Gravitational waves do not directly affect the hydrogen line. The hydrogen line refers to a specific spectral line in the electromagnetic spectrum associated with the transition of an electron in a hydrogen atom between two energy levels.
Gravitational waves, on the other hand, are ripples in the fabric of spacetime caused by the acceleration of massive objects. When a gravitational wave passes through space, it can cause a stretching and squeezing effect on objects, including the spacetime itself. However, this effect is extremely small for typical gravitational waves.
The interaction between gravitational waves and electromagnetic radiation, such as light, occurs at a higher-order level of physics. Gravitational waves can cause a phenomenon known as gravitational wave-induced birefringence, where the polarization of light passing through the gravitational wave is affected. However, this effect is very weak and difficult to detect.
So, in summary, while gravitational waves can have subtle interactions with electromagnetic radiation, they do not directly affect the hydrogen line or have a significant impact on atomic transitions. The hydrogen line remains a fundamental feature of atomic spectroscopy that is primarily governed by the electromagnetic interaction between electrons and photons.