“Negative time” exists, but is time travel possible: physicists found the answer 0 30

It turns out that quantum particles can behave in very strange ways. The time of their arrival indicates that they were together with other particles for a negative interval of time. Does this mean that time travel is possible? Physicists provide an answer, writes Focus.

Behavior of Photons in Atoms

In a new experiment, physicists used photons, which are quantum particles of light, that moved through a cloud of rubidium atoms to test a long-standing experiment involving "negative time." Rubidium atoms resonate with photons, meaning the energy of the photon can be temporarily transferred to the atoms in the form of atomic excitation. This allows the photon to remain in the cloud of atoms for some time before it exits. For this resonance to be effective, the photon must have a specific energy corresponding to the energy required to excite a rubidium atom.

However, according to the Heisenberg uncertainty principle, if the energy of the photon is defined, then the time of its appearance must be uncertain. The momentum of light, which is the photon, must have a large duration. This means that it is impossible to know exactly when the photon enters the cloud of atoms, but the average time of its entry can be determined.

Negative Time

If a photon is directed into a cloud of atoms, it is most likely that its energy will be transferred to the atoms, and then the photon will scatter and not exit. But if the photon does pass through, something strange happens. Based on the average time of the photon's entry into the cloud of atoms, one can calculate the expected average time of its arrival on the far side of the cloud when it travels at the speed of light. It turns out that the photon arrives much earlier. In fact, it arrives so early that it seemingly spends a negative amount of time inside the cloud to exit the cloud before it enters it.

This phenomenon was first discovered back in 1993, but physicists largely chose not to take this negative time seriously. This is because only the very front edge of the long-duration light pulse passes straight through the cloud of atoms, while the rest of the light scatters. This leads to the non-scattered photon arriving earlier than one would expect. Scientists believed that negative time was an artifact of the measurements.

The authors of the new study say that to confirm negative time, continuous measurement of the atoms during the photon's passage through the cloud of atoms is needed to determine whether the energy of the photon is there at that moment. But measurements in quantum physics inevitably distort the measured system. If it were possible to accurately measure whether the photon is in the atoms at every moment, then the interaction of the atoms with the photon would be prevented.

Is Time Travel Possible?

Instead, physicists decided to conduct an imprecise but still very finely tuned measurement. They directed a laser beam, unrelated to a single photon pulse, through the cloud of atoms and measured small phase changes in the light in the beam to check whether the atoms were excited.

Any individual run of the experiment provides only an approximate idea of whether the photon was in the atoms, but the average results of millions of runs give an accurate time of the photon's stay in the atoms.

It turned out that the time of stay when the photon passes straight through the cloud of atoms is exactly equal to the negative time, which is the average arrival time of photons in the cloud of atoms. Before this experiment, no one suspected that these two times, measured in completely different ways, would be equal.

Does this mean that time travel is possible? Unfortunately, no, scientists say. The results of the experiment are fully explained by standard physics. But the experiment showed that negative time is not an artifact of measurements and does indeed exist.