Undergrad Was the Universe Really Dark and Quiet After the Big Bang?

[russ_watters]

Astronomers do not generally consider infrared light, or even radio waves, to be "darkness".

Agreed. And as such, the term "dark ages" - per the definition Chronos provided - isn't meant to refer only to visible light. If it did, the timeline would be missing an epoch!

Who specifically coined this term in this context, and what s/he was thinking at the time, I do not know, but that's a question of psychology, not of physics.

I think the term makes a lot of sense from an astronomical point of view. It means that we can't "see" what happened during that time because there was no new "light" created then. Telescopes are windows into the past, and that time is "dark" to us, at all wavelengths.

 

[russ_watters]

There are quite a number of steps in between. The "Chronology of the universe" wiki article:
https://en.wikipedia.org/wiki/Chronology_of_the_universe
is a good introductory explanation.
It has a nice table which describes temperatures, energies, "time since BB" and what was happening.

In particular:
...
Recombination, 380k years...

Dark Ages, 380k...150M years - The time between recombination and the formation of the first stars. During this time, the only source of photons was hydrogen emitting radio waves at hydrogen line. Freely propagating CMB photons quickly (within ~500 ka) red-shifted to infrared, and Universe was devoid of visible light.
...

For me, this is fairly well written and understandable.

"The age without sources of visible light" just does not roll off my tongue as easily as "Dark Age".

I feel like you're still suggesting "dark ages" is referring specifically to visible light. Please note that if that were true, the timeline would be in error and there would be an epoch missing; from 380ka-880ka, with the "dark ages" starting at 880ka.

 

[mfb]

At 380,000 years the CMB had a temperature of 3000 K and z=1100. Things glow visibly to the naked eye down to ~800 K, or z=290, corresponding to about 3.2 million years. That is quite a significant range where the light would have been visible to human eyes.

 

[Wondermine]

You are jumping around between completely different periods of the big bang and between completely different questions about the existence of particles from post to post. In addition you misrepresent the answers given by others. That makes a discussion very difficult.

I disagree with your criticisms entirely. The questions referred to the nature and form of energy preceding the BB.
Subsequent time periods are related to that and contiguous with that energy environment. So called "jumping around" is simply referring to consequences of one state and time leading to another.

Secondly, mentor ship is the act of commenting, not criticism of what one may know or not.
You have failed in your role as mentor to comment on specifics in a lighthearted way (all mentor comments have done this in fact).
Mentoring is not proving how much more you know at the expense of others. It is unbecoming for you to exhibit impatience when there is ample time for replies that do not require burdensome lengths of time.
Thirdly, the need to comment on how much I may know or not know dominated all of your replies. My questions remain unanswered.
Valid questions as to the density of the "singularity" before the BB were not answered. Many astrophysicists refer to the period before the BB as a singularity therefore it is a waste of your time focusing on critic.ism of my comment using this term.
I asked how you would define this period and what name you would like to assign to it in terms of structure. This question was not answered.
I asked what the consequences would be on the net energy of that system and whether you felt the net energy would rise with decreased degrees of freedom or fall with decreased degrees of freedom(before the BB).
This question was not answered.
Both questions relate to the BB and subsequent time line in the terms of energy states.

 

[berkeman]

I disagree with your criticisms entirely. The questions referred to the nature and form of energy preceding the BB.
Subsequent time periods are related to that and contiguous with that energy environment. So called "jumping around" is simply referring to consequences of one state and time leading to another.

Secondly, mentor ship is the act of commenting, not criticism of what one may know or not.
You have failed in your role as mentor to comment on specifics in a lighthearted way (all mentor comments have done this in fact).
Mentoring is not proving how much more you know at the expense of others. It is unbecoming for you to exhibit impatience when there is ample time for replies that do not require burdensome lengths of time.

Well, we are indeed trying to help you. If it's not working so well so far, then ...

For example, you just referred again to the time "before the Big Bang". Did you read the links that I sent you that explained why we cannot say much about that period?

 

[Wondermine]

That time spans at least 40 orders of magnitude in time and at least 30 in energy, with several huge changes in the composition of the universe. You are jumping around between different points in time in this giant range of different conditions.At least three physicists working on topics connected to the big bang told you that it is unclear which time you are referring to where. You might reconsider if what you write was really as clear as you think.What do you mean by that? Degrees of freedom are not physical objects, they cannot cause something.
Net energy of what?

The net energy of the system immediately preceding the BB and what form(s) that energy is in. What states(particles) survive that extreme compression that is widely postulated and termed a "singularity).

Well, we are indeed trying to help you. If it's not working so well so far, then ...

For example, you just referred again to the time "before the Big Bang". Did you read the links that I sent you that explained why we cannot say much about that period?

There is an ample supply of mathematical models describing the "singularity" states associated with Black Holes. Why would it be assumed the "singularity" before the BB would be anything different in character? What reason would be presented to justify the difference.

Well, we are indeed trying to help you. If it's not working so well so far, then ...

For example, you just referred again to the time "before the Big Bang". Did you read the links that I sent you that explained why we cannot say much about that period?

Yes. Extreme and accelerated expansion infers extreme contraction.
Therefore questions about extreme densities and "before the BB" are entirely acceptable paths of inquiry in a general sense.

 

[russ_watters]

There is an ample supply of mathematical models describing the "singularity" states associated with Black Holes. Why would it be assumed the "singularity" before the BB would be anything different in character? What reason would be presented to justify the difference.

I can think of one obvious one: the Big Bang banged and black holes don't. So it is very likely that the vastly different results are the result of vastly different conditions.

 

[berkeman]

For example, you just referred again to the time "before the Big Bang". Did you read the links that I sent you that explained why we cannot say much about that period?

Therefore questions about extreme densities and "before the BB" are entirely acceptable paths of inquiry in a general sense.

It sounds like either you didn't read the links that I suggested, or are not happy with what you found there...

From the INSIGHTS article: https://www.physicsforums.com/insights/big-bang-happen/

According to standard cosmological models, which are based on general relativity and are found to agree well with observations, time and space did not exist before the Big Bang — or even at the time of the Big Bang, which is a point where the theory breaks down because various quantities (such as temperature and spacetime curvature) are infinite. Therefore these models do not describe the Big Bang as an explosion that happened at a particular point in a preexisting landscape of time and space.

These are only statements about a particular kind of model. The model incorporates various assumptions, and as we get closer and closer to the Big Bang, these assumptions become more and more uncertain. For example, it is possible that under conditions of very high density and temperature, matter has exotic behavior that causes gravity to become repulsive. If this happens, then it’s possible that the Big Bang was not a bang but a bounce, and then time could be extended farther back into the past.

But even if time existed before the Big Bang, there is still another reason not to imagine the Big Bang as happening at one point in a preexisting empty space. Observations of the universe show a nearly complete lack of structure on very large scales, and the cosmic microwave background is also extremely uniform (with fractional temperature differences on the order of 10-5). For this reason, realistic cosmological models must be almost exactly homogeneous, meaning that no point in space has properties that differ very much from those of any other point. Therefore the best evidence is that the Big Bang happened uniformly, everywhere at once.

Reference https://www.physicsforums.com/insights/big-bang-happen/

 

[PeterDonis]

The questions referred to the nature and form of energy preceding the BB.

And the short answer to that is: we don't know, but the primary current hypothesis appears to be that it was potential energy in the inflaton field.

Notice that this answer has nothing to do with any "singularity". Nor does it bear any resemblance to any of the suggestions you have been making. Nor does it have anything to do with the "Dark Age", which happened well after the Big Bang. So the reason you didn't get an answer earlier to the question quoted above is that you didn't ask that question; you've asked a bunch of other questions that are either not well posed at all or are not about "the nature and form of energy preceding the BB".

Many astrophysicists refer to the period before the BB as a singularity

Please give an actual valid reference--textbook or peer-reviewed paper--that says this. Many pop science sources say this, but that just shows you can't learn actual science from pop science sources. Some textbooks use this term in reference to a particular idealized model that is used for pedagogy, but nobody thinks it actually describes our actual universe.

What actual valid references say about our actual universe is that the period before the BB was a period of inflation, since, as noted above, that appears to be our best current hypothesis.

Mentoring is not proving how much more you know at the expense of others. It is unbecoming for you to exhibit impatience when there is ample time for replies that do not require burdensome lengths of time.

You need to stop complaining about the tone of people's replies and start reading the actual content of those replies. We are trying to explain to you why the mental model you appear to have of how the universe developed is wrong. This thread can't go anywhere until you understand why that is.

 

[Orodruin]

Mentoring is not proving how much more you know at the expense of others.

Learning is accepting that your preconceptions and imaginations may not be as solid as you imagined and listening to people who have actual experience with the topic.

As already stated, you have gotten advice from numerous people who work with related topics for a living, all saying that your preconceptions are false in one way or the other. Not accepting this is just making you appear stubborn and unwilling to learn by unlearning false premises.

 

[russ_watters]

[period before the BB is referred to as "singularity"]
Please give an actual valid reference--textbook or peer-reviewed paper--that says this. Many pop science sources say this, but that just shows you can't learn actual science from pop science sources. Some textbooks use this term in reference to a particular idealized model that is used for pedagogy, but nobody thinks it actually describes our actual universe.

I don't think this point is necessarily critical to the thread, but I think Steven Hawking is probably the source of many of the "popular" tellings we see. One of many examples, from a lecture (you didn't list qualified lectures as valid, but we generally consider them to be):

So the time of zero separation...

At this time, the Big Bang, all the matter in the universe, would have been on top of itself. The density would have been infinite. It would have been what is called, a singularity. At a singularity, all the laws of physics would have broken down.

http://www.hawking.org.uk/the-beginning-of-time.html

There are probably three items you would quibble with here:
1. That the singularity is being referred to at all.

2. For whatever reason people on PF don't like the zero volume/infinite density "feature" Hawking likes to say for a space-time singularity (in a black hole, too), but to me "infinity" and "approaches infinity" aren't far enough apart to be worth quibbling over. But perhaps more to the point, I think that given his his significant contribution to this exact issue, Hawking's wording should be considered acceptable (the inventor gets to decide the name of his invention).

3. It is common to cite the "Big Bang" as the earliest identifiable state after the singularity, not the singularity itself. But I'm not sure this is a distinction worth quibbling about either (the wiki article notes the slight differnece in usage). These slightly different labels are colloquial, not scientific, no matter where they are used; in a paper, a lecture a news article, or on PF.

[note: this lecture/link is not dated, so it is possible this is an obsolete position of his. The wiki article's section on the singularity cites a 1973 paper of his as the source for describing the initial state as a singularity.]

[edit]
This wiki article provides some history:

Hawking's singularity theorem is for the whole universe, and works backwards in time: in Hawking's original formulation, it guaranteed that the Big Bang has infinite density.[1] Hawking later revised his position in A Brief History of Time (1988) where he stated that "there was in fact no singularity at the beginning of the universe" (p. 50). This revision followed from quantum mechanics, in which general relativity must break down at times less than the Planck time. Hence general relativity cannot be used to show a singularity.

https://en.wikipedia.org/wiki/Penrose–Hawking_singularity_theorems

So it would appear the idea that the universe started with a singularity was a naive early view that has been superceded but still remains in popular literature and some wiki articles. Still, it is a little surprising it hasn't been taken out of the BBT wiki article.

 

[PeterDonis]

There are probably three items you would quibble with here:

No, the item I am objecting to is that the idealized model Hawking is implicitly referring to, the one that has an "initial singularity" and no inflation, is not the model cosmologists actually use to describe our actual universe. It's an idealized model that is used for pedagogy, not physics.

It is common to cite the "Big Bang" as the earliest identifiable state after the singularity

No, it is common (in actual peer-reviewed literature) to use the term "Big Bang" to refer to the earliest identifiable state at the end of inflation. That is the current best-fit model: a hot, dense, rapidly expanding state that is modeled as arising from "reheating" when inflation ends and the energy stored in the inflaton field is transferred to the Standard Model fields. This model does not even have an "initial singularity" at all; it is agnostic about the question of whether such a thing exists, and does not use it, or even limits approaching it, to make any predictions at all.

Unfortunately, cosmologists do very little to clarify this point when pop science articles talk about an "initial singularity" and give the impression that the term "Big Bang" refers to it, or to some state "just after" it. What's more, cosmologists obfuscate the issue further by commonly quoting "times after the Big Bang" to label events, when what they are actually doing is: estimating the temperature of the universe at some event (such as the end of inflation) based on the actual best-fit model, which, as noted above, includes inflation and does not assume an "initial singularity" even exists; figuring out what the comoving coordinate time after the initial singularity would be for such a temperature in an idealized expanding FRW universe with no inflation; and quoting that idealized time as the "time after the Big Bang" of the event.

 

[Orodruin]

No, it is common (in actual peer-reviewed literature) to use the term "Big Bang" to refer to the earliest identifiable state at the end of inflation.

I just have a minor issue with this. Inflation is not really necessary for the standard Big Bang (even if it is useful to explain a series of issues that would otherwise arise). I would just call it the earliest identifiable state and be agnostic about what came before.

 

[PeterDonis]

Inflation is not really necessary for the standard Big Bang (even if it is useful to explain a series of issues that would otherwise arise). I would just call it the earliest identifiable state and be agnostic about what came before.

Yes, that's a fair point.

 

[russ_watters]

No, the item I am objecting to is that the idealized model Hawking is implicitly referring to, the one that has an "initial singularity" and no inflation, is not the model cosmologists actually use to describe our actual universe. It's an idealized model that is used for pedagogy, not physics.

I added some additional history I found, to my previous post, as you were posting this...

It appears from the history that Hawking's verbiage is just a very early view from a "first pass" at the issue some 45 years ago and was quickly supplanted. Suprising that it remains (with its 45 year old reference) in the wiki article...and undated lectures don't help.

Unfortunately, cosmologists do very little to clarify this point when pop science articles talk about an "initial singularity" and give the impression that the term "Big Bang" refers to it, or to some state "just after" it. What's more, cosmologists obfuscate the issue further by commonly quoting "times after the Big Bang" to label events, when what they are actually doing is: estimating the temperature of the universe at some event (such as the end of inflation)...

Well, colloquial labels are imprecise by nature, and depending on the context of the discusion, and event can be a process (think car crash or explosion). I suspect it doesn't cause any real problems in the research.

 

[PeterDonis]

I suspect it doesn't cause any real problems in the research.

I'm sure you're right, since in the actual research all of the cosmologists involved know what they actually mean. The problem is that lay people who read pop science articles by those cosmologists don't, and as a result many lay people get an incorrect understanding of what our current best cosmological models actually say. In other words, it's an issue of communication of research results to the public, not research itself.

 

[nikkkom]

Come to think of it, "Dark Age" was a rather unique period of time when Universe was a very quiet place.

There were practically no radioactive elements. BB nucleosynthesis may have produced radioactive Be-10 with half-life of 1.4 million years, but in extremely tiny concentration of ~10^-15 relative to hydrogen.

There were no sources of high-energy particles or any kind (be it gamma and X-rays, or lepton or hadron cosmic rays). If you'd magically teleport any current particle detector into the past into Dark Age, it would detect absolutely not a single cosmic ray for years on end. It would probably only detect particles from decays of its own radioactive impurities. :D

The only (known to us) relativistic species at that time were CMB photons, 21-cm radio from hydrogen, and relic neutrino background from neutrino decoupling.