SEMANTICS OF THE EINSTEIN THEORY 653
endowed them with objective values of definiteness and rigidity, we dealt with 'absolute space' and with 'absolute time', which was 'unchanging' and 'the same for all'. In the older assumptions our velocities varied. If A had a velocity of 5 centimetres per second, for instance, and B was overtaking A with a velocity of 7 centimetres per second, the relative velocity between A and B would be 7 5 = 2 cm. per second. The units of 'space' and 'time' were definite, immutable and did not and could not vary, which followed directly from the assumptions of an 'objective' 'absolute space' and 'absolute time'.
In the case of light, we came in contact with a velocity which did not vary for any observer no matter what his relative motion. The velocity c was found to be constant, so the natural assumption to make is that our 'space' and 'time' vary for different observers.
In the above equations as they stand, 'absolute time', t=t, the 'same' for all observers is assumed, which made such equality impossible. Assuming dif-
sides t, which makes the equation impossible, whereas in the second equation we have on the left-hand side t and on the right-hand side a different t; namely, t'.
The above considerations mean that there is a definite structural discrepancy between the old language and the empirical world, requiring a fundamental structural linguistic revision. This revision has been accomplished, and is known as the Einstein theory. It is not implied that Einstein's work is final, but that it shows clearly the structural errors of the old elementalism to which we can never return.
In other words, in the older mechanics we had definite and permanent 'time' (absolute) and varying relative velocities. Dealing with light-waves we find experimentally that the velocity, c, of light does not vary with the relative motions of the observers and we must assume a variable time to preserve our equations.
An obvious objection can be raised to this: why alter our habitual notions of 'time'? Can we not keep the old s.r and find some other method of compensation, less bothersome and less revolutionary? The older physicists and Einstein give a long and convincing list of perfectly sufficient reasons for such a change; yet their arguments always leave us somehow in doubt, with the feeling of a lurking possibility that the old can be preserved.
What has already been said in this work about structure and semantic disturbances and the fact that the terms 'matter', 'space', and 'time' are not objects, which they cannot be, removes perhaps for good and all, the last doubt as to the revolutionary and epoch-making significance and value of the structural linguistic discoveries of Einstein. On these grounds alone the return to