If we can look at all the atoms in a copper wire between a point of zero volts and a point of, say, 10,000 volts and observe no difference in any of the atoms then where is the Voltage? Is it perhaps as with the kinetic energy of a brick raised to a great height with respect to the earth - a manifestation of the work done to move against the acceleration of gravity? i.e. the gravitational 'force' ? And in the case of electricity an 'electromagnetic force' ? i.e. a field that we observe only through its effects upon certain things we put in the field?