Karen Barad’s monumental book “Meeting the Universe Halfway” (subtitle: “Quantum physics and the entanglement of matter and meaning”, Duke University Press, 2007) currently receives more than 2700 citations per year (according to google scholar). That’s more than all my publications have received altogether over the years. Reason enough to read the book that promises a unified framework to think about quantum physics, philosophy, gender studies, ethics and more. Here is my review of it.

---

Imagine it’s late evening and after some energizing dinner with your best friend you decide to grab a beer in a bar around the corner. The beers come, and you quickly settle on one of these fundamental debates about what comes first: mind (idealism) or matter (materialism)? theory or experiment? wave or particle? culture or science? After the third beer you arrive at the chicken-or-egg dilemma, and the evening continues…

Who doesn’t remember such a situation and finds themselves in a position strongly arguing in favour of one of the two alternatives? But what if these questions are misconceived, and there is actually a third position? A position that shows that the “or” in these questions is not an “exclusive or” (XOR), a position that argues that neither of the two alternatives can stand alone, that they are somehow inseparably entangled, a position somewhere halfway in between. This is, loosely speaking, the main message of Karen Barad’s 500 pages book, which I’ve read around a year ago (skipping chapters 5 and 6).

Karen Barad’s philosophy-physics

The general philosophy of the book is guided by the ambition to dispose of binary thinking in many important questions, from the foundations of quantum physics, over the philosophy of science, to the generation of meaning in contemporary social debates. Instead of thinking that one of the two alternatives comes first or is primary, Barad argues that they are mutually co-constitutive: one can not exist without the other because each half gives meaning to the other half only in a joint, inseparable context. Barad calls these contexts phenomena.

And Barad doesn’t shy away from explicating their approach in detail to quantum physics, which also has a famous chicken-egg dilemma known as the measurement problem or, more broadly speaking, how to separate the observer from the observed system. Barad calls into question whether there is any such clean a priori separation and introduces the novel terminology “intra-action” instead of interaction to make this point clear. What does this mean?

The standard physicists way of thinking goes as follows: there exist various individual systems (electrons, atoms, cats, detectors, humans, etc.) and they can “talk to each other” via an interaction. But what if it is only the interaction that gives these individual systems any meaning in the first place? Indeed, without interaction two systems would be decorrelated forever, and, for example, neither the observer could claim to have “observed” anything nor would the system exist for that observer. Hence, Barad suggests to invert the logic and to put interaction—or now: intra-action—first. While intra-actions always combine entities into something larger, the right intra-action (as in an experiment) also allows to draw a boundary between them by giving each individual system meaning in relation to the other. This generation of a boundary and creation of meaning is called an agential cut by Barad.

From the fact that observers (including humans) are a part of the world they seek to understand, that they are co-constitutive for the phenomena that happen, Barad deduces that observers also have an ethical responsability for the world. That is, ethical responsability is not something optional that comes from reflecting over the right response to external circumstances—instead, ethical responsability is an unavoidable consequences of our entanglement with the world, of having only an inside perspective.

Fun anecdotes

The local hero of Barad’s book is Niels Bohr, the famous physicist known for proposing the first quantized model of the atom, the (infamous) Copenhagen interpretation of quantum physics, and almost endless debates with Einstein about its meaning. For Niels Bohr physics and philosophy were inseparable, and individual quantum systems had no ontological pre-existing properties without specifying an experimental context. That is, using our above terminology, the basis of Bohr’s ontology are phenomena that create the meaning for individual objects via intra-actions. All this, of course, resonates very well with Barad’s point of view, who extensively refers to and cites Niels Bohr, but corrects him by allowing phenomena, intra-actions and the creation of meaning also between inanimate objects (for Bohr humans stood out).

Barad’s book also contains a bunch of interesting historical anecdotes, perhaps worthy mentioning in a standard quantum mechanics curriculum. For instance, did you know that Heisenberg’s famous paper about his uncertainty relation contains an addendum, where, following a discussion with Bohr, he admits that he “overlooked essential points”? Indeed, in Heisenberg’s original view a quantum particle has a position and momentum that is, however, epistemologically not accessible to us humans because of some inevitable measurement disturbance. Instead, Bohr understands Heisenberg’s relation in ontic terms (and publishes his mathematically equivalent complementary relations in the same year): as a matter of fact a simultaneously determinate position and momentum simply does not exist (and as a consequence can also not be measured).

Another (to me unknown) anecdote refers to the Stern-Gerlach experiment. Usually, students are taught that this experiment was conducted to determine the spin of an electron, but this interpretation was given to it only three years later. Originally, Stern and Gerlach wanted to find out whether Bohr’s atom model is true and whether space itself is quantized (Bohr’s atom model predicts that electrons can only move on certain fixed orbits around the nucleus whereas they are forbidden to be somewhere in between the orbits). Perhaps the experimental findings of Stern and Gerlach would have never been published if they hadn’t fitted this other interpretation as well. What a lucky coincidence. Moreover, if Stern was not so poor and could only afford cheap cigars, they would never have even seen anything in the experiment. Sounds unbelievable? Well, I leave this as a teaser for you…

My opinion

I have much sympathy for the picture that Barad is painting. After all, the reason why there are endless debates about these yes-or-no, mind-or-matter, chicken-or-egg questions is, perhaps, that they are not resolvable using binary thinking, that this single-concept-superiority and the-winner-takes-it-all approach is detrimental for science and society. So, we should overcome it.

I also have to praise the book for its exposition of quantum physics to a broad audience (physicists are only one but not the main target audience of the book). Barad manages to do the seemingly impossible: to describe quantum physics (including state-of-the-art experiments) in an understandable way with almost no equations but without leaving out the details. I’ve certainly not seen such a description before.

However, there are also things I didn’t like. Let’s start with a criticism of the presentation:

• Even some of the 5-star ratings on Amazon will tell you that the book is very repetitive. While a certain amount of repetitiveness is helpful from a pedagogical perspective, in particular if one looks at a problem from many different angles as Barad does (or diffracts about the problem in their language, in contrast to reflecting about it), at some point it no longer helps to repeat the same points over and over again, in particular if they are repeated with more or less exactly the same words.
• While Barad did an insane job to explain quantum physics to non-physicists, she does a poor job to explain all this philosophy slang to non-philosophers. So, if you can not fluently distinguish between realism, positivism, naturalism, representationalism, materialism, instrumentalism, (post)structuralism, (post)humanism, etc. you might feel embarrassed at various points. My favourite wording is still “material discursive practices”. Until today I do not understand what this means (and not even what it not means).

Turning to the actual content, I criticize Barad for never attempting to develop a quantitative account of their theory. For instance, while I agree with Barad that observers or agencies shouldn’t be limited to humans, it remains totally unclear at which scale these “phenomena” manifest and at which point one can apply this “agential cut” (is a bacteria or a grain of sand sufficient? is this cut enacted by scale, mass, energy, entropy, complexity?). The only thing that Barad tells you is the following:

This cut […] is determined by the specific experimental arrangement, or material configuration.

(p. 337)

I promise it doesn’t get more quantitative than that.

Also their resolution of the quantum measurement problem can hardly count as a resolution in my view. To be clear, the quantum measurement problem requires one to explain not only why a coherent quantum superposition effectively behaves like a classical mixture or ensemble, but also why we only experience single, seemingly random measurement outcomes compatible with Born’s rule. While Barad seems to be well aware of that problem, she has nothing to offer here. All what they say is the following:

This agential separability is an unambiguous resolution of the ontological indeterminacy within the phenomenon. And this is precisely the insight we need to resolve the paradox.

Suppose we could ‘peek’ insight a phenomenon. What would we see? If we were to peek inside the phenomenon, we would find that the mark the ‘object’ makes indicates a specific definite value of the property being measured. […] This is precisely what we do when we perform a measurement—we are ‘peeking’ inside a phenomenon.

(p. 345, italics in original)

Note that Barad emphasizes that “there is no ‘collapse’” (also p. 345), but the only mentioning of Everett’s many worlds interpretation is degraded to a mere citation among many possible interpretations of quantum mechanics on page 287. Perhaps it is this “resolution” of the measurement problem why one barely finds any physicist among the 20,000+ citations?

Should you read the book?

If you are physicist who wants to get familiar with the foundations of quantum mechanics, philosophy and the ontology of the world, then you should give it a try. It is a demanding book, but it is definitely a book you can engage and grow with and learn from. Furthermore, if you are a philosopher who wishes to get acquainted with quantum physics, this book might be your first choice. If you are a physicist who has already a strong background in quantum foundations, you might be disappointed at the end, even though it is more than worth to consider Barad’s overall positions. If you are none of the above, I can’t tell you what to do.

---

Karen Barad (born 1956) is a distinguished professor of feminist studies, philosophy, and history of consciousness at the University of California at Santa Cruz. They did a PhD in theoretical physics about “Fermions in Lattice Gauge Theories” in 1984.