There is a bit of an online dust-up going on in the physics world. Personalities plus disagreements about research and theory, all done in public? I’m glad it’s not just anthropology…
I read this morning Skulls in the Stars’ post on the controversy, as well as on quantum theory and the Pauli exclusion principle more generally – Pauli, “armchair physicists”, and “not even wrong”. I really enjoyed the clear description of quantum theory, and how physicists deals with understanding the quantum world in both conceptual and empirical fashion.
And I’m going to jump in and do some armchair comparing of quantum physics and culture theory. A bit of a thought experiment, which is just the sort of thing blogs can be useful for doing. The last comparison of anthropology and physics – Anthropology, Science and Relativism – where I drew some parallels between relativity and relativism got plenty of people worked up, that’s for sure.
The parallel I want to draw today is between understanding particles as both individuals and part of larger dynamics, and culture theory, which also has individuals and larger dynamics. I think there are some interesting implications for how we try to measure culture, and also how we understand the role of local properties and dynamics in producing cultural outcomes.
Here’s an initial key part:
How do we explain that individual electrons act like particles but many electrons act like waves? The conventional interpretation is known as the Copenhagen interpretation, and was developed in the mid-1920s. In short: the wavefunction of the electron represents the probability of the electron being “measured” with certain properties. When a property of the electron is measured, such as its position, this wavefunction “collapses” to one of the possible outcomes contained within it. In the double slit experiment, for instance, a single electron (or, more accurately, its wavefunction) passes through both slits and has a high probability of being detected at one of the “bright” spots of the interference pattern and a low probability of being detected at one of the “dark” spots. It only takes on a definite position in space when we actually try and measure it.
So, culture theory and measurement? I think this is one of the major problems facing culture theory today, and is particularly apparent in lots of social psychology and epidemiological research. We measure individuals, and thus get a definite positions, but haven’t really figured out well how to measure the properties, even though as anthropologists we generally have a lot theoretical and empirical (through ethnography) insight into those properties.
The next part is on the properties of fields.
If the electric field of one photon is oscillating horizontally the other must be oscillating vertically, and vice-versa. However — and this is the important part — nothing distinguishes between the two photons on creation, and nothing chooses the polarization of one or another. Just like the position of the electron in Young’s double slit experiment is genuinely undetermined until we measure it, the polarization of the photons is undetermined until we make a measurement. Nevertheless, there is a connection between the two photons: we don’t know which one has which polarization, but we know for certain that the polarizations are perpendicular.
Here a key difference emerges, since historical and social forces do play a tremendous role in distinguishing which people end up where. But at the same time, I find it striking how the concept of polarization (an organizational property) is what organizes the field, and that it has certain consistent dynamics. And, again, that can be represented visually and theoretically, and then confirmed with measurements.
Next, the issue of entanglement. The photons demonstrate these sorts of properties because the “photons are said to be entangled; though their specific behavior is undetermined, the physics of their creation still forced a relationship between the two.” The piece then goes into the spookiness of entanglement at a distance – reminiscent to me of debates about globalization as a force, creating entanglements locally yet somehow connecting everyone too. In physics, this dilemma seems to be resolved by considering issues of separation in space, physical boundaries, and from there, whether relative position is more important than overall entanglement. For electrons on opposite sides of the universe, and people on opposite sides of the globe, relative position might be the more relevant approach.
But at a local level, things are more interesting. Things get distributed in local space in more specific ways, rather than ending up all the same.
The wave nature of matter also raises a new problem: electrons are now somewhat “squishy”! In larger atoms with multiple electrons orbiting the nucleus, it was readily found that only a finite number of electrons can fill each orbital position/energy level. One is naturally led to wonder why all the electrons don’t just fill the lowest energy state of the atom, the “n=1″ state; because the electrons are wavelike and “squishy”, there doesn’t seem to be anything prohibiting this.
This was one problem that Wolfgang Pauli (1900-1958) concerned himself with. The answer he developed became known as the Pauli exclusion principle: no two identical fermions can occupy the same quantum state. ”Fermions” include electrons, protons and neutrons: the constituent parts of ordinary matter…
The electrons in a piece of bulk material are all “squashed together”, just like the multiple electrons in a complex atom are all squashed together. In an individual atom, the electrons must stack up into the different quantum states (different energies, different spins) that are permitted by the electron/nucleus interaction. In a bulk piece of crystal, a similar argument applies: there are a large number of permissible quantum states allowed, in which electrons are “spread out” over the size of the crystal; Pauli’s principle indicates that each electron must be in a different state, and they end up filling a “band” of energies.
Culture theory also deals with this sort of problem. From an older uniform view of culture, where everyone in a group had “the culture,” we’ve come to realize that there is distribution in knowledge, social position, gender, and the like. People get squashed together, and because of historical pathways and the local dynamics/properties of culture, get differentially situated. In other words, they literally end up as different individuals.
Just a thought for the day. Now go measure some squishy properties… Or at least read Dr. SkySkull’s fascinating post on quantum physics.