Talk:Expansion of the universe

See also /Archive 1 -- to 30 September 2007.

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)

"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)

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)

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)

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.

--Tommac2