Talk:Cosmic variance

message: It seems to me that there are three distinct meanings of cosmic variance in widespread use, but before modifying the article to reflect this, I'd like to discuss it here to see if others agree.
* First, many astronomers (incorrectly, I believe) use the term to mean sample variance - i.e. the poissonian shot noise. So, one will read statements that source counts from different surveys differ because of cosmic variance (meaning sample variance).
* Second, some cosmologists use it to mean that we can only observe one realization of all the possible universes. For example, we can only observe one CMB, so the measured positions of the peaks in the WMAP spectrum are limited by the fact that WMAP can only see the observable Universe. The Universe next door might have the peaks in slightly different places, while still being consistent with the same physical laws, inflation, etc.
* Third, (and probably the most widespread use), is to use it to mean that measurements are affected by large-scale structure, so a measurement in any region of space may differ from a a measurement in a different region of space by an amount greater than the sample variance. 
I believe the current article confuses the second and third meanings, and it would be helpful to distinguish between them. Anybody disagree?
RayNorris (talk) 09:17, 27 February 2012 (UTC)
thread_title: Define three meanings of Cosmic Variance?

message: The speed with which other people read a new wikipedia page and make corrections in a way which shows they appreciate the work is truly amazing. It really makes writing something satisfying in a way unlike any other pedagogical writing, where you only hope that others will eventually find your effort useful. Thanks to adrian for the typo correction :). Boud 14:01 2 Jun 2003 (UTC)
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My problem is that it might only take me a couple of minutes to proofread but will now take several days to understand (or try to)!! :^) Adrian
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 :) Boud 14:14 2 Jun 2003 (UTC)
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Hi, I was unhappy with this statement "Since cosmic variance is an attempt to make a scientific statement about an unrepeatable scientific experiment (over the lifetime of any 21st century scientist remaining on Earth), this lies at the borderline between physcial cosmology and philosophical cosmology." and so I removed it. What lies at the borderline? Cosmic variance is a notion that cosmologists have to deal with in understanding how to deal with measurements that have a very small statistical sample, but it doesn't mean that these measurements are philosophy. The real philisophical problem cosmologists face is dealing with the anthropic principle. --Joke137 00:52, 12 Mar 2005 (UTC)
thread_title: Older Comments

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