Peering into the dark universe

By Tushna Commissariat

Catherine Heymans (Courtesy: University of Edinburgh)

Inquisitive minds from all over the city of Bristol (where Physics World HQ is based) met at the University of Bristol’s Peel Lecture Theatre last night to hear astrophysicist Catherine Heymans give a talk entitled “The Dark Universe”, in which she tackled dark matter, dark energy, the structure of our universe from the largest to the smallest scales, flying pigs and even astronomical tooth fairies!

Heymans’ lecture was the first of a number of talks to celebrate the 25th anniversary of Physics World that we will be running with the Bristol Festival of Ideas, which hosts special events, talks and screenings held throughout the year in the city.

This being the first time that Physics World has been directly involved with the festival, we were pleased that Heymans’ talk was entirely sold out. And having a particular interest in astronomy, I made sure to attend the event, which proved to be a great success.

Heymans – an astronomer at the University of Edinburgh who works on the KiDS and CFHTLenS dark-matter surveys – is not only friendly and charming, but also one of that rare breed of scientists who is also an excellent communicator. Undoubtedly her topic was a complex and difficult one, especially when talking to an audience with nearly no astronomical knowledge, but she proved to be engaging, entertaining, to-the-point and informative.

Heymans started off with a simple overview of dark matter – describing how and why we realized that 26.8% of matter in our universe is invisible to us. And to explain how the spin of our own galaxy tipped off astronomers to the existence of dark mater, Heymans used a small pink toy pig attached to a string as a “comedy prop”. (You can’t have a good science talk without a good prop!). Swinging the pig above hear head faster and faster, Heymans showed how much harder she had to work to keep the pig from flying off.

After talking about how scientists, including her group, had mapped the large-scale distribution of dark matter in our universe – and what the consequence of that are on where galaxies are located and  form – Heymans went on to tackle dark energy, which she describes as the evil twin sister of dark matter. “Together, these two dark entities play out a cosmic battle of epic proportions,” she exclaimed.

Dark-matter butterfly nets.

At one point, she asked all of us in the audience to hold up our thumbs and index fingers to make a ring for a few moments, forming what she called  our very own dark-matter butterfly nets. She then asked us to guess how many dark-matter particles we had caught and there was a collective gasp when she said that each of us had caught at least a billion particles in that moment.

I won’t go into much more detail about the talk because you can read all about what Heymans has to say on the topic in an article she wrote for Physics World‘s special 25th anniversary issue. But I will say that I was very impressed by how she also encouraged the audience to be sceptical of everything that she was telling us. Whether it was her work or other alternative theories that could explain our universe, Heymans always suggested that the answer could be completely different or that the researchers’ theories or observations could be wrong. In fact, she fondly referred to this as the “tooth fairy” they made up because they got their sums wrong!

Heymans ended her talk by saying that the mystery of the “dark universe” will be solved only by some new physics that will forever change our cosmic view.

Our next talk, which will see Nobel-prize-winning physicist Andre Geim talk about graphene, will be held on Wednesday 23 October.