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I have read this question:

This isn't some accounting trick, it means we will never see an event horizon form. At this point someone will usually pop up and say that means black holes don't really exist. In a sense that's true in our co-ordinate system, but all that means is that our co-ordinate system does not provide a complete description of the universe.

How can anything ever fall into a black hole as seen from an outside observer?

Now we actually have a real image of a black hole, M87. But as far as I understand, this is an image of an unformed black hole with an unformed event horizon. If the event horizon never forms when viewed in our frame here on Earth, then should this mean that light and information is still able to escape M87? Since the event horizon is unformed, the escape velocity is still less then the speed of light.

Should this mean that theoretically we would still be able to receive information from the inside?

As far as I understand, M87 is not black because of the event horizon (because that never forms), but because of redshift. So light and information still escapes the black hole, it just loses energy to the gravitational field when it tries to propagate outwards. So there could still be some information that we could receive (even if it is redshifted)? Theoretically it could still be possible to decode that information and (algorithmically) make up for the redshift. It could either just be hard to decode or theoretically impossible.

Question:

  1. If black holes never form (like m87) then does this mean that theoretically we could decode light and information that is still coming out of them?
Qmechanic
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Árpád Szendrei
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2 Answers2

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The black hole does form. The fact that we don't see the horizon or have a coordinate singularity in how we describe the universe doesn't change that. This was the critical part of what you originally quoted:

In a sense that's true in our co-ordinate system, but all that means is that our co-ordinate system does not provide a complete description of the universe.

That statement is very different than saying that the black hole doesn't form. In fact is a disclaimer stating how our view of the universe is incomplete exactly in the sense that we don't see the formation in the scenario described.

Brick
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From our frame of reference, infalling matter travels into regions outside the event horizon where time runs slower and slower as seen by us. Because of this, we see them falling slower and slower as they approach the horizon. By our clocks, it takes an infinite time to reach the horizon.

This also means that photons coming off the matter arrive at a slower and slower rate. As it approaches, all the photons that leave in a millisecond of in falling matter time would be received spread out over a second of our time. When it gets closer, the photons from a microsecond would be received in a second.

You can see the result of this progression. Soon photons would be arriving from such a short interval that the expected number in a second is $0$.

These extreme time stretches happen when the in falling matter is very close to the event horizon. That is to say, by its own clock, it will cross the event horizon within a very short time. The expected number of photons it will emit before it crosses becomes $0$.

A second point is that photons we do receive become more and more red shifted. Assuming you use a receiver with some lower frequency limit, the frequency would quickly too low to receive.

mmesser314
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