Physicists cannot see subatomic particles directly, for instance, so they verify their existence by watching for telltale tracks that the particles leave in cloud chambers.

• 例如物理学家无法直接观察次原子粒子，因此他们观察那些粒子在云雾室中的轨迹，轨迹证实它们的存在，并透露了它们的性质。