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The cathedral in Barcelona, a grand old lady. View in LinkedIn

THE STRETCH. “Our washing up is just like our language. We have dirty water and dirty dishcloths, And yet we manage to get the plates and the glasses clean. In language too, we have to work with unclear concepts and form a logic whose scope is restricted in an unknown way, and yet we use it to bring some clarity into our understanding of nature.” (Neils Bohr, page 4) https://lnkd.in/d_2R77E View in LinkedIn

EIGENSTATES. “Decoherence is a process that rapidly puts macroscopic objects (including tiny ones such as dust particles) that interact with their environment (even very slightly, such as with the microwave background radiation) into mixtures, whose components are, in typical cases, approximate position eigenstates. The process diffuses the interference terms characteristic of the macro-object’s initial superposition into the environment, so that its statistical behaviour is as if it is in a mixture—and a mixture of states that have definite values for familiar quantities like position, or quantities very ‘close’ to those like position.” https://lnkd.in/dMm_YkR View in LinkedIn

THE FOOTNOTE. “Decoherence is an important aspect of quantum theory’s ‘recovery’ of a classical realm.” https://lnkd.in/dMm_YkR View in LinkedIn

OTHER ISSUES. “But there are many interpretative issues about quantum theory, such as entanglement and non-locality, which we need not engage here.” https://lnkd.in/dMm_YkR View in LinkedIn

ONLY DEFINED BY RELATION. “So much the worse, it seems, for the relationist tradition, stemming from Leibniz through Berkeley and Mach, of denying that space, time (and space-time), and their parts, are objects; and of conceiving them instead as a system of spatiotemporal relations between bodies. For the bodies have become diaphanous and omnipresent fields, which are themselves complicated structures of properties and relations among spacetime points.” https://lnkd.in/dMm_YkR View in LinkedIn

SPACETIME AS OBJECTS. “And so it is natural to presume that all these are to be construed as properties of (and relations between) points, or higher-order properties and relations. In short, we arrive at the doctrine now called ‘substantivalism’: that spacetime points are genuine objects, indeed are the basic objects of physical theory.” https://lnkd.in/dMm_YkR View in LinkedIn

THE CHRONOGEOMETRY OF REALITY. “In short, the effect has been for matter to now play second fiddle to space and time. As these field theories, both classical and quantum, are presented to us, their basic objects seem to be just spacetime points. All else—matter, fields, and even the metrical structure of spacetime, the ‘chronogeometry’ of the world—are represented as mathematical structures defined on these points; in particular, as just emphasised, physical quantities for matter and fields are represented by structures defined point by point.” https://lnkd.in/dMm_YkR View in LinkedIn

TRANSMOGRIFICATION. “Furthermore, this assimilation of matter to the concept of a field continued with quantum theory. Even elementary quantum theory has a formulation (wave mechanics) which can be thought of as a field theory. And this picture deepens with the advent of quantum field theory: here physical quantities describing matter are again represented by a field; albeit in a transmogrified form in which an operator (rather than a simple real number) is associated with each space, or space-time, point.” https://lnkd.in/dMm_YkR View in LinkedIn

TIME IN QUANTUM GRAVITY. “On the other hand, the problem of time is about ‘finding’ a time in quantum gravity theories: and so not, in the first instance, about finding some kind of classical limit of, or classical approximation to, such theories.” https://lnkd.in/dMm_YkR View in LinkedIn