John opens the show by saying that nothing seems more basic or real than time, that indeed every momentconfirmsthe existence of time. He brings up metaphysician John McTaggart’s view of time being unreal, and Ken wonders why something as obvious as the reality of time is being disputed or considered news. John explains that philosophers are not the only ones who are doubting - physicists, too, are considering the unreality of time. Ken wonders what it means to say that time is unreal, whether it is, for example, a denial that there is a past, present, and future. John considers a very detailed calendar: the events it represents do occur, and the calendar is a structure imposes strict order onto these events, a past, a present, a future. But perhaps we are mistaken in thinking of time in this linear way, so the view we have of how events fit together might be false. If we look at the vastness of the cosmos or at quanta, says John, our framework of time, of a before and an after, seems flawed. Ken considers how change fits into John’s argument – change is real, and does that not imply that real time exists?

Ken and John are joined by guest Julian Barbour, Visiting Professor of Physics at the University of Oxford and author ofThe《时空终结:物理学的下一次革命. John first asks Julian what got him interested in the thrilling subject that is time. Julian explains his fascination with astronomy at a young age, which then translated into almost acquiring a PhD in Astrophysics. He changed learning course in his late 20s, when he became more interested in fundamental physics.

The accidental stumble upon a newspaper article about the work of theoretical physicist Paul Dirac, who was one of the major discoverers of quantum mechanics and who wanted to make a quantum theory of the universe and questioned the famous four-dimensional symmetry of Einstein’s theory of general relativity, inspired him to pursue concerns about time.

约翰问朱利安为什么物理学家在时间问题上有这样的问题:如果物理学是解释事件如何在时间中展开的科学，那么它怎么会背弃它的基本概念并怀疑它的真实性呢?朱利安解释说，在更大的范围内，有两个主要原因，那就是几十年来人们试图将爱因斯坦的广义相对论与量子力学结合起来。朱利安解释说，1905年，爱因斯坦决定不存在个体时间的概念，而是存在时空，这一观点在此后得到了无数实验的支持。在爱因斯坦的理论20年后，具有相当牛顿时间观念的量子力学被发现，这两种理论的调和直到今天都困扰着物理学家。朱利安还提到了布莱斯·德威特(Bryce DeWitt)的作品和《时间问题》(the Problem of Time)的创作。’

Ken说我们通常认为时间有三个阶段，即过去、现在和未来。他问朱利安，考虑到这个时态词汇指的可能是不存在的东西，它是否毫无意义。朱利安否认了这一点，并解释了他的观点，即有许多“现在”，许多瞬间都存在。What right, he wonders, does he have to say that from the perspective ofthisNow, this vibrant moment,thatNow, one which took place 5 minutes ago, does not exist any longer? At the same time, in this Now, he has memories of other Nows, Nows which are different. The crux of the question has to do with difference, not with moving between Nows. John asks whether future Nows are just as real as past Nows and whether that would undermine the idea that there is a future that is open and free. Julian explains it would not, bringing up the Many Worlds Interpretation from quantum mechanics and suggesting that there is no reason why there shouldn’t be many routes to take in the future.

Ken asks Julian to elaborate on the notion of time being either an emergent property or a secondary quality, that is, one that is in our minds. Is time a mental phenomenon or an actual, real thing? Julian explains that it is both: emergent in the sense of memories, a secondary quality when what is being considered is the flow of time. John then asks Julian whether on this view causation is also a secondary property, and Ken later asks how to reconcile being in different frames of reference, as Einstein suggested, with the universe having a determinate history, a view more embraced by quantum mechanics. Ken and John welcome audience participation, and topics such as McTaggart’s view, the arrow of time, the relationship between space and time, and whether time is merely a human conception, one not experienced by, for example, animals, are discussed. The conversation ends with the influence of Leibniz on Julian.

• Roving Philosophical Report(Seek to 5:55): Caitlin Esch talks to Jeffrey Hollis, member of the Antiquarian Horological Society in the UK, to get a clearer sense of how people throughout history and in different cultures have measured time. The etymology of the word clock and the history of telling time are contemplated, as are different types of clocks.
  
• 60-Second Philosopher(Seek to 46:25): Ian Shoales discusses how the fragmentation of time will be increased in the future: technological abbreviations of time will supposedly benefit shorter time and attention spans and lead to more positive back-and-forth collaboration.