Confirming the surprise: the many successes of dark energy
The idea that dark energy makes up 70% of the energy of the universe seems ludicrous at first sight (pun intended!). How is it that we’re so confident of so much that we cannot see?
CAASTRO Chief Investigator and “The Dark Universe” leader Professor Tamara Davis has run through all the many-varied ways in which we have now detected the influence of dark energy. Often the observations of supernovae in the late 1990s are touted as the big breakthrough that discovered that the expansion of the universe is accelerating. And indeed they were the first really decisive observations. However, the supernova discovery fell on fertile ground. There were already many simple hints that indicated dark energy should exist. Primary among them was that the universe appeared to be younger than the oldest stars – a problem for anyone who thought that the universe should be older than the things it contained! There were too many distant galaxies, and the curvature of the universe seemed all wrong. Acceleration (dark energy) fixed all of that. It makes the universe older than we thought, changes the volume so the number of galaxies is right, and flattens out the curvature.
Since the supernova results brought dark energy to the fore, the course of cosmology has changed, and over the last 16 years an enormous amount of effort has gone into testing dark energy in every way we could conceive. We have observed light from just after the big bang (the Cosmic Microwave Background or CMB), measured the distribution of galaxies across billions of light years, detected sound waves from the big bang (yes, there was once sound in space!), measured the motion of hundreds of thousands of galaxies, detected light being bent by the gravitational field around galaxy clusters, seen galaxy clusters collide, watched time running more slowly in the distant universe (time dilation), and much, much more! Every single one of these observations confirms that dark energy exists… Our challenge, now, is to explain what the dark energy is!
Tamara Davis in General Relativity and Gravitation (2014): “Cosmological constraints on dark energy”