Does Dark Energy really Exist?

For the past twenty years the greatest mystery in all of Science has been the Nature of Dark Energy, a unknown force that is accelerating the expansion of the Universe and whose energy makes up more than three quarters of everything there is. Now a new study by Cosmologists J.T.Nielsen, A. Guffanti and S. Sarkar has called into question the very existence of Dark Energy.

To understand what is going on we have to go back to 1929 when astronomer Edwin Hubble discovered that the galaxies he was studying were all receding from our milky way and that the further a galaxy was the faster it was receding. This is Hubble’s law for the expansion of the Universe and the rate of expansion is called Hubble’s constant.

Almost immediately after Hubble’s announcement physicists and astronomers began to theorize what could have caused this expansion and so they developed the Big Bang Theory which was finally confirmed by A. Penzias and R. Wilson in 1965. But if the Big Bang Theory was true then the gravitational attraction of the galaxies should be slowing the rate of expansion, Hubble’s constant should not be truly constant. Cosmologists also theorized that there could be two basic solutions. One, the gravitational attraction was strong enough that eventually the expansion would come to a stop and the entire Universe would enter a Big Crunch phase. The other solution was that the expansion was so great that the Universe had achieved escape velocity and would expand forever.

It was to discover which of these two alternative Universes was true that two teams of astronomers, one led by S. Perlmutter and the other by A. Riess and B. Schmidt used Type Ia supernova to try to measure the deceleration of Hubble’s constant. In 1998 these two teams independently announced their findings that the expansion of the Universe was in fact accelerating, a discovery that shocked the world of science and led to Perlmutter, Riess and Schmidt being awarded the 2011 Nobel Prize in Physics.

The search was now on for the cause of this acceleration, an unknown force that was quickly named Dark Energy although cosmologists prefer to call it Dark Pressure. Literally hundreds of theoretical papers have been written over the past two decades speculating on the nature of Dark Energy but little more observational detail was provided by astronomers.

Now a new study, using data from more than ten times as many Type Ia supernovas as was available to Perlmutter, Riess and Schmidt has called into question the very existence of Dark Energy, asserting that the discovery was if fact only a statistical fluctuation. This new study by astronomers J.T. Nielsen, A. Guffanti and S. Sarkar uses data from 740 Type Ia supernovas and concludes that “we find, rather surprisingly, that the data are still quite consistent with a constant rate of expansion.”

This result is something of a shocker, have cosmologists spent the last 18 years chasing a phantom? Personally I’ll wait and see. There is other indirect evidence for Dark Energy in the Cosmic Microwave Background so Dark Energy isn’t gone just yet. In fact the new study found that the evidence for Dark Energy is at the three sigma level but scientists prefer five sigma so we are talking statistical weights of evidence.

Still this is yet another example of just how difficult it is to get real, precise details on the nature of our Universe. We have learned a great deal but that knowledge has required great effort, and just as often great patience. I’ll keep you informed.

I’m going to try a little experiment of my own and try to insert the actual article by Nielsen et al into this post. Enjoy.