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Topic: Cosmic variance


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  Cosmic variance - Wikipedia, the free encyclopedia
Cosmic variance is the idea that we are only able to observe one universe, so it is difficult to make statistical statements about cosmology on the scale of the entire universe.
This variance is called the cosmic variance and is separate from other sources of experimental error: a very accurate measurement of only one value drawn from a distribution still leaves considerable uncertainty about the underlying model.
Cosmic variance is also the name of a collaborative weblog discussing astrophysics and fundamental physics, written by JoAnne Hewett, Clifford Johnson, Mark Trodden, Sean Carroll and Risa Wechsler.
en.wikipedia.org /wiki/Cosmic_variance   (636 words)

  
 Cosmic variance -- Facts, Info, and Encyclopedia article   (Site not responding. Last check: 2007-10-09)
Cosmic variance is the idea that we are only able to observe one universe, so it is difficult to make statistical statements about (The branch of astrophysics that studies the origin and evolution and structure of the universe) cosmology on the scale of the entire universe.
The standard ((cosmology) the cosmic explosion that is hypothesized to have marked the origin of the universe) big bang model is usually supplemented with (additional info and facts about cosmic inflation) cosmic inflation.
This variance is called the cosmic variance and is separate from other sources of experimental error: a very accurate measurement of only one value drawn from a (The act of distributing or spreading or apportioning) distribution still leaves considerable uncertainty about the underlying model.
www.absoluteastronomy.com /encyclopedia/c/co/cosmic_variance.htm   (517 words)

  
 Munch   (Site not responding. Last check: 2007-10-09)
As expected, the variance of the measured one-dimensional mass power spectrum is inversely proportional to the number of lines of sight that are sampled from each random field.
From the covariance, one will be able to determine the cosmic variance in the measured one-dimensional mass power spectrum as well as to estimate how many lines of sight are needed to achieve a target precision.
We vary 10 cosmological parameters (including two related to the trans-Planckian terms) and show that the amplitude of the tensor perturbations is directly correlated with the detectability of any trans-Planckian modulation.
home.fnal.gov /~bertone/DM/JC010305.html   (1707 words)

  
 Results for Variance   (Site not responding. Last check: 2007-10-09)
The variance is therefore equal to the second central moment mu_2.
The variance of a random variable is the square of its standard deviation.
The variance is a measure of the spread of data.
www.wikimoz.org /buscar/search/Variance   (224 words)

  
 Cosmic Shear   (Site not responding. Last check: 2007-10-09)
Thus a measurement of cosmic shear bridges the gap between theory, which is primarily concerned with dark matter, and observation, which generally probes only luminous matter.
A further issue arises from sample (or 'cosmic') variance, the impact of which can be limited by using numerous independent sightlines to complement panoramic imaging of a few selected areas.
A measurement of this quantity from cosmic shear is cosmologically valuable, as it represents a direct measure of the amplitude of mass fluctuations.
www.ing.iac.es:8080 /PR/SH/SH2003/shear.html   (666 words)

  
 Cross Correlation
The inherent statistical errors forced upon the ISW effect by cosmic variance at large angular scales severely limits the ability to extract information from it regarding the dark energy.
A seemingly promising method of pinning down the ISW effect despite the problem of cosmic variance is through the use of CMB polarization towards galaxy clusters.
As we have discussed at length, the limitations placed on observation of the ISW effect by cosmic variance are formidable.
cfcp.uchicago.edu /~davemilr/ISW/Cross_cor.htm   (1340 words)

  
 Dark Energy...
Explained extremely well by Kamionkowski and Loeb (1997) cosmic variance derives from the statistical nature of the effects one is trying to observe as they measure the CMB.
In fact, for the lowest multipoles, the scale for which the ISW effect becomes the most important, the error associated with cosmic variance is the limiting factor in extracting information from the power spectrum of anisotropy.
Despite this limitation, there are methods of subverting cosmic variance to which we will return in the next section.
cfcp.uchicago.edu /~davemilr/ISW/dark_energy.htm   (896 words)

  
 Kaiser et al., Large-Scale Cosmic Shear Measurements   (Site not responding. Last check: 2007-10-09)
We present estimates of the gravitational lensing shear variance obtained from images taken at the CFHT using the UH8K CCD mosaic camera.
Six fields were observed for a total of 1 hour each in V and I, resulting in catalogs containing approximately 20,000 galaxies per field, with properly calibrated and optimally weighted shear estimates.
Our most reliable estimator for cosmic shear is provided by the cross-correlation of the shear measured in the two passbands.
ifa.hawaii.edu /publications/preprints/00preprints/Kaiser_00-10.html   (179 words)

  
 RealClimate » Recent Warming But No Trend in Galactic Cosmic Rays
Globally, the variation of cloud cover during a sun cycle is around 2%, which can have a substantial influence on global temperatures.
Only if the cloud change is directly forced by some cosmic ray induced process would this be an extra forcing, however, the physical evidence so far of an actual mechanism for this is underwhelming.
And the highest variation of solar is in the stratosphere vs. GHGs in the lower troposphere.
www.realclimate.org /index.php?p=42   (2606 words)

  
 [140.06] Approaching the Reionization: Cosmic Variance in the Transmission of the IGM at z $\sim$ 5 -- 6   (Site not responding. Last check: 2007-10-09)
[140.06] Approaching the Reionization: Cosmic Variance in the Transmission of the IGM at z ~ 5 -- 6
The spectra show a considerable variation in the optical depth as a function of redshift at z > 5.
A clumpy and gradual transition to a fully reionized IGM is generically expected in models of early structure formation, as a consequence of the biasing and a gradual appearance and early evolution of the first luminous sources.
www.aas.org /publications/baas/v34n4/aas201/865.htm   (194 words)

  
 - Cosmic Log - MSNBC.com
Even people who have lost their hearing can experience the extreme form of earworms, known as "musical hallucinosis." That's because the earworms don't originate in your ears, but in the higher-level areas of your auditory cortex.
Those meddlesome melodies are known as sticky songs, or "earworms," and over the past couple of years, hundreds of Cosmic Log readers have sent in contributions to the earworm list.
At various points in the soundtrack, the music went silent for 3 to 5 seconds, and researchers watched how the brain responded.
www.msnbc.msn.com /id/7119148   (3451 words)

  
 Cosmic Violence | Cosmic Variance
I sort of get into the bad habit of thinking of those 13.5 billion years as astrophysics (which is not to devalue it in any way), and push the term “cosmology”; back earlier and earlier in the universe’s life… I shouldn’t.
Cosmic acceleration is a cosmological phenomenon of central importance, tied to fundamental physics in a deep way and effective at (and discovered by looking at objects that are at) redshifts less than 2.
I’d have thought that anything distant is useful because it helps fill in the gaps in structure evolution between decoupling (where the state of the universe is imprinted in the CMB) and the structure that we see today.
cosmicvariance.com /2005/09/12/cosmic-violence   (2073 words)

  
 Too many coincidences?
This can be achieved by means of complimentary data like cosmic shear from weak lensing [5] and cross-correlations with the polarization spectra [6].
Although these cosmic coincidences associated with the two currently observed phenomena namely, DE domination and CMB power suppression at horizon sized wavelengths, are dominantly displayed at low energies, for the reasons mentioned above it is reasonable to expect that they may originate from processes occurring in the very early universe.
String theory and quantum gravity are possible candidates of the unknown physics of the early universe.
www.phys.lsu.edu /mog/mog23/node7.html   (788 words)

  
 [No title]   (Site not responding. Last check: 2007-10-09)
Cosmic microwave background (CMB) anisotropies probe the primordial density field at the edge of the observable Universe.
There is a limiting precision (``cosmic variance'') with which anisotropies can determine the amplitude of primordial mass fluctuations.
In particular, the polarization of CMB photons scattered by the electron gas in a cluster of galaxies provides a measurement of the CMB quadrupole moment seen by the cluster.
cfa-www.harvard.edu /ep/preprint/julaug97/4578.html   (138 words)

  
 [26.10] Cosmic Variance in Chandra Fields: The First SEXSI Results   (Site not responding. Last check: 2007-10-09)
Using results from the thirteen moderate to deep fields included to date in our SEXSI program along with the handful of other published fields, we explore variations in source number counts as well as the magnitude distributions of optical counterparts.
One of the more striking anomalies is found for a field selected because it hosted a bent-double radio source at z=0.65; this field contains more than three times the number of X-ray sources within 8' of the target than expected from the mean source surface density at this flux limit.
Quantitative measures of cosmic variance will be presented, and their implications for the use of faint X-ray sources and the X-ray Background in constraining large-scale structure at intermediate and high redshifts will be discussed.
www.aas.org /publications/baas/v32n3/head2000/445.htm   (269 words)

  
 Cosmic Variance
It would be rather silly to waste money now on big money projects like LHC, or on hopeless crackpots like super string research, or the nonsense global warming theory (if you do not have any more oil to burn, it is unlikely you can increase the atmosphere CO2 much either!)
This blog is created in response to the fact that a bunch of so called experts are really not interested in pursuing scientific truth.
This is a paragraph of text that could go in the sidebar.
cosmicvariance.blogspot.com   (311 words)

  
 Cosmic Variance
Other studies, it should be mentioned, claim that α actually does not vary at all, and place an upper limit.
Lawrence is an extremely well regarded member of the physics community, whose research, popular writings and remarkable efforts to defend science against pseudoscience and political distortion have earned the respect of all of us.
I also understand that they may be entranced with various aspects of the ideas that have been developed.
cosmicvariance.com   (7760 words)

  
 Not Even Wrong » Blog Archive » Cosmic Hype   (Site not responding. Last check: 2007-10-09)
Over at Cosmic Variance, Clifford Johnson has a posting about an article in the Guardian about wacky science stories in the media by Ben Goldacre, who runs the Bad Science weblog devoted to this topic.
Progress was possible because the “obscure work”, for example Yang-Mills fields, were able to explain some aspect of the flood of experimental HEP data that the popular theories of the day could not.
One thing they don’t account for is the much more eglatarian basis of US education compared to many other countries, which essentially doom the majority of their population to trade labor at an early age.
www.math.columbia.edu /~woit/wordpress?p=252   (2565 words)

  
 'Cosmic' blog impacts media, perceptions of science
Since joining four other physicists and astrophysicists from different universities as a contributor to the group blog Cosmic Variance, Johnson has discovered many advantages of blogging.
His posts have received comments from various members of the media, including Annabelle Gurwitch from National Public Radio and K.C. Cole, a science writer and columnist for the Los Angeles Times who is now joining the USC Annenberg School for Communication as a visiting professor of journalism.
The posts on Cosmic Variance are often observations and commentary about everyday things, from shopping in Hollywood to the political news of the day.
www.ojr.org /ojr/blog/Sites/864   (366 words)

  
 Daily 3469   (Site not responding. Last check: 2007-10-09)
This wide field survey is essential to understand the interplay between Large Scale Structure {LSS} evolution and the formation of galaxies, dark matter and AGNs and is the one region of parameter space completely unexplored at present by HST.
The MDS image parameters, in particular the galaxy orientations and axis ratios, are such that any residual corrections due to errors in the PSF or jitter are much smaller than the measured signal.
We have also developed a statistical analysis procedure to derive unbiased estimates of cosmic shear from a large number of fields, each of which has a very small number of galaxies.
www.science-one.com /new-4548358-4257.html   (2820 words)

  
 Intermediate FAQs
In the standard theoretical pictures which people have for the CMB fluctuations, the large-angle variations are caused by gravitational red-shifts and blue-shifts from blobs sitting on the last-scattering surface.
An overdensity (ie a region with more matter than the average) causes a photon to lose energy on its way out: we say there is a "gravitational redshift" as the photon "climbs out of the potential well".
So if you're trying to determine the angular power spectrum, then at large angles you tend to be dominated by "Cosmic Variance", while at small angles you're dominated by instrumental noise.
www.astro.ubc.ca /people/scott/faq_intermediate.html   (1089 words)

  
 Majikthise : Cosmic Variance launched
Cosmic Variance is a group blog by five people who, coincidentally or not, all happen to be physicists and astrophysicists: Mark Trodden, Risa Wechsler, Sean Carroll, Clifford Johnson, and JoAnne Hewett.
Our day (and night) jobs notwithstanding, the blog is about whatever we find interesting — science, to be sure, but also arts, politics, culture, technology, academia, and miscellaneous trivia.
Thought I'd join the crowd and help announce the launch today of a new academic blog called Cosmic Variance, written by a group of five physicists.
majikthise.typepad.com /majikthise_/2005/07/cosmic_variance.html   (333 words)

  
 Technorati Tag: cosmic
Pathwork Lecture 149: Cosmic Pull Toward Union * Frustration There is a great pull in the manifest universe in which you live.
[klammer auf] She's just a cosmic girl from another galaxy My heart's at zero gravity She's from a cosmic world Putting me in ecstasy Transmitting on...
We were at Cosmic Cosmic Cantina, where they serve...
www.technorati.com /tag/cosmic   (621 words)

  
 CosmoCoffee :: View topic - [astro-ph/0504290] An indirect limit on the amplitude of primordial Gravitational Wave ...   (Site not responding. Last check: 2007-10-09)
While large scale cosmic microwave background (CMB) anisotropies involve a combination of the scalar and tensor fluctuations, the scalar amplitude can be independently determined through the CMB-galaxy cross-correlation.
Using recently measured cross-correlation amplitudes, arising from the cross-correlation between galaxies and the Integrated Sachs Wolfe effect in CMB anisotropies, we obtain a constraint $r < 0.5$ at 68 % confidence level on the tensor-to-scalar fluctuation amplitude ratio.
Our biggest concern however is not cosmic variance but determination of bias and systematics.
cosmocoffee.info /viewtopic.php?t=229   (1128 words)

  
 Christina's LIS Rant   (Site not responding. Last check: 2007-10-09)
One comment received was that all the variables might be useful in some study.
System variables were not rated as highly as the cognitive and affective user variables, in general.
Dichotomy: the most important variables were user-centric, but there was the most disagreement on how to measure them, or even statements that they can’t be measured.
christinaslibraryrant.blogspot.com   (4486 words)

  
 Orange Quark
My esteemed new co-contributors are; Sean Carroll (of the widely-read Preposterous Universe) - another particle cosmologist; Risa Wechsler, who is a cosmologist from the University of Chicago, Clifford Johnson - a string theorist from the University of Southern California, and JoAnne Hewett - a particle phenomenologist from the Stanford Linear Accelerator Center.
However, realistically, I can imagine that time constraints will mean that pretty soon I will focus exclusively on Cosmic Variance.
I'd like to hear what he has to say about the London attacks, on people using public transportation to get to their varied jobs around the city.
orangequark.blogspot.com   (2489 words)

  
 Mormon Philosophy & Theology
After various discussions about allowing people to nominate other people's writings, we've come up with a public nomination system.
May 09, 2005 05:23 PM Just a brief note that part of the reason I found Brandon's post so interesting was how it paralleled the two aspects of philosophy one finds in Kant.
Kant divided it into the Schulbegriff and the Weltbegriff, or the scholastic and the cosmic.
www.libertypages.com /clark/10503.html   (2721 words)

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