Posts Tagged ‘the universe’
on physics and the universe – what’s a neutrino?
more on the standard model later…
(Years ago, in the early 1980s, I bought the monthly magazine Scientific American regularly, to improve my education. A couple of books I read at the time brought this on – The Magic Mountain by Thomas Mann and The Selfish Gene by Richard Dawkins, probably in that order. I was then around the same age as Hans Castorp, Mann’s central character, which really helped me get into the novel. Call me Narcissus.
It wasn’t so much the whole (rather multifarious) novel that grabbed me, but a section in which the tubercular Hans, through his reading, reflects on the nature and origin of life, and then of matter itself. I have a romantic image of myself at the time jumping up from the book and pacing my bedroom, my mind abuzz with thoughts and wonderings. Science! Why is it so? How did it all begin? How did one become another?
Perhaps sadly, perhaps not, my reading of The Magic Mountain marked a fairly rapid switch in my reading habits, from fiction to non-fiction. And yet the big questions still elude me. I’m still very much an amateur, and I used to call this blog An autodidact meets a dilettante to mark my inexpertise. I changed the name to A bonobo humanity? because I hoped it would narrow my focus a bit, and of course because a female-dominated human world, a ‘world turned upside-down’, is a fantasy of mine, but one worth working towards. And yet, the even bigger issues stimulated by Hans Castorp’s reflections, like – why is there something rather than nothing? – still bug me. So, here goes…
What is a neutrino? I first read about them in a Scientific American magazine, which described experiments and facilities designed to detect them. They’re not so much rare as difficult to detect, and we don’t even know whether they have mass. But isn’t a massless particle a contradiction in terms? According to a Scientific American article from 1999, Wolfgang Pauli first postulated their existence in 1930, and they were first detected, as antineutrinos, in 1955. The article begins thus:
A neutrino is a subatomic particle that is very similar to an electron, but has no electrical charge and a very small mass, which might even be zero.
The weird idea that its mass might be zero is somewhat explained by this more recent intro to neutrinos from the US Department of Energy:
The neutrino is perhaps the best-named particle in the Standard Model of Particle Physics: it is tiny, neutral, and weighs so little that no one has been able to measure its mass [my emphasis]. Neutrinos are the most abundant particles that have mass in the universe. Every time atomic nuclei come together (like in the sun) or break apart (like in a nuclear reactor), they produce neutrinos. Even a banana emits neutrinos—they come from the natural radioactivity of the potassium in the fruit. Once produced, these ghostly particles almost never interact with other matter. Tens of trillions of neutrinos from the sun stream through your body every second, but you can’t feel them.
That last sentence is pretty mind-blowing! So, FWIW, neutrinos have 3 types, electron, muon and tau. They’ve been detected in human-constructed underground detectors such as the Sudbury Neutrino Observatory (SNO), a 1000 ton heavy water facility in Canada. And there’s still a lot to discover, apparently. As an amateur, and ‘knowing’ via Einstein that mass and energy are in a sense interchangeable, is it neutrinos as energy that are being detected, or neutrinos as mass? It seems that they’re being detected (and the neutrino type is relevant here) due to interactions with other matter particles more than anything else. There’s a sort of mathematical calculation called the Standard Solar Model (SSM), based on physicists’ understanding of stars in general, which predicts, inter alia, the outflow of solar neutrinos, and our inability to detect enough of these neutrinos early on became known as ‘the solar neutrino problem’. Virtually all the neutrinos detected in those early, pre-SNO days were electron neutrinos. Fuck knows why (but read on, as I learn…).
Neutrinos are fermions – elementary particles with a half-spin, like every other elementary particle – particles that aren’t composed of other particles (though not all fermions are elementary). There are bosons, hadrons and fermions, apparently. But particles also ‘exist’ as waves….
All of this has to do with the Standard Model, which recognises two types of elementary fermions – quarks and leptons. Neutrinos are a type of lepton. As mentioned, there are three types of neutrino, and another three particle types also known as leptons – electron, muon and tau. So each of these has a connected neutrino, making six lepton types in all. And then each has its antiparticle… As for the quarks, which combine to form hadrons, such as protons and neutrons, they come in types called flavours, of which there are six – up, down, strange, charm, top and bottom, which all sounds like Alice in Wonderland meets Willie Wanka and his Cocaine Factory, but no – all these particles, though often proposed through some kind of mathematical modelling (methinks), have been confirmed observationally.
I’m starting my explorations of particle physics and quantum mechanics and the magic of mass-energy with neutrinos only because I have to start somewhere, but what I’ve learned already poses questions. The zillions of neutrinos passing through our bodies all the time come from the sun, so they say. If we lived further from the sun, say on Mars, or even Jupiter, would we still be getting this flux of neutrinos? We amateurs tend to think of the space between planets, or ‘outer space’, as pretty vacuous.
My guess is that, assuming all the neutrinos in our solar system come from the sun, the only energy-generating source in our solar system, and since they radiate outward from that one source, they’ll be more thinly spread the further out they go, and that could be mathematically formulated, FWIW?
Apparently they’re all electron neutrinos. And their antiparticles, presumably. But neutrinos can change type, or ‘flavour’, as they travel (a more recently discovered fact which solved the Solar Neutrino Problem, as previous experiments could only detect electron neutrinos) – and this also indicates that they have some slight mass. But what’s most mind-boggling, to me, is that this thing called the Standard Model was formulated, back in the early 70s, from theoretical and experimental work done in the decades before, to explain all the matter in the universe, dividing it up into categories and subcategories – though presumably there’s still a big issue with the ‘missing’ dark matter.
So I suppose there’s no point in asking why neutrinos exist, or what ‘purpose’ they serve, we just have to accept they exist, in their three flavours and together with their anti-particles, as other leptons exist, and all fermions and baryons and bosons, which almost sounds as if I know what I’m talking about. But we know about them because of a lot of brilliant theorising and collective experimental activity which the vast majority of us would find very difficult to comprehend. But this is the universe that made us, for better or worse, and, while I don’t think it’s necessarily our duty to understand it, it helps to pass the time, and I can think of a lot more boring things to do. And so, dark matter…
References
Thomas Mann, The Magic Mountain, 1924
https://www.scientificamerican.com/article/what-is-a-neutrino/
https://en.wikipedia.org/wiki/Sudbury_Neutrino_Observatory
https://en.wikipedia.org/wiki/Standard_solar_model
https://en.wikipedia.org/wiki/Fermion
Solar neutrinos