Fine's Trilemma and the Reality of Tensed Facts

Fine (2005, 2006) has presented a ‘trilemma’ concerning the tense-realist idea that reality is constituted by tensed facts. According to Fine, there are only three ways out of the trilemma, consisting in what he takes to be the three main families of tense-realism: ‘presentism’, ‘(external) relativism’, and ‘fragmentalism’. Importantly, although Fine characterises tense-realism as the thesis that reality is constituted (at least in part) by tensed facts, he explicitly claims that tense realists are not committed to their fundamental existence. Recently, Correia and Rosenkranz (2011, 2012) have claimed that Fine’s tripartite map of tense realism is incomplete as it misses a fourth position they call ‘dynamic absolutism’. In this paper, I will argue that dynamic absolutists are committed to the irreducible existence of tensed facts and that, for this reason, they face a similar trilemma concerning the notion of fact-content. I will thus conclude that a generalised version of Fine’s trilemma, concerning both fact-constitution and fact-content, is indeed inescapable

Fine’s McTaggart: Reloaded

In this paper I will present three arguments (based on the notions of constitution, metaphysical reality, and truth, respectively) with the aim of shedding some new light on the structure of Fine’s (2005, 2006) ‘McTaggartian’ arguments against the reality of tense. Along the way, I will also (i) draw a novel map of the main realist positions about tense, (ii) unearth a previously unnoticed but potentially interesting form of external relativism (which I will label ‘hyper-presentism’) and (iii) sketch a novel interpretation of Fine’s fragmentalism (which I contrast with Lipman’s 2015, 2016b, forthcoming)

No ground for doomsday

ABSTRACTThe ability of providing an adequate supervenience base for tensed truths may seem to be one of the main theoretical advantages of both the growing-block and the moving-spotlight theory of time over presentism. However, in this paper I will argue that some propositions appear to be as problematic for growing-block theorists as past-directed propositions are for presentists, namely propositions stating that nothing will be the case in the future. Furthermore, I will show that the moving-spotlight theory can adequately address all the main supervenience challenges that can be levelled against A-theories of time. I will, thus, conclude that, at least as far as the supervenience principle is concerned, the moving-spotlight theory should be preferred over both presentism and the growing-block theory

Against 'Against 'Against Vague Existence''

Alessandro Torza argues that Ted Sider’s Lewisian argument against vague existence is insufficient to rule out the possibility of what he calls ‘super-vague existence’, that is the idea that existence is higher-order vague, for all orders. In this chapter it is argued that the possibility of super-vague existence is ineffective against the conclusion of Sider’s argument since super-vague existence cannot be consistently claimed to be a kind of linguistic vagueness. Torza’s idea of super-vague existence seems to be better suited to model vague existence under the assumption that vague existence is instead a form of ontic indeterminacy, contra what Ted Sider and David Lewis assume

Creation of nonlocal spin-entangled electrons via Andreev tunneling, Coulomb blockade and resonant transport

We discuss several scenarios for the creation of nonlocal spin-entangled electrons which provide a source of electronic Einstein-Podolsky-Rosen (EPR) pairs. The central idea is to exploit the spin correlations naturally present in superconductors in form of Cooper pairs. We show that nonlocal spin-entanglement in form of an effective Heisenberg spin interaction is induced between electron spins residing on two quantum dots with no direct coupling between them but each of them being tunnel-coupled to the same superconductor. We then discuss a nonequilibrium setup where mobile and nonlocal spin-entanglement can be created by coherent injection of two electrons in an Andreev tunneling process into two spatially separated quantum dots and subsequently into two Fermi-liquid leads. The current for injecting two spin-entangled electrons into different leads shows a resonance whereas tunneling via the same dot into the same lead is suppressed by the Coulomb blockade effect of the quantum dots. The Aharonov-Bohm oscillations in the current are shown to contain h/e and h/2e periods. Finally we discuss a structure consisting of a superconductor weakly coupled to two separate Luttinger liquid leads. We show that strong correlations again suppress the coherent subsequent tunneling of two electrons into the same lead, thus generating again nonlocal spin-entangled electrons.Comment: 15 pages, 6 figures; proceedings Spintronics conference 2001, Georgetown-University, Washington D

Fermionic and Majorana Bound States in Hybrid Nanowires with Non-Uniform Spin-Orbit Interaction

We study intragap bound states in the topological phase of a Rashba nanowire in the presence of a magnetic field and with non-uniform spin orbit interaction (SOI) and proximity-induced superconductivity gap. We show that fermionic bound states (FBS) can emerge inside the proximity gap. They are localized at the junction between two wire sections characterized by different directions of the SOI vectors, and they coexist with Majorana bound states (MBS) localized at the nanowire ends. The energy of the FBS is determined by the angle between the SOI vectors and the lengthscale over which the SOI changes compared to the Fermi wavelength and the localization length. We also consider double-junctions and show that the two emerging FBSs can hybridize and form a double quantum dot-like structure inside the gap. We find explicit analytical solutions of the bound states and their energies for certain parameter regimes such as weak and strong SOI. The analytical results are confirmed and complemented by an independent numerical tight-binding model approach. Such FBS can act as quasiparticle traps and thus can have implications for topological quantum computing schemes based on braiding MBSs

Fractional Fermions with Non-Abelian Statistics

We introduce a novel class of low-dimensional topological tight-binding models that allow for bound states that are fractionally charged fermions and exhibit non-Abelian braiding statistics. The proposed model consists of a double (single) ladder of spinless (spinful) fermions in the presence of magnetic fields. We study the system analytically in the continuum limit as well as numerically in the tight-binding representation. We find a topological phase transition with a topological gap that closes and reopens as a function of system parameters and chemical potential. The topological phase is of the type BDI and carries two degenerate mid-gap bound states that are localized at opposite ends of the ladders. We show numerically that these bound states are robust against a wide class of perturbations

Giant spin orbit interaction due to rotating magnetic fields in graphene nanoribbons

We theoretically study graphene nanoribbons in the presence of spatially varying magnetic fields produced e.g. by nanomagnets. We show both analytically and numerically that an exceptionally large Rashba spin orbit interaction (SOI) of the order of 10 meV can be produced by the non-uniform magnetic field. As a consequence, helical modes exist in armchair nanoribbons that exhibit nearly perfect spin polarization and are robust against boundary defects. This paves the way to realizing spin filter devices in graphene nanoribbons in the temperature regime of a few Kelvins. If a nanoribbon in the helical regime is in proximity contact to an s-wave superconductor, the nanoribbon can be tuned into a topological phase sustaining Majorana fermions