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In physics, there are four fundamental forces—gravitational, electromagnetic, strong, and weak. Each plays a vital role in how the universe works. For example, the strong force is what holds atoms together. For years, physicists have sought a single theory that explains how all the forces work together: the theory of everything. Even on his deathbed, Einstein was working on this problem. Some believe no solution exists. What notable physicist once believed it was possible, then changed his mind? Discuss
Source: The Free Dictionary