THE GROWTH OF PHYSICAL IDEAS 115 



rotating around the center of the earth with a velocity at the 

 equator of over a thousand miles an hour. It is also moving 

 around the sun with a velocity of about eighteen miles a 

 second, and the whole solar system is moving among the stars 

 with even higher velocity, the rotation of the galaxy cor- 

 responding to a velocity for the solar system of over one 

 hundred miles a second. To the occupant of a point on the 

 earth, all these motions are unperceived as motion. Einstein 

 expanded his special theory and stated in his general theory 

 of relativity that even accelerated motion cannot be ascer- 

 tained by physical experiment. Sitting in an elevator that is 

 completely sealed, an observer cannot distinguish whether 

 the elevator is moving with accelerated velocity or whether 

 it is restinor in a sravitational field. Einstein's Qreneral rela- 

 tivity theory uses this idea to reduce all physical laws to one, 

 namely, de Fermat's law that the path between t^vo events 

 separating two points in space-time has stationary value com- 

 pared with other paths possible in the gi^avitational fields 

 given by all the effective forces. This theory allows the laws 

 of classical physics to be expressed in a very simple form; 

 moreover, it makes it possible to relate mass to energy. For 

 the transformation of mass into energy, Einstein deduced the 

 relation E = Amc-, where Am is the change in the mass in 

 grams, E the energy produced in ergs, and c is the velocity of 

 light. Since the velocity of light is 3 X 10^^ centimeters per 

 second, c^ = 9 X 10-^ 



Attempts to introduce the atomic structure of matter and 

 energy into a general field theory have not yet been success- 

 ful. At the present time we have dual theories in all fields 

 of physics— a relativistic continuous field theory, which uses 

 disturbances (waves) periodic in time and space and explains 

 the phenomena of interference, polarization, and diffraction, 

 common to all matter and all forms of energy; and an atomic 

 theory of matter and energy, which is basically discontinuous 

 and the laws of which are statistical in nature. 



From the time of Newton to the beginning of the twen- 

 tieth century, astronomy was the science of position. It dealt 



