I vividly remember the first time I read one of Francis Halzen’s papers about high-energy neutrinos. It was the late 1990s, and I was an undergraduate student at the University of California, Berkeley. The field of astroparticle physics was young, and Halzen was making predictions that couldn’t be tested using conventional particle accelerators.

On 6 October, Halzen was awarded the Nobel Prize in Physics for his work on the IceCube Neutrino Observatory at the South Pole. The experiment uses sensors embedded in the ice to detect high-energy neutrinos (a type of fundamental particle) that have been blasted towards Earth from distant cosmic accelerators.

Nobel physics prize awarded for detection of cosmic neutrinos

Astroparticle physicists have lots of ideas for experiments that have the same discovery potential as IceCube. For example, the underwater Pacific Ocean Neutrino Experiment (P-ONE) — a collaboration between North America and Europe — is currently under construction off the coast of Vancouver Island, Canada. There are also several projects searching for dark matter (a substance that does not interact with or emit light), including the XLZD Collaboration (a European–North American consortium) and PandaX in China.

However, realizing these experiments is not easy. The story of Halzen and IceCube is a lesson not just about fundamental science, but also about what it will take to build the infrastructure that will support discoveries over the next few decades.

When I first read Halzen’s paper (F. Halzen et al. Astrophys. J. 527, L93–L96; 1999), IceCube was not yet built, but its predecessor, called the Antarctic Muon and Neutrino Detector Array (AMANDA), was running. The construction of AMANDA cost around US$7 million. This is much less than the $271 million it cost to build IceCube. Nevertheless, realizing experiments at this smaller scale can be difficult. They require more resources than an initial proof-of-concept project, but they are not large enough to make a discovery.

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Many countries face difficult decisions about research funding, and I am concerned that small and mid-scale projects could be an easy target for cuts. For example, the 2023 US particle physics strategic plan (P5) recommended creating a portfolio of small-scale experiments. However, because of budgetary constraints, it is unclear whether the proposed portfolio will go ahead.