Over time, researchers have identified several kinds of time crystals, each with unique properties that could be useful in different applications.

A New Sound-Levitated Time Crystal

Physicists at New York University have now created a new version of a time crystal. In this system, tiny particles float on a cushion of sound and interact by exchanging sound waves. During these interactions, the particles behave in a way that appears to break Newton’s Third Law of Motion, which states that for every action, there is an equal and opposite reaction (i.e., forces always occur in balanced pairs). In this experiment, however, the particles do not follow that balance. Instead, they move in a nonreciprocal way, meaning their interactions are uneven and not mirrored.

The results, published in Physical Review Letters, point to new possibilities for using time crystals in technology and industry. Unlike many previous experiments, this system is visible to the naked eye and operates on a compact device about one foot tall that can be held in your hand.

“Time crystals are fascinating not only because of the possibilities, but also because they seem so exotic and complicated,” says Physics Professor David Grier, director of NYU’s Center for Soft Matter Research and the paper’s senior author. “Our system is remarkable because it’s incredibly simple.”

Insights Into Biology and Circadian Rhythms

The study, carried out with Mia Morrell, an NYU graduate student, and Leela Elliott, an NYU undergraduate, may also help scientists better understand biological timing systems such as circadian rhythms. Similar to these time crystals, some biochemical processes in the body involve nonreciprocal interactions, including how the body breaks down food.

How Sound Waves Keep Particles Floating

The time crystal itself is made from small styrofoam beads, similar to packing material, that are held in place by sound waves. This setup acts as an “acoustic levitator,” allowing the beads to remain suspended and still in mid-air.

“Sound waves exert forces on particles — just like waves on the surface of a pond can exert forces on a floating leaf,” explains Morrell. “We can levitate objects against gravity by immersing them in a sound field called a standing wave.”

When the levitated beads interact, they do so by scattering sound waves between one another.

Uneven Forces and Broken Symmetry

Larger beads scatter more sound than smaller ones. As a result, a larger particle has a stronger effect on a smaller particle than the smaller particle has on the larger one. This creates an imbalance in how they influence each other.

“Think of two ferries of different sizes approaching a dock,” says Morrell. “Each one makes water waves that pushes the other one around — but to different degrees, depending on their size.”

Because these interactions are carried by sound waves, they are not limited by Newton’s Third Law. This allows the beads to begin oscillating on their own while floating in mid-air, producing a steady rhythm that reflects the unusual forces at play.

The research was supported by grants from the National Science Foundation (DMR-21043837, DMR-2428983).

An international research team led by Griffith University, Indonesia’s national research and innovation agency (BRIN), and Southern Cross University determined that these paintings on the island of Sulawesi were created at least 67,800 years ago.

Researchers say this breakthrough helps clarify when and how humans first reached Australia. The people who made the Sulawesi art were likely closely related to the ancestors of Indigenous Australians.

Ancient Handprint and Advanced Dating Techniques

The artwork was preserved in limestone caves in southeastern Sulawesi, on the nearby island of Muna. Scientists identified a partial hand stencil surrounded by much younger paintings.

To determine its age, the team used uranium-series dating, examining tiny mineral layers that had formed over and sometimes beneath the artwork in Liang Metanduno cave. This allowed them to establish when the paintings were created.

The hand stencil dates back at least 67,800 years, making it the oldest reliably dated cave art ever found. It is significantly older than another Sulawesi painting identified by the same team in 2024.

The findings also show that people continued creating art in this cave for a remarkably long time. Artistic activity spanned at least 35,000 years, lasting until around 20,000 years ago.

“It is now evident from our new phase of research that Sulawesi was home to one of the world’s richest and most longstanding artistic cultures, one with origins in the earliest history of human occupation of the island at least 67,800 years ago,” said Professor Maxime Aubert, an archaeologist and geochemist from the Griffith Centre for Social and Cultural Research (GCSCR), who co-led the study.

A Unique Claw-Like Handprint

The team noted that this hand stencil stands out as a unique variation of a common motif.

After it was first created, the image appears to have been intentionally modified. The outlines of the fingers were narrowed, giving the hand a claw-like appearance.

Professor Adam Brumm of Griffith University’s Australian Research Centre for Human Evolution (ARCHE), a co-leader of the study, said the meaning behind this alteration remains uncertain.

“This art could symbolize the idea that humans and animals were closely connected, something we already seem to see in the very early painted art of Sulawesi, with at least one instance of a scene portraying figures that we interpret as representations of part-human, part-animal beings,” Professor Brumm said.

Clues to Early Human Migration to Australia

Dr. Adhi Agus Oktaviana, a rock art specialist at BRIN and a team leader whose doctoral research at Griffith University contributed to the study, said the discovery has major implications for understanding the deep history of Australian Aboriginal culture.

“It is very likely that the people who made these paintings in Sulawesi were part of the broader population that would later spread through the region and ultimately reach Australia,” Dr. Oktaviana said.

For years, archaeologists have debated when humans first arrived on the ancient landmass known as Sahul, which once connected present-day Australia, Tasmania and New Guinea.

Some researchers support a short chronology, suggesting humans arrived around 50,000 years ago. Others favor a long chronology, placing their arrival at least 65,000 years ago.

“This discovery strongly supports the idea that the ancestors of the First Australians were in Sahul by 65,000 years ago,” Dr. Oktaviana said.

Migration Routes and Ongoing Research

Scientists have proposed two main pathways into Sahul. One is a northern route through Sulawesi and the ‘Spice Islands’ toward New Guinea. The other is a southern route that carried early seafarers more directly to Australia via Timor or nearby islands.

Professor Renaud Joannes-Boyau of the Geoarchaeology and Archaeometry Research Group (GARG) at Southern Cross University said the new evidence strengthens the case for the northern route.

“With the dating of this extremely ancient rock art in Sulawesi, we now have the oldest direct evidence for the presence of modern humans along this northern migration corridor into Sahul,” Professor Joannes-Boyau said.

“These discoveries underscore the archaeological importance of the many other Indonesian islands between Sulawesi and westernmost New Guinea,” said Professor Aubert, who continues working with colleagues to uncover more evidence of early human activity along this route with support from the Australian Research Council (ARC).

The ARC funding is part of a broader effort to study human origins. This includes the ARC Centre of Excellence for Transforming Human Origins Research, led by Griffith University, and the ARC Training Centre for Advancing Archaeology in the Resources Sector at Southern Cross University. These initiatives aim to expand knowledge of human evolution and help protect cultural heritage.

Additional support for the research came from Google Arts & Culture and the National Geographic Society.

The Sulawesi discoveries have also been featured in a documentary, ‘Sulawesi l’île des premières images,’ produced by ARTE and released in Europe.

The study, titled ‘Rock art from at least 67,800 years ago in Sulawesi,’ was published in Nature.