NOVA: Physics Laws Cannot Always Turn Back Time

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NOVA: Physics Laws Cannot Always Turn Back Time

Post by bystander » Mon Mar 23, 2020 4:24 pm

Physics Laws Cannot Always Turn Back Time
Netherlands Research School for Astronomy (NOVA) | 2020 Mar 23
Click to play embedded YouTube video.
Two computer simulations of 3 black holes that influence each other
Credit: NOVA / T. Boekholt et al., MNRAS 2020

If three or more objects move around each other, history cannot be reversed. That is the conclusion of an international team of researchers based on computer simulations of three black holes orbiting each other. ...

Most basic laws in physics have no problem with the direction in which they run. They are, as scientists call it, symmetric with respect to time, or time symmetric. In practice, however, everyone knows that time cannot simply be turned back. For example, a cup that falls into hundred pieces really does not fly back into your hand spontaneously and undamaged. Until now, scientists explained the lack of time symmetry by the statistical interaction between large numbers of particles. Three astronomers now show that only three particles are enough to break the time symmetry.

[Researchers] calculated the orbits of three black holes that influence each other. This is done in two simulations. In the first simulation, the black holes start from rest. Then they move towards each other and past each other in complicated orbits. Finally one black hole leaves the company of the two others. The second simulation starts with the end situation of two black holes and the escaped third black hole and tries to turn back the time to the initial situation.

It turns out that time cannot be reversed in 5% of the calculations. Even if the computer uses more than a hundred decimal places. The last 5% is therefore not a question of better computers or smarter calculation methods, as previously thought. ...

Gargantuan Chaotic Gravitational Three-Body Systems and Their Irreversibility
to the Planck Length
~ Tjarda Boekholt, Simon Portegies Zwart, Mauri Valtonen
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