Posts Tagged ‘multiverse’
how did the universe begin – or did it? And when will another one come along? And other conundrums
hypothetical stuff
I thought I’d relax and tackle some pretty basic stuff for a change.
Years ago, when I was foster caring, I had a particularly smart kid under my care. One day he asked me, ‘so if the world, or the universe, started with this big bang, what caused it? Something must have. So something must’ve existed before it.’ I just said something like, ‘Well that’s when time began, along with space, because space and time are intimately connected, according to Einstein…’ He wasn’t particularly satisfied, and neither was I, though I hid it better.
So what I learned, or heard, decades ago, was that there was a big bang theory and a steady state theory, and the big bang theory won, for some reason. I also recall reading, presumably in a science magazine, that the big bang was maybe the result of a collision between two entities called branes, I think. So I’ve just looked up branes and found that they’re ‘fundamental objects in string theory’. All I know about string theory is that it seems to be going out of fashion due to lack of progress in recent years, but I could be wrong. In any case, the idea of a universe created out of nothing seems a bit puzzling to me, and the brane thing may be neither here nor there.
Of course the big bang, or the big start-up, whatever, is an obvious corollary to an expanding universe – if we take it backwards, it contracts, presumably to nothing, or a supermassively massive and energetic dimensionless point…. A universe from nothing – I’ve heard that phrase before. Easy to say, impossible to comprehend. One vlogger or whoever speaks of ‘a tiny, infinitely dense, ball of matter’. It doesn’t take genius to recognise that this description makes absolutely no sense. ‘Immeasurably dense’, maybe, but not infinitely.
So there was nothing, then there was cosmological inflation, presumably of that same nothing. This just can’t be right. And I believe some cosmologists agree with me on this. Not surprisingly there are lots of speculations which will remain speculation – e.g. that this cosmic inflation somehow arose from, was ‘sparked’ from, a cold dark, very ancient universe, and that our universe will head in that cold dark direction until another big bang occurs – or am I just making this up?
So I’m sure there are people working frenetically, mathematically, on this, as well as others who just don’t care, and others who find it too mind-blowingly awesome to think too hard about, and then there are all the others. And even if you switch back to some version of the steady state model, or imagine a piano-accordion style expanding and contracting model (just because the current evidence is that the universe’s expansion is accelerating – if that’s what the current evidence is – doesn’t mean it won’t start decelerating and eventually going backwards and contracting, I presume), you can’t necessarily be sure that its future will be anything like what you think you have worked out about its past.
And then there’s the multiverse, which seems to be an imagined, or should I say theorised, consequence of quantum indeterminacy, perhaps among other things. Max Tegmark introduced me to this idea in his book Our Mathematical Universe, or rather he made it sound a little more plausible, but the more that book has faded from memory, the more absurd the idea has seemed. C’est la vie même.
Others seem to be saying that the many-worlds solution to the indeterminacy problem is just a mathematical nicety, a kind of elegant solution, the ‘real-world’ implications of which can be safely ignored, or something like that. Or that the world of sub-atomic particles, or wave-particles, or smeared-out wee thingies, just doesn’t behave like the macro-world, so it can be safely ignored by everyone except those condemned to study it. And yet…
What if we too are in super-positions, until a measurement of something like our co-ordinates? I don’t know what I’m talking about really, but I’m skeptical about any division between the macro and the apparently quantum world, of which we’re presumably made up. And I know that there are much more sophisticated and/or knowledgeable people than me, mathematically speaking, who are also dissatisfied with this situation. And then there are people, I mean physicists – the only people who matter when it comes to matter – who believe it really doesn’t matter, just shut up and calculate.
And speaking of matter, a large part of the universe’s share of the stuff is apparently dark, that’s to say not visible or even detectable to us but rather inferred, due I believe to the behaviour of stars swirling around far from the black holes at the centre of their galaxies. These stars should be travelling more slowly than the stars closer to the black hole, as gravity would predict, but that’s not happening, so some kind of matter is supposedly affecting their movements, gravitationally, but invisibly from our perspective. It doesn’t sound too convincing to a layperson like me. And as to dark energy…
Okay I’ll try coming to grips with dark energy in my small way. It has apparently to do with the acceleration of the universe’s current expansion. That’s to say, it is supposed to drive it, being energetic. This is all wrapped up in the lambda-CDM cosmological model. CDM stands for cold dark matter and lambda is a cosmological constant. According to this model, dark energy constitutes 68% of universal energy, while dark matter contributes 27% and ordinary (baryonic) matter contributes 5%, with those more or less massless particles, photons and neutrinos, contributing more or less nothing.
So how do we know that the universe is expanding, acceleratingly? By finding that distant galaxies are receding from we human observers at an increasing velocity, of course. And the fact that this verified discovery is known as the Hubble-Lemaître law suggests that it isn’t particularly new, at least from the perspective of modern post-Newtonian physics.
Apparently the standard view, pictured above, is that there was this initial period, known as ‘cosmic inflation’, which lasted for an infinitesimally tiny amount of time, the time it took, apparently, for nothing to become something, and which generated two types of wave, gravitational waves and density waves. What’s the difference between these two waves? Well, according to AI, which hasn’t quite become sophisticated enough to be completely deceptive, gravitational waves are ripples in space-time (which I believe we’ve detected with LIGO – the Laser Interferometer Gravitational-Wave Observatory), while density waves are ‘disturbances in the density of a medium’, like air or water.
We’re talking about a very energetic super-expansion, and mass and energy are e- mc2 counterparts, so it created everything particulate, the building blocks of matter, which were super-hot with all that energy. It’s a bit hard to believe to put it mildly, which isn’t to say that it isn’t true. And of course what brought about that ‘big bang’ super-expansion is unknown, and must leave many cosmologists a bit pissed.
So apparently – don’t trust me on this, or anything here – after or maybe during this expansion, matter formed, first as particles, let’s call them, then fusions of particles, all in less than a second, they say. But other theorists say there are/were ‘eternal inflations’, creating multiple universes, with all their different boundary conditions viv-a-vis light, gravity, mass-energy and such. Pretty easy to speculate, it seems.
Theorists also speculate, and even submit proofs, sort of, that there was a period before the big bang when everything was intensely cold (fancy!), and empty, except for space, which was enormous and somehow highly energetic, until the big bang happened and made this energetic enormousness even more energetic and enormous (wow!), but there are alternative theories that…. well there are alternate theories that are quite different, calculating initial conditions that would give rise to a big bang that creates different spatial dimensions that numbers of universes could inhabit….
And the maths really works…!
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