5 ms·

What I don't understand is how big bang could exist if such relatively "small" mass concentration creates black holes?

DevelopingElk 2y ago
The layman's answer is that since everywhere was very dense there wasn't a gravitational pull to one direction or another since it all cancelled out.
- btilly 2y ago
  Except that this answer does not make sense. General Relativity predicts that if you fill flat space-time with matter, it will start to contract due to gravity. It is not uniform density by itself that prevented the early Universe from forming a giant black hole. In fact one of the proposed cosmological models for our universe is that it has sufficient density to some day reverse its expansion and then fall in on itself into a giant black hole. See https://en.wikipedia.org/wiki/Big_Crunch https://en.wikipedia.org/wiki/Big_Crunch for more.
  - Loughla 2y ago
    My theory with zero study, math, or proper explanation is that this is exactly how the universe operates. It explodes outward until the explosion energy is cancelled out by gravity, wherein the universe then collapses on itself. The moment in which the last bit of matter and energy is consumed by the massive black hole that forms, it's enough to cause another explosion.
    - gavinray 2y ago
      My experiences with psychedelics agree with this baseless theory =)
btilly 2y ago
Excellent question. Gravity pulls things in by causing space-time to accelerate in a particular direction. In other words we accelerate towards the Earth at 9.8 meters per second per second because that is what space-time itself does. The space-time that is in our frame of reference accelerates down, carrying us with it. The floor pushes up on us, causing us to accelerate up. Balancing things out so that we remain where we are. A dense mass will cause flat space-time to start falling in. Enough mass, densely enough, will cause it to fall in so fast that not even light can escape. This is a black hole. However the Big Bang wasn't a flat space-time. The space-time that was the structure of the universe was moving apart extremely quickly. There was more than enough mass around to create a black hole today. But what it did is cause the expansion rate to slow. Not to stop, reverse, and fall back in on itself into a giant black hole.
- raattgift 2y ago
  > Gravity pulls things in by causing space-time to accelerate in a particular direction. Ok, how does this sketch work for a low-ellipticity eccentric orbit? > "The space-time that is in our frame of reference" Isn't throwing out general covariance (and manifold insubstantivalism) rather a high price for a simplification of Einsteinian gravitation? > the Big Bang wasn't a flat space-time Sure, it's a set of events in a region of the whole spacetime. If we take "Big Bang" colloquially enough to include the inflationary epoch, always assuming GR is correct, then at every point in that "Big Bang" region of the whole spacetime there is a small patch -- a subregion -- of exactly flat spacetime. However, these small patches must be small because most choices of initially-close pairs of test objects can only couple to timelike curves that wildly spread in one direction (and focus in the other). I don't know how to understand your two final sentences: how do you connect the period just before the end of inflation and the expansion history during the radiation and matter epochs?
  - fn-mote 2y ago
    I don't know enough physics to know whether the parent knows what they are talking about, but there is one piece of math that makes me think they do not. > at every point in that "Big Bang" region of the whole spacetime there is a small patch -- a subregion -- of exactly flat spacetime Can explain how you get a non-empty region of exactly flat space time around every point? Patching together curved things out of not curved things happens all of the time. The Earth looks flat around the point you are standing. I'm worried that just because it looks flat in my city doesn't mean it is actually flat in my city, if I measure carefully.
hinkley 2y ago
One of the theories is that the properties of the Higgs Field changed and so the laws of physics changed. And that if they ever change again that we'll likely be dead before we know to be afraid, since the change would propagate through the universe at the speed of light. We wouldn't even see the stars blink out before the molecules in our bodies stopped being the molecules in our bodies.
- dreamcompiler 2y ago
  "There is another theory which states that this has already happened." --Douglas Adams
somenameforme 2y ago
While not a direct answer in itself, I think it's noteworthy that the big bang already requires esoteric physics, like inflation [1], that have no known explanation, source, or parallel anywhere else in existence -- and in fact contradict everything we know about known physics. It's an entirely ad-hoc hypothesis that was largely developed to solve numerous other problems with a big bang, in particular our universe not fitting what would be expected following a "normal" big bang, such as the Horizon Problem. [2] And so looking for logical explanations for the big bang is already a nonstarter. At this point it remains highly dependent upon ad hoc constructions. [1] - https://en.wikipedia.org/wiki/Cosmic_inflation https://en.wikipedia.org/wiki/Cosmic_inflation [2] - https://en.wikipedia.org/wiki/Horizon_problem https://en.wikipedia.org/wiki/Horizon_problem
bufferoverflow 2y ago
Because space expanded faster than the speed of light.
cryptonector 2y ago
Well, imagine that the big bang is really something more akin to a white hole, which is a black hole running backwards: all the stuff has outward momentum, and lots of it, so it can't get pulled back. In standard cosmology the big bang happens not at a point (so it's not really like a white hole) but everywhere, but there's also really strong repellent forces that cause "inflation", which defeats the mass-energy's gravitational pull's attempt to collapse the whole thing. But still, perhaps the thought of a white hole might help you bridge the gap. Mind you, this is a pop science, handwavy explanation.

The layman's answer is that since everywhere was very dense there wasn't a gravitational pull to one direction or another since it all cancelled out.

btilly 2y ago
Except that this answer does not make sense. General Relativity predicts that if you fill flat space-time with matter, it will start to contract due to gravity. It is not uniform density by itself that prevented the early Universe from forming a giant black hole. In fact one of the proposed cosmological models for our universe is that it has sufficient density to some day reverse its expansion and then fall in on itself into a giant black hole. See https://en.wikipedia.org/wiki/Big_Crunch https://en.wikipedia.org/wiki/Big_Crunch for more.
- Loughla 2y ago
  My theory with zero study, math, or proper explanation is that this is exactly how the universe operates. It explodes outward until the explosion energy is cancelled out by gravity, wherein the universe then collapses on itself. The moment in which the last bit of matter and energy is consumed by the massive black hole that forms, it's enough to cause another explosion.
  - gavinray 2y ago
    My experiences with psychedelics agree with this baseless theory =)

btilly 2y ago

Excellent question. Gravity pulls things in by causing space-time to accelerate in a particular direction. In other words we accelerate towards the Earth at 9.8 meters per second per second because that is what space-time itself does. The space-time that is in our frame of reference accelerates down, carrying us with it. The floor pushes up on us, causing us to accelerate up. Balancing things out so that we remain where we are. A dense mass will cause flat space-time to start falling in. Enough mass, densely enough, will cause it to fall in so fast that not even light can escape. This is a black hole. However the Big Bang wasn't a flat space-time. The space-time that was the structure of the universe was moving apart extremely quickly. There was more than enough mass around to create a black hole today. But what it did is cause the expansion rate to slow. Not to stop, reverse, and fall back in on itself into a giant black hole.

raattgift 2y ago
> Gravity pulls things in by causing space-time to accelerate in a particular direction. Ok, how does this sketch work for a low-ellipticity eccentric orbit? > "The space-time that is in our frame of reference" Isn't throwing out general covariance (and manifold insubstantivalism) rather a high price for a simplification of Einsteinian gravitation? > the Big Bang wasn't a flat space-time Sure, it's a set of events in a region of the whole spacetime. If we take "Big Bang" colloquially enough to include the inflationary epoch, always assuming GR is correct, then at every point in that "Big Bang" region of the whole spacetime there is a small patch -- a subregion -- of exactly flat spacetime. However, these small patches must be small because most choices of initially-close pairs of test objects can only couple to timelike curves that wildly spread in one direction (and focus in the other). I don't know how to understand your two final sentences: how do you connect the period just before the end of inflation and the expansion history during the radiation and matter epochs?
- fn-mote 2y ago
  I don't know enough physics to know whether the parent knows what they are talking about, but there is one piece of math that makes me think they do not. > at every point in that "Big Bang" region of the whole spacetime there is a small patch -- a subregion -- of exactly flat spacetime Can explain how you get a non-empty region of exactly flat space time around every point? Patching together curved things out of not curved things happens all of the time. The Earth looks flat around the point you are standing. I'm worried that just because it looks flat in my city doesn't mean it is actually flat in my city, if I measure carefully.

hinkley 2y ago

One of the theories is that the properties of the Higgs Field changed and so the laws of physics changed. And that if they ever change again that we'll likely be dead before we know to be afraid, since the change would propagate through the universe at the speed of light. We wouldn't even see the stars blink out before the molecules in our bodies stopped being the molecules in our bodies.

dreamcompiler 2y ago
"There is another theory which states that this has already happened." --Douglas Adams

somenameforme 2y ago

While not a direct answer in itself, I think it's noteworthy that the big bang already requires esoteric physics, like inflation [1], that have no known explanation, source, or parallel anywhere else in existence -- and in fact contradict everything we know about known physics. It's an entirely ad-hoc hypothesis that was largely developed to solve numerous other problems with a big bang, in particular our universe not fitting what would be expected following a "normal" big bang, such as the Horizon Problem. [2] And so looking for logical explanations for the big bang is already a nonstarter. At this point it remains highly dependent upon ad hoc constructions. [1] - https://en.wikipedia.org/wiki/Cosmic_inflation https://en.wikipedia.org/wiki/Cosmic_inflation [2] - https://en.wikipedia.org/wiki/Horizon_problem https://en.wikipedia.org/wiki/Horizon_problem

bufferoverflow 2y ago

Because space expanded faster than the speed of light.

cryptonector 2y ago

Well, imagine that the big bang is really something more akin to a white hole, which is a black hole running backwards: all the stuff has outward momentum, and lots of it, so it can't get pulled back. In standard cosmology the big bang happens not at a point (so it's not really like a white hole) but everywhere, but there's also really strong repellent forces that cause "inflation", which defeats the mass-energy's gravitational pull's attempt to collapse the whole thing. But still, perhaps the thought of a white hole might help you bridge the gap. Mind you, this is a pop science, handwavy explanation.