Rainer Weiss: 1932-2025
September 2025 :
It is with great sadness we report the passing of the great physicist and educator (and Skyscrapers presenter!) Rainer Weiss on August 25, 2025. Rainer was central to two landmark experiments in astrophysics, opening up two of the most important fields of study: the measurement of the cosmic microwave background (CMB) and the detection of gravitational waves (the latter of which earned him the 2017 Nobel Prize in Physics. He was also a talented teacher and mentor, training several generations of experimental physicists as part of his professorship at MIT.
In both projects, Rainer demonstrated the importance of taking the long view of experiments. When he joined the Dicke lab at Princeton in 1962, the group was just beginning to design experiments to detect the remnant glow from the early Universe (Dicke’s group was “scooped” by Penzias & Wilson at Bell Labs in 1965). Rainer continued making improvements to CMB measurements, eventually (27 years later) co-founding the Cosmic Background Explorer (COBE) experiment that first detected the fluctuations in the background that are the signatures of the lumpiness in the Universe out of which all structures formed. Similarly, already in the early 1970s, Weiss had come up with the idea of using laser interferometers to measure gravitational waves. At the time, the technology was not mature enough to build what would eventually be the Laser Interferometer Gravity Observatory (LIGO). Through years of null results, Rainer and his collaborators persevered, culminating in LIGO’s first detection in September 2015, more than 40 years later.
Rainer was gracious and generous with his time. I personally treasure how he approached his visit to Seagrave with no pretensions, showing interest in everyone’s work and stories without any signs of pretentiousness and without stressing his status as a world-renowned physicist. Generations of physicists will miss working and talking with him.
