I am totally hanging out for this idea to be thrown out the window and explained adequately.

But dont forget, spaghettification (all hail FSM) happens AFTER the event horizon and at that point, all bets are off for einsteinian physics. Like newtons is einsteins equations for large values (ie you can derive netwons laws from einsteins equations), I am sure that einsteins will be a solution to some other more crazy thing yet to come. GUT anyone?

Please note the above is not a final word – it’s just me trying to make sense of all the stuff about gravity! The bottom line is that even in General Relativity, gravity always acts in regards to an object’s current position, without retardation due to light speed delays in propagation.

Note too that some people argue that this does mean gravity waves travel faster than light; some say much faster! They’re outsiders in the current world of physics, though their arguments are fascinating.

Thanks for that answer, it’s good to know- I will have to look up the part of ABHoT that gave me the nightmares to see what Hawking was saying.

When you say ‘gravity is instantaneous’, I was always under the impression that gravity propagated at the speed of light? As in, if the sun suddenly winked out (as happens in one of the Star Trek films), the earth would not be destroyed, or even notice anything was wrong at all, until eight minutes later- the ‘absence of gravity’ would come at the same time as the absence of light. Can any event be instant across multiple frames of reference, and if there is, could that be used to transfer information faster than light?

This isn’t really answered in Hawking’s book, but I’ll have a go – and I’m afraid the other guys were right. Time always seems to flow at the same speed to a particular observer – the clock you keep with you always seems to advance at one second per second no matter your speed or nearby massive objects. The difference in time is only apparent when introducing separate frames of reference. So it would seem the other persons would be right. But now the question is: where is the astronaut’s frame of reference? In her head? What if she’s looking at a watch on her wrist? To get even more specific, precisely where in her head is her frame of reference? It’s true that once you’re close enough to the black hole, even the atoms in the top of her head are experiencing significantly different gravitational effects to those a little lower down! (Truthfully, that’s all rather academic – you’ll be pulled apart physically long before you’re close enough for that to matter.)

The clincher, though, is that the effect of gravity is still instantaneous – however you model it, while light would take more time to reach the astronaut’s head, gravity would reach it at the same time as it reached her legs. So the spaghettification “starts” at both ends at once, with the effect increasing steadily as you fall closer and closer. Now, I know our astronaut is “immortal”, but I can’t think of any form of immortality that could protect you from a black hole, short of being a massless, energy-less consciousness unaffected by gravity. But in that case you won’t be spaghettified at all, and you represent an old-school absolute notion of space and time, and we’re back to square one.

So to summarize: if you’re falling into a black hole, you experience a finite amount of time, slowly getting stretched out, with the stretching getting faster and faster until you finally get torn to bits, probably long before you reach the singularity and oblivion (unless you prefer the Disney movie version of events). The amount of time relies on the mass and therefore size of the black hole (not all black holes are created equal!).

I’m not very familiar with BSG, so their teleport-style FTL travel is news to me, but travel which doesn’t involve going through intervening space breaks a lot of laws of physics! Presumably they wouldn’t experience relativistic time dilation, since no time (or the same, very small amount of time) passes for them and for outside observers during the trip. In that sense, they’re not able to travel into the future, at least not any faster than you or I. They can’t go back in time, either – really, all they can do is “pause” the universe while they travel, and I imagine they can’t affect anything while doing so.

This seems more or less consistent with wormwhole theory; while large, stable wormholes (and these would probably need to be manufactured) might be usable for time travel, that’s only possible if you can drag one end at relativistic speeds, such that the two ends are no longer synchronised in time.

I hope that helps – and I welcome other comments!

The schwarztchild radius is very cool