In this video Neil Degrasse Tyson compares the Observable Universe to a Black Hole…
…and how the mass of our observable universe within the Hubble Horizon indeed equals the size of an event horizon of a black hole containing a universe’s amount of mass. Is Our Universe Inside a Black Hole?
Nevertheless, has any astrophysicist/cosmologist worked in the Hubble Parameter into the formation of black hole/ event horizon physics? Hubble’s law - Wikipedia
I think this topic is generally called “black hole cosmology”, and it has its adherents though they’re not in the majority. I really like the theory. However, pleasing Napier isn’t much of a test of the merits of a theory.
I think there’s a version that, more or less, describes a parent universe with 11 orthogonal dimensions. Black holes that form in that universe have interiors with 9 dimensions, these interiors effectively being their own universes. In those universes, black holes form that have interiors with 7 dimensions. This cascades down to simpler and simpler universes, always losing two dimensions with each step. I don’t remember where I heard this and may have butchered it, so please feel free to correct me! In any case, I think this one is especially intriguing, but I don’t think it’s the mainstream.
Well, it is an agreed upon fact that a Black Hole is created from gravity so intense that the entire remaining mass of the exploded star collapses into a singularity. Not even light can escape because, apparently, the 300,000 km/s light speed isn’t escape velocity. Yet, it is another agreed upon fact that our universe is expanding at a tremendous rate, a rate even faster than light in some instances. Non sequitur. That “theory” makes no sense and sounds more like the earth is flat click bait than a serious theory.
Any discussion of modern cosmology has to involve dark energy (or the cosmological constant, or whatever you call it), which is the dominant factor (70%) governing the current evolution of the Universe, and which, unless something completely unexpected happens (which it very well might, given that we have basically no understanding of dark energy) will become even more dominant as time progresses. So any cosmological model which doesn’t include dark energy, these days, is a toy model at best: It might be useful as a simplification for teaching students how to approach models, but it definitely doesn’t describe reality.
The usual descriptions of black holes are set in asymptotically flat universes: That is to say, in the model, there’s nothing else in the Universe besides the black hole, and so space far from the black hole is completely flat. This works fine, for small black holes, because the distance from the black hole where the hole’s own effects become negligible is still far shorter than the distances at which cosmological effects become relevant: It’s not actually accurate, but the deviations from the real situation are a rounding error.
One can still set up the equations for a black hole in a space that’s not asymptotically flat, though, at least in some cases. And people have worked out formulas for the metric for a black hole in a space with uniform dark energy, and nothing else. But in those formulas, if the size of the black hole starts getting too large, things start getting really weird, in ways that nobody is quite sure how to interpret.
There are a lot of issues with this. First, black holes have nothing to do with escape speed. I know that you’ll find that explanation in lots of places, but it’s just plain wrong. A more accurate description would be that there is no path from the inside of a black hole to the outside, since any such path would be timelike and in the wrong direction. Furthermore, every path that does exist inside of a black hole eventually leads to the center of the hole, in the same way that any path through summer vacation eventually inevitably leads to September.
It’s an observed fact that the Universe is expanding, but you cannot describe the Universe’s expansion in terms of a speed. Rather, it’s a speed per distance: More distant objects are receding more quickly. For any given speed you care to name, there is some distance at which that’s the speed. This even includes the speed of light. In the models without dark energy (which, again, we now know to be inaccurate anyway, and have known for decades), the expansion of the universe must be decelerating, due to gravity. The relevant question then becomes how quickly it’s decelerating, which depends on how much matter (the source of gravity) there is in the Universe. If there’s too much matter, then the expansion of the Universe will eventually come to a stop, and then start falling back and contracting, ending in everything coming together in a Big Crunch. If that were the correct model for the Universe, then it would be impossible to avoid that Big Crunch singularity, because it would be everywhere, and every path would lead to it. The fact that the Universe is currently expanding is irrelevant to this eventual collapse. It works, in fact, exactly like the singularity in the center of a black hole.
Of course, English isn’t the correct language for discussing any of this. The actual serious discussion has to be had using mathematics. But it would take a very long time to teach all of the relevant mathematics, more than could be easily done over a message board.
Was it you that wrote (or did I read elsewhere) that it’s an unfortunate coincidence that the naive calculation of an escape velocity of c produces an answer of the right magnitude for the Schwartschild radius, because that gives the impression that the concepts are related?
It might have been me. The argument is flawed to begin with, because you can escape an object without ever reaching escape speed, if you have a constant source of thrust. But if you do try the calculation, flawed though it may be, and work through it, you’ll find that there are two different factors of 2 that don’t show up in Newtonian mechanics at all, and which cancel each other out.
AIUI, the edge of the observable universe is far beyond the Hubble Horizon. The furthest galaxy seen so far with the James Webb telescope has a redshift of z=14.32, which as far as I understand it, corresponds to an object receding at more than 14 times the speed of light.
If it is more complex than that, I’d be interested to know what the true situation is thought to be, and how this rapid expansion could be shoehorned into a black hole cosmology.
You have to be careful about defining your terms. That galaxy was in the observable Universe when the light we see left it. But any light leaving that galaxy now would never reach us.
It does, if you’re dealing with an extremely large black hole, in a universe with dark energy. That’s part of what nobody’s really sure how to interpret.
So do I, but I certainly don’t have the expertise to justify it.
As I see it, it provides a satisfying answer to the question about what preceded the Big Bang: the death of a star.
(This might be nonsense, but I’ll throw it out anyway. If the expansion of the universe is a result of being drawn towards an event horizon, and since space and time are interconnected, would that also explain the unilateral direction of time?)
I’m not sure that “explain” is the right word, but the fact that inside a black hole, progress towards the singularity is inexorable is exactly equivalent to progress towards the future being inexorable. Inside of the event horizon of a black hole, r is a timelike coordinate and t is a spacelike coordinate (if you continue to use the r and t coordinates as usually defined, which might or might not be the most convenient coordinates to use).
I assume the t coordinate being the one with opposite sign in the “distance” formula.
But what does this mean? Apparently you still can’t travel “back in time” to some place, because apparently you r distance will have to be smaller so while you can “move backwards” in time, you can’t get back to the same spot. So I guess causality is still protected.
Inside the black hole, r is the one with the opposite sign. That’s what “timelike” means, to a relativist.
Note that this swapping of r and t is, in some sense, just an artifact of the choice of coordinates. There are other choices of coordinates that are smooth everywhere, without that weird flip at the horizon.
Unfortunate yes, but one could argue against coincidence. By one view, the Buckingham pi theorem (which at its core is just a statement that physical laws can’t depend on unit-full quantities) would insist that the same dimensionless quantity of interest \frac{GM}{rc^2} appear in these two problems since the same gravitational constant G, mass M, and speed of light c appear in both. Said another way, both problems relate a particular speed specified up front with the gravitational potential at some radius, and there’s only one way to do this, up to dimensionless constants which have no reason here to be anything other than of order one. But, yeah, unfortunate that this allows an incorrect picture to give “the right answer”. (This sort of not-coincidentally-right answer via wrong — or even absent! — reasoning can happen in many places in physics, and it can be a useful tool.)
It’s a given that they’d be the same to within dimensionless quantities. But it’s an unfortunate coincidence that the dimensionless quantities happen to be the same.