John opens the show by saying that nothing seems more basic or real than time, that indeed every moment confirms the 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 of The End of Time: The Next Revolution in Physics. 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.  

John asks Julian why physicists are having such a problem with time: if physics is the science of explaining how events unfold in time, then how can it then turn its back on its basic concept and doubt that it is real? Julian explains that there are two main causes under the larger umbrella that is the several decade-long attempts to combine Einstein’s theory of general relativity with quantum mechanics. In 1905, Julian explains, Einstein resolved that there was no concept of individual time, that instead there was spacetime, something which has been supported by numerous experiments since. 20 years after Einstein’s theory, quantum mechanics, which has a rather Newtonian idea of time, was discovered, and the reconciliation of these two theories has troubled physicists to this day. Julian also brings up the work of Bryce DeWitt and the creation of ‘The Problem of Time.’

Ken says that we ordinarily think about time as having three phases, namely the past, present, and future. He asks Julian whether this temporal vocabulary is nonsense given that it refers to something that is possibly nonexistent. Julian denies this and explains his view that there are many ‘Nows,’ many instants that all exist. What right, he wonders, does he have to say that from the perspective of this Now, this vibrant moment, that Now, 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.