Various methods have been proposed for transporting large probes or colony ships through interstellar space to nearby stellar neighborhoods. All methods proposed thus far encounter monumental technological or engineering roadblocks, or even rely on speculative unknown science. In particular light of the recent public excitement and ensuing disappointment regarding the exotic “EM drive” we feel it worthwhile to point out that propellantless space travel is eminently possible based on well established physical principles. We propose a new mode of transport which relies on electric-field moderated momentum exchange with the ionized particles in the interstellar medium. While the application of this mechanism faces significant challenges requiring industrial-scale exploitation of space, the technological roadblocks are minimal, and are perhaps more easily addressed than the issues presented by light sails or particle beam powered craft.

Although black holes are objects of central importance across many fields of physics, there is no agreed upon definition for them, a fact that does not seem to be widely recognized. Physicists in different fields conceive of and reason about them in radically different, and often conflicting, ways. All those ways, however, seem sound in the relevant contexts. After examining and comparing many of the definitions used in practice, I consider the problems that the lack of a universally accepted definition leads to, and discuss whether one is in fact needed for progress in the physics of black holes. I conclude that, within reasonable bounds, the profusion of different definitions is in fact a virtue, making the investigation of black holes possible and fruitful in all the many different kinds of problems about them that physicists consider, although one must take care in trying to translate results between fields.

Reverse mathematics studies which subsystems of second order arithmetic are equivalent to key theorems of ordinary, non-set-theoretic mathematics. The main philosophical application of reverse mathematics proposed thus far is foundational analysis, which explores the limits of different foundations for mathematics in a formally precise manner. This paper gives a detailed account of the motivations and methodology of foundational analysis, which have heretofore been largely left implicit in the practice. It then shows how this account can be fruitfully applied in the evaluation of major foundational approaches by a careful examination of two case studies: a partial realization of Hilbert’s program due to Simpson [1988], and predicativism in the extended form due to Feferman and Schutte. Shore [2010, 2013] proposes that equivalences in reverse mathematics be proved in the same way as inequivalences, namely by considering only ω -models of the systems in question.

This is a brief, popular-level introduction to holographic entanglement. It was published in the newsletter of the International Centre for Theoretical Sciences, Bangalore.

The present study proposes the use of intelligent metasurfaces in the design of products, as enforcers of circular economy principles. Intelligent metasurfaces can tune their physical properties (electromagnetic, acoustic, mechanical) by receiving software commands. When incorporated within products and spaces they can mitigate the resource waste caused by inefficient, partially optimized designs and security concerns. Thus, circular economy and fast-paced product design become compatible. The study begins by considering electromagnetic metamaterials, and proposes a complete methodology for their deployment. Finally, it is shown that the same principles can be extended to the control of mechanical properties of objects, exemplary enabling the micro-management of vibrations and heat, with unprecedented circular economy potential.

In this paper I discuss the concept of physical time. I consider the thermal time hypothesis and I stress that thermal time could be not reducible to relativistic time. In the conclusive section, I explicitly claim that different times can be generated inside the different clocks employed for measuring durations. This hypothesis opens the possibility of a new foundation of the theory of physical time, and new perspectives in theoretical and philosophical researches.

Detection of gravitational waves by LIGO-Virgo observatories disclosed the agent of gravity (gravitons) and together with information paradox of black hole event horizon points to paradigm shift from non-quantum geometry to quantum gravity physics. Historical, philosophical, mathematical, physical and astronomical arguments are presented for demonstration that in the beginning of the 21st century we are on the verge of the forthcoming change in understanding of gravity nature, which will bring new ideas in performing gravitational experiments and interpretation of astrophysical phenomena.

This paper provides an overview of modern digital geometry and topology through mathematical principles, algorithms, and measurements. It also covers recent developments in the applications of digital geometry and topology including image processing, computer vision, and data science. Recent research strongly showed that digital geometry has made considerable contributions to modelings and algorithms in image segmentation, algorithmic analysis, and BigData analytics.

Quantum physics, which describes the strange behavior of light and matter at the smallest scales, is one of the most successful descriptions of reality, yet it is notoriously inaccessible. Here we provide an approachable explanation of quantum physics using simple thought experiments that deal with one- and two-particle interference. We derive all relevant quantum predictions using minimal mathematics, without introducing the advanced calculations that are typically used to describe quantum physics. We focus on the two key surprises of quantum physics, namely wave-particle duality, which deals with the counter-intuitive behavior of single quantum particles, and entanglement, which applies to two or more quantum particles and brings out the inherent contradiction between quantum physics and seemingly obvious assumptions regarding the nature of reality. We employ Hardy’s version of Bell’s theorem to show that so-called local hidden variables are inadequate at explaining the behavior of entangled quantum particles. This means that one either has to give up on hidden variables, i.e. the idea that the outcomes of measurements on quantum particles are determined before an experiment is actually carried out, or one has to relinquish the principle of locality, which requires that no causal influences should be faster than the speed of light. Finally, we describe how these remarkable predictions of quantum physics have been confirmed in experiments. We have successfully used the present approach in a course that is open to all undergraduate students at the University of Calgary, without any prerequisites in mathematics or physics.

Our paper discusses the epistemic attitudes of particle physicists on the discovery of the Higgs boson at the Large Hadron Collider (LHC). It is based on questionnaires and interviews made shortly before and shortly after the discovery in 2012. We show, to begin with, that the discovery of a Standard Model (SM) Higgs boson was less expected than is sometimes assumed. Once the new particle was shown to have properties consistent with SM expectations – albeit with significant experimental uncertainties -, there was a broad agreement that ‘a’ Higgs boson had been found. Physicists adopted a twopronged strategy. On the one hand, they treated the particle as a SM Higgs boson and tried to establish its properties with higher precision; on the other hand, they searched for any hints of physics beyond the SM.