The characteristics of gravitational waves that make them difficult to detect are
long wavelength and high energy
long wavelength and low energy
short wavelength and high energy
short wavelength and low energy
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UPSC Geoscientist – 2022
Gravitational waves are difficult to detect primarily because they interact very weakly with matter, resulting in incredibly small amplitudes (strains) by the time they reach detectors on Earth. This weak interaction is associated with low energy flux at large distances from the source. The relevant wavelengths for detectable sources are often quite long (hundreds to thousands of kilometers for ground-based detectors, much longer for proposed space-based detectors), which necessitates very large and sensitive instruments like interferometers.
The difficulty in detecting gravitational waves stems from their weak coupling to matter. This means they cause only tiny distortions (strains) in spacetime as they pass through. Even waves from catastrophic events like black hole mergers result in strains of only about 10⁻²¹ to 10⁻²². Detecting such minuscule changes requires extraordinarily sensitive instruments, isolated from environmental noise. The energy carried by the waves, while immense near the source, spreads out over vast cosmic distances, leading to extremely low energy flux at the detector.