all was air, while Xenophanes conceptualized all things as earth. Empedocles later proposed that, as opposed to being made from any one substances, the physical world was comprised of all four forces.
Since the time of Albert Einstein, physicists have pursued the hypothesis that the four known forces--gravity, electromagnetism, and the weak and the strong versions of the nuclear force--are derived from a single primordial energy, consistent with the concept of Heraclitus. Stephen Hawking contended that by joining the four primordial forces into a single theory, humankind may achieve a complete model of the universe, and thereby come to "know the mind of God."
In the contemporary period, public interest in electromagenetics ranges from the field of astrophysics to a concern over the potentially harmful effects of radiation from electric power lines. One popular theory holds that electromagnetic forces governing charged dust particles in cosmic plasmas may be more important than gravitation in the formation of bodies such as planets. The argument that gravity dominates the dynamics of the universe is a difficult proposition to accept for many astronomers. The laws of gravity are central to the explanations of phenomena ranging from the structure of planetary rings to the formation of stars. The concept of a universe shaped primarily by gravity, however, is beginning to attract researchers.
At the other end of the spectrum of public interest, an upsurge in public concern has developed "about the invisible fog of electromagnetism" in which contemporary society is said by some to exist. Every electric motor, appliance, and current-carrying wire radiates energy as a byproduct of normal operation, as does the use of radio waves in communication technology applications, and microwave ovens, electric blankets, and electric ranges in the home, and as does the radar equipment used by police, meteorologists, and military pers...