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The universe is immense and 13.8 Billion years has passed overall since it was formed in the Big Bang event.

If time greatly slows down inside a Black Hole (BH), then logically very much less than 13.8 Billion years has elapsed inside any BH that has formed since the Big Bang, in our universe.

Thus, inside a BH, has any matter had sufficient time inside the BH to transit from the event horizon to the center ?

I understand that time for the in-falling matter seems normal, but that doesn't mean it is unlimited. There is still the matter of the limited 13.8 Billion years in normal time outside the BH. Any slower time means less than 13.8 Billion years has elapsed inside the BH.

Maybe the age inside a BH is only a few seconds total elapsed time! From inside the BH's perspective, matter must be falling in at an infinitely fast rate and piling up into a very condensed shell at the event horizon!

IF that is true, then would not the BH be just a huge condensed matter shell only a few meters thick without any central singularity formed - in 13.8 Billion years viewed from our perspective outside ?

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  • $\begingroup$ The time slows down outside of the event horizon. Inside the black hole, the role of the radial coordinate and the time coordinate changes if the Schwarzschild metric is extrapolated into the black hole. It's not obvious for me that it further slows down, does it? $\endgroup$
    – p6majo
    Commented May 18, 2019 at 20:35
  • $\begingroup$ The idea of a black hole being a shell just outside the horizon is well known. However your personal theory of the shell being inside the horizon has nothing to do with physics, but is based on a lack of knowledge or understanding of the Schwarzschild metric. Time inside a black hole doesn't move slower relative to the universe. Instead, time inside a black hole moves in a different direction and for this reason can't be put in any reference at all to the time elsewhere in the universe, not "slower", not "faster", nothing. You can't race to the destination while moving in different directions. $\endgroup$
    – safesphere
    Commented May 20, 2019 at 5:59
  • $\begingroup$ Also a Schwarzschild black hole doesn't have a point-like center. The spacetime geometry inside the horizon is an infinitely long 3-cylinder with a rapidly shrinking circumference. While space in the universe is expanding, space inside a black hole is contracting at a very fast rate (just microseconds for a stellar size black hole). $\endgroup$
    – safesphere
    Commented May 20, 2019 at 6:29

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The most important feature of a black hole is the cosmic censorship, that means that the event horizon is a sort of screen which is entirely intransparent for our scientific methods. For this reason, the interior Schwarzschild is not corroborated by any experimental insight.

A black hole may not be imagined as a sophisticated world, in fact, according to our knowledge it has very little features – mass, position, diameter of event horizon, angular momentum, and - possibly - some Hawking radiation.

The existence of black holes may be observed, and by this we may assign an age to each black hole. In contrast, there is no information about the existence of some proper time of some hypothetical observer inside the black hole. All the contrary, we must admit that spacetime of general relativity ends at the event horizon of a black hole, and so does our definition of time.

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It is a misconception that mass creates time dilation, in reality it is stress energy, and the difference between the strength of stress energy of the black hole, and the rest of the universe (let's assume empty space).

Now you are correct that because of this difference in stress-energy, that causes time dilation, clocks at the black hole will seem to tick slower relative to clocks in empty space.

Now you are saying that you understand that infalling clocks and observers would seem their own clock to tick normally. It is only when they would compare it to clocks outside that they would see their own clock inside the hole ticks slowly.

But you say it cannot be unlimited. Now in reality, 13.8 billion years might seem a long time to us, but it might be just a second in the frame of an infalling observer in a black hole.

To clarify, there were no black holes 13.8 billion years ago, but let's disregard that and say that there was a black hole so long ago. Let's assume an infalling observer looked at his clock inside the hole at that point (again, assuming this would be already existed 13.8 billion years ago), and compared it with clocks outside the hole.

What he infalling observer would see, on his own clock, is that it ticks normally just 1 sec in this example, but if he compared it to clock outside the hole, those clocks ticked 13.8billion years already and here we are.

So 1 sec in the black hole might easily be 13.8 billion years outside the hole. So no, it is not neccesseraly true that all that matter that falls into the black hole would have reached the singularity by now (13.8 billion years later on an outside clock).

It is because 13.8billion years on an outside clock, might just be 1 sec inside the hole. In reality, we do not know if anything ever reached a singularity inside any black hole ever (that is any new matter infalling from outside the already formed black hole).

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  • $\begingroup$ So, Arpad Szendrei, you agree with me. My hypothesis is that BH's must, therefore, consist of SHELLS of condensed matter of some unknown thickness just beneath the event horizon due to extremely slow in-fall velocity and that singularities may not even exist (YET) in our 13.8 Billion year old universe - which was my whole point in this posting. It seems to me that almost all discussions of BH's by pass the time dilation problem, as if it does not exist, and continue on to discuss singularities as if that is the obvious conclusion! $\endgroup$
    – DoctorBill
    Commented May 19, 2019 at 1:58
  • $\begingroup$ @DoctorBill you are correct, though, I do not know what the requirements for the creation of a black hole are, among those might be a requirement of a singularity, but in reality nobody knows. $\endgroup$
    – Árpád Szendrei
    Commented May 19, 2019 at 2:31
  • $\begingroup$ "So 1 sec in the black hole might easily be 13.8 billion years outside the hole." - This is incorrect for a Schwarzschild black hole. Time inside a true black hole moves in a different direction and cannot be put in any relation (like "slower" or "faster") to time outside. However, if you consider an empty shell under a gravitational collapse, then, for any external observer, it would look like a black hole that is empty inside where time moves still in the same direction, but so slow that it is practically halted. $\endgroup$
    – safesphere
    Commented May 20, 2019 at 6:18
  • $\begingroup$ I find it SO INTERESTING that people discuss singularities and Spagetification and what someone would experience entering a BH, but - when I postulate that BHs are condensed Matter SHELLS, why then, suddenly "We cannot know what happens inside a BH !" $\endgroup$
    – DoctorBill
    Commented May 21, 2019 at 2:57
  • $\begingroup$ An infalling observer will not observe massive amounts of time dilation on an external clock. They will receive a finite amount of signals in the finite proper time it takes them to reach the singularity. Extreme time dilation occurs for radially stationary observers, that cannot exist (in GR) inside the horizon. $\endgroup$
    – ProfRob
    Commented May 10, 2022 at 22:56
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'Has any matter had sufficient time inside the BH to transit from the event horizon to the centre?'

One can regard the black hole and its contents as isolated from the rest of the universe, in that no information can be transferred (as of 18th May 2019!) from the black hole to the universe. In this sense the matter inside the black hole has had as long as the age of the black hole to progress to the 'singularity'.

Relative to our time, yes, the matter in the black hole has experienced a very small amount of time (much much smaller than the age of the black hole). The matter does fall in at a finite rate all the way up to the singularity.

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