It is theoretically possible that a foreign entity, such as an extraterrestrial civilization, could be transmitting data using wavelengths that are not yet discovered or understood by humans. Our understanding of the electromagnetic spectrum is based on the range of wavelengths and frequencies that we have been able to detect and study so far.
The electromagnetic spectrum encompasses a wide range of wavelengths, from radio waves to gamma rays. Humans have developed technologies to detect and utilize a significant portion of this spectrum, including radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Each portion of the spectrum has its own unique properties and interactions with matter.
However, it is entirely possible that there are other regions of the electromagnetic spectrum that we have not yet explored or discovered. If an alien civilization were to use wavelengths or frequencies that are outside the ranges we currently understand, we might not have the necessary technology or knowledge to detect or interpret their signals.
Discovering and understanding new portions of the electromagnetic spectrum would require advancements in our scientific knowledge, technological capabilities, and the development of new detection and communication systems. Scientists and researchers are continuously exploring and expanding our understanding of the electromagnetic spectrum, but there is still much more to learn.
So while it is within the realm of possibility that a foreign entity could be using unknown wavelengths for communication, until such wavelengths are discovered and studied, we can only speculate about their existence or potential use by extraterrestrial civilizations.