Cosmic rays are high-energy radiation coming from outside the solar system. The detection of cosmic rays of an energy past a threshold called the Greisen–Zatsepin–Kuzmin limit contradicts current theories in physics, so it is the aim of the SOLTA project to find out where these extremely high-energy cosmic rays are coming from. An advancement in knowledge about these types of cosmic rays is regarded as key in the refinement of current theory.
To get a better idea of what we’re dealing with when we talk about cosmic rays, check out this video done by Harvard Natural Science Lecture Demonstrations.
The trajectories of charged particles, including some cosmic rays, can be seen as they ionize the cooled alcohol vapour inside the cloud chamber.