From Quarks to the Cosmos

Tuesday 15th October, 2019

Our speaker for the evening was Prof Ian Shipsey from the Department of Physics at Oxford University and his talk was entitled "From Quarks to the Cosmos". He began by saying that although he is from London, he has spent most of his academic life in the USA and only came to Oxford five years ago. He is an experimental physicist as he works with other scientists on the data collected by the huge underground physics experiment called the Large Hadron Collider or LHC. This is a giant excavated circular tunnel located 175 km underground that stretches for 27 km and even crosses the French-Swiss border. It is used to accelerate tiny particles up to close to the speed of light and then purposefully collide them. The products of these collisions allow the scientists to understand more about the fundamental properties of particles and the high collision energies can even produce new particles.

Prof Shipsey then said that there have been a number of recent breakthroughs in physics. In 2012 the confirmation of the existence of a particle called the Higgs Boson was announced at the LHC using data collected by two experiments, named ATLAS and CMS. The existence of this particle was first proposed by the theoretical physicist Prof Peter Higgs (whom the particle is named after) along with several other physicists back in the 1960s. In 2013 Prof Higgs and Dr Francois Englert were jointly awarded the Nobel Prize for Physics for their work.

He then continued by saying that a huge leap forward had also occurred in 2016 when the Laser Interferometer Gravitational-Wave Observatory (LIGO) had successfully recorded gravity waves for the first time. This phenomenon was first proposed in 1905 by Henri Poincaré and predicted by Einstein on the basis of his General Theory of Relativity which explained how the movement of any mass can affect the space it sits in. Just as a stone thrown in a pond causes waves to spread outwards, the movement of a large mass in space can send a disturbance outward and these oscillations are known as "gravity waves". The only problem is that these waves are so tiny that it is incredibly difficult to pick them up as they are smaller than the width of an atom.

He then went on to explain that cosmologists are collaborating with particle physicists and scientists using LIGO as there is a natural limit to how far back in time even large professional telescopes can see. For, up until roughly 400,000 years after the Big Bang when space was filled with plasma, the Universe was opaque and any light waves were absorbed as soon as they were emitted. However, the LHC particle collisions can recreate the conditions at this early time and model the interactions. Also, unlike light, gravity waves still propagate in the dense fog-like conditions of the early Universe and can, in theory, penetrate this natural barrier.

Currently, other gravitational wave observatories are coming on-line around the world and the LIGO experiment has been upgraded and is now on its third observing run. The LHC is not working at present as it is having vital maintenance but will be back in 2021 for a final three-year run. This also allows for the embedded experiments such as ATLAS and CMS to be upgraded.