Jul 17, 2015 06:17 AM
https://www.sciencenews.org/article/arrow-time
EXCERPT: [...] the laws of physics do not forbid time to run backward. Equations that determine the acceleration of a rocket or the momentum of a billiard ball all work just as well with time flowing backward as forward. Yet [...] we remember the past but not the future. We get older but never younger. There is a distinct arrow of time pointing in one direction.
For nearly 140 years, scientists have tried to rule out the backward flow of time by way of nature’s preference for disorder. Left alone, nature transforms the neat into the messy, a one-way progression that many physicists have used to define time’s direction. But if nature prefers disorder now, it always has. The challenge is figuring out why the universe started out so orderly — thereby allowing disorder to grow and time to march forward — when the early universe should have been messy. Despite many proposals, physicists have not been able to agree on a satisfying explanation.
A new paper offers a solution. The secret ingredient, the authors say, is gravity. Using a simple simulation of gravitationally interacting particles, the researchers show that an orderly universe should always arise naturally at one point in time. From there, the universe branches in opposing temporal directions. Within each branch, time flows toward increasing disorder, essentially creating two futures that share one past. “It’s the only clear, simple idea that’s been put forward to explain the basis of the arrow of time,” says physicist Julian Barbour, a coauthor of the study published last October in Physical Review Letters.
It may be clear and simple, but it’s far from being the only idea attempting to explain the mystery of time’s arrow. Many scientists (and philosophers) over the decades have proposed ideas for reconciling nature’s time-reversible laws with time’s irreversible flow. Barbour and colleagues admit that the arrow of time issue is far from settled...
EXCERPT: [...] the laws of physics do not forbid time to run backward. Equations that determine the acceleration of a rocket or the momentum of a billiard ball all work just as well with time flowing backward as forward. Yet [...] we remember the past but not the future. We get older but never younger. There is a distinct arrow of time pointing in one direction.
For nearly 140 years, scientists have tried to rule out the backward flow of time by way of nature’s preference for disorder. Left alone, nature transforms the neat into the messy, a one-way progression that many physicists have used to define time’s direction. But if nature prefers disorder now, it always has. The challenge is figuring out why the universe started out so orderly — thereby allowing disorder to grow and time to march forward — when the early universe should have been messy. Despite many proposals, physicists have not been able to agree on a satisfying explanation.
A new paper offers a solution. The secret ingredient, the authors say, is gravity. Using a simple simulation of gravitationally interacting particles, the researchers show that an orderly universe should always arise naturally at one point in time. From there, the universe branches in opposing temporal directions. Within each branch, time flows toward increasing disorder, essentially creating two futures that share one past. “It’s the only clear, simple idea that’s been put forward to explain the basis of the arrow of time,” says physicist Julian Barbour, a coauthor of the study published last October in Physical Review Letters.
It may be clear and simple, but it’s far from being the only idea attempting to explain the mystery of time’s arrow. Many scientists (and philosophers) over the decades have proposed ideas for reconciling nature’s time-reversible laws with time’s irreversible flow. Barbour and colleagues admit that the arrow of time issue is far from settled...
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