i) Introduction ii) The No-One-Understands-Quantum-Mechanics Meme iii) The Copenhagen Interpretation & Anti-Realism iv) Schrödinger’s Cat v) Wavefunctions vi) Information and Spin States vii) Conclusion
In 2018, the science writer Philip Ball had a book published called Beyond Weird: Why Everything You Thought You Knew About Quantum Mechanics is Different. In that book he downplays the “weirdness” of quantum mechanics and stresses new approaches to its interpretation. This piece, however, doesn’t focus on Ball’s Beyond Weird. Instead it relies on his articles, blogs and a seminar he gave for The Royal Institution. That said, it does focus on the same issues.
More specifically, this piece concentrates on what Christopher Fuchs calls “the grimacing and posturing” that quantum mechanics often brings about. In that sense, it inevitably focuses on the Copenhagen interpretation; which Ball somewhat favours. It also deals with Schrödinger’s cat; the specifics of wavefunctions; and “informational theory” as it’s applied to quantum mechanics. All this is embedded within a discussion of philosophical anti-realism, which (to me) is a useful — and even ideal — position to adopt within the context of quantum mechanics. (Of course seeing the Copenhagen interpretation in anti-realist terms is hardly original.)
The No-One-Understands-Quantum-Mechanics Meme
The physicist Christopher Fuchs (as quoted by Philip Ball and referred to earlier) expresses the problem of quantum mechanics in terms of “all the posturing and grimacing over [its] paradoxes and mysteries”. In other words, for the layperson especially, that posturing and grimacing seems to have become the very essence of quantum mechanics… And perhaps this is even the case for some physicists too.
And from that quantum weirdness there follows the no-one-understands-quantum-mechanics refrain. That’s why Philip Ball uses Richard Feynman’s often-quoted words:
“I think I can safely say that no one understands quantum mechanics.”
Ball picks up on the bizarre nature of this statement when he says that
“[a]t that point, no one alive knew more than Richard Feynman about quantum mechanics”.
He concludes: “What hope is there, then, for the rest of us?”
So why, exactly, does no one understand quantum mechanics? Indeed is it the case that no one understands quantum mechanics? And what does it mean not to understand quantum mechanics?
To be honest, I find Feynman’s remark rhetorical; as I suspect Philip Ball does. After all, it’s fairly well-known that Feynman didn’t have too much time for the interpretations of quantum mechanics, let alone for the philosophy of quantum mechanics. In other words, Feynman knew all (or at least most) of the relevant mathematics. “The trouble was”, as Ball puts it, “that’s all he could do”.
On the other hand and from a purely scientific point of view, it’s easy to agree with Feynman. So it’s not a surprise that Ball says that “[s]ome scientists feel the same way today”. Many scientists (in the words — quoted by Ball - of the physicist David Mermin) also say “shut up and calculate”. Ball himself writes:
“Quantum theory works. It allows us to calculate the shapes of molecules, the behaviour of semiconductor devices, the trajectories of light, with stunning accuracy.”
Thus the “theory works”; though “without our knowing what it’s about”. And that surely wouldn’t be such a bad thing if physicists believed that there’s no real answer to the what-is-it-about? question. Perhaps some (or even many) do believe that.
So what do the words “What the maths mean”… mean? What does the maths describe? What is there beyond the maths (if anything)? Does the mathematics alone give us a full understanding?
The Copenhagen Interpretation & Anti-Realism
Albert Einstein famously asked whether the moon continued to exist when we stopped looking at it. He said:
“[I can’t accept quantum mechanics because] I like to think the moon is there even if I am not looking at it.”
Einstein’s moon is also a good way of putting the ostensible problem with philosophical anti-realism. However, no anti-realist has ever argued (as far as I know) that the moon ceases to exist when we stop looking at it. (That’s what idealists argue.) Instead, let Ball himself express the anti-realist position. He says:
“It now seems that something is there when we don’t look, but exactly what is there is determined only when we look.”
In other words, there’s no description of the moon “as it is in itself”. Everything we say about the moon is theory- and observer-relative. But this doesn’t in any way factor out the moon as a physical object which is, indeed, independent of minds.
To change direction.
My position is that the anti-realist stance on “the world” (or “nature”) is similar to the Copenhagen interpretation of quantum mechanics. However, whereas Niels Bohr and others might have mentioned measurements, experiments and whatnot; anti-realists have talked of verification, observation, the “public nature of meaning”, etc. Indeed these differences in jargon may not count for much; at least within this limited context.
So let Philip Ball put the “Copenhagenist” interpretation of quantum mechanics in its most graphic form:
“In this comment [from Niels Bohr] lurk all the notorious puzzles and peculiarities of quantum theory. It seems to be an incredibly grandiose, self-obsessed image of reality: nothing exists (or at least, we can’t say what does) until we bring it into being. Isn’t this the antithesis of science, which assumes an objective reality that we can examine and probe with experiments?”
One can see the problem with the Copenhagen interpretation when it’s expressed in that way. Yet Ball lays his cards on the table about both this interpretation and his positive view of it. He writes:
“It’s perhaps for this reason too that I think there are misconceptions about the Copenhagen interpretation. The first is that it denies any reality beyond what we can measure: that it is anti-realist. I see no reason to think this.”
Ironically, Ball then puts the anti-realist position in the most explicit way possible when he tells us that
“[a]t the root of the matter is the issue of whether quantum theory pronounces on the nature of reality (a so-called ontic theory) or merely on our allowed knowledge of it (an epistemic theory)”.
Perhaps Ball should brush up on his contemporary philosophy. Most (or even all) anti-realists don’t “deny any reality beyond what we can measure”. They say that this “mind-independent” reality (to put it simply) serves hardly any purpose. And anti-realists also believe this for similar reasons to that given by Niels Bohr (whom Ball then quotes). So perhaps, like so many others, Ball is guilty of fusing anti-realism with idealism — or even with postmodern quackery!
Indeed many (or all) anti-realists class their position as “epistemic” too. Or, rather, it can be seen as an epistemic position on ontology. (Some may see that as almost being oxymoronic.)
So since we have made that point, let Ball himself put the “epistemic” position of the Copenhagen interpretation. He writes:
“Ontic theories, such as the Many Worlds interpretation, take the view that wavefunctions are real entities. The Copenhagen interpretation, on the other hand, is epistemic, insisting that it’s not physically meaningful to look for any layer of reality beneath what we can measure.”
Philosophical anti-realists would be (more or less) happy with that passage. So, again, it’s odd that Ball seems to have a negative view of anti-realism. Perhaps this boils down to the brazen technical term that is “anti-realism”. After all, this term can be read as a philosophical position that’s against the real!
And in the following quote we can again see why so many people conflate both the Copenhagen interpretation of quantum mechanics and philosophical anti-realism with idealism. Ball writes:
“Pascual Jordan, one of the physicists working with Niels Bohr who helped to define the new quantum world view in the 1920s, claimed that ‘observations not only disturb what has to be measured, they produce it… We compel [a quantum particle] to assume a definite position.’ In other words, Jordan said, ‘we ourselves produce the results of measurements’.”
One can understand the idealist smell of the quote directly above. Nonetheless, the fact that “‘observations not only disturb what has to be measured, they produce it” doesn’t mean that that there wasn’t a reality (or a something) which was measured in the first place. There was. That something (perhaps John Locke’s “something, I know not what”?) was disturbed. So there’s an acceptance here that there was a something which was disturbed. It’s not as if this something was created out of the blue. After all, the very words “disturbed” and “measured” show us that there was something that was disturbed or measured! Stressing observations or measurements clearly doesn’t factor out what is that’s observed or measured.
“People might read [anti-realism!] into Bohr’s famous words: ‘There is no quantum world. There is only an abstract quantum physical description.’ But it seems to me that the meaning here is quite clear: quantum mechanics does not describe a physical reality. We cannot mine it to discover ‘bits of the world’, nor ‘histories of the world’. Quantum mechanics is the formal apparatus that allows us to make predictions about the world.”
More relevantly and importantly:
“There is nothing in that formulation, however, that denies the existence of some underlying stratum in which phenomena take place that produce the outcomes quantum mechanics enables us to predict.”
An anti-realist (again) wouldn’t have a deep problem with any of that. The anti-realist — and perhaps even Niels Bohr might have said - would say that we can’t know Kantian noumena (Bohr and Ball both mention Kant) — i.e., the world “as it is in itself”. Though, again, instead of the Copenhagen talk of “predictions”, anti-realists would simply emphasise verification, observations, intersubjectivity, etc. Bohr himself backed this up when he famously said (quoted by Ball) the following:
“‘It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.’”
We can now conclude by saying that there’s nothing beyond measurement (or beyond observation, verification, experiment, etc.). Or, rather, there is; though there may as well not be. Why? Because when it comes to noumena (for want of a better and more up-to-date word), there’s nothing we can say about it. (Though Kant did say a lot about noumena.)
According to Ball, Christopher Fuchs goes further than all this and says that
“standard Bayesian probability theory assumes, probabilities — including quantum probabilities — ‘are not real things out in the world; their only existence is in quantifying personal degrees of belief of what might happen’”.
“This view, he says, ‘allows one to see all quantum measurement events as little ‘moments of creation’, rather than as revealing anything pre-existent.’…”
In a certain sense, this is stronger than anti-realism in that an anti-realist would never feel the need to use a phrase like “moments of creation”. Thus we accept the “pre-existent” without also saying that we can “reveal” it in its complete fullness. Indeed if we don’t reveal the pre-existent, then what point does it play? Kant, for one, gave many reasons to accept the importance of noumena — or the pre-existent. Fuchs, on the other hand, appears to erase it from the picture.
This is very tricky.
If the pre-existent were different, then surely the “moments of creation” would be different too. And if that’s the case, then how can the pre-existent be entirely erased from the picture? Clearly these moments of creation can’t be autonomous. They are restrained by the pre-existent. Thus any creation carried out by a physicist is restrained by — and dependent upon — the pre-existent. In other words, if we take Fuchs literally and non-rhetorically, his position is essentially one of idealism!
Philip Ball applies more or less the same arguments found above to the specific and well-known case of Schrödinger’s cat. First of all Ball tells us that
“in neither the Copenhagen nor the Many Worlds interpretation is the cat ‘simultaneously alive and dead’”.
In more detail, Ball says that
“I think Bohr might have said something along the lines that ‘Observation allows us to speak about the classical state of the cat. And look, it is a dead one!’.”
In other words, until we get information about the cat, we don’t know if it’s alive or dead. It’s not the case that it’s both alive and dead at one and the same time (i.e., before we gain that information). However, until we get that information (as with anti-realism), the cat may as well be both alive and dead… in a manner of speaking!
Ball also offers up a more original take on the cat scenario. When one reads it, it seems extremely simple yet also powerful.
Basically, why the hell are we talking about an alive and dead cat in quantum mechanics in the first place? Sure, this was meant to be a colourful thought-experiment (i.e., against a certain take on quantum mechanics). However, it’s a thought-experiment which many people don’t really take to be a thought-experiment. In Ball’s own words:
“In order to be able to talk about the [cat] scenario in quantum terms, we need to be able to express it in quantum terms. But we can’t, because ‘live cat’ and ‘dead cat’ are not well-defined quantum states.”
I don’t know about “well-defined quantum states”: a live cat and a dead cat (both together or separately) don’t seem to be quantum states at all. Perhaps that doesn’t matter. After all, what’s happening here is that we’re applying a quantum-mechanical situation (or possibility) to the “real world” — to a cat! And what’s wrong with that?
Again, Ball’s point seems to be very simple. And, as with so much in philosophy, the simple only seems simple after it is stated. Thus Ball continues:
“What quantum property is it, exactly, that characterizes the superposition state, and that will enable you, unambiguously and in a single shot, to distinguish the two classical states? Live and dead are not quantum variables, and I’m not at all sure that they can be correlated even in principle with quantum variables that can be placed in superposition states.”
Yes; the question really is blindingly simple:
What exactly is it for a cat (or anything else) to be both alive and dead at one and the same time?
If we can’t even say what we mean in the first place, then what exactly are we talking about? This isn’t a philistine (or “positivist”) rejection of “modal theorising” or though-experiments: it’s just a demand that we define our terms, concepts or variables before we get the ball rolling.
Interestingly enough (especially in terms of philosophy), Ball focuses on logic and (sort of) plays down the maths of the quantum-mechanical cat scenario. Firstly he states:
“The paradox lies not in ‘two states at once’, but in ‘two contradictory states at once’. He [Schrödinger] was pointing not to ‘weird behaviour’ predicted by quantum theory, but to logical paradoxes.”
Forget paraconsistent or dialethic logics here (which can be deemed to be pragmatic logics when it comes to quantum mechanics — see W.V.O. Quine and Graham Priest), Ball is asking us logical questions here. We have some kind of clash between logic and maths. Thus:
“David Deutsch and Max Tegmark say, ah language! What should we trust more, language or maths? Contingent sounds, or timeless equations?”
Yet Ball argues that “here language is articulating something that underpins maths, which is logic”.
If you go with the maths rather than the logic (as it were), then we’ll inevitably have some strange scenarios to deal with. Ball cites the physicist Brian Greene’s position on the cat again. Greene is quoted as saying: “Your cat is dead, but your cat remains alive.” What’s more, Greene adds: “That is you too!”. Yes, “[t]hey are both you”!
Ball delves even more into logic when he says that “individual identity is a logical construct”. He then says that “[y]ou can’t wish it away with fantasies about ‘other yous’”. (I’m not sure this is entirely a case of logic trumping maths. Philosophy — or “conceptual analysis” — comes into the equation too.)
Philip Ball quotes physicist Maximilian Schlosshauer to back up his “Copenhagenist” position on wavefunctions. Like (it can be argued) Louis de Broglie and Max Born before him, Schlosshauer is quoted as saying that the
“whole talk of waves versus particles, quantization and so on has made many people gravitate toward interpretations where wavefunctions represent some kind of actual physical wave property, creating a lot of confusion”.
Indeed Schlosshauer concludes by saying that “[q]uantum mechanics is not a descriptive theory of nature”. In other words, there is no literal or physical reality which the wavefunction captures. The wavefunction is a product of our knowledge or “information” and also a “mathematical object”. And we only know any actualities (not the probabilities) when the wavefunction is “collapsed” — perhaps not even then.
According to Ball himself, a wavefunction doesn’t tell us what is. It tells us what “we would expect to find”. That is, if we do x, then we will find y or z. If we do y, then we will find something else.
There’s a temporal division here. We have a certain experimental state. A wavefunction is constructed (if that’s the correct way of putting it) and applied to that experimental state. That wavefunction tells us what “we would expect to find” given the many variables involved. Then the wavefunction is collapsed — i.e., a measurement is made. That means that there’s a gap between that original situation and the final measurement. (Indeed there’s also a gap between a measurement and how that measurement is interpreted.)
It actually seems like a crude mistake to conflate where particle x could be with that particle actually being in all the places it could be. Or, more correctly, it’s not a case of particle x possibly being in all the places it could be in: it’s seen as being in a lot of places at the same time. If this isn’t about probabilities but actualities, then there’s also a distinction to be made between where x could be and where x is. So how on earth can we argue that saying
x could be in many places.
is the same thing as saying that
x actually is in all these places it could be at the same time.
Thus a particle is not “in many places at once”. It could be in many different places — but not at one and the same time. Being in difference places at one and the same time is not the same as the possibility it could be in many different places.
In addition, particle x possibly being in either spin up or spin down, for example, isn’t the same as that particle actually being in spin up and spin down — at one and the same time.
Information and Spin States
Philip Ball also stresses the importance of what he and others call “information”. He contrasts information with “knowledge”. (Doesn’t one need knowledge about information?) Ball allows Christopher Fuchs (again) to express his own informational view. He writes:
“[Christopher Fuchs’] approach argues that quantum states themselves — the entangled state of two photons, say, or even just the spin state of a single photon — don’t exist as objective realities. Rather, ‘quantum states represent observers’ personal information, expectations and degrees of belief’, he says.”
In other words, a photon isn’t in both spin up and spin down at one and the same time. Instead, we simply have the “information” that it can be either in spin-state up or spin-state down. Until a measurement is made, we simply don’t know which one it is in.
As stated, all this ties into the stress which Ball places on information. Indeed, despite his view on philosophical anti-realism, information plays almost the same role as observation, verification and whatnot do in anti-realist philosophy.
“‘fundamentally a theory about the representation and manipulation of information, not a theory about the mechanics of nonclassical waves or particles’”.
Thus there’s a distinction between what is and the information we have about what is. This, again, is simple anti-realism.
Fuchs (as presented by Ball) also makes it explicit that this stress on information is on a par with anti-realism when he argues that it isn’t an “ontic” position. It is, instead, “epistemic”. In Ball’s words:
“Fuchs sees these insights as a necessary corrective to the way quantum information theory has tended to propagate the notion that information is something objective and real — which is to say, ontic. ‘It is amazing how many people talk about information as if it is simply some new kind of objective quantity in physics, like energy, but measured in bits instead of ergs’, he says. ‘You’ll often hear information spoken of as if it’s a new fluid that physics has only recently taken note of.’ In contrast, he argues, what else can information possibly be except an expression of what we think we know?”
I suppose that this means that stuff (as it were) gives off information, rather than stuff being information in and of itself. Yet this conflicts with what some philosophers and physicists see as information. That is, they believe (as Fuchs himself seems to say) that information is in no way mind-dependent. That is, they believe that information is information regardless of minds, persons, observers, experiments, etc. The philosopher John Searle, on the other hand, explicitly puts the information-for-us position. He writes:
“[I]nformation is typically relative to observers…These sentences, for example, make sense only relative to our capacity to interpret them. So you can’t explain consciousness by saying it consists of information, because information exists only relative to consciousness.”
It seems, therefore, that in accordance with the quote above, Fuchs is partly at one with Searle on this.
Philip Ball has a problem with what he calls (as already quoted) “the tired old cliches and metaphors” found in talk of quantum mechanics. So let’s offer an extreme scenario which also ends with a question:
i) If the mathematics of quantum mechanics fully accounts for what it is physicists are describing, ii) and we take away the maths, iii) then what do we have left?
Alternatively, if there is something over and above the maths, then what, exactly, is it? Is that above-and-above remainder accounted for by, say, philosophy? So here again we can state the following:
i) If the maths is indeed everything (though many people don’t realise that), ii) then there’s a danger of moving from Ball’s tired old cliches and metaphors to new cliches and metaphors if we don’t realise that.
This, then, may be the only route possible for Ball. However, it leaves the layperson — and even many physicists — will very little to say about quantum mechanics… beyond the mathematics.
1) To state the obvious: the interpretations of quantum mechanics are, well, interpretations. It’s hard to grasp what kind of standing a particular interpretation of quantum mechanics could actually have. The very word “interpretation” seems to deflate what it is that’s being done — at least from a scientific perspective. Does an interpretation become something else when it is proven, demonstrated or simply established as true or correct? Do any interpreters of quantum mechanics believe that their own interpretations can be proven? What would that mean?
2) In very broad terms, it can easily be argued that there is no “nature of reality” that can exist separately from — as Philip Ball puts it — “our allowed knowledge of it” . Indeed I would even suggest that the “ontic” position hardly makes sense. What does it mean to have a view of reality that is completely divorced from our tools for gaining knowledge of that reality?
3) To sum up. Philip Ball’s stance can be stated in this way:
Ball’s “if-isms” = metaphysical anti-realism Ball’s “is-isms” = metaphysical realism
4) John Searle argues that causes and effects — as well as the systems to which they belong — don’t contain or instantiate any information independently of minds. However, that doesn’t stop it from being the case that these causes and effects can become information due to direct observations, etc. of them. Searle’s position on information can actually be said to be an account of what’s called Shannon information. This kind of information is “observer-relative information”. In other words, it doesn’t exist as information until an observer takes it as information.