What does it mean for a cosmic ray to have an energy 1020 eV?
Physicists have learned that one way of understanding nature is by classifying it by sizes. Everyone sees small things and big things, but scientists quantify these notions. Here’s an example: A mouse is about 10 cm long. The Sun is about 10,000 million mice across. Now imagine if one day you ran across a mouse that was the size of the Sun. You might say: Cheese, I wonder how it got that big! Physicists are asking the same question when it comes to cosmic rays. On Earth we know what “everyday” fundamental particles, such as protons, are like. (We quantify them by measuring their mass-energy.) But when we study radiation from space, we find a few of them with as much more energy as the everyday ones on Earth, as the size of a mouse when compared to the size of the Sun. The curiosity of the situation is that cosmic rays and particles we find on Earth are both the same type of object. How is it that nature can produce such a variety?
