Superluminal transmission
2024-3-17
Definition:
Certain quantities travel faster than the speed of light in a vacuum.
Under certain conditions, the phase velocity or group velocity of light may be greater than the vacuum speed of light c. It seems that information can also be transmitted faster than the speed of light, but this is contrary to Einstein's theory of relativity, because this theory holds that super-light transmission violates causality. but. If you carefully study the existing physical theories (for example, Maxwell's theory of electromagnetic fields, Einstein's theory of relativity and quantum electrodynamics, etc.), you will find that super-light transmission does not have any non-causal effects. Anyone who tries to use traditional physical theory to explain this effect will run into a logical dilemma, because the problems in the middle are not easy to find.
Two relatively simple examples of apparently non-causal transmission are:
The phase velocity of X-rays or near-optical resonance atoms may be greater than c. Even very simple mechanical models (for example, a series of coupled pendulums) can yield phase velocities greater than c. However, the phase wavefront of a specific signal cannot be measured directly, and signal transmission requires some modulation method.
Information can be transmitted by sending pulses. At this time, the propagation speed of information is the group velocity, which is the peak propagation speed. A group velocity greater than c results in superluminal transmission, which can be obtained in tunnel experiments. However, errors are prone to occur in determining the peak value of the information-carrying pulses. For example, a Gaussian-shaped pulse is detected before the peak value is detected because the light intensity was detected some time before. Therefore, a different kind of signal needs to be considered, one in which no information is transmitted prior to detection. When using this kind of signal, the earliest time it can be detected is when it travels at the speed of light c in vacuum. A precursor's light travels at this speed, but is usually too weak to be detected, except in special circumstances.
Of course, existing physical theories, such as Einstein's theory of relativity, may also need to be reconsidered or replaced by new theories that even allow for faster-than-light transmission. Such a theory already exists, but so far there is no credible evidence to support replacing the relativistic theory with a new one.
Certain quantities travel faster than the speed of light in a vacuum.
Under certain conditions, the phase velocity or group velocity of light may be greater than the vacuum speed of light c. It seems that information can also be transmitted faster than the speed of light, but this is contrary to Einstein's theory of relativity, because this theory holds that super-light transmission violates causality. but. If you carefully study the existing physical theories (for example, Maxwell's theory of electromagnetic fields, Einstein's theory of relativity and quantum electrodynamics, etc.), you will find that super-light transmission does not have any non-causal effects. Anyone who tries to use traditional physical theory to explain this effect will run into a logical dilemma, because the problems in the middle are not easy to find.
Two relatively simple examples of apparently non-causal transmission are:
The phase velocity of X-rays or near-optical resonance atoms may be greater than c. Even very simple mechanical models (for example, a series of coupled pendulums) can yield phase velocities greater than c. However, the phase wavefront of a specific signal cannot be measured directly, and signal transmission requires some modulation method.
Information can be transmitted by sending pulses. At this time, the propagation speed of information is the group velocity, which is the peak propagation speed. A group velocity greater than c results in superluminal transmission, which can be obtained in tunnel experiments. However, errors are prone to occur in determining the peak value of the information-carrying pulses. For example, a Gaussian-shaped pulse is detected before the peak value is detected because the light intensity was detected some time before. Therefore, a different kind of signal needs to be considered, one in which no information is transmitted prior to detection. When using this kind of signal, the earliest time it can be detected is when it travels at the speed of light c in vacuum. A precursor's light travels at this speed, but is usually too weak to be detected, except in special circumstances.
Of course, existing physical theories, such as Einstein's theory of relativity, may also need to be reconsidered or replaced by new theories that even allow for faster-than-light transmission. Such a theory already exists, but so far there is no credible evidence to support replacing the relativistic theory with a new one.
