If someone else doesn't have this already, which they almost certainly do, I'm totally claiming this as Rhys' Law :
The value of a press release and the probability that the reported discovery is correct is anti-correlated with the grandiosity of the claims.
It's probably not a linear relation. Maybe more like a galactic hydrogen density profile : flat near the middle out to some quite large distance (importance of the claim), but then it drops precipitously beyond the stellar disc (as claims move from "probably" and "show" to "mystery solved" and "proof").
Tuesday, 29 November 2016
Friday, 25 November 2016
Publish or perish at least produces some hilarious author names
Hoover, a physicist at Lawrence Livermore National Lab, had tried unsuccessfully to get a paper published in two leading journals. So he added a co-author from a prestigious-sounding institute, the Institute for Advanced Studies at Palermo, Sicily, and resubmitted the work. Sure enough, the paper was accepted and published. He did this several times with the same result. But the name Hoover chose—Stronzo Bestiale—was a sly tell: In Italian, it means “giant asshole.” And yet Bestiale remains in the scientific literature, just like Hoss Cartwright. So does Galadriel Mirkwood, an Afghan hound that belonged to biologist Polly Matzinger of the National Institutes of Health. She was fed up with the use of passive voice in scientific papers, and decided to add her pup’s name to a paper in protest.
In astronomy the use of the passive voice is severely frowned upon... errr, I mean, we hates it, precious ! We hates it !
It’s tempting to laugh off some of these antics, which seem driven by ego and self-interest. But they also underscore a painful truth: Unless the evaluation of scientists—and the all-important doling out of funding—can be wrenched away from bean-counting metrics, history is likely to repeat itself. Tomorrow’s metrics gamers may come up with some other ruse, and spoofers like Morgenstern will invent the next Hoss Cartwright in response. Taking time to read and evaluate a selection of a job applicant’s papers takes far more time than plugging a bunch of numbers in to a matrix. But it’s precisely that output, not metrics, that science is supposed to be about. The agencies that fund grants and committees that hire and promote academic researchers need to get back to doing the hard job of assessing the value and quality of candidates’ scientific work rather than leaning on the crutch of overly simplified publication metrics.
It's the over-reliance on simplified metrics that's the problem here. A publication record is a useful thing, but relying on sheer numbers is a terrible idea. Hence my previous suggestion of a more nuanced journal/publication ranking system, where one could see how many papers of particular types and review quality a researcher has. Even then, to rely entirely on numbers would be a fatal mistake, because you can't quantify research quality. It's fundamentally impossible. All you can do is to try and make the current system better.
http://nautil.us/issue/42/fakes/why-fake-data-when-you-can-fake-a-scientist
In astronomy the use of the passive voice is severely frowned upon... errr, I mean, we hates it, precious ! We hates it !
It’s tempting to laugh off some of these antics, which seem driven by ego and self-interest. But they also underscore a painful truth: Unless the evaluation of scientists—and the all-important doling out of funding—can be wrenched away from bean-counting metrics, history is likely to repeat itself. Tomorrow’s metrics gamers may come up with some other ruse, and spoofers like Morgenstern will invent the next Hoss Cartwright in response. Taking time to read and evaluate a selection of a job applicant’s papers takes far more time than plugging a bunch of numbers in to a matrix. But it’s precisely that output, not metrics, that science is supposed to be about. The agencies that fund grants and committees that hire and promote academic researchers need to get back to doing the hard job of assessing the value and quality of candidates’ scientific work rather than leaning on the crutch of overly simplified publication metrics.
It's the over-reliance on simplified metrics that's the problem here. A publication record is a useful thing, but relying on sheer numbers is a terrible idea. Hence my previous suggestion of a more nuanced journal/publication ranking system, where one could see how many papers of particular types and review quality a researcher has. Even then, to rely entirely on numbers would be a fatal mistake, because you can't quantify research quality. It's fundamentally impossible. All you can do is to try and make the current system better.
http://nautil.us/issue/42/fakes/why-fake-data-when-you-can-fake-a-scientist
Tuesday, 22 November 2016
For the record...
I'm just going publically on the record to state that the EM drive does not work and it will go the way of cold fusion and all the other pseudoscientific claims before it. That is all. Have a nice day.
Thursday, 10 November 2016
Expecting the unexpected
Interesting project.
The case study of the Nobel-prize-winning discovery of pulsars by Jocelyn Bell is instructive. A talented and persistent PhD student studying interstellar scintillation (and thus expanding the observational phase space), and who knew her instrument intimately, recognised that ‘bits of scruff’ on the chart recorder could not be terrestrial interference, but represented a new type of astronomical object (Bell Burnell 2009). As a result, she discovered pulsars.
...A present-day Jocelyn Bell is unlikely to understand the instrument well enough to distinguish astrophysical phenomena from instrumental effects, and would not be able to sift through the petabytes by hand, searching for something unusual. On the other hand, failure to identify unexpected effects may mean missing out on the most important science to emerge from ASKAP. It is therefore necessary to plan explicitly to build techniques to make unexpected discoveries, rather than hoping to stumble across them.
We have therefore started a project called “WTF”, which explicitly aims to mine EMU data to discover unexpected science that is not part of our primary science goals, using a variety of machine-learning techniques and algorithms. Although targeted specifically at EMU, we expect this approach to have broad applicability to astronomical survey data.
https://arxiv.org/abs/1611.02829
The case study of the Nobel-prize-winning discovery of pulsars by Jocelyn Bell is instructive. A talented and persistent PhD student studying interstellar scintillation (and thus expanding the observational phase space), and who knew her instrument intimately, recognised that ‘bits of scruff’ on the chart recorder could not be terrestrial interference, but represented a new type of astronomical object (Bell Burnell 2009). As a result, she discovered pulsars.
...A present-day Jocelyn Bell is unlikely to understand the instrument well enough to distinguish astrophysical phenomena from instrumental effects, and would not be able to sift through the petabytes by hand, searching for something unusual. On the other hand, failure to identify unexpected effects may mean missing out on the most important science to emerge from ASKAP. It is therefore necessary to plan explicitly to build techniques to make unexpected discoveries, rather than hoping to stumble across them.
We have therefore started a project called “WTF”, which explicitly aims to mine EMU data to discover unexpected science that is not part of our primary science goals, using a variety of machine-learning techniques and algorithms. Although targeted specifically at EMU, we expect this approach to have broad applicability to astronomical survey data.
https://arxiv.org/abs/1611.02829
Wednesday, 9 November 2016
Visualising 3D data in arbitrary coordinates
I had a paper accepted. It doesn't seem very important now though, because America has decided to take all that was great and good about itself and crap all over it. Still, you can read the full version here.
https://arxiv.org/abs/1611.02517
https://arxiv.org/abs/1611.02517
Thursday, 3 November 2016
Spherical volumetric data in realtime
More experiments with all-sky HI data using frequency to set the radial distance. The realtime display in Blender gives a rather different appearance to the rendered views (see recent posts in this category) because faces are one-sided in the realtime view - so the opposite half of the spheres aren't visible. Gives a more interesting and subtle effect than the rendered view.
Tuesday, 1 November 2016
The Next Cat Fight ?
Lots of press releases lately about the expansion of the Universe not accelerating. This doesn't mean there's no dark energy (whatever that may be) continuing to drive the expansion - the expansion rate seems to be more of a constant, whereas without dark energy it should be slowing down.
Or is it ? Maybe not. According to this paper it's accelerating after all. They claim that the previous authors have done a shoddy bit of statistics on the data, ignoring selection effects at different distances and other independent evidence for the acceleration. I'm not going to comment on who's right because I'm nowhere near qualified enough to judge the statistical methods, but they conclude :
Even without external constraints, this work demonstrates that a more accurate model for the supernova analysis greatly increases the significance of acceleration. We conclude that the analysis in N16 is both incorrect in its method and unreasonable in its assumptions, leading the authors to question a result that is quite secure when addressed properly.
So there.
https://arxiv.org/abs/1610.08972
Or is it ? Maybe not. According to this paper it's accelerating after all. They claim that the previous authors have done a shoddy bit of statistics on the data, ignoring selection effects at different distances and other independent evidence for the acceleration. I'm not going to comment on who's right because I'm nowhere near qualified enough to judge the statistical methods, but they conclude :
Even without external constraints, this work demonstrates that a more accurate model for the supernova analysis greatly increases the significance of acceleration. We conclude that the analysis in N16 is both incorrect in its method and unreasonable in its assumptions, leading the authors to question a result that is quite secure when addressed properly.
So there.
https://arxiv.org/abs/1610.08972
Wednesday, 26 October 2016
The MDAR is completely normal in standard cosmology
A New Combatant Joins The Cat Fight And Tries Very Hard To Be Nice To Everyone
Well, at least this one is a respectable paper (submitted but not yet accepted) and not an angry rant.
To recap, recently it was shown that there's a very strong relation between the density of normal matter in a galaxy and its rotational speed. This has made a lot of people very angry, and was widely regarded as a bad move.
... or for those of you not following this regularly, it's a problem because the dynamics of galaxies - how fast they rotate and suchlike - should be dominated by their dark matter. Normal matter only makes up a few percent of their mass, so it shouldn't be able to affect their rotation speed much at all. That is, if you accept dark matter in the first place. The main alternative is that our understanding of gravity (or even dynamics in general) is fundamentally flawed. Modified gravity theories like MOND can explain this "mass discrepancy relation" very well without dark matter, whereas it's not obvious if the standard model can account for it.
Recently there was a paper submitted showing that actually, when you account for all the complex physics of the normal matter, yes you can. But there was a problem. That paper only used 18 simulations of galaxies which were all of similar mass, so it didn't show if this relation could also be explained for smaller galaxies as the observations show. It also didn't really refute MOND much, which also works over a huge range of masses. Unfortunately Milgrom, who came up with the idea of MOND, took the results very personally and wrote a nasty public letter pointing out the flaws with rather more force than is generally necessary.
This new paper improves things with a much larger sample of simulated galaxies, 150-200 or so which are re-simulated using varying parameters for the so-called "sub-grid physics". Essentially some aspects of the physics (like how much energy stars inject into the gas) occur on scales too small to resolve directly in the simulation, so they have to be manually calibrated. Since this calibration is uncertain, they perform simulations with a range of possible values. And their dark matter masses vary by a factor of at least 1000, so it should be good enough to address Milgrom's, err, concerns. Though I'm not sure if the baryon/dark matter ratio varies sufficiently, but I suspect it does.
What they find is that yes, again, you can reproduce this relationship just fine with standard cosmology. Varying the complex sub-grid physics doesn't make much difference - in this paper it's just a natural scaling relation rather than anything more complex. True, this doesn't rule out MOND (and this paper is much nicer in tone, stating that the possibility of MOND should be taken seriously), but it seems that this test just isn't useful to choose between MOND and the standard model.
It will be interesting to see McGaugh's response to all this, who first raised the issue with his silly claim of having discovered "a new law of nature". Now it looks increasingly that there's nothing particularly deep or profound about this observation after all.
https://arxiv.org/abs/1610.07663
Well, at least this one is a respectable paper (submitted but not yet accepted) and not an angry rant.
To recap, recently it was shown that there's a very strong relation between the density of normal matter in a galaxy and its rotational speed. This has made a lot of people very angry, and was widely regarded as a bad move.
... or for those of you not following this regularly, it's a problem because the dynamics of galaxies - how fast they rotate and suchlike - should be dominated by their dark matter. Normal matter only makes up a few percent of their mass, so it shouldn't be able to affect their rotation speed much at all. That is, if you accept dark matter in the first place. The main alternative is that our understanding of gravity (or even dynamics in general) is fundamentally flawed. Modified gravity theories like MOND can explain this "mass discrepancy relation" very well without dark matter, whereas it's not obvious if the standard model can account for it.
Recently there was a paper submitted showing that actually, when you account for all the complex physics of the normal matter, yes you can. But there was a problem. That paper only used 18 simulations of galaxies which were all of similar mass, so it didn't show if this relation could also be explained for smaller galaxies as the observations show. It also didn't really refute MOND much, which also works over a huge range of masses. Unfortunately Milgrom, who came up with the idea of MOND, took the results very personally and wrote a nasty public letter pointing out the flaws with rather more force than is generally necessary.
This new paper improves things with a much larger sample of simulated galaxies, 150-200 or so which are re-simulated using varying parameters for the so-called "sub-grid physics". Essentially some aspects of the physics (like how much energy stars inject into the gas) occur on scales too small to resolve directly in the simulation, so they have to be manually calibrated. Since this calibration is uncertain, they perform simulations with a range of possible values. And their dark matter masses vary by a factor of at least 1000, so it should be good enough to address Milgrom's, err, concerns. Though I'm not sure if the baryon/dark matter ratio varies sufficiently, but I suspect it does.
What they find is that yes, again, you can reproduce this relationship just fine with standard cosmology. Varying the complex sub-grid physics doesn't make much difference - in this paper it's just a natural scaling relation rather than anything more complex. True, this doesn't rule out MOND (and this paper is much nicer in tone, stating that the possibility of MOND should be taken seriously), but it seems that this test just isn't useful to choose between MOND and the standard model.
It will be interesting to see McGaugh's response to all this, who first raised the issue with his silly claim of having discovered "a new law of nature". Now it looks increasingly that there's nothing particularly deep or profound about this observation after all.
https://arxiv.org/abs/1610.07663
Tuesday, 25 October 2016
A gloriously angry rant about the MDAR
The Cat Fight Continues
Recently a paper by McGaugh et al. described a tight correlation between the density of normal matter in galaxies and how fast it's rotating. They claimed quite correctly that this is a challenge for standard models, which it seems (naively) predict that rotation speed depends on dark matter content. Normal matter (in standard cosmology) makes up only a small fraction (< 10% or so) of the total dark matter mass, so it can't play much of a role in setting rotation speed.
Unbeknownst to me, the McGaugh result was immediately and sharply criticised by Milgrom, the creator of Modified Newtonian Dynamics - a theory of modifying gravity as an alternative to dark matter. Unfortunately, instead of attacking some of the genuine silliness in the McGaugh paper ("We've discovered a new law of nature !" - yeah, sure, whatever) Milgrom instead vents his wrath upon the fact that McGaugh isn't supporting MOND strongly enough. Which is quite correct. The McGaugh paper is silly to play the importance of the results so strongly, but quite correct and careful to emphasise that there are different interpretations of the results.
Then there was that paper on Friday of Keller & Wadsley which claimed that this result can be explained in standard models after all. This new, umm, response by Milgrom challenges the challenges. But although this article is on astro-ph only (not submitted to any journal), it degenerates in the first line from merely being a bit dramatic (as McGaugh was) to downright unprofessional. "Keller and Wadsley (2016) have smugly suggested..."
Sigh. Milgrom has some good points, but unfortunately it's a ludicrous over-reaction to a challenging paper. "They then jump to the conclusion that ΛCDM is “fully consistent” with..." No, they don't. "And so, by further unwarranted extrapolation, they seem to imply...." Come on. You can't write, "they seem to imply" in a professional article. We've reach blog-esque ranting here, not a serious rebuttal.
However, Milgrom does have a very good point that the K&W paper only simulates 18 galaxies of similar masses, whereas the problematic relation described in McGaugh covered 153 galaxies spanning a huge range of masses. According to Milgrom, the reason the KW paper gets a good result is because it only deals with particles in a very particular acceleration regime, which is quite different to what you'd find in low-mass galaxies (MOND's predictions are more complicated - acceleration doesn't just depend on total mass). So if they included dwarf galaxies they might get a totally different result. This is a valid criticism, though it does not follow that they definitely would get a different result. Worse though, "it could be a result of various adjustments in the simulations over the years, which tended to make them look, in some restricted regards, like observed galaxies."
Ouch.
Milgrom makes a further, and in my view totally ridiculous, criticism that KW try and simulate the evolution of galaxies. Yes, he really criticises them for this, as though trying to simulate galaxy evolution were a hopeless and silly endeavour : "The simulation in question attempt to treat very complicated, haphazard, and unknowable events and processes taking place during the formation and evolution histories of these galaxies" . Oh come off it. This is true regardless of what theory of gravity you adopt - you have to make some guesses and assumptions in order to make progress !
Cat-fighting aside, I think there are some valid points here - but the sharp response to an ubpublished, un-refereed paper was just plain silly and unnecessary. We certainly haven't seen the last response to this - watch this space.
https://arxiv.org/abs/1610.07538
Recently a paper by McGaugh et al. described a tight correlation between the density of normal matter in galaxies and how fast it's rotating. They claimed quite correctly that this is a challenge for standard models, which it seems (naively) predict that rotation speed depends on dark matter content. Normal matter (in standard cosmology) makes up only a small fraction (< 10% or so) of the total dark matter mass, so it can't play much of a role in setting rotation speed.
Unbeknownst to me, the McGaugh result was immediately and sharply criticised by Milgrom, the creator of Modified Newtonian Dynamics - a theory of modifying gravity as an alternative to dark matter. Unfortunately, instead of attacking some of the genuine silliness in the McGaugh paper ("We've discovered a new law of nature !" - yeah, sure, whatever) Milgrom instead vents his wrath upon the fact that McGaugh isn't supporting MOND strongly enough. Which is quite correct. The McGaugh paper is silly to play the importance of the results so strongly, but quite correct and careful to emphasise that there are different interpretations of the results.
Then there was that paper on Friday of Keller & Wadsley which claimed that this result can be explained in standard models after all. This new, umm, response by Milgrom challenges the challenges. But although this article is on astro-ph only (not submitted to any journal), it degenerates in the first line from merely being a bit dramatic (as McGaugh was) to downright unprofessional. "Keller and Wadsley (2016) have smugly suggested..."
Sigh. Milgrom has some good points, but unfortunately it's a ludicrous over-reaction to a challenging paper. "They then jump to the conclusion that ΛCDM is “fully consistent” with..." No, they don't. "And so, by further unwarranted extrapolation, they seem to imply...." Come on. You can't write, "they seem to imply" in a professional article. We've reach blog-esque ranting here, not a serious rebuttal.
However, Milgrom does have a very good point that the K&W paper only simulates 18 galaxies of similar masses, whereas the problematic relation described in McGaugh covered 153 galaxies spanning a huge range of masses. According to Milgrom, the reason the KW paper gets a good result is because it only deals with particles in a very particular acceleration regime, which is quite different to what you'd find in low-mass galaxies (MOND's predictions are more complicated - acceleration doesn't just depend on total mass). So if they included dwarf galaxies they might get a totally different result. This is a valid criticism, though it does not follow that they definitely would get a different result. Worse though, "it could be a result of various adjustments in the simulations over the years, which tended to make them look, in some restricted regards, like observed galaxies."
Ouch.
Milgrom makes a further, and in my view totally ridiculous, criticism that KW try and simulate the evolution of galaxies. Yes, he really criticises them for this, as though trying to simulate galaxy evolution were a hopeless and silly endeavour : "The simulation in question attempt to treat very complicated, haphazard, and unknowable events and processes taking place during the formation and evolution histories of these galaxies" . Oh come off it. This is true regardless of what theory of gravity you adopt - you have to make some guesses and assumptions in order to make progress !
Cat-fighting aside, I think there are some valid points here - but the sharp response to an ubpublished, un-refereed paper was just plain silly and unnecessary. We certainly haven't seen the last response to this - watch this space.
https://arxiv.org/abs/1610.07538
Sunday, 23 October 2016
Geometrical Jiggery-Pokery
More fun with the all-sky HI data... sort of.
Recently I posted what the data looks like if you assume velocity is the same as distance. Of course it isn't really, but transforming it into true distance isn't so easy.
The data from the telescope consists of maps of the sky each one at a slightly different line-of-sight velocity. Knowing the position and velocity of each point in the map, it's possible to convert this into distance with some fairly ugly trigonometry.
There are some intrinsic limitations to this that can't be avoided. For instance, if the gas is closer to the centre of the Galaxy than the Sun, the equations give two equally valid solutions and there's no easy way to decide which is correct. So that data has to be chucked out. Another is that if you've looking directly towards or away from the Galactic centre, you don't get meaningful velocity information - we can only measure velocity along our line of sight, but at those angles gas is moving entirely across the sky except for some small random motions. So data at angles close to the centre and anti-centre needs to be thrown out too.
Then there's the problem of how to display the data. Previously I tried to convert the raw velocity cube to a distance cube by applying the equations to each pixel in the original data. So knowing position, velocity and intensity of any point gives a corresponding position, distance and intensity in the new data cube.
This creates an extra problem. Although the original data is fully sampled (that is, each map of the sky at each velocity channel is complete - every pixel has measured values), that isn't automatically the case for the output distance cube. To simplify, imagine that position x,y corresponds to i,j in the new data set. The problem is essentially that position x+1,y+1 corresponds to something like i+2,j+2 - there are gaps. You could try interpolating the missing values, but it's not so easy - and you still lose data, because in some regions in turns out that multiple points in the original coordinates correspond to the same point in the new coordinates. You need the resolution to be adaptive.
Which is where this funky geometry comes in. What we have here are a series of planes in Blender, each one corresponding to a different velocity channel. By transforming the vertices to the corresponding distance, the faces between them automatically interpolate the missing regions. The animation just overlays each successive velocity channel converted into distance.
.... or at least that's the idea. I'm really not sure if this is working correctly. The funky shape might be a consequences of the non-trivial equations, or I might have set something wrong. It's very hard to visualise what the equations look like in 3D, which is what this is supposed to help with. This requires further thought, but it's quite nice to watch (the flickering dark shadows are Blender rendering artifacts).
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