Quantum physics demonstrates many strange things and is often counterintuitive. This time, scientists made us remember the movie «Tenet» by discovering what can be called negative time.
The yet-to-be-peer-reviewed study, described in Scientific Americandescribes the observation of the strange temporal behavior of photons during the excitation of atoms. Photons directed into the cloud of atoms left the medium before entering it.
«Negative time dilation may seem paradoxical, but it means that if you built a «quantum» clock to measure the time that atoms spend in an excited state, the hand of the clock would move backwards rather than forwards» under certain circumstances, — says Josiah Sinclair of the University of Toronto. His early experiments formed the basis of the study, but he was not directly involved.
Photons, particles of light, can be absorbed by the atoms they pass through. When this happens, the energy they carry causes the electrons of the atoms to move to a higher energy state — this is called excitation.
But atoms can also get rid of their excitations and return to their normal state. One way this happens is by emitting energy in the form of photons. To an observer, this looks as if the light that passed through the medium was delayed. Scientists did not have a consensus on what actually happens to an individual photon during this delay, so they conducted a series of experiments.
During them, photon pulses were passed through a cloud of atoms at temperatures close to absolute zero. A strange thing happened: in the cases where the photons passed through without being absorbed, the ultracold atoms were already excited for the exact time interval as if they had already absorbed them. On the contrary, in cases where the photons were absorbed, they were re-emitted without delay or before the ultracold atoms could remove their excitation.
Scientists say that no laws of physics are violated here. Photons somehow travel faster through the atomic cloud when they excite atoms and are absorbed than when the atoms remain unchanged. Since photons do not carry information, causality remains intact, the researchers note. Quantum superposition leads to photons being in two states at the same time: for a detector that measures when they enter and leave a medium, this means that photons can have both positive and negative values. And hence, actually negative time.
This does not change our understanding of time, the researchers say. On the other hand, it does suggest, at least in the field of optics, that negative time has «more physical significance than» is generally thought to have, the study says.
Source: Futurism
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