[AnimalMuppet]

If I understand correctly, black holes do not play a large role in our model of the origins of the universe. So this doesn't (directly) lead to "rethinking the origins of the universe". Does this work call the big bang into question (or even our current models of the big bang)? Or is it just details like galaxy formation that it makes us rethink?

Another question: Something very massive and very small is at the center of our galaxy. At least, we sure think so. Does this make us question that? Or does this just make us question whether that massive thing is in fact a black hole?

[tjradcliffe]

Your first point is correct: the relationship between black holes and the initial state of the universe is not clear. Whether or not there was a primordial singularity or something else is an open question.

With regard to the question "If not black holes, then what?", this is a problem. There is a strict upper limit on neutron stars of about 1.4 solar masses. Beyond this, gravity is stronger than the repulsive core of the strong nuclear force, and the star should collapse. If the process described in this paper is what actually occurs, the star will shed mass due to Hawking radiation while collapsing. The end-state of that process must be either a neutron star (which can't have more than 1.4 solar masses) or something else. There doesn't seem to be any "something else" in the offing, which makes that million-solar-mass thing in the centre of our galaxy deeply mysterious.

A new theory that makes an old "settled" phenomenon mysterious is not all that uncommon in the sciences, so it's reasonable to take a wait-and-see attitude toward this idea, but I'm not enormously hopeful that it'll pan out very well in the long run.

[squozzer]

So it seems a cycle of collapse and Hawking radiation will occur until the star no longer has enough mass to collapse.

[danbruc]

The beginning of the universe and black holes have in common the singularity if you think about it naively. Besides that there is not much of a connection. And I think most physicist don't believe there are real singularities in black holes or at the beginning of the universe but quantum mechanics, quantization of space and time or something else kicks in and prevents the singularity.

And there is no(t much) doubt that very massive dark objects are out there, we can observe them indirectly. So even if the classical black hole creation process turns out to be not possible, there are still objects out there that a very much like classical black holes.

[lutusp]

> If I understand correctly, black holes do not play a large role in our model of the origins of the universe. So this doesn't (directly) lead to "rethinking the origins of the universe".

But it does, because one hypothesis about the Big Bang is that it commenced from conditions identical to a black hole's singularity. So our understanding of black holes is critical to at least one idea about the universe's beginnings.

> Or does this just make us question whether that massive thing is in fact a black hole?

The answer is that there is something like a black hole at the center of our galaxy, but people are free to theorize about what exactly it is.

[wuliwong]

I disagree completely. This calculation is about the formation of a black hole from a collapsing star. There is no theory stating that the singularity of which the big bang is theorized to expand from was brought into existence from a collapsing star.

Any theory about causes of that initial singularity are basically just conjecture at this point. My understand is that some of these high dimensional theories of quantum gravity postulate colliding 'membranes' and things but they are still very much in development and this calculation does nothing to further those theories along.

Another way I was thinking about it is that the initial singularity and creation of the universe is probably more a result of large scale, topological dynamics where this paper is concerned with more local, geometric dynamics. That's my own conjecture, there. :)

[lutusp]

> There is no theory stating that the singularity of which the big bang is theorized to expand from was brought into existence from a collapsing star.

Not an issue, only that a singularity can exist, and therefore might come into being in the present.

If in a consistent physical theory we grant the reality of a singularity arising from very high matter density, then this narrows the range of possibilities for their nonexistence in the present.

So we have conventional densities easily explained by current theory, and we have the possibility of a singularity as an endpoint of increasing matter density, which narrows the discussion to the means whereby a mass might collapse past the critical density. I'm just saying this increases the burden on those who try to argue that the transition isn't possible. Especially given the absence of evidence in favor of, and plenty of evidence against, the stated thesis.

[wuliwong]

Yes I agree with your first point. I think the author really oversteps their bounds. I don't see how this calculation speaks to the existence or lack of existence of a initial/primordial singularity.