Some fair number of weeks ago, my library loan of Saving Time by Jenny Odell expired, and I’d been waiting for my next turn to come around. Earlier this week it went on sale for $5.99, so I picked it up and have resumed by rewinding a bit to the start of Chapter 4, “Putting Time Back in Its Place”.

Early in the chapter, Odell describes coming to pay a different form of attention during the pandemic, when she wasn’t embedded in the same sort of flattened, online experience as everyone else.

If work and online life were Groundhog Day, then whatever I glimpsed through these slivers in the day felt very different. It started to remind me of something I had noticed when I was seventeen. In my journals from that time, where I usually complained about being bored or having too much homework, I would also mention occasional sightings of something I referred to as “it.” “It” was neither a thing in the environment nor an internal emotion (if such a thing is possible). Instead, it was some kind of gestalt, always unexpected and always fleeting—like catching a whiff of something for a split second and remembering something vast. Although my descriptions were sheepish and incomplete—it was always something that “wasn’t here,” or a time “outside time”

Odells turns to Henri Bergson:

For Bergson, time was duration—something creating, developing, and somewhat mysterious, as opposed to abstract and measurable.


Instead, his conception of time was one of interpenetrating and overlapping successions, stages, and intensities. In Creative Evolution, his model for this kind of movement is biological evolution, a process of branching and overlapping development where each step had to have been imminent in the last but where nothing about the process was deterministic.

Seeking ways to explicate this other sense of time, Odell turns to the flow of lava across flat ground.

Meanwhile, as you stand there thinking about it, the live edge of the lava is moving forward into the future, which is imminent in every present moment but also contains the history of everything that happened before.

Later in the chapter, Odells turns to someone we’ve seen here before, although less flatteringly in that case:

The geologist Marcia Bjornerud has called this sense “timefulness,” writing, “I see that the events of the past are still present….This impression is a glimpse not of timelessness but timefulness, an acute consciousness of how the world is made by—indeed, made of—time.”

Had I not had the long interruption in reading Saving Time, I’d not have restarted Chapter 4. That I did do this means that re-reading all of the above comes after having only just recently read three different articles about so-called Assembly Theory.

Technically, the Assembly Theory framing is meant to provide a new way to think about and understand what is and what is not life. In order to do this, however, its theorists talk a lot about time, in ways that make use of words such as “history” and “memory”.

Philip Ball, for Quanta Magazine

“We live in a recursively structured universe,” Walker said. “Most structure has to be built on memory of the past. The information is built up over time.”


Called assembly theory, the idea underpinning the pair’s strategy has even grander aims. As laid out in a recent series of publications, it attempts to explain why apparently unlikely things, such as you and me, even exist at all. And it seeks that explanation not, in the usual manner of physics, in timeless physical laws, but in a process that imbues objects with histories and memories of what came before them. It even seeks to answer a question that has perplexed scientists and philosophers for millennia: What is life, anyway?


“Constructor theory talks about the universe of tasks able to make certain transformations,” Cronin said. “It can be thought of as bounding what can happen within the laws of physics.” Assembly theory, he says, adds time and history into that equation.


The specific conditions in the prebiotic environment, such as temperature or catalytic mineral surfaces, could thus have begun winnowing the pool of life’s molecular precursors from among those in the Assembly Possible. According to assembly theory, these prebiotic preferences will be “remembered” in today’s biological molecules: They encode their own history. Once Darwinian selection took over, it favored those objects that were better able to replicate themselves. In the process, this encoding of history became stronger still.

This doesn’t yet really get at why the Odell had me thinking of Assembly Theory, but the other articles I’d read will help there.

Sara Walker and Lee Cronin, the Assembly Theorists themselves, for Aeon:

A new form of physics called assembly theory suggests that a moving, directional sense of time is real and fundamental. It suggests that the complex objects in our Universe that have been made by life, including microbes, computers and cities, do not exist outside of time: they are impossible without the movement of time. From this perspective, the passing of time is not only intrinsic to the evolution of life or our experience of the Universe. It is also the ever-moving material fabric of the Universe itself. Time is an object.


Evolution accurately describes changes observed across different forms of life, but it does much more than this: it is the only physical process in our Universe that can generate the objects we associate with life. This includes bacteria, cats and trees, but also things like rockets, mobile phones and cities. None of these objects fluctuates into existence spontaneously, despite what popular accounts of modern physics may claim can happen. These objects are not random flukes. Instead, they all require a ‘memory’ of the past to be made in the present. They must be produced over time – a time that continually moves forward.


These and other problems led us to develop a new way of thinking about the physics of time, which we have called assembly theory. It describes how much memory must exist for a molecule or combination of molecules – the objects that life is made from – to come into existence. In assembly theory, this memory is measured across time as a feature of a molecule by focusing on the minimum memory required for that molecule (or molecules) to come into existence. Assembly theory quantifies selection by making time a property of objects that could have emerged only via evolution.


In assembly theory, objects grow in their complexity over time through the process of selection. As objects become more complex, their unique parts will increase, which means local memory must also increase. This ‘local memory’ is the causal chain of events in how the object is first ‘discovered’ by selection and then created in multiple copies.


As the memory requirements increase, the probability that an object was produced by chance drops to zero because the number of alternative combinations that weren’t selected is just too high.


This complexity measurement is also known as an object’s ‘assembly index’. This value is related to the amount of physical memory required to store the information to direct the assembly of an object and set a directionality in time from the simple to the complex. And, while the memory must exist in the environment to bring the object into existence, in assembly theory the memory is also an intrinsic physical feature of the object. In fact, it is the object.


Complex objects with high copy numbers did not come into existence randomly but are the result of a process of evolution or selection. They are not formed by a series of chance encounters, but by selection in time. More specifically, a certain depth in time.


If the theory holds, its most radical philosophical implication is that time exists as a material property of the complex objects created by evolution. That is, just as Einstein radicalised our notion of time by unifying it with space, assembly theory points to a radically new conception of time by unifying it with matter.


Assembly theory treats time as fundamental and material: time is the stuff out of which things in the Universe are made. Objects created by selection and evolution can be formed only through the passing of time. But don’t think about this time like the measured ticking of a clock or a sequence of calendar years. Time is a physical attribute. Think about it in terms of Assembly, a measurable intrinsic property of a molecule’s depth or size in time.


If we follow those lineages back, beyond the origin of life on Earth to the origin of the Universe, it would be logical to suggest that the ‘memory’ of the Universe was lower in the past. This means that the Universe’s ability to generate high-Assembly objects is fundamentally limited by its size in time.


The consequences of objects having an intrinsic material depth in time is far reaching. In the block universe, everything is treated as static and existing all at once. This means that objects cannot be ordered by their depth in time, and selection and evolution cannot be used to explain why some objects exist and not others. Re-conceptualising time as a physical dimension of complex matter, and setting a directionality for time could help us solve such questions.


This makes assembly theory a causal theory of physics, because the underlying structure of an assembly space – the full range of required combinations – orders things in a chain of causation. Each step relies on a previously selected step, and each object relies on a previously selected object. If we removed any steps in an assembly pathway, the final object would not be produced. Buzzwords often associated with the physics of life, such as ‘theory’, ‘information’, ‘memory’, ‘causation’ and ‘selection’, are material because objects themselves encode the rules to help construct other ‘complex’ objects.


Thus, in assembly theory, time is essentially the same thing as information, memory, causation and selection. They are all made physical because we assume they are features of the objects described in the theory, not the laws of how these objects behave. Assembly theory reintroduces an expanding, moving sense of time to physics by showing how its passing is the stuff complex objects are made of: the size of the future increases with complexity.

Walker, to Thomas Lewton for New Scientist:

The fundamental objects in Assembly Theory are the emergent complex structures, not fundamental particles like quarks or electrons or photons. We define objects within an “assembly space”, which contains all of the ways of building up an object from its basic building blocks. So an object like a molecule isn’t defined by its three dimensional configuration that you might hold in your hand, and it’s not defined by its mass or electric charge. The object is actually the ways of building the molecule. These histories, which converge on a particular structure that we see, are the object.

Odell’s particular exploration related in Chapter 4 began as she tried to capture an ineffable “it”—“something that ‘wasn’t here’, or a time ‘outside time’”, and it led her to try to observe the world differently.

Odell, toward the end of the chapter:

This exercise in observation is an example of what I have come to think of as “unfreezing something in time.” To do this means releasing something or someone from their bounds as a supposed stable, individual entity existing in abstract time, seeing them not only as existing within time, but also as the ongoing materialization of time itself. Here, it’s important for me to note the difference between seeing the tree as evidence of time and seeing it as symbolic of time. While it is certainly possible to derive some fruitful thoughts about time and fate from the branching structure of a tree, what I’m talking about is different: The literal tree in front of you is encoding time and change at this literal moment.

Returning to Walker and Cronin in Aeon:

Einstein famously said that God ‘does not play dice’, and many physicists are still forced to conclude that determinism holds, and our future is closed. But the idea that the initial conditions of the Universe, or any process, determine the future has always been a problem. In assembly theory, the future is determined, but not until it happens. If what exists now determines the future, and what exists now is larger and more information-rich than it was in the past, then the possible futures also grow larger as objects become more complex. This is because there is more history existing in the present from which to assemble novel future states. Treating time as a material property of the objects it creates allows novelty to be generated in the future.

Odell wasn’t writing about Assembly Theory, but with its notions of history, memory, and of time being what things are made of, it feels like the last word should go to her: “This story is, finally, the signature of ‘it’: the restless, unstoppable, constantly overturning thing that makes it all go.”