Many macroscopic physical processes are known to occur in a time-directed way despite the apparent time-symmetry of the known fundamental laws. A popular explanation is to postulate an unimaginably atypical state for the early universe -- a "Past Hypothesis" (PH) -- that seeds the time-asymmetry from which all others follow. I will argue that such a PH faces serious new difficulties. First I strengthen the grounds for existing criticism by providing a systematic analytic framework for assessing the status of the PH. I outline three broad categories of criticism that put into question a list of essential requirements of the proposal. The resulting analysis paints a grim picture for the prospects of providing an adequate formulation for an explicit PH. I then provide a new argument that substantively extends this criticism by showing that any time-independent measure on the space of models of the universe must necessarily break one of its gauge symmetries. The PH then faces a new dilemma: reject a gauge symmetry of the universe and introduce a distinction without difference or reject the time-independence of the measure and lose explanatory power.

中文翻译：

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过去假说的新难点

尽管已知基本定律具有明显的时间对称性，但已知许多宏观物理过程以时间导向的方式发生。一个流行的解释是假设早期宇宙存在一种难以想象的非典型状态——“过去假设”（PH）——它为所有其他假设所遵循的时间不对称播种。我会争辩说，这样的 PH 面临着严重的新困难。首先，我通过提供一个系统的分析框架来评估 PH 的状态，从而加强现有批评的基础。我概述了三大类批评，这些批评对提案的基本要求清单提出了质疑。由此产生的分析描绘了为明确的 PH 提供适当公式的前景的严峻图景。然后我提供了一个新的论点，通过表明对宇宙模型空间的任何与时间无关的测量都必须打破其规范对称性之一，从而实质性地扩展了这一批评。PH 然后面临一个新的困境：拒绝宇宙的规范对称性并引入没有差异的区别，或者拒绝度量的时间无关性并失去解释力。