It’s been a while since I posted a question in the Cute Physics Problems folder so I thought I’d offer this one. It’s not particularly hard, but I think it’s quite instructive.
A thin spherical shell of radius r carrying a charge Q spread uniformly with constant surface density is split into two equal halves by a narrow planar cut passing through the centre as shown in the detailed diagram below:
Calculate the force arising from electrostatic repulsion between the two hemispherical shells, expressing your answer in terms of Q and r in SI units.
Answers through the Comments Box please. First correct answer wins a tomato*
It’s been far too long since I last shared another one of those interesting cosmology talks on the Youtube channel curated by Shaun Hotchkiss. This channel features technical talks rather than popular expositions so it won’t be everyone’s cup of tea but for those seriously interested in cosmology at a research level find them seriously informative.
In this one, Keir Rogers talks about Ultra-Light Dark Matter (ULDM; for a detailed review of this idea, see here). To summarize the argument, it seems that ULDM consisting of a single particle can’t be responsible for all the dark matter, but this doesn’t mean it can’t exist. Keir Rogers discusses how much of the dark matter could be of ULDM form.
Another issue discussed here relates to the parameter S8 quantifies the matter-density fluctuations on a scale of 8 h-1 Mpc. There is a Cosmology Talk discussing the state of play with this parameter here. The structure-suppressing properties of ULDM could also have implications for the S8 tension, i.e. maybe a small sub-component of ULDM is what is causing the apparently low S8 in local measurements?
The paper describing this work can be found on the arXiv here and here is the video:
Testing students’ ability to show their learning in a closed context is not preparing them for a future in which technology is ubiquitous. There are few professional contexts that require you to recall information in a specific time frame.
I agree to some extent with the conclusion of the article but for different reasons. In particular, I don’t think this conclusion has much to do with the arrival of new technologies such as ChatGPT. Exams that simply require the students to “recall information” and nothing else seem to me to be of limited value from an educational point of view and should indeed be scrapped, but I think exams can play a role in testing other, more important, skills such as problem-solving.
Over my lifetime the ratio of assessment to education in universities has risen sharply, with the undeniable result that academic standards have fallen especially in my own discipline of physics. The modular system encourages students to think of modules as little bit-sized bits of education to be consumed and then forgotten. Instead of learning to rely on their brains to solve problems, students tend to approach learning by memorizing chunks of their notes and regurgitating them in the exam. I find it very sad when students ask me what derivations they should memorize to prepare for examinations because that seems to imply that they think their brain is no more than a device for storing information. It became clear to me over the years that school education in the UK does not do enough to encourage students to develop their all-round intellectual potential, which means that very few have confidence in their ability to do anything other than remember things. It seems the same malaise affects the Irish system too.
On the other hand, a good memory is undoubtedly an extremely important asset in its own right.
I went to a traditional Grammar school that I feel provided me with a very good education in which rote learning played a significant part. Learning vocabulary and grammar was an essential part of their approach to foreign languages, for example. How can one learn Latin without knowing the correct declensions for nouns and conjugations for verbs? But although these basic elements are necessary, however, they are not sufficient. You need other aspects of your mental capacity to comprehend, translate or compose meaningful pieces of text.
The same considerations apply to STEM disciplines. It is important to have a basic knowledge of the essential elements of mathematics and physics as a grounding, but you also need to develop the skill to apply these in unusual settings. I also think it’s simplistic to think of memory and creative intelligence as entirely separate things. I seems to me that the latter feeds off the former in a very complex way. A good memory does give you rapid access to information, which means you can do many things more quickly than if you had to keep looking stuff up, but I think there’s a lot more to it than that. Our memories are an essential part of the overall functioning of our brain, which is not compartmentalized in such a simple way. For example, one aspect of problem-solving skill relies on the ability to see hidden connections; the brain’s own filing system plays a key role in this.
In recognizing the importance of memory I don’t mean that rote learning is necessarily the best way to develop the relevant skills. My own powers of recall are not great – and are certainly not improving with age – but I find I can remember things much better if I find them interesting and/or if I can see the point of remembering them and/or if I use them a lot. Remembering things because they’re memorable is far easier than remembering because you need to remember them to pass an examination!
Anyway, my point is that a good memory can help you learn, but is not in itself what should be assessed in an examination. I wish universities made more effort to educate students to understand that their brain can be much more than a memory device.
In yesterday’s post I asked the question whether anyone actually believes that it costs it costs £2310 to publish a scientific article online? I also posted the question on the Open Journal of Astrophysics Twitter account:
Only a few people responded to that question with a “yes”. Coincidentally all of them appear to be employed by the academic publishing industry. These people insist that the big publishers bring value to scientific papers. They don’t. Authors and referees do all the things that add value. What publishers do is take that value and turn it into its own profits. The fact that enormous profits are made out of this process in itself demonstrates that what the scientific community is being charged is nothing whatever to do with cost.
This reminds me of many discussions I had in my commie student days about surplus value, a concept explored in great detail by Karl Marx, in Das Kapital. According to the wikipedia page, the term “refers roughly to the new value created by workers that is in excess of their own labour-cost and which is therefore available to be appropriated by the capitalist, according to Marx; it allows then for profit and in so doing is the basis of capital accumulation.”
Engels is quoted there as follows:
Whence comes this surplus-value? It cannot come either from the buyer buying the commodities under their value, or from the seller selling them above their value. For in both cases the gains and the losses of each individual cancel each other, as each individual is in turn buyer and seller. Nor can it come from cheating, for though cheating can enrich one person at the expense of another, it cannot increase the total sum possessed by both, and therefore cannot augment the sum of the values in circulation. (…) This problem must be solved, and it must be solved in a purely economic way, excluding all cheating and the intervention of any force — the problem being: how is it possible constantly to sell dearer than one has bought, even on the hypothesis that equal values are always exchanged for equal values?
Marx’s solution of this economical conundrum was central to his theory of exploitation:
…living labour at an adequate level of productivity is able to create and conserve more value than it costs the employer to buy; which is exactly the economic reason why the employer buys it, i.e. to preserve and augment the value of the capital at his command. Thus, the surplus-labour is unpaid labour appropriated by employers in the form of work-time and outputs.
In the context of academic publishing, the workers are scientific researchers and the employers are the publishers. The workers not only produce the science in the first place, but also carry out virtually all of the actions that the employers claim add value. The latter are simply appropriating the labour of the former, which is exploitation. It needs to stop.
I got home this evening to find the sad news that legendary saxophonist Wayne Shorter has passed away at the age of 89. I only got to hear him live once, many moons ago, when he was part of a band led by drummer Jack de Johnette (I think that was in the early 1990s) but I have a big collection of CDs of him in various settings, including with Miles Davis, The Jazz Messengers, and, of course, Weather Report. As a tribute I feel it’s appropriate to post a great record he made as leader.
Speak No Evilwas recorded in 1964 and released as a Blue Note LP in 1966. It features a superb band, including Freddie Hubbard (tpt), Herbie Hancock (p), Ron Carter (b) and Elvin Jones (d) alongside Shorter himself on tenor saxophone. It’s one of the must-have jazz albums, and it demonstrates Shorter’s flair for composition as well as improvisation. In both respects his approach to this album is very different from that he took just a few years earlier with Art Blakey’s Jazz Messengers. Standout tracks on this album include the suave yet unsettling Dance Cadaverous, the brooding Fee-fi-fo-fum, and the curiously agitated Witch Hunt.
Every piece on this album was composed by Shorter and as a player he revels in the ambiguous harmonies he created alongside the melodies. Although his style is clearly influenced by Sonny Rollins and John Coltrane, his tone is unlike either of these other giants, and Shorter expresses his individuality through varying emphasis producing asymmetric phrases. His playing is very quick-witted, full of abrupt changes of mood and dashes of fierce humour. A good example is Infant Eyes, a theme made up of three 9-bar phrases, played at a leisurely pace, on which Shorter’s lines impose a sense of determined exploration when many other soloists would have dawdled.
Anyway, don’t take my word for it. You can listen to the full album as a playlist on Youtube. The track order is: Witch Hunt, Fee-Fi-Fo-Fum, Dance Cadaverous, Speak No Evil, Infant Eyes and Wild Flower.
As it was foretold, the Royal Astronomical Society has now officially announced that all its journals will be moving to Gold Open Access. The only thing that surprised me about this is the speed that it will be done – from January 1st 2024. The announcement confirms that the “rumour” I reported in 2020 was true (as I knew it was, given the reliability of the source). I did, however, think the timescale would be “within a few years” and it turns out to be much shorter than that.
For the journal of most relevance to myself, Monthly Notices of the Royal Astronomical Society (MNRAS) this decision means that authors will have to pay an Article Processing Charge (APC) at the (suitably astronomical) level of £2310 for each paper (although there will be exemptions in certain situations). Does anyone genuinely believe that it costs that much to publish an article online? Really?
I did actually laugh out loud when I saw the spin the RAS are trying to put on this decision:
The RAS is excited to be a key contributor to the open science movement, helping to drive discoverability and change.
Au contraire. Gold Open Access a serious hindrance to the open science movement, as it involves hugely inflated costs to the authors in attempt to protect revenue in the face of declining subscription income. Switching from a ‘fleece-the-libraries’ model to a ‘fleece-the-authors’ alternative can in no way be regarded as a progressive move.
Other notable astronomy-related journals, such as the Astrophysical Journal (ApJ) and Astronomy & Astrophysics (A&A), have levied “page charges” (effectively APCs by another name) for as long as I can remember, though in the latter case there is a waiver for researchers in “member” countries. ApJ and other journals also have a waiver scheme for those who cannot afford to pay. For those who have to pay, the fee is usually about $100 per page. For a long time MNRAS was the exception and indeed the only feasible choice for people who don’t have access to funding to cover page charges, including many in the developing world. More recently, however, MNRAS introduced a charge for longer papers: £50 per page over 20 pages, so a paper of 21 pages costs £50 and one of 30 pages costs £500, etc. Now there will be a flat fee of £2310 per paper.
It is true that some institutions will pay the APC on behalf of their authors, but that is hardly the point. If institutions have cash to pay for astronomy publications to be open access then they would do far more good to the research community by giving it to the arXiv rather than to the publishing industry. When authors themselves see how much they have to pay to publish their work, many will realize that it is simply not worth the money. (I refuse to pay any APC on principle.)
The Twitter feed for the Open Journal of Astrophysics (OJAp) was buzzing all day yesterday with negative reactions to the RAS announcement. Obviously I am biased in this matter, but I do encourage those thinking of switching to give it a try. The RAS has played into the hands of OJAp, which publishes papers (online only) in all the areas of Astrophysics covered by MNRAS, and more, but is entirely free both for authors and readers. The annual running costs of OJAp are substantially less than one APC at the level proposed by MNRAS.
The comments I have seen brought this image to my mind:
(The allusion to sharks is not accidental.)
The question for the Royal Astronomical Society, and indeed the other learned societies that fund their activities in a similar way, is whether they can find a sustainable funding model that takes proper account of the digital publishing revolution. If their revenue from publishing does fall, can they replace it? And, if not, in what form can they survive? I’d like to think that future operating models for such organizations would involve serving their respective communities, rather than fleecing them.
On February 29th 2020, Ireland identified its first case of the novel coronavirus, SARS CoV2, the virus that causes COVID-19. The World Health Organization declared the outbreak a pandemic on March 11th. On March 12th 2020 Schools and Colleges in Ireland were closed.
Since then, I have posted regular updates of the number of cases of COVID-19, initially daily and more recently weekly as the frequency of official announcements on the data hub decreased. The plotting the latest figures actually became a sort of ritual for me over this time and I even found mildly therapeutic.
Now, however, three full years have passed- can it really be three full years? – have since the (official) arrival of the pandemic in Ireland and, with the situation looking stable, I think it’s time to stop posting these updates. I made the decision to stop at the end of February 2023 unless something drastic happened to change my mind. Ironically, I just heard this morning that one of my colleagues has a new case of Covid-19 but that hasn’t changed my mind. I hope this makes it clear that I don’t think the pandemic is over: there are many people still suffering from new infections and the effects of “Long Covid”. I just don’t see the need to continue my updates here.
I will leave the data online here in case anyone is interested in the numbers, but I won’t be posting any further updates.
So here are the final graphs from me. The present 7-day moving average of new cases is just 89.6 per week, down from 103.0 last week and 36 deaths were recorded in the same period.
On a linear scale the cases look like this
The numbers for deaths on a linear scale look like this
Today is St David’s Day, and it seems apt to celebrate it with a poem by Dylan Thomas. I’ve loved this particular one since I first heard it when I was a student many years ago. I say “heard it” rather than “read it” because it was through buying a tape of the man himself reading his poems that got me hooked. I have posted this on St David’s Day before but that was many years ago and I hope you will forgive the repetition.
Fern Hill reflects about the passage of time, the loss of childhood happiness and the inevitability of death but its mood is defiant rather than gloomy. It’s full of vibrant imagery, but it’s also written with a wonderful feeling for the natural rhythms and cadences language. You can listen to Dylan Thomas reading this exactly as if it were music.
Fern Hill
Now as I was young and easy under the apple boughs
About the lilting house and happy as the grass was green,
The night above the dingle starry,
Time let me hail and climb
Golden in the heydays of his eyes,
And honoured among wagons I was prince of the apple towns
And once below a time I lordly had the trees and leaves
Trail with daisies and barley
Down the rivers of the windfall light.
And as I was green and carefree, famous among the barns
About the happy yard and singing as the farm was home,
In the sun that is young once only,
Time let me play and be
Golden in the mercy of his means,
And green and golden I was huntsman and herdsman, the calves
Sang to my horn, the foxes on the hills barked clear and cold,
And the sabbath rang slowly
In the pebbles of the holy streams.
All the sun long it was running, it was lovely, the hay
Fields high as the house, the tunes from the chimneys, it was air
And playing, lovely and watery
And fire green as grass.
And nightly under the simple stars
As I rode to sleep the owls were bearing the farm away,
All the moon long I heard, blessed among stables, the nightjars
Flying with the ricks, and the horses
Flashing into the dark.
And then to awake, and the farm, like a wanderer white
With the dew, come back, the cock on his shoulder: it was all
Shining, it was Adam and maiden,
The sky gathered again
And the sun grew round that very day.
So it must have been after the birth of the simple light
In the first, spinning place, the spellbound horses walking warm
Out of the whinnying green stable
On to the fields of praise.
And honoured among foxes and pheasants by the gay house
Under the new made clouds and happy as the heart was long,
In the sun born over and over,
I ran my heedless ways,
My wishes raced through the house high hay
And nothing I cared, at my sky blue trades, that time allows
In all his tuneful turning so few and such morning songs
Before the children green and golden
Follow him out of grace.
Nothing I cared, in the lamb white days, that time would take me
Up to the swallow thronged loft by the shadow of my hand,
In the moon that is always rising,
Nor that riding to sleep
I should hear him fly with the high fields
And wake to the farm forever fled from the childless land.
Oh as I was young and easy in the mercy of his means,
Time held me green and dying
Though I sang in my chains like the sea.
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In the Dark 