One year on

It has been a long month-and-a-bit since I last had the time to write a proper post here. Primarily this is because I am not very good at doing more than one thing at a time – at least while attempting to do those things properly – and I have been working on some real research papers, which I thought I should try to do properly. As a result science communication, and blogging in general, has had to wait. But I will get back in the swing of things very soon: there are some interesting new results, some interesting rehashes of old arguments about inflation, and one of my own papers that I will write about over the next couple of weeks.

One of the many things that I omitted to mention during this little break was the fact that Blank On The Map had its first anniversary a couple of weeks ago. All in all, I would say it has been quite a satisfying year of blogging, and, at least relative to my prior expectations, a reasonably successful one too. Blogger doesn't provide me with many detailed statistics, but it does tell me that despite the low recent rate of new postings, there have been roughly 23,000 clicks over the last twelve months. A sizeable portion of of this traffic came from one link on Peter Woit's blog (boy he must have a huge number of readers!) – though the majority appear to arrive via Google search, either by accident or design.

Anyway, to all those who have arrived here at some point over the last year, welcome! I hope you found what you were looking for, and enjoyed what you read. This explains what this blog is about. In case you haven't worked your way through the archives, here is a short selection of some highlights from the last year:

• Steven Weinberg and the 'Crisis of Big Science'
• An explanation of a dark matter controversy
• A question of probability
• The dog who climbed a mountain
• The Structure of a Scientific Revolution
• Explaining Planck by analogy

I should also use this post to try to get some feedback from (all three) regular readers. Do you think I should post more often? Less often? More posts about cosmology and fewer about mountaineering and other stuff in general? Or the other way round? Let me know through the comments box. Constructive criticism of the writing style or any other aspect of this blog will also be well received, though I can't promise to change ...

Unnecessary spin

A few people have asked me why I have not blogged about the recent announcement about, and publication of, results from the Alpha Magnetic Spectrometer, which were widely touted as a possible breakthrough in the search for dark matter.

The reason I have not is simply that there are many other better informed commenters who have already done so. In case you have not yet read these accounts, you could do worse than going to Résonaances, or Ethan Siegel, or Stuart Clark in the Guardian, who provide commentary at different levels of technical detail. The simple short summary would be: AMS has not provided evidence about the nature of dark matter, nor is it likely to do so in the near future. The dramatic claims to the contrary are spin, pure and simple. Siegel in fact goes so far as to say "calling it misleading is generous, because I personally believe it is deceitful" (emphasis his own).

So I'm not going to make any more comments about that.

However, since this incident brought it up again, I do want to comment on a related piece of annoying spin, which is the habit of physicists in the business of communicating science to the public of making vastly exaggerated claims about the possible practical applications of fundamental physics. The example that caught my attention this week occurred when Maggie Aderin-Pocock – who is apparently a space science research fellow at UCL – appeared on the BBC's Today programme on Thursday to discuss the significance of the AMS findings.

At one point in the discussion the interviewer John Humphrys asked a slightly tricky question: I understand that dark matter and dark energy are endlessly fascinating, he said, and that learning about the composition of the universe is very exciting. But what practical benefits might it bring? The answer Aderin-Pocock gave was that if we understood what dark matter and dark energy were, we might be able to use them to supply ourselves with energy – dark matter as a fuel source.

I'm sorry, but that is just rubbish.

Unfortunately, it's the kind of rubbish that is increasingly commonly voiced by scientists. You may argue that Aderin-Pocock was simply commenting on something she didn't understand – and if you  listen to the whole interview (available here for a few days; skip to the segment between 1h 23m and 1h 26m), including the cringe-worthy suggestion that dark matter and dark energy are the same thing really (because E=mc², apparently), it's hard to avoid that conclusion. But a few weeks ago I thought I heard Andrew Pontzen and Tom Whyntie suggest something similar about the Higgs boson on BBC Radio 5 (unfortunately this episode is no longer on the iPlayer so I can't check the exact words they used). And here is Jon Butterworth seeming to suggest (in the midst of an otherwise reasonable piece) that the Higgs could be used to power interstellar travel ...

Why do people feel the need to do this? It's patently rubbish, and they know better. Do we as a scientific community feel that continued public support of science is so important that we should mislead or deceive the public in order to guarantee our future access to it? Do we feel that there is no convincing honest case to be made instead? Or are we just too lazy to make the honest case, and so rely on the catchy but inaccurate soundbite instead?

I think the sensible answer to the question John Humphrys posed would go something like this. Discovering the nature dark matter is a fascinating and exciting adventure. Knowing the answer will almost certainly have no practical applications whatsoever. However, on the journey to the answer we will have to develop new technologies and equipment (made of ordinary matter!) which may serendipitously turn out to have spin-off applications that we cannot yet foresee. More importantly, the very fact that the search is fascinating is part of what draws talented and creative young minds to physics – indeed to science – in the first place, from where they go on to enrich our society in a myriad different ways, none of which may later be connected to dark matter at all. I tried to make this case at greater length here in the early days of this blog.

It's a more subtle argument than just throwing empty phrases about "energy source" around, and it might be hard to reduce to a sound-byte. But it is justifiable, and also honest. And since science is after all about careful argumentation, let's have less spin all round please.

What Planck has seen

Update at 16:30 CET: I've now had a chance to listen to the main science briefing, and also to glance at some of the scientific papers released today, albeit very briefly. So here are a few more thoughts, though in actual fact it will take quite some time for cosmologists to fully assess the Planck results.

The first thing to say – and it's something easy to forget to say – is just what a wonderful achievement it is to send a satellite carrying two such precise instruments up into space, station it at L2, cool the instruments to a tenth of a degree above absolute zero with a fluctuations of less than one part in a million about that, spin the satellite once per minute, scan the whole sky in 9 different frequency bands, subtract all the messy foreground radiation from our own galaxy and even our solar system, all to obtain this perfect image of the universe as it was nearly 14 billion years ago:

The CMB sky according to Planck.

So congratulations and thanks to the Planck team!

Now I said all that first up because I don't want to now sound churlish when I say that overall the results are a little disappointing for cosmologists. This is because, as I noted earlier in the day, there isn't much by way of exciting new results to challenge our current model of the universe. And of course physicists are more excited by evidence that what they have hitherto believed was wrong than by evidence that it continues to appear to be right.

There are however still some results that will be of interest, and where I think you can expect to see a fair amount of debate and new research in the near future.

Firstly, as I pointed out earlier, Planck sees the same large scale anomalies as WMAP, thus confirming that they are real rather than artifacts of some systematic error or foreground contamination (I believe Planck even account for possible contamination from our own solar system, which WMAP didn't do). These anomalies include not enough power on large angular scales ($\ell\leq30$), an asymmetry between the power in two hemispheres, a colder-than-expected large cold spot, and so on.

The problem with these anomalies is that they lie in the grey zone between being not particularly unusual and being definitely something to worry about. Roughly speaking, they're unlikely at around a 1% level. This means that how seriously you take them depends a lot on your personal prejudices priors. One school of thought – let's call it the "North American school" – tends to downplay the importance of anomalies and question the robustness of the statistical methods by which they were analysed. The other – shall we say "European" – school tends instead to play them up a bit: to highlight the differences with theory and to stress the importance of further investigation. Neither approach is wrong, because as I said this is a grey area. But the Planck team, for what it's worth, seem to be in the "European" camp.

The second surprise is the change in the best-fit values for the parameters of the simplest $\Lambda$CDM model. In particular the Hubble parameter is lower than WMAP's, which was already getting a bit low compared to distance-ladder measurements from supernovae. This will be a cause for concern for the people working on distance-ladder measurements, and potentially something interesting for inventive theorists.

And finally, something close to my own heart. A few days ago I wrote a post about the discrepancy in the integrated Sachs-Wolfe signal seen from very rare structures, and pointed out that this effect had now been confirmed in two independent measurements. Almost immediately I had to change that statement, because one of those independent measurements had been partially retracted.

Well, the Planck team have been on the case (here, paper XIX), and have now filled that gap with a second independent measurement (as well as re-confirming the first one). The effect is definitely there to be seen, and it is still discrepant with $\Lambda$CDM theory (though I'll need to read the paper in more detail before quantifying that statement).

So there's a ray of hope for something exciting.

 
11:30 am CET: Well, ESA's first press conference to announce the cosmological results from Planck has just concluded. The full scientific papers will be released in about an hour, and there will be a proper technical briefing on the results in the afternoon (this first announcement was aimed primarily at the media). However, here is a very quick summary of what I gathered is going to be presented:

• The standard Lambda Cold Dark Matter Model continues to be a good fit to CMB data
• However, the best fit parameters have changed: in particular, Planck indicates slightly more dark matter and ordinary (baryonic) matter than WMAP did, and slightly less dark energy. (This is possibly not a very fair comparison – my hunch is that the Planck values are obtained from Planck data alone, whereas the "WMAP values" that were quoted were actually the best fit to WMAP plus additional (non-CMB) datasets.)
• The value of the Hubble parameter has decreased a bit, to around 67 km/s/Mpc. Given the error bars this is actually getting a bit far away from the value measured from supernovae, whch is around 74 km/s/Mpc. I think the quoted error bars on the measurement from supernovae are underestimated.  
• The Planck value of the spectral tilt is a bit smaller than, but consistent with, what WMAP found.
• There is no evidence for extra neutrino-like species.
• There is no evidence for non-zero neutrino masses.
• There is no evidence for non-Gaussianity.
• There is no evidence for deviations from a simple power-law form of the primordial power spectrum.
• No polarisation data, and therefore no evidence of gravitational waves or their absence, for around another year.
• There is evidence for anomalies in the large-scale power, consistent with what was seen in WMAP. We'll have to wait and see how statistically significant this is – the general response to the anomalies WMAP saw could be summarised as "interesting, but inconclusive"; I don't think Planck is going to do a lot better than this (and the bigging-up of it in the press conference might have had more to do with the lack of other truly exciting discoveries), but I'd love to be surprised!

That's about all I got out of the media briefing. Obviously we are all waiting for more details this afternoon! 

Things to Read, 8th September

I have been neglecting this series over the summer, so there are rather a lot of things to highlight today.

Science items:

• The most interesting piece of physics news over the last few months has been that the wealthy Russian investor and physics fan, Yuri Milner, decided to award a 'Fundamental Physics Prize' to 9 theorists he chose himself. The amount of the award is a staggering $3 million each, wired overnight into the physicist's bank accounts — as many people have pointed out, this makes the prize worth far far more than the Nobel Prize. Suddenly being a physicist almost appears to be a lucrative career choice. The lucky physicists were Nima Arkani-Hamed, Alan Guth, Alexei Kitaev, Maxim Kontsevich, Andrei Linde, Juan Maldacena, Nathan Seiberg, Ashoke Sen and Ed Witten. All big names in theoretical physics.
• Unsurprisingly, the award of this prize generated a lot of debate. For one thing, it is a huge amount of money. For another, the prizes were awarded basically on the whim of one man, who is not a physicist himself. But perhaps the most controversial thing was reported in the New York Times:
  

  Unlike the Nobel in physics, the Fundamental Physics Prize can be awarded to scientists whose ideas have not yet been verified by experiments, which often occurs decades later.

  This was picked up on by Peter Woit, who is of course well-known for his dislike of some of the work on string theory that the said physicists are famous for, and was highly critical of the prize, including in an article for an Italian newspaper (English transcript from his blog). I guess most physicists would share his unease with the prize, if perhaps not with string theory itself. It was quite amusing to read Matt Strassler finding himself in a position of agreement with Woit but managing to attack him nevertheless (I get the feeling he really dislikes Woit).
• Motivated by this discussion, Strassler did put up a very interesting and nuanced personal defence of string theory. Whether you have an opinion on 'The String Wars' or not, you will probably have heard strong criticisms of string theory. This piece will provide some balance.
• Among the other worthwhile physics discussions were two guest posts at Cosmic Variance: by Terry Rudolph and Douglas Finkbeiner. Both discuss recent research work (in quantum mechanics and searches for dark matter, respectively) and both include interesting little insights into the world of academic publishing.
• Outside physics, I saw a piece by Dr. Dave Hone in the Guardian science section that includes the lines:

  [...] we have dinosaurs everywhere around us. We have dinosaurs nesting in trees in our gardens, tiny dinosaurs that can hover and fly backwards and feed on nectar, aquatic dinosaurs that live in Antarctica. There are dinosaurs that we eat, we have dinosaurs that can circle the globe without landing, intelligent and puzzle-solving dinosaurs, tall and flightless dinosaurs that can sprint at over 40 miles and hour, and brightly coloured and beautiful dinosaurs almost too numerous to mention.

Other items:

• Of course the big news over the summer has been the Olympics. It's been impossible to miss the outpourings of national pride in British newspapers at Team GB's medal tally and I have heard also of despondency in countries such as Russia and Australia. But what is the benefit to a nation from this arms race for medals? This was discussed, rather provocatively perhaps given the timing, by Ian Johnson in the New York Review of Books. 
• There's been a lot of discussion in the US about the Republican presidential ticket, and in the UK about the dire state of the national economy, now in a longer slump than during the Great Depression. Paul Krugman made the obvious connection, and labelled Chancellor of the Exchequer George Osborne "Britain's Paul Ryan." That post includes a graph that should be shown to everyone who still believes austerity in the recession is the answer to anything:
  
  
  
  One could forgive Krugman for feeling rather frustrated (and perhaps a little smug), because this is pretty much exactly what he predicted back in 2010:
  

  The British government’s plan is bold, say the pundits — and so it is. But it boldly goes in exactly the wrong direction.

  See also here.
• Of course some people might remember the 20 "leading economists" who wrote an open letter to The Sunday Times supporting George Osborne's fiscal plans back before the 2010 election. Well, some time ago the New Statesman had the bright idea to go back and ask them if they still stuck by their advice: 9 of the 20 had changed their minds, 10 refused to comment, and only one still agreed with himself.
• You might wonder what a poor politician is to do: if you have only a degree in History and an ideology as substitutes for genuine competence, you naturally rely on the advice of professional macroeconomists. But when the economists disagree with each other, which ones should you listen to? Jonathan Portes had a post laying out some sensible criteria for judging who to take seriously. Unsurprisingly, people like Krugman, Simon Wren-Lewis and Martin Wolf passed the test, but none of the Sunday Times economists did. Portes notes that not all those who pass his test always agree with each other — but he still always takes them seriously.
• The New York Review of Books carries a review of two books on the current global and American economic mess by Paul Krugman (End This Depression Now!) and Joseph Stiglitz (The Price of Inequality: How Today's Divided Society Endangers Our Future). What particularly interested me here was learning just how radical Stiglitz appears to be.
• Incidentally, for those who were interested in the Niall Ferguson episode featured here, John Cassidy in the New Yorker has a longer look at the arguments, and comes to the same conclusions: Ferguson is a lightweight who is being repeatedly knocked to the canvas, and this "isn't a fair fight".
• And finally, since I'd like to end on an uplifting note, here's a video to cheer us all up.

Things to Read, 28th July

Physics items:

• New results are in from the dark matter search at the XENON100 detector in Gran Sasso in Italy. See here for technical slides, or read the summaries at Quantum Diaries or Cosmic Variance. Basically, they see no dark matter events above the background expectation, so the exclusion limits on WIMP mass and cross-section are extended. As Sean Carroll points out, the results appear to be in some tension with some other experiments, but these things depend on theoretical assumptions about the nature of dark matter.
• In the Guardian, Jon Butterworth muses about the 'impact' of the discovery of the Higgs, and on the usefulness of 'impact' in general as a guide for deciding what scientific research to fund. There are some worthwhile points there, especially about who should get to decide which science has an 'impact' and which not. But I felt on some issues the piece was rather confused — he first seems to suggest that "a sense of progress" and the satisfaction of simply "adding to the body of human knowledge" are sufficient justification for funding fundamental research that may have no other forseeable benefit, but later says he disagrees with the statement that "the acquisition of knowledge is somehow morally or intellectually superior to the application or dissemination of knowledge". So which is it?
  I wrote about my own views on the justification for funding science research that has no obvious economic, medical or social payoff here. I do think it is justifiable, even if one can safely predict that there will never be any direct benefits from such research (serendipitous spin-offs, like the common examples of the internet or MRI, are a separate issue, but cannot be guaranteed). So it annoys me to see people constantly trying to justify studying the Higgs boson in terms of what hypothetical technological advances it might bring. Face it, there won't be any — if you don't believe me, here is Steven Weinberg saying much the same (among other interesting things!), or click here to see just how hard it is to come up with any remotely plausible technological speculations consistent with known physics.
  The point is that there already exist good enough reasons for funding fundamental research, so let's leave out all the rubbish about Higgs-powered spaceflight and so on, shall we?
• Readers may have already seen elsewhere the story of the physicist Paul Frampton, who has been in an Argentine jail for several months, facing charges of drug smuggling. It's a sad and frankly incredible story; I see (via Peter Woit) that Frampton expects he might be released soon (though he's been wrong about this before).

Other items:

• There is a fantastic super-slow-motion video of a lightning strike, shot at 7207 frames per second, available here, with a nice little explanation of the mechanism of the strike. I'd highly recommend it!
• A Canadian wonders whether the Euro is worth saving at all.
• Is there a magic button for the UK government to press? Do they want to press it?
• On a more cheerful note, some time ago Peter Coles posted Patrick Barrington's lovely comic poem I Had A Hippopotamus. It begins like this:

  I had a hippopotamus; I kept him in a shed
  And fed him upon vitamins and vegetable bread.
  I made him my companion on many cheery walks,
  And had his portrait done by a celebrity in chalks.
  
  His charming eccentricities were known on every side.
  The creature’s popularity was wonderfully wide.
  He frolicked with the Rector in a dozen friendly tussles,
  Who could not but remark on his hippopotamuscles.
  
  [...]

  Barrington's best known poem The Diplomatic Platypus is also great fun (and has a strangely similar theme).

An explanation of the recent dark matter controversy

About two weeks ago, I mentioned a recently published paper by Chilean authors Moni Bidin et al., claiming to have found no evidence for dark matter around our local neighbourhood in the Milky Way. Very soon afterwards, I pointed out a new pre-print by Bovy and Tremaine that rebutted this claim. Although I suppose I was fairly quickly on the scene, I wasn't particularly happy with the way I had reported this argument: just mentioning that some people disagree with each other without any explanation of the reasons is a bit closer to mere journalism than I was intending.

Since then, there have been several blog posts on this issue elsewhere — see Résonaances, Peter Coles, Matt Strassler and Sean Carroll among others — but to be honest I didn't think they actually did much more than report that people disagreed with each other either (although many of them did add some sociological comments). Which is fine as far as it goes, but if you were looking for someone to explain the science to you, you might have been disappointed. Jon Butterworth at least made a commendable effort in his Guardian blog, but he was perhaps limited by space and an inability to include any mathematics. In the end he simply said that he believed the Bovy and Tremaine result because Peter Coles believed it (and Peter Coles essentially told us to believe it because Scott Tremaine is an acknowledged world expert in galactic dynamics). Which is all very good and probably correct, but not very enlightening!¹

So eventually I've decided to fill this gap in the market myself: this post will attempt to summarise and explain both papers to a non-expert (i.e. anyone who doesn't actually work in the field of galactic dynamics). A major caveat before I start: I don't work in galactic dynamics either. I don't own, and had never read, the main reference work on this subject (by Binney and Tremaine; you see why people might trust Tremaine to be right on this one!). In preparation for writing this post I borrowed a copy and read a small amount of it — enough to feel I understood what was going on — but even so much of what I am about to write might be over-simplified, misrepresented or simply wrong. If you happen to spot any mistakes, please let me know.

Now that we've got that out of the way, let's start.

Links for the week: 20th May

I meant to put this out yesterday, but the supernova post took a bit longer to write than I was hoping. Anyway, here's a list of interesting links.

Physics links:

• Last week I linked to a paper by Moni Bidin, Carraro, Mendez and Smith that claimed to have detected no evidence for dark matter affecting the kinematics of stars in the solar neighbourhood. I mentioned that this was not without controversy, and indeed this morning there was a new preprint by Bovy and Tremaine on the arXiv, who claim the Moni Bidin et al result is due to a key assumption that is not supported by the data. I haven't had time to read the paper yet, so I'll just quote from the abstract:

"We show that this result is incorrect and that it arises from the invalid assumption that the mean azimuthal velocity of the stellar tracers is independent of Galactocentric radius at all heights; the correct assumption -- that is, the one supported by data -- is that the circular speed is independent of radius in the mid-plane."

• Suppose you have three upturned cups, and you are 90% certain that there is a ball under one of them. You turn two of them over and find no ball — how confident are you that the ball is under the third cup? Philip Gibbs gives a nice little argument illustrating Bayes' theorem, and uses it to argue that we shouldn't give up on SUSY yet.

• At Cross Sections, Rhys demonstrates that although neutrinos don't travel faster than light, they don't go a whole lot slower either.
• Last week would have been Richard Feynman's 94th birthday. Quantum Diaries carried a nice birthday tribute, and here's another, featuring a video of the great man himself.

Other links:

• The Guardian carried a pretty shocking report, called The wrong Carlos: how Texas sent an innocent man to his death.
• In the New York Review of Books, Jared Diamond reviews a new book by Acemoglu and Robinson on what makes countries rich or poor. Excellent reading.
• I recently discovered Simon Wren-Lewis's economics blog Mainly Macro, which I can highly recommend. Wren-Lewis is a professor at Oxford, in fact at my old college, Merton (though that isn't why I'm recommending his blog, and I don't think I ever even met him while I was there). Anyway, he asks Is it all Gordon Brown's fault? He also has several other interesting and well-argued pieces on economic policy here, here, here and here.
• Back in the Guardian, George Monbiot on more myths about marriage.

Links for the week - dark matter special

A longer blog posting should ready by the weekend, but is proving a little harder to write than I had hoped. In the meantime, here is a collection of interesting things to read elsewhere. I will make this sort of a roundup of worthwhile links a weekly feature on this blog, though it will make more sense to put it out at the weekend next time. Anyway, here you go:

Physics links:

• Dark matter detection experiments have been in the news a lot recently. A couple of pre-prints have claimed to have seen some tentative evidence for a dark matter annihilation signal in gamma-ray data from the Large Area Telescope on the Fermi satellite, that somehow wasn't seen by the Fermi guys themselves. Matt Strassler discusses the first of these papers here. Rhys provides a nice short summary of both; you may also want to read a more bombastic discussion on Lubos Motl's blog.
• The Cryogenic Dark Matter Search (CDMS) detection experiment earlier this year found no evidence for an annual modulation of dark matter interaction events in its detector, apparently contradicting earlier experiments DAMA and COGENT. A new pre-print from two members of COGENT claims CDMS mis-analysed their own data and there isn't a contradiction. (I'm not sure what to make of this: the argument seems pretty straightforward but I'm no expert so I might be missing some elementary things. Comments welcome!)
• To make the story murkier still, this paper accepted by the Astrophysical Journal claims to find no evidence for dark matter in the solar neighbourhood based on the dynamics of stars in our galaxy, which would presumably rule out the possibility of direct detection. There are a number of caveats, so caution is advised: see here and Matt Strassler's post above. But then this paper, accompanied by this press release, makes an even more inflammatory claim about the non-existence of dark matter. Peter Coles provides a sceptical review (and entertaining arguments in the comments section!).
• In case you are now thoroughly confused by the status of evidence for dark matter, Sean Carroll at Cosmic Variance gives us the transcript of a debate that sums up the main cosmological issues.

Phew, what a lot of dark matter. I realise some of the links above are not very recent — this blog is new and has some catching up to do! Now for other stuff.

Other links:

• In the Guardian, Barney Ronay has a brilliant piece recalling an inspiring Olympic moment: Michael Johnson breaking the 200 m world record at Atlanta '96. If, like me, you watched the race at the time, you will have it forever seared in your memory. If not, here's a video:

• Jonathan Portes uses charts and figures to illustrate why the UK government's economic policy is the opposite of sensible. See also here.
• Paul Krugman gets zapped by evil aliens.
• Peter Woit reviews a philosophical book on physics, and gives it a thumbs up. 
• Gary Wills on The Myth of Marriage.
• Private Eye lists some of the things Rupert Murdoch might have forgotten during his testimony to the Leveson inquiry.