Originally posted by Hurkyl
Because a FTL signal going forward in time in one reference frame will go backwards in time in some other reference frame.
Causality is the concept that events have a cause and effect relationship, meaning that one event causes another to happen. FTL (faster-than-light) signals, which are signals that appear to travel faster than the speed of light, can potentially violate causality by allowing information to be sent back in time.
Currently, there is no evidence to suggest that FTL signals are possible. According to Einstein's theory of relativity, the speed of light is the fastest possible speed for any object or signal. If FTL signals were to exist, they would violate this fundamental principle and have not been observed in any experiments.
Some theories suggest that FTL signals could exist in certain conditions, such as through the use of wormholes or quantum entanglement. However, these theories are still hypothetical and have not been proven to be possible.
If FTL signals were to exist and violate causality, it could lead to paradoxes and contradictions in the laws of physics. For example, it could allow for the possibility of traveling back in time and changing events, which could fundamentally alter the course of history.
The study of causality and FTL signals is important for understanding the fundamental laws of the universe and how they govern the behavior of matter and energy. It also helps us to explore the limits of what is possible and what may be beyond our current understanding. By studying these concepts, we may gain a deeper understanding of the nature of space, time, and the universe itself.