The Father of Physics, Sir Isaac Newton, was the great seventeenth-century English genius.  Newton, like others before him, developed a theory of atomic structure.  Newton's theory was that atoms were like marbles and were indestructible.  It was not until in the 1930s that he was proved wrong and that atoms were not indestructible, but rather a system of subatomic particles: electrons, protons, and neutrons.  In theory, according to Newtonian physics, the relationship of the subatomic particles is unstable and the atom should fall apart.  Yet it was clear from observation that the atom is very stable.  This puzzled many scientists until Niels Bohr, a young Danish physicist, broke through the contradiction.   He showed that the classic model which applies to the movement of planets did not work at the atomic level.  Bohr used the newly emerging quantum theory to explain how electrons can obtain a stable orbit around an atomic nucleus.  This earned Bohr the Nobel Prize in physics in 1922.
    The energy required to hold subatomic particles together brought increased interest and speculation.  Albert Einstein, a famous German physicist, who moved to America in 1933, became interested in the atomic physics.   Working in Switzerland, he came up with the idea that a tiny bit of mass equaled a vast amount of energy and developed the famous equation:

E=mc² (Energy equals mass times speed of light squared)

Expressed in standard units, the value of c² is 10²⁰.   It was said that the if the energy was released from a pound of water, there would be enough to run all the steam engines in the world for two weeks or that the energy released from a piece of metal the size of a fist could exceed all the explosive forces produced since gunpowder was invented.  But could this be done?  People could not comprehend what Einstein was saying.  Many scientists did not agree with Einstein's ideas and believed that the whole idea of converting matter to energy was more like something from a science fiction book.  Einstein and Ernest Rutherford, leaders of the scientific community, were both skeptical.
    Leo Szilard, a Hungarian physicist, devoted much of his time to thinking about the power locked inside an atom.  In 1932, the neutron particle was discovered which lead Szilard to wonder about the binding energy of the atomic nucleus.   He reasoned that the neutron particle, because it had no electrical charge, could penetrate through the atom to the nucleus and cause it to disintegrate to release a great amount of energy along with more neutrons which could disintegrate more atoms, thus causing a chain reaction.

1.  The electron directed at the atom is repelled by the electrons circling the atom.
2.  The proton directed at the atom penetrates the electron orbit but is repelled by the protons at the nucleus.
3.  The neutron is the only particle with no charge that can penetrate through to the nucleus, causing it to disintegrate.

    It was now shown that a chain reaction was indeed possible and scientists in Europe and America continued experimenting with nuclear energy.   Enrico Fermi, Italian physicist, and the team of Otto Hahn and Fritz Strassmann in Berlin worked independently.  They experimented with neutron bombardment of uranium 235.   The results were a variety of radioactive substances.  Scientists saw that the splitting of the uranium nucleus into two parts released a tremendous amount of energy.   Otto Frisch gave it the name fission, from the Latin word meaning split.  Word got around and scientists all over rushed to their laboratories to study the fission process.  This started the idea of an atomic bomb and fear of German aggression became the stimuli for America to build the bomb first.  This became known as the Manhattan Project.  To learn about the Manhattan Project, please continue onto the first atomic bomb and World War II.  If you want to learn about the physics of nuclear fission, please proceed to Nuclear Fission.