If you believe everything that is written on the Internet (including us), quantum physicists can be congratulated. Sounds cool: scientists (and even Russians) have turned back the clock. Straight "Back to the Future". It all started with an article in Scientific Reports with the provocative title "The Arrow of Time and Its Reversal on an IBM Quantum Computer." In it, the authors stated that they had conducted an experiment, which, according to them, opens up new directions for research on "time reversal and time reversal."
If you still don’t understand why the world hasn’t gone crazy with scientists making such amazing progress, don’t worry. They didn't get it.
Scientists have turned back the clock. True?
Some simple physical models are symmetric over time. Imagine an idealized version of the Earth orbiting the Sun, with each body represented by an ideal sphere. See how this system moves forward in time, and the Earth moves counterclockwise. "Reverse" the time and the Earth will move clockwise. Both events are equally realistic. Or imagine a collision of two billiard balls. You can skip the video in any direction and it will be physically believable.
The real world is not like that. Everything would not look so if time went back - entropy (a measure of disorder) grows. This is the law of physics and common sense.
What did these scientists do then if they didn't invent time travel?
Think about pressing the rewind button on a video. It "reverses the flow of time" in a sense. If you've never done this, do it, it's cool. You will see the steam flow back into the kettle, the cup collecting from the shards. The article of interest to us describes a quantum computational version of such a video, shown in reverse order.
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A closer analogy would be a lens like one found in a telescope, microscope, or glasses. The lens can be used to focus light - "inverting" the scattering of light that is out of focus. The authors of the article say that their technique can be useful for testing quantum programs. It is right. But this is far from a time machine.
As Scott Aaronson, director of the Quantum Information Center at the University of Texas at Austin, says, “If you simulate a time reversal on your computer, you can change the direction of time by changing the direction of your model. Taking a quick glance at the work, I confess I don't understand where this noise comes from if the simulation was done on an IBM quantum computer."
In general, no one created a time machine. Nobody violated the laws of thermodynamics, physics. This case could give quantum computing a bad name. Don't be confused. It can be difficult to explain the paradoxes that actually exist in quantum mechanics without sensational slogans. Time only moves forward.
Ilya Khel