Whenever any of this comes up I remember that physics professor’s speech on first day of quantum mechanics that got viral:
“Nobody understands quantum mechanics. The people who came up with it don’t understand it. I will do my best so that by the end of this course you don’t understand it either, and so you can got out to the world and spread our ignorance.”
I think the trick was to establish that disagreeing with the Copenhagen Interpretation makes you one of these idiots who can’t comprehend Quantum Mechanics. Idiots like… Albert Einstein? Or… Erwin Schrödinger? You know, real morons.
Because it’s part of reality, a foundational part of it even, it’s logical basically by definition. If it wasn’t, it would just mean our concept of logic is flawed.
Beyond that, we have perfectly logical and sensible descriptions for what is happening in quantum physics, the problem is just that we have more than one and don’t know which is right.
Whenever this picture comes up I remember that it’s wrong - both electrons on it have the same spin, one is just rotated 180°, but it says +½ for one and -½ for the other, is like a part of the joke?
All electrons have spin 1/2, that’s a property of it being an electron. They have a spin vector (the arrow shown) and whether it is in the same direction or opposite direction to the magnetic field it’s in determines where it is plus or minus.
Now you might think “but what if it is not entirely aligned with the field, then it wouldn’t be 1/2”, which is true, on aggregate for large numbers of electrons, but if you ever look at a single electron its spin will either be “up” or “down” never any other orientation.
This is the kind of thing people are referring to when they say “no one understands QM”, we know it is the case, we can measure it and predict it, but it makes no fucking sense.
I think where the sense starts to fall through is in remembering that it’s not a ball though. It’s a wave, and the spin only in one direction when interacting with something else, otherwise it’s akin to three parts spinning clockwise, and one part spinning counter-clockwise. 🫠
I’d say we understand quantum mechanics better than most things.
We know more about the behaviour of an electron than we know about the oceans, the Earth, the sun, the weather, the stock market, the human body, prime numbers, and so on.
Do you mean “why” as in “why did X cause Y” or as in “why are things the way they are”?
In the former case, quantum mechanics is our most precise theory for coupling causes and effects, predicting the outcome of experiments to an incredible degree.
In the latter case, do we really have a grasp of that for anything? Why is the gravitational constant the value that it is? Why is pi the ratio of a circle’s circumference and it’s diameter? Mostly we ultimately have to say that it is so because we can observe that it is so. For quantum mechanics it is the same.
Oceans: We know the basic mechanics of currents, tides, chemistry, where all that water came from in the first place, and while there are a few known-unknowns it doesn’t seem like a paradigm-shifting discovery is likely. They mystery is mostly because it’s huge and we just can’t look through it very well, and that there’s too many physical inputs to track them all so models are abstractions by necessity.
The same goes for most of your list (I will not speak to prime numbers, I am an Earth Sciences guy and bad at higher math) in that we may not have a perfect map but we know the shape of it and where the probable gaps in understanding are. So the “why” is questions like “why do waves happen” or “why does the sun look yellow” or “why do we have embryonic ‘gills’” and we have pretty good answers you can drill pretty deep into.
Pushing at the edges of physics is, I think, where the situation is flipped. We have very good models for the behavior of light but questions like “why is there a limit to the speed of information and why does light go that fast” and “why does it behave as a wave and also a mass-less particle” don’t seem to have satisfying answers or even a means to be answered. Admittedly physics beyond its applications to organic chemistry is outside my education (again, math) but I try to keep up.
We understand the “how” better than most things. Quantum mechanics is extremely well-supported mathematically and experimentally. I think that’s what they mean. The “why”, an understanding of what a system that generated those results looks like at a macro level, basically no clue.
The consensus seems to be that the math works, don’t try to figure out why.
There are plenty of simple ways to understand QM on a more ontological level than just the maths. The literature is filled to the brim with them these days. The problem is not so much that it’s difficult, but that there is no agreement. So discussions regarding it just lead to arguments that can’t be settled, and so professors get tired of it and tell people to just shut up and calculate.
It’s not so much that there’s no agreement, it’s that the different understandings all give the same empirical results, so there’s no way to decide on which understanding is “better”.
Settling the argument is a matter of taste, not science. At least for now.
No, it’s the lack of agreement that is the problem. Interpreting classical mechanics is philosophical as well, but there is generally agreement on how to think about it. You rarely see deep philosophical debates around Newtonian mechanics on how to “properly” interpret it. Even when we get into Einsteinian mechanics, there are some disagreements on how to interpret it but nothing too significant. The thing is that something like Newtonian mechanics is largely inline with our basic intuitions, so it is rather easy to get people on board with it, but QM requires you to give up a basic intuition, and which one you choose to give up on gives you an entirely different picture of what’s physically going on.
Philosophy has never been empirical, of course any philosophical interpretation of the meaning of the mathematics gives you the same empirical results. The empirical results only change if you change the mathematics. The difficulty is precisely that it is more difficult to get everyone on the same page on QM. There are technically, again, some disagreements in classical mechanics, like whether or not the curvature of spacetime really constitutes a substance that is warping or if it is just a convenient way to describe the dispositions of how systems move. Einstein for example criticized the notion of reifying the equations too much. You also cannot distinguish which interpretation is correct here as it’s, again, philosophical.
If we just all decided to agree on a particular way to interpret QM then there wouldn’t be an issue. The problem is that, while you can mostly get everyone on board with classical theories, with QM, you can interpret it in a time-symmetric way, a relational way, a way with a multiverse, etc, and they all give you drastically different pictures of physical reality. If we did just all pick one and agreed to it, then QM would be in the same boat as classical mechanics: some minor disagreements here and there but most people generally agree with the overall picture.
What value does such an agreement have? Why is it a problem that there’s a plurality of equivalent understandings? Does that plurality add to or subtract from our understanding of reality?
You say the different interpretations give drastically different pictures of physical reality, but not in an empirical sense. But can we really talk of an empirically unavailable physical reality? If pilot waves, multiverses and wave function collapses all lead to the same empirical reality, does it make any difference to physical reality which one you think about?
That is a somewhat narrow definition of “why”, I’d say. But indeed, the transition from quantum mechanics to classical mechanics is unclear.
There are several interpretations of quantum mechanics, but they are empirically equivalent, so you can just pick your favourite and move on. That’s not necessarily a big mystery. The math works, as you say, and that’s the whole point of a physical theory.
There are also several interpretations of statistics. Does that mean we don’t understand “why” a dice rolls results with a certain frequency?
Note that superconductivity and the quantum Hall effect are both macroscopic quantum effects, so we do know what a macroscopic quantum system looks like.
Whenever any of this comes up I remember that physics professor’s speech on first day of quantum mechanics that got viral:
“Nobody understands quantum mechanics. The people who came up with it don’t understand it. I will do my best so that by the end of this course you don’t understand it either, and so you can got out to the world and spread our ignorance.”
Or something to that effect.
The Many Worlds Interpretation must be rejected because it makes sense and we’ve already agreed that Quantum Mechanics is not supposed to make sense.
Well put. I will never understand how Bohr managed to persuade so many scientists to commit themselves to not making sense.
I think the trick was to establish that disagreeing with the Copenhagen Interpretation makes you one of these idiots who can’t comprehend Quantum Mechanics. Idiots like… Albert Einstein? Or… Erwin Schrödinger? You know, real morons.
Quantum mechanics is illogical and stuff that happens makes no sense but can be recrcreated through experimentation…as long as you don’t look at it.
The end
It’s perfectly logical, what happens makes sense, we just don’t know key facts about what is actually happening.
How can you know that
Because it’s part of reality, a foundational part of it even, it’s logical basically by definition. If it wasn’t, it would just mean our concept of logic is flawed.
Beyond that, we have perfectly logical and sensible descriptions for what is happening in quantum physics, the problem is just that we have more than one and don’t know which is right.
What definition of “logical” are you using here?
Coherent and coming from sound reasoning
Quantum mechanics is extremely logical - we understand the math extremely well, and the math describes reality better than any other theory.
It is, however, not intuitive.
I was just being cheeky
I’m so good at not understanding stuff. My time has come.
Whenever this picture comes up I remember that it’s wrong - both electrons on it have the same spin, one is just rotated 180°, but it says +½ for one and -½ for the other, is like a part of the joke?
All electrons have spin 1/2, that’s a property of it being an electron. They have a spin vector (the arrow shown) and whether it is in the same direction or opposite direction to the magnetic field it’s in determines where it is plus or minus.
Now you might think “but what if it is not entirely aligned with the field, then it wouldn’t be 1/2”, which is true, on aggregate for large numbers of electrons, but if you ever look at a single electron its spin will either be “up” or “down” never any other orientation.
This is the kind of thing people are referring to when they say “no one understands QM”, we know it is the case, we can measure it and predict it, but it makes no fucking sense.
That makes sence though, thanks for clearing that up
I think where the sense starts to fall through is in remembering that it’s not a ball though. It’s a wave, and the spin only in one direction when interacting with something else, otherwise it’s akin to three parts spinning clockwise, and one part spinning counter-clockwise. 🫠
Ah much better, thank you
I’d say we understand quantum mechanics better than most things.
We know more about the behaviour of an electron than we know about the oceans, the Earth, the sun, the weather, the stock market, the human body, prime numbers, and so on.
We generally have a grasp of “why” for that stuff though, even if the whole picture is currently hidden or too complex.
Do you mean “why” as in “why did X cause Y” or as in “why are things the way they are”?
In the former case, quantum mechanics is our most precise theory for coupling causes and effects, predicting the outcome of experiments to an incredible degree.
In the latter case, do we really have a grasp of that for anything? Why is the gravitational constant the value that it is? Why is pi the ratio of a circle’s circumference and it’s diameter? Mostly we ultimately have to say that it is so because we can observe that it is so. For quantum mechanics it is the same.
Or do you mean “why” in some other way?
Oceans: We know the basic mechanics of currents, tides, chemistry, where all that water came from in the first place, and while there are a few known-unknowns it doesn’t seem like a paradigm-shifting discovery is likely. They mystery is mostly because it’s huge and we just can’t look through it very well, and that there’s too many physical inputs to track them all so models are abstractions by necessity.
The same goes for most of your list (I will not speak to prime numbers, I am an Earth Sciences guy and bad at higher math) in that we may not have a perfect map but we know the shape of it and where the probable gaps in understanding are. So the “why” is questions like “why do waves happen” or “why does the sun look yellow” or “why do we have embryonic ‘gills’” and we have pretty good answers you can drill pretty deep into.
Pushing at the edges of physics is, I think, where the situation is flipped. We have very good models for the behavior of light but questions like “why is there a limit to the speed of information and why does light go that fast” and “why does it behave as a wave and also a mass-less particle” don’t seem to have satisfying answers or even a means to be answered. Admittedly physics beyond its applications to organic chemistry is outside my education (again, math) but I try to keep up.
We understand the “how” better than most things. Quantum mechanics is extremely well-supported mathematically and experimentally. I think that’s what they mean. The “why”, an understanding of what a system that generated those results looks like at a macro level, basically no clue.
The consensus seems to be that the math works, don’t try to figure out why.
There are plenty of simple ways to understand QM on a more ontological level than just the maths. The literature is filled to the brim with them these days. The problem is not so much that it’s difficult, but that there is no agreement. So discussions regarding it just lead to arguments that can’t be settled, and so professors get tired of it and tell people to just shut up and calculate.
It’s not so much that there’s no agreement, it’s that the different understandings all give the same empirical results, so there’s no way to decide on which understanding is “better”.
Settling the argument is a matter of taste, not science. At least for now.
No, it’s the lack of agreement that is the problem. Interpreting classical mechanics is philosophical as well, but there is generally agreement on how to think about it. You rarely see deep philosophical debates around Newtonian mechanics on how to “properly” interpret it. Even when we get into Einsteinian mechanics, there are some disagreements on how to interpret it but nothing too significant. The thing is that something like Newtonian mechanics is largely inline with our basic intuitions, so it is rather easy to get people on board with it, but QM requires you to give up a basic intuition, and which one you choose to give up on gives you an entirely different picture of what’s physically going on.
Philosophy has never been empirical, of course any philosophical interpretation of the meaning of the mathematics gives you the same empirical results. The empirical results only change if you change the mathematics. The difficulty is precisely that it is more difficult to get everyone on the same page on QM. There are technically, again, some disagreements in classical mechanics, like whether or not the curvature of spacetime really constitutes a substance that is warping or if it is just a convenient way to describe the dispositions of how systems move. Einstein for example criticized the notion of reifying the equations too much. You also cannot distinguish which interpretation is correct here as it’s, again, philosophical.
If we just all decided to agree on a particular way to interpret QM then there wouldn’t be an issue. The problem is that, while you can mostly get everyone on board with classical theories, with QM, you can interpret it in a time-symmetric way, a relational way, a way with a multiverse, etc, and they all give you drastically different pictures of physical reality. If we did just all pick one and agreed to it, then QM would be in the same boat as classical mechanics: some minor disagreements here and there but most people generally agree with the overall picture.
What value does such an agreement have? Why is it a problem that there’s a plurality of equivalent understandings? Does that plurality add to or subtract from our understanding of reality?
You say the different interpretations give drastically different pictures of physical reality, but not in an empirical sense. But can we really talk of an empirically unavailable physical reality? If pilot waves, multiverses and wave function collapses all lead to the same empirical reality, does it make any difference to physical reality which one you think about?
That is a somewhat narrow definition of “why”, I’d say. But indeed, the transition from quantum mechanics to classical mechanics is unclear.
There are several interpretations of quantum mechanics, but they are empirically equivalent, so you can just pick your favourite and move on. That’s not necessarily a big mystery. The math works, as you say, and that’s the whole point of a physical theory.
There are also several interpretations of statistics. Does that mean we don’t understand “why” a dice rolls results with a certain frequency?
Note that superconductivity and the quantum Hall effect are both macroscopic quantum effects, so we do know what a macroscopic quantum system looks like.