By "Present," We mean-- we will pick some part of the universe we want to study and we will ask, "What information do I need to know for that system at the initial time, like, right now, in order to be able to predict the future?"

我们所说的"现在",意思是,我们会选取客观世界某一部分来进行研究,然后我们就会问,我们需要什么信息去了解,初始时刻的系统,比如现在,进而能使我们能够预测未来呢

耶鲁公开课 - 基础物理课程节选