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Alan also saw that Einstein avoided philosophical discussions of what space and time 'really were', and instead concentrated on something that could in principle be done. Einstein placed great emphasis on 'rods' and 'clocks' as part of an operational approach to physics, in which 'distance', for instance, only had meaning in terms of some well-defined measuring operation, not as an absolute ideal. Alan wrote:
艾伦还看到，爱因斯坦避开了哲学式的关于"时间和空间到底是什么"的讨论，相反地，他把注意力集中在一些可以做到的事情上。爱因斯坦强调，"木棒"和"时钟"是物理学中可操作的研究手段，但像"距离"这样的东西，只有在一些严格定义的测量操作中才有意义，不能绝对理想化。艾伦写道：
Its are always the same distance apart, as you stipulate that that distance is your unit and your ideas have to go by that definition. … These ways of measuring are really conventions. You modify your laws to suit your method of measurement.
如果你站在自己的角度来定义距离，并让你的想法满足你的定义，然后你问，两个点之间的距离是否一样，这就是无意义的……
No respecter of persons, he preferred a piece of working of his own to that supplied by Einstein 'because in this way I think it should seem less “magicky”.' He reached the very end of the book, and gave a masterly derivation of the law* which in General Relativity would supplant Newton's axiom, that a body subject to no external force would move in a straight line with constant speed:
尽管如此，艾伦并不崇拜别人，相比于爱因斯坦的方法，他还是更喜欢他自己的方法。他说："这样我才会觉得它看起来不那么怪。"他看到书的最后几页，轻松地给出了一个推导，说广义相对论中的短程线运动定律，会取代牛顿的惯性定律：
He has now got to find the general law of motion for bodies. It will have, of course, to satisfy the general Principle of Relativity. He does not actually give the law, which I think is a pity, so I will. It is: 'The separation between any two events in the history of a particle shall be a maximum or minimum when measured along its world line.'
他现在知道了固体运动的一般规律。当然，这将满足广义相对论。他没有直接给出定理，我觉得这是个遗憾，所以将由我来给出。那就是："对于一个粒子发生的两个事件之间的间隔，当沿着其自身的世界线测量时，会取到最大值或最小值。"
