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ASSEMBLY
THEORY OF TIME
Abstract
TIME IS AN OBJECT: Not a backdrop, an illusion or an emergent
phenomenon, time has a physical size that can be measured in the
laboratory. Time is unidirectional forward.
ASSEMBLY THEORY:
Proposed by Sara Walker of the University of Arizona and Lee Cronin of
Glasgow in Scotland. Darwin’s Natural
Selection is at play here and Assembly Theory quantifies selection by making
time a property of objects that could have emerged only via evolution.
Life is evident when the space of possibilities is so large that the universe
must select only some of that space to exist. Assembly Theory can function as a universal life-detection
system that works by measuring the assembly indexes and copy numbers of
molecules in living or nonliving samples.
Discussion
Assembly theory explains evolved
objects that involve biospheres, molecules and computers. Such objects exist only along lineages
where information has been acquired specific to their discovery. The nature of these objects are explained
by Walker and Cronin as follows:
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If the lineages are followed back beyond the origin of life on Earth
to the origin of the universe, it would be logical to assume that the
memory of the universe was lower in the past, which means that the universe's
ability to generate objects of high Assembly is limited by its size in
time. Some objects are too large in
time to come into existence in intervals that are smaller than their
assembly index. For complex objects
such as computers to exist in our universe, many other objects had to form
first, such as stars, heavy elements, life, tools, technology and the
abstraction of computing. All this
takes time and is path-dependent due to the casual contingency of each
innovation that is made. The early
universe may not have been capable of computation, as we know it, because
not enough history had existed.
Time had to pass and be materially formed through the selection of
the computer's constituent objects.
This is also true for large language models, new pharmaceutical
drugs, the techno sphere or any other complex object.
The consequences of objects having an intrinsic material depth in
time are far reaching. In the block
universe, everything is treated as static and existing all at once, which
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 others
do not. Considering time as a
physical dimension of complex matter and setting directionality for time
should help solve such questions.
Making time material through assembly theory unifies several
philosophical concepts related to life in one measurable framework. Basic to this theory is the assembly
index, which measures the complexity of an object. It is a quantifiable way of describing
the evolutionary concept of selection by showing how many alternatives were
excluded to yield a given object.
Each step in the assembly process of an object requires information,
memory, to specify what should and should not be added or changed. A specific sequence of steps is required
to construct an object, and each misstep is an error. If too many errors are made a
recognizable object cannot result.
Copying an object requires information about the steps that were
previously needed to produce similar objects.
Assembly theory is a casual 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. Phrases that
are frequently associated with the physics of life, such as
"complexity, "information," "memory",
"causation," and "selection," are material because
objects themselves encode the rules to help construct other complex
objects. This process could be the
case in mutual catalysis where objects reciprocally make each other. Therefore, 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 that complex objects are made of: The size of the future increases with complexity.
Time is fundamental and this new conception of time might solve many
open problems in fundamental physics.
The first and foremost is the debate between determinism and
contingency. 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 richer in information than 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.
Novelty is critical for our understanding of life as a physical
phenomenon. Our biosphere is an
object that is at least 3.5 billion years old by the measure of clock time
(Assembly is a different measure of time).
But how did life get started?
What allowed living systems to develop intelligence and consciousness? Traditional physics suggests that life
"emerged." The concept of
emergence captures how new structures seem to appear at higher levels of
spatial organization that could not be predicted from lower levels. Examples include the wetness of water,
which is not predicted from individual water molecules, or the way that
living cells is made from individual nonliving atoms. However, the objects traditional physics
considers emergent become fundamental in assembly theory. From this perspective an object's
"emergentness" (how far it departs from a physicist's
expectations of elementary building blocks) depends on how deep it lies in
time. This idea points toward the
origins of life, but we can also travel in the other direction.
If this is the right track, assembly theory suggests time is
fundamental. It suggests change is
not measured by clocks but is encoded in chains of events that produce
complex molecules with different depths in time. Assembled from local memory in the vastness of combinatorial
space, these objects record the past, act in the present, and determine the
future, which means the universe is expanding in time, not space--or maybe
space emerges from time, as many current proposals from quantum gravity
suggest. Though the universe may be
entirely deterministic, its expansion in time implies that the future
cannot be fully predicted, even in principle. The future of the universe is more open-ended than we could
have predicted.
Time may be an ever -moving fabric through which we experience
things coming together and apart.
But the fabric does more than move--it expands. When time is an object, the future is
the size of the universe.
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REFERENCES:
Doran, D. E., E. Clarke, G. Keenan, E. Carrick,
C. Mathis & L. Cronin. 2021. Exploring the sequence space of unknown
oligomers and polymers. Cell Reports
Physical Science 2: 100685.
Liu, Y.
C. Mathis, M. D. Bajczyk, S. M. Marshall, L. Wilbraham & I.
Cronin. 2021. Exploring and mapping chemical space with
molecular assembly trees. Science
Advances 7: 3abm 2465.
Marshall, S. M. et
al. 2021.
Identifying molecules as biosignatures with assembly theory and mass
spectrometry. Nature Communications
12: 3033.
Marshall, S. M., D. G. Moore, A. R. G. Murray,
S. I. Walker & L. Cronin.
2022. Formalising the pathways
to life using assembly spaces.
Entropy 24: 884.
Sharma, A., D. Czegel, M. Lachmann, C. P.
Kempes, S. I. Walker & L. Cronin.
2023. Assembly theory explains
and quantifies the emergence of selection and evolution. Vol 3, arXiv: 2206. 02279.
Walker, Sara & Lee Cronin. 2023. Time is an object.
American Scientist III (5):
302-309.
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