The 2017 Nobel Prize in Physics was awarded for the **first observation of gravitational waves**. This discovery confirmed a major prediction of Albert Einstein’s general theory of relativity.

Gravitational waves are tiny ripples in space-time caused by massive cosmic events like black hole collisions. Scientists observed these waves using the LIGO detectors.

This breakthrough opened a new way of observing the universe. So, the correct answer is **First Observation of Gravitational Waves**.