The humble neutrino particle won its fourth Nobel Prize in physics this year (also in 2002, 1995 and 1988). Despite being millions of times smaller than other subatomic particles, it is of major importance in physics and could be the key to unravelling some of the universe’s best-kept secrets. So where is neutrino research heading next – and what could it discover?

Matter is made of fundamental particles. Most people will have heard of electrons, neutrons and protons – and perhaps even quarks, which make up the latter two. But to me, the neutrino is the most amazing fundamental particle. They are everywhere. About 65 billion neutrinos, produced by nuclear fusion in the Sun, pass through every square centimetre of area on Earth, every second (you could try and calculate that yourself), without doing anything.

Because neutrinos hardly interact with other matter, this year’s Nobel prize winners for physics, Takaaki Kajita and Arthur B McDonald, had to build vast detectors, filled with thousands of tonnes of water, in order to study them. What they found out was that the neutrino is even more interesting than we thought.

While travelling through space, a neutrino apparently continuously flips between different “types” of neutrino, changing the way they interact with matter. This is called neutrino oscillations. You might imagine this as a little fellow that, while running at nearly the speed of light, continuously changes the colour of its jacket by which you are trying to identify it. Neutrinos can only do this if they have mass. So until the results from these experiments were published, they were assumed to be massless. Clearly this was ground-breaking news.