Posts Tagged ‘atoms’
Carlo Rovelli, humanist extraordinaire, and Lucretius, ditto
Lucretius, apparently
I was, for a time, a member of the South Australian humanists, basically a meet-up group, but also a branch of the national organisation, the title of which I can’t remember, mea culpa. I might also claim to be a prominent member, as I gave three talks to the group, the first on free will (on which I’ve since changed my position), the second on the decline of religion in Australia, and the third on the birth and growth of international organisations. I write this purely to big-note myself, as nobody else will.
I believe that humanist group is no longer with us, but of course humanism lives on in many hearts and minds. I’ve been very much reminded of this as I read a collection of essays by the philosophical physicist Carlo Rovelli, with the grand and charming title, There are places in the world where rules are less important than kindness. And I must say, to my shame, that I only got the book via a ‘Dirty Santa’ game last Christmas. I filched the book from someone, as part of the rules of the game, largely to show off about how bookish I am (I also filched another book, to become the sole owner of the only book gifts available).
Strangely I knew the name, probably through my various researches for my writing, but I chanced to search my little library and found a slender Rovelli volume, Seven brief lessons on physics, which I can’t for the life of me remember buying, and have surely never opened – mea maxima culpa. So now I have two Rovelli essay collections to read, and they truly are gems, resurrecting my humanist interests as well as, if it’s not the same thing, making me want to be a better person, at last!
The most recent essay I’ve read, ‘De rerum natura’, rather excited me in anticipation, and I must tell a story about it, which I suspect I’ve written before, but never mind.
In my early twenties I was at a party at a friend’s house, a fairly raucous affair, with painfully loud music and painfully attractive women, and I found myself overwhelmed and wilting. My friend noticed and made some effort to revive me, but I told him I was in a dull mood and should go home. He suggested instead that I spend some time in his spare room, away from the noise, where there was a sofa bed and ‘lots of books’. He knew me well. So, shutting the door to the beats of Ian Dury, Elvis Costello et al, I perused a plethora of texts before more or less randomly selecting Lucretius. De Rerum Natura is generally translated as On the nature of things, or On the nature of the universe, though there may be other variants. It was written in the first century BCE, and, believe me, it’s an extraordinary work, which cuts through the centuries between then and now like a knife through air. After the first few pages I found myself laughing with incredulity. Though from the beginning he addresses the great goddess Venus, it didn’t strike me as a religious text, it was too full of the life of the nature around him, animate and inanimate, and the atoms this natural world was all made from. Yes, this was an early atomic theory, first posited by Democritus and Epicurus, though long before subatomic particles, quantum states, electromagnetism and field theory,
I was certainly bedazzled by this 2,000 year old claim about atoms, but other speculations seemed fascinatingly ‘modern’:
… if things were made out of nothing, any species could spring from any source and nothing would require seed. Men could arise from the sea and scaly fish from the earth, and birds could be hatched out of the sky… The same fruits would not grow constantly on the same trees, but they would keep changing: any tree might bear any fruit. If each species were not composed of its own generative bodies, why should each be born always of the same kind of mother? Actually, since each is formed out of specific seeds, it is born and emerges into the sunlit world only from a place where there exists the right material, the right kind of atoms. This is why everything cannot be born of everything, but a specific power of generation inheres in specific objects.
This is the very sniffter of an intuition about the origin of individual species, which went through me, as a young man, like a very mild and titillating electric shock. The passage, and others like it, appear in the first few pages of De Rerum Natura, and it may well be that I didn’t get much further on that night, given the circumstances, but they made a deep impression. Our thoughts, or those of the best of us, have been plumbing the depths of what’s what in terms of what we are, and everything living – and non-living – around us, for 2 thousand, or 20 thousand, or even 200 thousand years. Our sharing of these thoughts no doubt began with the development of language, and then writing, which boosted us to become the dominant species we now are.
So I note that I’ve got a copy of On the nature of the Universe on my bookshelves, but I likely haven’t read past Book One of six books. Time to make amends. Life begins at 69! Which reminds me – vive les bonobos!
References
Carlo Rovelli, There are places in the world where rules are less important than kindness, 2022
Carlo Rovelli, Seven brief lessons on physics, 2014
Lucretius, On the nature of the universe, trans by R E Latham, 1994
On electrickery, part 1 – the discovery of electrons
Canto: This could be the first of a thousand-odd parts, because speaking for myself it will take me several lifetimes to get my head around this stuff, which is as basic as can be. Matter and charge and why is it so and all that.
Jacinta: so let’s start at random and go in any direction we like.
Canto: Great plan. Do you know what a cathode ray is?
Jacinta: No. I’ve heard of cathodes and anodes, which are positive and negative terminals of batteries and such, but I can’t recall which is which.
Canto: Don’t panic, Positive is Anode, Negative Is Cathode. Though I’ve read somewhere that the reverse can sometimes be true. The essential thing is they’re polar opposites.
Jacinta: Good, so a cathode ray is some kind of negative ray? Of electrons?
Canto: A cathode ray is defined as a beam of electrons emitted from the cathode of a high-vacuum tube.
Jacinta: That’s a pretty shitty definition, why would a tube, vacuum or otherwise, have a cathode in it? And what kind of tube? Rubber, plastic, cardboard?
Canto: Well let’s not get too picky. I’m talking about a cathode ray tube. It’s a sealed tube, obviously, made of glass, and evacuated as far as possible. Sciencey types have been playing around with vacuums since the mid seventeenth century – basically since the vacuum pump was invented in 1654, and electrical experiments in the nineteenth century, with vacuum tubes fitted with cathodes and anodes, led to the discovery of the electron by J J Thomson in 1897.
Jacinta: So what do you mean by a beam of electrons and how is it emitted, and can you give more detail on the cathode, and is there an anode involved? Are there such things as anode rays?
Canto: I’ll get there. Early experiments found that electrostatic sparks travelled further through a near vacuum than through normal air, which raised the question of whether you could get a ‘charge’, or a current, to travel between two relatively distant points in an airless tube. That’s to say, between a cathode and an anode, or two electrodes of opposite polarity. The cathode is of a conducting material such as copper, and yes there’s an anode at the other end – I’m talking about the early forms, because in modern times it starts to get very complicated. Faraday in the 1830s noted a light arc could be created between the two electrodes, and later Heinrich Geissler, who invented a better vacuum, was able to get the whole tube to glow – an early form of ‘neon light’. They used an induction coil, an early form of transformer, to create high voltages. They’re still used in ignition systems today, as part of the infernal combustion engine
Jacinta: So do you want to explain what a transformer is in more detail? I’ve certainly heard of them. They ‘create high voltages’ you say. Qu’est-ce que ça veux dire?
Canto: Do you want me to explain an induction coil, a transformer, or both?
Jacinta: Well, since we’re talking about the 19th century, explain an induction coil.
Canto: Search for it on google images. It consists of a magnetic iron core, round which are wound two coils of insulated copper, a primary and secondary winding. The primary is of coarse wire, wound round a few times. The secondary is of much finer wire, wound many many more times. Now as I’ve said, it’s basically a transformer, and I don’t know what a transformer is, but I’m hoping to find out soon. Its purpose is to ‘produce high-voltage pulses from a low-voltage direct current (DC) supply’, according to Wikipedia.
Jacinta: All of this’ll come clear in the end, right?
Canto: I’m hoping so. When a current – presumably from that low-volage DC supply – is passed through the primary, a magnetic field is created.
Jacinta: Ahh, electromagnetism…
Canto: And since the secondary shares the core, the magnetic field is also shared. Here’s how Wikipedia describes it, and I think we’ll need to do further reading or video-watching to get it clear in our heads:
The primary behaves as an inductor, storing energy in the associated magnetic field. When the primary current is suddenly interrupted, the magnetic field rapidly collapses. This causes a high voltage pulse to be developed across the secondary terminals through electromagnetic induction. Because of the large number of turns in the secondary coil, the secondary voltage pulse is typically many thousands of volts. This voltage is often sufficient to cause an electric spark, to jump across an air gap (G) separating the secondary’s output terminals. For this reason, induction coils were called spark coils.
Jacinta: Okay, so much for an induction coil, to which we shall no doubt return, as well as to inductors and electromagnetic radiation. Let’s go back to the cathode ray tube and the discovery of the electron.
Canto: No, I need to continue this, as I’m hoping it’ll help us when we come to explaining transformers. Maybe. A key component of the induction coil was/is the interruptor. To have the coil functioning continuously, you have to repeatedly connect and disconnect the DC current. So a magnetically activated device called an interruptor or a break is mounted beside the iron core. It has an armature mechanism which is attracted by the increasing magnetic field created by the DC current. It moves towards the core, disconnecting the current, the magnetic field collapses, creating a spark, and the armature springs back to its original position. The current is reconnected and the process is repeated, cycling through many times per second.
A Crookes tube showing green fluorescence. The shadow of the metal cross on the glass showed that electrons travelled in straight lines
Jacinta: Right so now I’ll take us back to the cathode ray tube, starting with the Crookes tube, developed around 1870. When we’re talking about cathode rays, they’re just electron beams. But they certainly didn’t know that in the 1870s. The Crookes tube, simply a partially evacuated glass tube with cathode and anode at either end, was what Rontgen used to discover X-rays.
Canto: What are X-rays?
Jacinta: Electromagnetic radiation within a specific range of wavelengths. So the Crookes tube was an instrument for exploring the properties of these cathode rays. They applied a high DC voltage to the tube, via an induction coil, which ionised the small amount of air left in the tube – that’s to say it accelerated the motions of the small number of ions and free electrons, creating greater ionisation.
x-rays and the electromagnetic spectrum, taken from an article on the Chandra X-ray observatory
Canto: A rapid multiplication effect called a Townsend discharge.
Jacinta: An effect which can be analysed mathematically. The first ionisation event produces an ion pair, accelerating the positive ion towards the cathode and the freed electron toward the anode. Given a sufficiently strong electric field, the electron will have enough energy to free another electron in the next collision. The two freed electrons will in turn free electrons, and so on, with the collisions and freed electrons growing exponentially, though the growth has a limit, called the Raether limit. But all of that was worked out much later. In the days of Crookes tubes, atoms were the smallest particles known, though they really only hypothesised, particularly through the work of the chemist John Dalton in the early nineteenth century. And of course they were thought to be indivisible, as the name implies.
Canto: We had no way of ‘seeing’ atoms in those days, and cathode rays themselves were invisible. What experimenters saw was a fluorescence, because many of the highly energised electrons, though aiming for the anode, would fly past, strike the back of the glass tube, where they excited orbital electrons to glow at higher energies. Experimenters were able to enhance this fluorescence through, for example, painting the inside walls of the tube with zinc sulphide.
Jacinta: So the point is, though electrical experiments had been carried out since the days of Benjamin Franklin in the mid-eighteenth century, and before, nobody knew how an electric current was transmitted. Without going into much detail, some thought they were carried by particles (like radiant atoms), others thought they were waves. J J Thomson, an outstanding theoretical and mathematical physicist, who had already done significant work on the particulate nature of matter, turned his attention to cathode rays and found that their velocity indicated a much lighter ‘element’ than the lightest element known, hydrogen. He also found that their velocity was uniform with respect to the current applied to them, regardless of the (atomic) nature of the gas being ionised. His experiments suggested that these ‘corpuscles’, as they were initially called, were 1000 times lighter than hydrogen atoms. His work was clearly very important in the development of atomic theory – which in large measure he initiated – and he developed his own ‘plum pudding’ theory of atomic structure.
Canto: So that was all very interesting – next time we’ll have a look at electricity from another angle, shall we?