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Old Jan 13th 2016, 05:34 AM   #11
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I find distance starts to become a surprisingly slippery concept in a small but rapidly expanding universe.
I personally find it easier to consider the closely related "probability of interaction".
In the very early universe everything is interacting with everything, all the time, and there is no possibility of stability.
As the universe matures, the probability of interactions becomes smaller and the time between interactions becomes long enough for sensibly stable particles, then aggregations of particles, etc... to form.
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Old Jan 13th 2016, 07:45 AM   #12
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Originally Posted by kiwiheretic View Post
Black holes are so compressed and densely packed with matter that not even light can escape from beyond the event horizon. How could an even more dense region of space, such as the big bang "egg" explode if larger and less dense objects (black holes) cannot?
Why are you assuming that the existing black holes existed at the time of the Big Bang and weren't created after that from collapsed stars?
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Old Jan 13th 2016, 10:40 AM   #13
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One of the (perhaps rather fringe) theories I mentioned in post#3
is that a black hole is precisely the same as a Big Bang...

Every Black Hole in our universe is a Big Bang for a new universe,
and "our" Big Bang is a Black Hole in a progenitor universe.

Note that if you work out the relativistic time distortion effects of a black hole, you will find that the entire duration of our universe becomes but an instant "within" the black hole.
i.e. Time and Space in the new universe are completely disconnected from Time and Space in the progenitor universe.
This makes formulating any kind of sensible prediction of observable consequences that might result from this theory rather difficult...
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Old Jan 13th 2016, 11:12 AM   #14
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Originally Posted by MBW View Post
One of the (perhaps rather fringe) theories I mentioned in post#3
is that a black hole is precisely the same as a Big Bang...

Every Black Hole in our universe is a Big Bang for a new universe,
and "our" Big Bang is a Black Hole in a progenitor universe.

Note that if you work out the relativistic time distortion effects of a black hole, you will find that the entire duration of our universe becomes but an instant "within" the black hole.
i.e. Time and Space in the new universe are completely disconnected from Time and Space in the progenitor universe.
This makes formulating any kind of sensible prediction of observable consequences that might result from this theory rather difficult...
Whereas there is perhaps some truth to the argument that our Universe is contained inside some event horizon similar to a black hole, black holes are not known to explode. The singularity at the big bang is unique in that aspect, so far as we know, so I would hesitate to say that the big bang singularity is a black hole.

-Dan
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Old Jan 13th 2016, 11:15 AM   #15
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Originally Posted by Pmb View Post
Why are you assuming that the existing black holes existed at the time of the Big Bang and weren't created after that from collapsed stars?
I didn't make that assumption. How did you read that into my question? It was a statement purely about the ability, of a dense region of space, to explode once it exceeds a certain density. Sorry if that was unclear.
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Old Jan 13th 2016, 12:37 PM   #16
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Originally Posted by kiwiheretic View Post
...It was a statement purely about the ability, of a dense region of space, to explode once it exceeds a certain density. Sorry if that was unclear.
I think you are missing a significant difference between black holes and the Big Bang. A black hole is a finite-sized object that occupies a small amount of the universe; you can observe it from the outside, and think about the notion of it "exploding" like a bomb. When a bomb explodes the shrapnel is spewed out into the space around it. We can also talk about the time of the explosion - we can describe the state of a bomb at T minus 1 second, or at T=0, or at T plus 1 second. But the expansion of the universe following the Big Bang is not like that at all - it's not a case of the "cosmic egg" expanding out into space, but rather space itself that is expanding. And we can't talk at all about what may have been at T minus 1 second, or even at T=0, because the notion of time as we know it didn't exist. Whatever the mechanism was that caused this to happen, the analogy of an exploding black hole is not an appropriate one.
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Old Jan 13th 2016, 01:25 PM   #17
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Originally Posted by ChipB View Post
I think you are missing a significant difference between black holes and the Big Bang. A black hole is a finite-sized object that occupies a small amount of the universe; you can observe it from the outside, and think about the notion of it "exploding" like a bomb. When a bomb explodes the shrapnel is spewed out into the space around it. We can also talk about the time of the explosion - we can describe the state of a bomb at T minus 1 second, or at T=0, or at T plus 1 second. But the expansion of the universe following the Big Bang is not like that at all - it's not a case of the "cosmic egg" expanding out into space, but rather space itself that is expanding. And we can't talk at all about what may have been at T minus 1 second, or even at T=0, because the notion of time as we know it didn't exist. Whatever the mechanism was that caused this to happen, the analogy of an exploding black hole is not an appropriate one.
So what are you saying exploded? Not matter but space exploded? This is starting to feel like way too much hand waving.
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Old Jan 13th 2016, 01:45 PM   #18
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Originally Posted by MBW View Post
I find distance starts to become a surprisingly slippery concept in a small but rapidly expanding universe.
I personally find it easier to consider the closely related "probability of interaction".
In the very early universe everything is interacting with everything, all the time, and there is no possibility of stability.
As the universe matures, the probability of interactions becomes smaller and the time between interactions becomes long enough for sensibly stable particles, then aggregations of particles, etc... to form.
I don't get this at all. Quantum confinement has already happened by T+8 minutes so all the real (not virtual) protons and neutrons have formed. We have all the nuclei now. I realise they are tightly confined, perhaps, like marbles in a spherical glass jar. They cannot move yet, all potential energy and no kinetic energy. However the jar is growing and the walls of the jar are moving radially outwards at greater than the speed of light. Now we have vibrations in the nuclei as they are moving within the limits of the available space. I haven't started working out yet how fast the volume is growing yet but I am guessing it will be a factor of r^3 where r is the radius of a growing universe. Light travels at 3*10^8 metres/second. That gives you a lot of room for the nuclei to move after one second and in the next second there is more room still. What scenario are you positing in which they are still frequently bumping into each other (excluding virtual particles) after T+1 year?
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Old Jan 13th 2016, 03:54 PM   #19
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OK I was trying to develop a line of thought relating distance to interactions,
but I'm not sure now if the thought is going in a helpful direction...

I have just watched the presentation from your link in post#5 and, as is often the case, there are at least as many new questions as answers.
The key "magic" seems to be the period of inflation.
As you point out the big bang infinite density singularity and the black hole infinite density singularity seem to be essentially pretty much the same sort of thing.
However at the big-bang we get inflation, and a universe appears...
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Old Jan 13th 2016, 06:31 PM   #20
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Originally Posted by MBW View Post
The key "magic" seems to be the period of inflation.
As you point out the big bang infinite density singularity and the black hole infinite density singularity seem to be essentially pretty much the same sort of thing.
However at the big-bang we get inflation, and a universe appears...
Try to see it from my perspective. Someone who always thought there was a line of "cause and effect" reasoning from T = 0 to T = now. Now it just seems like some physicist is saying it must be true because after all, we exist, therefore it must have happened that way. From my uneducated perspective it seems that we could say "Pixies made the universe because we exist!" I am struggling to see why the current theory is better than sprinkling pixie dust and waving a magic wand except we dont have teams of people rushing to write mathematical papers on what properties the pixie dust has. Surely there is more substance to the big bang theory than that?!?

Why is the big bang better than its competing theories?
Why does it struggle to explain how to acheive high molecular interaction, amidst so much energy, in the incredibly large distances over a rapidly expanding volume? From where I am sitting it seems like these molecular interactions are the "elephant in the room". Surely there was more thought put into the inflationary model than just the dreaded anthropomorphic principle??

(Of course, you guys are still researching the answers and I do appreciate your input. Just I was hoping for physics rather than anthropomorphic answers no matter how subjective. Sorry for my frustration here but it seems to be difficult for me to convey my questions in a way they can be understood.)
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