Talk:Dark energy
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Rewrite
I decided to take a stab at reorganizing this page, rewriting much of it and adding content, per User:Pjacobi's suggestion below. I think a lot of work probably still needs to be done, but it will ultimately result in a better article. I have taken a first stab, drawing on material in the articles quintessence (physics), cosmological constant and accelerating universe, all of which I edited extensively over the past weeks. I think these articles, along with ultimate fate of the universe and Equation of State (Cosmology) should be retained, but should perhaps be more technical, with this sort of an umbrella page for this set of ideas. Please let me know what you think. P.S. Incidentally, if someone wants to move the old talk to an archive page, please go ahead. I don't know how, so I just nuked it. P.P.S. I added some, hopefully simple, equations in the cosmological constant section. Do you think the argument is comprehensible to the reader with little specialized knowedge? --Joke137 00:55, 4 Mar 2005 (UTC)
- I think you did a very good job with rewriting this article. There are a few places where I thought your presentation was ambiguous or imprecise, and I may try and do something about that, but overall a remarkably good effort. Dragons flight 01:27, Mar 4, 2005 (UTC)
- Thanks a lot. It is something I had been thinking about doing for a while. I've tried to touch it up a little bit, and will probably come back to it again in a few days once it has had some time to settle in my mind. Please edit away where you've found ambiguities. --03:07, 4 Mar 2005 (UTC)
I redirected the accelerating universe page to this one, since it now contains a more complete discussion of SN Ia etc. --Joke137 15:50, 10 Mar 2005 (UTC)
clarification
I made some edits to the article. I made what I think is an important clarification in the "Nature of phenomena" (whatever that means) section: the SN Ia data tell us the expansion of the universe is accelerating. The CMB tells us the universe is flat. Various things tell us that baryons + dark matter = 30% of the critical density. However, all three are required to suggest that dark matter makes up the extra 70%. --Joke137
- I assume, you want to say: However, all three are required to suggest that dark energy makes up the extra 70%.
- And put in the data on element abundances, as merging in the Big Bang nucleosynthesis constraints gives even smaller error bounds on the cosmological parameters.
- And, BTW: What's your opinion on having separate articles on Dark energy, Quintessence (physics), abd Cosmological constant? Seems some overlap to me.
- Pjacobi 00:49, 2005 Feb 7 (UTC)
- Well, I think there is plenty of overlap and they could probably be merged. I'm new, and I'm not really sure what the standard is re: when it's better to have one article, and when it's better to have three. --Joke137 06:09, 7 Feb 2005 (UTC)
- For what its worth, I vote for keeping the articles seperate. They clearly are related issues, and the quintessence / cosmological constant articles could use some polish, but they also seem to me to be sufficiently distinct ideas as to warrant elaboration on their own pages. Dragons flight 13:14, Feb 7, 2005 (UTC)
Split articles
Adding to the thread above: These articles must be seperated, I think! The Accelerating universe is an observational fact (with low proabaility of being incorrect), but the rest of the articles are theories to explain that fact! They can not be mixed, just like the observation of spectral lines can not be mixed up with Bohr's theory of the atom. Awolf002 15:59, 24 Mar 2005 (UTC)
Right now, there is a huge pressure against raising concerns about whether redshifts are entirely due to cosmological expansion (with small contributions from proper motion), or whether some redshifts might be intrinsic.
The question is whether the drop in luminosity is the result of simple distance, or if it is the result of the metrics of an expanding universe. -- Orionix 08:20, 1 Apr 2005 (UTC)
- What I advocate is to re-instate the article Accelerating universe in its own right, not having it as a redirect page! Observations should be kept separate from theories, at least as long as the latter are in a realistic competition. Your concerns (which I do not share) would also be better framed in such an article, instead of being in here. Awolf002 18:40, 1 Apr 2005 (UTC)
- I think it would be OK to have an accelerating universe page with a detailed technical discussion of the SNIa results, including figures. But I don't think it would be valuable unless it is much more extensive than that in the dark energy article. The problem is that our belief in dark energy comes from complementary sources: big bang nucleosynthesis, the cosmic microwave background, SNIa, large-scale structure of the cosmos etc. Dark energy is the unifying concept between these, the idea that 70% of the cosmic energy budget is unaccounted for, and has to be made up of something that doesn't cluster or evolve much with time, which GR therefore predicts will cause acceleration. If it were only the direct observation of an accelerating universe -- the supernova Ia measurements -- then we wouldn't believe in dark energy with nearly the confidence we have now. Systematic errors, such as a failure in the standardizability of SNIa populations or attenuation in the observed luminosity of supernovae by the intergalactic medium, would be much more worrisome. But the fact is that we have a number of indirect, independent checks, and together they make up something more general than the accelerating universe, called dark energy.
- As for keeping observations and theory seperate, I think that is misguided. While it is important to make it clear that we don't have an agreed-upon theory for dark energy, and that the Lambda-CDM model is merely a very good phenomenological model, it is still important to keep the proposed explanations in the same article as the observations, particularly since the cosmological constant, whatever its flaws, perfectly accounts for every observation by adding only one parameter to cosmology. --Joke137 19:37, 1 Apr 2005 (UTC)
- I hear what you're saying. The Lamda-CDM model is important and unique in the sense of explaining current observations with minimal changes. It should have its proper place. But I also think it would be worth while to have the Accelerating universe be an article focussing on the SNIa data and have some well written detail on its meaning and history, since this was the first hint of a discrepency from earlier models and had to survive some strong challenges before it was accepted. If I get the time, I will try my hand in this. Awolf002 15:47, 4 Apr 2005 (UTC)
Other explanations for an accelerating universe
2. Leaking gravity (into other dimensions)
3. A failure of general relativity. Spacetime curvature is fictitious and dark matter does not exist.
4. Incorrect interpretations. Hubble's law is not correct and redshift is not a reliable distance indicator.
The 3rd and 4rd options seem the most promising candidates to me in the future. -- Orionix 13:36, 31 Mar 2005 (UTC)
- The Lambda-CDM model is an excitingly successfull theory. Unless you can cite an alternate theory which passes the test of the scientific method, is not yet falsified but falsifiable, there aren't alternatives worthy mentioning in the article. Private speculations and opinions are better discussed on USENET. --Pjacobi 14:31, 2005 Mar 31 (UTC)
The PSR J0737-3039 is a good varification to general relativity but the fact that dark matter and gravitational radiation have never been directly detected is suspect to me. Just because general relativity makes correct predictions doesn't mean that gravitational waves really exist. These could just be geometrical entities. --Orionix 14:53, 31 Mar 2005 (UTC)
Gravitational waves almost certainly do exist, as was shown by measurements of binary pulsars. And they are "just" geometrical entities, as is all of general relativity. For 1, cosmic inflation and dark energy are hard to reconcile, because of the very different energy scales on which they occur. The recent attempt by Kolb to connect them seems to have been quickly refuted.
But 2 and 3 are good possibilities. Number 2 is another kind of dark energy, but coming from higher dimensional geometry. It is hard to precisely define the difference between number 3 and dark energy. They used to call a cosmological constant a failure of general relativity, but now write it on the other side of Einstein's equation and call it a new form of energy.
Hubble's law is well established, and it would be very surprising if 4 were the case. It could be the case, although it seems very unlikely, that there are systematic problems with supernovae, but that would not be a failure of Hubble's law, which is a robust prediction of any geometrical theory of an expanding universe. --Joke137 19:59, 1 Apr 2005 (UTC)
Negative Pressure
I've been working on a paper about dark matter and dark energy for a writing class I'm taking. I found a Scientific American article from January 2001 titled "The Quintessential Cosmos", and based on that article it appears that the discussion in this article about negative pressure could use a bit of work. It's probably correct in the case of the cosmological constant but details seem to be lacking. I'll probably edit it in a while (couple weeks) when I'm not so busy and sick of writing, but the key point is that when the ratio of pressure to energy density drops below -1/3, gravity becomes repulsive. --DonJuan 16:30, 2005 April 21 (UTC)
- What, specifically, are the problems with the discussion of negative pressure? I wrote that, as well as the more technical, detailed discussion in Equation of state (cosmology). I was trying to keep the article from getting technical, but in the case of the cosmological constant I couldn't resist putting a short, simple argument about the thermodynamics of a box of cosmological constant in. --Joke137 19:38, 21 Apr 2005 (UTC)
Correa Link
Let me start out by saying that I have no interest in spending my time debating whether dark energy is real. That is not the purpose of wikipedia. It suffices to say that it is a firmly established theory in cosmology.
I have moved to Correra article User:SamuelR to non-standard cosmology. I hope this is a suitable compromise. The article itself is pseudoscience, that displays a fundamental misunderstanding of dark energy and general relativity. Here are some points:
- by more recent so-called computations, this rate of expansion is accelerating, and one obtains all the ingredients for a modern scientific religion - a metaphysics of physics [...] but please remark further that, despite thousands of papers published on the subject, there is literally no experimental evidence for any of them. That is incorrect. Read the evidence for dark energy section. Type Ia supernovae, big bang nucleosynthesis and galaxy clustering are ample evidence.
- Indeed, the idea that the universe had a beginning is nothing more than an interpretation, and at that, one that is not legitimized by the First Law of Conservation of Energy. The conservation of energy is well established in general relativity, and satisfied by dark energy and the big bang model in particular. Since it is impossible to define the energy of the universe in Einstein's theory, it means that the stress-energy tensor is covariantly conserved.
- There could never be Dark Energy without mass. And there could never be massless energy. Not, at least, according to Albert. Anyway, this is a minor detail, since the Dark Energy that our particle physicists talk about is only 'massless' for laughs - it was 'massless' in a distant past, but is supermassive today. Nonsense. Mass has energy, sure, but energy doesn't need to be massive in the traditional bricks-and-rocks sense. Light is a perfectly good example.
- One first assumes a beginning for the universe and postulates, by dint of sheer interpretation, that the universe expands. Backwards. General relativity and observations clearly suggest the universe is expanding.
After that, I got sick of reading it. –Joke137 22:58, 23 May 2005 (UTC)
-- Response from SamuelR --
Let me start out by saying that I have no interest in spending my time debating whether dark energy is real. That is not the purpose of wikipedia. It suffices to say that it is a firmly established theory in cosmology.
I have moved to Correra article User:SamuelR <http://en.wikipedia.org/wiki/User:SamuelR> to non-standard cosmology <http://en.wikipedia.org/wiki/Non-standard_cosmology>. I hope this is a suitable compromise.
The name is Correa, not Correra.
The article itself is pseudoscience, that displays a fundamental misunderstanding of dark energy and general relativity.
Rather, the conventional theory of Dark Energy - along with Relativity -
are pseudoscience. Just because they are universally accepted does not
make them any less 'pseudoscience'. Many religions claim universal
acceptance but that does not make their dogmas true. Only fanatic
followers claim such nonsense.
It is truly remarkable that in a "community encyclopedia", a publication one of whose very purposes is to provide a vehicle for presenting our store of knowledge and understanding through open discourse, you would set yourself up as a watchdog of the "purity" of science-as-religious-dogma, as posited and promoted by the officiating "scientifc" institutions.
Here are some points:
* by more recent so-called computations, this rate of expansion is
accelerating, and one obtains all the ingredients for a modern
scientific religion - a metaphysics of physics [...] but please
remark further that, despite thousands of papers published on
the subject, there is literally no experimental evidence for any
of them. That is incorrect. Read the evidence for dark energy
section. Type Ia supernovae
<http://en.wikipedia.org/wiki/Supernova>,
big bang nucleosynthesis
<http://en.wikipedia.org/wiki/Big_bang_nucleosynthesis> and
galaxy clustering
<http://en.wikipedia.org/w/index.php?title=Galaxy_clustering&action=edit>
are ample evidence.
All three lines of evidence are interpretive. Even for Relativity there is no incontrovertible evidence. Other hypotheses can explain the same findings without recourse to the dogmas of Relativity.
* Indeed, the idea that the universe had a beginning is nothing
more than an interpretation, and at that, one that is not
legitimized by the First Law of Conservation of Energy. The
conservation of energy is well established in general
relativity, and satisfied by dark energy and the big bang model
in particular. Since it is impossible to define the energy of
the universe in Einstein's theory, it means that the
stress-energy tensor
<http://en.wikipedia.org/wiki/Stress-energy_tensor> is
covariantly conserved.
Einstein created formalisms that permitted the universe to run down while energy would be conserved. The question is whether the universe is or is not running down. The answer that it is running down is not a fact but an interpretation. Citing a mathematical model for an interpretation does not make it into a fact. A more consistent view of the universe, and moreover one that does not need to abandon simultaneity, is to conclude that the universe is neither running down nor had a beginning.
Since you cannot prove your contentions other than with suppression and interpretation, you are defending a faith (the 'Einsteinian faith'), not science.
* There could never be Dark Energy without mass. And there could
never be massless energy. Not, at least, according to Albert.
Anyway, this is a minor detail, since the Dark Energy that our
particle physicists talk about is only 'massless' for laughs -
it was 'massless' in a distant past, but is supermassive today.
Nonsense. Mass has energy, sure, but energy doesn't need to be
massive in the traditional bricks-and-rocks sense. Light
<http://en.wikipedia.org/wiki/Light> is a perfectly good example.
Light has never been demonstrated to have or not to have mass. It is an issue still open to contention. The notion that Dark energy was massless at the origins and became supermassive in contemporary time is built right into the Higgs model and the so-called unification of weak and electromagentic interactions. If you do not know this, that you are not even very cognizant of the interpretations that are foundational for your faith in relativity. So, you are repressive, a-scientific, and also ignorant.
Understandably, you fear that others might read the link and make their minds up by themselves. Your faith only has to lose and nothing to gain.
* One first assumes a beginning for the universe and postulates,
by dint of sheer interpretation, that the universe expands.
Backwards. General relativity and observations clearly suggest
the universe is expanding.
A suggestion is not a fact.
After that, I got sick of reading it. -Joke137 <http://en.wikipedia.org/wiki/User:Joke137> 22:58, 23 May 2005 (UTC)
You appropriately named yourself what you are - a joke. And since Dirac
and others are wrong about 137, the entire cosmos has put still another
joke on you and your fellow interpreters. It's 138, my dear Joke!
It is funny how a text that makes me laugh makes you sick. Maybe science is not for you.
Sam
An encyclopedia has to report the universally accepted view. New theories must battle for their acceptance or even superiority in academic discussion, not in Wikipedia articles and not on Wikipedia discussion pages. --Pjacobi 17:26, 2005 May 24 (UTC)
User:SamuelR, As I wrote on your talk page, I would appreciate it if you read no personal attacks and no original research. You will not win many friends on here if you suggest that I'm a Nazi, that I'm ignorant, that I'm gutless or that I'm a joke. You say
- It is truly remarkable that in a "community encyclopedia", a publication one of whose very purposes is to provide a vehicle for presenting our store of knowledge and understanding through open discourse, you would set yourself up as a watchdog of the "purity" of science-as-religious-dogma, as posited and promoted by the officiating "scientifc" institutions.
You have misunderstood the purpose of Wikipedia: it is not meant as a community for open discourse. I am merely following official Wikipedia policy. If the policy were any different, I would likely choose not to contribute. In case you don't care to refer to the latter page, let me quote:
- The phrase "original research" in this context refers to untested theories; data, statements, concepts and ideas that have not been published in a reputable publication [...] Reputable publications include peer-reviewed journals, books published by a known academic publishing house or university press, and divisions of a general publisher which have a good reputation for scholarly publications.
Finally, let me suggest that science is all interpretation and suggestion. You imply that it is possible to prove scientific theories, particularly ones so far outside the realm of everyday experience as cosmology and relativity, by some other means. I doubt that. I expect you could learn something about this on the philosophy of science page. –Joke137 17:44, 24 May 2005 (UTC)
No evidence for dark energy
I think that it was correctly stated in the header that dark energy is an hypothetical form of energy. Then, why does the first section have the title Evidence for dark energy? I would rather give it the title The dark energy puzzle or something that would not imply a so strong indication that dark energy at such actually must exist. It may turn out that the true explanation of the mystery won't be appropriately described by the term energy. Also, in the same section, instead of saying that The type Ia supernovae provide the most direct evidence for dark energy, I propose something like The dark energy hypothesis is able to explain the type Ia supernovae observations.. --Philipum 12:46, 27 May 2005 (UTC)
- Ahem, in scientific discourse, provide evidence and is able to explain, is nearly equivalent, with some portion of Occam's Razor added. As the Lambda-CDM model is beautifully d'accord with Occam's Razor, I don't see the need to change the formulation. --Pjacobi 13:45, 2005 May 27 (UTC)
newbie request
ok.. instead of having:
((supernova|type 1a supernovae))
shouldn't it be:
type 1a ((supernova|supernovae))
??