Was the great Albert Einstein right?
The German-born theoretical physicist who developed the theory of relativity, one of the two pillars of modern physics alongside quantum mechanics, is perhaps best known to the public for his mass-energy equivalents formula, E = mc2, dubbed the world’s most famous equation.
Scientists from the International Centre for Radio Astronomy Research (ICRAR) and the University of Western Australia (UWA) have put relativity to the ultimate test to date — setting a world record for the most stable transmission of a laser signal through the atmosphere, Phys.org reported.
In a study published in the journal Nature Communications, Australian researchers teamed up with researchers from the French National Centre for Space Studies (CNES) and the French metrology lab Systèmes de Référence Temps-Espace (SYRTE) at Paris Observatory.
The team set the world record for the most stable laser transmission by combining phase stabilization technology from Australia with advanced self-guiding optical terminals. Together, these technologies allowed laser signals to be sent from one point to another without interference from the atmosphere, the report said.
Why is this significant?
The researchers say their laser will allow science such as Einstein’s theory of general relativity to be tested more precisely than ever before.
In layman’s terms, Einstein’s theory of relativity is a theory of gravity.
According to a report in NBC News, the basic idea is that instead of being an invisible force that attracts objects to one another, gravity is a curving or warping of space. The more massive an object, the more it warps the space around it.
For example, the sun is massive enough to warp space across our solar system — a bit like the way a heavy ball resting on a rubber sheet warps the sheet. As a result, Earth and the other planets move in curved paths (orbits) around it.
This warping also affects measurements of time. We tend to think of time as ticking away at a steady rate. But just as gravity can stretch or warp space, it can also dilate time.
If your friend climbs to the top of a mountain, you’ll see his clock ticking faster compared to yours; another friend, at the bottom of a valley, will have a slower-ticking clock, because of the difference in the strength of gravity at each place.
Special relativity is ultimately a set of equations that relate the way things look in one frame of reference to how they look in another — the stretching of time and space, and the increase in mass. The equations involve nothing more complicated than high-school math.
General relativity is more complicated. Its “field equations” describe the relationship between mass and the curvature of space and dilation of time, and are typically taught in graduate-level university physics courses.
In 1971, scientists tested both parts of Einstein’s theory by placing precisely synchronized atomic clocks in airliners and flying them around the world.
A check of the timepieces after the planes landed showed that the clocks aboard the airliners were running a tiny bit slower than (less than one millionth of a second) than the clocks on the ground.
The disparity resulted from the speed of the planes (a special relativity effect) and their greater distance from the center of Earth’s gravitational field (a general relativity effect).
In 2016, the discovery of gravitational waves — subtle ripples in the fabric of spacetime — was another confirmation of general relativity.
Lead author Benjamin Dix-Matthews, a Ph.D. student at ICRAR and UWA, said the technique effectively eliminates atmospheric turbulence, the report said.
“We can correct for atmospheric turbulence in 3-D, that is, left-right, up-down and, critically, along the line of flight,” he said.
“It’s as if the moving atmosphere has been removed and doesn’t exist. It allows us to send highly stable laser signals through the atmosphere while retaining the quality of the original signal.”
The result is the world’s most precise method for comparing the flow of time between two separate locations using a laser system transmitted through the atmosphere, the report said.
ICRAR-UWA senior researcher Dr. Sascha Schediwy said the research has exciting applications.
“If you have one of these optical terminals on the ground and another on a satellite in space, then you can start to explore fundamental physics,” he said.
“Everything from testing Einstein’s theory of general relativity more precisely than ever before, to discovering if fundamental physical constants change over time.”
The technology’s precise measurements also have practical uses in earth science and geophysics, the report said.
“For instance, this technology could improve satellite-based studies of how the water table changes over time, or to look for ore deposits underground,” Dr. Schediwy said.
There are further potential benefits for optical communications, an emerging field that uses light to carry information.
Optical communications can securely transmit data between satellites and Earth with much higher data rates than current radio communications, the report said.
“Our technology could help us increase the data rate from satellites to ground by orders of magnitude,” Dr. Schediwy said. “The next generation of big data-gathering satellites would be able to get critical information to the ground faster.”
The phase stabilization technology behind the record-breaking link was originally developed to synchronize incoming signals for the Square Kilometer Array telescope.
The multi-billion-dollar telescope is set to be built in Western Australia and South Africa from 2021.