Talk:Age of the universe

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[edit] Old comments

Sorry, but some of this stuff really is too hard to make sense of by making minor corrections, so i've cut it out (today Boud 13:38, 3 Dec 2004 (UTC)) and pasted it here in case anyone wants to make sense of it:

This allows us to describe how the universe has evolved over time using an equation like this: $t = t 0 (1 + z) 3 (1 + w) / 2$ . As you can see, things are starting to get a bit more tricky, but this equation simply relates the age of the universe to the redshift. This particular example has an additional term w, which comes from something called the equation of state, relating the pressure and density of the universe (p=wdc^2, where p is pressure, d is density and c^2 is the speed of light squared).

For a standard model (cosmological constant = constant or zero, no quintessence), we have w = -1, and this equation gives t = t_0 (1+z)^0 = t_0 so time is constant and the universe doesn't expand at all. Maybe this is one of the early historical models with some minor error, but i don't recognise it. Boud 13:38, 3 Dec 2004 (UTC)

Things do start to get technical here, but there is a nice confirmation of this model which actually validates it against recent observations. Coming back to the math, the change in the distance is related to time with the redshift relation $t = t (1 + z) 2$ . However, there is an additional change in time related to redshift as $t = t o (1 + z) 1 / 2$ , which (the product of both) brings us back to the original form for our "dust" w=0 universe. The idea of time-variable time probably sounds bizarre, but this is expected since there is no "absolute" concept of time in General Relativity.

The two formulae look weird, i can't make sense of the discussion, and saying that there is no absolute concept of time in GR is misleading, since GR applied to the universe in the standard FLRW model very definitely has a favoured time axis in the comoving coordinates system.

The Planck stuff needs some checking too - i'm not familiar with stuff that theoretical, so i'm not sure whether it's meaningful or not. Boud 13:38, 3 Dec 2004 (UTC)

I was the originator of the discussion on the Talk:Universe page where a large part of this content came from. It wasn't meant to be turned directly in to an article, so the quality isn't great and there are some typos in the formulas. However, I would be glad to tidy up what currently exists in the article and hopefully resolve any remaining confusion. Nodem 00:23, 23 Feb 2005 (UTC)

[edit] CNO studies

Does anyone have citations for the "some recent studies" mentioned in the CNO section? —Joe Jarvis 14:43, May 24, 2005 (UTC)

I was about to post that question myself. If a section or statement does not have a citation, it is thus unverifiable by Wiki standards and should be removed. However, this section provides a valuable bit of information to the article so... we should try to find some peer-reviewed articles or texts that discuss the CNO statements (try Google Scholar). If we can't, the section should be removed. Astrobayes 22:53, 23 June 2006 (UTC)

Nobody? Ok, I'll find references for this section and add them myself. Cheers, Astrobayes 22:19, 30 June 2006 (UTC)

Hi, I moved this section to after the "Age Based on Cosmological Parameters" section. I think that since the CNO studies are speculative it's a good idea to put them after the generally accepted argument based on cosmological parameters and the Friedmann equation. This way the article flows a little better, since the canonical WMAP value gets explained more or less right away... Wesino 09:38, 15 November 2006 (UTC)

[edit] graviational

I do more basic proofreading than science, which led me to this apparent typo: "Obviously, the entropy increases (due to graviational in fall) and this has the effect that the universe has become cooler than this simple model predicts." I almost corrected it to "gravitational", but that makes the sentence look backwards. Gravitational in fall of a meteorite, for instance, would convert gravitational potential energy to heat energy, and get hotter, not cooler - although I agree that it would increase entropy. Did I discover a typo and/or a more serious mistake? Art LaPella 02:36, August 22, 2005 (UTC)

I do not know where you are looking. Please direct me to the page with "graviational" Pdn 16:28, 22 August 2005 (UTC)OOps I see the page and the item on it. I will ponder it and maybe consult someone if needed. Good call - it does look odd. Pdn 16:46, 22 August 2005 (UTC)

This whole section looks amateurish, but I am not sure I'm qualified to fix it. One example is that the author refers to the Planck temperature as "measurable" and tries to project forward from it. But that is trying to look way past where we can see - we can't see past the "surface of last scattering" of the CMB. The stuff about Planck temperature is all done by estimating backwards in time from then, and using particle physics, and so it cannot serve as a useful age marker. In fact, things ran so fast near the Planck temperature that the time interval to get way below it is inconsequential compared to the present age. I am not sure if I could get Ned Wright, for example, to fix this. (see [1]). There is a generic Wiki-problem here - there is a lot of good information out there already, and it is not clear that Wikipedia can attract authors who want to spend time on poorly supervised pages repeating what they have said elsewhere, or what is in books. Wikipedia may be turning into a forum for creationists, "General Semanticists" (General Semantics), and other cranks to vent their ideas. I mean, really, do you have to study the works of Korzybski to learn that dogs do not create handbooks or literature, or that words are to be distinguished from the objects they refer to? Pdn 16:58, 22 August 2005 (UTC)

I've experimented with Wikipedia:Template messages when dealing with something wrong that I can't fix - simple example, Baotou. Templates might embarrass this stuff away, or at least warn people not to believe it. Here are some templates that we might want to choose from for the "Age based on temperature" section here: (I removed templates afterwards - they made the talk page show up in categories. 8/27/05)

Beyond that, I think Wikipedia is too democratic. Nobody is really equal, even though some situations go smoother by pretending they are. In particular, I would establish a class of newbies, forbidden to edit except indirectly, on a new provisional edit page that has to be approved by others. A newbie could graduate if enough text or changes are substantially approved. A banned user returning as a Wikipedia:sock puppet would have to qualify all over again. Art LaPella 20:51, August 22, 2005 (UTC)

[edit] Temperatures

2943K the temperature of a dully-glowing poker? I think not: iron melts at a mere 1811K. I don't feel adequately qualified to edit the page, though.

I've done a bit of poking (heh) around other articles. Unless you're using a tungsten carbide poker (melting point 3143K), you don't really stand a chance of getting a poker anywhere near that hot. I thought for a bit that it might have been a mistake with someone mistaking fahrenheit for kelvin, but even if that were the case the poker would be far from dull (iron melts at 2800 degrees fahrenheit, and alloys like steel at less than that). Anyway, I'll edit it now. --Dom 01:10, 22 December 2005 (UTC)

[edit] Planck Temp

The bit about the Planck temperature and the comments following in the article are really a minefield of numbers and concepts that are not well described...and I do have the education to understand them, they're just poorly written. Would the original author of these statements please respond as to what she or he was trying to convey? It doesn't add much to the article as it stands and should be rewritten. If a scientist can't follow it, it will certainly turn away non-scientists who come here looking for interesting and educational material. Astrobayes 22:57, 23 June 2006 (UTC)

I don't understand it but I can trace the editing history. It was first written at the end of this edit by Nodem, followed by this correction, after which Zeimusu copied it when he started this article with this edit. Nodem hasn't edited lately but Zeimusu has. Art LaPella 03:33, 24 June 2006 (UTC)

I have rewritten this section, Wikified it, and given it an understandable basis. As it stood before, it was a mess and added nothing to the article. Now the opposite is true, while still retaining the original intention. I hope everyone enjoys it now. Astrobayes 22:19, 30 June 2006 (UTC)

I think the "derivation" of the age of the Universe in terms of its temperature should be removed not only because the argument is difficult to follow, but because it is just plain wrong. Here is why:

For a physically-motivated counter example, one can compare the age of two spatially flat universes with the same CMB temperature (2.7K), but where one model includes a cosmological constant and the other does not (where the matter density is adjusted appropriately to keep the curvature zero). You find that the universe with the c.c. has a larger age than the other. Therefore, because the ages are different but the temperatures are the same, the age of the universe cannot depend on the CMB temperature alone. Historically, the fact that the cosmological constant increases the age of the universe was one of the early arguments that suggested that a c.c. was necessary in the standard cosmological model, since there appeared to be globular clusters that were older than a matter-dominated Universe without a c.c. See Friedmann equations but there doesn't seem to be a reference to the age as a function of various other cosmological parameters that I can find.

A very much more elementary reason this argument cannot be correct is the following. Suppose the age of the universe t is inversely proportional to the square of the temperature (as asserted). Then since temperature is inversely proportional to the Scale factor (Universe) this implies that the scale factor a(t) goes like t^1/2. This is patently false for the vast majority of the history of the universe -- again see the Friedmann equation page (today the scale factor is growing nearly exponentially, and during matter domination between redshifts of about z=1 and z=10,000 it went like t^2/3). The only case where this argument is true is during radiation domination. Since the fraction of the Universe's total energy density in radiation is currently around 1 part in 10,000, this is clearly not the case today.

So the only reason that this argument can give anything close to the correct value is due to some kind of numerical coincidence.

Now, what is true is that if you do the integrals required to calculate the age of the universe carefully, they all turn out to be of the form 1/(Hubble parameter today) times (function of the fractions of matter, radiation, etc.) So a good back-of-the-envelope statement is that the age of the universe is roughly today's Hubble parameter. Inserting a reasonable value -- 72 km/s/Mpc -- in Google gives an age estimate of 13.6 Gyr, which is almost precisely correct (and for the right reasons!)

I would be happy to do the appropriate edits but it would be good to get some feedback from others who have contributed to this section before I do so... Wesino 16:20, 9 November 2006 (UTC)

So it's been about a week, and no defense of the "Age in terms of Planck Temp" section has appeared. So I decided to be bold and delete it. I think this is justified based on the comments made above. If anyone takes issue with this, then let's discuss it. Wesino 09:34, 15 November 2006 (UTC)

Hi Wesino. I don't have a problem with the section being deleted. It was part of a discussion that someone else posted into this article as is. I took a quick stab at updating it a while back, but I couldn't possibly do it justice in a Wikipedia page. It is derived from a principle and, in fact, not "some kind of numerical coincidence". I don't mind discussing it further if you are interested. Thanks Nodem 05:21, 27 November 2006 (UTC)

I'm glad you're OK with the edit, Nodem. I didn't mean to offend by calling it a "numerical coincidence." However that's the only reason I can think of for the calculation giving anywhere close to the right answer, except during radiation domination (which anyway is a poor approximation to our Universe at z < 10,000 or so).

It's possible that there's a principle behind it, but it seems that the principle must be false, or at least in severe conflict with observations. As explained above, the essential reason is that it gives a time-temperature relation, and thus a time-scale factor relation, that would

imply the universe is decelerating (since a(t) ~ t^1/2) in conflict with SNIa observations,

Without going into detail, the relationship a(t) ~ t^1/2 was from a normalized model and should not be interpreted in the context of the standard model. Also, the universe is not necessarily accelerating/decelerating. This is a conclusion drawn from one specific model using a set of assumptions. The standard model may be right, but until someone detects a WIMP, explains/resolves the various dark energy issues (like where theory and observation conflict by 120 orders of magnitude), I would stick to statements like: "The high-z SNIa appear to be fainter than a simple matter dominated FRW universe based on their observed host galaxy redshift. This may be due to the fact they are further away, which in turn could be that the rate of expansion has increased, which if due to some invisible force, that if we now insert into the mass/energy budget of the universe we could partially fix another problem, although at the expense of the cosmological principle". Statements of the type "the universe is doing this or that" can become a lot of rope from which one could easily hang. Yes, the current observations are very impressive (considering a decade or two ago there was almost nothing), but they are far from conclusive. Also note that there are some pretty bright folks developing alternatives (like MOND), so I'm not a minority voice in questioning the absolute truth of Lambda CDM.

disagree with observations of structure formation, which need a matter dominated epoch a(t) ~ t^2/3 followed by dark energy domination,

Again, the relationship a(t) ~ t^1/2 should not be treated in a comparison like this.

be in conflict with the cosmic microwave background anisotropy, and especially the location of the first peak (since this essentially measures the angular diameter distance to the surface of last scattering, which depends on the behavior of the scale factor since then),

ditto

require us to replace the Friedmann equations and thus Einstein gravity. In fact, since the radiation density is extremely tiny today, to get a(t) ~ t^1/2 matter could not gravitate at all -- definitely in conflict with observation.

ditto

All of this is pretty standard stuff, these arguments can be found on various Wikipedia pages (as well as in the scientific litertature and textbooks on cosmology).

True, I've taken all the classes and have quite a few textbooks at this point (I even had to read some of them... believe it or not). Nodem 16:50, 27 November 2006 (UTC)

If you want to talk further but don't want to do it here, you're welcome to post to my talk page. That way others can benefit from/contribute to the discussion if they wish. Wesino 09:50, 27 November 2006 (UTC)

From your responses to my points it seems like you're quite enthusiastic about this idea. Lambda-CDM has a few problems and perhaps someday a better theory will be found. But right now you're talking about a "principle," which is associated with a "normalized model" that can be compared to LambdaCDM as far as age calculations go, but can not be compared to classic LambdaCDM predictions or cosmological observations, apparently only predicts (or assumes?) an age-temperature relation, and -- perhaps most importantly for an encyclopedia -- isn't backed up by reliable sources. Perhaps someday it'll be worthy of a journal article or more. But I think we can both agree that for now it doesn't belong in an encyclopedia.

I want to say something more and please, please don't take it as condescension. If you've taken classes on this stuff, please go back and re-read your notes! The model accepted by the vast majority of cosmologists has gained its status by passing a HUGE number of nontrivial tests over decades of research. Any replacement will have to pass all of these, and more. And until one has demonstrated this, claiming to have an alternative in hand is dodgy business indeed. Wesino 17:41, 27 November 2006 (UTC)

Yes, dodgy business indeed! That's why I've not invested any time to this for the last year at least. My results don't actually agree with the currently accepted value for the Hubble parameter. I end up in the region of 63, so someone has got it wrong! It wasn't my intention to have this thing swept into a Wiki-article (I originated the "Strong Priors" section and this got sucked into a discussion). Nodem 18:10, 27 November 2006 (UTC)

...of course some would argue that the whole field was a bit dodgy. 63 isn't too far off -- who knows, maybe someday it'll be worth a Wiki article? Keep truckin', best, Wesino 22:01, 27 November 2006 (UTC)

[edit] Accuracy template

Some similar language was added long ago, as described above at #graviational. Now someone has deleted the warning language without fixing that problem, so I replaced it with an official Wikipedia template. Art LaPella 04:58, 15 December 2005 (UTC)

You can't leave a dispute template up on a page for two months without doing anything to fix it. The editing activity since that time has not addressed the dispute. What are you doing to fix this? Sections cannot be permanently disputed. --TreyHarris 20:58, 18 February 2006 (UTC)

As described above at #graviational, someone who knows this subject better than I do has decided that the entire section, in addition to the sentence I objected to, is nonsense. If I can't leave a dispute template indefinitely, then I hope Wikipedia has some other alternative procedure to being taken over by nonsense, just because no one still here understands the exact nature of the nonsense. Deleting the entire section would be OK with me. Art LaPella 22:44, 18 February 2006 (UTC)

Then you delete the nonsense. If somebody puts it back, you can engage them on this page, and you can have an actual dispute. "This section is disputed" means not that someone has at some point disagreed with the section, but that people, on the talk page, are disputing it at the moment in order to reach a consensus. Once the dispute ceases progress, the template goes; you can't just walk away from the dispute. --TreyHarris 23:49, 18 February 2006 (UTC)

OK (gulp!) Is there anyone out there who wants this paragraph to go back in? PDN didn't, as described above. Here is the major section I deleted:

Thanks to the bold one it's gone :-) I had stared at the section and modified a bit (see below) and thought: What's going on here?, but said to meself: Self, we don't know enuff 'bout this - leave it be. Onward, Vsmith 04:45, 19 February 2006 (UTC)

[edit] Age based on temperature

In its most basic form, the Big Bang theory is based on the idea that the universe was smaller, denser, and hotter in the past. Assuming, therefore, that the initial temperature of the universe is known, and that the change in temperature over time is accurately modeled, the age of the universe can be extrapolated from a measurement of the current temperature of the universe (approximately 2.7 K).

An expanding (or contracting) universe is given a scale factor to indicate its current size in relation to a fixed point. This could be a simple distance, or a dimensionless ratio of one distance (the size now) divided by a size in the past. In the case of a ratio like this, the present scale factor of the universe is one, and for an expanding universe, the scale factor in the past is less than one. Given a universe with scale factor $a$ , the redshift $z$ of an object in the universe is simply the inverse of the scale factor minus one: $z = 1 - (1 / a (t))$ , or $a (t) = 1 / (1 + z)$ .

The temperature of the universe at a given time is inversely proportional to its scale factor at that time; somewhat analogous to a gas that would cool down if expanded, or heat up if compressed, the temperature of the universe is thus related to redshift as $T = T 0 (1 + z)$ . We can do a quick test by using the current temperature of 2.7K and the redshift of CMB as 1089 to calculate the temperature of the decoupling surface $T = 2.7 * 1090 = 2943K$ (this is the temperature of the universe when the CMB was emitted.)

In a universe like our own, most of the contents is in the form that does not exert a pressure on its surroundings (clouds of hydrogen gas, stars, planets etc). This is a pressureless, or "dust" model. For this kind of cosmological model, the evolution of the universe (scale factor at a specific time) is $t = t 0 (1 + z) - 3 / 2$ . Putting in the redshift of 1089 for the cosmic microwave background and a current age of the universe $t_0 \approx 13.7$ Gyr indicates the CMB was emitted around 380,000 years after the birth of the universe.

The earliest measurable point in the evolution of the universe is the Planck time, when the universe would be at the Planck temperature. The Planck temperature represents the maximum attainable temperature in the physical universe and can only be attained via an extreme event, such as the evaporation of a black hole (the Planck temperature is the Hawking temperature of a black hole with a radius of the Planck length $4.5 \times 10^{30}$ K). Therefore $T p = T o (1 + z max)$ , where $T 0 = 2.725$ K and now $z max$ is the maximum redshift as if seen from the Planck time $t p$ . Using the radiation dominated formula above, we arrive at an age of the universe of 11.667 Gyr.

This is not the end of the story however: First we must take into consideration the matter domination, which in this calculation is equivalent to a change in the value of the Planck time itself. This is a fairly simple integration and results in an age one third greater at 15.556 Gyr. Finally, this model was also simplified by considering that the entropy of the universe is constant. Obviously, the entropy increases (due to graviational in fall) and this has the effect that the universe has become cooler than this simple model predicts. The difference here is around 13.5% (the temperature would be 6.5% higher if entropy had not increased, so the age difference is this squared). This adjustment finally brings the temperature calculated age down to the WMAP age.

[edit] 380, 000 Years

I would like to point out that the 380 000 year age seems to be here just to put a hole in the page. I did not edit the page because I do not fully understand the math he has used. The idea of using bad science to 'prove' a religous theory is not a new idea, it is little more than kicking over someone elses sand castle because you can not build one that stands on its own. [Richard Bailey]

I'm taking it out because it makes no sense. We have dinosaur fossils from over 65 million years ago. It's absurd to have something like that in this article.

er... read it again: current age of the universe approx 13.7 Gyr gives us around 380,000 years for the age of the universe when the CMB was emitted. Replaced the deleted para. Vsmith 20:56, 29 January 2006 (UTC)

[edit] Open Idiocy

380,000 years as the age of the Universe? This doesn't even deserve to be dignified with a proper response. It needs to be removed immediately - as it stands, it compromises the integrity and perception of empricism that Wikipedia holds dear. Justifications of ludicrous religious theories, regardless of how widespread they are, doesn't deserve a place in an encyclopaedia.

This trend in Wikipedia towards including right-wing political, religious and moral sensibilities as valid 'criticism,' no matter how outlandish or utterly falsified by modern science, is disturbing and an indication of intellectual laziness and misguided belief that simply because there are two opposing positions, the factual middle ground is somewhere evenly between the two. In reality, almost no respectably accreditted scientist supports Creationsim, yet it seems that we must always qualify an article on evolution with the 'opposing view' of Creationism. Really, these opposing opinions deserve no more place in Wikipedia than the 'stork theory' in human reproduction.

Idiocy is widespread and commonplace: this is no excuse, however, for it to be given equal footing with our current, rational understanding of the world.

(above post by 146.87.193.90 moved to bottom of page)

To repeat my comment from above in the section entitled 380,000 years:

er... read it again: current age of the universe approx 13.7 Gyr gives us around 380,000 years for the age of the universe when the CMB was emitted.

Perhaps we need to reword that bit as at least two users have mis-read it. Vsmith 03:05, 6 February 2006 (UTC)

OK, I reworded the offending sentence to, hopefully, avoid further confusion. The whole section needs a re-write as it is a bit much for the average user (me included :-) Vsmith 03:26, 6 February 2006 (UTC)

Should we perhaps link to an appropriate Wikipedia Creation Myth page?

[edit] The first sentence needs to be changed

I am a physicist, I have studied astrophysics, astronomy, and cosmology for years, and this is my suggestion: the first sentence of this article has to go, and asap. Because it is simply not true. It states, "Nothing is certain as to the extent of either the age or size of the universe..." That is factually at odds with the very laws of physics used to calculate the age of the Universe. Not only is there a currently accepted age of the universe, which is calculated in several different ways arriving at the same order of magnitude but in fact, the age of the universe is currently accepted within about 1.4% error. Since this is fact, it needs to be presented in this article as such; just click here for a clear and concise explanation of actual measurments of the age of the universe that are not based upon cosmological models for those measurments, such as the big bang. To leave the first sentence as it currently stands would be an egregious offense to the policies of WP to promote NPOV for this subject. I plan on making a change soon and I would like suggestions from those of you who have researched this subject, and understand a way to present it to a general audience for their maximum benefit. I realize how this can be a confusing issue for many people. To be able to do something as complex as measure the age of the universe requires advanced mathematics well beyond what most people are comfortable with, so there needs to be some way to balance the presentation of these measurments from their actual foundations, with a readability for a casual observer. I'd like to work on a solution to this as soon as possible and all feedback would be welcome. Thank you for your time. C.Melton 00:12, 11 February 2006 (UTC)

I agree. I am also an astrophysicist who has studied cosmology. The statement is equivalent to saying nothing is certain about the number of legs dogs have, when in fact the majority of evidence suggests that four is the number. Soloist 14:11, 17 February 2006 (UTC)

Me and my Mutt had a discussion and reached an agreement: the answer is four. Deleted the Nothing is certain... bit. Now you astrophysics guys go to work on it :-) Vsmith 15:27, 17 February 2006 (UTC)

Just did an edit on the first paragraph. It seemed to get overly technical "very" quickly. I think that a casual reader should be able to gather that the Age of the Universe is just the time between the beginning (=Big Bang) and today. But I think this casual reader could easily be lost in the sentences about integrating proper time along curves (which linked to the Minkowski space article, which makes no sense in this context). Also, the comments jumped directly in to the various alternative models without really explaining the consensus view first (which should really be the purpose of this article, right?).

So I changed things a bit and made the first two sentences as simple as possible to get the idea across. Then I tried to preserve some of the discussion of other possibilities (which were largely about universes without a big bang and infinite age; I added an example of a model with a big bang but of infinite age) as well as some of the comments about the ambiguity of defining time properly in SR/GR. Hope others find that this makes the opening paragraph clearer too Wesino 10:04, 15 November 2006 (UTC)

[edit] Problem With A Reference - Removed

I have a problem with this reference given in the article. It is only in the Pre-Print Archive - a database in which anyone can present any original research and it is hence not in a peer-reviewed professional journal (appropriate journals for this topic would include ones like Physical Review D or the Astrophysics Journal). Any source cited that argues problems with a scientific consensus on some issue bears the burden of proof and such can only be truly reliable if it is peer-reviewed research. There are plenty of articles that discuss the problems, drawbacks, or other limitations of one model or another in professional journals and therefore we should - in the interest of quality - include more peer-reviewed articles than non peer-reviewed articles. I have therefore removed the poor reference and replaced it with better ones. Astrobayes 11:18, 20 June 2006 (UTC)

[edit] Strong Priors Section

I have also added an additional comment, backed by several peer-reviewed journal articles and one peer-reviewed Ph.D. thesis, that adds a very important point to the editor's comment about strong priors. The impetus for adding these references and my comment was that the editor seemed to be saying that you cannot trust a conclusion or result unless you consider the model first, but this is not the entire story. The model used helps constrain the confidence interval, but does not invalidate the measurment if a different model obtains slightly different results - this amounts to correctly normalizing the data, not invalidating models which the original editor seemed to suggest. There are two branches of statistical tools used in science: frequency statistics (what most people are familiar with) and Bayesian statistics. Only the latter is a tool that adjusts statistical results based upon a model (i.e. prior) being used. Since this important tool is used so often in science (I used it quite frequently when I did astrophysics research as an undergraduate), it is important that it be mentioned because it constrains our confidence intervals for age of the Universe measurments. In other words, we cannot simply eliminate a particular scientific measurement we may or may not agree with just becuase it comes from one model and not another. If this edit is reverted, there should be an overwhelming support to the contrary cited by peer-reviewed research for as it stands, it adds important NPOV content to the article. Astrobayes 12:09, 20 June 2006 (UTC)

[edit] Age based on what time frame of reference?

While there are several methods to calculate the age of the universe as we know it and they have produced similiar results, one must wonder, what does this "age" really mean? Does that mean age in our time? Age in relative time? Age in warpped time? Since there's an age, there must be a start, and I believe the most commonly accepted theory is the Big Bang; in which case, while the universe is a singularity, the space-time is warpped at the point from the heavy gravitational fields, wouldn't the calculation of time (using our common time-units) be largely inaccurate as well? Even if we use String theory to avoid the singularity problem, the fact that time is messed up at the point doesn't seem to change. Allan Lee 16:08, 10 July 2006 (UTC)

[edit] Title - 'Age of the universe' vs 'Age of the Universe'

Shouldn't the title of this page be 'Age of the Universe', i.e. capitalized Universe as it's a noun (and there's only one of it)? If not, then the capitalization of the first sentence in the article needs to be changed... --Mike Peel 06:59, 1 August 2006 (UTC)

"Do not capitalize solar system and universe." ( http://www.science-teachers.com/articles/phpBB2/viewtopic.php?t=8 ) "It is not necessary to capitalize a word merely because there is only one thing it can possibly refer to: ... the words equator, north pole and universe need no capitals, because they aren't strictly proper names. Some people choose to capitalize them anyway; this is not wrong, but it's not recommended." ( http://www.cogs.susx.ac.uk/doc/punctuation/node27.html ) Googling the word "universe" shows that it's written as "universe" about twice as often as "Universe". So I would prefer not to capitalize either use of the word "universe", but the issue is close enough that I haven't uncapitalized any "Universe"'s either. Art LaPella 18:19, 1 August 2006 (UTC)

[edit] Seems the article may need adjusting

Something about the Carnegie Institute of Washington here: [2], I especially like that first sentence about the wrench on the universe's evolution bit, but that's just me. Homestarmy 23:52, 8 August 2006 (UTC)

No, this is just reporters who don't know what they're talking about, as usual. I especially like the "180 billion light years" figure, which was obtained by an incorrect calculation (naively adding 15%) applied to an incorrect value (156 billion light years, as widely misreported in the popular press a couple of years ago).

For an accurate report see Ned Wright's News of the Universe. -- BenRG 13:58, 9 August 2006 (UTC)

[edit] Reference removed

I've removed [3] Evolution of Population II Stars, as the link doesn't work (it redirects to the springerlink homepage). It's possibly DOI:10.1007/s001590050014, but I'm a bit doubtful about that. Mike Peel 19:43, 16 September 2006 (UTC)

[edit] What the hell is a Gyr?

For the first half of the article, the age of the universe is given in billions of years. Then the article switches to giving the age in "Gyr" units, whatever that is supposed to mean, and "Gyr" links to an article which also doesn't define it. Someone needs to fix this, or I'll just replace them all with "billion" and assume that is probably correct. --Xyzzyplugh 23:49, 27 September 2006 (UTC)

Gyr is a standard abbreviation for Giga-year or billions of years (aka

109

Julian rotation periods of the Earth around the Sun). Other abbreviations of SI prefixes that will probably be found in physics articles and the other natural sciences would be things like: Bly = "billion light years", pc = "parsec" which is another way of writing 3.26ly or "3.26 light-years." In the natural sciences, the numerical prefixes are used continually and the shorthand for those is to use the first letter of each, e.g. G for Giga, T for Tera, k for Kilo, c for Centi, f for Femto, etc. It was not a mistake in the article to use the abbreviation but I agree that the article would be best served by using consistent units. The Giga article now reflects this. I hope that helps! Cheers, Astrobayes 00:12, 28 September 2006 (UTC)

[edit] standard representation of ages

Could someone please reformat all the ages we have in this article in scientific notation for easy comparison, or perhaps create a table with the method of calculation & age with all the ages using the same exponent on 10? This would make it easy to see differences/similarities in the calculated values. As well, some measure of error for each value would be nice.

[edit] What came before the universe?

If the universe has only been around for a finite period of time, then what existed before the universe? What I mean is, if there was nothing before the universe, then how can something be created from nothing? Sounds impossible to me. But if there was something always there to begin with, then where did it come from? Can someone explain this to me like a 2 year old? :) Davez621 07:46, 7 November 2006 (UTC)

We don't know if there was anything before the Big Bang, according to the second paragraph of Big Bang. "Age of the universe" is to some extent a widely accepted misnomer for "time since the Big Bang". There are no experts on what happened before the Big Bang because we have no good ways of knowing. I can offer some philosophical mumbo jumbo: if the universe began with the Big Bang, which is a good guess, then we are like artificially intelligent chess programs programmed only for chess, asking how a chess game could have a finite past. What move could have come before move one, and which legal chess move could have placed the pieces on the board? Art LaPella 20:04, 7 November 2006 (UTC)

Mathematically, time itself started with the Big Bang, so there's no such thing as "before" the Big Bang, and there was never "nothing". thx1138 05:45, 19 November 2006 (UTC)

If you can prove that mathematical model represents the consensus view of reality, then I think you should rewrite the second paragraph of Big Bang. Art LaPella 05:57, 19 November 2006 (UTC)

I wasn't talking about the consensus view of reality, just about the mathematical view, which may or may not turn out to conform to reality. thx1138 06:14, 19 November 2006 (UTC)

[edit] Section on Cosmological Parameters

Just added a section on how the age of the universe is calculated based on knowledge of cosmological parameters. I hope this will be educational since it gives you an idea of how the $1 / H 0$ back-of-the-envelope calculation gives nearly the right answer, and how to correct it to get exactly the right answer.

In case anyone would like to build on what I've put down, I've placed a simple Python program that I used to calculate the age correction function, a Gnuplot script to make the plot, and some basic instructions on my user page User:Wesino. I'd be happy to answer any questions if someone would like to use those materials to improve the section. Wesino 14:16, 12 November 2006 (UTC)

[edit] billion?

First paragraph mentions age in billions of years, but the billion link can mean either thousand million or million million, so it should be stated here more obviously to which billion it is refering, or else change the link on billion to be more specific --anonymous coward. —The preceding unsigned comment was added by 203.54.206.36 (talk) 15:21, 8 December 2006 (UTC).

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