Perhaps the most mind-bending concept of physics is that light-and possibly even other forms of energy-might be able to travel backward in time. Recent experiments finally demonstrate that, under proper conditions, light indeed might experience some kind of temporal reversal, which very accurately challenges our perception of time and space.
The way light travels through time
To get a feel for how light might carry an information flow "backwards" through time, we must revisit one of the main principles in physics, which is called time symmetry. This is the idea that many physical processes can be said to run both forwards and forwards in time. Almost all the laws of physics-from Newton's mechanics to Maxwell's electromagnetism-are such that it is possible to run them backwards in time. But to our everyday experience, time only moves in one direction. The key is that most of the phenomena we can see are subject to influence by entropy-the tendency of systems to go from order to disorder-giving us the clear arrow of time.
However, if the photons are the matter of light, then this rule may not be as applicable for matter. Being massless, these particles might, in principle, "bounce back" without their entropy acting as a limiting factor. In fact, some quite recent experiments have begun to investigate just this hypothesis, and they have established that, under controlled conditions, photons behave as if they were moving backward in time as they retrace their path.
The Experiment
A team of physicists designed such a sophisticated optical system, which was meant to control the movement and action of photons. In doing so, they used a high-intensity laser together with the nonlinear crystal, which helped in achieving an effect called spontaneous parametric downconversion or SPDC. The effect enabled them to split a photon into two entangled photons; a phenomenon where two particles were linked even if separated by large distances.
In this setup, when they were measuring one photon, the effect was observed on its entangled counterpart only in a way that would make sense if it had already been measured. That's what physicists are now calling "temporal entangement." The behavior here speaks to the possibility that the measurement on one photon is influencing not only the present state of the entangled photon but perhaps retroacting to a point before the measurement was made.
Time-Reversing Photons Implication
If, after all, light could travel back in time, it would be some extraordinary implications. Perhaps it would change us completely from thinking about cause and effect in terms of quantum physics and about the invalid assumptions that Einstein had about the speed of light and time. This may also finally open up new forms of quantum communication, where information would get sent not only across space but perhaps even backwards in time.
The experiment, however, is not free from criticism. Some say that the phenomenon might be just an artifact of how quantum systems behave under observation, rather than being a change in nature of the time sense. Others believe that it could be the first step toward understanding the real nature of time and energy.
What Does This Implication Have in Terms of the Future of Physics?
This phenomenon, if true, would power physics into an utterly new world, with the promise of future technologies to utilize quantum variables, specifically time, as computational and communicative variables, and take us even further into the science fiction expanse, such as time travel and even retrocausality-in which the effect precedes the cause.
Now, this phenomenon is still in its infancy, and a
lot more research is required to understand the whole procedure of
time-reversal of photons in detail. A very probable outlook of this new
breakthrough suggests that mankind is far from unlocking the entire secrets of
how time, light, and the quantum world work. Probably, further experiments will
unravel even deeper mystery of the true reality with their total cosmos
implications.
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