Universality
This is a common theme in physics. Universality is found in dynamic systems where a certain property is found regardless of the details. More simply it is seen when one is modeling some system and a particular property has the same form whether the model uses more particles or less particles or even different particles.
Van der Waals Equation and Critical Points
The Van der Waals equation is parameterized for certain particles by the a and b constants. Due to these two constants every Van der Waals system is slightly different. However, these two constants can be replaced by the critical pressure, volume, and temperature. Once this is done one can graph the proportions of the actual pressure to the critical pressure versus the proportion of the actual volume to the critical volume. In this form all Van der Waals systems are identical. Also all Van der Waals systems exhibit the property that:
