# Pre-Big Bang < than a proton?

1. Jan 27, 2014

### megacal

I'm a microbiologist by training, and only have the basics of physics & math, so please bear with me.

Why do cosmologists assert that all the matter in the universe
was contained in a volume many times smaller than e.g. a proton
(or infinitely small?) prior to the Big Bang?

Why couldn't it have been a more "reasonable" size, e.g. the sun?

Everything we see that explodes has a reasonable volume....super novas,
sticks of dynamite, a nuclear bomb, etc. Isn't it reasonable to predict the
mass of the universe would only be stabile in a reasonable sized volume?

Just because you can extrapolate (theoretically) to an incredibly small volume
doesn't mean it was so.

(I have another question as about the assertion that everything expanded at
much greater than C, but will ask in another thread if necessary).

2. Jan 27, 2014

### Chronos

That figure ignores quantum gravity effects, which are not yet understood, and only applies to the observable universe, not the UNIVERSE

3. Jan 27, 2014

### megacal

Do you believe all the matter was contained in a volume infinitely smaller than a proton,
or is it possible it was something larger, e.g. the Milky Way, or a cubic lightyear, or the sun?

4. Jan 27, 2014

### Chronos

I think it is irrelevant without quantum gravity corrections.

5. Jan 28, 2014

### Chalnoth

In order for dark matter to be produced efficiently, the temperature of the early universe had to be above what we've probed in particle accelerators so far, or above about 1TeV. Our universe would have been at a temperature of 1TeV when the observable universe was contained within a radius of about 100 million kilometers, or a bit less than the distance from the Earth to the Sun.

That is the maximum possible minimum size of the visible universe when it was hottest. The natural expectation is that the starting temperature (at the end of inflation) of the very early universe would have been much, much higher than that. Some models, for example, put the temperature at around a hundred billion times that, which would have meant the observable universe would have fit within about a meter radius.

6. Jan 28, 2014

### megacal

Chalnoth,
I was going to ask what is the smallest volume that could contain all the
visible & dark matter (another problem for me, but will assume it exists for the purpose of this thread) in the universe prior to the BB.

Even a 2 meter diameter sphere is much more reasonable than something infinitely dense and infinitely smaller than a proton, which is what I've heard stated confidently as fact from several cosmologists without any qualification.

Do cosmologists consider what is "reasonable"? I.e. if something seems impossible, couldn't there
be a different explanation? E.g. that maybe there isn't any "dark matter" if we can't see it or measure it directly even though we're supposedly surrounded by it? (should I ask that question

Chronos,
"I think it is irrelevant without quantum gravity corrections",
but Chalnoth's answer was more in the ballpark of my understanding.

7. Jan 28, 2014

### Chalnoth

I think the distinction here is that the observable universe was indeed very much smaller than a proton in the very early universe. But at that time, it didn't have any matter around.

This would have been during cosmic inflation. The matter came about when inflation ended, and the field that drove inflation (the inflaton field) decayed into various particles. It is at this event that I'm talking about our universe being the hottest.

8. Jan 28, 2014

### Mordred

Chalnoth do you have a paper or article referencing the TEV level to form dark matter? If so I would be interested in reading it particularly if that paper defines the energy limits of its formation.

in regards to the quoted questions above, the evidence for dark matter is numerous, these include gravitational lensing, early universe large scale structure formation (without DM large scale structures would form much later than observed) and galaxy rotation curves (missing mass to explain rotation rates) threads on that subject are numerous on this forum.

The infinitely dense, infinitely small universe at the BB is a pop media misunderstanding of the singularity described in the BB model. More accurately the use of the singularity term in the BB model is merely a point at which our mathematics can no longer describe its nature (infinities).
The size of the universe at the BB is unknown and could be finite or infinite.

for the OP you may find these articles will help aid your understanding of current cosmology.

Misconceptions about the big bang by Lineweaver and Davis

http://www.mso.anu.edu.au/~charley/papers/LineweaverDavisSciAm.pdf

http://arxiv.org/abs/astro-ph/0310808 :"Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe" Lineweaver and Davies

http://arxiv.org/abs/1304.4446 :"What we have leaned from Observational Cosmology." -A handy write up on observational cosmology in accordance with the LambdaCDM model.

the last article is particularly handy as it describes cosmology without any mathematics in a manner of a Cosmology FAQ. However all 3 articles are fairly straight forward. More articles can be found in my signature "cosmology101 link."

9. Jan 28, 2014

### phinds

I'd suggest that you make an attempt to use proper terminology. You continue to say "the universe" when presumably you mean the OBSERVABLE universe.

"infinitely smaller than" is the same as "infinitely small", meaning no dimension at all, which I'm sure was not the case even when talking about only the observable universe.

10. Jan 28, 2014

### JesseM

The only reason astronomical objects like stars don't keep collapsing under their own gravity is that there are other non-gravitational forces that push outwards when the matter becomes too compressed, countering gravity--when these forces are in equilibrium the object can maintain a constant size. But for each of these non-gravitational forces, there is a limit to how much mass you can compress into a given region and have the outward force be strong enough to resist further collapse--for example, the outward pressure from "electron degeneracy pressure" can't resist gravity for a white dwarf (a type of dense remnant of the core of an exploded star) larger than the Chandrasekhar limit, and similarly the even stronger outward pressure from the "neutron degeneracy pressure" can't resist gravity for a neutron star larger than a certain limit. At a certain point there is no possible degeneracy pressure that can resist continued collapse, and in these cases general relativity (Einstein's theory of gravity) predicts that the matter will continue to collapse until the density approaches infinity in a finite time, creating a "singularity" at the center of a black hole. The same sort of idea would apply to the universe as a whole--if space were contracting so that all the matter in the universe was getting compressed into a smaller volume, general relativity predicts the density would become great enough that no form of outward pressure could resist continued collapse, and the whole universe would approach a state of infinite density in a finite time, an idea known as the Big Crunch (current observations suggest this won't happen in reality, that the universe will continue to expand forever because the mass density isn't great enough to overcome the expansion and start it collapsing, but this is a theoretical possibility in general relativity).

General relativity is a time-symmetric theory, meaning that the equations you'd use to predict the future state of a given system are the same as the ones you'd use to "retrodict" its past state, given knowledge of its present state. So, the Big Bang is just like a theoretical Big Crunch happening in reverse, and the same theoretical statements apply--if you keep extrapolating the present expansion backwards, general relativity predicts that there's no outward pressure that could avoid the conclusion that the density must have approached infinity at a finite time in the past.

So, that's what's predicted in general relativity, which is the current most accurate known theory of gravity that has a long history of its predictions being verified experimentally. But there are theoretical arguments that convince physicists that general relativity is likely to be only an approximation to a future theory of quantum gravity, and that the two theories will start to diverge significantly in their predictions at a scale of very high density of mass/energy (or very small units of distance and time) known as the Planck scale. So, physicists trust general relativity's prediction of increasing density further into the past right up to about the point where the density reaches the Planck density, before that general relativity isn't trustworthy and we can't know what would have happened without a theory of quantum gravity. I would guess the "size of a proton" statements are based on taking the estimated mass of the observable universe and figuring out how big it would be if squeezed to the Planck density.

Last edited: Jan 28, 2014
11. Jan 28, 2014

### Chalnoth

Sorry, but no. I'm just going by the fact that we've probed the behavior of matter up to around 1TeV or so in particle accelerators and not yet found any deviation from the standard model. There needs to be some rather significant deviation from the standard model to produce dark matter (and also for baryogensis, now that I think about it).

So this is just an extremely loose bound. The true maximum temperature was almost certainly much, much higher.

12. Jan 28, 2014

### megacal

Many thanks to all for taking time to answer my questions.

Mordred,
Yes, BUT.... we still haven't got a piece of it in hand.
Thanks for the links.....I'll review them before posting again.

JesseM,
thank you for that very clear & straightforward overview (with links!)...very helpful.

phinds,
Thanks for the correction. I assumed "universe" vs "Universe" was understood, but will be careful in the future to specify "observable universe"....presuming "observable" needn't be in all caps.

BTW, found your page on the Balloon Analogy, etc, and will spend time there. I tried to get on the "same page" here a year or so ago, and gave up......will have another go at it.....thanks.

Last edited: Jan 28, 2014
13. Jan 30, 2014

### JesseM

I just did a calculation on another thread which suggests where the "size of a proton" estimate probably comes from:

Last edited: Jan 30, 2014
14. Jan 31, 2014

### megacal

Thanks Jesse...the math says "way" but my brain says "no way".

Will have to mull it over with what limited tools I have. ;)

15. Jan 31, 2014

### megacal

I printed out and read through "Misconceptions about the Big Bang" by Lineweaver & Davis.

Very interesting and raises even more questions....

E.g. re: the Big Bang....
....??????

How large is "everywhere"?
What's wrong with a pre-existing void? If nothing is there, it's a void, right?
There is no limit or edge to the Universe as I understand it, though there is an
boundary to the observable uiniverse, which is a smaller structure within the Universe.....that's my perception anyway.

Lineweaver & Davis's Scientific American article is dated 2005. I didn't see any updates.....does that mean their article is still accurate 9 years later?

Does anyone take exception with anything they wrote? I have no way to dispute what they
claim.

BTW, they referred to "the universe" 29 times before specifying "observable universe" (but who's counting?) I'll leave it to someone else here to gently point that out to them. I don't know how well received it would be coming from a noob like me. :tongue2:

Last edited: Feb 1, 2014
16. Jan 31, 2014

### phinds

In the "big bang theory" model, there WAS no pre-existing ANYTHING. There are other theories that say there was but they are talking about the big bang theory.

"Everywhere" means exactly that. Everywhere. If the universe was finite at the time of the singularity, then "everywhere" is that big and if it was infinite at the time of the singularly then "everywhere" is infinite.

They use "universe" because they MEAN "universe". When they start talking about the observable universe, they say so.

Last edited: Jan 31, 2014
17. Feb 1, 2014

### megacal

....are or are not?

If it's critical for clarity to distinguish between "the universe" vs "the observable universe", especially
for the general public, it should be made at the beginning of any article, rather than 30 instances later.

18. Feb 1, 2014

### Mordred

Although its an older article, its still highly recommended and often cited in current research papers. The hot big bang model today is represented by the $\Lambda$CDM model. Which is the hot big bang with cold dark matter and the cosmological constant added to the energy content of the universe. However as Phinds pointed out there are other models. LCDM is still accurate and yet to be disproved, another contender is LQG (loop quantum gravity) which involves a bounce from a previous universe. I'll let others answer questions on that model as I'm more familiar with LCDM.
There have been countless other models, some more lavish than others such as our universe being inside a black hole, MOND (which tries to model without dark energy) etc.

The problem is that other models with the exception of LCDM and potentially LQC, simply do not fit observational data overall. Most times they work better in specific circumstances but poorly in others. MOND is excellent for predicting rotation curves of specific small galaxies. However loses accuracy when it comes to other galaxies and early large scale structure formation.

Unfortunately most papers and articles assume you know they are referring to the observable universe. Gathering data beyond the observable can only be done via an influence. Thus far no conclusive evidence has been detected. Therefore its assumed to be the same as our observable as there is no evidence to assume its any different. The policy of defining universe as meaning our observable derives from those reasons. Loosely put our universe is defined as "anything we can observe and measure" however that is a loose definition.

the term void unfortunately describes an energy state with space, that energy state being the lowest possible energy density. This has particular influences of surrounding space google ( false vacuum for one example).

In essence we can only speculate on anything outside of the observable universe. Any statements beyond the observable is simply conjecture and speculation.

Last edited: Feb 1, 2014
19. Feb 1, 2014

### megacal

Mordred,

Actually, I assumed that when reading Lineweaver & Davis's
article, and when I referred to the universe earlier.

Also, I checked all the links you gave me earlier....much to mull over.

Lineweaver & Davis's paper at Cornell was several orders of magnitude
above my level of comprehension. But I'm grateful they edited it
it for Scientific American so I could digest most of it....choked on just a few concepts...
will chew on them more.

20. Feb 1, 2014

### Mordred

keep at it, this forum is excellent for any questions you may have so feel free to ask for more recommended material and aid.:thumbs:

21. Feb 1, 2014

### phinds

Sorry. That was confusingly stated. I did mean "are" because the "they" I was referring to was Lineweaver & Davis, not the other theories I was bringing in. Very poor choice of wording on my part.

22. Feb 1, 2014

### petergreen

Correct calculation... interesting...

23. Feb 1, 2014

### JesseM

I think they are discussing how things work in the FLRW metrics which is how cosmologists have traditionally modeled the expanding universe in general relativity, but which doesn't take into account newer ideas like eternal inflation in which new "universes" can inflate out from tiny regions of preexisting ones (a full treatment of such ideas might require a theory of quantum gravity, or at least a better understanding of the quantum fields involved in the inflationary process). Just in the context of these traditional theoretical models, the density of matter/energy is assumed to be perfectly uniform throughout all of space (not just the observable part), which can be either finite (in the case of a "closed" universe with positive spatial curvature) or infinite (in the case of an "open" universe with zero or negative spatial curvature). In this sort of model there is nothing "outside" the matter filling space, the Big Bang is more like an expansion of space itself.

We can understand this more intuitively through a lower-dimensional analogy, imagining a universe with only 2 spatial dimensions as in the famous old book Flatland. In this case, for a finite "closed" universe of positive curvature you can imagine that the 2D surface is curved into the surface of a sphere, and the sphere itself is expanding so all the 2D matter on its surface gets less dense over time. In the case of an infinite universe with zero curvature, you might imagine something like an infinite chessboard drawn on a flat plane where the squares can all simultaneously get larger over time, but the amount of matter in each square stays constant, so the density again decreases with time (and going back in time, each square approaches a size of zero as you approach the Big Bang singularity, so the density of matter in each square approaches infinity--but this happens throughout all of infinite space, with no central location). For an infinite universe with negative curvature, you'd have to picture something like an infinite chessboard drawn on a 2D surface curved into a sort of "saddle shape"--you can see pictures of the 2D analogues of each type of geometry in part 3 of Ned Wright's cosmology tutorial.

24. Feb 1, 2014

### Mordred

This article covers the geometry aspects of the FLRW metric mentioned by JesseM. I tied to keep it as uncomplicated as possible yet still accurately describe Universe geometry in accordance to the FLRW metric. Ned Wright's site (link in JesseM's post) is also an excellent reference

25. Feb 1, 2014

### Mordred

I should mention that eternal inflation is an older but still valid inflationary model, in fact there is over 60 still valid inflation models, many of which derived from "old Inflation" or false vacuum by Allen Guth. The problem with old inflation, new inflation and eternal chaotic inflation. Is that they lacked a mechanism that would stop inflation ("Runaway Inflation"). Later models use a slow roll mechanism to limit inflation and attempt to stop inflation.

the Slow roll approximation is more commonly used as a benchmark model for other inflationary models as it has a tighter fit to observational data. Although eternal chaotic inflation is still within marginal error and therefore still valid.

Personally I prefer the Higg's inflation with 3 goldstones or the zero scalar Higg's inflation, as the Higg's inflation accomplishes similar results without introducing any exotic processes or particles such as the inflaton. Higg's inflation is gaining weight thanks to CERN's discovery of the Higg's boson.

Natural inflation is another personal interest of mine though finding good articles on it specifically has proven daunting.

Keep in mind their are tons of variations of inflation but inflation itself is a specific era in cosmology. Inflation is an extremely rapid expansion of space-time that occurred approximately within the 1st second of the universe. The exact time depends on the model but all models must solve several key problems. Googling each with the term cosmology used in the search will provide numerous links on each problem.

-monopole problem
-flatness problem
-horizon problem

Further information on the problems above can be found in the "What we have learned from Observational cosmology link provided in my first post.

This article has a listing of still valid models. the first section covers the requirements to match observational data. So provides a coverage of those problem. I wouldn't bother trying to read the full article but rather study the specific models your interested in.

http://arxiv.org/abs/1303.3787

the first 4 or 5 models I would however recommend reading, as they cover the history of how the early inflation models were developed historically.