Experimental physicist Daniela Angulo poses with a device in her physics lab at the University of Toronto.
Scientists have long known that light can sometimes appear to leave a material before it enters it, but this effect can be interpreted as an illusion caused by how waves are distorted by the material. It has been ignored.
Now, through innovative quantum experiments, researchers at the University of Toronto have shown that “minus time” is not just a theoretical concept, but exists in a concrete physical sense that deserves closer scrutiny. states that it has been demonstrated.
The findings, posted on the preprint server arXiv but not yet published in a peer-reviewed journal, have attracted both global attention and skepticism.
The researchers stress that these puzzling results highlight a quirk of quantum mechanics rather than a fundamental change in our understanding of time.
“This is difficult for us to talk about, even with other physicists. We get misunderstood all the time,” said Ephraim Steinberg, a professor at the University of Toronto who specializes in experimental quantum physics.
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Although the term “negative time” may sound like a concept lifted from science fiction, Steinberg defended its use, hoping it would spark a deeper discussion about the mysteries of quantum physics. There is.
laser experiment
A few years ago, the team began investigating the interaction between light and matter.
When particles of light, or photons, pass through an atom, some are absorbed by the atom and are later re-emitted. This interaction changes the atoms, temporarily placing them in a high-energy or “excited” state before returning to their normal state.
In a study led by Daniela Angulo, the researchers set out to measure how long these atoms remain in an excited state. “That time turned out to be negative,” Steinberg explained. That is, the duration was less than zero.
To visualize this concept, imagine a car entering a tunnel. Before the experiment, the physicists realized that while the average entry time for 1,000 cars might be noon, the first car could leave a little earlier, say at 11:59 a.m. Ta. This result was previously dismissed as meaningless.
What Angulo and colleagues demonstrated is similar to measuring carbon monoxide levels in a tunnel after the first few cars showed up and finding that the readings were preceded by a minus sign. Ta.
Relativity remains the same
The experiments took more than two years to optimize in an underground laboratory cluttered with equipment wrapped in wire and aluminum. The laser used had to be carefully calibrated to avoid distortion of the results.
Still, Steinberg and Angulo were quick to clarify that no one is claiming that time travel is possible. “I don’t want to say anything has gone backwards in time,” Steinberg said. “That’s a misunderstanding.”
The explanation lies in quantum mechanics, where particles like photons behave in vague and probabilistic ways rather than following strict rules.
Rather than following a fixed timeline of absorption and re-release, these interactions occur over a range of possible time periods, some of which are counterintuitive to everyday life.
Critically, the researchers say this does not violate Einstein’s special theory of relativity, which states that nothing can travel faster than light. These photons carried no information and bypassed the cosmic speed limit.
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A controversial discovery
The concept of “negative time” has attracted both interest and skepticism, especially from prominent figures in the scientific community.
As an example, German theoretical physicist Sabine Hossenfelder criticized the study in a YouTube video viewed by more than 250,000 people, saying, “The negative time in this experiment has nothing to do with the passage of time.” “It’s just a way to explain how photons move.” through the medium and how their phases change. ”
Angulo and Steinberg pushed back, arguing that their work addresses a critical gap in understanding why light doesn’t always travel at a constant speed.
Steinberg acknowledged the controversy surrounding the paper’s provocative headline, but noted that no serious scientist had disputed the experimental results.
“We chose what method we thought would be useful to explain the results,” he said, adding that although practical application remains difficult, the discovery opens new avenues in the exploration of quantum phenomena. added.
“To be honest, I don’t see any path to application from what we’ve been considering so far,” he admitted. “We’ll keep thinking about it, but we don’t want to get people’s expectations up.”
Further information: Daniela Angulo et al., Experimental evidence that photons can spend negative time in atomic clouds, arXiv (2024). DOI: 10.48550/arxiv.2409.03680, arxiv.org/abs/2409.03680
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