A model for exploring the truths of the universe – the Standard Model.
Eight ring magnets for cern's ATLAS detector. Image source: Maximilien Brice.
This article was originally published in The Conversation, which recommended it to Space's Expert Voices: Op-Ed & Insights.
Aaron McGowan: Principal Lecturer in Physics and Astronomy at the Rochester Institute of Technology.
If you ask a physicist like me to explain how the world works, my unruly answer would probably be, "It follows the Standard Model." “
The Standard Model explains the fundamental physical principles of the universe's operation. Although experimental physicists continued to explore flaws in the model's fundamentals, it withstood more than 50 trips around the sun.
With a few exceptions, it stood firm and passed experimental tests again and again with contact performance. But this extremely successful model is conceptually flawed, suggesting that there is still some knowledge to be learned about how the universe works.
I am a neutrino physicist. Neutrinos represent 3 of the 17 elementary particles in the Standard Model, and they penetrate everyone on Earth all the time. I study the properties of the interaction between neutrinos and particles of normal matter.
In 2021, physicists around the world have done some experiments studying the Standard Model. The team measured the model's basic parameters more precisely than ever before. Others investigated the edges of knowledge and found that the best experimental measurements did not exactly match the predictions of the Standard Model. Finally, the teams built more powerful techniques designed to push models to their limits and potentially discover new particles and fields. If these efforts succeed, they could lead to a more complete theory of the universe in the future.
The Standard Model of Physics allows scientists to make incredibly accurate predictions about how the world will work, but it doesn't explain everything. (Image source: CERN)
Closes the holes in the Standard Model
In 1897, J. J. Thomson J Thomson) discovered the first elementary particle, the electron, using only glass vacuum tubes and wires. More than 100 years later, physicists are still discovering new parts of the Standard Model.
The Standard Model is a predictive framework that can do two things. First, it explains what the elementary particles of matter are. These things, like electrons and quarks, make up protons and neutrons. Second, it uses "messenger particles" to predict how these particles of matter interact. These are called bosons—they include photons and the famous Higgs boson—and they convey the fundamental forces of nature. After decades of working at CERN, Europe's giant particle collider, the Higgs boson was not discovered until 2012.
The Standard Model is very good at predicting many aspects of how the world works, but it does have some holes.
It is worth noting that it does not include any gravity description. Although Einstein's theory of general relativity describes how gravity works, physicists have yet to discover a particle that transmits gravity. A proper "theory of everything" would do everything the Standard Model could do, but also include messenger particles that communicate how gravity interacts with other particles.
Another thing the Standard Model can't do is explain why any particle has a certain mass — physicists have to measure the mass of particles directly through experiments. Only after experiments have given physicists these precise masses can they be used for prediction. The better the measurement, the better the predictions that can be made.
Recently, physicists from a team at CERN measured the strong sensations of the Higgs boson. Another team at CERN also measured the mass of the Higgs boson more accurately than ever before. Finally, progress has also been made in measuring the mass of neutrinos. Physicists know that neutrinos have a mass above zero, but are lower than the number that is currently detectable. A team in Germany continues to refine the technology, allowing them to directly measure the mass of neutrinos.
Projects such as the Muon g-2 experiment highlight the differences between experimental measurements and Standard Model predictions that point to problems somewhere in physics. (Image credit: Reidar Hahn/Wikimedia Commons)
Clues to new forces or particles
In April 2021, members of the Muon G-2 experiment at Fermilab announced their first measurement of the magnetic moment of the μ meson. μ are one of the elementary particles in the Standard Model, and one of its properties has been the most accurate to date. This experiment is important because the measurements do not exactly match the standard model predictions of the magnetic moment. Basically, μ behaves abnormally. The discovery may point to undiscovered particles interacting with μ.
But at the same time, in April 2021, physicist Zortan Fodor and his colleagues showed how they could use a mathematical method called lattice QCD to accurately calculate the magnetic moments of μ. Their theoretical predictions, unlike those of the old ones, are still valid in the Standard Model and, importantly, match the experimental measurements of μ.
Before physicists can know whether an experimental result actually exceeds the Standard Model, the divergence between previously accepted predictions, this new result, and the new prediction must be reconciled.
The new tool will help physicists find dark matter and other things that could help explain the mysteries of the universe. (Image credit: Mattia Di Mauro (ESO/Fermi-Lat))
Upgrade physics tools
Physicists must vacillate between developing distorted ideas about reality that make up theories and advancing techniques to the point where new experiments can test those theories. 2021 is a big year to advance the tools of physics experiments.
First, the world's largest particle accelerator, CERN's Large Hadron Collider, was shut down and undergoing some substantial upgrades. Physicists just restarted the facility in October, and they plan to begin the next data collection effort in May 2022.
The upgrade increased the power of the collider, allowing it to produce collisions at 14 TeV, higher than the previous 13 TeV limit. This means that batches of tiny protons orbiting circular accelerators in beams carry the same amount of energy as an 800,000-pound (360-kilogram, 360-ton) passenger train traveling at 100 miles (160 kilometers) per hour. At these incredible energies, physicists may find that new particles are too heavy to be seen at lower energies.
To help find dark matter, a number of other technological advances have been made. Many astrophysicists believe that dark matter particles that don't currently fit the Standard Model can answer some of the unanswered questions about the way gravity bends around stars — called gravitational lensing — and how fast the stars spin in spiral galaxies. Projects like cryogenic dark matter search have yet to find dark matter particles, but the teams are developing larger, more sensitive detectors for deployment in the near future.
Particularly relevant to my work using neutrinos is the development of huge new detectors, such as the top-level Hyper-Kamiokande and Dune (DUNE). Using these detectors, scientists are expected to answer questions about fundamental asymmetries in neutrino oscillations. They will also be used to observe proton decay, which some theories predict should occur.
2021 highlights some of the ways in which the Standard Model fails to explain every mystery in the universe. But new measurements and new technologies are helping physicists make progress in their search for a theory of everything.
BY: Aaron McGowan
FY: Green mountains and green water
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