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Signatures of Universe’s Extra Dimensions Could Be Hiding in Gravitational Waves

In a paper published in the Journal of Cosmology and Astroparticle Physics (arXiv.org preprint), German physicists investigate the effects due to Universe’s extra dimensions — the existence of which is a critical but as yet unproven element of string theory — on ‘ripples’ in the fabric of space and time called gravitational waves, and discuss whether these effects could be observed.

Gravitational waves observed by Laser Interferometer Gravitational-Wave Observatory (LIGO) twin detectors were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole. Image credit: T. Pyle / LIGO.

Gravitational waves observed by Laser Interferometer Gravitational-Wave Observatory (LIGO) twin detectors were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole. Image credit: T. Pyle / LIGO.

LIGO’s observations of gravitational waves in September and December 2015, and January 2017 are impressive experimental results and groundbreaking scientific achievements.

They provide physicists with a new observational tool, allowing them to probe nature and test theories in completely innovative manners.

“Now it looks like with this new tool we cannot only trace black holes and other exotic astrophysical objects but also understand gravity itself,” said study co-author Dr. David Andriot, from the Max Planck Institute for Gravitational Physics in Germany.

“Compared to the other fundamental forces like, e.g. electromagnetism, gravity is extremely weak.”

“The reason for this weakness could be that gravity interacts with more than the three dimensions in space and one dimension in time that are part of our everyday experience.”

Extra dimensions, which are hidden because they are very small, are an indispensable part of string theory, one of the promising candidates for a theory of quantum gravity.

A theory of quantum gravity, unifying quantum mechanics and general relativity, is sought after in order to understand what happens when very large masses at very small distances are involved, e.g. inside a black hole or at the Big Bang.

“Physicists have been looking for extra dimensions at CERN’s Large Hadron Collider, but up to now this search has yielded no results,” said co-author Dr. Gustavo Lucena Gómez, also from the Max Planck Institute for Gravitational Physics.

“But gravitational wave detectors might be able to provide experimental evidence.”

According to the team, Universe’s extra dimensions should have two different effects on gravitational waves: they would modify the ‘standard’ gravitational waves and would cause additional waves at high frequencies (above 1,000 Hz).

“However, the observation of the latter is unlikely since the existing ground-based gravitational wave detectors are not sensitive enough at high frequencies,” the authors said.

“On the other hand, the effect that extra dimensions can make a difference in how ‘standard’ gravitational waves stretch and shrink space-time might be easier to detect by making use of more than one detector.”

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David Andriot Gustavo Lucena Gómez. Signatures of extra dimensions in gravitational waves. Journal of Cosmology and Astroparticle Physics, published online June 23, 2017; doi: 10.1088/1475-7516/2017/06/048