TORONTO: Researchers at the University of Toronto say they have confirmed the existence of “negative time” in a tangible physical sense, challenging traditional perceptions of how time works.
For years, scientists have observed that light can sometimes appear to leave a material before it has even entered, which is often dismissed as a distortion caused by the waves’ interaction with matter.
However, the team’s latest experiments suggest that this phenomenon is not an illusion but a measurable reality.
The findings, which have not yet been published in a peer-reviewed journal, have attracted both global attention and skepticism.
The researchers emphasize that these puzzling results highlight a quirk of quantum mechanics rather than a radical change in our understanding of time.
“This is a difficult thing, even for us, to talk to other physicists. We get misunderstood all the time,” said Aephraim Steinberg, a University of Toronto professor specializing in experimental quantum physics.
While the term “negative time” may seem like a concept straight out of science fiction, Steinberg defends its use, hoping that it will spark deeper discussions about the mysteries of quantum physics.
laser experiments
Years ago, the team began exploring interactions between light and matter.
When light particles, or photons, pass through atoms, some are absorbed by the atoms and then re-emitted. This interaction changes the atoms, temporarily putting them in a higher energy or “excited” state before they return to normal.
In research led by Daniela Angulo, the team set out to measure how long these atoms remained in their excited state. “That time turned out to be negative,” Steinberg explained, meaning a duration less than zero.
To visualize this concept, let’s imagine cars entering a tunnel: Before the experiment, physicists recognized that while the average entry time for a thousand cars might be, say, noon, the first cars might leave a little earlier, say at 11:59 am. This result was previously discarded as meaningless.
What Angulo and his colleagues demonstrated was similar to measuring carbon monoxide levels in the tunnel after the first cars emerged and finding that the readings had a minus sign in front of them.
Relativity intact
The experiments, conducted in a cramped basement lab packed with aluminum-wrapped cables and devices, took more than two years to optimize. The lasers used had to be carefully calibrated to avoid distorting the results.
Still, Steinberg and Angulo are quick to clarify: no one claims that time travel is a possibility. “We don’t want to say that anything has traveled back in time,” Steinberg said. “That’s a misinterpretation.”
The explanation lies in quantum mechanics, where particles like photons behave in confusing and probabilistic ways rather than following strict rules.
Rather than adhering to a fixed schedule for absorption and re-emission, these interactions occur across a spectrum of possible durations, some of which defy everyday intuition.
Crucially, the researchers say, this does not violate Einstein’s theory of special relativity, which dictates that nothing can travel faster than light. These photons carried no information, circumventing any cosmic speed limit.
A divisive discovery
The concept of “negative time” has sparked both fascination and skepticism, especially among prominent voices in the scientific community.
German theoretical physicist Sabine Hossenfelder, for her part, criticized the work in a YouTube video viewed by more than 250,000 people, noting: “The negative time in this experiment has nothing to do with the passage of time; it is just a way “to describe how photons travel through a medium and how their phases change.”
Angulo and Steinberg responded, arguing that their research addresses crucial gaps in the understanding of why light does not always travel at a constant speed.
Steinberg acknowledged the controversy surrounding the provocative headline of his paper, but noted that no serious scientist has questioned the experimental results.
“We have chosen what we believe is a fruitful way to describe the results,” he said, adding that while practical applications remain elusive, the findings open new avenues for exploring quantum phenomena.
“I’ll be honest, I currently don’t have a path from what we’ve been looking for to the applications,” he admitted. “We’re going to keep thinking about it, but I don’t want to get people’s hopes up.”
