B Questions about the Timeline of the Big Bang

  • Thread starter Cerenkov
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Hello.

I'm trying to obtain a better understanding of the earliest epochs of the universe's evolution and have been looking here...


Now to my questions.

1.
Am I correct in thinking that all the listed information in these timelines about epochs prior to Recombination is based upon inference and extrapolation, rather than direct observation?

2.
Hawking and Penrose's seminal paper on singularity theory, "The Singularities of Gravitational Collapse and Cosmology' https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.1970.0021, if still applicable, would apply to which epoch/s of the very early universe?

3.
mfb has kindly pointed me to these links... https://en.wikipedia.org/wiki/Big_Bang_Observer and https://arxiv.org/abs/1808.01892
My last question is therefore this. Would gravitational waves and/or neutrinos be able to probe back to the epoch/s that the Hawking - Penrose singularity theorems were designed to describe?

Many thanks in advance for any help given. Please note that my level of competence in PF is 'Basic' and I would therefore appreciate any replies being pitched at that level, please.

Thank you.

Cerenkov.
 

phyzguy

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Now to my questions.

1.
Am I correct in thinking that all the listed information in these timelines about epochs prior to Recombination is based upon inference and extrapolation, rather than direct observation?

Many thanks in advance for any help given. Please note that my level of competence in PF is 'Basic' and I would therefore appreciate any replies being pitched at that level, please.

Thank you.

Cerenkov.
Let me take just the first question. I think the answer is no. As the timeline shows, recombination happened about 380,000 years after the big bang. At a much earlier time, about 2 minutes after the big bang, the universe cooled enough for the first nuclei to form. This period is called the era of Big Bang Nucleosynthesis. After this time, a few minutes after the big bang, the primordial abundances of the light elements was "frozen in". We can measure the abundances of these light elements by measuring their abundance in the earliest stars, and the abundances agree quite well with the predictions of the standard model of cosmology(see figure below, from this site.). These measurements of the light element abundances clearly constitute observations, not "inference and extrapolation". It is true there is a smal discrepancy in the abundance of lithium-7, but as the graph shows, it is not that far off, and this problem is still being worked on.
BBNS-sm.gif
 
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Hawking and Penrose's seminal paper on singularity theory, "The Singularities of Gravitational Collapse and Cosmology' https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.1970.0021, if still applicable, would apply to which epoch/s of the very early universe?
It doesn't apply to any of them. It is a mathematical theorem about what happens if you extrapolate a model of an expanding universe backwards far enough, but the model the theorem applies to is an idealized model that does not correctly describe our actual universe. Our actual universe at early enough times--the inflation epoch--violates at least one of the premises of the singularity theorems, the energy conditions. So the "time zero" quoted in all of your references (none of which are textbooks or peer-reviewed papers, btw) is not an actual "initial singularity" that anyone really thinks occurred. It's just a feature of the idealized model which is used for convenience to define a time scale.
 
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Let me take just the first question. I think the answer is no. As the timeline shows, recombination happened about 380,000 years after the big bang. At a much earlier time, about 2 minutes after the big bang, the universe cooled enough for the first nuclei to form. This period is called the era of Big Bang Nucleosynthesis. After this time, a few minutes after the big bang, the primordial abundances of the light elements was "frozen in". We can measure the abundances of these light elements by measuring their abundance in the earliest stars, and the abundances agree quite well with the predictions of the standard model of cosmology(see figure below, from this site.). These measurements of the light element abundances clearly constitute observations, not "inference and extrapolation". It is true there is a smal discrepancy in the abundance of lithium-7, but as the graph shows, it is not that far off, and this problem is still being worked on.
View attachment 249399
I see phyzguy. So, despite the fact that we cannot actually see beyond the Epoch of Recombination, because these measured abundances are in good agreement with the predictions of theory, they qualify forensically as observations. Much as a geologist can have confidence in plate tectonics, even though they cannot travel back in time to actually visit Pangaea or Gondwanaland. Is that a reasonable summary of what you're saying?

Thank you.

Cerenkov.
 
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It doesn't apply to any of them. It is a mathematical theorem about what happens if you extrapolate a model of an expanding universe backwards far enough, but the model the theorem applies to is an idealized model that does not correctly describe our actual universe. Our actual universe at early enough times--the inflation epoch--violates at least one of the premises of the singularity theorems, the energy conditions. So the "time zero" quoted in all of your references (none of which are textbooks or peer-reviewed papers, btw) is not an actual "initial singularity" that anyone really thinks occurred. It's just a feature of the idealized model which is used for convenience to define a time scale.
Thank you, Peter.

As you can probably tell from the length of time I've been struggling with this issue, I'm still having problems differentiating between what a mathematical theorem is and what a physical theorem is. Between where the former applies and where it doesn't. Quite why this is I don't know. Are there any sites that you know of that can help me further, please?

Yes, I do realize that none of my cited references came from peer-reviewed papers or textbooks. But if I've recently been advised by other members of PF to use Google for my 'initial research' (their wording) then what else can I do but use the fruits of my Googling in my questions? Furthermore, because my level in this forum is Basic, surely I'm not expected to quote from textbooks or peer-reviewed papers that I cannot understand, when asking my questions?

Putting that niggle aside Peter, if my cited references don't make the cut, then I'd be very happy if you could rectify the situation by pointing me to ones that do and then explaining them to me in ways that I can understand.

Thanks again.

Cerenkov.
 

phyzguy

Science Advisor
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I see phyzguy. So, despite the fact that we cannot actually see beyond the Epoch of Recombination, because these measured abundances are in good agreement with the predictions of theory, they qualify forensically as observations. Much as a geologist can have confidence in plate tectonics, even though they cannot travel back in time to actually visit Pangaea or Gondwanaland. Is that a reasonable summary of what you're saying?
Yes, I think that's a good summary.
 

Ibix

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As you can probably tell from the length of time I've been struggling with this issue, I'm still having problems differentiating between what a mathematical theorem is and what a physical theorem is. Between where the former applies and where it doesn't.
Think of the singularity theorem as analogous to the claim that 2+2=4, and cosmology as analogous to the question of how many objects you have in your hands.

2+2=4 is a true result, and it was of interest because our best evidence was that you have two objects in your left hand and two in your right. Developments in observation, however, now suggest that you have three objects in your left hand. That doesn't mean that 2+2=4 is false or disproven - only that we now think it's not relevant to the real world.

Similarly, we were interested in the singularity theorems because they had implications for the type of spacetime we believed we live in. Developments in observation now suggest that the universe is not the type of spacetime that the singularity theorems talk about. They aren't wrong, just irrelevant.

At least, I think that's it.
 
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Please forgive my denseness in this matter but my only excuse is that I am literally a half century out of College and I haven't used much beyond rudimentary calculus in any job I've worked. From my learning integers are perfect abstractions because they are constructed and defined that way. I cannot grasp how 2 + 2 = 4 is irrelevant to the real world when it seems obvious that if one has two (2) containers, each containing two (2) of something, if one wishes to combine them into one (1) container that container must measure four (4) of that thing. What am I missing in this?
 

Ibix

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From my learning integers are perfect abstractions because they are constructed and defined that way. I cannot grasp how 2 + 2 = 4 is irrelevant to the real world when it seems obvious that if one has two (2) containers, each containing two (2) of something, if one wishes to combine them into one (1) container that container must measure four (4) of that thing. What am I missing in this?
You are pushing the analogy further than I intended.

In the analogy, 2+2=4 is irrelevant because the real world situation is that he has two objects in one hand and three in the other. We need urgent research into the value of 2+3. 2+2 is no longer of physical interest. :wink:

Putting it slightly less childishly, the singularity theorems are simply a statement about solutions to a system of differential equations given certain constraints on the solutions we will accept. It was of physical interest because the differential equations describe the dynamics of spacetime and its contents, and the constraints were physically reasonable. More recent study, however, leads us to believe that the constraints aren't correct for the early universe. So while the singularity theorems remain true as far as we are aware, we are no longer certain that they are talking about the universe we live in.
 
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What am I missing in this?
The fact that not all containers have two objects in them and not all combinations of containers are combinations of exactly two containers. If you're not combining two containers with two objects in them, then the fact that 2 + 2 = 4, while mathematically correct, is irrelevant.

Similarly, as @Ibix says, if the conditions required for the singularity theorems to apply are not valid in our actual universe at early times, then the fact that the singularity theorems hold under those conditions, while mathematically correct, is irrelevant.
 
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Whew! Gentlemen, thank you.... that helped. For a minute there I was beginning to imagine giant caterpillars smoking hookas might be real ;)
 
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I don't think they're explicitly forbidden by the field equations...
I haven't seen any literature on a "giant caterpillar smoking hookah solution", so I think it will be difficult to find a valid reference supporting it for discussion... :wink:
 
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My thanks to Ibix and Peter Donis for their helpful replies.

I'd like to respond to Ibix first, about something he wrote to enorbet.

Ibix, in both your responses to enorbet you use the number of objects he has in his hands to illustrate your point. That's fine. You also say that he notices the change in the number of objects he's holding. Therefore, he must have observed this change. You've answered his question well enough, but using the notion of "observing a change" cannot really apply to my question about how the Hawking - Penrose singularity theories do or don't apply to earliest epochs of the universe's evolution

Why? Because we cannot observe these epochs. In this thread... https://www.physicsforums.com/threads/can-we-observe-anything-beyond-the-cmb-wall.976974/ I asked about information coming to us through the CMB 'wall' and was advised that no electromagnetic radiation from earlier than 380,000 after the Big Bang can be observed by us.

Ok, I realize that you were answering enorbet's query and not mine, but I'm still left somewhat bemused and confused by this issue.

I shall see if Peter can help me.

Thanks again.

Cerenkov.
 
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Hello Peter.

In your reply to enorbet you say that "the conditions required for the singularity theorems to apply are not valid in our actual universe at early times". I accept that there must be a good reason for this and recently you've explained to me that certain energy conditions necessary for singularities are violated in inflationary spacetimes. Following up on this I found this paper...
http://strangebeautiful.com/papers/curiel-primer-energy-conds.pdf and sure enough in section 3.2 Violations, page 80, SEC violations, # 6... we see that the Strong Energy Condition is necessarily violated by cosmological inflation.

My current understanding of this situation is therefore a kind of parallel to the one I outlined to phyzguy in post # 4. In that case he and I discussed the abundances of elements as being a kind of forensic observation of conditions prior to the CMB wall. I've applied that mode of thinking to the issue of the conditions that prevailed in the very early universe and come up with this.

There must be some observations that favor inflationary cosmology which, if taken to apply to the very early universe, would appear to indicate that the conditions for a Hawking - Penrose singularity were violated. While the singularity theorems are mathematically correct, they do not agree with our observations and do so are irrelevant.

Is that a fair summary of the issue?

Thank you.

Cerenkov.
 
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I'm still having problems differentiating between what a mathematical theorem is and what a physical theorem is.
There is no such thing as a "physical theorem". There are mathematical theorems, whose premises are satisfied in some physical models but not others. Obviously a mathematical theorem can't apply to a physical model in which its premises are not satisfied.
 
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what else can I do but use the fruits of my Googling in my questions?
And if the fruits of your Googling are giving you pop science references that give misleading or wrong presentations of the issue, what else can we do but remind you that PF has a policy about acceptable sources for a reason?

my level in this forum is Basic, surely I'm not expected to quote from textbooks or peer-reviewed papers that I cannot understand, when asking my questions?
No, but you might have to accept that there might be no references that you can understand at the Basic level that will give you a correct presentation of the issue you're interested in. Which means that the only way to get one might be to increase your level of knowledge by working through textbooks or peer-reviewed papers until you do understand them.

We understand that that can be a long process. Unfortunately, there often are no shortcuts.
 
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sure enough in section 3.2 Violations, page 80, SEC violations, # 6... we see that the Strong Energy Condition is necessarily violated by cosmological inflation.
Yes.

In that case he and I discussed the abundances of elements as being a kind of forensic observation of conditions prior to the CMB wall.
Yes, that's a valid way of describing it. We can't see directly past the CMB using electromagnetic radiation (although if we figure out how to detect neutrinos or gravitational waves from earlier times, that would give us a way of seeing to those earlier times), but we can infer what conditions were at earlier times based on other observations.

There must be some observations that favor inflationary cosmology which, if taken to apply to the very early universe, would appear to indicate that the conditions for a Hawking - Penrose singularity were violated. While the singularity theorems are mathematically correct, they do not agree with our observations and do so are irrelevant.

Is that a fair summary of the issue?
Yes.
 
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And if the fruits of your Googling are giving you pop science references that give misleading or wrong presentations of the issue, what else can we do but remind you that PF has a policy about acceptable sources for a reason?
Peter,
Of course I cannot challenge you on any matter concerning PF policy. But I would answer your, "What else can we do?" with,"What else could I have done?" I was advised, in good faith, to use Google for initial research, by other members of PF and I took that advice at face value.

If it's incumbent upon me to check the advice I'm given, to see if it falls within PF policy, then please let me know. I'll then do my best to check the advice I'm given to see if it conforms to your policies.

It also seems that in following the above advice, I failed to understand that the content of my own initial research falls outside the guidelines of PF. If that's so then I apologize for breaching the rules.


No, but you might have to accept that there might be no references that you can understand at the Basic level that will give you a correct presentation of the issue you're interested in. Which means that the only way to get one might be to increase your level of knowledge by working through textbooks or peer-reviewed papers until you do understand them.
My understanding is inching forward very slowly. But I am still pleased that the general direction is forward.
 
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Yes.

Yes, that's a valid way of describing it. We can't see directly past the CMB using electromagnetic radiation (although if we figure out how to detect neutrinos or gravitational waves from earlier times, that would give us a way of seeing to those earlier times), but we can infer what conditions were at earlier times based on other observations.

Yes.
Thank you Peter.
 
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@Cerenkov, please use the quote feature as it was designed. I have edited your post #20 so that your responses to what you quoted from me do not appear in the quote box. If your responses appear in the quote box that defeats the whole purpose of the quote box.
 
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was advised, in good faith, to use Google for initial research
For initial research, yes. That means you look at the search results you get for further links that will eventually lead you to good sources. You should not expect that the items that come up in the Google search will already be good sources. That will often not be the case. But if, for example, you get to a Wikipedia article from Google, even if the article itself is not a good source (which Wikipedia articles often are not), it will probably have links to references which are better ones.

In short, you were not being advised to Google and treat whatever links come up in the search results as good sources. You were being advised to use Google as a tool to help you find good sources using a process in which Google as a tool is only the first step.
 
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Thank you Peter.

I understand these things now and will endeavor to sharpen up my questions,quotes and citations accordingly.

All the best.

Cerenkov.
 

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