- #1
jaketodd
Gold Member
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Why didn't the big bang just become a black hole?
Thanks,
Jake
Thanks,
Jake
Usually the defining characteristic of a black hole is taken to be the existence of an event horizon that forms a closed surface, and the event horizon is defined as the surface from inside which it's impossible to escape to infinitely far away (where we typically assume that spacetime becomes flat). In a homogeneous and isotropic cosmological model, there is nothing to break the symmetry and single out one particular surface as a spherical event horizon, nor is it clear to me how to apply the definition of the event horizon, since there isn't any asymptotically flat background at infinite distances.jaketodd said:Why didn't the big bang just become a black hole?
Can you explain more? Are you talking about standard GR, or quantum gravity? This seems implausible to me in GR. Obviously it can't be a Schwarzschild black hole, since a Schwarzschild black hole is a vacuum solution. Also, we observe that tidal forces vanish, and there is no evidence of inhomogeneity or the existence of geodesics that are incomplete in the future.HallsofIvy said:What makes you think it didn't? There is a theory that we, and all of the universe that we could possibly observe are inside a black hole.
Hard to know if that was what jaketodd had in mind, but if one was visualizing the Big Bang as an explosion at a localized point in a preexisting space, then it would certainly be sensible to imagine that it would have made a black hole.narrator said:Have I got that right guys?
bcrowell said:Hard to know if that was what jaketodd had in mind, but if one was visualizing the Big Bang as an explosion at a localized point in a preexisting space, then it would certainly be sensible to imagine that it would have made a black hole.
Antiphon said:I'm not sure that's correct. Theres no amount of pressure that would prevent a black hole from forming once the event horizon can form.
And that's the key. The universe was the size of say a marble. Not the stuff, but the space and the stuff. No matter how high the energy density, there's no event horizon if the energy is uniformly distributed through all of space.
In order to get a black hole, the matter or energy has to start clumping in a larger emptier space. No clumping, no black holes.
narrator said:This is where it gets a bit confusing.. if the universe was once the size of a marble, how is it infinite? lol Unless it has something to do with that video game analogy where you move off the left side of the screen and reappear on the right side, making spacetime like a sphere though space itself isn't. ohh.. my head hurts
phinds said:I don't understand that at all. The EH is just the place where light can't overcome the gravity of the BH. If you have enough matter all in one place to create that amount of gravity, don't you HAVE a black hole? Maybe the EH is more complex than I understand?
narrator said:This is where it gets a bit confusing.. if the universe was once the size of a marble, how is it infinite? lol Unless it has something to do with that video game analogy where you move off the left side of the screen and reappear on the right side, making spacetime like a sphere though space itself isn't. ohh.. my head hurts
Well, assuming it's not spatially closed. But anyway I agree with the thrust of what you said in #12.Drakkith said:Even at the 1st attosecond after the big bang the universe was still Infinite in extent.
Drakkith said:Don't think of the universe at the big bang as the "size" of something. That isn't the case. Instead, realize that what they mean is that the DISTANCE BETWEEN POINTS IN SPACE was much much much smaller back then. Even at the 1st attosecond after the big bang the universe was still Infinite in extent. But because the distance between everything was smaller, that means that all the energy was effectively compressed.
GOD__AM said:Whether all the mass of our current observable universe was ever the actual size of a marble, or some of these marble sized areas were bound by gravity quickly enough to not be forced apart by inflation I'm not clear on. It makes more sense to me to think the latter. Even two points inside this marble sized area would have different observable universes which extend beyond what each point could see, or be affected by
bcrowell said:FAQ: Is the universe finite, or is it infinite?
...If it is exactly flat, then it is a special case lying between the more general open and closed cases...
bcrowell said:FAQ: Is the universe finite, or is it infinite?
...Current observations of the cosmic microwave background's anisotropy show that our universe is very nearly spatially flat (on the cosmological scale)...
http://www.lightandmatter.com/html_books/genrel/ch08/ch08.html#Section8.2narrator said:I've wondered how this is worked out. Could you explain (or offer a link) how cosmologists worked out that "our universe is very nearly spatially flat"?
The former.narrator said:And does that "very nearly" mean "as flat as we can currently work out but we may know better in the future" or does it mean that some small degree of curvature has been found?
No, curvature is observable. For example a bug living on the surface of a sphere can determine from measurements confined to the surface that the Pythagorean theorem fails.narrator said:And lastly, isn't everything flat to the observer?
mdmaaz said:The Big Bang didn't become a black hole because a black hole occurs when lots of mass is compressed into a small amount of space. But in the case of the big bang, the matter, along with empty space was squeezed down. But most of it was empty space, which is why it didn't become a black hole. Also keep in mind if the big bang were to become a black hole, how would it ever explode into the big bang. Think about that.
mdmaaz said:The Big Bang didn't become a black hole because a black hole occurs when lots of mass is compressed into a small amount of space. But in the case of the big bang, the matter, along with empty space was squeezed down. But most of it was empty space, which is why it didn't become a black hole. Also keep in mind if the big bang were to become a black hole, how would it ever explode into the big bang. Think about that.
Reg E said:I recently thought of the same question and asked a friend.
He suggested that gravity was not a force yet.
It is suspected that there was a unified force at that time and that gravity, electromagnetism, the weak nuclear force, and the strong nuclear force only occurred later.
Seemed like a reasonable suggestion to me. Does this seem logical?
HallsofIvy said:What makes you think it didn't? There is a theory that we, and all of the universe that we could possibly observe are inside a black hole.
The initial singularity indicates that the theory is not operative at that point -- it signals a breakdown of the theory. There is no actual singularity in big bang cosmology, so it makes no sense to talk about "gravity" being "inside the singularity"; any statements about the physics of t=0 are pure speculation, and those concerning the singularity are wrong.mannygonzales1 said:Hey dude not to say any of these people are wrong cause they aren't but they're making it a little complicated.
Black holes are formed when an object like a massive star collapses in on itself due to the amount of gravity pushing on it. The reason the Big Bang didn't become a black hole is because gravity was inside the singularity that eventually became the Big Bang. Also, it wasn't even a "bang" It was an inflation. Like blowing air into a balloon. So there is no way it could have collapsed IN on itself when it's motion and gravity were hurdling outward.
I'm sorry, but I have to strongly disagree with what you're saying here and point out that this is not the conventional view of the big bang cosmology as held by modern cosmologists. The singularity is *not* part of the theory. The creation of the universe is not currently a scientific question -- no well-meaning cosmologists ever talks seriously about what banged, or how it banged, or why it banged, or even if anything banged at all. The big bang model, as it is currently conceived, is a model of the early universe describing its expansion from a hot, dense, young state to the universe of the present-day -- nothing more.mannygonzales1 said:Saying there was no 'singularity' would indicate that the universe was formed from nothing. Which is a very big misconception when talking about the Big Bang. There was essentially a singularity according to the Standard Theory of course. A singularity is thought to be at the core of a black hole. Meaning it has infinite density and infinite matter. (the singularity) Before the big bang the universe was thought to be an infinitesimally small, infinitely hot, infinitely dense, something or.. a singularity. Where it came from or why is a question physicists are very soon going to figure out.
Now you can't have something that has matter without gravity. So there is no possible way gravity wasn't present with this singularity when and before it expanded. Also, time doesn't determine if gravity is present or not. Matter does. So, t=0 has nothing to do with gravity being present with this singularity.