This talk briefly reviews three types of time-asymmetry in physics, which I classify as universal, macroscopic and microscopic. Most of the talk is focussed on the latter, namely the violation of T-reversal invariance in particle physics theories. Talk presented at Discrete ’08 Conference, Valencia, Spain December 11, 2008 SLAC–PUB–13518 This work is supported by the Department of Energy under ...

An experimental study is performed on electromagnetic time reversal in highly scattering environments, with a particular focus on performance when environmental conditions change. In particular, we consider the case for which there is a mismatch between the Green’s function used on the forward measurement and that used for time-reversal inversion. We examine the degradation in the time-reversal...

An embodied language-learning system is presented that can learn the correct deictic meanings for the words “I” and “you.” The system uses contextual clues from already understood words and sensory information from its environment to determine the most likely grounding for a new word. The system also serves as a model for the phenomenon of pronoun reversal among congenitally blind children, as ...

A mathematical study of the focusing properties of acoustic fields obtained by a time-reversal process is presented. The case of time-harmonic waves propagating in a nondissipative medium containing sound-soft obstacles is considered. In this context, the so-called D.O.R.T. method (decomposition of the time-reversal operator in French) was recently proposed to achieve selective focusing by comp...

2. (Jordan) A transitive permutation group of degree n > 1 contains a derangement. In fact (Cameron and Cohen) the proportion of derangements in a transitive group G is at least 1/n. Equality holds if and only if G is sharply 2transitive, and hence is the affine group {x 7→ ax + b : a, b ∈ F, a 6= 0} over a nearfield F. The finite nearfields were determined by Zassenhaus. They all have prime po...

In this paper I draw the distinction between intuitive and theory-relative accounts of the time reversal symmetry and identify problems with each. I then propose an alternative to these two types of accounts that steers a middle course between them and minimizes each account’s problems. This new account of time reversal requires that, when dealing with sets of physical theories that satisfy cer...

Processes mediated by small nucleophilic catalysts are currently experiencing a renaissance. In addition to competing with well-established metal-catalyzed reactions, there is a tempting opportunity to invert conventional reactivity patterns by exploiting the concept of polarity reversal (umpolung). Following this strategy, aldehydes can be turned into acylanion equivalents through covalent act...