Sunday, May 19Royal Holloway's offical student publication, est. 1986

The Hunt for the Unseen

Throughout it’s history, the human race has delved far into the mysteries of the Universe: why are we here? Where did the Universe come from? What is the Universe made of? These questions have sparked interest and exploration for millennia, and we have come a very long way in that time. It has been approximately 2500 years since the Ancient Greeks started to formulate their ideas about the Universe we live in. Since then the human race has become to probe the true nature of the Universe itself to answer these questions, and it is the final question that has the whole physics community stumped: what is the Universe made from?

An experiment named WMAP measured the Cosmic Microwave Background (CMB) Radiation of the Universe, which is made from photons that have been travelling since the beginning of the Universe. This experiment concluded that the Universe was flat and thus 30% of the energy of the Universe was contained in matter. Further investigation showed that of this 30%, only approximately 15% of this matter was stuff that we can see. This result is quite shocking: more than 95% of the energy density of the Universe has never been directly detected in a laboratory! So what do we know about the rest of the Universe? The problem is, we know practically nothing about 95% of the Universe’s energy. We do know that 25% is made from Cold Dark Matter, and the rest is Dark Energy, but what makes up these mysterious entities we do not know. The word ‘dark’ is used because this matter does not release any detectable electromagnetic radiation, and our current detection techniques rely on this. 

So where do we go from here? Deep into the Earth is where we have started. Physicists working on experiments such as DEAP-3600 at the SNO laboratory in Canada are searching for Dark Matter particles. They expect these particles to be very illusive, and very weakly interacting. This means that they pass through most things in the Universe without effecting a thing. Their technical term is a Weakly Interacting Massive Particle, or WIMP for short. This is only one candidate for what Dark Matter could be made from. The field is rich in theories of new, exotic particles that could exist. Physicists believe that these new, unseen particles, could solve the problem of Dark Matter and perhaps shine light on the Dark Energy of the Universe. 

There are many experiments looking for a direct detection of Dark Matter, but as of yet none have succeeded. Despite this, the evidence is compelling that Dark Matter is out there somewhere, just waiting to be found. Maybe we’re just looking in the wrong place? Never the less, solving the mystery of Dark Matter is one of the most prevalent pursuits in the particle physics world, and one that could rewrite physics as we know it.

With thanks to the International Dark Matter Day.