Why didn't the big bang just become a black hole?

[jaketodd]

Why didn't the big bang just become a black hole?

Thanks,

Jake

 

[HallsofIvy]

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.

 

[bcrowell]

Why didn't the big bang just become a black hole?

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.

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.

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.

-Ben

 

[narrator]

Jake, are you thinking of the universe as a finite thing? If you are, your question is more understandable to this layman. But as I now understand the more popular model, the big bang wasn't an event in a single place, which grew out from that spot, but rather (and in my simple words) one moment it wasn't there, then the next moment the universe was there, everywhere, infinite in every direction. I'm not sure if that nullifies the possibility that it once was a black hole, possibly under a form of the old recycling universe idea, but to this layman that makes it less plausible. Have I got that right guys?

 

[bcrowell]

Have I got that right guys?

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.

 

[phinds]

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.

Right ... this sounds to me more like a consideration of what I thought he mean, which is, to restate in my words (or maybe I'm asking something a little different that what he meant):

Black holes form because huge amounts of matter in a very small area condense to a black hole, and the early U was a huge amount of matter in a small space, so why didn't it become a black hole?

Answer: because it had WAY too much energy for gravity to overcome the pressure --- black holes form when a clump of mass is (1) big enough and (2) doesn't have, or no longer has, enough energy for the pressure to overcome gravity.

 

[Antiphon]

I'm not sure that's correct. there's 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.

 

[phinds]

I'm not sure that's correct. there's 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.

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]

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

 

[GOD__AM]

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

My understanding is elementary at best, but I think analogies relating to the size of the universe at any point in time can only refer to the observable universe of a location. Two marbles may be only be separated by a small distance, but each marble's center has its own observable universe which may or may not overlap with the other.

Since gravity is (assumed?) to travel at the speed of light, and inflation was greater than the speed of light (I think this is correct) it's no wonder that the whole of the universe didn't collapse into a black hole.

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.

That being said anyone feel free (and I know you will ;P) to correct my misconceptions.

 

[bcrowell]

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?

What would break the symmetry and make one surface (the event horizon) different from any other surface?

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

FAQ: Is the universe finite, or is it infinite?

Standard cosmological models come in two flavors, open and closed. The open type has negative spatial curvature and infinite spatial volume. The closed one has positive curvature and finite spatial volume; spatially, it is the three-dimensional analog of a sphere. Since both types are mathematically self-consistent solutions to the Einstein field equations, the finiteness or infiniteness of the universe is something that cannot be determined by solely logic but only by observation.

Current observations of the cosmic microwave background's anisotropy show that our universe is very nearly spatially flat (on the cosmological scale). If it is exactly flat, then it is a special case lying between the more general open and closed cases. The flat case has infinite volume. However, the range of uncertainty in the curvature is wide enough to be consistent with either positive or negative curvature, so right now the finiteness or infiniteness of the universe is an open question.

Sometimes people use the word "universe" when they really mean "observable universe." The observable universe is finite in volume because light has only had a finite time to travel since the Big Bang.

 

[Drakkith]

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.

 

[bcrowell]

Even at the 1st attosecond after the big bang the universe was still Infinite in extent.

Well, assuming it's not spatially closed. But anyway I agree with the thrust of what you said in #12.

 

[narrator]

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.

"the DISTANCE BETWEEN POINTS IN SPACE was much much much smaller back then"

Do you mean like a lot of clumps with bigger distances eventually spreading out to fill the spaces between, or ALL of it compressed? If the latter, and an infinite, flat model, where did it spread out to, if not within itself?

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

Kind of like an infinite array of 3D Venn diagrams?

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...

Isn't that like being somewhere between pregnant and not?

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)...

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"?

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?

And lastly, isn't everything flat to the observer? If yes, then how can we deduce curvature if it's "out there", so to speak?

Many thanks for the input folks... I'm enjoying stretching this relatively old brain.

 

[bcrowell]

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"?

http://www.lightandmatter.com/html_books/genrel/ch08/ch08.html#Section8.2
See subsection 8.2.9.

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?

The former.

And lastly, isn't everything flat to the observer?

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]

thanks bc :)

"The observed relative abundances of hydrogen, helium, and deuterium cannot be reconciled with the density of “dust” (i.e., nonrelativistic matter) inferred from the observational data."

What's relativistic matter? I have some idea, but I'd rather not just assume.

 

[mdmaaz]

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.

 

[phinds]

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.

I'm pretty confident that this is all totally incorrect. There was no space getting "squeezed" into the big bang, space and matter were being created by the BB and the initial density at the plank time was high beyond human comprehension (I don't want to get into whether it was infinite at t=0 because physics breaks down there and we really don't know WHAT was going on). The reason it did not collpase was purely because it was far too energetic.

As to "... if the big bang were to become a black hole, how would it ever explode into the big bang" that is in fact the question that I believe the OP was posing, not an answer to his question.

 

[Reg E]

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?

 

[ImaLooser]

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.

At the Big Bang there was no empty space. There was no empty space whatsoever for quite a long time, since everything was crammed with matter. Eventually the density dropped enough that voids appeared.

 

[ImaLooser]

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?

Not really. A unified force would still be a force.

 

[Mordred]

what your referring to is the theory of everything. when all 4 forces are combined

http://en.wikipedia.org/wiki/Theory_of_everything.

In grand unification theory only the 3 forces gravity excluded are combined.

this is a symmetry breaking concept in TOE the sum of the forces combined must have a net force of zero. Otherwise it is not complete. To date no known theory exists that obtains TOE.

Now as to our universe being born from an exploded singularity, this is not the mainstay view point of the inflationary model. the inflationary model is considered as a rapid expansion of spacetime. we do not know what occurs prior to 10^-43 seconds as the maths breaks down at that point.
However CMB measurements in its even distribution do not infer an explosion type beginning, such a beginning would show a hotter region towards a preferred direction as thermodynamics from an explosion radiate out from the source being hotter towards the starting point and cooler on the outside regions. This is not what we measure.

Also if we did explode from a singularity the amount of mass from such an explosion would quickly pull all the matter back to a singularity unless continuous energy is supplied as gravity would take effect. This did not happen
Like its been stated we do not know if the universe was infinite in the past or present nor do we know if its finite. However if its infinite now it was infinite in the past.
So the big bang is best represented as expansion not an explosion

 

[Chronos]

Here is the deal, the universe is 'real'. I assume we can all agree on that. We have this abiding desire to define 'real', which is absurd. How do you attempt to define a 'beginning' of the universe when it, by nature, assumes there was a 'time' that preceeded the universe? I find that ... disturbing.

 

[Adrian07]

I asked this same question many moons ago possibly on another but similar site. The answer I got then was that gravity did not exist until after the BB, a bit of a cop out I felt.

 

[Double-Slit]

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.

What theory is that i`m very interested in it,because it would not make any sense.Look at Hawking's work he proved that BH have a high state of entropy, yet the universe at it's beginning had a very low state of entropy,so how that would make sense ?
Also that would imply white holes (none which has been detected) ,and if you say the big bang was the white hole,then you contradict yourself by saying the universe is in a BH.
On the other hand what about the extreme gravity,you can't ignore that right,if we would be inside a black hole we would be moving to a single point the singularity,becoming closer and closer to each other until we merge in a 0 dimensional point ,and not expand and move away from each other.
And what about our black holes? Black hole in a black hole ,WTF? And many more reasons why this theory is rubbish.

 

[Mordred]

The theory that we are formed from inside a BH event horizon is by Poplowkii. Its often referred to as a torsion model. Not sure on the correct name.

 

[bapowell]

I don't understand why this debate always renews every year. Instead of speculating about why the big bang did not become a black hole, why doesn't someone first show that the big bang conforms to the Schwarzschild solution? The Friedmann-Robertson-Walker model, on which the big bang cosmology is based, lacks the symmetries of a black hole spacetime. So why would the big bang form a black hole?

 

[Mordred]

Blame pop media portrayals.

 

[mannygonzales1]

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.

 

[bapowell]

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.

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.

Your balloon analogy is right on, but one shouldn't think of the universe "hurtling outward" due to any sort of force: the expansion of the early universe is essentially just a boundary condition. The early universe would have been just as happy contracting!