# Talk:Universe/Archive 1

 Archive 1 Archive 2 Archive 3 Archive 4

## Questions on the shape of the universe and other things

If the universe is expanding like an expanding balloon, why wouldn't the universe have all stars and galaxies on the surface of the balloon and have a big hole of empty space in it? Is there any reason for galaxies to move away from the center faster or slower? Would some matter still be at the exact location as all matter was originally placed? Like the center of a bomb that just stayed right where the bomb was placed? I e is the universe a balloon filled with stars or are they pretty much plastered along a spherical surface leaving empty space within the sphere?

You're carrying the analogy too far. The balloon analogy is only supposed to illustrate the idea that things can grow farther from each other without moving away from anything in particular. It doesn't even do a very good job of that, because people inevitably get the idea that things are expanding away from a point in the middle of the balloon, which is totally wrong. Best to just forget the analogy. There's no center of expansion of the universe. -- BenRG 17:56, 14 July 2007 (UTC)
Totally wrong? What's the point of a Big Bang Theory if the expansion of the
Universe from one point in space is "totally wrong"? --Denton22 15:25 5 Feb. 2007

In the case that most stuff would be at the outer edge of space: if you looked out from the balloon you wouldn't see anything for there wouldn't be anything there. But now it seems like you see equal amounts of stuff in all directions from the earth, or do you? And why in that case?

Even if all stuff did not move away from the center at the same speed since the big bang you would definitely have some objects moving in almost opposite direction from each other and some objects along each other, like the Milky Way and Andromeda, right? So light from the stuff on the opposite side of the balloon would take much longer to reach us since we're moving apart so quickly? While the Milky Way and its closest galaxies are moving apart very slowly, right?

Check out The Local Group. The Milky Way and Andromeda are not just "moving along eachother" —Preceding unsigned comment added by Denton22 (talkcontribs) 03:35, 6 February 2008 (UTC)

In any way, can anybody find an illustration of what the universe might have looked like all the time to now? And how the objects and formations would be located in relation to each other? Not because anybody definitely know, but just a best guess, that would be really good.

On the age of the universe: For a person sitting on a ball that flew out from the center at big bang it would have felt like 14bn years till today? If the person had a 14bn years half-life in his own time he would have halved till today? How long would it have felt like for a person still sitting at the same place in the center of the big bang till today? Let's say the other person was moving away from him at maximum speed. Would it be 14bn years in that persons own time to? -- JR, 18:54, 19 May 2007 (UTC)

On the Hubble constant: Is it really a constant, is it not decreasing with distance? If it's about 0,022 m/s per light year (0,071 m/s per parsec) that gives a moving away speed of more than light speed at a distance of 14 billion light years. 0,022*14E9 = 308 Mm/s. Is that a problem? I saw that z factors (of red shift) of 6 have been seen. That would give a comoving distance of 19bn light years from a relation between the distance and z-factor i saw. So a good guess is that those stars are moving away at about 400 Mm/s? The distances of 45bn light years mentioned in the article, were those mesaured from red shifts? With the hubble constant they would be moving away at more than 900 Mm/s then? -- JR, 13:41, 29 May 2007 (UTC)

In theory Hubble's law applies to arbitrarily large distances (it has to, because of homogeneity). The speed exceeding c is not a problem. This is a different kind of speed from the kinematical speed in special relativity that can't exceed c. A redshift of 6 corresponds to a comoving distance of 27 billion light years, not 19, according to Ned Wright's cosmology calculator. (The relationship between redshift and comoving distance is not linear.) Multiplying by Ho gives a speed of 600 Mm/s or 2c. Distances like 45bn light years are inferred indirectly by fitting parameters of the model. Redshift is one of the most important sources of empirical data we have, so you could say that the distances are inferred from redshifts in some sense. The most distant part of the universe we can see (via the CMBR) has a comoving speed of about 3.3c. -- BenRG 17:56, 14 July 2007 (UTC)

## False Analogy in 'Shape' Section

The analogy used to show that the universe may have no boundary but be finite is false-- spheres may not have an edge, but they are bounded. The universe is supposed to be unbounded, so we're looking for something to show that an unbounded space may be finite. The analogy given does not do this; it is false. I won't remove it because someone smarter would put it back up. Please consider this and remove it.

I agree. The 'Shape' section is full of false statements, unspoken assumptions, and poor wording. I threw in qualifiers ("may," "if," "conceivably"), but it still lacks rigor and clarity. I don't think anyone who is not already familiar with the concepts described would learn anything from the section. It needs to be rewritten completely. 24.27.9.13 03:52, 8 January 2007 (UTC)

## Our Universe name

Why there is no name for our universe? And is the universe=everything? If universe =everything then what we call this (the 1.9 × 1033 cubic light years)

Is there is a good name for “everything”?

Now if we ever found that the space is a lot bigger then what we thank, and patterns of our universe exist in millions, shouldn’t we name our universe?!

Uh, I think it's just "The Universe." Other universes would just be "Other Universes." It's not like we really need a name for our universe, as we aren't really going to be travelling to other ones. Sorry. Citizen Premier 02:12, 25 October 2005 (UTC)

The good name for "everything" is "universe" :) Chris M. 00:09, 12 January 2006 (UTC)
This is not acceptable. Please come up with a good name. --einexile 00:41, 28 June 2007 (UTC)
Bob is fine with me Denton22 —Preceding unsigned comment added by Denton22 (talkcontribs) 03:37, 6 February 2008 (UTC)

I removed the paragraph

But some of the objects outside of the observable universe can, in principle, be observed indirectly. For example, it is theoretically possible to meet an observer located near the end of our observable universe, who in his past has observed some galaxies that left our observable universe because of expansion.

I'm a mathematician not a physicist but this seems to contradict the paragraph above about Causality.

It's a poorly phrased version of the statement that things that were once in the observable universe can leave it. This hasn't actually happened in our universe, because between cosmic inflation and dark energy domination, it wasn't expanding fast enough, and we were able to observe more and more things. However, in the future, things will pass outside the event horizon, and be irretrievably lost to us. – Joke137 23:58, 17 July 2005 (UTC)

## Meaning of Universe

The Universe is the whole spacetime continuum in which we find ourselves, together with all the matter and energy within it.

Different words have been used throughout history to denote "all of space", including the equivalents in various languages of "heavens", "cosmos" and "world".

For a large fraction of the twentieth century, the word Universe, with an upper case "U", was used to mean the whole spacetime continuum in which we find ourselves, together with all the matter and energy within it.

However, since the standard Big bang model has become well established observationally during the last few decades of the twentieth century, theoretical cosmologists have come up with new ideas of "the whole spacetime continuum" which are much, much larger than the "Universe" corresponding to the Big bang model. For this reason, the word universe can now be used in the plural and with a lower case "u" when discussing theories about all of space-time. There is no clear consensus on what new word to use for the whole spacetime continuum (though some like the term multiverse), and as long as there is no conceivable method of measuring anything beyond the observable horizon (formally speaking, the particle horizon), this is a seen as a moot point (irrelevant) for empirical scientists, and is of interest only to philosophy.

## infinite universe?

It is not known whether the Universe is finite or infinite in spatial extent and volume, although current theories favor an infinite Universe.

although the majority of theorists presently favor an infinite Universe.

Rubbish. The majority of theorists currently favour an infinite Universe, but this is a matter of personal taste and sociology and historical fashion and nothing to do with physics.
I certainly also sense theorists favoring an infinite Universe. I disagree that it is a matter of taste.
http://www.sciam.com/article.cfm?articleID=000F1EDD-B48A-1E90-8EA5809EC5880000 "Parallel Universes" Not just a staple of science fiction, other universes are a direct implication of cosmological observations. By Max Tegmark.
NealMcB 17:46, 2004 May 4 (UTC)
That's why it's stated as "the majority" Chris M. 00:11, 12 January 2006 (UTC)

if the universe is infinite, there would have to exist a piece of matter that is infinte in size, so wouldnt i be able to see it o.O —Preceding unsigned comment added by 64.230.7.12 (talk) 02:18, 10 March 2008 (UTC)

## size of universe

48 billion (48 ? 109) light years.

50x10^9 light-yr = 5x 10^10 *0.3 pc = 1.7x 10^10 pc = 17 Gpc = 12 /h Gpc (where h=0.7 is the Hubble constant) OK :), this is approximately correct for Omega_m=0.3, Omega_Lambda =0.7, though 10/h Gpc is closer. In any case, i'll round to 50 since it's no more than 10% precise.

I'm glad the way this is improving - and i love the desire to avoid ambiguity. Wikipedia is definitely a good tool for spreading relatively wellunderstood information to outsiders without expecting them to waste hours and hours to sort through ambiguous jargon.

--boud

How can the universe be at least 48 billion light years across when the age as we know it is 13.7 billion years? If the current theory is still the big bang then the universe could conceivably be no greater than 27.4 billion light years. --98.200.62.240 (talk) 21:08, 29 December 2007 (UTC)

• The only restriction is that matter cannot travel through space faster than the speed of light in a vacuum. There is no known upper limit on the speed with which space itself can expand. Try taking an empty balloon, and use a marker to put dots all over it. Those dots are the galaxies. Now blow up the balloon. As you blow it up, the distance between the dots increases, however are the dots really moving, or is it that the material between them is stretching? More info here: Metric expansion of space. — BRIAN0918 • 2007-12-29 22:25Z

I see various estimates of the number of particles in the observable universe, e.g. the claim in Wikipedia talk:Size comparisons that It is accepted by astrophysicists that the number of particles in the observable universe? is currently in the 1085 range. This seems like the place to document that. Does anyone have some good references? NealMcB 18:27, 2004 May 4 (UTC)

"...it is estimated to be about 78 billion light years (7.4 × 1023 km)."

Interesting....just based on what did this 'estimated value' came from? At least a note should be provided for this kind of 'data'. LegolasGreenleaf 11:26, Nov 7, 2004 (UTC)

"...billion ..."

What kind of billion?, I meen, 10^9 or 10^12? I know that wikipedia uses 10^9 "if don't state otherwise" but I think that talking about science and to avoid ambiguity, is better 10^9 or the prefixes "giga" or "tera" see wikipedia, long scale alternative approaches

I agree. Jimp 09:21, 28 February 2006 (UTC)
I've never seen a scientist use 10^12 as a billion; short scale is always used. Just like m/sec is always used instead of feet/sec. Gopher65 (talk) 19:59, 16 March 2008 (UTC)

Is it not possible that we are concentrating on the universe as a ball instead of a balloon. Could we not be an outer layer petering out and as for the big bang it is very much like the opposite of the current theory involving black holes, so theoretically could not ours have started from a black hole reaching a set limit then exploding outwards. Baloons inside balloons. So size isn't what is worrying, it's rate of decreasing depth? Based on Sighn's work (hope spelled this right, his signiture is awful!)

This section really needs to be synched to the main article (Observable universe). --Pascal666 02:28, 21 January 2006 (UTC)

To me, it is a logical choice that the universe is infinite.

Here's an explanation: You have space, which is nothing, but is infinite in dimensions. Then you have matter and energy. Matter likes to collect into clumps. Heres the simple question that made me understand why the universe must be infinite. If we did not have a universe with infinite matter and energy, where would it all be? Exactly, one single point.

The Big Bang: A measurable amount of matter crammed into a fine point such as what happened before the big bang needs to interact with something else to disturb its finely packed equilibrium. Think about it; Billions of galaxies packed into a small sphere. Where would the particles be distributed? Protons and neutrons would sink, and the electrons would float. Cut a ball of this tightly packed matter in half with something of comparable mass, and the packed particles are going to scatter outward real fast, and create an expanding cloud of hydrogen gas.

Forgive my rambling.

Djedi81 12:01, 2 October 2007 (UTC)

             Absolute BS!, the singularity that comprised the Big Bang was packed tighter than
"normal matter" would ever allow, thats precisely why we call it a singularity.


In reply to the previous response.. That is the current theory of the big bang, true. I'm simply thinking outside the box of that theory. Throughout the history of theories, they have been challenged, and some of them later found to be either partially or totally wrong. I'm simply stating my opinion. Also, I don't understand what you mean by "normal matter", isn't all matter 'normal'? To me, matter is 'something', where as space is 'nothing', and energy is just a property of matter.

In response to your reply, matter can be packed as tight as the given amount of matter can be under its own gravity. I stand by my theory about the pre-big bang event having two (or more) parts involved. Every action has an equal and opposite reaction. An equilibrium exists in everything to keep it the way it is. If it is suddenly disrupted, well, it changes. Depending on how BIG it is, and how BIG the equilibrium was that maintained its state, well, you can only imagine what will happen. A single ball of matter didn't just spontaneously explode by itself without any outside influence.

The universe, or everything, (including everything that our biggest telescopes can't see) contains an infinite amount of matter. It is impossible to cram infinite of something into a measurable volume. The universe can be labeled a singularity as a whole, but it will never exist within a measurable amount of space. You would probably think of me as an idiot if I say this, but the ratio of space to matter is 1:1. It's the distribution of matter vs space that is completely random, but measurable within a given area.

If the universe did have a finite amount of matter, it would all be at one point somewhere in the emptiness of space. We would not exist, and the universe would be completely boring, no wait, it wouldn't be boring because the term 'boring' wouldn't exist.

I'm rambling again!

Djedi81 09:34, 3 December 2007 (UTC)

## Seeing around the universe

For the time being, I am removing the following statement from the article, because I don't see how it can be true:

"Therefore, strictly speaking, we should call the stars and galaxies "images" of stars and galaxies, since it is possible that the Universe is finite and so small that we can see once or several times around it, and the real number of physically distinct stars and galaxies could be a little smaller. There are observations underway to determine whether this is true."

If the universe were so small that one could see even once around it, wouldn't the night (and day) sky be completely bright? If the universe were unbounded yet sufficiently finite, wouldn't the "image" of the sun exist in every direction that one looked?Johnstone 13:31, 8 May 2004 (UTC)

I'd put it back in. You bring up Olbers'_paradox. See that article for reasons why the sky isn't all bright. But that doesn't depend on whether the universe is bent or flat. It's more about whether you can see an infinite distance. NealMcB 16:16, 2004 May 8 (UTC)
I was aware of that paradox, though I didn't know it had a name. It was in the back of my mind when I decided to question the material I removed. As you say, that paradox is not about the idea of seeing "around" the universe, so it does not necessarily relate to my question. However, I was thinking of the universe as a "spherical space"; I have re-read the sentences in question, and now I realize that my objections do not apply for most non-spherical geometries. I've tweaked a few words to (hopefully) clarify their meaning. Johnstone 22:51, 10 May 2004 (UTC)
What I recall reading is that it would take all time (from Big Bang to Big Crunch) for a photon to traverse a whole universe and return to its original position. Jimp 09:24, 28 February 2006 (UTC)

## universe (fiction)

It might be nice to have an article on "Universe (fiction)" or something -- the sense of the word where somebody says "Many of the Marvel Comics series take place in the same universe" or "The SERRAted Edge novels are set in the same universe as the Bedlam Bards novels". Cwitty

http://www.cs.appstate.edu/~sjg/class/1010/wc/geom/finitespace.html "Is Space Finite?" by Jean-Pierre Luminet, Glenn D. Starkman and Jeffrey R. Weeks

Or not. 80.42.216.244 (talk) 03:25, 26 April 2008 (UTC)

## Shape of the Universe

Hi, I'd like to question the analogue of the shape of the Universe and the shape of the Earth. There are no current experimental hints, that the Universe is not flat. This is stark contrast to our experience on Earth, where it is rather easy to find that it is not flat (ships under horizon etc.) We should change/improve that sentence. Awolf002 23:17, 10 May 2004 (UTC)

Uh, what exactly do you mean? How could the universe be flat? Assuming you're sitting in a three-dimensional chair typing on a three-dimensional computer with three-dimensional fingers, you must not mean completely flat... do you mean very wide and not very tall? And if so, why? A spherical universe seems most logical, if based on nothing but the fact that you can stand anywhere on earth, look up and see celestial bodies in all directions. Another shape would have to be based on contradictory evidence, but that applies to anything, so why specifically flat? I don't see the basis of flatness being any kind of default assumption.

## At least 156 billion light-years?

According to http://www.space.com/scienceastronomy/mystery_monday_040524.html , the universe is at least 156 billion light-years across.

I changed the article accordingly. If someone thinks it was too early and we should wait until the new estimate becomes widely accepted, change it back.Paranoid 12:50, 28 May 2004 (UTC)
while changing from 50 to 78 Bly in radius, it looks like you left unchanged the language The observable universe contains about 7 × 1022 stars, organized in about 1010 galaxies,. Anyone know where that estimate came from? Based on applying the local density to the total volume? Based on observations of deep fields? Something else? If based on density, these numbers would also need to be adjusted based on the new volume. And this all relates to my question above about the number of particles in the universe. --NealMcB 00:04, 2004 May 29 (UTC)

The universe is not 156 billion light years large. That would mean that it expanded past the speed of light which would be impossible given the general theory of relativity. A period of such speed may have been achieved billionths of a second after the Big Bang, but not for long.

## Age - forever uncertain

According to http://www.sciencenews.org/articles/20040522/fob1ref.asp , physicists from National Laboratories of Gran Sasso found the age to be 14.7, not 13.7.

Well, kind of... You need to understand, that the age of the Universe can (and should) be obtained by many independent methods. Each of these methods has its own assumptions and systematic errors. So it is very unlikely you get the exact same numbers from all of these measurements. If the theory about the Universe (on which these numbers are based on) is correct, then these numbers should agree within their uncertainties!
The article seems inconsistent. We have one paragraph stating the age is 13.7 (or 14.7) +-.2, and another saying it is 15.556 +- 0.024 billon years. These numbers aren't agreeing within their uncertainties. We need to square this somehow, at least we should point out the inconsistency. Zeimusu 16:17, 2004 Jun 15 (UTC)
I suspect the 15.556 one is less reliable. If we knew the age with such precision, nobody would be discussing it, doing research and publishing paper about it.Paranoid 18:00, 15 Jun 2004 (UTC)

Does anyone know who wrote that stuff about "the age is the inverse square of the temperature"? I know quite a bit about cosmology, and never heard of such a formula - and actually I think that this claim makes no sense.

In another article on the age of the universe it says that "the age is the inverse square of the temperature" when measuring the universe's age in planck(not sure of spelling) units. From the description in that article these units are based on the temperature of the universe after the big bang.

WRT the 14.7 billion years, I think that was misreported in the popular science media. What the people actually showed that the age of stars and globular clusters is 1 billion years more than previously thought - but adding that 1 billion years simply to the WMAP result makes no sense, since the WMAP result does not depend in any way on the age of the stars. There could possibly be problems now that the age of some stars seems to be older than the age of the universe, but AFAIK, this is not the case, despite this age correction for the stars.

Accordingly, I have deleted this paragraph. If anyone feels it must be reinstated, lets discuss it here first. Zeimusu 12:27, 2004 Jul 23 (UTC)

well, I can claim that the universe is 20 billion years old and you CANNOT prove me wrong...=) while we may have a vague figure of the visible universe, what is beyond what our vision could reach is anyone's guess...who's to say that the next second the Hubble telescope will not see a 'boundary' somewhere beyond the deep field... I think i'm a lil bit drunk... but this stuff is fun to think about — LegolasGreenleaf 11:34, Nov 7, 2004 (UTC)

## Age of Universe - Observation and Theory

The often quoted age of 13.7+/-0.2 Gyr for the age of the universe comes from the first year WMAP results: This measurement is made by using the location of the first acoustic peak in the microwave background power spectrum to determine the size of the decoupling surface (size of universe at the time of recombination). The light travel time to this surface (depending on the geometry used) yields a pretty good age for the universe. Assuming all the various models used are valid in getting to this number, the accuracy of actual data allows a margin of error around 1%.

However, this age is only accurate if the assumptions built into the various models being used are also accurate. This is referred to as “strong priors” and essentially involves stripping the potential errors in other parts of the model to render the accuracy of actual observational data directly into the concluded result. Although this is not a totally invalid procedure in certain contexts, it should be noted that the caveat, “based on the fact we have assumed the underlying model we used is correct”, then the age given is thus accurate to the specified error (since this error represents the error in the instrument used to gather the raw data input into the model).

The age of the universe based on the “best fit” to WMAP data “only” is 13.4+/-0.3 Gyr (the slightly higher number of 13.7 includes some other data mixed in). This number represents the first accurate “direct” measurement of the age of the universe (other methods typically involve Hubble law and maximum age of stars, etc). There is a sense of triumphantism in the scientific community surrounding results like this, and therefore a more careful analysis of the methods and assumptions used, tend to be overlooked.

This, of course, is a classic example of how different methods for determining the same parameter (in this case – the age of the universe) can give different answers with no overlap in the “errors”. It is quite common to see two sets of uncertainties, one related to the measurement and other the related to the systematic errors of the model. In some cases, this can not be done (in theoretical a prediction), but it is not evident why WMAP were not able to do this?

Worth checking out is Science 299 (2003) 1532-1533, available here http://arxiv.org/abs/astro-ph/0303180

There is a purely theoretical approach to calculating the age of the universe which I can outline in more detail here. This comes from a very recent development and hasn't been published yet. Even after publication, it can take some years before a new result like this makes its way into the mainstream (so don't be surprised if you have not heard about this yet.) It is probably best to leave this development out of the main page until such time as it gains greater acceptance. For now this discussion forum should suffice for a preview however:

The redshift of an object in a dynamic universe is related to a scale factor of that universe by the relation R=Ro/(1+z). Where R represents the “scale” of the universe as seen at the redshift z, where the current scale is Ro. The “scale” is just a device to measure the size of the universe, it can be thought of as the radius, but most people use the “scale factor” a=R/Ro, which would be dimensionless regardless of how you represented R.

The temperature of the universe is inversely proportional to its scale; 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=To(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 - around the dull red glow of a hot poker.)

One of the most important cosmological models, is based on the Friedmann equations. This allows you to describe how the universe has evolved over time using an equation like this: t=to(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).

In a universe like our own, most of the contents is in the form of stuff that does not exert much pressure on its surroundings (clouds of hydrogen gas, stars etc). In this model, w=0 and is known as a pressureless, or “dust” model. Here t=to(1+z)^-(3/2), and throwing in our redshift of 1089 and a current age of the universe to=13.7 Gyr gives us around 380,000 years for the age of the universe when the CMB was emitted. This may not seem so tricky after all, but unfortunately, it is not quite that simple.

Embedded in these models is an assumption about time and an interpretation of metric distance which is not entirely correct. That is not to say that they are entirely wrong either: The metric distance defined between two points in an expanding universe increases over time. However, the General Theory of Relativity does not explicitly state how that change in distance should be interpreted. It is entirely valid to consider this change as a fundamental change in the underlying “concept” of distance (and the same situation would also apply to the concept of time).

This type of model immediately solves an important problem relating to our CMB calculation above. If the photons in the CMB went from being hot enough to fry a burger, how come those same photons can't even defrost one today? Where did all that energy go? Of course, this comes back to our idea of the change in the distance scale: These universe expands by a change in the unit system, so the temperature likewise changes with the unit system. In this context, the temperature/scale of the universe can be thought of as being constant over the history of the universe, with no loss of energy in the CMB.

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=to(1+z)^-2. However, there is an additional change in time related to redshift as t=to(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 (even though it seems people try and introduce this idea in most models.)

So this was a very round about way of saying that we can relate the temperature of the universe to the age of the universe. Since we can measure the current temperature and have a model to extrapolate back, all we need to know now is the origin of the graph and read off the age. The earliest valid point in the evolution of the universe if the Planck time. At this time, the universe had the Planck temperature at a state of essentially zero entropy. The Planck temperate is the maximum attainable temperate in the universe and can be thought of as the Hawking temperature of black hole with a radius of the Planck length.

The Planck temperature Tp comes out to around 4.5x10^30K, and we can state Tp=To(1+zmax), where To=2.725K and zmax=1.65x10^30 is the maximum redshift at the Planck time tp. We know that tp=to(1+zmax)^-2, so putting in the Planck time gives us a n age of the universe of 11.667 Gyr. This is not the end of the story however: If time was absolute and never changed, then this would be the correct value, but we need to take into consideration of the change in time over the age of the universe. This is a fairly simple integration and results in a age one third as much at 15.556 Gyr. The CMB temperature is known to a 2mK accuracy, and with some error in things like the Planck units (mainly from G), the accuracy of this age determination is around 24 Myr.

There is a simplification where if expressed in Planck units, the temperature is equal to the inverse square. Dividing To/Tp gives the current temperature expressed in the amount of the Planck temperature 6x10^-31. Taking the inverse square gives 2.72x10^60 which is the age in Planck units. Multiplying by the Planck time gives the 11.667 Gyr again. There is mainly other simple relations like this, including the critical density as the Planck temperature raised to the forth power. In Planck units, the density is 1.3x10^-121, which multiplied by the Planck density is 3.3x10^-30 g/cm^3.

This was a very stripped down and somewhat mangled explanation, but hopefully it has shed some light on the “age of the universe” question.

I notice that you not only snipped my questions and chose to ignore them; you also left our discussion in sci.astro. I count that as a defeat. You call our discussion "fruitless" - you are right there, but you might consider *who* was the one who kept ignoring questions and arguments, and thereby made the discussion fruitless...Bjoern 14:52, 3 Dec 2004 (UTC)
Not so much a defeat, as a waste of time; your questions and arguments didn't warrant the time required to address them. However, if you are still interested, I will be presenting this work at the annual meeting[1] of the American Association for the Advancement of Science on February 20th 2005 (so I need to focus my attention on that presentation for the time being).
Wow, more discussion than I was expecting! I wonder if that can be incorporated into this page or another, it was worth reading. The universe page should have 13.7 billion years as its value for the age of the universe, but I'm going to copy some of your caveats to the main page. Zeimusu 14:41, 2004 Jul 27 (UTC)

My thoughts about the age of the universe... It's infinitely old, and I can't prove it, because I don't have a telescope that can see infinitely. (snicker) Djedi81 (talk) 06:01, 11 February 2008 (UTC)

I want to apologize to Djedi81. I hastily deleted his/her comment, thinking it was on the article page then reinstated it when I saw my mistake. I've GOT to stop doing Wikipedia editing on my coffee break!(BTW some people say I'm older than the universe.)Trilobitealive (talk) 15:03, 11 February 2008 (UTC)
MEANY Head. I find it so hard to understand the scope of the known universe and then go read ardicles like M Theory and find that Theorists think there are multiple universes(Plural?) floating around in a kind of 'soup' just like Cells on a microscope slide! Everything we know as small is replicated as the most massive there is. In theory of course. Anyways, my 2¢.Ziros (talk) 17:04, 11 February 2008 (UTC)

## Capitalizaton

I asked this question on Talk:Kardashev scale but I'm still not confident. this article mizes and matches the use of Universe and universe. Is there a distinction between the two forms or is this a formatting error? Many articles have the word Universe capitalized but this article starts out by uncapitalizing it and then shifts to upper case. The title: Size of Universe and observable universe seems to be using both versions in one line. If it isn't an error there should be a note about it somewhere. Comments? [[User:BrokenSegue|BrokenSegue]] 03:27, 19 Nov 2004 (UTC)

Could it be that the Big Bang is what happens on the 'otherside/inside' of a Black Hole? (Hawking temp) That would provide a starting event for the expansion of this know universe and contribute to the theory of Infinity; an 'infinity of universes'; the only constant being Change/Flux.

## I don't like...

Much of this article depends on the reader subscribing to the Big Bang theory for it to be anything other than nonsensical...other equally (or more) plausible theories concerning the genesis of everything exist, so should they not also be given the spotlight by this article? Redxela Sinnak 16:45, July 10, 2005 (UTC)

Fringe views belong in their own articles. Until the article on time discusses Gene Ray's Time Cube hypothesis, or Earth discusses modern geocentrism or modern Flat Earth views, this article shouldn't discuss fringe views. --brian0918 16:55, 10 July 2005 (UTC)
I was in no way referring to "fringe theories". Please read comments more clearly in future. Anyone else? Redxela Sinnak 11:45, July 19, 2005 (UTC)

What are the other "equally (or more) plausible" theories? I don't think any of the other scientific theories have been tested with nearly the precision of the big bang. –Joke137 13:38, 19 July 2005 (UTC)

Redxela I agree. It seems to me that the current focus on BB and the continual reference to anything other than BB as being 'fringe' stems from the simple fact that most astrophysicists, physicists, and astronomers are simply not educated in the history and dynamics of the scientific method in general. No doubt most are unsure of what the word 'paradigm' even means, completely blind to the fact that the majority of their world-view is restricted to one. (this is now a fragment.. continue with 'BB is viewed..')
Surely, you must be joking!! Are you saying, the people who work on creating a scientific theory day by day are "not educated" to address all these issues? Do you really believe, most scientists would not follow a potentially Nobel Prize winning new explanation for the genesis of the Universe? All this makes me think, that you are talking about non-scientific theories. Please, prove me wrong and give us an example. Awolf002 17:34, 9 August 2005 (UTC)
It is a rare physicist that is educated in the history of the circumstances of his science. How often where you taught in your training to go back to the fundamentals and research the original history and cultural circumstances? Here in the US most physics curriculums simply train in the presently known science with no attempt to portray the cultural and historical background of the science. Im not sure where you got the idea that I think scientists dont follow potentially nobel prize winning theories, because it seems thats all they do, regardless of their foundations and factuality! --Ionized 20:40, August 9, 2005 (UTC)
BB is viewed as correct through biased perception that simply will not be able to see it as anything other than correct. Nearly all 'tests' which verify the BB are constructed from within the BB paradigm itself. The study of the history of the field is of utmost importance, researching original papers from the pioneers themselves such as Hubble can greatly clarify which events lead to the popular acceptance of any one theory over another. Unfortuneatly, most main-stream researchers don't even question the foundations hence would never bother to take the time to research them, and indeed simply discount anyone who has done the research and knows more about it. The history behind Hubble is one of the greatest examples, for he didn't come up with Hubbles law entirely by himself, he was lead into it by colleagues. He observed a relation between luminosity and redshift, it was only latter interpretted by others as 'velocity and distance', and indeed before his death Hubble fought hard to bring this information back into the community. He didn't believe it was recessional velocity at all, there where historical circumstances which forced that interpretation upon it. Anyhow, its a shame that BB is the current focus of the major funding in the field, if all of the funding was taken away and redirected, no doubt the popular conception would start noticing the already existing evidence against the standard paradigm. --Ionized
Good to hear an echoing of my thoughts, fellow music lover ;) Quite shamefully, I cant back up my thoughts as I lost the original source of "genesis dispute". I can assure anyone reading this that it that the points raised in that article were valid. Not to put too fine a point on it, but someone better educated than me must follow up this lead. --Redxela Sinnak 11:04, August 9, 2005 (UTC)

Can someone please make space (of the universe) seem less technical? It is very confusing for the average person to understand, and it seems like the knowledge of physics is mandatory to understand any of it. Please change this.

Try checking out the article in Simple English

SEASONS GREETINGS 2005/2006 <spam removed-- JeremyA 01:46, 25 December 2005 (UTC)>. Thanks.

## Sum of matter and energy

This is a confusing statement that is not necessarily true (especially in regards to the disambig at top referring to the observable universe). Do not continuing inserting this statement. Thanks,--ScienceApologist 16:38, 18 December 2005 (UTC)

The universe consists of energy in various forms , one of them matter ... The sum of energy in the universe is constant. Why do you disagree with that ?

The sum of the energy in the universe need not be constant -- especially if this is about the observable universe (which is continually expanding). --ScienceApologist 03:48, 19 December 2005 (UTC)

According to science the sum of energy (including matter) in the universe is constant.Energy can not be created from nothing.Energy can not be destroyed into nothing.

I know many religious people do not like the results from science - are you making religious censorship ????

I think maybe we are having a problem with English not being your first language. In any case, the article already makes the expression needed. --ScienceApologist 19:41, 19 December 2005 (UTC)

I am taking the liberty to copy the two sentences in contention:

1 - The definition of the Universe is everything that exists. Nothing exists beyond the universe.
2 - The Universe consists of energy and matter, the sum of energy and matter is always constant.

I find it rather difficult to find consensus about them with just the above arguments. Awolf002 20:21, 19 December 2005 (UTC)

## Capitalization revisited

Why is universe capitalized in much of this article? Do sources outside Wikipedia capitalize it? My dictionary doesn't. Neither do any of the external web sites the article links to, at least as far as a cursory inspection reveals. — Knowledge Seeker 04:39, 11 January 2006 (UTC)

Agree that universe would be better lower case for an encyclopedia type article on 'universe'. Could be UK tendency to capitalize many nouns but I think we usually try to keep the style already on existing pages. Possibly, considering the type of vandalizing the page suffers, there appear agendas involving the promotion of The Universe here and related articles. --Eddie | Talk 09:34, 11 January 2006 (UTC)
I've put it in lowercase. The use of uppercase, especially in phrases such as "known universe," is non-standard and the explanation given for the use of lowercase for "parallel universes" alone is original research, to put it charitably. (And no, this is not a UK tendency.) ProhibitOnions 14:05, 11 January 2006 (UTC)

## Update Tag

I was somewhat reluctant to tag it this way at first, but I feel that as the current community of physicists and other scientific disciplines dealing with cosmological principles have well advanced the theories of Albert Einstein (no offense intended there, sorry if it comes off like that) that some more modern sources are required (maybe some more current than 1952). In fact, because this Einstein source is the sole work in the bibliograpical section, I imagine that all of the subjects within the greater subject of the concept of a universe were not in Einstein's original paper. I don't have access to it at this moment but I will dig for it and retract this tag and comment if there is any discrepancy from what I feel is true.

JuniorMuruin 01:06, 18 March 2006 (UTC)

## where is our universe?

on what plane of existence does our universe live on? is there someother plane bigger than universe that hold all other universes as well? if so, they where is that plane? at what point does the universe stop expanding, and what happens when that occurs?

When the universe stops expanding depends on the shape of the universe. If the universe is open, it will continue to expand until the Big Rip(Actually, even after the Big Rip, it will continue to expand). This can also lead to the Heat death of the universe. If the universe is a sphere, it may retract until it beomes a singularity. There are many more factors that will affect the universe's fate. If you are interested, see the Ultimate fate of the universe. Funnybunny (talk/Counter Vandalism Unit) 02:53, 21 May 2006 (UTC)

## Expanding universe...

If the Universe is expanding, then what is it expanding into? Alexrushfear 17:14, 12 May 2006 (UTC)

hehehehehe72.144.128.40 19:30, 20 July 2007 (UTC)

Gods aching sphincter. —Preceding unsigned comment added by 83.70.163.71 (talk) 16:42, 13 December 2007 (UTC)

## Incomplete beginning of the article

The article should start with a paragraph treating "Does the universe exist?". Its perceived existence should not be taken at face value. it could be a mere reflection or an insignificant detail of something bigger that actually exists. Refer to the ending scene of Man in Black for a much dramatized illustration.

## Grammar errors

The sentence "There is controversy over which came first in the universe: matter or energy." Just doesn't seem to fit in. I know it's not the biggest mistake in the world but could someone fix that sentence to be correct?

Uh, could you? You did add the sentence in. Splintercellguy 20:24, 10 July 2006 (UTC)

## "Universe and Mind Embodiment"?

This section was added by 24.90.214.20. I'm not sure that the Wikipedia "Universe" article is the place for touchy-feely new-age hippy speculation such as this. It throws around a lot of big words but ultimately says very little. It is not scientific or supported by any other articles. I feel that this section should be removed. Any objections? I've read that fringe theories belong in their own articles, so perhaps the person who wrote this would like to create a new article or stub in the future. Bvanderveen 22:02, 16 July 2006 (UTC)

Seconded. `'mikka (t) 23:01, 16 July 2006 (UTC)

## Clarifying the universe

This should add to better understanding of many aspects of the univese.

Two wrong and harmful assumptions

There are two basic reasons for the mysteries in the standard model of the universe – and they are due to two wrong assumptions that should be corrected in order to really understand our universe.

The first wrong fundamental assumption about our universe is that Newton’s laws and gravitational constant (only derived from observations in our solar system) are also valid at galactic distances outside our solar system.

The second wrong fundamental assumption is that the observed red shifts of stars show that the stars are receding and that the universe is expanding.

It is important that the scientific community take careful consideration of these two basic assumptions in order that many capable scientists do not waste any more of their precious years of research following ideas and trails that will be discarded by future generations.

The consequences of these assumptions (for over seven decades) are that they directed many excellent physicists into beliefs about the universe that are strange, wrong, and not really productive. There now are serious errors in the commonly accepted model of the universe.

GRAVITY AND DARK MATTER

The first wrong assumption is the implicit belief that Newton’s law of gravity is also valid at cosmic distances. There are no observational proofs for this assumption. In fact when used together with early observations of the motion of groups of galaxies (reported by F. Zwicki), and the motion of stars in spiral galaxies (by V. Rubin), these observations according to Newton’s laws need massive amounts of missing matter, now called Dark Matter, to explain the many observations.

The equations describing the rotation of the stars in spiral galaxies, balancing the gravitational and centrifugal force, result in M*G = r*v*v where M is the central force and G is Newton’s gravitational constant.

In regions where the rotation velocity curves are flat (constant) this requires that either M increases linearly with distance r, or that G increases linearly with distance in the region of constant rotation velocity. The usual assumption is that a linear invisible mass is the explanation for the unusual observations thus leading to a need for massive amounts of dark matter.

Actually my simple extension of the gravitational constant G consisting of an additional term linear in distance, A*r, can explain the observations without needing to search for dark matter. (This is different from the interesting MOND theory of M. Milgrom that involves acceleration.) Note that with this extension of the gravitational constant with large distances, Newton’s laws and Einstein’s General Relativity are still valid in our solar system at the smaller distances. The observed gravitational lenses are also explained without needing dark matter.

MEANING OF THE RED SHIFT

The second, and more critical, wrong assumption is that the observed red shifts are only due to the Doppler effect and presumably show that the stars with red shifts are receding.

This wrong assumption concerning the causes and meaning of the red shift has resulted in a number of even more serious errors, including the apparent expansion of the universe, the supposed initial inflation, the apparent acceleration of the expansion, and the need for Dark Energy, the wrong age of the universe based upon the Hubble constant, the big bang, Inflation, and the explanation for the Cosmic Microwave Background and its low temperature. A number of Nobel prizes were awarded based upon excellent works that unfortunately were based upon these wrong assumptions.

The red shift initially termed by Hubble as an “… apparent Doppler effect …” is supposed to measure the apparent receding velocity of remote stars, leading to the conclusion that the universe is expanding. This apparent expansion encouraged Einstein to remove his cosmological constant, which he previously had inserted into his equations to support his belief (wish) for a static universe.

Actually, there are three additional contributions to the red shift and they are only due to gravity. The first is for photons leaving large masses. The results are that massive quasars can appear to have large energy output, and transverse (angular, “proper”) velocities greater than the velocity of light. This is because the apparently large distances determined from the red shift make the quasars appear to be further away. This also explains why galaxies that appear to be connected by streams of stars (H. Arp) also show different red shifts indicating large differences in distance (a massive black hole in the further galaxy adding to the red shift).

The second contribution to the red shift is for photons traveling large interstellar distances and is due to gravitational drag by interstellar dust and gas (without collisions or absorption and reemission that would blur images). This is similar to the gravitational drag by our moon on Earth tides causing the moon to lose energy, without needing blurring effects on the photons.

The third contribution is due to the long-range drag by the extended gravitational constant (related to the apparent dark matter), and adds a new logarithmic term, ln(r) as a contribution to the red shift. The logarithmic term arises from the integration of the force with the inverse r term in the extended gravitational constant with respect to distance to determine the loss of photon energy.

The apparent accelerating expansion of the universe is due to the observations that very remote stars are dimmer (and further away) than predicted from their observed red shifts based upon the Hubble linear relation ship between red shift and distance (S. Perlmutter). The result is the apparent need for Dark Energy to power the acceleration.

For very remote stars, determination of distance from red shift and the Hubble constant is no longer linear and should be corrected by the ln(r) contribution for the extreme distances. This error makes the distance for very remote stars based upon intensity much larger than expected from the assumed linear red shift. The wrong interpretation of distance based upon observed red shifts and distances of very remote stars resulted in the wrong concepts of accelerating expansion, and dark energy to provide the reason for the differences between red shift distance and the light intensity determination.

The cosmic microwave background is caused by the effect of gravity on photons traveling long distances to reduce the photon energy to the microwave range. Gravitational interactions will equilibrate the microwave photon energy to thermal equilibrium with the very low (2.7 K) temperature of interstellar gas and dust.

The loss of photon energy traveling from very remote stars will shift the wavelength out of the visible range – and this explains Olbers paradox (why the sky is black in spite of the vast number of stars).

SUMMARY

A careful, open minded review of the points raised here could be beneficial to the future progress of the scientific community although the results could be upsetting to many intelligent and productive experts working in this field.

If you feel that these explanations have merit, please feel free to send a copy of this document (unchanged) to your friends and colleagues.

508/651-0140 itgplus@earthlink.net To be updated: http://inventing-solutions.com/simplified-universe.htm

That's interesting stuff and I would be happy to see it on the main page... once it's published in a peer-reviewed scientific journal. SheffieldSteel 19:14, 1 March 2007 (UTC)
Can we just paraphrase all that by saying that "photons are shagged-out after their long journey". Makes sense to me. Far Canal (talk) 05:45, 12 December 2007 (UTC)

Where is Null under See Also fit in? I'd fix it but i can't figure it out.

## When was the density equal to water?

How long after the big-bang did it take for matter in the universe to reach a density equal to that of water? Also, how long until a density equal to that of air at sea-level was achieved? Thanks

## Problem in para - anyone know what this is supposed to mean??

I edited out this rather confused segment, be grateful if someone can (a) explain what it's all about and (b) make some sense of it in the right page context:

"== Hisgalaxy formation theory predict more nearby small galaxies than observed.

passes through the intervening gas clouds. The ionization of these gas clouds is determined by the number of nearby bright galaxies, and if such galaxies are spread around, the ionization level should be constant. It turns out that in galaxies from the period after cosmic reionization there are large fluctuations in this ionization level. The evidence seems to confirm the pre-ionization galaxies were less common and that the post-ionization galaxies have 100 times the mass of the dwarf galaxies. [citation needed] tory of the universe ==" MarkThomas 19:54, 26 August 2006 (UTC)

## This whole theory is illogical

Question #1: If there is a Big Bang, where did everything come from before that? And the answer that it all shrunk down to some superball only leads to "where did that come from?"

In fact, the entire theory makes absolutely no sense, except to say that we do not understand the core nature of both mathematics and of physics.

Far too much money is wasted on this meaningless research, really, while the pseudo-intellectuals debate the trivialities of Big Bang and other theories, what's really needed on this planet are solutions on this planet, and not idylls of the rich wasted money on what is nothing more than a trick to avoid the needed responsibilities. Not unlike kings and emperors playing darts while large portions of their populations go starving, or worse, are used for another game, genocidal chess.

AHEM. The self irony of just what you've written. above! Followed by even funnier stuff in which you expect us to waste our time paying attention to what YOU think about such matters, which you've just said aren't themselves really important enough to warrant attention. Hmmm.

Listen, Bub, FYI this TALK section is for the "special interest group" of people who are interested in the Wiki article on the Universe. If you're interested in other stuff, go attend to them. Don't come and bother us, HERE. Next, there's actually no place on WIkipedia for your pet unified physics theories. Put them on your web page. I'm SURE that HERE is not the place for them. So I'll be deleting them. Anybody interested in them can recover them from this page's history. SBHarris 20:09, 10 February 2007 (UTC)

sbharris... What's "pet unified physics theories" supposed to mean? do you get a kick out of belittling people like that? Let me inform you sir, that the Big Bang Theory is just a Theory and so long as its a theory it's nothing but an opinion emphasized and agreed upon a wide amount of pompous scientists. Why don't you draw your own conclusions instead of being so EASILY influenced by a piece of paper claiming the existence of the Big Bang Theory. Maybe i shouldn't make such a big deal out of this but i tend to find your kind quite rude and arrogant.
At the risk of aggravating a squabble that otherwise never really got started, despite the best efforts of our anonymous lecturer here, I wonder if in the case of this article - as with other subjects that tend to attract particular vitriol from those of a certain religious bent, such as evolution - it might be worth placing a little more information about just what a 'theory' is, scientifically speaking, in the article itself. I realise that there's already a specific article on scientific theory, but since this misunderstanding (deliberate or otherwise) is the basis of a large percentage of the anti-scientific arguments ("it's only a theory so that means no-one actually knows"), would it be better to push that info at every end and turn, rather than expecting someone who probably isn't all that interested in what 'theory' really means to make the effort to go and find out for themselves? Or, on the other hand (and the reason I haven't added it myself), is that in itself pandering to the anti-science (usually religious) lobby more than is healthy? Incidentally, for honesty's sake, I consider myself religious - but I know that doesn't mean I have to be anti-science. - Shrivenzale 14:05, 1 December 2007 (UTC)

## A Map of the Universe

A recent publication :: http://arxiv.org/abs/astro-ph/0310571 :: includes a link (on page 50, http://www.astro.princeton.edu/~mjuric/universe ) to the various maps produced by the analysis. The linked-to page includes statements to the effect that the maps may be reproduced for 'classroom wall' display. Could/should they be incorporated into the wiki Universe article, i wonder? ed. (newolder)

## Origin of name, "Universe"?

Kent Hovind said the name, Universe literally means a single spoken sentince. Uni meaning one, and verse meaning a single spoken sentence. As such he insinuates that the word, "universe" comes from the idea of god creating the universe by speaking it in one sentence. Is there any truth to this? Inforazer 14:00, 20 September 2006 (UTC)

I have found two etymologies, but not that one (yet). Most commonly, dictionaries state something like "From Latin universa, unus or uni one + versus from vertere turn Via Old French univers. Originally literally all turned into one." rossnixon 09:36, 13 October 2006 (UTC)

Kent Hovind made up a lot of things including his own tax system. Due to the shortsightedness of the Federal government he's continuing his bold researches in a prison cell. 83.70.163.71 (talk) 16:48, 13 December 2007 (UTC)

## uni verse = one word or all things accomplished in one word

Also, see this: Special Dispensation for the Big Bang theopsis

--CyberSongs 20:02, 16 October 2006 (UTC)

## "Seems nonsensical"

My edits to the section "Size of the universe and observable universe" were just reverted with the comment "seems nonsensical". I'm concerned about this, because an encyclopedia article isn't very useful if it reads like nonsense. The fact is, though, that a lot of the old information in this section was just wrong, and it desperately needed rewriting.

The old content of the section was longer and had two references, both of them to poorly researched, inaccurate web articles distributed by general news sources. My revised version is much shorter and has only one reference (to an actual research paper). I deliberately reduced the size to avoid duplicating information that's already on the Observable universe page. I also updated Observable universe to explain why the numbers previously quoted in this section are wrong.

There's an unusually large amount of misinformation about big bang cosmology in the popular press, and I want to impress on people that just because you read in BBC News or Discover magazine that the universe is 156 billion light years wide doesn't mean that it actually is, or even that any cosmologist has claimed that it is. -- BenRG 15:15, 18 November 2006 (UTC)

## Failed GA on 12/3/06

I'm sorry, but this article has a few issues (and one glaring problem) that need to be corrected before it can become a Good Article. As per WP:WIAGA:

• 1(a)- well-written/prose: A lot of individual phrases needed to be changed. To wit:
• From "Expansion": "...the farther away from us galaxies are, the faster they move away from us." Writing should never be done in the first person; in this case, "us" should be "Earth."
• From "Expansion": "As with most things in physics, that certainly wasn't the end of the story, as attested by the update and reissue of The First Three Minutes in 1993." This is an incredibly unencyclopedic sentence. I certainly do not want to sound condescending, as a lot of hard work has obviously been put into this article, but "that certainly wasn't the end of the story" is simply unacceptable.
• From "Pre-matter soup": "..the first hundredth of a second was a bit of a mystery." Again, "a bit" should be changed. Ditto to "Fast forwarding to after the existence of matter..." from "First galaxies," "...there is no reason to believe that this bound is anywhere near right" from "Size," and a handful of other phrases that need to be improved in tone.
• 1(c)- WP:MOS adherence: There are no real style problems, except for there being far too many external links. Please see WP:EL; external links should be kept to a minimum and only added when necessary, which many of these are not. In addition, it would be a good idea to list what source each link comes from, as opposed to simply including the article's title. This is not a big deal (one could simply scroll over the link to see the address), but it's a little touch that can go a long way.
• 2- factually accurate and verifiable: The big one. The article currently has two {{citation needed}} tags, but there could be many more. For a topic this expansive, having only four references equals not having nearly enough references. I doubt there are any Good Articles within all of Wikipedia that contain so few references.

I know that this article could easily be a GA if a little more work is put into it. There are a lot of things to like about this article- it's very comprehensive, it's got an excellent image, and it's NPOV, touching on many different theories. Best of luck, and feel free to resubmit to WP:GAC when the above issues are addressed. -- Kicking222 16:25, 3 December 2006 (UTC)

## How many stars in the universe?

I didn't see an mention of how many estimated stars in the universe (i.e. how many total stars in all galaxies). Any idea? --Calan 19:57, 23 December 2006 (UTC)

From star, "A typical galaxy contains hundreds of billions of stars, and there are more than 100 billion galaxies in the observable universe." So it's about 10^22, and should probably be in the article. Xiner (talk, email) 22:35, 3 January 2007 (UTC)

Gott et al, in their mind-buggeringly good paper 'A Map of the Universe' [2] say "the currently observable universe is home to of order 6 * 10^22 stars". Excellent guess, Xiner! -- Tom Anderson 2008-01-13 21:27 +0000 —Preceding unsigned comment added by 62.56.80.10 (talk)

## Etymology

I just added the etymology info from Wiktionary, which I assume is kosher. I don't know if it's necessary (or even welcome) to cite taking info from a sister project. Drooling Sheep 09:46, 4 January 2007 (UTC)

## footnote one

"It is not known whether the whole Universe is observable . . ." To me this seems like an unnecessary sentence. In any case, footnote one, which is the reference citation for it, does not make a statement about this that I can see. Sincerely, Mattisse 19:10, 4 January 2007 (UTC)

Whether or not the whole Universe is observable makes a huge difference. Please read the reference again, and read the review papers listed in that reference. Thanks. Boud 14:52, 5 January 2007 (UTC)
I don't see this in the article anymore, so I suspect that it was removed in the past year sometime (I wonder how you archive a talkpage. This one certainly needs to to be done). But anyway, it is expressedly known that the entire observable universe is not observable, so it would be wrong statement in any case.Gopher65 (talk) 20:11, 16 March 2008 (UTC)

## introduction reworked

i've done a major reworking of the introduction, trying to retain the various contributions of different editors while also trying to make it short, correct and complete. This is not easy, because practising cosmologists are not always careful about their use of terms - partly because people doing research know the concrete meanings of the terms, while researchers talking to or writing for the general public have to simplify things, which is difficult to do without saying things that are incorrect, confusing or misleading. But hopefully this wikipedia entry will soon be correct, clear and reasonably complete. :)

TODO:

• Some of the bits of the introduction should probably be expanded in the main part of the article.
• We should check usage to see if "observable Universe" or "observable universe" is more frequently used in scientific articles. http://arxiv.org/find/astro-ph
• The present version is a bit English (language)-centric. Many languages do not have articles, so the distinction between "the" and "a" universe does not exist in those... universes ;). Many scripts do not have upper/lower case, in which case there's no way to distinguish "Universe" from "universe". On the other hand, most modern cosmologists publish nearly all of their articles in English. This is too much detail for the introduction - but can we omit it totally?
• Cosmologists frequently switch between space-time thinking and comoving space thinking. Is this done correctly and clearly (for those who wish to know the difference) in the present version?
• i'm not quite sure where to put: Philosophy deals with the related philosophical notion of the world.
• i've removed this bit since i think it's redundant and the intro is long, though i understand the motivation (to make it clear that this is a physics model not a postmodernist or religious intuition or poetry). Both theorists and observers base their models by assuming fundamental theoretical principles and laws that govern matter, energy, space, and time (all of which are tightly interrelated to one another). These principles and laws are constantly tested empirically.

Boud 15:19, 9 January 2007 (UTC)

The opening sentence shouldn't be the origins of the word. Ideally it should be of the form 'The Universe is...'. I don't think it's necessary to bog the intro down with excessive collaries, such as 'Physicists' concept', given that there is a disclaimer at the top.--Nydas(Talk) 17:03, 9 January 2007 (UTC)
A couple of comments per the WP:MoS:
Thanks. — RJH (talk) 18:43, 9 February 2007 (UTC)

## Failed "good article" nomination

This article failed good article nomination. This is how the article, as of February 10, 2007, compares against the six good article criteria:

1. Well written?:-The lead section needs a lot of work (the universe in philosophy is not mentioned in the body). There is also a tag complaining about the informal tone in the article.
2. Factually accurate?:-There are citation tags all over the article. The lack of citations make some elements at least seem like original research such as the place underneath the formal tone tag. I would ask that you refrain from putting an article for a GA nomination with tags on the article, even if it is after an AID.
3. Broad in coverage?:-This article fails to consider philosophical and religous views on the origin of the universe.
4. Neutral point of view?:-Lack of citations and selective information would give the indication of POV, but I believe this is more a verifiability and broad in coverage problem.
5. Article stability?-No edit war that I can see
6. Images?:-Good amount of images

When these issues are addressed, the article can be resubmitted for consideration. Thanks for your work so far.

GA review (see here for criteria)
1. It is reasonably well written.
a (prose): b (MoS):
2. It is factually accurate and verifiable.
a (references): b (citations to reliable sources): c (OR):
3. It is broad in its coverage.
a (major aspects): b (focused):
4. It follows the neutral point of view policy.
a (fair representation): b (all significant views):
5. It is stable.
6. It contains images, where possible, to illustrate the topic.
a (tagged and captioned): b lack of images (does not in itself exclude GA): c (non-free images have fair use rationales):
7. Overall:

--Jorfer 17:17, 10 February 2007 (UTC)

confused :/

tried to rewrite no avail plz tell me what matter-soup is ? Pipsqueak007 00:37, 16 March 2007 (UTC)pipsqueak007Pipsqueak007

The original review by Jorfer used an older version of GAList: I substitute it below. Geometry guy 21:13, 7 November 2007 (UTC)

GA review (see here for criteria)
1. It is well written.
a (prose): b (structure): c (MoS): d (jargon):
2. It is factually accurate and verifiable.
a (references): b (inline citations): c (reliable): d (OR):
3. It is broad in its coverage.
a (major aspects): b (focused):
4. It follows the neutral point of view policy.
a (fair representation): b (all significant views):
5. It is stable.
6. It contains images, where possible, to illustrate the topic.
a (tagged and captioned): b (lack of images does not in itself exclude GA): c (non-free images have fair use rationales):

## Beginning and End

Hello, I am into black holes, universe, astronomy;; to answer your question;; where did Big Bang come from, first of all, that waas never proven, it's still and will remain theory and even hypothesis, ok. Its possible there were many big bangs. And there may be more. The visible Universe we see goes back no more than 20 000 000 000 years. It's possible there are other universes, within multiple universes, multiverse. Same question remains if God has no beginning and no end, who created him, too much to know... But is there better theory than Big Bang? How many r there? User_talk:Researchlady

Be careful, very careful, if you are "into black holes". They are hard to escape from. rossnixon 02:31, 5 April 2007 (UTC)
Very likely simply we're living inside an immense computer whose sole purpose is to determine the meaning of life and existence. We don't ever want to find the answer though as that will bring the program to an end. Sleep well... ;-) — RJH (talk) 22:42, 27 April 2007 (UTC)

Please do not make statements about whether or not theories will remain as theories. The Big Bang theory is not a hypothesis. That is why it is called the Big Bang theory and not the 'Big Bang hypothesis'. Additionally, The Macquarie Dictionary defines hypothesis as 'a mere assumption or guess' and the The Concise Oxford Dictionary as 'a groundless assumption'. This is not the case with the Big Bang theory as there is evidence to support it. 'God', or the notion of any 'divine creator', is completely and utterly irrelevant to science and, consequently, this page. Please specify what a "better theory than Big Bang" entitles. Are you asking how many theories there are - or 'Big Bang's? Lastly, it is not "very likely" that we exist "inside an immense computer". --F Notebook (talk) 10:58, 19 May 2008 (UTC)

## Universe and Dimension

Is there any difference between a universe and a dimension? I do think so, but since when you go to the disambiguation page for dimension, it says, at the bottom, that it might refer to simply an alternate universe. Tom@sBat 01:49, 9 May 2007 (UTC)

## No cite of evidence for this

"During the early phases of the big bang, equal amounts of matter and antimatter were formed."

I believe this to be an assumption until shown otherwise. Brian Pearson 20:56, 30 May 2007 (UTC)

Well, isn´t there always an equivalent amount of matter and anti-matter? Tom@sBat 21:32, 7 June 2007 (UTC)
I don't know. I've often heard it said that there's always been the same amount of each, but since then I've questioned it as possibly an assumption which somehow transmuted to "common knowledge". I'd like to see evidence showing this equivalence. Brian Pearson 04:21, 19 June 2007 (UTC)
The number of CMB photons compared to the number of baryons is all the evidence required to show this. See baryogenesis for more. --ScienceApologist 13:22, 19 June 2007 (UTC)
As a layman, I'll need a bit more convincing. BTW, I was reading about how they were estimating the size of the observable universe. They did not try to estimate the unobservable universe, which to my mind, would encompass a sphere having a diameter of 32 billion light years. It seems to me we should be able to estimate the whole, given what we can see. Brian Pearson 00:39, 24 June 2007 (UTC)
If the universe was closed and had a measurable curvature, it might have been possible to estimate a size of the unobservable universe. However the universe appears to be flat or open, so there is no evidence that it is of finite size. The equal amounts statment may have to be changed to say that there was slightly more matter than antimatter, otherwise there has to be an explanation of why is there more matter in later times as we observe now? However it says 'formed', and if the matter/antimatter was formed from photons, that would be the case. But was there always more matter than antimatter? GB 03:27, 24 June 2007 (UTC)
I was just reading some of the earlier comments. One person posted a link [3] in which there was an estimated diameter of 156 billion light years. BTW, I find it incomprehensible that we would have an infinite universe with an infinite amount of mass. I would think that a 'Bang' would produce a spherically shaped universe. Brian Pearson 16:33, 27 June 2007 (UTC)

## Speculative Questions

I'm unsure if there are scientists out there who have looked into these questions, but if there are could you give possible ideas/theories about these questions: 1. What is at the edge and beyond the Universe and then whats beyond that? 2. Where did it come from and what was in the space before the Universe?

I find it all facinating, its just annoying that we probably won't have many answers in my lifetime. (Simon.uk.21 10:27, 14 July 2007 (UTC))

Yes, it is extremely annoying. But from what I've read, it seems after awhile, the path of light emitted outword, eventually curves back. Therefore spacetime, at some point, "peters out". Distance becomes meaningless. Just the same, I'd like to speculate that somewhere out there, there are other universes -- maybe an infinite number of them. But, we may as well be talking about an exchange of information from someone inside a black hole. There can be no information from other such universes to ours which would verify that. Brian Pearson 16:48, 17 July 2007 (UTC)
In some versions of FLRW cosmology, light eventually returns to its starting point (assuming it isn't absorbed or deflected en route). But that's not because space "peters out", it's because space has a spherical geometry and the light circumnavigates the sphere. The total volume of space is finite in this case. This doesn't appear to be the case in the real world. It's just possible that space might have a spherical geometry, but even so the light wouldn't return because of runaway expansion.
As for what's at the edge, (a) there might not be an edge, (b) there might be an edge with nothing beyond it (not even empty space), or (c) there might be an edge with something beyond it whose nature we don't know. In the time direction, there might not have been anything before the current expansion (not even time), or there might have been something whose nature we don't know. There's no apparent way to settle these questions, at least for now. There might be other universes, but there's no apparent empirical way to detect them, so that's also not a scientific question, at least for now. Of course, it's just as unscientific to claim that they don't exist as to claim that they do. -- BenRG 17:22, 17 July 2007 (UTC)
The curvature, or the path that light takes, would define the "edge", I suppose. Then, there would be no "spacetime" Beyond that. Brian Pearson 04:43, 23 July 2007 (UTC)

## U and u

The first sections spend too much time discussing naming conventions. Can we make a Capitalization of universe (or similar) section that discusses the opposing uses, and then chooses the most neutral and readable naming convention for the rest of the article? Zojj 09:31, 15 July 2007 (UTC)

I moved all the U vs u discussion to one section. Zojj 08:22, 18 July 2007 (UTC)

## I Have a Question, Universe Age/Size

Expansion[4] of the universe is not just the galaxies physically moving apart. Spacetime, itself, is expanding, but I believe most of this expansion was nearer the beginning of the universe. Brian Pearson 02:20, 11 August 2007 (UTC)
I was hoping that a good explanation could be added to the page itself, since I believe that this would be a common question. I am not sure that I understand your answer, all objects in the universe were in one location at the time of the Big Bang, and now they are further apart than should be possible without traveling faster than light. I was expecting some relativistic answer, (like it has been longer from the perspective of the items furthest apart, or the like) but you seem to be implying that items can get further apart in less time than the speed limit of light allows IF space itself expands under them. Since space is defined by distances, force, and time, (and the force required to cause acceleration to get one item to another in a certain amount of time) I guess that I can't quite wrap my brain around how space can expand without simply meaning that the only items IN space spread out, thus expanding space/time. If it is the expansion of the items that caused the expansion, then how can we use that expansion to explain their super light speed movement? If the expansion of space/time means something other than this, then what does it mean? --Jlc46 00:47, 13 August 2007 (UTC)
I agree it should be written so people who are less familiar with the topic can better understand it. Brian Pearson 04:03, 13 August 2007 (UTC)
Basically this is a magic/pseudoscientific "fudge factor". These are often required in science to fill in gaps that otherwise would require the existence of God to explain. rossnixon 02:41, 13 August 2007 (UTC)
You might be interested in reading the big bang article. The 'Bang' was not an explosion like dynamite, but an explosion of spacetime, probably with emphasis on the fourth dimension, space. Brian Pearson 13:31, 13 August 2007 (UTC)
Have you seen this "New Scientist" article [5] from 2004? rossnixon 02:30, 14 August 2007 (UTC)
Yes I have. It is not factual. Example: A star that is 13 billion years old [6] No 'fudge factor' needed. Brian Pearson 03:49, 14 August 2007 (UTC)
Full size galaxies 12 billion light-years distant discovered last week? [7] - this was supposed to take billions of years - maybe we need to "think outside the bang". rossnixon 11:09, 15 August 2007 (UTC)
Did you even read the article? It's about how there's still more to know about galaxy formation. There's nothing about disproving the big bang. You read into that yourself. GSlicer (tc) 02:52, 16 August 2007 (UTC)
It's difficult to know how to explain this without getting into the details of the FLRW model, but maybe the following two points will help:
• Special relativity is a good approximation in many situations, but it's totally wrong at cosmological scales; you really need to use general relativity. Many concepts from special relativity don't carry over. For example, it's simply not true, in any meaningful sense, that light that has been traveling for a time t has traveled a distance ct.
• The distances like 78 billion and 46.5 billion light years are "comoving distances", which means they're measured in terms of the size of the universe in the present era. For very distant objects, the light we see was emitted when the universe was much smaller, and so its travel early on "counted for much more" than it would now. Instead of thinking of the universe as being smaller in the past, you can think of the speed of light as being larger; it amounts to the same thing.
Is this helpful? Should it be added to the article? -- BenRG 23:30, 18 August 2007 (UTC)
I recently read that the bang took place in the first few seconds (how 'long' those seconds were, relative to seconds today, are another question), but I've also read that there is still a certain amount of expansion above and beyond that as explained by inertia or dark matter, and blue shifts or red shifts. I think some clarification would be helpful to the reader, but I recognize that there may still be some questions about what we know. It's possible those 'in the know' find it hard to see a perfectly good piece of writing from a novice's point of view. On the other hand, I can see how the size of an article can be too large, just trying to explain every detail. The interested reader should be expected to explore links and sources up to a point. I guess the whole thing comes down to a kind of balance. Since I'm not an experienced editor, I wouldn't be able to make that call. I do wonder how many people look at a given article and scratch their heads. Brian Pearson 01:37, 19 August 2007 (UTC)
It's been a long time since I was in school. But it seems to me light emitted from comoving sources would fit the Special Theory, while at the same time, the General Theory wouldn't rule out what you are saying. I'm a little vague on that. It seems the GT mostly deals with gravity. Brian Pearson 01:20, 21 August 2007 (UTC)

I did not take the time to observe all of your comments upon this particular subject, the law that you are arguing states that matter can not exceed celetaris in current space time. Theoretically space-time did not exist until the begginging of the universe nor outside its boundaries, therefore the Universe could have traveled faster the speed of light in expansion. This law only applies to known particles, mainly matter: photons, quarks, gluons, electrons etc. Derek Yoda's friend (talk) 02:15, 23 February 2008 (UTC)

## How to say Universe in German

The German language has a beautiful, poetic word for Universe: das All. Normally I'd think "universe" is an advanced concept and so would be polysyllabic in every language (monosyllables being reserved for basic concepts like: man, child, eat, run). Not in German: Das All. I would mention this in the Universe#Other terms section but I can't think of an economical way to work it in. I'll leave it for someone who has time. -- JEBrown87544 15:10, 6 September 2007 (UTC)

## Definition Problems

Wikipedia’s present definition of the universe is “The universe is the summation of all particles and energy that exist and the space-time in which all events occur.” I’m OK with the words in that definition until it reaches the word summation. If the people who think the universe is infinite are right, summation is out the window.

The next troublesome word is particles. Basically there are two kinds of particles: elementary particles that contain no component particles and composite particles that do contain them. Didn’t the definers realize that the present day elementary particles are those of the standard model of particle physics, a model that does not account for gravitational force? Without gravity there would be no sun, moon, or stars, not even air to breathe. Until somebody comes up with elementary particles that account for gravity, we can forget about elementary particles.

As for composite particles, if you add a composite particle to the sum, the definition‘s "all particles" requires you to also add its component particles to the sum. That’s like being charged twice for the same automobile (once for the auto and then for each of its components). You shouldn’t let a car dealer or a cosmologist get away with it. Whether elementary or composite, scratch particles from the definition.

If particles can’t be summed, how in the world can their gravitational and kinetic energies be summed? Goodbye energy.

We are left with space-time, which is a construct of an abstract mathematical model. Constructs and models exist only in the mind; they don’t belong in a definition of the world outside the mind. Space-time vanishes, leaving the following definition: the universe is the ______ of all ______ and ______ that exist and the ______.

Definers, back to the drawing board!

Nafyladok 15:13, 18 September 2007 (UTC)

Defining terms like "life" and "the universe" is effectively impossible. I don't much like the current definition, but it's probably unreasonable to expect anything better.
"Summation" is being used in its ordinary English sense, which is closer to mathematical set union than to mathematical summation. It could be replaced with "sum total" or "collection" or "aggregate" or just deleted (along with the two bracketing words).
The distinction between elementary particles and composite particles isn't important here, provided you interpret summation in its colloquial sense. The universe contains both valence electrons and atoms. I imagine gravity was supposed to be included in "the space-time in which all events occur." "Particles and energy" is arguably redundant.
Spacetime is as real as elementary particles are. -- BenRG 16:07, 18 September 2007 (UTC)
Per your suggestion let’s delete summation and its two bracketing words, redefining the universe as all particles and energy that exist and the space-time in which all events occur. Shall we use the word all in its collective or distributive sense? Here’s an example of the collective sense: “The weight of all the rice grains in that bag is one kilogram.” The collective sense of all implies mathematical summation, which, as I have shown, leads to universe definition problems.
In the sentence “All cats are gray in the dark.” the word cats refers to the abstract class of which each member is a cat. Here the word All is used in its distributive sense meaning any or each and no summation is implied. If all is taken in its distributive sense for the universe definition, the universe would be an abstract class (the universe class) whose membership consists of all particles and energy that exist and the space-time in which all events occur. While we’re at it, if we’re making the universe merely an abstract class, let’s just say the universe is the class of all things that exist. That way the universe could include the sun, moon, stars, galaxies, clusters, atomic nuclei, orbital electrons, particles, energy, and even you and me. If space-time exists we can throw that in as well.
But, defining the universe as a class is not without problems. Once the rules for membership in a class are specified, that class can never change. To change the membership rules is to define a different class. The universe class, being an abstract notion, cannot have physical properties such as density or age, let alone temporal variation of properties. Defining the universe as an abstract class is obviously not satisfactory for cosmologists. They need a definition of the universe as a thing that is as real as a star, galaxy or cluster, so it can also have real properties.
Definers, back to the drawing board? -- Nafyladok 14:18, 27 September 2007 (UTC)

The definers went back to the drawing board. The previous definition was relegated to the disambiguation page. Here is the current definition.

“The Universe is most commonly defined as everything that physically exists: the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and constants that govern them.”

That most common definition seems to make sense at first glance, but fails on further scrutiny. The word ‘everything’ in that most common definition causes its failure. Here are dictionary definitions of ‘everything’:

1. Every thing; all things; all; as everything in human life is interesting.
2. Every single thing; every particular of an aggregate or total; all.

These definitions clearly indicate that ‘everything’ is used only in a distributive sense.

Here are dictionary definitions of ‘every’:

1. All, as of the items or individuals constituting an aggregate, considered separately; each, taken as part of an aggregate.
2. Being one of a group or series taken collectively; each: We go there every day.

‘Every’ is also only used in a distributive sense.

Note that though ‘all’ appears in the definitions of ‘every’ and ‘everything’, only the distributive sense of ‘all’ is intended. See my previous post for the senses of the word ‘all.’

That most common definition of the universe means the universe is each thing that physically exists. A speck of lint on my mouse pad physically exists. It is not meaningful to say that the universe is that speck of lint. That most common definition, failing to delimit the meaning of the word ‘universe,’ is a meaningless definition. Definers, back to the drawing board? -- Nafyladok (talk) 17:25, 30 January 2008 (UTC)

The present Wikipedia definition of the Universe is “The Universe is everything that exists: the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and physical constants that govern them.”

If the Universe is a thing that exists, then the term everything that exists includes the Universe. It follows that everything that exists is equal to the Universe and every other thing that exists.

The definition, then, is equivalent to “The Universe is the Universe and every other thing that exists.” However, no thing, not even the Universe, can be greater than itself, nor can it be defined in terms of itself. The present definition fails to define the Universe. A definition such as "The Universe is everything that exists except the Universe” fails because it defines the Universe in terms of itself. If the Universe exists it cannot be defined in terms of everything that exists

If the Universe were considered to merely be the abstract class of things that exist, though it could not then have physical existence, it could at least have mental existence and be a member of itself. However, as indicated in my post of 14:18, 27 September 2007 (UTC) above, cosmologists need a definition of the Universe as a physical thing.

As for the other unresolved problems raised by the continued inclusion of the word everything in the definition, see my previous posts. Nafyladok (talk) 13:20, 27 June 2008 (UTC)

## Neutrality

I don't see any mention of Creationism here. This article doesn't meet the neutrality policy, IMO. --Agüeybaná 23:27, 26 October 2007 (UTC)

What sort of mention did you want to see? It's hard to know what to say about it except "some people believe that the universe was created by some form of deity; see creationism." It might be reasonable to link to creationism in the "See also" section. -- BenRG 14:53, 27 October 2007 (UTC)
There's already a link to religious cosmology - I don't see a reason to give undue weight to creationism by specifically including it and not other alternative viewpoints as well. Ciotog 16:28, 27 October 2007 (UTC)
I don't see a link to Flying Spaghetti Monsterism either. If Creationism has to be mentioned, I demand my religion gets equal time as well.Rglong 03:50, 29 October 2007 (UTC)
but this is absurd! Agüeybaná is no longer wanting to contribute to wikipedia anyway! What possible remote reason is there for this tag? This is, IMHO, close to vandalism. I request an administrator to take a look at this ASAP. does anyone know how to request this?--Snideology 01:17, 30 October 2007 (UTC)
ok further research shows that user Agüeybaná clearly states that he is NO LONGER a contributor to wikipedia. he has offered no followup, and appears to have an agenda. does anyone who is NPOV have an issue with me removing the tag?
i believe this tag was placed outside wikipedia policies--Snideology 01:31, 30 October 2007 (UTC)
WTF?? I'm more active than you, man... Neutrality means "representing fairly and, as much as possible, without bias all significant views." Creationism is a view held by almost every major religion; I think it deserves the same, if not more, mention in the article as the Big Bang theory. Be careful when calling someone a vandal, my friend. I did not spend 6 months of my life here to put up with this... --Agüeybaná 01:49, 30 October 2007 (UTC)
As nobody seems interested in making this article neutral, I have asked that it be reassessed at WP:GAR. --Agüeybaná 02:28, 30 October 2007 (UTC)
WP:V indicates that scholarly journals that rely on provable facts are the best sources for articles, which suggests that creationism, although popular, isn't necessarily suited for expansion in this article. Besides, it has its own article. Nevertheless I've moved the links to religious and philosophical cosmologies to the lede where they'll get more notice. (note I was writing this while Agüeybaná posted his message) Ciotog 02:36, 30 October 2007 (UTC)
point of personal privilege! Agüeybaná has claimed he is more active than i, when his own user page claims to no longer be interested in editing wikipedia. also, i take offense to the acronym "WTF" in a dedicated wikipedia talk page. further, i did not refer to Agüeybaná as a "vandal" as accused - i called the addition of a misused tag as "close to vandalism". i take offense, too, at the assertion that activity level is automatically equated with veracity or accuracy--Snideology 03:44, 30 October 2007 (UTC)
further accusations or inflammatory language of this sort will be reported. however, since, as you, Agüeybaná, state that you are no longer an editor, this certainly will not bother you...n'est-ce pas ?--Snideology 03:44, 30 October 2007 (UTC)
If a report is filed because a user decided to use "foul language" that wasn' directed towards you it will most likely be ignored, even if he said the phrase entirely. - Caribbean~H.Q. 22:33, 30 October 2007 (UTC)
well, frankly, the foul language wasn't of major concern; it was the context of the entirety. but i am mollified, since the entire point of a talk page isn't to resolve personal conflict, but to improve the quality of the main page, and that has been done. i hope, since most editors seem to feel the neutrality is no longer an issue, that this entire subject can be dropped?--Snideology 23:29, 30 October 2007 (UTC)
My only concern with adding information about religious cosmologies to the article is that there are an awful lot of them. The article feels overlong and poorly organized already, and a whole new category of content would make the situation much worse. How do people feel about turning Universe into a disambiguation page? The current content could be moved to Universe (physical cosmology), and other cosmologies could be covered by a new article or by existing articles like Religious cosmology. -- BenRG 16:27, 2 November 2007 (UTC)
good point. it is lengthy, and ignoring religious philosophy is not acceptable. but i must take issue with changing this to a disambiguation page itself, since it is likely that most who visit for research are probably more concerned (at that moment) with answering a scientific question. but do not some pages list not only a 'for other uses see' line, but another 'for xxxxx see' line for a second-most common quest? thus, while i support your thesis, i feel the mission of imparting knowledge may best be served thus. should we also not continue this as a new topic? this is also getting lengthy, and seems only tangentially related to the tag issue--Snideology 05:54, 9 November 2007 (UTC)

This is a page about the Universe, not about human religious interpretations of the Universe's origin. I myself am a Heathen, yet I wouldnt dream of having the Lore listed on this page. Religious interpretations should be seen under the pages for each faith in question. Science is cold, hard fact. If I drop an apple, it falls to the ground. The same goes true, regardless of the religion of the person who dropped the apple. It will not fall for a Heathen, and then float away for a Buddhist, nor will it orbit around a Christian, and explode for a Muslim. Understand how this works, Agüeybaná? Ƿōdenhelm (talk) 13:29, 4 February 2008 (UTC)

## Article removed from GA list

By a clear consensus of many editors at good article reassessment, this article has been removed from the good article list. Please see the discussion at Wikipedia:Good article reassessment/Archive 32 for improvements that are needed to help this article reach good article standards.--Jayron32|talk|contribs 06:36, 10 November 2007 (UTC)

## Core Contest entry

I see that User:WillowW has taken up my challenge for improving this article. It could easily be improved. I would start by adding {{fact}} to any statements that say "some people believe" or "some say". Then expand the theory section, dwarfing the attention spent on the Multiverse theory (which is only even mentioned due to its popularity in tv/movies). Then get rid of any random pop culture nonsense, expand and source the stub sections, etc. — BRIAN0918 • 2007-11-27 16:40Z

## Just for discussion

I have read that some scientist like Gödel believe the Universe is rotating. Hawking feels that it can't be rotating because heavenly bodies on the edge would eventually have to rotate at the speed of light (or faster) to keep up with the rotation of the whole. What I wonder is how large would the Universe have to expand to before the edge approached lightspeed? I realize it would be dependent on the rotation rate as well as the size of the Universe. As matter excelerates its mass increases. According to Einstein it can never reach the speed of light because there would not be enough energy. (You would need an infinite amount of energy.) One wonders that if this would act as a brake or governor and keep matter just below the speed of light at the edge of the Universe? Also, the increased mass of all material at the edge of the universe would cause gravity to pull on the interior of the Universe and increase the expansion of the Universe. The rate of expansion would not be constant, but would slowly increase. Mass at the edge of the Universe would reach a fixed rate of rotation due to this energy limit. However, the Universe could still exand. The only limitor would be the rotational speed of the edge. Carrying this to the next step, one wonders what would happen eventually as all matter would reach the edge of the Universe and reach incredible mass? What effect would this have in causing the Universe to have a Bang-Crunch-Bang cycle? I may be absolutely wacko on this posting and would very much like some enlightenment. Everything seems to rotate in this crazy world anyway!Dane Sorensen (talk) 00:44, 29 November 2007 (UTC)—Preceding unsigned comment added by Dane Sorensen (talkcontribs) 00:35, 29 November 2007 (UTC)

Gödel found a solution to general relativity in which everything rotates around everything else. I don't know whether he believed the real world was like that. In any case, astronomical observations have shown that it isn't. I find it hard to believe that Hawking said what you attribute to him (do you have a citation?). General relativity can describe an infinite rotating universe in which there's no center to the rotation and no edge beyond which things move (locally) faster than light, just as it can describe an infinite expanding universe with those properties.
I'm afraid your cosmology makes virtually no sense. The big problem is that you're thinking in terms of special relativity, which fails completely on cosmological scales. I agree with your last sentence, though. Everything in this crazy world does rotate, and it is surprising and interesting that the universe as a whole doesn't. -- BenRG (talk) 04:12, 30 November 2007 (UTC)

Thank you BenRG for your thoughts. Hawkings statement about the Universe not rotating is to be found in his book "The Universe in a Nutshell." How does the Universe show that it is not rotating? I would love to see the proof for that. I wonder if rotation may fit in with Mr. Peter Lynds ideas? Now there is a guy thinking out of the box. Dane Sorensen (talk) 00:24, 8 December 2007 (UTC)

Imagine a young universe exploding outward. Due to quantum flux, matter is not evenly spread. Gravitational forces are not balanced. This imbalance causes matter to move in other directions beyond the initial direction caused by the big bang. The aggregate movement would eventually show up as a rotation in a closed system. Centrifugal force would eventually become a force acting on all matter in the universe. Dane Sorensen (talk) 06:14, 30 December 2007 (UTC)

Probably worth considering Mach's principle here - it's possible that if the entire universe were rotating, you wouldn't be able to tell, i think. Or that it's logically impossible for the entire universe to have net rotation, any more than it can have net velocity. But i could be completely wrong. Sega! -- Tom Anderson 2008-01-13 2145 +0000 —Preceding unsigned comment added by 62.56.80.10 (talk) 21:45, 13 January 2008 (UTC)

I think that this is stated, assuming the Universe is acting as a singular object— which it isnt. Merely looking at our own Solar System would show how the rotation (revolution) would work... those closer to the center would go faster, while those towards the outside would be slower, rotating at different speeds. Ƿōdenhelm (talk) 13:35, 4 February 2008 (UTC)

I don't think the Universe and a solar system are comparable. It still may be that the extra expansion we see is only due to a rotating Universe. Dane Sorensen

## The hole in the universe

Is it pertinent to mention the hole in the universe they found in August [8] in this article ? Rosenknospe (talk) 17:32, 29 November 2007 (UTC)

## Observable portion section - "tiny speck"?

The observable portion section currently contains the following statement:

If it is infinite, the observable Universe is just a tiny speck of the whole universe.

This makes no sense; if something is infinite, it makes no sense to reference the size of the whole in a comparison. It's the same as saying "the numbers ending in 1 are a tiny speck of all numbers". Most likely an accidental mistake, but still harmful to an article dealing with hard science.

I'll remove that sentence, please revert if necessary. 83.172.207.188 16:05, 2 December 2007 (UTC)

## Is this a typo ?

In the lead, there is a line of text that says "even objects initially at rest to one another will appear to fly apart as new space is created between them" which seems to be grammatically incorrect and should read "at rest with respect to one another" or "at rest in relation to one another". I'm loathe to change it though, as I imagine that thousands of readers must have scanned it and thought it looked OK. Is this a US grammatical construct that I haven't previously encountered? Far Canal (talk) 05:30, 12 December 2007 (UTC)

I removed the whole clause because I don't think it was even factually accurate. -- BenRG (talk) 08:45, 24 December 2007 (UTC)
I'm not sure if I understand what you mean by "factually accurate"? The problem, I fear, is that the mathematical results are precise, but the language to describe them imprecise or inadequate. Thus, we can agree that Friedmann equation describes the changes in the scale factor R(t) in the Robertson-Walker metric; we can agree on the possible solutions of this equation given various parameters, and that R(t) is increasing at a particular moment t. Where we encounter difficulties is in describing that increase; for example, shall we say that "the space between objects is expanding" or that "space is being created between objects"? In general, I've been using the former, although I'm open to other suggestions. Willow (talk) 15:28, 3 January 2008 (UTC)
Here's the clause I removed:
[The Universe is expanding] in the sense that space itself is enlarging with time; even objects initially at rest to one another will appear to fly apart as the space between them is enlarged.
I think the part after the semicolon is incorrect for any reasonable definition of initial rest. In a Friedmann universe with two spatial dimensions suppressed (${\displaystyle ds^{2}=dt^{2}-a(t)^{2}dr^{2}}$), the curvature scalar is ${\displaystyle R=-2{\ddot {a}}/{a}}$. In traditional models without a cosmological constant this is always nonnegative, and I'm pretty sure that means that test particles initially at relative rest and following geodesics will always get closer together, or in limiting cases stay the same distance apart. In Lambda-CDM the particles do separate at late enough t, but it's not generally true that they separate; that's not what expanding space is "about". My subjective description would be that (sans cosmological constant) the galaxies move apart because of inertia, and the curvature of spacetime acts only against the expansion. Gravitationally bound objects have already completely overcome their initial inertial expansion, and there's nothing trying to push them apart any more (except for the cosmological constant). -- BenRG (talk) 01:16, 7 January 2008 (UTC)
I'm still not sure if I understand you, especially your idea of galaxies moving apart because of inertia. As I understand them, traditional cosmological models assume that the all the matter in the universe is at rest (technically, that their 3-velocities v are all exactly zero), as you may find in the following references: S. Weinberg (1972), p. 472; Rindler (1977), p. 227; and Landau and Lifshitz (1975), p. 363. To assume that the matter anywhere had a velocity would violate the cosmological principle of isotropy, since the velocity would favour one direction over another, no?
Perhaps we might understand one another better if we agree first on the math? Using R(t) to denote the cosmological scale factor in the Robertson-Walker metric (which you call a(t), the Friedmann equation reads (e.g., Rindler, p. 228)
${\displaystyle {\dot {R}}^{2}={\frac {M}{R}}+{\frac {c^{2}\Lambda R^{2}}{3}}-kc^{2}}$
where M is a constant proportional to the amount of (mass-)energy in a given fraction of the universe. This equation may be integrated using separation of variables
${\displaystyle \int dt=t=\int {\frac {dR}{\sqrt {{\frac {M}{R}}+{\frac {c^{2}\Lambda R^{2}}{3}}-kc^{2}}}}}$
Setting the cosmological constant Λ to zero, I'm sure that you can verify that for k=1 (a closed, "3-spherical" universe) the solution is a cycloid
${\displaystyle R\propto 1-\cos \psi }$
where the time t is also defined by the parameter ψ
${\displaystyle t\propto \psi -\sin \psi }$
Thus, in this example, space expands and then contracts; extrapolating backwards gives the Big Bang when R=0 and extrapolating forwards gives the Big Crunch when R returns to zero. The distance between otherwise stationary galaxies varies in synch with R(t), making them appear to fly apart and then come together, even though none of them feels any acceleration or considers itself to be moving.
Part of our misunderstanding might lie in my feeble English explanations of those mathematical results? I was trying to convey the "3-velocity v is zero" idea by saying that two local galaxies were at rest relative to one another, but that they could move apart (without feeling any acceleration) due to the expansion of space. Perhaps you were thinking that their apparent relative velocity can only decrease because the second derivative of R(t) is always negative, which I totally agree with. But I want to get across to the reader that the galaxies can fly apart even if they have no "proper" motion of their own, do you see what I mean? I think that's important for explaining the paradox that SqueakBox and others have been asking about. I'm totally open to new and better ways of explaining it in English, though! :) Willow (talk) 18:29, 7 January 2008 (UTC)
I agree with all of your math. (Well, I didn't check it carefully, but if there's a problem it's an unimportant detail.) But I don't think any cosmologist would say that objects moving with the Hubble flow are at relative rest. They're at rest with respect to a physically meaningless coordinate system, but they're moving apart in a real physical sense: the metric distance between them is increasing with cosmological time. And their separation is by ordinary inertial motion -- the physics that governs the separation of the galaxies is the same as the physics that governs the separation of objects a meter apart. This is a fact about general relativity, not an interpretation of it. Special relativity is a better approximation for the latter case than the former, but it isn't exactly right for either. There's no transitional scale at which special relativity gives way to general relativity.
It's interesting to look at the zero-density limit of the FLRW metric. When ${\displaystyle \Omega \approx 0}$ you can take ${\displaystyle k=-1}$ and ${\displaystyle a(t)=t}$ and write the metric as ${\displaystyle ds^{2}=dt^{2}-t^{2}\left({\frac {dr^{2}}{1+r^{2}}}+r^{2}d\theta ^{2}+r^{2}\sin ^{2}\theta d\phi ^{2}\right)}$. Space is hyperbolic (${\displaystyle k=-1}$) and expands forever at a constant rate (${\displaystyle a(t)=t}$). But spacetime is flat (the Riemann tensor is zero everywhere). In fact, this case of the FLRW metric is a coordinate reparameterization of part of Minkowski spacetime. You can map it to Minkowski polar coordinates ${\displaystyle T,R,\Theta ,\Phi }$ by
${\displaystyle {\begin{array}{l}T=t{\sqrt {1+r^{2}}}\\R=tr\\\Theta =\theta \\\Phi =\phi \end{array}}}$.
The constant t surfaces in FLRW coordinates map to hyperboloids of revolution in Minkowski coordinates, and the stationary worldlines (Hubble flow) in FLRW coordinates map to future-directed timelike rays from the origin in Minkowski coordinates. In Minkowski coordinates this cosmology looks like a bunch of (highly rarefied) matter exploding outward from a central point, with the edge of the explosion moving at the speed of light. In this special case, the Hubble separation actually is special relativistic inertial motion. As you increase ${\displaystyle \Omega }$ the special relativistic description becomes less and less accurate, but there's no transition point at which the nature of the Hubble flow becomes fundamentally different.
You can introduce perturbations into the ${\displaystyle \Omega \approx 0}$ solution. If you push a bit of matter so that it's moving toward another bit, that's that; it will forget its former state of motion and continue to approach the other bit until it's acted upon again. There's no force trying to make it return to the Hubble flow. It's the same with the galaxies. They mostly move away from each other only because the primordial matter that formed them was mostly moving apart.
As before I ignored the cosmological constant, which does push things apart. I also ignored the CMBR, which does (by friction) encourage things to move with the Hubble flow. -- BenRG (talk) 09:35, 9 January 2008 (UTC)
Thanks BenRG! I think we're beginning to understand one another, and I appreciate your efforts to educate a relative newbie. I had read up a little on Milne's theory, and also on the pseudo-Newtonian interpretation in relativistic cosmology, although I can't claim to have understood them perfectly, and I do realize that the objects are really separating as R(t) (or, if you prefer, a(t)) increases. For me, the problem is that if M and/or Λ are not zero, then the rate of change of R is not constant; the objects will appear to "accelerate" relative to each other, although none of them will feel any force. That's why I think it seems preferable to grant that each one is in their own rest frame, and that their separation is due to space expanding, not inertial motion being slowed by gravity. (For simplicity, let's assume perfect isotropy and homogeneity for now.) Do you see where I'm coming from? Willow (talk) 12:10, 9 January 2008 (UTC)

This phenomenon has resulted in the imagination and theories for space time travel. The time lag paradox is among the most famous ones. For example: In a pair of twins, one of them (Twin A) is sent to the space for a considerable period of time and the other one (Twin B) is present on the earth, the "Twin A" who was in the space or on some different planet would have experienced the local time there and the Twin B on Earth is bound by the rotations and revolutions of the earth i.e. experiencing the time on earth. Case 1: Now if the time was going faster for Twin A than Twin B, on return after some considerable period of time - Twin A would be older than Twin B. Case 2: If time was slower for Twin A on a different planet, on return after considerable period of time - Twin A would be younger than Twin B. Karthik Kannan.M M karthikkannan (talk) 07:33, 14 December 2007 (UTC)

## Creation stories flawed

By some very weird reason, under "Creation stories", there's not a word about christian creation stories, which is really odd since it's one of the most common creation myths. Why isn't that added? It's just as much a myth as any other religious creation story myth. Ran4 (talk) 12:26, 23 December 2007 (UTC)

Perhaps you missed it? It's there near the end of that paragraph
That should be OK, right? Willow (talk) 09:35, 5 January 2008 (UTC)

I just created Template:UniverseNavSmall for the reasons listed at Template talk:UniverseNav. I just realized it has the same links as Template:Earth's location, but in an (less polished) vertical format suitable for "series" navigation. I don't find the horizontal template to be prominent enough (partly because I didn't even notice it existed before I re-created it), but I thought I'd ask if others agree, before I go through all the linked articles and remove the old template and add the new one.

If not, would something like Template:UniverseNav be a useful addition to the body of this or other articles, or would it be a good link to add to "Earth's location"? -- Beland (talk) 05:26, 2 January 2008 (UTC)

Hi, I appreciate where you're coming from, but I'll confess that I'm not fond of the new template in the lead. First, it makes the lead text-heavy and basically image-less; the microwave distribution in the {{cosmology}} navigational template doesn't count, since it's unexplained. I think the older Hubble picture did a good job of setting the cosmic scale, even though it shows only the luminous matter in the observable universe. Second, I think the focus in the lead should be on the subject of the article, the universe as a whole; the reader shouldn't get distracted with smaller-scale structures such as the Earth. Would you be OK with moving your template into the body of the article, perhaps where we discuss the size of the universe? Willow (talk) 15:16, 3 January 2008 (UTC)
Well, I agree the intro is too texty. I liked the picture that was there, and while it made things look pretty, I didn't find it particularly clarifying. It wasn't a picture of the whole universe; it was a picture of some random corner of it, and it was difficult to get a sense of the scale of the objects one was looking at. I'm trying to make sure that the various articles are understandable by someone who is thinking to themselves, "What is the difference between the universe, the galaxy, and the solar system?" because apparently there are well-educated adults running around who don't know. I think by the time these people hit the phrase "path-integral formulation of quantum mechanics" in the first paragraph, they will have given up trying to figure that out.
Usually the "finder map" for geographic entities on the Earth is next to the intro, to give readers immediate locational context. The only way I can think of to give readers a sense of how big the universe is, is to run through the set of structures between the whole universe and something on a familiar scale (the Earth). It's sort of an inverse "finder map", since the entity being described is larger than the familiar geography, not smaller. Perhaps instead of the purely textual table, something graphical would be appropriate. Though the article Life has a similar textual table in its introductory infobox, it also has Image:Biological classification L Pengo.svg, which is a more colorful graphical depiction of the tree of life. Perhaps something similar could be constructed from various existing resources, such as the maps at atlasoftheuniverse.com, pictures of galaxies and stars, etc.? -- Beland (talk) 05:47, 5 January 2008 (UTC)
I see your point. Maybe we could use the fourth dimension to our advantage? I'm dreaming of a "powers of ten" type of animation, where we zoom in logarithmically from 13 billion light years to the Earth and then go back out again. It'd be hard to produce, but not impossible; I'm learning Blender, so anything seems possible to a little fool who blithely rushes in... ;) Willow (talk) 09:42, 5 January 2008 (UTC)

## Logic inconsistency

If nothing travels faster than the speed of light and the earth is 13.7 billion years old how can it be 93 billion light years wide, even half that figure, 46.5 billion, would mean light having to travel having to travel more than 3 times faster than it does. Or am I missing something. Thanks, SqueakBox 02:08, 7 January 2008 (UTC)

Hi SqueakBox! :)
Here's the solution to that apparent paradox. The law that objects cannot move faster than the speed of light relative to one another is a consequence of special relativity. According to general relativity, however, the laws of special relativity are exactly true only in flat space-time; when space-time is curved, special relativity breaks down on length scales longer than the length-scale that characterizes the local curvature. As an analogy, consider the Earth; it seems flat when you only look at distances less than (say) 200 miles; once you start going to larger distances, the curvature of the Earth becomes apparent. For example, two surveyors both heading north to lay out "square" county lines in North America, might find that their northern county line is shorter than the southern one; meridians of longitude get closer as you approach the North Pole.
The characteristic curvature length-scale might be quite short near a black hole, but for the universe as a whole, the curvature starts becoming noticeable above 300 million light years (100x the typical distance between neighbouring galaxies). So, beyond that length scale, there's no requirement that things move more slowly than the speed of light. Galaxies can separate faster than light, not because they're moving (each one feels itself at rest), but rather because the space between them is expanding. I'm about to give a technical derivation above to BenRG — stay tuned! :)
I'll probably incorporate something like this into the article, since so many people wonder about it. If you had any suggestions on how to present it, I'd be very grateful, SqueakBox! :) Willow 17:54, 7 January 2008 (UTC)

Thanks, SqueakBox 21:16, 9 January 2008 (UTC)

PS. I have the feeling that I'm misleading you slightly with the above explanation. The central idea is not curvature per se, but that special relativity applies exactly only on infinitesimally small regions, and that when you get to larger scales and longer times, all bets are off re: the speed of light. At least that's my understanding right now. Willow (talk) 01:22, 10 January 2008 (UTC)
Maybe I can clarify: as Willow says, it isn't directly to do with curvature. Nothing can move faster than the speed of light, but all motion is relative, so the question is, relative to what? The answer is that nothing can move faster than the speed of light relative to any nearby objects. However, the universe is expanding (insert traditional picture of blowing up a balloon here ;), so objects that are a long way away can be receding from us faster than the speed of light, simply because the space inbetween is expanding. Any light they emit now will never reach us, which is one reason that the observable universe and the universe are very different concepts. On the other hand, the expansion of the universe also implies that objects which are far away now were once much closer together. Light which reaches us now after a journey of a 13 billion years came from an object which, 13 billion years ago, was closer to us than 13 billion light years. However that very same object is now much further away from us than 13 billion light years.
(To try and convey the idea, I am using words such as "now" and "years ago" which don't actually make sense in terms of general relativity, but only have definitions in terms of cosmological models of the universe.) Geometry guy 20:27, 11 January 2008 (UTC)

A bold user has recently changed the LEAD to only a single paragraph, which is rather too much of an revision and shortening edit for a subject as encompassing as this ;). However, he has a point, inasmuch as the present LEAD is too long and detailed for a good summary. According to the style manual, good LEADs are 3 to 4 paragraphs, and usually paragraphs need a topical sentence plus perhaps 5 sentences. So the challenge: Can anybody reduce this present long LEAD section on the entire universe (!) to 5 paragraphs, each of 5-6 sentences = 30 sentences or so, max? SBHarris 19:41, 9 January 2008 (UTC)

Do you mean that the lead must be replaced by 30 sentences, or so? Or should a different lead be added, and the current lead be put under a different section? - Caco_de_vidro —Preceding unsigned comment added by Caco de vidro (talkcontribs) 21:10, 9 January 2008 (UTC)
Per WP:LEAD, the lead should summarize the article, but that the body of the article should not be redundant. The guidelines suggest that four paragraphs would be good for an article of this length, although there's no fixed number. The major topics here would seem to be the definition, the observational data, the theoretical models, the creation accounts, and "multiverse" ideas, which is five paragraphs. The multiverse stuff could perhaps be worked into the definition paragraph, though. I'll think it over and try to draft something shorter and less detailed by tomorrow, and I would welcome any suggestions from anyone else! :) Willow (talk) 01:22, 10 January 2008 (UTC)
P.S. It's so nice to see you again, SBHarris; it's been a while, no? :) Willow (talk) 01:22, 10 January 2008 (UTC)
Nice to see you, too. I'd go for 5 reasonable-sized paragraphs, as surely on THIS topic, nobody will complain that we stretched a bit. Yes, I like your suggestions. It's 1) definition (lead of the lead), 2) objective data (observations), 3) modern theoretical interpretation (, 4) History (creation myths perhaps blending into scientific history before modern ideas, and finally 5) Context in terms of larger stuff, which in this case is a little hard, but would include some wayout multiverse theorizing. History and context can also be lumped, as they are in a modern scientific paper. The problem here is that a lot of the history is pre-scientific, so the frank pre-science emythology almost demands its own section. So you start the history with the scientific history (Giordano Bruno, maybe?). One could argue that Creation Mythologies really demands its own article (and has one), and only needs a mere mention in this article (and not in the LEAD) as the "universe" ought to direct to the scientific topic according to policy, just as it does for (say) "water (substance)" or "Earth (planet)", which are chemistry-based and geophysical-based articles, and not much on what the Greeks thought water was, or stuff about when people thought the Earth was flat. SBHarris 03:14, 10 January 2008 (UTC)
I don't agree. I think the lead is fine. It should just be cut to pieces. This is an encyclopedia. People want answers fast and don't want to search though large lumps. If other people want to read though a lump then they can just ignore the topics I added. Please respond to this and tell me what is wrong with subtopics? And don't refer to formalisms please.User_talk:Caco_de_vidro —Preceding comment was added at 15:32, 12 January 2008 (UTC)

The lead is certainly far too long. I tried to read it last night, but gave up half-way through— not because it is poorly written, I hasten to add, but simply because there is so much stuff happening. The guidelines of WP:LEAD exist for a reason: we need a concise summary of the topic, not a "touch all bases" approach.

On the other hand, I have just remembered that this is the same article that was delisted at GAR in early November. Wow, it has seriously improved since then: I read through the body of the article today and was most impressed! Geometry guy 16:37, 14 January 2008 (UTC)

## Stupid question

In the lead: "the universe is 13.7±0.2 billion years old and at least 93 billion light years across". How is this possible? Wouldn't the maximum size of the universe be 28 billion light years across? Since the maximum speed for matter and light is the speed of light in vacuum, and it all started from 'a point'? Randomblue (talk) 10:54, 14 January 2008 (UTC)

See the discussion two sections up. Geometry guy 11:02, 14 January 2008 (UTC)
Just to amplify on that. Our current understanding of the universe, combined with evidence on the density of matter and energy, suggests that the universe is actually infinite in extent, and has been since the big bang. This sounds implausible and is very difficult to visualize. Things were much easier when scientists thought we lived in a "closed" universe. Then the idea of a universe expanding from a point could be visualized more easily in terms of an inflating balloon. So the question is not so stupid... Geometry guy 15:56, 14 January 2008 (UTC)
What indications or evidence is there that the universe is infinite in extend. I know that 3-space is roughly flat, but that does not mean that 3-space is globally Eucleadian or infinite in extend. Take for example the 3-torus. See Shape_of_the_universe#Flat_universe. Or are there other considerations? - Caco —Preceding comment was added at 19:09, 14 January 2008 (UTC)
Please read the geometry guy comment and the artcle. There isn't enough mass in the universe to close it, even if you count the dark matter inferred from galaxy rotation. In addition, the rate that the universe is expanding seems to be increasing with time, which also means it can't be closed. So closed shapes like 4-spheres and 4-toruses (which are possible with a closed universe) are out. SBHarris 19:41, 14 January 2008 (UTC)
We had an edit conflict which the software (remarkably) resolved. The above is not quite right: in the spherical and flat cases, the topology would be the product of a 3-sphere (or some other lens space) or 3-torus (or some other flat 3-manifold) with time. However, even in the hyperbolic case, a universe of finite diameter is possible, as I explain below. Geometry guy 20:21, 14 January 2008 (UTC)
Unfortunately this is something that we may never know for sure, since our observations are limited to the observable universe (obviously), which is finite. All we know is that the observable universe is approximately homogeneous, isotropic, and (according to the current evidence) hyperbolic (but close to flat, as you say). Assuming this is true for the entire universe, a spacelike slice could be a hyperbolic 3-manifold of finite diameter. However, if it is, then all the evidence to date suggests that this diameter is close to or larger than the observable universe (otherwise we would see patterns in the sky because light will have had time to travel all the way around the universe). So if the universe is finite, we will never know it, and there are loads of hyperbolic 3-manifolds (both finite and infinite in extent) with no way to know which one the universe looks like. So pretty much the only thing we can do is appeal to Occam's razor, and prefer the simplest hypothesis. In this case, one might argue that the simplest hypothesis is that the universe is simply connected. In which case the hyperbolic 3-manifold is the hyperbolic ball which is infinite in extent. That's what I meant by "suggests".
There is hope that a new fundamental theory of physics (such as string theory) will provide a theoretical model which pins down the shape of the universe (for instance by relating fundamental constants to the topology), but for any such theory, there could be another which is equally consistent with experiment but predicts a different shape! So again, we would probably still have to rely on the empirical observation which underlies Occam's razor: the universe seems to be rather elegant! Geometry guy 19:42, 14 January 2008 (UTC)
This is all nicely explained in the article itself (see the sections on "Size, age, contents, structure, and laws" and "Solving Einstein's equations"). Geometry guy 16:41, 14 January 2008 (UTC)

## Universe "created"

I notice that in a number of places, the past participles "created" and "formed" are used, with the passive voice, as, for example, "...space itself was created ex nihilo...". The passive voice does avoid the need to say who the creator or former is; but it does still imply that there is or was a creator. I think that this implication is inappropriate here. —Preceding unsigned comment added by 76.250.119.79 (talk) 19:05, 21 March 2008 (UTC)

## Very slight change

I made a slight change in the introductory paragraph. Instead of The universe is 13 billion years old, I've made it The universe is at least 13 billion years old. I daresay that our scientific and technological achievements to date are not sufficient to pinpoint the exact age of the universe. 99.240.217.191 (talk) 12:33, 27 April 2008 (UTC)

Strictly speaking, it is the age of the observable universe, which we can measure. Mike Peel (talk) 20:44, 27 April 2008 (UTC)

## Galaxy 40 billion light years away?

What Galaxy is observed at 40 billion light years away? Most articles and websites will say the most distant observed objects is between 13-14 billion light years. Another says the most distant object is quasar PK 1247 +3406 at 5000 Megaparsecs. If I calculated correctly that is about 16 billion light years- far short of 40 billion. I'm going to delete this sentence until cited and verified: "This expansion accounts for how Earth-bound scientists can observe the light from a galaxy 40 billion light years away, even if that light has traveled for only 13.7 billion years; the very space between them has expanded." —Preceding unsigned comment added by 71.15.106.102 (talk) 05:32, 29 April 2008 (UTC)

71.15.106.102 (talk) 22:31, 28 April 2008 (UTC)

I'm pretty sure we've never seen a galaxy 40 billion light years away (comoving distance). That would be a redshift around 50 and an era of around 50 million years after the big bang. I restored the sentence but changed 40 to 30, which is closer to the right ballpark. The 13-14 billion light year figures are probably light-travel-time distance. -- BenRG (talk) 11:48, 29 April 2008 (UTC)
If the 30 billion light years is the result of more accurate calculation then this is a step in the right direction. However, I'm not challenging the number. The sentence is still confusing and with no citation, hard to clarify. An average reader may be challenged to find out what galaxy the sentence is referring to and who made the discovery. I know I was. I'm still looking and like I said before: the most distant observed galaxies are around 13-14 billion light years away. Without an understanding of comoving distance this conflict cannot be easily resolved by the average reader. Notice this sentence is one of only a few in the paragraph that does not have a hyperlink or citation. I originally thought deletion was an adequate remedy because it did not effect the flow of the rest of the paragraph. Taking your lead, Would adding in parathesis (comoving distance) with hyperlink be better?

71.15.106.102 (talk) 02:58, 30 April 2008 (UTC)

## It makes no sense to say that the universe has a beginning

A beginning implies a previous point in time where the universe does not exist, but, by definition, all points in time are within the universe. Therefore there is no "beginning" of the universe. If there is no beginning of the universe, it follows that the universe has always existed. Therefore, it makes no sense to say that the Big Bang was the beginning of the Universe. Please make the appropriate changes in the article. --70.55.187.162 (talk) 01:10, 29 April 2008 (UTC)

To clarify, the universe has always existed in the sense that there is no point in time when the universe did not exist because all points in time are within the universe, but that is not to say that the duration of existence of the universe is infinite and cannot be measured (app. 15 billion years). To say that there is no point in time when the universe did not exist is one thing, to say that the duration of existence of the universe is infinite is another. --70.55.187.162 (talk) 01:47, 29 April 2008 (UTC)
That is a philosophical point on etymology. You should cite the book/show/lecture/magazine/peer-reviewed article that comes from and we'll look it over. Jok2000 (talk) 02:31, 29 April 2008 (UTC)
Only potentially controversial material needs to be sourced. There is no possible controversy regarding this matter. Furthermore, it addresses a common mistake that people make when they talk about the Universe and the Big Bang. 2 + 2 = 4 (Do I need a source?).--70.53.141.111 (talk) 10:50, 29 April 2008 (UTC)
You're assuming an extrinsic notion of beginning ("there was a time when it didn't exist"), but physicists use an intrinsic definition ("there was an earliest time when it existed"). There's no problem with applying this to the whole universe, and I don't think it does any violence to the intuitive notion of "beginning". In fact it is my intuitive notion of beginning; yours seems unnatural to me since it unnecessarily involves entities other than the one under discussion. At any rate physicists do use the word this way. -- BenRG (talk) 11:42, 29 April 2008 (UTC)
What are you on about? I want to read the source where you got this belief. 2+2 = 10 base 4. Jok2000 (talk) 11:22, 29 April 2008 (UTC)
To respond to BenRG, there is no time before which the universe didn't exist. Therefore, you cannot say that the universe has a beginning. All you can say is that the universe has existed for say about 15 billion years. It's a paradox. To Jok2000, "2+2 = 10 base 4" doesn't need to be sourced right? I didn't find this stuff anywhere. It's a logical deduction. --70.55.176.177 (talk) 12:03, 29 April 2008 (UTC)
To clarify, there can be no "earliest time when the universe existed", if there is no time before which the universe didn't exist. For something (X) to begin to exist requires a point in time when X does not exist and a point in time when X exists. But there is no point in time when the universe did not exist. Therefore the universe never began to exist. --XUniverse (talk) 12:29, 29 April 2008 (UTC)
Do you understand what I mean by intrinsic and extrinsic? Your objection is very much like saying that spacetime can't be curved because there's nothing outside of spacetime for it to curve into. That would be fair enough except that "curved" in this context refers to intrinsic curvature, which can be defined without reference to anything outside the manifold. Imagine a last-Thursdayist universe which is like our Lambda-CDM universe but with all the points at cosmological time t < t0 removed, where t0 is some time last Thursday. In this universe the points at t = t0 have no past neighborhood; they're on the boundary; they're uncaused. That's an intrinsic beginning. -- BenRG (talk) 13:21, 29 April 2008 (UTC)
Thanks for the clarification. What you wrote should be clearly indicated in the article, otherwise, it's misleading to say that the universe began 15 millions years ago, based on the common meaning of "beginning". Nevertheless, I'm very suspiscious of the term "intrinsic beginning". It's like creating the term "special existence" to describe the "Flying Spaghetti Monster". --XUniverse (talk) 14:05, 29 April 2008 (UTC)

The universe has always existed and will always exist; the question is in what state, for how long. Some more theist-inclined Big Bang cosmologists view the Big Bang as a something-from-nothing act of creation, rather than a transference of one mode of existence into another. El_C 12:20, 29 April 2008 (UTC)

To the anon who hasn't cited a philosophy book (maybe never?). Logic itself is subject to philosophical analysis, perhaps more so in physics than any other science, as the actual nature of space and time is not known, just that there is a best-fitting model that works rather well. Also, the point of 2+2=4 or 10 depending on base was to show you that meaning depends on context. (context being base 4 or base 10). That you did not notice suggests to me you should pick up a book on logic & meaning, also maybe "time". Jok2000 (talk) 13:38, 29 April 2008 (UTC)

## Strange Gibberish

Someone had inserted random little quips of gibberish in the opening section of the article, an example being "The Universe was founded by a German lunatic in 1934." I removed what I came across but I did not look over the entirety of the article. It seemed relatively harmless in nature but nonetheless if anymore is found it should be promptly removed.--96.231.165.182 (talk) 14:23, 4 May 2008 (UTC)

Thank you for your help. I've tidied up the rest. SHEFFIELDSTEELTALK 14:32, 4 May 2008 (UTC)

## Age of the universe

I have found a news article according to which it has been found that the universe is 350 million years younger than previously estimated. Should this be added to the article? --Eleassar my talk 18:14, 7 May 2008 (UTC)

## Theory

The Big Bang is just a theory that has not been proven. Please do not talk like it is a fact —Preceding unsigned comment added by 166.87.255.131 (talk) 13:38, 18 May 2008 (UTC)

Theories don't get proven right, they get proven wrong. Please let us know when you find some evidence contrary to the theory. 121.216.136.243 (talk) 10:06, 19 May 2008 (UTC)

## Cap up pronouns for God

WP:MOS#Religions, deities, philosophies, doctrines and their adherents has "Pronouns and possessives referring to figures of veneration are not capitalized in Wikipedia articles, even when they traditionally are in a religion's scriptures. They are left capitalized when directly quoting scriptures or any other texts that capitalize them." Reverting. --Old Moonraker (talk) 14:39, 12 June 2008 (UTC)

## SI Unit usage

"SI units should be secondary, and we should use REAL SI units (Xm?)" (editing comment by Arthur Rubin)

Hi there!

I agree that Metres are a better unit than Kilometres.

But I was just wondering why SI units should be secondary? Just about every known person in the universe uses Metres, and pretty much only astronomers use light-years. Astronomers make up a pretty small percentage of people.

Which brings me to a point: The kind of people that use light-years to measure things are the kind of people who probably already have a pretty fair idea of how big the universe is. The remaining people who look at this article are probably the type who view the light-year as some kind of science-fiction unit, or possibly even a unit of time. For the sake of the majority of people (non-astronomers), it would seem reasonable to list SI units first, and then list Light-years next.

You might argue that the light-year is a natural unit for measurement, since many calculations of universal dimensions are based on measurements of the distance light has travelled, but I would counter that the unit is still inherently arbitrary in using the Earth-specific "year" as a point of reference.

What do you think? InternetMeme (talk) 06:32, 17 June 2008 (UTC)

In cosmology, light-years and years seem to be the natural units of space and time (respectively). In any case, they're most commonly used in publications and by experts in the field. "93 billion light-years (880 Ym)" seems better than "880 Ym (93 billion light-years)", especially since we'd need to link Ym somehow. — Arthur Rubin (talk) 07:03, 17 June 2008 (UTC)
I agree that the speed of light is a natural unit in cosmology (and any other field). But I see no reason whatsoever that the year should be thought of as a natural unit in any field outside of farming. It has no conceivable relevance whatsoever outside our planet as far as I can see. Therefore the light-day, light-month, or light-martian-year might all present themselves as equally suitable candidates. I think the only reason that the light-year could be seen as a natural unit would be due to many years of entrenched and arbitrary habit within the astronomical community. Is there another explanation? And if there isn't another explanation, why should any field outside of cosmology perpetuate the usage of this unit?
My main point, though is one of practicality: What percentage of Wikipedia's readership have an idea of the length of the metre/kilometre? I'd suggest over 75%. What percentage have an idea of the length of a light-year? I'd expect 10% at best. For this reason alone, it makes seven times more sense to present the diameter of the universe in metres/kilometres. Also, although SI prefixes are very useful, I think the usage of a reasonably familiar term such as "trillion" would be more useful than the "atto" prefix. InternetMeme (talk) 14:13, 18 June 2008 (UTC)
Perhaps we should Wikilink light-years? I think using non-SI terminology for SI units is specifically forbidden strongly discouraged by the MoS. As it stands, because of the short and long scales problem, "billion" and "trillion" are technically ambiguous, and Ym is probably recognized by fewer people than recognize light-year. I certainly think light-year should be primary, but that still leaves us with discussion the proper format of the metric unit.
880 Ym
880 septillion metres (note, spelling out the word and using the unit abbreviation is bad)
880 ×1024 m 8.8 ×1026 m
I think the last is probably most understandable. — Arthur Rubin (talk) 14:31, 18 June 2008 (UTC)
Indeed, I didn't even know what a Ym was until I started reading this discussion. If I'm talking about a number that big I use scientific notation, not Yotta. Using a prefix is just silly in this case. I suspect that no normal person knows what a Ym is, and that few abnormal people do. Think about it: when you talk about the distance between galaxies, what units do you use? Ym, or parsecs/light-years? I've *never* used metres or kilometres to talk about inter-galactic distances. I say "Alpha Centauri is the nearest star, and it's 41 trillion km away! That's like, 4 light-years or so. And the nearest major galaxy is two and a half MILLION light-years away!". That's the only way you can give any real sense of scale. Saying that Andromeda is 2.4*10^18 km away is meaningless to almost everyone, as is saying that it is 2.4 exakilometres away. "Say waaaa...?". People don't understand numbers bigger than trillion (shortscale), because they never come across them in their everyday lives.
I would also argue that light-year is a commonly understood term. People know what light is, and that it moves fast. They know what a year is. Putting the two together to get a *relative* measure of distance in their own mind shouldn't be that hard.Gopher65talk 16:58, 18 June 2008 (UTC)
Well, in reply to the second-to-last post; people don't really understand numbers bigger than a billion either. So, rather than trying to relate that kind of distance on ANY scale, why not just write "The universe is big. Really big." And leave it at that? Also, I agree that the yotta prefix isn't very meaningful here. In fact, the entirity of what I'm suggesting here is that we try to convey a sense the size of the universe using only terms that are familiar to the average person. "billions of light-years" and "trillions and trillions of metres" are both difficult quantities to deal with, but at least metres are familiar to most people. Even miles would be more suitable than light-years in that respect.
In reply to the post above, I don't think it's the case that any normal person has any idea of the speed of light. For instance: How long does it take light to get from one end of the room to the other? How long does it take for light to get in to town? What about how long it takes to circle the globe? Now, if you could answer any of those questions without a calculator, then maybe I'm wrong. But I'm betting the average person has no idea of the answers. Therefore, using the speed of light as a reference is basically meaningless to the average person. As an aside, I think it takes light about a seventh of a second to get around the world : ) InternetMeme (talk) 11:59, 22 June 2008 (UTC)
The speed of light is a nanosecond a foot, of course, showing, once again that English units are preferable to metric.
</sarcasm>Arthur Rubin (talk) 14:47, 22 June 2008 (UTC)
Well, when asked just how fast light is, I usually say something like "It takes us about 3 days to get to the moon. It takes light about 1.5 seconds. It's fast." (Or is 1.5 seconds for a round trip? I can never remember.) When dealing with an article like this, which is clearly a low-information beginner article, I think what we're going for is a relative distance. I mean, the distances involved are too much for any of us to truly understand. Even thinking about the distance between planets is mind-boggling if you try to hold it all to scale while you think about it. So we aren't trying to convey an absolute sense of distance, but rather a relative sense of distance.
I would use light-years as the primary unit, and metres in scientific notation as the secondary unit. But even if everyone agrees to that, it brings up another problem: a surprising number of people don't understand scientific notation. Of course, they won't understand any prefix bigger than trillion either. (Which is what I meant earlier. People know what trillion (short scale) is, even if they have difficulty conceptualizing it.) So What do we use? They don't know exactly what a light-year is, so it is just a random, relative unit to them. They don't understand big prefixes at all, so we can't say exametre or yottametre. They don't understand scientific notation, so we can't say 2.4*10^18, cause that is just a meaningless string of numbers to them. So since we have no meaningful way of really conveying these big numbers, I say we just use whatever units we are most comfortable with, and anyone who doesn't understand them can click the blue link and read up, just like the rest of us do on subjects that we aren't familiar with.Gopher65talk 15:33, 22 June 2008 (UTC)

## Big Bang?

We are not certain that the universe started with the "big bang". —Preceding unsigned comment added by Deathbydsgn (talkcontribs) 14:40, 17 June 2008 (UTC)

Apologies, I missed the earlier topic regarding this. —Preceding unsigned comment added by Deathbydsgn (talkcontribs) 14:43, 17 June 2008 (UTC)