A term coined in 1927 by the British astronomer Arthur Eddington to describe the “one-way direction” or “asymmetry” of time.
For most people, the notion that time passes only in one direction is a given. There are multiple reasons for taking this point of view : cause and effect, ageing etc etc. And on the cosmic scale, extensive and varied measurements have shown that the universe is relentlessly progressing in the direction of more disorder. (Therefore, for, imagining backwards in time, the universe was previously more ordered)
But at the atomic and subatomic scale, quantum theory insists that particles can ‘travel’ either forwards or backwards in time with equal probability.
And further, Albert Einstein’s theories of relativity, incorporating Time as another dimension, insist that there is no single and special present - all moments are equally real.
Quote from New Scientist Nov. 1997
“The past is gone, remembered perhaps, but unalterable. The future has yet to come into being, and is still open. Only the present moment is truly real. All this seems like common sense. Yet many scientists and philosophers are adamant that we have got it all wrong. They insist that time does not flow at all. ”
More reference :Wikpedia
Also see (“Physicists can’t agree on whether the flow of future to past is real or a mental construct.”) an Atlantic Magazine article July 2016, about the Time in Cosmology conference at the Perimeter Institute for Theoretical Physics in Waterloo, Canada.