Talk:Cosmological principle

message: :However, the European Space Agency has concluded, based on data from the Planck Mission showing hemispheric bias in 2 respects: one with respect to average temperature, the second with respect to larger variations in the degree of perturbations. i.e. temperature fluctuations, i.e. densities, that these anisotropies are, in fact, statistically significant and can no longer be ignored .[8] 
--Logical Gentleman (talk) 05:06, 30 July 2016 (UTC)
thread_title: Should this sentence be moved to Criticism?

message: What observations and axioms support this. Hackwrench 18:08, 1 November 2005 (UTC)
replies: text: My understanding, and perhaps someone can correct/expand as needed, is that the cosmological principle is itself taken as an axiom, but there is experimental evidence as well.  The best evidence for isotropy is the [cmb] which is isotropic to one part in 10,000.  I think for homogeneity, we can look at other galaxies/clusters and see that the physics there appears to be the same, and galaxies on average are the same. Threepounds 06:54, 26 November 2005 (UTC)
thread_title: Support for this

message: OK, I'll bite:  Under what logic does the Cosmological principle disprove the Anthropic principle?  Do sources exist for such claims? ----Jasonuhl 21:26, 13 October 2005 (UTC)
replies: text: I've removed this sentence.  The link between this and the Anthropic principle seems tenuous at best, and a claim that one disproves the other without any attempt at explanation adds nothing but confusion.  ----Jasonuhl 23:42, 21 February 2006 (UTC)
thread_title: This vs. Anthropic

message: I found a link in Timeline of cosmology that said Milne "formalized" this cosmological principle.  While I agree that he did, I don't think that the gist of his argument is well presented here.  For instance, Milne did not like the idea of a finite universe, nor did he like the idea of expanding space.
Milne says in Relativity, Gravitation, and World Structure "I am well aware that some mathematicians believe that such difficulties are at once swept awy if we use the concept of 'curved space.'  I have examined such attempts at explanation with the greatest care, and I have found that in all cases the proposed explanations break down at some point.  Two-dimensional analogies with hypothetical inhabitants on the surface of a sphere fail as soon as we recall that a survey of the astronomical universe is made by taking a photograph with a telescope and camera, and that, for a telescope of arbitrarily large light-gathering power, either the number of nebulae that can be counted is finite and therefore contains one faintest and so presumably most distant member, or it is infinite, in which case either the same nebula is photographed as an infinite number of separate spots or the total number of actual nebulae in existence is infinite.  The latter will be our eventual conclusion.  Here I am only concerned to argue that the phrase 'curvature of space' used in connexion with astronomical photographs merely involves a mist of mysticism.  Such photographs can always be interpreted in flat space, and then the assumption of a finite number of density-maxima inevitably leads to some kind of accessible edge of the universe."  
In this book, at least, Milne eventually concluded that the universe was not finite in terms of number of nebulae.  He did not conclude that space was curved. JDoolin 16:27, 27 August 2006 (UTC)
replies: text: I guess you mean Olbers' paradox.  You don't even need a large telescope because the number of galaxies increases with distance as fast as the light dims. Cosmo0 (talk) 22:56, 18 November 2007 (UTC)
thread_title:  Milne's Formalization of the Cosmological Principle 

message: Guys, this doesn't read at all well for someone not well versed in cosmology/physics. I imagine it is quite complex but is it possible to be expresed in more simple terms, or at least to explain the concept a little better? Some parts of it read almost like the article was created with the intention of being as obscure as possible. :-) Diliff   | (Talk)   (Contribs) 23:47, 21 August 2007 (UTC)
replies: text: Unforunately, Diliff, many articles are obscuranist like this.  I've added a line to the intro that, hopefully, makes things a little clearer.--Michael C. Price talk 18:27, 24 August 2007 (UTC)
replies: text: I agree (well, imbecile is taking it a bit far).  That's what the links to the articles on homogeneity and isotropy are for. Cosmo0 10:27, 23 September 2007 (UTC)
thread_title: In layman's terms

message: I don't get it. An isotropic fractal is an oxymoron then, or am I missing something? (it's not unlikely that I am) --Extremophile 19:25, 8 October 2007 (UTC)
replies: text: I'm no expert, but as I understand it, fractal means that something looks the same viewed at different scales - it doesn't say anything about how it appears when viewed from different directions, so I imagine an isotropic fractal is possible.  But a fractal that is smooth on large scales but not on small scales isn't, by definition. Cosmo0 21:18, 8 October 2007 (UTC)
thread_title:  "smooth (i.e.: not fractal)" 

message: There is a big hole in the sky! Although you can't see it with the naked eye it actually covers almost 3 degrees of the sky, and to put that into perspective the full Moon covers about half a degree!
Until recently no-one was sure how big or far away this void was but the latest calculations suggest it is 900 million light-years across and 8,000 million light-years away.
So can we still say the universe is homogeneous and isotropic? Is the Big bang theory still true?
24 November 2007 
IN AUGUST, radio astronomers announced that they had found an enormous hole in the universe. Nearly a billion light years across, the void lies in the constellation Eridanus and has far fewer stars, gas and galaxies than usual. It is bigger than anyone imagined possible and is beyond the present understanding of cosmology. What could cause such a gaping hole?
— Preceding unsigned comment added by 202.42.202.67 (talk) 06:39, 30 November 2007
:See here for the details of the story.  Structures on many scales have been discovered before (e.g. the Great Wall and the Sloan Great Wall); their existence doesn't invalidate the cosmological principle, which only requires the universe to be asymptotically homogeneous on very large scales.  This particular result is interesting because it is judged to be very unlikely in the standard cosmology (although it's difficult and dangerous to draw statistical inferences from a sample of one) and because it explains a previously unexplained feature in the cosmic microwave background. Cosmo0 (talk) 09:30, 30 November 2007 (UTC)
replies: text: I already did.Kmarinas86 (talk) 18:18, 5 December 2007 (UTC)

text: If it's asympotically homogeneous, all that would really mean is that if the hole is bigger, then it must be farther away. That's the same as a fractal.Kmarinas86 (talk) 18:23, 5 December 2007 (UTC)
thread_title:  Is the cosmological principle still true? 

message: :Peculiar velocities of clusters of galaxies can be measured by studying the fluctuations in the cosmic microwave background (CMB) generated by the scattering of the microwave photons by the hot X-ray emitting gas inside clusters. While for individual clusters such measurements result in large errors, a large statistical sample of clusters allows one to study cumulative quantities dominated by the overall bulk flow of the sample with the statistical errors integrating down. We present results from such a measurement using the largest all-sky X-ray cluster catalog combined to date and the 3-year WMAP CMB data. We find a strong and coherent bulk flow on scales out to at least > 300 h-1 Mpc, the limit of our catalog. This flow is difficult to explain by gravitational evolution within the framework of the concordance LCDM model and may be indicative of the tilt exerted across the entire current horizon by far-away pre-inflationary inhomogeneities. -- Kashlinsky, A., et al. (2008) "A measurement of large-scale peculiar velocities of clusters of galaxies: results and cosmological implications." Astrophysical Journal Letters (Science Daily, Space.com)
Spring Back (talk) 05:25, 24 September 2008 (UTC)
thread_title:  Looks like this one is on its way out 

message: The article should present how the principle emerged into cosmological physics, including opposition and criticism. __meco (talk) 10:58, 2 May 2010 (UTC)
thread_title:  History missing 

message: as described here
http://phys.org/news/2013-03-planck-reveals-universe.html
and discussed in 2008 here
http://blogs.discovermagazine.com/cosmicvariance/2008/07/17/a-new-cmb-anomaly/
basically the Planck data has confirmed the CMB anisotropy first seen in the WMAP data, but now in very fine detail.  There is an axis to the Universe, and in one direction the contrast of background temperature variations is higher than in the other direction.  It's very close to the ecliptic.
This data throws a wrench in the Cosmological principle.  the " uniformity of conclusions drawn from observation" is not the same, and we know it now.  Far in one direction the Universe is different than far in the other direction.
signed: jmdugan 66.109.99.16 (talk) 02:52, 25 March 2013 (UTC)
thread_title:  Needs updates from Planck Data 

message: The criticism seems a bit disingenuous since the cosmological principle is just an assumption not something that has ever been considered a fact. Is the opinions of Popper really relevant in an article about cosmology? 85.230.137.182 (talk) 16:32, 27 February 2014 (UTC)
replies: text: The entire study of the Big Bang was based on the assumption that the cosmological principle is true. If the cosmological principle had never been adopted, cosmology would be open to a greater diversity of explanations, and that would have been a great thing for science.siNkarma86—Expert Sectioneer of Wikipedia86 = 19+9+14 + karma = 19+9+14 + talk 03:47, 23 March 2014 (UTC)
replies: text: What Popper didn't seem to get (based on what this article is saying) is that the 'comsmological principle' isn't 'adopted' in a strict sense (it's not considered an undisputable fact or axiom) it's simply a commonly made assumption. No-one is being prevented from making different assumptions, cosmology is wide open to any explanation that agrees with experimental data. 85.230.137.182 (talk) 04:00, 31 March 2014 (UTC)
replies: text: "No-one is being prevented from making different assumptions, cosmology is wide open to any explanation that agrees with experimental data." In theory, what you say is correct, but in practice, it's not. The Big Bang theory is presented in almost a monopolistic way. For every cosmologist that rejects the cosmological principle there is perhaps 100 cosmologists whose work requires that it's true.siNkarma86—Expert Sectioneer of Wikipedia86 = 19+9+14 + karma = 19+9+14 + talk 22:22, 31 March 2014 (UTC)
replies: text: But that is true for every theory: they are derived from a bunch of assumptions. If experimental results agree with what the theory is predicting people tend to think the assumptions are correct, That doesn't mean the assumptions are dogma. The fact that people aren't as open-minded as we might like has more to do with human psychology. 85.230.137.182 (talk) 11:18, 2 April 2014 (UTC)
replies: text: True that. As per usual, Popper was scoring a cheap point that really amounted to nothing. The academic-sociological background to this is that many folk still smart from the fact that our modern knowledge of the universe shows us up as "nothing special" and hence this pretend-deep sort of criticism plays very well. Add to that the fact that academic philosophers not are not only ignorant of science these days, but also immensely proud of it, I predict that this kind of stupid will have legs and legs and legs. 2A01:CB0C:CD:D800:4DCF:8A84:9B04:97AC (talk) 12:33, 20 April 2019 (UTC)
thread_title:  Karl Popper Criticism 

message: There is some material in the lead that is both incorrect and out of place:
:"The second implicit qualification is that "looks the same" does not mean physical structures necessarily, but the effects of physical laws in observable phenomena."
This is followed by a discussion about upper limits on variations in the fine structure constant. This is just plain wrong. The cosmological principle certainly *does* refer to physical structure. What the author of this material is talking about is referred to as local position invariance (LPI), which is closely related to the equivalence principle. There is nothing inherently cosmological about LPI; it can be tested on both laboratory scales and cosmological scales. You can have LPI without the cosmological principle. I'm going to remove this incorrect material from the lead.--76.169.116.244 (talk) 23:29, 10 May 2015 (UTC)
thread_title: incorrect material in lead

message: The Universe is expanding at a superluminal rate if we compare afar regions. This superluminal mean distance will shrink to point expansion everywhere, the omni-singularity or Big Bang. Big Bang is default space at the ultimate apex of decohesion, thus there is no need to transform any quantum information so that will get homogeneous. There is only one form of "default space", and it always explodes Big Bang way. Homogeneity is derived via superlumic defaulting spacetime (apex of decohesion fills the gaps expansion created because absolute decohesion among the universal components is not allowed).  — Preceding unsigned comment added by 2A02:587:410E:8300:5C60:852E:2E99:DF75 (talk) 02:57, 24 February 2016 (UTC)
thread_title: De facto homogeneity

message: The article has quotes like:
: ... 'Viewed on a sufficiently large scale, the properties of the universe are the same for all observers.' ... the part of the universe which we can see is a fair sample ... the universe is knowable and is playing fair with scientists ... the same physical laws apply throughout ... the cosmological principle [means that] the universe looks the same whoever and wherever you are ... 
That sound like just homogeneity though, doesn't it.
The explanation of isotropy given is:
:Isotropy means that the same observational evidence is available by looking in any direction in the universe ("the same physical laws apply throughout").
How do we get there from 'the same physical laws apply throughout'? That's not the obvious reading of that phrase. --174.116.141.16 (talk) 12:23, 27 September 2016 (UTC)
replies: text: It's talking about the laws of physics, specifically conservation. Taking the entire universe as a control mass, no matter from where it's measured, it will have a constant value. Similarly, if the momentum of the universe as a whole (traveling through the void beyond), it would have the same vector if the same coordinate system is used. Which really would equal zero if one assumes there is no void and the universe is infite or non-expanding.
In other words, the flux or change in any of the universes physical properties is equal to zero.
TittilateMyTasteBuds (talk) 09:57, 15 February 2020 (UTC)
thread_title:  Homogeneity vs isotropy 

message: This is written under the criticism heading:
"In September 2016, however, studies of the expansion of the Universe that have used data taken by the Planck mission show it to be highly isotropical, reinforcing the cosmological principle."
However my understanding of the referenced paper was that if homogeneity is assumed, the we can say that the universe is very likley (121,000:1) expanding in an isotropic way.  — Preceding unsigned comment added by Dextrion (talk • contribs) 19:57, 30 October 2016 (UTC)
thread_title:  Understanding of a Cited Paper 

message: There are 2 paragraphs here about the results of the Planck mission that seem to contradict:
: ″Data from the Planck Mission shows hemispheric bias in 2 respects: one with respect to average temperature (i.e. temperature fluctuations), the second with respect to larger variations in the degree of perturbations (i.e. densities). Therefore the European Space Agency (the governing body of the Planck Mission) has concluded that these anisotropies are, in fact, statistically significant and can no longer be ignored.[12]"
: - Added 16 May 2015 (Note: You can find this using WikiBlame)
I read this as: The Planck data showed lots of anisotropies that cannot be ignored, suggesting a potential rethink regarding the Cosmological constant.
: "In September 2016, however, studies of the expansion of the Universe that have used data taken by the Planck mission show it to be highly isotropical, reinforcing the cosmological principle[17]"
: - Added 13 September 2016
I read this as: The Planck data showed lots of isotropy, so there's no need to rethink the Cosmological constant.
The second paragraph starts with "however", implying that it contradicts, but supersedes, the points presented just before it about large observed structures. Yet I don't understand how these things are related. If there are these large structures, how come the Planck mission didn't pick them up as well? Perhaps the Planck mission was measuring a different thing. In that case, why should the Planck data override the existence of these structures?
It sounds like the second sentence is just given as a convenient conclusion to tie up the loose ends introduced by the "Inconsistencies" section.
Perhaps the paragraphs can be brought together, using something like "The Planck data showed mostly a lot of uniformity, though it did find some discrepancies".
Spur (talk) 20:11, 24 May 2017 (UTC)
thread_title:  Contradiction on Planck data 

message: Please add information on these two papers (or their subjects along with information on related papers) to section "Inconsistencies":
* "Probing cosmic isotropy with a new X-ray galaxy cluster sample through the LX–T scaling relation"(press release) (news articles: ,,...)
* "Four direct measurements of the fine-structure constant 13 billion years ago"(press release) (news articles: ,,...)
Here is what I added to the article 2020 in science:
*Scientists publish a study which suggests that the Universe is no longer expanding at the same rate in all directions and that therefore the widely accepted isotropy hypothesis might be wrong. While previous studies already suggested this, the study is the first to examine galaxy clusters in X-rays and, according to Norbert Schartel, has a much greater significance. Beyond the potential cosmological implications, it shows that studies which assume perfect isotropy in the properties of galaxy clusters and their scaling relations can produce strongly biased results.
*Scientists report verifying measurements 2011-2014 of what seem to be discrepancies in four measurements of the fine-structure constant, a basic physical constant used to measure electromagnetism between charged particles, which indicates that there might be directionality with varying natural constants in the Universe which would have implications for theories on the emergence of habitability of the Universe and be at odds with the widely accepted theory of constant natural laws and the standard model of cosmology which is based on an isotropic Universe.
Also see Fine-structure constant#Is the fine-structure constant actually constant?
--Prototyperspective (talk) 14:24, 23 May 2020 (UTC)
thread_title:  Add to section "Inconsistencies": indications of spatial variations of the fine-structure constant and the rate of the expansion of the Universe 

message: In the section above, Looks like this one is on its way out, the quoted article uses the abbreviation CMB, but it is in parentheses and is immediately preceded by the phrase it abbreviates. Our encyclopedia article omits what seems to me to be a common courtesy, for the first use of an abbreviation to be in parentheses, immediately following the phrase it abbreviates. Would such a well-defined appearance of the abbreviation, rather than just throwing the abbreviation into the text as in our encyclopedia article, be a violation of some Wikipedia stylistic tic with which I am unfamiliar? 
As a convenience to you, I quote the referenced section, where the preferred usage (at any rate, my preferred usage) appears in a quotation from a journal article:
:...studying the fluctuations in the cosmic microwave background (CMB) generated by the scattering Larry Koenigsberg (talk) 03:47, 22 December 2021 (UTC)
thread_title:  CMB 

message: There is a significant problem in the phrasing of some of these claims, and the choice of references. The reality is that these claims are all controversial, but many of them are just listed as factual.  Other sections use rather partial language instead of a neutral tone, for example:
"The European Space Agency (the governing body of the Planck Mission) has concluded that these anisotropies are, in fact, statistically significant and can no longer be ignored."
The source says nothing about "ignored", this is very unscientific language. The sources cited in the CMB dipole section are particularly biased, the article doesn't weight this discussion at all or even hint that these claims may be controversial. There are no papers cited on the other side of the argument, several studies have been able to recover the amplitude of the kinematic dipole. This section is entirely one sided, but it does not reflect the state of the field today. The other issue is that all of these references are primary sources. LazyAstronomer (talk) LazyAstronomer (talk) 10:06, 27 July 2023 (UTC)
thread_title:  NPOV problems in observational sections 

message: The section "Violations of homogeneity" includes a list of "violations" but such primary evidence is not encyclopedic. The list is de facto synthetic original research WP:SYNTH. The section should have secondary references reviewing and analyzing the individual claims. Johnjbarton (talk) 17:42, 15 January 2024 (UTC)
thread_title:  "Violations of homogeneity"