Ten years ago today, on Sept. 14, physicists detected gravitational waves rippling through the cosmos for the first time.
When such massive objects accelerate — such as when two black holes collide — they would send ripples through the cosmos, called gravitational waves, he posited.
But if a gravitational wave was passing by, Weiss reasoned, these beams would be ever-so-slightly out of phase.
That’s because gravitational waves temporarily smoosh and stretch space-time, thereby creating fluctuations in the length of the passageways through which the laser beams travel.
And in September 2025, scientists from the LIGO Collaboration validated Stephen Hawking’s decades-old theory about black holes, linking quantum mechanics and general relativity.
Today, September 10, is ten years ago. 14. For the first time, physicists saw gravitational waves rippling across the universe.
This discovery has roots that go back a century. Space-time would be warped by massive objects, according to Albert Einstein’s general theory of relativity. He proposed that gravitational waves are ripples that travel through the universe when such massive objects accelerate, like when two black holes collide.
Because the distortion of space-time brought about by these waves would be much smaller than that of a single atom, Einstein never believed that we could detect them.
But MIT physicist Rainer Weiss, who passed away in August, suggested in the 1970s that it might be possible to find these microscopic ripples from massive black hole collisions.
The interferometer, which would divide a laser light beam, was essential to his plan. After passing through two different routes, the light would bounce off hanging mirrors and recombine at its source, where its arrival would be measured by a light detector. It would be normal for these two beams to return simultaneously if the paths were of equal length.
Weiss reasoned that these beams would be ever-so-slightly out of phase if a gravitational wave were passing by. The reason for this is that gravitational waves cause space-time to momentarily squish and stretch, which causes variations in the length of the passageways that the laser beams pass through.
Weiss suggested attempting to measure these elusive waves, as did Caltech physicist Kip Thorne. They claimed that in order to pick up such small signals, the detector pathways had to be extremely lengthy. Additionally, the project would require two widely separated detectors in order to help localize the source of cosmic collisions and rule out the possibility that signals were caused by nearby disturbances.
Two identical L-shaped detectors, each with arms 2.5 to 5 miles (4 kilometers) long, were constructed in Livingston, Louisiana, and Hanford, Washington, respectively, after the Laser Interferometer Gravitational-Wave Observatory (LIGO) project was approved in 1990.
Detectors found nothing for years. In order to make LIGO more sensitive to ever-tinier signals, it was upgraded. In order to prevent the signals from the far-off universe from being obscured, a large portion of that involved shielding the equipment from vibrations brought on by nearby traffic, aircraft, or distant earthquakes.
The scientists activated the upgraded instruments in September 2015.
Spend the night in September. 14. Researchers made an intriguing discovery at both LIGO sites.
“I approached the computer and examined the screen. And, lo and behold, there is this amazing image of the waveform, and it appeared to be precisely what Einstein had envisioned,” Weiss stated in a documentary about the finding.
The detector arms’ length fluctuated, producing a powerful “chirp” that was a thousand times smaller than a nucleus’s diameter.
On Feb. On November 11, 2016, researchers revealed that the event they had caught was caused by the collision of two enormous black holes that occurred roughly 1 point 3 billion years ago. Virgo, a gravitational wave experiment in Europe, discovered the same thing.
The discovery opened up a whole new avenue for researching the most extreme occurrences in the universe. LIGO’s detectors, the Japanese Kamioka Gravitational Wave Detector (KAGRA), and its European counterpart experiment Virgo have detected about 300 collisions since that initial discovery. These collisions include triple black hole mergers and collisions between black holes and neutron stars. A group of researchers declared in June 2023 that pairs of black holes veering toward collision throughout space and time are responsible for the faint “gravitational wave background” that permeates the universe. Additionally, researchers from the LIGO Collaboration confirmed in September 2025 that Stephen Hawking’s long-held theory about black holes—which connected general relativity and quantum mechanics—was correct.
