Bohr’s quantum postulate and time in quantum mechanics

In this paper I shall consider the concept of time used in the quantum theory from the perspective of Bohr’s ideas as presented in what he called the quantum postulate and some of its consequences. In particular, Bohr’s views on the role of the experimental arrangement that defines the context in which we can consider the state of the quantum system to be defined – and the related interpretation of the quantum wave function –, enables a view on the time concept being used in the theory that makes compatible the discontinuous changes in individual physical systems with a continuous description in time of the behavior of an ensemble of systems. A crucial aspect will be to show that Bohr’s ideas are coherent with the use of an external classical time

The relation between classical and quantum electrodynamics

In this article it is presented the idea that quantum electrodynamics presents intrinsic limitations in the description of physical processes that makes it impossible to recover from it the type of description we have with classical electrodynamics. In this way I cannot consider classical electrodynamics as reducing to quantum electrodynamics and being recovered from it by some sort of limiting procedure. Quantum electrodynamics has to be seen not as an independent theory but just as an upgrade of classical electrodynamics and the theory of relativity, which permits an extension of classical theory in the description of phenomena that, while being clearly related to the conceptual framework of the classical theory – the description of matter, radiation, and their interaction –, cannot be properly addressed from the classical theory

The Dirac equation, the concept of quanta, and the description of interactions in quantum electrodynamics

In this article the Dirac equation is used as a guideline to the historical emergence of the concept of quanta, associated with the quantum field. In Pascual Jordan’s approach, electrons as quanta result from the quantization of a classical field described by the Dirac equation. With this quantization procedure – also used for the electromagnetic field – the concept of quanta becomes a central piece in quantum electrodynamics. This does not seem to avoid the apparent impossibility of using the concept of quanta when interacting fields are considered together as a closed system. In this article it is defended that the type of analysis that leads to so drastic conclusions is avoidable if we look beyond the mathematical structure of the theory and take into account the physical ideas inscribed in this mathematical structure. In this case we see that in quantum electrodynamics we are not considering a closed system of interacting fields, what we have is a description of the interactions between distinct fields. In this situation the concept of quanta is central, the Fock space being the natural mathematical structure that permits maintaining the concept of quanta when considering the interaction between the fields

Time in the theory of relativity: on natural clocks, proper time, the clock hypothesis, and all that

When addressing the notion of proper time in the theory of relativity, it is usually taken for granted that the time read by an accelerated clock is given by the Minkowski proper time. However, there are authors like Harvey Brown that consider necessary an extra assumption to arrive at this result, the so-called clock hypothesis. In opposition to Brown, Richard T. W. Arthur takes the clock hypothesis to be already implicit in the theory. In this paper I will present a view different from these authors by recovering Einstein's notion of natural clock and showing its relevance to the debate

The renormalization of charge and temporality in quantum electrodynamics

In this article it is intended a closer look at the renormalization procedure used in quantum electrodynamics to cope with the divergent integrals that appear in higher-order calculations within the theory. The main focus will be the charge renormalization that reveals, in a clearer way than the mass renormalization, structural limitations present in quantum electrodynamics that are even more aggravating than the ones usually pointed at when considering the renormalization procedure. In this way we see that the possibility of charge renormalization is due to limitations of the theory in the temporal description of the interactions

Life history and mating systems select for male biased parasitism mediated through natural selection and ecological feedbacks

Males are often the "sicker" sex with male biased parasitism found in a taxonomically diverse range of species. There is considerable interest in the processes that could underlie the evolution of sex-biased parasitism. Mating system differences along with differences in lifespan may play a key role. We examine whether these factors are likely to lead to male-biased parasitism through natural selection taking into account the critical role that ecological feedbacks play in the evolution of defence. We use a host-parasite model with two-sexes and the techniques of adaptive dynamics to investigate how mating system and sexual differences in competitive ability and longevity can select for a bias in the rates of parasitism. Male-biased parasitism is selected for when males have a shorter average lifespan or when males are subject to greater competition for resources. Male-biased parasitism evolves as a consequence of sexual differences in life history that produce a greater proportion of susceptible females than males and therefore reduce the cost of avoiding parasitism in males. Different mating systems such as monogamy, polygamy or polyandry did not produce a bias in parasitism through these ecological feedbacks but may accentuate an existing bias.Comment: 18 pages, 4 figure

Verified Correctness and Security of mbedTLS HMAC-DRBG

We have formalized the functional specification of HMAC-DRBG (NIST 800-90A), and we have proved its cryptographic security--that its output is pseudorandom--using a hybrid game-based proof. We have also proved that the mbedTLS implementation (C program) correctly implements this functional specification. That proof composes with an existing C compiler correctness proof to guarantee, end-to-end, that the machine language program gives strong pseudorandomness. All proofs (hybrid games, C program verification, compiler, and their composition) are machine-checked in the Coq proof assistant. Our proofs are modular: the hybrid game proof holds on any implementation of HMAC-DRBG that satisfies our functional specification. Therefore, our functional specification can serve as a high-assurance reference.Comment: Appearing in CCS '1