Scientists observe ‘negative time’ in quantum experiments

Scientists have long known that light can sometimes appear to exit a material before entering it — an effect considered an illusion caused by the way waves are distorted by the material.

Now, researchers at the University of Toronto, through innovative quantum experiments, claim to have demonstrated that “negative time” is not just a theoretical idea: it exists in a tangible physical sense, worthy of closer examination. in-depth.

The findings, job on the preprint server arXiv but not yet published in a peer-reviewed journal, have attracted both attention and skepticism around the world.

The researchers point out that these puzzling results highlight a particular oddity quantum mechanics rather than a radical change in our understanding of time.

“It’s a difficult question, even for us, to talk about with other physicists. We’re misunderstood all the time,” said Aephraim 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 from Science fictionSteinberg defends its use, hoping it will spark deeper discussions about the mysteries of quantum physics.

Laser experiments

Years ago, the team began exploring the interactions between light and matter.

When particles of light, or photons, pass through atoms, some are absorbed by the atoms and then re-emitted. This interaction changes the atoms, temporarily placing 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 less than zero.

To visualize this concept, imagine cars entering a tunnel: before the experiment, physicists recognized that if the average entry time for a thousand cars could be, say, noon, the first cars could exit a little earlier, say at 11:59. This result had previously been dismissed as meaningless.

What Angulo and his colleagues demonstrated was akin to measuring carbon monoxide levels in the tunnel after the first cars emerged and discovering a minus sign in front of them.

Relativity intact

The experiments, conducted in a cluttered basement laboratory bristling with wires and devices wrapped in aluminum, took more than two years to optimize. The lasers used had to be carefully calibrated to avoid distorting the results.

However, Steinberg and Angulo are quick to clarify: no one claims time travel is a possibility. “We don’t want to talk about time travel,” Steinberg said. “That’s a misinterpretation.”

The explanation lies in quantum mechanics, where particles like photons behave in a fuzzy, probabilistic manner rather than following strict rules.

Instead of adhering to a fixed schedule of uptake and re-emission, these interactions occur over a spectrum of possible durations, some of which defy everyday intuition.

According to the researchers, this does not violate Einstein’s theory of special relativity, which states that nothing can travel faster than light. These photons carried no information, bypassing any cosmic speed limit.

A discovery that divides

The concept of “negative time” arouses both fascination and skepticism, particularly from prominent figures 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 of describing how photons move. through a medium and how their phases change.

Angulo and Steinberg countered, arguing that their research filled crucial gaps in understanding why light doesn’t always travel at a constant speed.

Steinberg acknowledged the controversy surrounding the provocative title of his paper, but stressed that no serious scientist has disputed the experimental results.

“We made our choice on what we think is a fruitful way to describe the results,” he said, adding that while practical applications remain elusive, the results open new avenues for exploring quantum phenomena.

“I’ll be honest, I don’t currently have any path forward between what we’ve looked at and the applications,” he admitted. “We’ll continue to think about it, but I don’t want to give people hope.”

© 2024 AFP