Quasars might be more damaging that originally believed.
When you are in a gravity well, you are falling. Suppose get into a balloon, rise to the edge of space, and jump off. You are not in orbit. You are going to fall for all practical purposes straight down. As your speed increases while you plummet to the earth time slows down.
When you are in orbit around a black hole, your falling down but also moving to the side. To stay in orbit close to a gravity well you have to be moving very fast and time will slow down. Suppose you are not in orbit and just using rocket thrusters to keep from falling into a black hole. Well you might be stationary relative to the singularity. Relative to the space itself that is rushing by you as it falls into the black hole, you are moving quit fast through that space and time will slow down. Think of a speed boat at the edge of a water fall using its motor to keep itself from being carried by the water down the water fall. From the shore the boat may appear stationary, but it is actually moving through water at a very high rate of speed.
Hope that helps.
6 million years ago, which is essentially a split second ago on astronomical time scales, the earth was/is in a nice quiet part of a barred spiral galaxy. Humans (or our ancestors) were limited to the planet earth. When the Milky Way and Andromeda collide what ever life that descends from us may populate every nook and cranny of our galaxy. The collision will destroy this nice barred spiral and for a time what galaxy exists will be quite irregular. A quasar going off in barred spiral isn't going to hit much because its going to be pointed 90 degrees away from the galactic plane. A quasar(possibly two quasars for a time), going off in an irregular galaxy that is almost entirely populated with life could easily blow off the atmosphere someone's planet.
I referenced the Iron Stars episode only because that is where I heard Isaac make a claim that strikes me as being wrong and I remembered the specific episode. The claim being: over infinite time lines anything that can happen will happen. To be fair, I hear that claim fairly often so If it is an error, it is a common one. In most circumstances, like the transmutation of the atomic constituents of dead stars, it is probably true that given enough time they will all turn into iron.
I do seemed to remember an episode where Isaac was discussing how in the future we could make copies of ourselves. I recall him making a comment along the lines that if enough time passed eventually some series of calamities would come along which did all your copies in; the ability to make copies of yourself, doesn't bring you some kind of immortality. I wish I remembered what specific episode that was so I could review it again for the sake of this discussion. The ability to make copies of yourself and spread yourself throughout the cosmos means it is plausible that over time the probability of some random set of calamities doing all of your copies in decreases over time. If the probability decreases over time I don't think it is a given you'd be wiped out over an infinite time line(setting aside heat death of course).
I get that Isaac is a science popularizer and he needs to explain things in broader terms with out going into every exception. This isn't an obscure exception but rather one that has a lot practical application. It is a folly for a degenerate gambler to decide to stop his self destructive behavior only after he breaks-even regardless if the gambler has an infinite amount of time and money to pursue such a quest. There is some positive probability X that earth will be ravaged by nuclear war. If we can't get the probability of X to be 0 is humanity doomed or do we have some hope? Well if we continue to decrease X we have a chance....there is hope. Because there is hope, we've got to try to continuously reduce X.
In that episode, Isaac claimed, "Over an infinite period of time, anything that can happen will happen...". I agree that if the probability of that thing that "can happen" is static, then it will happen. What if the probability of that thing is not static but decreases over time? Will that thing happen eventually?
Imagine this game. You have a magic die that begins with 6 numbered sides. You win the game if you roll a 1. At the start of the game you have a 1 in 6 chance of winning. If you don't win the game after the first roll, the magic die increases by 1 side so on the next trial you have a 1 in 7 chance of winning. If you go on to a third trial the die has 8 sides, On the forth trial it has 9 sides and so on. Is it possible to roll such a die an infinite number of times and never roll a 1(win the game)? Its always possible to win the game but does an infinite number of tries guarantee you will win it?
Admittedly the above thought experiment is contrived. Nevertheless similar situations do happen in real life. Can a roulette player who starts a quest to quit gambling when he/she is even when they are currently down by $10000 ever have a winning steak that takes them back to even if they play the game for eternity? It could happen, but is it guaranteed? If they play for an eternity they will certainly have winning streaks that clear $10000 in losses. The problem for our degene gambler is while he/she is chasing that streak his/her losses our very likely to grow. After a billion spins our roulette player might have to run into a 100 billion dollar winning streak to get back to even and that is a much harder thing to accomplish..