"Modern" physics introduced B. C. E. Think of bringing back to the civilizations before the common era physics that could practically be used. For instance, an electric magneto might be fashioned by ancient peoples with access to magnetite and copper. Using his laws, planetary motion could easily be forcast accurately long before Kepler. They might be able to isolate radioactive compounds. Even a crystal radio transmitter and receiver would be constructible then. What modern physics would you share with the people of the past that they might implement?