Physicists measured the smallest gravitational field ever recorded, in an experiment that could help in the search for a unified physical theory.
Of the four fundamental forces known to physics – the weak and strong interaction, the electromagnetic force and gravity – only gravity remains unchanged in the playbook of physics, called the standard model, which describes how the zoo of subatomic particles behaves. Gravity is rather described by Einstein’s general theory of relativity, but if it breaks down on the quantum scale, our best picture of the universe is divided into two.
As a result, physics still cannot describe how gravity works on subatomic scales, what makes physicists scratch their heads when it comes to the singularities that lie in the middle of black holes, or why gravity is so much weaker than all the others. the other forces.
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But a new experiment that measured the minimum gravity between two small golden spheres, which is only 2 millimeters wide, may be the first of many to give directions on how gravity works on this scale.
“It was proof of concept experimentation to create a sensor that could measure very small accelerations and to determine methods that would enable us to detect even smaller gravitational forces,” studied co-author Jeremias Pfaff, ‘ a doctoral student at the University of Vienna, told Live Science. “In the long run, we want to answer what the gravitational field of a quantum object in a superposition looks like there, but there is a lot that needs to be done on the way there,” Pfaff said, referring to gravity experiencing a subatomic experience. particle that is in two quantum states simultaneously.
To get a glimpse of how gravity works on a small scale, the researchers used a small version of a torsional balance – a device first designed by English scientist Henry Cavendish in 1798 to measure the density of the Earth, and hence the strength of the gravitational constant called G.
A torsion balance is a horizontal rod that hangs at its center through a wire with two masses, in this case golden spheres, attached to each side. This means that if a small force is mounted along the horizontal axis of the rod, the wire will rotate and scientists can measure the force applied based on how much the rod has rotated. By bringing a third golden sphere in close proximity to one of those attached to the end of the rod, the researchers were able to measure the gravity between it and the attached sphere.
The power the researchers were looking for was small. At about 9 × 10 ^ minus 14 newtons it would be the force that one third of a human blood cell would experience in the Earth’s gravitational field. The experiment therefore had to be incredibly sensitive, and the researchers had to limit exposure to outside noise, make sure no stray charges had built up on the device, and find a way to detect the desired signal.
“The urban environment is also far from ideal,” Pfaff said. “It was amazing to see that we are not only sensitive to small earthquakes, but also to the local tram and some buses. We could even see the Vienna City Marathon in our data.”
They got rid of stray charges by flooding the area around the device with ionized nitrogen before placing it in a vacuum. They also made the small gravitational signal they were looking for stand out more by slowly moving the two spheres closer and further apart.
In the same way that a flashing light is more conspicuous than a constant, the growing and shrinking force of gravity between the spheres was much easier to select than when it was stationary. This enabled the researchers to find the strength of the gravitational force between the two spheres and also to find their own measurement for the gravitational constant.
So far, on the scale they measured, gravity has followed the same predictable rules as on larger scales. The physicists now hope to make their experiment even more sensitive, allowing them to record smaller signals of masses at least 1000 times lighter and at shorter distances. It can provide important clues for a theory that explains gravity on a small and large scale, along with insights into other mysteries, such as the existence of dark matter, a mysterious form of matter that does not yet emit light.
On a smaller scale, the researchers were able to begin to discover completely new ways in which matter interacts through gravity – ways that follow the much more bizarre rules of the quantum world. If that does happen, physics can finally begin to bridge the gap between our big and small pictures of the universe.
“Expanding our knowledge about this elusive force can help us gather tips to find a more fundamental understanding of our physical reality,” Pfaff said.
Originally published on Live Science.