I took my first degree in the Natural Sciences Tripos at the University of Cambridge. This involved doing a very general first year comprising four different elements that could be chosen flexibly. I quickly settled on Physics, Chemistry and Mathematics for Natural Sciences to reflect my A-level results but was struggling for the fourth. In the end I picked the one that seemed most like Physics, a course called Crystalline Materials. I didn’t like that at all, and wish I’d done some Biology instead – Biology of Cells and Biology of Organisms were both options – or even Geology, but I stuck with it for the first year.
Having to do such a wide range of subjects was very challenging. The timetable was densely packed and the pace was considerable. In the second year, however, I was able to focus on Mathematics and Physics and although it was still intense it was a bit more focussed. I ended up doing Theoretical Physics in my final year, including a theory project.
My best teacher at School, Dr Geoeff Swinden, was a chemist (he had a doctorate in organic chemistry from Oxford University) and when I went to Cambridge I fully expected to specialisze in Chemistry rather than Physics. I loved the curly arrows and all that. But two things changed. One was that I found the Physics content of the first year far more interesting – and the lecturers and tutors far more inspiring – than Chemistry, and the other was that my considerable ineptitude at practical work made me doubt that I had a future in a chemistry laboratory. And so it came to pass that I switched allegiance to Physics, a decision I am very glad I made.
(It was only towards the end of my degree that I started to take Astrophysics seriously as a possible specialism, but that’s another story…)
Anyway, when I turned up at Cambridge over 40 years ago to begin my course, and having Chemistry as a probable end point, I bought all the recommended text books, one of which was Physical Chemistry by P.W. Atkins. I found a picture (above) of the 1982 edition which may well be the one I bought (although I vaguely remember the one I had being in paperback). I thought it was a very good book, and it has gone into many subsequent editions. I also found the Physical part of Chemistry quite straightforward because it is basically Physics. I even got higher marks in Chemistry in the first year than I did in Physics but that didn’t alter my decision to drop Chemistry after the first year. When I did so, I followed tradition and sold my copy to a new undergraduate along with the other books relating to courses that I dropped.
Yesterday I found out that Peter Atkins has decided to make one of his books available to download. The book concerned is however not the compendious tome I bought, but a shorter summary called Concepts in Physical Chemistry, which was published in 1995. This is no doubt a very useful text for beginning Chemistry students so I thought I’d pass on this information. You can download it here, although you have to do it chapter by chapter in PDF files.
P.S. Chemistry in Spanish is ‘Química’. Since Physics and Chemistry share the same building in the University of Barcelona, where I am currently working, I frequently walk past rooms with doors marked ‘Quim’ (but I have never taken the opportunity to enter one).
I was intrigued to see this graphic accompanying an article about hurling. Notice that the left hand side shows the field equations of Einstein’s General Theory of Relativity and some expressions to do with quantum mechanics. Hurling is indeed an extraordinary – and extraordinarily fast – sport but is the article implying that classical physics is inadequate to describe it? Perhaps it is implying that through hurling we will at last arrive at a Theory of Everything?
Here’s another video in the Cosmology Talks series curated by Shaun Hotchkiss. This one very timely after yesterday’s announcement. Here is the description on the YouTube page:
The Dark Energy Spectroscopic Instrument (DESI) has produced cosmological constraints! And it is living up to its name. Two researchers from DESI, Seshadri Nadathur and Andreu Font-Ribera, tell us about DESI’s measurements of the Baryon Acoustic Oscillations (BAO) released today. These results use one full year of DESI data and are the first cosmological constraints from the telescope that have been released. Mostly, it is what you might expect: tighter constraints. However, in the realm of the equation of state of dark energy, they find, even with BAO alone, that there is a hint of evidence for evolving dark energy. When they combine their data with CMB and Supernovae, who both also find small hints of evolving dark energy on their own, the evidence for dark energy not being a cosmological constant jumps as high as 3.9σ with one combination of the datasets. It seems there still is “concordance cosmology”, it’s just not ΛCDM for these datasets. The fact that all three probes are tentatively favouring this is intriguing, as it makes it unlikely to be due to systematic errors in one measurement pipeline.
My own take is that the results are very interesting but I think we need to know a lot more about possible systematics before jumping to conclusions about time-varying dark energy. Am I getting conservative in my old age? These results from DESI do of course further underline the motivation for Euclid (another Stage IV survey), which may have an even better capability to identify departures from the standard model.
P.S. Here’s a nice graphic showing the cosmic web showing revealed by the DESI survey:
Here’s an interestingly different talk in the series of Cosmology Talks curated by Shaun Hotchkiss. The speaker, Sylvia Wenmackers, is a philosopher of science. According to the blurb on Youtube:
Her focus is probability and she has worked on a few theories that aim to extend and modify the standard axioms of probability in order to tackle paradoxes related to infinite spaces. In particular there is a paradox of the “infinite fair lottery” where within standard probability it seems impossible to write down a “fair” probability function on the integers. If you give the integers any non-zero probability, the total probability of all integers is unbounded, so the function is not normalisable. If you give the integers zero probability, the total probability of all integers is also zero. No other option seems viable for a fair distribution. This paradox arises in a number of places within cosmology, especially in the context of eternal inflation and a possible multiverse of big bangs bubbling off. If every bubble is to be treated fairly, and there will ultimately be an unbounded number of them, how do we assign probability? The proposed solutions involve hyper-real numbers, such as infinitesimals and infinities with different relative sizes, (reflecting how quickly things converge or diverge respectively). The multiverse has other problems, and other areas of cosmology where this issue arises also have their own problems (e.g. the initial conditions of inflation); however this could very well be part of the way towards fixing the cosmological multiverse.
The paper referred to in the presentation can be found here. There is a lot to digest in this thought-provoking talk, from the starting point on Kolmogorov’s axioms to the application to the multiverse, but this video gives me an excuse to repeat my thoughts on infinities in cosmology.
Most of us – whether scientists or not – have an uncomfortable time coping with the concept of infinity. Physicists have had a particularly difficult relationship with the notion of boundlessness, as various kinds of pesky infinities keep cropping up in calculations. In most cases this this symptomatic of deficiencies in the theoretical foundations of the subject. Think of the ‘ultraviolet catastrophe‘ of classical statistical mechanics, in which the electromagnetic radiation produced by a black body at a finite temperature is calculated to be infinitely intense at infinitely short wavelengths; this signalled the failure of classical statistical mechanics and ushered in the era of quantum mechanics about a hundred years ago. Quantum field theories have other forms of pathological behaviour, with mathematical components of the theory tending to run out of control to infinity unless they are healed using the technique of renormalization. The general theory of relativity predicts that singularities in which physical properties become infinite occur in the centre of black holes and in the Big Bang that kicked our Universe into existence. But even these are regarded as indications that we are missing a piece of the puzzle, rather than implying that somehow infinity is a part of nature itself.
The exception to this rule is the field of cosmology. Somehow it seems natural at least to consider the possibility that our cosmos might be infinite, either in extent or duration, or both, or perhaps even be a multiverse comprising an infinite collection of sub-universes. If the Universe is defined as everything that exists, why should it necessarily be finite? Why should there be some underlying principle that restricts it to a size our human brains can cope with?
On the other hand, there are cosmologists who won’t allow infinity into their view of the Universe. A prominent example is George Ellis, a strong critic of the multiverse idea in particular, who frequently quotes David Hilbert
The final result then is: nowhere is the infinite realized; it is neither present in nature nor admissible as a foundation in our rational thinking—a remarkable harmony between being and thought
But to every Hilbert there’s an equal and opposite Leibniz
I am so in favor of the actual infinite that instead of admitting that Nature abhors it, as is commonly said, I hold that Nature makes frequent use of it everywhere, in order to show more effectively the perfections of its Author.
You see that it’s an argument with quite a long pedigree!
Many years ago I attended a lecture by Alex Vilenkin, entitled The Principle of Mediocrity. This was a talk based on some ideas from his book Many Worlds in One: The Search for Other Universes, in which he discusses some of the consequences of the so-called eternal inflation scenario, which leads to a variation of the multiverse idea in which the universe comprises an infinite collection of causally-disconnected “bubbles” with different laws of low-energy physics applying in each. Indeed, in Vilenkin’s vision, all possible configurations of all possible things are realised somewhere in this ensemble of mini-universes.
One of the features of this scenario is that it brings the anthropic principle into play as a potential “explanation” for the apparent fine-tuning of our Universe that enables life to be sustained within it. We can only live in a domain wherein the laws of physics are compatible with life so it should be no surprise that’s what we find. There is an infinity of dead universes, but we don’t live there.
I’m not going to go on about the anthropic principle here, although it’s a subject that’s quite fun to write or, better still, give a talk about, especially if you enjoy winding people up! What I did want to say mention, though, is that Vilenkin correctly pointed out that three ingredients are needed to make this work:
An infinite ensemble of realizations
A discretizer
A randomizer
Item 2 involves some sort of principle that ensures that the number of possible states of the system we’re talking about is not infinite. A very simple example from quantum physics might be the two spin states of an electron, up (↑) or down(↓). No “in-between” states are allowed, according to our tried-and-tested theories of quantum physics, so the state space is discrete. In the more general context required for cosmology, the states are the allowed “laws of physics” ( i.e. possible false vacuum configurations). The space of possible states is very much larger here, of course, and the theory that makes it discrete much less secure. In string theory, the number of false vacua is estimated at 10500. That’s certainly a very big number, but it’s not infinite so will do the job needed.
Item 3 requires a process that realizes every possible configuration across the ensemble in a “random” fashion. The word “random” is a bit problematic for me because I don’t really know what it’s supposed to mean. It’s a word that far too many scientists are content to hide behind, in my opinion. In this context, however, “random” really means that the assigning of states to elements in the ensemble must be ergodic, meaning that it must visit the entire state space with some probability. This is the kind of process that’s needed if an infinite collection of monkeys is indeed to type the (large but finite) complete works of shakespeare. It’s not enough that there be an infinite number and that the works of shakespeare be finite. The process of typing must also be ergodic.
Now it’s by no means obvious that monkeys would type ergodically. If, for example, they always hit two adjoining keys at the same time then the process would not be ergodic. Likewise it is by no means clear to me that the process of realizing the ensemble is ergodic. In fact I’m not even sure that there’s any process at all that “realizes” the string landscape. There’s a long and dangerous road from the (hypothetical) ensembles that exist even in standard quantum field theory to an actually existing “random” collection of observed things…
More generally, the mere fact that a mathematical solution of an equation can be derived does not mean that that equation describes anything that actually exists in nature. In this respect I agree with Alfred North Whitehead:
There is no more common error than to assume that, because prolonged and accurate mathematical calculations have been made, the application of the result to some fact of nature is absolutely certain.
It’s a quote I think some string theorists might benefit from reading!
Items 1, 2 and 3 are all needed to ensure that each particular configuration of the system is actually realized in nature. If we had an infinite number of realizations but with either infinite number of possible configurations or a non-ergodic selection mechanism then there’s no guarantee each possibility would actually happen. The success of this explanation consequently rests on quite stringent assumptions.
I’m a sceptic about this whole scheme for many reasons. First, I’m uncomfortable with infinity – that’s what you get for working with George Ellis, I guess. Second, and more importantly, I don’t understand string theory and am in any case unsure of the ontological status of the string landscape. Finally, although a large number of prominent cosmologists have waved their hands with commendable vigour, I have never seen anything even approaching a rigorous proof that eternal inflation does lead to realized infinity of false vacua. If such a thing exists, I’d really like to hear about it!
I can’t speak about the American Institute of Physics or the American Physical Society but in the context of the Institute of Physics – of which I am a Fellow and in whose house magazine the article appears – I draw your attention to the last sentence of the above excerpt which contains a commitment to “invest funds generated from publishing back into research” (my emphasis).
Really? The IOP invests in research? That’s news to me. How do I apply for a grant? Will they fund my next PhD student?
The IOP invests its funds in many things – many of them worthy – but it does not spend a significant part of the vast income it generates from its publishing house on research. The claim that it does is just dishonest. There’s point in mincing words.
This is an important distinction, particularly so that publishing in most IOP journals now requires the payment of a hefty Article Processing Charge (APC; Artificial Profit Charge would be more apt) which often has to be paid for out of research grants. Previously the revenue of IOP Publishing was appropriated from library budgets through subscriptions, so physicists were less aware of just how much the IOP was raking in. Now that researchers are having to find the funds themselves from research grants it has become more obvious that the IOP is actually a drain on research funds, not a source of them. The APC is a levy on research, designed to generate funds for other things. I think this model is indefensible. What gives the IOP the right to impose charges that far exceed the cost of disseminating scientific results in order to appropriate funds for its other activities?
Moreover, even if the IOP did fund research, what benefit would that be to a researcher in Spain, South Korea or Singapore or indeed anywhere outside the UK and Ireland?
The slogan for the initiative described in the article is “Purpose-led Publishing”. That reminds me of an old saying from systems theory: the Purpose Of a System Is What it Does (POSIWID). What the system does in this case is to raise funds for the IOP. That’s its purpose. Everything else is just marketing spiel.
The claim that IOP Publishing does not make a profit is disingenuous too. It does make a substantial profit. The only difference between it and the likes of Elsevier is where the profits go. A true not-for-profit publisher would charge only at the level to cover the costs of publication. The Purpose that should be leading Publishing in physics is the dissemination of scientific results, not the generation of revenue for sundry other things.
I have avoided publishing in IOP journals for many years because I think the approach of IOP Publishing is unethical. Now I have decided that I no longer wish to be associated with the IOP in any way. I have paid the subscription for 2024 but when that lapses I won’t renew it. Enough is enough.
At the annual AAS Meeting in New Orleans last week there was an announcement of a result that made headlines in the media (see, e.g., here and here). There is also a press release from the University of Central Lancashire.
Here is a video of the press conference:
I was busy last week so didn’t have time to read the details so refrained from commenting on this issue at the time of the announcement. Now that I am back in circulation, I have time to read the details, but unfortunately was unable to find even a preprint describing this “discovery”. The press conference doesn’t contain much detail either so it’s impossible to say anything much about the significance of the result, which is claimed (without explanation) to be 5.2σ (after “doing some statistics”). I see the “Big Ring” now has its own wikipedia page, the only references on which are to press reports, not peer-reviewed scientific papers or even preprints.
So is this structure “so big it challenges our understanding of the universe”?
The Big Ring (blue) and another large structure (red)Spot the Ring in the actual data
Based on the available information it is impossible to say. The large-scale structure of the Universe comprises a complex network of walls and filaments known as the cosmic web which I have written about numerous times on this blog. This structure is so vast and complicated that it is very easy to find strange shapes in it but very hard to determine whether or not they indicate anything other than an over-active imagination.
To assess the significance of the Big Ring or other structures in a proper scientific fashion, one has to calculate how probable that structure is given a model. We have a standard model that can be used for this purpose, but to simulate very structures is not straightforward because it requires a lot of computing power even to simulate just the mass distribution. In this case one also has to understand how to embed Magnesium absorption too, something which may turn out to trace the mass in a very biased way. Moreover, one has to simulate the observational selection process too, so one is doing a fair comparison between observations and predictions.
I have seen no evidence that this has been done in this case. When it is, I’ll comment on the details. I’m not optimistic however, as the description given in the media accounts contains numerous falsehoods. For example, quoting the lead author:
The Cosmological Principle assumes that the part of the universe we can see is viewed as a ‘fair sample’ of what we expect the rest of the universe to be like. We expect matter to be evenly distributed everywhere in space when we view the universe on a large scale, so there should be no noticeable irregularities above a certain size.
This just isn’t correct. The standard cosmology has fluctuations on all scales. Although the fluctuation amplitude decreases with scale, there is no scale at which the Universe is completely smooth. See the discussion, for example, here. We can see correlations on very large angular scales in the cosmic microwave background which would be absent if the Universe were completely smooth on those scales. The observed structure is about 400 Mpc in size, which does not seem to be to be particularly impressive.
I suspect that the 5.2σ figure mentioned above comes from some sort of comparison between the observed structure and a completely uniform background, in which case it is meaningless.
My main comment on this episode is that I think it’s very poor practice to go hunting headlines when there isn’t even a preprint describing the results. That’s not the sort of thing PhD supervisors should be allowing their PhD students to do. As I have mentioned before on this blog, there is an increasing tendency for university press offices to see themselves entirely as marketing agencies instead of informing and/or educating the public. Press releases about scientific research nowadays rarely make any attempt at accuracy – they are just designed to get the institution concerned into the headlines. In other words, research is just a marketing tool.
In the long run, this kind of media circus, driven by hype rather than science, does nobody any good.
P.S. I was going to joke that ring-like structures can be easily explained by circular reasoning, but decided not to.
Some important cosmological results have just been announced by the Dark Energy Survey Collaboration. I haven’t had time to go through them in detail but I thought it was worth doing a quick post here to draw attention to them. The results concern a sample of Type Ia supernovae (SN Ia) discovered during the full five years of the Dark Energy Survey (DES) Supernova Program, which contains about 1500 new Type Ia Supernovae that can be used for cosmological analysis. The paper is available on the arXiv here; the abstract is:
The key numerical result of interest is the equation-of-state parameter for dark energy, designated by w, which occurs in the (assumed) relationship between pressure p and effective mass density ρ of the form p=wρc2. A cosmological constant – which for many cosmologists is the default assumption for the form of dark energy – has w=-1 as I explained here. This parameter is one of the things Euclid is going to try to measure, using different methods. Interestingly, the DES results are offset a bit from the value of -1, but with quite a large uncertainty.
While the results for the equation-of-state parameter are somewhat equivocal, one thing that is clear is that the new SNIa measurements do confirm the existence of dark energy, in that the data can only be described by models with accelerating expansion, as dramatically demonstrated in this Figure:
I think this figure – or versions of it – will very rapidly appear in public talks on cosmology, including my own!
In the foyer of the Physics Department at the University of Barcelona you will find, as well as a fine refracting telescope, an example of the Atwood Machine. For some years before my current sabbatical I have been teaching Newtonian Mechanics to first-year students in Maynooth and used this as a simple worked example. I have to admit I’ve never seen an actual Atwood machine before, and what I’ve done in lectures is the simplified form on the right rather than the actual machine on the left.
Atwood Machine
The illustration on the right depicts the essential elements, but you can can see that the actual machine has a ruler which, together with a timing device, can be used to determine the acceleration of the suspended mass and how that varies with the other mass. You can work this out quite easily in the simplest case of a frictionless pulley by letting the tension in the string (which is light and inextensible) be T (say) and then eliminating it from the equations of motion for the two masses. I leave the rest as an exercise for the reader. A more interesting problem, for the advanced student, is when you have to take into account the rotational motion of the pulley wheel…
When I was a lad, during the 1970s, the term Spanish Practices was used pejoratively in a union-bashing sense to describe restrictive practices in the workplace. Until recently I thought it was a modern invention that relied on a stereotypical view of Spanish people as being lazy. In fact it seems the term dates back to Tudor times and is religious in origin, referring to Roman Catholic rites, in contrast to the simpler Protestant forms of worship. Anyway, none of that is what this post is about. I just used the title as clickbait.
I’ve been here in Barcelona, and working in the University of Barcelona, for four weeks now and I thought I’d share a few observations about differences in practice here and in the Ireland (and the UK).
The other night I went out for dinner with colleagues from the Department. The restaurant was much closer to the University than to my flat so instead of going home first I stayed in my office and walked straight there. My route out of the building takes me past a number of teaching rooms. During this warm weather, most of the rooms have the doors open so it’s easy to have a quick look at what’s going on inside. On my way out at about 7.30pm I was surprised to see a number of classes still going on, and they weren’t sparsely attended either.
In Maynooth the latest regular lectures finish at 6pm. Even during the 5pm to 6pm lectures, many students have to leave before the end to catch the one and only bus back to their place of residence. Here the public transport system is so good that isn’t really an issue even for those who don’t live near the campus. As far as I know lectures start at 9am, so students potentially have a very long day. They work hard.
I have to say that I wouldn’t like to have teach late in the evening. I used to do that on Fridays at Queen Mary for the MSc course and didn’t enjoy it. I don’t mind doing 9am lectures, though, but I don’t think students agree – partly because of the difficulty of getting to campus at that time.
In the Faculty of Physics, all the lecture halls, classrooms and laboratories are in one building rather than spread around the campus like they are in Maynooth (and many places in the UK). Fortunately, the building has been designed with students in mind and there is plenty of space for students to use socially or for private study between teaching sessions.
In this picture you can see the inner courtyard of the building occupied by the Faculties of Chemistry and Physics. It’s a big open space, with teaching rooms, etc, on either side. In the far right-hand corner there is a café/bar where one can buy lunch, a coffee, or even a beer, to be consumed either inside or in the seating area in the courtyard. Many students seem to prefer bring their own lunch and eat it in this space., although the food available is pretty good and cheap compared to back home.
As well as being able to eat and drink here, there is plenty of room for students simply to hang out or to study, either alone or in groups. If they don’t feel like that they can use the tram, bus or Metro to go home, and come back later if they have a long gap between classes. None of this is possible at Maynooth.
This particular kind of open space would not work so well in Ireland or the UK because of the weather, though you can probably see in the picture that there had been a bit of rain before I took the photograph, but I hope I’ve made the point that having social spaces makes a huge amount of difference to the student experience, not least because it feels that the University has thought about them. In the neoliberal system that dominates in the UK and Ireland, students are simply a commodity, a source of revenue, to be crammed into every available space and processed as cheaply as possible. In Maynooth students have been, and are being, forced to pay an extra levy for a notional student centre that will probably never be built.
The contrast is very disheartening.
Getting back to educational matters, another thing I’ve noticed walking past classrooms is that it’s not unusual to see a student standing at the blackboard in front of the class going through a problem. I’ve seen that a number of times with quite large classes. Sometimes we ask students to do that sort of thing in tutorials, but I’ve never done so in a full lecture. I think our students would be shocked if we asked, but it’s clearly not unexpected here. That’s a Spanish Practice I’d be quite happy to try.
I spent quite a lot of this morning trying to get my internet connections to work and trying to sort out an office key, not with 100% success. I am currently in the office of a member of staff who happens to be away today instead of the office I was allocated, and my email address here is not yet activated – probably because I did something wrong in the registration process. I’m hopeful that these minor issues will be resolved tomorrow. Even Eduroam acted up for a while before finally letting me connect. Such is life.
Anyway, my first impression on arriving in the building was of a huge difference in scale in Physics activity here at the University of Barcelona (UB) as compared to Maynooth (and indeed the UK Physics departments I have worked in). That’s not just the size of the building, which the Faculty of Physics shares with the Faculty of Chemistry. Physics and Chemistry also share a building in Maynooth, in fact, so the sharing was not in itself a surprise. The Science Building in Maynooth is very small, however, and it was a bit of a shock seeing how much space there is here compared with Maynooth, and also finding out how easy it is to get lost among the 7 floors. The sense of space is very refreshing, actually, as cramped accommodation is a constant reminder of financial and other constraints.
That’s not the only difference, though. There is enough activity in Physics in the University of Barcelona for it to be an entire Faculty. The UB Faculty of Physics contains Departments, covering the following areas: Electronic & Biomedical Engineering; Quantum Physics & Astrophysics; Condensed Matter Physics, and Applied Physics. It is also home to ICCUB, an interdisciplinary research institute that sits outside the Department structure and some of whose staff are paid from external agencies rather than the University itself.
In Maynooth there is a Faculty of Science and Engineering that covers all disciplines represented in the list above, and more besides. It would amuse my colleagues back in Ireland to see that Electronic Engineering is considered a small subset of Physics in Barcelona, whereas in Maynooth it is a free-standing department which is larger than Physics.
P.S. I just thought I’d mention another difference: that it is very warm here (26° C) so I may need to stop for a beer on the way home…
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In the Dark 