Light Signals, the Special Theory of Relativity, and Reality

Alfred Arthur Robb

Günter Nimtz

Superluminal signal velocity is widely assumed to confront Einstein causality and thus the Special Theory of Relativity (STR). Actually, there is only the tunneling mechanism known to permit superluminal signal velocities at present. The demonstrated negative group velocity experiments don't represent superluminal signal velocities. In those experiments only the signal's peak traveled faster than light and the signal was reshaped. In this Note we shall discuss why tunneling allows superluminal signal velocities. However, opposed to text books on STR we have shown that a superluminal signal beam does not allow the design of a time machine.

John Lighton Synge

Won-Young Hwang

We prove a special case of Helstrom theorem by using no-signaling condition in the special theory of relativity that faster-than-light communication is impossible.

Gerhard Grössing

Jose Javier Garza Cuartero

The speed of light, c, is the best-confirmed constant in physics. Within Special Relativity, it defines the causal structure of spacetime and no experiment has ever recorded an object exceeding it. This paper does not dispute any of that. What this paper argues is that quantum entanglement constitutes direct experi­mental evidence that the extrapolation of c to a universal limit across all layers of physical reality is not justified by the data. c is the fundamental limit of rel­ativistic spacetime. Whether it is also the limit of whatever substrate gives rise to that spacetime is a question the experiments force us to take seriously—and that current physics leaves genuinely open. Bell-test experiments, confirmed from Aspect (1982) to the Large Hadron Col­lider (2023), show that entangled correlations cannot be explained by any local model. Something produces those correlations without any mechanism that re­spects c. The no-communication theorem shows that this cannot be exploited for signalling today, within the current framework. It does not show that c gov­erns the mechanism that produces the correlations. Those are different claims, and conflating them has allowed a mathematical result about signal statistics to carry unwarranted ontological weight. This is a conceptual and philosophical analysis grounded in experimental results. It does not propose a new theory. It argues that the evidence we already have is sufficient to challenge the extrapolation that treats c as an absolute limit across all layers of physical reality. That extrapolation is not forced by the data. It is a theoretical choice and a contestable one.