The Dynamic Theory of Time and Time Travel to the Past

I argue that time travel to the past is impossible, given a certain metaphysical theory, namely, The Dynamic Theory of Time. I first spell out my particular way of capturing the difference between The Dynamic Theory of Time and its rival, The Static Theory of Time. Next I offer four different arguments for the conclusion that The Dynamic Theory is inconsistent with the possibility of time travel to the past. Then I argue that, even if I am wrong about this, it will still be true that The Dynamic Theory entails that you should not want to travel back to the past. Finally, I conclude by considering a puzzle that arises for those who believe that time travel to the past is metaphysically impossible: What exactly are we thinking about when we seem to be thinking about traveling back in time? For it certainly does not feel like we are thinking about something that is metaphysically impossible

A Defense of Presentism

∗ Apologies to Mark Hinchliff for stealing the title of his dissertation. (See Hinchliff, A Defense of Presentism. As it turns out, however, the version of Presentism defended here is different from the version defended by Hinchliff. See Section 3.1 below.)

Doctor of Philosophy

dissertationIn this work we focused on the electronic processes in active materials used in organic photovoltaics. Films of several electron donors, acceptors, and their blends were investigated by means of steady state optical and magnetic resonance probes. The efficiency of organic photovoltaics depends on film morphology, charge mobility and light absorption. Therefore we studied common donor materials with very different morphology: RR P3HT (regioregular poly(3-hexylthiophene)) and RRa P3HT (regio-random poly(3-hexylthiophene)). The charge transport is affected by regioregularity and molecular weight. Consequently, we examined RR P3HT polymers with various molecular weights. We learned that a polaron band at low photon energy only appears in the photoinduced absorption spectrum of low molecular weight RR P3HT. We studied two main approaches for improving the efficiency of organic photovoltaics: modifying the lowest (highest) unoccupied (occupied) molecular orbital, LUMO (HOMO) of the donor (acceptor) materials; as well as synthesizing polymer donors with low optical gap. TAES-V is a low-band gap polymer composed of three co-polymers having the structure of „donor-acceptor-donor?. Its record power conversion efficiency (~7%) when blended with PC70BM is partially due to the significantly red-shifted absorption. Our results show that an intrachain charge transfer exciton (CTE) is long-lived in this polymer and that it persists in the blend with PC70BM. In addition we studied three fullerene derivatives. The LUMO of a fullerene derivative can be changed by the addition of functional side groups to the fullerene cage that improves the organic solar cells performance. The addition can also lead to hindering of aggregation in the films, which consequently decreases the charge transport in solar cells. In the study of polymer/fullerene blends we mixed RR P3HT with three different fullerene derivatives. We conclude that higher power conversion efficiency of a blend is mainly due to the higher LUMO level and improved open circuit voltage. We also compared DOO-PPV (H-polymer) with DOO-PPV enriched with deuterium (D-polymer). We show that hyperfine interaction is weaker in the D-polymer and that the spin relaxation rate is four times smaller than in H-polymer. Consequently, the longer spin diffusion length makes the D-polymer better suited for higher performing organic spin-valves

Software Engineering Research/Developer Collaborations in 2004 (C104)

In 2004, six collaborations between software engineering technology providers and NASA software development personnel deployed a total of five software engineering technologies (for references, see Section 7.2) on the NASA projects. The main purposes were to benefit the projects, infuse the technologies if beneficial into NASA, and give feedback to the technology providers to improve the technologies. Each collaboration project produced a final report (for references, see Section 7.1). Section 2 of this report summarizes each project, drawing from the final reports and communications with the software developers and technology providers. Section 3 indicates paths to further infusion of the technologies into NASA practice. Section 4 summarizes some technology transfer lessons learned. Section 6 lists the acronyms used in this report

On language and the passage of time

Since the early part of this century there has been a considerable amount of discussion of the question 'Does time pass?'. A useful way of approaching the debate over the passage of time is t