Ammersee, Bavaria; 1934. Photo by Herbert List/Magnum



How to think about time

This philosopher’s introduction to the nature of time could radically alter how you see your past and imagine your future

Ammersee, Bavaria; 1934. Photo by Herbert List/Magnum





Graeme A Forbes

spent 10 years as an academic philosopher, and is now a freelance philosophical consultant. He has two books on philosophy of time in press: Philosophy of Time: The Basics (2024) and The Growing Block View (forthcoming, Bloomsbury). He lives in Canterbury, UK.

Edited by Sam Dresser





Need to know

Change and variation

Stretch out your arms to their fullest extent getting the tips of your fingertips on your right hand as far from the fingertips on your left hand as you can. Depending on where you are reading this, that might have been embarrassing, but you will feel like you’ve taken up more space than when you scrunch yourself into a tiny ball. Now do the equivalent in time…

You can’t, right? We can spread out in space, but not in time. In time, we experience one thing after another, in a sequence of episodes. This is one of the striking things about time. It does something that space doesn’t do. It passes.

You live in time, and whether or not you think about it, this difference between space and time affects how you act, what you can choose to do, and poses challenges of how to deal with the things you didn’t do or should have done differently. As Augustine of Hippo observed, it seems like we understand time until we try to articulate what it is.

When you stretched your arms out just now (you can take them down, if you haven’t already), you were varying across space. Your body filled up a region of space, but how it filled it was different in different places. Some of that space had fingers in it, some an arm, some an elbow, some a shoulder. Is change just different events filling up different bits of time? This view would be that your birth is in one bit of time, your reading this in another, and your death (hopefully) in another, much later time. Sure, we experience these as a sequence of episodes, but that’s something about how people experience things, rather than about what change really is. Let’s call this the temporal variation view. It goes with a ‘static’ view of time. Things vary across time, but they don’t change how they vary.

The other view is that change has no spatial analogue. Time passing might involve varying across space, but there is something fundamentally different about it. Let’s go back to your birth being at one time and your reading this article at another. We can represent them on a timeline. But that’s missing something. It’s missing the change. And that missing ingredient, whatever it is that the timeline with different events at different places lacks, is what is required for time to really pass. Call this view of change ‘McTchange’ after the early 20th-century philosopher J M E McTaggart, who argued that change couldn’t be mere temporal variation (and, also, that change is contradictory). It goes with a dynamic view of time, because time itself McTchanges as stuff successively happens.

Past and future

Once stuff has happened, it becomes the past. And there’s a sense in which you’re stuck with it then. You can dress it up in different ways, but whether you got out of bed and did the training, whether you said those hurtful things, and whether you crossed the finish line on the day, are now unalterable things that happened. In addition to the difference between change over time and variation across space, there’s a difference between the past and the future. We’re stuck with the past in a way we might not be stuck with the future. Maybe there’s nothing you can do about the future; perhaps you’ve set off a sequence of events that are now unfolding outside of your control. But at least sometimes you can influence the future, right? Your chances of making something happen in the future seem a lot higher than your chances of making something happen in the past. This contrast is called ‘the open future’, where, usually, it is assumed the past isn’t similarly open.

We’re stuck with the past. But you can dress it up in different ways. Often, what happened in the past is affected in the future because ‘what happened’ depends on how things turn out. Whether some past purchase was a lucrative investment decision depends on what happens to the investment after the decision. Even if you reasoned really well, if your prediction didn’t pan out, you lose the money. If you met someone for a coffee and it turns out that this was the first meeting of the relationship that defines your life, then the coffee was a different kind of event than of a coffee meeting that leads nowhere and has no later significance. This needn’t be a failure of knowledge on your part. Whether or not it counts as a significant event in your life might hinge on how things go subsequently. There may be no clues that you can spot at the time. So there you are, sitting in a café, nervously reading an online magazine, unaware of the significance of the event you are waiting for – because there is no fact yet!

Why think about all this? After all, if time passes, it does so whether you think about it or not. One reason is simply that it’s puzzling. How does something so familiar manage to be so hard to explain? But another is that it is the time of our lives. It provides context for our hopes and regrets. Understanding time helps us understand how to assess lives lived within time.

Think it through

The nature of time and your experience of it

We experience the world from inside time and attempt to think about what time is like generally. We know what it is like round here, for us. But what is it like in other parts of the Universe, for other creatures, indeed for the other people we live with? You might have been in a situation where you were really excited and, when you look at the clock, it’s hours later than you were expecting. Or you might have been in a hospital waiting room, with every minute seeming to last an hour. The experience of lengths of time varies according to different moods in the same person, and it often varies between people, and among different animals. When we ask if time really passes, we want to escape the peculiarities of you and me to say something more general.

The problem is that, if we think there is McTchange, it’s really hard to say what it is. It looks like our best bet is to point at some change and say it’s like that. But if the disagreement is between people who think that change is temporal variation, and those who think there is a missing ingredient, at least pointing at a clock ticking, or an apple ripening, or an election result announced on the news, is something both parties can do. But the debate won’t be settled by looking intently at examples of change to see if they contain some fizzy, flowing quality. The debate is about how to think about difference in clocks, apples, governing parties, etc over time.

The Gods eye view

In the Middle Ages, this debate had a theological twist. It was about how God experienced the world. Does God experience the world like you and I do, as a sequence of events, or does God experience the world with time spread out like space is spread out before us? In fact, the options for God’s experience of the world got a lot more complicated than this, but even if you don’t believe in God, thinking about these questions can be useful. For one thing, scientists who developed our modern scientific worldview, such as Isaac Newton, thought in these terms, and the way they frame these problems has a lasting legacy. If we substitute appeal to an objective scientific understanding of the world for God, we get something very like the contemporary debate.

Here are a bunch of views to consider, then:

1a. Although for us it seems like time passes, for God variation across time is no different than variation across space.
1b. Although we experience change over time, our scientific theories have no role for change distinct from variation across time. (This is the common ‘scientific’ view.)
2a. Even God exists in time and is subject to change over time.
2b. To give an objective scientific description of the world, one has to appeal to change in a way that isn’t captured by a range of acceptable values in a time variable.

There’s another option:

3. The very idea that science can offer an objective view of the world is mistaken. The demand for ‘objectivity’ is a demand to abstract from a bunch of features of the world, to an impersonal, value-free, timeless view from nowhere, and there cannot be an adequate description of the world so divorced from the context required to make sense of things.

Science versus subjective experience

In April 1922, there was a debate between Albert Einstein, the famous physicist, and Henri Bergson, the (slightly less) famous philosopher. Einstein defended something like view 1b, and Bergson defended something like view 3. Defenders of Einstein claim that Bergson didn’t understand the physics. Defenders of Bergson claim that Einstein didn’t understand the point about seeing time in the context of lived experience. The rumour is that after this debate Bergson used his influence to prevent Einstein getting a Nobel Prize for the Theory of Relativity.

Since then, it has become reasonably standard to set up the debate about time as one of science against common sense, with common sense often derided as ‘more or less rubbish’. But the debate also reverberates within science itself. A scientist might adopt view 2b, instead of 1b. Medicine is a science interested person-centred, value-laden projects like making people healthier. Engineering is applied science interested in making structures out of materials that don’t collapse unexpectedly on people’s heads. The disagreement between view 1b and view 3 seems to be to concede that the kind of abstract, impersonal, value-free science that some theoretical physicists do is the only kind that counts as objective. But applied science plausibly still counts as science, and that allows for view 2b to be a scientifically respectable view. The debate can be framed as one within science, then, rather than as a choice between accepting science and rejecting objective thought.

Relativity says there is no way of specifying a universal now

Why is view 1b often taken to be the ‘scientific’ view? It’s because of the Theory of Relativity, which shows that we have no physically meaningful way of establishing simultaneity – that is, two events happening at the same time – independent of some inertial frame (ie, the coordinate system based on what we consider to be not moving). What pairs of events occur at the same time is relative to these inertial frames and, according to one inertial frame, two particular events are at the same time, while, according to another, those same two events are at different times. This is a really well-confirmed scientific theory, and Einstein deserved a Nobel Prize for it regardless of what Bergson thought. It shows that there is no physically meaningful way of establishing an objective ‘now’ that spans the Universe. If you ask ‘What’s happening on Mars now?’ there is no physically meaningful way of giving a perspective-independent answer. Give me an inertial frame, and I can make sense of the question (I still might not know the answer) but, so far, we have no objective way to pick one inertial frame as the correct one that’s remotely plausible.

If you think that change over time is a matter of a Universe-wide now changing location as time passes, our inability to provide a physically meaningful perspective-independent universal now looks like a problem. And what relativity shows is that we can’t provide a perspective-independent now, not that there is no such thing as change. The role of change in physics is still hotly debated. Some of our best theories of matter, spacetime and gravity have no role for time in them at all (not even temporal variation), whereas others claim the passage of time is the ‘birth of spacetime atoms’. But something like view 1b is probably the majority view among physicists and philosophers of physics.

We need change to make sense of doing things

These considerations might prompt you to ask if time does really pass in the first place? Time passing helps a lot for doing things. A lot of the time, when you do something, you are aiming to bring about a change. Much of the rest of the time, you are trying to stop something from changing. Thinking in terms of a way things are now, and the way things are supposed to be after you’ve carried out your plans, is really useful. Experiencing things episodically is part of this. Pretty much everyone accepts that it is useful for us to think like this. But is it useful because we are trapped in an ‘embedded perspective’, where we see things embedded within time, and couldn’t make sense of acting otherwise? Or is it useful because we’re capable of really changing things (or preventing them changing), and we need to keep track of those changes over time? Are we just stuck thinking like this, or do we think like this because change is something that we can control (some of the time)?

If everything is on a timeline – laid out without changing – what happens when someone tries to change something? It looks like there’s one bit of the timeline before they change something, and one bit after. It’s when we attempt to do something or refrain from doing it that the question of ‘real’ change appears. On the timeline, we have no change; just one thing after another. If physics is missing a story about what happens when we intervene on the world, there’s a question about why we should believe scientific experiments give us evidence for their claims. Experiments are attempts to bring about change, after all.

We do things to change the future, not the past

Change isn’t the only feature of time that is puzzling. Change has a directedness to it. We can remember the past and, when we do archaeology, or geology, or astronomy, we can find out what things were like beyond living memory, or even before humans existed. We can’t do that in the future direction. When we do an experiment, we usually think that the effect will be after the cause (notwithstanding some puzzling quantum phenomena). We think that we can affect the future but not the past.

We don’t have a difference like that in space, where we can remember in one direction and act in the other. McTchange, if there is any, affects what we can know, and what it’s possible to do. If there is no McTchange, we need an alternative explanation of why it seems to us like time involves a change from what’s up to us to what we’re stuck with. Perhaps the explanation is that we are equally stuck with the future and we just don’t know what it is yet.

So we have two perplexing things to make sense of: first, that time seems different to space and, second, that the past seems different to the future. Any decent view of time has to explain these differences, or else explain them away.

There are lots of specific views of time to choose from, such as:

  • eternalism (all times exist equally, and presentness is a matter of perspective);
  • presentism (only the uniquely objective present exists);
  • the growing block (the past exists, the future doesn’t, and the passage of time is stuff coming into existence); and
  • the moving spotlight (past, present and future all exist, but there is a uniquely objective present).

These and other views all have their defenders. But they are all attempts to respond to questions about whether and in what sense time passes, and whether and in what sense the past differs from the future, so those questions are the place to start.

Our emotions are directed at what was, what might be, and what wasnt/wont be

Not only do we have theories about time but we live in it. Our emotional lives are directed out from the present into the past and future in myriad ways. We regret the past. This makes sense only if we can’t undo our past actions, but can learn from them. We hope for the future. Hope makes sense only if there’s a chance our hopes will be fulfilled. But it’s not just the past and future that we direct our emotions toward. Often we’re directed towards ‘pasts’ that never happened, as in nostalgia, and we fantasise about ‘futures’ that are no longer possible (or never were). We ask ‘What if?’ questions about how the Universe would have been had we born richer, not inherited particular genes from our parents, not suffered particular trauma, or had met people at a different time in our lives. When we think about time, we include thinking about past, present or future. To complete the set, we have to add thinking about what could have happened but didn’t and won’t. Understanding the differences and choosing which ones we think about can make a great difference to our happiness and our ability to make our lives better.

As we live our lives, we tell ourselves stories about what we are doing. Those stories are often based on plans for the future. But the meaning of a story can change depending on what happens later. Pride and Prejudice would be a very different story if there were an additional chapter involving the Darcys getting an acrimonious divorce. This relationship is worth investing in because it’s going somewhere, you might say. It’s worth saving money now for a comfortable future, you might tell yourself. Whether those plans are good ones depends on how likely they are to succeed. That can change drastically with one new piece of information, and then change back with a second, leading to a stressful emotional rollercoaster, if you let it. You are stuck with the past, but what role it plays in the story of your life is still up for grabs. That’s because what kind of story you’re writing is still up for grabs.

Key points – How to think about time

  1. Change and variation. Whether or not change is variation across time or something more, you experience change – indeed, you can’t live without changing.
  2. Past and future. You’re stuck with the past. What happened happened. But because the future is open, the meaning and significance of the past is itself subject to change.
  3. The nature of time and your experience of it. When thinking about time, we’re trying to say something general about it, freed from your subjective experience of time, shaped by your particular moods, hopes, fears, interests and so on.
  4. The God’s eye view. In the Middle Ages, debates about time were largely concerned with the nature of God. Even if today we are more interested in an objective, scientific understanding of the world, the Middle Ages remain a useful way of framing views about time.
  5. Science versus subjective experience. The classic, modern formulation of the debate about time pits Einstein, representing the scientific approach to time, against Bergson, who argued in defence of ‘common sense’.
  6. Relativity says there is no way of specifying a universal now. The theory – well tested and universally endorsed by scientists – supports the view that our scientific theories have no role for change distinct from variation across time.
  7. We need change to make sense of doing things. A lot of the time, when you do something, you are aiming to bring about a change. Much of the rest of the time, you are trying to stop something from changing.
  8. We do things to change the future, not the past. Any theory of time must account for two puzzling things. First that, time is fundamentally different from space and, second, that the future is fundamentally different from the past.
  9. Our emotions are directed at what was, what might be, and what wasn’t/won’t be. The past is unchangeable and the future is always ahead of you. But the meaning of both are constantly in flux and change as the story of your own life changes.

Why it matters

Time passes whether or not you want it to, and whether or not you think about it. But understanding it may make better sense of how you live in it. You’re embedded in time and that means you have to deal with change, accept the past and make the best of the future. It is only from this embedded perspective that your life can make sense, so we had better hope that the embedded perspective isn’t misguided, or pointless, simply because it is a perspective. The debate about the nature of time matters because it bears on that question of how our embedded perspective relates to a wider context that might reframe the context against which we attempt to make sense of our lives. Do I have grandchildren who are existing in the distant future the way I have a sister in distant Australia? Are these real future grandchildren stuck with decisions I haven’t even made yet, the way I can’t change the decisions my grandparents made 75 years ago? Whether the future is lying in wait for me, despite my ignorance of it, or is something I bring about, through my action or apathy, seems to make a difference to how I ought to feel about it.

You have a choice (at best) between different futures, but we often spend our lives absorbed by possibilities that might have been, and pasts that never were, sometimes at the expense of the lives that we are living now. Living based on an imagined past can have a rosy glow, but tends to disappoint in the end, and ruminating about futures that aren’t possible for you can lead to bitterness at the options that you can choose between. We can get traumatised by the near-misses, even though nothing actually happened. We can find hope through knowing that things can change, even if they don’t. And we don’t get the chance to go back and try again, the way, in computer games, you can reload a saved game.

We also judge others harshly, because we forget that swirling mass of possibilities and plans they were confronted with at the time they were acting. The past has a tendency to appear as if it inevitably led to the present. It is easy to forget that you didn’t know how things would turn out when you were younger, and that some of the things you devote your energy to now won’t make sense in 10 years. This is because, when looking at other times ‘objectively’, we often slip into thinking of them as a sequence of events on a timeline, when that’s not how they are lived, or could be lived.

Links & books

The episode ‘Does Time Exist?’ (2020) of the BBC Radio 4 show The Infinite Monkey Cage discusses whether time passes, according to physics.

The episode ‘Time for Philosophers’ (2008) of the Australian radio show The Philosopher’s Zone features the philosopher of time David Braddon-Mitchell.

The novel Slaughterhouse-Five (1969) by Kurt Vonnegut is an anti-war novella with time-travel as a metaphor for PSTD, but with a brilliant discussion of how our emotions relate to our experiences of time in literature.

The book What Makes Time Special? (2017) by Craig Callender won the Lakatos Award for an outstanding contribution to the philosophy of science; it argues for the view that our experience of time is ‘more or less rubbish’ as a guide to what time is really like.

The book Out of Time (2022) by Samuel Baron, Kristie Miller and Jonathan Tallant provocatively argues that, for all we know, our best theories of physics don’t have any role for time at all.

The book The Physicist and the Philosopher (2015) by Jimena Canales takes a historical approach to the philosophy of time through the debate between Einstein and Bergson.

The book Philosophy of Physics: Space and Time (2012) by Tim Maudlin offers an introduction to the physics of spacetime, with a focus on the philosophical questions rather than the mathematical formulas.

My book Philosophy of Time: The Basics (2024) is a textbook, forthcoming in May, that expands on these themes.