What Would it Look Like to Fall into a Black Hole?

In summary: But light that is further from the singularity would be visible even though it is inside the event horizon.In summary, the videos show a simulation of an observer falling into a black hole. The light from the outside becomes increasingly redshifted as the observer approaches the singularity, with the redshift diverging to infinite as the singularity is reached.
  • #1
Hornbein
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There are a number of videos of simulations of this. They all end with complete blackness. This seems wrong to me because light is concentrated by the black hole. There should be more light closer to the center.

On second thought I guess it is OK. While the observer would encounter more light, it would all be from behind or the side while the perspective in the videos is straight ahead.

It would be better to approach the black hole obliquely. Not only is this a lot more likely than a direct hit, but then a forward view would show the strong light that is inside the object. Or so I suppose.

Or maybe both a front and rear view. The rear view would shrink into a very bright dot, I would think.
 
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  • #2
Hornbein said:
light is concentrated by the black hole. There should be more light closer to the center.
Inside the hole this viewpoint does not work. There is no "center" as regards a point in space. The locus ##r = 0##, the singularity, is a moment of time, not a place in space, and light is not "concentrated" at this moment of time.
 
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  • #3
PeterDonis said:
Inside the hole this viewpoint does not work. There is no "center" as regards a point in space. The locus ##r = 0##, the singularity, is a moment of time, not a place in space, and light is not "concentrated" at this moment of time.
OK, then what do you think would be "seen" by our imaginary pointlike observer? What light would intersect that point from which direction?
 
  • #4
Hornbein said:
what do you think would be "seen" by our imaginary pointlike observer?
It would depend on what light sources were present and how they were moving. The hole itself is vacuum so it is not a source of light.

If you mean as the observer approaches the singularity, light sources would be expected to disappear from the observer's field of vision (because the region of space that is in the past light cone of the event where the observer hits the singularity gets smaller and smaller).
 
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If you look backwards you would see the sky outside shrinking towards a point, I think. It would be bright due to the concentration of the light into a small angular subtense, but dimmed due to redshift. It's the wrong side of midnight at the moment for me to figure out which effect wins...
 
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  • #6
Ibix said:
If you look backwards you would see the sky outside shrinking towards a point, I think. It would be bright due to the concentration of the light into a small angular subtense, but dimmed due to redshift. It's the wrong side of midnight at the moment for me to figure out which effect wins...

Both the light and the observer are falling into the black hole so your relative motion is unchanged and no shift is seen, such is my guess.
 
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  • #7
PeterDonis said:
It would depend on what light sources were present and how they were moving. The hole itself is vacuum so it is not a source of light.

If you mean as the observer approaches the singularity, light sources would be expected to disappear from the observer's field of vision (because the region of space that is in the past light cone of the event where the observer hits the singularity gets smaller and smaller).
I'm thinking the sights would be fixed stars.

So the observer crosses the event horizon. Everything closer to the singularity than is the falling observer would be invisible and black. But light that is further from the singularity would be visible even though it is inside the event horizon. I'm interested in light that is originally from a star but has been so curved by the black hole that its essentially of random origin and forms a sort of haze. I would think that the closer one got to the singularity the more concentrated and brighter this haze would be. You seem to be saying that this isn't correct, which certainly could be.

I was also thinking that dust and junk would be cofalling, scattering light, making it possible to see what is going on and making the light more random, and that said dust would become more concentrated closer to the center. But perhaps I am wrong about that.
 
  • #8
Hornbein said:
Both the light and the observer are falling into the black hole so your relative motion is unchanged and no shift is seen, such is my guess.
You should not guess. You should do the math. When you do, you will find that, to an observer free-falling into the black hole, light from the outside becomes increasingly more redshifted as the singularity is approached, with the redshift diverging to infinite as the singularity is reached.

Hornbein said:
Everything closer to the singularity than is the falling observer would be invisible and black.
Once again, the singularity is not a place in space. It's a moment of time. You are thinking of it as a place in space, which is wrong; and any reasoning you do based on that premise will also be wrong.

As far as "space" inside the hole is concerned, for the purposes of the scenario we are considering here, it can be considered to be infinite. It is certainly not the case that "space gets smaller" as the singularity is approached. So any reasoning you do based on that premise (which appears to be a premise that is implicit in a number of the things you say) will also be wrong.
 
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  • #9
PeterDonis said:
You should not guess. You should do the math.
Well duh. I have tried and I cannot do it. Thank you for helping a layman out, which I believe to be one of the main purposes of physicsforums.
 
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  • #11
Hornbein said:
Both the light and the observer are falling into the black hole so your relative motion is unchanged and no shift is seen, such is my guess.
No, because you and a light pulse that passes you at some instant took different paths through spacetime to get where you are, so the cumulative effects are different.
 
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  • #12
Ibix said:
No, because you and a light pulse that passes you at some instant took different paths through spacetime to get where you are, so the cumulative effects are different.
Aha. But then wouldn't the shift be randomly either blue or red?
 
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  • #13
Hornbein said:
Aha. But then wouldn't the shift be randomly either blue or red?
No. Where would randomness come from?
 
  • #14
Ibix said:
No. Where would randomness come from?
From the different paths.
 
  • #15
Hornbein said:
From the different paths.
Why would they be random? GR is a deterministic theory.
 
  • #16
Ibix said:
Why would they be random? GR is a deterministic theory.
The light from different sources -- or even the same source -- would take different paths.
 
  • #17
Hornbein said:
The light from different sources -- or even the same source -- would take different paths.
So? Why would that randomly induce red or blue shift? It's a bit like thinking that if you throw balls in different directions some of them will fly upwards.
 
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  • #18
Ibix said:
So? Why would that randomly induce red or blue shift? It's a bit like thinking that if you throw balls in different directions some of them will fly upwards.
OK, I'll take your word for it, red shift only.
 
  • #19
Hornbein said:
OK, I'll take your word for it, red shift only.
You don't have to take my word for it - PeroK linked to a calculation.
 
  • #20
Ibix said:
You don't have to take my word for it - PeroK linked to a calculation.
There's no way in h that I would ever be able to understand that calculation. I am perfectly willing to take your word for it.
 

1. What exactly is a black hole?

A black hole is a region in space where the gravitational pull is so strong that nothing, including light, can escape from it. This is due to the fact that a black hole has an incredibly large mass packed into a very small space, creating a powerful gravitational force.

2. What would happen if I fell into a black hole?

If you were to fall into a black hole, you would experience something called "spaghettification". This is when the gravitational force of the black hole is so strong that it would stretch your body into a long, thin shape. As you get closer to the center of the black hole, the force would become stronger and stronger, until you eventually reach the singularity, where the laws of physics as we know them break down.

3. Can we see what it would look like to fall into a black hole?

Currently, we do not have any direct observations of what it would look like to fall into a black hole. However, scientists use mathematical models and simulations to predict what might happen. These simulations show that as you approach the event horizon (the point of no return), the light around you would appear distorted and the colors would shift due to the intense gravitational forces.

4. Is it possible to survive falling into a black hole?

Based on our current understanding of black holes, it is highly unlikely that anyone could survive falling into one. The immense gravitational forces would be too strong for any known material to withstand. Additionally, the intense radiation and tidal forces would also be fatal.

5. Are there different types of black holes?

Yes, there are three main types of black holes: stellar black holes, intermediate black holes, and supermassive black holes. Stellar black holes are formed from the collapse of a single massive star, while intermediate black holes are thought to form from the merging of smaller black holes. Supermassive black holes, on the other hand, are found at the center of most galaxies and are millions or even billions of times more massive than our sun.

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