Your previous post was good, but this one seems to be eliding a few too many issues. If you took a poll of physicists asking them to explain what their fundamental model — quantum mechanics — actually tells us about the world (surely a simple enough question), there would be disagreement comparable to that regarding the philosophical questions you mentioned. The survey you cite is also obviously unhelpful, in that the questions on that survey were chosen because they’re controversial. Most philosophical questions are not very controversial, but for that very reason you don’t hear much about them. If we hand-picked all the foundational questions physicists disagreed about and conducted a popularity poll, would we be rightly surprised to find that the poll results were divided?
(It’s also worth noting that some of the things being measured by the poll are attitudinal and linguistic variation between different philosophical schools and programs, not just doctrinal disagreements. Why should we expect ethicists and philosophers of mathematics to completely agree in methodology and terminology, when we do not expect the same from physicists and biologists?)
There are three reasons philosophers disagree about foundational issues:
(1) Almost everyone disagrees, at least tacitly, about foundational issues. Foundational issues are hard, and our ordinary methods of acquiring truth and resolving disagreements often short-circuit when we arrive at them. Scientific realism is controversial among scientists. Platonism is controversial among mathematicians. Moral realism is controversial among politicians and voters. Philosophers disagree about these matters for the same basic reasons that everyone else does; the only difference is that philosophers do not follow the same social conventions the rest of us do that dictate bracketing and ignoring foundational disagreements as much as possible. In other words...
(2) … philosophy is about foundational disagreement. There is no one worldly content or subject matter or methodology shared between all the things we call ‘philosophy.’ The only thing we really use to distinguish philosophers from non-philosophers is how foundational and controversial the things they talk about are. When you put all the deep controversies in a box and call that box Philosophy, you should not be surprised upon opening the box to see that it is clogged with disagreement.
(3) Inasmuch as philosophical issues are settled, they stop getting talked about. So there’s an obvious selection bias effect. Philosophical progress occurs; but that progress gets immediately imported into our political systems, our terminological choices and conceptual distinctions, our scientific theories and practices, our logical and mathematical toolboxes. And then it stops being philosophy.
That said, I agree with a lot of your criticisms of a lot of philosophers’ practices. They need more cognitive science and experimentalism. Desperately. But we should be a lot more careful and sophisticated in making this criticism, because most philosophers these days (even the most metaphysically promiscuous) do not endorse the claim ‘our naive, unreflective intuitions automatically pick out the truth,’ and because we risk alienating the Useful Philosophers when we make our target of attack simply Philosophy, rather than a more carefully constructed group.
LessWrong: Start tabooing the word ‘philosophy.’ See how it goes.
If you took a poll of physicists asking them to explain what their fundamental model — quantum mechanics — is actually asserting about the world (surely a simple enough question), there would be disagreement comparable to that regarding the philosophical questions you mentioned.
A major problem with modern physics is that there are almost no known phenomena that are known to work in a way that disagrees with how modern physics predicts they would work (in principle; there are lots of inferential/computational difficulties). What physics asserts about the world is, to the best of anyone’s knowledge, coincides with what’s known about most of the world in all detail. The physicists have to build billion dollar monstrosities like LHC just to get their hands on something they don’t already thoroughly understand. This doesn’t resemble the situation with philosophy in the slightest.
You’re speaking in very general terms, and you’re not directly answering my question, which was ‘what is quantum mechanics asserting about the world?’ I take it that what you’re asserting amounts to just “It all adds up to normality.” But that doesn’t answer questions concerning the correct interpretation of quantum mechanics. “x + y + z . . . = normality.” That’s a great sentiment, but I’m asking about what physics’ “x” and “y” and “z” are, not questioning whether the equation itself holds.
you’re not directly answering my question, which was ‘what is quantum mechanics asserting about the world?’
I’m pointing out that in particular it’s asserting all those things that we know about the world. That’s a lot, and the fact that there is consensus and not much arguing about this shouldn’t make this achievement a trivial detail. This seems like a significant distinction from philosophy that makes simple analogies between these disciplines extremely suspect.
(I agree that I’m not engaging with the main points of your comment; I’m focusing only on this particular aside.)
So your response to my pointing out that physicists too disagree about basic things, is to point out that physicists don’t disagree about everything. In particular, they agree that the world around us exists.
Uh… good for them? Philosophers too have been known to harbor a strong suspicion that there is a world, and that it harbors things like chairs and egg timers and volcanoes. Physicists aren’t special in that respect. (In particular, see the philosophical literature on Moorean facts.)
physicists don’t disagree about everything. In particular, they agree that the world around us exists. … Philosophers too have been known to harbor a strong suspicion that there is a world
Physicists agree about almost everything. In particular, they agree about all specific details about how the world works relevant (in principle) to most things that have ever been observed (this is a lot more detail than “the world exists”).
They agree about the most useful formalisms for modeling and predicting observations. But ‘formalism’ and ‘observation’ are not themselves concepts of physics; they are to be analyzed away in the endgame. My request is not for you to assert (or deny) that physicists have very detailed formalisms, or very useful ones; it is for you to consider how much agreement there is about the territory ultimately corresponding to these formalisms.
A simple example is the disagreement about which many-worlds-style interpretation is best; and about whether many-worlds-style interpretations are the best interpretations at all; and about whether, if they are the best, whether they’re best enough to dominate the probability space. Since the final truth-conditions and referents of all our macro- and micro-physical discourse depends on this interpretation, one cannot duck the question ‘what are chairs?’ or ‘what are electrons?’ simply by noting ‘chairs are something or other that’s real and fits our model.’ It’s true, but it’s not the question under dispute. I said physicists disagree about many things; I never said that physicists fail to agree about anything, so changing the topic to the latter risks confusing the issue.
Is the truth of many-worlds theory, or of non-standard models, a purely ‘philosophical’ matter? If so, then sure. But that’s just a matter of how we choose to use the word ‘philosophy;’ it doesn’t change the fact that these are issues physicists, specifically, care and disagree about. To dismiss any foundational issue physicists disagree about as for that very reason ‘philosophical’ is merely to reaffirm my earlier point. Remember, my point was that we tend to befuddle ourselves by classifying issues as ‘philosophical’ because they seem intractable and general, then acting surprised when all the topics we’ve classified in this way are, well, intractable and general.
It’s fine if you think that humanity should collectively and universally give up on every topic that has ever seemed intractable. But you can make that point much more clearly in those simple words than by bringing in definitions of ‘philosophy.’
It seems that the matters you’re arguing that scientists disagree on are all ones where we cannot, at least by means anyone’s come up with yet, discriminate between options by use of empiricism.
The questions they disagree on may or may not be “philosophical,” depending on how you define your terms, but they’re questions that scientists are not currently able to resolve by doing science to them.
The observation that scientists disagree on matters that they cannot resolve with science doesn’t detract from the argument that the process of science is useful for building consensuses. If anything it supports it, since we can see that scientists do not tend to converge on consensuses on questions they aren’t able to address with science.
The observation that scientists disagree on matters that they cannot resolve with science doesn’t detract from the argument that the process of science is useful for building consensuses.
Agreed. It’s not that scientists universally distrust human rationality, while philosophers universally trust it. Both groups regularly subject their own reasoning faculties to tests and to distrust. (And both also need to rely at least somewhat on human reasoning, since one can only fairly conclude that a kind of reasoning is flawed by reasoning one’s way toward that conclusion. Even purely ‘empirical’ or ‘factual’ questions require some amount of interpretive work.)
The reason philosophers seem to disagree more than scientists is very simple, and it’s the same reason physicists trying to expand the Standard Model disagree more than physicists working within the Standard Model: Because there’s a lack of intersubjectively accessible data. Without such data for calibration, different theoretical physicists’ inferences, intuitions, and pattern-matching faculties in general will get relatively diverse results, even if their methodologies are quite commendable.
I think you are reading too much into my comment. It totally wasn’t about what humanity should collectively give up on, or even what anybody should. And I agree that philosophy is effectively defined as a collection of problems which are not yet understood enough to be even investigated by standard scientific methods.
I was only pointing out (perhaps not much clearly, but I hadn’t time for a lengthier comment) that the core of physics is formalisms and modelling and predictions (and perhaps engineering issues since experimental apparatuses today are often more complex than the phenomena they are used to observe). That is, almost all knowledge needed to be a physicist is the ordinary “non-philosophical” knowledge that everybody agrees upon, and almost all talks at physics conferences are about formalism and observations, while the questions you label “foundational” are given relatively small amount of attention. It may seem that asking “what is the true nature of electron” is a question of physics, since it is about electrons, but actually most physicists would find the question uninteresting and/or confused while the question might sound truly interesting to a philosopher. (And it isn’t due to lack of agreement on the correct answer, but more likely because physicists like more specific / less vague questions as compared to philosophers).
One can get false impression about that since the most famous physicists tend to talk significantly more about philosophical questions than the average, but if Feynman speaks about interpretation of quantum mechanics, it’s not a proof that interpretation of quantum mechanics is extremely important question of physics (because else a Nobel laureate wouldn’t talk about it), it’s rather proof that Feynman has really high status and he can get away with giving a talk on a less-than-usually rigorous topic (and it is much easier to make an interesting lecture from philosophical stuff than from more technical stuff).
Of course, my point is partly about definitions—not so much the definition of philosophy but rather the definition of physics—but once we are comparing two disciplines having common definitions of those disciplines is unavoidable.
I don’t think we disagree all that much; and I meant ‘you’ to be a hypothetical interlocuter, not prase. All I want to reiterate is that the line between physics and philosophy-of-physics can be quite fuzzy. The ‘measurement problem’ is perhaps the pre-eminent problem in ‘philosophy of physics,’ but it’s not some neoscholastic mumbo-jumbo of the form “what is the true nature of electron?”. Rather, it’s a straightforward physics problem that happens to have turned out to be especially intractable. Specifically, it is the problem that these three propositions form an inconsistent triad given our Born-probabilistic observations:
(1) Wave-function descriptions specify all the properties of physical systems.
(2) The wave function evolves solely in accord with the Schrödinger equation.
(3) Measurements have definite outcomes.
De-Broglie-style interpretations (‘hidden variables’) reject (1), von-Neumann-style interpretations (‘objective collapse’) reject (2), and Everett-style interpretations (‘many worlds’) reject (3). So far. there doesn’t seem to be anything ‘unphysical’ or ‘unphysicsy’ about any of these views. What’s made them ‘philosophical’ is simply that the problem is especially difficult, and the prospects for solving it to everyone’s satisfaction, by ordinary physicsy methods, seem especially dim. So, if that makes it philosophy, OK. But problems of this sort divide philosophers because they’re hard, not because philosophers ‘trust their own rationality’ more than physicists do.
I find it a bit tricky to formulate problems in propositions like yours (1) - (3) and insist that at least one must be rejected because of mutual inconsistency. The problem is that the meaning of the propositions is not precise. What exactly does “all properties of physical systems” denote? Is it “maximum information about the system that can be obtained in principle” (subproblem: what does “in principle” mean), or is it “information sufficient to predict all events in which the system is involved, if there is no uncertainty external to the system involved”, or is it something else?
We know that the conditions under which we prepare the system can be summarised in a wave function and we know how to calculate the frequencies of measurement outcomes, given a specific wave function. We know that the knowledge of wave function doesn’t let us predict the measurements with certainty. We even know, due to Bell’s inequalities and the experimental results, that if there is some unknown property of the system which determines the measurement outcome prior to actual measurement, then this property must be non-local. We know that the evolution of systems under observation isn’t described by Schrödinger equation only. All this is pretty uncontroversial.
Now the interpretations tend to use different words to describe the same amount of knowledge. Instead of saying that we can get unpredictably different outcomes from a measurement on a system with some given wave function, one may say that the outcome is always the same but our consciousness splits and each part is aligned only with a portion of the outcome, or one may say that the outcome is not “definite” (whatever it means). This verbal play is the unphysicsy thing with the given propositions.
What exactly does “all properties of physical systems” denote? Is it “maximum information about the system that can be obtained in principle”
You seem to be trying to explain something rather clear with something less clear. The sentence in question is simply affirming that the wave function captures everything that is true of the system; thus (if you accept this view) there are no hidden variables determining the seemingly probabilistic outcomes of trying to measure non-observables. There’s nothing mysterious about asserting that there’s a hidden cause in this case, any more than science in general is going Mystical when it hypothesizes unobserved causes for patterns in our data.
To say that the outcome is not “definite” is to say that it is false that a particular measurement outcome (like ‘spin up’), and not an alternative outcome (like ‘spin down’), obtains. “Definite” sounds vague here because the very idea of “many worlds” is extremely vague and hard to pin down. One way to think of it is that the statistical properties of quantum mechanics are an epiphenomenon of a vastly larger, unobserved reality (the wave function itself) that continues merrily on its way after the observation.
Say there are no hidden variables and the evolution is probabilistic. Does then the wave function capture everything that is true of the system? It seems to me that it doesn’t: it is true that the system will be measured spin up in the next measurement, but the wave function is as well compatible with spin down. But you seem to assert that if I don’t believe in hidden variables then the wave function does capture everything that is true of the system. Thus I don’t find it rather clear. Neither does “epiphenomenon of a vastly larger reality” seem clarifying to me even a little bit.
Say there are no hidden variables and the evolution is probabilistic. Does then the wave function capture everything that is true of the system?
At a given time, yes. But over time, the way a wave function changes may (a) be determined entirely by the Schrödinger equation, or (b) be determined by a mixture of the Schrödinger equation and intermittent ‘collapses.’ Given (a), the apparently probabilistic distribution of observations is somehow mistaken, and we get a many-worlds-type interpretation. Given (b), the probabilities are preserved but the universe suddenly operates by two completely different causal orders, and we get an ‘objective collapse’ interpretation. These are the two options if the wave function captures all the variables.
I am now interested in clarification of “everything that is true of the system”. I have an electron whose spin I am going to measure five minutes from now. Does the proposition “the spin will be measured up” belong to “everything that is true about the electron”? Presume that the spin will indeed be measured up (or I will perceive the world in which it was up or whatever formulation will suit you the best). To me it appears as a true proposition, but there may be philosophical arguments to the contrary (problem of future contingents comes to mind).
Physics-inclined people tend to be 4-dimensionalists, so I don’t think they’ll object to describing wave functions in terms that account for them at all times. Even indeterminists (i.e., collapse theorists) can accept that we can talk about what will be true of electrons in the future, though we can’t even in principle know some of those facts in advance.
Does the proposition “the spin will be measured up” belong to “everything that is true about the electron”?
de Broglie sez: “Yes, that belongs to everything that is true (about the electron’s wave function). But at least one truth about the electron (its position at any given time) is not accounted for in the wave function. (This explains why the Schrödinger equation, although a complete description of how wave functions change, is not a complete description of how physical systems change.)”
von Neumann sez: “Yes. And the wave function encompasses all these truths. But there is no linear dynamical equation relating all the time-slices of the wave function. There are more free-floating brute facts within wave functions than we might have expected.”
Everett sez: “Yes… well, sort of. The formalism for ‘the spin will be measured up’ is a component of a truth. But it would be more accurate and objective to say something like ‘the spin will be measured up and down’ (assuming it was in a prior superposition). Thus the wave function encompasses all the truths, and evolves linearly over time in accord with the Schrödinger equation. Win-win!”
Inasmuch as philosophical issues are settled, they stop getting talked about.
Why exactly? I mean, there is no controversy in mathematics about whether 2+2=4, and yet we continue teaching this knowledge in schools. Uncontroversial, yet necessary to be taught, because humans don’t get it automatically, and because it is necessary for more complicated calculations.
Why exactly don’t philosophers do an equivalent of this? It is because once a topic has been settled at a philosophical conference, the next generations of humans are automatically born with this knowledge? Or at least the answer is published so widely, that it becomes more known than the knowledge of 2+2=4? Or what?
Start tabooing the word ‘philosophy.’ See how it goes.
First approximation: Pretended ability to make specific conclusions concerning ill-defined but high-status topics. :(
I mean, there is no controversy in mathematics about whether 2+2=4, and yet we continue teaching this knowledge in schools.
Yes, and we continue teaching modus ponens and proof by reductio in philosophy classrooms. (Not to mention historical facts about philosophy.) Here we’re changing the subject from ‘do issues keep getting talked about equally after they’re settled?’ to ‘do useful facts get taught in class?’ The philosopher certainly has plenty of simple equations to appeal to. But the mathematician also has foundational controversies, both settled and open.
Pretended ability to make specific conclusions concerning ill-defined but high-status topics. :(
So if I pretend to be able to make specific conclusions about capital in macroeconomics, I’m doing philosophy?
Your previous post was good, but this one seems to be eliding a few too many issues. If you took a poll of physicists asking them to explain what their fundamental model — quantum mechanics — actually tells us about the world (surely a simple enough question), there would be disagreement comparable to that regarding the philosophical questions you mentioned. The survey you cite is also obviously unhelpful, in that the questions on that survey were chosen because they’re controversial. Most philosophical questions are not very controversial, but for that very reason you don’t hear much about them. If we hand-picked all the foundational questions physicists disagreed about and conducted a popularity poll, would we be rightly surprised to find that the poll results were divided?
(It’s also worth noting that some of the things being measured by the poll are attitudinal and linguistic variation between different philosophical schools and programs, not just doctrinal disagreements. Why should we expect ethicists and philosophers of mathematics to completely agree in methodology and terminology, when we do not expect the same from physicists and biologists?)
There are three reasons philosophers disagree about foundational issues:
(1) Almost everyone disagrees, at least tacitly, about foundational issues. Foundational issues are hard, and our ordinary methods of acquiring truth and resolving disagreements often short-circuit when we arrive at them. Scientific realism is controversial among scientists. Platonism is controversial among mathematicians. Moral realism is controversial among politicians and voters. Philosophers disagree about these matters for the same basic reasons that everyone else does; the only difference is that philosophers do not follow the same social conventions the rest of us do that dictate bracketing and ignoring foundational disagreements as much as possible. In other words...
(2) … philosophy is about foundational disagreement. There is no one worldly content or subject matter or methodology shared between all the things we call ‘philosophy.’ The only thing we really use to distinguish philosophers from non-philosophers is how foundational and controversial the things they talk about are. When you put all the deep controversies in a box and call that box Philosophy, you should not be surprised upon opening the box to see that it is clogged with disagreement.
(3) Inasmuch as philosophical issues are settled, they stop getting talked about. So there’s an obvious selection bias effect. Philosophical progress occurs; but that progress gets immediately imported into our political systems, our terminological choices and conceptual distinctions, our scientific theories and practices, our logical and mathematical toolboxes. And then it stops being philosophy.
That said, I agree with a lot of your criticisms of a lot of philosophers’ practices. They need more cognitive science and experimentalism. Desperately. But we should be a lot more careful and sophisticated in making this criticism, because most philosophers these days (even the most metaphysically promiscuous) do not endorse the claim ‘our naive, unreflective intuitions automatically pick out the truth,’ and because we risk alienating the Useful Philosophers when we make our target of attack simply Philosophy, rather than a more carefully constructed group.
LessWrong: Start tabooing the word ‘philosophy.’ See how it goes.
A major problem with modern physics is that there are almost no known phenomena that are known to work in a way that disagrees with how modern physics predicts they would work (in principle; there are lots of inferential/computational difficulties). What physics asserts about the world is, to the best of anyone’s knowledge, coincides with what’s known about most of the world in all detail. The physicists have to build billion dollar monstrosities like LHC just to get their hands on something they don’t already thoroughly understand. This doesn’t resemble the situation with philosophy in the slightest.
You’re speaking in very general terms, and you’re not directly answering my question, which was ‘what is quantum mechanics asserting about the world?’ I take it that what you’re asserting amounts to just “It all adds up to normality.” But that doesn’t answer questions concerning the correct interpretation of quantum mechanics. “x + y + z . . . = normality.” That’s a great sentiment, but I’m asking about what physics’ “x” and “y” and “z” are, not questioning whether the equation itself holds.
I’m pointing out that in particular it’s asserting all those things that we know about the world. That’s a lot, and the fact that there is consensus and not much arguing about this shouldn’t make this achievement a trivial detail. This seems like a significant distinction from philosophy that makes simple analogies between these disciplines extremely suspect.
(I agree that I’m not engaging with the main points of your comment; I’m focusing only on this particular aside.)
So your response to my pointing out that physicists too disagree about basic things, is to point out that physicists don’t disagree about everything. In particular, they agree that the world around us exists.
Uh… good for them? Philosophers too have been known to harbor a strong suspicion that there is a world, and that it harbors things like chairs and egg timers and volcanoes. Physicists aren’t special in that respect. (In particular, see the philosophical literature on Moorean facts.)
Physicists agree about almost everything. In particular, they agree about all specific details about how the world works relevant (in principle) to most things that have ever been observed (this is a lot more detail than “the world exists”).
They agree about the most useful formalisms for modeling and predicting observations. But ‘formalism’ and ‘observation’ are not themselves concepts of physics; they are to be analyzed away in the endgame. My request is not for you to assert (or deny) that physicists have very detailed formalisms, or very useful ones; it is for you to consider how much agreement there is about the territory ultimately corresponding to these formalisms.
A simple example is the disagreement about which many-worlds-style interpretation is best; and about whether many-worlds-style interpretations are the best interpretations at all; and about whether, if they are the best, whether they’re best enough to dominate the probability space. Since the final truth-conditions and referents of all our macro- and micro-physical discourse depends on this interpretation, one cannot duck the question ‘what are chairs?’ or ‘what are electrons?’ simply by noting ‘chairs are something or other that’s real and fits our model.’ It’s true, but it’s not the question under dispute. I said physicists disagree about many things; I never said that physicists fail to agree about anything, so changing the topic to the latter risks confusing the issue.
You are basically saying that physicists disagree about philosophical questions.
Is the truth of many-worlds theory, or of non-standard models, a purely ‘philosophical’ matter? If so, then sure. But that’s just a matter of how we choose to use the word ‘philosophy;’ it doesn’t change the fact that these are issues physicists, specifically, care and disagree about. To dismiss any foundational issue physicists disagree about as for that very reason ‘philosophical’ is merely to reaffirm my earlier point. Remember, my point was that we tend to befuddle ourselves by classifying issues as ‘philosophical’ because they seem intractable and general, then acting surprised when all the topics we’ve classified in this way are, well, intractable and general.
It’s fine if you think that humanity should collectively and universally give up on every topic that has ever seemed intractable. But you can make that point much more clearly in those simple words than by bringing in definitions of ‘philosophy.’
It seems that the matters you’re arguing that scientists disagree on are all ones where we cannot, at least by means anyone’s come up with yet, discriminate between options by use of empiricism.
The questions they disagree on may or may not be “philosophical,” depending on how you define your terms, but they’re questions that scientists are not currently able to resolve by doing science to them.
The observation that scientists disagree on matters that they cannot resolve with science doesn’t detract from the argument that the process of science is useful for building consensuses. If anything it supports it, since we can see that scientists do not tend to converge on consensuses on questions they aren’t able to address with science.
Agreed. It’s not that scientists universally distrust human rationality, while philosophers universally trust it. Both groups regularly subject their own reasoning faculties to tests and to distrust. (And both also need to rely at least somewhat on human reasoning, since one can only fairly conclude that a kind of reasoning is flawed by reasoning one’s way toward that conclusion. Even purely ‘empirical’ or ‘factual’ questions require some amount of interpretive work.)
The reason philosophers seem to disagree more than scientists is very simple, and it’s the same reason physicists trying to expand the Standard Model disagree more than physicists working within the Standard Model: Because there’s a lack of intersubjectively accessible data. Without such data for calibration, different theoretical physicists’ inferences, intuitions, and pattern-matching faculties in general will get relatively diverse results, even if their methodologies are quite commendable.
I think you are reading too much into my comment. It totally wasn’t about what humanity should collectively give up on, or even what anybody should. And I agree that philosophy is effectively defined as a collection of problems which are not yet understood enough to be even investigated by standard scientific methods.
I was only pointing out (perhaps not much clearly, but I hadn’t time for a lengthier comment) that the core of physics is formalisms and modelling and predictions (and perhaps engineering issues since experimental apparatuses today are often more complex than the phenomena they are used to observe). That is, almost all knowledge needed to be a physicist is the ordinary “non-philosophical” knowledge that everybody agrees upon, and almost all talks at physics conferences are about formalism and observations, while the questions you label “foundational” are given relatively small amount of attention. It may seem that asking “what is the true nature of electron” is a question of physics, since it is about electrons, but actually most physicists would find the question uninteresting and/or confused while the question might sound truly interesting to a philosopher. (And it isn’t due to lack of agreement on the correct answer, but more likely because physicists like more specific / less vague questions as compared to philosophers).
One can get false impression about that since the most famous physicists tend to talk significantly more about philosophical questions than the average, but if Feynman speaks about interpretation of quantum mechanics, it’s not a proof that interpretation of quantum mechanics is extremely important question of physics (because else a Nobel laureate wouldn’t talk about it), it’s rather proof that Feynman has really high status and he can get away with giving a talk on a less-than-usually rigorous topic (and it is much easier to make an interesting lecture from philosophical stuff than from more technical stuff).
Of course, my point is partly about definitions—not so much the definition of philosophy but rather the definition of physics—but once we are comparing two disciplines having common definitions of those disciplines is unavoidable.
I don’t think we disagree all that much; and I meant ‘you’ to be a hypothetical interlocuter, not prase. All I want to reiterate is that the line between physics and philosophy-of-physics can be quite fuzzy. The ‘measurement problem’ is perhaps the pre-eminent problem in ‘philosophy of physics,’ but it’s not some neoscholastic mumbo-jumbo of the form “what is the true nature of electron?”. Rather, it’s a straightforward physics problem that happens to have turned out to be especially intractable. Specifically, it is the problem that these three propositions form an inconsistent triad given our Born-probabilistic observations:
(1) Wave-function descriptions specify all the properties of physical systems.
(2) The wave function evolves solely in accord with the Schrödinger equation.
(3) Measurements have definite outcomes.
De-Broglie-style interpretations (‘hidden variables’) reject (1), von-Neumann-style interpretations (‘objective collapse’) reject (2), and Everett-style interpretations (‘many worlds’) reject (3). So far. there doesn’t seem to be anything ‘unphysical’ or ‘unphysicsy’ about any of these views. What’s made them ‘philosophical’ is simply that the problem is especially difficult, and the prospects for solving it to everyone’s satisfaction, by ordinary physicsy methods, seem especially dim. So, if that makes it philosophy, OK. But problems of this sort divide philosophers because they’re hard, not because philosophers ‘trust their own rationality’ more than physicists do.
I find it a bit tricky to formulate problems in propositions like yours (1) - (3) and insist that at least one must be rejected because of mutual inconsistency. The problem is that the meaning of the propositions is not precise. What exactly does “all properties of physical systems” denote? Is it “maximum information about the system that can be obtained in principle” (subproblem: what does “in principle” mean), or is it “information sufficient to predict all events in which the system is involved, if there is no uncertainty external to the system involved”, or is it something else?
We know that the conditions under which we prepare the system can be summarised in a wave function and we know how to calculate the frequencies of measurement outcomes, given a specific wave function. We know that the knowledge of wave function doesn’t let us predict the measurements with certainty. We even know, due to Bell’s inequalities and the experimental results, that if there is some unknown property of the system which determines the measurement outcome prior to actual measurement, then this property must be non-local. We know that the evolution of systems under observation isn’t described by Schrödinger equation only. All this is pretty uncontroversial.
Now the interpretations tend to use different words to describe the same amount of knowledge. Instead of saying that we can get unpredictably different outcomes from a measurement on a system with some given wave function, one may say that the outcome is always the same but our consciousness splits and each part is aligned only with a portion of the outcome, or one may say that the outcome is not “definite” (whatever it means). This verbal play is the unphysicsy thing with the given propositions.
You seem to be trying to explain something rather clear with something less clear. The sentence in question is simply affirming that the wave function captures everything that is true of the system; thus (if you accept this view) there are no hidden variables determining the seemingly probabilistic outcomes of trying to measure non-observables. There’s nothing mysterious about asserting that there’s a hidden cause in this case, any more than science in general is going Mystical when it hypothesizes unobserved causes for patterns in our data.
To say that the outcome is not “definite” is to say that it is false that a particular measurement outcome (like ‘spin up’), and not an alternative outcome (like ‘spin down’), obtains. “Definite” sounds vague here because the very idea of “many worlds” is extremely vague and hard to pin down. One way to think of it is that the statistical properties of quantum mechanics are an epiphenomenon of a vastly larger, unobserved reality (the wave function itself) that continues merrily on its way after the observation.
Where’s the ‘verbal play’?
Say there are no hidden variables and the evolution is probabilistic. Does then the wave function capture everything that is true of the system? It seems to me that it doesn’t: it is true that the system will be measured spin up in the next measurement, but the wave function is as well compatible with spin down. But you seem to assert that if I don’t believe in hidden variables then the wave function does capture everything that is true of the system. Thus I don’t find it rather clear. Neither does “epiphenomenon of a vastly larger reality” seem clarifying to me even a little bit.
At a given time, yes. But over time, the way a wave function changes may (a) be determined entirely by the Schrödinger equation, or (b) be determined by a mixture of the Schrödinger equation and intermittent ‘collapses.’ Given (a), the apparently probabilistic distribution of observations is somehow mistaken, and we get a many-worlds-type interpretation. Given (b), the probabilities are preserved but the universe suddenly operates by two completely different causal orders, and we get an ‘objective collapse’ interpretation. These are the two options if the wave function captures all the variables.
I am now interested in clarification of “everything that is true of the system”. I have an electron whose spin I am going to measure five minutes from now. Does the proposition “the spin will be measured up” belong to “everything that is true about the electron”? Presume that the spin will indeed be measured up (or I will perceive the world in which it was up or whatever formulation will suit you the best). To me it appears as a true proposition, but there may be philosophical arguments to the contrary (problem of future contingents comes to mind).
Physics-inclined people tend to be 4-dimensionalists, so I don’t think they’ll object to describing wave functions in terms that account for them at all times. Even indeterminists (i.e., collapse theorists) can accept that we can talk about what will be true of electrons in the future, though we can’t even in principle know some of those facts in advance.
de Broglie sez: “Yes, that belongs to everything that is true (about the electron’s wave function). But at least one truth about the electron (its position at any given time) is not accounted for in the wave function. (This explains why the Schrödinger equation, although a complete description of how wave functions change, is not a complete description of how physical systems change.)”
von Neumann sez: “Yes. And the wave function encompasses all these truths. But there is no linear dynamical equation relating all the time-slices of the wave function. There are more free-floating brute facts within wave functions than we might have expected.”
Everett sez: “Yes… well, sort of. The formalism for ‘the spin will be measured up’ is a component of a truth. But it would be more accurate and objective to say something like ‘the spin will be measured up and down’ (assuming it was in a prior superposition). Thus the wave function encompasses all the truths, and evolves linearly over time in accord with the Schrödinger equation. Win-win!”
Why exactly? I mean, there is no controversy in mathematics about whether 2+2=4, and yet we continue teaching this knowledge in schools. Uncontroversial, yet necessary to be taught, because humans don’t get it automatically, and because it is necessary for more complicated calculations.
Why exactly don’t philosophers do an equivalent of this? It is because once a topic has been settled at a philosophical conference, the next generations of humans are automatically born with this knowledge? Or at least the answer is published so widely, that it becomes more known than the knowledge of 2+2=4? Or what?
First approximation: Pretended ability to make specific conclusions concerning ill-defined but high-status topics. :(
Yes, and we continue teaching modus ponens and proof by reductio in philosophy classrooms. (Not to mention historical facts about philosophy.) Here we’re changing the subject from ‘do issues keep getting talked about equally after they’re settled?’ to ‘do useful facts get taught in class?’ The philosopher certainly has plenty of simple equations to appeal to. But the mathematician also has foundational controversies, both settled and open.
So if I pretend to be able to make specific conclusions about capital in macroeconomics, I’m doing philosophy?
Really? Can you name a few philosophical questions whose answers are uncontroversial?