Talk:Hubble's law

From Wikipedia, the free encyclopedia

↓ Skip to table of contents ↓
Good articles Hubble's law has been listed as a good article under the good-article criteria. If you can improve it further, please do.
If it no longer meets these criteria, you can delist it, or ask for a review.
WikiProject Astronomy
Portal:Astronomy
 Astronomy Portal
This article is within the scope of WikiProject Astronomy, which collaborates on articles related to astronomy, and WikiProject Physics, which collaborates on articles related to physics.
Good article GA This article has been rated as GA-Class on the assessment scale.

This article has been rated but has no comments. If appropriate, please review the article and leave comments here to identify the strengths and weaknesses of the article and what work it will need.
WikiProject Physics
Portal:Physics
 Physics Portal
This article is within the scope of WikiProject Physics, which collaborates on articles related to physics.
Good article GA This article has been rated as GA-Class on the assessment scale.
High This article is on a subject of High importance within physics.

This article has been rated but has no comments. If appropriate, please review the article and leave comments here to identify the strengths and weaknesses of the article and what work it will need.
Hubble's law is included in the 2006 Wikipedia CD Selection, or is a candidate for inclusion in the next version. Please maintain high quality standards and, if possible, stick to GFDL-compatible images.

Contents

[edit] Question

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

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)

[edit] 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

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

  • 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

the accelerating universe and cosmological constant seem to cover this. -- April

  • 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

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

[edit] 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)

[edit] 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)

[edit] 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 :) )

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)


[edit] 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)

[edit] 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?...

[edit] +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)


[edit] 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)

[edit] 15 percent off?

Someone should add a discussion of the Alceste Bonanos team calculations: [1]

[edit] 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 Wikipedia: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#Another_reason, why Wikipedia sucks, Wikipedia talk:Citing sources#When not to cite
--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)

[edit] 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. Tolkein) 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)

[edit] 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.

[edit] 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)
Retrieved from "http://en.wikipedia.org../../../h/u/b/Talk%7EHubble%27s_law_dab8.html"