As the universe expanded and cooled, it crossed transition temperatures at which forces separated from each other. These cosmological phase transitions can be visualized as similar to condensation and freezing phase transitions of ordinary matter. At certain temperatures/energies, water molecules change their behavior and structure, and they will behave completely differently. Like steam turning to water, the fields which define the universe's fundamental forces and particles also completely change their behaviors and structures when the temperature/energy falls below a certain point. This is not apparent in everyday life, because it only happens at far higher temperatures than usually seen in the present-day universe.