Hold out your thumbnail. In the second it takes to read this, billions of tiny particles will pass straight through it, then through the floor, the planet, and out the other side.
About 10 billion neutrinos cross every square centimetre of Earth each second. You will never feel a single one, and neither will almost anything else. This year, one man won the Nobel Prize for catching them anyway, using a giant cube of ice at the bottom of the world.
The ghost nobody wanted to invent
In 1930, the physicist Wolfgang Pauli had a problem. Energy seemed to vanish during radioactive decay, so he proposed an invisible particle that was quietly carrying it away.
He worried he had invented something no one could ever detect. It took 26 years, and a nuclear reactor producing neutrinos in huge numbers, before anyone proved him wrong.
Why they slip through everything
Neutrinos have no electric charge and almost no mass. They ignore the forces that make matter feel solid, so to a neutrino, a planet is mostly empty space.
A neutrino could cross a wall of lead light-years thick and still have a fair chance of coming out untouched. That is why scientists call them ghost particles.
How to catch a ghost
You cannot make a neutrino more willing to interact, but you can give it more chances. If only one in a trillion bumps into an atom, you need an enormous target and a great deal of patience.
When a neutrino does strike an atomic nucleus, it sets off charged particles that race through the material faster than light can travel in it. The result is a faint blue flash, the optical cousin of a sonic boom.
Why the South Pole?
In 1988, Belgian-born physicist Francis Halzen of the University of Wisconsin–Madison had a bold idea. Deep Antarctic ice is crushed so hard by the weight above that its air bubbles are squeezed out, leaving it clearer than almost anything on Earth.
It is also pitch dark, perfectly still and free of earthquakes. In other words, it is the ideal place to watch for those faint blue flashes.
Building Ice Cube
Engineers used hot water to drill deep holes into the ice and lowered strings of light sensors into them before the water refroze. More than 5,000 sensors now sit between about 1.5 and 2.5 kilometres down, spread through a full cubic kilometre of ice.
The idea took 23 years to become reality, with Ice Cube completed in 2011. Remarkably, the detector often looks downward, using the whole Earth as a filter so that only neutrinos make it through from below.
Finding the needle
Most of what Ice Cube records is local noise. Every day it detects more than 100 million particles created when cosmic rays strike the air above Antarctica.
The breakthrough was picking out the rare, ultra-high-energy neutrinos that come from deep space. Because neutrinos travel in straight lines and pass-through dust and gas, they point back to their source like arrows.
Messages from black holes
In 2013, IceCube reported the first convincing high-energy neutrinos from beyond our solar system. In 2017, a single neutrino was traced to a blazar, a galaxy with a jet-firing supermassive black hole about four billion light-years away.
Later work linked neutrinos to the active galaxy NGC 1068. The team also produced the first neutrino picture of our own Milky Way.
The Nobel
On 6 October 2026, Francis Halzen was awarded the Nobel Prize in Physics for his decisive role in IceCube and the discovery of high-energy neutrinos from space. He is the first person to win the physics prize alone since 1991.
The Nobel committee praised his tenacity and vision for opening a new kind of astronomy. At 82, he shows no sign of slowing down, and on the day of the announcement he said he was busy working on a proposal.
The Byte to Remember
The most elusive particle in the universe was caught by turning a kilometre of Antarctic ice into an eye. That eye looks through the Earth itself and sees black holes billions of light-years away.
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Sources: NobelPrize.org, Physics World, Kathmandu Post / Reuters, Times Higher Education, Qatar Tribune / DPA, WUNC / AP, Berliner Zeitung.
