If all physical laws are time-reversible, then how can black holes have an event horizon, a point of no return?
• 69. Sean’s experimental science in a space he can’t access « Society with Jimmy Crankn Says: December 5th, 2007 at 10:29 pm […] get to the meat of what I want to highlight. In Arrow of Time FAQ, Sean says, The arrow of time is hot, baby. I talk about it incessantly, of course, but the buzz is […] • 70. Greg Egan Says: December 5th, 2007 at 11:19 pm Miller (#68): In the spacetime geometry of a black hole, at the event horizon the only timelike vectors that point radially outwards also point backwards in time (in the sense defined as “backwards” for the external universe). So to escape from a black hole, you either have to travel along a spacelike vector (i.e. travel faster than light), or you have to travel backwards in time — which doesn’t violate any physical laws, but is essentially impossible for thermodynamic reasons. (By “travel backwards in time”, I don’t mean jump in some magic machine and emerge in the past, I mean experience everything along your world line backwards, re
