University of Copenhagen team contributes to an Antarctic large-scale experiment striving to search out out if gravity also exists on the quantum level. A unprecedented particle in a position to travel undisturbed through space seems to carry the reply.
Several thousand sensors distributed over a square kilometer near the South Pole are tasked with answering considered one of the massive outstanding questions in physics: does quantum gravity exist? The sensors monitor neutrinos — particles with no electrical charge and almost without mass — arriving on the Earth from outer space. A team from the Niels Bohr Institute (NBI), University of Copenhagen, have contributed to developing the strategy which exploits neutrino data to disclose if quantum gravity exists.
“If as we imagine, quantum gravity does indeed exist, this may contribute to unite the present two worlds in physics. Today, classical physics describes the phenomena in our normal surroundings corresponding to gravity, while the atomic world can only be described using quantum mechanics. The unification of quantum theory and gravitation stays some of the outstanding challenges in fundamental physics. It could be very satisfying if we could contribute to that end,” says Tom Stuttard, Assistant Professor at NBI.
Tom Stuttard is co-author of a scientific article recently published by the journal Nature Physics. The article presents results from a big study by the NBI team and American colleagues. Greater than 300,000 neutrinos have been studied. Nonetheless, these aren’t neutrinos of essentially the most interesting type originating from sources in deep space. The neutrinos on this study were created within the Earth’s atmosphere, as high-energy particles from space collided with Nitrogen or other molecules.
“Taking a look at neutrinos originating from the Earth’s atmosphere has the sensible advantage that they’re by much more common than their siblings from outer space. We would have liked data from many neutrinos to validate our methodology. This has been achieved now. Thus, we’re able to enter the following phase during which we are going to study neutrinos from deep space,” says Tom Stuttard.
Travelling undisturbed through the Earth
The IceCube Neutrino Observatory is situated next to the Amundsen-Scott South Pole Station in Antarctica. In contrast to most other astronomy and astrophysics facilities, IceCube works the perfect for observing space at the other side of the Earth, meaning the Northern hemisphere. It is because while the neutrino is perfectly able to penetrating our planet — and even its hot, dense core — other particles will probably be stopped, and the signal is thus much cleaner for neutrinos coming from the Northern hemisphere.
The IceCube facility is operated by the University of Wisconsin-Madison, USA. Greater than 300 scientists from countries world wide are engaged within the IceCube collaboration. University of Copenhagen is considered one of greater than 50 universities having an IceCube center for neutrino studies.
For the reason that neutrino has no electrical charge and is sort of massless, it’s undisturbed by electromagnetic and powerful nuclear forces, allowing it to travel billions of lightyears through the Universe in its original state.
The important thing query is whether or not the properties of the neutrino are actually completely unchanged because it travels over large distances or if tiny changes are notable in spite of everything.
“If the neutrino undergoes the subtle changes that we suspect, this is able to be the primary strong evidence of quantum gravity,” says Tom Stuttard.
The neutrino is available in three flavors
To know which changes in neutrino properties the team is on the lookout for, some background information is known as for. While we confer with it as a particle, what we observe as a neutrino is absolutely three particles produced together, known in quantum mechanics as superposition. The neutrino can have three fundamental configurations — flavors as they’re termed by the physicists — that are electron, muon, and tau. Which of those configurations we observe changes because the neutrino travels, a really strange phenomenon often known as neutrino oscillations. This quantum behavior is maintained over hundreds of kilometers or more, which is known as quantum coherence.
“In most experiments, the coherence is soon broken. But this is just not believed to be brought on by quantum gravity. It’s just very difficult to create perfect conditions in a lab. You would like perfect vacuum, but someway just a few molecules manage to sneak in etc. In contrast, neutrinos are special in that they’re simply not affected by matter around them, so we all know that if coherence is broken it’s going to not be resulting from shortcomings within the human-made experimental setup,” Tom Stuttard explains.
Many colleagues were sceptical
Asked whether the outcomes of the study published in Nature Physics were as expected, the researcher replies:
“We discover ourselves in a rare category of science projects, namely experiments for which no established theoretical framework exists. Thus, we just didn’t know what to anticipate. Nonetheless, we knew that we could seek for a few of the general properties we would expect a quantum theory of gravity to have.”
“Whilst we did have hopes of seeing changes related to quantum gravity, the undeniable fact that we didn’t see them doesn’t exclude in any respect that they’re real. When an atmospheric neutrino is detected on the Antarctic facility, it’s going to typically have travelled through the Earth. Meaning roughly 12,700 km — a really short distance in comparison with neutrinos originating within the distant Universe. Apparently, a for much longer distance is required for quantum gravity to make an impact, if it exists,” says Tom Stuttard, noting that the highest goal of the study was to ascertain the methodology:
“For years, many physicists doubted whether experiments could ever hope to check quantum gravity. Our evaluation shows that it’s indeed possible, and with future measurements with astrophysical neutrinos, in addition to more precise detectors being in-built the approaching decade, we hope to finally answer this fundamental query.”
