Talk:Hubble's law/Archive 1

Question
I think the first sentence is incorrect; Hubble's law is an approximately linear relationship between two observational quantities, the redshift and brightness of distant galaxies, therefore i suggest replacing the word "distance" with "brightness" 136.159.208.33 (talk) 21:50, 15 February 2008 (UTC)

--Avramov 08:36, 4 November 2005 (UTC) Isak Avramov avramov@ipc.bas.bg


 * The fundamental relationship is between redshift and distance. The fact that brightness (generally) decreases as objects get further away depends on the objects initially having the same intrinsit brightness. Kiyo.masui (talk) 20:59, 4 December 2009 (UTC)

My question concerns the following news: "Astronomers have detected a faint glow from the first stars to form in the Universe, Nature journal reports. This earliest group of stars, called Population III, probably formed from primordial gas less than 200 million years after the Big Bang."

If we see now light emitted from a star 200 million years after the Big Bang, the light should have traveled about 13 billion years. This means that by the emitting time the radius of the universe cannot be less 13 billion light years! This is possible only if the expansion rate of the Universe exceeded the speed of light on average 65 times. How is this possible!


 * The stars were outside of our particle horizon before 200 million years ago. Cosmic inflation accounts for the enormous size of the total universe. Joshuaschroeder 08:52, 4 November 2005 (UTC)
 * I'm troubled by this answer. I think the time taken for the light to get back to us is ignored, bear in mind that a clock carried on the back of a photon shows no time passing. These Population III stars are travelling at some 0.9c, so will have travelled another 10bn light years maybe since we see them. I don't think you can add the distances and say the Universe is 'now' in some meaningful sense say 23bn light years in radius. I'm not sure that inflation, strictly so called, is involved here - it terminated after an initial phase well before any star formation. Open to correction, I think we need a professional cosmologist to make sense of this paradox. Brian, 22:49, 23 Feb 2012  — Preceding unsigned comment added by 86.141.172.87 (talk)

H(t)
Hubble's constant does indeed decrease over time, even in the presence of a non-zero cosmological constant. The cosmological constant causes Hubble's constant to decrease slower (resulting in an accelerating expansion), but a constant or even increasing Hubble's constant is not contained in any of the current models, and would have extremely strange consequences. --AxelBoldt
 * The Hubble parameter can remain constant, for $$q=-1$$, or increase over time, for $$q<-1$$. ~ Tsumetai 20:51, 14 December 2005 (UTC)

You are right, sorry. I forgot that hubble parameter is (da/dt)/a, not just da/dt.--AN

Pardon me, I'm quite confused by this, how can a "constant" change over time? does everyone else not realize how crazy that sounds? (ie. doublespeak)

66.222.226.248 (talk) 18:37, 20 February 2008 (UTC)
 * It's not a constant, this is just nomenclature. We call it a constant because it doesn't change on time scales relevant to humansKiyo.masui (talk) 20:59, 4 December 2009 (UTC)

I removed this:
 * although some cosmologists have wondered if the expansion of universe is uniform throughout the whole universe. These speculations have been driven in part by the observation that the expansion of the universe seems to be accelerating at least in our section of it.

Have people seriously conjectured that the universe is not homogeneous? Why would the acceleration lead to that conjecture? AxelBoldt

the accelerating universe and cosmological constant seem to cover this. -- April
 * My understanding is that on large scales, it's been observed to be remarkably homogeneous. (I'm thinking of the cosmic microwave background here.)  Fluctuations in the microwave backgrounds are on scales of thousandths (or less!) of the mean value.  The distribution of matter is of course not homogenous, but I can't say I've ever run across serious suggestions that the expansion of spacetime might be unequally distributed.  Comments on


 * I might add that the whole apparatus of cosmology now rest on the cosmological principle: the statement (assumed true for the construction of the theory) that the Universe is isotropic and (at least at large scales), homogeneous. AstroNomer


 * But this is almost a universal assumption by science, isn't it? That there are no special points in spacetime. Physicists assume that an experiment done on Friday in Berkeley will come out the same if done on Monday in Munich; biologists assume that the laws of chemistry were valid millions of year ago; astronomers assume that the nuclear reactions in distant stars are the same as the ones observed on Earth etc. Of course, this is not just an arbitrary assumption, because many things make eminent sense when interpreted with this assumption. AxelBoldt

NO, AxelBoldt it is not. Observations are extrapolated to situations where we are unable to "test" directly. Without getting sucked into the horrors of philosophy: we OBSERVE that chemistry, biology, mechanics, electronics, etc. work identically at the Equator or North Pole and on Mars or orbiting Saturn. The chemistry and physics in the solar system is consistent with the Laws. In Cosmology, the assumption is used to confirm/justify models. Occam's razor (yes an assumption/paradigm of all science ) requires us to assume things are the same unless there is reason to believe they aren't. There are plenty of reasons to believe that 13.7 billion years ago the Universe was substantially different from today. We KNOW it was. There is no argument there, right? So, the problem is that the results are strongly dependent on the assumption of isotropy (which is arguably NOT what the observations show - matter is not homogeneously distributed, microwave BG HAS part per thousandths inhomogeneities, spacetime is not flat, gravitational lensing is common, dark matter is concentrated,density was higher, ...) while in most physical science the fact that a Law IS a Law is due to the observation of its (parochial) universality. The conclusion of universiality for most of science is turned on its head and used to justify the other conclusions in cosmology. I am not claiming that the assumption should not be made; I am claiming that because the results are highly dependent on that assumption, it is just that more difficult to "trust" those results. I see no better alternative, however. 69.40.254.33 (talk) 13:16, 30 May 2009 (UTC)


 * Certainly on the scale we have been able to observe well to date. It is my understanding that the view the universe has homogenous physical laws (universal laws) has essentially been postulated but never proven.  Some would say no violation of homogeneous unviversal distribution of physical laws (spellling?) such as those in thermodynamics has ever been observed.   Black holes lead to all sorts of speculation because while we can predict their behavior and appearance from the outside and test against observation we have extremely limited information coming back out with which to conduct scientific  inquiry.


 * For conjecture Vernor Vinge is your man. Also, David Brin has some pretty wild thoughts published as science fiction, he is a professional P'hd physicist.  Likewise Poul Anderson and others.  Plenty of conjecture but no evidence.  user:mirwin

When objects reaches a speed near the speed of light, due to the hubble effect, relativly to an observer, wouldnt they appear to smother out into some weird form of "inverse event horrizon" or something??? :b! (that would in turn lead to a conclusion that there is a end of the universe, that it is not infinitly large.. That if something reach too far away from you, it would end up at the *edge* of the universe, where it flattens out and bla bla bla.. //Noone

I have a question concerning my homework? The first sentence in the paragraph is not clear to me what does it mean??? —Preceding unsigned comment added by 72.21.233.211 (talk) 01:00, 28 May 2009 (UTC)

Hubbles Constant
Hubbles Law gave us the picture of an expanding universe. The expanding universe is the result of the big bang. Everything in the universe is expanding away fom this source. Simple calculation can esimate the minimum velocity of expnsion at 0.5c. Because of the expansion from a central point, there can be no constant that will identify the rate of expansion for all conditions. Assuming the minimum velocity away from the big bang is 0.5c, the velocity of recession of two groups of galaxies would be:

Vr=Vo+[Vx(Cos Angle)]

Where: Vr= Velocity of recession for galaxies o and x, Vo is the velocity of galaxy o from the big bang, Vx is the velocity of galaxy x from the big bang and Cos Angle is the angle the light from galaxy x intersects galaxy o.

This formula can be simplified to:

Vr=0.5c(1+Cos Angle).

J. Chwastyk@comcast.net


 * There is no central point in the Big Bang model. There is no "source." It is not an explosion, as such. Chris Mid 23:59, 22 Jun 2005 (UTC)
 * I don't think this is right. The Big Bang originated from a cosmic singularity - a central point and an explosion par excellence, though unlike any other. But that central point cannot be located with reference to the space time we now inhabit or our coordinates in it, or anyone else's. It was somewhere and it was everywhere. Brian, 21:52, 23 Feb 2012  — Preceding unsigned comment added by 86.141.172.87 (talk)

Please elaborate
"Furthermore, if one takes Hubble's original observations and then use the most accurate distances and velocities currently known, one ends up with a random scatter plot with no discernable relationship between redshift and distance. Nevertheless the relationship was confirmed by observations after Hubble."


 * Confirmed by what? Please elaborate. - Omegatron 21:15, Aug 4, 2004 (UTC)

Recent value for Hubble's constant
http://wmap.gsfc.nasa.gov/m_uni/uni_101expand.html

" The initial results show the Hubble Constant to be 71 (km/sec)/Mpc, +0.04/-0.03. (...) Last updated: Thursday, 12-15-2005"

It should be updated, shouldn't it? (sorry for having inserted the message here; move it to the bottom if you know how :) )

Hubble's parameter vs. Hubble's constant
IMHO what this article is talking about, is "Hubble's parameter". "Hubble's constant" is the dimensionless parameter $$h = \sqrt{2(\omega_b + \omega_{cdm})/(\Omega_t+\Omega_d)}$$. OTOH it's rather late local time, and I may be confused. --Pjacobi 00:32, 2005 Jan 24 (UTC)

Correction: Red sunset is not a redshift.
Deleted: "this is also why the sun appears redder at sunset than when high in the sky)"

This isn't true. Red sunset is due to preferential scattering of blue light off oxygen, nitrogen, and dust. Known as Rayleigh scattering. (More correctly Tyndall effect, John Tyndall, 1859)

Reference at Physics FAQ Chris Mid 23:07, 22 Jun 2005 (UTC)

needs improving
I am improving the article. Joshuaschroeder 30 June 2005 13:49 (UTC)

I have finished with my overhaul for now, but may return later with more information. The history section, in particular, I think needs improving as does the measuremet section. I have tried to be very pedantic about the distinction between the Hubble constant, Hubble parameter, etc. as well as tying this altogether with general relativity considerations. I think with a little work we can make this a featured article.

It would be good to put in some pictures. One obvious one would be the famous picture of Einstein at Mount Wilson. Hubble's journals are publicly available, but I don't have access right now. If someone could include that first graph that he made of the hubble law, that would be great! Other images would be appreciated too. Also we need some references. The Big Bang article has some that are probably transferrable.

Joshuaschroeder 30 June 2005 17:19 (UTC)

Question
How can i use V=Hr to prove the earth is not at the centre of the universe?


 * You can't. However, it does show that, if the Earth is at the centre of the Universe, all distant galaxies are receeding from it at a velocity proportional to their distance from it. According to Occam's razor, if one theory says that the expansion of the Universe is uniform throughout whereas the other says that it isn't then, all other things being equal, the former is preferable since the latter introduces the notion of acceleration varying with position without giving a reason for it. As far as we can tell, the Universe seems to be more or less uniform on very large scales, whereas an Earth-centred Universe contradicts that notion.


 * For that matter, Occam's razor would seem to preclude the possibility of an Earth-centred Universe by asking the question: "Why should it be?"


 * Sorry if I've gone into rather too much detail or overcomplicated things. Robin S 01:06, 12 March 2007 (UTC)

Hubble's interpretation is missing in Interpretation of Hubble's law!
Amazing but true (or I'm struck with blindness of course!). Please whoever has the sources about this at hand, add it to the article (I don't have them available at the moment and I'm too busy elsewhere). Harald88 19:49, 3 May 2006 (UTC)


 * We have to be careful with how we do this. In fact, there is a level of dispute as to what Hubble's interpretations of his law actually were. As an observationalist and not a particularly gifted mathematician or physicist, Hubble was not overly concerned with the physical models that described his law. In particular, Hubble welcomed with open arms the visit by Einstein. This visit was heralded by the press at the time as an extraordinary meeting of the minds that indicated the peculiar intersections that were occuring in the physical sciences. At no time during that encounter were there any indications that Hubble disagreed with the implications that his law was part-and-parcel to FLRW formulations. --ScienceApologist 20:03, 3 May 2006 (UTC)


 * I think to have read a publication of his - that should do it (but I don't have it ready, even I'm not sure to have it - I'll check). Apart of that, I read "[...], Hubble was not overly concerned with the physical models that described his law" as the personal and unsupported opinion of a fellow editor (in lawyer terms: not to be taken into account for the article's contents).
 * Anyway, perhaps you mean to say that he didn't publish a lot about his interpretation, and that may be right; or that his opinion doesn't need a long elaboration, and that also looks correct to me. It's just the complete absence that is inappropriate. Harald88 21:37, 4 May 2006 (UTC)


 * Hubble wasn't clear about his "interpretation" one way or the other. In any case, his support of general relativity and FLRW cosmology seems to be fairly straightforward to demonstrate. --ScienceApologist 21:50, 4 May 2006 (UTC)

I've read Hubbles book, "The realm of the Nebulae" and it doesn't support the expanding universe theory. In the final chapters he presents alternative suggestions for the brightness-redshift relation. 66.222.226.248 (talk) 18:45, 20 February 2008 (UTC)

Another Question(s)
OK - I understand the concept of the doppler effect on light and how the redshifts are interpreted to mean that the galaxies are moving farther away from eachother...

But what I don't understand is how anyone can know that "the universe" or "space" itself is expanding as opposed to simply matter moving through space. In other words, what if 15 billion (or how ever many) years ago, instead of there being a "big bang" there was simply a bang within a larger existing universe. And ever since then, all this stuff has been expanding out into a really gigantic void which it still hasn't finished crossing after all these years?

What makes physicists so sure that "space" and time and everything began then? How do they know that what we observe as "the universe" isn't simply a small part of something much larger? For all we know, couldn't all the known universe simply exist as part of a subatomic particle in some larger "universe?"

Anyone?...

Think about this: If we lived close to a supermassive black hole, wouldn't it appear as if the universe was expanding slower? Is it possible that the redshift in hubble's law is really due to gravitational redshift, and that what we think is the rate of expansion of the universe actually reflects our local position within the gravitational potential of the universe? 66.222.226.248 (talk) 18:52, 20 February 2008 (UTC)


 * The only way to account for the Doppler shift is either that the Earth is the centre of the expanding universe, or that everything is expanding from everything else. We find no evidence that the Earth is "special", and so this assumption is one of the bases of physics (cosmological principal).  Of course, there could be nothing outside the observable Universe (a "void"), but we see no sign of it - we can see stuff as far away as we can look (see WMAP).  —Preceding unsigned comment added by 81.106.89.232 (talk) 16:49, 15 September 2008 (UTC)

The only way? It seems to me that the big bang theory rests almost entirely on this assumption, that only the Doppler effect can explain the red shifts. That's actually a pretty bold statement to make. You're willing to believe that the whole universe originated from a microcsopic point in a huge explosion that created everything, but you won't consider other reasons why frequencies of light could be shifted? Have people considered basic things like refraction? (ie, the index of refraction inside a galaxy is slightly higher than outside a galaxy) Or there could be some reason no one has ever thought of, that doesn't require such an outlandish theory as the big bang. - Paul Wolf
 * This should not be allowed to pass. Refraction through other galaxies would be negligible, refraction through this galaxy would not be proportional to the distance beyond this galaxy. As the article explains, actually the Doppler effect is only an approximate explanation for comparatively local sources; the real explanation is the cosmic expansion which 'stretches' the wavelengths. The Big Bang theory is thhe only show in town now I'm afraid - though there is still debate about many other essentials such as 'inflation'. Brian, 21:52, 23 Feb 2012 — Preceding unsigned comment added by 86.141.172.87 (talk)

+2.4/-3.2.
" 70 (km/s)/Mpc, +2.4/-3.2."

What does +2.4/-3.2 mean??? Fresheneesz 05:53, 9 June 2006 (UTC)


 * These are error bounds. The most likely guess is 70, but it could be anywhere from 66.8 (70 - 3.2) to 72.4 (70 + 2.4). --Christopher Thomas 06:31, 9 June 2006 (UTC)

Original Data Added
As a great (and fun) illustration for this article, I've added the graph of Hubble's data from his seminal 1929 paper. This paper is referenced by this article in the first paragraph so I'm editing out the reference I tagged onto it. Astrobayes 21:33, 30 June 2006 (UTC)

15 percent off?
Someone should add a discussion of the Alceste Bonanos team calculations:

GA Re-Review and In-line citations
Note: This article has a small number of in-line citations for an article of its size and currently would not pass criteria 2b. Members of the WikiProject Good articles are in the process of doing a re-review of current Good Article listings to ensure compliance with the standards of the Good Article Criteria. (Discussion of the changes and re-review can be found here). A significant change to the GA criteria is the mandatory use of some sort of in-line citation (In accordance to WP:CITE) to be used in order for an article to pass the verification and reference criteria. It is recommended that the article's editors take a look at the inclusion of in-line citations as well as how the article stacks up against the rest of the Good Article criteria. GA reviewers will give you at least a week's time from the date of this notice to work on the in-line citations before doing a full re-review and deciding if the article still merits being considered a Good Article or would need to be de-listed. If you have any questions, please don't hesitate to contact us on the Good Article project talk page or you may contact me personally. On behalf of the Good Articles Project, I want to thank you for all the time and effort that you have put into working on this article and improving the overall quality of the Wikipedia project. Agne 01:03, 26 September 2006 (UTC)

Commenting on question left on my talk page You need to say how many inline citations are required. Vague responses are not appreciated. There are currently two. How many more are needed? Reply on Talk:Hubble's law--ScienceApologist 01:08, 26 September 2006 (UTC Reply: I apologize if you think my notice was vague. I linked to all applicable policies and discussion on what exactly is expected. To put it in a nutshell response, It needs as many as it needs in order to pass criteria 2 of the Good Article Criteria, which is 2. It is factually accurate and verifiable. In this respect:
 * (a) it provides references to any and all sources used for its material;
 * (b) the citation of its sources using inline citations is required;
 * (c) sources should be selected in accordance with the guidelines for reliable sources;
 * (d) it contains no elements of original research.

The key here is ease of verification per WP:V and WP:CITE. Unfortunately, at this time I can not give a full review of each and every little detail that would need a cite. Most glaring is the complete absence of citations in the Discovery section as well as the bulk of Interpretation. With this lack of verifiable in-line citation references, the article would currently fail the GA criteria. My notice above is to simply give the editors of this article time to bring the article back up to GA standards before a reviewer will come along and delist it for failing criteria 2. Agne 01:19, 26 September 2006 (UTC)


 * Asking for citations to sections is not helpful. Please reference actual facts and we'll discuss which ones need citations and which ones are common knowledge. This kind of general criticism is far from helpful and actually is a waste of editors time. --ScienceApologist 17:45, 26 September 2006 (UTC)


 * If you prefer, we could just delist pretty much every article Agne has commented on so far, we have recently changed the Good Article criteria after much discussion, and warning articles to convert to inline citations instead of just delisting them just, at least to me, seems a more fair idea. Homestarmy 18:19, 26 September 2006 (UTC)


 * No, I prefer that we discuss whether or not articles live up to the standards. The new standards say that articles need inline citations. It doesn't say how many. If there is a minimum number, let it be known, otherwise it's clear that since this article has inline citations it fulfills at first glance all of the criteria outlined. Specific review criticisms are welcomed. Vague, unclear criticisms are meaningless. --ScienceApologist 18:27, 26 September 2006 (UTC)


 * Actually forking off the physics and mathematics articles as CH and Anville have suggested would be the best idea. This in-line cite nonsense, even for textbook science is just the last hint, that we're wrong here.
 * See also Wikipedia_talk:WikiProject Physics, Wikipedia talk:Citing sources
 * --Pjacobi 18:37, 26 September 2006 (UTC)
 * It's true it doesn't say how many citations, but it still does say that the article must be well-referenced, and while that is certainly subjective, (as it should be) it doesn't stop the objection from having merit if enough people agree that an article isn't, in actuality, well-referenced. This discussion doesn't actually matter, however, unless someone really pushes the issue for this article's status, which could happen if someone hits this article on a sweep and doesn't feel its well-referenced or something, or if a review is opened concerning this article. Homestarmy 18:42, 26 September 2006 (UTC)

Vaguely claiming an article isn't "well-referenced" is only meaningful if the reviewer can point to specific instances. Right now at Talk:Special relativity there are people trying to claim that basic scientific facts need to be inline-referenced. Utter baloney and hogwash. What needs referencing is history of subjects and unique, original published research. No science editor in their right mind would in-line reference "blue light has a higher energy than red light" for example, so ignorant reviewers who are looking for a particular density of in-line references need to have their wings clipped when they head over to science articles. --ScienceApologist 18:58, 26 September 2006 (UTC)

I have made a request regarding this issue here. --ScienceApologist 21:02, 26 September 2006 (UTC)
 * ScienceApologist you are trying to bully - others are making valid points and you're shouting them down. (Sorry it's taken me 6 years to spot this!) eg I read 2.2 about observability and the suggestion that the models allow for movement of an object since the time when the light was released. I fully understand the need for a resolution of the apparent paradox of proportionality between recession speed and observed distance, but in 40 years as an amateur cosmologist I have never come across this one. My understanding has always been that this parameter falls out even under close analysis using classical physics and maths - even without relativity - the object took that time to get to where you see it and the time for the light to get back here is ignored. But there is no reference to help me whether to trust the source or not. Brian, 22:16, 23 Feb 2012  — Preceding unsigned comment added by 86.141.172.87 (talk)

Fact tags added without discussion
Please, user:Agne27, explain each of your inclusions in this article. What about each sentence would you like to verify. --ScienceApologist 18:07, 27 September 2006 (UTC)
 * Most of the cite needed tags are reasonable, although there may be a few exceptions They've been put on specific historical facts, or the research results obtained specific people, or numbers released recently by a scientific experiment.  It's not all textbook stuff. -- SCZenz 00:19, 28 September 2006 (UTC)

The inclusions of the tags were in response to ScienceApologist request made on my talk page from September 26. "Offering helpful criticisms like "please include references for the following facts:" is appreciated." So I responded to that request. The items I tagged where items that I felt, as a layperson, I would like to be able to verify. My initial notice above was intentionally general because, as the articles editors, I felt that you were in better position to see what cited would be needed for WP:V as laid out in WP:CITE. What I didn't anticipate was the divided canyon of thought of what a science article needs to be considered "well referenced" and what other Wikipedia articles (such as J. R. R. Tolkien) need. While I regret and apologize for the strife this has caused, I am hopeful that the resulting dialogue will help clarify ambiguity that is spread across several guidelines and Project standards. If in the end, a better encyclopedia emerges, then this will not be for naught. Agne 23:20, 29 September 2006 (UTC)


 * Compared to the citation warriors we recently saw, I must say Agne27, you are much more reasonable. I still would like to encourage you to actually discuss the citation tags you would like to see. What in particular about the sentences would you like to see cited? It isn't clear from a simple fact tag what we as editors should cite. Your input can be valuable, but you have to give it for it to be recognized as such. --ScienceApologist 23:32, 29 September 2006 (UTC)


 * I appreciate the invite. On the WP:CITE page, Joke made a reasonable approach to the "elementary science data" when he said At the start of the article, cite a prominent review or textbook or two from which many of the (relatively speaking) "elementary" facts in the article can be mentioned. but I would modify it a bit. I'm sure that there are particular chapters in said text or review book that deal particularly with the subject matter (like Hubble's law), it would be helpful to utilize that text as a single in-line ref to place at the end of the section or paragraph with a note to the effect of "Elements in this section incorporate basic knowledge of physics and mathematics that can be referenced in [Name of Book and ideally chapter]". I think could be a worthwhile compromise in that a single cite at the end of the paragraph should not be off-putting as several cites throughout the section but for a layperson you would still have an area to go to for reference and verifiability. Having it connected to the specific section of the article and the specific chapter of the text is a lot more "reader friendly" then a reference listing at the bottom for the entire article or a general exhortation to get some kind of science text book. As for the non-text book stuff, I would love to have a link or some direction to the particular experiment or report that resulted in an important result. Historical items can be cited to biographies about the scientist or other historical record. Not only would this benefit verifiability but it would also be an excellent resource for those interested in learning more about the subject. Agne 23:48, 29 September 2006 (UTC)

These comments make a lot of sense to me. Whether to do it by section or by article is something that I think would go section-by-section and article by article. When I was working on the references to big bang yesterday, I added a citation to Kolb and Turner to several sections, because it has a particularly good discussion of these topics. For other articles, I could envision that one text would be appropriate for almost an entire article.

Your comments are reassuring – I think that, a few editors aside, people's feelings about these things are quite compatible. –Joke 00:59, 30 September 2006 (UTC)


 * I think we all have the same goal on the horizon- to make the best encyclopedia we can. I think we encountered a sort of parallax (to use a science metaphor :p) in how the two sides viewed that horizon. The more I read, the more I realize that science articles do need to be looked at in a different way then other articles. It also seems that the more the science editors talk about it, the more they see a need for a little more referencing to keep us lay folks from being lost in the dark. :) Within this space there is fertile room for compromise. I have no problem with being referred to a text book for aspects of the article that are considered "text book" stuff, but it would be nice to have an idea of what that general text book would be and maybe where in that mammoth thing I could find that info. (My fiance is an MIT grad, those texts could crush a person with their weight). I think we all made errors along the way (Myself certainly included) but I am excitedly optimistic that real progress will be made. Agne 05:25, 30 September 2006 (UTC)

Hi, I tried to move the photos down a little so they wouldn't overlap the text. It seemed to work in the preview, but it reverted to the overlap when I selected "save page". Could someone move the photos down a line? I learned a lot reading the article. Thank you for writing it! Michele123 14:07, 1 December 2006 (UTC)

90 or 500
Form the figure of the original work of Hubble in 1929 it is obvious from the slope, that a value as high as 500 (km/s)/Mpc was expected by Hubble.

Olber's Paradox
The sentence: "According to the Big Bang theory, both effects contribute (the finite duration of the Universe's history being the more important of the two)" seems to be in contradiction with the Olber's Paradox article, which says, "The current scientific consensus is that effects of general relativity relating to the Big Bang and the finite age of the Universe do indeed give a finite size for the observable universe, but that it is the astronomical redshift relationship which really explains the dark sky at night." And it follows with, "The works of experts[1] suggests that if just the assumption that the universe is infinite is dropped the paradox still holds. Though the sky would not be infinitely bright, every point in the sky would still be like as the surface of a star." 75.71.216.222 04:21, 10 January 2007 (UTC)
 * You're right -- a steady state universe would still have a dark night sky. --Michael C. Price talk 04:38, 10 January 2007 (UTC)
 * Corrected this article and Olbers' paradox. --Michael C. Price talk 09:33, 10 January 2007 (UTC)

The "tired light hypothesis" holds that light slows as it passes thru the universe and this is the cause of the red shift. As light passes thru a gravitational/electromagnetic field, it is slowed as is evidenced by the bending of the photon's path. The photon must slow more on the side toward the mass in order to bend. The slowing is not restricted to only the proximal edge of the photon, but the entire photon. The interaction of photons and electrons is not elastic, as is evidenced by the absorption and emission of photons in fluorescence and in heat. The photon losses a small amount of energy to this passing interaction and the photon red shifts slightly. The electron absorbs the energy as heat of the host atom. As a photon passes thru the universe (if not absorbed by an atom it strikes), it red shifts all the way into the microwave. Microwave is the light we are looking for in Olber's paradox. We see the microwave light everywhere. When the microwave photon strikes any matter it contacts it is brought to an end as heat. My Flatley (talk) 06:15, 8 October 2009 (UTC)
 * I don't think the light is slowed, it can't slow in a vacuum it continues to travel at the speed of light. Yes it may lose energy in the course of interactions, but the point is it's wavelength is extended. Brian, 22:22, 23 Feb 2012 — Preceding unsigned comment added by 86.141.172.87 (talk)

error?
"We may define the 'Hubble age' (also known as the 'Hubble time' or 'Hubble period') of the universe as 1/H0, or 978000 million years/[H0/(km/s/Mpc)]. The Hubble age comes to 14000 million years for H0=70 km/s/Mpc, or 13800 million years for H0=71 km/s/Mpc."

this seems to be contradictory... define it as 978 billion then immediately say it is 14 billion Agoodspellr 18:49, 15 July 2007 (UTC)

Controversy
There is no mention whatsoever of the discussion in cosmology around the counter evidence to the hubble law, and rethinking of previous data interpretations that were done to fit big bang theory -- for example, stellar observations of Markarian 205, Stephan's Quintet, NGC 4319, and NGC 7603 are all examples of apparently connected observables with widly different redshifts. Unfortunately, I'm not an cosmology expert, so it is not clear if this is simply a loud but extreme minority making such claims or if there is a real controversy starting to re-evaluate the red-shit/distance connection. Anyone else have more expertise here? For example, there is a professional documentarty called cosmology quest (http://www.amazon.com/UNIVERSE-Cosmology-Quest-Dr-Halton/dp/B0006HU2VY), and pages like this http://www.astr.ua.edu/keel/galaxies/arp.html, http://www.astronomy-mall.com/Adventures.In.Deep.Space/arpredshift.htm 64.142.101.135 20:47, 11 August 2007 (UTC)

Hello, any cosmologists out there? No one has commented... All the work of Friedman was done based on the current understanding that the velocity interpretation of Hubble's measurements was correct - ie, that recessional velocity due to spacetime expansion was correlated with distance as measured from standard candle measurements. If these measurements were collected and interpreted with today's data, the whole assumption of the Hubble constant as a "real velocity" would be highly suspect. As far as I can tell, the velocity interpretation is an  essential lynchpin in the whole scientific field of cosmology - and that this is an unverifiable assumption, and more recently with a nontrival body of counterevidence. While there is a significant body of observation that is consistent with the velocity interpretation, there are not any measurements I can find that actually support it (please point to these/papers/etc if they exist). This whole kooky story about 25% dark matter and 70% "dark energy" are pinned on Friedman's equations, which are pinned on the velocity interpretation of redshift+standard candle = Hubble law. If the velocity interpretation is wrong, then Friedmans equations are wrong, and the dark energy hooha starts looking less troubling. Can anyone with significant knowledge of cosmology comment? The deeper I look into this, the worse it looks (meaning it looks like a lot of results and careers piled onto one assumption). 64.142.101.135 05:48, 1 October 2007 (UTC)


 * Check out nonstandard cosmologies for information on your ideas. ScienceApologist 18:54, 2 October 2007 (UTC)

Comoving Distance?
Under the mathematical expression for Hubble's Law, D is defined as the comoving distance (i.e. the distance which is unaffected by expansion). But if it really is the comoving distance then dD/dt would essentially be zero as it would just be the comoving velocity of the distant galaxies, not their recession velocity due to expansion. Is this a mistake? Waofy (talk) 14:11, 20 December 2007 (UTC)
 * According to the article D is the proper distance. Brian, 22:30, 23 Feb 2012

KATIE ROSE LOVES YOU! —Preceding unsigned comment added by 65.185.101.216 (talk) 19:33, 9 February 2008 (UTC)

I corrected cosmotology time to cosmological time HTH69.40.254.33 (talk) 12:41, 30 May 2009 (UTC)

I am neither a mathematician nor cosmologist but Hubble´s Law just does not feel right. This double the distance double the speed feels like a simple illusion based on a red shift concept of distance when an alternating or impaired light speed could have the same effect. The big bang boys always avoid the question of what came before and what lies beyond? There may be a sign for infinity but it does not exist. If time and space are one then how can you measure distance without time? Anyone care to tell me whats going on? Thanks,
 * There are a lot of misunderstandings here! I'm afraid you can't evaluate a theory by whether it 'feels right' to you or me! What do you mean by alternating or impaired light? It is red shifted light, either by Doppler effect or in this case cosmological expansion. What came before is much discussed by Hawking, Penrose and many others. Space and time are not one, space has three dimensions, time is the fourth dimension in space-time. Space is one but you can still measure height, width and length independently, and of course you can measure time and distance - or infer them from obseervations - though they differ between frames of reference. Brian, 22:34, 23 Feb 2012

—Preceding unsigned comment added by 79.149.215.87 (talk) 14:23, 31 January 2010 (UTC)

"$$H_0$$ should not be given in Hz. It is equal to ... aHz"
It is stated in article that the Hubble constant should not be given in hertz. However before (in introduction) it is given in hertz. Please choose one option (can be given in Hertz or not) and clear the article. Uzytkownik (talk) 21:17, 27 March 2008 (UTC)

As a cosmologist I agree that the Hubble constant/parameter should not be quoted in Hertz or aHz. It is nearly always quoted in (km s^-1) Mpc^-1, which makes physical sense as the change in velocity per Mpc for more distant galaxies. Since most readers (and indeed most non-cosmologist physicists) wouldn't find these units natural, I guess it should also be quoted here in SI units, but it would have to be in s^-1 (as these quantities are not frequencies, as might be suggested by using Hz). Does *anyone* think the intro should be left with aHz(?!) or can it please be changed to s^-1 ? --Kyuzo2000 (talk) 16:05, 10 April 2008 (UTC)

Superluminal Speeds
The interpretation of special relativity in this section is way off. The appearance of superluminal speeds does not violate special relativity because we are not necessarily moving relative to the other. It is true that no object can move faster than the speed of light with respect to another object, but the reason that superluminal speeds appear to be achieved is that spacetime is expanding between the two, thus giving the appearance of moving apart.

The correct way to state this section would be to say that special relativity does not apply at galactic scales where the expansion of the universe is no longer negligible.

150.243.67.58 (talk) 16:06, 4 April 2008 (UTC)

H0
How come there is no clear and stand-out value for H0, without needing to read the article?

If anyone knows how to introduce it, it would be helpful for people like me that comes to wiki as first place for such purposes. —Preceding unsigned comment added by 128.139.226.36 (talk) 12:39, 20 November 2008 (UTC)

History of constant definitions
It would be good for someone to construct an graph depicting the history of the Hubble constant refinements like what is found in this book:


 * Conceptions of cosmos: from myths to the accelerating universe : a history page 191

WilliamKF (talk) 21:13, 22 September 2009 (UTC)

"Hubble Flow"?
I was redirected to this page from Milky Way after clicking a link for Hubble Flow, but the word "flow" is found nowhere in the text of this article and I have no clue where to begin looking. Great Attractor also links to Hubble Flow in its article summary, so it seems as though this topic is well-known in astronomy. A little clarification would be nice. —Preceding unsigned comment added by KHAAAAAAAAAAN (talk • contribs) 18:28, 4 November 2009 (UTC)

Agree, there should be a explanation if it redirects here, I had a similar problem when searching wikipedia for hubble flow, only to find no mention of it in the page I'm redirected to. Georgeryall (talk) 19:25, 1 June 2010 (UTC)

SDSS estimates
It would be nice if the sdss estimates for H_0 were included.Kiyo.masui (talk) 20:59, 4 December 2009 (UTC)

Hubble's Law
Along with other readers, there is more confusion generated per article than help. There is no definition of what is meant by "THE UNIVERSE". From the various, Maths in action, it appears to be the 1% visible matter contained in star/galaxies. How does the behaviour of this small, specialised sample, be defined to represent the other 3% matter and the 96% Dark Matter/Dark Energy? As some galaxies are not dissipating into the never/never, is there an inference of space contraction for blue shift galaxies? Given recent deep field observations suggest an inferred Universe diameter of 80 Billion light years can 'inflation' support this value 58.161.199.95 (talk) 12:31, 24 April 2010 (UTC) JEM

Hubble-Reynolds Law
Hubble-Reynolds Law redirects to Hubble's Law but they are not the same: the former refers to a formula for surface brightness of elliptical galaxies, and should have its own entry. —Preceding unsigned comment added by Fuelmonty (talk • contribs) 11:45, 30 July 2010 (UTC)

Question
Assumptions:
 * 1) The principles of physics are valid in the entire universe
 * 2) Speed of light is limited
 * 3) No information can be transmitted faster than the speed of light.

Observation: The light emitted by the farthest galaxy is shifted to the red.

Thesis: Universe expands and the speed of propagation is proportional to the distance from the observer. (That is, the farther from us the more the universe expands.)

According to me there is an error: What we see is not the current state of the object, but a condition in which the object was within the time specified by the distance from the observer. We have no information about how galaxies observed now look and behave but, just as they did (how fast were moving) some billions of years ago. Observation of far facilities enables us to retreat in time. The more distant an object, the earlier the condition observed.
 * Please see my recent post under GA Re:Review above. Brian, 22:39, 23 Feb 2012

So the only thesis, which can be working on the basis of observation, IMHO is this:

The speed of moving objects in the universe decreases. Am I right?
 * I think this is a non-sequitur, but you may be right depending what you mean. The universe is expanding at an accelerating rate or appears to be, the peculiar motions of bodies relative to that expansion are, doubtless, very gradually slowing down and losing energy. Brian, 22:41, 23 Feb 2012

Sfuj (talk) 18:31, 4 August 2010 (UTC)

Hubble time
the article says

"a naive interpretation of the Hubble time is that it is the time taken for the universe to increase in size by a factor of e"

but if the diameter of the universe is simply increasing at a constant rate

then the Hubble time (1/H = 13.8 BY) is the time it has taken to reach its current diameter

(The age of the universe is 13.75 ± 0.13 billion years since the Big Bang)

Just granpa (talk) 10:21, 11 June 2011 (UTC)

Who was the 1931 MNRAS censor of Lemaitre?
See my question at User_talk:RockSolidCosmo and the two recent arXiv papers linked there. Boud (talk) 07:49, 30 June 2011 (UTC)

Misleading and Incorrect - Hubble was NOT the "first to observe".
It is quite clear that Hubble was not the first to "observe" galactic redshift. The very first paragraph of this is wrong and misleading. Concatenation of several CONCLUSIONS that Hubble did reach do not change the fact that the data he worked with was largely the work of others. Those others, including Slipher, take precedence in the discovery. Not trying to diminish Hubble's accomplishemnets, but get the history right please.71.31.151.178 (talk) 04:00, 28 September 2011 (UTC)