4 ms·

So what's new here ? We always knew if you travel really fast, time slows down for you, and people on Earth have aged faster. We always knew time moves at a d

• Jun8 16y ago
  You're right, that classical special theory of R, but I don't think that's what people have in mind when they think about time travel. If they're so inclined (like me), they think of it as a way to visit a person from the past, e.g. Cleopatra in her imperial boat. Or, going to the year 2500. As far as I understand, the crucial physical and philosophical problem is: Why is time's direction one way? Why can't we reverse it. Some physicists explain this by saying time moves in the direction of increasing entropy. But WHY does it have to be so? There's no inherent physical law, AFAIK, that says that this must be the case. In your example the direction is still the same for both people, it's just the difference of inertial frames.
  • Tamerlin 16y ago
    That's actually also true. The only thing that physicists have identified so far as being linked to time's directionality is entropy. Pretty much every other aspect of physics works with time's arrow pointed in either direction. So from a physical point of view, the only thing keeping the egg you dropped from putting itself back together is the slope of the entropy curve associated with that event.