Drunken solution to the chaotic three-body problem
Dec 2021, phys.org
This one is a real mind-bender.
Two objects orbiting each other like the Earth and Moon, can be precisely predicted. Newton helped with that one. Add a third, and all hell breaks loose. It's called the three-body problem, although it's also called chaos, and the best we can do is to say that the future trajectories of these bodies is essentially random.
We know that at some point, the third body will be ejected into space. When, where, how fast, etc, we can't know; it's too chaotic. But these researchers model this using the theory of random walks (or the "drunkard's walk") --
This series of close encounters could be regarded as a drunkard's walk. Like a drunk's step, a star is ejected randomly, comes back, and another (or the same star) is ejected to a likely different random direction (similar to another step taken by the drunk) and comes back, and so forth, until a star is completely ejected and never returns (akin to a drunk falling into a ditch).
And --
Instead of predicting the actual outcome, they calculated the probability of any given outcome of each phase-1 [chaotic] interaction. While chaos implies that a complete solution is impossible, its random nature allows calculation of the probability that a triple interaction ends in one particular way rather than another. Then, the entire series of close approaches could be modeled by using the theory of random walks, sometimes called "drunkard's walk."
So they use probability and work their way backwards from there?
via Technion - Israel Institute of Technology: Yonadav Barry Ginat et al, Analytical, Statistical Approximate Solution of Dissipative and Nondissipative Binary-Single Stellar Encounters, Physical Review X (2021). DOI: 10.1103/PhysRevX.11.031020
Image credit: On the Way to Paradise, Dainbramage on Fractal Forums, 2017
Post Script:
A three-qubit entangled state has been realized in a fully controllable array of spin qubits in silicon
Sep 2021, phys.org
via RIKEN: Kenta Takeda et al, Quantum tomography of an entangled three-qubit state in silicon, Nature Nanotechnology (2021). DOI: 10.1038/s41565-021-00925-0
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