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Standard Problems (old)

I hope I'm not reopening old wounds, but I felt the introduction to the Standard Problems sections was inaccurate so I rewrote it to make the following clear and make it, if anything, more neutral:

1 - most physicists accept the basic picture of the big bang

2 - dark matter, dark energy and inflation have not yet been detected in a way that would make a particle physicist happy, so they remain somewhat controversial (dark matter less so)

The most convincing argument seems to be Occams razor: A rather simple theory with not that much free parameters gives a good fit to current observations of the microwave background and large scale structure surveys.

In fact some recent reviews, have focused on the information theoretic aspect of this. Standard, flat, Lambda-CDM model plus plain vanilla inflation gives such a good fit, that adding more parameters doesn't make the fit better, compared to the amount of input to the formalus.

Pjacobi 00:01, 2005 Feb 5 (UTC)

dark matter, dark energy and inflation have not yet been detected in a way that would make a particle physicist happy -- the cross-sections and energy regimens for probing these phenomena are not touched by particle physics yet. I'm sorry if they are unhappy, but the burden is on them to show and observation that will shed light on the phenonmena, not on the cosmologists. 67.172.158.8 04:05, 7 Feb 2005 (UTC)

Hi, I made the above modifications, and I stand by them. The statement I added: "However, dark energy and dark matter are only known through their gravitational effects, whereas cosmic inflation is only known for setting the initial conditions for the big bang. There is not yet a consensus on their particle physics origin." is a fair representation of the views of almost all workers in the physics community, particle physicists and cosmologists included.

Cosmic inflation has evidence through the anisotropies of the CMB. This isn't simply a boundary condition (which is different from an initial condition, by the way). This is actually demanded of from the parameter fitting. Without inflation, the CMB data doesn't match with other observations. Joshuaschroeder 16:45, 7 Feb 2005 (UTC)

The boundary condition article discusses initial conditions. The initial conditions that inflation sets are: a flat, empty universe which is homogeneous on vastly superhorizon scales, and a nearly-scale invariant spectrum of scalar curvature perturbations with amplitude $\delta \rho /\rho =10^{-5}$.

Correct, but not the entire story. Inflationary scenarios drive the universe toward this (as we observe the universe now to be). It's not really an initial condition at all. Joshuaschroeder 00:51, 8 Feb 2005 (UTC)

I meant from the point of view of the hot big bang, it is an initial condition. For example, when you integrate the Boltzmann equation to get the CMB spectrum, the initial conditions are a nearly scale invariant spectrum. --Joke137 05:14, 8 Feb 2005 (UTC)

The simplest, most robust models of inflation include a spectral index around .95 and a specific amplitude for the tensor modes. This says nothing about where the particle physics of inflation should come from. Just because inflation is the best-established theory to acheive these initial conditions doesn't mean it should be accepted into the canon of the big bang along with such well-tested and understood theories as big-bang nucleosynthesis and structure formation.

Well, the problem is if infation didn't happen, the thing that did happen looks so much like it, it's like arguing over whether Newtonian gravity or GR describe the orbits of the planets. Nobody is seriously proposing any alternatives to inflation that don't let the universe expand exponentially. In fact, there's a mathemtical proof by Linde that given any of a series of universes (even without the scalar field assumption) inflation has to happen. Joshuaschroeder 00:51, 8 Feb 2005 (UTC)

Jim Peebles -- I doubt one could find a more trusted authority -- says in [1]: "The accompanying evidence for flat space sections was welcomed as a prediction of inflation, but you can count that welcome as an effect of social pressure because inflation is a social construction, which is to say that it is a promising working hypothesis that awaits searching scientific tests." --Joke137 23:36, 7 Feb 2005 (UTC)

I don't disagree with Peebles, his experience with the CMB discovery is illustrative for to what the above quote refers. The predictions of inflation are for the most part "post-hoc", but the fact is that there are inflationary tests (including gravitational waves and polarization of the CMB) that may very well provide the tested predictions to which Peebles is refering. If inflation happened in a non-vanilla way, this criticism will be satisfied. The danger is if we fall into a parameter space where the kind of inflation that happened is not well constrained. Then there's not much left that people have thought to test. Still, this is a highly nuanced issue and can't really captured well for a general audience. Joshuaschroeder 00:51, 8 Feb 2005 (UTC)

The nearly-scale invariant spectrum is an extremely important prediction of inflation. Gravity waves and B-modes in the CMB haven't yet be measured, and when they are they will constrain inflation. That still leaves a number of problems: nobody has yet found a natural way to fit inflation into the standard model. Moreover, it looks that the slow-roll conditions of inflation are incredibly hard to satisfy, because inflationary potentials in quantum field theory get renormalized to be much too steep. String theory also seems to have trouble producing inflation. In the face of this, alternatives need to be investigated: things like infrared modifications of gravity, ekpyrotic models, holographic cosmologies like Banks-Fischler. --Joke137 05:14, 8 Feb 2005 (UTC)

Slow-roll inflation as it is normally taught is almost certainly incorrect. However, that's not the only kind of inflation available (though it's the easiest to understand conceptually). Infrared gravity has real problems reproducing large-scale structure observations. The ekpyrotic and holographic cosmologies have their own versions of inflationary scenarios. In short, I don't see what you think is so risky about claiming inflation occurred.

In terms of only gravitational effects, this isn't quite true either. CDM is known to work through detail considerations of the time of decoupling which isn't a gravitational effect at all. Dark energy is known to work through structure formation which is more detailed than simply a "gravitational effect". Joshuaschroeder 16:45, 7 Feb 2005 (UTC)

No, these are both absolutely gravitational effects. They do not involve CDM or dark energy coupling through any force other than gravity. In the same paragraph, Peebles continues:

No, decoupling is purely a particle physics effect. Structure formation is tied to gravity, but includes other terms in the Vlasov equation. It isn't purely gravitational. Joshuaschroeder 00:51, 8 Feb 2005 (UTC)

"It is important that there are independent lines of evidence for the detection of Lambda, mainly from measures of the angular size distance as a function of redshift, and from the WMAP measurement of the CBR anisotropy. The latter is somewhat beclouded by its dependence on a structure formation model with anomalies that, if real, will drive adjustments of the model and maybe of the constraint on Lambda, and it is beclouded also by the puzzle of the quantum vacuum energy density, which might drive adjustments of the world picture or of the gravity theory and the interpretation of the cosmological tests. One can make a similar list of hazards for each estimate of Omega_m, of course; the big difference is in the lengths of the lists of independent evidence. The issue of Einstein’s cosmological constant has been under discussion since 1917. I suggest we wait a few more years to see how the evidence develops ... before making a definite decision about the reality of this curious term."

I think Peeble's conservatism in this regard is admirable. There is, however, no question that he is stating that the thoroughly independent measurements of lambda, for example, are not dependent on single parts of physics as you have claimed. Joshuaschroeder 00:51, 8 Feb 2005 (UTC)

I don't think you're understanding what I say. Decoupling, surely, is not purely gravitational. Most of the formation of large-scale structure, which is governed by CDM, is, but baryonic processes can be non-gravitational. However, these do not involve postulating any non-gravitation interaction for CDM or dark energy. In these models, CDM is a pressureless, non-dissipative non-interacting gas, and dark energy is either a cosmological constant or a very light scalar field with equation of state less than < -1/3. It both cases, in the model, they do not couple to the visible sector we observe other than through the curvature of space. --Joke137 05:14, 8 Feb 2005 (UTC)

Neither couples today. However, the times when coupling is important are probed in ways other than direct astronomical or particle physics observations. Joshuaschroeder 05:26, 8 Feb 2005 (UTC)

Lambda and inflation are promising working hypotheses, and standard parts of the most accurate working model of the big bang, but most people would reserve judgment on the extent to which, and certainly the way in which they are a part of our universe. I have trouble understanding what is objectionable about my original quote. --Joke137 23:36, 7 Feb 2005 (UTC)

There are, unfortunately, a few things incorrect about your original quote (for example claiming that evidence for CDM only comes from gravitational effects). I have tried to include the correct and valid arguments you made in the article. Joshuaschroeder 00:51, 8 Feb 2005 (UTC)

There are many candidates for non-baryonic dark matter, although none have been confirmed, and thus it seems like the theory is well ground, but nobody has yet come up with a fundamental theory of dark energy or cosmic inflation, and I think it is important to point this out, to separate what has been established in the big bang from what is still speculative. --Joke137 06:05, 7 Feb 2005 (UTC)

The observational evidence for dark matter and dark energy are well-established. The details of them are not, but that is already mentioned in the article. Joshuaschroeder 16:45, 7 Feb 2005 (UTC)

Again, I suggest you look at the text I recommend adding. It does not contradict what you're saying. I think it is important to maintain a distinction in the article between the canonical features of the big bang, and what is still likely to change substantially. --Joke137 23:36, 7 Feb 2005 (UTC)

This may be a bit of missing the forest for the trees. That the global properties of the effects of inflation, CDM and Lambda will be around in the final draft of the Big Bang is not up for debate. As to what form they will have, we aren't exactly sure. While science is cautious, we cannot simply make the claim that these areas are going to change "substantially". When I think of "substantially" I think of a change in substance. Brane cosmology, for example, doesn't claim to change the substance of dark matter, but only recast it in terms of higher physics.

To put it another way, imagine writing an article in the late 19th century about gravity. Nobody yet knew about relativity, but the predictive power of Newton's Laws were unmistakable. GR didn't change the major face of non-relativistic gravity, but it was still a major paradigm shift. I wouldn't call the change, however, "substantial" since Newtonian gravity still worked for the regime in which it was considering. Classical physics was, however, a "substantial" change over Aristotlean physics. They actually predicted substantively different things for all regimes.

Maybe this is the old argument about linear theory. Is the first order-approximation a substantial difference from the second order? I say no. Joshuaschroeder 00:51, 8 Feb 2005 (UTC)

I agree that we are missing the forest for the trees, and I agree that in the final draft of the big bang we will see something with the same effects as CDM, inflation and Lambda. Perhaps we disagree about what substantial means. I am suggesting that it should be made clear in the article that the community, as yet, does not put inflation and dark energy on quite the same footing as, say, the prediction of acoustic peaks in the CMB, structure formation, BBN, the quark-gluon plasma, decoupling, reionization, etc. Baryongenesis and dark matter are perhaps somewhere in between, the ideas are in place but the details have yet to be revealed. --Joke137 05:14, 8 Feb 2005 (UTC)

Since WMAP, the concordance model astrophysics is really quite intertwined with each other. Denying Dark energy and inflation would require the skeptic to explain WMAP, something I have yet to see done. Right now, the only thing that is fishy in the big picture is the high-optical-depth to reionization. I suppose the "house of cards" could fall completely, but our probes of this era are not the best and Tegmark claims that we can patch it up anyway. Joshuaschroeder 05:26, 8 Feb 2005 (UTC)

I'm going to be a curmudgeon and just write my comments at the end. I don't think slow-roll inflation, as it is usually taught, is almost certainly wrong. Sure, it seems incompatible with QFT but I don't see anything better supplanting it, and it has a great advantage over every other model of inflation: it makes robust predictions. It is true that the holographic cosmology needs inflation to push perturbations outside the horizon, but ekpyrotic cosmologies do not (although the cyclic model has dark energy, the perturbations are generated in a slowly contracting phase). But this is beside the point, I think.

Regarding dark matter and dark energy, you say: "Neither couples today. However, the times when coupling is important are probed in ways other than direct astronomical or particle physics observations." I disagree, Lambda+CDM or DE+CDM models used to do simulations of structure formation generally do not include any coupling at any epoch. I encourage you to look in the literature. This in important -- as far as we know, CDM could be anything from WIMPs, to 10⁶ solar mass black holes, to some non-dissapative matter on a hidden brane, to superpartners, to an IR modification of gravity, each of which would have very different properties. Some components of dark matter, like neutrinos, do, of course, interact, but they don't make up the non-baryonic ~25%. Even less is known about dark energy, other than some constraints on its homogeneity, energy density and equation of state. I said it above: "in the final draft of the big bang we will see something with the same effects as CDM, inflation and Lambda." I don't pretend they will go away (incidentally, I think the large value of tau will), but given that we only have a very limited window on them, it is crucial to keep an open mind. --Joke137 14:52, 8 Feb 2005 (UTC)

Other models make robust predictions too. Tegmark's paper on the subject was particularly elucidating on the matter. It seems that traditional slow-roll is almost entirely excluded form WMAP parameterspace consideration (to something like the 4 or 5 sigma level).

Strucuture formation simulations are not the only theoretical work being done in cosmology. Of course, there is no reason to include dark energy or dark matter coupling in them. By the way, we know that the blackhole model doesn't work because the hierarchical clustering model fails with dark matter chunks that big. Brane-dark matter would still see a decoupling event that would make it non-baryonic CDM just as predicted from current observations.

The open mind is, of course, always important. I think the article as it is makes that point. Joshuaschroeder 00:53, 9 Feb 2005 (UTC)

I am a bit confused by what you are suggesting Tegmark said. Can you give me the astro-ph phone number of this paper? WMAP does claim to rule out the simplest phi^4 models of inflation, but as with anything in the CMB, I think you can bring them back into the contours by adding more parameters to your MCMC. In any case, the charm of vanilla slow roll inflation, as far as I am concerned, is that there isn't much room to muck with the spectrum. A lot of other theories seem designed to account for any possible observation in the future: isocurvature, non-gaussianity, running spectral index etc... These theories are not easily falsifiable, which makes them less useful as models than simple things like lambda and slow-roll. Ordinary slow roll inflation is falsifiable, and has the additional benefit that it hasn't been falsified yet but could be in the near future (e.g. by finding n_s=1.00 to good accuracy, or not finding B-modes).

I miswrote. It's not a Tegmark paper, but rather a talk he gave at two AAS conferences ago. here is a paper which constrains slow-roll to WMAP results. Simplest slow-roll is ruled out. We're on the same page here. phi^4 models are what I usually call slow-roll, but obviously second and third order corrections might be (and indeed are) claimed to be slow roll as well. Joshuaschroeder 00:47, 13 Feb 2005 (UTC)

I think inserting a sentence or two in the Standard Problems section that indicates some of the problems with dark matter, dark energy and inflation have not yet been resolved is important. My original sentences are fair and correct: "However, dark energy and dark matter are only known through their gravitational effects, whereas cosmic inflation is only known for setting the initial conditions for the big bang. There is not yet a consensus on their particle physics origin." Here is a more modest version: "There is not yet a consensus on the particle physics origin of dark matter, dark energy and inflation. While their gravitational effects are understood observationally and theoretically, they have not yet been incorporated into the standard model of particle physics in an accepted way." This is important, because these are three of the biggest problems in particle physics today. An earlier writer put: "the cross-sections and energy regimens for probing these phenomena are not touched by particle physics yet." That is not true, particularly in the case of dark matter there have been plenty of opportunities to detect such a particle, and we have not, ruling out swathes of parameter space. Nobody knows how to detect dark energy or the inflaton yet, since their interactions are not known, so it is not yet even a problem of energies and cross sections. --Joke137 18:56, 11 Feb 2005 (UTC)

dark energy and dark matter are only known through their gravitational effects -- again, I disagree with this statement. They are also known through other effects that are not gravitational. Since the parameter space is dependent on a variety of details, it's not quite correct to claim they are only known by gravitational effects. Joshuaschroeder 00:47, 13 Feb 2005 (UTC)

I still disagree with this, but I think we are probably arguing about semantics.

"There is not yet a consensus on the particle physics origin of dark matter, dark energy and inflation. While their gravitational effects are understood observationally and theoretically, they have not yet been incorporated into the standard model of particle physics in an accepted way." This I like much better. Please put this into the article. Joshuaschroeder

Sure!

particularly in the case of dark matter there have been plenty of opportunities to detect such a particle, and we have not, ruling out swathes of parameter space. --> True before WMAP, I think now, though, that the CDM has to be so collisionless as to be outside the range of our particle accelerators. Joshuaschroeder

I didn't realize WMAP constrained dark matter interactions -- is it something to do with free-streaming and structure formation?

Yes. In order for the hierarchical model to be correct, CDM had to decouple from the field way too soon for us to observe it in the lab -- though we're getting close to reaching it. In some sense, it was really COBE (or technically BOOMERanG) that nailed it since they were the ones that actually determined how small the anisotropies were. Joshuaschroeder 06:26, 13 Feb 2005 (UTC)

Nobody knows how to detect dark energy or the inflaton yet, since their interactions are not known, so it is not yet even a problem of energies and cross sections. --> Inflation not being dependent on cross-sections I agree with. However, the energy density of dark energy is well known, and it's tiny. We cannot probe changes in energy density on such scales at this time. Joshuaschroeder 00:47, 13 Feb 2005 (UTC)

Yes, I agree absolutely. --Joke137 01:08, 13 Feb 2005 (UTC)

Don't wanting to disturb your conversation, but wouldn't it be a good option to give a more elaborate discussion of cosmological parameters, including which observations implies what, and subsequent consequences for inflation models in another article. It seems best to me, to let Big Bang be the overview articles, including history and all that, and the details should go elsewhere. Perhaps to Lambda-CDM model? --Pjacobi 00:59, 2005 Feb 12 (UTC)

I think this is a great idea to expand the Lambda-CDM article in this way. I don't have time to write this now, but maybe in the summer. --Joke137 01:08, 13 Feb 2005 (UTC)

Problems with the introduction

First, let me say that this is a fine article and my comments may well be nitpickish, but - I think the introduction is too technical in style. Cosmology is difficult to understand. However, the fundamental concept of the theory of a non-static universe, specifically, an expansion of space itself, should be described explicitly, because that is one of the aspects that many might understand more easily than the rest of he theory. I have tried to rewrite the introduction, but upon some more consideration it looks like my command of the English language is insufficient to improve the style. Please could somebody give it a try? Kosebamse 10:12, 23 Feb 2005 (UTC)

Historical material

The Medieval Jewish scholar Nachmanides (1194-1270, in his commentary on Genesis 1:4) states that the universe started "the size of a mustard seed" (i.e. something tiny) and increased in size afterwards. While I concede that this is not a scientific observation, he did argue against the then-prevalent Aristotleian steady-state approach and may be notable. What are the other authors' feelings on this matter? JFW | T@lk 14:33, 23 Feb 2005 (UTC)

In principle, this can be mentioned in the Deistic/Jewish section of Philosophical and Religious implications section. Something along the lines of what is written in the Islam section might suffice. User:Joshuaschroeder

Removed material

I am not at my computer right now, and cannot login, but I removed some edits:

• evolution is not a dirty word and will be used in the article as that is the word used by scientists.
• Gap creationism may be interesting, but says nothing about the Big Bang per se. We aren't just talking about what people do to accomodate the Big Bang in their religious traditions but what the implications of the Big Bang ARE on said traditions.
• Space is not "created" in the Big Bang. It's just rulers streching.

161.97.202.103 20:32, 23 Feb 2005 (UTC) (User:Joshuaschroeder

Evolution is a biological concept. The Universe, and galaxies, are not biological. It is a misapplication of the word to use it outside of a biological context. To apply it outside of biology is just a secular humanistic POV jab at creationists.

The encyclopedia should not be used to enforce your POV on others. To promote the idea that evoution happens outside of biology is just propoganda.

My edit is going back. The word "development" is perfectly appropriate in place of the word "evolvolution".

KeyStroke 16:34, 2005 Feb 24 (UTC)

The first usage of the word "evolution" in English is recorded in the mid-17th century. Clearly it can be used in a way that has nothing to do with biology, which is the way that astrophysicists use it when talking about "galactic evolution." This is a standard usage and should be restored. It is not propoganda: using the word evolution does not imply that selection happens. --Joke137 17:22, 24 Feb 2005 (UTC)

The only thing you gain by using "evolution" over the word "developement" is to further your POV agenda against creationists. Using the word "development" takes nothing away from the meaning of the article. But using "development" does clean up the article by removing the humanistic secualarist idea that we are all on some grand evolution to a higher state of being. Which is a religion made out of quasi-science. KeyStroke 12:31, 2005 Feb 25 (UTC)

It seems like the only agenda here is yours. Re-read my previous comments. The word evolution, in physics, means change over time. Look in the OED or Google "galactic evolution" and "galactic development:" evolution gets more than one hundred times more hits. It is absurd to avoid such a standard usage in wikipedia because of prejudice against the word. --Joke137 15:03, 25 Feb 2005 (UTC)

Using "development" in place of "evoution" does not detract from the meaning of the article in the slightest. The fact that there is at least one person (me) that sees the use of the word "evolution" as confusing the concepts being discussed should be enough to justify replacing "evolution" with "development".

You don't have any need to keep "evolution" except to promote a secular humanist agenda. And you can't even demonstrate the honesty to admit that. KeyStroke 21:42, 2005 Feb 25 (UTC)

Evolution is the term most often used in scientific papers on this subject. --Pjacobi 22:03, 2005 Feb 25 (UTC)

Oscillating universe

I added something to the history section about the oscillating universe, which was removed by User:Joshuaschroeder. The truth is, that before the mid sixties and Hawking's work on the singularity theorems, the big bang was not generally understood as it is today: many physicists were convinced it did not mark the start of time, as we now understand it, and Lifshitz and Khalatnikov were occupied with trying to prove that singularities were not a generic feature of general relativity, Misner was trying to show that Mixmaster behavior set the initial conditions for the big bang, etc.

At the beginning of their classic 1965 paper, Dicke, Peebles, Roll and Wilkinson wrote: "One of the basic problems of cosmology is the singularity characteristic of the familiar cosmological solutions of Einstein's field equations. Also puzzling is the presence of matter in excess of antimatter in the universe [...] We can distinguish three main attempts to deal with these problems:

"1. [The steady-state model]

"2. The assumption [due to Wheeler] that the creation of new matter is intimately related to the existence of the singularity, and the resolution of both paradoxes may be found in the quantum mechanical treatment of Einstein's field equations.

"3. The assumption that the singularity results from a mathematical over-idealization, the requirement of strict isotropy or uniformity, and that it would not occur in the real world. [Wheeler, Lifshitz and Khalatnikov]"

Option two corresponds very roughly to our understanding of the big bang today, and option three corresponds to Richard Tolman's oscillating universe scenario. It wasn't until Hawking's work on singularities that cosmologists were forced to accept option two. It is pseudo-historical (similar to how quantum mechanics is often taught) to put things so simply. --Joke137 22:25, 21 Mar 2005 (UTC)

It's not true that Hawking eliminated option 3. We can, in fact, still match a DeSitter Waist onto a universe before the Planck Time because the GR-solutions allow us to do so. Thus, claiming that the oscillating universe is no longer viable is incorrect. Joshuaschroeder 16:04, 23 Mar 2005 (UTC)

Yes, it is true that if you start violating energy conditions, you can have a bouncing universe, and that there is no a priori reason to assume the energy conditions are satisfied, except that we have always known them to be. Tolman's oscillating universe picture didn't postulate any extraordinary physics to cause the reversal from contraction to expansion, however: it was assumed general relativity would do it with ordinary matter. (It was also ruled out because entropy would build up in the horizon.)

Incidentally, the de Sitter waist is unstable to small perturbations: it will form a singularity instead of a waist if slightly perturbed. That's the reason that past-eternal inflation doesn't work. --Joke137 17:43, 23 Mar 2005 (UTC)

Although Tolman's first try at the oscillating universe didn't require "Speculative physics beyond the Big Bang" we should be careful to keep the article NPOV with respect to the option that we might still live in a different kind of oscillating universe that would look superficially similar. While I understand there are "fine-tuning" arguments against the simplest patch allowing for an oscillating universe, the whole point of speculation pre-inflation is we don't know all the conditional arrangements of the universe. This is due primarily to the fact that no one has a consistent theory of quantum gravity. To be perfectly honest, we should keep the osciallting universe in the Speculative physics section. I also think the mention of it in the history section is a bit too great, but that's an editorial opinion.

Good point. I've added it back in. I think the speculative physics section is the weakest link right now, and could stand some expansion and revision. As for the mention in this history section, it is a matter of taste. I think it is important to keep it in because I think it affected how we see the universe in nearly as profound a way as discarding the static and steady state models. --Joke137 00:40, 24 Mar 2005 (UTC)

Confused about nucleosynthesis

I'm having trouble with the following paragraph:

"Measurements of primordial abundances for all four isotopes are consistent with a unique value of that parameter, and the fact that the measured abundances are in the same range as the predicted ones is considered strong evidence for the Big Bang. There is no obvious reason outside of the Big Bang that, for example, the universe should have more helium than deuterium or more deuterium than ³He."

Since a previous guess I made was wrong, here's my suggested rewrite:

"The measured abundances are in the same ranges as the predicted ones. This in itself is considered strong evidence for the Big Bang, as without it the Big Bang there is no obvious reason that, for example, the universe should have more helium than deuterium or more deuterium than ³He. As further evidence, measured primordial abundances of all four isotopes are consistent with a unique value of the baryon-to-photon ratio."

I agree, it is kind of obtuse as written. I like your revision, but I can't understand what the last sentence adds. How about:

The measured abundances all agree with those predicted from a single value of the baryon-to-photon ratio. This is considered strong evidence for the Big Bang, as the theory is the only known method that explains the relative abundances of light elements.

Okay, I'm about to use that, a little more concise ("the only known explanation for"), and I'm going to try to keep the point that other methods don't even get the orders of magnitude right, which I think is what the original author was saying. —JerryFriedman 15:33, 27 Apr 2005 (UTC)

And are we really talking about measurements of primordial abundances, or are the measurements made now and assumed to be the same as the primordial amounts, or extrapolated backwards somehow? —JerryFriedman 19:17, 26 Apr 2005 (UTC)

Yes. All that. --Joke137 21:09, 26 Apr 2005 (UTC)

Got it. —JerryFriedman 15:33, 27 Apr 2005 (UTC)