Physicists have found proof of the existence of "negative time": what it means

Physicists have long known that light can sometimes appear to leave a material before it enters it. This effect has been dismissed as an illusion caused by the way waves are distorted by matter.

However, researchers at the University of Toronto say they can prove that "negative time" is not just a theoretical idea using innovative quantum experiments. They say it actually exists in a tangible, physical sense, and it deserves to be studied in more detail, Phys.org writes.

The researchers emphasize that their findings emphasize a particular quirk of quantum mechanics, not a radical change in our understanding of time.

"This is a difficult thing, even for us, to talk about with other physicists. We are misunderstood all the time," said Ephraim Steinberg, a professor at the University of Toronto who specializes in experimental quantum physics.

Laser experiments

Many years ago, a team of scientists began to study the interaction between light and matter.

When light particles, or photons, pass through atoms, some of them 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 their normal state, scientists say.

In a study led by Daniela Angulo, a team of scientists decided to measure how long these atoms remained in their excited state. This time turned out to be negative, meaning that the duration was less than zero.

To visualize this concept, experts advise imagining that cars are entering a tunnel. Before the experiment, physicists recognized that while the average entry time for a thousand cars might be, for example, noon, the first cars might leave a little earlier, say, at 11:59 am. This result had previously been dismissed as meaningless.

What Angulo and her colleagues demonstrated was akin to measuring carbon monoxide levels in a tunnel after the first few cars have entered and finding that the reading has a minus sign in front of them.

Unchanging relativity

The scientists spent more than two years optimizing the experiments. The lasers used had to be carefully calibrated to avoid distorting the results, the researchers say.

"No one is claiming that time travel is possible or that anything has traveled back in time," Angulo and her colleague Steinberg emphasized.

According to the researchers, their explanation lies in quantum mechanics. Instead of following a fixed schedule for absorption and re-emission, these interactions occur over a spectrum of possible durations, some of which go against everyday intuition.

Importantly, 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, bypassing any cosmic speed limit.

Discovery

The concept of "negative time" has aroused both fascination and skepticism among some scientists.

German physicist Sabine Hossenfelder criticized the work in a YouTube video viewed by more than 250,000 people, saying: "Negative time in this experiment has nothing to do with the passage of time – it's just a way of describing how photons travel through a medium and how their phases shift."

Angulo and Steinberg responded that their research addresses key gaps in understanding why light does not always travel at a constant speed.

However, Steinberg noted that no serious scientist has challenged the results of the experiments. He added that although practical applications remain elusive, the discoveries open up new avenues for the study of quantum phenomena.

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