The physics world has been in a tizzy for the last few weeks as tweets and rumors suggest that scientists may have detected long-sought ripples in space-time called gravitational waves. While some of this is speculation, there is some evidence to suggest that researchers at the Laser Interferometer Gravitational-Wave Observatory (LIGO) may have come across the first direct evidence for these waves since Albert Einstein proposed their existence a century ago in his general theory of relativity.
Here are five things to know about gravitational waves to prepare for the upcoming announcement.
What are they?
If you think of the universe as a vast ocean, gravitational waves are like ripples caused when an object is dropped on its surface. According to Einstein’s theory, changes in the acceleration of massive objects in space, like neutron stars and black holes, start these radiating ripples through the fabric of space-time—with the most dramatic effects from collisions, Joshua Sokol writes for New Scientist.
Why are they such a big deal?
Gravitational waves would not only further support relativity, they could also help scientists study many mysterious phenomena in the cosmos. Astronomers right now scan the skies using the electromagnetic spectrum, which reveals different types of objects depending on the wavelength. Gravitational waves would be “the most direct way of studying the large fraction of the universe which is dark,” LISA Pathfinder scientist Bill Weber tells Gizmodo. The waves pass though otherwise difficult-to-spot bodies, providing a glimpse into the mysterious forms that would be akin to seeing them in a whole new wavelength.
Though elusive, these ripples are also central to many theories about the universe’s earliest beginnings. Calculations show that the universe went through a period of rapid expansion in the seconds after the Big Bang. Gravitational waves created in this speedy inflation period would have twisted through the cosmic microwave background, the earliest radiation that permeates the universe. The ripples would leave a mark like a fingerprint that could be traced to the very beginnings of existence. LIGO is designed to detect more recent waves, cosmically speaking, but just proving they exist would be a big step.
How do scientists look for them?
Most gravitational wave detectors work by attempting to spot minute changes in the distance between objects separated by a known amount, reports Maddie Stone for Gizmodo. The idea is that a wave passing through Earth would wrinkle space-time in a way that changes that distance.
There are several ongoing experiments based all over the world, each testing different techniques. LIGO, for example, has two detectors located almost 2,000 miles apart, and it aggregates data from 75 observatories around the world to detect and triangulate possible signals from gravitational waves passing through Earth. Other researchers have proposed using highly sensitive atomic clocks to detect temporal distortions, and the European Space Agency recently launched a satellite that will test technology that could help scientists devise new ways to measure miniscule fluctuations in space.
Why are they so hard to detect?
When you drop a stone into a body of water, the ripples get smaller the farther they move from the epicenter. Gravitational waves follow the same basic principle. Space is vast, and scientists believe that many of the sources of gravitational waves are bodies that hover on the edges of the universe, which means any signals that reach Earth would be extremely faint and hard to isolate. Most observatories searching for gravitational waves have to comb for miniscule distortions in the fabric of space-time—the LIGO detectors, for example, can measure shifts as small as one ten-thousandth the diameter of a proton, Sokol writes.
Wait, why does this sound familiar?
This isn’t the first time scientists have announced the discovery of gravitational waves. In 2014 astronomers working with the BICEP2 observatory near the South Pole said that they had found evidence for gravitational waves from the dawn of the universe. But that turned out to be a false alarm caused by cosmic dust. LIGO has also had its own false positives in the past. In 2010, before the observatory was upgraded to its current sensitivity, researchers detected what they thought might be evidence for a gravitational wave, but later realized it was just a signal their own scientists made to test whether they could tell the difference between a fake signal and the real thing.
While we won’t know for sure what happened at LIGO until Thursday, there is evidence in the observatory’s public logs that suggests they might really be onto something this time. Since the current experiment began last September, logs show that LIGO researchers have followed up on at least three leads in different parts of the sky, Sokol reports. It could be yet another false alarm, but for now, physicists, astronomers and space enthusiasts are waiting with mounting excitement.