Signs of extra dimensions may reveal themselves in the way they impact gravitational waves. Scientists hope that further study of these waves might allow for a single, coherent theory of the universe.
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.
For years, scientists have been baffled by a weird anomaly far away in space: a mysterious “Cold Spot” about 1.8 billion light-years across. It is cooler than its surroundings by around 0.00015 degrees Celsius (0.00027 degrees Fahrenheit), a fact astronomers discovered by measuring background radiation throughout the universe.
Previously, astronomers believed that this space could be cooler simply because it had less matter in it than most sections of space. They dubbed it a massive supervoid and estimated that it had 10,000 galaxies fewer than other comparable sections of space.
But now, in a recently published survey of galaxies, astronomers from the Royal Astronomical Society (RAS) say they have discovered that this supervoide could not exist. They now believe that the galaxies in the cold spot are just clustered around smaller voids that populate the cold spot like bubbles. These small voids, however, cannot explain the temperature difference observed.
To link the temperature differences to the smaller voids, the researchers say a non-standard cosmological model would be required. “But our data place powerful constraints on any attempt to do that,” explained researcher Ruari Mackenzie in an RAS press release. While the study had a large margin of error, the simulations suggest there is only a two percent probability that the Cold Spot formed randomly.
“This means we can’t entirely rule out that the Spot is caused by an unlikely fluctuation explained by the standard model. But if that isn’t the answer, then there are more exotic explanations,” said researcher Tom Shanks in the press release. “Perhaps the most exciting of these is that the Cold Spot was caused by a collision between our universe and another bubble universe.”
If more detailed studies support the findings of this research, the Cold Spot might turn out to be the first evidence for the multiverse, though far more evidence would be needed to confirm our universe is indeed one of many.