If we view events occurring on a star that is collapsing to become a black hole, do we see time speeded up or slowed down?
ANSWER: From special relativity, we already know how time slows down for different inertial observers according to their velocities. But general relativity tells that, time also slows down by gravitational fields. And as we know that stars and objects like black holes bend the spacetime a lot, so that if an outside observer sees any event near these massive objects, then he will observe a huge time lag or time dilation. But when a star is getting converted to a black hole, the mass does not change. As the mass is same, so the spacetime bending will also be same. Because the bending is independent of the size of the object and only depends on the mass and energy. Definitely the distant observer will observe a time delay between his clock and the clock near the black hole. Because time is relative, and it is the proper time which is the invariant quantity. But, the time delay will not change anymore, as the mass of the star does not change after getting converted to a black hole. The time lag will remain same. All this is true for the events outside the event horizon of the black hole. The inside horizon events are forbidden to the rest of the universe and we have absolutely no idea how time behaves inside the event horizon.