Archive for the The Universe and Stuff Category

Precision Cosmology!

Posted in Books, The Universe and Stuff with tags , , on April 28, 2017 by telescoper

Well, look what the postman brought me today!

Hot off the press, here is a textbook by my friend and erstwhile collaborator Bernard Jones. As you will see, it even has an endorsement by me on the back cover. I think its a very fine book indeed and it will be immensely useful for cosmologists young and old alike!

PhD Opportunities in Data-intensive Physics & Astrophysics!

Posted in The Universe and Stuff on April 24, 2017 by telescoper

I’m back from my little holiday having accumulated a very long to-do list, near the top of which are a number of things related to our new STFC-funded Centre for Doctoral Training involving the Universities of Cardiff, Bristol and Swansea. This will be coordinated by the Data Innovation Institute at Cardiff University and it covers  a wide range of data-intensive research in particle physics, astrophysics and cosmology carried on at the three member institutions. ‘Data-intensive’ here means involving very big data sets, very sophisticated analysis methods or high-performance computing,  or any combination of these.

The Centre for Doctoral Training is being coordinated by the Data Innovation Institute at Cardiff University. It will commence in September 2017. Applications have been open for a couple of weeks and we will be starting to make selections very soon so if you’re interested in this opportunity you will have to get your skates on! In fact, to secure a PhD place at this STFC CDT administered by the DII you’d better apply PDQ!

For further information on the programme, including details of some of the projects on offer at Cardiff, please see here. Follow that link if you want some more information about the application process.

By the way, for  this special programme, STFC have relaxed the  rules relating to  nationality, so full funding is potentially available for  non-UK citizens under this scheme – that isn’t normally the case for PhD studentships funded by the UK research councils.

If you’re looking to do a PhD in data-intensive physics or astrophysics, get your application in now!

 

The Einstein Theory of Relativity

Posted in Film, The Universe and Stuff with tags , on April 21, 2017 by telescoper

I thought you might find this film interesting. I think it’s rather wonderful, actually, though it’s silent and definitely pre-CGI. It’s also a bit dodgy on the science in a few places.

However, made way back in 1923 by Max FleischerThe Einstein Theory of Relativity  has to be one of the first science films ever made. Who can think of an earlier one?

P.S. Bonus points if you can name the soundtrack music!

 

Going NUTs

Posted in The Universe and Stuff, Uncategorized with tags , , , on April 5, 2017 by telescoper

If you’ve studied General Relativity the chances are that you’ve come across the Taub-NUT exact solution discussed in this post. It’s generally regarded as something of an oddity in that it’s a bit contrived, but provides a counter-example to some well-known results. For example, in the context of a Black Hole solution, it violates the No Hair Theorem (by violating the assumption of asymptotic flatness).

When I saw this post at CQG, however, I was reminded of a paper published a few years ago discussing this in a cosmological context, where it can be seen as a special case of the Bianchi IX geometry.

CQG+

By Paul I. Jefremov and Volker Perlick.


Among all known solutions to Einstein’s vacuum field equation the (Taub-)NUT metric is a particularly intriguing one. It is that metric that owing to its counter-intuitive features was once called by Charles Misner “a counter-example to almost anything”. In what follows we give a brief introduction to the NUT black holes, discuss what makes them interesting for a researcher and speculate on how they could be detected should they exist in nature.

paul jefremov-and-volker Volker Perlick and Pavel (Paul) Ionovič Jefremov from the Gravitational Theory group at the University of Bremen in Germany. Volker is a Privatdozent and his research interests are in classical relativity, (standard and non-standard) electrodynamics and Finsler geometry. He is an amateur astronomer and plays the piano with great enthusiasm and poor skills. Paul got his diploma in Physics at the National Research Nuclear University MEPhI in Moscow, 2014. Now he…

View original post 901 more words

The Bayesian Second Law of Thermodynamics

Posted in The Universe and Stuff with tags , , , on April 3, 2017 by telescoper

I post occasionally about Bayesian probability, particularly with respect to Bayesian inference, and related applications to physics and other things, such as thermodynamics, so in that light here’s a paper I stumbled across yesterday. It’s not a brand new paper – it came out on the ArXiv in 2015 – but it’s of sufficiently long-term interest to warrant sharing on here. Here’s the abstract:

You can download the full paper here. There’s also an accessible commentary by one of the authors here.

The interface between thermodynamics, statistical mechanics, information theory  and probability is a fascinating one, but too often important conceptual questions remain unanswered, or indeed unasked, while the field absorbs itself in detailed calculations. Refreshingly, this paper takes the opposite approach.

 

 

 

Is there a kinematic backreaction in cosmology?

Posted in The Universe and Stuff with tags , , , , , on March 28, 2017 by telescoper

I just noticed that a paper has appeared on the arXiv with the confident title There is no kinematic backreaction. Normally one can be skeptical about such bold claims, but this one is written by Nick Kaiser and he’s very rarely wrong…

The article has a very clear abstract:

Kaiser

This is an important point of debate, because the inference that the universe is dominated by dark energy (i.e. some component of the cosmic energy density that violates the strong energy condition) relies on the assumption that the distribution of matter is homogeneous and isotropic (i.e. that the Universe obeys the Cosmological Principle). Added to the assumption that the large-scale dynamics of the Universe are described by the general theory of relativity, this means that we evolution of the cosmos is described by the Friedmann equations. It is by comparison with the Friedmann equations that we can infer the existence of dark energy from the apparent change in the cosmic expansion rate over time.

But the Cosmological Principle can only be true in an approximate sense, on very large scales, as the universe does contain galaxies, clusters and superclusters. It has been a topic of some discussion over the past few years as to whether the formation of cosmic structure may influence the expansion rate by requiring extra terms that do not appear in the Friedmann equations.

Nick Kaiser says `no’. It’s a succinct and nicely argued paper but it is entirely Newtonian. It seems to me that if you accept that his argument is correct then the only way you can maintain that backreaction can be significant is by asserting that it is something intrinsically relativistic that is not covered by a Newtonian argument. Since all the relevant velocities are much less than that of light and the metric perturbations generated by density perturbations are small (~10-5) this seems a hard case to argue.

I’d be interested in receiving backreactions to this paper via the comments box below.

Science for the Citizen

Posted in Education, Open Access, The Universe and Stuff with tags , , , , , , on March 20, 2017 by telescoper

I spent all day on Friday on business connected with my role in the Data Innovation Research Institute, attending an event to launch the new Data Justice Lab at Cardiff University. It was a fascinating day of discussions about all kinds of ethical, legal and political issues surrounding the “datafication” of society:

Our financial transactions, communications, movements, relationships, and interactions with government and corporations all increasingly generate data that are used to profile and sort groups and individuals. These processes can affect both individuals as well as entire communities that may be denied services and access to opportunities, or wrongfully targeted and exploited. In short, they impact on our ability to participate in society. The emergence of this data paradigm therefore introduces a particular set of power dynamics requiring investigation and critique.

As a scientist whose research is in an area (cosmology) which is extremely data-intensive, I have a fairly clear interpretation of the phrase “Big Data” and recognize the need for innovative methods to handle the scale and complexity of the data we use. This clarity comes largely from the fact that we are asking very well-defined questions which can be framed in quantitative terms within the framework of well-specified theoretical models. In this case, sophisticated algorithms can be constructed that extract meaningful information even when individual measurements are dominated by noise.

The use of “Big Data” in civic society is much more problematic because the questions being asked are often ill-posed and there is rarely any compelling underlying theory. A naive belief exists in some quarters that harvesting more and more data necessarily leads to an increase in relevant information. Instead there is a danger that algorithms simply encode false assumptions and produce unintended consequences, often with disastrous results for individuals. We heard plenty of examples of this on Friday.

Although it is clearly the case that personal data can be – and indeed is – deliberately used for nefarious purposes, I think there’s a parallel danger that we increasingly tend to believe that just because something is based on numerical calculations it somehow must be “scientific”. In reality, any attempt to extract information from quantitative data relies on assumptions. if those assumptions are wrong, then you get garbage out no matter what you put in. Some applications of “data science” – those that don’t recognize these limitations – are in fact extremely unscientific.

I mentioned in discussions on Friday that there is a considerable push in astrophysics and cosmology for open science, by which I mean that not only are the published results openly accessible, but all the data and analysis algorithms are published too. Not all branches of science work this way, and we’re very far indeed from a society that applies such standards to the use of personal data.

Anyway, after the day’s discussion we adjourned to the School of Journalism, Media and Cultural Studies for a set of more formal presentations. The Head of School, Professor Stuart Allan introduced this session with some quotes from a book called Science for the Citizen, written by Lancelot Hogben in 1938. I haven’t read the book, but it looks fascinating and prescient. I have just ordered it and look forward to reading it. You can get the full-text free online here.

Here is the first paragraph of Chapter 1:

A MUCH abused writer of the nineteenth century said: up to the present philosophers have only interpreted the world, it is also necessary to change it. No statement more fittingly distinguishes the standpoint of humanistic philosophy from the scientific outlook. Science is organized workmanship. Its history is co-extensive with that of civilized living. It emerges so soon as the secret lore of the craftsman overflows the dam of oral tradition, demanding a permanent record of its own. It expands as the record becomes accessible to a widening personnel, gathering into itself and coordinating the fruits of new crafts. It languishes when the social incentive to new productive accomplishment is lacking, and when its custodians lose the will to share it with others. Its history, which is the history of the constructive achievements of mankind, is also the history of the democratization of positive knowledge. This book is written to tell the story of its growth as a record of human achievement, a story of the satisfaction of the common needs of mankind, disclosing as it unfolds new horizons of human wellbeing which lie before us, if we plan our new resources intelligently.

The phrase that struck me with particular force is “the democratization of positive knowledge”. That is what I believe science should do, but the closed culture of many fields of modern science makes it difficult to argue that’s what it actually does. Instead, there is an increasing tendency for scientific knowledge in many domains to be concentrated in a small number of people with access to the literature and the expertise needed to make sense of it.

In an increasingly technologically-driven society, the gap between the few in and the many out of the know poses a grave threat to our existence as an open and inclusive democracy. The public needs to be better informed about science (as well as a great many other things). Two areas need attention.

In fields such as my own there’s a widespread culture of working very hard at outreach. This overarching term includes trying to get people interested in science and encouraging more kids to take it seriously at school and college, but also engaging directly with members of the public and institutions that represent them. Not all scientists take the same attitude, though, and we must try harder. Moves are being made to give more recognition to public engagement, but a drastic improvement is necessary if our aim is to make our society genuinely democratic.

But the biggest issue we have to confront is education. The quality of science education must improve, especially in state schools where pupils sometimes don’t have appropriately qualified teachers and so are unable to learn, e.g. physics, properly. The less wealthy are becoming systematically disenfranchised through their lack of access to the education they need to understand the complex issues relating to life in an advanced technological society.

If we improve school education, we may well get more graduates in STEM areas too although this government’s cuts to Higher Education make that unlikely. More science graduates would be good for many reasons, but I don’t think the greatest problem facing the UK is the lack of qualified scientists – it’s that too few ordinary citizens have even a vague understanding of what science is and how it works. They are therefore unable to participate in an informed way in discussions of some of the most important issues facing us in the 21st century.

We can’t expect everyone to be a science expert, but we do need higher levels of basic scientific literacy throughout our society. Unless this happens we will be increasingly vulnerable to manipulation by the dark forces of global capitalism via the media they control. You can see it happening already.