My issues with quantum physics often sounding like anti-realism or nonrealism. Realism vs. antirealism. Realism is the commonsense belief that scientific theories describe true things about the world—a real world that exists whether or not we’re looking—and that electrons, quarks, dark matter, and whatever other objects appear in our best theories, whether or not they can be observed directly, are real objects, the true ontological furniture of a singular, mind-independent world. Antirealism is an umbrella category for all sorts of ideas that reject realism in one way or another. I would Challenges many of the interpretation quantum mechanics saying they are not scientific realism. So in that way they are kind of like religion misinterpretations of reality or eroding of our true justified belief in reality’s mostly fixed truth with nonrealism untruth. Challenges many of the interpretation quantum mechanics are: Difficulties reflect a number of points about quantum mechanics: Abstract, mathematical nature of quantum field theories Existence of apparently indeterministic and yet irreversible processes Role of the observer in determining outcomes Classically unexpected correlations between remote objects Complementarity of proffered descriptions Rapidly rising intricacy, far exceeding humans present calculational capacity, as a systems size increases The mathematical structure of quantum mechanics is based on rather abstract mathematics, like Hilbert space. In classical field theory, a physical property at a given location in the field is readily derived. In Heisenbergs formalism, on the other hand, to derive physical information about a location in the field, one must apply a quantum operation to a quantum state, an elaborate mathematical process. Schrödingers formalism describes a waveform governing probability of outcomes across a field. Yet how do we find in a specific location a particle whose wavefunction of mere probability distribution[disambiguation needed] of existence spans a vast region of space? The act of measurement can interact with the system state in peculiar ways, as found in double-slit experiments. The Copenhagen interpretation holds that the myriad probabilities across a quantum field are unreal, yet that the act of observation/measurement collapses the wave function and sets a single possibility to become real. Yet quantum decoherence grants that all the possibilities can be real, and that the act of observation/measurement sets up new subsystems. Quantum entanglement, as illustrated in the EPR paradox, seemingly violates principles of local causality. Complementarity holds that no set of classical physical concepts can simultaneously refer to all properties of a quantum system. Here are some thoughts from the book: Trespassing on Einstein’s Lawn: A Father, a Daughter, the Meaning of Nothing and the Beginning of Everything, by Amanda Gefter. 2014 In class, we debated the merits of realism and antirealism. Realism is the commonsense belief that scientific theories describe true things about the world—a real world that exists whether or not we’re looking—and that electrons, quarks, dark matter, and whatever other objects appear in our best theories, whether or not they can be observed directly, are real objects, the true ontological furniture of a singular, mind-independent world. Antirealism is an umbrella category for all sorts of ideas that reject realism in one way or another. a common position among physicists, who always seemed to squirm at any mention of the R-word. It’s the philosophers’ job to worry about reality, they’d say. We just calculate and predict and test. No matter how many times I heard that, it always struck me as total bullshit. Okay, maybe if you were an electrical engineer or a surgeon or a meteorologist you’d just be concerned with predictions and the outcomes of experiments, but the people I was hearing this from were physicists. Theoretical physicists. People who were dealing with black holes and multiple universes and glitches in the simulation. Maybe when you work in theoretical physics, you feel the need to overcompensate by pretending to be as no-nonsense as a refrigerator repairman, but at the end of the day, who are you kidding? You stay awake nights worrying about how matter behaves at length scales a millionth of a billionth of a billionth of a billionth of a centimeter in six extra dimensions undetectable by any foreseeable experiment, but you don’t care at all what reality is? Please. Given my propensity for worrying about simulations and shadows and butterfly dreams, I wouldn’t have guessed that I would find myself advocating a strict realist view. Then again, I was a self-proclaimed reality hunter, so entertaining any antirealist ideas would be like shooting myself in the foot. Besides, at times the arguments for antirealism struck me as utterly absurd. “Both quantum mechanics and relativity profoundly challenge our intuitive idea that the world is made of objects,” he said. “Quantum particles have all sorts of problems about their individuality: entangled states, quantum statistics. Then in general relativity, spacetime points don’t seem to be the ultimate reality; the reality is something more like a metric field. In both cases we are pushed away from an ontology according to which you drill down and find little things that everything is built of.” It was a good point. Not only were quantum statistics weird, but they made it pretty much impossible to think of particles as “things.” If you have two electrons, there’s no way to distinguish between them. Electrons have no known substructure; they’re defined solely by their rest mass, spin, and charge, which are the same for every electron. Electrons, by definition, are identical. Of course, you’d think you could distinguish them just by their locations in space and time—an electron here is not the same particle as an electron there, by virtue of their being in different places. That trick might have worked in classical physics, but not quantum. Quantum particles don’t have well-defined positions in spacetime, only probabilities for appearing in various locations, the locations themselves smeared out by uncertainty. The result is that quantum physics renders elementary particles literally indistinguishable, a fact that becomes pretty important when you’re calculating probabilities. If each of the seven rats in my flat inevitably ended up stuck to a glue trap, then I’d say there was a one in seven chance of finding a given rat on a given trap. But if the rats really were quantum, there would be a 100 percent chance of finding any rat on any given trap. If you’re placing bets, knowing whether you’re dealing with classical or quantum statistics makes a pretty big difference. And what would it even mean to call a rat a “thing” if it has no individuality on which to pin its “thingness”? General relativity only exacerbated the situation. My father had taught me that to keep accelerated and inertial reference frames on equal footing—to turn a curve into a line—you have to bend the paper. The problem is that you can bend it in endlessly different ways and produce the same results, a fact made possible by Einstein’s central principle, general covariance. Different configurations of the paper can all correspond to the exact same physics, a kind of underdetermination that led not only Ladyman but also Einstein himself to believe that the paper itself—the “thingness” of spacetime—wasn’t ultimately real. The only reality lay in the spatiotemporal relationships traced by the paper’s curves. The metric. The structure. The more I thought about it, I realized that such underdetermination in ontology runs rampant in physics. It reminded me of Dirac’s holes. In the early days of quantum mechanics, Paul Dirac had come up with an equation that made the Schrödinger equation compatible with special relativity. The only problem was that the equation allowed particles such as electrons to have negative energy, something that clearly didn’t happen in the real world. To save his equation, Dirac imagined that the quantum vacuum was a sea in which every possible negative energy state was already filled, leaving only positive energy states accessible to electrons. But a new problem arose when Dirac realized that, if excited, the negative energy states could transform into positive energy states, leaving an empty hole in the negative energy sea. The hole would have all the properties of an electron, but with a positive charge. With his holes, Dirac had predicted the existence of antiparticles. What Dirac had considered a positively charged hole physicists nowadays think of as a positron—an object in its own right, not merely a hole. But the point is, the math never changed. Only the interpretation did. Physicists could just as well stick with the hole picture and they’d still come up with all the predictions for anything they might test in a lab. You can think of a positron as a thing or as an absence, two ontologies about as opposite as you can find, but from the point of view of mathematical structure, they’re exactly the same. I wanted to run to philosophy class to tell my classmate the good news: You don’t have to talk about particles as little balls! You can talk about them as holes! “How do you define structure?” I asked Ladyman. “I’d say it’s a system of relations. But then people say, ‘Well, a system of relations is among objects so related,’ ” he said, echoing Worrall’s critique. “But quantum mechanics and general relativity don’t seem to be based on an ontology of objects first and then relations between them sort of sitting on top. It’s really more the other way round. The objects are just nodes in the relational structure or something.” Balls and holes are merely descriptions; they’re instantiations of structure, not the structure itself. The real thing is a mathematical relationship. If you’re a realist about structure, the underdetermination crisis is averted. “Does that mean the physical world is made of math?” “It might be that at a certain level of description it becomes impossible to adequately represent the world other than mathematically. If you read popularizations of, say, quantum field theory, at a certain point the writer has to say, ‘We can’t explain this but it turns out that such and such . . .’ The resources they’ve got to communicate are not adequate because they make people think that we’re talking about little particles, and we’re not. So the more fundamental a description of reality becomes, the more mathematical it becomes, and the distinction between the abstract and the concrete becomes sort of unstable. On the other hand, I don’t want to say that the concrete universe is made of maths. But its nature might be so far removed from our common-sense notion of a concrete physical object that maybe it is less misleading to say it’s made of maths than to say it’s made of matter. These are very difficult issues. I really don’t know.” “The way I picture it is like reality is the bottom layer, and then you have a layer of mathematics on top, and there’s a one-to-one mapping between the two,” I said. “And on top of that you have language, but there’s not a one-to-one mapping between the mathematics and language, so something gets lost in translation, like you said. But then my question is, if there’s really a one-to-one mapping between math and reality, doesn’t that by definition mean that they are the same thing?” “I suppose the problem at the moment is that we don’t have a one-to-one mapping, because even our best theories aren’t completely accurate,” Ladyman said. “So yeah, you might think, if we eventually did have a one-to-one mapping, what would be the grounds for denying that reality was mathematical? I’m not really sure. I suppose I’m very skeptical of anything in philosophy that purports to explain the difference between abstract maths and maths that’s substantiated. Because in the end, what could we possibly explain that difference in terms of? Like, I reject the question, ‘What breathes fire into the equations?’ Because anything you say is just gonna be figurative, right? Because you’d say, ‘Well, there’s the abstract maths and then the actual universe is a sort of substructure of all the possible structure there could be. So what’s the difference between the uninstantiated structure and the instantiated structure?’ Well, the philosopher will say there’s a primitive instantiation relation or something—you could invent some metaphysical language to talk about it, but to me that’s no different from saying that some of the maths has pixie dust in it. It’s not going to do any work. Because what could it possibly connect to that would have any meaning? If you ask questions in science like ‘What causes an earthquake?’ you appeal to conceptual resources and those are nonempty because they’re tied to observation. But maths—pure maths isn’t tied to observation. If the theory of everything is a mathematical theory, how would you test it? It would have to have some content that has to do with something other than mathematics.” “I’ve heard some people say that if you really had a theory of everything, it wouldn’t be testable,” I offered up. “Right, hmmm,” Ladyman said, thoughtful. “That’s interesting.” I could hardly believe I was defending the notion that the world was made of math, given my teenage years as a strict nonbeliever. I was glad my mother wasn’t there to get the satisfaction. But like Ladyman, I didn’t see what the other option could be, not if we followed Worrall’s advice and listened to “what our current theories tell us.” As far as I could see, our current theories really were telling us that reality is made of math. That objects give way to equations, that thingness melts to abstraction. Given the drastic underdetermination of ontology in general relativity and quantum mechanics, Ladyman’s version of structural realism seemed to be the only lifeboat capable of keeping us afloat in a sea of existential crisis and contradiction. As I thought about it, I realized how surprising that was. I mean, you’d think it would be the other way around—that as our theories of physics got better, snowballing ever closer to ultimate reality, they’d offer us increasingly clearer pictures of the objects that ultimately constitute reality. Instead it seemed that the only clear-cut message they offered was that “objects” aren’t the right ontology at all. Not only was physics undermining every intuition we have about the world, it was also weeding out philosophies. From where I was sitting in a nondescript room in a nondescript hotel, ontic structural realism seemed to be the only one left standing. As I walked the London streets, the sky a dull gray overhead, the pavement slick with rainwater, I looked around at the so-called world. It was crazy to think that everything—the majestic townhouses and double-decker buses, the sprawling green of Hyde Park and the white stone at Marble Arch—was made not of physical things, but of math. Then again, wasn’t that exactly what Wheeler had been saying all along? It from bit: the world is made of information. Not described by information, but made of information. A house is made of bricks but the bricks are made of information. And what was information if not mathematical structure? Being a realist about objects was kind of like believing that love and amor are two totally different things just because they look and sound different. You have to know the rules of translation between English and Spanish to discover that the two words are equivalent—there’s a one-to-one isomorphic mapping from one word to the other, a mapping that preserves some underlying structure, not love or amor but the concept to which they both refer. Love and amor are words. Descriptions. What’s real is what survives the translation, the structural relationship between them. We can’t give it a name. Giving it a name would trade structure back for description. Giving it a name would require choosing a single language, a preferred coordinate system, violating general covariance, breaking the symmetry of a linguistic spacetime. Science is about structure. The stories we tell and the images we create to describe the structure are up to us. The key is to not mistake description for reality. But how do we sort them out? We have to look at all the varied descriptions and find their common denominators, the structure they share, the thing that remains unchanged when you go from one description to the next. scientificamerican/article/schrodingers-rats-and-the-search-for-ultimate-reality-excerpt/
Posted on: Mon, 14 Jul 2014 18:45:40 +0000
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