That discussion seems to reduce to "as little new and exotic physics as possible". - Edit 1
Before modification by Joel at 02/05/2011 01:35:03 AM
If that's the basis for exotic dark matter I can support it, but if it's simply a case of "your alternative to my new and exotic physics requires new and exotic physics, and I prefer mine" that's a competition of biases, not theories.
I'm going to link to a discussion that cites much more data to demonstrate that RAMBOs, like MACHOs, can't account for the vast majority of dark matter.
The simpler explanation should be preferred only when it explains the evidence just as well as the more complicated explanation. In this case, it really clearly doesn't.
Also, I hope you see that this statement: "Meanwhile, I'm not sure how convinced I am by a visual search failing to find extremely faint and distant objects." launches your preferred explanation right into the realm of unfalsifiability, which is exactly the problem you claim to have with exotic dark matter. Of course, as I pointed out in my reply to the branch above this one, direct detection of exotic dark matter is known to be hard if it's possible; observation of microlensing is not known to be so hard, and the results just didn't show up. That's when it's time to move on.
At the risk of scientific heresy, I dare say it's possible that all roads lead to unfalsifiability, at least for the foreseeable future. However, what I meant was that an exclusively visual search doesn't strike me as the best way to find mass producing/reflecting little or no visual light. If that were the only way to detect mass we wouldn't be having this discussion. A gravitational search seems more promising, particularly when it's such a popular means for detecting potential exotic dark matter.
The problem is that unless I'm misunderstanding the conclusions MACHOs were ruled out as the primary dark matter because we haven't seen enough gravitational lensing from the perimeter of the Milky Way. That means there's little matter, dark or otherwise, causing lensing there; it doesn't mean MACHOs aren't causing the lensing that IS observed elsewhere. Saying that MACHO theories predict far more of them should surround the Milky Way and thus more lensing should be observed doesn't rule out MACHOs as the primary dark matter; it could just mean that MACHO theories overpredict the number that should exist around the Milky Way, and need refinement, which is still simpler than positing new and exotic types of matter.
It may sound odd coming from me, but I'm leery of elevating any part of science to an article of faith, let alone a new one so poorly defined that there are still widely disparate interpretations (I admit I'd never heard of dark galaxies until browsing Wikipedia just now, but if the candidates are being detected by hydrogen emissions that sure sounds like normal baryonic dark matter). Do the research and observations, by all means, and let the chips fall where they may--just don't get so committed to validating the theory that you insist on continuing past the point where it's possible. Let's bear in mind that the whole basis for dark matter, exotic or otherwise, was negative: Not that a new phenomenon motivated a search for its cause, but that measurement of an existing phenomenon didn't conform to theoretical predictions of its magnitude.
That's the parallel with theoretical particle physics that makes me nervous; if theory is found wanting reevaluating the theory is at least as justified as trying to patch it. The biggest scientific advances have come from the former, and the last thing any of us wants is a dogmatic refusal to do so that makes exotic dark matter the modern version of epicycles.
I'm not opposed to radical reevaluation or even rejection of accepted theory where warranted, but I am opposed to radical and tortuously convoluted variations on it solely to preclude such reevaluation. In a way, that dark matter and dark energy DON'T fundamentally change existing theory is my concern: They add new radical terms to an equation whose results are changing, to prevent changing old standard terms. If the current equations terms don't match the results I prefer reconciling that within existing terms or seeking a new equation rather than simply adding new terms and hoping we someday find proof they actually exist.
At the bottom of the Wikipedia page is a link to one on RAMBOs, described thus:
So, they're baryonic dark clusters, and the last sentence implies they could account for any dark matter halo around the Milky Way. So now there's yet another new proposal for dark-but-normal matter that could fit the bill without anything more exotic than very distant and/or non-luminous but quite familiar brown and/or white dwarfs.
Meanwhile, I'm not sure how convinced I am by a visual search failing to find extremely faint and distant objects. The theoretical argument is more compelling, but it depends on our current understanding of the Big Bang being correct, and that sems as likely to contain key errors as it is to rule out baryons accounting for all dark matter.
But, yeah, by all means test the theory; you have to, and if it's fully vindicated I'll accept that. Just don't spend so much effort devising more and more tests for a theory that defies proof that you overlook a simpler (and accurate) explanation.
In astronomy, a RAMBO or robust association of massive baryonic objects is a dark cluster made of brown dwarfs or white dwarfs.
RAMBOs were proposed by Moore and Silk in 1995. They may have effective radii between 1 and 15 pc, with masses in the range 10–100,000 solar masses.
Dynamics
The dynamics of these objects, if they do exist, must be quite different from that of standard star clusters. With a very narrow mass range (all brown dwarfs or white dwarfs), the evaporation rate of these RAMBOs should be very slow as predicted by the evolution of simulated mono-component cluster models. Theoretically, these very long-lived objects could exist in large numbers. The presence of a clustered thick disk-like component of dark matter in the Galaxy has been suggested by Sanchez-Salcedo (1997, 1999) and Kerins (1997).
RAMBOs were proposed by Moore and Silk in 1995. They may have effective radii between 1 and 15 pc, with masses in the range 10–100,000 solar masses.
Dynamics
The dynamics of these objects, if they do exist, must be quite different from that of standard star clusters. With a very narrow mass range (all brown dwarfs or white dwarfs), the evaporation rate of these RAMBOs should be very slow as predicted by the evolution of simulated mono-component cluster models. Theoretically, these very long-lived objects could exist in large numbers. The presence of a clustered thick disk-like component of dark matter in the Galaxy has been suggested by Sanchez-Salcedo (1997, 1999) and Kerins (1997).
So, they're baryonic dark clusters, and the last sentence implies they could account for any dark matter halo around the Milky Way. So now there's yet another new proposal for dark-but-normal matter that could fit the bill without anything more exotic than very distant and/or non-luminous but quite familiar brown and/or white dwarfs.
Meanwhile, I'm not sure how convinced I am by a visual search failing to find extremely faint and distant objects. The theoretical argument is more compelling, but it depends on our current understanding of the Big Bang being correct, and that sems as likely to contain key errors as it is to rule out baryons accounting for all dark matter.
But, yeah, by all means test the theory; you have to, and if it's fully vindicated I'll accept that. Just don't spend so much effort devising more and more tests for a theory that defies proof that you overlook a simpler (and accurate) explanation.
I'm going to link to a discussion that cites much more data to demonstrate that RAMBOs, like MACHOs, can't account for the vast majority of dark matter.
The simpler explanation should be preferred only when it explains the evidence just as well as the more complicated explanation. In this case, it really clearly doesn't.
Also, I hope you see that this statement: "Meanwhile, I'm not sure how convinced I am by a visual search failing to find extremely faint and distant objects." launches your preferred explanation right into the realm of unfalsifiability, which is exactly the problem you claim to have with exotic dark matter. Of course, as I pointed out in my reply to the branch above this one, direct detection of exotic dark matter is known to be hard if it's possible; observation of microlensing is not known to be so hard, and the results just didn't show up. That's when it's time to move on.
At the risk of scientific heresy, I dare say it's possible that all roads lead to unfalsifiability, at least for the foreseeable future. However, what I meant was that an exclusively visual search doesn't strike me as the best way to find mass producing/reflecting little or no visual light. If that were the only way to detect mass we wouldn't be having this discussion. A gravitational search seems more promising, particularly when it's such a popular means for detecting potential exotic dark matter.
The problem is that unless I'm misunderstanding the conclusions MACHOs were ruled out as the primary dark matter because we haven't seen enough gravitational lensing from the perimeter of the Milky Way. That means there's little matter, dark or otherwise, causing lensing there; it doesn't mean MACHOs aren't causing the lensing that IS observed elsewhere. Saying that MACHO theories predict far more of them should surround the Milky Way and thus more lensing should be observed doesn't rule out MACHOs as the primary dark matter; it could just mean that MACHO theories overpredict the number that should exist around the Milky Way, and need refinement, which is still simpler than positing new and exotic types of matter.
It may sound odd coming from me, but I'm leery of elevating any part of science to an article of faith, let alone a new one so poorly defined that there are still widely disparate interpretations (I admit I'd never heard of dark galaxies until browsing Wikipedia just now, but if the candidates are being detected by hydrogen emissions that sure sounds like normal baryonic dark matter). Do the research and observations, by all means, and let the chips fall where they may--just don't get so committed to validating the theory that you insist on continuing past the point where it's possible. Let's bear in mind that the whole basis for dark matter, exotic or otherwise, was negative: Not that a new phenomenon motivated a search for its cause, but that measurement of an existing phenomenon didn't conform to theoretical predictions of its magnitude.
That's the parallel with theoretical particle physics that makes me nervous; if theory is found wanting reevaluating the theory is at least as justified as trying to patch it. The biggest scientific advances have come from the former, and the last thing any of us wants is a dogmatic refusal to do so that makes exotic dark matter the modern version of epicycles.
I'm not opposed to radical reevaluation or even rejection of accepted theory where warranted, but I am opposed to radical and tortuously convoluted variations on it solely to preclude such reevaluation. In a way, that dark matter and dark energy DON'T fundamentally change existing theory is my concern: They add new radical terms to an equation whose results are changing, to prevent changing old standard terms. If the current equations terms don't match the results I prefer reconciling that within existing terms or seeking a new equation rather than simply adding new terms and hoping we someday find proof they actually exist.