Tag: physics

In Our Time: Perpetual Motion

Perpetual motion would be a wonderful thing, if only it were possible – being able to set some machine going and then it would power itself and just carry on & on without end. Free energy from nothing! Which is, of course, why it is impossible – but this wasn’t provable until relatively recently. Discussing the search for, and disproof of, perpetual motion on In Our Time were Ruth Gregory (Durham University), Frank Close (University of Oxford) and Steven Bramwell (University College London).

Before the modern understanding of physics there didn’t seem to be any reason why perpetual motion should necessarily be impossible. In the Aristotelian view of the universe the stars were in perpetual motion in the heavens – so there must surely be some way to replicate this on earth with earthly machinery. This wasn’t (solely) the province of charlatans – people like Leonardo da Vinci, Robert Boyle and Gottfried Leibniz were all involved in attempts to design machines that could power themselves forever. Various approaches were tried – like trying to design a waterwheel that not only ground corn but also pumped the water back uphill so it could flow down again. Or a bottle that siphoned liquid out of itself in order to refill itself. Or some sort of machine that was constantly over-balancing – like an Escher drawing of a waterwheel with buckets labelled 9 travelling down one side, and when they reach the bottom they flip round to now read 6 so they’re lighter. Which works beautifully in the illusory world of Escher’s art but rather less so in our mundane reality. As well as people genuinely trying to investigate the possibility there were also those who claimed to have achieved success – normally with machines that conveniently couldn’t be inspected to expose their charlatanry.

Once physicists started to gain a greater understanding of how the universe worked it became clear that perpetual motion machines were fundamentally impossible. All proposed perpetual motion machines violate either the first or second law of thermodynamics. Before moving on to explain how these laws affect perpetual motion machines they digressed slightly to explain some of the background to the formulation of the laws of thermodynamics. First they gave us the technical meaning of the word “work” in a physics context – important in understanding the rest of the discussion. Work is the energy that is applied to do something. For instance if you want to move something then work = force x distance. Or if you’re heating something up then work refers to the energy you need to cause the temperature change. Experiments by Joule were key to showing a link between heat and energy. Before his work the prevailing theory was that heat was a thing (called calor) that could be transferred between objects – so a fire heated a pot because calor was transferred from flames to pot. But Joule showed that you could generate heat using energy, and later it was realised that heat was a form of energy. Reception of his work at the time (the mid-19th Century) was mixed – the temperature changes he was study were very small and not everyone believed it was possibly to accurately detect them.

The First Law of Thermodynamics is that energy must be conserved in a closed system. I.e. you don’t get something for nothing. When work is done it all turns into motion or heat or some other form of energy. Many perpetual motion machines violate this law, and they are termed “perpetual motion machines of the first kind”. An example of this is a waterwheel that both grinds corn and pumps the water back up to the top to start over again. In order to pump all the water back up you need to use just as much energy as it generated for you on the way down – so there none left over for your corn grinding, even if your machine is perfectly efficient (see below).

The Second Law of Thermodynamics is that entropy always increases or remains the same, it never decreases. Gregory used the example of a room that’s either tidy (a single ordered state) or untidy (many possible disordered states). In order to move from disordered to ordered you need to do work, otherwise over time the random chance will move objects from their positions in the room and it will become more disordered. The Second Law of Thermodynamics is associated with time – it provides directionality to the universe, if things are getting more disordered then they’re moving forwards. Perpetual motion machines which violate this law are categorised as “perpetual motion machines of the second kind”.

Another way that perpetual motion machines can violate the laws of physics is by being too efficient. I touched on that above – in the real world no machine operates without losing some energy (generally in the form of heat due to friction). And so even if you aren’t trying to do anything useful with the energy other than keep the machine moving you’ll still fail to achieve perpetual motion as you won’t have quite enough energy to return to the starting point.

So perpetual motion is impossible, as it would violate the laws of physics. There are some loopholes at the quantum level (aren’t there always?). Implications of the Heisenberg Uncertainty Principle mean that it’s possible to “borrow” energy temporarily from the future, which means the First Law of Thermodynamics doesn’t quite apply. But at the macro level these laws are inviolable and perpetual motion is impossible. They finished by saying that if a way to make a perpetual motion machine work was found then it wouldn’t just be a case of minor tweaks to physics-as-we-understand-it. Instead it would require a re-writing of pretty much all science we’ve ever conceptualised – the laws of thermodynamics are that fundamental to our understanding of the universe.

In Our Time: The Science of Glass

Glass is odd stuff. We’ve been making it so long that one tends to forget that it’s both artificial and really quite odd. The In Our Time episode about glass talked both the science of glass and glass-making, and the history of it. The experts discussing it were Dame Athene Donald (University of Cambridge, current Master of Churchill College, my old college, but here in her context as a physicist), Jim Bennett (University of Oxford) and Paul McMillan (University College London).

On the programme they intertwined the historical and the scientific discussion, but I thought the joins showed rather more than they usually do and so I’m going to split the threads up in my writeup. We first know of glass manufacturing about 5,000 years ago, by the ancient Egyptians who made beads of it initially. Over time they learnt to make larger and more complex objects like bottles & ornaments. The Romans developed the technology further. They invented most of the techniques that were used before the Industrial Revolution, like glass blowing for example. In ancient Egypt glass was primarily used for decorative or luxury goods, but the Romans used glass for both everyday and finer objects – including wine bottles (which struck me as an awfully modern way to store wine!).

In the Renaissance era the Venetians were famed for making particularly fine quality glass. The city attempted to keep a monopoly on glass-making by keeping their methods secret & forbidding glass-makers to leave the city. Which didn’t entirely work, unsurprisingly. One of their secrets was a way of making very transparent glass which was useful for lenses. Something I learnt from this programme was that spectacles first appear in the 13th Century AD which is much earlier than I’d assumed. Once lenses were being made to correct people’s sight it was only a relatively short step to making lenses for scientific instruments. Glass is part of the Enlightenment’s scientific revolution – not just lenses but also for making scientific instruments or vessels. There is a feedback loop between the demands of the scientific experiments driving new glass making technology and better glass instruments expanding the possible experiments that can be done. Industrial production of glass as we know it today begins in the Industrial Revolution.

The whole of the history discussion was very Eurocentric so I had a little look on wikipedia after we’d listened to the programme to see whether this was a fair reflection of the world history of glassmaking. The answer (based on a tiny amount of effort on my part) is … maybe? Glass making in China appears to’ve arrived late – during the Han Dynasty and probably influenced by trade goods from the Roman Empire. I didn’t find anything about the Americas, so I don’t know if that means they didn’t invent glass making or if no-one cared enough to add it to wikipedia. It’s odd to think that something so ubiquitous today might’ve been discovered once & once only.

Making glass (not good glass, just glass) is deceptively simple. In essence the process is to heat up sand till it melts, and then cool it very quickly and you end up with the transparent solid that we call glass. One of the experts pointed out that the necessary temperatures are those that would be reached by a bonfire on a beach – so it was probably discovered in Egypt by people (briskly) putting out campfires in the desert. Although a large body of empirical knowledge of how to make glass was built up over the next 5,000 years it was only relatively recently that we gained any understanding of what is actually going on, and the science of glass & glass-making is still not entirely understood. It’s actually more difficult to make glass out of pure sand than when there are impurities present, pure sand needs a quicker cooling step. So when making glass other things are often added – like potash or lime.

One of the complicated things about glass formation is that the phase transition from liquid sand to glass is not well defined – which is an oddity in physics. An example of a well defined phase transition is that from liquid water to ice: it happens at 0°C no matter how you cool the water. But the point at which liquid sand becomes glass depends on the precise starting conditions and the precise heating & cooling regimen – and it isn’t predictable using the current state of knowledge. Glass isn’t even a usual solid – it’s not crystalline, and that’s why the speed of cooling is important. If it cools too slowly it will crystalise and you don’t get glass. So instead of the atoms lining up in neat little rows they appear to just stop where they are. This non-crystalline nature of glass is what gives it some of its characteristic properties. It is brittle because there are no planes of atoms able to spread over each other when pressure is applied. I think they also said that the transparency is down to there being more routes for light to take through the structure, but I’m not sure that makes sense to me so I may’ve mis-remembered.

Glass in the technical sense is a broader term than just silicon glass (the stuff we generally call glass). You can make a glass using sugar – that’s what sweets like glacier mints are made of. And something I knew but had never really thought about is that spectacles & things like motorbike crash helmet visors aren’t made from silicon glass. Instead they are made using large polycarbon molecules – these can never crystallise so are much easier to work with. And the glass produced is not prone to fracturing, which is obviously important in those usages. I assume there are other downsides which mean we don’t use these glasses for all applications.

From the title I hadn’t expected this to be as interesting as it was – I didn’t realise how much wasn’t known about glass (nor how unique a discovery it was).

In Our Time: The Earth’s Core

Despite being relatively close to us the inside of the Earth, and particularly the core of the Earth, is difficult to investigate. Primarily because we can’t just look at it – and the deepest mines or boreholes are only 10km deep which is tiny compared to the 6,000km that is the Earth’s radius. So everything needs to be logically deduced from the readings that we can take. Discussing what we know about the Earth’s core and how we know it on In Our Time were Stephen Blundell (University of Oxford), Arwen Deuss (Utrecht University) and Simon Redfern (University of Cambridge).

Prior to the 19th Century the assumption was that the Earth was the same all the way through – rocks where we can see, so rocks everywhere. But in the 19th Century scientists realised that the theory of gravity required a denser Earth than is possible if it’s just rocks and so they postulated an iron core. This was also the time when scientists began to be interested in how the Earth was formed. The consensus at the time was that it formed by condensation out of a hot cloud, and it was still cooling. This explained (at a time when radioactivity wasn’t known) why it got warmer the further you went underground. So at the time the best explanation for the structure of the Earth was that it had a hot liquid iron rich core surrounded by a rocky shell.

However even in the 19th Century it was clear that there were problems with this explanation. If you spin an uncooked egg, it wobbles – so why doesn’t the earth? During the 20th Century it began to be postulated that the core was two phase – a solid core with a liquid coating. One of the experts on the programme, Arwen Deuss, used seismological readings to show that this was the case. When there is an earthquake seismographs on the other side of the Earth detect the shockwaves that have travelled through the planet. Before Deuss’s work it was thought that there was a shadowzone where no waves were detected because they had failed to pass directly through the centre of the Earth – so it was thought that the core was a different phase to the rest of the planet and the waves couldn’t travel through it. Deuss showed that there are very faint delayed waves detectable in that shadow zone, and that mathematically the best model to describe how these waves are delayed and how they are diminished is one where the core is solid but it is surrounded by liquid. The seismic waves cannot travel through liquid in the same state as they travel through solid, and each transition between states uses up some of the energy in the wave. A wave that travels directly through the core will transition from solid to liquid to solid to liquid and lastly to solid again. As well as each transition using up energy it takes time (hence the delay) and changes direction (so the waves aren’t in quite the same places you’d expect if they had no transitions).

The current theory is that the inner core is an iron crystal that is forming out of a less pure molten iron fluid around it. This iron crystal is about the size of the Moon, a fact which I find mind-boggling. The crystal is still growing and this is not a consistent process, sometimes it grows more quickly and sometimes more slowly. The experts said there is evidence of some sort of discontinuity that formed 500 million years ago, but no-one knows what caused it. The crystal is also split into two pieces. One of the experts made an analogy with the land/sea divide up here on the crust, but I didn’t really follow that. The crystal is also different in the north/south direction as compared to the east/west direction – seismic waves take longer to travel east & west than they do north & south. It’s not known why this is: perhaps to do with crystal alignment, or perhaps it tells us something about the shape of the core.

This solid iron crystal is rotating within the liquid it sits in, I think at a slightly different (quicker?) speed than the whole of the Earth rotates. It’s this rotation that is the cause of our magnetic field (which is another piece of evidence in favour of the two phase theory). And the magnetic field is what protects us from cosmic radiation so in some sense you can say that the two-phase spinning core of the Earth is why there is life on Earth. The current theory is that Mars and Venus have cores that are too solid or too small to generate enough of a magnetic field to protect against radiation. That’s an untested hypothesis, and so Deuss would like to put seismographs on one (or both) of the other planets to see what she can detect about their internal structure.

Bragg closed up the programme by attempting to encourage them to talk about practical uses that have come out of this blue-skies research – but it seems at the moment this is still in the blue-skies phase.

In Our Time: The Photon

The episode on In Our Time about photons was summed up near the end by all the experts agreeing with an Einstein quote that if you think you understand what a photon is then you’re deluding yourself! So that makes it a trifle daunting to write up the episode but is reassuring in that the reason the subject feels slippery & hard to grasp is because it is 🙂 The three experts who joined Melvyn Bragg in discussing photons were Frank Close (University of Oxford), Wendy Flavell (University of Manchester) and Susan Cartwright (University of Sheffield).

Close opened the discussion by giving a summary of the 19th Century view of light. The key idea at this time was that light was a part of the electromagnetic spectrum. The electromagnetic spectrum is the name given to waves formed electromagnetically – an electrical field builds up, which generates a magnetic field, the electrical field fades away as the magnetic field builds up, and a new electrical field builds up as the magnetic field fades away. These waves can have any frequency, and scientists showed the light was a part of this spectrum (i.e. that this is what light is). The existence of non-visible frequencies was predicted after this.

This didn’t, however, explain all the known observations of light. Cartwright discussed the “black body problem”: as you heat something up it starts to emit light, first red, then yellow and so on up to the bluer wavelengths. Planck figured out that this sequence can be explained if you assume that the light comes in little packets of energy (quanta), and that the amount of energy in each packet is determined by the frequency of the electromagnetic light wave. I don’t think I’d heard of the “black body problem” before, but I was aware of the existence of Planck’s constant – which is part of this theory.

At the time Planck was thinking about this problem it was assumed that the quanta were a property of the heated object and not of light itself – after all it was “known” that light was a wave and waves don’t come in discrete particles. Flavell explained that Einstein suggested that light might need to be thought of as a particle as well, but most people thought that was ludicrous. It wasn’t until after experiments done by Compton on interference patterns, which produced results that could only be caused by light being made up of particles, that it became accepted that photons are both waves and particles.

Having brought us up to speed on the history behind the theory of light’s paradoxical existence as both a wave & a particle the experts moved on to discuss more of the properties of photons. Photons are massless, consisting only of energy. This is why they travel at “the speed of light” – that’s the speed of a massless particle, anything with mass must travel slower. Photons are bosons one of the two broad classes of particles – the other being fermions. The classes are distinguished by how many can exist in the same quantum state at the same time. There can only be one fermion in each quantum state (and this is why we don’t fall through matter), but there can be more than one boson in each quantum state. Photons are also the mechanism by which the electromagnetic force is transferred around between objects.

The wave/particle duality of photons is one of the pairs of things that can’t be measured at the same time. This is the Heisenberg Uncertainty Principle, which I had heard of before but hadn’t realised applied to more than position/speed of particles. The experiments that demonstrate this practically are some of the weirder experimental data I’ve heard of, a proper demonstration of the counter-intuitive nature of quantum physics. If you look at light passing through a diffraction grate, then you see interference patterns – this is light acting as a wave. However, if you measure it at the level of single photons passing through, then you have “forced” the light to act like a particle by counting them and there are no interference patterns. And bizarrely if you measure like this and then delete the data the patterns reappear!?

My write-up of this has definitely not done the subject justice – physics is my weakest subject by far, especially quantum physics. Still interesting to learn a bit about, tho 🙂

In Our Time: Robert Boyle

I know of Robert Boyle because of Boyle’s Law (which I must’ve learnt in GCSE physics about 25 years ago although I couldn’t give you the details now), but as In Our Time explained his part in developing the scientific method is probably the more important part of his legacy. And in his own time his piety and religious writings were also important. The three experts who discussed it were Simon Schaffer (University of Cambridge), Michael Hunter (Birkbeck College, University of London) and Anna Marie Roos (University of Lincoln).

Robert Boyle was born in 1627 as the 14th child and 7th son of Richard Boyle, 1st Earl of Cork. The Boyles were fabulously wealthy. Not all of the children survived to adulthood, of those that did the daughters were married off advantageously (although not always happily) and the sons inherited their father’s land. Robert Boyle as the youngest son probably had the least lands and income, but this still inclued lands in County Limerick and a manor in Dorset. And an income of around £3,000/year (if I remember right) which made him ludicrously wealthy at the time. An anecdote the experts used to illustrate this was that Boyle funded Hooke’s telescope for the Royal Society, which was almost not built because it was too expensive and Hooke couldn’t secure funds – Boyle stepped in and paid, and the programme gave the impression that this wasn’t a stretch for him.

Boyle was educated at Eton for a few years starting when he was 8 years old, just after his mother died. Then in his mid-teens he went abroad, with a tutor, and spent several years in Continental Europe including France and Italy on a sort of Grand Tour. During that time he began to develop an interest in science, but more important to him he had the opportunity to debate religion with various scholars of the day. At some point in these years abroad he had a type of religious conversion experience during a thunderstorm in which he thought he might die. On his return to Ireland (and then England) in the 1640s he began to write essays about his understanding of religion, seeing this as his life’s work. One of the experts, Hunter I think, said that if this was all Boyle had done then we probably wouldn’t remember him – his style and his thinking weren’t particularly novel or readable.

Boyle’s practice of religion was a fairly practical matter. He was part of a school of thought that felt the best way to live a godly Christian life was to carefully examine your past to determine if you’d taken the actions most pleasing to God (and then presumably you have a pattern for the future). It’s an ongoing process and would require meticulous attention to detail and thinking about other alternative things you could’ve done and so on. His scientific interests were also an outgrowth of his piety – a belief that the best way to learn about God was to learn about his creation. Bragg asked a few times if there had been a “scientific conversion” moment to match Boyle’s religious turning point, but either Hunter or Schaffer pointed out that our division between religion and science as separate things with different spheres of relevance is anachronistic when thinking about the 17th Century.

During the 1650s and later Boyle became involved with a group of men who met regularly in Wadham College, Oxford and who would later form the nucleus of the Royal Society. They were mostly university educated, and so Boyle was a bit of an outlier (although I think not the only one) with his lack of formal education past his schooling at Eton. Whilst here he formed a close working partnership with Robert Hooke, who was particularly gifted at building apparatus and the practical side of chemistry & physics experimentation. The work Boyle is remembered for on air and gases was done in collaboration with Hooke. Boyle also corresponded with one of his sisters, Lady Ranelagh, about his work – and in later life he moved to London and lived in her household (which didn’t include her husband, her marriage hadn’t been a happy one).

Boyle was meticulous about writing down his experiments, and also wrote about how one should both carry out and record scientific experiments. Roos pointed out that modern day Materials and Methods sections in scientific papers are the direct descendants of Boyle’s ideas about the scientific method. He said that one should write down exactly what had been done, so that another person could do the same experiment again. He also said that the experimenter should come to the experiment with an open mind, instead of already already decided what they expected to happen. Hunter finished up the discussion by saying that this initial development of the scientific method is Boyle’s greatest legacy.

Boyle turns out to’ve been a much more interesting man than I’d expected from my half memory of his law about the relationship between gas volume & pressure!

Heart vs Mind: What Makes Us Human?; The First World War; How to Get Ahead; Precision: The Measure of All Things

We finished three different series over the last week so I wasn’t going to write about any of the one-off programmes as well, but Heart vs Mind: What Makes Us Human? irritated me sufficiently that I wanted to say why! The premise of this film was that the presenter, David Malone, had always thought of himself as a wholly rational person but then his life had become derailed – his wife had started to suffer from severe depression and it was as if the person she had been no longer existed. In the wake of that, and his responses to it, he started to think emotions were more important to what makes us human than he’d previously thought. So far, so good – I mean I might quibble about how it’s a known thing that no-one’s really totally rational and we know that the mind affects the body & vice versa; and I might wonder what his wife thinks about being talked about as if she might as well be dead. But those are not why I found this programme irritating.

I found it irritating because the argument he was putting forward had the coherency and strength of wet tissue paper. He took the metaphorical language of “brain == reason; heart == emotion” and then looked for evidence that the physical heart is the actual source of emotions. There was some rather nice science shown in the programme – but whenever a scientist explained what was going on Malone would jump in afterwards and twist what was said into “support” for his idea.

For instance, take heartbeat regulation. It is known that there are two nerves that run from the brain down to the heart and they regulate the speed of the heartbeat. There is a physiologist in Oxford (I didn’t catch his name) who is looking at how that regulation works. It turns out there is a cluster of neurones attached to the heart which do the actual routine “make the heart beat” management. The messages coming from the brain tell the heart neurone cluster “speed up” or “slow down” rather than tell the heart muscle to “beat now; and now; and now”. Interesting, but not that astonishing – I think there are other examples of bits of routine tasks being outsourced to neurones closer to the action than the brain is (like the gut, if I remember correctly). Malone took this as proof that the heart had its own mini-brain so it would be possible for it to generate emotions. And so it’s “like a marriage between heart and brain with the brain asking the heart to beat rather than enslaving it and forcing it to beat.”

There were other examples of his failure to separate metaphor from reality – indeed his failure to realise that there were two things there to separate. Take, for instance, the metaphor of the heart as a pump. Malone hated this metaphor, so industrial and mechanical and soulless. Practically the root of everything wrong with modern society! (I exaggerate a tad, but not much.) However, the heart undeniably does pump blood round the body. So he looked at visualisations of blood flowing through his heart (another awesome bit of science) and talked about how beautiful this was – as the blood is pumped around the shape of the heart chambers encourages vortices to form in the flow which swirl in the right way to shut the valves after themselves on the way out. Which is, indeed, beautiful and rather neat – and I learnt something new there. However Malone then carried on about how we shouldn’t keep saying the heart is a pump because the complexity of the heart’s pumping mechanics are too beautiful to be reduced to what the word pump makes him imagine. Er, what? Saying you can only imagine pumps as simple metal cylinders with pistons says more about paucity of your imagination than the pumpness of the heart.

I think part of my problem with this was that I’m not actually that much in disagreement with him so it was irritating to watch such a poor argument for something reasonable. I too believe Descartes was wrong – you can’t separate mind from body. The mind is an emergent property of the body. And there is feedback – our mental state, our emotions and beliefs, affect the body and its functions. Our physical health and physical state affects our minds. It’s not surprising to me that it’s possible to die of a broken heart (ie mental anguish can affect the physical system including disrupting heartbeat potentially fatally in someone whose heart is already weak). But this is not because the metaphor of the heart as the seat of emotions is a physical reality. It’s because mind and body are one single system.

None of us are rational creatures. Emotions are a central part of what makes us human. And metaphors do not need to be based in a physical truth to be both useful and true.

(I also get grumpy about people who think that explaining something necessarily robs it of beauty but that’s a whole other argument. As is the one where I complain about the common equation of industry with ugliness.)

Moving on to what I intended to talk about this week: we’ve just finished watching the BBC’s recent 10 part series about The First World War. This was based on a book by Hew Strachan, and used a combination of modern footage of the key places, contemporary film footage, photographs and letters to tell the story of the whole war from beginning to end. Although obviously the letters were chosen to reflect the points the author wanted to make, using so many quotes from people who were there helped to make the series feel grounded in reality. It was very sobering to watch, and the sort of programmes where we frequently paused it to talk about what we’d just seen or heard. It wasn’t a linear narrative – the first couple of episodes were the start of the war, and the last couple were the end, but in between the various strands were organised geographically or thematically. An episode on the Middle East for instance, or on the naval war, or on the brewing civil unrest in a variety of the participating countries.

I shan’t remotely attempt a recap of a 10 episode series, instead I’ll try and put down a few of the things that struck me while watching it. The first of those was that there is so much I didn’t know about the First World War. This wasn’t a surprise, to be honest, I’ve not really read or watched much about it and didn’t spend much time on it at school (having given up history pre-GCSE). But I’d picked up a sort of narrative by osmosis – the Great War is when Our Men went Over There and Died in a Brutal Waste of Life. And that’s true as far as it goes, but it doesn’t go anywhere near far enough. Even for the Western Front – the British narrative is all about it being “over there” but (obviously!) for the French and the Belgians this was happening in their country and in their homes. One of the sources used for this part of the war was a diary of a French boy – 10 years old at the start, 14 by the end – which really brought that home. And (again obviously) the Western Front and the French+British and German troops weren’t the only participants nor the only areas of conflict. I thought separating it out geographically & thematically was well done to help make that point.

It was odd to note how much the world has changed in the last century. Because there was film footage of these people – dressed a bit too formally, but looking like ordinary people – the casual anti-Semitism and racism in their letters and official communications was more startling than it would’ve been from more distant seeming people. Things like referring to Chinese or African troops as “monkeys” in relatively official documents. I’m not saying that racism or anti-Semitism have vanished in the modern world, but there’s been a definite change in what’s acceptable from politicians and so on.

Throughout the whole series the shadow of the Second World War loomed. Obviously no-one knew at the time how things would turn out (tho it seems one of the French generals did make some rather prescient remarks about only getting 20 years of peace at the end of the First World War). But it’s rather hard to look at it now without the knowledge that hindsight gives us. Which ties in with my remark about anti-Semitism above, because one of the things that changed cultural ideas of “what you can say about Jews” is the Holocaust. And other hindsight spectres included the situation in the modern Middle East as set up in large part by the First World War, and of course the Balkans too.

Interesting, thought provoking, and I’m glad I watched it.

Very brief notes about the other two series we finished:

How to Get Ahead was Stephen Smith examining three different historical courts and looking at both the foibles of the monarch and the ways a courtier at that court would need to behave & dress in order to succeed. He picked out a selection of very despotic rulers – Richard II of England, Cosimo Medici of Florence and Louis XIV “the Sun King” of France. I wasn’t entirely convinced about Smith as a presenter, a few more jokes in his script than he quite managed to pull off, I think. But good snapshots of the lives of the elite in these three eras/areas.

Precision: The Measure of All Things was Marcus du Sautoy looking at the various ways we measure the world around us. For each sort of measurement (like length, or time) he looked at how it had evolved throughout history, and at how greater precision drives on technology which in turn can generate a need for even greater precision. I think I found this more interesting than J, because I think it’s kinda neat to know why seemingly arbitrary units were decided on when they could’ve picked anything. I mean the actual definition settled on for a meter is arbitrary (the distance light travels in a vacuum in 1/299,792,458 of a second) but there’s a rationale for why we decided on that particular arbitrary thing (the definition before the definition before the current one was that it was 1/10,000,000th of the distance from the north pole to the equator).

Other TV watched this week:

Episode 2 of Churches: How to Read Them – series looking at symbolism and so on in British churches.

Krakatoa Revealed – somewhat chilling documentary about the 19th Century eruption of Krakatoa and what we’re learning about the certainty of future eruptions of Krakatoa.

24 Hours on Earth – nature documentary looking at the effects of the diurnal cycle on animals and plants. Lots of neat footage and a voiceover with somewhat clunky and distracting metaphors (“Soon the sun’s rays will flip the switch and it will be light” !?)

Episode 1 of David Attenborough’s First Life – series about the origins of life and the evolution of animals.

In Our Time: The Invention of Radio

Sunday morning we listened to the In Our Time episode about the invention of radio, which we’ve had sitting on the ipod for a while – it’s not a subject that caught either of our imaginations in advance. It did turn out to be interesting, but it also felt like a series of vignettes – this person, this date, this advance, now move on to the next – so I’m approaching writing it up with some trepidation! The three experts on the programme were Simon Schaffer (University of Cambridge), Elizabeth Bruton (University of Leeds) and John Liffen (Science Museum, London).

At the beginning of the show Bragg introduced the subject by talking about Marconi and the patents he filed in the early 20th Century that mean he is often credited as the father of radio. When they discussed him, towards the end of the programme, they talked about how he liked to present himself as coming up with the whole thing himself. He didn’t give many (if any) of the people who’d previously worked in the field credit for their achievements. But as the programme had just demonstrated, radio wasn’t invented in a single flash of genius but was instead the result of an accumulation of nearly a century of small advances.

Before the 19th Century if you wanted to send a complex message a long way, then it could only travel as fast as you could transport a person carrying it. Experiments with electromagnetism in the early 19th Century started to change this, and by the 1830s a system of transmitting messages along a wire had been developed – the telegraph. At first the pioneers of this technology had envisioned something that would twist a needle to point at the required letter of the alphabet, but the work of Morse & others established a technically easier method involving a simple code. The telegraph took off pretty rapidly, but developing a wireless method would take much longer.

James Clerk Maxwell came up with a theory of electromagnetism that predicted electromagnetic waves. At first this was purely in the realm of theory, and proving it experimentally posed a variety of technical problems. You have to design and build apparatus to emit these waves, which was eventually done in the form of a spark-gap transmitter – I don’t think they explained how this worked on the programme. And then having done this you need to reliably detect the resulting waves. They talked about a few of the ways that were developed, but I didn’t really follow any of them and so have forgotten the details :/ Over a period of several years successive scientists and engineers made their own contributions to the field, but the definitive experimental proof came from the work of Hertz in the late 1880s.

This is still science rather than technology – none of the people involved so far in the story were thinking in terms of commercial applications, it was just an interesting phenomenon to investigate and try to explain. The Post Office, in Britain, oversaw the domestic telegraph network and was beginning to be interested in possible applications of wireless technology. However there was some pushback because the telegraph system worked so well, so why develop something new? There was a similar thought process at work in the early days of the telephone system too – the postal system worked so well, why would anyone need a phone?

Even once it was known to be theoretically possible to transmit and receive electromagnetic waves wirelessly there were still several practical obstacles that needed to be overcome. For instance at first transmitters transmitted across a wide range of frequencies – so if there were two transmitters relatively close together then their signals would overlap and a receiver wouldn’t be able to pick out the message from one or the other. So one of the advances that had to be made was in the concept of tuning – restricting the transmitter to a particular subset of frequencies and then only listening to one of these bands. Another obstacle to be overcome was in the sensitivity of detectors. This was done in part by a man called Bose, who was working in Calcutta. The detectors used didn’t operate as well in the humid environment of India, and so Bose had to develop a modification of the design – which was then better in other environments too.

And we’re back to where Marconi enters the story. He was a young man from a wealthy Italian family, and despite his protestations otherwise what he did was to put together all the various prior work on wireless technology and figure out a commercial product. He’s helped in this by the fact that he’s rich, well connected and good at publicity. He also came up with a niche for the technology – ships! Obviously it’s not practical to trail a telegraph wire after a ship that’s sailing across the Atlantic, so this is an application where wireless has obvious answers to the “why bother?” question. Most people at that time (including people like Tesla) thought that electromagnetic waves would move in straight lines, so this is a case where Marconi not really understanding the science worked out in his favour – he just set up trials at doing a transatlantic transmission from Cornwall to the US. This was a success and he was then able to market his devices for use in shipping.

These radios were still transmitting code rather than sound. The programme didn’t spend much time covering the next stage because it was getting towards the end of the time they had available. But basically instead of transmitting bursts of waves, instead this built on the work of Tesla (I think) and transmitted a continuous radio signal. The modulations of this signal were then used to carry information that could be decoded into the original soundwaves recorded by the microphone.

I’m not sure I’ve done the programme justice with this write-up – in particular there were a lot of little biographical snippets for the various figures involved in the story that made them come alive as people, and I haven’t conveyed that at all.

In Our Time: Cosmic Rays

We’re back to listening to episodes of In Our Time on Sunday mornings. The one we listened to this week was about that staple of 1930s science fiction – cosmic rays. The three experts who were talking about the reality of this phenomenon were Carolin Crawford (University of Cambridge), Alan Watson (University of Leeds) and Tim Greenshaw (University of Liverpool).

Cosmic rays were discovered about a century ago. The first indications that they existed came from detection of increasing radiation levels as you go higher up in the Earth’s atmosphere. At first they were assumed to be photons and the name “cosmic rays” was coined. This turns out to be a misnomer, they are in fact charged particles – bits of atoms. Some of them are atomic nuclei, some are electrons and some are more exotic things like positrons. They travel at a variety of speeds, from a variety of sources. Crawford told us that they are categorised into three broad groups. The first of these are relatively slow-moving particles that come from relatively local sources – the sun for instance – and are very common. These are the particles that are involved in creating the Aurora Borealis. The next group are moving more quickly, and come from further away – generally these are thought to be generated as as side-effect of supernova explosions. And the last group are the fastest moving and are thought to be from outside our galaxy, these are the rarest type of particle.

The particles aren’t detected directly (on Earth) instead what we detect is the side-effects of these particles hitting the Earth’s atmosphere. As the particles collide with atoms in the upper atmosphere they generate a shower of secondary particles and it’s these that are detected. The types and numbers of these particles can be used to work out what hit the atmosphere, how fast it was going and the direction it was travelling. We know they are charged particles (and which charge) because of the effects of the Earth’s magnetic field – the number of particles hitting the atmosphere varies with latitude with most of them at the poles. This is also why the Aurora Borealis are mostly at the poles. That phenomenon is formed by the particles exciting the electrons in atmospheric atoms, when the electrons return to their original energy states they emit light. They went off into a slight digression on the programme when talking about this – predicting the Aurora Borealis requires prediction of solar weather and that’s being worked on because particularly bad solar weather can lead to EMPs that can affect satellites.

All three experts agreed that the fastest moving group are the most interesting – in part because we still don’t know much about where they come from or how they’re generated. They’re pretty rare, so a normal sized detector (I don’t think they said how big) would only detect about one a century – so Watson was talking about a project he helped set up that built a detector the size of Luxembourg and this detects 3 or 4 of these rare particles a year. One theory of where they come from is that they are generated in galaxies with super massive black holes at the centre. Another is that they have something to do with dark matter.

Particle physics as a discipline grew out of the study of cosmic rays. The Large Hadron Collider does under controlled conditions what cosmic ray particles do when they hit the atmosphere. This is another reason why the fastest particles are the most interesting – they travel at a much higher speed than the LHC can achieve. The fastest moving particles travel faster than the speed of light in air, generating Cherenkov radiation. Again the programme took a little digression to explain this. Light travels at different speeds in different media – and so these particles aren’t travelling faster than light does in a vacuum (like the space the particle was just travelling through), it’s just that they don’t slow down when they enter the atmosphere. So the radiation that is released in front of the particle is moving slower than the particle and so can’t move away from the particle. It’s effectively being pushed along in front of the particle and that’s what we detect as Cherenkov radiation. It’s a bit like the sonic boom you get when something breaks the speed of sound.

As an aside – something I didn’t know before was that 14C dating is a direct result of cosmic rays. The 14C in the atmosphere is generated by cosmic ray particles hitting nitrogen atoms, if cosmic rays didn’t exist we’d not have such a good way of dating organic material (like bones).

Future work on cosmic rays is quite concentrated around figuring out what the fast ones are. There is also data being gathered more directly on the particles involved. The ISS currently has a cosmic ray detector fitted to the side of it, which has been gathering data since 2011 and is planned to continue for ten years.

In Our Time: Exoplanets

The first planet orbiting a star other than the Sun wasn’t discovered until 1992 and since then the subject of exoplanets has gone from being something you argue about the existence of to a rapidly expanding field with new discoveries all the time. The experts who discussed exoplanets on In Our Time were Carolin Crawford (University of Cambridge), Don Pollacco (University of Warwick) and Suzanne Aigrain (University of Oxford).

One of the reasons it took so long to discover any extra-solar planets, despite people speculating about their existence for centuries, is that they are very hard to directly see. In fact I think they were saying that none of the known ones have actually been seen. Instead a variety of more indirect techniques are used to detect them, and these required both sophisticated technology & sophisticated knowledge of physics before they could be used. The technology needed to develop to a point where small differences in stars could be measured accurately and consistently over time. And the physics is required to both predict how a star without planets would behave and then to figure out what the differences from this prediction mean.

In the programme they ran through a variety of techniques used to detect planets. One of these is to look at the colour of the star’s light and see if it’s changing between blue-shifted & red-shifted over time. If the star has no planets then you won’t detect that. When there’s a planet orbiting the star it’s not quite as straightforward as the planet circling the star, actually the star and the planet are both circling a point between them (that’s a lot lot closer to the centre of the star than it is to the planet). So the star will seem to move back & forth relative to us observing it. This is biased towards detecting more massive planets, as they’ll move the centre of gravity from the centre of the star more – so-called “hot jupiters” for instance, which are planets the mass of Jupiter that orbit close to their star.

Another method is to look for the changes in the star’s light caused by the transiting of a planet across the face of the star. Obviously this is only possible to detect if the planet is orbiting in the right plane for us to see it. But if you have one transiting where we can detect it then you can detect the existence of other planets in that system by looking at the perturbations of the orbit of the one that transits. You can also detect things about a planet’s atmosphere with this method. The changes in the light of the star can be used to tell you something about the size of the planet (in terms of diameter), and if you look at different wavelengths of light then you’ll see varying diameters. This tells you when the atmosphere of the planet is thin enough to be transparent to that wavelength, and different gases absorb different wavelengths differently so you can figure out the gases that are present. Apparently you can even detect the presence of clouds using this technique.

Another method uses the phenomenon of gravitational lensing. If the light from a distant star passes by a closer to us star on it’s way to the telescope then it will be bent by the gravity of the middle star. A planet orbiting that middle star will affect the lensing effect, and you can figure out things about the size & distance from the star by exactly how the lensing is affected.

If you use the first two methods together you can tell things about the density of the planet. Is it small & heavy? Is it big & fluffy? Or even small & fluffy? There seem to be a wide variety of planet types out there, not all of which are represented in our own solar system. There are also a wide variety of types of solar system out there – Pollaco pointed out that one reason there was argument about the reality of the first exoplanet discovered was because people were assuming that our own solar system was a good model for “all systems everywhere”. It turns out it’s not. The example they used in the programme was systems that have hot jupiters – the first exoplanet was one of these, and the very idea of a Jupiter type planet orbiting with a periodicity of only 4 days was almost unthinkable. They also talked about planetary systems detected around brown dwarves – stars which weren’t quite massive enough to ignite at the end of the formation process. And planets around pulsars (again like the first ones detected) – and one of the experts (I think it was Crawford?) made a throwaway remark about how these are probably not the first planetary system for the star in question. Before a star becomes a pulsar it goes through a supernova explosion, which would probably destroy any original planets – the ones orbiting afterwards are probably secondary captures.

They also discussed looking for planets which might be habitable. Bragg asked if we are thinking about life like ourselves, or germs. The answer was (paraphrasing) “yes”. At the moment no-one knows enough to know what we’re looking for in terms of life on other planets, and at first we’re obviously limited to things we know about life on Earth as a starting point for what to look for. So looking for rocky planets which are neither too big nor too small, that are in the right zone for liquid water. And other things about our own solar system might’ve been necessary – like the presence of Jupiter which draws away some of the comets that could bombarded Earth & wipe out all life. I think it was Aigrain who talked about other ways of detecting life – looking at what we can tell about the atmospheres of the planets. If there are very reactive gases present then they must be being made constantly – some of these we only know of biological processes that make them. So if one could detect such gases that’d be a sign of life.

It was a little bit of an odd In Our Time episode, because there was less of a sense of a narrative than they normally have. It felt like this is because the study of exoplanets is in its infancy – we’re at a point where most of the work is data gathering. I mean in the sense that a lot of planets are being discovered and categorised, but as yet they’re not classified and grouped into types. Nor are there overall theories about how solar systems in general work or were formed – it’s now clear that the one we know isn’t the only sort there can be, nor is it particularly typical of what we’re detecting now.

In Our Time: Relativity

Physics is one of those subjects where I can very clearly see the boundaries of my understanding – as soon as we get to quantum physics or Einstein’s theories of relativity I can follow the surface level explanations & analogies, but I’m always aware I don’t understand it on a deeper level. I assume the same is actually true of all subjects at some point – I’m not a genius, and I spread my self-education widely among many subjects rather than deeply delving into one – but for physics I can see the fence. It’s a peculiar sensation.

The three experts who talked about Einstein’s theories of relativity on In Our Time were Ruth Gregory (Durham University), Martin Rees (Astronomer Royal and University of Cambridge) and Roger Penrose (University of Oxford). The programme started with a bit of context: in 1905 Einstein published four papers, including one on Special Relativity. At the time he was working as a clerk in a patent office & was previously unknown as a physicist. Ten years later he published a paper extending Special Relativity into General Relativity.

Prior to Einstein’s theories of relativity the assumption was that there was some sort of objective measure of time in the universe, the same no matter how it was observed. Einstein theorised that the motion of the observer affected the observation of the passage of time – hence relativity. Apparently he later regretted using that word for his theories because it’s been used since to imply that physics is all just subjective & depends on your point of view, but actually there is still an objective physical reality which can be described mathematically & rigorously it’s just that within the system the point of view of the observer is important for the observations made.

One of the things that Einstein’s theories grew out of was the observation that the speed of light remains constant no matter what direction you’re travelling in or how fast you’re travelling. This seems to be a paradox. Say you think about driving a car towards or away from another car that’s driving towards you – when you’re travelling towards it, it gets closer to you quicker than if you’re travelling away from it. (I hope that makes sense.) But with light if you’re travelling towards it it appears to be travelling the same speed as it travels if you’re travelling away from it. Einstein’s theory explains how this happens by explaining how time is running differently (I think).

Special Relativity implied that time is another dimension like the spatial dimensions, and Minkowski built on this theory to mathematically describe spacetime. Einstein then used this mathematics as part of his theory of General Relativity. One of the key insights of General Relativity is that spacetime is curved by the presence of mass and this curvature explains why gravity exists. Gregory used an analogy I’ve heard before to describe spacetime & its curvature – thinking of spacetime as being like a four-dimensional version of a two-dimensional rubber sheet. If you have your rubber sheet suspended as a flat horizontal plane and then you put something large like a bowling ball on it, the sheet will be distorted & curved where the ball weighs it down. Then if you roll a marble across it it will accelerate down the slope towards the bowling ball – or if you get your angles and speed right you can make it orbit the bowling ball.

There was some discussion of the twin paradox at two different points in the programme. This is a thought experiment where you have twins one of which remains on Earth, and the other one travels away to a different star system at close to the speed of light, and then returns. When the twins meet again the one that stayed on Earth will be older than the one that went to the stars and back. This is a staple of science fiction, and I think the first time I ran into the idea was in “Time for the Stars” by Robert A. Heinlein which I read when I was at middle school. The first time it was discussed on the programme was in the context of Special Relativity as the way of demonstrating what Einstein is talking about. And they mentioned that this has actually been shown experimentally – by getting a very accurate clock (synchronised with a matching clock) and putting it on a plane and flying it to the other side of the world & back. Then when you compare the two clocks the one that travelled has measured less time than the one that stayed put. Gregory pointed out that the observations demonstrate both the effects of relative motion and the effects of distance from a massive object (the maths needs to take into account that the plane is up in the air while the other clock is on the ground). I had no idea prior to this programme that the effects were measurable on such a human scale.

The second time the twin paradox came up was in the context of talking about the geometry of spacetime. Penrose was explaining that with his theories Einstein was trying to explain the universe in geometrical terms. Spacetime is four-dimensional, three dimensions are the familiar spatial ones that can be explained using Euclidean geometry. For the fourth dimension, time, Einstein (and Minkowski?) showed that you could use almost the same geometric rules only needing to reverse a sign – turn a plus to a minus. The way Penrose explained what he meant by this was to use the twin paradox – one twin is moving from event A to event B along a straight line in the time dimension, the other is moving from A to B on a curved line in the time dimension. For the spatial dimensions a curved line is a longer path than a straight line, for the time dimension a curved line is a shorter path than a straight line. (And this is what I mean by being able to see the edge of my understanding – I can write that last sentence as a fact and accept it is true, but I don’t understand why or how.)

I know I’ve missed out various things they discussed but I shall only mention another couple before I finish the post. Firstly there are real world applications of the theories of relativity, it doesn’t just help physicists understand the universe – it’s an important part of the underpinning of how GPS works. The other thing was that Rees was saying that Einstein was in some ways more like an artist than a scientist. By this he meant that for an artist their work is generally unique, if they didn’t exist no-one else would produce the same artworks. But for science generally if one person doesn’t come up with the theory or do the experiment then someone else would not long after. Rees thought (and the other two agreed) that while Special Relativity would probably have been thought of by someone else soon after, General Relativity was such a large jump that if Einstein hadn’t thought of it then we might still have not thought of it.