A team of physicists at Stockholm University has come up with a groundbreaking proposal: a method to detect single gravity. Interestingly, “those elusive particles were considered too difficult to observe” until now.
For context, gravitons are theoretical particles believed to be the building blocks of gravity. Scientists have long struggled to bridge the gap between gravity and quantum mechanics.
“If we believe in the quantum theory, even gravity must be made of small, quantized particles – gravitons,” the researchers say.
But “single gravitons do not interact with anything at all. They pass almost all objects as they cross the universe. Detecting them seemed impossible,” the researchers added in a press release.
Suggested solution
Now, a team of researchers, led by Stevens physics professor Igor Pikovski, “has worked out how to make a single graviton detector” that could enable the detection of gravitons.
Their method promotes recent developments in the field of quantum sensing and the study of quantum macroscopic objects.
These objects, large enough to be seen with the naked eye but exhibiting massive behavior, are ideal for detecting gravity due to their strong interaction with gravity.
The team’s proposal is based on existing technologies, such as sound generators and Weber bars.
The detector works by cooling a super-quantum object to its lowest energy state and then subjecting it to gravitational waves.
“We need to cool the material and then monitor how the energy changes in one step, and this can be achieved through quantum sensing,” explained postdoctoral researcher Sreenath Manikandan.
The gravito-phonetic effect
Scientists speculate that when a graviton interacts with an object, it will cause a unique change in its energy, something they call a “quantum jump.”
These distortions are usually too small to detect, but by carefully tracking these quantum jumps, the team believe they can determine the absorption of a single graviton.
This “gravito-phonetic effect” reflects the photoelectric effect, in which light interacts with matter by coherent action or photons.
“Our solution mimics the photoelectric effect, but we use acoustic resonators and gravitational waves that pass through the Earth,” said PhD student Germain Tobar. “We call it the ‘gravito-phononic’ effect.”
Using LIGO data
To increase their chances of detecting gravity, the team proposes to use data from the Laser Interferometer Gravitational-Wave Observatory (LIGO). LIGO is known for its basic detection of gravitational waves, but it cannot directly detect gravity itself.
In particular, according to the team, detecting single gravity requires very strong gravitational waves. This is because the interaction between a single graviton and matter is expected to be very weak.
Besides, we can’t just create gravitational waves whenever we want in the lab. They are produced by massive cosmic events such as colliding black holes or neutron stars.
However, by carefully combining the LIGO data with measurements of the proposed detector, the researchers believe they can isolate and confirm the signature of a single graviton interaction.
“We can solve both problems using existing observations of gravitational waves,” claimed PhD student Thomas Beitel.
“We are waiting until LIGO detects a passing gravitational wave and observe how it produces quantum jumps in our detector at the same time.”
In search of a unified theory
Although the theoretical framework for the experiment is robust, the technology to detect this attraction remains a major challenge. The required level of quantum sensing capability has not yet been fully developed.
That said, the team is optimistic and is now aiming to design a real experiment using data from gravitational waves detected on Earth.
Research to detect gravitons has been going on for over a century. Einstein’s theory of relativity revolutionized our understanding of gravity, describing it as a curvature of space-time.
However, gravity remains the only fundamental force not fully explained by quantum theory. The successful discovery of the graviton would mark an important step toward a “unified theory of everything.”
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