Saturday, July 28, 2012

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).

Wednesday, July 25, 2012

Be very, very afraid

Paul Krugman cannot believe the lack of terror among German politicians about the spectre of a Greek exit from the Euro. Do they really think that if Greece is forced out, Spain will not be forced to follow?

In fact the disturbing news from Germany has got most economists spooked — or at least most economists who aren't willfully blinkered. Some time ago, I noted here that Simon Wren-Lewis was holding out some hope for the survival of of the Euro, because he felt sure Eurozone officials would eventually see that hard-line moral posturing was detrimental to their own interests (apart from being wrong). Sadly, it appears not even he is so optimistic any more:
Sometimes it seems as if Germany and its supporters are like a poker player with a very weak hand, who has managed to convince all the other players that their hand is much stronger than it is. But there is a danger that you may get so good at playing this bluff, that you may stop looking at your cards and actually believe you have a strong hand. Or worse still, that although your hand is weak, you deserve to have the better cards, and therefore you do have the better cards.
The situation with German public opinion is now so dire that although he is careful not to explicitly say so, I think Wren-Lewis now agrees with Greek economist Yanis Varoufkis' assessment that Germany actually doesn't want to solve the Eurozone crisis.

Which brings us back to Krugman's take on the foolish lack of terror.

Tim Duy agrees, asking whether a panic button even exists in Europe:
I doubt we will need to wait much longer to learn the outcome of Grexit. But the devastating train that is the debt crisis keeps rolling right along, currently crashing through Spain's economy.

And make no mistake, European policymakers have learned nothing from the Greek experience. One gets the sense that policymakers think the prescription was correct, but that the patient was simply unwilling to take the medicine. Where Greece failed, Spain will succeed, or at least so it is hoped [...] Spain is doing the right thing, apparently. It's just the markets that have it all wrong [...] And in return for this bailout, Spain will be pushed further down the same path of never ending recession as Greece. Because if once you don't succeed, try, try again. European policymakers will pursue the same path because they know of no other [...]

In my view, the lack of panic is downright scary. Is Europe completely devoid of new ideas? Or is everyone simply on vacation?
Surely, you feel, we will wake up soon and learn this was all a dream? Surely somebody will remember which country's banks it was that lent the money to Greece, Spain, Ireland, Italy, Portugal et al. in the first place, and which country's banks therefore stand to lose most if they collapse? Surely someone will remember who was "the sick man of Europe" before the introduction of the Euro helped turn their economy around?

But no. The words 'face', 'spite', 'chop' and 'nose' come to mind.

Saturday, July 21, 2012

How to update your beliefs in light of new evidence

This post is the second in a series on probability and statistical inference, and follows this one, in which I asked readers a question that I had once put to applicants to Oxford in physics interviews. If you have not yet answered the question in the poll, you should click on the link above and try it first! The poll will remain open for anyone who would like to try answering the question before reading the answer below.

Monday, July 16, 2012

Things To Read, 16th July

When I first decided to start collecting together links to interesting things on the internet and putting them into one blog post per week, I was envisaging something like a less frequent version of this. Instead these posts have become something slightly different: longer, because I like to add short comments on the articles I link to; and perhaps more selective. This meant that these posts were becoming a little too much work! I also don't always find enough physics links to highlight each week.

So I have decided to embrace the change: these posts will remain a regular feature, but no longer necessarily a weekly feature. Instead I shall put them out as and when I have collected enough items I'd like to point out and briefly comment on. The title of the series will also be amended to reflect this.

Anyway, since I have already started writing something for today, I will include a few items:
  1. I was particularly interested in this little post by Julianne Dalcanton at Cosmic Variance, about the employment chances for physicists who choose to, or for whatever reason have to, leave the world of academia. The statistics — at least in the US — appear to be relatively encouraging, and somewhat better than for "lab-based" biologists or chemists. Julianne has her speculations as to why this should be so; I suppose they sound quite plausible.
    I think the other point she makes is really important too — students enrolling for physics PhD programmes really ought to be aware that the odds against them ever getting a permanent academic position equivalent to that of their advisor are very small. Say the average professor sees one student through to a PhD every two years. Over a career of 40 years, that's 20 completed PhDs, and yet when that professor retires, only one permanent faculty position becomes available. Odds like that mean that, unlike the UK government, every sensible PhD student should be aware of the need to have a Plan B. This applies also to those of us who have been lucky enough to get a foot on the ladder in the form of a post-doc job (though I don't seem to have taken my own advice yet!).
  2. Tucked away in the Guardian, I saw this report on the treatment in Pakistan of Nobel-Prize-winning particle theorist Abdus Salam, both before and after his death in 1996.
  3. Anyone who has been following the US Presidential elections will know that there has been some amount of kerfuffle recently about who was in charge of which company when. You could see this for a little perspective, or doubtless there are countless other places you could read about it. Anyway, that's not what interests me: I don't have a vote in this election, and if I did, I wouldn't need stories about Bain Capital to know that Romney is a ridiculous candidate.
    Instead, I think the significant occurrence from the last week was this quote from Barack Obama:
    [I]f you’re a head of a large private equity firm or hedge fund, your job is to make money. It’s not to create jobs. It’s not even to create a successful business – it’s to make sure that you’re maximizing returns for your investor. Now that’s appropriate. That’s part of the American way. That’s part of the system. But that doesn’t necessarily make you qualified to think about the economy as a whole ...
    Phew. At last some politician has come out and said something sensible. I would have thought it was fairly obvious that the analogy between running a country and running a business was completely wrong — after all, I doubt there is a company anywhere in the world that sells its product primarily to its own employees — but still most politicians continue to treat people like idiots. This is not restricted to the US: in Britain the analogy used by the Tories is different — that government budgets are like family budgets, complete with credit cards and tightening belts — but the underlying fallacy is basically the same (which family buys goods and services primarily from itself?). I don't know exactly what rhetorical devices politicians use in Germany, Spain, Greece and the like, but from the utter mess they have made of the Euro, one can surmise that they must be equally stupid. So one-and-a-half cheers for Obama for attempting to right that trend.

Sunday, July 15, 2012

A question of probability

In my post today, I'd like to ask readers of this blog a little question on probability that we* used a few years ago as an interview question for Oxford physics admissions.

The Oxford interview process is quite famous — or notorious, depending on your point of view — in the UK, and every year, come admissions time, newspapers run stories containing collections of "impossible" or eccentric questions that have supposedly been asked of candidates by malicious interviewers. In some newspapers the slant then given to the story is that the entire interview process is, by design or by coincidence, weighted against applicants from state schools, who are less well prepared for such shocks and are reduced to nervous wrecks.

I don't wish to enter into such a political discussion here, but in case any prospective interview candidates were to read this blog post I'd like to assure them that the interviews — at least in physics and at least in my experience — are certainly not like this. Interviewers realise that nervous applicants do not reflect their true potential, so they do not deliberately add to the tension and will in most cases attempt to create as relaxed an atmosphere as possible. They also realise that interviews, because of their highly subjective nature, are statistically not very good indicators of the true physics ability of the student. It is well-known that performance in the physics aptitude test applicants are required to take is a better predictor of their subsequent performance when at Oxford, so test results are substantially weighted up relative to interview scores when making decisions on who to admit. (You're also probably better off reading Oxford's own guide to sample interview questions than anything in the press!)

Anyway, I digress. The point of this post was the question of probability, not a discussion of admissions procedures. I thought the question was quite a nice one, but as it turned out no interviewees answered it correctly when it was first put to them, and after being given a gentle hint or two, almost all of them got to the right answer. So it was pretty useless at distinguishing between applicants and as a result not a very successful interview question. On top of that, I've also recently discovered that it is explained in great detail in a best-selling popular book on probability, so it probably won't be used again — which is why I feel it is safe to disclose it here! So here it is, slightly reworded:
You learn about the existence of some rare disease, X, which is known to affect 1 in every 10,000 people. Being a bit of a hypochondriac, you are afraid that you may have disease X, so you go to your doctor for a blood test. The doctor tells you that the test for this disease is accurate 99.9% of the time. To your horror, the test result comes back positive. What is the probability you have disease X?
I won't give the answer immediately (update: the answer is now explained here), because I'd first really like to know how readers of this blog would answer it. So I'd like to encourage everyone who reads this post to vote in the following poll -

What is the likelihood you have disease X?

Please don't be shy about voting! If you get it wrong, well, you've done no worse than some of the brightest A-level students in the UK. On the other hand, you could have the satisfaction of getting it right and displaying your knowledge to the world (the poll's completely anonymous, but still). Feel free also to comment on this post, but please don't give the answer away if you know it.

The reason that I've posted this question and the reason I'd like to know people's answers is that although it wasn't a good interview question, I think it is still a good way to get people to think about probability, and the question of how to deduce information from limited evidence. These are topics which I would like to discuss in a series of further posts over the next few weeks, so I'll use this as a starting point.

* I took part in admissions interviews between 2007 and 2010 as part of a tutoring job while finishing my doctorate. This particular question was one suggested by my (senior) colleague for use in one of those years.

Monday, July 9, 2012

LftW: 9th July

Physics links:
  • Update: Another link worth highlighting this week is a background piece on the Higgs by Steven Weinberg from the New York Review of Books, taken from the introduction to a book due to be published next month. As ever, Weinberg is clear, precise and interesting.
  • Perhaps inevitably given the momentous nature of the results announced at CERN last week, there has been much discussion about who should be awarded the Nobel Prize for (a) the discovery of the Higgs and (b) the theoretical prediction of the Higgs around 50 years ago. Of course, the existence and future discovery of the Higgs was regarded as so certain that (b) has already been a topic of much debate for several years. For those who have not already read it, Frank Close's book The Infinity Puzzle provides an excellent summary, and (somewhat surprisingly) Mark Thoma's economics blog quotes some of the relevant sections. Summarised in a sentence, the problem is that six theorists including Peter Higgs can claim to have predicted the mechanism by which the Higgs boson gives mass to elementary particles, but the Nobel can only be awarded to three at most, leaving a complex decision for the committee to make. Close has recently been reiterating his recommendations and urging haste, since Nobels cannot be awarded posthumously. Already only five of the six survive.
  • The problem of who should get the prize for (a) is perhaps even more difficult. Although it is hard to imagine anything more Nobel-worthy than the discovery of a new elementary particle, Nobel Prizes can only be awarded to individuals, not collaborations, and most commentators seem to agree that it would be hard to single out any especially deserving individuals from the excellent team efforts of ATLAS or CMS. (This has been done before, for instance when John Mather and George Smoot got the 2006 Prize for their roles in COBE, but the choice now is less clear-cut.) Peter Woit wants the rules to be changed so the prize can be awarded to both complete groups and also CERN engineers, which I suspect is unlikely to happen. He would also like the award to be made this October, which is probably also unlikely, given that the detailed papers on the discovery will not even be submitted to a journal until the end of this month. (And I would guess it is even more unlikely for a theory prize to be awarded in October as Frank Close wants, since strictly speaking it isn't yet proven that the discovered particle is the Standard Model Higgs boson. But of course mine is a relatively uninformed opinion!) 
Other links:

Wednesday, July 4, 2012

Found the Higgs, not the mermaids

Once again not a long post — in fact I was in the middle of typing a simple congratulatory message when I noticed that Rhys got there before me. The facts to take home from today's presentations can of course be found on many physics blogs: basically, a particle has been found, at a mass of around 125 GeV, it is a boson, so far it behaves as we would expect a Standard Model Higgs to behave (there are some small discrepancies which may or may not be indications of the deviations that all theorists would love to see). So, as Rhys says: congratulations to everyone, and we hope to learn more soon.

In the meantime though, I notice (h/t Rob) that the most popular science articles on the BBC website at the moment are the following:
Higgs discovery at CERN and mermaid non-discovery in the US
We've found the Higgs, but not the mermaids.
Which suggests that although science marches on, science education still has some way to go.

Tuesday, July 3, 2012

What is the Higgs, and why is tomorrow's announcement important?

Although the title suggests this will be a long, detailed post full of explanations of particle physics, it actually won't. This is partly because I haven't the time or inspiration to write one, but mostly because it has been done much better elsewhere. Instead I'd like to draw your attention to a few excellent background pieces so that you can be well-prepared for what promises to be a very important press conference tomorrow (indeed Peter Woit now suggests that ATLAS and CMS will each present nearly-5-sigma evidence).

The first of these is a new post by Shaun at partner blog The Trenches of Discovery, which provides a nice layman-level overview of why discovering the Higgs would be cool, but theorists hope it isn't just the Higgs. A similar theme was discussed by Jester (Adam Falkowski) at Résonaances. He has also got a series of countdown posts, each explaining some aspect of Higgs physics, but these posts are all at a more technical level than Shaun's. At Cosmic Variance, John Conway has reprised an old Higgs overview post (from 2007) which is again aimed at the non-expert. There are other pieces I won't link to now, because these cover most of the bases for anyone interested.

Monday, July 2, 2012

LftW: 2nd July

Physics links:
  • The important physics event of the next week will be the CERN press conference on the Higgs search analyses coming up on Wednesday at 9 am CEST. Peter Woit provides a preview, summarising what we might expect to hear. At Quantum Diaries, Aidan Randle-Conde explains why we might not want to combine the significances of detection obtained from ATLAS and CMS in order to obtain the magical "5 sigma" standard for detection. The official results probably won't provide a combined significance for this reason, but doubtless various bloggers and others will do so.
  • On the day itself, this blog will not be the best place to get your news. Instead, you might wish to go here, or to one of the other links down the right-hand panel.
  • On Friday, there was an intriguing paper uploaded to the arXiv, proposing a new type of dark matter detector made out of gold foils and single-stranded DNA. I don't know what to make of this paper: it sounds a little crazy, but then I don't know much about the molecular biology of using ssDNA. Two of the physicist authors — Katherine Freese and David Spergel — are well-known, serious scientists. I presume the other authors are biologists.
  • Peter Coles put up a nice set of "order-of-magnitude" physics problems to have a go at, including for instance "How much brighter is sunlight than moonlight?"
Other links:
Victor Keegan's Guardian report on Beatle myths in 1969
Victor Keegan's Guardian report on mysterious phone calls from the US ...