The main evidence that suggests neutrinos are different is the phenomenon of neutrino oscillation. This is when neutrinos change from one type (or "flavor") to another as they travel through space. This can only happen if the neutrinos have mass, which was previously thought to be impossible.
The evidence of neutrino oscillation was discovered through several experiments, including the Super-Kamiokande and Sudbury Neutrino Observatory experiments. These experiments used large detectors to observe the behavior of neutrinos coming from the sun and from supernovae. The results showed that the number of neutrinos detected was lower than expected, indicating that they were changing into different types.
Neutrinos were previously thought to be all the same because they have very little interaction with matter and are difficult to detect. This made it challenging to study their properties and behavior. Additionally, the Standard Model of particle physics, which describes the fundamental particles and forces in the universe, did not include the possibility of neutrino oscillation.
The discovery of neutrino oscillation has greatly impacted our understanding of the universe. It has confirmed that neutrinos have mass, which was previously not accounted for in the Standard Model. This can lead to new theories and explanations for the behavior of particles and the structure of the universe. It also opens up the possibility for new experiments and discoveries related to neutrinos.
The discovery of neutrino oscillation has potential applications in a variety of fields. For example, it can help us better understand the processes happening in the sun and other stars, as well as in supernovae. It can also potentially lead to new technologies, such as more precise detectors or even neutrino-based communication systems. Additionally, it may have implications for our understanding of dark matter and dark energy, two mysterious components of the universe that make up a large portion of its mass and energy.