Archive for August, 2012

Short but sweet – Higgs (1964)

Posted in The Universe and Stuff with tags , , , , on August 31, 2012 by telescoper

In the light of all this Malarkey about the (claimed) discovery of the Higgs Boson at the Large Hadron Collider, I thought you might be interested to see the original paper by Higgs (1964) in its entirety. As you can see, it’s surprisingly small. The paper, I mean, not the boson…

p.s. The paper is freely available to download from the American Physical Society website; no breach of copyright is intended.

p.p.s. The manuscript was received by Physical Review Letters on 31st August 1964, i.e. 48 years ago today.

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Cosmogony

Posted in Music with tags , , on August 31, 2012 by telescoper

And now for something completely different, from the extraordinary whirlwind of creativity actually named   Björk Guðmundsdóttir, but known throughout the Universe simply as Björk.

Laura

Posted in Film, Jazz with tags , , , on August 30, 2012 by telescoper

Last week’s post about Vincent Price reminded me of the film that really established him as a movie actor, the classic film noir Laurain which he played the parasitic boyfriend of the eponymous heroine. If you’ve never seen the film, you should because in my opinion it hasn’t dated at all even though it was made in 1944. A song with the same name written for the film in 1945 (after the filming was completed) became a popular hit at the time as well as a favourite for jazz musicians, spawning numerous cover versions including one by the great Charlie Parker. Those of you who associate Bird with jagged bebop tunes played at a frenetic pace might be surprised to hear his take on this romantic ballad, particularly as it involves him playing with strings. The Charlie Parker with Strings session recorded in 1950 received mixed reviews from the critics, primarily because many of the arrangements are a bit bland, but while  I don’t like all these tracks, I do think Parker’s version of  Laura is a gem in which he  reveals a sensitive side to his music-making that isn’t often appreciated.

A-level Chemistry Examination Paper, Vintage 1981

Posted in Education with tags , , , on August 29, 2012 by telescoper

I don’t know how many followers of this blog are interested in Chemistry, but I thought I’d continue my irregular series of postings of old examination papers with my Chemistry A-level. This particular Paper was Paper 1 of 2 (although I did also take the “special” Paper 3). As you can see Paper 1 was of multiple-choice format, with 40 questions to answer in 75 minutes, which seems a bit stiff! Looking over the exam just now I can’t believe that there was a time when I actually knew this stuff. Nowadays I can only really do the first few questions – because they’re really physics – and I don’t even remember what most of the words mean in the other questions!

Anyway, as usual,  any comments from people who’ve done A-level Chemistry more recently would be very welcome through the Comments Box, e.g. is there anything  in this paper that you wouldn’t expect to see nowadays? Is it easier, harder, or about the same as current A-level Chemistry papers?

The Importance of Being Homogeneous

Posted in The Universe and Stuff with tags , , , , , , , , on August 29, 2012 by telescoper

A recent article in New Scientist reminded me that I never completed the story I started with a couple of earlier posts (here and there), so while I wait for the rain to stop I thought I’d make myself useful by posting something now. It’s all about a paper available on the arXiv by Scrimgeour et al. concerning the transition to homogeneity of galaxy clustering in the WiggleZ galaxy survey, the abstract of which reads:

We have made the largest-volume measurement to date of the transition to large-scale homogeneity in the distribution of galaxies. We use the WiggleZ survey, a spectroscopic survey of over 200,000 blue galaxies in a cosmic volume of ~1 (Gpc/h)^3. A new method of defining the ‘homogeneity scale’ is presented, which is more robust than methods previously used in the literature, and which can be easily compared between different surveys. Due to the large cosmic depth of WiggleZ (up to z=1) we are able to make the first measurement of the transition to homogeneity over a range of cosmic epochs. The mean number of galaxies N(<r) in spheres of comoving radius r is proportional to r^3 within 1%, or equivalently the fractal dimension of the sample is within 1% of D_2=3, at radii larger than 71 \pm 8 Mpc/h at z~0.2, 70 \pm 5 Mpc/h at z~0.4, 81 \pm 5 Mpc/h at z~0.6, and 75 \pm 4 Mpc/h at z~0.8. We demonstrate the robustness of our results against selection function effects, using a LCDM N-body simulation and a suite of inhomogeneous fractal distributions. The results are in excellent agreement with both the LCDM N-body simulation and an analytical LCDM prediction. We can exclude a fractal distribution with fractal dimension below D_2=2.97 on scales from ~80 Mpc/h up to the largest scales probed by our measurement, ~300 Mpc/h, at 99.99% confidence.

To paraphrase, the conclusion of this study is that while galaxies are strongly clustered on small scales – in a complex `cosmic web’ of clumps, knots, sheets and filaments –  on sufficiently large scales, the Universe appears to be smooth. This is much like a bowl of porridge which contains many lumps, but (usually) none as large as the bowl it’s put in.

Our standard cosmological model is based on the Cosmological Principle, which asserts that the Universe is, in a broad-brush sense, homogeneous (is the same in every place) and isotropic (looks the same in all directions). But the question that has troubled cosmologists for many years is what is meant by large scales? How broad does the broad brush have to be?

I blogged some time ago about that the idea that the  Universe might have structure on all scales, as would be the case if it were described in terms of a fractal set characterized by a fractal dimension D. In a fractal set, the mean number of neighbours of a given galaxy within a spherical volume of radius R is proportional to R^D. If galaxies are distributed uniformly (homogeneously) then D = 3, as the number of neighbours simply depends on the volume of the sphere, i.e. as R^3, and the average number-density of galaxies. A value of D < 3 indicates that the galaxies do not fill space in a homogeneous fashion: D = 1, for example, would indicate that galaxies were distributed in roughly linear structures (filaments); the mass of material distributed along a filament enclosed within a sphere grows linear with the radius of the sphere, i.e. as R^1, not as its volume; galaxies distributed in sheets would have D=2, and so on.

We know that D \simeq 1.2 on small scales (in cosmological terms, still several Megaparsecs), but the evidence for a turnover to D=3 has not been so strong, at least not until recently. It’s just just that measuring D from a survey is actually rather tricky, but also that when we cosmologists adopt the Cosmological Principle we apply it not to the distribution of galaxies in space, but to space itself. We assume that space is homogeneous so that its geometry can be described by the Friedmann-Lemaitre-Robertson-Walker metric.

According to Einstein’s  theory of general relativity, clumps in the matter distribution would cause distortions in the metric which are roughly related to fluctuations in the Newtonian gravitational potential \delta\Phi by \delta\Phi/c^2 \sim \left(\lambda/ct \right)^{2} \left(\delta \rho/\rho\right), give or take a factor of a few, so that a large fluctuation in the density of matter wouldn’t necessarily cause a large fluctuation of the metric unless it were on a scale \lambda reasonably large relative to the cosmological horizon \sim ct. Galaxies correspond to a large \delta \rho/\rho \sim 10^6 but don’t violate the Cosmological Principle because they are too small in scale \lambda to perturb the background metric significantly.

The discussion of a fractal universe is one I’m overdue to return to. In my previous post  I left the story as it stood about 15 years ago, and there have been numerous developments since then, not all of them consistent with each other. I will do a full “Part 2” to that post eventually, but in the mean time I’ll just comment that this particularly one does seem to be consistent with a Universe that possesses the property of large-scale homogeneity. If that conclusion survives the next generation of even larger galaxy redshift surveys then it will come as an immense relief to cosmologists.

The reason for that is that the equations of general relativity are very hard to solve in cases where there isn’t a lot of symmetry; there are just too many equations to solve for a general solution to be obtained.  If the cosmological principle applies, however, the equations simplify enormously (both in number and form) and we can get results we can work with on the back of an envelope. Small fluctuations about the smooth background solution can be handled (approximately but robustly) using a technique called perturbation theory. If the fluctuations are large, however, these methods don’t work. What we need to do instead is construct exact inhomogeneous model, and that is very very hard. It’s of course a different question as to why the Universe is so smooth on large scales, but as a working cosmologist the real importance of it being that way is that it makes our job so much easier than it would otherwise be.

P.S. And I might add that the importance of the Scrimgeour et al paper to me personally is greatly amplified by the fact that it cites a number of my own articles on this theme!

Sonnet of the Sweet Complaint

Posted in Poetry with tags , , , on August 28, 2012 by telescoper

Never let me lose the marvel 
of your statue-like eyes, or the accent 
the solitary rose of your breath 
places on my cheek at night.
I am afraid of being, on this shore, 
a branchless trunk, and what I most regret 
is having no flower, pulp, or clay 
for the worm of my despair.
If you are my hidden treasure, 
if you are my cross, my dampened pain, 
if I am a dog, and you alone my master,
never let me lose what I have gained, 
and adorn the branches of your river 
with leaves of my estranged Autumn.

by Federico Garcia Lorca (1898-1936).

This poem is from a collection called Sonetos del amor oscuro (“Sonnets of Dark Love”), which contains the last verses ever written by Lorca. They were written to a young man, with whom the poet had a secret love affair, whose identity remained unknown until earlier this year (2012) when letters and other documents were found which revealed him to be the (then) 19-year old Juan Ramírez de Lucas.

Open Journal of Astrophysics: Update

Posted in Open Access with tags , , , , , on August 27, 2012 by telescoper

Regular readers of this blog (Sid and Doris Bonkers) may recall that a few weeks ago I posted an item in which I suggested setting up The Open Journal of Astrophysics. The motivation behind this was to demonstrate that it is possible to run an academic journal which is freely available to anyone who wants to read it, as well as at minimal cost to authors. Basically, I want to show that it is possible to “cut out the middle man” in the process of publishing scientific research and that by doing it ourselves we can actually do it better.

I have been unwell for much of the summer, so haven’t been able to carry this project on as much as I would have liked, and  I also received many messages offering help and advice that I have been unable to reply to individually. But I can assure you that I haven’t forgotten about the idea, nor have I quietly withdrawn the financial backing I suggested in my earlier post. Indeed, my interest in, and excitement, about this project has grown significantly over the summer as new possibilities have been suggested and my resentment about how the academic publishing industry hijacked the Finch Report has deepened.

In fact, quite a lot of effort has already been put in by people elsewhere thinking about how to set this journal up in the best way to make maximal use of digital technology to produce something radically different from the stale formats offered by existing journals.  I hope to be able to report back soon with more details of how it will work, when we propose to launch the site, and even what its name will be, Open Journal of Astrophysics being just a working title. I think it’s far better to wait until we have a full prototype going before going further.

In the meantime, however, I have a request to make. The Open Journal of Astrophysics will need an Editorial Board with expertise across all astrophysics, so they can select referees and deal with the associated correspondence.  The success of this venture will largely depend on establishing trust with the research community and one way of doing that will be by having eminent individuals on the Editorial Board. I will be contacting privately various scientists who have already offered their assistance in this, but if any senior astronomers and/or astrophysicists out there are interested in playing a part please contact me. I can’t offer much in the way of remuneration, but I think this is an opportunity to get involved in a venture that in the long run will benefit the astronomical community immensely.

Oh, and please feel free pass this on to folks you think might be interested even if you yourself are not!