The question of where gravity comes from is a seemingly eternal one among theoretical physicists, and most answers involve dark matter, which can't be accounted for by regular physics. But a new theory offers an explanation that can be explored with existing equations: Gravity might originate in the quantum vacuum.
This vast region of space contains only fleeting, charged particles. Suggesting that the quantum vacuum could surround large bodies such as planets, a paper published March 18 in Monthly Notices of the Royal Astronomical Society proposes that the environment of the quantum vacuum is conducive to fostering gravitational fields.
One in a series of studies, the new paper explains how, just like a magnet, there would exist an intuitive force in the vacuum between a positive particle and a negative one, called an antiparticle. The catch is that because this "magnet" is analogous to a gravitational field, the negative half would require negative gravity, which isn't thought to exist in the observable universe. That's because gravity is always considered positive, or attractive. A negative version would reflect opposite effects — if gravity was reversed on Earth, humans would be ejected into space.
However, study author Dragan Hajdukovic, a professor of physics who worked at the European Council for Nuclear Research for more than 20 years and currently works at the Institute of Physics, Astrophysics and Cosmology, in Montenegro, explained that the charge limitation doesn't appear to exist in the quantum vacuum.
"There are unexpected phenomena, like 'islands,' of the quantum vacuum, with a negative effective gravitational charge," he told The Academic Times. "Islands like small invisible planets that repel the surrounding matter."
He continued, "We can exactly calculate where we have to look for these islands. And if these islands exist, it's a confirmation of [the] theory."
In classical physics, a vacuum is thought to indicate a region of utter nothingness: no matter, force or light.
Quantum physics has a separate interpretation. A quantum vacuum is almost completely empty, except for something called virtual quantum particles — the charged particles that make up Hajdukovic's proposed gravitational fields.
"There [are] quite different states of matter and energy," he said, referring to solids and liquids. "Quantum vacuum is the most surprising state that emerged from the quantum field theory. And now, we know for sure that it exists."
These virtual particles appear and disappear extremely quickly. That's because they're not really particles at all, but are more like minor disturbances, or fluctuations, in electromagnetic waves found within the vacuum. It would also be inevitable for the virtual quantum particles to interact.
If these particles carry both positive and negative gravitational effective charge, each interaction would generate a minor gravitational force, Hajdukovic said. Also called a gravitational dipole, he terms those forces "magnetic needles."
"Imagine billions and billions of magnetic needles aligning with the magnetic field of the Earth," he said. "A single needle can change nothing, but if there are billions of needles, they will contribute to the magnetic field of the Earth."
If Hajdukovic is correct, the mystery of the invisible force would finally be solved — and thoroughly, because his theory offers a rare backing for gravity that is comprehensible in the realm of human physics.
"So far, we've had two revolutions in our understanding of gravity: Newton's and Einstein's," Hajdukovic explained. "For both of them, [bodies] are in an empty space. In my theory, bodies are not immersed in the empty space, but in the quantum vacuum."
Newton's contribution to gravity theory is that large masses in space attract each other; the bigger the mass, the greater the attraction. That's called the law of universal gravitation.
Einstein's general relativity theory says that gravity isn't a force at all. Rather, it's a consequence of the distortion of space and time. As the fabric of the universe curves, things curve with it; his work says that's perceived as gravity.
Beyond what Newton and Einstein found, many believe that normal physics can't explain gravity. As a result, scientists usually seek something new to understand the omnipresent force. That's where dark matter comes in.
But Hajdukovic has reservations about that method.
"We don't know what [it is], and we are not able to detect any dark matter particles," he said. "Each time when we have a problem, we assume an ad hoc hypothesis."
The quantum vacuum theory doesn't need dark matter to be dissected; it can even be tested within the solar system, he says in an upcoming paper. The researcher further proposes that the theory can be used to explain hypothetical dark matter itself.
"I was thinking in a different direction," Hajdukovic said. "Maybe there is a hidden way to explain it by our known physics."
He added, "The impact of the quantum vacuum is minuscule compared with Newtonian — and general relativistic — gravitational fields. But at large distances, gravitation caused by quantum vacuum can become larger than gravitation caused by [a] body."
He also suggests that the antiparticle in the dipole could be attributed to the phenomenon of antimatter, which is just like conventional matter, except it has negative protons and positive electrons.
In fact, Hajdukovic's association with CERN stems from it being the only place in the world with access to antimatter. He hopes to see whether the elusive matter contributes to his theory.
Acknowledging that the quantum vacuum theory is not in the mainstream of physics, Hajdukovic believes that such diversity of ideas might be a good thing, because only one theory needs to work for the whole of physics to have a breakthrough.
"If you have one idea, if I have one idea, if many people have different ideas, and one of these different ideas works in nature," he said, "it's the victory of the whole generation."
The paper, "Gravitational polarization of the quantum vacuum caused by two point-like bodies," was published March 18 in Royal Astronomical Society. It was authored by Dragan Slavkov Hajdukovic and Sergej Walter, INFI.