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The Cosmological Evidence – 25 Years Ago

Posted in Biographical, The Universe and Stuff with tags , , , on July 15, 2020 by telescoper

Today Facebook reminded me that the picture below is now 25 years old. I have posted it before and it has done the rounds at a number of cosmology conferences (usually to the accompaniment of lots of laughter), but I thought I’d circulate again as a bit of nostalgia and also to embarrass all concerned with this image. The picture was taken at a graduate school in cosmology in Leiden (in The Netherlands) in July 1995. In my memory that was a sweltering hot summer, which is my excuse for the informality of my attire.

Anyway, various shady characters masquerading as “experts” were asked by the audience of graduate students at a summer school to give their favoured values for the cosmological parameters. from from top to bottom these are:

  • the Hubble constant H0;
  • density parameter Ω0 (not split into dark matter and `ordinary’  matter as is now customary);
  • cosmological constant Λ0,
  • curvature parameter k
  • and age of the Universe t0.

 

From left to right we have Alain Blanchard (AB), Bernard Jones (BJ, standing), John Peacock (JP), me (yes, with a beard and a pony tail – the shame of it), Vincent Icke (VI), Rien van de Weygaert (RW) and Peter Katgert (PK, standing). You can see on the hi-tech digital display screen blackboard that the only one to get anywhere close to correctly predicting the parameters of what would become the standard cosmological model was, in fact, Rien van de Weygaert. Actually he was the only one of us to include a non-zero cosmological constant. My own favourite model at the time was a low-density model with negative spatial curvature.

Nobody is suggesting that panel discussions are the right way to settle scientific questions, of course, but it is interesting to see the diversity of opinions that were around in 1995.

P.S. Note that not all the combinations of parameters presented there are consistent with a Friedman model, but nobody said they had to be!

 

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Cosmology Examination Results

Posted in Education, Maynooth, The Universe and Stuff with tags , , , , on July 14, 2020 by telescoper

The examination season in Maynooth being now over, and the results having been issued, I thought I’d pass on the results not for individual students but for the Universe as a whole.

As you can see Dark Energy is top of the class, with a good II.1 (Upper Second Class). A few years ago this candidate looked likely to get a mark over 70% and thus get First Class Honours, but in the end fell just short. Given the steady performance and possible improvement in future I think this candidate will probably be one to reckon with in a future research career.

In second place, a long way behind on about 27%, is Dark Matter. This candidate only answered some of the questions asked, and those not very convincingly. Although reasonably strong on theory, the candidate didn’t show up at all in the laboratory. The result is a fail but there is an opportunity for a repeat at a future date, though there is some doubt as to whether the candidate would appear.

At the bottom of the class on a meagre 5% we find Ordinary Matter. It seems this candidate must have left the examination early and did not even give the correct name (baryons) on the script. Technically this one could repeat but even doing so is unlikely even to get an Ordinary Degree. I would suggest that baryons aren’t really cut out for cosmology and should make alternative plans for the future.

 

P.S. Photons and neutrinos ceased interacting with the course some time ago. Owing to this lack of engagement they are assumed to have dropped out, and their marks are not shown.

 

 

 

 

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Viva Zoom!

Posted in Biographical, The Universe and Stuff with tags , , , , on July 13, 2020 by telescoper

They say that there’s a first time for everything and this morning I conducted my first ever viva voce examination as an External Examiner via Zoom. Given the Covid-19 restrictions it was inevitable that I’d have to do this at some point! As it turned out candidate in question happened to be at University College London.

For those of you not familiar with how this sort of examination usually works, at least in the UK and Ireland, a PhD involves doing research into a particular topic and then writing up what you’ve done in a thesis. The thesis is a substantial piece of work, often in the region of 100,000 words (200 pages or so), which is then assessed by two examiners (one internal to the university at which the research was done, and one external). They read copies of the thesis and write preliminary reports assessing its suitability. Then the candidate has to defend the thesis in an oral examination, which was what happened today, after which the examiners make a final recommendation to the university about whether the degree should be awarded.

There aren’t many rules for how a viva voce examination should be conducted or how long it should last, but the can be as short as, say, 2 hours and can be as long as 5 hours or more. The examiners usually ask a mixture of questions, some about the details of the work presented and some about the general background. The unpredictable content of a viva voce examination makes it very difficult to prepare for, and it can be difficult and stressful for the candidate (as well as just tiring, as it can drag on for a long time). However, call me old-fashioned but I think if you’re going to get to call yourself Doctor of Philosophy you should expect to have to work for it.

As it happens, my own PhD examination (almost 30 years ago!)  was quite long (about 4hrs 30 minutes) and my external examiner was John Peacock. Today’s was a bit shorter – around three hours – and the internal examiner was Andrew Pontzen. Obviously I can’t give details of what went on in the examination except that the internal examiner Andrew Pontzen and I agreed to recommend the award of a PhD to the candidate, Krishna Naidoo. Although it was slightly strange doing this over Zoom instead of in person, it worked out OK. The only thing really missing was a blackboard or whiteboard. I also found it a bit awkward having the PDF thesis and videoconference on the same screen, but that was my fault for not appropriating a spare monitor.

At UCL as in most UK universities, the PhD examiners simply make a recommendation to a higher authority (e.g. Board of Graduate Studies) to formally award the degree, but only in very rare and peculiar circumstances do they not follow the recommendation.

The sad thing about these times of social distancing is that not being there in person I couldn’t shake the hand of the candidate at the end of the examination nor could I join him and his friends and colleagues for a drink afterwards. I’m sure they’ll find a way of celebrating. I couldn’t even join them remotely as I had another Zoom call to make. ..

P.S. If you want an idea of what is in  Krishna’s thesis you could have a look at one of the papers to come from it.

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The Joy of Penguin Faeces

Posted in The Universe and Stuff with tags , , , on July 4, 2020 by telescoper

Last night my attention was drawn to an important article on the ArXiv in the domain of biophysics. The title is Projectile Trajectory of Penguin’s Faeces and Rectal Pressure Revisited*.

Here is the abstract:

We discuss a trajectory of penguins’ faeces after the powerful shooting due to their strong rectal pressure. Practically, it is important to see how far faeceses reach when penguins expel them from higher places. Such information is useful for keepers to avoid the direct hitting of faeceses. We estimate the upper bound for the maximum flight distance by solving the Newton’s equation of motion. Our results indicate that the safety zone should be 1.34 meters away from a penguin trying to poop in typical environments. In the presence of the viscous resistance, the grounding time and the flying distance of faeces can be expressed in terms of Lambert W function. Furthermore, we address the penguin’s rectal pressure within the hydrodynamical approximation combining Bernoulli’s theorem and Hagen-Poiseuille equation for viscosity corrections. We found that the calculated rectal pressure is larger than the estimation in the previous work.

That is amusing enough (though admittedly the English isn’t great) but the diagrams are an absolute joy!

*In case you’re wondering about the “revisited” at the end of the title, the authors of the present work present a critique of earlier work by Meyer-Rochow & Gal (2003) in which “the projectile trajectory of the faeces is not taken into account”. This previous paper was awarded the Ignobel Prize in 2005.

One should not pooh-pooh research on this topic and now that we have got to Number Two I for one hope for the speedy production of further outputs in this area.

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The Open Journal of Astrophysics & INSPIRE

Posted in Open Access, The Universe and Stuff with tags , , , , on July 1, 2020 by telescoper

After a busy morning I’ve got time for an update or two about the Open Journal of Astrophysics.

As well as the NASA Astrophysics Data System (ADS) many papers in astrophysics are also indexed by INSPIRE HEP the analogous information management system for high energy physics. Here is the logo for the latter:

Being indexed in INSPIRE  is particularly relevant for authors of papers in astroparticle physics and cosmology, but papers in other areas of astrophysics are also listed on INSPIRE HEP. I am given to understand that, e.g., postdoc selection committees often look at INSPIRE for bibliometric information about applications so this is potentially important for early career researchers.

I am very grateful to staff at Inspire for ensuring that all our papers are now fully indexed in INSPIRE HEP as refereed articles with metadata fully consistent with NASA/ADS. The back catalogue having been dealt with manually we can now set up a feed to ensure that future papers are indexed automatically by NASA/ADS and Inspire HEP.

It is worth noting that because our papers are only published online we do not use the standard referencing style of volumes and pages. We have volumes: Volume 3 is 2020, Volume 2 is 2019, and everything before that is Volume 1. Each paper published in a given year is allocated an numerical id which is just an integer.

For an example of this style, see here.

The main thing for proper cross-referencing and citation is the Digital Object Identifier, which is displayed on the overlay for each paper.

The final thing I wanted to say is that I’m now reliably informed that the correct name to be use for the form of Open Access Publishing offered by the Open Journal of Astrophysics is not Green (which has come to mean author self-archiving of papers) but Diamond Open Access, which means that neither authors nor readers are charged.

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Watch “Why the Universe is quite disappointing really – Episode 6” on YouTube

Posted in The Universe and Stuff, YouTube with tags , , on June 30, 2020 by telescoper

I had to suspend the production of these videos for a month or so while I dealt with examination matters, but after that short hiatus, here is Episode 6 during which I explain just how weak and feeble the force of gravity really is. Combined with the fact that the Universe has such a low density (see Episode 5), the weakness of gravity means that the cosmos evolves extremely slowly.

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R.I.P. Olivier Le Fèvre (1960-2020)

Posted in The Universe and Stuff with tags , , , , , on June 29, 2020 by telescoper

Olivier Le Fèvre (1960-2020)

The international cosmological community was deeply saddened last week to hear of the death on 25th June after a long illness of Olivier Le Fèvre. He was 59 years old.

Olivier was a specialist in astronomical spectroscopy and as such he made important contributions to cosmology through galaxy redshift surveys. He was Director of the Laboratoire d’Astrophysique de Marseille from 2004 to 2011. In latter years he was involved, among many other things, in the Euclid space mission.

You can find a full obituary and appreciation of Olivier’s life and work here. His funeral takes place this morning and there is an online book of condolence here to send messages of condolence and support to his family, friends and colleagues at this difficult time.

Rest in peace, Olivier Le Fèvre (1960-2020).

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Another Open Day Preview – General Science at Maynooth

Posted in Education, Maynooth, The Universe and Stuff with tags , , , on June 26, 2020 by telescoper

I thought I’d put up another post following on from yesterday’s post about Open Day at Maynooth coming up on Saturday 27th June which, owing to Covid-19 restrictions still being in place,  is once again a virtual event. It will take place between 10am and 2pm and be online for that period to answer queries about Theoretical and Mathematical Physics at Maynooth University. You can sign up for the event here.

Yesterday’s post was about our denominated degree programme in Theoretical Physics and Mathematics, but I also recorded a separate video for students interested in studying Mathematical Physics  (or Theoretical Physics – we use the terms interchangeably) through our General Science programme, MH201, so here’s a little presentation about how to study Mathematical physics at Maynooth that way:

Currently, most students doing Science subjects here in Maynooth enter on the General Science programme (codename)  a four-year Omnibus science course that involves doing four subjects in the first year, but becoming increasingly specialised thereafter. That’s not unlike the Natural Sciences course I did at Cambridge, except that students at Maynooth can do both Mathematical Theoretical Physics and Experimental Physics in the first year as separate choices. Other possibilities include Chemistry, Computer Science, Biology, etc.

In Year 1 students do four subjects (one of which has to be Mathematics). That is narrowed down to three in Year 2 and two in Year 3. In their final year, students can stick with two subjects for a Joint Honours (Double Major) degree, or specialise in one, for Single Honours.

I like this programme very much because it does not force the students to choose a specialism before they have had a taste of the subject, and that it is flexible enough to accommodate Joint Honours qualifications in, e.g., Theoretical Physics and Mathematics. It also allows us to enrol students onto Physics degrees who have not done Physics or Applied Mathematics as part of the Leaving Certificate.

I think Mathematical Physics has a particular value in the first year of this course, even for students who do now wish to continue with beyond that level. The material we present in the first year focusses on Mechanics, which is perfect for students to learn how to apply concepts from the Mathematics courses in calculus and linear algebra (especially vectors). It obviously complements Experimental Physics and I would recommend all students who want to do Experimental Physics to do Mathematical Physics too, but  basic mechanics comes up in a wide range of contexts in science, including Biology and Chemistry, so it is relevant for students taking a wide range of pathways through this very flexible programme.

 

 

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New Publication at the Open Journal of Astrophysics!

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , on June 25, 2020 by telescoper

Proving further the point that the The Open Journal of Astrophysics is definitely fully open we have published yet another paper. This one was actually published yesterday, which means that we had two in two days..

This one is in the Cosmology and Nongalactic Astrophysics section and is entitled Source Distributions of Cosmic Shear Surveys in Efficiency Space. The authors are Nicolas Tessore and Ian Harrison, both from the University of Manchester. The paper is concerned with the extraction of cosmological information from cosmic shear surveys.

Here is a screen grab of the overlay:

You can find the arXiv version of the paper here.

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What kind of thing is GW190814?

Posted in The Universe and Stuff with tags , , , , , , , on June 24, 2020 by telescoper

There’s been a lot of interest in the past day or two over an event that occurred in the LIGO detectors last August, entitled GW190814. A paper has appeared declaring this to be “the observation of a compact binary coalescence involving a 22.2–24.3 M ⊙ black hole and a compact object with a mass of 2.50–2.67 M ⊙“. That would be interesting of course because the smaller object is smaller than the black holes involved in previous detections and its mass suggests the possibility that it may be a neutron star, although no electromagnetic counterpart has yet been detected.  It’s a mystery.

I was quite excited when I saw the announcement about this yesterday but my enthusiasm was dampened a bit when I saw the data from the two LIGO detectors at Hanford and Livingston in the USA and the Virgo detector in Italy.

Visually, the Livingston detection seems reasonably firm, but the paper notes that there were thunderstorms in the area at the time of  GW190814 which affected the low-frequency data. There doesn’t look like anything at all but noise in the Virgo channel. The Hanford data may show something but, according to the paper, the detector was “not in nominal observing mode at the time of GW190814” so the data from this detector require special treatment. What you see in the Hanford channel looks rather similar to the two (presumably noise) features seen to the left in the Livingston plot.

I know that – not for the first time – I’m probably going to incur the wrath of my colleagues in the gravitational waves community but I have to sound a note of caution. Before asking whether the event involves a black hole or a neutron star you have to be convinced that the event is an event at all.  Fortunately, at least some of the data relating to this have been released and will no doubt be subjected to independent scrutiny.

Now I’m going to retreat into my bunker and hide from the inevitable comments…

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