Based on Einstein’s theory of general relativity, new tool allows researchers to take into account ripples in spacetime, making the most accurate simulations yet

Scientists have created the most accurate way yet of simulating the way the universe expands.

Dubbed “gevolution”, the tool will for the first time allow researchers to take into account the effect of ripples in spacetime - known as gravitational waves - and could help shed light on dark energy, the mysterious force driving the universe’s accelerated expansion.

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“I think it is an important step forward,” said Professor Jo Dunkley of the University of Oxford, who was not involved in the study. “It’s something that people have been trying to work towards for a while.”

While many models of the universe currently exist, simulations are typically based on those built on Newton’s theory of gravity. The new tool, however, is based on Einstein’s theory of general relativity, allowing scientists to create computer simulations based on a far wider range of models. Dr Julian Adamek, one of the paper’s authors now based at the Observatoire de Paris in Meudon, says that offers exciting possibilities. “You can see now a simulation of how spacetime is dragged around - the ‘frame-dragging’ effect - by the movement of matter and also how gravitational waves would be generated by the matter which moves around,” he says.

“Surprisingly, you can calculate - to really good accuracy - what the large-scale structure of the universe should look like by just using simple Newtonian gravity. Hence virtually all the large computer simulations we use to date just work with Newton’s laws,” says Dr Tessa Baker, also from the University of Oxford. However the new tool, she says, goes further. “It allows one to calculate the small deviations from Newtonian gravity that weren’t captured by any simulation to date.”

Published in the journal Nature Physics, the paper, led by scientists at the University of Geneva, also points out that the tool will allow researchers to delve deeper into the nature of dark energy - the mysterious phenomenon responsible for the acceleration of the expansion of the universe. While dark energy is often given a value known as the cosmological constant, Adamek is quick to add that it is still an enigma. “If it is not [described by the cosmological constant], if it is something else, you need to know what kind of implications [it would] have and for this, simulations would be a nice way,” says Adamek.



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But not everyone is so enthusiastic. “Einstein’s general relativity is our best description of gravity, but the equations are complicated and expensive to solve - in the sense that it takes a great deal of computer time,” says Dr David Seery from the University of Sussex. “To study growth of structure on cosmological scales we can usually make do with the older Newtonian theory of gravity.” Indeed, while the new tool could offer advantages, Seery believes it has yet to usher forth revelations. “Their computer software is an impressive piece of work, but at this stage the results don’t amount to significant changes in our understanding of the growth of structure.”

However, with large cosmological surveys in the offing, including the European Space Agency’s Euclid satellite, Dunkley believes the simulations will yet prove valuable. “This is really timely because we are just about to embark on this whole wealth of new data - we will need these computer simulations available if we want to learn new physics from the new data that is coming,” she says.

Baker agrees. “Capturing these general relativistic effects is important because as our telescope technology is improves, so does the accuracy of our astronomical data. They may be only small corrections to the Newtonian predictions, but we should include them to make totally rigorous calculations for the next generation of telescopes.” She adds: “Also they have a bearing on ruling out models of dark matter and dark energy, arguably the biggest problems in current cosmology.”