The dark side of The Universe
There is a lot of ‘stuff’ in our universe: just five percent of it is the normal matter we’re used to – the matter that makes up you and me, the planets and the stars. Twenty-seven percent of it is ‘dark matter’, found in the midst of our galaxies, and the rest is known as ‘dark energy’.
Both dark matter and dark energy are barely detectable. So how do we know about them? In 1978, astronomers set out to measure the mass of several spiral galaxies and found that the mass of these galaxies was much greater than the mass of the visible stars and gases alone. It is this missing matter that we call dark matter. On the other hand, dark energy is invoked to make sense of our expanding universe. In 1929, when Edwin Hubble discovered that our universe is expanding, scientists guessed that the rate of expansion would be decreasing over time, slowed down by the pulling effect of gravity. However, in 1998, cosmologists discovered that that our universe is actually expanding at an accelerating rate. This indicated the existence of something driving the expansion, counteracting the effect of gravity, and it is this that we call dark energy.
Because dark matter and dark energy are barely detectable, we know very little about them. In the current standard model of cosmology, it is assumed that the amount of dark energy in The Universe is constant, an assumption that has correlated reasonably well with observations, until recently.
Earlier this year, researchers from the University of Portsmouth and the University of Rome found evidence to suggest that the amount of dark energy in The Universe is in fact increasing, and they suggest that it may be increasing by feeding on dark matter. Their research appeared in Physical Review Letters. Professor David Wands, a member of the research team, says: “it appears that the standard model is no longer sufficient to describe all of the data. We think we’ve found a better model of dark energy.”
If this model turns out to be correct, it has big implications on the fate of our universe. Professor Wands explains: “Dark matter provides a framework for structures to grow in the universe…if dark energy is growing and dark matter is evaporating we will end up with a big, empty, boring universe with almost nothing in it.”
There is much more work to be done before this can be considered a solid result, and indeed there is a long way to go until we really understand what dark matter and dark energy are. But what we can be sure of is that, though we can barely detect them, dark matter and dark energy are fundamental to our understanding of cosmology and key to the way our universe works.
Image: ‘Space’ by Sweetie187 under creative commons license