What Next? A Time Machine!

2
877
The Arrow of Time historyofthingstocome.blogspot.com

Physicists Reverse Time for Tiny Particles Inside a Quantum Computer

By Meredith Fore, Live Science Contributor

Video: Reversing Time

Time goes in one direction: forward. Little boys become old men but not vice versa; teacups shatter but never spontaneously reassemble. This cruel and immutable property of the universe, called the “arrow of time,”is fundamentally a consequence of the second law of thermodynamics, which dictates that systems will always tend to become more disordered over time. But recently, researchers from the U.S. and Russia have bent that arrow just a bit — at least for subatomic particles.

In the new study, published Tuesday (Mar. 12) in the journal Scientific Reports, researchers manipulated the arrow of time using a very tiny quantum computer made of two quantum particles, known as qubits, that performed calculations. [Twisted Physics: 7 Mind-Blowing Findings]

At the subatomic scale, where the odd rules of quantum mechanics hold sway, physicists describe the state of systems through a mathematical construct called a wave function. This function is an expression of all the possible states the system could be in — even, in the case of a particle, all the possible locations it could be in — and the probability of the system being in any of those states at any given time. Generally, as time passes, wave functions spread out; a particle’s possible location can be farther away if you wait an hour than if you wait 5 minutes.

Undoing the spreading of the wave function is like trying to put spilled milk back in the bottle. But that’s exactly what the researchers accomplished in this new experiment.

“There is basically no chance of this happening on its own,” lead researcher Valerii Vinokur, a physicist at Argonne National Laboratory in Illinois, told Live Science. “It is like that saying, where if you give a monkey a typewriter and a lot of time, he may write Shakespeare.” In other words, it’s technically possible but so unlikely it may as well be impossible.

How did the scientists make the essentially impossible happen? By carefully controlling the experiment.

“You really need a lot of control to make all the broken pieces of a teacup come back together,” Stephen Bartlett, professor of physics at the University of Sydney, told Live Science. Bartlett was not involved in the study. “You have to have a lot of control over the system in order to make it do that … and a quantum computer is something that lets us have a huge amount of control over a simulated quantum system.”


The researchers used a quantum computer to simulate a single particle, its wave function spreading out over time like a ripple in a pond. Then, they wrote an algorithm in the quantum computer that reversed the time evolution of every single component of the wave function, essentially pulling that ripple back into the particle that created it. They accomplished this feat without increasing entropy, or disorder elsewhere in the universe, seemingly defying the arrow of time.

“You really need a lot of control to make all the broken pieces of a teacup come back together,” Stephen Bartlett, professor of physics at the University of Sydney, told Live Science. Bartlett was not involved in the study. “You have to have a lot of control over the system in order to make it do that … and a quantum computer is something that lets us have a huge amount of control over a simulated quantum system.”

The researchers used a quantum computer to simulate a single particle, its wave function spreading out over time like a ripple in a pond. Then, they wrote an algorithm in the quantum computer that reversed the time evolution of every single component of the wave function, essentially pulling that ripple back into the particle that created it. They accomplished this feat without increasing entropy, or disorder elsewhere in the universe, seemingly defying the arrow of time.

After running the program, the system went back to its original state 85 percent of the time. However, when a third qubit was introduced, the experiment succeeded only 50 percent of the time. The researchers said the complexity of the system likely increased too much with the third qubit, making it harder for the quantum computer to maintain control over all aspects of the system. Without that control, entropy can’t be held in check, and the time reversal is therefore imperfect. Still, they’re aiming for bigger systems and bigger quantum computers for their next steps, Vinokur told Live Science.

“The work is a nice contribution to the foundations of physics,” James Whitfield, a professor of physics at Dartmouth College in New Hampshire, who was not involved in the study, told Live Science. “It reminds us that not all applications of quantum computing must be application-oriented to be interesting.”

“This is exactly why we’re building quantum computers,” said Bartlett. “This is a demonstration that quantum computers can allow us to simulate things that should not occur in the real world.”


EDITORIAL DISCLOSURE
All content herein is owned by author exclusively.  Expressed opinions are NOT necessarily the views of VT, authors, affiliates, advertisers, sponsors, partners, technicians or Veterans Today Network (VT).  Some content may be satirical in nature. 
All images within are full responsibility of author and NOT VT.
About VT - Read Full Policy Notice - Comment Policy

2 COMMENTS

  1. One does not need to move into the esoteric domain of quantum computers or entropy to conceptually understand why the arrow of time only moves in one direction and is impossible to reverse or labeled irreversible.
    Think about what is going on or what would have to go on to reverse the time evolution of a process. Using the example of a glass or clay object. We made such objects in art class in the 5th grade. One shaped pliable clay into different shapes, painted them and baked them at high temperatures. They were allowed to cool to beautiful cups or glasses or hot plates dishes, etc. What if you drop one on a floor which when struck exerts forces on the object which cause it to break apart into many pieces visible to the eye, but many other smaller pieces less visible, and even smaller pieces visible only with a microscope and possibly even smaller pieces of molecular dimensions. Imagine having a slow motion moving photograph of this process as it develops in time. What does the phrase “time reversal” mean? It does not mean going through the initial process of making the object in the oven again. It means having the physical ability to “put Humpty Dumpty” back together again by reversing the order of everything exactly that broke him in the first place! And think about this: Every, and I mean every physical part of the object, down to the smallest molecule must be recovered and replaced in exactly the same position it was in to begin with! This is a tall order. In fact suppose some of the molecules, which could not be seen by the naked eye anyway, had an excess charge on them, which then resulted in them being pulled out of the area where you recovered the broken pieces. How would you find and recover them? What kind of machine would you design to put Humpty Dumpty back together again? Whatever the machine is, it is evidently much much much more complicated, or at least as complicated than the machine which created Humpty Dumpty in the first place isn’t it? Now multiply all this to the complexity of the world around at any time in history and the myriad of physical and chemical and biological… processes going constantly. Isn’t it obvious why we will never be able to move backward in time except in running a motion picture projector backwards, or pictures or books or artifacts documenting the past? Have you ever met any human being on Earth smart and intelligent enough to make such a machine? Neither have I.