Archive for the The Universe and Stuff Category

New Publication at the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , , , , , , , on March 24, 2021 by telescoper

Time to announce another publication in the Open Journal of Astrophysics. This one was published yesterday, actually, but I didn’t get time to post about it until just now. It is the third paper in Volume 4 (2021) and the 34th paper in all.

The latest publication is entitled Dwarfs from the Dark (Energy Survey): a machine learning approach to classify dwarf galaxies from multi-band images and is written by Oliver Müller  of the Observatoire Astronomique de Strasbourg (France) and Eva Schnider of the University of Basel (Switzerland).

Here is a screen grab of the overlay which includes the abstract:

 

You can click on the image to make it larger should you wish to do so. You can find the arXiv version of the paper here. This one is in the Instrumentation and Methods for Astrophysics Folder, though it does overlap with Astrophysics of Galaxies too.

It seems the authors were very happy with the publication process!

Incidentally, the Scholastica platform we are using for the Open Journal of Astrophysics is continuing to develop additional facilities. The most recent one is that the Open Journal of Astrophysics now has the facility to include supplementary files (e.g. code or data sets) along with the papers we publish. If any existing authors (i.e. of papers we have already published) would like us to add supplementary files retrospectively then please contact us with a request!

The Hubble Constant from Gravitational Waves

Posted in The Universe and Stuff with tags , , , , on March 22, 2021 by telescoper

Some time ago I blogged about how one can use gravitational waves to estimate the Hubble Constant, H0. Well, about a month ago the LIGO people produced a user-friendly update on progress in that regard which you can find here.

The full paper (i.e. author list plus a small amount of text) can be found here. Here are two plots from that work.

The first shows the constraints from the six loudest gravitational wave events selected for the latest work, together with the two competing measurements from Planck and SH0ES:

As you can see the individual measurements do not constrain very much. The second plot shows the effect of combining all relevant data, including  a binary neutron star merger with an electromagnetic counterparts. The results are much stronger when the latter is included

Obviously this measurement isn’t yet able to resolve the alleged tension between “high” and “low” values described on this blog passim, but it’s early days. If LIGO reaches its planned sensitivity the next observing run should provide many more events. A few hundred should get the width of the posterior distribution shown in the second figure down to a few percent, which would be very interesting indeed!

Basic Research in Ireland

Posted in Science Politics, The Universe and Stuff with tags , , on March 21, 2021 by telescoper


I realised today that I hadn’t yet posted a reaction to theannouncement earlier this month by Science Foundation Ireland (SFI) of a new five-year strategic plan. Although much of the document Shaping Our Future is fairly bland – as strategic plans usually are – there are some very welcome things in it.

Currently Ireland spends just 1.1% of its GDP on scientific research and development and SFI currently has a heavy focus on applied research (i.e. research aligned with industry that can be exploited for short-term commercial gain). This has made life difficult for basic or fundamental science and has driven many researchers in such areas abroad, to the detriment of Ireland’s standing in the international community.

The new strategy, which will cover the period from now to 2025, plans for 15% annual rises that will boost the agency’s grant spending — the greater part of the SFI budget — from €200 million in 2020 to €376 million by 2025. Much of this is focused in top-down manner on specific programmes and research centres but there is at least an acknowledgement of the need to support basic research, including an allocation of €11 million in 2021 for early career researchers.

The overall aim is to increase the overall R&D spend from 1.1% of gross domestic product, well below the European average of 2.2%, to 2.5% by 2025.

One of the jobs I had to do last week was to write the Annual Research Report for the Department of Theoretical Physics at Maynooth University. I am very pleased that despite the Covid-19 pandemic, over the last year we managed to score some notable successes in securing new grant awards (amounting to €1.3M altogether) as well as doubling the number of refereed publications since the previous year. This is of course under the old SFI regime. Hopefully in the next few years covered by the new SFI strategic plan we’ll be able to build on that growth still further, especially in areas related to quantum computing and quantum technology generally.

Anyway, it seems that SFI listened to at least some of the submissions made to the consultation exercise I mentioned a few months ago.

Non-Solutions to the Hubble Constant Problem…

Posted in The Universe and Stuff with tags , , , , on March 18, 2021 by telescoper

A rather pugnacious paper by George Efstathiou appeared on the arXiv earlier this week. Here is the abstract:

This paper investigates whether changes to late time physics can resolve the `Hubble tension’. It is argued that many of the claims in the literature favouring such solutions are caused by a misunderstanding of how distance ladder measurements actually work and, in particular, by the inappropriate use of distance ladder H0 priors. A dynamics-free inverse distance ladder shows that changes to late time physics are strongly constrained observationally and cannot resolve the discrepancy between the SH0ES data and the base LCDM cosmology inferred from Planck.

For a more detailed discussion of this paper, see Sunny Vagnozzi’s blog post. I’ll just make some general comments on the context.

One of the reactions to the alleged “tension” between the two measurements of H0 is to alter the standard model in such a way that the equation of state changes significantly at late cosmological times. This is because the two allegedly discrepant sets of measures of the cosmological distance scale (seen, for example, in the diagram below  taken from the paper I blogged about a while ago here) differ in that the low values are global measures (based on observations at high redshift) while the high values of are local (based on direct determinations using local sources, specifically stars of various types).

That is basically true. There is, however, another difference in the two types of distance determination: the high values of the Hubble constant are generally related to interpretations of the measured brightness of observed sources (i.e. they are based on luminosity distances) while the lower values are generally based on trigonometry (specifically they are angular diameter distances). Observations of the cosmic microwave background temperature pattern, baryon acoustic oscillations in the matter power-spectrum, and gravitational lensing studies all involve angular-diameter distances rather than luminosity distances.

Before going on let me point out that the global (cosmological) determinations of the Hubble constant are indirect in that they involve the simultaneous determination of a set of parameters based on a detailed model. The Hubble constant is not one of the basic parameters inferred from cosmological observations, it is derived from the others. One does not therefore derive the global estimates in the same way as the local ones, so I’m simplifying things a lot in the following discussion which I am not therefore claiming to be a resolution of the alleged discrepancy. I’m just thinking out loud, so to speak.

With that caveat in mind, and setting aside the possibility (or indeed probability) of observational systematics in some or all of the measurements, let us suppose that we did find that there was a real discrepancy between distances inferred using angular diameters and distances using luminosities in the framework of the standard cosmological model. What could we infer?

Well, if the Universe is described by a space-time with the Robertson-Walker Metric (which is the case if the Cosmological Principle applies in the framework of General Relativity) then angular diameter distances and luminosity distances differ only by a factor of (1+z)2 where z is the redshift: DL=DA(1+z)2.

I’ve included here some slides from undergraduate course notes to add more detail to this if you’re interested:

The result DL=DA(1+z)2 is an example of Etherington’s Reciprocity Theorem. If we did find that somehow this theorem were violated, how could we modify our cosmological theory to explain it?

Well, one thing we couldn’t do is change the evolutionary history of the scale factor a(t) within a Friedman model. The redshift just depends on the scale factor when light is emitted and the scale factor when it is received, not how it evolves in between. And because the evolution of the scale factor is determined by the Friedman equation that relates it to the energy contents of the Universe, changing the latter won’t help either no matter how exotic the stuff you introduce (as long as it only interacts with light rays via gravity). In the light of this, the fact there are significant numbers of theorists pushing for such things as interacting dark-energy models to engineer late-time changes in expansion history is indeed a bit perplexing.

In the light of the caveat I introduced above, I should say that changing the energy contents of the Universe might well shift the allowed parameter region which may reconcile the cosmological determination of the Hubble constant from cosmology with local values. I am just talking about a hypothetical simpler case.

In order to violate the reciprocity theorem one would have to tinker with something else. An obvious possibility is to abandon the Robertson-Walker metric. We know that the Universe is not exactly homogeneous and isotropic, so one could appeal to the gravitational lensing effect of lumpiness as the origin of the discrepancy. This must happen to some extent, but understanding it fully is very hard because we have far from perfect understanding of globally inhomogeneous cosmological models.

Etherington’s theorem requires light rays to be described by null geodesics which would not be the case if photons had mass, so introducing massive photons that’s another way out. It also requires photon numbers to be conserved, so some mysterious way of making photons disappear might do the trick, so adding some exotic field that interacts with light in a peculiar way is another possibility.

Anyway, my main point here is that if one could pin down the Hubble constant tension as a discrepancy between angular-diameter and luminosity based distances then the most obvious place to look for a resolution is in departures of the metric from the Robertson-Walker form. The reciprocity theorem applies to any GR-based metric theory, i.e. just about anything without torsion in the metric, so it applies to inhomogeneous cosmologies based on GR too. However, in such theories there is no way of defining a global scale factor a(t) so the reciprocity relation applies only locally, in a different form for each source and observer.

All of this begs the question of whether or not there is real tension in the  H0 measures. I certainly have better things to get tense about. That gives me an excuse to include my long-running poll on the issue:

Matter and forces in quantum field theory – an attempt at a philosophical elucidation

Posted in Maynooth, The Universe and Stuff with tags , , , on March 16, 2021 by telescoper

I thought the following might be of general interest to readers of this blog. It’s a translation into English of an MSc thesis written by a certain Jon-Ivar Skullerud of the Department of Theoretical Physics at Maynooth University. I hasten to add that Dr Skullerud hasn’t just finished his MSc. It just appears that it has taken about 30 years to translate it from Norwegian into English!

Anyway, the English version is now available on the arXiv here. There isn’t really an abstract as such but the description on arXiv says:

This is a translation into English of my Masters thesis (hovedoppgave) from 1991. The main topic of the thesis is the relation between fundamental physics and philosophy, and a discussion of several possible ontologies of quantum field theory.

I note from here that hovedoppgave translates literally into English as “main task”.

I haven’t read this thesis from cover to cover yet – partly because it’s in digital form and doesn’t have any covers on it and partly because it’s 134 pages long –  but I’ve skimmed a few bits and it looks interesting.

 

 

Reminder: What is Quantum Technology? – A Public Lecture by Prof. Sir Peter Knight

Posted in Maynooth, The Universe and Stuff with tags , , , , on March 10, 2021 by telescoper

I thought I’d post a quick reminder that tomorrow, Thursday March 11th (at 7pm), the Maynooth University Faculty of Science and Engineering will present its first ever Dean’s Lecture.of the Faculty of Science and Engineering. This is a public event, consisting of a talk followed by a Q&A session. I’m told that over 350 people have signed up for this talk but there’s still room for a few more.

The topic of the talk is quantum technology and it is presented by Prof. Sir Peter Knight who is Senior Research Investigator at Imperial College London. He retired in 2010 as Deputy Rector (Research) at Imperial. He was knighted in 2005 for his work in optical physics. Knight was the 2004 President of the Optical Society of America and 2011-2013 President of the Institute of Physics. He is Editor of Contemporary Physics, Chair of the UK National Quantum Technology Programme Strategy Advisory Board, chairs the Quantum Metrology Institute at the National Physical Laboratory, was until 2010 chair of the UK Defence Scientific Advisory Council and remains a UK Government science advisor. His research centres on quantum optics and quantum technology. He has won the Thomas Young Medal and the Glazebrook Medal of the Institute of Physics, the Ives Medal and the Walther Medal and Prize of the OSA, the Royal Medal of the Royal Society and the Faraday Prize of the IET.

Here is a description of the talk:

We already live in a quantum-enabled world with devices powered by quantum mechanics affecting our everyday world (lasers, telecoms semiconductor chips, and much more). But we are now poised to exploit a hitherto largely unexplored technology capability enabled by some of the stranger aspects of quantum physics: quantum coherence and entanglement. These new capabilities include novel sensing, timing, imaging, and of course computing. I will describe these new quantum coherence capabilities and plans to develop the next generation of quantum technologies. Quantum Information Science is advancing our understanding of the physical world in remarkable ways. But it is also driving novel and disruptive technologies. I will describe plans for ensuring the advanced quantum science and demonstrator platforms in imaging, sensing, communications, and computing developed over the past five years or so will drive the formation of the quantum technology sector and embed quantum technology in a broad range of industries.

The event is free but you will need to register here.

P.S. I will have a small part in this event – welcoming people to it and generally directing traffic.

Assembly on the Mountain

Posted in The Universe and Stuff with tags , , , on March 9, 2021 by telescoper

Here’s a video showing the arrival and installation of the Top End Assembly (TEA) of the Simonyi Survey Telescope at the Vera C Rubin Observatory site on top of Cerro Pachón in Chile. The Vera C Rubin Observatory was previously known as the Large Synoptic Survey Telescope but was subsequently renamed in honour of the late Vera Rubin.

It’s fantastic to see this project progressing to this stage. I have been around long enough to remember when LSST, as it then was, seemed to be in the impossibly distant future (along with e.g. JWST). The fact that it is now really happening makes me feel extremely old! It’s still great to see though.

 

Hawking and the Mind of God

Posted in Books, Talks and Reviews, Science Politics, The Universe and Stuff with tags , , , , , on March 3, 2021 by telescoper

There’s a new book out about Stephen Hawking which has triggered a certain amount of reaction (see, e.g., here) so I thought I’d mention a book I wrote, largely in response to the pseudo-religious nature of some of Hawking’s later writings.

I have in the past gone on record, both on television and in print, as being not entirely positive about the “cult” that surrounds Stephen Hawking. I think a number of my colleagues have found some of my comments disrespectful and/or churlish. I do nevertheless stand by everything I’ve said. I have enormous respect for Hawking the physicist, as well as deep admiration for his tenacity and fortitude, and have never said otherwise. I don’t, however, agree that Hawking is in the same category of revolutionary thinkers as Newton or Einstein, which is how he is often portrayed.

In fact a poll of 100 theoretical physicists in 1999 came to exactly the same conclusion. The top ten in that list were:

  1. Albert Einstein
  2. Isaac Newton
  3. James Clerk Maxwell
  4. Niels Bohr
  5. Werner Heisenberg
  6. Galileo Galilei
  7. Richard Feynman
  8. Paul Dirac
  9. Erwin Schrödinger
  10. Ernest Rutherford

The idea of a league table like this is of course a bit silly, but it does at least give some insight into the way physicists regard prominent figures in their subject. Hawking came way down the list, in fact, in 300th (equal) place. I don’t think it is disrespectful to Hawking to point this out. I’m not saying he isn’t a brilliant physicist. I’m just saying that there are a great many other brilliant physicists that no one outside physics has ever heard of.

It is interesting to speculate what would have happened if the list had been restricted to living physicists. I’d guess Hawking would be in the top ten, but I’m not at all sure where…

And before I get accused of jealousy about Stephen Hawking’s fame, let me make it absolutely clear that if Hawking was like a top Premiership footballer (which I think is an appropriate analogy), then I am definitely like someone kicking a ball around for a pub team on a Sunday morning (with a hangover). This gulf does not make me envious; it just makes me admire his ability all the more, just as trying to play football makes one realise exactly how good the top players really are.

I am not myself religious but I do think that there are many things that science does not – and probably will never – explain, such as why there is something rather than nothing. I also believe that science and religious belief are not in principle incompatible – although whether there is a conflict in practice does depend of course on the form of religious belief and how it is observed. God and physics are in my view pretty much orthogonal. To put it another way, if I were religious, there’s nothing in theoretical physics that would change make me want to change my mind. However, I’ll leave it to those many physicists who are learned in matters of theology to take up the (metaphorical) cudgels with Professor Hawking.

Anyway, this is the book I wrote:.

And here is the jacket blurb:

Stephen Hawking has achieved a unique position in contemporary culture, combining eminence in the rarefied world of theoretical physics with the popular fame usually reserved for film stars and rock musicians. Yet Hawking’s technical work is so challenging, both in its conceptual scope and in its mathematical detail, that proper understanding of its significance lies beyond the grasp of all but a few specialists. How, then, did Hawking-the-scientist become Hawking-the-icon? Hawking’s theories often take him into the intellectual territory that has traditionally been the province of religion rather than science. He acknowledges this explicitly in the closing sentence of his bestseller, A Brief History of Time , where he says that his ultimate aim is to know the Mind of God . Hawking and the Mind of God examines the pseudo-religious connotations of some of the key themes in Hawking’s work, and how these shed light not only on the Hawking cult itself, but also on the wider issue of how scientists represent themselves in the media.

I’m sure you’ll understand that there isn’t a hint of opportunism in the way I’m drawing this to your attention because my book is long out of print so you can’t buy it unless you get a copy second-hand…

Postgraduate Programmes in Theoretical Physics at Maynooth University

Posted in Education, Maynooth, The Universe and Stuff with tags , , on March 2, 2021 by telescoper

We have a (virtual) Postgraduate Open Day coming up on Tuesday 9th March at Maynooth University (for which you can register here). To go with that here is a short video of our new Postgraduate Coordinator Dr John Regan answering some frequently asked questions about the programmes we offer in the Department of Theoretical Physics:

If you have any other questions then you can register for the Open Day where we will have staff on hand to answer them in a live Q&A session.

You could also follow the Department’s Twitter feed here:

Particle Physics Masterclass at Maynooth

Posted in Education, Maynooth, The Universe and Stuff with tags , , on February 26, 2021 by telescoper

I have already informed you of a Masterclass in Astrophysics & Cosmology at Maynooth that will take place on March 25th 2021. For more information on that event including instructions on how to book see here.

Now it’s time to announce the International Masterclass on Particle Physics. The  Department of Theoretical Physics has hosted such event for secondary school students each Spring, apart from last year when it was cancelled because of Covid-19.  The next event will take place online on 21 and 22 March 2021. You can find more information, including instructions on how to book a place, here.

These Masterclasses give secondary school students the opportunity to discover the world of quarks and leptons for themselves, by performing measurements on real data from CERN, meeting active particle physics researchers and linking up with like-minded students from other countries.  We will join thousands of other secondary school students at more than 100 universities and laboratories around Europe and worldwide in a programme stretching over four weeks.

Physics at the most fundamental level – the smallest and most basic building blocks of matter – is an exotic world.  But a few introductory talks and working with data from CERN will give the students insight into the fundamental particles of matter and the forces between them, as well as what went on during the Big Bang.

On Sunday afternoon, the students are introduced to particle physics, experiments and detectors in lectures given by active particle physics researchers.  On Monday, after a virtual visit to the ALICE detector at CERN, they work on their own with data from ALICE Afterwards they participate in a video conference with students from other countries and moderators at CERN, where they discuss and compare their results.

For more information on the Particle Physics Masterclasses, see the International Masterclasses web site.

I don’t know. You wait ages for a Masterclass in Physics at Maynooth University, and then along come two in quick succession!