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bunker9603
2010-Jul-04, 12:41 PM
I am almost embarassed to ask, but here goes.

When a star collapses a black hole is formed, so my question is was a black hole formed when the BB ocurred?

WayneFrancis
2010-Jul-04, 02:19 PM
Don't be embarrassed. It is a good question. While the energy density of the early universe was as high or higher then when could be found inside the event horizon of a black hole there are other conditions that don't match the conditions of a black hole. One thing is there is no "outside" that has less gravity. So while there might be a very deep gravity well it isn't like a bowl because there is mass every where.

George
2010-Jul-04, 07:51 PM
When a star collapses a black hole is formed,... [Just to "eschew obfuscation" ;), I assume you mean when a star of sufficent mass collapses, since the vast majority of stars are not massive enough to have their cores collapse into black holes.]


...so my question is was a black hole formed when the BB ocurred?
One of the major additions, and likely the most important, to the original theory ("Primeval Atom") was Inflation theory. Almost instantly after the beginning, space violently expanded at unimaginable speeds, much faster than the speed of light -- space is allowed to do that even though objects and light itself can't as this things are traveling through space. Such expansion would also be a problem for any hope for blackhole formation.

Tensor
2010-Jul-04, 08:17 PM
I am almost embarassed to ask, but here goes.

When a star collapses a black hole is formed, so my question is was a black hole formed when the BB ocurred?

Along with the other answers, there are the nature of the singularities involved to consider also. To quote Ned Wright, In a black hole, you have a singularity that occurs through all time at a single point and with the Big Bang, you have a singularity that extends through all space at a single instant. This site (http://www.weburbia.com/physics/universe.html) might help you with the differences. Here ( http://www.astro.ucla.edu/~wright/cosmology_faq.html) is Ned Wrights FAQ on Cosmology, if you want a good "quick" explanation of several of the most asked questions about cosmology.

Kwalish Kid
2010-Jul-04, 11:18 PM
One of the major additions, and likely the most important, to the original theory ("Primeval Atom") was Inflation theory. Almost instantly after the beginning, space violently expanded at unimaginable speeds, much faster than the speed of light -- space is allowed to do that even though objects and light itself can't as this things are traveling through space. Such expansion would also be a problem for any hope for blackhole formation.
My goodness, this reply above shows the gross philosophical and physical problems with inflationary reasoning! In GR, there is no need to avoid the problem of everything collapsing initially because there is an initial condition: the rate of expansion of the universe. This rate must be overcome before any black hole could form (as it presumably is in various pockets of inhomogeneity in the universe). Inflation does absolutely nothing to address this issue and is entirely superfluous, even though it is often trotted out for a number of non-problems.

It may be that we should adopt some sort of inflationary scenario for the early universe, but not on this sort of reasoning.

George
2010-Jul-05, 02:50 AM
My goodness, this reply above shows the gross philosophical and physical problems with inflationary reasoning![ Hardly. Inflation serves an example of why it makes little sense to look for black holes during this early period. Consider it hyperbole for effect when compared to expansion.

If it is reasonable to consider a kind of gravitational repulsion as causal to inflation, then it becomes even more clear why a black hole is problematic as it is a result of gravitational attraction. Am I wrong?

blueshift
2010-Jul-05, 03:41 AM
In a black hole entropy is in saturation. With a BB entropy is quite low.

astromark
2010-Jul-05, 04:26 AM
At precisely that moment when a group of cosmologists announce that the Universe can never implode back to a singularity... Whomp ! It did.

Yes,. according to Douglas Adams... It is important to have a understanding of both Newtonian and GR...

A Black Hole could only exist after a period of expansion.

Relativity must be maintained... I am qualified to tell you that there may not have been a beginning.

The initial expansion allowed no place or time for a Black Hole.

As the density of the expanding universe prohibited time. t = 0.

Until that happened time and the universe did not exist.

Not even a Black Hole.

I agree with George's post #6, and 3.

astromark
2010-Jul-05, 06:11 AM
I am almost embarassed to ask, but here goes.

When a star collapses a black hole is formed, so my question is was a black hole formed when the BB ocurred?

On reflection... I am embarrassed to admit that I may have answered a question you did not ask... You do not need to be embarrassed.

That is a good question. The answer is, No.

At the outset of this Universe the expansion was such that mater as we understand it could not behave as we might expect it to...

Only when the density and temperature of the universe fell below the plasma state where electrons had not yet formed...

Could such mater begin to distort the space it was in... Gravity. Before that happened no star or black hole could have formed...

Jeff Root
2010-Jul-05, 07:05 AM
The main reason that the Universe was not a black hole at the moment
of the Big Bang, probably sufficient by itself even if there aren't any other
reasons, is what Wayne said back in post #2: Gravity depends on the
distribution of mass-energy. If the mass-energy involved in the Big Bang
filled all of space uniformly, then there could not have been any gradient
in the gravitational field, so there was no net gravity. Analogous to equal
quantities of positive and negitive electric charges in matter resulting in
zero net electric charge. From any location in space, there was no
direction that could be considered to be "down", no location that was
"lower" gravitationally than any other location, no "well" to fall into.

-- Jeff, in Minneapolis

bunker9603
2010-Jul-05, 07:12 AM
Along with the other answers, there are the nature of the singularities involved to consider also. To quote Ned Wright, In a black hole, you have a singularity that occurs through all time at a single point and with the Big Bang, you have a singularity that extends through all space at a single instant. This site (http://www.weburbia.com/physics/universe.html) might help you with the differences. Here ( http://www.astro.ucla.edu/~wright/cosmology_faq.html) is Ned Wrights FAQ on Cosmology, if you want a good "quick" explanation of several of the most asked questions about cosmology.

Thank you for those sites they are exactly what I was looking for. I want to thank everyone else who answered also as I have watched so many Big Bang and Black Hole shows on the History Channel, NatGeo and Through the Wormhole lately that I was getting myself confused.

It seemed like there were some similarities between the two so I thought I would ask.

RussT
2010-Jul-05, 11:01 AM
Watch "Seeing Black Holes" and pay close attention to what Michio Kaku says toward the end about Singularities and Infinity + Infinity + Infinity...everybody is VERY confused ;>))

Kwalish Kid
2010-Jul-05, 02:11 PM
Hardly. Inflation serves an example of why it makes little sense to look for black holes during this early period. Consider it hyperbole for effect when compared to expansion.
Initially, it seemed that you were offereng is as an explanation (not needed) of why the initial universe did not collapse into a black hole. If you meant to address the subject to the presence of black holes in the early universe in general, this is OK, though it still does not seem to be a better answer than initial conditions.

If it is reasonable to consider a kind of gravitational repulsion as causal to inflation, then it becomes even more clear why a black hole is problematic as it is a result of gravitational attraction. Am I wrong?
I'm not sure of your reasoning here. There is no explanation required for why the early universe did not collapse into a black hole, adding new repulsive forces to that mix cannot make an explanation any less required.

blueshift
2010-Jul-05, 02:39 PM
The main reason that the Universe was not a black hole at the moment
of the Big Bang, probably sufficient by itself even if there aren't any other
reasons, is what Wayne said back in post #2: Gravity depends on the
distribution of mass-energy. If the mass-energy involved in the Big Bang
filled all of space uniformly, then there could not have been any gradient
in the gravitational field, so there was no net gravity. Analogous to equal
quantities of positive and negitive electric charges in matter resulting in
zero net electric charge. From any location in space, there was no
direction that could be considered to be "down", no location that was
"lower" gravitationally than any other location, no "well" to fall into.

-- Jeff, in MinneapolisBoth posts #2 and #10 seem the best explanations, one extending a touch on the other. Thank you Wayne and Jeff!

Cougar
2010-Jul-05, 06:06 PM
Watch "Seeing Black Holes" and pay close attention to what Michio Kaku says toward the end about Singularities and Infinity + Infinity + Infinity...everybody is VERY confused ;>))

Well, Kaku tends to emphasize the "confusing" and "weird" of quantum- and astrophysics.

Spaceman Spiff started a thread (http://www.bautforum.com/showthread.php/103516-The-Universe-is-Not-a-Black-Hole?highlight=black+hole) awhile ago specifically designed to answer the OP question:


When a star collapses a black hole is formed, so my question is was a black hole formed when the BB ocurred?

I thought I picked out a good point from the link to Sean Carroll's discussion on the topic:





Although the approximate mass and radius of the visible universe might fit pretty well into the formula for the Schwarzschild radius, as Carroll writes....




You may have noticed that the universe is actually expanding, rather than contracting as you might expect the interior of a black hole to be.

Tough to argue against that one, all right. He notes our universe is more like the opposite of a black hole, i.e., a white hole. I always kind of thought (to myself) that the idea of a white hole was pretty ridiculous... I didn't realize I could be living in one.

George
2010-Jul-05, 06:52 PM
I'm not sure of your reasoning here. There is no explanation required for why the early universe did not collapse into a black hole, adding new repulsive forces to that mix cannot make an explanation any less required. When the force of gravity was repuslive (i.e. Inflation) instead of attractive, what mechanism could possibly allow the formation of a black hole?

Jeff Root
2010-Jul-05, 07:41 PM
When the force of gravity was repulsive (i.e. Inflation) instead
of attractive...
Is that your understanding of Inflation, or is it only one possible
interpretation of what happened in Inflation? I don't think the
idea that gravity momentarily reversed and become much
stronger is a popular explanation of Inflation.

-- Jeff, in Minneapolis

Tensor
2010-Jul-05, 07:47 PM
Thank you for those sites they are exactly what I was looking for.

The FAQ by Ned Wright is attached to a cosmology tutorial. This will help you understand a few other things


I want to thank everyone else who answered also as I have watched so many Big Bang and Black Hole shows on the History Channel, NatGeo and Through the Wormhole lately that I was getting myself confused.

Watching a lot of popular science show can do that. They are aimed at different audiences, use different analogies (which may contradict each other) and generally are aimed at the lowest common denominator. As those who come here are usually on the higher side of the intelligence measure, they ask a lot of questions about those analogies and contradictions. You may understand why we get frustrated at popular science treatments around here.


It seemed like there were some similarities between the two so I thought I would ask.

If you're thinking, then you will see the similarities. You have to do a lot more thinking and a bit of learning to understand the differences. Congratulations on increasing your knowledge.

Cougar
2010-Jul-05, 07:52 PM
When the force of gravity was repuslive (i.e. Inflation) instead of attractive, what mechanism could possibly allow the formation of a black hole?

Even beyond that: the surface of last scatter, 400,000 yrs after nucleosynthesis, is too smooth to allow any such large "gravitational anomalies," particularly having just come out of a state of thermal equilibrium. There must have been some pretty large gravitational infalls throughout the universe fairly soon after that, though, I would think....

George
2010-Jul-05, 09:02 PM
I don't think the
idea that gravity momentarily reversed and become much
stronger is a popular explanation of Inflation. I am not that well versed in inflation, admittedly. It just seems so logical that repulsive gravity would make for such a nice explanation of such a fantastically inflationary event. What causal explaination is now mainstream?

Here (http://www.phys.cwru.edu/events/grav_ws/guth-st-thomas.pdf) is a brief presentation from Guth's Eternal Inflation model. Note that he shows that negative pressure is repulsive gravity. What am I missing?

George
2010-Jul-05, 09:05 PM
Even beyond that: the surface of last scatter, 400,000 yrs after nucleosynthesis, is too smooth to allow any such large "gravitational anomalies," particularly having just come out of a state of thermal equilibrium. There must have been some pretty large gravitational infalls throughout the universe fairly soon after that, though, I would think.... I am unclear what you mean here. Are you saying that there may have been some black holes shortly after recombination due to the anisotropies observed?

Kwalish Kid
2010-Jul-05, 09:31 PM
When the force of gravity was repuslive (i.e. Inflation) instead of attractive, what mechanism could possibly allow the formation of a black hole?
You are misrepresenting inflationary theory. The inflation field might operate gravitationally, but it operates slightly differently from what we identify as ordinary gravity. We can say today that gravity is repulsive because that's how it works for long distances, as given by our measurements of the cosmological constant. However, we can still recognize the vanilla operation of gravity on most scales of interest to us. The same can be said for the way the inflation field works, as it is possible that there were initial conditions such that there were regions where the inflation field was not able to overcome the local energy density.

Regardless, this is still an appeal to something that is unnecessary: we do not need an inflation field to explain why the early universe did not collapse into a black hole.

Now what is interesting is that some inflationary scenarios tell us what inhomogeneities we should expect to see in the surface of last scattering. This might be a way to test inflationary hypotheses.

George
2010-Jul-06, 04:23 AM
The inflation field might operate gravitationally, but it operates slightly differently from what we identify as ordinary gravity. We can say today that gravity is repulsive because that's how it works for long distances, as given by our measurements of the cosmological constant. However, we can still recognize the vanilla operation of gravity on most scales of interest to us. Yes, but the OP suggests the idea of a BH forming at the moment just after BB. Expansion, inflation or post-inflation, would prevent their formation. I'm not saying that there aren't other reasons, but it is the one that I like.


Regardless, this is still an appeal to something that is unnecessary: we do not need an inflation field to explain why the early universe did not collapse into a black hole. Inflation is helpful to get a feel of the expansive dynamics that were taking place. According to Alan Guth, per my link, he calls it "repulsive gravity". "Gravity" may or may not be the best term to use, but is he really that wrong? [Did you see my link to his short work?] I realize there have been improved models since his original one, so is he ATM with this 2006 presentation?

Jeff Root
2010-Jul-06, 06:43 AM
I don't know or understand why Guth called it "repulsive gravity".
I should find out.

If aside from expansion, including Inflation, conditions had been right
for the formation of a black hole, then the black hole would likely
have prevented the expansion. This is awfully similar to the question,
"What happens when an irresistable force meets an immoveable object?"

-- Jeff, in Minneapolis

Cougar
2010-Jul-06, 01:10 PM
I am unclear what you mean here. Are you saying that there may have been some black holes shortly after recombination due to the anisotropies observed?

I'm saying very large stars apparently formed fairly quickly. They burned through their hydrogen and helium quickly, fusing heavier metals, then went supernova, spreading the metals around and (each) forming a black hole. With everything closer together back then, apparently there were lots of interactions, black hole mergers, etc. Details are sketchy, but I base this scenario on the fact that there are now galaxies all over the place, and have been for a long time.

Kwalish Kid
2010-Jul-06, 02:26 PM
I'm saying very large stars apparently formed fairly quickly. They burned through their hydrogen and helium quickly, fusing heavier metals, then went supernova, spreading the metals around and (each) forming a black hole. With everything closer together back then, apparently there were lots of interactions, black hole mergers, etc. Details are sketchy, but I base this scenario on the fact that there are now galaxies all over the place, and have been for a long time.
The current wide-spread theory on early galaxy formation is that galaxies formed in areas of high matter density. The high density was primarily dark matter density.

Kwalish Kid
2010-Jul-06, 02:33 PM
Yes, but the OP suggests the idea of a BH forming at the moment just after BB. Expansion, inflation or post-inflation, would prevent their formation. I'm not saying that there aren't other reasons, but it is the one that I like.
Only with certain initial conditions would inflation stop black holes from forming. If there were a region of the universe of extremely high density, inflation could not stop that from turning into a black hole.

Inflation is helpful to get a feel of the expansive dynamics that were taking place. According to Alan Guth, per my link, he calls it "repulsive gravity". "Gravity" may or may not be the best term to use, but is he really that wrong? [Did you see my link to his short work?] I realize there have been improved models since his original one, so is he ATM with this 2006 presentation?
Guth is correct that an inflation field can act just like the cosmological constant. But just like the cosmological constant, the gravitational action associated with the inflation field increases with distance while the action of the standard gravity remains and decreases with distance. This is just something not included in Guth's slides. Indeed, Guth is appealing to anthropic reasoning because it allows us to assume that there are regions of the universe where inflation could not overcome the creation of black holes (and other weird regions), it's just that we don't find ourselves in this area because our kind of life wouldn't develop in such an area.

George
2010-Jul-06, 04:53 PM
Guth is correct that an inflation field can act just like the cosmological constant. But just like the cosmological constant, the gravitational action associated with the inflation field increases with distance while the action of the standard gravity remains and decreases with distance. This is just something not included in Guth's slides. Indeed, Guth is appealing to anthropic reasoning because it allows us to assume that there are regions of the universe where inflation could not overcome the creation of black holes (and other weird regions), it's just that we don't find ourselves in this area because our kind of life wouldn't develop in such an area. Ah, that helps much. The inflationary force is accumlative with distance much like pressue is with increasing ocean depths. Thus, a near point-source mass/energy with high density would not be prevented by inflation alone from forming a BH. This is still a bit confusing since I thought Inflation was instrumental in explaining the isotropy, which would minimize such a possible high density spot. Is this not correct?

George
2010-Jul-06, 04:57 PM
I'm saying very large stars apparently formed fairly quickly. They burned through their hydrogen and helium quickly, fusing heavier metals, then went supernova, spreading the metals around and (each) forming a black hole. With everything closer together back then, apparently there were lots of interactions, black hole mergers, etc. Details are sketchy, but I base this scenario on the fact that there are now galaxies all over the place, and have been for a long time. Ok, that makes sense, though I have assumed the OP was asking about the earliest moments of Big Bang when mass/energy densities were so huge.

Kwalish Kid
2010-Jul-06, 05:52 PM
Ah, that helps much. The inflationary force is accumlative with distance much like pressue is with increasing ocean depths. Thus, a near point-source mass/energy with high density would not be prevented by inflation alone from forming a BH. This is still a bit confusing since I thought Inflation was instrumental in explaining the isotropy, which would minimize such a possible high density spot. Is this not correct?
Inflation can explain the isotropy that we see by scattering inhomogeneities so far and wide that what we see in our region appears isotropic, even though spacetime overall has no such requirement. There is still an appeal to initial conditions in this reasoning, but many feel that this is a better appeal, though so far there is no rigourous support for this intuition.

George
2010-Jul-06, 06:08 PM
Inflation can explain the isotropy that we see by scattering inhomogeneities so far and wide that what we see in our region appears isotropic, even though spacetime overall has no such requirement. Ok, but assuming the inflation period took a proton-sized universe and expanded it to something about the size of a grapefruit, aren't even quantum-sized areas stretched rather than just carried along? If so, wouldn't this minimize the chances for BH development?

Kwalish Kid
2010-Jul-06, 06:56 PM
Ok, but assuming the inflation period took a proton-sized universe and expanded it to something about the size of a grapefruit, aren't even quantum-sized areas stretched rather than just carried along? If so, wouldn't this minimize the chances for BH development?
Well, you are welcome to set the initial conditions and the assumptions for just how inhomogeneous the initial conditions were to whatever you want. There is always a threshold of a density that will not be significantly broken up by an inflationary field.