The Growing Block

In our study of time, we compare four leading theories: Presentism, Eternalism, Growing Block Theory, and Branching Tree Theory. We aim to show in a future post that a metaphysics of time anchored in the work of Thomas Aquinas is superior. Let’s take a closer look at the Growing Block Theory (GBT) of time.

In Favor of the Growing Block. C.D. Broad[1] was an early proponent of GBT. He speaks of the Specious Present[2] as a thin slice of time that is his experience of the present, which then appends to the receding past as the time block grows. “When an event, which was present, becomes past, it does not change or lose any of the relations which it had before, it simply acquires, in addition, new relations which it could not have before, because the terms to which it now has these relations were then ‘simply non-entities.’” The future is nothing until it becomes the present. The sum total of existence is always increasing and this gives time its order.

Though not its motivation, application of GBT is evident in Sara Walker’s description of the Origin of Life in her recent book.[3] Walker (and her colleague Lee Cronin) makes a case for life’s emergence via Assembly Theory (AT). According to AT, objects are things that can be assembled from elementary building blocks. These objects have causal powers, not because of their parts, but because of properties that emerge from their assembly. Life evolves and expands with the assembly index (A-I), which essentially measures the steps in the process. The A-I also describes the size of an object in time. As the universe expands, its capacity for complexity increases. Accordingly, “complex matter is complex because it has a physical extent not just in space, but in time too.” For Walker, time is a material. Life’s possibilities enlarge with the ever-expanding front of the present. “The size of an object in time…is a material property.”

Against the Growing Block. Anti-realist Michael Dummett[4] argues that past events are fixed. Neither the present nor the future can change these past facts. Accordingly, GBT theorists need to justify why the present occupies a privileged position. The present does not sustain the past.

Flaws in Assembly Theory. Scientific support for a philosophy of time is potentially helpful if the science has merit. Unfortunately, AT widely misses the mark. A-I measures the number of steps in a sequence of molecular attachments that lead from the simple (amino acid) to the complex (functional protein). However, the estimated A-Is that are achievable via random processes are generously in the range of 10-50. The average protein is 300 amino acids long, and it is more likely that the next sequence of amino acids will attach to the side of the polypeptide chain than to its ends. Human designers construct cars, aircraft engines, and satellite networks with A-Is in the thousands. Life needs A-Is many orders of magnitude larger![5]

Implications. Giving agency to the “present” may produce intricate patterns, but there is no direction guiding the work of natural selection. Evolution is famously non-transitive.[6] GBT describes the capacity for growth, not its motivation. The universe of Richard Dawkins,[7] guided by “blind pitiless indifference,” simply does not care. Clearly, a better theory of time is needed.