Archive for February 17, 2017

Emergent gravity in galaxies and in the Solar System [GA]

Posted in The Universe and Stuff with tags , , on February 17, 2017 by telescoper

I’ve been meaning to do a blog post about Erik Verlinde’s  very interesting “Emergent Gravity” theory since it was first aired in November 2016, but never got round to it. However, this recent paper suggests that the new theory fails badly on scales of the Solar System. And when I say “badly”, I mean by seven orders of magnitude. That’s pretty bad.

Unless there’s something wrong with this analysis, this looks pretty terminal …


It was recently proposed that the effects usually attributed to particle dark matter on galaxy scales are due to the displacement of dark energy by baryonic matter, a paradigm known as emergent gravity. This formalism leads to predictions similar to Modified Newtonian Dynamics (MOND) in spherical symmetry, but not quite identical. In particular, it leads to a well defined transition between the Newtonian and the modified gravitational regimes, a transition depending on both the Newtonian acceleration and its first derivative with respect to radius. Under the hypothesis of the applicability of this transition to aspherical systems, we investigate whether it can reproduce observed galaxy rotation curves. We conclude that the formula leads to marginally acceptable fits with strikingly low best-fit distances, low stellar mass-to-light ratios, and a low Hubble constant. In particular, some unobserved wiggles are produced in rotation curves because of the dependence of the transition on the…

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Le Vin herbé

Posted in Opera with tags , , on February 17, 2017 by telescoper

Last night I went to the Wales Millennium Centre in Cardiff for the opening night of Welsh National Opera’s new production of Le Vin herbé  by Swiss-born composer Frank Martin. This isn’t a work with which I was previously familiar so I wasn’t sure what to expect, but then that’s why I usually particularly hard to get to see departures from the standard repertoire. It’s not that I’m at all bored with Mozart, Puccini et al but that it’s always good to keep an ear open for new things.  In fact there is only one performance of this piece in Cardiff this year before it goes on tour. Fortunately I was able to make it.

Le Vin herbé is based on the story of Tristan and Iseult ; the title refers to the potion that the two lead characters accidentally drink which makes them fall in love and thus betray King Mark of Cornwall, who is Tristan’s uncle and Iseult’s husband-to-be. Naturally tt all ends in disaster, with the two lovers both dying. But if the story makes you think of Wagner’s epic operatic telling of this legend, Tristan und Isolde then you need to think again, as this is a very different piece. Le Vin herbé is a much more intimate work, with a relatively small case and a band of just eight musicians (a piano and seven string players) who, in this production, were at centre stage throughout the performance rather than in the pit. The main characters are played by tenor Tom Randle (Tristan) and soprano Caitlin Hulcup (Iseult) – both of whom were brilliant – and some of their lines are also sung by the chorus and there are also solo storytellers to provide bits of the narrative. The set and staging is very minimal. In fact it’s more of a chamber oratorio than an Opera. Also the entire performances lasts under two hours, with no interval. Quite a lot shorter than Wagner’s version!

I think the instrumental music by Frank Martin is very fine indeed, and very well played by the musicians directed by James Southall, and the principals and chorus were in good voice. Having said that I think Martin’s writing for voices is less successful. The vocal lines consciously evokes mediaeval plainsong, which works quite well for the chorus but makes it difficult for the soloists to generate any melodic drive. It’s not helped by the libretto either, which is rather dry and undramatic. On the way home from the performance I couldn’t help wondering what it might have been like had the text been in mediaeval Latin! The staging was at times effective: some of the scenes between Tristan and Iseult were very moving, but the stage was too busy and confusing when the whole chorus got involved.

This probably sounds very critical, but I don’t mean it to be. There’s much to enjoy in this production, so I’d encourage you to go and form their own opinion. It’s on tour in Bristol, Milton Keynes, Llandudno, Plymouth and Southampton. Last night’s performance got a very warm reception from a pretty full house which, for an unusual work like this, is a very good sign.