Physicists have a problem with time.
 
 Whether through Newton's gravitation, Maxwell's electrodynamics, Einstein's special and general relativity or quantum mechanics, all the equations that best describe our universe work perfectly if time flows forward or backward.
 
 Of course the world we experience is entirely different. The universe is expanding, not contracting. Stars emit light rather than absorb it, and radioactive atoms decay rather than reassemble. Omelets don't transform back to unbroken eggs and cigarettes never coalesce from smoke and ashes. We remember the past, not the future, and we grow old and decrepit, not young and rejuvenated. For us, time has a clear and irreversible direction. It flies forward like a missile, equations be damned.-http://www.scientificamerican.com/article/2-futures-can-explain-time-s-mysterious-past/?WT.mc_id=SA_WR_20141210