The possibility of time travel by optical methods has been denied by scientists from Hong Kong. However, there is still a hypothetical possibility of creating a time machine using supergravity regions, as in black holes or "wormholes"
One hypothetical way of time travel is to travel at speeds on the order of, or even faster than, the speed of light. Despite one of the fundamental statements of Einstein's theory of relativity, which is that it is impossible to achieve a speed greater than the speed of light, over the past ten years a discussion has developed in the scientific community, the essence of which boils down to the fact that single photons can be "superluminal".
Proving the existence of such photons would mean the theoretical possibility of time travel, since these photons would violate the principle of causality.
This principle in classical physics means the following: any event that occurred at time t 1 can affect the event that occurred at time t 2 only if t 1 is less than t 2. In the theory of relativity, this principle is formulated in a similar way, only conditions associated with relativistic effects are added to it, due to which time depends on the selected frame of reference.
The reason for the resumption of the discussion about the existence of "superluminal" photons appeared in January 2010. Then an article by American scientists was published in the Optic Express magazine, about which the science department of Gazeta. Ru spoke. In their experiment, the researchers sent photons through a stack of materials of various natures.
By alternating between layers of high and low refractive indices, scientists have detected that individual photons pass through a 2.5 micron plate at seemingly superluminal speeds.
The authors of the work tried to explain this phenomenon from the standpoint of the corpuscular-wave nature of light (after all, light is both a wave and a stream of particles-photons at the same time) without violating the theory of relativity, arguing that the observed speed is some kind of illusion. In this experiment, light both begins and ends its journey as a photon. When one of these photons crosses the boundary between layers of material, on each surface it creates a wave - an optical precursor-precursor (for clarity, you can compare an optical precursor with an air wave that occurs in front of a moving train). These waves interact with each other, creating an interference pattern: that is, the wave intensities are redistributed, creating a pattern of clear highs and lows, likeas in the case of oncoming waves in the ocean, a tidal layer is formed - a thrust of water. At a certain location of the H- and L-layers, the interference of the waves causes the effect of "early arrival" of a part of the photons. But other photons, on the contrary, arrive much later than usual due to the appearance of interference minima in the picture. For the correct speed detection, it is necessary to register all the photons passing through the layers, then averaging will give the usual speed of light.
To confirm this explanation required observations of a single photon and its optical predecessor.
The corresponding experiment was carried out by a group of scientists led by Professor of the Hong Kong University of Science and Technology (HKUST) Du Chengwang.
In their experiment, the researchers created a pair of photons, after which one of them was directed into a medium consisting of rubidium atoms cooled to low temperatures. By creating the effect of electromagnetically induced transparency (where a medium that absorbs radiation becomes transparent when an appropriate field is applied to it), Du and colleagues have successfully measured the velocities of both the photon itself and its optical precursor. “Our results show that the causality principle holds true for individual photons, says the abstract of an article published in Physical Review Letters.
Thus, this work put an end to the scientific discussion about whether there can be individual "superluminal" photons.
In addition, the experiment of Hong Kong scientists is important for the development of quantum optics, a better understanding of the mechanism of quantum transitions and, in general, some principles of physics.
Well, people who dream of traveling back in time should not despair.
Violation of the principle of causality by individual photons was not the only hypothetical possibility for creating a time machine.
In an interview with the Toronto Star, Du Chengwang stated:
“Time travel using photons or optical methods is not possible, but we cannot rule out other possibilities such as black holes or wormholes.
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