We get to the bottom of some modern physics. When two particles collide, there is no way that the energy can get to any other particles that may be a nearby. For centuries, physicists have had the idea of particles and waves. Particles are like small bullets, they hurt when they hit you and when they hit each other they bounce off. Waves on the other hand, can pass through each other and through matter.
Waves can interfere with each other, and they can spread out, unlike particles.
The problem came around the turn of the century. An effect known as the photoelectric effect turned a lot of the conventional wisdom on its head. The photoelectric effect is where light is shone on to a metal. Much of the time nothing happens. However, if the light is of a high enough frequency then electrons are emitted from the metal.