Can time be negative? Scientists working in a field as counterintuitive as quantum mechanics claim that it does. At least, for photons in their laboratories.
Quantum effects and photons
Quantum mechanics is a branch of science that studies the world at the level of individual atoms and elementary particles and constantly encounters situations that contradict our everyday experience. A study was recently published in the journal Physical Review Letters in which negative time was discovered.
In fact, this phenomenon was first observed as far back as 1993. It requires a source of photons (quantum particles of light) and several rubidium atoms. And also a screen for recording the arrival times of these photons after they pass through these atoms.
When a photon strikes a cluster of atoms, it may pass right through it, or it may interact with the particles, exciting them to an energy-higher state, and after a short time, it is re-emitted in a random direction without hitting the target.
The only problem is that Heisenberg’s uncertainty principle applies to these photons. We can precisely determine the exact energy a photon must have in order to excite a rubidium atom, but in that case, the light particles must be emitted over a very roughly defined time interval.
Reverse time
But there’s nothing stopping us from taking a statistical approach: we could simply emit a large number of photons and determine the average time it takes for them to reach the rubidium, as well as the time it takes for a subset of them to reach the target with the highest possible precision. In theory, if light particles did not interact with atoms in any way, they should travel at the speed of light.
Well, a 1993 experiment showed that photons travel from rubidium atoms to the target in the time that they were theoretically expected to take. As if they had spent some kind of negative time there. This result has been verified many times, but physicists have found an explanation for it.
The point is that the time of arrival at the rubidium barrier—and, consequently, the time taken to travel from there to the target—is calculated as an average, and it was not primarily the photons that reached the atoms first that interacted with them. Negative time seems somewhat abstract, but in the context of statistical studies of the quantum world, almost everything is like that.
New study
However, one of the study’s authors, Aephraim Steinberg, was not satisfied with this explanation as early as 1993 and decided to approach the problem from a different angle. The excitation of rubidium atoms can also be measured, thereby determining the duration of the interaction between the photons and the atoms.
However, the rules of the quantum world once again pose an obstacle here. According to these rules, a precise measurement of a parameter is possible only by altering the state of the system. Thus, when we accurately measure the excitation of atoms, we simultaneously destroy it.
However, the scientists found a solution. They used a very weak laser and simultaneously measured the state of the atoms very roughly, which allowed them to estimate how many photons were present in the rubidium. And it turns out that this time, in a surprising way, corresponds in meaning to the “negative time” described earlier. In other words, the latter isn’t all that virtual, but scientists aren’t sure exactly how it works.
According to phys.org
