1. Time and Eternity

Within the vast literature on the subject of ‘time and eternity,’ I’ll touch on three schools of thought and their assumption of flowing time. 1) In 20th century Trinitarian theologyeternity is no longer limited to either of two traditional ideas: timelessness (the opposite of temporality) or unending time (time without fulfillment). Instead eternity is understood in a far richer, more complex way: God as eternal is the supra-temporal source of the temporality of the world and its eschatological future. According to Karl Barth, God is “supremely temporal.” The divine eternity is “authentic temporality, and therefore the source of all time.” Eternity is ‘pre-, super-, and post-temporality.Wolfhart Pannenberg claims that the doctrine of the Trinity provides the needed basis for the relation between God and creaturely temporality. Moreover, the temporal events of God’s saving economy in the world are constitutive of the imminent nature of God.Jenson has expressed similar views.2) Process theologians interpret God’s ‘consequent nature’ as the way God experiences the temporal occasions of the world. Suchocki writes that “The actualities of the world shall be felt by God through the consequent nature, and integrated into the harmony of God, the primordial nature...God, as well as finite reality, is a unification, a becoming.”Charles Hartshorne captures this through his concept of “the divine relativity” and its dialectic relation to the absolute character of God as the “self-surpassing of all.”3) Scholars forging a revised natural theology argue that God is both eternally transcendent to and temporally immanent within the world. As a dipolar theist, Polkinghorne stresses that God experiences the world in the universal present moment; the future is simply not there for us, or for God.As a panentheist, Peacocke takes a similar approach: the future does not yet exist, leaving God to create each instant of physical time.Across deep theological and philosophical differences, then, these three schools of thought represent what is generally true in theology, namely the assumption of a unique, flowing, global present which divides the past shared in common from a common future --- whether or not God is then thought of as experiencing the world through that present moment.

This underlying view of time is based on both ordinary experience and classical, Newtonian physics: namely linear, flowing time, with a universal and uniformly moving present that separates the global past from the global future. Special relativity (“SR” c. 1905) directly challenges this view in two ways. It undercuts both the notion of a universal present and the assumption of a uniform rate of time’s passage. Instead, according to SR, observers in relative motion define their own ‘present’ and its universal ‘past’ and ‘future’; moreover, observers in relative motion move into the future at different rates. Because of this and other facts, SR can lead to a ‘block universe’ interpretation.

Science minisummary: Special relativity. There are many ways to discuss special relativity (SR); one is to start with empirical data 

1.‘Time dilation’ and the “downfall of the present” Ideal clocks can be imagined as a pack of firecrackers of identical size, composition, and fuse.If they are all lit at once, we would expect that the firecrackers would explode at the same time, let’s say, one second later. Well, they do, when they are at rest with respect to each other. But what if we throw them to the left and right so they’re moving at different velocities v with respect to each other, and keep one at rest at the origin? Stunningly, the actual result is that they do not explode simultaneously! Instead, identical clocks (i.e., ‘firecrackers’) in relative motion run at different rates than identical clocks at rest, a fact called “time dilation”, and thoroughly verified throughout the twentieth century. So the ordinary idea of a ‘present moment’ that moves equally into the future for everyone just doesn’t hold! But there’s more: the faster they move away from us, say along the x axis, the more time t passes before they explode. In fact the events in space x and time t where they explode are all related to each other and to the time (here one second) when the firecracker we kept at rest exploded. Let’s call this time “proper time” τ. Then τ² = t² - x²/c², where c is the speed of light.Still these are identical clocks, so what’s happening? Perhaps we should say that they each tick at the same rate in their own reference system, but the way we measure time and space itself must be reconsidered. Physicists refer to the proper time as an “invariant spacetime interval” since it represents an identical ‘distance’ or ‘interval’ between the origin of the experiment and the events in space and time where the one-second proper time ticks occurred (i.e., the firecrackers exploded). 

2. Synchronization and the “downfall of the present”. Time dilation leads inexorably to the “downfall of the present”. Suppose, instead, that there were a physically significant global present, a universal “now” as classical physics and common sense hold. How would we specify it, i.e., how would we synchronize clocks A and C in relative motion to tell what event along the worldline of clock C corresponds to the “now” along the worldline of clock A? An obvious answer would be synchronize a third clock at rest with respect to A, then move it from A to C, set C’s time to match it, and thus to match A. The problem is time dilation: if we move identical and synchronized clocks around to different positions as just described, they will no longer be synchronized!In fact, there is no physically significant way of determining a global present according to SR. Instead of a universal, unique “present”, there is only a “present” defined by each moving observer in an equivalent way. 

3. Implications: The immediate implications are a variety of ‘paradoxes’, most of which represent variations on the themes of time dilation and what is its converse, ‘length contraction.’In effect, all such “paradoxes” arise because we so naturally look at the world as “3+1", i.e., as a 3-dimensional spatial universe changing in time, a perspective lodged in both ordinary human experience and the classical physics of Newton and Galileo. Instead, SR invites us to look at the union of space and time in “spacetime”, often referred to as “3+1 --> 4". Here, though time and space measurements vary between moving observers, the measure of the ‘spacetime interval’ between events is invariant. 

4. The invariance of causality: The speed of light is not only a constant in SR; it functions as a limitation on which events in my future I can effect, namely those which I can reach with light signals or slower-moving phenomena. This means that the order of events along any worldline moving past me is invariant: all observers in relative motion will agree with this order.(For General Relativity see below.)

Given the seriousness of the challenge of SR to our classical view of a universal, flowing present and its routine incorporation into theology, it is surprising how little attention SR has received. One notable exception is Hartshorne, who was willing to acknowledge that, to neo-classical theism, special relativity posed “the most puzzling (challenge) of all.”

Some scholars in theology and science, though, have addressed the challenge in detail.The crucial step, as Polkinghorne points out, is to recognize that the theological implications of relativity depend critically on its philosophical interpretation, and this in turn can take at least two forms. In a recent debate, Polkinghorne defended a ‘flowing time’ interpretation that accords with our everyday experience of temporality and Chris Isham supported the ‘block universe’ view which claims to undercut it.

A) Polkinghorne argues for a ‘flowing time’ interpretation in which the problem of the downfall of the universal present is epistemic, not ontological. Here God truly experiences the world in its open and flowing temporality. Indeed God cannot know the future since there is no future to be known. Defending “flowing time,” Polkinghorne stressed the independence of kinematics, the abstract rules for coordinating measurements between observers in relative motion such as classical physics and SR offers, and dynamics, the concrete theories about how natural processes and forces work. For example, we can use classical kinematics in both deterministic dynamics (classical mechanics) and indeterministic dynamics (non-relativistic quantum mechanics interpreted indeterministically). Similarly we can use relativistic kinematics in both deterministic dynamics (classical electromagnetism) and indeterministic dynamics (relativistic quantum mechanics and quantum electrodynamics). This means that the use of SR does not commit us to a deterministic view of the future and a timeless view of nature as entailed by the “block universe”. Theologically, Polkinghorne suggests that omniscience may be taken to refer to a particular spatial domain and a special sequence of spatial frames of reference, and that the overall cosmic background radiation in Big Bang cosmology might suggest a cosmic present (see “cosmology” below).

B) Isham defends a Platonic ‘block universe’ interpretation: all events in spacetime are equally ‘real’Thus Isham ontologizes all of spacetime homogeneously and places God outside of time in a timeless view of the eternal present. Chris Isham sees the “flowing time” view of nature as illusory. “If the speed of light had been much smaller, reality would presumably have seemed very different to us and we would never have fallen into the error of assuming that, at each moment of our experience, the whole universe divides into events that have not yet happened, and those that have.” As a “unashamed Platonist,” Isham sees “the eternal reality of the spacetime manifold...as a single mathematical entity” as the essence of relativity. He avoids being charged as reductionist, since physics studies matter, not the human mind. Still his main objection is about reference to “the future” or “the past”. Which future? “If it is the future of the entire universe this seems to be equivalent to the idea of a ‘passing now’ which is incompatible with both special and general relativity.” Clearly the light-cone structure for each point-event along a given world-line provides a valid division of spacetime into past, future, and elsewhere. This ‘changing’ point-event and its changing division of spacetime can be thought of as a ‘passing now’ for the entity moving along a given worldline. Moreover, one could posit a special sequence of spatial reference frames through which God experiences physical reality. But this leads to Isham’s main challenge: “(Polkinghorne claims) that God acts on the world in such a way as to preserve the requirements of relativistic physics, and this may by correct. But is it possible to construct a model of such an interaction? It is not easy to add any external influence on the physical world and maintain the full fabric of relativity.” In essence, Isham asks whether opponents of the block universe “seek merely to reinterpret the existing theories of physics, or do they make the much stronger claim that their metaphysical views can be sustained only by changing the (scientific) theories?”

Variations on the argument for ‘flowing time’ have also been pursued recently. David Griffin has collected numerous articles by scientists and philosophers which challenge the block universe view of SR.Barbour has stressed that SR points to a universe both “dynamic and interconnected” and yet suggestive, through its lightcone structure, of “a new form of separateness and isolation.” Responding to Hartshorne’s concern, Barbour claimed that God’s immanence in all events can be thought of as the way God is omnipresent, the way God knows all events and also influences each in terms of its own causal past as this past is uniquely defined according to SR.Lawrence Osborn interprets relativity in terms of flowing time and connects this with the Trinity and the creation of real temporal relations.John Lucas, like Polkinghorne and Barbour, argues that we need to posit a divine ‘frame of reference’ by which God experiences the real temporal flow of the universe. Lucas is open to the possibility that such a view might actually challenge SR. My approach is to construct a more complex interpretation of SR with two goals in mind: to re-conceptualize “past” and “future” not as the ontological status of events but as relations between events,and to deploy an inhomogeneous ontology for spacetime. I then suggest we integrate these into a Trinitarian understanding of eternity, and explore whether such a relativistically correct reconstructed Trinitarian view of eternity may have empirical implications for science.

These issues involving SR, temporality and eternity, then, clearly lie at the cutting edge of research in theology and science today, and they spill over into related issues such as divine action, free will, and theodicy.

Contributed by: Dr. Robert Russell