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© 2024. All rights reserved.
Site created with
Hakyll.
Modified theme
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based on
Lanyon.
Niels Bohr wasn’t a philosopher by trade, but he was an exemplar of a scientist who approached his scientific practice in a reflective and philosophical fashion. Bohr’s work in physics was driven by philosophical vision; and what he learned by doing physics fed back into his worldview. Most notably, Bohr frequently referred to “the epistemological lesson of quantum physics”. Whether or not we agree with Bohr about what the philosophical lessons of quantum physics are,1 surely we can admire his attempt to align his worldview with the deliverances of the empirical sciences. In short, Bohr committed his life to science, and he developed a philosophy of life that was in harmony with that commitment.
While we want to understand what Bohr’s “philosophy” was, it has not proven helpful to try to put Bohr into the classificatory boxes that analytic philosophers have created. For example, it’s hardly interesting to ask whether Bohr was a “realist” or “antirealist” if philosophers cannot make up their mind about what those words mean.2
Niels Bohr thought hard about the foundations of quantum theory for fifty years. He traded ideas with the greatest minds of the times, often dealing with severe criticism. Nonetheless, these days, discussions of the foundations of quantum theory often begin with dismissive phrases such as “we won’t consider the Copenhagen interpretation”.
Let’s set aside the fact that the “Copenhagen interpretation”, as it emerged after World War II, is hardly what Niels Bohr was pushing for.3 Why should we not consider the view of one of the main players in the development of quantum physics — and, admittedly, the most philosophically reflective of those players? Could we please have a hint about the basic mistake or misconception in Bohr’s point of view? Where does he go wrong? Adding some citations, to substantiate the attribution of a view to Bohr, would just be icing on the cake.
Sarcasm aside, we were trained to think that it takes some work to figure out what the good ideas are. We were also trained to read charitably, paying attention to context and linguistic subtleties. Bohr has not received much of this kind of careful reading in recent years, so it seems that somebody ought to do it.4
Bohr also opined on some of the biggest questions in philosophy — e.g. free will, the aims of science, etc. Surely it could be interesting to learn what he thought about such topics.
A good tree cannot bring forth evil fruit; neither can a corrupt tree bring forth good fruit. Wherefore by their fruits ye shall know them. (Matthew 7)
There are some decent books out there about Niels Bohr’s philosophy — by Murdoch, Honner, Folse, and Faye, among others. But what is a person’s philosophy? Let’s distinguish two ways of thinking about it, with reference to a famous philosopher (David Lewis) and a fictional character (Mette the banker).
David Lewis had philosophical views about many things, including things that 99% of human beings never think about. Lewis had views about whether numbers exist. He also had views about what the laws of nature are. And he believed that there are other complete universes that actually exist. The list could go on and on and on. Lewis was a person with a system of well-articulated metaphysical views.
In contrast to David Lewis, Mette the banker has never heard about the thesis of Humean supervenience. If asked whether she believed whether Humean supervenience is true, she would be puzzled by the question. If you spelled it out in detail for her, she might say that she hadn’t thought about it, and couldn’t see what difference it would make. That’s the key phrase there: “what difference it would make”. Mette is not a logical positivist, and she is not claiming that Humean supervenience is unverifiable and hence meaningless. What she is saying is that she can’t immediately imagine any future choice where what she chose would depend on her belief (or disbelief) in Humean supervenience. Mette doesn’t see how the question connects into her agency.
This doesn’t mean that Mette is an unreflective person. In fact, Mette might spend a lot of time thinking about the meaning of life and what’s important to her. She might wonder whether it’s rational to believe in God, or whether democracy is an ideal form of government. What she reflects upon is very likely connected to the choices she has to make in life, e.g. about whether to attend church, or who to vote for in the next election.
We claim that Niels Bohr is like Mette, only the choices he had to make in life often related to his practice as a scientist and as an administrator of a scientific institute. Bohr was faced with decisions about which papers to write, which calculations to perform, whom to hire as a postdoc, etc. Some metaphysical, epistemological, and ethical issues were of direct importance for Bohr’s scientific practice; but some of the more abstruse metaphysical issues surely were not. In fact, Bohr seems simply to have been agnostic about some of the issues that exercise today’s metaphysicians and philosophers of science.
So we claim that Bohr did have a philosophy — it’s just that having a philosophy is not the same as having a metaphysical system.
Q: Did Bohr think that the wavefunction collapses upon measurement?
Bohr never says that the wavefunction collapses upon measurement. However, he does say that the very notion of a system’s state makes sense only in the idealization where the system is not under active observation. [add citation!]
Based on a 1990s classification of interpretations of QM, Bohr then adopts a “no collapse” interpretation.
Update: There is some new textual evidence that suggests that this issue is more nuanced.
Q: Did Bohr think that the world is split into two parts — a quantum part and a classical part?
No, not really. Or more accurately: no, not ontologically. Bohr says explicitly that the entire world is quantum, including the measuring devices we use to probe the quantum world. Nonetheless, Bohr says that the goal of physics is to produce objective descriptions, and that such descriptions ultimately bottom out in the words of everyday language such as “here” or “there”.
(Camilleri and Schlosshauer 2015) describe Bohr’s view in a clarifying way: the measuring device is described from a functional point of view.
for Bohr, such a cut [between measuring apparatus and observed quantum system] did not originate in dynamical (ontological) considerations, but rather in functional (epistemological) considerations.
I think that’s almost right, but I would say that the measuring device is used to describe something else — not that it is being described. The cut isn’t in the object being described, it is between the subject and the object.
There are interesting connections between Bohr’s discussion of the role of measuring devices and Einstein’s discussion of clocks and rods — e.g. in “Geometry and experience” (Einstein 1921). Einstein notes that clocks and rods must themselves obey the laws of relativity. But if, e.g., a rod is bent by gravitational force, how can it be the standard for straightness of other rods?
The years 1900 to 1930 were an extraordinary time in physics and much has been written about it — by historians of science and philosophers, as well as by popular science writers. (Jammer 1966)
The Niels Bohr Archive in Copenhagen prepared a thirteen volume set of Niels Bohr’s Collected Works.
A few books have been written before about Bohr’s philosophical outlook: (Murdoch 1987; Meyer-Abich 1984; Faye 1991; Favrholdt 2009). The book by Favrholdt is unfortunately unavailable in English, but it comes the closest to “getting into Bohr’s head”, from a philosophical point of view. Favrholdt was convinced that Bohr was one of the most interesting and innovative philosophers in history.
(Pais 1991) is the only real biography of Niels Bohr in English. (There is an old biography by Ruth Moore, but it doesn’t pretend to go deep into Bohr’s way of thinking.) In German, there is a biography by Röseberg (Röseberg 1992).
Many contemporary philosophers look to physics primarily for ontological lessons, i.e. lessons about what exists and how it moves. The assumption seems to be that questions about our epistemological situation are of secondary importance, or ought to be answered by the complete theory of the physical world. It’s an old philosophical dilemma: should we first produce a theory of what there is and then figure out what we’re capable of knowing, or should we first figure out what we’re capable of knowing and then produce a theory of what there is?↩︎
By some standards, Bohr was clearly a scientific realist. For example, he says that the existence of atoms and their parts has clearly been demonstrated. By other standards, Bohr was clearly a an antirealist. For example, he says that it’s impossible to achieve a God’s eye view of reality. (Bernard Williams indicates in a few places that if you don’t believe that science can provide the “absolute conception”, then you’re not a realist.)↩︎
(Howard 2004; Camilleri 2009)↩︎
All credit to the pioneers who tried to make sense of Bohr’s ideas long before it was cool to do so: Don Howard, Henry Folse, and Jan Faye, among a few others. Credit also to those who have contributed new insights in recent years: Scott Tanona, Kristian Camilleri, Guido Bacciagaluppi, and Michael Cuffaro, among a few others.↩︎