The possibility of being able to travel either forwards or backwards in time has been discussed by philosophers, thinkers and writers for centuries.
More recently, discussions have also featured in the physics community - especially since Albert Einstein's discovery and description of 4-dimensional spacetime.
At quantum scales, it's now routine to assume that sub-atomic particles can freely move both forwards and backwards in time.
At larger scales, time travel forwards in time is also now regarded by physicists as routine. Einstein's theories insist that any object which is accelerating through 3-D space (relative to others) has its local time slowed down - thus, in effect, traveling forwards in time when compared to the non-accelerating objects.
This concept has been so extensively tested that there is no longer any doubt about its validity. Though, on a scale large enough to be of any practical significance to humans who wish to 'export' themselves to the future, it currently remains impractical.
Large-scale time travel backwards in time is much more problematic. Though many physicists assert that the current understanding of the laws of physics doesn't appear to rule it out, it raises so many paradoxes that there is currently no agreement within the advanced physics community as to whether it's theoretically possible or not. Even if it is theoretically possible, there are currently no practical ways to achieve it.
For an extensive discussion on the the physical and philosophical implications of time travel, see Wikipedia
Also see : Arrow of Timeplugin-autotooltip__plain plugin-autotooltip_bigArrow of Time
inexplicable
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 apparently expanding universe will irrevocably progress in the direction of more disorder. (Th…