Talk:Big Bang

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Features and problems subsections order[edit]

I care a lot about wikipedia article sections and subsections being organized in a logical order. With respect to 'Features and problems' subsection, I think we ought to either have an alphabetical order or a going-from-more-significant-features-slash/problems-to-the-less-important-ones order. I prefer the latter. Currently, the order seems to vaguely be the latter, but not quite. For example, while 'Horizon problem' and 'Flatness problem' are the first subsections and seem like the most important features/problems, 'Globular cluster age' seems like the least important issue (because it's pretty much been resolved and never really posed much of a problem for the theory), but it doesn't go last.

I'm curious what you guys think about what the subsection order should be. If we go with the important-to-less-important issues idea, then I think the order should be something like this (based on what the subsections currently say, although admittedly I'm not too knowledgeable on these issues):

Horizon problem, Flatness problem, Dark energy, Dark matter, Magnetic monopoles, Baryon asymmetry, Globular cluster age.

What are your thoughts on this issue? Would you prefer alphabetical? Etc. Byelf2007 (talk) 12 April 2012

Assumption: Cosmological principle[edit]

I think the discovery of the Hercules-Corona Borealis Great Wall should be included, it seems to be a structure which can not be explained by this principle. --RicardAnufriev (talk) 02:03, 19 March 2014 (UTC)

The exact nature of the Great Wall's formation is curious, but the studies done do not suggest that this invalidates the big bang. 74.128.43.180 (talk) 02:34, 15 April 2014 (UTC)

Image/caption[edit]

Evidence of gravitational waves in the infant universe may have been uncovered by the microscopic examination of the focal plane of the BICEP2 radio telescope.[refs]

In the Problems subsection there's an image, which I've reproduced here, showing the BICEP2 detector undergoing microscopic examination. The first problem is that the caption seems to imply that evidence of gravitational waves in the infant universe (a groundbreaking discovery, to be fair) was found by looking at the instruments, rather than using these instruments to observe the universe. Or have I read that wrong? The second problem, and the reason why I've elected not to fix the first problem myself, is that this image has no place being in that section and really ought to be removed. I'd remove it myself but I thought it might seem ill considered. It's an interesting image of an impressive detector that has since made an amazing discovery, but that isn't sufficient reason to shoehorn it in here, is it? nagualdesign (talk) 02:18, 25 March 2014 (UTC)

The image is relevant to the inflationary theory, but it was not clear how. I've moved it to the "Other lines of evidence" section that clarifies how gravitational waves are related to the big bang theory.
As for the difference between looking at the instruments and using the instruments to observe the universe, I don't see the problem; the first is necessary to achieve the second. Can you please suggest a better wording that would address your concern? Diego (talk) 11:29, 15 April 2014 (UTC)
I think this image simply is not very suitable for this article. It does not illustrate anything useful. It does not give the reader any idea of the nature of the BICEP experiment (in fact it is more likely to give the wrong idea). I suggest just dropping the image.TR 20:07, 15 April 2014 (UTC)

Simplifying the lede[edit]

I think it this point the lede (and in particular the first paragraph) is more complicated than it needs to be. Given the mass appeal of the subject, we should be aiming to make the lede accessible to as large an audience as possible. In the process we should be looking to see if we can make the lede a bit shorter as it is a bit longish. (At a glance there is some detail there that is need absolutely necessary. I have made a start at reducing the huge amount of wikilinks in the lede, which hamper readability (we do not need to link every other word). Similarly, there were way to may references for some single facts which I trimmed.

One suggestion would be to have one or two sentences after the first sentence that summarize the core of the ideas behind the Big Bang theory. For example,

The main idea is that the universe is expanding. Consequently, the universe was denser and hotter in the past. In particular, the Big Bang model suggests that at some moment all matter in the universe was contained in a point. Modern measurements place this moment at approximately 13.82 billion years ago, which is thus considered the age of the universe.

I am not quite happy with this yet, but it does put into focus the main idea behind the BB: the universe is and was expanding. I am not quite sold on inlcuding the singularity bit, partly because the singularity falls outside the Big Bang theory per se. However, some how including the fact that the big bang theory suggests the universe (as we know it) has a beginning seems desirable.TR 14:02, 15 April 2014 (UTC)

That sounds good. Be careful with removing too many links; the lede section admits a higher density of wikilinks, as any jargon term should be either explained or linked to. Diego (talk) 14:59, 15 April 2014 (UTC)

Big bang vs black hole, universal expansion vs light speed[edit]

I have 2 questions which do not seem to be explained:

1. How does the early universe, or significant portions of it, avoid being considered a black hole?

2. It appears that the outward spread of light is not the same as the expansion of the universe. If the outward spread of light does not effectively cause the universe to grow, then where does the light go (I know I didn't express that well)? Hmm, I guess this is answered by the universe wrapping around.

Scott McNay (talk) 03:11, 18 April 2014 (UTC)

The short answer to your first question: "because it expands" or "because it is not dense enough".
The slightly longer answer is that expansion of spacetime and gravitational collapse are two competing effects with in the case of our (visible) universe expansion winning. The condition for the visible universe to collapse or keep expanding is exactly the question whether the density is lower or higher than the critical density as discussed in the section on the future according to the Big Bang.
It is of course possible that in some regions the density was big enough to win out from the expansion. This regions would have collapsed to form primordial black holes.
The second question, just seems a matter of confusion about what is meant with "expansion". The universe is not expending into anything.It is space itself that is expanding. As far we can tell the universe is completely homogenous, consequently there is no such notion as "outward". In particular there is no outward spread of light. (At any point, there is about same amount of light travelling in any direction. Well, at least if you average over a large enough scale.) The article attempts to address this in the section title "FLRW metric".TR 09:52, 18 April 2014 (UTC)