Talk:Expansion of the universe/Archive 2

Archive 1

Archive 2

Archive 3

Lorentz factor

Is it the case that the parts of the Universe that are expanding faster than the speed of light are doing so because of bending space, the lorentz factor, and other aspects of relativity exclusively or at least more so than to do with newtonian motion? 206.109.195.126 (talk) 05:44, 21 August 2009 (UTC)

Please understand that the speed of light is measured within space-time. Expansion is taking place to space-time. To say it differently, every place in the universe is NOT MOVING. Both the place here and the place there are standing still, but they are moving apart because the space between them is getting larger. It used to take light a few seconds to move from here to there, but now it takes a little longer because here and there are farther apart. And, the light is slightly red shifted because the space it was moving through stretched it by expanding while it was traveling from here to there. During that time the light was always traveling at the speed of light. - Allyn — Preceding unsigned comment added by 97.65.82.66 (talk) 21:31, 24 June 2011 (UTC)

I hope someone can elaborate on how objects aren't moving from eachother. Perhaps you were refering to how the Big Bang wasn't a blast of objects, which is ok. If space between the objects (herby galaxy clusters) are getting larger, it also indicates that the objects are receeding from eachother. It follows that space exerts a tug on the objects. How can space exert a tug, when such require mass? Siggy G (talk) 12:23, 5 May 2013 (UTC)

Expanding Raisin Bread

Don't we need to include an explanation of why the bread is expanding but the ruler isn't?

    What're you talking about? The ruler is expanding to suit the larger size of the bread, 
    and the distance between the raisins.
       (talk) 18:46, 12 April 2011 (UTC)

I disagree. The space (bread) is expanding, but the ruler is not getting larger because it is made up of atoms that stay the same size because the orbits of their parts around each other are continually returning to their stable distances. So the ruler stays the same size. - Allyn

New section

First of all sorry for adding my comment into your thread, but I was unable to find the "new thread" button.

Added Hubble's personal views upon the subject, with sources and references, and removed 'famous' from the 'famous Friedmann equations', since I cannot see why a famous equation should be better than an unfamous one. All in all this article is a terrible piece.

Jeppe —Preceding unsigned comment added by Jjjjc (talk • contribs) 10:04, 11 September 2008 (UTC)

Lack of evidence

This article is intended for the general public, however, the section on observational evidence is somewhat lacking. There are two principles, and 4 evidence points in the is section (2 of which support the principles).

The principles, while supported by evidence may be correct, but are not evidence for metric expansion. Evidence supporting the principles are not evidence for expansion: eg isotropic distribution across the sky is NOT evidence of expansion, and for the 4th point, redshift on the microwave background is consistent with the expansion assumption, however, it also is not observational evidence... if somehow it is evidence, then the point needs to explain how it is, but from my understanding of science, the redshift argument from Hubble law defines our understanding of the age of the universe, and thus makes this observation consistent, not evidence.

The second point of evidence is about homogeneity: when we look far away, that galaxies appear not so lumpy as they do in close measurements. How is this evidence of metric expansion? Only if you already believe the story does this look like evidence - without the assumption of the big bang, then this is simply consistent with the story.

Which brings me to the first point of evidence, both which depends on redshift, and Hubble's Law. The first sentence is flat wrong, Hubble DID NOT demonstrate that, in fact he it very clear he published the redshift+standard candle correlation, and it was interpretation that lead to the velocity assumption. Instead of evidence, metric expansion is an explanation for this assumption - not observational evidence.

This sentence: "Additionally, scientists are confident that the theories which rely on the metric expansion of space are correct because they have passed the rigorous standards of the scientific method." is an affront to reason. If it is so, then we must point to a review article, point to even one actual scientific study that got data, analyzed is and the result was metric expansion.

Here is the problem, we have a story about how light behaves over many many light years, and we have never done any experiments passing light through many light years of open space. All our experiments have been either completely enclosed in our galaxy, or on the receiving end of light that came from distant galaxies. Bluntly, there is no way we could have done controlled experiments on light traveling through interstellar distances.

I'd like to start a discussion of what the real evidence is for metric expansion, cite the section better with it, and if lacking, change the tone of the section (like the brash, arrogant assertion of the first sentence) to reflect that metric expansion is a consistent story with observation for which there is no direct evidence.

64.142.101.135 06:18, 1 October 2007 (UTC)

The fact is that the only solutions offered to the observations outlined are a uniformly expanding universe. Support for the description comes from the evidence outlined. "Direct evidence" as you put it is a blatant misnomer and not based in the actual way theory gets formulated to explain observations. ScienceApologist 18:52, 2 October 2007 (UTC)

Wow, this article could be the biggest load of bollocks I've come across on Wikipedia. Not only is it biased in tone and presentation, it provides almost no supporting evidence and misinterprets basic scientific ideas (like the Copernican principle). Further, the amount of weasel words employed to present this theory as having even a modicum of scientific acceptance is truly astounding.

The author should be ashamed. If you want to float a theory you support, there are better places than Wikipedia.

I support the assertions of 64.142.101 completely. ScienceApologist, you need to realize that science doesn't need an apologist: it needs evidence. You may think this theory explains certain observations, but if it doesn't make testable predictions or isn't supported by direct evidence, then it is pseudoscientific nonsense. I'll be coming back soon for a major rewrite.

I suggest that you do not rewrite this article without some pretty hefty sourcing for your opinions. In particular, I expect you to use authorities who are recognized in the field. ScienceApologist (talk) 23:15, 17 November 2007 (UTC)

(Okay. Just so it doesn't look like he's alone here...) I'm completely behind ScienceApologist on this one. The metric expansion of space really is very broadly accepted by mainstream scientists, with no other serious candidates theories. Any edit suggesting that metric expansion is suspect would only be damaging to the article. It may be wrong, but it reflects current scientific concensus, which is all that belongs in a Wikipedia article.

The obvious analogy here is with the evolution "debate". We can't do an experiment showing that complex animals including humans indisputably evolved from single-celled organisms over billions of years. Nonetheless, most scientists do accept the theory as fact because there are so many consistent observations -- essentially, because theories that rely on it have "passed the rigorous standards of the scientific method." If you want to argue about metaphysics, there are better places than Wikipedia. --131.215.123.98 (talk) 00:00, 18 November 2007 (UTC)

If "the expansion of space is unobservable", how can you say that it's happening? If it's unobservable, it hasn't passed the standards of anything. I think the problem is that people are assigning a physical meaning to the co-ordinates. A metric can undergo a change of co-ordinates and still describe the same space so it's hard to see that the co-ordinates do have a physical meaning. Can the article be renamed to 'expansion of the universe'? Neodymion (talk) 07:49, 12 April 2010 (UTC)

"The metric expansion of space really is very broadly accepted by mainstream scientists..." "It may be wrong, but it reflects current scientific concensus..." "Nonetheless, most scientists do accept the theory as fact..." Consensus science is not science. Data is proof. Consensus of scientific opinion is still opinion and, therefore, should not be posited as proof. —Preceding unsigned comment added by 198.203.192.166 (talk) 19:53, 15 March 2008 (UTC)

I also must support the assertions of 64.142.101. I just read "A Diatribe On Expanding Space" by J.A. Peacock that- at least to me- scientifically demonstrates the fallacy of expanding space. Not only is this "expanding space" unobservable, but Peacock also throws it in doubt with his equations and explanations.

We surely cannot posit the concept of expanding space as though it were some irrefutable truth when there is absolutely no direct evidence to support it. —Preceding unsigned comment added by 174.0.138.157 (talk) 15:58, 31 July 2010 (UTC)

Metrics

Coming back to this article after a while, this section still bothers me slightly. Are we really explaining "metrics" well? Could we be more cogent for the lay-reader? Or is it just a technical term that is hard to explain?

The concern being, metrics are a term needed to understand this idea in cosmology, but for a background "pre-article information thats useful" it's quite long. Does an explanation of metrics need to be explained in this length, before moving to the "meat" of the article and its actual topic? Could we explain it simpler and shorter in any other way? FT2 ^{(Talk | email)} 08:25, 28 October 2007 (UTC)

The only reason "metric" is complicated is because it refers to the shortest distance between two events (the geodesic). Since every event is defined by four coordinates (t,x,y,z) there are sixteen terms in the metric for describing how to get from event A to event B. Some of these terms may become redundant depending on what kind of symmetries are invoked, (for example, rotational symmetry, radial symmetry, etc.) but generally speaking that's where we have to go.

Metric expansion happens in a theoretical sense because there is a term called the scale factor which relates (t) to (x,y,z) without changing the overall symmetries invoked for an appropriate cosmology. Now, this scale factor could be any number of values. Einstein's static universe effectively chose a value for the scale factor that was the square root of a cosmological constant: a technique which removed any dynamical features for spacetime. One could introduce a scale factor that was independent of (t) which would effectively mean there was no metric expansion of space. The point is that you have to go and measure the scale factor in order to answer the question. That's where Hubble's observations come in.

Does this explain why "metrics" are needed? ScienceApologist 15:09, 28 October 2007 (UTC)

• Are there any exceptions to the rule - that is, something is actually hurtling toward us or other objects in violation of the model? --71.245.164.83 (talk) 01:31, 3 December 2010 (UTC)

Delisted from GA

In order to uphold the quality of Wikipedia:Good articles, all articles listed as Good articles are being reviewed against the GA criteria as part of the GA project quality task force. While all the hard work that has gone into this article is appreciated, unfortunately, as of February 15, 2008, this article fails to satisfy the criteria, as detailed below. For that reason, the article has been delisted from WP:GA. However, if improvements are made bringing the article up to standards, the article may be nominated at WP:GAN. If you feel this decision has been made in error, you may seek remediation at WP:GAR. As with many articles passed before the good article criteria where updated in 2006, this article has insufficient inline citations. Current criteria state that at minimum articles must provide "in-line citations from reliable sources for direct quotations, statistics, published opinion, counter-intuitive or controversial statements that are challenged or likely to be challenged". I've listed this article with the unreferenced good article task force. --jwanders^Talk 03:56, 15 February 2008 (UTC)

Dark Matter and the Expansion of Space

I was wondering what is the proof that the universe is expanding? Is it because the redshift on standard candles? Is there other proof?

My understanding is that gravity can bend space. If a great mass passes in front of light could one see a redshift since the distance now is farther than it was? the speed of light should be constant but I think that it relatively has to go father in the same time. thus the redshift. Is this correct?

Also if the above is correct. What would be the effect of mass that was spread over great distances. Where I am going with this is :

Could dark matter spread out over billions of light years cause a red shift in the light from a star that is not moving away from us in absolute terms? The thought is that the amount of dark matter that the light passed through could have quite a bit of gravity. Thus making far away objects appear that they are moving farther away from us quicker than they actually are.

From the article:

Edwin Hubble demonstrated that all galaxies and distant astronomical objects were moving away from us ("Hubble's law") as predicted by a universal expansion.[2] Using the redshift of their electromagnetic spectra to determine the distance and speed of remote objects in space, he showed that all objects are moving away from us, and that their speed is proportional to their distance, a feature of metric expansion. Further studies have since shown the expansion to be extremely isotropic and homogenous, that is, it does not seem to have a special point as a "center", but appears universal and independent of any fixed central point.

Couldnt this also be the proof that dark matter can effect redshift? The farther something is away from us the more dark matter it would need to pass through and that would create more of a red shift. —Preceding unsigned comment added by 69.249.66.67 (talk) 05:19, 22 March 2008 (UTC)

I just was discussing things on another page. And it seems like a passing gravitational field will create a red shift as the light passes into it then a blue shift when the light passes out. So lets take this a step farther. Lets say that the amount of dark matter in the universe is growing at a constant rate equally distributed accross the universe. That means that the amount of dark matter that the light from a distant star passes through is increasing. Thus the light is effected by an increasingly larger net gravitational field. In theory couldnt that cause a permanent red shift? --Tommac2 —Preceding unsigned comment added by 207.45.240.18 (talk) 14:07, 24 March 2008 (UTC)

--Tommac2

Light and the Expansion of Space

Another theory of the source of the expansion comes from Geometric Algebra. Geometric Algebra models particles (such as light) and interactions between particles (such as light absorption by an atom) the same way. The model is somewhat quaternion like, but has many more terms. The state of a particle is a 16-tuple which can be grouped as {1, (1+3), (3+3), (3+1), 1} = {scalar, vector, bi-vector, tri-vector, pseudo-scalar}. The different elements can be associated approximately to {scalar, (time+space), (velocity+orientation), (angular-rate+volume), space-time}. All interactions between particles simply become essentially multiplications. In the Geometric Algebra model, whenever two elements are multiplied, two different elements are generated (e.g. two vectors multiply to give a scalar and a dot product [bi-vector]). In this representation what happens when light is absorbed the result is both an impartation of momentum and an increase of space-time. That is to say, the absorption of light is the cause of the increase in the total amount of space-time.

Look at the picture depicting the history of the size of the universe. Early on while everything was electrically charged, hot and closely packed together, lots of light was absorbed almost immediately and the universe was in hyper-inflation. As soon as everything paired up to make electrically neutral atoms, the CBR light was able to pass by the atoms and inflation almost immediately stopped. Shortly stars began coalescing and absorbing light and inflation began increasing again. Inflation continues to increase as the amount of interstellar trash increasingly absorbs more light. Maybe what we have been calling dark is actually light. --Allyn

Expanding relative to what?

If the universe is expanding is it expanding at all points?

In any case if space time is effected by gravity an expanding universe could be from the effects of more gravity right? It would have to be taken in relative terms ( I guess relative to earth ). Would the addition of mass / gravity be the same as an expanding universe? Time space would bend.

--Tommac2 —Preceding unsigned comment added by 69.249.66.67 (talk) 05:15, 22 March 2008 (UTC)

expansion of the universe = growth of gravitational field?

Could one way of looking at the expansion of the universe be that the net gravitational field is increasing? Does that mean that there is more energy / mass?

I was trying to think of what is meant by an expanding universe. I was trying to picture what happens to the fabric of time-space as the universe is expanding. Lets think about a universe without any gravitational field? I would state that the universe would not exist and that a universe could only exist relative to fields of gravity. The fabric of time space IS gravity!?

The expansion of space would really only mean that the fabric of space-time been warped in a way that the distance between all matter relative to time is growing. Could this also mean that the net gravitational field in the universe is growing?

Can time-space even be percieved without including gravity in the equation? --Tommac2 —Preceding unsigned comment added by 207.45.240.18 (talk) 16:59, 31 March 2008 (UTC)

Incorrect statement - please fix the article

Hi,

At some place in the article you say:

"... in our diagram, this means that light beams always make an angle of 45° with the local grid lines...."

But that is incorrect. The diagram actually pictures the metric

ds^2 = dt^2 - R(t)^2*dx^2

or approximately, in the case of ideal cone where R=h*t

ds^2 = dt^2 - h^2*t^2*dx^2

(constant h is analogue to the Hubble constant)

Here, x is effectively an "angular" coordinate (x = const are the radial lines of the cone starting from the vertex)

Light rays are represented by ds^2=0, or for these holds

dt^2 = h^2*t^2*dx^2

i.e.

dx/dt = 1/(h*t)

Obviously, because the derivative of x(t) with respect to t changes with time as 1/(h*t), and it is equal to tg(alpha), it is not possible (and it is not true) that "angle with the local grid lines is always 45°". In fact, as t grows and it goes farther from the BB (vertex of the cone), lightrays get more and more parallel to the constant angular coordinates x (vertical lines through the vertex).

The "local" speed is calculated as R*dx/dt; i.e. in for lightrays it is always +-1.

However, this is not "immediately visible" on the image, and can to be deduced from the cone in the following way: As the time grows, the curcumference of the cone gets larger and larger. I.e. between two neigbour constant x-coordinates, "local distance" gets more and more - and for the same lapse of the time interval, as we go up the cone, the ligh passes less and less part as percentage of the neighbour constant x-coordinates (vertical lines) - but, it continues to pass the same real distance (as pure length) for this lapse of time, all the time.

Another way to illustrate this, is to imagine the cone is closed. At the thin parts of the cone (close to the vertex), say light will do full circle for the 10 time periods. Next 10 time periods, the curcumference is larger (we moved up the cone), and if light again makes full circle around for the same 10 periods, it has to travel locally (around the cone) with higher local speed - which is impossible.

Please correct this. You may need to correct the picture too, if you originated from that lightrays must keep constant 45 deg. angle with the grid. (on the picture, it should not be like that)

Excuse me I did not correct the article myself - my english is not very good, and I am not very familiar with Wikipedia.

UPDATE: I corrected it myself, the sentence now reads: "... According to the equivalence principle of general relativity, the rules of special relativity are locally valid in small regions of spacetime that are approximately flat. In particular, light always travels locally at the speed c; in our diagram, this means that light beams always make same real curcumferencial distance for a small lapse of time (but as the time grows and universe expands, beams trajectory gets more and more parallel to vertical grid lines)." —Preceding unsigned comment added by 206.248.171.64 (talk) 05:59, 11 July 2008 (UTC)

Thanks,

Dzver —Preceding unsigned comment added by 206.248.171.64 (talk) 04:31, 11 July 2008 (UTC)

Hi, I'm sorry I didn't reply earlier, I've been on vacation. The light geodesic does make a 45° angle with the grid lines everywhere. It's true that dx/dt decreases as the scale factor increases, but dx isn't a measure of distance on the surface. The embedding I used is

${\begin{aligned}r&=a(t)R\\\phi &=x/R\\z&=\int {\sqrt {1-a'(t)^{2}R^{2}}}\,dt\end{aligned}}$.

(Note I'm using a(t) where you used R(t), and I use R for a different purpose.) To make the analysis easier let me use Cartesian coordinates $v=r\cos \phi ,w=r\sin \phi ,z=z\,\!$ in terms of which the embedding is

${\begin{aligned}v&=R\,a(t)\cos {\frac {x}{R}}\\w&=R\,a(t)\sin {\frac {x}{R}}\\z&=\int {\sqrt {1-R^{2}a'(t)^{2}}}\,dt\end{aligned}}$.

The tangent space at $x=x_{0},t=t_{0}\,\!$ is

${\begin{aligned}dv&=R\,a'(t_{0})\cos {\frac {x_{0}}{R}}\,dt-a(t_{0})\sin {\frac {x_{0}}{R}}\,dx\\dw&=R\,a'(t_{0})\sin {\frac {x_{0}}{R}}\,dt+a(t_{0})\cos {\frac {x_{0}}{R}}\,dx\\dz&={\sqrt {1-R^{2}a'(t_{0})^{2}}}\,dt\end{aligned}}$.

By symmetry I might as well take $x_{0}=0\,\!$, which gives

${\begin{aligned}dv&=R\,a'(t_{0})\,dt\\dw&=a(t_{0})\,dx\\dz&={\sqrt {1-R^{2}a'(t_{0})^{2}}}\,dt\end{aligned}}$.

Normalized tangent vectors to the grid lines at this point are $(0,1,0)\,\!$ and $(R\,a'(t_{0}),0,{\sqrt {1-R^{2}a'(t_{0})^{2}}})$ in (v,w,z) order. The light geodesic at this point satisfies $dx=dt/a(t_{0})\,\!$, to which a tangent vector (unnormalized) is $({\tfrac {dv}{dt}},{\tfrac {dw}{dt}},{\tfrac {dz}{dt}})=(R\,a'(t_{0}),1,{\sqrt {1-R^{2}a'(t_{0})^{2}}})$. The grid line tangent vectors are orthonormal and the light tangent vector is their sum, so the light geodesic makes a 45° angle to each grid line in the 3D Euclidean embedding space. The fact that I Euclideanized the FLRW metric before embedding it is important. If I had embedded the 1+1 metric in 2+1 dimensions and then Euclideanized the embedding space, the minus under the radical would have been a plus and the (Euclidean) angle would not have been 45° in general.

I'll undo your changes for the time being, but let me know if I've missed something. -- BenRG (talk) 11:49, 22 July 2008 (UTC)

isn't it false??

"For much of the universe's history the expansion has been due mainly to inertia."

inertia relative to what??? —Preceding unsigned comment added by 89.60.192.103 (talk) 15:29, 13 November 2008 (UTC)

That line doesn't make much sense to me either. That whole section seems a bit suspicious to me. I haven't studied this field in much depth, but it seems at odds with how expansion effects the energy density of radiation. At any rate, the book I learned cosmology from (Dodson) never talked about expansion in these terms. --75.90.223.53 (talk) 21:20, 18 October 2009 (UTC)

layman questions

I am not a physicist but it seems to me that there are many interesting, qualitative layman questions about the metric expansion of space, including whether and how it impacts observables in our galaxy. Does metric expansion of space affect:

the energy of cosmic rays and photons (CMB, light, gamma, etc.); 
the rest mass of hadrons, including intergalactic hydrogen nuclei; 
a hydrogen atom in ground state;
the rest mass of leptons;
conservation of momentum, energy, and angular momentum;
relativistic Doppler effect and red shift.

The effects of metric expansion of space are dominated by other factors within a galaxy but have they been modeled and simulated at the periphery of a galaxy or assumed away? Could metric expansion of space affect galactic rotation curves? How about the evolution of stars at the periphery of galaxies? Is the distance at which metric expansion effects become negligible dependent upon the mass of the supermassive black hole differently than on the mass of the galaxy as a whole? At what radius might we expect a transition region between dark matter dominance and dominance of metric expansion of space? Has this been observed in relativistic jets?

Could the "negligible" effect of metric expansion of space on Earth affect any of the universal constants that we measure to eight or more significant digits?

I would be interested in finding one or two layman-tolerant general relativists who could help me to understand these issues qualitatively. I would appreciate any readable references.

best wishes, WalterU (talk) 14:13, 1 January 2009 (UTC)

The most important thing to understand about the expansion of the universe is that it's just relative motion. Some things are moving towards each other, some away, but if you average it out over very large scales you get an overall motion apart. Nothing is being pushed; we don't live in an Aristotelian universe where things need to be continually pushed to keep moving. I don't think the article makes this point nearly as well as it should. The article title is part of the problem—"metric expansion of space" sounds like a phenomenon that's independent of the stuff occupying space. It would probably be better at "expansion of the universe".

The cosmological constant (if there really is one) is a bit different. You can think of it as a repulsive force. That's not necessarily the best way to think of it, but it is a valid way, and you can reasonably ask whether it would have a noticeable effect on galaxy rotation, for example. The repulsion is proportional to distance and the proportionality constant is about 10⁻³⁵ s⁻². The radius of the galactic disk is about 60,000 light years, so the repulsion between the center and the edge due to the cosmological constant is about 60,000 × 10⁻³⁵ light years / s² ≈ 10⁻¹⁴ m/s². The galaxy completes a rotation about once every t = 250 million years, so the net acceleration at the edge is (2πr/t)²/r ≈ 10⁻⁹ m/s². So the effect is actually fairly large in this case, but I think it's far too small to be detectable given the uncertainties in the ordinary+dark matter distribution in the galaxy. The effect at the scale of a hydrogen atom is ridiculously small, less than 10⁻⁶⁰ of the electromagnetic force at that range. Note also that most experiments take place on the Earth's surface, where the acceleration of gravity exceeds the acceleration due to the cosmological constant by at least 30 orders of magnitude—and even the acceleration of gravity can be neglected in a lot of these experiments.

So much for galaxies and hydrogen atoms. The Doppler effect (redshift) is intimately tied in to spacetime geometry, and since spacetime isn't flat (unlike special relativity's spacetime) the special relativistic redshift formula doesn't make sense at cosmological scales (not because it gives wrong numbers, but because the distances and relative velocities that go into it can't even be sensibly defined in cosmology). Energy is a frame-dependent concept. The big bang model breaks the symmetry of spacetime, and with respect to the natural reference frame it defines (basically, the reference frame in which the CMB is isotropic), you can say that objects lose energy as the universe expands and this energy goes into the gravitational field. But in a deeper sense, there's no right answer. Conservation laws are tricky. They are associated with symmetries of spacetime (Noether's theorem) and the spacetime of the real world doesn't have any exact symmetries, so at some level there are no exact conservation laws. At another level you can recover exact conservation laws by attributing energy, momentum and angular momentum to spacetime itself (as I mentioned above for energy), but that breaks general covariance. There's a somewhat technical essay about it here. -- BenRG (talk) 01:41, 5 January 2009 (UTC)

__

"we don't live in an Aristotelian universe where things need to be continually pushed to keep moving."

From a Digital physics perspective, let a universal Turing machine boot Aristotle's prime mover and notice every celestial object is in motion and remains in motion with nothing pushing them. "Natural" movement is a teleological effect of movers thinking about thinking and dedicated movers are hard coded for each celestial sphere. Alas, the metaphysics failed to rival more pedestrian solutions; powered directly by some god du jour qua gerbil.

With apologies for any lack of relevance, we could use some help with Talk:Cosmological argument#Scientific positions on philosophy. Thanks—Machine Elf 1735 (talk) 09:49, 14 April 2010 (UTC)

Weird Question: Is Time Expanding?

As I understand it, space expanding means that there is more distance between two points now than at some point in the past. And from what I understand about space-time, the idea is that time really is a dimension like space, although different in that entropy happens "along" time but not along space. (Hawking talks about the arrow of time in those terms.)

So, is time expanding too? Is there somehow more time between two locked events -- atomic decay or something -- now than there had been in the past? How would we measure that?

I appreciate it's probably a goofy question that reflects a mis-conception of one or more of the terms -- if so, I'd appreciate a quick debugging of the thought process.(71.101.53.18 (talk) 03:23, 25 May 2009 (UTC))

The answer is yes. As for a quick debugging however, I don't know what to tell you, other than to keep that thought while pulling back from whatever reference frame is causing you the confusion. --Neptunerover (talk) 23:09, 26 December 2009 (UTC)

Relative size

To better understand the vast numbers of cosmological distances and to make the metrics easier to understand. Lets say you have a sphere or cube volume of 1 meter. How much is the expansions and acceleration of the volume of space-time over lets say 100 years relative to the same volume today. Is it as small as plank scale or nanometers? I have not found this calculation and may help others understand the scale of expansion and acceleration. SG —Preceding unsigned comment added by 67.167.4.135 (talk) 15:58, 1 March 2009 (UTC)

Two points a distance d apart would have a relative speed of H_od; after a time t they will have separated by H_odt; as a fraction of the initial separation that's H_odt/d = H_ot. Over 100 years that's about seven parts per billion—pretty high. Another way to see it is that it's about 100 years divided by the age of the universe. But it's misleading to talk about a separation of 1 meter because things that size aren't expanding, even by a few parts per billion. Only the relative speed of galactic superclusters follows Hubble's law.

The acceleration, i.e. the change in Hubble's constant over that 100 years, is similar, about 3 parts per billion if I calculated right. (So it only affects H_ot by a few parts in 10¹⁸.) -- BenRG (talk) 14:47, 26 March 2009 (UTC)

Issue with "Local Perturbations" Section

In describing the impact of expansion on small scale dynamics, the article distinguishes between models with and without a Cosmological Constant:

"These stars and galaxies do not subsequently expand, there being no force compelling them to do so. ... This situation changes somewhat with the introduction of a cosmological constant."

This statement is misleading, since the dynamics of objects are completely determined by the geodesic equation and the geodesic equation depends only upon the metric, and not directly upon the details of the field equation that led to the metric (that is, whether contained a zero or non-zero Cosmological Constant).

Furthermore, since the Cosmological Constants can be absorbed into the stress-energy tensor term of the field equation through a redefinition of pressure and density, its not apparent why the two cases should lead to fundamentally different dynamics.

Bill Menke Columbia University —Preceding unsigned comment added by William.menke (talk • contribs) 21:32, 28 January 2010 (UTC)

could it be a different type of expanding ?

It occurred to me that the expansion of the universe might be explained differently. We think of the universe expands as all galaxies move away from us and thus as we cannot explain this wonder if dark energy can explain this..as a kind of contra force to gravity. But what if these galaxies where not pushed away, but the space in between grows in volume, while the particles inside do not grow. (or because that's matter of perspective, the space doesnt grow, but the particle shrink). The reason for growing, could be something to do with dimensions; if the big bang created time and dimensions. Its not sure that these dimensions are static on a big scale, it might be they grow slowly, we know of process that convert mass to energy. Its known what lightspeed does do to geometry of fast moving objects, so its not strange if geometry is not a static factor. It might be that mass / or energy waves could expand empty space as well, (as to which reference point does an object has light speed?). Such a universe would look the same as an expanding universe, but with no dark energies, and basicly it never went bigger then the first seconds after the big bang. Because allready then the explosion of empty space /or shrinking matter.. happend.

Well i wonder if such model has ever been thought of 82.217.115.160 (talk) 19:02, 28 February 2010 (UTC)

Re. the section "Other models of expansion"

As the lead sentence in the section says all these models do not include the time dimension in their workings. The problem with these models are that the reason for the increasing distance between ojects is that a reference frame has expanded. This does not pertain well to the basic principle that everything in the universe is relative. It's the same as explaining the universe is expanding because the aether medium that everything is sitting on is expanding. These models are specious explanations: they make it easier for the mass populace to comprehend the ideas, but they are not really accurate. 222.153.245.28 (talk) 03:55, 5 February 2010 (UTC)

pseudo space expansion

Should it ever be observed that all galaxies are members of a rotating group, rotating around some common point. As the angular velocity, per group, would be approx. the same value. Then those farthest from the central point would have higher velocities (as observed) without any need for space expansion. This would also allow for galactic collisions between members of different rotating groups without the need for "space compression??!!" BUT no metric Expansion either? 58.161.196.6 (talk) 12:18, 13 March 2010 (UTC)John

Changes by Systemizer

Can you explain the reasons for changing the name of the page and deleting most of the content, references, etc.? There doesn't seem to be a single accepted explanation for how this works, so removing tons of external links and explanation seems premature. —ShadowRanger ^(talk|stalk) 18:04, 18 March 2010 (UTC)

To be clear, simply calling them "vacuous" isn't enough. —ShadowRanger ^(talk|stalk) 18:05, 18 March 2010 (UTC)

Also, while I have found some references to "impansion" (explosion:implosion :: expansion:impansion), it's not a particularly common word, and it conveys the opposite meaning; you need an explanation and references to justify it. —ShadowRanger ^(talk|stalk) 18:07, 18 March 2010 (UTC)

Revision of the Page Title

Here the word "space" is used as an equivalent to word "universe". Space has several meanings. I recommend to use its mathematical meaning in this page, as reference coordinate (cubic, spherical, etc.) for measuring expansion of the universe. In this case, space is fixed (not expanding). So the main title should be changed to "expansion of universe". Then there is no need for the word "metric" in the title, either. K.Hamze (talk) 18:48, 2 April 2010 (UTC)

Misleading redirections

The redirections from "Expanding Universe" or "Expansion of the Universe" are misleading. The "metric expansion of space" is just an interpretation of the phenomenon of the universal expansion and is currently under debate. Moreover, the very notion of "metric expansion of space" is far from being widely accepted by the community, or even used. This can be easily checked on NASA ADS.

The main article should be "Expansion of the Universe". Metric expansion could be given just as one of the interpretations.

--Q (talk) 17:08, 18 April 2010 (UTC)

It is outrageous that "it is a fact that space is expanding" is apparently not allowed to be edited off. Orphadeus (talk) 12:50, 10 May 2011 (UTC)

I don't see why increasing redshift of more distant objects means that expansion is increasing...

I may be looking at this is simple terms but I can think of two scenarios where the more distant an object is, the more redshifted it is.

1) Isn't it a fact that the more distant the object that you observe the further back in time you are seeing it - due to the length of time the light has had to travel to reach us? That's the way I understood it. Well to me that means that the light being more redshifted on those distant galaxies than the light of closer galaxies (which we are seeing less far back in time) means that expansion was faster in the past and that the light was redshifted way back in the past when the universe was expanding very quickly, now it slowing down and the fact that light reaching us from nearer objects isn't so redshifted surely demonstrates this?

2) An alternative that I've considered related to the 'dough with raisins in it' theory of space expanding between all of the objects in the universe is that if this is the case then doesn't the net effect of increasing space between objects have a knock on effect meaning that objects are 'displaced' by a greater factor as you move towards the boundary due to the cumulative affect of the increases within therefore these outer objects cover greater distances in the same time and are therefore redshifted more? This doesn't mean that the expansion is increasing, it just looks like that due to the consolidated effect of all of the local expansions.

A simplistic example is a bunch of dots equally spaced on a ruler. If the space between each dot is expanded by one additional unit the knock on effect to the adjacent dots means that on the outer edge, the dots have moved by a much greater degree but the expansion has been no greater between them and the objects local to them. Using this model, the outer objects have travelled greater distance during the same timeframe - effectively moving at a greater velocity. This doesn't however indicate that the expansion itself is increasing.

I don't know, this seems pretty simple to me - maybe too simple?

Micktruss (talk) 08:48, 24 July 2010 (UTC)

First of all, Wikipedia does not allow original research to be included in articles, and Wikipedia is not a forum. Second, scientists can make observations across time. This seems to be how an accelerating universe was ascertained. Increasing redshift from an identical target over time cannot be explained by your model. Third, the knock off affect may well be behind the big rip idea.--Jorfer (talk) 17:18, 24 July 2010 (UTC)

Dfflick319 (talk) 22:47, 10 Feb 2011 (UTC)

Increasing redshift from an identical target over time can, however, be explained by a formerly expanding universe that is now contracting. This idea is growing in popularity in some circles. I am rather disappointed that the article at this point does not specify more alternate theories, contracting universe included. Dfflick319 (talk) 22:52, 10 February 2011 (UTC)Dfflick319

Misconception that objects receding faster than the speed of light are not observable

In the paragraph

"While special relativity constrains objects in the universe from moving faster than the speed of light with respect to each other, there is no such theoretical constraint when space itself is expanding. It is thus possible for two very distant objects to be moving away from each other at a speed greater than the speed of light (meaning that one cannot be observed from the other)."

the word "meaning" in the parenthesis suggests the same misconception that is discussed in reference 1 given a few lines below (misconception #3).

And the "thus" in the next sentence,

"The size of the observable universe could thus be smaller than the entire universe."

then connects the two statements in a way that appears to confuse the Hubble sphere with the particle horizon.

Perhaps this would better be linked to the similar paragraph in: The Universe versus the observable universe.

Rainer Bartoldus (talk) 16:23, 23 October 2010 (UTC)

Justification of changes

If you really have to justify changing, "it is a fact that space is expanding," its very exasperating. Ok, try this - there are a number of other possibilities. To the people on here - and I can see you are there - who are capable of thinking, nice to see you. Orphadeus (talk) 00:58, 10 May 2011 (UTC)

I would say we should put a concerted effort in to remove, "It is a fact that space is expanding". Its the least likely of 3 explanations.

1. As Hubble said

2. The photon, not in its light packet, minus its gluon, dark and unseen, is travelling approx twice the speed of light directly from the Big Bang. Galaxies further away from the epicentre have more catchment to the energy from the Big Bang. Radiative cooling simply reflects that energy from the Big Bang (X = Y x Xes, it can come from anywhere even if there is an epicentre) is at current lower (or at least that aspect), which may be fluctuation.

3. Space is expanding

There may be others. In my opinion, the least likely is the 3rd. That opinion is irrelevant, the point is that the 3rd has not been proved. We should not appease them. 94.193.97.139 (talk) 01:22, 10 May 2011 (UTC)

Nowhere does the article use the wording "It is a fact that space is expanding". What the article does and should make clear is that the vast preponderance of third-party reliable sources agree that evidence for the standard cosmological model is extremely strong, and this model includes expansion, which is measured to high precision.

I have reverted your changes and added a source from a very notable author in a very reliable publication. There are plenty of other similar sources. I also reworded two sentences for neutrality, which I agree were too strongly worded against potential alternatives. To contest the current wording or make substantial changes, you are going to have to find consensus with others and base your proposed changes on reliable sources. There are various places you might look for others' opinions, such as the physics project or the neutral point of view noticeboard if you are alleging that the article is biased. Continuing to revert against consensus is likely to make your experience here frustrating and possibly short-lived as well. Tim Shuba (talk) 04:47, 10 May 2011 (UTC)

Breakdown of changes in this edit

• "is said to support ... is claimed to be ... presented as evidence" - using the passive voice in this way serves as weasel wording. The attribution for the evidence presented after that paragraph is provided by the sources for each point. The nebulous wording change urges the reader towards a certain reading of those sources without itself providing sources to justify this.
• "(please source, Figure 5a is not a source)" - Figure 5a is just a diagrammatic representation of the points in that section, and is not intended as a source. For future reference, the image in question is the one at Metric expansion of space#Observational evidence; I am removing the figure label per the Manual of style, as trying to keep labels synchronized does not work very well on a collaborative project such as this (which is probably why none of the other figures carry such identifiers).
• "A possible explanation ... an alternate explanation" - this well and truly fails at providing a fair representation of the collective opinion of the astrophysics community, in violation of the Neutral point of view policy. An epicenter for the Big Bang is strongly excluded by observational evidence. This page is not an appropriate place to rewrite modern cosmology; Wikipedia follows reliable sources, it does not lead in any debate.
• removed "the only theory which coherently explains ..." - this is just tying together the preceding points, which otherwise stand as apparently unconnected observations. Some statement as to why an article about the metric expansion of space would discuss those points is necessary.
• "some believe" - see above
• removed "determined that" - removing this misrepresents the cited source by making it appear to support something that it does not.
• "notwithstanding Hubble's personal opinion" - Edwin Hubble died in 1953, and should not be cited as representing the modern cosmology community. His views would be relevant to a History or Development section devoted to detailing how the theory and its reception have evolved. For instance, the subsection devoted to his interpretation of the data. A vague uncited insinuation has no place in the Observational evidence section.
• "or other possibilities such as the photon travelling twice the speed of light directly from the Big Bang" - um? This is either very unclearly written, or very, very odd.
• "many scientists believe" see above, again.

I am accordingly restoring the earlier version of the article. Per WP:BURDEN, please justify any changes here and wait for discussion to reach consensus before restoring disputed material. - 2/0 (cont.) 07:46, 10 May 2011 (UTC)

Theres a problem

Lets take the hypothesis that space is infinite. In the same way that the photon manifests in a vacuum, so energy from the Big Bang can come from everywhere, even in the form of cosmic background radiation. Now lets take the hypotheses that the cosmic background radiation coming from the Big Bang is currently less, and so we have Radiative Cooling. Can you please desist from citing Radiative Cooling as proof of space expanding. Also, lets take the hypothesis that the measurements are correct and that galaxies are accelerating away faster that the speed of light. Some might take the view that energy from the Big Bang travelling faster than the speed of light (galaxies further from the epicentre have more catchment to the energy) is at least as valid a theory as space expanding. That aside, its not hypothetical, at what point did the expanding space company prove Hubble and Einstien's doubts about the measurements wrong? Orphadeus (talk) 15:03, 11 May 2011 (UTC)

Could there be electromagnetic interference with wavelength? If so, the more light years away, the more the interference. Orphadeus (talk) 18:08, 11 May 2011 (UTC)

I've added a 'Theres a problem' section to that. I would suggest that if no-one has coherently countered within 5 days, we should consider there is a general consensus that the Metric expansion of space page should be edited. Orphadeus (talk) 14:21, 12 May 2011 (UTC)

(Moved from the archive, and from the top of the page. I thought the meaning of the word "archive" was obvious...) Ian.thomson (talk) 18:37, 12 May 2011 (UTC)

@Orphadeus I've moved your latest post to the correct place at the end of this page. I've restored the previous attempt to move the new posts you made on Talk:Metric expansion of space/Archive 1 over here to the current talk page, (where people will see them). I've also reverted your revert to Archive 1, and I've moved a second copy of your posts here. FYI, consensus is against the article edits you attempted to make and your 5-day suggestion isn't going to work out like you're hoping...—Machine Elf ¹⁷³⁵ 09:10, 13 May 2011 (UTC)

---

I've added a 'Theres a problem' section to that. I would suggest that if no-one has coherently countered within 5 days, we should consider there is a general consensus that the Metric expansion of space page should be edited. Orphadeus (talk) 14:21, 12 May 2011 (UTC)

Thanks Machine Elf, there does appear to be quite a lot of logical unrest at 'It is a fact that space is expanding'. As such, I would suggest that if nobody can say at which point Hubble and Einstein's doubts about the measurements were proved wrong, if nobody can site evidence that there is not energy from the Big Bang travelling faster than the speed of light, if nobody can provide evidence against that some Cosmic Background Radiation comes from the Big Bang in infinite space and the energy coming from the Big Bang is currently lower; 'It is a fact that space is expanding' should be considered an unscientific statement that should be amended. With respect, you have basically said, "I'm not going to let you" (going by many of the posts, you may be in a minority), rather than coherently explained why it would be wrong to edit to such as, "It is believed by many scientists that space is expanding." 94.194.100.228 (talk) 12:14, 13 May 2011 (UTC)

I won't stop you and you're welcome to be in the majority... Actually, what I said was "your 5-day suggestion isn't going to work out like you're hoping..." That's because you need to cite WP:RS to make those changes to the article, other editors don't need to provide "evidence" to revert them. However, if you're only challenging that particular statement, you should simply tag it with Template:Citation needed and I'm sure someone would happily oblige.—Machine Elf ¹⁷³⁵ 15:14, 13 May 2011 (UTC)

Thanks for the advice. There was a claim of studies where Template:Citation needed would have been appropriate but it appears someone other than me has moved the claim. I think there are a couple of WP:RS that can be included, perhaps in a 'Criticism' section, to give the page better balance. This is one and a mention of Dr Baldev Raj, who believes space was always there, is another. It would be good to include Arp's photo of image of Galaxy NGC 7319, perhaps that photo could be mention with a link to the page. It would be nice it someone could get hold of that photo in isolation to put on the page, but unless someone more technical than me is able to do that, having a mention of that particular photo with the link should be uncontroversial. Orphadeus (talk) 13:15, 15 May 2011 (UTC)

Theres a problem 2

Lets take the hypothesis that space is infinite. In the same way that the photon manifests in a vacuum, so energy from the Big Bang can come from everywhere, even in the form of cosmic background radiation. Now lets take the hypotheses that the cosmic background radiation coming from the Big Bang is currently less, and so we have Radiative Cooling. Can you please desist from citing Radiative Cooling as proof of space expanding. Also, lets take the hypothesis that the measurements are correct and that galaxies are accelerating away faster that the speed of light. Some might take the view that energy from the Big Bang travelling faster than the speed of light (galaxies further from the epicentre have more catchment to the energy) is at least as valid a theory as space expanding. That aside, its not hypothetical, at what point did the expanding space company prove Hubble and Einstien's doubts about the measurements wrong? Orphadeus (talk) 15:03, 11 May 2011 (UTC)

Could there be electromagnetic interference with wavelength? If so, the more light years away, the more the interference. Orphadeus (talk) 18:08, 11 May 2011 (UTC)

We could source Dr Raj Baldev, who believes space is not expanding and appears to believe that Dark Energy from the Big Bang is travelling faster than the speed of light. Also dark flow surely should be added, whatever the implication. My understanding is that Wikipedia is supposed to be neutral. Orphadeus (talk) 13:21, 13 May 2011 (UTC)

Some of you will be better able to evaluate Liou_Scwartz' stretch effect than me. —Preceding unsigned comment added by Orphadeus (talk • contribs) 14:36, 13 May 2011 (UTC)

This talkpage is not a forum for general discussion of the topic. Please restrict your posts to discussion of specific improvements to the article or proposed sources.

See Interference (wave propagation); did you mean some other term here?

The first is not an appropriate source for this article; please see WP:SCIRS. Likewise the AngelFire page. Dark flow was still fairly controversial last I checked (huge project, minuscule statistics - it was bound to happen); it concerns the observable universe rather than the universe as a whole, so I am not sure there is a strong case for treating it here. It did need to be linked at the Observable universe article, though, so I have taken care of that.

I believe that you may be laboring under a misapprehension of the meaning of the term neutral in this context. As explained at the Neutral point of view policy, we are required to provide an accurate reflection and summary of the gamut of sources without introducing our own editorial biases. In the particular case of this article, this means that we must present the theory as well-accepted by cosmologists. - 2/0 (cont.) 14:44, 13 May 2011 (UTC)

Thanks for the reply. Could you explain why Dr. Baldev Raj BE (Ravishankar Univ.) Ph.D.(IISc) FNAE, FASc., FNASc., HFICNDT, HFISNT, HFBINDT, FIIM,FUSI, FASI, Director of Indira Gandhi Centre for Atomic Research (IGCAR) is not an appropriate source?

Interference (wave propagation); was along the line of what I was theorising. Thats not allowed, other than by a few authorised persons, although if the logic is strong it perhaps should be a factor when considering whether to state something else as an absolute. Perhaps someone authorised has theorised about it, in which case there would be a source.

Something that hopefully can be included is Alton Arp's discovery: 'Arp believes that the observed redshift value of any object is made up of two components: the inherent component and the velocity component.' For and against Arp could be put. Orphadeus (talk) 17:28, 13 May 2011 (UTC)

Possibly of particular interest among the Arp photos is the image of Galaxy NGC 7319 if you scroll down, which gives a strong impression of a quazer 'over 90 times further away' infront of the Galaxy, particularly the magnified picture. Orphadeus (talk) 18:06, 13 May 2011 (UTC)

It appears to be devestating stuff. I'm a bit of a technophobe so if anyone wants to improve the page..

The Redshift research has gone well. Now I'm trying to find a source for that cosmic background radiation is at current coming from the Big Bang. I think I'm correct in saying I am refering to something like the photon manifesting in a vacuum. If I understood, here is confirmation that the photon currently manifests in a vacuum, that being the case, cosmic background radiation is currently coming from the Big Bang. 94.193.97.139 (talk) 00:16, 14 May 2011 (UTC)

Dissent

'In this situation, variations in galaxy age, metallicity, and dust (reddening) will cause the largest changes in the redder color due to changes in the slope of the ultraviolet continuum.'

That is a direct quote. Is the repeated removal of 'Dissent' not vandalism? Orphadeus 94.193.97.141 (talk) 17:03, 18 May 2011 (UTC)

The person who is doing the removal makes 3 claims:

1: Arp is not a source. 2. Thunderbolts is not a source. 3. The words quoted fro the report co-authored by Jane C. Charlton do not mean what they say

The 2nd point might have some merit other than that it is a reasonable source to source the photo to Jane C. Charlton. Furthermore, there are 2 references given at the point, and the other, which is a reasonable source, does not credit for the who took the photo. All in all, I think the complaints do not stand and would be grateful if any decent person could reinstall. Orphadeus (talk) 17:12, 18 May 2011 (UTC)

That quote has nothing to do with redshift, nor with the standard cosmology. You appear to be confusing reddening due to dust extinction, which is what the quoted passage is about, with redshift due to the metric expansion of space. Please stop adding links to thunderbolts.info and Arp's homepage to cosmology articles, as they are not Reliable Sources for cosmology. - Parejkoj (talk) 17:18, 18 May 2011 (UTC)

'Indeed, Lowenthal et al. (1997) found a number of highredshift galaxies selected nearby, but not within, the nominal region of high-redshift color space within the HDF. On an empirical basis alone, this indicates that the current selection methods may be somewhat incomplete. There are several other reasons to expect that the precise selection function for high-redshift galaxies is complicated and not yet well deÐned. While variations in SEDs play a critical role in determining the color-based selection criteria for selecting high-redshift galaxies, the intervening opacity is as important. To meet the dropout criterion in a twocolor diagram, ideally the bluest band (alone) samples below 1216 AŽ in the galaxyÏs rest frame. In this situation, variations in galaxy age, metallicity, and dust (reddening) will cause the largest changes in the redder color due to changes in the slope of the ultraviolet continuum.' Check Orphadeus (talk) 17:28, 18 May 2011 (UTC)

Yes, that passage is talking about determining the reddening values of high redshift galaxies. In fact, the whole passage wouldn't make sense outside the standard cosmology, where redshift and distance are related. Please read the wikipedia page on reddening. - Parejkoj (talk) 19:34, 18 May 2011 (UTC)

Can you confirm that redshift ie wavelength is determined by colour? Consider:

'Indeed, Lowenthal et al. (1997) found a number of highredshift galaxies selected nearby, but not within, the nominal region of high-redshift color space within the HDF.'

Can you explain why reddening caused by galaxy age and metallicity has nothing to do with the redshift of galaxies? According to Wikipedia Schools, 'In physics (especially astrophysics), redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum.' (perhaps you need to edit that). From the same study quote previously:

'Note, however, that while the mean and distribution of bluer colors changes with increasing internal NH I the redder colors in Figures 10a and 10b do not. This is because in the redder bands for the redshifts displayed, the absorption produced by the internal neutral hydrogenÏs discrete Lyman series lines does not compete with the forest of Lyman series lines integrated along the sight line, i.e., at different redshifts or different observed wavelengths.'

It certainly appears to me a clearly stated link. Orphadeus 94.193.97.141 (talk) 20:37, 18 May 2011 (UTC)

Redshift is generally measured via emission and absorption lines. Reddening is caused by a reduction in the amount of short wavelength flux compared to long wavelength flux; it does not shift the positions of emission and absorption lines, and thus does not result in a redshift. The two Wikipedia articles are correct, and the reddening article even says, "not to be confused with the quite separate phenomenon of red shift." Perhaps you have a suggestion on how to edit one or the other of them to make them clearer to you? - Parejkoj (talk) 13:30, 19 May 2011 (UTC)

The atom will be split. Orphadeus (talk) 14:05, 19 May 2011 (UTC)

'Extinction is the technical term for the dimming of starlight by interstellar dust' and 'Interstellar grains block blue light (wavelength=0.4µm) effectively, but red light (wavelength=0.7µm) can get through more easily'. source

What has that got to do with galaxy age and metalicity?

As a seperate point, the conclusions here seem to me to indicate that the dust shows up in the redshift. Orphadeus (talk) 14:42, 19 May 2011 (UTC)

Where are you finding these papers? I suggest that you spend some time studying a textbook on astronomy before jumping around in research papers, as you seem to have a number of points of confusion.

To answer your question, galaxy age and metalicity help determine the amount and type of dust in the galaxy, and thus the amount and nature of its effective reddening. Santiago et al. talk about "Galactic extinction," i.e. extinction of background sources by dust in our own galaxy. This affects the "selection function"--whether a given galaxy is picked to have its redshift measured or not--because galaxies viewed through different amounts of Galactic dust are reddened differently. This is an important effect to take into account when doing redshift surveys, but does not mean that redshift and reddening are related concepts: they aren't.

Again, I recommend that you study a textbook before trying to interpret research papers. The reference list at the end of the Redshift article has many good suggestions. - Parejkoj (talk) 15:43, 19 May 2011 (UTC)

Arp argues that redshift is primarily a function of age, I believe he is refering to what I quoted: 'In this situation, variations in galaxy age, metallicity, and dust (reddening) will cause the largest changes in the redder color due to changes in the slope of the ultraviolet continuum.' [1]

Notwithstanding the unquantifiable effect dust reddening has on redshift; Can you give us a reference for your statement that 'galaxy age and metalicity help determine the amount and type of dust in the galaxy'? Orphadeus 87.194.33.95 (talk) 20:02, 19 May 2011 (UTC)

Arp is not a Reliable Source for cosmology, and his ideas about redshift (which you are also misinterpreting, as even he doesn't believe that redshift and reddening are the same thing) are wildly incorrect. You are also taking the other articles out of context. Again: I strongly recommend you familiarize yourself with some basic texts on astronomy before trying to interpret research papers. A good place to start would be:

Carroll, Bradley W. and Dale A. Ostlie. An Introduction to Modern Astrophysics.

which is listed in on the Redshift page. You should be able to find it at a local library. It has chapters discussing both redshift and reddening and the properties and formation mechanisms of interstellar dust, all at an undergraduate level. The wikipedia page on Reddening could perhaps use some reddening, but I would prefer focused, relevant questions. - Parejkoj (talk) 05:33, 20 May 2011 (UTC)

Arp is Hubble's former assistant. Furthermore, it is beyond debate that a sourced article by Arp is a reasonable source to establish there dissent from Arp. Regarding the Thunderbolts source, the alternative is that Jane C. Charlton is not credited with the photograph. Doing that is churlish. As such, the Thunderbolts is a reasonable source to establish that the photo is believed to have been taken by her, I will reword accordingly. Orphadeus (talk) 12:22, 20 May 2011 (UTC)

Whether or not Arp was Hubble's assistant doesn't matter. His views, and those of the owners of thunderbolts.info are WP:FRINGE and do not belong on this page. There is already a section of the Non-standard cosmology page devoted to his views. Your interpretation of the papers you are citing is incorrect, and I again strongly urge you to read a textbook on astronomy before trying to understand research papers. You seem to hold a number of misunderstandings regarding astronomical topics. - Parejkoj (talk) 18:41, 20 May 2011 (UTC)

I concur that the Non-standard cosmology article is probably a better place for these dissenting opinions, as that article is focused on a high-level viewpoint and it covers the topic more comprehensively. There's not much point in having a dissent section on multiple cosmology-related articles if they are just going to repeat similar viewpoints. As for this page, I'd like to suggest that all we really need is a link to the above topic in a "See also" section. Thanks. Regards, RJH (talk) 18:51, 20 May 2011 (UTC)

Stick your necks out and tell us about that specific quasar (theres an amazing photograph). Orphadeus (talk) 19:07, 21 May 2011 (UTC)

Yes that is interesting and I'm sure astronomers will study it further. But an article talk page isn't the place to debate the subject. Thanks. Regards, RJH (talk) 18:58, 22 May 2011 (UTC)

Speaking as an astronomer, there is nothing particularly interesting about that paper, except the fact that it probably shouldn't have passed peer review. It is poorly written and their conclusions are not supported by their data. RJHall is correct that this talk page is not a place to discuss it. Orphadeus is pushing a very WP:FRINGE viewpoint here. - Parejkoj (talk) 20:11, 23 May 2011 (UTC)

RobotRollCall

Please inject some RobotRollCall into this article and remove as much jargon as possible. The article is supposed to be for an audience who doesn't understand this matter. Now, it's written like a summary for those who already studied this subject. http://www.reddit.com/user/robotrollcall?sort=top Her simple explanations make stuff understandable. 93.172.56.90 (talk) 05:59, 26 May 2011 (UTC)

Do you have some more specific suggestions? The introduction doesn't use much jargon, and what it does use, it explains. - Parejkoj (talk) 14:27, 26 May 2011 (UTC)

Layman here. There are way too many tidbits clumped up in the intro, especially from the third paragraph and on.

The first paragraph gives a very dry definition, which is confusing. At first, I thought it talked about some sort of property because the wording "is the increase..." I think it should somehow emphasize that this is a phenomenon. Also, I think the point it's between two distant objects is incorrect because the increase in distance happens everywhere, and it's just that with distant objects that don't attract much each other back together this phenomenon is evident. But again, I'm not a physicist.

The second paragraph makes absolute sense once you get the subject. It means nothing if you still haven't. I think the key issue to explain here is that the universe makes distances grow between (all) objects (or points in space), even if the objects in question don't move relative to each other.

The third paragraph is where the bombardment starts: Is it really necessary pointing out in the intro that ME is modeled with FLRW metric? Then come a bunch of facts that make no sense unless you are a cosmologist (valid in present era, the expansion is due partly to inertia, Lambda-CDM model, etc.) It should definitely be included in the article, just not in the intro.

The fourth paragraph is written backwards. At the end of it, comes the important point, presented as it was obvious what the previous commonly accepted hypothesis was. At the beginning comes the explanation leading to the point, but you don't really know why you are suddenly being lectured about the constraints of special relativity.

The fifth paragraph starts to explain a special case but stops short of actually explaining it. The second to last sentence about the confusion is entirely unnecessary. Many subjects cause confusion to everyone. We're trying to help. The last sentence is meaningless without detail, as every single part of physics is subject to debate and interpretation.

93.172.229.46 (talk) 07:33, 11 June 2011 (UTC)

Not buying it either

I think the § "Hubble's personal opinion upon interpretation of the data" should be expanded to make clear how this conflict was resolved. Quick scan of the lede of False vacuum left me with a feeling that the old Euclidean space was demoted like Pluto. So that it, common sense empty space, was demoted in favor of "real space" which is the thing with stuff in it. Apparently it can't be space without the stuff. Don't pay any mind to the stuff though, it's this new real ™ space-time that is expanding. Perhaps some more exposition of the overall historical development from Hubble's time till now can help laypersons like myself understand this. Lycurgus (talk) 03:37, 30 May 2011 (UTC)

Whose trademark would that be? Aristotle's? Although from "space-time", (never mind "expanding"), seemingly not.—Machine Elf ¹⁷³⁵ 02:31, 31 May 2011 (UTC)

It was a rhetorical device. I am in general revolt against the notion that space, a purely abstract concept, has physical properties other than relations to entailed concepts such as "extension". I think this a symptom of the fact that in this time science is still without a philosophical grounding, and further is generally blithely unaware of the fact or worse thinks that in fact it does have one. Which is how, IMO, "physically expanding space", i.e. an active physical property assigned to nothingness, comes to be taken seriously. I did look for an Aristotelian and at the Kantian treatment of Space, but not referring to either. Not advocating the inclusion of such a POV in the article of course, but rather its opposite. I.e. current text leaves the matter of Hubble's interpretation hanging and that can I believe be supplied with a sentence or two expressing current physics orthodoxy and that heterodoxy which is not considered "fringe". Lycurgus (talk) 15:26, 31 May 2011 (UTC)

Some folks still just seem to have their hearts set on instrumentalism (aka “shut-up and calculate”). I do think it's a shame, really, as there's no shortage of... folks who are delighted that physicists decided to bow out of the competition.

And yes, no thanks to Kant, certainly. Aristotle's discussion of place was somewhat confusing... I'd just recently come across yet another website that felt the need to try and “debunk” him for believing Democritus' void, (vacuum), would be filled by Democritus' “atoms”. (Not that you meant anything of the sort). Someday, maybe he'll be forgiven for not inventing calculus if wanted to explain all change in terms of locomotion. Aristotle, I mean... <sigh>.

Anyway, the article does seem to be clear, at least, on “the space into which the universe is expanding” being a mathematical abstraction, relative internally to all the stuff far away getting farther away.—Machine Elf ¹⁷³⁵ 17:33, 31 May 2011 (UTC)

Glaring Invalid Inference

The mention of the Copernican principle in Observational Evidence is not a valid application of said principle. The principle only applies to phenomenon which are or could be distributed. The origin of the universe is not currently accepted as being anything other than a point or a relatively small region centered on one. Breaking this out from placement in the prior thread as it's a positive defect at least as important as the negative one that thread notes. Also note in re the article subject Reification_(fallacy)#Fallacy_of_misplaced_concreteness . Lycurgus (talk) 19:17, 31 May 2011 (UTC)

Sirs! is it expanding?

Has anybody considered and will anybody accept that there is no expansion of space. The observed phenomena are due to the acceleration in the velocity of the flow of time. KK (78.146.56.15 (talk) 11:35, 7 October 2011 (UTC))

I believe you'd need that objects are shrinking as well as time accelerating so it all gets a bit silly. We can't really discuss new ideas, this is an encyclopaedia not a research journal or scientific forum. Before getting here any ideas would need to be published in a refereed journal first. Dmcq (talk) 12:36, 7 October 2011 (UTC)

Object ARE srinking (gravitational radiation!) Obviously what is needed is understanding of the correct cosmology. KK (78.146.64.106 (talk) 14:47, 22 October 2011 (UTC))

This is an encyclopaedia not a discussion board or a venue to discuss new ideas. May I point you to WP:Reliable sources and WP:Original research and WP:NOTAFORUM. Dmcq (talk) 17:30, 22 October 2011 (UTC)

I doubted it too, and still am ready say that it's a possible misinterpretation of fact but just ran across the core empirical fact, or one view of it and the critical missing piece of info in re the Hubble constant, which is the observed number that quantifies the expansion (at about 73 km/s/Mpsc). It operates at the supercluster level and below that level gravity dominates. So the problem is with language/philosophy and the reification of the concept of space, but the underlying thing, I now see must be real albeit perhaps awaiting a more satisfying physics. As I've noted above. In fine, there's problems with the newtonian concepts of space and time (and derivative concepts like force) which aren't making it well into language yet, at least not to anything like the people level .

So here KK, is my understanding of it: flat Euclidean space, in which physical reality can still be just as validly situated as ever is not subject to deformation. However the space concept that actually works best for physics is. Since no concept or abstraction is any more real than another, nothing real changed, the new deformable space is not anymore real than its predecessor even if it is the right one for physics. Physicists are gobsmacked by this latter result and fail to understand the impact on a public of the non-disclosure and/or have nothing to disclose. Lycurgus (talk) 09:28, 30 December 2011 (UTC)

Obviously you know that what you are saying is correct - but only within the framework of todays knowledge. Naturally I cannot ecxplain the properties of space using the corrct cosmology if only because it would clash too strongly with vested interests. Please be patient. Surely you can think of some simple qauestions relating to space (spaces) which we can discuss. KK (78.147.253.29 (talk) 18:11, 30 December 2011 (UTC))

(Adjusted your indent). Also, I'm seeing, for example in mention of objects which are presumed to be from the first billion years, in addition to their distance being 13 billion ly, a "proper" and I guess comoving distance which would be more than twice that, which I take to be a Euclidean distance. When you think that it's less than a hundred years since the existence of other galaxies was confirmed ... 72.228.177.92 (talk) 07:44, 31 December 2011 (UTC)

Please make an adjustyement to your ideas on space for the fact that there is no chnage of position in space in straight line. Changes follow converging spiral. This disposes of Euclidean space in cosmology. KK (78.147.242.66 (talk) 14:07, 31 December 2011 (UTC))

Please take this conversation elsewhere. Wikipedia is not a forum. - Parejkoj (talk) 15:44, 31 December 2011 (UTC)

Expansion of the universe discovered before Hubble

I suggest info from this source be condensed and included in the article. Suraj T 04:47, 15 November 2011 (UTC)

Space is not curved.

According to NASA, the universe is flat with a 0.5% margin of error. http://map.gsfc.nasa.gov/universe/uni_shape.html Unless there are some complaints, i'll update the page shortly. 74.132.249.206 (talk) 02:05, 6 March 2012 (UTC)

That is an almost totally meaningless statement. I guess there was some actual document that was mangled in the production of that 'Universe 101' page. Dmcq (talk) 10:47, 6 March 2012 (UTC)

Misleading statement at the end of the "Observational Evidence" section

It states:

"Using standard candles with known intrinsic brightness, the acceleration in the expansion of the universe has been measured using redshift as H0 = 73.8 ± 2.4 (km/s)/Mpc. For every million parsecs of distance from the observer, the rate of expansion increases by about 74 kilometers per second."[13][14]

But isn't this number supposed to be the velocity at which objects are moving away from us due to the expansion of space, not the acceleration?

Charliewantsfacts (talk) 06:22, 27 April 2012 (UTC)::

The text is correct. As objects are further away, their recessional velocities are higher. Junjunone (talk) 18:55, 24 September 2012 (UTC)

No, the poster is correct. The statement wikilinks "acceleration" to accelerating universe, which discusses the expansion due to dark energy. However, The second sentence is entirely about the Hubble flow and thus isn't related to the dark energy driven expansion at all. Hubble velocities change with distance and the Hubble flow as a whole should slow down with time (for a flat universe with no dark energy), but neither of those things are what people mean when talking about the "acceleration in the expansion of the universe". The discussion is mixing multiple things together in a way that isn't clear. Dragons flight (talk) 21:07, 24 September 2012 (UTC)

I think that in this case there shouldn't be a link to acceleration universe which is a different concept. Junjunone (talk) 00:22, 25 September 2012 (UTC)

Where do the 4 billion light years come from?

Layman here. In the example of the isometric embedding, it is mentioned that the distance between the earth and the quasar of 4 billion light years when the light was emitted. But of course, looking at the picture, they are separated by the same 28 line grids (although much closer back then), which means that the comoving distance has always been 28 billion years. So how can we make sense of the 4 billion light years in the diagram? I found it confusing. At least some explanation would be needed here Epovo (talk) 12:02, 31 October 2012 (UTC)

The distance between the grid is larger at the top than at the bottom. It's not the number of gridpoints that matter: it's the actual length between point A and point B. Counting gridpoints as you are doing is akin to using comoving coordinates. Junjunone (talk) 01:21, 1 November 2012 (UTC)

Great article

Thanks for a great article and also for dealing with fringe ideas respectfully but firmly. As a scientist (but a layman in cosmology) I could follow the text without difficulty. Excellent work. — Preceding unsigned comment added by 46.65.91.22 (talk) 23:19, 23 November 2012 (UTC)