Do the laws of physics forbid the operation of time machines?

We address the question of whether it is possible to operate a time machine by manipulating matter and energy so as to manufacture closed timelike curves. This question has received a great deal of attention in the physics literature, with attempts to prove no-go theorems based on classical general relativity and various hybrid theories serving as steps along the way towards quantum gravity. Despite the effort put into these no-go theorems, there is no widely accepted definition of a time machine. We explain the conundrum that must be faced in providing a satisfactory definition and propose a resolution. Roughly, we require that all extensions of the time machine region contain closed timelike curves; the actions of the time machine operator are then sufficiently “potent” to guarantee that closed timelike curves appear. We then review no-go theorems based on classical general relativity, semi-classical quantum gravity, quantum field theory on curved spacetime, and Euclidean quantum gravity. Our verdict on the question of our title is that no result of sufficient generality to underwrite a confident “yes” has been proven. Our review of the no-go results does, however, highlight several foundational problems at the intersection of general relativity and quantum physics that lend substance to the search for an answer.     

Personality self-concept affects processing of trait adjectives in the self-reference memory paradigm

We combined personality, social cognitive, and cognitive paradigms for researching the self. Specifically, we examined whether personality trait assessments are associated with variation in the cognitive processes that produce the self-reference effect in memory. We found that self-reported, but not indirectly assessed, trait orderliness (Study 1; N = 98) and openness (Study 2; N = 92) were associated with slower free recall when corresponding trait adjectives were self-referenced, but not when adjectives were encoded in control tasks. The slower recall showed mixed predictive validity. Results suggest that personality congruent adjectives elicit more elaborative processing in the form of propositions that arise during self-reference, which counter-intuitively slows recall in a manner consistent with random search memory models and cue overload theory.     

Prior sensitivity in theory testing: An apologia for the Bayes factor

A commonly voiced concern with the Bayes factor is that, unlike many other Bayesian and non-Bayesian quantitative measures of model evaluation, it is highly sensitive to the parameter prior. This paper argues that, when dealing with psychological models that are quantitatively instantiated theories, being sensitive to the prior is an attractive feature of a model evaluation measure. This assertion follows from the observation that in psychological models parameters are not completely unknown, but correspond to psychological variables about which theory often exists. This theory can be formally captured in the prior range and prior distribution of the parameters, indicating which parameter values are allowed, likely, unlikely and forbidden. Because the prior is a vehicle for expressing psychological theory, it should, like the model equation, be considered as an integral part of the model. It is argued that the combined practice of building models using informative priors, and evaluating models using prior sensitive measures advances knowledge.     

Sensitivity analysis in factor analysis: Difference between using covariance and correlation matrices

Influence curves of some parameters under various methods of factor analysis have been given in the literature. These influence curves depend on the influence curves for either the covariance or the correlation matrix used in the analysis. The differences between the influence curves based on the covariance and the correlation matrices are derived in this paper. Simple formulas for the differences of the influence curves, based on the two matrices, for the unique variance matrix, factor loadings and some other parameter are obtained under scale-invariant estimation methods, though the influence curves themselves are in complex forms.The authors are most grateful to the referees, the Associate Editor, the Editor and Raymond Lam for helpful suggestions for improving the clarity of the paper.     

Development of the Drooling Infants and Preschoolers Scale (DRIPS) and reference charts for monitoring saliva control in children aged 0–4 years

ObjectivesTo develop and validate a parent questionnaire to quantify drooling severity and frequency in young children (the Drooling Infants and Preschoolers Scale – the DRIPS). To investigate development of saliva control in typically developing young children in the age of 0–4 years. To construct sex-specific reference charts presenting percentile curves for drooling plotted for age to monitor the development of saliva control in infancy and preschool age.Study designThe DRIPS was developed consisting of 20 items to identify severity and frequency of drooling during meaningful daily activities. Factor analysis was performed to test construct validity. A piecewise logistic regression was followed by a piecewise linear regression to construct sex-specific reference charts.ResultsWe obtained 652 completed questionnaires from parents of typically developing children. The factor analysis revealed four discriminating components: drooling during Activities, Feeding, Non nutritive sucking, and Sleep. To illustrate the development of saliva control, eight sex-specific reference curves were constructed to plot the scores of the DRIPS by age group, at the 15th, 50th, 85th and 97th percentile. About 3–15% of the preschoolers in our cohort did not acquire full saliva control at the age of 4 years.ConclusionsWith the DRIPS it is possible to validly compare and visualize the development of saliva control in an individual infant or preschooler and allow clinicians to timely initiate individually targeted interventions if children outperform.     

Predicting Growth Curves of Externalizing Behavior Across the Preschool Years

Hierarchical linear modeling was used to examine 2 facets of externalizing behavior: its level at age 6 and its rate of change from age 2 to 6 among 299 boys from low-income families. As for age-6 level of externalizing behavior, maternal depressive symptoms, maternal acceptance of child behavior, parental conflict, and the interaction between maternal acceptance and maternal depressive symptoms were each uniquely associated with this outcome. Regarding the interaction, maternal acceptance was associated with externalizing behavior primarily when maternal depressive symptoms were low, and maternal depressive symptoms were related to externalizing behavior only when maternal acceptance was high. Externalizing behavior gradually decreased between ages 2 and 6; interactions between infant negative emotionality and maternal depressive symptoms and between parental conflict and maternal acceptance were associated with rate of change. Plots suggested a protective effect of low infant negative emotionality when maternal depressive symptoms were high and a larger effect of maternal acceptance when parental conflict was low compared to when it was high. Results add to a small but growing literature regarding predictors of continuity and change in early child externalizing behavior.     

Time ordering in frontal lobe patients: a stochastic model approach

Frontal lobe patients reproduced a sequence of capital letters or abstract shapes. Immediate and delayed reproduction trials allowed the analysis of short- and long-term memory for time order by means of suitable Markov chain stochastic models. Patients were as proficient as healthy subjects on the immediate reproduction trial, thus showing spared encoding and short-term memory. They failed, instead, on the delayed trials with capital letters, but not with random shapes, suggesting that their long-term memory impairment did not depend on primary deficits for ordering, but on inability to benefit from the organisational strategies that improve the retention and retrieval in normal subjects.     

Don't be afraid of irrelevant words: The emotional Stroop effect is confined to attended words

The emotional Stroop effect denotes slower responses to the colour of negative words (e.g., death) compared to neutral words (e.g., mug). Popular explanations assume a general power of negative words to capture visual attention. However, in the typical task, the irrelevant word stimulus and the relevant colour stimulus are perceptually integrated. We compared interference from negative words, which were part of the relevant visual object, to interference from negative words that were part of an irrelevant object, or occurred in the background, respectively. Results showed that only negative words in the relevant object delayed colour-naming responses, compared to neutral words. Negative words outside the relevant object failed to affect performance. This finding is at odds with the claim that negative words could capture spatial or object-based mechanisms of visual attention. However, the finding is consistent with the idea that negative words interfere with the allocation of dimensional attention to different features of an attended object.