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Wikipedia:Peer review/Cosmic inflation/archive1

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Cosmic inflation

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NASA WMAP press release image

I am slowly trying to improve this article to the point where I can nominate it for FA. It is certainly an important article for a general audience, because it is one of the linchpins of the big bang theory. It is hard, because it deals with a somewhat technical topic that, while old, is still very much a topic of current research, particularly with recent developments in string theory. My feeling about the article right now is that it works well as a literature review, but it is still much too technical for the general reader. I also know that the last four subsections in "Theoretical status" could use some work (they are stubs), and the article is probably getting to be on the long side. More illustrations would help, but I'm not sure what to add: there used to be an image from a WMAP press release, but I'm unsure of whether it really teaches the reader anything. Any comments would be much appreciated: I sometimes feel a bit like I'm working in a vacuum. –Joke 03:23, 1 November 2006 (UTC)[reply]

Yes it's a pretty good article. But unfortunately it reads more like a refresher to the subject than an introduction. In many cases the article pretty much assumes pre-existing knowledge on the part of the reader. I think it needs to slow down a little and explain matters to a lay reader who is not already familiar with the concepts of cosmology. Thus concepts such as "de Sitter universe", "causally-connected", "radiation dominated universe", "exotic heavy particles", "universe is flat", "bubbles nucleated", "near-scale invariance", "Planck unit", "21 centimeter radiation", "quadrupole moment", "Higgs field", "scalar field rolling down a potential energy hill" and "curvature redshifts away more slowly than matter and radiation" need to be clarified without necessarily requiring the reader to drill-down to new topics.
Some more comments:
  • Please link: inhomogeneities, anisotropies, curvature of space, domain walls, and adiabatic (which type: thermodynamic or quantum?)
  • The description for the illustration in the history section is unclear.
  • Most of the paragraph on normal distribution of fourier modes is going to be over the heads of most people who haven't taken advanced college-level math.
  • What are "B-modes"?
  • The "21 centimeter radiation" measurements could be explained in terms of the dark epoch prior to reionization. Likewise dark energy in terms of the accelerating universe.
  • The middle paragraph in "Initial conditions" is much too long and could use some judicious paragraph breaks.
  • Spelling or grammar issues:
    • "thie"
    • "could eliminated the" => eliminate (drop the "d")
    • "conditions are necessary for inflation occurs in tunneling"
    • "bring it back up the potential"
    • "Inflation and string theory" section is missing a closing parenthesis at the end of the section.
Thanks! — RJH (talk) 17:06, 1 November 2006 (UTC)[reply]
Thank you for your suggestions. I have incorporated nearly all of them. I didn't link "adiabatic" or "isentropic" because the links are relevant in an obvious way – the better link was thermal equilibrium; I also haven't worked on the string theory section, for lack of time and because it needs a major rewrite. If you have any more comments, they would be greatly appreciated. –Joke 20:42, 3 November 2006 (UTC)[reply]
  • For a general audience, this article confuses the shit outta me. This is basically re-iterating what RJH said, but I'm not going to try to explain it, as my knowledge of the area is zero - and perhaps most pertinently, still is. The article doesn't grab me, as a layman, and I believe that is part of the criteria of being a GA - compelling prose. Simplification, for me, is vital. Seegoon 20:55, 2 November 2006 (UTC)[reply]
Yes, but simplification is difficult, because you have to tread the thin line between being too technical and stating things that are actually wrong. I'm looking for ways to improve the prose without compromising technical correctness – do you have any suggestions? –Joke 20:42, 3 November 2006 (UTC)[reply]
  • On the one hand, don't dumb this down too much; it's a subject that some readers just won't have the background to understand, and targeting them would be a mistake. On the other hand, it's a good article about an interesting subject and it currently sounds more like a review of the topic than an introduction to it. There are a lot of things that could use expansion or clarification without detracting from the main point of the article.
  • Right from the first sentence: "negative pressure vacuum energy density" - "negative pressure" and "vacuum energy density" are both understandable phrases, but one as a modifier of the other isn't clear to me. Are there some hyphens missing here?
  • The last sentence in the lead should specify that the inflaton is hypothetical.
  • I diagram would be nice to illustrate exponential expansion. In particular, I'm not sure how the distance between observers is expanding exponentially but the "rate of expansion" is described as constant - rate with respect to what? Also, the first paragraph of the overview says the Hubble parameter is constant, but the third paragraph says it changes "only very slowly".
    Yes, this is absolutely a problem. The idea is that two observers are moving apart an an accelerating rate because as they move further apart their relative velocity increases. However, at any point in time two points a fixed distance apart will seperate with the same velocity. It's very much like a bank account with a fixed interest rate. If you leave the interest in the account, then interest will compound, so the interest earned at the end of this month will be larger than the interest earned the month before. However, if you withdraw your interest, you will continue to receive the same interest payment month after month. I'm not really sure how best to clarify this in the article. It is a subtle point that can easily trip up the reader. –Joke 21:22, 5 November 2006 (UTC)[reply]
Ah, I understand now. I think incorporating your second sentence here into the article would help clarify things. A diagram or animation would be excellent if you could make one. Opabinia regalis 04:03, 7 November 2006 (UTC)[reply]
  • There could be more consistency in the description of the inflaton. There's mention of the inflaton's energy density, and also in the last paragraph of the overview, there's a reference to the decay of "inflaton particles", though the lead says "particle or field". Later there's "tiny quantum fluctuations in the inflaton". I think some of the reason this article is so dense is minor terminological variations.
    Yes, these are all technical distinctions that I will have to put some thought into clarifying. –Joke 21:22, 5 November 2006 (UTC)[reply]
  • I don't really like the question-mark sidebox. It has a weird 'textbook that's trying too hard' implication and the cutesy icon contrasts with the technical detail in the article.
    Neither do I. On the other hand, someone added it as part of a series about unsolved problems in physics, so I don't think I should remove it. I did move it to a more appropriate place. –Joke 21:22, 5 November 2006 (UTC)[reply]
  • Since the de Sitter space comes up so often in the article, a straightforward explanation (more complete than "metric expansion of space") would be useful. Maybe incorporate the diagram from that article.
    I agree. This, along with the idea of "exponential expansion" and "rate of expansion" need to be clarified. Perhaps I can make an animation that would help? Another thing that would be nice to explain graphically is the idea of "causally connected" region (also called a Hubble patch or Hubble volume). –Joke 21:22, 5 November 2006 (UTC)[reply]
Good idea. Opabinia regalis 04:03, 7 November 2006 (UTC)[reply]
  • Piles of multiple citations on the same sentence could be bundled into one footnote for improved readability.
    Is this preferred? It would certainly look better. Sometimes multiple citations always come together, but other times I cite the same paper a couple of times in different contexts – is there a simple solution? –Joke 21:22, 5 November 2006 (UTC)[reply]
It looks neater, but I don't know of a good way to do it when some of the references in the pileup are used more than once. You could use a "notes" system for the footnotes and list the specific references separately (I believe the military history articles do this a lot, but it's more useful when there are dozens of notes to different pages/sections in the same text.) I thought photon did a good job with the references, if you're looking for ideas. Opabinia regalis 04:03, 7 November 2006 (UTC)[reply]
  • Don't just put Cauchy data in parentheses - even a very brief explanation
  • Occasional odd word choise - "it is inconceivable that they have equilibrated"? Impossible sure, but inconceivable? "This problem is now even more acute" - in any other context this would be a ridiculous question, but what do you mean by "now"? At the present time in the universe, or is the problem more acute due to recent data?
  • Maybe a diagram of what a magnetic monopole would do in a magnetic field? ("Knot" isn't very descriptive.) This section is also a bit redundant, "copiously produced" is used twice, but this section doesn't explicitly state (as I think was said previously) how inflation resolves the monopole issue.
    Again, I'll give some thought to the best way of handling this. –Joke 21:22, 5 November 2006 (UTC)[reply]
  • "Future measurements of the cosmic microwave background will tell us more about inflation" - we/us is awkward writing, but the real problem here is the definitive statement about the future. A few sentences later there's an admission that the measurements might be overwhelmed by noise (though presumably more sensitive instruments would eventually be built).
  • I don't think, after reading the section, that I understand the fine-tuning problem. Is it just that the theory requires certain values to fall within rather narrow ranges? If so, it's more of a philosophical than a substantively scientific problem.
    It is, in some sense, philisophical problem, but one that very much concerns physicists. If you have to make a bunch of baroque adjustments to make your model work, it makes your model look implausible, particularly since particle physics has no reason to "want" to choose parameters that would allow inflation to occur (in fact, based on renormalization, it actively wants to choose parameters that make inflation impossible). If your mechanism is quite natural, then it has more explanatory power. So far, inflation is an incredibly simple idea, but there seems to be some key insight missing to see how this simple idea can arise naturally in particle physics. –Joke 21:22, 5 November 2006 (UTC)[reply]
Hmm, if it's not too lengthy, it might be worth going into more detail on the parameters that don't match and why. Opabinia regalis 04:03, 7 November 2006 (UTC)[reply]
  • Some of the very last sections on problems with the model are quite short, and could use either expansion or possibly merging.
    Yes, these sure need some work. I am still thinking about what to do with them. –Joke 21:22, 5 November 2006 (UTC)[reply]
  • Two-column format for the references would make the list easier to wade through.
    Done, but it doesn't show up as two columns in Safari for some reason. –Joke 21:22, 5 November 2006 (UTC)[reply]

Opabinia regalis 04:57, 4 November 2006 (UTC)[reply]

Thanks very much for your comments. They're very helpful! The ones I haven't responded to specifically I've just gone ahead and fixed. As you can see, some of the others seem to require a bit of thought. –Joke 21:22, 5 November 2006 (UTC)[reply]
Glad they were useful. I'd like to see more technical subjects get such thorough treatment. Opabinia regalis 04:03, 7 November 2006 (UTC)[reply]
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