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Comment by aurareturn | Hacker News Reader

On the topic of black holes, there is a recent paper on black holes potentially converting mass into dark energy: https://iopscience.iop.org/article/10.1088/1475-7516/2024/10...

I'm not a physicist but it's interesting to think about the implications:

1. No singularity at the center of a black hole

2. Universe's expansion rate is not constant because it's blackholes powering it with matter

3. Eventually expansion slows, stops and reverses

And now my own crazy ideas:

1. Maybe the universe is a inside a black hole

2. Maybe the big bang was a result of the birth of another black hole somewhere else, and that the rapid expansion rate of the early universe was due to the a huge amount of matter converted into dark energy by this black hole

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The universe is not inside a black hole. Inside black holes the radial coordinate is time like, which is definitely not true in our universe, where the time coordinate is timelike, and the radial coordinate is space like.

Inside of black holes looks nothing like ordinary spacetime. Inside black hole, everything in your future is with decreasing radial coordinate, which means space is shrinking until you hit the singularity where radial coordinate is zero and you have no future.

No, this depends on your choice of coordinate system - has been debunked N times on physics reddit in virtually every thread that it comes up. The EH itself is not a singularity in the observers reference frame as they cross it nor do they particularly notice when they do.

I never said EH is a singularity. I said you could notice you're inside as your timelike coordinate becomes the radial coordinate. That's something you could easily notice if you look around, it would correspond to a shrinking universe, and our universe is expanding.

The "you won't notice crossing the event horizon" troupe is true only in a very local sense. If you move around and observe the geometry around you, you can definitely tell you're inside a black hole.

As the black hole getting larger, it is more difficult to notice this difference (of crossing the event horizon or “observe the geometry around you”.) and as we are talking about the whole visible universe being inside a black hole, we are in this extreme large scale.

Also, I’m not sure why you’re arguing about the radial coordinate being time-like. You can only measure in your own local reference frame. You wouldn’t necessarily be able to transform between your own local reference frame to the blackhole’s if you don’t know you’re in one.

The universe as a black hole is actually a very old idea: https://en.wikipedia.org/wiki/Black_hole_cosmology

I’m not saying we are in one, but I’m saying it is not as obviously false as you might be arguing.

https://www.reddit.com/r/askscience/s/vwCegmNdOE ?

The fact that radial coordinate is timelike inside the event horizon doesn't change when you change coordinate systems. The radial direction remains timelike in kruskal coordinates. Direction being space like or time like is independent of coordinate system.

I think for this to be a complete explanation, it needs to be shown that what was "the time" coordinate is not expanding in some sense.

Does volume even make sense in GR?

Thought experiment here would be: suppose me and you appeared stationery (from the point of view of the outside reference frame) just above the horizon of a non-rotating black hole in the manner of Boltzmann brains. We immediately start falling and cross the horizon. Now will you see me receding from you or going at you? Will I be red-shifted or blue-shifted?

There is a singularity in our past. Are we in a white hole?

Is your crazy idea not effectively the oscillating universe theory proposed by Einstein?

It's not crazy. I'm no physicist, but I understand the math of the Big bang is similar to that of a White hole.

What gets a little mind bending for me is the idea that the physics inside the black hole can differ slightly from the ancestor universe. So black holes will preferentially create descendant universes that prefer to create more black holes.

This is a different multiverse theory than the quantum many worlds theory. The limitation of quantum many worlds is that the physics doesn't change. But in the ancestor black hole many worlds theory it does.

When you put these together, you can get an even larger multiverse, where anything that can happen does happen, but only if the laws of physics allow for black holes. That may mean the Marvel Cinematic Universe, is out there somewhere, so long as those laws of physics allow for black holes. Right? Again not a physicist.

According To Tegmark's reasoning the MCU could be out there, black holes not a prerequisite but

"there are all sizes of infinity, some infinities are bigger than others. The infinity of Real numbers is bigger than the infinity of all positive numbers, and it should be noted that while the infinity of all positive numbers is infinite the number 3 only shows up in it once."

https://medium.com/luminasticity/the-marvel-cinematic-multiv...

Not even close. There’s an infinite amount of numbers in between 0 and 1. But in an infinite multiverse for each of those numbers, you could never see 2.

If I spend long enough, I can count whole numbers to infinity. I cannot possibly count all the numbers between 0 and 1. This so why real numbers have a whole different magnitude of infinity from integers.

Thanks, this is helpful.

So first we need to answer does math follow physics or does physics follow math?

If math follows physics, and the physics is changing across universes in the multiverse in question, then no you're assertion is wrong.

If physics follows math, then we would have to go up the level higher, and we're not talking about that right now.

> Maybe the big bang was a result of the birth of another black hole somewhere else, and that the rapid expansion rate of the early universe was due to the a huge amount of matter converted into dark energy by this black hole

There is actually a theory that black holes create universes inside them, and that our universe could be underneath countless layers of black holes forming universes that form black holes ad infinitum.

There is a Kurzgestadt video[0] that discusses the theory in more detail. Granted, this is in the realm of science where we have no idea if this is remotely true, but that's part for the course when black holes are involved.

[0] https://youtube.com/watch?v=71eUes30gwc

>There is actually a theory that black holes create universes inside them

Calling it a "theory" is kind of wrong, it's not a "theory" according to the classical definition of the word. The word has been diluted over time to mean any thought anyone has about anything, but it used to mean something that has been proven by observation and empirical evidence. Yes, I'm being pedantic.

>A "classical" definition of a theory refers to a well-established, comprehensive explanation of a phenomenon, based on a body of evidence and often including clearly defined principles or laws, signifying a robust and widely accepted understanding of a subject, as opposed to a mere hypothesis or speculation; essentially, a "theory" in the true scientific sense

>Granted, this is in the realm of science where we have no idea if this is remotely true, but that's part for the course when black holes are involved.

I'm not sure this qualifies as "science". It's more like stoner speculation.

Science is defined as:

>"The systematic study of the structure and behavior of the physical and natural world through observation, experimentation, and the testing of theories against the evidence obtained."

There is no observation, experimentation, or testing of theories that could ever happen for these notions about black holes and the universe(s).

It could be that the universe is a giant egg laid by a giant chicken, and that is just as plausible as "black holes create universes inside them" as far as we know.

Theories are always in a sense speculative, as they build upon other theories and measurements. And as measurements aren't definitive, but just a standardized way of comparing results, theories are just an abstract framework how we have a shared understanding of the world around us.

Theories usually are just based on other theories and just create a theory from the current available data. The less data you have, the larger the possible space that your theory might lie in.

Hypotheses are usually things that rework theories because we have some new data that showed that our theories were inaccurate/false/invalid and builds a new framework that more accurately models the data and theories that we have.

Take this just with grain of salt, this is just a philosophical view of the meanings of the words as I understand them.

If that’s the case, why was it a bang instead of a slow leak?

The initial collapse of a star into the black hole would have been the big bang.

you might enjoy some of Lee Smolin's writing on the "Fecund Universes Theory"

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