Are we getting closer to dark energy and dark matter?

Much of the universe is shrouded in darkness. Dark matter is the mysterious, invisible glue which we hypothesise must be driving strange gravitational effects out in the cosmos we can’t explain by calculations involving visible matter alone. It’s responsible for things like galaxies we can see spinning faster than they ever “should,” or light bending as it travels through space filled with… something. Whatever it is, it doesn’t interact with light, and so we don’t know what it is...

Dark matter seems to pull things together. Dark energy on the other hand is the placeholder name used when discussing the way matter is being driven apart. We know by observing other galaxies that the universe is expanding and the expansion is accelerating. Whatever is causing this repulsive acceleration we call dark energy.

These phenomena appear to have separate sources as they have opposite effects: attraction and repulsion, hence the distinction. Together, they make up 95% of the mass-energy content of the universe. So where are we in trying to unpick the nature of these glaring holes in the study of cosmology?

Recently a collaboration of scientists, including those at the University of Cambridge, released a paper placing constraints on our current model. In other words, by pooling their data, scientists have put tighter limits on how much dark matter exists and how it’s spread out. The paper uses data from the Dark Energy Survey, Atacama Cosmology Telescope and Planck satellite.

The Dark Energy survey quantified some of the gravitational effects caused by dark matter, and allows us to narrow the possible ranges of a few properties. For example, the value for the proportion of the universe that is dark matter was refined, and the amount of dark matter associated with each galaxy was more accurately quantified. The results are consistent with previous studies which is a promising start, however it does raise a question…

In a time where there seems to be a never-ending stream of these new studies and new data which refine the properties slightly, are we actually any closer to finding solutions to the dark matter and dark energy problems?

At first glance the answer appears to be no.

There have been no instances of detection of dark matter particles, most of our theories have issues, and there haven’t been any changes in approach. Naturally, there is a serious lack of information. The very nature of these unknown entities is such that we only have their gravitational effects to go off. More measurements quantifying these effects, as taken by the Dark Energy survey, is the obvious first step. Then we are faced with no other option but to start eliminating possibilities: to refine the properties we do know and to attempt to find evidence for specific theories.

Take dark matter. For a long time, scientists thought it might have been made of WIMPs (weakly interacting massive particles.) These were well-motivated theoretically, but as more and more masses were tested and no WIMP found, scientists were forced to turn to other options. Freed from the confines of WIMP tunnel vision, scientists are starting to move on and get creative. Perhaps it’s going to take more radical ideas to kickstart a breakthrough.

Going forwards, there is hope in the search for solutions to arguably the biggest mysteries in modern physics, although it is likely to be a slow and painful process. As more telescopes and means of detection come about we can only hope that we get lucky sooner rather than later.