Which type of noise with non-zero spectral density centered around fc can be bypassed by nature?

The question pertains to types of noise in signal processing and communication systems. The correct answer, Gaussian noise, is often characterized by its constant power spectral density, which remains uniform over a range of frequencies.

Gaussian noise exists in many natural processes and measurements, and its statistical properties make it highly predictable and manageable in various applications. This predictability contributes to its significant role in communication theory, where it is commonly assumed for signal analysis and design.

The other types of noise mentioned—Galactic noise, External noise, and Atmospheric noise—have specific origins and characteristics that may not align with the concept of being 'bypassed by nature.' Galactic noise is the noise originating from celestial sources, while external noise refers to noise from sources outside the system being analyzed. Atmospheric noise includes phenomena caused by weather and ionospheric conditions. Each of these noise types possesses unique properties and spectra, making them less uniform and manageable compared to Gaussian noise.

Thus, Gaussian noise serves as a theoretical foundation in signal processing, explaining its relevance in this context.