Can information be transferred faster than light? II. The relativistic Doppler effect on electromagnetic wave packets with suboptic and superoptic group velocities

1988 ◽  
Vol 18 (6) ◽  
pp. 625-638 ◽  
Author(s):  
William Band
Keyword(s):  
Electromagnetic Wave ◽  
Doppler Effect ◽  
Wave Packets ◽  
Group Velocities ◽  
Faster Than Light

scholarly journals Optical wave-packet with nearly-programmable group velocities

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Zhaoyang Li ◽  
Junji Kawanaka
Keyword(s):  
Wave Packet ◽  
Group Velocity ◽  
Wave Packets ◽  
Bessel Beam ◽  
Propagation Path ◽  
Uniform Motion ◽  
Optical Wave ◽  
Straight Line ◽  
Line Trajectory ◽  
Group Velocities

AbstractDuring the process of Bessel beam generation in free space, spatiotemporal optical wave-packets with tunable group velocities and accelerations can be created by deforming pulse-fronts of injected pulsed beams. So far, only one determined motion form (superluminal or luminal or subluminal for the case of group velocity; and accelerating or uniform-motion or decelerating for the case of acceleration) could be achieved in a single propagation path. Here we show that deformed pulse-fronts with well-designed axisymmetric distributions (unlike conical and spherical pulse-fronts used in previous studies) allow us to obtain nearly-programmable group velocities with several different motion forms in a single propagation path. Our simulation shows that this unusual optical wave-packet can propagate at alternating superluminal and subluminal group velocities along a straight-line trajectory with corresponding instantaneous accelerations that vary periodically between positive (acceleration) and negative (deceleration) values, almost encompassing all motion forms of the group velocity in a single propagation path. Such unusual optical wave-packets with nearly-programmable group velocities may offer new opportunities for optical and physical applications.

Faster-than-light group velocities and causality violation

1970 ◽  
Vol 316 (1527) ◽  
pp. 515-524 ◽  
Keyword(s):  
Wave Equations ◽  
Signal Propagation ◽  
Necessary Condition ◽  
Speed Of Light ◽  
Frequency Range ◽  
Classical Analysis ◽  
Causality Violation ◽  
Light Group ◽  
Group Velocities ◽  
Faster Than Light

The classical analysis of Brillouin and Sommerfeld has shown that the appearance, in some frequency range, of group velocities in excess of the speed of light does not imply causality violation. The group velocity is not always identical with the velocity of signal propagation. We show that a necessary condition for causality violation is that the infinite- frequency limit of the phase velocity shall exceed the speed of light. Application of the theorem leads to the conclusions ( a ) that all Lorentz-invariant wave equations (and in particular the Feinberg ‘tachyon’) are causal, and ( b ) that the quasi-acoustic branch of the Bludman-Ruderman model is causal.

scholarly journals Redshift effect implications on revised models of Stephan’s Quintet

2019 ◽  
Vol 35 (01) ◽  
pp. 1950342
Author(s):  
Mohamed Lamine Abdelali ◽  
Noureddine Mebarki
Keyword(s):  
Compact Group ◽  
Gravitational Waves ◽  
Doppler Effect ◽  
Significant Contribution ◽  
Numerical Models ◽  
Gravitational Interaction ◽  
Simulation Data ◽  
Group Members ◽  
Group Velocities

Recent observations of Stephan’s Quintet (SQ) gave new indications on its formation scenario. Older formation and role of NCG 7317 should be considered in revised numerical models of the compact group. Velocities of group members to recreate are estimated from redshift measurements. Several effects contribute to observed redshifts and a new effect is predicted to be the result of the gravitational interaction between photons and constant magnetic fields creating gravitational waves. The energy carried by these waves is manifested as redshifts of the photons. Cosmological simulation data are used to prove the significant contribution of our effect. The analysis of synthetic observations created from those simulations has shown that redshifts of SQ members could be misinterpreted as caused only from Doppler Effect. The revised models of the group should consider a new method to recreate the formation scenario based on redshift patterns and not mis-estimated velocities.

scholarly journals The Connection between Coherent Structures and Low-Frequency Wave Packets in Large-Scale Atmospheric Flow

2004 ◽  
Vol 61 (21) ◽  
pp. 2616-2626 ◽  
Author(s):  
Daniel Hodyss ◽  
Terrence R. Nathan
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Wave Packets ◽  
Low Frequency ◽  
Wave Groups ◽  
Atmospheric Flow ◽  
Subsequent Formation ◽  
Frequency Wave ◽  
Wave Focusing ◽  
Group Velocities

Abstract A theory is presented that addresses the connection between low-frequency wave packets (LFWPs) and the formation and decay of coherent structures (CSs) in large-scale atmospheric flow. Using a weakly nonlinear evolution equation as well as the nonlinear barotropic vorticity equation, the coalescence of LFWPs into CSs is shown to require packet configurations for which there is a convergent group velocity field. These LFWP configurations, which are consistent with observations, have shorter wave groups with faster group velocities upstream of longer wave groups with slower group velocities. These wave group configurations are explained by carrying out a kinematic analysis of wave focusing, whereby a collection of wave groups focus at some point in space and time to form a large amplitude wave packet having a single wave front. The wave focusing and the subsequent formation of CSs are enhanced by zonal variations in the background flow, while nonlinearity extends the lifetimes of the CSs. These results are discussed in light of observed blocking formation in the Atlantic–European and South Pacific regions.

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