[SPOILERS] some questions regarding Interstellar's black hole

[sndrtj]

So I went to Interstellar last night. I have some questions regarding the end of the movie, both related to the black hole.

1) At the end of the movie Cooper falls in the black hole and has his epiphany. However, how could one subjectively actually fall in a black hole? From a reference point far from the black hole, one of course can see things falling into a black hole, but how is this possible from the reference point of the falling object itself? As I understand relativity and orbital mechanics, one likely approaches light speed when very near the event horizon, which means time dilation basically becomes infinite, and the object will never actually experience passing the event horizon. Or is this some kind of paradox here? The only way I can figure out Cooper being aware of himself falling would be if he would have killed most of his velocity (good luck with that with relativistic speeds), and falling sort of straight into the black hole.

2) Just before Cooper enters the black hole, the Endurance is slingshotting past the black hole, upon which Amelia remarks "This little trick costs us 51 years". Wouldn't this have to mean they would be orbiting Gargantua for 51 years as seen from a reference point far from the black hole? That no longer seems like a slingshot - unless Gargantua is truly insanely huge - but rather like a stable orbit around it. Wouldn't a real gravitational slingshot just last several seconds from a time-dilated reference frame?

[Moss]

1) It's a movie.

2) Both.

[andrewas]

1) You have it backwards. Cooper falls into the black hole in roughly the time you would expect. I think. Certainly, he falls in in a finite time. For an outside observer, he seems to slow and you'll never see him cross the event horizon. This does mean that the scene in the tesseract must take place in the very distant future, but the aliens can manipulate wormholes so there's still no difficulty in returning Cooper home to the right time.

2) Again, duration for the Endurance is a few minutes, duration for an outside observer is 51 years. If you watched Endurance from a distance, it would do the slingshot maneuver but very slowly.

[Bill Phil]

I believe she said "trip" but I could be mistaken.

Plus it's relativity and time dilation and they were really close to the black hole: practically in the debris cloud.

[sndrtj]

1) You have it backwards. Cooper falls into the black hole in roughly the time you would expect. I think. Certainly, he falls in in a finite time. For an outside observer, he seems to slow and you'll never see him cross the event horizon. This does mean that the scene in the tesseract must take place in the very distant future, but the aliens can manipulate wormholes so there's still no difficulty in returning Cooper home to the right time.

2) Again, duration for the Endurance is a few minutes, duration for an outside observer is 51 years. If you watched Endurance from a distance, it would do the slingshot maneuver but very slowly.

How does that work? Time dilation slows down the subjective clock of Cooper/Endurance, not the clock of a far-away observer. If they're close to the black hole, musn't they actually go extremely fast (whole fractions of c)? The closer you get to a black hole, the greater your speed, the slower your clock goes, isn't that true? So how can you then pass the horizon? I get that your acceleration as measured by a far observer must be extremely tiny - and decreasing - since you would be asymptotically approaching c. Would that means that the acceleration is so tiny it would take them a burn of (as seen by a far observer) 51 years? But would said observer not see them orbiting Gargantua for the same amount of time?

There is something here I don't quite understand. Wikipedia seems to tell me you can't see an object passing the horizon, because you can't actually see that event happening (hence the name event horizon). In stead, the object would red-shift forever (which, eventually means that for all practical purposes you're going to loose sight of the object, since your instruments won't be able to detect nearly infinitely red-shifted light).

[sndrtj]

It's already late, but I guess I might have found my problem: I think I forgot that because Cooper's clock seems to go slower from the far-away observer's point of view, the amount of (visible) work on Cooper/Endurance can also only be (very) small per time unit for the far-away observer's point of view. As he goes faster and faster, the amount of observed work dwindles to nothing, which means the observer sees Cooper approaching but never quite reaching the black hole. But for himself, even if takes a billion years from the observer's point of view, he will eventually cross it in a relatively short finite time from his point of view. I think I get it now :-).

Reference frames, reference frames. Blah .

[K^2]

I think you are picturing this a bit wrong. If you are in a frame of reference that's severely dilated and your clock slows, do you expect to watch the clock actually run slower? No, you are time-dilated as well. Your internal clock slows as well. All of your thoughts run slower. Your metabolism runs slower, everything. From perspective of your brain, the clock runs at the same rate. It's everything else in the universe that appears to run faster.

Edit: Heh, ninja'd. Yeah, you got it.

[Aningaaq]

1) You have it backwards. Cooper falls into the black hole in roughly the time you would expect. I think. Certainly, he falls in in a finite time. For an outside observer, he seems to slow and you'll never see him cross the event horizon. This does mean that the scene in the tesseract must take place in the very distant future, but the aliens can manipulate wormholes so there's still no difficulty in returning Cooper home to the right time.

2) Again, duration for the Endurance is a few minutes, duration for an outside observer is 51 years. If you watched Endurance from a distance, it would do the slingshot maneuver but very slowly.

There are no aliens in this movie. The aliens turn out to be humans in the future. At least, that is Cooper's hypothesis.