Antimatter

Today was biology day, beginning with 2 talks by Pulitzer-prize winning science historian Ed Larson: ‘The Reception of Darwinism’ and ‘Darwinism, Eugenics and Religion’ . I won’t say much about the first (see the video here), except how refreshing it is to hear a science historian who carefully distinguishes between evolution, general modification, natural selection and neo -Darwinism from the very start. There was also a very nice discussion of the initial problems with the theory, e.g. the age of the earth according to Kelvin’s calculations, the precise mechanism of natural selection, the absence of early fossils and the gaps in the record…

The second talk was quite shocking, as Prof Larson detailed how the work of Francis Galton and others quickly led to the dominance of eugenics over theories such as ‘soft’ heredity and ‘blended heredity’ – the result was the emergence of repressive legislation on reproduction for the mentally deficient (segregation and sterilization) throughout northern Europe and the U.S.
Thankfully, the idea went out of fashion almost as quickly as it appeared, partly because of the horrors of Nazi Germany, and partly because of the emergence of scientific evidence that the model was deeply flawed.

Denis Alexander, the director of the Faraday Institute, then gave a talk on ‘God and Memetics’, which consisited of an analysis of Dawkin’s theory of memes, and a discussion of the Dawkins description of religion as a ‘virus’. This was always going to be a lively talk and so it was. Dr Alexander had a field day dissecting the ‘virus’ theory in analytic terms (your humble correspondent pointed out at question time this might be a little unfair, as Dawkins probably uses the term in a metaphorical sense). More seriously, Denis also dissected the Dawkins ‘meme’ theory unmercifully, which I’ve seen a few biologists do recently. That said, he was very complimentary of many of Dawkin’s other ideas…more tolerant than vice versa anyway!

Phew! Quite a day. Oxford historian Peter Harrison kicked off with two excellent talks, ‘Religion and the Rise of Science’, followed by ‘The Fall of Man and the Foundations of Science’. I can’t do justice to either in a brief post, but Peter’s basic thesis is that, historically speaking, religion actually facilitated the rise of science, essentially by providing the stability it needed to flourish.

The first talk broke this idea down into areas such as

– social legitimacy for scientific enquiry

– presuppositions about nature (natural laws etc)

– motivation of discovery

– criteria for choosing between different theories etc.

He contrasted the rise of science in the west with that in China and the Islamic world, pointing out that the established Church gave legs to early scientific discovery.

The third talk dealt with a rather different encounter between science and religion – a superb overview of the Galileo affair by Prof Ernan McMullin of Notre Dame. Ernan had many insights I had not heard before – in particular, the role of the reformists. He started with a simple summary of Galileo’s telescopic findings, and then explained the context of the warning in 1616. Galileo’s timing was pretty terrible, as the rise of Luther and Calvin had by then forced a revised literal interpretation of the Bible throughout the Church – not the time for supporting the Copernican universe! Another point frequently overlooked is that the Church was not rejecting mainstream science – at the time, Galileo’s support for the Copernican was pretty way out there!

Just as I had always understood, the1633 trial itself consisted of a simple question – whether or not Galileo had supported a doctrine that contradicted a literal interpretation of Scripture – which was always going to give a positive result. Given the hegemony of he bible at the time, it could be said that he got off likely.

At question time, I made the comment that this is exactly what worries most people about the trial – the Church were simply not interested in the veracity of the claim, but simply whether it contradicted their precious doctrine…not the way to find out about the world…

Ernan also gave a great answer to the perennial question of why Galileo did not quote Kepler in his defence – because Kepler was a Lutherian! Of course! This would hardly be a source the Church wanted to hear from..

Ernan’s book on the Galileo affair received rave reviews

After the talk, we got a ‘science tour’ of Cambridge, concentrating on the colleges where famous science had been done. Hugely impressive tradition, from Trinity (Newton, Sedgewick, Darwin etc), St John’s (Dirac), Gonville and Caius (Stephen Hawking) to the Cavendish (Thompson, Rutherford, Cockroft, Walton etc). What a legacy…

The Cavendish

And there I was moaning at having to leave the surf for a conference at Cambridge

In fact, Cambridge is fabulous, a lovely town. Having arrived by coach from Stansted, I decided to walk to the college (St Edmund’s) from the town centre. Most impressed to see all those famous colleges right in the centre – St John’s, Jesus, Magdalane, Trinity etc. The colleges give the town a lovely student atmosphere, great buzz and bicycles everywhere. I like the contrast between the beautiful ancient college buildings and the modern shops on the high street too, quite nice. It’s not at all a stuffy town either, tons of foreigners and tourists about.

St Edmund’s is obviously one of the newer colleges, but very nice. One big difference with Trinity College Dublin is that the rooms are lovely modern rooms, not 400 years old!

We’ve just had dinner -I’d love an afterdinner walk, but I’d better get swotting for Peter Harrison’s talk on religion and the rise of science tomorrow morning..

St John’s College

Typical. On my last day in Dingle, Co. Kerry, the surf was up at last -just as I was leaving for Cambridge.

Nothing like it said on the radio (9 ft waves?- more like 2 ft) – but a nice clean wave at Inch all the same, after a week of poor surf. Plus the sun came out to play. It’s hard to beat, when you get both good surf and sun in the west of Ireland – a rare combination.I had a great last day.

The forecast is a nice big swell for the whole week. Meanwhile yours truly is off to a week long conference on science and religion at Cambridge University. Seemed like a good idea at the time.

Sigh. Not too many waves over at Cambridge, I imagine.

Last wave at Inch

There’s a very interesting conference going on at Lake Constance (der Bodensee) this week, the Nobel Laureate Meeting in Lindau. There are a whole bunch of talks by Nobel laureates on diverse aspects of science, with several excellent talks on physics. The talks can be viewed on-line here.

For those interested in particle physics, there was a panel session devoted to expectations for the LHC experiments at CERN. I got these links from Peter Woit’s weblog NOT EVEN WRONG, and Peter has a discussion of the LHC session on his blog.

As regards the online Lindau lectures, the best I have found so far is David Gross’s talk on the future of particle physics (here). I just sat through the talk in its entirety, absolutely excellent. He gives a very good overview of particle physics, the Standard Model and the concept of supersymmetry. I particularly enjoyed his ‘big three’ reasons for SUSY, and his view of difficulties in detection at LHC. He predicts definite observation of a Higgs particle, and says he has taken bets that supersymmetry will be seen, at 50-50 odds. I wonder who his bet was taken with….

Official pic from Lindau website – is that E.? No, it’s Schweitzer

This evening, I’m looking forward to taking notes from ‘The Development of Particle Physics’ by Veltman, and tomorrow I think I’ll settle down with ‘The Beginning and Development of the Universe’ by George Smoot.

What a find!

Update

I’ve just sat through Martin Veltman’s talk. It is also very good, though he takes a totally different approach to Gross. Instead of a history of particle physics, it’s really a history of accelerator physics. Of course, some of the story of particle physics emerges naturally from the experimental narrative, but not as well as in Gross’s case (mental note for teaching – Ed).

That said, there are some great anecdotes. Almost the first physicist to be credited is the Irish priest Nicholas Callan, who developed the first high voltage transformer. I knew this, but I didn’t know Callan tested his instrument on hapless students until he was ordered to switch to turkeys! Veltman then goes on to the Rhumkoff transformer and its use by Roentgen in the discovery of X-rays. He descibes the discovery of radioactivity and the nuclear experiments of Rutherford as the true beginning of particle physics. Another Irishman, Walton, gets great credit for the invention of the Cockroft-Walton tube, and its use even in today’s machines is described.

There is a nice description of the role of cosmic rays, and the next generation of accelerators, including the development of the klystron, the synchrotron and finally the storage ring. Overall, it’s a very interesting talk for anyone in particle physics, if less so for non-professionals.

The end of the talk contains some interesting comments – Veltman points out that we are ending the end of an era, as accelerators reach circumferences in 10s of km. As the energy is determined by circumference, it’s hard to see how we’re going to increase energy further using this technology….

All the more reason to hope for interesting results at CERN

Update II

I sat through George Smoot’s talk this morning. Entitled ‘ The beginning and development of the universe’, it promised a lot more than it delivered. This was definitely what I call a type II lecture – everything was probably there somewhere, but not in any order one could make much sense of.

Smoot mentions the acceleration of the universe early on, without any discussion of the universe expansion. or Hubble’s law. Similarily, he launches into a description of measurements of the cosmic microwave background without giving any explanation of its importance as a snapshot of the early universe. Finally, while there was plenty of talk of both the COBE and WMAP satellite experiments, there is no mention of the ‘why’ – i.e. the advantages of satellite measurements over ground-based observation.

In fact, this talk was strangely reminiscent of a talk given by Smoot’s co-laureate John Mather at Trinity College Dublin last year. There should be a law – if you’re going to give a public talk about your area (cosmology), you need to spend a few minutes on the basics – univ. expansion, nucleosynthesis, backgound radiation and inflation models. That’s hat I think anyway.

I’m fairly sure any members of the audience not familiar with BB theory left that lecture no wiser than before…

The success of the unification of the weak- and electromagnetic interactions (see SM post below) soon led to attempts to extend the program to include the strong interaction, i.e. a search for one unified scheme that could describe all three non-gravitational forces (known as Grand Unified Theory) .

However, the GUT program soon ran into serious trouble, with a clutch of ‘no-go’ theorems from mathematicians such as McGlynn, O’Raifeartaigh, Coleman and Mandula showing that such unification could not be achieved using similar gauge methods to that of the electro-weak program. In response, a dramatic new type of symmetry was proposed in the 1970s.

The theory of supersymmetry was a new type of gauge symmetry, and is called ‘super’ in the sense of an ultimate gauge symmetry. Supersymmety (SUSY) supposes a deep connection between two classes of particles that had previously thought to be unrelated – the particles that make up matter (quarks and leptons) and the particles that act as ‘force carriers’ (photons, W and Z bosons ). A very significant difference between the two sets is their spin – quarks and leptons have 1/2 integer spin (called fermions) and obey Fermi-Dirac statistics in consequence. They follow the Pauli Exclusion Principle which states that no two fermions with identical quantum numbers can occupy the same state. ‘Force-carrying’ particles like the photon have integer spin (called bosons ) obey no such rule, and basically behave completely differently.

In essence, supersymmetry posits that every fermion has a corresponding boson sibling and vice versa – in other words, for every quark and lepton there exists a supersymmetric sibling (squarks and sleptons), and every boson also has a supersymmetric partner.

Unfortunately, no-one has ever seen such particles, either in cosmic rays or in particle acceleraor experiments. Hence, if SUSY exists, it must be a broken symmetry, i.e. the supersymmetric partners must have different decay schemes to ‘normal’ particles, and must be much heavier than their ‘normal’ cousins (otherwise we would have seen them). The only way to see if SUSY particles ever existed is to try re-creating them at extremely high energies in particle accelerators (much as we create anti-particles). This is one of the things the new collider at CERN was built to look for.

That said, theoreticians claim that there are indirect hints that SUSY , or something like it, might be right. The first is the convergence of the three non-gravitational forces. While these forces appear completely different at low energy, they have a different energy dependence, and may in fact converge at high enough energies. However, detailed calculations show that they converge to a point only if supersymmetry is allowed for. Unfortunately, this is a purely theoretical conjecture – you can see from the diagram below that the convergence is expected to occur at energies way beyond the reach of current accelerators.

GUT convergence including supersymmetry

The second is a hint from cosmology – we are pretty sure that well over 2/3 of the matter of the universe is ‘dark matter’, i.e. only seen by its gravitational effect (see post below). Such matter must be massive and yet weakly interacting (WIMPS) – an idea that fits supersymmetric particles very nicely. In fact, the favoured candidate for dark matter is the lightest SUSY particle, the neutralino (see post below).

Hence the search for SUSY particles at CERN, and the search for Dark Matter in cosmology are experiments that complement each other. Progress on either front will probaby have implications for the other, a fantastic convergence of particle physics and cosmology.

The post below made reference to the theory of supersymmetry and this weblog is long overdue a post on the subject. However, as supersymmetry is proposed as an extension of the Standard Model (SM) of particle physics, we’d better have a few words about the SM first…

As we said before, one of the big discoveries of 20th century physics is that there exist only four independent forces or interactions. These are gravity, electromagnetism (the unification of electricity and magnetism achieved by Maxwell in the 19th century), the strong nuclear force (that holds the protons and neutrons together in the nucleus), and the weak nuclear force (responsible for nuclear decay and radioactivity).

Physicists have long suspected that the four fundamental forces are not truly independent, but deeply connected. The idea is that at the tremendous energies of the Big Bang, a single superforce existed, which gradually split off into the four seperate entities we see today as the universe cooled. This idea received a great boost in the 1970s, when Salaam, Weinberg and Glashow established a strong theoretical connection between the electromagnetic and the weak nuclear interactions, using the methods of gauge symmetry. The theory predicted the existence of new particles (W and Z bosons), which were subsequently discovered in high-energy experiments at CERN in the 1980s…ever since we talk about the electro-weak interaction as a single entity.

Shortly before this, the first comprehensive theory of the strong nuclear force had also emerged – the key idea being Gellman’s prediction that the nuclear particles (protons and neutrons) are in fact made up of quarks, and the strong nuclear force is really an interquark force. This was verified by scattering experiments at Stanford in 1979, and the theory of the strong interaction is now known as quantum chromodynamics

Putting the two theories together gave rise to the Standard Model – a model that has been fantastically accurate at predicting the masses and properties of all particles discovered so far. However, the model contains several shortcomings

– there is no real unification between the electro-weak and strong interactions, they are treated in parallel

– gravity doesn’t appear at all

These shortcomings led to new theories that attempted to unify the strong nuclear force with the electro-weak interaction (known as Grand Unified Theories), and even more ambitious attempts to unify all three with gravity (Theories of Everything). To accomplish either of these, some new mathematical approaches would be needed….see next instalment…

Update

I forgot to mention another shortcoming of the Standard Model – namely that one particle, necessary to the model, has never been observed (thanks, tankers!). The Higgs boson plays a central role in the SM as the Higgs field gives the mechanism for other particles to acquire the masses we observe. Unfortunately, no evidence of the Higgs particle has been seen in accelerator experiments so far. Most theoreticians are convinced this is simply because we need higher energies than currently available to create it (i.e. it has a large mass), and expect to see evidence of Higgs bosons in the next round of accelerator experiments due to begin at the new accelerator in CERN next year – the Large Hadron Collider.

The alternative is that we’ll see something quite different, which would be even more interesting!

I learned at lunchtime on Monday that Professor Tim Sumner of Imperial College was booked to give a talk in Trinity College that very evening on the search for Dark Matter (DM). Prof Sumner is one of the project directors of the well-known UK Zeplin DM experiment, so I jumped in my car and drove up to Dublin. It’s not every day you get to hear a lecture from a player at that level….

It was certainly worth the drive, it was a cracking lecture. The seminar was organised by Astronomy Ireland, so there were quite a few non-professionals in the audience (I didn’t spot many staff from Trinity Maths or Physics, perhaps the talk wasn’t terribly well advertised). Of course, there’s something slightly ironic about an astronomical society hosting a seminar on Dark Matter as you’re not to likely to see DM through a telescope, but good for AI ! In the event, Tim gave a thorough overview of the whole area before describing current experiments to detect DM.

Recall that Dark Matter is thought to account over 2/3 of the matter of the universe (not to be confused with dark energy). Although we can’t see it, we’re pretty sure it exists because of its gravitational effect on the matter that we can see. I said in a previous post that the phenomenon was first suggested by Fritz Zwicky, but according to Tim, the suggestion first came from a scientist whose name I didn’t catch (Oert?).

The seminar was divided in four parts –

I. Indirect evidence of DM from gravitation effects

II. Indirect evidence of DM from cosmological models

III. DM candidates

IV. Current DM experiments

In part I, Tim gave a comprehensive account of the gravitational evidence, explaining the discrepancy between the expected velocity of stars and galaxies to that measured, working from smaller scales to the largest e.g. local stellar dynamics, galaxy rotation, galaxy cluster dynamics, X-ray halos, gravitational lensing and cluster streaming. I was only aware of a few of these so this was very interesting.

Calculations for galaxy rotation (curve A) and experimental points (curve B)

There was also a brief discussion of the alternative explanation, that our laws of gravity (both Newtonian and Einsteinian) need to be modified (MOND) and why this idea has lost ground recently

Part II concerned the role of DM in analysis of the cosmic microwave backgound (CMB). Tim explained the challenge to relate the temperature perturbations seen in the CMB to galaxy formation, and how all current models rely heavily on the postulate of DM…he also explained how the postulate is necessary to provide enough gravity to explain the geomety of the universe as observed.

Part III concerned the various candidates for DM. Such particles are expected to be weakly interacting (otherwise we would see them) and probably massive – i.e. weakly interacting massive particles or WIMPs. Tim then explained that the most likely candidates are thought to be certain supersymmetric particles. (As we saw before, the theory of supersymmetry (SUSY) arises out of attempts to unify three of the fundamental forces – the theory postulates that every normal particle has a heavier supersymmetric partner). Anyway, it turns out the most likely candidiate for DM is the neutralino, the lightest SUSY particle which cannot decay further.

In part IV, Tim described current experiments. He gave a full description of the recent galactic bullet cluster phenomenon, and was very positive about their results. He also mentioned the DAMA-LIBRA experiment, but was a lot less positive about this. The problem seems to be that their technique is less, not more, sensitive than other experiments, none of which have detected similar results. He confirmed that many in the community are sceptical that the DAMA result is really DM-related at all. Tim then finished with a brief overview of his own group’s attempt to detect WIMPS by their nuclear interactions in underground detectors in a mine over 1km deep, the Zeplin III experiment. There is a very good overview of the Zeplin experiment here .

The photomultiplier tubes of the ZEPLIN III detector

In summary, this was a super overview of the search for Dark Matter. There is always something to learn in such seminars, and things I particularly liked were

1. The lecturer took the time for a thorough overview of the whole area

2. There was time for a description of the experiments of other groups

3. There was great emphasis on the ‘double-whammy”. For many years, many scientists have scoffed at the idea of SUSY particles, as none have so far been seen in our particle detectors. Others have scoffed at the idea of Dark Matter, seeing it as a fudge. If DM turns out to be made up of SUSY particles, that solves both conundrums beautifully – and confirms supersymmetry as the way forward in unified field theory. It would also represent another step in the fantastic convergence of particle physics and cosmology, two of the most fundamental areas of physics.

4. There were plenty of questions afterwards – always interesting. In my case, I asked Tim about mass constraints put on SUSY particles by recent experiments in particle physics (accelerators). In fact, one of his slides showed that the ZEPLIN results so far are in agreement with accelerator experiments, ie. suggest candidate particles lying well within the ‘mass window’ provided by accelerator studies…the key slide was basically an updated version of the slide shown below – the predicted red curve (labelled Zeplin III) is now a reality (note that the vertcial line at 60 GeV is the lower mass limit set by accelerator experiments).

The above is written from my own notes at the talk, I may have missed a few points. Astronomy Ireland will provide a webcast and a DVD of the talk on their website and there is a very good overview of the worldwide search for DM here

Update:

I just read on the Cosmic V ariance blog that the GLAST satellite has just successfully launched (see earlier post on GLAST). Among other things GLAST will look for DM, by looking for gamma-rays produced by DM annihilation…there is a very nice discussion of this on their blog. I meant to ask Prof Sumner about the prospect of success of DM detection by this method but I forgot..

What are you doing for the summer? Like most academics, I’m asked this question regularly, by people envious of our holidays. I sometimes think they’re more interested in my holidays than I am myself.

But what will I do? I used to head back to my alma mater Trinity College as soon as term ended, doing experimental work in the magnetic resonance lab. These days, I find myself doing more and more writing about science, and less and less labwork. Truth is, I always liked writing papers more than getting the results…

This summer, I intend to make a start on a short book on particle physics, aimed at the layman – The Story of Atoms. I’ve noticed that while there are lots of good introductory books on cosmology, there are fewer such books on particle physics. Also, I’ve always had an interest in the area and l teach an introductory course in high-energy physics. Of course, particle physics probably doesn’t have quite the popular appeal of cosmology – but there’s enough convergence between the two fields to draw in plenty of readers. Plus, it’d be great to get a simple introductory book on particle physics out in time for expected dramatic results at CERN sometime next year. (I’m sure no-one else has thought of this – Ed).

Apparently one needs an outline, chapter headings and at least one full chapter to get a publisher interested. I think I’ll use the summer break to get the structure organised and bang out the first chapter, ready to send off to a few publishers by the time term starts up again.

‘Course I won’t spend the entire summer on it – all work and no play makes Albert a very dull boy. I intend to travel, and hole up somewhere where I can surf in the mornings and work in the afternoons (and socialize in the evenings). Anywhere really, so long as it’s outside Ireland, for God’s sake.

Garret Lisi, the surfer dude with the exceptionally simple theory of everything, has already been in touch with a list of suitable surf spots in California as long as your arm – thanks Garrett!

Mind you, I suspect what Garrett considers ‘suitable’ is probably life-threatening.

Tip – try not to land on the board when you wipeout

So that’s the summer plan.

1. Get started on a pop science book that will eventually make me rich and famous

2. Get back surfing

3. Meet someone nice. You’d be amazed how many academics are single, it’s frightening. All I ask is that a girl can surf and handle complex equations…

Good luck with all that – Ed

Incredibly, the cold fusion controversy is with us again. Physics World, normally a reputable source of news in physics, have a posting by Jon Cartwright on their weblog concerning claims that Japanese physicist Yoshiaki Arata of Osaka University may have demonstrated cold fusion.

To understand how startling – and controversial- such a claim is, you only have to call things by their proper names. ‘Cold fusion’ is media-speak for nuclear fusion at low energy, a process most physicists consider pretty much a contradiction in terms (it’s very difficult to achieve nuclear fusion even at extremely high temperatures and energies, with certain well-understood exceptions).

The dream of ‘cold fusion’ first hit the news in 1989, when chemists Fleischmann and Pons claimed to have observed a dramatic, unexplained heating effect in a chemical reaction, and attributed it to nuclear fusion processes ocurring at normal temperatures. The discovery made headlines around the world, because it offered the dream of a clean, cheap energy source on a small scale (nuclear fusion is a very different process from nuclear fission). However, the whole field was controversial from the very start.

Most physicists felt the jump from an unexplained heating effect to the assumption of nuclear fusion was highly speculative. Secondly, the effect was publicized (and funding received) long before the results were published in recognized journals, one of the first times this happened. Worst of all, when physics labs around the world rushed to reproduce the results, no discernible heating effect was found. The end result was a withdrawal of funding and a great career blow to the experimenters…and prompted a serious debate on the importance of peer review before going to the press!

Fusion in a beaker – the Fleischmann apparatus

It’s probably too early to say, but the current Japanese story bears many resemblances to the Fleischmann fiasco – a great deal of talk in the press (now web), a paucity of peer-reviewed results, and a great deal of copy written by non-physicists. In particular, I notice that most descriptions of the experiment focus once more on the benefits of ‘fusion energy’, (cheap, clean energy etc) with only a few lines concerning the skepticism of mainstream scientists.. (see this thread on the Richard Dawkins website for example)

There is also the question of biased opinion. For example, Cartwright’s article states ‘I also received a detailed account from Jed Rothwell, who is editor of the US site LENR (Low Energy Nuclear Reactions) and who has long thought that cold-fusion research shows promise’. Hmm. Not exactly an unbiased opinion, then. Indeed, a glance at the LENR website suggests that the above is not likely to represent the mainstream view…This is exactly the sort of press that caused such a problem the first time around…