Exploring Physics at the Event Horizon of a Black Hole

[tribdog]

Okay, let's say I'm orbiting a black hole right near the event horizon. If I take a long stick and poke the black hole what happens? If time stops for the end of my stick as it reaches the event horizon how can I keep pushing on my end? For that matter if I jump in feet first doesn't my head see my feet freeze in time? I know that my feet don't notice any time difference, but my head notices it for my feet doesn't it?

 

[mathman]

The idea of time "stopping" is in the frame of a distant observer, not moving with respect to the black hole. If you are moving, things are different. For example if you fall past the event horizon, you wouldn't notice anything unusual right away, particularly if the black hole is very large.

 

[xmavidis]

I don't think that the time stops on time an object enter the horizon. The space-time is curved as much as the "distance" of object-anomaly is getting smaller.

 

[Enigma007]

you probably wouldn't notice a difference at all from your frame or reference

 

[sudhirking]

as in my theory of everything.. which i ddnt get a chance to finsh on here.. space-time is very relative and as space-time streches, the "fibrs" also strech casung adistortion of perception dependinf\g on your view

 

[LURCH]

Regarding all these "you wouldn't notice any difference" responses:

If the end of the stick enters the black hole, it cannot come out again. However, the rest of the stick can move away from the event Horizon, as can the person holding it. It seems likely that this effect would be quite noticeable.

 

[Khursed]

I think people are losing sight of a few facts here.

For one, no one could hold any stick in such a way that one end is safely out of the event horizon, and another part is in it.

The gravitational pull on the stick itself would probably exert force far beyond the mechanical strength of any material.

Time doesn't stop for anyone, that's confusing illusion with reality.

A safe observer would get the illusion because of how light behaves so close to a black hole, that the image of the stick is not moving anymore, however that stick is long gone, having probably hit the black hole with the strength of an H-bomb.

Imagine a stick long as the distance between the sun and neptune, that's 4.55 billion km. a steel stick of roughly 3cm in radius, would weight, 22.2 tons per kilometer, or 101 billion tons.

Even such a long stick would not stop at one point and keep on falling toward the black hole at another.

It would probably be a hell of an experience to try, but something tells me that once it starts to move toward the black hole, and one points reaches the event horizon, the rest of the stick is doomed to end up in the black hole.

The event horizon is not a tangible place, its merely a concept, meaning at that distance from the black hole, nothing has enough energy to escape its gravitational pull.

Try using a 1 kilometer stick made of steel and making it stand up straight, and you'll understand that if Earth's gravity can claim your stick, a black hole would make short work of it.

 

[LURCH]

I don't think people are confusing illusion with reality when they say that time slows for one obsever and not for another. Most of the people in this discussion (and in these Forums in general) seem to have a fairly good grasp of General Relativity. One of the main points of GR is that time dilation is as real as anything else.

But I certainly agree that no stick made of any material could withstand the G-forces involved. This is not just a comment on the structural integrety of all known materials, but a statement of the limits of what strengths are theoretically possible for any imaginary material existing in real space.

 

[Chronos]

The event horizon of a black hole would look very unremarkable to an approaching observer. The rest of the universe would, however, look very strange indeed. Objects behind you would be blue shifted!

 

[Tzemach]

We know that in the centre of stars matter becomes so condensed that the electron shells disintegrate so that mass becomes degenerate matter, similar reactions occur within a black hole. So although you would not notice anything as Chronos said the rest of the universe would appear pretty strange and the gravitational field would distort shapes and colour. Even though you thought you were pushing the stick into the black hole generations of distant observers would see that you were not moving and to them you would appear frozen in time except for the energy stripped away as you and the atoms of your stick collapsed into the black hole.

 

[LURCH]

But this assumes that both the person and the stick are very near the EH. If the stick were quite long, the person holding it would be the "distant observer." I think the OP was trying to come to grips with the idea that there is unbroken spacetime between the EH and the "distant obnsever" position. What would happen if we used a stick to physically bridge that distance, putting the distant observer into direct contact with an object that is in direct contact (or nearly so ) with the EH?

On the one hand, time dilation near the EH seems to say that that end of the stick would never cross the EH. So, I could push on my end with all my might, and it just wouldn't go any further.

So, no amount of pushing force I coulod generate would make it move inward.


On the other hand, the overwhelming gravitational forces involved seem to suggest that the stick would fall in, and at rather high speeds. If I could generate the forces required to hold my end still, the stick would break, no matter what it was made of.

So, no amount of force I could generate would keep it from moving inward.

Certainly I don't experience any effects of time dilation just because I'm holding onto the stick.

 

[Nabeshin]

You're confusing the Event Horizon of a black hole with the singularity. Time does not stop at the event horizon, it stops at the singularity. The Event Horizon is known as such for one reason: it represents the radius at which light (and therefore any information) cannot escape. Therefore, poking a stick through it would be no whoop, assuming we're ignoring tidal forces. Unfortunately, you would not be able to see the stick anymore as what of it is beyond the black hole would not be able to radiate any light outwards. Good luck keeping a grip on it to, because the force of gravity is enough to make a photon curve in on itself, save a massive object such as a stick.

 

[LURCH]

But most modern BH models state that a distant observer will never see an object cross the EH. So, if the "distant observer" is holding one end of the stick and pushing so that the other end crosses the EH, he will see the other end of the stick slowing down to a crawl (and turning red), but will he feel that slowing from his end? If I see the other end of the stick apearing to slow down, I would expect to feel resitance on my end, decelerating the stick. But, since the other end of the stick is being subjected to strong gravitational forces, I would expect to feel a strong pull, accelerating the stick.

These two scenarios cannot both be true. I would expect that the pull on the stick continues to increase, despite the fact that, from my perspective, the end of the stick has ceased to move.

 

[korinteren]

Nothing will happend

Ignoring the fact that the observers hand-movement will move with the speed of sound through the sticks material, and therefore makes the setting even a bit more shady:
My guess is that if time was different in one end of an object than the other, how would that have any effect on how "easy" the stick is to move? If time goes against zero, it does not mean that it stops moving in the slow-time side of the stick. The stick does not "notice" any difference, as every event is still happening in the same relative order and speed for the stick in its local environment (including speed of sound). (not that I know what the h... I am talking about)

 

[Nabeshin]

But most modern BH models state that a distant observer will never see an object cross the EH. So, if the "distant observer" is holding one end of the stick and pushing so that the other end crosses the EH, he will see the other end of the stick slowing down to a crawl (and turning red), but will he feel that slowing from his end? If I see the other end of the stick apearing to slow down, I would expect to feel resitance on my end, decelerating the stick.

I don't think so. Appearances can be deceiving, especially when we're near black holes. Just because it looks to slow down does not mean there is some magical "Event-Horizon" force pushing back on the stick.
Also, will the gravity at the EH inevitably tear your stick? I don't think this is a question of how strong your material is. If not even light can escape, your stick (the part inside the EH) should be pulled off, yes?

 

[LURCH]

I don't think so. Appearances can be deceiving, especially when we're near black holes. Just because it looks to slow down does not mean there is some magical "Event-Horizon" force pushing back on the stick.

Yes, that's what I conclude, as well. The appearance of deceleration at the far end of the stick would be rather like the appearance of bending at the point where the stick passes through the surface of some water, having no effect on the forces one would feel while holding the stick.

Also, will the gravity at the EH inevitably tear your stick? I don't think this is a question of how strong your material is. If not even light can escape, your stick (the part inside the EH) should be pulled off, yes?

Definitely. This is true not only for real materials, but any imaginary material, because it is not a question of the structural integrity of the material itself. The space that the material occupies is so curved that all "future paths" point toward the singularity. Any material that occupies that space must also be curved to such an extent as to be severed from the rest of the universe outside the event horizon.

 

[sudhirking]

You're confusing the Event Horizon of a black hole with the singularity. Time does not stop at the event horizon, it stops at the singularity. The Event Horizon is known as such for one reason: it represents the radius at which light (and therefore any information) cannot escape. Therefore, poking a stick through it would be no whoop, assuming we're ignoring tidal forces. Unfortunately, you would not be able to see the stick anymore as what of it is beyond the black hole would not be able to radiate any light outwards. Good luck keeping a grip on it to, because the force of gravity is enough to make a photon curve in on itself, save a massive object such as a stick.

actually.. time doesn't stop at the singularity..
since- according to astronomers and physicists- space time cannot rip(i DON NOT BELIEVE THAT) so that would mean that the fabrics of space time would strech so much in the singularity, that it would seem timeless, but in truth itsn't really timeless

 

[sudhirking]

YOUR STICK- due to the very intense gravitational forces would be vaporixed out of your hand becasue every atom is streched to nearly infinite and since light cannot be seen due to the gravitational ppull, so you wuold fell everything is the same as usual but in truth you are a very large size

 

[Algr]

So the short answer is:

Your stick would break.

And it would happen so fast you'd hardly see anything.

 

[Nabeshin]

actually.. time doesn't stop at the singularity..
since- according to astronomers and physicists- space time cannot rip(i DON NOT BELIEVE THAT) so that would mean that the fabrics of space time would strech so much in the singularity, that it would seem timeless, but in truth itsn't really timeless

I realize that the time dilation is rather asymptotic, but for all practical purposes time stops. It just doesn't have the same zing to say "time dilation increases without bound as one approaches the singularity"!