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dcl all the posts in my post below speedfreeks where aimed at him
dcl you said... I think these values have the values that they do merely because we wouldn't be here to ask the question if they were different,,,,, which i translated into ... just to say well im here so that explains it... anyway i tend to agree with all of you great posts guys esp cougar ,,,thanks 4 the Alex Vilenkin mention.... i like this idea.. ![]() |
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It may indeed seem doubtful that the fundamental domain (the whole universe) is smaller than our observable universe, but we have to do what we can to test for it and the least we can do is search our observable universe for evidence for it so that we can count it out. So far we have only counted it out across a co-moving diameter of 78 billion light years and our observable universe has a co-moving diameter of 92 billion light years so there is a little way to go yet before we can confidently state that the whole universe is larger than our observable portion of it. Until we can, there remains the possibility that we might find evidence for a non-trivial topology. Should we only look for evidence for the most plausible model? Is that good science? As you are so convinced that the hypersphere is the only plausible shape for the universe I must assume you have studied the mathematics of hyperspheres and so you should be familiar with both the Poincaré conjecture and, perhaps more pertinently, the Poincaré homology sphere, which is also known as Poincarés dodecahedral space. |
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Cougar: Here [in running the movie backward] your answer is incorrect. We can't get anywhere near 10^-43 sec. From my recent reading on the subject, many major names in the field all seem to agree on how the movie would rewind back to 1 second.
dcl: I suggest you broaden your reading. There are any number of respected sources that give that 10^-43 figure. That figure comes from the Standard Model of particle physics, not from accelerator experiments. Cougar: Ha ha! Now that is truly funny. Would you like to peruse my Recent Reading list? I believe the misunderstanding about what we currently know [about] when the universe was 10^-43 seconds old is yours. dcl: I note your long list of references, most of which appear to be either outdated or totally irrelevant to the question of how far back in time the history of the Universe has been traced via the Standard Model of particle physics. It suffices for me to cite just one reference to rebut your assertion that the movie can be rewound only to 1 second. On page 155 of James S. Trefil, "The Moment of creation", Macmillan, New York, 1983. You can find the following statement, quoted verbatim from page 155 of this book.: . "We will call the period from 10^-43 second to 10^-35 second after the Big Bang the GUT, or Grand Unification Theory, era." Trefil is a professor of physics at Stanford University. Perhaps you'd like to challenge him on that figure. His response should be even funnier than was yours to my earlier statement. Last edited by dcl; 11-June-2008 at 03:03 AM.. |
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Everyone is entitled to his own opinion, but not his own facts. |
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It's deductions from the Standard Model of particle physics, not accelerator data, that tell of what we think we know about conditions in the early Universe. I am not a particle physicist, so I am not qualified to judge how valid these deductions are, but when the community of particle physicists tells us that they are confident that theory has enabled them to extrapolate physical phenomena back to 10^-43 second, I'm inclined to accept their statements at least tentatively as well-founded. These statements are not made lightly: They are not published in reputable journals until other physicists up to date on the latest findings endorse them through the peer review process. I cited only one place where the 10^-43 second figure for the beginning of the GUT era can be found. I've seen it in a number of different publications.
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speedfreek: Your reference to the Poincare conjecture induced me to Google it to find out what it claims. I had of course heard of it earlier but had never managed to find out what it claimed, even after it had made a big splash in the news several years ago on finally being proven. I had supposed it to be an abstract idea in pure mathematics of no immediate interest to cosmologists.
The same seemed to apply to the supposed relevance of the dodecahedron to cosmology. From the reference you cited, I learned that the conceivable relevance of the dodecahedron is the same as for the 3-torus when parallel faces or the former are "glued" in the topological sense. I still feel that the glued dodecahedron, like the 3-torus, is too implausible to be taken seriously as a possible model for the Universe. |
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Well sometime around 2003 we found what looked like a repeating pattern in WMAP data that indicated that the universe might be shaped like a Poincare dodecahedral space, which is why we were investigating these models. There was some observational evidence of a non-trivial topology that required further investigation and that investigation isn't finished yet.
If you were in charge, would you have said the shape is too implausible to investigate, bearing in mind that we already had some data that seemed to indicate that shape? |
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See Timeline of the Big Bang. Note the caveat at the beginning of the section on the very early universe: All ideas concerning the very early universe (cosmogony) are necessarily speculative. As of today no accelerator experiments probe energies of sufficient magnitude to provide any insight into the period. All proposed scenarios differ radically, some examples being: the Hartle-Hawking initial state, string landscape, brane inflation, string gas cosmology, and the ekpyrotic universe.
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Everyone is entitled to his own opinion, but not his own facts. |
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In the following, I quote speedfreek and Cougar and comment on their comments: The first paragraph by one of us is preceded by that person's pseudonym. Succeeding paragraphs by the same person are not so labeled.
speedfreek: Well sometime around 2003 we found what looked like a repeating pattern in WMAP data that indicated that the universe might be shaped like a Poincare dodecahedral space, which is why we were investigating these models. There was some observational evidence of a non-trivial topology that required further investigation and that investigation isn't finished yet. If you were in charge, would you have said the shape is too implausible to investigate, bearing in mind that we already had some data that seemed to indicate that shape? dcl: Without meaning to be derogatory in any way, I'm interested in knowing whether by "we" you mean a research group of which you are a member. If so, I am impressed and hope to learn from you. Can you refer me to a description of what was found in 2003 that would be accessible on the Internet? Alternatively, can you summarize briefly what was found? What group is or was doing this investigation? Cougar: I don't believe any particle physicist has said that, certainly not confidently. 10-43 is the Planck Time. (Actually, it's 5.39 x 10-44.) It is supposedly a barrier beyond which measurement cannot go, even in principle. See http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang Note the caveat at the beginning of the section on the very early universe: "All ideas concerning the very early universe (cosmogony) are necessarily speculative. As of today no accelerator experiments probe energies of sufficient magnitude to provide any insight into the period. All proposed scenarios differ radically, some examples being: the Hartle-Hawking initial state, string landscape, brane inflation, string gas cosmology, and the ekpyrotic universe." dcl: I've seen the equivalent of that statement and number in a large enough number of different sources that I've assumed, possibly erroneously, that it was factual. I'd appreciate your citing statements to the contrary if you can. I appreciate your referring me to the Wikipedia article you cited. Incidentally, it gives 10 exp -43 second not as the Planck era but as the end of the Planck era. It gives the interval starting at 10 exp -43 second and ending at 10 exp -36 second as the Grand Unification Era. |
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Sorry if it misled you, I often write that way when the subject is about scientific discoveries - "We have discovered a new planet", "We think the universe is 13.7 billion years old" etc.This is the original story - Is the universe a dodecahedron? And the paper that followed the original story - A Hint of Poincaré Dodecahedral Topology in the WMAP First Year Sky Map A research group then pursued the issue but they found no evidence for any non-trivial topology across a diameter of 78 billion light years (24 Gigaparsecs) and so we can confidently state that the fundamental domain of the whole universe is at least that large. These figures are based on the WMAP data representing a sphere around us that has now grown to 46 billion light years in radius (92 billion light years diameter). They intend to continue the search until they have reached ~28 Gigaparsecs. They have discounted the dodecahedral model as the universe would have had to have had a fundamental domain only 30 billion light years across for that to work. This is the paper with their findings - Extending the WMAP Bound on the Size of the Universe. I actually agree with you about the universe probably being a hypersphere but if the fundamental domain of the universe is indeed larger than our observable portion of it, as seems likely, we will never know for sure. If the fundamental domain were smaller however (and that is a possibility), we might find evidence that allows us to determine the overall topology. (See I'm doing the we thing again - I just fall into it naturally!) Until they have finished the study, I wouldn't want to commit myself either way, even if I thought the most plausible shape was an S3 hypersphere. The reason is simple - if they find no evidence for a non-trivial topology at all then the whole universe must be larger than our observable portion of it. The topology will therefore always be subject to speculation. |
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Thank you, speedfreek, for your references. The article cited in the following is from one of them.
-------- "We use optimal filtering and the combination statistic to rule out the infamous 'soccer ball universe model'" This statement is quoted directly from the last sentence in the abstract for the article entitled "Extending the WMAP Bound on the Size of the Universe" by Joey Shapiro Key, Neil J. Cornish, David N. Spergel, and Glenn D. Starkman, submitted in Apr 2006, downloadable from http://arxiv.org/abs/astro-ph/0604616). Until this article is withdrawn by the authors or its substance refuted by other articles, I'd think it should stop speculation about the Universe's having the geometry of a dodecahedron with opposite faces "glued" in the topological sense, which had impressed me from the first time I heard of it as too improbable to be taken seriously. I see the possibility of Universe's having the geometry of either a 3-torus or Dr. Gay's doughnut as equally improbable. I'm not at all convinced that the Universe has the geometry of a four-dimensional hypersphere either, but I've tried unsuccessfully to find any plausible argument for rejecting it and find that it seems to readily provide plausible answers to every question I've been able to come up with.. If anyone can provide a plausible argument against the four-dimensional hypersphere Universe, I'd like to be told of it. It envisages the Universe as having originated at a point or at least within an extremely small three-dimensional volume at the center of a four-dimensional hypersphere the three-dimensional "surface" of which is the curved and finite expanding three-dimensional Universe that we seem to find ourselves in. I feel that people are too quick to jump on the infinite flat Universe model that people have read into the WMAP data. As I see it, WMAP has thus far found the Universe so nearly flat as to be unable to detect any curvature, allowing people to jump to the unwarranted conclusion that the Universe is precisely flat and infinite. I'd like to consider any plausible models for which others would argue. |
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Yes, as I said in my above post they have discounted the "soccer ball universe" (dodecahedral space) as the fundamental domain seems too large to allow it. They have not so far been able to totally discount other non-trivial topologies.
My original point was that it seems to me if it were up to you they shouldn't have even been following up possible evidence of the dodecahedral model as you deem that model implausible and preposterous and I am wondering if that is good science or not. That paper also states that they have only found space to be within 2% of being flat, so there may indeed be large scale curvature but the radius of that curvature would be larger than our observable universe. The paper below may interest you - it examines and eliminates some other non-trivial topologies but concludes that although we still have no evidence for a non-trivial topology, we still cannot discount it. However, the best fit to the data is the flat, simply-connected Lambda-CDM model. Imprints of spherical non-trivial topologies on the CMB |
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Unfortunately, it seems that the simplest possibilities are the hardest to eliminate.
If we never find enough evidence to confidently state the shape of the universe, but along the way we find hints for some of the less simple topologies, are you saying that we shouldn't investigate these, if not just so that we can eliminate them? This is what we (humans!) have been doing. |
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speedfreek, I think your thinking is sound, and I have no problem with it. In particular, I have no problem with people wanting to test hypothetical models for shape of the Universe that can be eliminated or confirmed as plausible only through a reasonable amount of testing. If they test those models and find persuasive evidence for their validity, the effort will have been justified. If the effort fails, the onus will be on them and the sponsors of their research to justify the cost, time, and manhours spent on the effort that might have been expended on some other research. I would not deny them the right to test their ideas, no matter how outlandish they seem to me.
I'm saying only that all of the models of the Universe that I am aware of as having been proposed other than the four-dimensional hypersphere that I and presumably others have proposed impress me as being so improbable that I myself dismiss them out of hand, but I have no problem with others who feel differently looking for evidence to support their models. As for what constitutes good science, I'll leave that to others to say. If people want to invest time, effort, and money on studies that seem to others to be destined to produce negative results, I say let them go ahead if those with the money to fund the effort are willing to provide the money. If they fail, they will at least have provided an answer to a question. As for the glued dodecahedron model, I would have been most astonished if convincing evidence had been found for it. |
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