Scientists Successfully Sent A Particle Back in Time Using A Quantum Computer

Time travel was fiction before Einstein, but his calculations took us into the quantum world and we were introduced to a more complex picture of time. Einstein's equations permitted time travel into the past, as Kurt Gödel discovered. The issue? None of the hypothesized time travel systems were ever physically feasible.

So, before sending a particle back through time, Argonne National Laboratory, Moscow Institute of Physics and Technology, and ETH Zurich scientists wondered, “Why stick to physical grounds?

Many physics laws treat the future and the past as continuous. A closed system progresses from order to disorder according to the second rule of thermodynamics (or entropy). If you scramble an egg to produce an omelet, you've added a lot of chaos to the closed system that was the egg.

The arrow of time is an essential consequence of the second law. A process that develops entropy, like whisking an egg, is irreversible. An omelet won't turn back into an egg, and billiard balls won't spontaneously reassemble a triangle. Entropy, like an arrow, goes in one direction, and we see it as time.

The second rule of thermodynamics holds us captive, but an international team of scientists sought to test it in the quantum world. Since nature cannot do such a test, scientists utilized an IBM quantum computer.

Ordinary computers, such as the one you're reading this on, work with bits of data. A bit is either a 1 or a 0. A qubit is a fundamental unit of information used by quantum computers. A qubit may be both a 1 and a 0, allowing the system to process data considerably quicker.

The researchers used qubits to simulate subatomic particles in a four-step experiment. They entangled the qubits first, such that whatever occurred to one affected the others. Then they utilized microwave radio pulses to evolve the quantum computer's initial order into a more sophisticated state.

A specific algorithm changes the quantum computer to bring order out of chaos. They're zapped by another microwave pulse, but this time they go back to their old selves. That is, they are de-aged by a millionth of a second.

Argonne National Laboratory researcher Valerii M. Vinokur compares it to pushing against a pond's waves to restore them to their source.

Success was not guaranteed since quantum mechanics is about probability. In a two-qubit quantum computer, however, the algorithm accomplished a time leap 85 percent of the time. With three qubits, the success rate decreased to around 50%, which the scientists blamed on flaws in current quantum computers.

The findings were just reported in Scientific Reports.

The results are exciting but don't go buying flux capacitors just yet. This experiment also illustrates that manipulating even a simulated particle in time is difficult. Our ability to produce such an external force to influence even one quantum wave is limited.

To time-reverse even ONE quantum particle is impossible for nature alone, says research author Vinokur.  “The system comprising two particles is even more irreversible, let alone the eggs — comprising billions of particles — we break to prepare an omelette.”

A press release from the Department of Energy notes that the “timeline required for [an external force] to spontaneously appear and properly manipulate the quantum waves” to appear in nature and unscramble an egg “would extend longer than that of the universe itself.” In other words, this tech specifically binds to quantum computation. 

But the study isn't just a high-tech exercise. While the approach won't help us build real-world time machines, it will improve quantum computation.

Einstein's equations don't prohibit time travel, but they make it a difficult task, as Kurt Gödel demonstrated.


The New York Times | For a Split Second, a Quantum Computer Made History Go Backward | Arrow of time and its reversal on the IBM quantum computer

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