Rob Sheldon comments. But first, in the interests of explaining time’s arrow, researchers go back to the Big Bang:
The researchers have discovered simple, so-called “universal” laws governing the initial stages of change in a variety of systems consisting of many particles that are far from thermal equilibrium. Their calculations indicate that these systems — examples include the hottest plasma ever produced on Earth and the coldest gas, and perhaps also the field of energy that theoretically filled the universe in its first split second — begin to evolve in time in a way described by the same handful of universal numbers, no matter what the systems consist of.
The findings suggest that the initial stages of thermalization play out in a way that’s very different from what comes later. In particular, far-from-equilibrium systems exhibit fractal-like behavior, which means they look very much the same at different spatial and temporal scales. Their properties are shifted only by a so-called “scaling exponent” — and scientists are discovering that these exponents are often simple numbers like 12 and −13. For example, particles’ speeds at one instant can be rescaled, according to the scaling exponent, to give the distribution of speeds at any time later or earlier. All kinds of quantum systems in various extreme starting conditions seem to fall into this fractal-like pattern, exhibiting universal scaling for a period of time before transitioning to standard thermalization.Natalie Wolchover, “The Universal Law That Aims Time’s Arrow” at Quanta
The idea is that time’s arrow’s direction got set during a prescaling period.
Our physics color commentator Rob Sheldon offers:
People sometimes wonder why physicists think so much about the arrow of time. but I’ll try to guess at their motivations:
a) The usual suspects.
Physicists are an arrogant lot, and part of the schtick is sounding erudite, edgy, and incomprehensible. Time travel, wormholes, multiverses, mirror matter, and time going backward are all good candidates for impressive cocktail conversations. And strangely enough, the public eats it up. Having dispensed with religion and its priests, they are starved for something that sounds quasi-mathematical (to exclude the crystals and incense crowd), and cloak physicists with the vestments of authority. Physicists, for their part, rarely turn down the role.
b) The unusual suspects.
The myth and worldview that we and the universe are an accident (the marriage between the Big Bang and Darwin), has been hard to sustain recently. Too many events in the history of the universe seem designed or caused. If causation can be eliminated, then design can be sidestepped. One way to eliminate causation is to have time go backward. Hence there is a perverse attempt to do away with time, because it supports causation and a Designer. As an added bonus, doing away with causation also does away with morality, sin and guilt.
Hey, it might even lead to time travel, someone is sure to say.
See also: Would backwards time travel unravel spacetime?
Economist: Can time go backwards?
Astrobiologist: Why time travel can’t really work
Carlo Rovelli: Future time travel only a technological problem, not a scientific one. Rovelli: A starship could wait [near a black hole ] for half an hour and then move away from the black hole, and find itself millennia in the future.
Rob Sheldon’s thoughts on physicists’ “warped” view of time An attempt to force complete symmetry on a universe that does ot want to be completely symmetrical
At the BBC: Still working on that ol’ time machine… BBC: “But using wormholes for time travel won’t be straightforward.” Indeed not. Unless everything is absolutely determined, some wise person from the future has already gone back through a wormhole and altered the present so that we can’t go anywhere.
Is time travel a science-based idea? (2017)
Apparently, a wormhole is our best bet for a time machine (2013)
Does a Time Travel Simulation Resolve the “Grandfather Paradox”?
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