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The Observed Universe, Our Universe, Our Big Bang.
Op dinsdag 15 juli 2014 09:37:24 UTC+2 schreef Phillip Helbig:
In article , Nicolaas Vroom writes: The question is: are "Our observable Universe" and "all what is created as a result of the Big Bang" identical concepts No. The former is the observable universe and the latter the universe. Or, in Tegmark's terminology, the former is the universe and the latter is the Level I multiverse. The issue is that IMO our primarily interest should be in what you call "the universe". I would call that "Our universe" created by "Our Big Bang" completely indepent of any human "behaviour". The word "our" is only there to allow for more Big Bangs. Accordingly to Tegmark at page 121: As we saw inflation predits that there is even more. By this he means that inflation predicts that the universe is much larger than the observable universe, perhaps infinitely larger. By "simplest example" he means what he calls the Level I multiverse. What I understand is that before inflation the observable universe was small and equally in size as the (our) universe but after inflation the (our) universe became much larger as the observable universe. If that picture is correct it makes sense to first study the larger part. The question arises where is this larger part? before the CMB radiation or after the CMB radiation? (relevant to our position) what the simulation shows that in general in the early universe the density is always close to the critical density and that this is no prove that inflation theory is correct. This is a generic feature of non-empty big-bang models. etc This does not prove that inflation is correct. See your document: http://arxiv.org/pdf/1112.1666v2.pdf Equation (1) is the starting point used in my simulations. Interestingly you raises the question if there is a flatness problem in the first place. For Alan Guth the most impressive piece of evidence is the flatness problem This is what Alan Guth describes in his book at page 185. When you study study figure 10.6 my interpretation is, that with inflation the size is the same but the age is a fraction of a second younger. I don't follow you here. Fig 10.6 shows horizontal the time axis in seconds (between 10^-43 and present. Vertical it shows the Radius of the Observed Universe in meters. The figure shows the Standard Theory and the Inflationary Theory in two lines. Both lines start from the left (time 10^-43) untill present. The ST line starts at Radius 10^-3 and finishes with radius 10^20. (angle 15 degrees) The IT line starts with radius 10^-57, almost goes straight up around 10^-35 seconds untill 1 meter and than becomes the same as the ST line. The text reads: Figure 10.6 Solution to the horizon problem: the size of the observed universe in the standard and inflationary theories. If you compare the two lines starting after 10^-30 seconds both are identical. That means the age of the universe without inflation is only a fraction older. Ofcourse this is a very unimportant issue. Important is what are the physical implications of this small period of rapid expansion and which specific observations are an idication that this is true. The same problem exists with the horizon problem. First "we" assume a problem. Next we "predict" a theory which solves this problem. Next we claim that there is no problem anymore (more or less). An even stronger claim is that this proves that the theory is correct. What is so important for the inflation theory is that the details of the theory are impossible to observe nor predicted observations with and without the theory. This type of science is completely different compared to the medical industry where the influence of a medicine is tested with thousand patients with or without the medicine What worries me about Figure 10.6 is that it shows the observed radius and not the true radius which includes all what is changed after the Big Bang. Nicolaas Vroom |
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The Observed Universe, Our Universe, Our Big Bang.
In article , Nicolaas Vroom
writes: The issue is that IMO our primarily interest should be in what you call "the universe". I would call that "Our universe" created by "Our Big Bang" completely indepent of any human "behaviour". The word "our" is only there to allow for more Big Bangs. I don't think anyone disagrees with this, but we have to keep in mind that we can infer things directly about the observable universe only. What I understand is that before inflation the observable universe was small and equally in size as the (our) universe but after inflation the (our) universe became much larger as the observable universe. Right. If that picture is correct it makes sense to first study the larger part. IN PRACTICE, one can't study what is by definition not observable, except theoretically. The question arises where is this larger part? before the CMB radiation or after the CMB radiation? (relevant to our position) I guess you mean "before" and "after" spatially, not temporally. The CMB is at a redshift of about 1000 and the big bang at infinite redshift. That means that a photon just reaching us now from the big bang (assuming this were possible in practice; it is not since the universe became transparent only at a redshift of 1000) has travelled the maximum distance possible. This is the definition of the observable universe. Things farther away than that---and hence farther away than the CMB---are in the non-observable part of the universe. See your document: http://arxiv.org/pdf/1112.1666v2.pdf Equation (1) is the starting point used in my simulations. Interestingly you raises the question if there is a flatness problem in the first place. Right. That's the point of the paper. As I mention, though, I am not the first to claim that the flatness problem is exaggerated and/or misunderstood. See the references to Lake and various combinations of Coles, Ellis and Evrard. For Alan Guth the most impressive piece of evidence is the flatness problem He's built his career on it. Bird feathers did not evolve for flying, but for temperature regulation. So, inflation can still be a useful concept no matter what the original motivation was. (Actually, Guth was studying the monopole problem and realized that inflation could solve the flatness problem as well.) This is what Alan Guth describes in his book at page 185. When you study study figure 10.6 my interpretation is, that with inflation the size is the same but the age is a fraction of a second younger. OK, I get it now. The current size is fixed so, of course, any theory has to have the current size now. Because of inflation, expansion very early on was faster so, yes, it is slightly younger. Very slightly. The same problem exists with the horizon problem. First "we" assume a problem. There is definitely a problem: Why do two widely separated areas of the sky have the same CMB temperature even though they have not been in causal contact? Next we "predict" a theory which solves this problem. A theory which solves the problem is more interesting, but inflation was not constructed to solve the horizon problem. Next we claim that there is no problem anymore (more or less). If inflation solves it. An even stronger claim is that this proves that the theory is correct. In general, one can never prove a theory. One can disprove a theory. However, observational and other evidence can increase our confidence in a given theory. |
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The Observed Universe, Our Universe, Our Big Bang.
On 7/20/14, 1:55 AM, Phillip Helbig---undress to reply wrote:
I guess you mean "before" and "after" spatially, not temporally. The CMB is at a redshift of about 1000 and the big bang at infinite redshift. That means that a photon just reaching us now from the big bang (assuming this were possible in practice; it is not since the universe became transparent only at a redshift of 1000) has travelled the maximum distance possible. This is the definition of the observable universe. Things farther away than that---and hence farther away than the CMB---are in the non-observable part of the universe. Observable universe is still an open question in terms of high energy Cosmic Rays. At what redshift are they produced? Some data is available: Indications of Intermediate-Scale Anisotropy of Cosmic Rays with Energy Greater Than 57 EeV in the Northern Sky Measured with the Surface Detector of the Telescope Array Experiment http://arxiv.org/abs/1404.5890 Although the Telescope Array Experiment observed Cosmic Rays with Energy Greater Than 57 EeV appear with an anisotropic hotspot, their rate fall within an isotropic generation of ~ 1/km^2/year Richard D Saam |
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