Do you ever die when you fall into a black hole?

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Originally Posted by Seismosaur

No, the light would sit there forever until the universe ends.

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The light would "sit there" forever, but we would stop seeing it. The object's trip passed the event horizon would take it to a point where the photons would never reach our eyes, rendering it invisible. That is precisely why we do not see the huge blobs of mass that give black holes their gravitational pull (the collapsed star). It is not because they are invisible. It is because the light never bounces off of them and reaches us. It hits the object, tries to bounce off, but gets drawn back by the insane gravitational pull of the object, which is the same thing that happens to anything that travels passed the event horizon - including the hypothetical dancing man.

No, the light never reaches the "actual" black hole, so you will still be able to see the object forever.

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Originally Posted by Seismosaur

No, the light never reaches the "actual" black hole, so you will still be able to see the object forever.

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What do you mean the light never reaches the "actual" black hole? The light passes through the event horizon and gets sucked directly to the "actual" black hole. This is why it doesn't escape, no?

No, it stops.

Everything that goes into a black hole just sits around it.

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I believe that is incorrect.

The outside observer would be basing his/her opinion on what he saw from the photons that left the event horizon and reached his eye. So, if the person in question entered a black hole, and the visual of his being spaghettified took x amount of time to reach the outside observer, it would be because the photons showing the person in question getting S-ified would take longer to reach the observer (if ever). That would not mean that the observer would be right in saying that the person in question wasn't already S-ified. Frame of reference does not change the absolution of whether or not that person has already been stretched/split into sections that no longer sustain human life. It's either happened and he's no longer intact, or it hasn't happened, and he is.

It's the same as someone saying "A star that we see with our naked eye does not actually exist anymore." We, as observers, may still see it, but that does not mean the star still exists, as it could have been destroyed light years ago. If that was the case, the person saying that it still exists (regardless of whether or not we could still see it) would, in fact, be wrong.

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No..?

So many people seem to refute relativity, it's strange... it's all there in the name. Completely ignoring photons and information flow and that kind of thing; time for the outsiders would not progress at the same rate as the person in the black hole. It's got nothing to do with how long it takes signals to reach observers. They have different 'whens'.

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Originally Posted by Xei

No..?

So many people seem to refute relativity, it's strange... it's all there in the name. Completely ignoring photons and information flow and that kind of thing; time for the outsiders would not progress at the same rate as the person in the black hole. It's got nothing to do with how long it takes signals to reach observers. They have different 'whens'.

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I'm not refuting relativity. I'm simply saying that relativity must be looked at for what it is (a different frame of reference). Something can seem to still be existent, to someone outside of that frame of reference, but whether something does or does not exist, cosmically, is much more absolute, is it not? (As far as the relativity, I'm honestly asking, as I'm not 100% sure).

But, to call my initial analogy into question once again: If we (here, on Earth) can see a star with our naked eye that was, in fact, destroyed hundreds of light years ago (and the light from that explosion just hasn't hit us yet, so we still see the star as intact), would we be right in saying that star still exists? Or would it just be an error of perception?

I think so. The star does not exist any more, according to our now. If we put a mirror out of the direct line between us and that star that reflected its light towards us (ie increased the time it takes for the light to get here), following that logic we'd have to say that the star is simultaneously at two different points in its life according to us. What is true is that both things we are seeing are actually wrong, and that the star is indeed objectively dead at that time, even though we might not know it. Relativity and how long it takes to see something are separate.

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Originally Posted by Xei

I think so. The star does not exist any more, according to our now. If we put a mirror out of the direct line between us and that star that reflected its light towards us (ie increased the time it takes for the light to get here), following that logic we'd have to say that the star is simultaneously at two different points in its life according to us. What is true is that both things we are seeing are actually wrong, and that the star is indeed objectively dead at that time, even though we might not know it. Relativity and how long it takes to see something are separate.

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Ok, good. That was exactly my point in the previous post. No matter where we are, and what frame of reference we are observing from, there has to be a cosmic truth (in this case, at least). As is the case with the dancing man falling into a black hole. The question of whether or not the man is alive or dead (due to spaghettification) is not necessarily relative. There is an absolute truth (which would, most accurately, be determined by the reference point of the man who's actually undergoing the S-ification). When he's dead - from his own frame of reference - he's dead, no matter what an outsider sees.

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Originally Posted by Seismosaur

No, it stops.

Everything that goes into a black hole just sits around it.

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I never addressed this one directly, but you are both right and wrong. The light (just as everything that goes into a black hole) just sits around the black hole. That part is true (well, sort of true, because most things that get sucked into a black hole are turned to cosmic dust, because the gravity is too great for anything to just "sit" there without being atomized). But it's not the light's existence, alone, that makes us able to see objects. It is light bouncing off of a surface and into our eyes that allows us to see it.

If an object gets sucked into a black hole, then the light that bounces off of it does not bounce back into our eyes. It tries to, but it gets drawn back to the original object because of the gravitational field of the black hole. This, again, renders both the collapsed star and the object in question invisible. That is why black holes are black. If the light bounced off and into our eyes, we would see the remnants of a collapsed star, and not a black void.

This is also how "invisible cloak" technology works. Fiber-optics bend the light around an object so that the photons don't bounce directly off the object into our eyes and, instead, they are funneled to another direction, rendering the wearer of the cloth "invisible."

I think the theoretical dancing man would be spaghettified to a more than fatal extent long before he reached the event horizon. After all, the event horizon is where gravity is so strong, not even light can escape its pull.

I also think that if death did happen after the event horizon, and the outside observers see the man freeze in place still alive, they would be incorrect to assume that he is still alive. While he may be frozen in time in their frame of reference, in his frame of reference, he is nothing but small particles.

An interesting thing to consider is that to the dancing guy, time for the outside observers at the moment he crosses the event horizon and is frozen in the outside observer time; he would see time pass for them (if he could see them at all) at an infinitely fast rate.

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Originally Posted by Schmaven

I think the theoretical dancing man would be spaghettified to a more than fatal extent long before he reached the event horizon. After all, the event horizon is where gravity is so strong, not even light can escape its pull.

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Very good point.

There seems to be some lingering confusion here.

Both the outside observer and the falling person are correct in what they experience, even if they don't agree.

The falling observer does hit the singularity in a finite amount of time.

The outside observer will see all falling objects crowded around the even horizon, frozen in time. However, this freezing of time also produces a huge red shift and so the outside observer will have trouble actually seeing them.

Now, the issue of light is complicated. Light does still travel at the speed of light close to the event horizon and even inside the event horizon. What varies is the curvature of spacetime. Inside the event horizon, spacetime is so curved, that light, which travels straight in its own frame, will actually have a decaying orbit around the singularity. Outside the even horizon, light passing by will have its path bent as it enters and exits the region of severely warped spacetime.

When the outsiders see the man as frozen, for them he is not dead.
He is traveling into the future. After an infinite amount of time has passed to the ousiders, he will die in their time frame. Because an infinite amount of time will never pass, he will never die in their time frame.
He however will die in his own timeframe, and his friends that he left behind will be then dead too, as they will be an infinite number of years old.

That's right, dodo. Although practically speaking he would be dead. But if we're talking theoretically, then yes.

Actually, black holes make very good time machines. Not just for traveling forward but also for going into the past. But that's even more complicated and off-topic.

The problem I see with using black holes as time machines (in any direction) is that their gravity is too strong for anything we can make to survive. All matter breaks down at the speed of light.

Does being in a strong gravitational field in free space kill you though? All that happens as far as I can see is that all your atoms are accelerated at the same rate.

But you can't travel backwards in time anyway, drewmandan.

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Originally Posted by Schmaven

The problem I see with using black holes as time machines (in any direction) is that their gravity is too strong for anything we can make to survive. All matter breaks down at the speed of light.

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No, it doesn't matter what speed a thing is going. Speed is relative. The gravity would be a problem, of course, but I'm just speaking theoretically.

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Originally Posted by Xei

Does being in a strong gravitational field in free space kill you though? All that happens as far as I can see is that all your atoms are accelerated at the same rate.

But you can't travel backwards in time anyway, drewmandan.

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A constant gravitational field does nothing, but the gravitational field close to a black hole has a noticeable divergence, or in layman's terms, changes a lot over small distances. Thus, if you were falling feet first into a black hole, the gravity at your feet would be stronger than the gravity at your head, and this difference would become strong enough to rip you apart. Like that dude in the video said, this is the same thing that causes ocean tides on Earth.

And there is a theoretical way to travel backwards in time, using a spinning black hole.

http://en.wikipedia.org/wiki/Kerr_metric

Yeah, that was my point; only if there was a difference in G and hence F=Gm then there would be an overall tension force pulling you apart. If you're in an immensely strong but constant field then I don't see how any harm could come to you, you'd just accelerate...

I didn't know about Kerr metric, interesting. I have a gut feeling it's wrong because it'll allow for temporal paradoxes, but who knows.

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Originally Posted by Xei

Yeah, that was my point; only if there was a difference in G and hence F=Gm then there would be an overall tension force pulling you apart. If you're in an immensely strong but constant field then I don't see how any harm could come to you, you'd just accelerate...

I didn't know about Kerr metric, interesting. I have a gut feeling it's wrong because it'll allow for temporal paradoxes, but who knows.

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Space time isn't distorted with a constant depression, it is curved, but with black holes, this curvature of space time would be so great that the forces at your feet would be significantly greater than at your head. So basically, your feet are trying to accelerate faster than your head. All the while, the space-time is becoming more constricted, so you are not only being pulled apart but also squeezed.

Hence the term, Spaghettification.

Also, as general relativity predicts, if the black hole is spinning, you get further distortion of space and time, as in additional torque and shearing forces. In general, Black Holes are brutal.

Yes it's all there in my first sentence.

'Accelerating faster than your head' is a bit misleading though, for a time the tension force between your head and legs will stop that happening. Only when that force difference overcomes the forces holding bits of your body together will you start to stretch. Actually I'd imagine your flesh would be ripped off first and organs, followed by your limbs snapping off...

lel, physics is so dispassionate.

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Originally Posted by Xei

I didn't know about Kerr metric, interesting. I have a gut feeling it's wrong because it'll allow for temporal paradoxes, but who knows.

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Temporal paradoxes only exist in the old Jules Verne model of time travel, which unfortunately is used in sci-fi even to this day. The quantum model, called the Many Worlds Interpretation, has no paradoxes. So which model do you think is correct, the one invented by a 19th century author or the one developed using modern physics?

Come on, you know that's wrong. The many worlds interpretation (you know what that word means..?) is one of the many interpretations of quantum theory, and actually it's currently a minority view.

It is one of the interpretations of quantum theory, but in terms of time travel, it's the leading theory, other than simply saying you can't time travel.

You can't ignore all theories which say you can't go back in time. :undecided:

Obviously discussions about time travel have to be consistent which current physical theory, that's the point.

Well, actually my main point is your giant strawman of a post above which was basically entirely wrong. But ya.

The physical theories which allow for wormholes do not have any specific quantum interpretation assosciated with them (considering quantum theory is currently completely separate from relativity) so the possibility of paradoxes has to be considered.