Physicists are pretty comfortable with using a four-dimensional model for the universe — three spatial dimensions and one dimension of time — on the macro-scale, but when it comes to understanding the universe on the tiniest of scales, the model has its limits. In fact, according to string theory, one of the more promising theories about the fundamental nature of the cosmos, at least 10 dimensions are required to make the theory work.
But it's one thing to imagine the existence of extra dimensions, and another thing for those dimensions to actually exist. If hidden dimensions do exist in our universe, scientists have yet to discover them. That could soon change, thanks to the recent detection of subtle ripples in the fabric of spacetime, also known as gravitational waves.
The Laser Interferometer Gravitational-Wave Observatory (LIGO) recently detected its fourth set of gravitational waves, which came from two massive black holes colliding about 3 billion light-years from Earth. The resulting black hole has a mass about 53 times that of our sun, according to LIGO, which is operated by California Institute of Technology and the Massachusetts Institute of Technology.
In all four cases, LIGO's two detectors sensed gravitational waves from the "tremendously energetic mergers of black hole pairs," LIGO said. "These are collisions that produce more power than is radiated as light by all the stars and galaxies in the universe at any given time."
The latest gravitational wave was the first one identified by a new detector (called the Virgo detector) located near Pisa, Italy; LIGO's twin detectors are in Livingston, Louisiana, and Hanford, Washington.
“This is just the beginning of observations with the network enabled by Virgo and LIGO working together,” David Shoemaker of MIT said in a press release. “With the next observing run planned for Fall 2018 we can expect such detections weekly or even more often.”
Opening new dimensions
According to a theory proposed by physicists Gustavo Lucena Gómez and David Andriot from the Max Planck Institute for Gravitational Physics in Germany, the signatures of extra dimensions might be observable in the ways that gravitational waves undulate through the universe.
“If there are extra dimensions in the universe, then gravitational waves can walk along any dimension, even the extra dimensions,” explained Gómez to New Scientist.
In other words, just as waves of gravity can travel through the four known dimensions of space and time, so too should they be capable of traveling through any extra dimensions. If we follow the behavior of gravitational waves close enough, we might be able to "surf" them right into the other dimensions.
“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,” said Gómez.
Gómez and Andriot have devised a mathematical model that predicts how the effects of hidden dimensions ought to look as they act on the gravitational waves flowing through them. To test their theory, we only need to look for these subtle rippling patterns in the gravitational waves that we detect.
Unraveling another mystery
Interestingly, the existence of extra dimensions could also help explain another long-standing mystery: why gravity appears to be such a weak force compared to the other fundamental forces of nature. Perhaps the reason that gravity is so weak is because it has been "leaking" into these other extra dimensions; its strength is lost because it has been stretched so thin traveling between so many dimensions.
For now, we'll have to wait to see if Gómez' and Andriot's model holds up to scrutiny before it can be tested. We'll also have to wait for technology to advance. Currently, our only gravitational wave detector, known as LIGO (Laser Interferometer Gravitational-Wave Observatory), is not sensitive enough to see the subtle ripples that might be caused by extra dimensions.
Eventually, though, we might have to completely re-think our understanding of the universe to make room for weird new dimensional features. If you thought that thinking about time as another dimension was a mind-warp, you might want to sit out this next round out...
The research has been pre-printed at the website arXiv.org.
Editor's note: This story has been updated with new information since it was originally published in May 2017.