China have a demonstrated ability to kill a satellite. Why not use this to get Hubble, or for that matter, any other satellite down?
Eh? In case you're actually serious about this, (a) The US demonstrated ASAT capability over 20 years ago, and (b) ASAT capability is completely irrelevant, as such attacks don't deorbit the satellite, but result in tens of thousands of pieces of debris that are dangerous to other satellites.
In any case, casting aspersions on NASA's ability based on Hubble is ridiculous, as it's been by any measure a spectacularly successful instrument, which even 17 years after launch has capabilities not matched by any foreseeable ground-based instruments (no, not even with adaptive optics) or by any planned space instrument.
...there is some reason to believe that the flat rotation curves of spiral galaxies are due to baryonic dark matter, although it would have to be in the form of small clumps of matter like comets or dead stars or something to not do any significant scattering of light.
Microlensing surveys have already placed upper limits of well under half the dark matter in a typical galactic halo being baryonic.
Dark matter on larger scales is completely unrelated to galactic dark matter--the use of the single term "dark matter" for these totally unrelated problems is unfortunate and confusing, as I point out every time this topic comes up on/.
On what, exactly, are you basing this statement? It's certainly not the majority scientific view.
To clump in the manner observed, extra-galactic dark matter has to have some mechanism for losing energy.
Do you have a citation for this? To the best of my knowledge, none of the (generally quite successful) structure formation simulations include any interaction for dark matter besides gravity.
I'm not criticising (yet), but you're making what appear to be claims based on evidence, and I'm wondering what that evidence is.
Every time an article regarding dark matter is posted on Slashdot, there are nonsense "fudge factor!!1!" postings like the above. And every time, like-thinking idiots mod them up as "Insightful" or "Interesting". And every time, I suspect, people like me get the urge to go through and respond to every single one, but have to limit ourselves.
So let's start at the beginning, shall we? Galaxy rotation curves indicate that there is more mass in galaxies than would be inferred from the luminous matter. How do we know that it's not clouds of cold gas? Because that's ruled out by 21cm observations and by studying the absorption spectra of extragalactic objects. How do know that it's not clouds of hot gas? Becasue that's ruled out by UV and X-ray observations. How do we know that it's not brown dwarfs and black holes? Because that's ruled out by microlensing surveys.
Now, studies of galaxy dispersion velocities in clusters indicates that there's more mass in galaxy clusters than than would be inferred from the galaxies themselves, plus the intracluster medium which is observed in the X-ray. This is verified to high accuracy (i.e., the estimates of the total cluster mass are in close agreement) by hydrostatic X-ray mass measurements and by weak lensing observations. How do we know that it's not clouds of cold gas? Because that couldn't coexist with the hot gas, and because the dark matter spatial distributions are clearly different from the gas distributions. How do we know that it's not clouds of hot gas? See "intracluster medium" above. How do we know that it's not brown dwarfs and black holes? Because there's no mechanism for moving large numbers of objects out of the galaxies into the ICM (there are some intracluster stars, yes, but relatively very few--and the number of those gives us hints as to the number of non-luminous objects similarly ejected). How do we know that it's not neutrinos? Because neutrinos are experimentally shown to be too light and too fast, and cosmological constraints show that too few would have been produced in the Big Bang.
Now, studies of cosmological structure formation indicate that the size and number of galaxy clusters in the universe are not consistent with what would be expected given an all-baryonic universe. How do we know that...er...well, that's that. Cold collisionless dark matter is required to make the simulations work.
How do we know that modified gravity isn't the answer? See multiple independent lines of evidence above. There are no theories of modified gravity that come even close to explaining all of the above. The MOND people cheerfully acknowledge this, even if their advocates on Slashdot don't.
Look, the history of physics is replete with things whose existence was inferred long before they could be directly observed--neutrinos, quarks, atoms themselves, and much, much more. It's simply asinine to suggest that "we haven't directly measured it" means "it doesn't exist". Heck, we only really "see" subatomic particles because of the photons given off when they interact with one thing or another--"seeing" dark matter via measurements of its gravitational effects is hardly less direct.
And we'll just ignore the nonsensical "fitting facts to the data".
The bottom line is, there are multiple, independent lines of evidence that dark matter exists, and that it is non-baryonic. Uninformed posters on Slashdot can pat themselves on the back for their intelligence as much as they want, but they're only fooling themselves.
Well, AFAIK even most of the MOND folks have acknowledged that some dark matter is necessary. E.g., even when a MOND theory looks like it can explain galactic rotation curves, it doesn't fully explain galaxy clusters or come close to explaining cosmological observations.
The MOND people (generally) aren't kooks. They're just pushing in different directions, which is a good thing. But yes, this does make it even harder for them.
This, unfortunately, is what happens when you try to wrap a scientific definition around a cultural concept. It seems pretty clear that the simplest and most logical option (demote Pluto) was deemed unpalatable to the general public. Which, really, is what this is all about; solar system research will go on the same regardless of what the things are being called. Since the textbooks will be rewritten anyway, why go for such an unwieldy change? No one now cares that Ceres, Pallas, Juno, and Vesta were all initially designated as planets before their nature was realized and the term "asteroid" was coined; I suspect that if Pluto were redesignated then its former status would likewise be forgotten in a few decades.
In any case, let's note that this isn't official yet; it will be voted on at the IAU symposium in the next couple of days. Let's hope that enough present have the good sense to send this back to committee.
The "VERY rarely hear of research failing" bit has already been addressed--of course things that don't work don't get published and announced. It's certainly not true that things never fail--I know way too many people who have been involved in projects that didn't work out for years and were abandoned (and yes, funding lost), and this at a school that's regarded as the best in the world in their subfield. And in fact, negative results are often as interesting as--or more so--than getting what you expected. I'm coming up on two years spent on a project that started as a one month "let's make sure this is really what happens" exercise--surprise, that isn't what really happens.
And I can't really believe that you've read the scientific literature, given your last paragraph. Of course papers state their relevence to their particular area, but you can't seriously look through journals (except perhaps Science or Nature, which are supposed to be publishing only the ground-breaking stuff) and get the idea that these people believe that their work is earth-shattering. We all know that the vast majority of us are adding only little bits and pieces to the overall puzzle.
Except that China first did it in 2003, before SpaceShipOne's flight. So they were third.
And, of course, despite all the hype the SpaceShipOne flight really wasn't comparable, being suborbital with no reasonable extension that would make it orbital.
The astro-ph listing claims that the paper has been submitted to the Astrophysical Journal. Another poster noted that the manuscript is not prepared in ApJ style, so I was inspired to check the future papers listing. It doesn't show up as submitted or accepted; I've published/submitted a few times in ApJ, and this listing is not something that one opts in/out of. So either the paper was withdrawn, it was never submitted in the first place, or it wasn't submitted to ApJ (which would be an odd mistake to make; also, it's not shown as accepted in Phys Rev D, the other logical place to publish).
Now, I don't mean to imply that the authors are cranks or similar; I'm not in the GR community, and I've no reason to believe that they're anything but sincere and competent. But it does add fuel to the fire, and something for the "I've always known dark matter is a crock"/"those scientists don't know what they're doing"/"they're repressing alternative ideas" folks to consider.
Oh, please. There are numerous independent chains of evidence pointing to the existence of dark matter. Not just galaxies, but galaxy clustes, distribution of large scale structure, cosmic microwave background anisotropies, gravitational lensing, and so on. It was *not* accepted quickly...more than three decades passed between Fritz Zwicky postulating its existence (due to studies of the velocities of galaxies in clusters) and its widespread acceptance (due primarily to Vera Rubin and Kent Ford's investigation of galaxy rotation curves). These are rigorous, quantitative theories; it is simply not a case of "well, we don't know, so let's say there's dark matter".
And to act as if no one is questioning it is nonsense. Do a search for, e.g., modified Newtonian dynamics if you don't belive it. These are serious, respected scientists doing serious science--i.e., quantitatively checking theories, not sitting around complaining that their ideas are being "stifled". This is an active area of research.
Slashdot Mirror
Since Hubble was orbited using Discovery, I doubt it.
Eh? In case you're actually serious about this, (a) The US demonstrated ASAT capability over 20 years ago, and (b) ASAT capability is completely irrelevant, as such attacks don't deorbit the satellite, but result in tens of thousands of pieces of debris that are dangerous to other satellites.
In any case, casting aspersions on NASA's ability based on Hubble is ridiculous, as it's been by any measure a spectacularly successful instrument, which even 17 years after launch has capabilities not matched by any foreseeable ground-based instruments (no, not even with adaptive optics) or by any planned space instrument.
Microlensing surveys have already placed upper limits of well under half the dark matter in a typical galactic halo being baryonic.
Dark matter on larger scales is completely unrelated to galactic dark matter--the use of the single term "dark matter" for these totally unrelated problems is unfortunate and confusing, as I point out every time this topic comes up on /.
On what, exactly, are you basing this statement? It's certainly not the majority scientific view.
To clump in the manner observed, extra-galactic dark matter has to have some mechanism for losing energy.
Do you have a citation for this? To the best of my knowledge, none of the (generally quite successful) structure formation simulations include any interaction for dark matter besides gravity.
I'm not criticising (yet), but you're making what appear to be claims based on evidence, and I'm wondering what that evidence is.
So let's start at the beginning, shall we? Galaxy rotation curves indicate that there is more mass in galaxies than would be inferred from the luminous matter. How do we know that it's not clouds of cold gas? Because that's ruled out by 21cm observations and by studying the absorption spectra of extragalactic objects. How do know that it's not clouds of hot gas? Becasue that's ruled out by UV and X-ray observations. How do we know that it's not brown dwarfs and black holes? Because that's ruled out by microlensing surveys.
Now, studies of galaxy dispersion velocities in clusters indicates that there's more mass in galaxy clusters than than would be inferred from the galaxies themselves, plus the intracluster medium which is observed in the X-ray. This is verified to high accuracy (i.e., the estimates of the total cluster mass are in close agreement) by hydrostatic X-ray mass measurements and by weak lensing observations. How do we know that it's not clouds of cold gas? Because that couldn't coexist with the hot gas, and because the dark matter spatial distributions are clearly different from the gas distributions. How do we know that it's not clouds of hot gas? See "intracluster medium" above. How do we know that it's not brown dwarfs and black holes? Because there's no mechanism for moving large numbers of objects out of the galaxies into the ICM (there are some intracluster stars, yes, but relatively very few--and the number of those gives us hints as to the number of non-luminous objects similarly ejected). How do we know that it's not neutrinos? Because neutrinos are experimentally shown to be too light and too fast, and cosmological constraints show that too few would have been produced in the Big Bang.
Now, studies of cosmological structure formation indicate that the size and number of galaxy clusters in the universe are not consistent with what would be expected given an all-baryonic universe. How do we know that...er...well, that's that. Cold collisionless dark matter is required to make the simulations work.
How do we know that modified gravity isn't the answer? See multiple independent lines of evidence above. There are no theories of modified gravity that come even close to explaining all of the above. The MOND people cheerfully acknowledge this, even if their advocates on Slashdot don't.
Look, the history of physics is replete with things whose existence was inferred long before they could be directly observed--neutrinos, quarks, atoms themselves, and much, much more. It's simply asinine to suggest that "we haven't directly measured it" means "it doesn't exist". Heck, we only really "see" subatomic particles because of the photons given off when they interact with one thing or another--"seeing" dark matter via measurements of its gravitational effects is hardly less direct.
And we'll just ignore the nonsensical "fitting facts to the data". The bottom line is, there are multiple, independent lines of evidence that dark matter exists, and that it is non-baryonic. Uninformed posters on Slashdot can pat themselves on the back for their intelligence as much as they want, but they're only fooling themselves.
Well, AFAIK even most of the MOND folks have acknowledged that some dark matter is necessary. E.g., even when a MOND theory looks like it can explain galactic rotation curves, it doesn't fully explain galaxy clusters or come close to explaining cosmological observations.
The MOND people (generally) aren't kooks. They're just pushing in different directions, which is a good thing. But yes, this does make it even harder for them.
TRealFA: here (the dark matter bragging) and here (details on the lensing observations). Perhaps certain folks will take the time to read and understand them before blathering about "fudge factors" and "modern ether". But probably not.
This, unfortunately, is what happens when you try to wrap a scientific definition around a cultural concept. It seems pretty clear that the simplest and most logical option (demote Pluto) was deemed unpalatable to the general public. Which, really, is what this is all about; solar system research will go on the same regardless of what the things are being called. Since the textbooks will be rewritten anyway, why go for such an unwieldy change? No one now cares that Ceres, Pallas, Juno, and Vesta were all initially designated as planets before their nature was realized and the term "asteroid" was coined; I suspect that if Pluto were redesignated then its former status would likewise be forgotten in a few decades.
In any case, let's note that this isn't official yet; it will be voted on at the IAU symposium in the next couple of days. Let's hope that enough present have the good sense to send this back to committee.
And I can't really believe that you've read the scientific literature, given your last paragraph. Of course papers state their relevence to their particular area, but you can't seriously look through journals (except perhaps Science or Nature, which are supposed to be publishing only the ground-breaking stuff) and get the idea that these people believe that their work is earth-shattering. We all know that the vast majority of us are adding only little bits and pieces to the overall puzzle.
And, of course, despite all the hype the SpaceShipOne flight really wasn't comparable, being suborbital with no reasonable extension that would make it orbital.
Now, I don't mean to imply that the authors are cranks or similar; I'm not in the GR community, and I've no reason to believe that they're anything but sincere and competent. But it does add fuel to the fire, and something for the "I've always known dark matter is a crock"/"those scientists don't know what they're doing"/"they're repressing alternative ideas" folks to consider.
Oh, please. There are numerous independent chains of evidence pointing to the existence of dark matter. Not just galaxies, but galaxy clustes, distribution of large scale structure, cosmic microwave background anisotropies, gravitational lensing, and so on. It was *not* accepted quickly...more than three decades passed between Fritz Zwicky postulating its existence (due to studies of the velocities of galaxies in clusters) and its widespread acceptance (due primarily to Vera Rubin and Kent Ford's investigation of galaxy rotation curves). These are rigorous, quantitative theories; it is simply not a case of "well, we don't know, so let's say there's dark matter". And to act as if no one is questioning it is nonsense. Do a search for, e.g., modified Newtonian dynamics if you don't belive it. These are serious, respected scientists doing serious science--i.e., quantitatively checking theories, not sitting around complaining that their ideas are being "stifled". This is an active area of research.