Talk:Big Bang/Archive 3

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Archive 3
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Contents

Personal pronouns

In the introduction, I noticed a reference to "you", so I'm changing it to "one." Is that proper? -Thorns among our leaves, 14:50 7 November 2004 (UTC)

Crank

I notice Geoffrey Burbidge was mentioned in Popular Scientist. Apparently some people think he's a crank because of his controversial views on big bang theory. Accroding to Popular Science, "On the rare occasions he’s asked to speak at a conference, zealots shout him down while the rest of the audience snickers. He endures constant insult from young upstarts such as Sean Carroll of the University of Chicago, whose blog belittles big-bang deniers: “They just aren’t, for the most part, very smart.” Burbidge takes refuge in his native British stoicism. “It’s just the road to conformity,” he says. “They’re all happier thinking alike.”" [1] Can anyone comment? - Ta bu shi da yu 13:28, 23 Nov 2004 (UTC)

(William M. Connolley 14:12, 23 Nov 2004 (UTC)) According to the article, he believes "In his view, the universe is a natural oscillator, expanding and contracting alternately—and infinitely—over time.". Not knowing the details, I could see this as being indistinguishable from BB from our POV - its just a what-came-before question.
Oops, meant to add: assuming there isn't more than one (there is a B, EM too but thats not the one I mean) then he has a decent publications list. Inc some with Arp.
Here's a very critical page on Burbidge's work. It looks as if he started out as a steady-stater, and has been gradually modifying his steady-state model by superimposing an expansion-contraction cycle until it's almost indistinguishable from the standard Big Bang... except that where it is distinguishable, it still falls down. --Matt McIrvin 15:36, 11 Dec 2004 (UTC)

Reasons of the Big Bang

Why/how did Big Bang occur?

Cons of energy / JimJast

(William M. Connolley 22:08, 5 Dec 2004 (UTC)) I'm moving this here:

Also the need for the Big Bang would be invalidated if energy were conserved: It has been shown already in 1985 that Einstein's theory of gravitation predicts that if energy were conserved then the light coming from distant galaxies were redshifted in such a way that it would create an illusion of accelerating expansion. The effect is known in astrophysics as dynamical friction. The amount for photons in a stationary universe, calculated from Einstein's theory, equals within observational error to what is actually observed in the universe as its "accelerating expansion".
In the Big Bang theory it is assumed though that "accelerating expansion" of the universe is real and so it is tacitly assumed that this tiny amount of energy that is needed to compensate for dynamical friction of photons (that otherwise would be responsible for the observations of "accelerating expansion") is constantly created from nothing. This is one of the reasons why it has to be assumed in the Big Bang theory that energy is not conserved "in general relativity". It is interesting though why the nature creates from nothing only the amount of energy that is needed to keep the Big Bang afloat and seems to keep energy strictly conserved in all the other situations? Jim 21:45, 5 Dec 2004 (UTC)

partly because Jim signed it (so I assume it was meant to be here) and partly because I'm doubtful. AFAIK energy is convsered in GR (except at the moment of Big Bang?).

The astronomy students are already taught that "energy is not conserved in GR" so you may ask them if you don't believe me (despite that I'm one of them, hopefully with degree in astrophysics in the near future). If you don't know any students then ask at news group sci.physics.research or ask Prof. John Baez, gravity physicists, a moderator in this group. I don't think that you need a higher authority than that. Jim
(William M. Connolley 19:43, 6 Dec 2004 (UTC)) I'll try User:Lumidek instead, he seems to be quite good at this stuff.
Hey William! They're right, the energy conservation in GR is a very subtle thing - which is my fast answer, still a better one than "yes/no". OK, let's say a couple of things about the energy in GR. Energy is, according to Noether's theorem, a conserved quantity associated with a specific symmetry, namely the time-translation symmetry. Therefore if you consider GR describing a spacetime that looks "asymptotically flat", much like the spacetime in special relativity, you may define the so-called ADM energy, and it will be conserved. However, in the most general time-dependent case, the energy in GR is not conserved. For example, in the inflationary models, the vacuum energy density is roughly constant - it's the cosmological constant - but the volume of the universe grows exponentially, and therefore the "total energy" grows like R cubed where R is the typical length scale (radius) of your Universe. On the other hand, the total energy of "dust" - matter with very small velocity - is conserved even in cosmology. However, no real system can be "pure dust". As long as the system emits some radiation, for example, there will be non-conservation. Let's say one more example: in a radiation dominated Universe (radiation is anything whose speed is close to the speed of light), the wavelength of a photon or another quantum of the radiation grows with the size of the Universe, which also means that the energy of the photon (or any wave) is decreasing inversely proportionally to R (the energy of a photon is inversely proportional to the wavelength). These arguments hold even classically, so the total energy of the Universe dominated by radiation will decrease like 1/R.
What you may have been thinking about, William, is the continuity equation for the stress-energy tensor - the covariant divergence of the stress-energy tensor is zero in GR. However, it is not possible to convert this identity into a global conservation law, exactly because the derivative is covariant and not partial.
Even in the case where the total energy is conserved - the asymptotically flat space, for example - the energy in GR is subtle. Although you may define the total energy, there is actually no canonical way to define this energy as an integral of a local quantity. You know that the gravitational waves can also carry energy, so you must consider both the stress energy tensor of the matter fields (like electromagnetic field) as well as the gravitational field (the metric tensor). However the "total" stress-energy tensor, obtained by varying the full action with respect to the metric tensor, is of course zero because the variation with respect to *any* dynamical field must vanish - because this defines the field equations of motion. So let's summarize: the "total" energy is only conserved in GR if we required some asymptotic shape of the background which is time-independent (such as the flat Minkowski space), and even in this case, it is not possible to define the total energy as an integral of a uniquely defined local quantity (energy density). --Lumidek 22:05, 6 Dec 2004 (UTC)
(William M. Connolley 22:55, 6 Dec 2004 (UTC)) Thanks. That was interesting. Given how far that was outside what I was competent to describe (or knew), I think I'll bow out of this debate until I've read a bit more...
So, if you don't mind, I put the text (edited a little bit to a form that you might accept now) back where it belongs. So not only we know that energy isn't conserved in GR and why, but the readers as well. I hope that if you want to remove some of my texts only because I sign them you try to consult the matter with me first. Jim

While energy isn't globally conserved in GR, the "photon dynamical friction" business mentioned in that section seems to be some sort of "tired light" model, and therefore subject to the usual criticisms of tired light models, which bear no relation to standard cosmology.

I might have mentioned that tired light is not dynamical friction (even if it looks similar) but I hoped that if people suspect tired light effect they might look at the page which explains it where it is specificly stated that it isn't physics and why, but only a lame hypohesis. Jim

Also, the phrase "Einstein's theory of gravitation predicts that if energy were conserved..." makes no sense, since, as we all just said, Einstein's theory of gravitation doesn't predict that energy is conserved, so it can say no such thing. (You can come up with definitions of energy that are conserved in GR, but in general they are somewhat contrived and only useful in special cases; it isn't as if conservation of energy is a switch you can turn on and off in GR to get different physical effects. Certainly this tired-light-through-dynamical friction notion is not part of any GR-based cosmology.)

You're right that "Einstein's theory of gravitation doesn't predict that energy is conserved" since the conservation of energy is a separate issue and energy is either conserved or isn't. But then one may have two versions of GR: with and without it. Of course I agree that the present version is without it, but the text we are talking about is in a section that is meant to present any possible objections to the Big Bang theory, more or less viable. The dynamical friction of photons despite that it is not addressed in the Big Bang, has to have non vanishing value if energy is conserved. Of course it may be exactly zero, as it is assumed in the Big Bang theory, only if non conservation of energy is in the picture. As it is. Jim

Since there seems to be a low-speed edit war going on here, I'm not going to wade into it just now, but participants ought to take this into consideration, and have a gander at Ned Wright's tutorial and the relevant sections of the Physics FAQ. --Matt McIrvin 15:58, 11 Dec 2004 (UTC)

I dont' know about the war and the other participants but I read Wright's tutorial and agree with him on the tired light. BTW, it was Wright who told me about the dynamical friction when I wanted to know long time ago how the astrophysicists call the effect under consideration. Now I'm myself in a process of becoming an astrophysicist so I'd appreciate any data that you know about and I don't. Jim 20:57, 12 Dec 2004 (UTC)

Overall bad shape of the article

Having had a second look at this article, IMHO it is in general bad shape. It is littered with badly written "Critics say..." disclaimers, which ignore the current academic discussion and mis-quote there sources. Also some paragraphs are duplicates after the last edits. This version [2] from Oct 04 looks rather superior.

What's going on here?

Pjacobi 19:49, 2005 Jan 8 (UTC)

See Talk:Quasar for a more elaborate discussion, why I removed the "quasar in our galaxy" criticism paragraph. --Pjacobi 20:32, 2005 Jan 8 (UTC)
I've fixed some of the problems; I'll work on the rest later. Ben Standeven 08:15, 11 Jan 2005 (UTC)
I can't imagine how the following portion of the introduction can be modified to be relevant enough to the Big Bang theory to include so prominently. This excerpt is strictly a (poorly written, in my opinion) cosmogony discussion which the current Big Bang theory does not encompass. Could someone make modifications to this portion of the article which would make it relevant? Otherwise I'll delete it in a few days. --JHG 07:32, 2005 Jan 13 (UTC)
There are actually many theories about the Big Bang. Some theories purport to explain the cause of the Big Bang itself (First cause), and as such have been criticized as being modern creation myths. Some people believe that the Big Bang theory lends support to traditional views of creation, for example as given in Genesis, while others believe that all Big Bang theories are inconsistent with such views. The relationship between religion and the Big Bang theory is discussed below.

Merged with Critiques of Big Bang.

I have merged the old Big Bang Critiques article with this one; but we need to do some serious trimming, since the article is now 54K. Ben Standeven 00:35, 15 Jan 2005 (UTC)

Thanks for yout tedious efforts!
Some quick, first impressions, how to proceed:
  • It would help a lot, to setup a 'master plan' how to divide the stuff between the different cosmology articles. Isn't there a WikiProject page, where we cas set up the co-ordination?
  • Perhaps the "See also" section can be trimmed down first, be eliminating all links, which are already linked in the article text?
  • Criticism and ideas, which are seriously out of sync with current observational astronomy, can perhaps find a place in History of cosmology?
Pjacobi 12:00, 2005 Jan 15 (UTC)

Massive overhaul

I have massively overhauled this page, mercilessly editting out commentary that was either irrelevant, unrelated, or tangential. I don't think any of the stuff should be included here, but someone might be able to work it into another article. The obvious choice would be non-standard cosmology, which is an article that is itself in a shambles The major stuff I took out I post here Joshuaschroeder 00:52, 16 Jan 2005 (UTC):

I have also now merged with content from Beyond the standard Big Bang model. Joshuaschroeder 03:30, 16 Jan 2005 (UTC)

Alternative theories

Theories which assert that the universe has an infinite life such as the steady state theory fail to account for the abundance of deuterium in the cosmos, because deuterium easily undergoes nuclear fusion in stars and there are no known astrophysical processes other than the Big Bang itself that can produce it in large quantities. Hence the fact that deuterium is not an extremely rare component of the universe suggests that the universe has a finite age.

Theories which assert that the universe has a finite life but that the Big Bang did not happen have problems with the abundance of helium-4. The observed amount of 4He is far larger than what could be created via stars or any other known process. By contrast, the abundance of 4He are very insensitive to assumptions about baryon density changing only a few percent, as the baryon density changes by several orders of magnitude. The observed value of 4He appears to be within the range calculated.

This having been said, there are three theoretical issues with Big Bang nucleosynthesis which have some potential of undermining the theory. The first is that the baryon concentration necessary to get an exact match with the current abundances is inconsistent with a universe with mostly baryons. The second is that the Big Bang predicts that no elements heavier than lithium would have been created in the Big Bang, yet elements heavier than lithium are observed in quasars, which presumably are some of the oldest galaxies in the universe. The third problem is since big bang nucleosynthesis produces no elements heavier than lithium, then we ought to see some long lived remnant stars which have no heavy elements in them. We don't.

The standard explanation for the first are that most of the universe isn't composed of baryons. This explanation fits nicely with other evidence of dark matter such as galaxy rotation curves. The standard explanation for the second and third is that the universe underwent a period of massive star formation creating large high mass stars and that without heavy elements, forming low mass red dwarf stars is impossible. This explanation has the feature that it predicts a class of stars that, as of 2004, have not been observed. Hence, in a few years we should have either seen them, which would support the big bang scenario, or we won't, in which case there is a possibility that we will have to fundamentally alter our views of the universe.

Critics of the big bang argue that there may be some other means by which deuterium can be generated. They further claim that there is no evidence that deuterium is being depleted by stellar fusion.

Intrinsic Redshifts

There also remain small numbers of astrophysicists, including Hans Alfven, Y.P. Varshni and Halton Arp, who argue that redshifts in galaxies do not correlate with distance and/or are not due to the Doppler effect, and that this invalidates the need for the Big Bang.

Halton Arp, one of the most famous of these astrophysicists, bases his alternative theory on observations made by himself and his team from as far back as 1960. Arp has observed a handful of correlations between quasars (and more recently, X-ray sources from Chandra data) and AGN (Active Galactic Nuclei) which he claims demonstrates that quasar redshifts are not entirely due to the expansion of the universe, but contain a local, or non-cosmological, component. Arp claims that clusters of quasars have been observed around many galaxies which all have some properties in common:

  • The active galaxy always has a lower redshift than any of its associated quasars.5
  • The quasars tend to lie within a narrow conical zone centered about the minor (rotational) axis of the associated active galaxy.6
  • Schematically, the quasars' redshifts are inversely proportional to their angular distances from the AGN, i.e. as apparent distance from the AGN increases, the redshift of the quasars decrease.7
  • Some of the quasars occur as pairs on either side of an AGN, particularly the X-ray sources appearing in the Chandra data.

These observations indicate to Arp that a relationship may exist between quasars (or at least a certain type of quasar) and AGN that is completely unrelated to the standard explanation that quasars are AGN at cosmological distances.8 Arp claims that certain quasars originate as very high redshift objects ejected from the nuclei of active galaxies, and gradually lose their non-cosmological redshift component as they evolve into galaxies.9 This stands in stark contradiction to most accepted models of galaxy formation.

The biggest problem with Arp's analysis is that today there are tens of thousands of quasars with known redshifts discovered by various sky surveys. The vast majority of these quasars are not correlated in any way with nearby AGN. Indeed, with improved observing techniques, a number of host galaxies have been observed around quasars which indicates that those quasars at least really are at cosmological distances and are not the kind of objects Arp proposes. Arp's analysis, according to most scientists, suffers from being based on small number statistics and hunting for peculiar coincidences and odd associations. In a vast universe such as our own, peculiarities and oddities are bound to appear if one looks in enough places. Unbiased samples of sources, taken from numerous galaxy surveys of the sky show none of the proposed 'irregularities' nor any statistically significant correlations that Arp suggests exist.

In addition, it is not clear what mechanism would be responsible for such high initial redshifts, or indeed its gradual dissipation over time as the quasar evolves. It is also unclear why objects ejected from a galaxy should never seem to produce a blue shift. Moreover it is unclear how nearby quasars would explain some features in the spectrum of quasars which the standard model easily explains. In the standard cosmology, the clouds of neutral hydrogen between the quasar and the earth at different red shifts spikes between the quasar redshift and the rest frequency of Lyman alpha in a feature known as the Lyman-alpha forest. Moreover, in extreme quasars one can observe the absorbion of neutral hydrogen which has not yet been reionized in a feature known as the Gunn-Peterson trough. Most cosmologists see this missing theoretical work as sufficient reason to explain the observations as either chance or error. Arp himself proposes Narlikar's variable mass hypothesis, which contains alternative explanations of various observed cosmological features, but it remains, at best, incomplete.

A consequence of Arp's proposed AGN-origin of quasars would be that quasars would be much closer, much larger, and much less luminous than currently supposed and their heavy element composition would no longer require primaeval Population III stars. Such a theory would predict that the heavy element composition of quasars would be similar to the associated AGN, though observed metal lines in quasars are notoriously weaker than AGN. Variable luminosity and absorption phenomena such as the Lyman-alpha forest would both be explained by as yet theoretically undeveloped "local means".

Another traditional alternate explanation of the redshift is dynamical friction of photons; the photon's gravitational interactions with stars and other material will progressively reduce their momentum, thus producing a redshift. However, this process will also tend to blur images of distant objects, and no such blurring has been detected [3].

Note that in the General Theory of Relativity, dynamical friction does not apply to photons (basically, because photons are massless). This does not contradict the conservation laws, because in the general theory they apply only locally, and dynamical friction is inherently non-local.

The effects that dark matter has on Big Bang calculations generally do not depend on the detailed properties of the dark matter. The main property of dark matter which influences cosmology is whether the dark matter consists of particles that are heavy and hence slow-moving, called cold dark matter, it consists of particles that are light and hence fast-moving, called hot dark matter, or it consists of ordinary baryonic matter.

Quasi steady-state theory and plasma cosmology have been put forward as alternatives that rely on explanations other than dark matter to explain a limited number of observations that are associated with dark matter in standard models. In some versions of plasma cosmology, for instance, the observed galaxy rotation curves are accounted for by the additional electro-magnetic forces and interactions.1 It is claimed that by treating the arms of galaxies as plasma filaments interacting with electromagnetic fields, the filamentary structure of galaxy clusters and superclusters can be viewed as a result of the self-amplifying nature of currents in plasmas.2 In this way, plasma cosmology proports to explain two observations often attributed in the standard cosmological models as due to dark matter. However, proponents of the Big Bang theory claim that no non-standard cosmology explains in detail the totality of proposed evidence for dark matter.

Alternate explanations of the Cosmic Microwave Background

Alfven, Lerner and others working within plasma cosmology have claimed that the temperature, isotropy, and non-polarisation of the CMB can be readily explained as the diffusion of galactic radio emission by the magnetic fields of intervening plasma filaments. Electrons travelling along the large, weak magnetic field lines of a galaxy can absorb radio, and re-emit it in a different direction. This scatters the radiation, much as light from the sun is scattered in a dense fog. This can also explain the observed decrease in radio brightness of galaxies relative to their IR luminosity with increasing redshift. Lerner explains that radiation from distant galaxies successively interacts with the magnetic fields of many intervening galaxies, nebulae, supernova remnants and so on, resulting in an isotropic scatter.3 However, standard cosmologists have been able to model in detail not only these global features, but also the detail measurements of anisotropies and polarization of the CMB and identify a number of features such as peaks and valleys in its power spectrum which correspond to cosmological quantities.

With regards to anisotropy studies, the WMAP experiment has been especially fruitful in providing a goldmine of data that is interpreted easily by the standard cosmological models. The inability thus far of plasma cosmologies to come up with a theory that replicates these features in detail remains a major hurdle for the models to overcome.4

A second alternative explanation, favoured by Steady State theorists, is that the intergalactic medium contains microscopic iron dust particles or whiskers, which can also scatter radio in the same manner to produce an isotropic CMB. However, observational evidence for the existence of these iron particles is yet to appear.

Either or both of these explanations are sometimes employed by supporters of other alternative cosmological models since, if either were true, they would no longer need to explain the isotropy of the CMB.

Notes

  1. While it is true that in astrophysics plasma and magnetic effects are considered very important in determining the structure of gas and dust within a galaxy, it is unclear by what mechanism magnetic fields would change galaxy rotation curves and velocity dispersions. Galaxy velocity dispersion measurement come in part from observations of halo stars and it is unclear how a magnetic field would change the orbital motion of a star in an area where there is very little gas and dust.
  2. The structure of the filaments seen in cosmological galaxy surveys are very different than the structure of filaments seen in most plasma processes, and there is no proposed mechanism offered by the alternative model as to why the size of the structures has an upper-limit.
  3. Lerner fails to explain why the electrons should reemit in the best measured blackbody spectrum observed in all of science and how the entire plasma can become thermalized with exposure to anisotropic radiation fields.
  4. There was recently some excitement on the part of certain plasma cosmology adherents over an analysis of WMAP results by researchers at the University of Durham. This analysis proported to show certain variations of microkelvin anisotropies in the WMAP data correspond to the locations of local galactic clusters and superclusters. Fans of Eric Lerner claim that his model predicted similar types of associations. However, this association was predicted in the Big Bang model to be due to the Sunyaev-Zeldovich effect, and the investigation was designed with that in mind.
  5. As quasars are considered by most astronomers to be highly luminous, distant cores of AGN, it isn't surprising that the AGN whose galaxy is more easily observable would have a lower redshift.
  6. Some astrophysicists believe that gravitational lensing might be responsible for some examples of quasars in the immediate vicinity of AGN, but Arp and others argue that gravitational lensing cannot account for the quasars' tendency to align along the host galaxies minor axis.
  7. It has been pointed out that it is impossible for this relationship to continue indefinitely. It is a purely observational coincidence in the minds of the vast majority of astrophysicists.
  8. The question of whether quasars are cosmological or not was an active controversy in the late 1960s and early 1970s, but by the late 1970s most astronomers had considered the issue settled. The main argument against cosmological distances for quasars was that the energy required was far too high to be explainable by nuclear fusion, but this objection was removed by the proposal of gravity powered accretion disks.
  9. Arp and others who agree with him have been known to support the argument for a varying non-cosmological redshift by referring to a so-called "magnitude-redshift discrepancy". When a Hubble Law-type plot of quasar magnitudes versus redshift is made, a graph with a diffuse scatter and no clear linear relation is generated. However, since absolute magnitudes can only be independently calibrated to an upper limit using size constraints from variability and an Eddington luminosity, it is likely that quasars are exhibitting differing luminosities that cannot neccessarily be derived from such simplistic first principles. Arp, Burbidge, and others maintain that the scatter in these plots further supports the idea that quasars have a non-cosmological component to their redshift, but nearly everyone else in the field accepts that quasars have variable luminosity.

References to Big Bang Critiques

"See also" section is redundant...

...and should thus be removed. Topics already covered in text clearly need not be repeated, and related topics are handled by the category system. Fredrik | talk 01:51, 18 Jan 2005 (UTC)

Finite universe

Maybe something should be added about the misconception that the Big Bang theory implies a finite-size universe? - Fredrik | talk 13:56, 30 Jan 2005 (UTC)

I hadn't heard about that misconception. Whether the universe is finite size or not is a question that cannot be answered from the context of the Big Bang. Joshuaschroeder 15:07, 30 Jan 2005 (UTC)
My experience (I did a brief presentation about the shape of the universe in high school, and the possibility of infiniteness surprised most listeners) is that people commonly visualize an expanding universe as a finite, three-dimensional ball of space that grows from an initially infinitesimal three-dimensional ball of space. Fredrik | talk 15:28, 30 Jan 2005 (UTC)
In fact, given a positive cosmological constant, not only the observable universe's size, but also its entropy, is bounded. --Pjacobi 18:25, 2005 Jan 30 (UTC)
Well, the misconceptions about the size and shape of the universe notwithstanding, I think that the section on the future of the universe gives a pretty good guideline for saying the true answer to the boundaries of the universe: we just don't know -- if they are there, they're outside our observable horizon. Joshuaschroeder 19:50, 30 Jan 2005 (UTC)