I can mention a significant scientific discovery up until my understanding.
One notable scientific discovery in recent years is the detection of gravitational waves, which was announced in 2016. Gravitational waves are ripples in the fabric of spacetime caused by the acceleration of massive objects. Their existence was predicted by Albert Einstein's general theory of relativity in 1915, but it took nearly a century to directly detect them.
The Laser Interferometer Gravitational-Wave Observatory (LIGO) made the groundbreaking observation of gravitational waves on September 14, 2015. LIGO detected the gravitational waves generated by the merger of two black holes, which resulted in a distinctive pattern of oscillations in space and time. This discovery not only confirmed Einstein's theory but also opened up an entirely new way of observing and studying the universe.
Since then, additional gravitational wave detections have been made, including signals from the merger of neutron stars and other black hole mergers. These discoveries have provided valuable insights into astrophysics, allowing scientists to study phenomena that were previously inaccessible through traditional astronomical observations.
It's important to note that there have been numerous significant scientific discoveries in various fields over the past five years. However, the determination of the "most important" discovery can be subjective and can vary depending on the specific field of study and the perspective of different individuals.