Physics Guy wrote: ↑Thu Apr 06, 2023 7:39 am
I don't know why there is anything rather than nothing and I don't believe anyone knows.
So much stuff does exist. Moreover things are just as they are, although they seemingly could have been different in so many ways. If reality were an argument it would seem to be a vast begging of the question. One has to assume so much, just to get started. In physics and elsewhere it is considered more reasonable to make fewer arbitrary assumptions, but reality itself seems to violate this principle so badly that it shakes my faith in the principle. The most reasonable, undemanding assumption would be that nothing should exist. That's so wrong that for me it takes the shine off the whole strategy of making undemanding assumptions.
The hardest thing to understand, for me, isn't why we have something rather than nothing, but why we have something in particular rather than anything else. The main thing that nothing has going for it is that it avoids having to pick any one thing in particular. As soon as you have anything at all, rather than just nothing, you're faced with this enormous choice among all the possible somethings. How did the one thing that we do have get picked?
One possible answer is that nothing got picked, because every possible reality is in fact real, somewhere. The various "multiverse" theories all go in this direction. I'm not impressed. Having to imagine so many perfectly undetectable additional universes, without even the possibility of any evidence at all for them, just leaves me cold. It answers the question so perfectly that it doesn't even feel like an answer at all, just a dismissal.
The multiverse may be dressed up in language about quantum mechanics and inflationary cosmology but it walks and talks exactly like the turtle theory of Russell's crazy old lady, or the hypothesis that everything was created ten seconds ago including all of our memories, or that I'm a brain in a vat. I can't refute it but I also can't take it seriously. If you really don't want to think about the question, fine, don't—but don't kid yourself that you have a good scientific answer to it. Scientific answers are things you can work with. Physics talks and papers almost always end with an "Outlook" discussion about what to do next. Often there is no obviously winning next move, but at least there are some suggestions. The Outlook statement from the multiverse is that there can't be possibly be anything at all to do next.
What I believe is that there exists a good answer of some kind for why we have, not only something rather than nothing, but the particular something we have rather than other somethings. And I suspect that this belief, vague though it may sound, is tantamount to believing in creation by God, whether or not one uses those words.
. He subtitles Chapter 8
and creates a scenario where a hypothetic physist father and his daughter have a discussion about her work in physics. let me see if I can quote enough to make sense of it. I thought it was a pretty good hypothetical dialogue.
Alice nodded. “Well, it depends on how we define ‘simple,’ of course. My philosophy colleagues sometimes cast this as a worry about ‘ontological commitment’—roughly, the amount of stuff we need to imagine is contained in all of reality, just to describe our observed portion of it.”
“So wouldn’t Occam’s razor suggest that having too many ontological commitments is an unattractive feature in a fundamental theory?”
“Sure, but you have to be a little careful about what that commitment actually is. Many-Worlds doesn’t assume a large number of worlds. What it assumes is a wave function evolving according to the Schrödinger equation. The worlds are there automatically.”
Her father objected. “What do you mean by that? It’s literally called the Many-Worlds theory. Of course it assumes a large number of worlds.”
“Not really,” replied Alice, becoming more animated as she warmed to the subject. “The ingredients used in Many-Worlds are ingredients that are used by every other version of quantum mechanics. To get rid of the other worlds, alternatives need to posit additional assumptions: either new dynamics in addition to the Schrödinger equation, or new variables in addition to the wave function, or an entirely separate view of reality. Ontologically speaking, Many-Worlds is as lean and mean as you can possibly get.”
“You’re kidding.”
“I’m not! A much more respectable objection, to be honest, is that Many-Worlds is too lean and mean, and it’s therefore a nontrivial task to map the formalism onto the messiness of our observed world.”
Her father seemed to contemplate this. His cocktail sat temporarily neglected.
Alice decided to press the point. “I’ll explain what I mean. If you believe that quantum mechanics is saying something about reality, you believe that an electron can be in a superposition of spin-up and spin-down, for example. And since you and I and our measuring apparatuses are made of electrons and other quantum particles, the simplest thing to assume—the thing that Occam’s razor would suggest that you do—is that you and I and our measuring apparatuses can also be in superpositions, and indeed that the whole universe can be in superpositions. That is what is straightforwardly implied by the formalism of quantum mechanics, like it or not. It’s certainly possible to think about complicating the theory in various ways to get rid of all those superpositions or render them unphysical, but you should imagine William of Occam looking over your shoulder, tut-tutting with disapproval.”
“Seems like a bit of sophistry to me,” her father grumbled. “Philosophizing aside, a bunch of in-principle-unobservable parts of your theory doesn’t seem very simple at all.”
“Nobody can deny that Many-Worlds involves, you know, many worlds,” Alice conceded. “But that doesn’t count against the simplicity of the theory. We judge theories not by the number of entities they can and do describe but by the simplicity of their underlying ideas. The idea of the integers—‘-3,-2,-1, 0, 1, 2, 3 . . .’—is much simpler than the idea of, I don’t know, ‘-342, 7, 91, a billion and three, the prime numbers less than 18, and the square root of 3.’ There are more elements in the integers—an infinite number of them—but there is a simple pattern, making this infinitely big set easy to describe.”
“Okay,” said her father. “I can see that. There are a lot of worlds, but there is a simple principle that generates them, right? But still, by the time you actually have all those worlds, it must take an enormous amount of mathematical information to describe all them. Shouldn’t we be looking for a simpler theory where they just aren’t needed at all?”
“You’re welcome to look,” replied Alice, “and people certainly have. But by getting rid of the worlds, you end up making the theory more complicated. Think of it this way: the space of all possible wave functions, Hilbert space, is very big. It’s not any bigger in Many-Worlds than in other versions of quantum theory; it’s precisely the same size, and that size is more than big enough to describe a large number of parallel realities. Once you can describe superpositions of spinning electrons, you can just as easily describe superpositions of universes. If you’re doing quantum mechanics at all, the potential for many worlds is there, and ordinary Schrödinger evolution tends to bring them about, like it or not. Other approaches just choose to somehow not make use of the full richness of Hilbert space. They don’t want to accept the existence of other worlds, so they need to work hard to get rid of them somehow.”
“Fine,” muttered her father, not fully convinced but apparently ready to move on to the next question. He took a sip of his drink and peered at his phone. “Isn’t there also a philosophical problem with the theory? I’m no philosopher myself, but Karl Popper and I both know that a good scientific theory is supposed to be falsifiable. If you can’t even imagine an experiment that might prove your theory wrong, it’s not really science. That’s exactly the situation with all these other worlds, isn’t it?”
“Well, yes and no.”
“That’s the go-to answer to any philosophy question.” “The price we pay for being notorious sticklers for precision.”
Alice laughed. “Sure, Popper had this proposal that scientific theories must be falsifiable. It was an important idea. But in the back of his mind he was thinking about the difference between theories such as Einstein’s general relativity, which made definite empirical predictions for the bending of light by the sun, and those like Marxist history or Freudian psychoanalysis. The problem with the latter ideas, he thought, was that no matter what actually happened, you could cook up a story to explain why it was so.”
“That’s what I thought. I haven’t read Popper myself, but I appreciate that he put his finger on something crucial about science.”
Alice nodded. “He did. But to be honest, most modern philosophers of science agree that it isn’t the complete answer. Science is messier than that, and what separates science from non-science is a subtle issue.”
“Everything is a subtle issue for you people! No wonder you never make any progress.”
“Now, now, Dad, we are getting at something significant here. What Popper was ultimately trying to pinpoint is that a good scientific theory has two characteristics. First, it is definite: you can’t just twist the theory to ‘explain’ anything at all, as Popper feared you could do with dialectical materialism or psychoanalysis. Second, it is empirical: theories are not deemed true by sheer reason alone. Rather, one imagines many different possible ways the world could be, each corresponding to a different theory, and then one chooses among the theories by going out and actually looking at the world.”
“Exactly.” Her father seemed to think that the advantage was his on this one. “Empirical! But if you can’t actually observe those worlds, there’s nothing really empirical about your theory at all.”
“Au contraire,” Alice replied. “Many-Worlds embodies both of these features perfectly. It is not a just-so story that can be adapted to any observed set of facts. Its postulates are simple: the world is described by a quantum wave function that evolves according to the Schrödinger equation. Those postulates are eminently falsifiable. Just do an experiment showing that quantum interference doesn’t occur when it should, or that entanglement really can be used for superluminal communication, or that a wave function really does collapse even without decoherence. Many-Worlds is the most falsifiable theory ever invented.”
“But those aren’t tests of Many-Worlds,” her father protested, unwilling to concede ground on this one. “Those are just tests of quantum mechanics generally"
"Right! But Everettian quantum mechanics is just pure, austere quantum mechanics without any additional ad hoc assumptions. If you do want to introduce extra assumptions, then by all means we can ask whether those new assumptions are testable.”
“Come now. The defining feature of Many-Worlds is the existence of all those worlds out there. Our world can’t interact with them, so that particular aspect of the theory is untestable.”
“So what? Every good theory makes some predictions that are untestable. Our current theoretical understanding of general relativity predicts that the force of gravity will not tomorrow suddenly turn off for a period of one millisecond in a particular region of space ten meters across and twenty million light-years away. That’s a completely untestable prediction, of course, but we maintain a very high credence that it’s true. There’s no reason for gravity to behave in that way, and imagining that it did leaves us with a much uglier theory than the one we have. The additional worlds in Everettian quantum mechanics have exactly this character: they are inescapable predictions of a simple theoretical formalism. We should accept them unless we have a specific reason not to.
“And besides,” Alice rushed on, “the other worlds could be detected in principle, if we got incredibly lucky. They haven’t gone away, they’re still there in the wave function. Decoherence makes it fantastically unlikely for one world to interfere with another, but not metaphysically impossible. I wouldn’t suggest applying for grant money to do such an experiment, though; it would be like mixing cream into coffee and waiting around for them to spontaneously unmix themselves.”
“Don’t worry, I wasn’t planning on it. I just don’t think Karl Popper would be very happy with your approach to the philosophy of science.”
“I’ve got you there, Dad,” said Alice. “Popper himself was a harsh critic of the Copenhagen interpretation, which he called a ‘mistaken and even a vicious doctrine.’ In contrast, he had good things to say about Many-Worlds, which he accurately described as ‘a completely objective discussion of quantum mechanics.’”
“Seriously? Popper was an Everettian?”
“Well, no,” Alice admitted. “He ultimately parted ways with Everett because he couldn’t understand why the wave function would branch but branches wouldn’t later fuse back together. I mean, that’s a good question, but it’s one we can answer.”
“I’m sure you can. Where did he come down on the foundations of quantum mechanics?”
“He developed his own formulation of quantum mechanics, but it never really caught on.”
“Ha! Philosophers. Yeah. We’re better at telling you why your theory is wrong than at proposing better ones.”
Ahh..ran out of time. I'll add more later, when I get a chance.
