If quantum gravity exists, scientists think they’ll find it at the South Pole

In the realm of physics, one of the most perplexing questions revolves around the existence of quantum gravity. A team of scientists has embarked on a pioneering study, utilizing data from thousands of neutrino sensors near the South Pole, to unravel this mystery.

Their findings, recently published in the prestigious journal Nature Physics, shed light on the potential to unite the two distinct worlds of physics: classical and quantum mechanics.

Quest for quantum gravity

Tom Stuttard, Assistant Professor at the Niels Bohr Institute (NBI), University of Copenhagen, is part of the team that has contributed to developing a method that exploits neutrino data to reveal the existence of quantum gravity.

“If as we believe, quantum gravity does indeed exist, this will contribute to unite the current two worlds in physics. Today, classical physics describes the phenomena in our normal surroundings such as gravity, while the atomic world can only be described using quantum mechanics,” Stuttard explains.

“The unification of quantum theory and gravitation remains one of the most outstanding challenges in fundamental physics. It would be very satisfying if we could contribute to that end,” he said.

Turning to atmospheric neutrinos for answers

The study, a collaboration between the NBI team and American colleagues, analyzed more than 300,000 neutrinos. However, these neutrinos were not the most intriguing type originating from deep space sources.

Instead, they were created in the Earth’s atmosphere when high-energy particles from space collided with nitrogen or other molecules.

“Looking at neutrinos originating from the Earth’s atmosphere has the practical advantage that they are by far more common than their siblings from outer space,” Stuttard notes.

“We needed data from many neutrinos to validate our methodology. This has been accomplished now. Thus, we are ready to enter the next phase in which we will study neutrinos from deep space,” he continued.

Data from the IceCube Neutrino Observatory

The study was conducted using data from the IceCube Neutrino Observatory, situated next to the Amundsen-Scott South Pole Station in Antarctica.

Unlike most other astronomy and astrophysics facilities, IceCube works best for observing space on the opposite side of the Earth, specifically the Northern hemisphere.

This is because while neutrinos can easily penetrate our planet, including its hot, dense core, other particles are stopped. This results in a much cleaner signal for neutrinos coming from the Northern hemisphere.

Unique properties of neutrinos

Neutrinos are unique particles with no electrical charge and nearly no mass, allowing them to travel billions of light-years through the Universe in their original state, undisturbed by electromagnetic and strong nuclear forces.

The key question the team is exploring is whether the properties of neutrinos remain completely unchanged as they travel over vast distances or if subtle changes can be detected.

“If the neutrino undergoes the subtle changes that we suspect, this would be the first strong evidence of quantum gravity,” Stuttard emphasizes.

Neutrino oscillations and quantum coherence

To understand the changes in neutrino properties that the team is searching for, it is essential to grasp some background information.

While referred to as a particle, what we observe as a neutrino is actually three particles produced together, known in quantum mechanics as superposition.

The neutrino can have three fundamental configurations, or flavors: electron, muon, and tau.

The observed configuration changes as the neutrino travels, a peculiar phenomenon known as neutrino oscillations. This quantum behavior, referred to as quantum coherence, is maintained over thousands of kilometers or more.

“In most experiments, the coherence is soon broken. But this is not believed to be caused by quantum gravity. It is just very difficult to create perfect conditions in a lab,” Stuttard explains.

“In contrast, neutrinos are special in that they are simply not affected by matter around them, so we know that if coherence is broken it will not be due to shortcomings in the human-made experimental setup,” he continued.

Searching for quantum gravity in uncharted territory

When asked about the expectations for the study’s results, Stuttard admitted, “We find ourselves in a rare category of science projects, namely experiments for which no established theoretical framework exists. Thus, we just did not know what to expect. However, we knew that we could search for some of the general properties we might expect a quantum theory of gravity to have.”

“Whilst we did have hopes of seeing changes related to quantum gravity, the fact that we didn’t see them does not exclude at all that they are real,” Stuttard clarifies.

“When an atmospheric neutrino is detected at the Antarctic facility, it will typically have travelled through the Earth. Meaning approximately 12,700 km – a very short distance compared to neutrinos originating in the distant Universe. Apparently, a much longer distance is needed for quantum gravity to make an impact, if it exists,” Stuttard continued.

Future of quantum gravity research

The study’s top goal was to establish the methodology for detecting quantum gravity. “For years, many physicists doubted whether experiments could ever hope to test quantum gravity. Our analysis shows that it is indeed possible, and with future measurements with astrophysical neutrinos, as well as more precise detectors being built in the coming decade, we hope to finally answer this fundamental question,” Stuttard concludes.

In summary, this important study led by Tom Stuttard and his colleagues marks a significant milestone in the quest to unravel the mysteries of quantum gravity. By establishing a methodology to detect quantum gravity using neutrino data, the team has opened up new avenues for future research.

As scientists continue to study neutrinos from deep space and develop more precise detectors in the coming years, they inch closer to answering one of the most fundamental questions in physics.

This study brings us closer to understanding the elusive nature of quantum gravity and holds the potential to bridge the gap between the two distinct worlds of classical and quantum mechanics, ultimately leading to a more unified understanding of our universe.

The full study was published in the journal Nature Physics.

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