Dark energy gets attention from Nobel Prize in Physics

*picture from NASA

Three American-born physicists won the Nobel Prize in Physics on Tuesday. Thirteen years ago they first made the startling announcement that the universe is expanding at an accelerating rate. They made the discovery by measuring the brightness of type 1a supernovae, explosions of small stars known as white dwarfs that can outshine an entire galaxy and can radiate as much energy as our sun will in its entire lifetime. The measurements showed that the supernovae were dimmer than what was expected, suggesting that galaxies were moving apart at an increasing rate.

At the time scientists were skeptical of the results – the prevailing view was that the universe was slowing down in its expansion. Yet two teams in competition with each other (one led by Saul Perlmutter of the Lawrence Berkeley National Laboratory, and the other headed by Brian Schmidt of the Australian National University in Canberra and Adam Reiss of the Space Telescope Science Institute and Johns Hopkins University) used independent lines of evidence to reach the same results.

The Nobel Prize brings attention to the study of a mysterious component of the universe called dark energy.


What is dark energy?

The simple answer: we don't really know, but physicists believe that dark energy is the “thing” that causes the universe to accelerate in its expansion. It's a little unbelievable that dark energy makes up about 73% of the universe, and yet we know so little about it. There are three properties to note. First, look at the name: dark. It is 'dark' because we don't see it; we do not observe dark energy interacting with matter at all. Second, it is smoothly distributed. The density of dark energy is uniform throughout space. And third, it is persistent. Unlike particles of matter, dark energy doesn't cluster together or dilute away.

The difference between dark energy and dark matter

Dark energy is not the same thing as dark matter. Again, look at the name. Dark energy is energy – it doesn't consist of particles. Dark matter consists of particles of matter. Physicists think it's there but they have yet to directly detect the particles.  However, they have observed gravitational influences (in settings like galaxies, clusters, large-scale structure, and microwave background radiation) that they attribute to clusters of dark matter.

Dark matter makes up about 23% of the universe. Actual matter – the stuff that the Earth is made up of, and the stuff that you and me interact with on a day-to-day basis – makes up less than 5% of the universe. Crazy.

More to come soon...