By Lucine Avanesian
Even if you were able to determine the positions of three black holes as accurately as physically possible, you would still not know where the black holes will go. The dynamic dance of such a trio can be so chaotic that the movements are essentially unpredictable, shown by recent computer simulations.
Based on their locations and speeds at one point in time, the paths of three black holes circling each other can be determined. In certain situations, however, the orbits depend so sensitively on the exact locations of the black holes that the uncertainty of quantum physics comes into play. Tiny quantum uncertainties in determining object positions will explode as the gyrations of black holes proceed over tens of millions of years, Tjarda Boekholt, an astrophysicist, and colleagues published in the Royal Astronomical Society's April Monthly Notes. Thus, it is difficult to predict the distant future of the orbits of black holes.
Such intense vulnerability to initial circumstances is called chaos. In the case of three black holes, the latest research indicates "quantum mechanics imprints at the fundamental level into the chaos of the universe," says astrophysicist Nathan Leigh of Universidad de Concepción.
Tiny adjustments can produce wildly different results in chaotic systems. A butterfly flapping its wings is the classic example, thus altering weather patterns, likely creating a distant tornado that would not have evolved otherwise. In the orbits of three black holes and other sets of three or more objects, this chaos often occurs, making those orbits difficult to measure, a conundrum known as the three-body problem.
To test whether the motions of the black holes were predictable, Boekholt, of the University of Coimbra, and colleagues tested whether they could run both forward and backward computer simulations of the orbits and obtain the same result. Starting with a specified set of positions for three initially stationary black holes, tens of millions of years in the future, the researchers built those orbits forward in time to an endpoint. Then, the simulation rewound, reversing the motions to see whether the black holes ended up where they started from.
There is a small degree of precision in computer simulations. In this case, for example, only a certain number of decimal places is considered to be the positions of black holes. Over millions of years of simulation, the tiny imprecision will balloon.
It is impossible to determine the location of any object, according to quantum mechanics, better than an utterly small distance called the Planck range, approximately 1.6 times 10-35 metres, or 16 billionths of a trillionth of a trillionth of a millimetre (SN: 4/8/11). However, even with the size of the Planck duration being right, the researchers found that when the simulation was reversed, the three black holes did not return to the same spots around 5 percent of the time. That means you couldn't rewind and figure out where they came from, even though you calculated where the black holes were to the quantum mechanical limit.
"Fundamentally, these systems are irreversible," says Boekholt. For these 5 percent of processes in existence, you can not go forwards and backward. And that was a very unexpected outcome."
The outcome is theoretical, says astrophysicist Nicholas Stone of the Hebrew University of Jerusalem, and can't be generalized to actual black holes. For instance, the meaning of quantum physics will be swamped by measurement errors. "But that doesn't detract from the significance of the study," he says: "From a philosophical viewpoint, it is still very important."
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