To understand the Center’s work, it’s important to understand its name: “spacetime symmetry.” In physics, spacetime refers to a model in which 3D space and time are connected. That is to say, every action has both a “when” and “where.” Symmetry is a more familiar term. To describe it, Associate Director of the IUCSS and Associate Scientist of Physics, Ralf Lehnert held up a blank piece of paper. “If I show you this paper” he said, “and then rotate it 180º,” he added while turning the sheet, “it looks exactly the same. You have no way of telling me that this paper is different from what I originally showed you.”
Putting the two concepts together, spacetime symmetry is the idea that the laws of physics are consistent (symmetrical) throughout all of spacetime. If you threw a ball into the air in Bloomington, for example, it would behave the same as a ball thrown in London. The laws of physics don’t change depending on where you are, when the experiment is performed, or a variety of other transformations, specifically those which leave light speed unchanged. At least, that is what physicists have traditionally believed. Mike Snow, director of the IUCSS and professor of physics, explained, “page one of the theory books says, ‘we assume this is correct.’” However, in the late 1980’s a team of IU researchers led by Distinguished Professor of Physics Alan Kostelecký started asking, “What if it’s not?”
The team’s study of such violations of spacetime symmetries started to pick up pace, and in 2010 it became clear that this idea harbored the seeds to ignite a new area of physics research. The IUCSS was founded that same year and quickly garnered the attention of researchers in Bloomington and beyond. “It surprised me how many people came out of the woodwork to get interested in the particular subject we were attacking,” said Professor Snow. “It seemed to strike a chord among various people.”
Today, the Center has more than 20 faculty and 40 student members, not to mention dozens of collaborators outside of the university. And, reflected Snow, those numbers will only continue to grow: “As we’ve made progress on the theoretical side, it’s opened up intellectual questions in new areas.” Researchers from a wide variety of subfields within physics are starting to consider how violations of spacetime symmetry could appear in their discipline.
Research at the Center generally falls into two categories: theoretical and experimental. Professor Lehnert tackles the theoretical side. He asks questions like: if there are perturbations in spacetime symmetry, what would they look like? Using mathematical and physical models, Lehnert can measure how much a phenomenon differs from what you would expect based on spacetime symmetry. His calculations pave the way for experimental studies, showing researchers what violations of spacetime symmetry would look like in their field.
On the experimental side, the key is precision. Violations of spacetime symmetry, if there are any, will be extremely small and difficult to find. In the words of Lehnert, “It would be like finding a single penny in the whole budget of the US.” To do this, researchers use highly sensitive experiments. Snow, for example, works at the subatomic level. He studies neutrons and their interactions with the matter around them. Working in such a small system, even the tiniest irregularity matters.
Any deviation from what spacetime symmetry predicts would be groundbreaking. For Snow, that’s the thrill of the field. “We could fail (to find an exception to Einstein’s idea)!” He said, “We could completely get zero. We have for decades. But physicists are stubborn, we don’t give up so easily. We say, ‘You never know.’” Even if researchers don’t find any violations of spacetime symmetry, they’ve still made lasting contributions to the field. As Snow put it: “The minimum thing we can say is ‘Don’t touch this law, it’s strong’.”
Aside from its benefit to science, the IUCSS is also an impressive asset to the University. The Center hosts workshops and conferences to bring together “scientists from all over the world who never usually see each other,” creating opportunities for new collaborations and ideas, said Lehnert. It also allows IU faculty to push the boundaries of their field and pass on the next generation of physics knowledge to their students.
You can stay up-to-date with the Center’s work and events on their website. Graduate students can participate in “Summer School:” a program offered every 3 years with presentations from researchers in the field and mentoring on a project related to violations of spacetime symmetry. The Center also hosts a variety of workshops and meetings on spacetime symmetry, with the next events planned for May 2023.
