Faster-than-light

Summary

Faster-than-light (also FTL, superluminal or supercausal) travel and communication are the conjectural propagation of matter or information faster than the speed of light ('''c'''). The special theory of relativity implies that only particles with zero rest mass (i.e., photons) may travel at the speed of light, and that nothing may travel faster. Particles whose speed exceeds that of light (tachyons) have been hypothesized, but their existence would violate causality and would imply time travel. The scientific consensus is that they do not exist. "Apparent" or "effective" FTL, on the other hand, depends on the hypothesis that unusually distorted regions of spacetime might permit matter to reach distant locations in less time than light could in normal ("undistorted") spacetime. As of the 21st century, according to current scientific theories, matter is required to travel at slower-than-light (also STL or subluminal) speed with respect to the locally distorted spacetime

Official source

https://en.wikipedia.org/wiki/Faster-than-light

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An invisibility cloak should completely hide an object from an observer, ideally across the visible spectrum and for all angles of incidence and polarizations of light, in three dimensions. However, until now, all such devices have been limited to either small bandwidths or have disregarded the phase of the impinging wave or worked only along specific directions. Here, we show that these seemingly fundamental restrictions can be lifted by using cloaks made of fast-light media, termed tachyonic cloaks, where the wave group velocity is larger than the speed of light in vacuum. On the basis of exact analytic calculations and full-wave causal simulations, we demonstrate three-dimensional cloaking that cannot be detected even interferometrically across the entire visible regime. Our results open the road for ultrabroadband invisibility of large objects, with direct implications for stealth and information technology, non-disturbing sensors, near-field scanning optical microscopy imaging, and superluminal propagation.

2019

cRacklet: a spectral boundary integral method library for interfacial rupture simulation

Fabian Barras, Jean-François Molinari, Thibault Didier Roch

The study of dynamically propagating rupture along interfaces is of prime importance in various fields and system sizes, including tribology (nm to m), engineering (mm to m) and geophysics (m to km) (Armstrong-Hélouvry et al., 1994; Ben-Zion, 2008; Vanossi et al., 2013). Numerical simulations of these phenomena are computationally costly and challenging, as they usually require the coupling of two different spatio-temporal scales. A fine spatial discretization is needed to represent accurately the singular fields associated with the rupture edges. Besides, the problems of interest usually involve a larger length scale along which rupture will propagate driven by long-range traveling elastic waves. The physical phenomena at play also occur at different timescales, from the slow process of rupture nucleation to the fast propagation of crack front close the elastic wave speeds. Large and finely discretized spatio-temporal domains are required, which are computationally costly. In addition, the behavior of such interfaces can be highly non-linear thus increasing the problem complexity. The use of boundary integral methods reduces the dimensionality of the problem. This enables to focus the computational efforts on the fracture plane and allows for a detailed description of the interfacial failure processes.

2022

Light Controlling Light in an Optical Fibre: From Very Slow to Faster-Than-Light Speed

Sang Hoon Chin, Kwang-Yong Song, Luc Thévenaz

2007