By considering situations from the paradox of the twins in relativity, it is shown that time passes at different rates along different world lines, answering some well-known objections. The best explanation for the different rates is that time indeed passes. If time along a world line is something with a rate, and a variable rate, then it is difficult to see it as merely a unique, invariant, monotonic parameter without any further explanation of what it is. Although it could, conceivably, be explained by the flow of something, it is better explained by the passing of a point present, which faces the problem that there is no absolute simultaneity in special relativity so that the present for an object is confined to just that object. This raises problems about presentism, eternalism, simultaneity, and special relativity. These issues are addressed first by giving accounts of presentism and eternalism and then an account of existence and times for objects relative to world lines. Finally, an analogy between a world of relativistic objects and Leibniz’s ontology of monads.

通过考虑相对论中双胞胎悖论的情况，表明时间沿着不同的世界线以不同的速度流逝，回答了一些众所周知的反对意见。对不同利率的最好解释是时间确实在流逝。如果沿着世界线的时间是具有速率和可变速率的东西，那么很难将它仅仅视为一个独特的、不变的、单调的参数，而不对其是什么做任何进一步的解释。虽然可以想象，它可以用某种东西的流动来解释，但最好通过一个现在点的经过来解释，它面临的问题是狭义相对论中没有绝对同时性，因此一个物体的现在仅限于那个对象。这引发了关于现在论、永恒论、同时性和狭义相对论的问题。这些问题首先通过给出现在主义和永恒主义的说明来解决，然后是相对于世界线的物体的存在和时间的说明。最后，将相对论对象的世界与莱布尼茨的单子本体论进行类比。