131–140 of 170 posts
The right frame of mind is not "shut up and calculate", it's "shut up and make testable hypotheses and then invalidate them experimentally".
But what if "make testable hypotheses and then invalidate them experimentally" is wrong to begin with?
Earlier quoted context omitted.
This notion does not explain how the thermal bath appears. I.e. why the system interacts with a particular bath and not a superposition of such baths? At best the decoherence can try to explain how appearance of a sufficiently big classical object may trigger appearance of other objects, but it does not explain how the initial object appears.
> This notion does not explain how the thermal bath appears. The point of the bath is it's a generic model of a large system with lots of states and interactions. > I.e. why the system interacts with a particular bath and not a superposition of such baths? The bath can be in a superposition state at the start, that's fine. (Indeed the whole model would be pretty useless otherwise).
In universe-as-a-wave-function there is no external bath. The system as whole is always coherent and is described by a single wave function.
Then the idea of the decoherence is that perhaps during evolution of this big wave function it is possible to find a subsystem that looks like it is approximately decoherent during some time interval. Then one claim that our visible universe is just such subsystem.
The trouble is that so far nobody came up with a model where such temporary approximately classical subsystem appears.
Perhaps we have not tried hard enough or this is a really difficult problem, but at this point I am rather skeptical that decoherence is the right approach at all.
Especially interesting point I'd love to read more is that "Because QM is a (the?) generalization of probability theory to involve complex numbers, whose squared absolute values are probabilities. It includes probability as a special case."
The main issue I have with the prevailing perspective on QM (including this Zen one, which is more widely accepted than the article makes it sound), is just that it's rather pessimistic and slightly unscientific. When declaring that the world works on this foundation of pure mathematical randomness, you are effectively stating that's the end of the line, there's nothing below to explain the phenomena. Probability is a tool to meaningfully reason about incomplete information, but the information is not fundamentally unknowable.
You could for instance say that wether a child will be male or female is purely mathematically random. For all intents and purposes, it is random in the sense we cannot hope to predict it before conception in a single instance. It's not uniformly random, there are external factors that may affect the probability, but it would still be correct to model it as a random variable.
But we must never forget it is a model. We do actually (mostly) know why it looks random from a macro scale: (being very simplistic, I might be quite wrong here) we have many molecules with a certain temperature wizzing past each other with Brownian motion, and it is effectively impossible to predict which will react with which, leading to a certain gene to be selected. We cannot predict it, but we can explain it and prove it by experimental means. It's a chaotic system ruled by relatively simple rules, and we can do a lot of meaningful work with that.
I'm sure many professional physicists also treat QM as an abstraction and model, and there are people trying to peek under the rug. But the community has mostly failed to express this perspective when communicating with a wider audience, and possibly between themselves and their students, for the last century.
Physicists like to redefine the word "real" as to mean "the mathematical model that currently best fits observations", but that is not the common sense of the word. It is merely a pragmatic excuse to focus students on actual publishable research and prevent them from getting constantly philosophical. But it does also make it slightly heretical to keep researching how these phenomena emerge from underlying laws. Which, to an outsider, is kind of the whole point of physics.
To be fair, it is becoming exceedingly expensive to do any experimental work in this area. And as long as we don't have a good number of strong measurements that differ from the theory's predictions, we can only formulate plausible but mostly unprovable theoretical models. I understand why the community is pushing students away from such folly with a small sprinkling of dogmatism.
Earlier quoted context omitted.
In the absence of charges, Maxwell's equations reduce to `\nabla^2 F = d^2/dt^2 F`, (where F is the electromagnetic field tensor) which has solutions given by superpositions of traveling waves. What I suspect you want, however, is some sort of substance or essential nature that makes the thing go. If that's the case, then the answer is that there are no such things. Not for light, not for ordinary classical mechanics…
Right that’s the point of my original post. I see lots of people trying to understand how QM “works” when it’s just a thing that’s works the way it does. I have never seen anyone trying to understand how light moves in a vacuum, which (at least to me) seems just as mysterious if you were to try and understand it in some sort of intuitive macro physical sense.
People have been doing this since pre-helenics, "what is the medium where everything operates" or along the questions of "what is the medium that contains vacuum".
It's not that anyone isn't trying to understand that, it's just that thinking about unprovable things is boring and uninteresting from science point of view. At that level we may as well accept we all live in the Rabbit's Hole with Magic.
All is clear and logical except the part where Aaronson endorses the opinion that Everett isn’t wrong, but grandiose (whatever this means). In justification, it seems he is pushed into further twisted locutions. He speaks of what “breathes fire” into branches of the wave function and says that the question of existence of other branches is “above the pay grade of physics”. Breathing fire and pay grade of physics?
How much simpler to just assert that yes evolution is unitary at all times and, yes, this implies many classical branches.
Earlier quoted context omitted.
Wait isn't that the common assumption? That the universe is just an algorithm and we're trying to figure which is it?
No, the common assumption is that we attempt to describe the universe with precise tools like mathematics, but the map isn’t the territory and all models are incomplete, some are just less incomplete. The universe being mathematical is a form of Platonism, which is the belief that mathematical and abstract objects are real.
It might be a distinction without a difference, but I always understood the idea to be that objects we believe to be real are actually mathematical structures.
I see it as sharing some ideas from the we-are-living-in-a-simulation idea. If we were in a simulation, you wouldn’t say data structures and objects are real but would say the table in front of you is actually just data.
I like the many-interpretations interpretation of quantum. It says that you should believe all of them, or rather, choose a different interpretation based on your mood. For the optimistic, it's many-worlds. If you are going out tonight & hoping to get lucky, it better be Copenhagen. If you are falling into despair then it's going to be superdeterminism for you.
They are just tools to facilitate thought. But they are not models that can be accepted as scientific "reality" (as physicists use the word), since they cannot be experimentally verified by design (they do not lead to different predictions from the accepted theory), they are merely plausible.
> OK, but are the quantum states “ontic” (really out in the world), or “epistemic” (only in our heads)? Scott's answer to this seems like a cop-out. He's basically saying "I can't tell which things are epistemic or ontic, and this all seems very complicated, so I'm going to assume the distinction doesn't exist."
Scott Aaranson:
"OK, but are the quantum states “ontic” (really out in the world), or “epistemic” (only in our heads)?" ... "Bad dichotomy."
Daniel Harlow #16:
"silliness of the ontic/epistemic discussion"
Mateus Araújo #50:
"The crucial distinction between ontic versus epistemic entities is that the latter don’t have to respect the laws of physics."
"If quantum states are epistemic, the unphysical collapse is not a problem. If they are ontic, well, we can’t have them collapsing, can we?"
Scott #88:
"There’s the state that I ascribe to the system I’m measuring, which does collapse when I measure it (more epistemic), and then there’s the state that I’d hypothetically ascribe to the entire universe including myself, which never collapses (more ontic)"
Mateus Araújo #97: "Both of your examples are trivially ontic states, the state of the system in your branch of the wavefunction, and the state of the whole wavefunction." "... you can’t even understand what people mean when they say they’re epistemic."
Scott #108: ?
Mateus Araújo #124: ?
Scott #129: no-go theorems => epistemicists should give up
Mateus Araújo #138: Agrees with #129 but lists some epistemicists (including Bohmians).
Scott #187: Are Bohmians epistemicists?
Mateus Araújo #199: "I think calling them (Bohmians) epistemicists is fair, though perhaps an oversimplification."