Although time may not materially exist, most of us still measure it out using clocks and calendars. From the creation of days to the atomic clock, this episode explores how the abstract concept of time became a countable “reality” — and why metric time worked its way to the heart of Western society.

This episode in brief:

1. Mapping calendrical time | 03:15

The countable time we use in our everyday life is a social construction. This section takes a look at how different cultures divided the abstract concept of time into days, weeks, months and years. We consider the mathematical limitations of basing units on environmental cues like the Earth’s rotation. From the 10-day weeks of ancient China to the alternative names for months in modern Turkmenistan, we explore how our calendars are as much cultural creations, as empirical tools.

2. The evolution of clock time | 10:55

This section explores the heritage of smaller units for tracking time — like hours, minutes and seconds. We trace the colourful history of time keepers, from water clocks and obelisks to the complex machinery of drive weights, pendulums and vibration. We see how our most precise timepiece — the atomic clock — still falls victim to the inconsistencies of nature; that the quest for a mathematically pure time will always be at odds with the realities of our material universe.

3. The global standardization of time | 18:10

Ever wondered where time zones came from? How the US settled on its four standard time belts? Or when the global organization of time began? This section explains all. It lays out the local origins of time standardization, through to the governmentally-sanctioned version of universal clock time we use today. We consider the pressures of local organization, industrialization, expanding transport and communications networks in the drive to create a coordinated social framework for time.

4. Living with metric time | 23:40

While we may run our lives according to clocks and calendars, that’s not to say we have an easy relationship with them. This section takes a closer look at the social implications of metric time to consider what it means today. Historian Paul Glennie deconstructs the disciplinary narrative of clock time — with its ties to 19th century industrialism — to show why it only represents one part of the social time picture. Using more contemporary examples, we explore what metric time means for our consumer services, personal aspirations and social etiquette.

Time isn’t just lived in the brain; it’s stamped into the very cells of our being. With insights from neuropsychologist Marc Wittmann, this episode explores how bodily clocks, illness and age all impact how we experience time. We'll see how social time inventions, like daylight saving, can clash with our highly individual biological time.

This episode in brief:

1. What is biological time? | 02:50

We all have a silent clockwork inside us governing what we feel and how our bodies operate. This section introduces the biological clocks that keep us ticking over — focusing on those which have captured our imagination most: circadian rhythms. We explore how ultradian rhythms work, from those that are stamped into our cells to those that respond to our external environment.

2. Sleep cycles: our master clock | 07:00

Ever considered where the whole “early bird”/”night owl” classification comes from? Or why teenagers find it so hard to get up in the mornings? This section takes a closer look at how our individual “clock genes” influence out master circadian rhythm: the sleep/wake cycle. We consider how social designs for time — like daylight savings and work schedules — impact biological time, and the potentially dangerous consequences of the “social jetlag” they create.

3. How our body impacts how we experience time | 10:45

In our last episode, we explored how our psychology can impact how we experience time, but our bodies also play a huge part in this too. Neuropsychologist Marc Wittmann helps explain how bodily states can act as time keepers in their own right — and how pain, temperature, illness, drugs and basic sensory stimuli all affect our conscious experience of time.

4. The“phenomenal self” and time | 14:40

The “material self” is one of our primary tools for cataloguing and understanding our life, but it’s only possible as an entity over time. This final section considers how our bodily signals constitute the most basic feature of our conscious self — as a stream of information that is forever updating — and how feeling states could function as an inner measure of duration itself.

Since we can’t prove that time physically exists, it must live somewhere inside the human mind. With the help of neuropsychologist Marc Wittmann, this episode takes a closer look at subjective time — the time we ‘feel’ — to see how our brains create our sense of time, and why it’s constantly speeding up and slowing down.

This episode in brief

1. How we are able to perceive time | 02:30

Time processing plays a role in almost all aspects of our cognitive function. But what exactly is happening in our brain? This episode introduces the core mechanism of time perception, from the 3-second perceptual moment, to the combined role of memory, attention and anticipation. We see that our brain is constantly throwing out predictions based on previous experience and testing them against new information in our environment.

2. How the brain keeps time | 08:45

Even though we can’t see, touch or hear time, our brains can still track its passage. We know what minutes and hour feel like, even when sat in a windowless meeting room. But how do we do this? This section explores some of the theories around how and where the brain predicts duration — both when consciously paying attention to time passing, or reconstructing a sense of it after the fact.

3. Why does time speed up and slow down? | 12:50

Unlike clock time, the time you directly experience isn’t steady and constant. It’s continually speeding up and slowing down, and as we age time seems to get faster. But what causes this flux? With the help of neuropsychologist Marc Wittmann, we explore how memory density, novelty, signpost events, attention to time, drugs affecting dopamine and emotional states all impact our perception of time. We see that perceiving time in so many ways is not a design flaw, but an essential part of our humanity.

Time is seen as part of the fundamental grammar of the world. Yet there is little evidence proving it actually exists. With the help of quantum physicist Carlo Rovelli, this episode seeks to mop up some of the biggest misconceptions surrounding time — exploring the theories and hypotheses shaping our current scientific understanding of it.

This episode in brief

1. Absolute Newtonian time | 03:00

We often think of time as a substance that lives outside of us and flows from past to future. But while useful, there is no strong scientific evidence showing this physical view of time is actually true. This section considers the origins of a universal “true time”, popularized by Isaac Newton, and the enduring impact it has had on the concept of time.

2. The challenge of Einstein’s relativity | 05:20

Einstein’s theories of relativity completely reimagined physical time, ushering a whole new level of existentialism into the theory of time. This chapter highlights some of his biggest points — like the illusion of universal clock time and simultaneity, and the idea of a 4D block universe which fixes all events ever to occur in time.

3. Directional time and entropy | 10:40

We consider time to be a fundamental part of our universe, but there is in fact only one natural law suggesting it exists and has a direction. This section lays out the idea of entropy — the tendency towards disorder within nature — as possible proof for “moving” time, as well as its limitations. It acknowledges how even objective scientific laws are subject to intrusions by our own subjective human perspective.

4. The quantum perspective with Carlo Rovelli | 14:00

When we study the smallest physical quantities of the universe, our popular notions of time quickly lose meaning. Drawing from his latest book, The Order of Time, world-renown physicist Carlo Rovelli proposes a new model for thinking about time. He explains why the answer to time’s mystery arguably has as much to do with how humans work as with the manner of the cosmos.

“Time” is the most frequently used noun in the English language. But what are we actually talking about when we talk about time? This episode looks at time representations and referencing systems used by different cultures, to explore how far language can shape how we think about time.

This episode in brief:

1.The spatial language of time | 03:45

Many cultures use the graphical model of space to understand time, but there are some pretty interesting differences in how the world’s languages conceptualize time. This section explores examples from Western European and Scandinavian languages to Mandarin Chinese, Aymara, and the aboriginal language of the Pormpuraaw community in Australia.

2. Event-based time | 13:10

While countable “clock time” seems like second-nature for the West, in some cultures it doesn’t exist. Starting with the Amazonian Amondawa community, this section considers languages who use events to index and talk about time. Anthropologist Vera da Silva Sinha draws insights from her latest research on three Brazilian tribes — the Huni Kuĩ, Awetý and Kamaiurá — who don’t count age, celebrate birthdays or use spatial metaphors to speak about time.

3. Languages without tense | 21:55

English – like most European languages – is a tensed language. But many languages do not use tense at all. This section explores how “tenseless” languages like Mandarin Chinese use aspect to indicate time, as well as the conceptual limitations our own three-tensed grammar imposes on how we communicate time.