Sunday, February 12, 2017

Tests May Solve Einstein’s Great Riddle

A graphical representation of the expansion of the universe with the inflationary epoch represented as the dramatic expansion of the metric seen on the left. Credit: NASA/WMAP Science Team

Advanced technology could resolve a long-standing puzzle over what is driving the accelerated expansion of the Universe. Researchers have long sought to determine the mechanism behind the expansion of our universe. Calculations in a new study could help to explain whether dark energy, as predicted by Einstein, or a revised theory of gravity are responsible.

Einstein’s theory describes gravity as distortions of time and space. This included a mathematical element known as a Cosmological Constant. Einstein originally introduced it to explain a fixed universe, but discarded the idea after it was discovered that our universe is expanding. Research carried out two decades ago showed that this expansion is accelerating. This suggests that Einstein’s Constant may still have a part to play in an explanation of dark energy.

Without dark energy, the acceleration implies a failure of Einstein’s theory of gravity across the largest distances in our Universe.

Scientists from the University of Edinburgh, UK, have discovered that the puzzle could be solved by experiments to determine the speed of gravity in the cosmos. The researchers’ calculations show that gravitational waves – ripples in space-time in the universe - may hold the key. If these are found to travel at the speed of light, this would rule out theories without dark energy. It would also support Einstein's Cosmological Constant. If, however, their speed differs from that of light, then Einstein’s theory must be revised.

The experiment could be carried out by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US. Its twin detectors, 2000 miles apart, detected gravitational waves in 2015.

Experiments conducted at the facility this year could resolve the question in time for the 100th anniversary of Einstein's Constant.

"Our results give an impression of how this will guide us in solving one of the most fundamental problems in physics," said Lucas Lombriser of the University of Edinburgh.

The study was published in Physics Letters B.

It was supported by the UK Science Technology Facilities Council, the Swiss National Science Foundation and the Portuguese Foundation of Science and Technology.

Credit: ed.ac.uk

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