Taming the Delayed Choice Quantum Eraser

I discuss the delayed choice quantum eraser experiment (DCQE) by drawing an analogy to a Bell-type measurement and giving a straightforward account in standard quantum mechanics. The delayed choice quantum eraser experiment turns out to resemble a Bell-type scenario in which the paradox's resolution is rather trivial, and so there really is no mystery. At first glance, the experiment suggests that measurements on one part of an entangled photon pair (the idler) can be employed to control whether the measurement outcome of the other part of the photon pair (the signal) produces interference fringes at a screen after being sent through a double slit. Significantly, the choice whether there is interference or not can be made long after the signal photon encounters the screen. The results of the experiment have been alleged to invoke some sort of 'backwards in time influence'. I argue that this issue can be eliminated by taking into proper account the role of the signal photon. Likewise, in the de Broglie-Bohm picture the particle's trajectories can be given a well-defined description at any instant of time during the experiment. Thus, it is again clear that there is no need to resort to any kind of 'backwards in time influence'.Comment: Published version; 19 pages, 4 figure

Exploring lexical patterns in text : lexical cohesion analysis with WordNet

We present a system for the linguistic exploration and analysis of lexical cohesion in English texts. Using an electronic thesaurus-like resource, Princeton WordNet, and the Brown Corpus of English, we have implemented a process of annotating text with lexical chains and a graphical user interface for inspection of the annotated text. We describe the system and report on some sample linguistic analyses carried out using the combined thesaurus-corpus resource

ON CLIMATE CHANGE AND ECONOMIC GROWTH

The economic impact of climate change is usually measured as the amount by which the climate of a given period will affect output or GDP in that period. This paper draws attention to some of the dynamic effects through which climate change may affect economic growth and hence future output. In particular, the paper looks at saving and capital accumulation. With a constant savings rate, a lower output due to climate change will lead to a proportionate reduction in investment which in turn will depress future production (capital accumulation effect). If the savings rate is flexible, forward looking agents may change their savings behavior to accommodate the impact of future climate change. Again this alters growth prospects (savings effect). In an endogenous growth context, the two effects may be exacerbated through changes in labour productivity and the rate of technical progress. Simulations using a simple climate-economy model suggest that the capital accumulation effect is important, especially if growth is endogenous, and may be larger than the direct impact of climate change. The savings effect is less pronounced and its sign is ambiguous. In most cases, the savings effect is negative, that is, faced with climate change households increase current consumption rather than saving more to compensate for future damages. The indirect effects are relatively larger for smaller direct effects; the indirect effects are also relatively larger for growth mechanisms more prevalent in richer countries. Ignoring the growth effects of climate change thus leads to a substantial underestimate of the impacts of climate change, particularly in richer economies.economic growth, climate change

Der Betreuungsunterhalt - Zur Spurensuche und -deutung anhand von Materialien

In den vergangenen 20 bis 30 Jahren ist es im Bereich des Familienrechts zu zahlreichen Revisionen gekommen, wobei in den letzten zehn Jahren die Kadenz der Novellen noch weiter angestiegen ist. Es erstaunt deshalb nicht, dass die jüngsten Reformprojekte von der Praxis zuweilen als wenig koordiniertes und nicht vertieft reflektiertes Flickwerk wahrgenommen wurden5. Folge davon sind vermehrte Auslegungsschwierigkeiten und damit auch stets die Frage, wie Materialien der Gesetzgebung bei der Auslegung im allgemeinen und für das neue Kindesunterhaltsrecht im speziellen zu berücksichtigen sind

How to make UK energy policy more predictable again

A series of policy U-turns have made aspects of British energy policy unpredictable. With such reversals having been politically motivated, state involvement must be revisited if the industry is to re-establish its credibility, argues Sam Fankhauser. He explains that making strategy and decision-making more transparent, and delegating regulation to independent bodies, are some steps that will depoliticise the energy sector and increase investor trust

Gravitational redshift, inertia, and the role of charge

I argue that the gravitational redshift effect cannot be explained purely by way of uniformly accelerated frames, as sometimes suggested in the literature. The concepts in need of clarification are spacetime curvature, inertia, and the weak equivalence principle with respect to our understanding of gravitational redshift. Furthermore, I briefly discuss gravitational redshift effects due to charge. Considering charge and mass together seems to give rise to a way of (locally) shielding gravity

Taming the Delayed Choice Quantum Eraser

In this paper I discuss the delayed choice quantum eraser experiment by giving a straightforward account in standard quantum mechanics. At first glance, the experiment suggests that measurements on one part of an entangled photon pair (the idler) can be employed to control whether the measurement outcome of the other part of the photon pair (the signal) produces interference fringes at a screen after being sent through a double slit. Significantly, the choice whether there is interference or not can be made long after the signal photon encounters the screen. The results of the experiment have been alleged to invoke some sort of 'backwards in time influences'. I argue that in the standard collapse interpretation the issue can be eliminated by taking into account the collapse of the overall entangled state due to the signal photon. Likewise, in the de Broglie-Bohm picture the particle's trajectories can be given a well-defined description at any instant of time during the experiment. Thus, there is no need to resort to any kind of 'backwards in time influence'. As a matter of fact, the delayed choice quantum eraser experiment turns out to resemble a Bell-type measurement, and so there really is no mystery

Taming the Delayed Choice Quantum Eraser

In this paper I discuss the delayed choice quantum eraser experiment by giving a straightforward account in standard quantum mechanics. At first glance, the experiment suggests that measurements on one part of an entangled photon pair (the idler) can be employed to control whether the measurement outcome of the other part of the photon pair (the signal) produces interference fringes at a screen after being sent through a double slit. Significantly, the choice whether there is interference or not can be made long after the signal photon encounters the screen. The results of the experiment have been alleged to invoke some sort of 'backwards in time influences'. I argue that in the standard collapse interpretation the issue can be eliminated by taking into account the collapse of the overall entangled state due to the signal photon. Likewise, in the de Broglie-Bohm picture the particle's trajectories can be given a well-defined description at any instant of time during the experiment. Thus, there is no need to resort to any kind of 'backwards in time influence'. As a matter of fact, the delayed choice quantum eraser experiment turns out to resemble a Bell-type measurement, and so there really is no mystery

William Beveridge's sixth giant: environmental sustainability

Today, William Beveridge would worry about the environment, writes Sam Fankhauser. He reflects on the LSE's Beveridge Festival and explains why environmental sustainability needs to be prioritised with the determination, leadership, and strong government commitment that Beveridge envisaged in 1942 - only this time at a global scale