## landmark LIGO Observation Confirms Hawking’s Black hole Area Theorem with Unprecedented Precision
Recent observations by the Laser Interferometer Gravitational-wave Observatory (LIGO) have provided the strongest confirmation yet of a fundamental theorem proposed by the late Stephen hawking: the black hole area theorem. This theorem states that the total area of a black hole’s event horizon can never decrease over time, even when black holes merge.
The confirmation stems from the analysis of gravitational waves emitted during the merger of two black holes, designated GW250114 – a signal detected on January 14, 2025. While similar to LIGO’s first detection in 2015 (GW150914), involving black holes approximately 1.3 billion light-years away with masses 30 to 40 times that of our sun, the GW250114 signal was significantly clearer due to a decade of advancements in detector technology. These improvements have made the LVK detectors – LIGO, Virgo, and KAGRA – the most precise measurement tools ever created, capable of detecting distortions in spacetime smaller than 1/10,000 the width of a proton. (Virgo and KAGRA were offline during this specific observation.)
By meticulously analyzing the frequencies of the gravitational waves,the LIGO team was able to provide the best observational evidence to date supporting Hawking’s theorem. The team focused on the “ringdown” phase of the merger - the period after the black holes coalesce when the newly formed black hole vibrates, analogous to a struck bell.
Researchers were able, for the first time, to confidently identify two distinct gravitational-wave modes within this ringdown phase. These modes, similar to the different tones a bell produces, decay at different rates and are notoriously arduous to distinguish.Extracting these modes allowed the team to precisely calculate the mass and spin of the resulting black hole,and subsequently,its surface area.
This new analysis achieved a confidence level of 99.999%, a substantial improvement over a previous test performed in 2021 using the GW150914 data, which yielded a confidence level of 95%.The confirmation is particularly poignant given hawking’s long-held belief in the testability of his theorem using gravitational wave detectors. Nobel Laureate Kip Thorne recounts Hawking inquiring about LIGO’s potential to verify the theorem shortly after the initial gravitational wave detection in 2015. Sadly, Hawking passed away in 2018 and did not live to witness the observational confirmation of his work. Thorne noted that Hawking “would have reveled in seeing the area of the merged black holes increase.”
The research, published in *Physical Review Letters* (https://doi.org/10.1103/kw5g-d732), represents a significant milestone in our understanding of black holes and the fundamental laws governing the universe.
