The universe "remembers" probably every gravitational wave

The universe can "remember" gravitational waves long after they pass.

This is the principle of a theoretical article published April 25 in the journal Physical Review D. Gravitational waves, light ripples in space and time that humanity has been able to detect only in recent years, tend to move very quickly. But the authors of the paper showed that after the passage of the waves, they could leave a slightly altered region, leaving behind a kind of memory of their crossing.

These changes, which the researchers termed "persistent gravitational wave observables," would be even weaker than the gravitational waves themselves, but these effects would last longer. Objects can be slightly moved. The positions of particles drifting in space could be modified. Even the weather itself could be slightly out of sync and operate briefly at different speeds in different parts of the Earth. [9 Ideas About Black Holes That Will Blow Your Mind]

These changes would be so tiny that scientists would barely be able to detect them. The researchers wrote in their article that the simplest method to observe these effects could involve two people "carrying around small gravitational wave detectors" – a joke because the detectors are big enough.

But there are ways for researchers to detect these memories. Here is the most obvious: look for changes in the existing gravitational wave detector mirrors.

At the present time, scientists can detect gravitational waves by building observatories that emit laser beams that are immobile and stable over long distances. When the beams move slightly, this is the sign that a gravitational wave has passed. By studying maneuvers, physicists can measure the waves. The first detection of this type took place in 2015 and since then the technology has improved so that observatories detect gravitational waves once a week.

These waves come from massive events, such as when black holes and neutron stars collide very far in space. By the time they reach Earth, however, the waves are barely noticeable. Their long-term effects are even less obvious.

But the mirrors of the detectors are constantly measured so precisely that, over time, the displacements caused by the gravitational waves could become so intense that the researchers will be able to locate them. The researchers have developed a mathematical model that predicts how much the mirrors should move in time at each passing wave.

Other methods that humans could use to detect these long-term effects involve atomic clocks and rotating particles.

Two atomic clocks placed at a distance from each other would perceive a gravitational wave differently, including its temporal dilation effects: as time would be slower for one clock than for the other, subtle differences in their readings after a past wave can leave the wave in the local universe.

Finally, a tiny spinning particle could change behavior before and after the passage of a wave. Hang it in a lab room and measure its speed and direction of rotation; then measure it again after passing a wave. The difference in behavior of the particle would reveal another type of wave memory.

This theoretical article, at the very least, offers scientists an intriguing new way of designing construction experiments to study gravitational waves.

Originally published on Science live.