Hunting for Extra Dimensions
As important as gravity is to us here on Earth, it is actually surprisingly weak in comparison to other fundamental forces in our universe, such as electromagnetism. In fact, as researchers struggle to unite quantum effects and gravity in single theories that make sense, they find that extra dimensions, usually with gravity, are implied.
However, theorizing the existence of these extra dimensions is much easier than actually proving that they exist. Scientists were hopeful that the Large Hadron Collider (LHC) might reveal evidence of their existence. After all, the device gives them the ability to run specialized experiments searching for massive particle traces, microscopic black holes, and missing energy caused by the migration of gravitons to higher dimensions. So far, however, definitive proof has not been discovered with the LHC.
In their search for answers, researchers Gustavo Lucena Gómez and David Andriot at the Max Planck Institute for Gravitational Physics in Potsdam, Germany, have honed in on two strange effects: high frequency gravitational waves and the “breathing mode,” a modification of how gravitational waves stretch space.
The researchers calculated that extra dimensions should result in the creation of extra, high frequency gravitational waves. Unfortunately, we don't currently have observatories that can detect frequencies in the range they predict, nor are any in development.
However, we do have the tech needed to observe the breathing mode. Space changes shape as it reacts to gravity passing through it. The breathing mode is seen when, in addition to stretching and squishing, space expands and contracts in reaction to additional gravitational waves. “With more detectors we will be able to see whether this breathing mode is happening,” Lucena Gómez told New Scientist.
Based on the researchers' calculations, the additional waves at high frequencies would point decisively to extra dimensions. However, the breathing mode could have explanations beyond those theoretical dimensions, but its detection would be a significant clue pointing toward their existence.
Explaining Our Universe
Even without definitive proof, we're making progress in our hunt for other dimensions. Since 2015, scientists have been able to observe gravitational waves, and because gravity probably exists in other dimensions, observing and analyzing the behavior of these waves under different conditions might provide clues about those extra dimensions. The existence of another dimension makes weak gravitational force more understandable — if gravity exists throughout all of these extra dimensions as well, it should be weaker.
Put another way, the existence of extra dimensions would allow for a coherent, comprehensive theory of the universe. It would also explain uncertainties about the nature of gravity. It would even put us on the road to explaining why the universe is expanding faster and faster. “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,” explained Lucena Gómez.
Proof of an extra dimension would be extraordinarily exciting for physicists working to explain the laws of the universe with a single, coherent theory. If we were able to reconcile the conflicts between quantum field theory and general principles of relativity, for example, things like antigravity, instantaneous communication and transport, transmutation of matter, and faster-than-light travel might all be possible. For now, we don't have a definitive answer, but understanding the behaviors of gravitational waves would be a remarkable step in the right direction.