The mixed temporal directions of the photon will help physicists investigate the nature of black holes.
What did you do
scientists?
By dividing a photon using a specialoptical crystal, two independent groups of physicists have achieved what they call a quantum time revolution. In this state, the photon exists in both forward and reverse time states. In simple terms, scientists have proven that light moves simultaneously forward and backward in time.
The effect arises as a result of combining two strange principles of quantum mechanics.
The first oddity is quantum superposition
The first principle, known as quantumsuperposition, allows tiny particles to exist in many different states or different versions of themselves simultaneously until they are observed. There's a simple thought experiment that helps understand this really strange concept. We are talking about the famous Schrödinger's cat.
Schrödinger's Cat, Science Centre, Singapore. Photo: Sharon Hahn Darlin
In 1935, it was proposed by one of the creatorsquantum mechanics Erwin Schrödinger during a discussion of the physical meaning of the wave function. In a thought experiment, a cat is placed in a sealed box containing a vial of poison, the release of which is controlled by the radioactive decay of an alpha particle. Radioactive decay is a quantum mechanical process that occurs randomly.
That is why it is initially impossible to know whathappened to a cat who is in a superposition of states, being both dead and alive. In any case, until an observer joins the process - a person who opens the box and finds out the truth.
The second oddity is quantum symmetry
The second principle that was usedscientists —CPT-invariance. This is the fundamental symmetry of physical laws during transformations involving the simultaneous inversion of charge conjugation (Charge, C), parity (Parity, P) and time (Time, T).
CPT is the only combination of C, P and T thatis the exact symmetry of nature at a fundamental level. According to this principle, any system containing particles will obey the same physical laws. This will happen even if the particle charges, spatial coordinates and movement in time are inverted, as in a mirror.
"Arrow of Time"
By combining these two principles, physicists created the photon,which seemed to simultaneously move along the “arrow of time” and back. This is a philosophical term that is used to explain the direction and irreversibility of time. This concept is visually shown as a time axis or arrow. It moves straight and only forward, from the past to the future.
However, an experiment with a photon changes things:physicists managed to “deceive” time. Scientists published the results of two experiments (first, second) on the arXiv preprint server. The results have not yet been peer-reviewed.
In general, despite its logicThe concept of the “arrow of time”, which people observe every day in the macroscopic world, actually contradicts many fundamental laws of physics, scientists are sure. They are, in general, symmetrical in time and therefore they do not have a “favorite” direction of time.
Entropy problem
According to the second law of thermodynamics, thatthe entropy of the system must increase. Acting as the “arrow of time,” entropy is one of the few quantities in physics that causes time to move in a certain direction.
For example, this trend toward increasing clutterin the Universe explains why it is easier to mix ingredients than to separate them. It is because of growing disorder that entropy is so closely tied to our sense of time. A famous scene in Kurt Vonnegut's novel Slaughterhouse-Five demonstrates how entropy affects the direction of time in different ways: during World War II, bullets are sucked out of the wounded; the fires “shrink” and the reversed arrow of time destroys the disorder and devastation of war.
Diagram explaining entropy. Illustration: BlyumJ, CC BY-SA 4.0, via Wikimedia Commons
The problem is that entropy isPrimarily a statistical concept, it does not apply to individual subatomic particles. In fact, every particle interaction scientists have observed so far (including the up to a billion interactions per second that occur inside the world's largest atomic accelerator, the Large Hadron Collider) maintains CPT invariance. Thus, particles that appear to move forward in time are indistinguishable from those in the mirror system of antiparticles traveling “back into the past.” Of course, the antimatter that emerged from matter in the Big Bang doesn't actually move backwards in time. It just behaves as if it were following the arrow of time, the opposite of ordinary matter.
How did the experiments go?
As you know, the superposition we wrote aboutabove, is difficult to observe experimentally. To achieve this, both teams of physicists designed similar experiments to split a photon into a superposition of two separate paths through a crystal. As a result, the photon moved along one path through the crystal as usual, but another was configured to change the polarization of the photon or its point in space. The goal is to make it move as if it were traveling back in time.
Photons outside and inside calcite. Photo: Jan Pavelka, CC BY-SA 4.0
After recombination of superimposed photons, passingUsing them through another crystal, physicists measured the polarization of the photons in several repeated experiments. As a result, they observed a quantum interference pattern that consisted of light and dark bands. It could only exist if the photon split and moved in both directions of time. As the authors of the experiments explain, this superposition of processes is more like an object that rotates simultaneously clockwise and counterclockwise.
How will this help science?
It is noteworthy that physicists have created a uniquephoton with inverted time just out of curiosity. But subsequent experiments showed that both directions of time can be connected to reversible logic gates to provide simultaneous calculations in either direction. This paves the way for quantum processors with increased processing power.
Scientists' discovery will influence the future of the theoryquantum gravity, which will unite the general theory of relativity and quantum mechanics (High-Tech previously wrote in detail about these two fundamental theories). It should include particles with mixed time orientation, as in the new experiments. If this succeeds, then scientists will be able to study some of the most mysterious phenomena in the Universe. For example, look into black holes or understand whether time travel is possible.
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