Related papers: Faster-than-c signals, special relativity, and cau…
From a mathematical point of view velocities can be larger than c. It has been shown that Lorentz transformations are easily extended in Minkowski space to address velocities beyond the speed of light. Energy and momentum conservation fixes…
The possibility is discussed of superluminal motion of non-tachyonic (i.e. moving with the instantaneous speed v<c) bodies within general relativity. It is shown that in some occasions quantum field theory apparently prohibits such motion,…
In sonic models of special relativity, the fact that the sonic medium violates (ordinary) Lorentz symmetry is apparent to observers external to the sonic medium but not to a class of observers existing within the medium itself. We show that…
The notion of Einstein causality, i.e. the limiting role of the velocity of light in the transmission of signals, is discussed. It is pointed out that Nimtz and coworkers use the notion of signal velocity in a different sense from Einstein…
Some recent experiments led to the claim that something can travel faster than light in vacuum. However, such results do not seem to place relativistic causality in jeopardy. Actually, it is possible to solve also the known causal…
Causal "superluminal" effects have recently been observed and discussed in various contexts. The question arises whether such effects could be observed with extremely weak pulses, and what would prevent the observation of an "optical…
We calculate the delay in the propagation of a light signal past a massive body that moves with speed v, under the assumption that the speed of propagation of the gravitational interaction c_g differs from that of light. Using the…
Non-tachyonic superluminal sectors of matter (superbradyons), with critical speeds in vacuum much larger than the speed of light, can quite naturally exist and play an important role in both cosmic-ray physics (anomalous high-energy events)…
Recent results demonstrating superluminal group velocities and tachyonic dispersion relations reopen the question of superluminal signals and causal loop paradoxes. The sense in which superluminal signals are permitted is explained in terms…
A particular problem about special kind of two light pulses propagation has been considered in cases of inertial motion, constant homogeneous gravitation field and progressive non-inertial motion with constant acceleration. A contradiction…
One may believe that front velocities of waves in a given theory coincide with the UV limit of phase velocities for any dispersion relations. This implies that IR physics is irrelevant to the discussion of propagation speed of waves. We…
We extend Kramers-Kronig relations beyond the optical approximation to dielectric functions that depend not only on frequency but on the wave number as well. This implies extending the notion of causality commonly used in the theory of…
Within an axiomatic framework, we prove that the existence of faster than light particles is consistent with (does not contradict) the dynamics of Einstein's special relativity.
The state equation of strangeon matter is very stiff due to the non-relativistic nature of and the repulsing interaction between the particles, and pulsar masses as high as $\sim 3M_\odot$ would be expected. However, an adiabatic sound…
The apparent superluminal propagation of electromagnetic signals seen in recent experiments is shown to be the result of simple and robust properties of relativistic field equations. Although the wave front of a signal passing through a…
We investigate the causal hierarchy in various modified theories of gravity. In general relativity the standard causal hierarchy, (key elements of which are chronology, causality, strong causality, stable causality, and global…
Present low-energy bounds on Lorentz symmetry violation do not allow to exclude the possible existence of superluminal particles (superbradyons) with critical speed in vacuum $c_i \gg c$ (c = speed of light) whose kinematical properties…
We consider pulse propagation in a linear anomalously dispersive medium where the group velocity exceeds the speed of light in vacuum (c) or even becomes negative. A signal velocity is defined operationally based on the optical…
We propose a brand-new formalism for the propagation of relativistic cosmic ray (CR) particles. The propagation of CRs has often been described using the diffusion approximation, which has the drawback that the propagation speed of CRs near…
We reconsider a thought experiment that employs the entanglement of the gravitational field with position space quantum states as a means for faster-than-light signaling. We present a protocol that includes the excitation to a higher…