Viewing a spaceship entering a black hole

I’m watching one of the universe shows and they talk about the effects of going into a black hole. Then they show the standard diagram which resembles water swirling down a drain. When the spaceman enters he disappears from view, of course, because he went down into the depression. Then it dawned on me that that was a 2D explaination of what happens in 3D. In reality there is no “down” in a black hole. So my question is:

If you are watching a spaceship entering a black hole (with a really swell yet to be developed telescope) does it simply vanish before your eyes at some point?

I’m guess that it would but that just seems to go against common sense.

[sup]For the sake of this question lets assume a super massive black hole so we can ignore witnessing the ship being torn apart part.[/sup]

A black hole is a spherical object, but since it (well, the black ‘surface’ that we can see, known as the event horizon) is basically featureless, it will look the same in any direction (provided it’s not rotating really fast and squishing itself, but you get the idea). If we watched a spaceship fall into it, it would be basically as you describe, now you see it, now you don’t.

Well, that’s the general idea anyway. What actually happens is that the black hole’s intense gravity causes time dilation and redshift, so not only does the ship appear to fall slower and slower as it gets closer, but it gets harder and harder to see as the light from it gets dimmer and dimmer. It’ll disappear into the infrared before we see it fall in, but if we could use a detector to keep track of it, we’ll never actually see it disappear completely. From our point of view, the spaceship will take literally forever to fall past the event horizon. From the ship’s own point of view it’s long gone, of course.

What happens when a black hole evaporates? Does the object that takes apparently infinite time to get “sucked” in just go “poof” or does something else happen? (i.e. witnessing it happen in fast forward, second coming of Jesus etc) My thoughts are seriously drifting towards the former, but what’s the result? Or rather, considering I doubt we’ve witnessed a black hole eating something disappear, what’s the theory.

An object entering a black hole does reach the singularity in finite proper time – it doesn’t just hang around the event horizon, even though it may look that way.
However, the question what happens to the object is a very interesting, and still not completely resolved, one: Hawking radiation (which is the process by which the black hole evaporates) is believed to be thermal, i.e. it contains no retrievable information, because of the ‘No Hair’-theorem, which states that a black hole is characterised by only three (externally) observable properties: mass, electric charge, and angular momentum. Thus, two black holes for which those quantities are the same are physically indistinguishable, which implies that the information about what they’ve snacked on during their existence is lost for good.
However, information is also very strongly assumed to be conserved in quantum mechanics, so we’re presented with a paradox – the aptly named black hole information paradox.
As of now, I’m not aware of any widely-accepted resolution; in fact, it is still subject of an ongoing bet (wikipedia has an article for everything) between Kip Thorne, Stephen Hawking and John Preskill, though Hawking has since conceded, believing the solution to lie in the fluctuation of the event horizon; Kip Thorne is still unconvinced, however.

Damn it! Can I ever ask a physics question that DOESN’T boil down to a presently irreconcilable paradox? :frowning:

Anyway, thanks for the explanation.

Part of the problem with evaporating black holes is that, before a black hole disappears entirely, it must at some point reach a size where quantum gravity becomes relevant. What we know about things like Hawking radiation just breaks down completely at that point, and ceases to be even a back-of-the-envelope guesstimate. Unfortunately, we don’t yet really have any better theories to use instead in that regime, so mostly all we’re left with is a bunch of head-scratching.

But that’s the best part!

As far as I’m concerned no truer words have ever been spoken.

It’s true that the EH singularity is only a coordinate one, but nonetheless it still seems that to a stationary far away observer, time really does come to a stop there.

Finkelstein frame or no, if an observer is lowered close to the EH his watch will show a smaller passage of time when he returns to the hovering rocket.

I understand that an infalling observer goes right in but it still seems that to the faraway observer a black hole really is a frozen star – even though he can’t actually see anything at the horizon because of infinite red shift.

What am I missing?

Poul Anderson wrote a short story using this idea ages ago, circa 1972. It wass called “Krie”, and it assumed (purely for the sake of the story) that telepathy a.) was a fact and b.) that it’s essentially not subject to physical laws – no falloff with distance, not affected by curvature of space, etc.

At the end of the storey, an alien space creature that a human is in telepathic contact with falls into a black hole. Since, from our point of view, that person is perpetually falling into the black hole, the human hears the alien’s death scream for the rest of her life. And can’t get away from it, no matter where she goes.

This is one reason I’m voting that telepathy follow at least a few of the laws of physics.

Nothing, so far as I can see. What is it about what you said that leads you to think you’re missing something?

But… but… you’re CHRONOS, don’t you govern all this messed up stuff that relates to time in any fashion!? Shouldn’t you know this to a T?

Titan my ass…


I’d off myself real quicklike in that scenario, not that suicide is a good thing, but I think I’d make an exception.

I’ve read many times that a black hole could not be considered a frozen star and that the Finkelstein FoR proves this. It’s been a long time since I’ve read Kip Thorne’s Black Holes and Time Warps, but I believe he states it in there.

In other words to a far away stationary observer time does not come to a stop at the EH.

Here’s a pretty good description of what I mean.

Erm…I thought a singularity was always in your future (or our past in the case of the Big Bang singularity)?

A black hole can not be considered absolutely a frozen star. So far as we can tell, the poor schlub falling in, in his frame of reference, just keeps on falling right past the event horizon until he, in short order, hits the singularity and goes splat. However, in our comfortable, safe frame of reference far away from the event horizon, there never comes a time when the schlub (or the matter of the original star) has ever quite passed the horizon.

Now, of course no poor schlub has ever reported back after having fallen into a black hole, so observations made from outside cannot actually verify what happens to the infalling observer. It’s possible that our Universe doesn’t actually contain any true black holes, just things that look exactly like one from the outside (and in fact, this idea is seriously floated occasionally in scientific circles: See gravitars). But our current theoretical understanding doesn’t allow for any mechanism for these not-quite-black-holes to exist, so absent any evidence to the contrary, we assume that what we have really are black holes, the horizon of which an infalling observer really can pass.

Again I thought that even the hapless guy falling in never actually reaches the singularity. The singularity represents an infinite curvature of spacetime. You just never quite catch up to it (IIRC I recall someone saying if you charted its light cone it is moving into the future at light speed…or something like that but the implication being you’ll never catch it).

Whack-a-Mole I think what’s screwing you up is that the light cone abruptly tips when passing the event horizon (in Schwarzschild coordinates), and therefore the time axis and the space axis change orientations wrt the singularity.

So the singularity is now in your future. But this doesn’t mean tomorrow doesn’t ever get here, it just means you’re absolutely, fer sure, very soon, going have a truly bad day.

No argument from me on this statement, but what about the faraway observer? In his frame does the guy falling in ever really cross the EH. I know he couldn’t actually see this, but what is the underlying reality? If time comes to a stop at the EH for the FAO then how can any object, including the star itself, get in there?

Personally, I don’t think anyone really knows. I think, as Jragon says you Titans of space and time are just making all this crapola up :slight_smile:

BTW the FAO is us!

Oops, sorry, I somehow or other missed this part of your post. Does this mean there’s a discontinuity between our proper time and the infalling guy’s proper time?


Sorry for my plethora of posts. I think what your referring to is: as the guy falling in approaches the EH he can either consider the horizon to be approaching him at light speed or that he’s approaching it at light speed. However, this doesn’t mean that he can’t pass through the horizon. It just means he passes through it faster than hell.

ETA: And he and his light cone continue towards the singularity at c.