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#1
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Galaxies without dark matter halos?
In article , greywolf42
writes: I neither claimed nor implied mass estimates were based on earlier 'dark matter' measurements. They are based on 'big bang' DISTANCE measurements. We are attempting to determine whether 'dark matter' exists, based on lensing estimates. Dark matter is inferred whenever we compare two disparate mass estimates. The first is when we calculate a mass of a galaxy based on it's apparent visible stars (actually overall absolute luminosity) -- which roughly 'counts' the number of visible stars and (through theory) low-luminosity normal matter objects. This mass estimate requires us to know the distance to the galaxy. Distances to galaxies (those used in lensing papers) are determined SOLELY through the assumption of the big bang -- that the measured redshift converts directly to a distance. The second mass estimate is based on the 'gravitational lensing' of a second galaxy behind the first. The amount of lensing (angle of bend) is based on two distances -- both determined solely by the big-bang theory (redshift IS distance). The apparent bend of the light is then used to infer a mass of the galaxy with the smaller redshift (presumed to be closer). Now if the redshift - distance postulate is not universally correct under all conditions, then (at the truly cosmic distances indicated) then not only is the 'visible mass' estimate in error, the deflection angle (and the 'total mass' estimate) are both going to be incorrect. The big bang relies upon dark matter to stay viable (otherwise omega is nowhere near 1). Thus, "your mass estimates are worthless for the purpose of discriminating between dark matter and non-dark matter." This is a valid point. Whenever discussing "alternative theories", one has to take care that everything is calculated self-consistently. John Barrow, for example, has often pointed this out. (He is a "mainstream cosmologist" who has frequently investigated "alternative theories" such as non-constant constants of nature etc.) I'm not aware of any preponderance of evidence for the big bang. Every time there is a new observation at odds with the big bang (i.e. omega = .02 instead of 1, Hubble constant failure at high redshift), a "new" physical phenomenon is invented to patch up the structure ('dark matter', 'dark energy'). You are making a big mistake here, confusing "The Big Bang" with some statement about the value of Omega. It is easy to set up a straw man (big bang implies Omega is near 1) then question the big bang when it is found that Omega is not near one. But the big-bang theory (the universe evolved from a dense, hot state, perhaps even a singularity) says NOTHING about the value of Omega. How about one that predicted the hubble constant failure at high z, instead of creating 'dark energy' as the latest epicycle (ad hoc)? Start with the book "The Big Bang Never Happened", by Lerner. Then we can discuss the measurements that you feel weigh more heavily on one side or the other. If you read Lerner's book, read this as well: http://www.astro.ucla.edu/~wright/lerner_errors.html |
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Galaxies without dark matter halos?
Phillip Helbig---remove CLOTHES to reply
wrote in message ... You are making a big mistake here, confusing "The Big Bang" with some statement about the value of Omega. Nope. The value of omega was quite a serious problem for one of the earlier incarnations of the big bang. It is easy to set up a straw man (big bang implies Omega is near 1) then question the big bang when it is found that Omega is not near one. I'm not setting up a straw man. I'm reporting one of the 'problems' of earlier big bang theory. The early proponents of the big bang (which doesn't include me) insisted that omega had to be near 1.0 to avoid some nasty contradictions with observation. But the big-bang theory (the universe evolved from a dense, hot state, perhaps even a singularity) says NOTHING about the value of Omega. Today (with all the new epicycles) there may be 'no problem.' However, this used to be called the 'flatness problem' in cosmological circles. It also affected the 'anisotropy problem.' Alan Guth 'solved' the 'flatness problem' by postulating 'inflation.' Which arbitrarily increased the size of the universe for a brief period for no other reason but to avoid the problem. But this meant that omega 'must' be 1.0. Hence, there 'must' be dark matter -- since the observed matter only made omega equal to 0.02 or 0.03. If you read Lerner's book, read this as well: http://www.astro.ucla.edu/~wright/lerner_errors.html I've read it. What's your point? Have you read TBBNH, or not? Or would you care to begin by discussing Ned Wright's mudfest? (You'll need TBBNH to do so, however.) greywolf42 ubi dubim ibi libertas [Mod. note: quoted text trimmed. Please do this yourself -- mjh] |
#3
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Galaxies without dark matter halos?
Phillip Helbig---remove CLOTHES to reply
wrote in message ... You are making a big mistake here, confusing "The Big Bang" with some statement about the value of Omega. Nope. The value of omega was quite a serious problem for one of the earlier incarnations of the big bang. It is easy to set up a straw man (big bang implies Omega is near 1) then question the big bang when it is found that Omega is not near one. I'm not setting up a straw man. I'm reporting one of the 'problems' of earlier big bang theory. The early proponents of the big bang (which doesn't include me) insisted that omega had to be near 1.0 to avoid some nasty contradictions with observation. But the big-bang theory (the universe evolved from a dense, hot state, perhaps even a singularity) says NOTHING about the value of Omega. Today (with all the new epicycles) there may be 'no problem.' However, this used to be called the 'flatness problem' in cosmological circles. It also affected the 'anisotropy problem.' Alan Guth 'solved' the 'flatness problem' by postulating 'inflation.' Which arbitrarily increased the size of the universe for a brief period for no other reason but to avoid the problem. But this meant that omega 'must' be 1.0. Hence, there 'must' be dark matter -- since the observed matter only made omega equal to 0.02 or 0.03. If you read Lerner's book, read this as well: http://www.astro.ucla.edu/~wright/lerner_errors.html I've read it. What's your point? Have you read TBBNH, or not? Or would you care to begin by discussing Ned Wright's mudfest? (You'll need TBBNH to do so, however.) greywolf42 ubi dubim ibi libertas [Mod. note: quoted text trimmed. Please do this yourself -- mjh] |
#4
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Galaxies without dark matter halos?
In article , greywolf42
writes: Phillip Helbig---remove CLOTHES to reply wrote in message ... You are making a big mistake here, confusing "The Big Bang" with some statement about the value of Omega. Nope. The value of omega was quite a serious problem for one of the earlier incarnations of the big bang. "One of the earlier incarnations". What is an incarnation? Somebody's pet theory du jour, intentionally confusingly deemed to be "part of the big-bang theory" to lend it credibility. I don't debate the fact that some people had great emotional problems when their favourite value of Omega turned out to be wrong. But it is a false dichotomy to say either one believes the big bang with the value of Omega which is currently favourable, or, if that value turns out to be wrong (in conflict with observations), then that brings down the whole big bang theory. Simply not true. What's the point in playing with words? Your line of argumentation is similar (but not identical) to the question "Have you stopped beating your wife?"---the statement or question itself makes invalid assumptions so that the other party is prohibited from giving the truly correct answer. I'm not setting up a straw man. I'm reporting one of the 'problems' of earlier big bang theory. The early proponents of the big bang (which doesn't include me) insisted that omega had to be near 1.0 to avoid some nasty contradictions with observation. OBSERVATIONS have never pointed to Omega = 1, at least not without very large error bars or hidden assumptions (such as a flat universe) or both. There WAS a lot of THEORETICAL PREJUDICE in favour of Omega = 1, but it was just that, and never was essential to any version of the big-bang theory. Sure, someone could come up with a theory of big bang + some value of Omega, but disproving that value of Omega disproves that theory, not the big bang per se. Going back to the original, pure big bang can hardly be called an epicycle. Today (with all the new epicycles) there may be 'no problem.' However, this used to be called the 'flatness problem' in cosmological circles. It also affected the 'anisotropy problem.' Alan Guth 'solved' the 'flatness problem' by postulating 'inflation.' Which arbitrarily increased the size of the universe for a brief period for no other reason but to avoid the problem. But this meant that omega 'must' be 1.0. Hence, there 'must' be dark matter -- since the observed matter only made omega equal to 0.02 or 0.03. First, you are confusing the big bang with inflation. The big bang is practically a certainty. Whether or not inflation occurs is still open. Also, if anything inflation favours a flat universe, hence only favours Omega = 1 if one ASSUMES that there is no cosmological constant. Sure, some people made this assumption and some didn't make this clear enough, but the fact that this particular version has been ruled out says nothing about the validity of the big bang per se. |
#5
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Galaxies without dark matter halos?
In article , greywolf42
writes: Phillip Helbig---remove CLOTHES to reply wrote in message ... You are making a big mistake here, confusing "The Big Bang" with some statement about the value of Omega. Nope. The value of omega was quite a serious problem for one of the earlier incarnations of the big bang. "One of the earlier incarnations". What is an incarnation? Somebody's pet theory du jour, intentionally confusingly deemed to be "part of the big-bang theory" to lend it credibility. I don't debate the fact that some people had great emotional problems when their favourite value of Omega turned out to be wrong. But it is a false dichotomy to say either one believes the big bang with the value of Omega which is currently favourable, or, if that value turns out to be wrong (in conflict with observations), then that brings down the whole big bang theory. Simply not true. What's the point in playing with words? Your line of argumentation is similar (but not identical) to the question "Have you stopped beating your wife?"---the statement or question itself makes invalid assumptions so that the other party is prohibited from giving the truly correct answer. I'm not setting up a straw man. I'm reporting one of the 'problems' of earlier big bang theory. The early proponents of the big bang (which doesn't include me) insisted that omega had to be near 1.0 to avoid some nasty contradictions with observation. OBSERVATIONS have never pointed to Omega = 1, at least not without very large error bars or hidden assumptions (such as a flat universe) or both. There WAS a lot of THEORETICAL PREJUDICE in favour of Omega = 1, but it was just that, and never was essential to any version of the big-bang theory. Sure, someone could come up with a theory of big bang + some value of Omega, but disproving that value of Omega disproves that theory, not the big bang per se. Going back to the original, pure big bang can hardly be called an epicycle. Today (with all the new epicycles) there may be 'no problem.' However, this used to be called the 'flatness problem' in cosmological circles. It also affected the 'anisotropy problem.' Alan Guth 'solved' the 'flatness problem' by postulating 'inflation.' Which arbitrarily increased the size of the universe for a brief period for no other reason but to avoid the problem. But this meant that omega 'must' be 1.0. Hence, there 'must' be dark matter -- since the observed matter only made omega equal to 0.02 or 0.03. First, you are confusing the big bang with inflation. The big bang is practically a certainty. Whether or not inflation occurs is still open. Also, if anything inflation favours a flat universe, hence only favours Omega = 1 if one ASSUMES that there is no cosmological constant. Sure, some people made this assumption and some didn't make this clear enough, but the fact that this particular version has been ruled out says nothing about the validity of the big bang per se. |
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Galaxies without dark matter halos?
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#7
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Galaxies without dark matter halos?
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#9
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Galaxies without dark matter halos?
In article ,
(Starblade Darksquall) writes: What does 'flatness' mean? That the geometry of space is familiar Euclidean geometry, as opposed to being positively or negatively curved. The analogues in two dimensions are a plane, the surface of a sphere and the surface of a saddle. Positive curvature implies a closed universe, negative or zero curvature (flatness) an open universe. "Open" and "closed" here refer to SPACE. Sometimes "open" is used to mean a universe which expands forever and "closed" is used to mean that it will collapse in the future. One could think of these terms as being temporal rather than spatial in this case, but I think it is best to use the terms to refer to the spatial properties and use other terms---"expands forever", "will collapse again" to refer to the history of the expansion (or contraction) of the universe. Better yet, don't use the terms at all, but use "positive curvature" and "negative curvature" to classify the spatial aspects. (Note for the experts: I am assuming a simple topology here.) What is the difference between the shape of the universe - IE whether it is infinite without boundary or finite without boundary - and whether it's closed, open, or flat, which has to do with it being on the boundary of open or closed, and where open and closed, and flat, have to do with the expansion of the universe? I take it that these questions are related, but that their answers are not bound to one another. In general, the shape of the universe and its expansion history are independent in the sense that all combinations are possible. In particular, the values of Omega and lambda determine both. Let me plug my own version of explaining this: http://www.astro.multivax.de:8000/he...ngsiz_guide.ps or, to save bandwidth, http://www.astro.multivax.de:8000/he...iz_guide.ps-gz Some confusion has arisen because, as one can see from the diagram on page 3 of the above reference, in the case of a vanishing cosmological constant, positive curvature implies collapse, negative implies expansion forever and flatness implies that the expansion speed asymptotically approaches zero. An absolute must-see web page for anyone interested in this kind of stuff is http://www.jb.man.ac.uk/~jpl/cosmo/f....html#solution |
#10
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Galaxies without dark matter halos?
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