"Unified Field Theory"

The Strong Nuclear Force  

​Scientists are aware of four fundamental forces- gravity, electromagnetism, and the strong and weak nuclear forces.  Most people have at least some familiarity with gravity and electromagnetism, but not the other two.  How is it that scientists are so certain that two additional forces exist?  In this video, Fermilab’s Dr. Don Lincoln explains why scientists are so certain that the strong force exists.

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Notes: 
http://aether.lbl.gov/elements/stellar/strong/strong.html