114 THE PATH OF SCIENCE 



of very careful investigations and no difference was found. 

 Repetitions of the experiment with Edward Morley, from 

 which it is generally known as the Michelson-Morley experi- 

 ment, gave essentially the same result. The ether is station- 

 ary ^vith regard to the earth, and, at the same time, no evi- 

 dence can be found that it is dragged with the planets. The 

 first solution of this paradox was given by Einstein in his 

 special relativity theory, in which he re-examined the founda- 

 tions of Newtonian mechanics. 



The conception of space and time as independent frame- 

 works presupposes that we can compare time in different 

 points of space, and that the meaning of simultaneity at 

 points separated in space can be clearly defined. If we had 

 instantaneous signals, this would be self-evident; but even 

 light needs time to travel from one point to another. Ein- 

 stein took the fundamental result of the Michelson-Morley 

 experiment, that light has a velocity independent of the mo- 

 tion of the observer, as the basis of his new theory. AV^ith 

 the help of this definition, we can define the simultaneity of 

 t^vo events for a given observer. The laws of physics become 

 laws in space-time. The difference from classical physics is 



given by a correction factor . /l wherein c is the ve- 

 locity of light and v the relative velocity of the object with 

 respect to the observer. Since the velocities of matter are 

 mostly very small compared to the velocity of light, the cor- 

 rection factor can be neglected in most practical cases, thus 

 leaving the bulk of physical experience uncorrected. How- 

 ever, it has served to explain some phenomena, such as the 

 motion of the perihelion of Mercury, and is of importance 

 in connection with the structure of spectral lines that arise 

 from the motion of electrons. 



The classical laws of motion teach that no physical experi- 

 ment can distinguish a state of uniform velocity from a state 

 of rest. The rapid and complicated movement of a point on 

 the earth, for instance, is not felt as movement by the in- 

 habitants of the earth in spite of the fact that the point is 



