Can someone tell me what time does in equations describing entanglement?

There is an arrow of time from the past to the present and future, but there is also an arrow of time from the future to the present, with the past walled off.

But the present becomes the past(and at an ever increasing rate, the older you get), so that wall is being breached continuously.

I assume, then, that if we turn this sort of diagram upside down, it shows what would happen to the ingoing light rays in the case of a white hole which formed via time-reversed Hawking radiation and then later blew apart as a time-reversed collapsing star, as seen in the outgoing or ‘retarded’ Eddington-Finkelstein coordinates described on pp. 829-831 of MTW (where it’s the outgoing light rays that are always represented as diagonals). So, this also helps me see what you meant at the end of #132 when you said “if you let yourself fall freely towards the white hole produced by the reversal, you never cross the horizon; rather, after a finite proper time, you collide with the time-reversed collapsing star emerging from the white hole.” This also suggests a sense in which a black hole could be differentiated from a white hole regardless of the arrow of time of matter outside–even if we had a black hole that formed via converging light that looked just like time-reversed Hawking radiation, so that its formation and growth appeared symmetrical with its shrinking and evaporation in the ingoing Eddington-Finkelstein coordinates (including a reversal of the thermodynamic arrow outside the hole at its moment of maximum size), it could still be differentiated from its own time-reversed white hole because a freefalling observer on the outside could cross the black hole’s event horizon in a finite time, while for the white hole they’d be flung forward in time on a path that hugged the outside of the event horizon until the white hole had evaporated under them (probably in an amount of proper time comparable to the proper time it took the first observer to fall into the event horizon of the black hole from the same distance, although I’m not sure about that).

The only thing that’s still a little confusing to me is what the black hole would look like in outgoing/retarded Eddington-Finkelstein coordinates, or what the white hole would look like in ingoing/advanced Eddington-Finkelstein coordinates. It almost seems as though in these cases the holes would have to form and evaporate in zero coordinate time in order for the distant observer’s light cones to come out right. I think maybe what was confusing me before was the thought that if a black hole’s formation and growth were symmetrical with its shrinking and evaporation as plotted in the ingoing/advanced coordinate system, then the drawing of its event horizon would look exactly the same in the outgoing/retarded coordinate system, but I suppose there’s no reason to expect that should have to be true. At some point I need to either study a GR textbook on my own or go to graduate school, so I can figure out how to do these sorts of plots myself…

There is an arrow of time from the past to the present and future, but there is also an arrow of time from the future to the present, with the past walled off.

Qubit

I don’t want to comment further on this until I’ve done some more reading, but if you want to see a Penrose diagram (aka conformal diagram) of an evaporating black hole, there’s one on page 413 of Wald’s General Relativity. (BTW, in the Wikipedia article I just linked to, they do actually call the infinite Schwarzschild geometry a “grey hole”.) Penrose diagrams are a great way of keeping track of causal relationships, and if you know when light signals can get from one event in spacetime to another, you also know that any material particles around will have to travel between the two sides of the (two-dimensional version of the) light cones.

It is a pleasant surprise to see someone else questioning whether time is fundamental. The institutional effect on science makes it acceptable to project established theory in the most fantastical, convoluted and complex forms imaginable, but fresh insights based on basic observation are too pedestrian to consider.
The discussion of black and white holes is a good example; Gravitation contracts. Radiation expands. Everything else is detail, perspective, or some combination thereof and when the two columns are added up and the loose ends tied together, there won’t be any need for all the supernatural phenomena currently proposed, from extra universes and additional meta-dimensions, to Big Bang theory and its various patches, from Inflation to Dark energy.

To those whom this may offend, it is another attempt to crack the facade and start a discussion. Surely I’m too stupid to be right and with all the intelligent people in this conversation, someone should have the wherewithal to set me straight. I may be too thick to understand, but it would be good test of communication skills.