Scientists shed new light on dark energy

European Cosmologists may have shed new light on one of astronomy’s greatest mysteries: how to measure dark energy, writing in the Monthly Notices of the Royal Astronomical Society, the
scientists from Durham University, UK, ran a series of computer simulations to generate snapshots of the entire universe.

The results of these simulations, carried out by a team co-led by Professor Carlos Frenk, show how to measure dark energy – a force that counteracts gravity and could decide the ultimate fate
of the cosmos.

The force is delicate and yet so all-pervasive that it will determine the fate of the universe. However, scientists lack the knowledge of what it is, where it is and even its very existence.

The discovery of evidence of dark energy in 1998 was unexpected and understanding its nature is one of the biggest problems in physics, explains Professor Frenk.

Most scientists believe that dark energy, which makes up 70% of the Universe, is driving its accelerating expansion. If this trend continues it could eventually lead to a Big Freeze as the
Universe is pulled apart and becomes a vast cold expanse of dying stars and black holes.

The simulations took 11 days to run on Durham’s Cosmology Machine computer. They looked at tiny ripples in the distribution of matter in the universe made by the sound waves that echoed around
the cosmos a few hundred thousand years after the Big Bang.

By charting how the ripples shaped the universe over its growth, the researchers discovered that the ripples appeared to change in length; crucial intelligence for the measurement of dark
energy.

Professor Frenk explains that the simulation of what remnant of the ripples should be seen today can be used as a ‘gold standard’. By comparing the universe today with the standard ‘we can work
out how the universe has expanded and from this figure out the properties of the dark energy.

‘Astronomers are stuck with the one universe we live in. However, the simulations allow us to experiment with what might have happened if there had been more or less dark energy in the
universe,’ he said.

The research was funded by the UK’s Science and Technology Facilities Council (STFC) and the European Commission.

In the next decade a number of experiments are planned to explore dark energy. The findings will provide vital input into the design of a proposed satellite mission called SPACE – the
SPectroscopic All-sky Cosmic Explorer – that could unveil the nature of dark energy. The Durham simulation demonstrates the feasibility of the SPACE satellite mission.

The project has been put forward to the European Space Agency (ESA) by an international consortium of researchers, including the Durham team. The project is already through to the second round
of assessment.

Co-principal investigator Professor Andrea Cimatti, of Bologna University, said: ‘Thanks to the ICC simulations it is possible to predict what SPACE would observe and to plan how to develop the
mission parameters in order to obtain a three-dimensional map of the Universe and to compare it with the predictions of the simulations.

‘Thanks to this comparison it will be possible to unveil the nature of dark energy and to understand how the structures in the Universe built up and evolved with cosmic time’ he added.

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