[thunder-blue-3]

I've been following this news for the past couple of weeks-- in essence your statement is what they are hypothesizing, and that the "something at the center that unites the two poles" might be that we are within a black hole. https://en.wikipedia.org/wiki/Black_hole_cosmology for the curious.

[askonomm]

It was my understanding that if two black holes collide, they just form a bigger black hole, but we know there's a black hole in our universe, which then would mean that there's a black hole inside of a black hole that did not merge with the parent black hole, right? Is that something that is considered possible?

[lupusreal]

I'm under the impression that we really have no clue what's going on inside of black holes, so the most we can really say with confidence is that when two black holes collide they appear from the outside to now be a single black hole.

[colejohnson66]

It’s a reasonable assumption. If two solar masses collide, their masses tend to combine[^]. Just “look” at planets that smash into each other. Ergo, a more massive black hole.

[^]: Ignoring ejections. But black holes also don’t “eject” mass. Or maybe they do? Hawking Radiation is weird.

[soulofmischief]

Actually, they can shoot out relativistic jets at the poles. https://www.nustar.caltech.edu/page/relativistic-jets

[colejohnson66]

But there, the black hole is ejecting other mass near it, not its own.

[soulofmischief]

Mm, I didn't correctly interpret their comment. You're absolutely correct.

[blueflow]

The inner black hole did not come from the outside, it formed inside and if i had to guess, it is stuck in the inside together with all the other matter, unable to interact with the outside of the outer black hole.

[askonomm]

Just thinking about this infinite recursion gives me the mental equivalent of a stack overflow.

[blueflow]

I don't think it is infinite - each universe can only have that mass/energy that fell into the outer black hole in the parent universe. At some level you'll inevitably have black holes with universes that do not have enough mass to form another inner black hole.

[soulofmischief]

Unless, although there's no reason to currently believe this, the energy requirements for physics are relative within each black hole, sort of (but not strictly) like how the speed of light is relative for all observers. And we can get a little crazier, and imagine a meta universe that is sort of like a Klein bottle in that it doesn't just recurse all the way down but somehow folds back into itself. Again, no current reason to believe anything like this but it's a mind-boggling to visualize.

[idiotsecant]

How much mass is required to form a black hole in a new universe with perhaps different physical constants? It could be that 'ability to make black holes' is a prerequisite for successful universes in the way way that good genes are a prerequisite for successful organisms. The universes that fail to spawn black holes are 'dead ends' so any life is statistically likely to find itself in a black hole spawning universe.

Maybe there is an 'incentive' for universes to form with physical constants tuned to produce black holes with the available energy in that universe.

[IngoBlechschmid]

This circle of ideals seems to be known as: https://en.wikipedia.org/wiki/Cosmological_natural_selection

[jfengel]

The trick is that bigger black holes are less dense. Supermassive black holes can have the density of water. If the universe is gravitationally closed, it would have the density of... well, just look up at night. (Actually much less than that; you see more stars because you're inside a galaxy.)

The density makes the scale recursion less mysterious.

[drusenko]

That’s interesting! When you are referring to density, are you referring to average density within the event horizon? Isn’t most (effectively all) matter concentrated in the singularity? Would love to hear you elaborate on this thought further.

[jfengel]

We can't really talk about what's inside a black hole. From outside, it has a volume and a mass, and that's all there is to know.

We can say that any particle inside the horizon is inevitably headed to the center. (That's why we can't say any more: no other information can escape.) That does lead to a problem in that all of the mass would be concentrated at a single point at the center, whose density is division-by-zero.

But I wouldn't put too much weight on that. We already know from quantum mechanics that there isn't really any such thing as a "point". The math is still a problem, but the solution almost certainly lies in that direction.

[jug]

Maybe generating a stack overflow was the true depiction of God!

[nashashmi]

“The universe is an orb and that orb is rotating causing all the other stuff to spiral.” This was a long held theory of mine because I could not understand why a galaxy would spiral.

I think there is a men in black scene, where an alien is rotating the universe globe like a toy they are playing.

[rdtsc]

> This was a long held theory of mine because I could not understand why a galaxy would spiral.

I think in general it would be unusual if they didn’t rotate. Any large non-uniform mass of gas or rocks when colliding will induce some rotation. What is odd though is that for galaxies we see more of them spinning one way than another.

[soulofmischief]

Ok but what is making the universe spin? This kind of theory is turtles all the way down.

[irrational]

Is this getting into questions like "Where did the singularity come from?" and "What came before the singularity?". We don't have a way to answer these kinds of questions.

[soulofmischief]

My point is that it's not much helpful to say, "galaxies spin a certain way because the universe spins", because it shifts the problem without actually answering the "why". "Turtles all the way down" is a saying about such infinite regress. https://en.wikipedia.org/wiki/Turtles_all_the_way_down

And yes, I'm familiar with Dawkins' famous retort when someone asked how magnets repel things.

[thaumasiotes]

> And yes, I'm familiar with Dawkins' famous retort when someone asked how magnets repel things.

I'm not. I was unable to substantiate that anyone named Dawkins, Richard or otherwise, made or is popularly associated with a comment about magnets. What was the retort?

[soulofmischief]

I deeply apologize, it was late and I mixed up my Richards. :)

https://youtube.com/watch?v=36GT2zI8lVA

[eightysixfour]

Doesn’t it have to spiral? Think of the gravity well, anything not orbiting is just falling. The only things not racing towards the black hole at the center of the galaxy are the ones that are orbiting.

[nashashmi]

It can be directly sucked into the center. A spiral implies a lateral movement plus a centripetal force

[eightysixfour]

Right, I guess what I am saying is if it didn't spiral, it wouldn't be a galaxy for "long." It would just be a super massive black hole.

[lolc]

The trick to having a galaxy is for mass to fall towards the black hole and miss it all the time.

[bencyoung]

From what I remembe of Undergrad physics this isn't actually possible. According to GR, within an event horizon, space-like pths become "time-like" which effecitvely means the singularity is unavoidably "in the future". No matter how big a black hole is, you can't just drift around inside it as literally all paths lead downward (hence even light not escaping)

If you were inside a black hole you wouldn't be able to see light from "deeper" because it wouldn't be able to travel towards you.

This is not what we see within the universe, so I don't think we can be inside a black hole

[kadoban]

All paths _eventually_ lead downward. Is there any limit to how long? Can't we just be near the outside of the blackhole and can't see the doom yet?

[bencyoung]

There are no stable orbits inside the event horizon, and my understanding is even things like atom vibration can't move further from the sigularity so I'm guessing timespans would be limited!

[kadoban]

Interesting, thanks. That does sound like you could tell from inside if you there or not.

I'll have to read up on that, I always had the vague sense that on ~finite scale of time there existed a region of space where you couldn't really tell the difference if you're inside of a big enough black hole or not.

Which sounds like I'm probably just wrong.

[bencyoung]

It's the usual rabbit hole if you search for it, but there are some useful comments here: https://astronomy.stackexchange.com/questions/58610/would-it...

The way I see it is every surface inside an event horizon is another slightly "stronger" event horizon