Posts Tagged ‘gravity’
Neutrinos – tough to think about
the standard model – pre-Higgs
I recently told myself that I would focus more on my ‘main topic’, bonobos and human culture, patriarchy and matriarchy and all that stuff, and yet…
I can’t keep to the script. Now I’m thinking about physics, and whether neutrinos have mass. But how can a particle not have mass? Light is described in terms of waves and their lengths, but also in terms of photons, particles that have no mass. But surely that makes no sense, or at least common sense. In order to comprehend this you have to start thinking about the equation of mass with energy, and perhaps stop thinking of a photon as a particle, but instead as an energy package. Quantised energy? Einstein’s famous theory related mass to energy, and light-speed. We can only get to light-speed by converting our mass to ‘pure’ energy. And it’s best to think of these things abstractly, rather than worrying about weight-loss. When we leave Earth’s gravitational field, we float, as if ‘weightless’. Yet we have mass, of course. And then what? What does ‘float’ mean? Would we just stay in the same position, eternally, or would we drift, attracted by the gravity of the nearest large object, or suspended between two gravitational fields? The Moon is spiralling away from the Earth, very very slowly, and is tidally locked to us, and as it spirals away, the Earth’s rotation slows, with an equal and somehow related slowness. Would our bodies finally be drawn to a spinning planet, and be caught in an orbit like the moon? One question leads to another, and I have no answers.
But I’m getting carried away, rather too literally. But thinking of the moon, and our orbiting body – if the moon is spiralling away (and it definitely is), will it one day cease to orbit, and will our Earth’s axial spin grind to a halt? It’s definitely slowing down, and was, according to astrophysicist Madelyn Broome, referenced below, spinning at a rate fast enough to make for a five-hour day when the moon first formed. But we’re talking billions of years here, and the sun will apparently begin to die long before the moon-Earth system becomes problematic for future Earthlings, whatever they may be…
So, where was I?
Massless particles. It was neutrinos that started it all (or was it photons?). They appear to be something of a problem for the standard view of particle physics. A tiny-teeny mass has been attributed to them (or some of them? – there are three different ‘flavours’, I’ve heard, but more of that later). Here’s what the Melbourne Theoretical Particle Physics research group has to say:
A striking fact about the neutrino masses is that while they are nonzero, they are really tiny, at least a million times smaller than the electron mass, which is itself a small quantity. The suspicion is that neutrinos acquire their masses via a quite different mechanism from the other particles. We do not know what that mechanism is.
The famous or infamous Standard Model of particle physics describes or hypothesises three neutrino types/flavours – electron, muon and tau. We know (by which I mean they know) that neutrinos stream out of the Sun in vast numbers as a result or by-product of nuclear fusion. I’m guessing that this huge stream, which hits the Earth, and us, is what inspired physicists to build underground detectors – and yet we/they know, apparently, that gazillions of these neutrinos are passing through our bodies right now, so they must already have detected them, right? Or do they just pass through us theoretically?
The good thing about neutrinos, if you can call it that, is that very very smart people who’ve worked on them for decades are just as mind-boggled by them as I am, or almost – familiarity may be breeding a touch of contempt, who knows? I mean, they know, so they say, that trillions of neutrinos are streaming through my body undetected or felt by me every (name any super-short period of time). They’re ghostly, insubstantial, and yet essential, presumably. They play a fundamental role, an essential role, in the make-up of the universe. Thank dog we discovered them. We’re going to try and use them, they say, to solve the mystery of dark matter…. heaven help us.
References
https://www.livescience.com/space/the-moon/will-earth-ever-lose-its-moon
gravitational mysteries 2 – it’s not a force, but…
this has something to do with it all…
So I mentioned in my previous post that the Moon is tidally locked to the Earth, keeping the same face to us, presumably for eons. I left it there, without an explanation from Dr Google or anyone else. Does it have anything to do with that gravity thing?
There’s an answer on Eos, an Earth Sciences magazine I’ve shamefully never heard of, so thanks to Caroline Hasler:
A tidally locked object rotates around its axis exactly once during its orbit around a host planet or star. This physical quirk affects many planets and moons, including Earth’s Moon…
This tidally locked state is a consequence of gravity. As the Moon orbits Earth, Earth’s gravity tugs at it. This force deforms the Moon, reshaping it from a perfect sphere into something a little more akin to an American football: slightly squashed at the poles, with a bulge at its equator facing Earth and another on its far side. The same sort of deformation manifests itself in Earth’s oceans, where the Moon’s tidal forces produce watery bulges that travel around Earth as it rotates, leading to alternating high and low tides.
So gravity, this curvature of space-time, deforms the moon, and presumably the oblate spheroid that is the Earth, and billions of other bits of flotsam and jetsam spewed out by our messy universe. Interestingly, though, Hasler describes gravity as ‘this force’, while so many others, such as Veritasium and the PBS SpaceTime presenter, insist that it’s not a force… the point being that it’s hard, it seems, even for those who understand the physics of gravity (though I sometimes wonder if anybody really does), not to describe it in forceful terms. Anyway it’s this gravity spacetime curvature that ‘forces’ the Moon to be locked into facing the Earth without ‘turning away’. And yet the Earth isn’t tidally locked to the Sun. This is partly because the Earth is too far away, and partly because it’s already tidally locked to the Moon.
Exoplanets have been found that, due to their closeness to their stars, are tidally locked to them. Mercury is apparently ‘semi-tidally locked’ to the Sun at present (it has what they call a 3:2 spin-orbit resonance, rotating 1.5 times for every orbit) but presumably this tidal locking will gradually unlock as Mercury spirals away from the Sun over time – an awful lot of time. Which suggests that planets like Earth are getting further from their stars, very very gradually. And so eventually the Moon will gradually unlock itself from the Earth. As to why this is happening, I don’t know – as yet. In the planets’ case, it’s probably because the Sun is gradually losing mass. You can’t get energy out of nothing.
I’m watching Leonard Susskind’s online lectures on special relativity – or rather, I’m watching the first lecture, and I’m already lost. I’ve also bought and had a go at Susskind and Friedman’s book, Special Relativity and Classical Field Theory: The Theoretical Minimum, but haven’t got very far. I’ll keep trying, I think, and then I’ll die. It’s the maths that tends to trip me up.
So let’s go with the book, which is easier to continually refer to. It starts by telling me that special relativity is all about reference frames.
In general, reference frames are about perspectives. Everybody’s perspective is different, due to the time and place of their birth, their upbringing, which has decisively affected their neural development and so forth. All very complex, so we’re narrowing the term to refer to location in time and space. In the Cartesian sense, we have spacial co-ordinates on three axes, x, y and z, as well as an origin from which we can measure distances. And then there’s a t axis for time. So at this stage we have to imagine that time is synchronised for everyone – same starting point and same rate.
So these reference frames, in terms of space, vary individually (we can shift them around) and from other reference frames. They can be moving or (relatively!) stationary. Time, though, seems a bit trickier:
The assumption that all clocks in all frames of reference can be synchronised seems intuitively obvious, but it conflicts with Einstein’s assumption of relative motion and the universality of the speed of light.
Susskind & Friedman, Special Relativity and Classical Field Theory, p5
So we have coordinates to pin down events. The laws governing those events are apparently the same in all inertial reference frames (IRFs) – i.e in which a body, subject to no forces, moves in a straight line with uniform velocity. So, in a fast moving plane, you will be subject to the same laws as you’re subject to on the (rotating) ground, as long as your velocity is uniform. Everything’s in movement, one might say, but if your movement is uniform, then it’s as if you’re at rest. You’re in an IRF.
Now I want to jump, if it’s a jump, to Lorentz transformations, which I’ve been trying unsuccessfully to understand. Here’s how Wikipedia clarifies the matter:
In physics, the Lorentz transformations are a six-parameter family of linear transformations from a coordinate frame in spacetime to another frame that moves at a constant velocity relative to the former. The respective inverse transformation is then parameterized by the negative of this velocity.
I’ve taken out all the links, which, if followed, might enlighten me further, but clearly this is v complicated stuff, which I need to understand for an understanding of special relativity. I expect to fail, valiantly, so first I will say that Hendrik Lorentz was an intellectual giant in what became the transformative physics of the early 20th century, making vital contributions to the understanding of electromagnetism, electrons, the aberration of light and much much else.
Lorentz transformations are transformations within inertial reference frames. What about non-inertial reference frames? They would include accelerating and decelerating motion (obviously non-constant velocity), and, apparently, a rotating reference frame. But isn’t the Earth’s rotation something we don’t feel because of the constant velocity of that rotation? But then, doesn’t the Earth, or a ball, rotate at different rates around the axis of rotation? Isn’t it obvious that a person on the equator is moving at a faster pace than someone close to the rotational axis? Apparently, the cognoscenti define this as ‘a special case of a non-inertial reference frame that is rotating relative to an inertial reference frame’.
Actually, there are times when I really do wish I was a bonobo.
I’ll stop here for now, having so far avoided the mathematics. Maybe next time, or maybe not, but I must add here something consoling I read today in Richard Dawkins’ most recent book, Book do furnish a life:
… practising scientists do need years of training. But you can enjoy music, appreciate music even at quite a sophisticated level, without being able to play a note. Similarly, I think you can appreciate and enjoy science at quite a sophisticated level without being able to do science. I want to encourage people to treat science in the same kinds of way they would treat music or art or literature: as something to be enjoyed, not at a superficial level, but at quite a deep level, without necessarily being able to tell one Bunsen burner from another or integrate a function.
R Dawkins, Books do furnish a life: reading and writing science, 2021, pp 109-10
References
Tidally Locked and Loaded with Questions
Why are planets not tidally locked with the sun?
byu/Neotheo inaskscience
Richard Dawkins, Books do furnish a life, 2022 (paperback edition)
gravitational mysteries – part one, maybe
what happens when you fall for gravity…
I don’t understand gravity, and I doubt that memorising equations will be of much help.
Gravity, I’m told, is a killer. If I fall from a high cliff, or a multi-storey building, onto hard ground below, I’ll most certainly die, due to gravity (and carelessness, because I know what falling onto hard ground, even just from a standing position, can do to a person). So gravity should be treated with gravity.
But then, gravity has benefits. It keeps us on the ground, prevents us from flying away. In fact, gravity has essentially formed our bodily structure. We have muscular legs which with some small effort we can lift from the ground and plonk down in another place in a tiny ongoing battle with gravity, which we’ll eventually lose.
So I suppose it could be said that gravity is a given. An essential element in the development of all living things that creep over the earth and even fly in the sky just above it. We just have to deal with it.
And yet, I hear things about gravity that don’t make much sense to me. I hear that gravity pins humans to the Earth, but also pins our planet to the Sun, and pins the Moon to our planet. And yet it doesn’t. The Moon hasn’t fallen to the Earth in the way that my body would fall to Earth from a tall building. It circles the Earth. In fact it is spiralling slowly away from the Earth. Something else must be happening, surely?
So what do I do when I don’t know? I consult people who claim to know. And what do they say? Well, in terms of the Moon’s spiral, it’s about velocity. Here’s an explanation designed for children, or children at heart like me:
From Earth, it might look like the moon is stationary, meaning it is not moving, but in reality, each year the moon gets 3 cm [further] away from Earth. Without having the force of Gravity from earth [the] moon would have just floated away from us. The moon’s velocity and distance from Earth allow it to make a perfect balance between fall and escape.
In case the velocity of rotation of the moon was a little bit faster, it would have escaped the Earth’s Gravity. On the other hand, if it’s a little bit slower, it would have fallen on Earth. That’s why the moon doesn’t fall on Earth.
So that’s a good start, but why is the Moon revolving around the Earth at just such a speed that it keeps at (almost) the same distance? Isn’t that just too convenient? I also hear that the Moon is ‘tidally locked’ to the Earth, keeping the same ‘face’ to us all the time. That means it rotates on its axis over the same time-frame as a single orbit around Earth. Or nearly so, because the Moon’s orbit isn’t perfectly circular, which seems to be the case with every other orbit we know of. I suppose a precisely circular orbit would be a wonder, but then again…
Anyway, our Earth isn’t precisely globular either, and I’m betting it’s the same for the Moon, and every other planet and moon out there. I’m beginning to sense a pattern in this lack of a pattern. Or this approximation of a geometric pattern which doesn’t quite get there with the purity of mathematics.
Not that this is a bad thing. I’ve written previously about Milankovic cycles, variations in the eccentricity and tilt of Earth’s orbit around the Sun, which add spice to our planet’s climate. It’s like we use mathematics to understand the universe’s endless play with mathematics.
But getting back to that cliff fall. I’ve more than once heard the tale that Einstein’s ‘happiest thought’ was of such a scenario. Nothing to do with sadism or masochism, nothing to do with the landing. It occurred to him that, though the falling fellow might feel the force of the air swishing by him, he would not feel any ‘force’ of gravity. In a vacuum he wouldn’t feel any force at all. He might as well be stationary. Gravity, according to my good mate Wiki,
… is most accurately described by the general theory of relativity, proposed by Albert Einstein in 1915, which describes gravity not as a force, but as the curvature of spacetime, caused by the uneven distribution of mass, and causing masses to move along geodesic lines.
Which all sounds pretty radical, especially for 1915, when Fokkers had only just become a thing. So I get that mass is very unevenly distributed. At night we see clumps of stars here and there, with lots of apparently blank space in between. And though we can see for miles and miles and miles, this messy distribution of matter and space extends way beyond what we can see, perhaps even with our most inventive gadgetry. But ‘curvature of space-time’ still smacks of science fiction after all these decades.
Einstein had of course come up with this marriage of space and time 10 years earlier with his very special theory of relativity. So there are three dimensions of space and one of time. But are there? What exactly is dimensionality? Is it more than a human invention? In looking this up I’ve come up immediately with an essay ‘The invention of dimension’, on the naturephysics website. So that answers that question. Or does it? Here’s a quote from the start of the essay:
The modern concept of dimension started in 1863 with Maxwell, who synthesized earlier formulations by Fourier, Weber and Gauss. In doing so he added a nuance that we acknowledge today whenever we refer to the dimensions of, say, g (≈ 9.81 m s−2) as distance over time squared, rather than just the dimensional exponents (1, −2). By referring to the dimensions of a quantity, Maxwell seemed to imply that real things have natural dimensions. In the same spirit he designated units of mass, length and time as ‘fundamental units’.
Distance over time squared is a formula for constant acceleration, which again takes me back to gravity. When we fall from a cliff or a plane we constantly accelerate (leaving aside prevailing winds etc) until we hit the ground, but until that moment we’re not feeling any force upon us, according to Einstein. So acceleration isn’t a force? Apparently not. Is it the result of a force – the effect of a causal force? Well it can’t be an effect of gravity, because gravity isn’t a force.
So our acceleration in the above example is caused by a distortion of space-time which in turn is caused by the mass of planet Earth. But if we had fallen not from a plane but from a spacecraft much much further away, say the distance of the Moon from Earth, what would happen? Would we fall at all? We have satellites and a space station up there (I’m not exactly sure where), so would we just go into orbit like they do? Or are they carefully put into orbit by exquisitely precise mathematical calculations?
But, returning to Einstein’s not-so-happily falling fellow. The only thing he has to worry about is the landing. But the landing, and the force of the landing, is caused by the Earth’s mass. Presumably if we lived on a life-sustaining planet with the mass of Jupiter, which Dr Google tells me is over 300 times that of Earth, we’d be falling, or accelerating at a much faster rate (I’m tempted to say 300 times faster, but the mathematics is always more complicated). But then we couldn’t even live on Jupiter because our weight would be 300 times greater than that on Earth, just as the twelve men who walked on the Moon weighed, for a few days, only one sixth of what they weighed at home. So for life to have evolved on a planet like Jupiter (mass-wise) it would have to be made from very different stuff, molecularly. None of those heavy bones and dense tissues, like brains. An elephant’s brain weighs about 6 kilograms, and on Jupiter it would weigh 1800 kilos. So I suppose it’s important to think about planetary or lunar mass when we’re looking for extraterrestrial life, or alternatively, to think about different building blocks….
Anyway, it’s fascinating to note where thinking about gravity can take you, even when you know virtually eff all about the science. But I do want to learn more, and I’ll keep plugging away at it….
References
https://www.vedantu.com/physics/why-doesnt-the-moon-fall-into-the-earth#
https://en.wikipedia.org/wiki/Tidal_locking
aspects of climate change – Milankovic cycles
Dummies on dark matter 2: there are problems…
from Forbes website, see below
Canto: So there are candidates for dark matter, and there are also those who think that, though there is a serious problem in cosmology, to do with mass and energy, ‘dark matter’ won’t be the fix.
Jacinta: By the way, I was chatting with another dummy on this topic recently, who had the excuse of being much much younger than myself, and she asked if dark matter had anything to do with black holes. I wasn’t able to give a very effective answer, but Sabine Hossenfelder, one of our heroes, says in a video linked below that black holes and brown dwarfs (whatever they are), and other such exotic objects ‘would make too many gravitational lenses, which have not been seen’, to be candidates. Also black holes are so called because they ‘swallow’ light, that’s to say, light-emitting particles. So they really are black, in a sense, whereas ‘dark’ matter is more transparent than anything, according to Hossenfelder.
Canto: Well, getting back to Peter Fisher’s Royal Institution talk, he talks about the 1980s as a time of confusion and excitement in theoretical physics and cosmology when so many things weren’t adding up. At the same time a concept called super-symmetry was being mooted. It ‘predicted all kinds of heavier particles that we wouldn’t have observed in accelerators because they weren’t powerful enough’, according to Fisher. He also presented, what I’ve heard before, a conjecture that there must be this ginormous halo of dark matter surrounding galaxies to make up the missing mass and to account for the behaviour of visible matter at the edge of galaxies. In other words, this dark matter must have a gravitational effect on the outer arms of these galaxies.
Jacinta: I know that Hossenfelder is no great fan of bigger and more expensive accelerator-colliders in the hope of discovering more teensy-tiny but ultra-ultra numerous particles to fit the dark matter bill, but Fisher also goes on to talk about the Standard Model and how effective it has been, without dark matter screwing it up…
Canto: Yes it’s been very effective for accounting for some 4% of the mass-energy of the universe. Anyway Fisher helped to debunk a theory regarding ‘heavy neutrinos’ as a candidate for dark matter in the late eighties, which seems to this dilettante like an absurdity – neutrinos being near-massless, which presumably helps them to pass through planets as if they’re not there.
Jacinta: I think this heavy neutrino thing might’ve morphed, in theory, into the idea of weakly interacting massive particles, or WIMPs, and they’re still looking for em, for example on the International Space Station. They’re also looking for theoretical particles called axions, using special detectors. No luck so far for WIMPs or axions.
Canto: Fisher describes another source, black holes, via work done by Stephen Hawking, but I found it difficult to follow, so I’ll try roughly quoting:
In the beginning of the universe there was all this mass around, it’s very dense, and in a regime where quantum mechanics is very important, so the density is… fluctuating and changing, and [Hawking] thought, could it be that the density would be high enough to form a black hole? He did some rough calculations and found that, yes they could collapse into a black hole, and there’d be a lot of black holes, but there must be a way of getting rid of them, because we don’t see them. Over time, he invented a mechanism by which black holes radiate light at a very low level, a concept now called Hawking radiation, a remarkable notion, as it suggests the only connection we currently have between gravity and quantum mechanics.
The connection with dark matter is that there still may be ‘primordial’ black holes with a lot of mass but tiny in size. No luck in finding them either, needless to say.
Jacinta: So now let’s focus on Sabine Hossenfelder’s RI talk. It seems to me she goes into a lot more detail about the anomalies in what we observe, ascribed to the missing matter. For example, structure formation in the universe – which I remember being fascinated by when Carl Sagan presented it image-wise in his Cosmos series. Here are two points she makes on structure formation:
- Dark matter cannot build up radiation pressure and therefore starts forming structures sooner than normal matter
- normal matter on its own does not produce sufficient structures on short scales to be compatible with observation
And I have no idea what they mean. She mentions things that we can see, such as ‘galactic filaments, and so on and forth’. So, thinks me, wtf are galactic filaments? Well, Wikipedia calls them galaxy filaments, and they’re the largest known structures in the universe…
Canto: This is actually exciting – how could I have lived so long without knowing about these things?
Jacinta: Haha well Wikipedia is pretty good on this stuff:
In cosmology, galaxy filaments are the largest known structures in the universe, consisting of walls of galactic superclusters. These massive, thread-like formations can commonly reach 50/h to 80/h Megaparsecs (160 to 260 megalight-years) — with the largest found to date being the Hercules-Corona Borealis Great Wall at around 3 gigaparsecs (9.8 Gly) in length — and form the boundaries between voids. Due to the accelerating expansion of the universe, the individual clusters of gravitationally bound galaxies that make up galaxy filaments are moving away from each other at an accelerated rate; in the far future they will dissolve.
Galaxy filaments form the cosmic web and define the overall structure of the observable universe.
Canto: Great. What’s a void?
Jacinta: Cosmic voids, doncha know, are those vast spaces between filaments that contain few or no galaxies. But to return to Hossenfelder, who’s a theoretical physicist, and a lot more proficient in maths than we are, as we’ll see. She’s also something of a dark matter skeptic, it seems. She highlights four problems that dark matter doesn’t solve, and we should try to understand them:
- the brightness of galaxies is strongly correlated with the (asymptotic) rotational velocity (‘Tully-Fisher Law’). Dark matter doesn’t explain this
- dark matter leads to density peaks in galactic centres which badly fits with observations (‘galaxy cusps’)
- dark matter predicts too many dwarf galaxies
Canto: Okay let’s start with asymptotic rotational velocity. Asymptotic analysis, in mathematics, is about describing behaviour of functions as they approach a limit, such as infinity. So galactic velocity presumably has some sort of limit, which can be calculated mathematically. The Tully-Fisher Law, or Relation, from Wikipedia:
is a widely verified empirical relationship between the mass or intrinsic luminosity of a spiral galaxy and its asymptotic rotation velocity or emission line width. Since luminosity is distance-dependent, the relationship can be used to estimate distances to galaxies from measurements of their rotational velocity.
So the point Hossenfelder makes here, I think, is that rotational velocity correlates well with brightness, which correlates with distance, as measured from Earth. Dark matter appears to be irrelevant to these calculations. Of course I may be getting this all wrong.
Jacinta: I wouldn’t know. But it seems that dark matter and its supposed halo should be interfering with orbital velocities and so interfering with calculations, but it isn’t?
Canto: Hmmm.. Anyway, second point. Galaxy cusps takes me to the ‘cuspy halo problem’, which I’ll try to explain in my own words. It’s also called the core-cusp problem, which, broadly speaking, is a discrepancy found in small, low-mass galaxies, according to different measurement systems or predictions. ‘Cuspy’ represents an energy-mass distribution which is denser at small radii, whereas most dwarf galaxies have a more flat ‘core’ distribution.
Jacinta: These are all just the beginnings of our explorations of this topic. In a hundred years or so we’ll be fully conversant with the issues. As to dark matter predicting too many dwarf galaxies, aka the dwarf galaxy problem, apparently we’ve observed and identified some 38 of these dwarf galaxies in our Local Group (a dumbbell-shaped group of galaxies with the Milky Way and Andromeda forming the two lobes), instead of the 500 or so predicted by dark matter simulations, and that’s just around the Milky Way.
Canto: Okay, we’re doing well, sort of. Final problem – the alignment of satellite galaxies. Essentially, they form a disk rather than a halo. Perhaps surprisingly, the Forbes website has what seems to me an excellent article on the subject. Dark matter simulations produce halos merging together in spiral formations surrounded by sub-halos in a variety of orientations. But that’s not what we see – we see satellite galaxies in the same orientation as their ‘hosts’, and co-rotating with them. This has been observed for the Milky Way, Andromeda and most satellite galaxies observed, such as Centaurus A. So what accounts for these discrepancies?
Jacinta: You don’t know? Well, we’ll have to look at that next time, or not. I suspect there might end up being hundreds of these dark matter posts. We might even have to learn some maths….
References
Is Dark Matter Real? – with Sabine Hossenfelder (Royal Institution video)
What is dark matter? – with Peter Fisher (Royal Institution video)
https://en.wikipedia.org/wiki/Galaxy_filament
https://en.wikipedia.org/wiki/Void_(astronomy)
https://en.wikipedia.org/wiki/Tully–Fisher_relation
https://en.wikipedia.org/wiki/Cuspy_halo_problem
https://en.wikipedia.org/wiki/Local_Group
Journey into dark matter , iTelescope Webinars, with Dr Maggie Lieu
is the moon really a harsh mistress?
Ummmmmm……..nah
Eons ago, as a relatively young perpetual student type, I was wide awake late at night in my upper storey bedroom, my mind a blooming buzzing confusion of I know not who’s ideas. All I can really recall is that I couldn’t sleep for love nor money. I paced about my tiny enclosure like the sad polar bear did, in those years, in our local zoo.
Somehow, I managed to rise above myself for an instant and gaze out of the window. A perfectly full moon hung low and large in the sky. Eureka! It struck me like moonlightning – lunatics, werewolves, somnambulism, witches and warlocks. I was spellbound.
Well, not really. But for a wee while, this teensy personal experience affected my thinking about the power of the moon. But my skepticism, or what others have called my contrarian disposition, was soon doing battle with these loony feelings. All of this occurred well before the advent of the internet, but as a child I became addicted to encyclopaedias. We had a couple of full sets in the family home, and I loved disappearing into them on a regular basis. And this tendency to arm oneself with facts against the world – or not – is generally fixed from an early age.
So all of this is a preamble to a conversation I recently had with a young person who insisted that the full moon had distinct, if somewhat unquantifiable, effects on our behaviour, due to gravity, essentially. And water.
Of course, the reference here was to the moon’s tidal effects. These effects are quite powerful, and we are mostly made up of water, ergo…
And apparently it isn’t just about water. Gravity is one of the fundamental forces of nature, it’s exerted everywhere, and particularly by massive bodies. The moon is massive, ergo…
So let me take up the gravitational effects first. Why would there be any relationship between the moon’s gravitational effects and its fullness? A full moon is simply more visible, due to reflected light from the sun, not more massive or more proximal. Thus the gravitational effects are more or less constant. The moon’s orbit is not precisely circular, of course, though it’s very nearly so, and in any case its varying distance from the earth is is no way connected to its ‘fullness’ or otherwise.
However the moon is the principal cause of oceanic tides. The Geographical Society explains:
The moon’s gravitational pull is the primary tidal force. The moon’s gravity pulls the ocean toward it during high high tides. During low high tides, the earth itself is pulled slightly toward the moon, creating high tides on the opposite side of the planet.
So we have two effects here. The moon’s gravitational effect on the tides and any other earthly phenomena, and the moon’s psychological, and other, effects on subjects (including non-human species) due to the amount of light it reflects from the sun.
the moon’s gravity
The moon circles the earth while the earth circles (or orbits) the sun. Picture, then, the moon’s movements tracing something like a spring as it revolves around the revolving earth. Our planet, like all the others in our system, orbits the sun due to the enormous gravitational pull caused by its mass. But tidal forces are more closely related to distance than to mass. Also the tidal force, which is a calculable value*, is different from the actual tides, which are affected by many variables, such as the distribution of land and water over the earth, ocean depths, and endlessly changing weather conditions. The moon has a gravitational pull on land as well as sea, but fluids are far easier to move.
The tidal force causes oceanic waters to bulge towards the moon, when the moon is on that side. The force is at its greatest on the side of the earth closest to the moon, and at its weakest on the furthest side. It averages out around the centre. But interestingly, the oceans on the side opposite the moon also bulge out, as described in the Geographical Society quote above, causing two high tides and two low tides each day, as the earth rotates through the bulges. This is because the earth itself is distorted slightly by the tidal force, on a daily basis.
So much for the tides. The moon’s gravitational effect on humans, individually, is minuscule, and any effect would be constant, since the moon’s distance from earth is essentially unchanging (actually it’s spiralling away from us at a rate of just under 4cm per year, but don’t worry). It certainly doesn’t matter that we’re mostly water, because even the largest non-oceanic bodies of water exhibit barely discernible tidal effects. So, no, our blood doesn’t slosh about to a tidal rhythm.
Ah but hang on. It so happens that a full moon (and a new one) does have a planetary effect – but not due to light. The sun also affects us gravitationally, to a lesser degree, but sometimes in cahoots with the moon, so to speak. The SciJinks website explains:
When the earth, moon, and sun line up—which happens at times of full moon or new moon—the lunar and solar tides reinforce each other, leading to more extreme tides, called spring tides. When lunar and solar tides act against each other, the result is unusually small tides, called neap tides. There is a new moon or a full moon about every two weeks, so that’s how often we see large spring tides.
So much for gravity, by far the weakest of the four fundamental forces known today.
*Specified as the moon’s gravitational pull in a specific location on Earth, minus the moon’s average gravitational pull over the whole Earth
the full moon’s strange powers
So the other question is, does the full moon affect us (and/or wolves) psychologically, either due to tidal effects or, more likely, due to the light it floods us with every 29.5 days?
How to find out? It’s fair to say that, in the days before we lit up the earth’s surface with our inventions, the full moon’s regularly monthly light had a much greater impact than it does now. ‘Ill met by moonlight’, complained Oberon to proud Titania, and certainly a flood of moonlight would make secret nightly trysts and/or avoidings a trickier proposition, but such effects would be indirect rather than direct. As to direct effects, they might be expected to show up in statistics – more untoward activity (from murders to mad mutterings) showing up under full moons than not.
Well, the evidence so far is mixed and unconvincing. It would be impossible to list the number of studies, small and large, rigorous or otherwise, that have tried to establish or quantify a full moon effect, so I will simply briefly refer to some of the scientific articles trying to make sense of this mish-mash. The articles themselves are in the references.
Scientific American‘s 2009 article ‘Lunacy and the Full Moon’ provides fun historical detail, and a lot of stuff about the claim that the moon affects our waters, including our very watery brain. This goes at least as far back as Pliny the Elder. Their conclusion – the lunar lunacy effect is ‘a cultural fossil’.
An undated article from Healthline (presumably from the US) is rather more open-minded, if that’s the term. It mentions one study that found ‘nearly 81 percent of mental health professionals believe the full moon can make people ill’. Unsurprising but not very helpful. It also describes statistics which indicate no correlation between full moons and homicides, assaults or suicides. However, there is some evidence of a link between full moons and increased sleep latency – ‘the period between when you first fall asleep and when you enter the first stage of REM sleep… Increased latency means it takes a longer time to get to REM sleep’. Interesting, but not exactly a clincher for serious lunar impacts. Another small study (17 subjects!) suggested a link between the full moon and enhanced bipolar disorder.
Wikipedia is comprehensive and skeptical as always these days – I love Wikipedia! The very first sentence of its article ‘Lunar Effect’ gives an indication of what’s to come:
The lunar effect is a purported unproven correlation between specific stages of the roughly 29.5-day lunar cycle and behavior and physiological changes in living beings on Earth, including humans.
It gives short shrift to the lunacy claims, and reports on sleep studies:
A 2015 study of 795 children found a three-minute increase in sleep duration near the full moon, but a 2016 study of 5,812 children found a five-minute decrease in sleep duration near the full moon. No other modification in activity behaviors were reported, and the lead scientist concluded: “Our study provides compelling evidence that the moon does not seem to influence people’s behavior.”
Other possible lunar effects, on bad behaviour, health issues (including epilepsy), accidents, birth rates, and even the stock market, were found to be unproven at best. Effects on non-human creatures are largely limited to coastal species obviously affected by tides. Increased light levels during full moons may have some slight effect on plant growth.
Finally, New Scientist has a recent (albeit very brief) article which bucks the trend – at least for oysters. But maybe for other species too. A researcher, Frank Brown, decades ago, noted that oysters opened their shells for feeding at high tide, not surprisingly. He wondered whether the moon had anything to do with this, so he removed a bunch of oysters far from their location to see what would happen:
Brown kept the shellfish in a sealed darkroom, shielded from changes in temperature, pressure, water currents and light. At first, the oysters kept their rhythm, feeding each day in time with the New Haven tides. Then, something strange happened – their feeding times gradually shifted until they lagged 3 hours behind. Brown was mystified, until he realised that they had adapted to the local state of the moon: they were feeding at times when Evanston, if it were by the sea, would experience high tide. Despite having no obvious environmental cues, it seemed these shellfish were somehow tracking lunar cycles.
The article goes on to say that, though Brown’s evidence was largely dismissed, recent and growing evidence from ‘a range of fields’ backs him up. Unfortunately, no detail is provided. Disappointing.
All in all, the evidence for the moon’s effects on human behaviour is scant and rarely corroborated. Still, it makes for pleasant poetry, and all that.
References
https://www.nationalgeographic.org/media/earths-tides/
https://www.bbc.com/news/science-environment-12311119
https://www.scientificamerican.com/article/lunacy-and-the-full-moon/
https://www.healthline.com/health/full-moon-effects
reading matters 10
New Scientist 3244 August 24 2019
Canto: Being dilettantes and autodidacts, we engage endlessly in educational reading, bootless or otherwise, so I thought we might take the effort to talk/write about, and expand on, what we’re learning from the texts we’ve perused, rather than providing ‘content hints’ as before.
Jacinta: Well of course science mags cover a wide range of topics at very various depths, so we’re going to limit ourselves to the ‘cover story’, if there is one.
Canto: So today’s topic comes from a New Scientist that’s been hanging around for a while, from a year ago, but since quantum theory is more or less eternally incomprehensible, that shouldn’t matter too much.
Jacinta: Yes I’ve heard of Lee Smolin, and in fact we can listen to many of his online interviews and lectures via youtube, and he’s described as a ‘realist’ in the field, which doesn’t mean much to me at present, but neither of us know much about quantum mechanics, in spite of having read numerous articles on the topic.
Canto: You probably have to ‘do the math’, as the Yanks weirdly say.
Jacinta: Well we won’t be doing much of that. The cover story is titled ‘Beyond weird’, and Smolin’s idea is that we need to move beyond quantum weirdness to something more coherent and unifying. He describes current quantum mechanical theory as comprised of two different laws:
The first… describes quantum objects as wave-like entities embodied in a mathematical construction known as a wave function. These objects evolve smoothly in time, exploring alternative realities in ‘superpositions’ in which they aren’t restricted to being in any one place at any one time. That, to any intuitive understanding of how the world works, is distinctly odd. The second law applies only under special circumstances called measurements, in which a quantum object interacts with a much larger, macroscopic system – you or me observing it, for example. This law says that a single measurement outcome manifests itself. The alternative realities that the wave function says existed up to that point suddenly dissolve.
Canto: So both of these laws – and of course I’m in no position to doubt or to verify their mathematical exactitude or explanatory power – make little sense from a ‘common-sense’ or ‘realist’ perspective, in which objects must always be objects and waves waves, and, if objects, they must be in a particular place at a particular time, regardless of anything observed. So it seems perfectly cromulent to me that Einstein and no doubt many others found something incomplete about quantum theory, in spite, again, of its apparently vast explanatory power. Like it was an intellectual placeholder for something more real or coherent.
Jacinta: Well Smolin seems to be one of those dissatisfied physicists, – he mentions de Broglie and Schrödinger as others – pointing out that the two laws are in apparent contradiction, with the second law unable to be derived from the first. The theory also ‘seems to’ violate the principle of locality, in which forces are dependent on distance. Quantum entanglement does away with that principle. So Smolin sees a way out by trying to incorporate gravity into the quantum world, or at least trying to connect the general theory of relativity and quantum theory into a seamless whole, as their current incompatibility constitutes a major problem. General relativity presents ‘a smooth, malleable space-time’, while quantum theory suggests ‘discrete chunks, or quanta, of space or space-time’. String theory and loop quantum gravity are some of the attempts to bridge this divide, but these are currently untestable theories. Also, apparently general relativity is compatible with our perception of the flow of time, whereas quantum theory is more problematic, an issue which, I think, Gerard ‘t Hooft attempts to address in his essay ‘Time, the Arrow of Time, and Quantum Mechanics‘ .
Canto: Yes, he feels that time, with its arrow pointing eternally forward, with no need for or possibility of reversibility, must be an essential element of a grand physical theory.
Jacinta: Maybe. He’s saying I think, that any explanation of our world, any theory, is arrow-of-time dependent, as it necessarily involves preceding causes and antecedent consequences. But let’s just stick to Smolin’s article. He argues that both relativity and quantum theory have issues with the conceptualisation of time. And there are problems, such as dark matter and dark energy, which don’t easily fit within the standard model. So he feels we need to go back to first principles, ‘in terms of events and the relationships between them’. So, according to these principles, space is an emergent property of a network of causal relationships through time.
Canto: Well to keep more strictly to Smolin’s description, he has five hypotheses. One – the history of the universe consists of events and relations between them. Two – that time, as a process of present causes and future consequences, is fundamental. Three – that time is irreversible, cause can’t go backwards and ‘happened’ events can’t unhappen. Four – that space emerges from this cause-consequence chain. Five – that energy and momentum are fundamental, and conserved in causal processes.
Jacinta: Good, and this is an ‘energetic causal set model’ of the universe, as he and others describe it, to which he’s added a sixth hypothesis, derived from ‘t Hooft, which says that ‘when two-dimensional surfaces are defined in the emerging geometry of space-time, their area gives the maximum rate by which information can flow through them’.
Canto: Now that sounds horribly mathematical. I do note that area = space and rate = time, and so this hypothesis somehow marries space-time with information flow?
Jacinta: Yes, it’s all threatening to move beyond our brains’ event horizon here. Smolin says that ‘in this picture’, and I’m not sure if he’s talking about the ‘picture’ derived from the sixth hypothesis or by all six taken together, but ‘in this picture, every event is distinguishable by the information available to it about its causal past’. This he calls the event’s sky, because the sky, or what we see (speaking about horizons) at any one instant, is what he calls ‘a view of its own causal past’. This has to do with the speed of light – we can’t see what we can’t see. And this sixth hypothesis, combined with the first law of thermodynamics, can apparently be used to derive the equations of general relativity, bringing gravity into the picture.
Canto: I don’t get the laws of thermodynamics.
Jacinta: The first law is about energy used in a closed-system process, which can be transformed in that process but is always conserved. Anyway, we’ll try to quit before we get in too much deeper. We know that there’s a ‘measurement problem’, a problem of causality in quantum mechanics, in which it is said that a measurement, or observation, ‘collapses the wave function’ to define a particle’s specific place at a specific time. This is counter-intuitive, to put it mildly, and highly unsatisfactory to many physicists, because it seems to make a mockery of how we understand causality. It seems to be a long-standing impasse to the unification of the two major theories. So we’ve only described a fraction of what Smolin has to say here, and there’s also the problem of entanglement. In ‘classical physics’ proximity matters in a way that it doesn’t in quantum theory. Smolin describes, or mentions, a lot of work being done on ‘ensembles’ in an attempt to solve this measurement problem.
Canto: I think one of the issues that the ‘realists’ are concerned with, but perhaps deliberately not mentioned in Smolin’s piece, is the many worlds hypothesis, or the multiverse, embraced for example by Max Tegmark in Our mathematical universe. Neil Turok is another skeptic of this apparent solution to the causality impasse.
Jacinta: Yes, I don’t think Smolin is an embracer of the multiverse, tantalising though it is in a sci-fi sort of way. Of course we don’t have the mathematical wherewithal to give an informed view one way or another, or to know whether mathematical wherewithal is what’s really needed. I’ve heard it said – possibly by Tegmark – that a multiverse fits so neatly with the mathematical equations that we need to accept it against our intuitions, which have been wrong in so much else. I don’t know… we’ll just have to watch with interest this intellectual battleground, and see if anything decisive crops up in what remains of our lifetimes.
Canto: Singular or plural…
Other references
https://www.frontiersin.org/articles/10.3389/fphy.2018.00081/full
The universe within, by Neil Turok, 2012
Our mathematical universe, by Max Tegmark
https://en.wikipedia.org/wiki/First_law_of_thermodynamics
How do trees transport water such long distances? Part 2: the mechanism remains a mystery (to me)
and I still haven’t found what I’m looking for…
So scientists have learned a lot, though not everything, about water’s travels from soil to leaf in a plant or tree. It’s a fascinating story, and I’m keen to learn more. But the real mystery for me is about energy. As the excellent Nature article, upon which I’m mostly relying, points out, animals have a pump-based circulatory system to distribute nutrients, oxygen and so forth, but plants are another matter, or another form of organised matter.
I actually posed two questions in my last post. How do plants – and I think I should specify trees here, because the massive distance between the soil and their top leaves makes the problem more dramatic – move water such large distances, and how do they know they have to transport that water and how much water to transport?
So let’s look at the Nature Education explanation:
The bulk of water absorbed and transported through plants is moved by negative pressure generated by the evaporation of water from the leaves (i.e., transpiration) — this process is commonly referred to as the Cohesion-Tension (C-T) mechanism. This system is able to function because water is “cohesive” — it sticks to itself through forces generated by hydrogen bonding. These hydrogen bonds allow water columns in the plant to sustain substantial tension (up to 30 MPa when water is contained in the minute capillaries found in plants), and helps explain how water can be transported to tree canopies 100 m above the soil surface.
Notice how we’re again returning to the explanations questioned by Wohlleben – transpiration and capillary action. But we’re introduced to something new – the C-T mechanism. The thesis is that water’s cohesiveness through hydrogen bonding creates a tension (the tension that makes for capillary action) that enables water to be shifted up to 100 metres – all because of the minuteness of capillaries found in plants. And trees? Somehow, I just can’t see it. Perhaps the key is in the phrase ‘helps explain’. There must surely be more to this. The thesis also mentions ‘negative pressure’ generated by transpiration. This is the signalling I wrote about before. Somehow the plant’s chemistry recognises that there’s an imbalance, and of course this happens in all living things, regardless whether they have a complex nervous system. So maybe there’s no need to worry about ‘knowing’. All living organisms respond to their ever-changing environment by altering their internal chemistry, by opening or closing barriers, by selectively adding or subtracting nutrients, and there are unknowns everywhere about precisely how they do that. It’s a kind of organised chemistry that seems like everyday magic from the outside, whether we’re focusing on a beech tree or our own intestines.
The C-T mechanism is only new to me I should add. It can actually be traced back to 1727 and a book by Stephen Hales, in which he pointed out that without what he called perspiration the water in a plant would stagnate, and that it was also required to allow for the capillary movement of water, because ‘the sap-vessels are so curiously adapted by their exceeding fineness, to raise [water] to great heights, in a reciprocal proportion to their very minute diameters’. But this ‘reciprocal proportion’, according to Wohlleben, as quoted in the last post, can only account for a maximum of 3 feet of upward force in ‘even the narrowest of vessels’.
The water transport system, referred to in the last post as the water potential difference or gradient, also has another name, the Soil Plant Atmosphere Continuum (SPAC). I also mentioned something about an ‘apoplastic pathway’. Water enters the tree by the roots, which are divided and subdivided much like branches and twigs above-ground, with the thinnest examples being the fine root hairs. Water enters through the semi-permeable cell walls by osmosis. Cell-to-cell osmosis carries the water deeper into the root system, and thence into an apoplastic pathway. According to this video, this pathway provides an uninterrupted flow of water (no cell wall barriers) which allows a mass flow ‘due to the adhesive and cohesive properties of water’. This is the cohesion-tension theory again. Apparently, due to evaporation, a tension is created in the apoplast’s continuous stream, leading to this ‘mass flow’.
This makes absolutely no sense to me. What I’m so far discovering is that it’s pretty hard to start from scratch as an amateur/dilettante and get my head around all this stuff, and in my reading and video-watching I’ve yet to find a straightforward answer to the how of long distance, fast transport of water in plants/trees – there probably isn’t one.
I’ll try again after a diet of videos – so far I’ve found a large number of videos in Indian English, and their accents defeat me, I’m sad to say. No transcripts available. Meanwhile, I’ve compiled a little glossary (from various sources) to help myself…
apoplast – within plants, the space outside the plasma membrane within which material can diffuse freely. It is interrupted by the Casparian strip in roots, by air spaces between plant cells and by the plant cuticle.
Casparian strip – a band of cell wall material deposited in the radial and transverse walls of the endodermis, which is chemically different from the rest of the cell wall – the cell wall being made of lignin and without suberin – whereas the Casparian strip is made of suberin and sometimes lignin.
cortical cells – in plants, cells of the cortex, the outer layer of the stem or root of a plant, bounded on either side by the epidermis (outer) and the endodermis (inner).
exudation – An exudate is a fluid emitted by an organism through pores or a wound, a process known as exuding.
guttation – water loss, when water or sap collects (at times of low evaporation, dawn & dusk), at tips of grass, herbs (not to be confused with dew, caused by condensation).
hydrostatic pressure – the pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity. This increases in proportion to depth measured from the surface because of the increasing weight of fluid exerting downward force from above.
lignin – a class of complex organic polymers that form important structural materials in the support tissues of vascular plants and some algae. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity and do not rot easily.
osmosis – the movement of water from an area of high to low concentration through a semi-permeable membrane. ‘Pumps’ in the cell membrane transport the specific ions into the cell which means water moves in by osmosis thus maintaining hydrostatic pressure.
phloem – the living tissue that transports the soluble organic compounds made during photosynthesis and known as photosynthates, in particular the sugar sucrose, to parts of the plant where needed. This transport process is called translocation.
plasmodesmata – narrow threads of cytoplasm that pass through the cell walls of adjacent plant cells and allow communication between them.
root pressure – the transverse osmotic pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves. Root pressure occurs in the xylem of some vascular plants when the soil moisture level is high either at night or when transpiration is low during the day
sap – a fluid transported in xylem cells (vessel elements or tracheids) or phloem sieve tube elements of a plant. These cells transport water and nutrients throughout the plant.
suberin – an inert impermeable waxy substance present in the cell walls of corky tissues. Its main function is as a barrier to movement of water and solutes.
symplast – the network of cytoplasm of all cells interconnected by plasmodesmata. The movement of water occurs from one cell to another through plasmodesmata
tracheid – a type of water-conducting cell in the xylem which lacks perforations in the cell wall.
vascular (plants) – also known as tracheophytes and also higher plants, form a large group of plants (over 300,000 accepted known species) that are defined as those land plants that have lignified tissues (the xylem) for conducting water and minerals throughout the plant.
xylem – one of the two types of transport tissue in vascular plants, phloem being the other. The basic function of xylem is to transport water from roots to shoots and leaves, but it also transports some nutrients.
On the Trump’s downfall. What a memo. One wonders if the DoJ is running out of patience with the wannabe dictator and his imbecilities, which may bring things to a head sooner rather than later. But those in the know say that Mueller is always thorough and unlikely to be distracted, so I shouldn’t project my own impatience onto him. Dog give me strength to suffer the horrorshow for a while longer.