Dennis Overbye in the NYT:
Using an IBM quantum computer, they managed to undo the aging of a single, simulated elementary particle by one millionth of a second. But it was a Pyrrhic victory at best, requiring manipulations so unlikely to occur naturally that it only reinforced the notion that we are helplessly trapped in the flow of time.
Most of us already sense that the atoms of a scrambled egg can’t be unscrambled back inside a pristine shell. Now it seems that, under general conditions, even a single particle probably can’t go backward without help and careful tinkering.
“We demonstrate that time-reversing even ONE quantum particle is an unsurmountable task for nature alone,” Valerii M. Vinokur, of Argonne National Laboratory, said in an email message; he is one of the five aspiring time lords led by Gordey B. Lesovik of the Moscow Institute of Physics and Technology.
On paper, the basic laws of physics are reversible; they work mathematically whether time is running forward or backward. But if time is just another dimension of space-time, as Einstein said, it’s a strange one-way dimension. In the real world we can climb out of the subway and turn left or right, but we don’t have the choice of going forward or back in time. We are always headed toward the future.
We seem to be at the mercy of the second law of thermodynamics, which states that disorder and complexity only increase in a closed system such as, say, the universe. Thus, the atoms in an egg never unscramble themselves, in part because there are countless more ways for them to be thoroughly scrambled than successfully reassembled.