Do parallel universes exist? Gravitational waves could be the key to discovering an extra dimension

by Shivali; Mail Online

Physicists believe that some gravity is escaping into extra dimensions
An extra dimension would create a ‘tower’ of high frequency waves
It would also change the way that gravitational waves stretch space
If these changes can be detected, it could help discover an extra dimension

The existence of parallel universes has long been one of the biggest mysteries of the universe.

Now, scientists believe they have found a way to some day detect hidden dimensions.

Physicists think that unknown dimensions could cause ripples through reality by modifying gravitational waves – changes in the space-time fabric.

And since gravity is likely to occupy all dimensions that exist, its waves are a promising way to detect unknown dimensions.

GRAVITATIONAL WAVES

The universe is made up of a ‘fabric of space-time’.

This corresponds to Einstein’s General Theory of Relativity, published in 1916.

Objects in the universe bend this fabric, and more massive objects bend it more.

Gravitational waves are considered ripples in this fabric.

They can be produced, for instance, when black holes orbit each other or by the merging of galaxies.

Gravitational waves are also thought to have been produced during the Big Bang.

Physicists believe the waves can offer insights into fundamental physics.

For instance, they could shed light on the idea that, at one point, most or all of the forces of nature were combined into a single force.

While we are aware of the three dimensions that surround us on a daily basis – length, width and depth – physicists have long believed that there may be more.

In the hopes of understanding whether another dimension does exist, researchers from the Max Planck Institute for Gravitational Physics in Potsdam are looking at gravitational waves – ripples in space-time, caused by the motion of massive objects.

Gravity is weaker than other fundamental forces, and experts have long wondered whether this is because some of it is escaping into an extra dimension.

Speaking to New Scientist, Gustavo Lucena Gomez, who is leading the study, said: ‘If there are extra dimensions in the universe, then gravitational waves can walk along any dimension, even the extra dimensions.’

The researchers set out to calculate how an extra dimension would affect gravitational waves, and found two strange effects – extra waves at high frequencies, and a change in how gravitational waves stretch space.

As gravitational waves move through an extra dimension, the researchers found that they should generate a ‘tower’ of extra gravitational waves with higher frequencies.

But observatories are currently unable to detect frequencies that high, and instead focus on lower frequency gravitational waves.

This could make spotting the gravitational wave towers a challenge.

But detecting the change in how gravitational waves stretch space could be easier, according to the researchers.

Dr Lucena Gomez said: ‘If extra dimensions are in our universe, this would stretch or shrink space-time in a different way that standard gravitational waves would never do.’

Gravitational waves stretch space as they ripple through the universe a bit like a rubber band – the ellipse gets longer in one direction and shorter in the other, before returning to its original shape.

But an extra dimension could add another way for gravitational waves to stretch space, called a breathing mode.

HOW WOULD GRAVITATIONAL WAVES AFFECT AN EXTRA DIMENSION?

The researchers set out to calculate how extra dimension would affect gravitational waves, and found two strange effects – extra waves at high frequencies, and a change in how gravitational waves stretch space.

As gravitational waves move through an extra dimension, the researchers found that they should generate a ‘tower’ of extra gravitational waves with higher frequencies.

But observatories are currently unable to detect frequencies that high, and instead focus on lower frequency gravitational waves.

This could make spotting the gravitational wave towers a challenge.

But detecting the change in how gravitiational waves stretch space could be easier, according to the researchers.

Gravitational waves stretch space as they ripple through the universe a bit like a rubber band – the ellipse gets longer in one direction and shorter in the other, before returning to its original shape.

But an extra dimension could add another way for gravitational waves to stretch space, called a breathing mode.

In the same way that lungs expand as you breathe, gravitational waves cause space to expand and contract, in addition to stretching.

The researchers hope that this breathing space could soon be detcted by an observatory.

In the same way that lungs expand as you breathe, gravitational waves cause space to expand and contract, in addition to stretching.

Dr Lucena Gomez said: ‘With more detectors we will be able to see whether this breathing mode is happening.’

Dr Emilian Dudas, from the Ecole Polytechnique in France told New Scientist: ‘Extra dimensions have been discussed for a long time from different points of view.

‘Gravitational waves could be a new twist on looking for extra dimensions.’

Last year, researchers at the Large Hadron Collider suggested that there could be nine dimensions, and black holes might be the key to reaching them.

A few theories in particle physics suggest there is much more to our universe than meets the eye – and these extra dimensions could answer questions ranging from quantum physics to gravity.

One of these, called ‘brane theory’, suggests multiple dimensions could be hiding extra universes.

‘Brane theory is part of a larger theory called string theory, which attempts to explain how all the forces and particles we see fit into one single description,’ Dr Chris White, a physicist from the Queen Mary University of London, told MailOnline.

STRING THEORY

At its most basic level, string theory, also known as the ‘theory of everything,’ proposes that all objects in our universe are composed of vibrating filaments (strings) and membranes of energy.

The theory suggests that each so-called fundamental particle contains a tiny, vibrating, one-dimensional loop of string. The vibration of the string determines the charge and mass of the greater particle.

String theory works in ten or eleven dimensions and we only experience four.

Scientists have theorised that the missing dimensions are curled up into a compact space. If the space is tiny, on the scale of the strings, then we would be unable to detect them.

Scientists are hopeful that string theory will solve one of the biggest mysteries of the universe; how gravity and quantum physics work fit together.

‘It suggests that the basic building blocks of nature, instead of being particles, can instead be strings, planes and higher dimensional generalisations collectively called ‘branes’.

‘The equations of string theory, which necessarily includes branes, only make sense in 9 space dimensions, rather than the 3 we appear to observe.’

Strings live in a 9-dimensional space, and when time is included as another dimension, this makes ten.

In his book ‘The Universe in Your Hand’, Dr Christophe Galfard describes a thought experiment, that shows what it might look like if we were able to travel between these dimensions.

‘You see what you think might be black holes linking nearby branes through a tube of distorted spacetime, with gravity from each brane attracting others’ he said.

‘You suddenly wonder if, by any chance, there might be other people living in those branes.

‘Could the black holes be a passage between your world and theirs?’

Using the Large Hardon Collider at CERN in Geneva, researchers are now looking for signs of extra dimensions, and one of these is tiny black holes.

‘The LHC could make small black holes if there are extra dimensions of the right size,’ Dr White added.

‘These would decay very quickly but leave a dramatic burst of radiation in the detectors!’

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