The forces that keep reacting atoms together include: electromagnetic, strong, weak, and gravitational forces. 

1. The strong nuclear forcebinds the particles within an atomic nucleus. This force attracts neutrons and neutrons, protons to protons, protons to neutrons within the nucleus. 
2. Gravity dictates how matter comes together to form galaxies and shapes the course of the universe's evolution from its creation in the big bang. 
3. The electromagnetic forceis responsible for holding negatively charged electrons in orbit around positively charged atomic nuclei and it is the force behind the bonding between atoms, allowing the generation of bulk matter. 
4. The weak nuclear forceplays a crucial role in the interactions between subatomic particles. It influences particles such as protons, neutrons, and electrons. Unlike the strong force, the weak force functions over extremely short ranges and is responsible for processes such as beta decay.