113 Years of Discovery
From Victor Hess's balloon flights to modern multi-messenger astronomy.
1912
Victor Hess ascends to 5,300m in a hydrogen balloon and discovers radiation increases with altitude — proving extraterrestrial origin. He wins the Nobel Prize in 1936.
1932
Carl Anderson discovers the positron in cosmic ray tracks — the first evidence of antimatter. This earns him a share of the 1936 Nobel Prize with Hess.
1938
Pierre Auger discovers that cosmic rays create cascades of billions of secondary particles — extensive air showers spanning kilometers. This enables ground-based detection.
1962
John Linsley detects the first cosmic ray above 10²⁰ eV at Volcano Ranch, New Mexico — energy equivalent to a baseball pitch compressed into a single proton.
1966
Greisen, Zatsepin & Kuzmin independently predict cosmic rays above 5×10¹⁹ eV should be absorbed by CMB photon interactions, limiting sources to ~100 Mpc.
1991
The Fly's Eye detector in Utah observes a cosmic ray at 3×10²⁰ eV — about 40 joules in a single particle. It remains the highest energy ever recorded.
2004
The world's largest cosmic ray detector begins operation in Argentina: 3,000 km² with 1,600 water Cherenkov detectors and 27 fluorescence telescopes.
2008
Northern Hemisphere's largest cosmic ray detector achieves full operation in Utah, providing complementary full-sky coverage with Auger.
2015
LIGO detects gravitational waves from merging black holes — opening multi-messenger astronomy and enabling correlation studies with cosmic rays.
2017
Pierre Auger confirms a ~6.5% dipole anisotropy above 8 EeV at 5.2σ significance — first strong evidence that the highest-energy particles are extragalactic.
2021
Pierre Auger releases 10% of cosmic ray data publicly, including the 100 highest-energy events with full reconstruction parameters.
2023
Telescope Array detects a 2.4×10²⁰ eV cosmic ray — the second-highest energy ever. Its arrival direction points toward the Local Void, deepening the mystery.
2025
After 113 years, the origin of ultra-high-energy cosmic rays remains unknown. New multi-messenger approaches may finally crack the puzzle.