bang, 14 billion years ago. Gravity acts against this expansion and so, depending upon the amount of matter in the Universe, we would expect the expansion to eventually slow down, or even stop. In the 1990s, observations of very distant supernova explosions were used to show that the expansion rate is not slowing at all - rather, it's speeding up!

Something has to be providing the push and causing this acceleration - that "something" is what's referred to as dark energy. There are different theories as to what it might be: maybe a new force, or particle, or a property of space itself. There are many projects in the works to provide better measurements and more insight into the problem (including space missions like WFIRST and JWST, and ground-based telescopes like the LSST), but for now, the true answer is really a mystery.

-Jamie Holder