Just Three Orbiting Black Holes Can Break Time-Reversal Symmetry, Physicists Find
Michelle Starr
ScienceAlert
Mar 2020
Nifty work.
At some point "micro chaos" "bubbles up" to give temporal irreversibility, albeit in a round-about way here. — jorndoe
I'm not clear about this. I've always assumed (and I could be very mistaken) that "time reversibility" is just a quirk arising when describing a physical process using mathematics. The two are not the same.
"And they have shown that the problem is not with the simulations after all."
Well, they're doing computer simulations in an environment of exceptional chaotic behavior. So I don't know what to think about reversing the actions. — jgill
As a concrete application of our result, we consider three black holes, each of a million solar masses, and initially separated from each other by roughly one parsec. Such a configuration is not uncommon among supermassive black holes in the concordance model of cosmology and hierarchical galaxy formation... [W]e estimate that the closest approach between any two black holes is on average between 10^{-2.5} and 10^{-2} parsec, during which the Newtonian approximation still holds. A parsec equals 10^{51} Planck lengths. Hence... we estimate that up to 5 percent of triples with zero angular momentum are irreversible up to the Planck length, thus rendering them fundamentally unpredictable. — Boekholt et al.
There could be a thread on the concept of time-reversibility. There seems to be a slight conflation here between forward and backward dynamics. — jgill
This is distinct from chaotic behavior (which is, in a technical sense, reversible) — SophistiCat
QM effects are already non-reversible... — VagabondSpectre
.The movement of the three black holes can be so enormously chaotic that something as small as the Planck length will influence the movements," Boekholt said. "The disturbances the size of the Planck length have an exponential effect and break the time symmetry.
The main idea of our experiment is the following. Each triple system has a certain escape time, which is the time it takes for the triple to break up into a permanent and unbound binary-single configuration. Given a numerical accuracy, , there is also a tracking time, which is the time that the numerical solution is still close to the physical trajectory that is connected to the initial condition. If the tracking time is shorter than the escape time, then the numerical solution has diverged from the physical solution, and as a consequence, it has become time irreversible. Only the systems with the smallest amplifications factors will pass the reversibility test. However, by systematically increasing the numerical accuracy (decreasing epsilon), we aim to increase the tracking time of each system. An increasing fraction of systems will obtain a tracking time exceeding its escape time, thus gradually decreasing the fraction of irreversible solutions
In the limit of infinite accuracy (epsilon → 0) we retrieve the microscopic time-reversibility of Newton’s equations of motion. In the presence of perturbations of size epsilon, whether numerical or physical, a fraction of systems becomes irreversible...
Explain what you mean by "which is, in a technical sense, reversible". Please provide a reference. — jgill
"In mathematics, a dynamical system is time-reversible if the forward evolution is one-to-one" — jgill
Fixed not floating, then? (And fixed by Planck length, if I understand you.) — bongo fury
The internet told me floating was sig figs not dp? — bongo fury
Planck length would be through fixed rather floating? — bongo fury
But fewer people would care about the paper if it didn't suggest (with plausible deniability in that typical academic way) that it has something to say about time irreversibility of physical/natural trajectories as opposed to time irreversibility of numerical algorithms representing them. — fdrake
The main idea of our experiment is the following. Each triple system has a certain escape time, which is the time it takes for the triple to break up into a permanent and unbound binary-single configuration. Given a numerical accuracy, , there is also a tracking time, which is the time that the numerical solution is still close to the physical trajectory that is connected to the initial condition. If the tracking time is shorter than the escape time, then the numerical solution has diverged from the physical solution, and as a consequence, it has become time irreversible.
If your intuition is that the Planck length is represented as fixed because it is a physical constant, — fdrake
What if we put in an error threshold of the Planck length, — fdrake
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