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Accelerating research into dark energy

2016-07-07 13:20
This false-colour image of the large-scale structure in a computerised Universe reveals the process behind the new technique. On the left, a regular virtual universe has the locations of galaxies highlighted in blue, showing how they cluster together. In the early Universe (centre) the relationship between these blue regions and the orange regions that expand into empty voids was symmetric. This allows a reverse version of the cosmos to be built (right) where the galaxies now inhabit the very regions that used to be empty voids. The latest results show how combining results from the original and reverse virtual Universe is a quick way to make accurate predictions for the real cosmos.

This false-colour image of the large-scale structure in a computerised Universe reveals the process behind the new technique. On the left, a regular virtual universe has the locations of galaxies highlighted in blue, showing how they cluster together. In the early Universe (centre) the relationship between these blue regions and the orange regions that expand into empty voids was symmetric. This allows a reverse version of the cosmos to be built (right) where the galaxies now inhabit the very regions that used to be empty voids. The latest results show how combining results from the original and reverse virtual Universe is a quick way to make accurate predictions for the real cosmos.

A quick method for making accurate, virtual universes to help understand the effects of dark matter and dark energy has been developed by CEFCA and UCL scientists. Making up 95% of our universe, these substances have profound effects on the birth and lives of galaxies and stars and yet almost nothing is known about their physical nature.

The new approach, published today in Monthly Notices of the Royal Astronomical Society is twenty-five times faster than current methods but is just as accurate, allowing scientists more computer power to focus on understanding why the universe is accelerating and galaxies are positioned where they are.

"New exciting ventures, including the Javalambre Physics of the Accelerating Universe survey and the Large Synoptic Survey Telescope, are about to measure the position of hundreds of millions of galaxies. By comparing these measurements with computational models, we will be able to learn about the nature of dark energy and dark matter", explained Dr Raul Angulo (CEFCA, Spain).

Joint author Dr Pontzen (UCL Physics & Astronomy, UK) continued: "But every computer simulation we run gives a slightly different answer. We end up needing to take an average over hundreds of simulations to get a ‘gold standard’ prediction. We’ve shown it’s possible to achieve the same model accuracy by using only two carefully-constructed virtual universes, so a process that would take weeks on a superfast computer, can now be done in a day."

The scientists say their method will speed up research into the unseen forces in the universe by allowing many model universes to be rapidly developed to test alternate versions of dark energy and dark matter.

"Our method will allows us to interpret cosmological observations in much more precise ways. For instance, we will be able to create millions of virtual universes with different laws of gravity and models of dark energy, and find those that best explain the data obtained by big telescopes", added Dr. Angulo.

The new method removes the biggest uncertainties in the model universe by carefully adjusting the ripples of the early universe and by comparing its properties with an ‘inverted’ version. In the inverted model universe, galaxies are replaced by empty voids, and the empty voids of space with galaxies. The scientists tried this approach after noticing a mathematical symmetry linking the two seemingly different pictures.

When they compared the output of the paired universes to that of the gold standard method – which averages 300 virtual universes to remove uncertainties – they found the results to be very similar. The new approach showed less than 1% deviation from the gold standard, suggesting the new approach makes predictions that are accurate enough to use in forthcoming experiments.

The team now plan on using the new method to investigate how different forms of dark energy affect the distribution of galaxies through the universe. "Because we can get a more accurate prediction in a single shot, we don’t need to spend so much computer time on existing ideas and can instead investigate a much wider range of possibilities for what this weird dark energy might really be made from," said Dr Pontzen.

Video: This false-colour video of the large-scale structure in a computerised Universe reveals the process behind the new technique. At the start, a regular virtual universe has the locations of galaxies highlighted in blue, showing how they cluster together. The video shows how these regions can be traced back to the early Universe, where the relationship between these blue regions and the orange regions that expand into empty voids was symmetric. From here, a reverse version of the cosmos is built where the galaxies now inhabit the very regions that used to be empty voids. The latest results show how combining results from the original and reverse virtual Universe is a quick way to make accurate predictions for the real cosmos.