Cosmo FAQ

Frequently asked, and infrequently answered questions about dark matter, dark energy, astrophysics and all manner of cosmological phenomena.

What is Dark Matter?

Dark Matter is a type of substance made of particles that are able to attract objects to themselves through gravity, when they are added up in bulk. In this arena, it acts in the same way that the Sun does when it attracts the planets. But, unlike the Sun, it does not shine. As far as we can tell this type of matter gives off no electromagnetic radiation at all, hence we call it “dark”. We know it exists because we can track its gravitational pull in our own Galaxy and in distant galaxies, but we still don’t know what type of substance it is.

What is Dark Energy?

Currently this is a mystery. This mystery is what motivated the Dark Energy Survey project. Even though we don’t know what Dark Energy is, we know what it does: it make the expansion of the Universe speed up. If you think of the rate of expansion as the speed of a car – the car was slowing down for about 8 billion years and then “someone” put their foot on the “accelerator” and it started speeding up again. So, for the last 6 billion years the Universe has been getting bigger at an ever increasing rate.

Current estimates are that 70% of the matter-energy budget of our Universe is in the form of Dark Energy. Most of the rest is in the form of Dark Matter.

What is the Dark Energy Survey?

It is a project to make a map of a large part of the night sky. The map will be very detailed and will allow scientists to find hundreds of millions of galaxies that have never been seen before. One of the primary purposes of the survey is to study how the Universe has changed over the last 14 billion years. The survey is being carried out from a mountaintop in Chile using a 4 metre telescope and the world’s largest digital camera.

The project is a collaborative effort of over 300 scientists from 25 institutions in 7 countries. We are using four different techniques to study Dark Energy: Supernovae, the spatial distribution of galaxies, Galaxy Clusters, and Weak Gravitational Lensing. The project started over 10 years ago. Once the camera, and other optical elements, had been built and shipped to Chile, DES started taking images of the sky, and has been doing so since August 2012. It will take until 2018 before all the data have been collected.

Why is the experiment in Chile?

Because the Chilean Andes are a great location for telescopes: they are extremely high and dry with some of the least precipitation in the world, and the place DES is located is very remote from towns (hence minimizing light pollution).

Are Dark Matter and Dark Energy related to each other?

Not as far as we know. It would be nice if they were two sides of the same coin, because then Physicists would only have to come up with one theory that would cover both. But it doesn’t seem as though that is the case. They do different things to the Universe: dark matter slows down the expansion rate, dark energy speeds it up. The history of Universe is very much dependent on both the amount of dark matter and the amount of dark energy (oddly, so far as we can tell currently, the history doesn’t depend all that much on what dark matter and dark energy are).