Amy’s Everyday Astronomy: Quantum Physics and Time Travel

If you’ve ever seen a Back to the Future movie, you’ve probably been tantalized by the idea of going back in time to change things for the better. And if you’re an avid Star Trek fan, you probably understand a great deal about the fundamentals of temporal mechanics. Yet, here in the real world, time travel is all but impossible, depending on who you ask.

A recent article in the New York Times talks about how quantum physicists are trying to tackle the possibility of time travel, at least on a quantum level.

Quantum physics can be a real head-spinner for most people. After all, dealing with the subatomic world can be difficult to comprehend when you’re talking about things that are so small, they cannot be seen and only barely measured. Especially when you must consider Einstein’s “spooky action at a distance” and the Schrödinger equation.

Here’s how these work:

Einstein supposed that two particles could become linked by the strange quantum property of entanglement. These two particles become entangled when they are created at the same place and time in space.

Over time, these particles are separated. However far apart they get from one another makes no difference. According to mathematics, whatever happens to one of the particles affects the other despite the distance between the two. And that is known as spooky action at a distance.

The Schrödinger equation is a differential math equation that is used to describe quantum mechanical behavior. Sometimes referred to as the Schrödinger wave equation, it is used to measure how the wavefunction of a physical system evolves over time.

Basically, this will tell you the probability of finding a particle at a given point (position). Keep in mind that Schrödinger also postulated that if you put a cat in a box with something that could kill it (a radioactive element, for example) and sealed the box, you would not know the true fate of the cat until you opened the box and observed it.

So, until you did that, the cat would exist as simultaneously both alive and dead.
So, how does this tie into the work done by the quantum physicists? Using computers, of course.

A regular computer, much like one you are likely using to read this, processes a series of ones and zeros (bits), known as binary code. As it does this, each bit can only be a one or a zero at a given time. But in a quantum computer, these bits become qubits. This means that the processing code can be a one AND a zero at the same time.

This allows it to perform thousands of calculations simultaneously, as long as no one tries to look at the answer until the end (like Schrödinger’s cat). Using a quantum computer, the quantum physicists attempted to make a wavefunction go backward.

Google’s top of the line quantum computer has 72 qubits. For the experiment, the physicists used an IBM that only had 5, utilizing only 2-3 of these at a time. They put the qubits into an entangled state while mimicking a virtual (artificial) atom.

In this way, using the spooky action at a distance ideal, they were able to tap one of the qubits with a series of microwave pulses, which directly affected its counterpart. After a millionth of a second, they applied another microwave pulse to put a halt on the “evolution” program in hopes of reversing their phase so the qubits could devolve to their more youthful states.

In layman’s terms, they tapped a qubit, causing it and its spooky counterpart to vibrate. Then they tapped them again to stop the vibration and hoped that the qubits would show no signs of ever having been tapped in the first place.

And this actually worked 85% of the time when using only two qubits. But when the scientists used three qubits, they only achieved their goal 50% of the time.

“It remains to be seen whether the irreversibility of time is a fundamental law of nature or whether, on the contrary, it might be circumvented,” the team wrote in their February paper posted online.

In the end, it will take computers with hundreds of qubits in order to achieve the lofty ambitions of quantum mathematicians. At which time, the team’s time-reversal algorithm could be used to test them. Until then, reversing the aging process of a single particle will remain too complicated for even nature, herself.


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