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#11
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Galaxies without dark matter halos?
Phillip Helbig---remove CLOTHES to reply
wrote in message ... In article , greywolf42 writes: They are 'explained' by the current model of the big bang. However, the 'big bang' is really a set of different theories that include one basic event: the expansion of the 'cosmic egg.' (Lemaitre, I believe.) "Red shift" was the foundation of the original theory termed 'big bang'. There is some serious confusion here. Yes, Lemaitre was the first to extensively discuss the "cosmic egg". The redshift was predicted somewhat earlier by de Sitter and for a time the cosmological red**** was known as the "de Sitter effect". There is no confusion at all. We agree that the big bang is essentially the theory that the universe expanded from a hotter, denser state---the cosmic egg, if you like. That is the commonality between the various theories that are often lumped together as the 'big bang.' This was renovated by adjusting contants to match observed light elements (big bang, version 2.0). This was later upgraded to BB 3.0: CMBR. There is nothing 'wrong' with ad hoc adjustments of a theory. But such 'observations' are not substantive support for a theory -- as they've been put in 'by hand' to match the observations, after the fact. For this reason, prediction is preferred to ad hoc adjustment. You have it backwards. The CMBR was PREDICTED (by Gamow in 1948 or so) long before it was observed (Penzias and Wilson, 1965 or so). Flatly untrue, though commonly believed. This is one of the myths of science. See the thread "Gamow's CMBR 'prediction' claims finally put to rest?" on the following thread: http://groups.google.com/groups?selm...0nntp2.onemain. com Similarly, predictions of the relative abundances of light elements were on the record before these were observed. Your statement contradicts the texts I've seen. Please identify the specific reference(s) that first predicted the abundances of the light elements. It did NOT happen that some arbitrary values were observed and then the big-bang theory made to fit them, as if it could be made to fit any values. (Gamow also did some work on element synthesis.) Your claim is unsupported, and -- I believe -- incorrect. I await substantiation of the 'light element' claim. greywolf42 ubi dubium ibi libertas |
#12
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Galaxies without dark matter halos?
In article , greywolf42
writes: They are 'explained' by the current model of the big bang. However, the 'big bang' is really a set of different theories that include one basic event: the expansion of the 'cosmic egg.' (Lemaitre, I believe.) "Red shift" was the foundation of the original theory termed 'big bang'. There is some serious confusion here. Yes, Lemaitre was the first to extensively discuss the "cosmic egg". The redshift was predicted somewhat earlier by de Sitter and for a time the cosmological red**** was known as the "de Sitter effect". There is no confusion at all. `"Red shift" was the foundation of the original theory termed 'big bang'' is what I was referring to as confusion. The cosmological redshift comes from expansion; there are non-big-bang models (both within the context of Friedmann-Lemaitre models and outside them) which have redshift but no big bang. Flatly untrue, though commonly believed. This is one of the myths of science. See the thread "Gamow's CMBR 'prediction' claims finally put to rest?" on the following thread: http://groups.google.com/groups?selm....onemain .com In sci.physics.relativity, OK. Dicke certainly had predicted it and was so confident in his prediction that he started to look for it, then got scooped (his words) by Penzias and Wilson. Your statement contradicts the texts I've seen. Please identify the specific reference(s) that first predicted the abundances of the light elements. Can you please name the "texts you've seen"? If they appear non-crackpot, I'll dig up the references, otherwise it's a waste of my time. |
#13
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Galaxies without dark matter halos?
In article , greywolf42
writes: They are 'explained' by the current model of the big bang. However, the 'big bang' is really a set of different theories that include one basic event: the expansion of the 'cosmic egg.' (Lemaitre, I believe.) "Red shift" was the foundation of the original theory termed 'big bang'. There is some serious confusion here. Yes, Lemaitre was the first to extensively discuss the "cosmic egg". The redshift was predicted somewhat earlier by de Sitter and for a time the cosmological red**** was known as the "de Sitter effect". There is no confusion at all. `"Red shift" was the foundation of the original theory termed 'big bang'' is what I was referring to as confusion. The cosmological redshift comes from expansion; there are non-big-bang models (both within the context of Friedmann-Lemaitre models and outside them) which have redshift but no big bang. Flatly untrue, though commonly believed. This is one of the myths of science. See the thread "Gamow's CMBR 'prediction' claims finally put to rest?" on the following thread: http://groups.google.com/groups?selm....onemain .com In sci.physics.relativity, OK. Dicke certainly had predicted it and was so confident in his prediction that he started to look for it, then got scooped (his words) by Penzias and Wilson. Your statement contradicts the texts I've seen. Please identify the specific reference(s) that first predicted the abundances of the light elements. Can you please name the "texts you've seen"? If they appear non-crackpot, I'll dig up the references, otherwise it's a waste of my time. |
#14
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Galaxies without dark matter halos?
Phillip Helbig---remove CLOTHES to reply
wrote in message ... In article , greywolf42 writes: There are two sides to the "problem". One is whether inflation is needed to explain why the universe is (nearly) flat. Coles and Ellis conclude "...we do not need to invole an additional ad hoc mechanism to `explain' this calue. In this sense, \emph{there is no flatness problem} in a purely classical cosmological model." Isn't that sort of like declaring victory and pulling out? The whole point of the 'flatness problem' is that the universe is not observed to be nearly flat. Omega is only .02 to .03. I think there is some confusion here. Yes, Omega (matter) is 0.3 or so. If you count galaxies, you count matter. You count apparent luminosity, not matter. And you convert that apparent luminosity to absolute luminosity based upon a theory of distance-vs-redshift. If your theory is wrong, so is your absolute luminosity. (The absolute-luminosity vs morphology relation is also based on the assumption of the big bang.) If your absolute luminosity is wrong, then so is your mass estimate (which may have other errors, as well). Other observations (CMB) indicate that the universe is flat. If you start with some versions of the BB theory, yes. The CMB may have other meanings if you assume different theories. That implies 0.7 in lambda. OK, take these values and the value of H, independently found to be 71 from the CMB and the HST key project (which agrees well with the value from gravitational-lens time delays), and calculate the age of the universe. Using what theory? What's the point of assuming an 'age of the universe' that requires BB, if the point is to determine the BB? It is somewhat older than the age of the oldest objects we know. What numbers do you come up with? The 10-15 billion years required by the (post Hipparcos) Hubble shift is significantly younger than the 18 billion year old globular clusters. All is quite consistent. This "standard model" is also compatible with the m-z diagram for supernovae. Only if you assume 'dark energy' as an additional ad hoc assumption. Where is the problem? I've listed several, above. Inflation might have occurred, but it (or some other mechanism) is not REQUIRED to explain the "extremely improbable" situation of a flat universe. How do C&E explain the fact that the universe is *not* observed to be flat? See above. They don't have to explain it. They point out that THERE IS NO REASON TO EXPECT IT TO BE FLAT. Their book is concerned mostly with measuring Omega (matter). At the time, there was no strong evidence for a cosmological constant, so they favoured a model with lambda=0, pointing out even then that lambda=0.7 also fits the data and would be a viable choice. The universe doesn't have to be flat, but it CAN be flat, or close to it, as current observations seem to indicate. I thought that GUTs require omega = 1.0. Are they all wasting their time? And why did the 'big bang' efforts of 20 years ago all focus on the necessity of 'flatness.' The other question is whether Omega + lambda 1 is a problem for inflation. Of course, if inflation isn't needed, that is a rather uninteresting question. It seems to me that if inflation occurred, then the most likely result would be a very nearly flat universe. Since that is what observations seem to be indicating, there is no conflict. The conflict is that the universe is not observed to be flat. Or rather, that the Big Bang theory cannot take us from one observation (omega = ..02 or ..03) to other observations (CMBR, etc). This is the core of the 'problem.' Merely stating 'we observe the universe *is* flat' simply avoids the theoretical conflict. These are two separate questions. No, they are linked. We all agree that Omega (matter) is 0.3. BUT WE DON'T KNOW WHAT MOS OF THIS MATTER IS. Then there's little basis for the agreement, don't you think? Most astronomers agree that lambda is 0.7. What lambda "IS" is a separate question. It's not seperate at all. If you don't know what it 'IS', then you can't know what the measurement of that unknown is. Denying that lambda is 0.7 since we don't "understand" lambda is as absurd as denying that Omega is 0.3 since we don't know what the dark matter is. Neither position is 'absurd.' The point is, that if you don't know what X is made of (on the basis of the fundamental theory), then you know nothing about X. What you are describing is an ad hoc process (which is valid). You have a theory (BB) which doesn't match observation -- unless an arbtrary new term is added with a particular value. This 'saves' the theory from observation. But until that ad hoc material is actually observed, the theory stands at odds with observation. And if it can't be disproved (ab initio), then you don't have a scientific theory. To summarise: if the present observations Observations of what, specifically? See any of a number of papers on "cosmic concordance". I meant the observations to which *you* were referring. I don't insist on a complete list. Just a few examples. It's kind of like the measurement of Avagadro's number a hundred years ago; more than any one observation, this proof that atoms are real came mostly from several independent methods giving the same result. Actually, atomic theory was fought tooth-and-nail by the positivists. However, it was 'prediction' (prior to experiment) of the atomic/molecular theory that paved the way to acceptance. Not ad hoc changes to the theory, based on a series of unpredicted observations. hold up and the universe is found to be very, very near the flat case, then this would be evidence in favour of inflation. No, that would be evidence of a problem with the big bang theory. Inflation is the ad hoc assumption needed to bridge the gap. The big-bang theory itself makes not statement about the values of Omega and lambda. That depends on which 'Big Bang' theory you refer to when you say "THE" big-bang theory. "THE" (most popular) BB theory contains inflation. Which makes statements of the values of omega and lambda. The classical flatness problem, that something like inflation is needed to keep Omega from being 1000000 or 0.00000001, is based on a misunderstanding of the mathematics of classical cosmology, as Coles and Ellis point out. I don't believe that's the 'classical' flatness problem. I thought the classical flatness problem is based on the exceedingly short lifetime of the universe if omega is significantly different from 1.0. No. THIS is precisely the misunderstanding that Coles and Ellis discuss in their book. So Coles and Ellis do not share the commonly-accepted view that there really *was* a 'flatness problem.' However, everyone understands what the 'classical flatness problem' *was.* Even if Coles and Ellis believe that this 'problem' was more 'myth' than 'problem.' greywolf42 ubi dubium ibi libertas |
#15
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Galaxies without dark matter halos?
Phillip Helbig---remove CLOTHES to reply
wrote in message ... In article , greywolf42 writes: There are two sides to the "problem". One is whether inflation is needed to explain why the universe is (nearly) flat. Coles and Ellis conclude "...we do not need to invole an additional ad hoc mechanism to `explain' this calue. In this sense, \emph{there is no flatness problem} in a purely classical cosmological model." Isn't that sort of like declaring victory and pulling out? The whole point of the 'flatness problem' is that the universe is not observed to be nearly flat. Omega is only .02 to .03. I think there is some confusion here. Yes, Omega (matter) is 0.3 or so. If you count galaxies, you count matter. You count apparent luminosity, not matter. And you convert that apparent luminosity to absolute luminosity based upon a theory of distance-vs-redshift. If your theory is wrong, so is your absolute luminosity. (The absolute-luminosity vs morphology relation is also based on the assumption of the big bang.) If your absolute luminosity is wrong, then so is your mass estimate (which may have other errors, as well). Other observations (CMB) indicate that the universe is flat. If you start with some versions of the BB theory, yes. The CMB may have other meanings if you assume different theories. That implies 0.7 in lambda. OK, take these values and the value of H, independently found to be 71 from the CMB and the HST key project (which agrees well with the value from gravitational-lens time delays), and calculate the age of the universe. Using what theory? What's the point of assuming an 'age of the universe' that requires BB, if the point is to determine the BB? It is somewhat older than the age of the oldest objects we know. What numbers do you come up with? The 10-15 billion years required by the (post Hipparcos) Hubble shift is significantly younger than the 18 billion year old globular clusters. All is quite consistent. This "standard model" is also compatible with the m-z diagram for supernovae. Only if you assume 'dark energy' as an additional ad hoc assumption. Where is the problem? I've listed several, above. Inflation might have occurred, but it (or some other mechanism) is not REQUIRED to explain the "extremely improbable" situation of a flat universe. How do C&E explain the fact that the universe is *not* observed to be flat? See above. They don't have to explain it. They point out that THERE IS NO REASON TO EXPECT IT TO BE FLAT. Their book is concerned mostly with measuring Omega (matter). At the time, there was no strong evidence for a cosmological constant, so they favoured a model with lambda=0, pointing out even then that lambda=0.7 also fits the data and would be a viable choice. The universe doesn't have to be flat, but it CAN be flat, or close to it, as current observations seem to indicate. I thought that GUTs require omega = 1.0. Are they all wasting their time? And why did the 'big bang' efforts of 20 years ago all focus on the necessity of 'flatness.' The other question is whether Omega + lambda 1 is a problem for inflation. Of course, if inflation isn't needed, that is a rather uninteresting question. It seems to me that if inflation occurred, then the most likely result would be a very nearly flat universe. Since that is what observations seem to be indicating, there is no conflict. The conflict is that the universe is not observed to be flat. Or rather, that the Big Bang theory cannot take us from one observation (omega = ..02 or ..03) to other observations (CMBR, etc). This is the core of the 'problem.' Merely stating 'we observe the universe *is* flat' simply avoids the theoretical conflict. These are two separate questions. No, they are linked. We all agree that Omega (matter) is 0.3. BUT WE DON'T KNOW WHAT MOS OF THIS MATTER IS. Then there's little basis for the agreement, don't you think? Most astronomers agree that lambda is 0.7. What lambda "IS" is a separate question. It's not seperate at all. If you don't know what it 'IS', then you can't know what the measurement of that unknown is. Denying that lambda is 0.7 since we don't "understand" lambda is as absurd as denying that Omega is 0.3 since we don't know what the dark matter is. Neither position is 'absurd.' The point is, that if you don't know what X is made of (on the basis of the fundamental theory), then you know nothing about X. What you are describing is an ad hoc process (which is valid). You have a theory (BB) which doesn't match observation -- unless an arbtrary new term is added with a particular value. This 'saves' the theory from observation. But until that ad hoc material is actually observed, the theory stands at odds with observation. And if it can't be disproved (ab initio), then you don't have a scientific theory. To summarise: if the present observations Observations of what, specifically? See any of a number of papers on "cosmic concordance". I meant the observations to which *you* were referring. I don't insist on a complete list. Just a few examples. It's kind of like the measurement of Avagadro's number a hundred years ago; more than any one observation, this proof that atoms are real came mostly from several independent methods giving the same result. Actually, atomic theory was fought tooth-and-nail by the positivists. However, it was 'prediction' (prior to experiment) of the atomic/molecular theory that paved the way to acceptance. Not ad hoc changes to the theory, based on a series of unpredicted observations. hold up and the universe is found to be very, very near the flat case, then this would be evidence in favour of inflation. No, that would be evidence of a problem with the big bang theory. Inflation is the ad hoc assumption needed to bridge the gap. The big-bang theory itself makes not statement about the values of Omega and lambda. That depends on which 'Big Bang' theory you refer to when you say "THE" big-bang theory. "THE" (most popular) BB theory contains inflation. Which makes statements of the values of omega and lambda. The classical flatness problem, that something like inflation is needed to keep Omega from being 1000000 or 0.00000001, is based on a misunderstanding of the mathematics of classical cosmology, as Coles and Ellis point out. I don't believe that's the 'classical' flatness problem. I thought the classical flatness problem is based on the exceedingly short lifetime of the universe if omega is significantly different from 1.0. No. THIS is precisely the misunderstanding that Coles and Ellis discuss in their book. So Coles and Ellis do not share the commonly-accepted view that there really *was* a 'flatness problem.' However, everyone understands what the 'classical flatness problem' *was.* Even if Coles and Ellis believe that this 'problem' was more 'myth' than 'problem.' greywolf42 ubi dubium ibi libertas |
#16
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Galaxies without dark matter halos?
In article , greywolf42
writes: I think there is some confusion here. Yes, Omega (matter) is 0.3 or so. If you count galaxies, you count matter. You count apparent luminosity, not matter. And you convert that apparent luminosity to absolute luminosity based upon a theory of distance-vs-redshift. If your theory is wrong, so is your absolute luminosity. (The absolute-luminosity vs morphology relation is also based on the assumption of the big bang.) If your absolute luminosity is wrong, then so is your mass estimate (which may have other errors, as well). No. Estimating the density by measuring luminosity and assuming a mass-to-light ratio (such as that of our galaxy), also known as Oort's method, takes place in the LOCAL universe. Redshift-based distances don't play much of a role here. (The fact that one gets the same result as with more global methods is another argument in favour of the (current, but probably relatively robust) standard model.) Other observations (CMB) indicate that the universe is flat. If you start with some versions of the BB theory, yes. The CMB may have other meanings if you assume different theories. Yes, the heavens could be full of angels with flashlights emitting microwaves. That implies 0.7 in lambda. OK, take these values and the value of H, independently found to be 71 from the CMB and the HST key project (which agrees well with the value from gravitational-lens time delays), and calculate the age of the universe. Using what theory? What's the point of assuming an 'age of the universe' that requires BB, if the point is to determine the BB? The point, here, was to show that all is consistent. If I have a theory in which different lines of investigation lead to the same result within that theory, without inserting this result from the start, then that is an argument in favour of that theory. It is somewhat older than the age of the oldest objects we know. What numbers do you come up with? The 10-15 billion years required by the (post Hipparcos) Hubble shift is significantly younger than the 18 billion year old globular clusters. This estimate for globular-cluster ages is obsolete. What's your reference? All is quite consistent. This "standard model" is also compatible with the m-z diagram for supernovae. Only if you assume 'dark energy' as an additional ad hoc assumption. It's not an assumption, it's an observation. Suppose someone gives me a paper bag, and I don't know if it is full of air or lead. If it feels heavy, I can say that there is something inside other than air, even if I don't know what it is. "Dark energy" is just a modern sexy name for the cosmological constant (with the possibility that the equation of state is perhaps different than that of a pure cosmological constant). You make it sound like ANY observed m-z diagram could be made compatible with the data. This is not true. (In addition, it looks like the equation of state is that of a pure cosmological constant.) See above. They don't have to explain it. They point out that THERE IS NO REASON TO EXPECT IT TO BE FLAT. Their book is concerned mostly with measuring Omega (matter). At the time, there was no strong evidence for a cosmological constant, so they favoured a model with lambda=0, pointing out even then that lambda=0.7 also fits the data and would be a viable choice. The universe doesn't have to be flat, but it CAN be flat, or close to it, as current observations seem to indicate. I thought that GUTs require omega = 1.0. Are they all wasting their time? Are you taking it as an established fact that GUTs are true---in contrast to the big bang? Give me some evidence that I should believe that a GUT---in particular, one requiring omega = 1.0---is true. And why did the 'big bang' efforts of 20 years ago all focus on the necessity of 'flatness.' Because it was perceived to be a problem. That's why Coles and Ellis wrote their book, to set the record straight. We all agree that Omega (matter) is 0.3. BUT WE DON'T KNOW WHAT MOS OF THIS MATTER IS. Then there's little basis for the agreement, don't you think? No. If the lights go out, we all agree that it is dark, though we might not know the cause, and our best guesses might disagree. Most astronomers agree that lambda is 0.7. What lambda "IS" is a separate question. It's not seperate at all. If you don't know what it 'IS', then you can't know what the measurement of that unknown is. Rubbish. If I weigh a container, I know its weight, even if I don't know what is inside. See any of a number of papers on "cosmic concordance". I meant the observations to which *you* were referring. I don't insist on a complete list. Just a few examples. Those ARE the observations to which I am referring. It's kind of like the measurement of Avagadro's number a hundred years ago; more than any one observation, this proof that atoms are real came mostly from several independent methods giving the same result. Actually, atomic theory was fought tooth-and-nail by the positivists. And they lost. That depends on which 'Big Bang' theory you refer to when you say "THE" big-bang theory. "THE" (most popular) BB theory contains inflation. Which makes statements of the values of omega and lambda. At most, it would claim that the sum is 1. However, even if it is ruled out, the evidence for the big bang still stands. So Coles and Ellis do not share the commonly-accepted view that there really *was* a 'flatness problem.' However, everyone understands what the 'classical flatness problem' *was.* Even if Coles and Ellis believe that this 'problem' was more 'myth' than 'problem.' It is no longer "commonly accepted" except among those who have not followed the progress of science in this field. |
#17
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Galaxies without dark matter halos?
In article , greywolf42
writes: I think there is some confusion here. Yes, Omega (matter) is 0.3 or so. If you count galaxies, you count matter. You count apparent luminosity, not matter. And you convert that apparent luminosity to absolute luminosity based upon a theory of distance-vs-redshift. If your theory is wrong, so is your absolute luminosity. (The absolute-luminosity vs morphology relation is also based on the assumption of the big bang.) If your absolute luminosity is wrong, then so is your mass estimate (which may have other errors, as well). No. Estimating the density by measuring luminosity and assuming a mass-to-light ratio (such as that of our galaxy), also known as Oort's method, takes place in the LOCAL universe. Redshift-based distances don't play much of a role here. (The fact that one gets the same result as with more global methods is another argument in favour of the (current, but probably relatively robust) standard model.) Other observations (CMB) indicate that the universe is flat. If you start with some versions of the BB theory, yes. The CMB may have other meanings if you assume different theories. Yes, the heavens could be full of angels with flashlights emitting microwaves. That implies 0.7 in lambda. OK, take these values and the value of H, independently found to be 71 from the CMB and the HST key project (which agrees well with the value from gravitational-lens time delays), and calculate the age of the universe. Using what theory? What's the point of assuming an 'age of the universe' that requires BB, if the point is to determine the BB? The point, here, was to show that all is consistent. If I have a theory in which different lines of investigation lead to the same result within that theory, without inserting this result from the start, then that is an argument in favour of that theory. It is somewhat older than the age of the oldest objects we know. What numbers do you come up with? The 10-15 billion years required by the (post Hipparcos) Hubble shift is significantly younger than the 18 billion year old globular clusters. This estimate for globular-cluster ages is obsolete. What's your reference? All is quite consistent. This "standard model" is also compatible with the m-z diagram for supernovae. Only if you assume 'dark energy' as an additional ad hoc assumption. It's not an assumption, it's an observation. Suppose someone gives me a paper bag, and I don't know if it is full of air or lead. If it feels heavy, I can say that there is something inside other than air, even if I don't know what it is. "Dark energy" is just a modern sexy name for the cosmological constant (with the possibility that the equation of state is perhaps different than that of a pure cosmological constant). You make it sound like ANY observed m-z diagram could be made compatible with the data. This is not true. (In addition, it looks like the equation of state is that of a pure cosmological constant.) See above. They don't have to explain it. They point out that THERE IS NO REASON TO EXPECT IT TO BE FLAT. Their book is concerned mostly with measuring Omega (matter). At the time, there was no strong evidence for a cosmological constant, so they favoured a model with lambda=0, pointing out even then that lambda=0.7 also fits the data and would be a viable choice. The universe doesn't have to be flat, but it CAN be flat, or close to it, as current observations seem to indicate. I thought that GUTs require omega = 1.0. Are they all wasting their time? Are you taking it as an established fact that GUTs are true---in contrast to the big bang? Give me some evidence that I should believe that a GUT---in particular, one requiring omega = 1.0---is true. And why did the 'big bang' efforts of 20 years ago all focus on the necessity of 'flatness.' Because it was perceived to be a problem. That's why Coles and Ellis wrote their book, to set the record straight. We all agree that Omega (matter) is 0.3. BUT WE DON'T KNOW WHAT MOS OF THIS MATTER IS. Then there's little basis for the agreement, don't you think? No. If the lights go out, we all agree that it is dark, though we might not know the cause, and our best guesses might disagree. Most astronomers agree that lambda is 0.7. What lambda "IS" is a separate question. It's not seperate at all. If you don't know what it 'IS', then you can't know what the measurement of that unknown is. Rubbish. If I weigh a container, I know its weight, even if I don't know what is inside. See any of a number of papers on "cosmic concordance". I meant the observations to which *you* were referring. I don't insist on a complete list. Just a few examples. Those ARE the observations to which I am referring. It's kind of like the measurement of Avagadro's number a hundred years ago; more than any one observation, this proof that atoms are real came mostly from several independent methods giving the same result. Actually, atomic theory was fought tooth-and-nail by the positivists. And they lost. That depends on which 'Big Bang' theory you refer to when you say "THE" big-bang theory. "THE" (most popular) BB theory contains inflation. Which makes statements of the values of omega and lambda. At most, it would claim that the sum is 1. However, even if it is ruled out, the evidence for the big bang still stands. So Coles and Ellis do not share the commonly-accepted view that there really *was* a 'flatness problem.' However, everyone understands what the 'classical flatness problem' *was.* Even if Coles and Ellis believe that this 'problem' was more 'myth' than 'problem.' It is no longer "commonly accepted" except among those who have not followed the progress of science in this field. |
#18
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Galaxies without dark matter halos?
In article , greywolf42
writes: I thought that GUTs require omega = 1.0. Are they all wasting their time? No GUT ever required Omega_matter = 1 in any meaningful sense. (As I said before, at most one could argue that inflation---which might be the consequence of some GUT---could point to Omega_matter + lambda = 1.) What used to happen is that the GUT guys would come up with their particle du jour and suggest it as a dark matter candidate, suggesting that its predicted mass would be about right to explain the "missing mass", or even make Omega_matter = 1. (Of course, my feeling is that they looked up the answer in the back of the book to get the numbers to come out right.) This is brilliantly described he http://www.astro.umd.edu/~ssm/mond/flowchart.html Ten years ago, I was as critical of the confidence of many cosmologists in the then standard model as greywolf is at present. I'm not critical as a matter of course, but only when I think something is wrong. My own view is that, in the last 10 years, driven primarily by data but also by arguments such as those of Coles and Ellis, the amount of dogma has decreased and, partly as a result, the current standard model looks quite promising. Again, the difference is that today's standard model is driven primarily by data, while 10 years ago the then standard model was driven primarily by theoretical prejudice. |
#19
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Galaxies without dark matter halos?
In article , greywolf42
writes: I thought that GUTs require omega = 1.0. Are they all wasting their time? No GUT ever required Omega_matter = 1 in any meaningful sense. (As I said before, at most one could argue that inflation---which might be the consequence of some GUT---could point to Omega_matter + lambda = 1.) What used to happen is that the GUT guys would come up with their particle du jour and suggest it as a dark matter candidate, suggesting that its predicted mass would be about right to explain the "missing mass", or even make Omega_matter = 1. (Of course, my feeling is that they looked up the answer in the back of the book to get the numbers to come out right.) This is brilliantly described he http://www.astro.umd.edu/~ssm/mond/flowchart.html Ten years ago, I was as critical of the confidence of many cosmologists in the then standard model as greywolf is at present. I'm not critical as a matter of course, but only when I think something is wrong. My own view is that, in the last 10 years, driven primarily by data but also by arguments such as those of Coles and Ellis, the amount of dogma has decreased and, partly as a result, the current standard model looks quite promising. Again, the difference is that today's standard model is driven primarily by data, while 10 years ago the then standard model was driven primarily by theoretical prejudice. |
#20
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Galaxies without dark matter halos?
Phillip Helbig---remove CLOTHES to reply
wrote in message ... In article , greywolf42 writes: I think there is some confusion here. Yes, Omega (matter) is 0.3 or so. If you count galaxies, you count matter. You count apparent luminosity, not matter. And you convert that apparent luminosity to absolute luminosity based upon a theory of distance-vs-redshift. If your theory is wrong, so is your absolute luminosity. (The absolute-luminosity vs morphology relation is also based on the assumption of the big bang.) If your absolute luminosity is wrong, then so is your mass estimate (which may have other errors, as well). No. Estimating the density by measuring luminosity One cannot 'measure luminosity.' It's simply not possible without first making several assumptions. We *can* measure 'brightness' or 'apparent luminosity.' To measure 'luminosity' (which for your uses means 'absolute luminosity'), one must first determine the distance and net extinction of the source. This requires at least two theoretical models. and assuming a mass-to-light ratio (such as that of our galaxy), also known as Oort's method, takes place in the LOCAL universe. I'm not discussing multiple-universe theories. "Local" in true distance-measuring systems only extends to 300 light-years or so (after Hipparcos). Beyond that, we make theoretical assumptions. Redshift-based distances don't play much of a role here. You are incorrect. There are about a couple of dozen galaxies where we have the ability to resolve Cepheid variables -- which are our only reliable distance "standard candles" (pre-supernovae -- which is another bag of worms). All distances to other galaxies are measured by assuming the BB and Hubble constant. (The fact that one gets the same result as with more global methods is another argument in favour of the (current, but probably relatively robust) standard model.) What are the 'more global methods' to which you refer? Other observations (CMB) indicate that the universe is flat. If you start with some versions of the BB theory, yes. The CMB may have other meanings if you assume different theories. Yes, the heavens could be full of angels with flashlights emitting microwaves. The point is that CMB measurements only indicate 'flatness' for the BB. No matter how you denigrate competing theories. That implies 0.7 in lambda. OK, take these values and the value of H, independently found to be 71 from the CMB and the HST key project (which agrees well with the value from gravitational-lens time delays), and calculate the age of the universe. Using what theory? What's the point of assuming an 'age of the universe' that requires BB, if the point is to determine the BB? The point, here, was to show that all is consistent. If I have a theory in which different lines of investigation lead to the same result within that theory, without inserting this result from the start, then that is an argument in favour of that theory. True. However, there are no 'independent' lines of investigation here. If the BB theory is incorrect, then the masses used are incorrect. And the 'dark matter' amounts are incorrect. And the 'dark energy' amounts are incorrect. Historically, every one of these 'new' additions to the theory are ad hoc -- to avoid another 'problem' with the BB. It is somewhat older than the age of the oldest objects we know. What numbers do you come up with? The 10-15 billion years required by the (post Hipparcos) Hubble shift is significantly younger than the 18 billion year old globular clusters. This estimate for globular-cluster ages is obsolete. What's your reference? It is not sufficient merely to claim an observation is 'obsolete,' and then avoid my question entirely. Again, what specific numbers to you come up with for age of the universe and age of globular clusters? All is quite consistent. This "standard model" is also compatible with the m-z diagram for supernovae. Only if you assume 'dark energy' as an additional ad hoc assumption. It's not an assumption, it's an observation. "Dark Energy" may not be observed. The observation is that the Hubble constant is not linear at far distances. "Dark Energy" is the ad hoc rationale to account for the observation (the new epicycle). Suppose someone gives me a paper bag, and I don't know if it is full of air or lead. If it feels heavy, I can say that there is something inside other than air, even if I don't know what it is. Who said that it only held air or lead? 10 pounds of air is the same as 10 pounds of lead. Or a microgram of air and a microgram of lead. "Dark energy" is just a modern sexy name for the cosmological constant (with the possibility that the equation of state is perhaps different than that of a pure cosmological constant). You make it sound like ANY observed m-z diagram could be made compatible with the data. This is not true. No need to distort my position with a strawman argument. I simply note that the "amount" and 'characteristics' of "dark energy" are backfit to the observed m-z diagram. (In addition, it looks like the equation of state is that of a pure cosmological constant.) Equations of state are theoretical constructs. The observation is simply that the "Hubble constant," isn't constant. See above. They don't have to explain it. They point out that THERE IS NO REASON TO EXPECT IT TO BE FLAT. Their book is concerned mostly with measuring Omega (matter). At the time, there was no strong evidence for a cosmological constant, so they favoured a model with lambda=0, pointing out even then that lambda=0.7 also fits the data and would be a viable choice. The universe doesn't have to be flat, but it CAN be flat, or close to it, as current observations seem to indicate. I thought that GUTs require omega = 1.0. Are they all wasting their time? Are you taking it as an established fact that GUTs are true---in contrast to the big bang? Give me some evidence that I should believe that a GUT---in particular, one requiring omega = 1.0---is true. Another strawman argument. No, I'm not assuming GUTs are true. But they are popular. Frankly, since the all predicted the decay of the proton -- and protons have not been seen to decay -- I conclude that GUTs are false. (Someday I may be proved wrong. But after three major theoretical 'revisions' to get out from under observation, I'm not holding my breath.) And why did the 'big bang' efforts of 20 years ago all focus on the necessity of 'flatness.' Because it was perceived to be a problem. That's why Coles and Ellis wrote their book, to set the record straight. Excellent. Another physics myth torpedoed. We all agree that Omega (matter) is 0.3. BUT WE DON'T KNOW WHAT MOS OF THIS MATTER IS. Then there's little basis for the agreement, don't you think? No. If the lights go out, we all agree that it is dark, though we might not know the cause, and our best guesses might disagree. Then there's little basis for the agreement as to the cause of the blackout. All we know is that there is something wrong. Most astronomers agree that lambda is 0.7. What lambda "IS" is a separate question. It's not seperate at all. If you don't know what it 'IS', then you can't know what the measurement of that unknown is. Rubbish. If I weigh a container, I know its weight, even if I don't know what is inside. If you don't agree on the theory used to 'weigh' the container, you don't even know that much. See any of a number of papers on "cosmic concordance". I meant the observations to which *you* were referring. I don't insist on a complete list. Just a few examples. Those ARE the observations to which I am referring. *What* are the observations to which you are referring, specifically? It's kind of like the measurement of Avagadro's number a hundred years ago; more than any one observation, this proof that atoms are real came mostly from several independent methods giving the same result. Actually, atomic theory was fought tooth-and-nail by the positivists. And they lost. And yet "modern physicists" continued to apply the positivistic method. Equations are all. That depends on which 'Big Bang' theory you refer to when you say "THE" big-bang theory. "THE" (most popular) BB theory contains inflation. Which makes statements of the values of omega and lambda. At most, it would claim that the sum is 1. However, even if it is ruled out, the evidence for the big bang still stands. To which specific 'Big Bang' theory(ies) are you referring? So Coles and Ellis do not share the commonly-accepted view that there really *was* a 'flatness problem.' However, everyone understands what the 'classical flatness problem' *was.* Even if Coles and Ellis believe that this 'problem' was more 'myth' than 'problem.' It is no longer "commonly accepted" except among those who have not followed the progress of science in this field. But you still understand what the perceived problem was. Hence, there is no need to imply that there never was a perception of the problem. And no need to denigrate others for addressing the 'problem.' greywolf42 ubi dubium ibi libertas |
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