Ten Years of the European Research Council

Posted in Politics, Science Politics with tags , , , , on February 9, 2017 by telescoper

This little video reminded me that we’re coming up to the tenth anniversary of the founding of the European Research Council (ERC).

 

In my opinion the ERC has been an outstanding success that has revitalized science across the continent and here in the United Kingdom. Sadly the UK government has decided that the United Kingdom will play no further part in ERC-funded schemes or any other programme funded by the EU.  The participation of UK scientists has already started to diminish and when it dries up completely there will be a significant loss of research income, especially for fundamental science. I’m grateful to Paul Crowther for pointing out that over the past decade there have been no fewer than 176 ERC awards to UK physics departments, meaning over  1/3 of a billion Euros in research funding.

I estimate that most physics & astronomy departments in the UK will lose 20-30% of their research income as a result of leaving the EU. Most also have a similar fraction of staff who are EU nationals, many of whom will leave because of the UK government’s shocking refusal to guarantee their right to remain. I find it sad beyond words that we as a nation are not only about to throw away our leading role in so many excellent research projects but also destroy our own credibility as a civilized nation by the mean-spirited way we are behaving.

But the ERC will at least offer British scientists two ways to continue their involvement with EU programmes. The first is that existing grants are portable, so principal investigators who decided to relocate to an EU country can take their funding with them. The second is that future ERC grants are open to applicants from any country in the world who wish to carry out their research within the EU.

As Niels Bohr famously remarked “prediction is very difficult, especially about the future”. I don’t know whether there will be a significant brain drain to the EU from the UK as a result of BrExit, but I do know many colleagues are talking about it right now. As for myself, if someone were to offer me a job in Europe I’d definitely take it.

(My CV is available on request).

 

 

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One Hundred Years of the Cosmological Constant

Posted in History, The Universe and Stuff with tags , , , , , , on February 8, 2017 by telescoper

It was exactly one hundred years ago today – on 8th February 1917 – that a paper was published in which Albert Einstein explored the cosmological consequences of his general theory of relativity, in the course of which he introduced the concept of the cosmological constant.

For the record the full reference to the paper is: Kosmologische Betrachtungen zur allgemeinen Relativitätstheorie and it was published in the Sitzungsberichte der Königlich Preußischen Akademie der Wissenschaften. You can find the full text of the paper here. There’s also a nice recent discussion of it by Cormac O’Raifeartaigh  and others on the arXiv here.

Here is the first page:

cosmo

It’s well worth looking at this paper – even if your German is as rudimentary as mine – because the argument Einstein constructs is rather different from what you might imagine (or at least that’s what I thought when I first read it). As you see, it begins with a discussion of a modification of Poisson’s equation for gravity.

As is well known, Einstein introduced the cosmological constant in order to construct a static model of the Universe. The 1917 paper pre-dates the work of Friedman (1923) and Lemaître (1927) that established much of the language and formalism used to describe cosmological models nowadays, so I thought it might be interesting just to recapitulate the idea using modern notation. Actually, in honour of the impending centenary I did this briefly in my lecture on Physics of the Early Universe yesterday.

To simplify matters I’ll just consider a “dust” model, in which pressure can be neglected. In this case, the essential equations governing a cosmological model satisfying the Cosmological Principle are:

\ddot{a} = -\frac{4\pi G \rho a }{3} +\frac{\Lambda a}{3}

and

\dot{a}^2= \frac{8\pi G \rho a^2}{3} +\frac{\Lambda a^2}{3} - kc^2.

In these equations a(t) is the cosmic scale factor (which measures the relative size of the Universe) and dots are derivatives with respect to cosmological proper time, t. The density of matter is \rho>0 and the cosmological constant is \Lambda. The quantity k is the curvature of the spatial sections of the model, i.e. the surfaces on which t is constant.

Now our task is to find a solution of these equations with a(t)= A, say, constant for all time, i.e. that \dot{a}=0 and \ddot{a}=0 for all time.

The first thing to notice is that if \Lambda=0 then this is impossible. One can solve the second equation to make the LHS zero at a particular time by matching the density term to the curvature term, but that only makes a universe that is instantaneously static. The second derivative is non-zero in this case so the system inevitably evolves away from the situation in which $\dot{a}=0$.

With the cosmological constant term included, it is a different story. First make \ddot{a}=0  in the first equation, which means that

\Lambda=4\pi G \rho.

Now we can make \dot{a}=0 in the second equation by setting

\Lambda a^2 = 4\pi G \rho a^2 = kc^2

This gives a static universe model, usually called the Einstein universe. Notice that the curvature must be positive, so this a universe of finite spatial extent but with infinite duration.

This idea formed the basis of Einstein’s own cosmological thinking until the early 1930s when observations began to make it clear that the universe was not static at all, but expanding. In that light it seems that adding the cosmological constant wasn’t really justified, and it is often said that Einstein regard its introduction as his “biggest blunder”.

I have two responses to that. One is that general relativity, when combined with the cosmological principle, but without the cosmological constant, requires the universe to be dynamical rather than static. If anything, therefore, you could argue that Einstein’s biggest blunder was to have failed to predict the expansion of the Universe!

The other response is that, far from it being an ad hoc modification of his theory, there are actually sound mathematical reasons for allowing the cosmological constant term. Although Einstein’s original motivation for considering this possibility may have been misguided, he was justified in introducing it. He was right if, perhaps, for the wrong reasons. Nowadays observational evidence suggests that the expansion of the universe may be accelerating. The first equation above tells you that this is only possible if \Lambda\neq 0.

Finally, I’ll just mention another thing in the light of the Einstein (1917) paper. It is clear that Einstein thought of the cosmological as a modification of the left hand side of the field equations of general relativity, i.e. the part that expresses the effect of gravity through the curvature of space-time. Nowadays we tend to think of it instead as a peculiar form of energy (called dark energy) that has negative pressure. This sits on the right hand side of the field equations instead of the left so is not so much a modification of the law of gravity as an exotic form of energy. You can see the details in an older post here.

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Anachronic Anthropology

Posted in Jazz with tags , , , , on February 7, 2017 by telescoper

I’m struggling a bit with a heavy cold (or at least I hope that’s what it is) and I had a two-hour lecture earlier today so I’m going to go home and crash out. To keep my readers (Sid and Doris Bonkers) amused, I decided to repost this piece which I’ve actually posted before almost eight years ago. It’s an oddity, but quite an interesting one I think.

The Anachronic Jazz Band is, I think, now defunct but they were from Paris originally. The style they played in could probably be described as like the New York style of the late 1920s, with definite touches of Bix Beiderbecke. On the other hand, the tunes they played all came from the bebop era of modern jazz, such as this one which is the Charlie Parker classic Anthropology. 

You might think that an uncompromising bebop number like this would pose unsurmountable challenges for a traditional jazz outfit, but I think they pull it off rather well. I think though that they were probably helped by the fact that this tune, like many modern jazz compositions, is actually based on a chord progression belonging to a much more familiar tune. In this case the harmonies actually derive from George Gershwin’s standard I Got Rhythm….

Anyway, perhaps the efforts of this fine little band go some way to showing that there’s more continuity between traditional and modern jazz than one might suppose…

 

 

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A Challenge for Inflationary Cosmologists

Posted in The Universe and Stuff with tags , , on February 6, 2017 by telescoper

A few days ago I wrote a very sceptical post about an alternative to the present standard cosmological which is called the holographic universe. After an interesting discussion thread on that post I thought I’d pose a challenge here. It might be a bit specialist as it is for inflationary theorists and model-builders (a club to which I do not belong) but I thought I’d try it as it might prove education for me as for other readers.

Anyway, the point is that in the inflationary paradigm there is a fairly generic prediction that the primordial scalar power spectrum (related to the spectrum of density fluctuations) takes the form of a power law:

equation-1

The wavenumber is denoted q. There are two free parameters here: the spectral index ns (which is usually close to unity); and an overall normalization amplitude parametrised here at an arbitrary “pivot” scale q*.

In the holographic model the functional form of the spectrum is quite different:
equation-2

This has two different free parameters: g and β, both of which relate to properties of a dual Quantum Field Theory which appears in the model.

The second model is motivated by very different considerations from those behind the inflationary model, but my suspicion is that in fact one could create a version of inflation that produces a spectrum of the form (2) rather than (1). There is an imtimate relationship between the scalar perturbation spectrum and the inflationary dynamics which means that there is considerable freedom to “design” the perturbation spectrum by building features into the potential.

Anyway, that’s the challenge. Would any cosmologists out there with time on their hands please make me an inflationary model that produces the spectrum (2). Alternatively, if this can’t be done, give me a proof why it can’t!

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Farewell, Captain Cook

Posted in Cricket with tags , , on February 6, 2017 by telescoper

So Alastair Cook has resigned from his post as Captain of the England (and Wales) Cricket team, having been skipper for 59 test matches since 2012. After their drubbing in India this is hardly surprising, but I hope he finds his form and continues as an opening batsman. He’s only 32 so should have a few more years in him.

When he started as captain I felt that he was far too cautious, something perhaps he inherited from his predecessor Andrew Strauss. I think he got marginally better as time went by, but I always felt he didn’t have sufficient presence on the field to be a great team leader and too often let things drift when England were fielding. Anyway, I don’t want to be too harsh – he did lead England to two Ashes victories!

Farewell, then, Alastair Cook. But who should take his place? Is it the youngster, Joe Root? Or should Geoffrey Boycott come out of retirement to wield his stick of rhubarb in the corridor of uncertainty once more?

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Fire and Ice 

Posted in Poetry with tags , , , on February 5, 2017 by telescoper

Some say the world will end in fire,
Some say in ice.
From what I’ve tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To say that for destruction ice
Is also great
And would suffice.

by Robert Frost (1874-1963)


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Enough work…

Posted in Uncategorized on February 4, 2017 by telescoper

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Boogie Woogie Boogie – Errol Garner

Posted in Jazz with tags , , on February 3, 2017 by telescoper

I have lately posted a number of classic boogie woogie and blues performances by the great Jimmy Yancey. Here’s a piece that’s related but really very different, recorded in 1944 by a musician not usually associated with boogie woogie at all, Errol Garner, who was 23 when this track was made.  The story I heard about this is that the studio bosses leant on the young and impressionable pianist to do play some things that he wasn’t keen on, including a bit of boogie woogie. Eventually Garner acceded to their request, and produced what I think is a minor masterpiece called Boogie Woogie Boogie. Note the way he doesn’t stick to the same left-hand figures throughout the track which makes this much more varied than most recordings in this genre. I particularly like the transition at about 1:35 where it all goes a bit “Batman”!  It also has a distinctively dark minor-key feel to it, which is rather atmospheric.

Have a good weekend!

 

 

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The Dipole Repeller

Posted in The Universe and Stuff with tags , , , , , , on February 2, 2017 by telescoper

An interesting bit of local cosmology news has been hitting the headlines over the last few days. The story relates to a paper by Yehuda Hoffman et al. published in Nature Astronomy on 30th January. The abstract reads:

Our Local Group of galaxies is moving with respect to the cosmic microwave background (CMB) with a velocity 1 of VCMB = 631 ± 20 km s−1and participates in a bulk flow that extends out to distances of ~20,000 km s−1 or more 2,3,4 . There has been an implicit assumption that overabundances of galaxies induce the Local Group motion 5,6,7 . Yet underdense regions push as much as overdensities attract 8 , but they are deficient in light and consequently difficult to chart. It was suggested a decade ago that an underdensity in the northern hemisphere roughly 15,000 km s−1 away contributes significantly to the observed flow 9 . We show here that repulsion from an underdensity is important and that the dominant influences causing the observed flow are a single attractor — associated with the Shapley concentration — and a single previously unidentified repeller, which contribute roughly equally to the CMB dipole. The bulk flow is closely anti-aligned with the repeller out to 16,000 ± 4,500 km s−1. This ‘dipole repeller’ is predicted to be associated with a void in the distribution of galaxies.

The effect of this “void in the distribution of galaxies” has been described in rather lurid terms as “Milky Way being pushed through space by cosmic dead zone” in a Guardian piece on this research.

If you’re confused by this into thinking that some sort of anti-gravity is at play, then it isn’t really anything so exotic. If the Universe were completely homogeneous and isotropic – as our simplest models assume – then it would be expanding at the same rate in all directions.  This would be a pure “Hubble flow“, with galaxies appearing to recede from an observer with a speed proportional to their distance:

slide7

But the Universe isn’t exactly smooth. As well as the galaxies themselves, there are clusters, filaments and sheets of galaxies and a corresponding collection of void regions, together forming a huge and complex “cosmic web” of large-scale structure. This distorts the Hubble flow by inducing peculiar motions (i.e. departures from the pure expansion). A part of the Universe which is denser than average (e.g. a cluster or supercluster) expands less  quickly than average, a part which is less dense (i.e. a void) expands more quickly than average. Relative to the global expansion rate, clusters represent a “pull” and voids represent a “push”. That’s really all there is to it.

The difficult part about this kind of study is measuring a sufficient number of peculiar motions of galaxies around our own to make a detailed map of what’s going on in the local velocity field. That’s particularly hard for galaxies near the plane of the Milky Way disk as they tend to be obscured by dust. Nevertheless, after plugging away at this for many years, the authors of the Nature paper have generated some fascinating results. It seems that our Galaxy and other members of the Local Group lie between a dense supercluster (often called the Shapley concentration) and an underdense region, so the peculiar velocity field around us has an approximately dipole structure.

They’ve even made a nice video to show you what’s going on, so I don’t have to explain any further!

 

 

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You have the power to change someone’s life – Time to Talk Day 2017

Posted in Mental Health with tags , , on February 2, 2017 by telescoper

time-to-talk-day

Today, 2nd February 2017, is Time to Talk Day, which means that it’s time for the nation’s biggest conversation about mental health.

One in four adults and one in ten young people will experience a mental health problem every year. Talking about it doesn’t have to be difficult but can make a big difference. It’s easy to have a conversation about mental health, and it could change someone’s life (including yours). You don’t have to be an expert to help: sometimes just asking  how they are is all you need to do to help someone who’s having a hard time.

Here’s a little video about Time to Talk Day:

For more information on how to get involved see here.

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