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Time as Object
Assembly theory’s boldest claim is not methodological but metaphysical. Time is not a backdrop against which objects exist, not an illusion to be reduced away, not merely emergent from thermodynamics — but a material property of objects with measurable size, encoded in their construction history.
“Time is the stuff out of which things in the Universe are made.” (Walker and Cronin, Aeon, 2023.)
This is the version of the theory most contested — by hostile critics and sympathetic readers alike.
Against three existing conceptions
The authors explicitly set assembly theory against three conceptions of time.
Newton: time as absolute backdrop. Time is a fixed, external container in which events happen. It exists independently of the objects in it and flows uniformly. Assembly theory rejects this: time is not external to objects but constitutive of them.
Einstein: time as block universe. In special and general relativity, past, present, and future coexist in a four-dimensional block. The flow of time is, in Einstein’s phrase, a “stubbornly persistent illusion.” Assembly theory rejects this too: the future is not already there, because the combinatorial space of possible constructions has not yet been explored.
Thermodynamics: time as emergent from entropy. The arrow of time arises from the second law — the tendency of systems to move from low-entropy to high-entropy states. Time is not fundamental but emergent from statistical mechanics. Assembly theory rejects the reduction: time is fundamental and material, not an epiphenomenon of entropy increase.
Assembly theory proposes a fourth position: time is material and fundamental, encoded in objects through their construction history. An object’s assembly index measures its size in time.
The identity claim
In assembly theory, time is identified with memory, information, causation, and selection — not by analogy but as the same material feature of objects viewed from different angles. Memory is the retention of construction history. Information is the content of that history. Causation is the path-dependent sequence that produced the object. Selection is the process that found and retained viable pathways through combinatorial space.
These identifications are load-bearing. They are what allows the theory to claim unification across physics and biology — and they are what the critics dispute most directly. The AIT debate challenges whether the information claim is mathematically novel; the mineral exchange challenges where the selection boundary falls.
The contingency claim
The future is determined but not until it happens. The laws of physics are deterministic, but the combinatorial explosion of possible construction paths means that what actually gets built is radically underdetermined by initial conditions.
The size of the future — the space of possible constructions — grows with complexity. The early universe had a small future: few construction paths were available. As objects with deeper construction histories accumulated, the space of what could be built next expanded. The present is larger than the past; the future is larger than the present.
This is assembly theory’s account of determinism-vs-contingency: deterministic laws, radically open outcomes. The framing reaches into cosmology — the universe expands in time as well as space, and novelty becomes possible because accumulated construction history opens paths that did not previously exist.
The Einstein-sequel framing
The authors’ own framing in the Aeon essay and in Walker’s Life As No One Knows It (2024) positions assembly theory as a sequel to Einstein’s unification of space with time. Einstein showed that space and time are aspects of the same geometric structure. Assembly theory proposes to show that time and matter are aspects of the same construction-historical structure.
This framing is contested even by sympathetic readers. Jaeger’s middle-ground critique accepts the theory’s methodological contribution while pushing back on the scale of the metaphysical claims. The broader reception ranges from interest in the formal apparatus to scepticism that the metaphysical framing is warranted by the evidence.