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#11
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Facts against BB Theory
On Tuesday, April 29, 2014 4:17:10 PM UTC-4, Robert L. Oldershaw wrote:
What would have been truly spectacular is if some theory had actually *predicted* the vast filamentary cosmic web/void structure before there were observations that revealed this important cosmological clue. My impression is that observations and computer simulations of the large scale void structure have developed concurrently over the past 10 years. While the simulations have improved, due to both faster computers and improved algorithms, the input physics ingredients have not changed and are not subject to a theorist's whim. But if you would like a very clear example of a theoretical prediction of standard cosmology followed by observational confirmation, then look at the closely related topic of baryon acoustic oscillations. Quoting from the discovery paper of Eisenstein et al (2005, http://arxiv.org/abs/astro-ph/0501171 ) on the observed large-scale galaxy correlation function: "We find a well-detected peak in the correlation function at 100h^{-1} Mpc separation that is an excellent match to the predicted shape and location of the imprint of the recombination-epoch acoustic oscillations on the low-redshift clustering of matter. This detection demonstrates the linear growth of structure by gravitational instability between z=1000 and the present and confirms a firm prediction of the standard cosmological theory. " These first observations have since been confirmed and much improved ( http://www.sdss3.org/surveys/boss.php ) and are in excellent agreement with the oscillations observed in the microwave background. --Wayne |
#12
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Facts against BB Theory
On Thursday, April 24, 2014 4:02:19 AM UTC-4, Robert L. Oldershaw wrote:
Matt Strassler's informed discussion of conventional cosmological thinking provides an open-minded starting point for useful discussions. http://profmattstrassler.com/2014/03...-are-reliable/ I agree that this is an excellent discussion of the uncertainties in big bang cosmology. In particular, what he classifies as "very high confidence" results (green zone, 1 second after the big bang) includes nearly all of classical big-bang cosmology, e.g. that the universe is ~13.7 billion years old, that the light elements were formed in primordial nucleosynthesis, that the cosmic microwave background is a relic of the hot early universe that has since cooled by expansion. The orange zone (t ~ 10^-35 seconds) includes the period of cosmic inflation and is more speculative. While the inflation models can provide an excellent fit of the angular spectrum of the cosmic microwave background, there are other models (e.g. the ekpyrotic universe) that can also do this. But if the recent BICEP2 observations are confirmed, then it may rule out all alternatives to inflation, and this regime may be moved to the green zone. Any theory discussing events before inflation are currently in the red zone (scientific guesswork) both because that regime is currently inaccessible to observations, and because we are not certain of what physics applies. This includes ideas that the universe arose from quantum fluctuations or a multiverse. Strassler notes individual scientists may mean different things by the term "big bang" and some don't consider the events before cosmic inflation as part of the big bang. --Wayne |
#13
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Facts against BB Theory
In article , wlandsman
writes: What would have been truly spectacular is if some theory had actually *predicted* the vast filamentary cosmic web/void structure before there were observations that revealed this important cosmological clue. My impression is that observations and computer simulations of the large scale void structure have developed concurrently over the past 10 years. Right, although the filament-void structure was first seen in the real universe, not in simulations. While the simulations have improved, due to both faster computers and improved algorithms, the input physics ingredients have not changed and are not subject to a theorist's whim. Right. Dark-matter simulations are well understood and there are really no free parameters. Actually, what makes them relatively easy is the lack of other interactions, i.e. only gravity. But if you would like a very clear example of a theoretical prediction of standard cosmology followed by observational confirmation, then look at the closely related topic of baryon acoustic oscillations. Quoting from the discovery paper of Eisenstein et al (2005, http://arxiv.org/abs/astro-ph/0501171 ) on the observed large-scale galaxy correlation function: "We find a well-detected peak in the correlation function at 100h^{-1} Mpc separation that is an excellent match to the predicted shape and location of the imprint of the recombination-epoch acoustic oscillations on the low-redshift clustering of matter. This detection demonstrates the linear growth of structure by gravitational instability between z=1000 and the present and confirms a firm prediction of the standard cosmological theory. " Essentially all of the features in the CMB spectrum were first derived theoretically then observed. There are only about 6 free parameters. One cannot fit anything with 6 parameters, so there is real constraint. Also, the derived values agree with other methods of measuring the same parameters. |
#14
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Facts against BB Theory
In article , wlandsman
writes: Matt Strassler's informed discussion of conventional cosmological thinking provides an open-minded starting point for useful discussions. http://profmattstrassler.com/2014/03...-are-reliable/ I agree that this is an excellent discussion of the uncertainties in big bang cosmology. In particular, what he classifies as "very high confidence" results (green zone, 1 second after the big bang) includes nearly all of classical big-bang cosmology, e.g. that the universe is ~13.7 billion years old, that the light elements were formed in primordial nucleosynthesis, that the cosmic microwave background is a relic of the hot early universe that has since cooled by expansion. Right. So the various newsgroup pundits who claim that the big bang never happened, that Eric Lerner is right and Ned Wright is wrong and so on are disputing what Strassler (and practically everyone) considers to be known with "very high confidence". The orange zone (t ~ 10^-35 seconds) includes the period of cosmic inflation and is more speculative. While the inflation models can provide an excellent fit of the angular spectrum of the cosmic microwave background, there are other models (e.g. the ekpyrotic universe) that can also do this. But if the recent BICEP2 observations are confirmed, then it may rule out all alternatives to inflation, and this regime may be moved to the green zone. At least this is a reasonably robust prediction of inflation and confirmation of the BICEP2 result would dramatically increase confidence in inflation. The scalar-to-tensor ratio R was firmly predicted long before there were even any hints as to what it might be observationally. |
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Facts against BB Theory
On Thursday, May 1, 2014 8:11:54 AM UTC-4, Phillip Helbig---undress to reply wrote:
In a sense, this is what happened. The theory is Newtonian gravitation. It just happened that observations were more advanced than computing technology, so they were discovered before they were simulated and hence predicted from the theory. You can be sure that Newtonian gravity was not modified in any way in order to fit the observations. ------------------------------------------------- In 1910 Newtonian gravitation had been around for a long time. Ask yourself a simple question: Did Newtonian theory predict that matter would be organized into "island universes" we call galaxies? No! Not a chance! Neither did Newtonian ever predict that the larger scale distribution of matter would be organized into a vast cosmic web of filaments and huge voids. I think the type of post facto reasoning in the claims made above is common, but unscientific. Ask yourself another question: Was de Vaucouleurs' Superclustering of galaxies welcomed with open arms? Just the opposite! He had to battle to convince people of the hierarchical organization of galactic systems. I am becoming increasingly aware of how physicists deceive themselves, and yet they seem virtually oblivious to the fact that they are doing so. This is why definitive predictions [prior, feasible, quantitative, non-adjustable and unique to the theory being tested] are so important. It's a "lost art" but it is the only thing that keeps us from deluding ourselves. |
#16
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Facts against BB Theory
Le 28/04/2014 22:13, wlandsman a ecrit :
For example, Sutter et al. (2013,http://arxiv.org/abs/1310.7155) find nearly 1000 voids in the Sloan survey, and compare these with their cosmological simulations, and conclude: "Our void abundances, ellipticity distributions, and radial profiles all indicate that voids in theory have the same sizes, shapes, and interior contents as observed voids." Thanks for this reference Mr Landsman. Sorry for the delay in answering but it took me quite a few readings to start understanding this text and its context. :-) This paper has two parts. The first is a study of the voids as such, and a method of finding those voids. This part looks ok to me, even if there is a heated discussion between astronomers about Sutter's catalog (Nadathur and Hotchkiss, ArXiv 1310.2791, and the answer of Mr Sutter in ArXiv 1310.5067) There is also a web site about voids (http://www.cosmicvoids.net). This is quite interesting but nowhere are the explanations for the questions I asked. The second part (that you make reference as a proof for BB theory) is that the catalog is very similar to orthodox cosmology simulations realized in software. And this is where I disagree with the author of the paper. I read paragraphs like this, for instance: quote In Figure 7 we compare the number function of voids in the CMASS Mid data sample to all our mocks. First, the unmasked N-body Mock simulation hosts roughly three times as many voids per unit volume than the data, even though they have similar galaxy populations. This occurs at all scales, though there are approx 4 times as many small voids in the unmasked mock as in the data. end quote So, the raw data doesn't at all fit with the simulation. Then, he applies his mask, what is probably OK if the mask used is the SAME as the mask he used with his data. But I did not find that sentence in the paper and can't be sure of that fundamental fact. Besides that, a few lines below, the paper says... quote As found in Sutter et al. (2013), the best match to voids in low-density galaxy surveys comes from adjusting the "void parameter" Dv to -0.015. end quote There we start massaging the data so that it fits whatever we want it to fit, sorry. Why is the simulation a low density survey? Maybe I did not understand everything but the article is vague here. Let's go on: quote While the number function roughly agrees with the order of magnitude of the full N-body Mock void population, it overestimates the number of voids in all size ranges considered here. It also does not fall off as steeply as in the mocks, though this might be influenced by finite-volume effects. end quote So, he must acknowledge that the data just DOESN'T FIT! Next sentence after acknowledging that? quote Still, the correspondence of these curves shows that theoretical modeling can qualitatively match unmasked void populations, but further adjustments must be made to match void statistics from masked volumes. end quote Excuse but there is NO WAY that THIS can be presented as an exact correpondence between the data and the BB models!!! The two sentences: one that says the data doesn't fit, and the very next one where he concludes that the survey supports BB theory just DO NOT MAKE SENSE! In the surface the conclusions of the paper are very "orthodox". The devil is in the details however. And this repeats itself in each paper that is supposed to "prove" BB theory. Thanks again for your answer. jacob |
#17
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Facts against BB Theory
In article , "Robert L.
Oldershaw" writes: In 1910 Newtonian gravitation had been around for a long time. Ask yourself a simple question: Did Newtonian theory predict that matter would be organized into "island universes" we call galaxies? No! Not a chance! The fact is that no-one had calculated it. Such computing power did not become available until the late 1970s. While a prediction is more emotionally satisfying than a postdiction, one shouldn't put too much weight on historical contingency which determined whether theory or observation was first. This is why definitive predictions [prior, feasible, quantitative, non-adjustable and unique to the theory being tested] are so important. It's a "lost art" but it is the only thing that keeps us from deluding ourselves. Several have been mentioned in this thread, such as the features in the CMB spectrum. |
#18
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Facts against BB Theory
In article , jacob navia
writes: The second part (that you make reference as a proof for BB theory) is that the catalog is very similar to orthodox cosmology simulations realized in software. And this is where I disagree with the author of the paper. I read paragraphs like this, for instance: quote In Figure 7 we compare the number function of voids in the CMASS Mid data sample to all our mocks. First, the unmasked N-body Mock simulation hosts roughly three times as many voids per unit volume than the data, even though they have similar galaxy populations. This occurs at all scales, though there are approx 4 times as many small voids in the unmasked mock as in the data. end quote Excuse but there is NO WAY that THIS can be presented as an exact correpondence between the data and the BB models!!! The two sentences: one that says the data doesn't fit, and the very next one where he concludes that the survey supports BB theory just DO NOT MAKE SENSE! In the surface the conclusions of the paper are very "orthodox". The devil is in the details however. And this repeats itself in each paper that is supposed to "prove" BB theory. In EACH paper? In EACH AND EVERY PAPER? This seems to be an exaggeration on your part. You seem to be throwing the baby out with the bathwater. What is "the big-bang theory"? It is the idea that the universe is expanding from an earlier state which was very hot and very dense. During this expansion, structure evolves. This is a complicated process and not all details are understood. When there is a discrepancy between theory and observation, you a) automatically conclude that the theory is wrong (observations can also be wrong, misinterpreted, misunderstood etc---witness all the wrong measurements of the Hubble constant, for example) and b) don't think that just the details of structure formation are wrong but want to chuck out the entire big-bang theory, essentially ignoring all other evidence in support of it. |
#19
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Facts against BB Theory
In article , Phillip
Helbig---undress to reply writes: In article , "Robert L. Oldershaw" writes: In 1910 Newtonian gravitation had been around for a long time. Ask yourself a simple question: Did Newtonian theory predict that matter would be organized into "island universes" we call galaxies? No! Not a chance! The fact is that no-one had calculated it. Such computing power did not become available until the late 1970s. While a prediction is more emotionally satisfying than a postdiction, one shouldn't put too much weight on historical contingency which determined whether theory or observation was first. Let me give another example. QED is one of the most successful theories ever. I don't know what the current state is, but theory and observation agree to 20 digits or whatever. When studying electrodynamics, the professor mentioned that, at that time, the agreement was 12 places or whatever. I asked whether the observations weren't more exact or whether the theory broke down at that level. The answer was neither, but rather that one hadn't CALCULATED more digits yet. These calculations are straightforward (i.e. everyone agrees on how to do them and there are no free parameters) but quite expensive numerically. Now, someone could calculate, say, 100 digits and this would be a prediction and perhaps some day g-2 will be measured to this precision and the prediction will be confirmed. However, what has usually been the case in the past is that more digits are calculated after experimental precision has correspondingly increased. Is this somehow worse for the theory? Should experimentalists always intentionally measure less accurately than the current prediction? Is it OK to calculate measure something as long as the theorists don't know about it? Of course, if the theory is amended IN ORDER TO get a particular experimental result, this makes a bad impression, especially if it is the case that, or is at least unclear whether, the theory could reproduce ANY experimental result. However, that is definitely not the case with QED. So, in summary, you seem to be setting the bar too high. My claim is that with something like QED, where it is clear that there is NO WAY to amend the theory to get an arbitrary result, a postdiction is just as valid a test of the theory as a prediction is. In this sense, n-body dark-matter simulations are like QED. The fact that voids and filaments were first observed then calculated is an accident of history. |
#20
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Facts against BB Theory
On 5/2/2014 10:23 AM, Phillip Helbig---undress to reply wrote:
In , "Robert L. writes: In 1910 Newtonian gravitation had been around for a long time. Ask yourself a simple question: Did Newtonian theory predict that matter would be organized into "island universes" we call galaxies? No! Not a chance! The fact is that no-one had calculated it. Such computing power did not become available until the late 1970s. While a prediction is more emotionally satisfying than a postdiction, one shouldn't put too much weight on historical contingency which determined whether theory or observation was first. There are "dictions" with several levels of strength: 1) The theory predicts it and later it is observed. 2) The theory *predated* the observation but only afterwards the postdiction is made (case above!) 3) The theory is formulated *after* the observation and is able to postdict the observation without effort. 4) The theory predated the observation but needs to be extensively fitted to match one new observation. 5) The theory is formulated after the observation and still needs to be extensively fitted to match it. It sounds reasonable to say that cases 1 and 2 are actually equivalent (and 4 and 5 are suspicious..) -- Jos |
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