标题： 泡泡碰撞与多重宇宙的测量 显示英文标题

标题： Bubble collisions and measures of the multiverse

摘要： 为了计算永恒膨胀多元宇宙中的观察者看到的气泡碰撞光谱，必须选择一个覆盖发散时空体积的测度，包括选择一个“初始”超曲面，在其下方没有气泡成核事件。 先前的计算集中于初始超曲面被推到非常遥远的过去的情况。 有趣的是，所观测到的光谱依赖于初始超曲面的方向，然而，观察到这种效应的能力随着气泡内外膨胀哈勃率之比的增加而迅速下降。 我们研究了在更普遍的情况下是否可以避免这一结论，特别是将观察者的气泡放置在初始超曲面附近。 我们发现这是不可能的。 作为参考，附录中详细回顾了永恒膨胀测度问题的相关方面。 显示英文摘要

摘要： To compute the spectrum of bubble collisions seen by an observer in an eternally-inflating multiverse, one must choose a measure over the diverging spacetime volume, including choosing an "initial" hypersurface below which there are no bubble nucleations. Previous calculations focused on the case where the initial hypersurface is pushed arbitrarily deep into the past. Interestingly, the observed spectrum depends on the orientation of the initial hypersurface, however one's ability observe the effect rapidly decreases with the ratio of inflationary Hubble rates inside and outside one's bubble. We investigate whether this conclusion might be avoided under more general circumstances, in particular placing the observer's bubble near the initial hypersurface. We find that it is not. As a point of reference, a substantial appendix reviews relevant aspects of the measure problem of eternal inflation.