Barad's Chapter 7 really is good, and I have now investigated in more detail. Take the quantum eraser experiments, for example (310F). It starts by considering the peculiar behaviour of particles when detectors are switched on and off as a kind of disturbance, not a structured interference, but this could be tested by switching off the detector and thus undoing the pattern that was produced. One possibility is that when we switched off the detectors, the original information might return. We can now actually do a more rigourous experiment, however, not only erasing, but even doing so 'after the atom has passed through the slits and registered its mark on the screen' (311) waiting until the atom has gone through the entire apparatus before we switch off which path information. Astonishingly, the original interference pattern can be retrieved. We have to think what happens when we have apparently erased information. The original apparatus recorded which path information by letting an atom passed through a double slit and then recording the traces left in either the upper or lower cavity (a trace in the form of a 'tell-tale photon', designed to remove the human observer). We can modify this by replacing the wall between the cavities with a 'photo detector – shutter system' — a photodetector is shielded from exposure to either cavity by putting shutters in front of it, closing the shutters to block the photodetector. Apparently, this also preserves the photon in the cavity, I think because the photodetector will absorb the photon. If this is so, and we open both shutters, a photon in a particular category will be absorbed by the detector and thus we will lose information about whether there is a photon in a cavity or not — 'the which path information is thereby "erased" (there is a nice diagram on page 314). If we close both the shutters we get a curved trace representing a 'full set of data points', corresponding to a state in which all which path information has been erased, bringing together those cases where photons have been raised, and those cases where they have not entered a cavity in the first place. When we reinstate shutters, however we get a different pattern, in effect two separate curves, one where we do have which path information and those where we don't: in effect, the curve in the first case is decomposed into two components (interesting shape for these two curves and the way they're superimposed implying that peaks in one curve are smoothed out by troughs in the other until we get the familiar bell-shape). If we look just at the curve produced when the which path information was raised we still see an interference pattern (lots of peaks and troughs), just as predicted by Bohr. Bohr himself never actually saw this experiment, but we can reconstruct his explanation by tracing an essay in which he says the system has not been mechanically disturbed but there has been some influence on 'the conditions which define the possible types of predictions regarding the future behaviour of the system' (313) we need to examine the whole phenomenon, 'the entire experimental system' in the words of some later physicists. Another experimental group has claimed that their results '"corroborate Bohr's view that the whole experimental setup determines the possible experimental predictions' (315). For Barad, this shows that 'the objects and the agencies of observation are inseparable parts of a single phenomenon', atoms are not separate individual objects, nor is the detecting system. The confusion arises from an approach that tries to separate these elements out from the phenomenon which has 'ontological priority'. Any other explanation will result in 'an utter mystery'. Nor is there any need for action at a distance between individual particles. Barad wants to generalise and say that '[all] space and time are phenomenal, that is, they are interactively produced in the making of phenomena; neither space nor time exist as determinate givens outside of phenomena' (315) [one thing springs to mind for me. What would happen if we kept adding bits of apparatus, another laser perhaps, or if we did the experiment in space. The laboratory set up seems to carefully exclude a lot of variables as well, presumably by sticking it all in a Faraday cage, for example, because that would produce what would be agreed to be distortions? This is the boundary problem?] It is an old metaphysics that sees this as a problem of instantaneous communication, which depends on there being individual entities from the outset. This experiment therefore calls into question those basic assumptions. In each case, we have 'inseparable parts of a single phenomenon', not individuals with fixed spatial positions. Instead '"individual" is ontologically and semantically indeterminate in the absence of an apparatus that resolves the inherent indeterminacy' (316) similarly, mysteries arise if we are working with conventional notions of space time and matter, an individualist notion in particular that suggests that objects occupy single positions in space and time. Earlier interpreters necessarily referred to erasure of memories of passage, and the recovery of earlier information. But technically, we have not recovered the original but observed 'the new interference pattern' produced by apparatus that now includes photo detection. It's not that the memory of the event has been erased. Instead, the memory is held in the phenomenon and that modifies the apparatus. [absolutely astonishing claim, equally mysterious to me]. Overall, the argument is that time space and matter are phenomenal, integral parts of phenomena and that interactive practices can be iterative when they constituting phenomena. Thus past and future are 'iteratively reconfigured and enfolded through one another' (316) and phenomena should be seen as 'material entanglements that "extend" across different spaces and time' (317) [very strange 'material' indeed, that now includes memory and permits iteration]. Overall, Bohr's central notion of indeterminacy is confirmed and demonstrated by this experiment.