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❓Big Questions❓ — Math&Physics

Time and Causality - What's The origin of change in Physics

Conceptual and ontological relationship between causality and time. The origin of change in Physics (relativity, quantum gravity, thermodynamics), metaphysics (temporal ontology, process philosophy), and cosmology (pre-time origins, first causes).

,   and  Eduardo Bergel
38 min read

Table of Contents

Introduction

What is more fundamental – the flow of time or the chain of cause and effect?

This question cuts to the core of how reality is structured. Time and causality seem intimately connected: causes precede effects in time, and without the passage of time, it is hard to imagine events influencing one another. Yet, philosophers and physicists have long debated whether one of these concepts underlies the other, or whether both emerge from something deeper. Is time merely a measure of change (with causation driving those changes), or is causality only possible given a temporal order to events? This essay explores these issues by examining insights from physics (relativity, thermodynamics, quantum mechanics, quantum gravity), metaphysics (the nature of temporal reality), cosmology (the origin of time), and theology (the idea of a first cause). We will ask whether causation could exist in a timeless realm, whether time could “flow” without causal relations, and whether either concept could exist independently. By analyzing these perspectives, we aim to clarify whether time or causality holds a more fundamental place in the structure of reality.

Time and Causality in Physical Theories

Classical and Relativistic Views

In classical Newtonian physics, time was treated as an absolute background that exists in its own right. Sir Isaac Newton famously described “absolute, true, and mathematical time” as something that “flows equably without relation to anything external” (Time: Physical and Biological Aspects | Encyclopedia.com). In this substantival view, time is like a container in which events occur; it would continue even if nothing changed. Causality in Newton’s framework was straightforward: causes produce effects in sequence, and time provides the universal clock for ordering those events. Newton’s rival, Gottfried Leibniz, argued the opposite – a relational view – that time is not an entity on its own but just the order of events. In Leibniz’s perspective (later echoed by Ernst Mach and others), if there were no events or change, time would have no meaning; time is essentially a way to compare and sequence changes. Indeed, St. Augustine reached a similar conclusion: “time is a measure of change” and “there can be no time without creation”, meaning time began with the first change or event (St. Augustine and the Beginning of Time). On this view, causation (the happenings and changes in the world) is primary, and time is an abstraction from the succession of those changes.

Einstein’s theory of relativity in the 20th century dramatically changed the understanding of time and causality. Relativity joined space and time into spacetime and showed that there is no single universal “now.” Events that are simultaneous in one frame may occur at different times in another, undermining Newton’s absolute time. However, relativity does enforce an invariant causal order for events that are directly connected. In relativity, a cause must lie in the past light cone of an event to influence it, and an effect must lie in the future light cone of its cause (Causality (physics) - Wikipedia) (Causality (physics) - Wikipedia). In other words, no effect can occur before its cause in any frame of reference – a cause cannot influence outside its future light cone or travel faster than light to create an effect (Causality (physics) - Wikipedia). This principle builds causality into the fabric of spacetime. Unlike Newton, Einstein did not see time as flowing on its own; all events past, present, and future can be viewed as part of a four-dimensional spacetime “block.” Nevertheless, the causal structure (the pattern of which events can influence which others) is fundamental in relativity. The speed of light acts as a cosmic speed limit ensuring a consistent cause-effect ordering for all observers (Causality (physics) - Wikipedia). If one were to violate this (e.g. by sending signals faster than light or traveling in a closed time loop), paradoxes could arise (an effect influencing its own cause). General relativity permits solutions with closed timelike curves (time loops), but such scenarios threaten to break causality. Most physicists suspect some yet-unknown constraint (Stephen Hawking’s “chronology protection conjecture”) prevents these causal paradoxes, preserving the consistency of cause and effect in our universe. Thus, in relativity, time and causality are tightly interwoven: time provides the coordinate ordering of events, but the allowable ordering is governed by causal relations (light-cone structure). Indeed, it has been proven that given the causal ordering of events (and the volume measure of spacetime), one can in principle reconstruct the spacetime geometry itself (Causal sets - Wikipedia). This is exemplified by the theorem of Malament and others that in a well-behaved spacetime, the causal order plus scale determines the spacetime metric (Causal sets - Wikipedia). Such results suggest that the causal structure of events might be as fundamental as – or more fundamental than – the continuum of time and space in which those events are embedded.

The Thermodynamic Arrow of Time

While the microscopic laws of physics (both classical mechanics and quantum mechanics) are largely time-symmetric (they do not care about a forward or backward direction of time), our macroscopic experience of time is highly asymmetric. We remember the past, not the future; causes precede their effects; we were younger in the past and older now. This one-way flow is often called the arrow of time (Arrow of time - Wikipedia) (Arrow of time - Wikipedia). In physics, the thermodynamic arrow of time is defined by the Second Law of Thermodynamics: entropy (disorder) tends to increase with time in an isolated system (Arrow of time - Wikipedia). As Sir Arthur Eddington noted, entropy increase gives a direction: it distinguishes past (lower entropy, more order) from future (higher entropy) (Arrow of time - Wikipedia). This entropy arrow aligns with our perceived direction of causality – we see causes leading to effects in the same direction that entropy grows. For example, a cup falls off a table and shatters (cause precedes effect); in doing so, the entropy of the system increases (the pieces are more disordered than the intact cup). We never see the reverse (shards gathering to form a cup) because that would require entropy to decrease. In general, past events are the causes of future events, not vice versa, and this correlates with the fact that entropy was lower in the past and is higher in the future (Arrow of time - Wikipedia) (Arrow of time - Wikipedia). Many physicists believe this is not coincidence: the causal asymmetry we observe is a consequence of special initial conditions of the universe (a low-entropy beginning – sometimes called the “Past Hypothesis”). The fundamental laws themselves don’t mandate an arrow; rather, a low-entropy starting state means entropy can increase, thereby defining a direction in time along which ordered causes produce more disordered effects. In this view, the flow of time we experience (with a fixed past and an open future) is closely tied to the growth of entropy and the causal structure that comes with it. As one source succinctly puts it, “the increase of entropy gives time its direction, creating a causal structure that helps define the arrow of time.” (The Arrow of Time: Entropy, Human Consciousness, and the Future ...). If we hypothetically reversed the arrow of causality, making effects precede causes, we would also reverse the thermodynamic arrow – entropy would decrease going “forward” in time, which appears to be physically forbidden (Arrow of Causality and Quantum Gravity | Phys. Rev. Lett.). Thus, from a physical standpoint, time’s direction (past-to-future) is deeply linked to causality’s direction (cause-to-effect), both of which seem to arise from conditions like entropy increase. However, it’s worth noting that this arrow is an emergent, statistical phenomenon. At the level of fundamental equations (general relativity, electromagnetism, quantum dynamics), there is symmetry between time forward and backward (Arrow of time - Wikipedia) (Time: Physical and Biological Aspects | Encyclopedia.com). The laws themselves do not distinguish cause from effect – it is the boundary conditions (like the Big Bang’s orderly state) that inject an asymmetry. This raises an interesting thought: if the arrow of time (and thus the usual direction of causality) is not built into the core laws but emergent, then perhaps neither time’s flow nor causation’s arrow is truly “fundamental” but a derived feature of a deeper, time-symmetric reality. In everyday terms, though, as long as entropy defines an arrow, time is the medium in which causality unfolds: one can measure time by change (clocks tick by some physical process), and that change is governed by causal evolution (physical interactions obeying cause→effect).

Quantum Mechanics and Causal Puzzles

Quantum physics brings new subtleties to the time–causality interplay. On one hand, relativistic quantum field theory upholds the principle of relativistic causality: no information or influence travels faster than light, and operators corresponding to measurements at spacelike-separated events commute (meaning neither can causally affect the other) (Causality (physics) - Wikipedia). In this sense, causality remains a fundamental constraint – even quantum entanglement, which produces strong correlations between distant particles, cannot be used to send signals or cause-and-effect influences faster than light. Any measurement on one entangled particle has no instantaneous causal influence on the other in a way that could transmit information; it merely updates correlations. So the basic requirement that cause precede effect in time still holds in quantum theory’s predictions and observed reality.

On the other hand, quantum mechanics challenges classical intuitions about causation. For example, in quantum processes the order of events can be indeterminate. Recent experiments have demonstrated scenarios of “indefinite causal order” in which it is impossible to say in which sequence two events occur – effectively, event A and event B happen in both orders at once, as a superposition (Quantum Mischief Rewrites the Laws of Cause and Effect | Quanta Magazine). One such demonstration uses a “quantum switch,” where two operations (like two quantum gates or two measurements) are arranged in a superposition of orders. The result is a situation where both “A causes B” and “B causes A” are simultaneously true in the quantum sense (Quantum Mischief Rewrites the Laws of Cause and Effect | Quanta Magazine). While this does not allow any logical paradoxes or time-travel absurdities (once you measure the order, you get a consistent outcome), it suggests that causality might not be a fixed backbone at the quantum level – the causal sequence of events can become fuzzy, much like other properties in quantum mechanics. Some physicists even speculate that causality might be an emergent classical concept, and that on the quantum level “cause” and “effect” may dissolve into more primitive correlations (Quantum Mischief Rewrites the Laws of Cause and Effect | Quanta Magazine). This is a speculative area, but it highlights that time and causation in quantum theory are subtle: quantum theory usually treats time as an external parameter (especially in ordinary quantum mechanics – Schrödinger’s equation runs on an external time variable), yet the theory’s implications (like entanglement and potential retro-causal interpretations in some interpretations of quantum mechanics) blur strict causal narratives. For instance, certain interpretations of quantum phenomena (like Wheeler’s delayed-choice experiments or the transactional interpretation) toy with influences that seem to transcend the normal order of time, though these remain interpretations without consensus.

Crucially, even where quantum mechanics challenges our notion of a single fixed causal order, it does not outright violate causality in the sense of producing contradictory cause–effect loops or observable influences backwards in time. The causal consistency of the world is preserved – quantum correlations are strange, but they respect the relativistic timing of causes and effects. In fact, one could argue that quantum entanglement hints at a deeper level of interconnection that underlies both time and causality. Some researchers have proposed that time itself might emerge from quantum entanglement in certain contexts. In a notable 2013 experiment related to the Page–Wootters mechanism, physicists showed that a clock particle entangled with a system can exhibit evolution as if time is emerging from their entanglement (Quantum Experiment Shows How Time ‘Emerges’ from Entanglement | by The Physics arXiv Blog | The Physics arXiv Blog | Medium). The headline of that work was “Time is an emergent phenomenon that is a side effect of quantum entanglement” (Quantum Experiment Shows How Time ‘Emerges’ from Entanglement | by The Physics arXiv Blog | The Physics arXiv Blog | Medium). In simple terms, if you have a large quantum system in an overall timeless state (e.g. the universe described by the Wheeler–DeWitt equation, which sets the global quantum state’s Hamiltonian to zero, implying no conventional time evolution), subsystems can still experience an effective flow of time relative to each other through entanglement and correlations. This provocative idea suggests that at the deepest level, the universe might be static or “timeless,” and what we call time (and the ordered chain of causes and effects) could arise from the way parts of the universe are correlated with one another. If so, causality (as an ordered sequence of events) would also be an emergent property of an underlying timeless reality.

These quantum considerations reveal that the question of fundamentality is non-trivial. In everyday conditions and in established physics, time and causality appear as two sides of the same coin – we identify causes by their earlier times and effects by later times, and we enforce that ordering through physical principles. Yet quantum physics invites the thought that perhaps the coin has another face entirely: a realm where the usual conceptions of time and causation break down or give way to something more fundamental (like a static wavefunction of the universe, or a probabilistic web of correlations). If so, deciding which of time or causality is “more fundamental” might require a theory of that deeper realm.

Time in Quantum Gravity – Is Time Fundamental?

The quest for a quantum theory of gravity (which would unify general relativity with quantum mechanics) has led researchers to seriously consider that time itself may not be fundamental at the deepest level of physical reality. One striking clue comes from the Wheeler–DeWitt equation in canonical quantum gravity, which (roughly speaking) says $H\Psi = 0$, where $H$ is the Hamiltonian constraint of the universe. This equation, which was an attempt to quantize the Einstein field equations, has the peculiar feature that it does not contain an explicit time parameter – it implies a “frozen” universe in which the quantum state of the cosmos doesn’t evolve in time. Physicists call this the Problem of Time: our most naive application of quantum principles to the whole universe suggests nothing ever happens (contradicting our experience of change) (Quantum Experiment Shows How Time ‘Emerges’ from Entanglement | by The Physics arXiv Blog | The Physics arXiv Blog | Medium). A possible resolution is that time is not fundamental in such a theory, but rather something that emerges from correlations within the state (as mentioned with entanglement clocks). In the 1980s, Don Page and William Wootters proposed that while the global state of the universe might be static, an observer within the universe could still experience the passage of time by becoming entangled with subsystems (Quantum Experiment Shows How Time ‘Emerges’ from Entanglement | by The Physics arXiv Blog | The Physics arXiv Blog | Medium) (Quantum Experiment Shows How Time ‘Emerges’ from Entanglement | by The Physics arXiv Blog | The Physics arXiv Blog | Medium). Experiments and toy models have lent some credence to this idea, showing how an effectively classical time parameter can arise for subsystems of a static quantum universe.

Another leading approach that puts causality at the forefront is the Causal Set Theory in quantum gravity. This approach posits that “spacetime is fundamentally discrete … and spacetime events are related by a partial order,” namely the causal order (Causal sets - Wikipedia). The slogan of causal set theory, coined by Rafael Sorkin, is “Order + Number = Geometry” (Causal sets - Wikipedia). In other words, if you know which events causally precede which (the order) and how many discrete “ticks” occur (the number of elements, giving volume), you can reconstruct spacetime. Here, causality (the ordering relation) is taken as more fundamental than continuum spacetime or continuous time. The flow of time would just be the growth of this causal set – as new events are added in order, time and history emerge. In such a picture, if we ask “what exists fundamentally?”, it’s a web of relations (“x is before y”) rather than a continuous time variable. The passage of time could be thought of as the accumulation of new events in the causal order (some have likened this to a “growing block” universe, where the past and present exist and the future is not yet, as new events come into being). Notably, causal set theory aligns with a key insight from relativity: the causal structure encodes the spacetime. It radicalizes that insight by dispensing with continuous time and space at the fundamental level – keeping only discrete causation. If this program (still under development) is correct, causality is literally the structural backbone of reality, and clock time, distances, etc., are secondary concepts that emerge from counting and ordering those fundamental events.

Other quantum gravity approaches also often diminish the fundamental role of time. Loop Quantum Gravity, for instance, has formulations where spatial relationships are quantized and time can become just a parameter derived from change in something else (like matter fields serving as “clocks”). Some approaches (e.g. cosmological models inspired by Euclidean quantum gravity or the AdS/CFT correspondence in string theory) suggest that time as we know it might “emerge” from a timeless theory – in AdS/CFT, for example, time in a gravitational bulk can correspond to the renormalization scale (not an explicit time) in a dual field theory. These are active research areas, but a common theme is time may not stand on its own at the most fundamental level. There are even proposals that the laws of physics themselves might be reversible and timeless, and that irreversibility (hence a directed causality) appears only once certain conditions (like entropy gradients or decoherence) are in place (Time: Physical and Biological Aspects | Encyclopedia.com) (Time: Physical and Biological Aspects | Encyclopedia.com).

In summary, modern physics provides two nearly opposite hints about our question. Relativity teaches that an event’s place in time is meaningful mainly via its causal relations (what can affect it and what it can affect), suggesting causality is fundamental to defining time. Quantum gravity hints that time might be an emergent concept, perhaps derived from causality or correlations (as in causal sets or entanglement scenarios). And thermodynamics suggests that the direction of time (and thus the directedness of causation) is an emergent feature of special initial conditions. All these perspectives entangle time and causality together. We rarely, if ever, find one without the other in physics: time without causal order is either meaningless (as in a completely static universe) or empty, and causation without time to order it is similarly incoherent in physical descriptions. This interdependence in physics sets the stage; to dig deeper, we turn to philosophy and metaphysics.

Metaphysical Perspectives: The Nature of Temporal Reality and Causation

A-Theory vs B-Theory: Being and Becoming

In the philosophy of time, a central debate is between A-theory (or tensed theory) and B-theory (tenseless theory). This debate concerns whether temporal becoming (the passage of time, the distinction between past, present, future) is fundamental to reality or an illusion. A-theorists hold that the present is objectively real and time truly “flows” or unfolds – the universe is in a continual process of becoming. In contrast, B-theorists maintain that all moments in time are equally real (past, present, future are just positions in time, like places on a map) and the flow of time is a subjective or emergent phenomenon, not something fundamental. This maps closely to presentism vs eternalism: presentism says only present objects/events exist, eternalism says past and future entities exist in a tenseless 4D block.

If one adopts B-theory/eternalism, time is often compared to another dimension of space – the universe can be seen as a static spacetime manifold with events laid out within it. In such a picture, what is causality? Causality would not be a process of “producing” new events (since all events already exist in the block); instead, causation is an ordering relation between events in the block. One event can be earlier in the time dimension and stand as a cause of a later event, but those events’ existence is not in question – only the relation “earlier than” distinguishes cause from effect. Many B-theorists indeed maintain that the distinction between cause and effect is a perspectival or higher-level concept, since the fundamental description just has a tenseless network of events. Notably, the relativistic view of time strongly supports something like the B-theory: Einstein himself, consoled by the death of a friend, wrote that “for those of us who believe in physics, the distinction between past, present and future is only a stubbornly persistent illusion.” (What Did Einstein's Theories Say About the Illusion of Time? | Discover Magazine). In a block-universe view consistent with relativity, the flow of time is not fundamental – it’s an “illusion” in Einstein’s words – and thus one might suspect causality (at least the feeling that the present causes the future) is also an emergent or perspective-dependent feature. To a godlike observer of the block, there is no coming-into-being of events; there is just the entire spacetime. However, even in a block universe, one can define causality as the partial order of events (again the light-cone structure). The B-theorist would say that while we perceive time flowing and causes coming before effects, in reality the universe just is, with a tenseless earlier-later structure. Causality can thus be given a tenseless definition: for example, event E is causally dependent on event C if and only if E lies in C’s future light cone and appropriate physical links connect them. But nothing becomes or produces in the literal sense; cause and effect are fixed relations in the block.

By contrast, A-theorists (presentists and others) argue that time’s flow is fundamental – the passage from a real present into a non-existence past is an ontological feature of the world. In this view, the universe is more like a process than a thing. Presentists say only the present moment exists; the past did exist but is now nothing, and the future does not yet exist. For an A-theorist, causation is a real process that brings about new events – causes truly generate effects as time unfolds. The present moment is the arena of reality where causes operate to produce new outcomes that then become the new present, and so on. If presentism is correct, one might argue time is more fundamental, in the sense that only the flowing “now” is real, and causality is basically the rule or pattern of how reality changes from one moment to the next. On this view, time isn’t just an ordering of events – it is an active dimension of reality in which only the moving present is ontologically real. The laws of nature connect one present state to the next, which is essentially causation in action. Some A-theorists (like proponents of process philosophy) explicitly elevate process and causation to the fundamental level: reality is not made of things but events, and those events are essentially causal processes of becoming. Philosopher Alfred North Whitehead’s process metaphysics, for instance, describes reality in terms of “actual occasions” – each a momentary event of experience that grows out of prior ones and causes effects in successors. Whitehead argued that “perception in the mode of causal efficacy” – the way each event feels the influence of past events – “is by far the most significant and fundamental mode of causation” in the world (Process Philosophy | Internet Encyclopedia of Philosophy). In other words, he considered the direct causal influence of one event on another to be the bedrock of reality (even more fundamental than our immediate perception of the present moment). This process-oriented view implies that causality is the driver of temporal becoming. Time is essentially the successive creative acts of causation; without causes bringing about new effects, time would not advance. Henri Bergson, another process thinker, criticized the spatialized view of time (the B-theory) and emphasized duration – the lived, flowing time – which he saw as the source of novelty and causation in the universe. These views resonate with the idea that causality (as genuine production of effects) is ontologically prior, and time is essentially the framework of that production.

However, A-theory faces challenges too. Special relativity’s lack of a universal present makes presentism hard to reconcile with physics ( Time (Stanford Encyclopedia of Philosophy) ) ( Time (Stanford Encyclopedia of Philosophy) ). Moreover, if only the present is real, how do we make sense of statements like “World War II caused the end of the Great Depression”? That cause and effect are both in the past now, yet we assert a causal relation. The worry is that in presentism “there are no non-present objects to be the relata of those relations” ( Time (Stanford Encyclopedia of Philosophy) ) – if only the present exists, past events like World War II don’t exist to have any properties, including causal relations. Presentists typically respond that past events did exist and left traces or records that exist now, and causation can be understood in terms of those traces (for example, the economic conditions at the end of the Depression bear the imprint of the war’s effects). But this is a subtle metaphysical issue: does causation require both cause and effect to exist at once in some sense (which B-theory provides, since both are in the block), or can a cause that no longer exists still somehow produce an effect that does exist? The presentist might say causation is a two-stage picture: a cause existed and produced a certain outcome; once the cause passes, only the outcome and perhaps an abstract relation “produced by” remain. Eternalists avoid this issue by saying the cause and effect co-exist in the four-dimensional tapestry of spacetime, linked by causal relations.

Causation: Dependency vs Production

There is also a rich philosophical literature on causation itself – what it means for one event to cause another. Some philosophies (like Hume’s empiricism) suggest that causation is not a fundamental “glue” in the world but rather a description of regular succession. David Hume famously argued we never directly observe a necessary causal power; we only see one event followed by another, and our mind projects a causal connection due to habit. If Hume is right in a deep sense, then causality might not be a fundamental feature of reality at all – it could be a way humans interpret temporal sequences. In such a view, time (as the dimension of sequence) might be more fundamental, and causality just a useful concept for patterns in time. However, most philosophers of science and metaphysicians think there is more to causation – something like a counterfactual dependency (if the cause hadn’t happened, the effect wouldn’t have either) or a transfer of energy or information. These accounts still tie causation to time: the cause is earlier and brings about the effect under some law of nature.

One interesting angle is the idea of atemporal causation – can causation make sense outside of time? In everyday terms, a cause always precedes its effect in time. But some metaphysical or theological contexts consider causation that is not temporal sequence but a sort of dependence. For example, in theology, God’s act of creation is often said to be outside time (God being eternal or timeless), yet God is considered the cause of the universe. This is sometimes called an atemporal cause or a cause “from eternity.” As Thomas Aquinas explained, “God is before the world by duration. The term 'duration' here means the priority of eternity, not of time.” (Time: Religious and Philosophical Aspects | Encyclopedia.com). In other words, God’s priority to creation isn’t like an earlier event, but a different kind of priority (logical or ontological priority). Aquinas and most medieval thinkers held that time itself began with the creation of the world, as reflected in his statement that “the heavens and earth were created together with time” (Time: Religious and Philosophical Aspects | Encyclopedia.com). For them, asking “what happened before time began?” is meaningless in a literal sense, just as (to use Stephen Hawking’s analogy) asking “what’s north of the North Pole?” is meaningless (Stephen Hawking - Wikipedia) (Stephen Hawking - Wikipedia). Nonetheless, they attribute a cause (God) to the beginning of time. This implies causation is being used in a broader sense of ontological dependence: the universe depends on God for its existence, even though there isn’t a prior moment where God ‘pulled the trigger’ in time. Can we consider such dependence causation? Many would say yes, it’s a cause–effect relationship, just not one that unfolds within time. In philosophical cosmology, similarly, one might contemplate a timeless law or principle causing the universe. For instance, some proposals in quantum cosmology suggest the universe arose from a “quantum fluctuation” in some timeless state. The “cause” (a quantum tunneling from nothing, or a vacuum instantiation) isn’t a prior event in time, but rather a feature of a timeless quantum state that yields time and space. This blurs the line between cause and initial condition.

Theologically, Augustine argued that time itself was part of creation, so there was no “before” creation for a cause to act in – yet he attributes creation to God’s eternal will (St. Augustine and the Beginning of Time). He even admonished not to envision God doing something before creation: “there can be no time without creation” and “what times would there be that were not made by you [God]?” (St. Augustine and the Beginning of Time). So for Augustine and Aquinas, time began with the first event, and the cause of that event exists in an eternal (timeless) realm. This viewpoint suggests causality (in the form of a sustaining or originating cause) might not require time as we know it – causality could be a more general concept of dependency, with temporal causation just one species of it. If one accepts this, one might say causality is more fundamental because one can conceive of causation without time (God causing a universe, or a timeless law causing a big bang), whereas time without any causation (just an empty container with nothing happening) seems physically and metaphysically less meaningful. On the other hand, a skeptic might respond that invoking “cause” in a timeless context is stretching the concept – perhaps it’s better seen as a logical explanation rather than causation per se, since cause as normally defined requires a temporal process.

Could Time Exist Without Causality?

Another way to probe fundamentality is to imagine one without the other. We’ve considered causality without time (e.g. a static dependence). What about time with no causality? If time is just a bare dimension and nothing causes anything, what would that be like? Perhaps a universe that is completely chaotic or one in which events happen but with no lawful regularities linking them – so you couldn’t infer causes. If literally nothing caused anything, events would be uncorrelated random flashes. Time could still tick, but the concept of causation wouldn’t apply. Is that a coherent scenario? It’s hard to imagine physics or any structured reality in such a world; it would be a film of random frames with no storyline. Some philosophers have entertained the notion of an uncaused universe – not just at the first moment, but entirely: a reality where things “just happen” for no reason at all. But even in such a reality, if events “just happen,” they still happen in time, and one could still label earlier and later. However, you would lack any causal order beyond the temporal order. This seems to violate what we find in our universe: we see regularities and persistence of objects, which we explain through causation. A world with time and change but no causation would be a strange, lawless place.

We might also contemplate a universe with a single, unchanging state. Would time exist there? Newton might say yes – time flows regardless of change. But empirically, if nothing at all changes or happens, there is no way to measure time or even define it operationally. In Einstein’s general relativity, one can have solutions where nothing evolves (a static universe); time in those solutions is a coordinate with no physical signification because all observables are constant. That suggests that without events or causation, time becomes unobservable – it might exist as a mathematical parameter, but it has no physical meaning. This echoes the relational view: time has meaning only as the measure of change. Thus, time devoid of any causally connected sequence of events might be empty.

In contrast, a universe with events and laws (so causation) but no sense of an external time could potentially be modeled as a causal network or a logical structure. Some have even speculated that the universe could be fundamentally timeless (as in Julian Barbour’s proposal of “Platonia,” where all possible moments or configurations exist and what we call time is the illusion of movement through this set). In Barbour’s view, each moment (each configuration of the universe) is complete and timeless; our sense of continuity and causation comes from the correlation between configurations (some contain records of others) (Julian Barbour: timeless complexity and the records of the universe) (What are Time Capsules in Julian Barbour's theory of a Timeless ...). This again suggests causation (correlation between configurations) might be more fundamental, with time being a way to label sequences of configurations that have mutual records. There is even a Bayesian or decision-theoretic notion of “timeless causality” where one can define cause–effect relations without embedding them in time, by how certain variables probabilistically depend on others (Timeless Causality - LessWrong). These ideas are highly theoretical, but they open the door to causation as a concept independent of time’s flow.

Cosmological and Ultimate Origins: Time, Causality, and the Universe

The Beginning (or Absence) of Time

Cosmology provides a testing ground for these ideas because we confront the origin of time and the need (or not) for a first cause. The Big Bang theory, extrapolating general relativity back in time, suggests the universe (as we know it) began about 13.8 billion years ago in a hot, dense state. In classical general relativity, there is a singularity at “time zero” – a boundary beyond which time cannot be extended. Many take this to mean time itself began at the Big Bang. If time began, one might ask: what caused the Big Bang? But if cause requires a prior time, the question becomes tricky. Stephen Hawking famously stated that asking what happened before the Big Bang is like asking what is north of the North Pole – it’s not that there’s something there; it’s that the question itself breaks down because “before the Big Bang, time did not exist” (Stephen Hawking - Wikipedia). In Hawking and Hartle’s no-boundary proposal, the universe has no initial boundary in imaginary time; the concept of a start is replaced by a smooth rounding-off (like the North Pole being the top of the world with no further north) (Stephen Hawking - Wikipedia). In such models, the universe doesn’t have a singular first event that needs a cause; the question of “what caused the Big Bang?” might be moot, as the Big Bang isn’t an event emerging in a prior time. Time “turns on” as the universe emerges. So one approach in cosmology is that the universe may not require an external cause in time – it could be self-contained. The causal principle (every event has a cause) might simply not apply to the origin of time, because there is no earlier state. This is reminiscent of Augustine’s stance that it’s meaningless to speak of times before creation (St. Augustine and the Beginning of Time). It could be that the universe’s existence is a brute fact or explained by a timeless law (like a law of physics that allowed a universe to appear quantum-mechanically). Here, time is fundamental in that it’s part of the universe’s fabric from the start, and causality as we know it only operates after time begins. The “first cause” in a temporal sense doesn’t exist – time starts and with it starts causally connected events.

Alternatively, some cosmological arguments (especially in philosophy of religion – the Kalam cosmological argument) assert that everything that begins to exist must have a cause, so if the universe began to exist, it must have a cause. If time began with the universe, that cause cannot be a prior physical event; proponents often suggest an eternal (timeless) agent or condition caused the universe. This circles back to the idea of an atemporal cause. Whether one finds that coherent or not often depends on how strictly one defines causation. Some argue such a cause can be thought of as bringing the universe into being simultaneously with the beginning of time. For instance, one might say a timeless Creator willed the universe and at t=0 the universe appears – the causal relation holds not in time but “at the boundary” of time. Others prefer to avoid talk of a “before” and instead say the initial state of the universe could be self-caused or explained by some principle like a quantum cosmological spontaneous creation, which is not a cause in the traditional sense but a natural mechanism.

Modern cosmology also entertains models where time might be cyclic or have a before: for example, in eternal inflation or cyclic ekpyrotic models, what we think is the Big Bang might be just a transition, and time could stretch infinitely far back with repeated causal processes (e.g., bubble universes budding off a multiverse, or oscillatory expansions and contractions). In eternal inflation, there is a kind of causal generation of new “pocket universes,” so causality extends beyond our Big Bang (though time might be differently defined in the multiverse context). In cyclic models, time is eternal and events repeat in cycles, so there was no first event, and thus perhaps no need for a first cause – but causality still operates within each cycle. These scenarios complicate the question of origin: if time is eternal, you don’t need a cause for time’s beginning, but you might still wonder if the whole sequence has a cause or explanation. Possibly, one could imagine an infinite regress of causes – every event is caused by a prior event ad infinitum. This avoids any uncaused “first” but at the cost of an infinite series (which some find problematic, others not). If such an infinite causal chain is possible, then neither time nor causality has a singular beginning; they’ve “always” been there. One might then say both are equally fundamental in that context (or equally derivative, as one might still ask “why does this infinite causal process exist at all?”).

Laws of Nature and a Deeper Substrate

Another perspective comes from considering the laws of nature themselves as a bedrock. Laws link cause and effect by describing how the state at one time produces the state at a later time. In that sense, laws presuppose time (they often are differential equations evolving in time), but they are also the source of causal relations (they tell us which causes yield which effects). One might ask: are the laws of nature outside of time or within it? If one believes laws are timeless truths (perhaps Platonic in a sense), then they exist in a conceptual realm and give structure to temporal processes. This could imply a timeless framework that yields time and causation as emergent. Some speculative ideas suggest information or mathematical structures are fundamental. For example, John Wheeler’s “it from bit” hypothesis posits that information underlies physical reality. If so, time and causality might both emerge from information processing or logical structure. The universe could be akin to a computer where the program (information and rules) exists in a timeless way, but when executed, it produces the simulation of a dynamic, time-evolving world with cause and effect. This is a very speculative analogy, but it illustrates one way both time and causality could derive from a deeper level of description.

Another idea is symmetry breaking at cosmic origins: perhaps time was not initially distinguished (maybe there was a more symmetric state with no distinction between space and time, or between forward and backward time), and some symmetry-breaking event or condition created an “arrow.” For instance, some Grand Unified Theories in physics suggest that at very high energies, the laws are symmetric under time reversal, but as the universe cools and symmetries break (like the CP violation in weak interactions, or the collapse from a quantum gravity state to a classical spacetime), an arrow of time could be set. If some process “chose” a time-direction (akin to how a marble rolling off a symmetric dome chooses a direction randomly), then that could be considered the “first event” that established a causal arrow. In such a picture, time as a dimensional parameter existed, but it was the content of the universe (and its state) that gave time a sense of direction and thus allowed a stable notion of causality to take hold. In a perfectly time-symmetric universe with no entropy gradient, the distinction of cause and effect would blur – one could run processes backward or forward with equal legitimacy. The fact that we have a low entropy past is a sort of initial symmetry-breaking condition that allows a consistent assignment of cause→effect aligned with the growth of entropy (Time: Physical and Biological Aspects | Encyclopedia.com) (Arrow of time - Wikipedia). Thus, one might say the “first cause” in the physical universe was not a particular event, but the special low-entropy condition itself which set the stage for all future causal processes. That special condition isn’t a cause in the usual sense (nothing within the model causes it, it’s an external hypothesis), but it’s what generates the arrow of time, and thereby the distinction between past causes and future effects.

Ultimately, cosmology still faces “known unknowns” about time’s origin. Whether time is finite or infinite, emergent or fundamental, is not settled. Likewise, whether causality is an inviolable principle at all scales or an emergent regularity (that might break down in quantum gravity or at singularities) is also unsettled. We speculate responsibly when we say perhaps neither time nor causality is the single fundamental cornerstone – it could be that something else (like quantum events, or a timeless law, or a meta-time in a multiverse) underlies both. It is conceivable that time and causality co-emerge from a deeper reality: for example, a boiling quantum foam that has no classical time or definite causal relations might, as it cools into a classical spacetime, give birth to both time and the usual causal order in one sweep. In such a scenario, picking one as prior to the other might be like asking “what’s more fundamental, the egg or the chicken?” when both arise together through an underlying process (in that analogy, perhaps the evolutionary process is the deeper explanation that produces both eggs and chickens).

Conclusion

So, what is more fundamental – time or causality? After surveying perspectives from physics, metaphysics, cosmology, and beyond, the honest answer is that they are profoundly interconnected, and it’s difficult to crown one as absolutely primary. In every domain we examined, time and causality appear as two facets of the same underlying reality:

  • In physics, the very definition of a causal relation depends on temporal order (cause precedes effect), yet the structure of time in relativity is defined by causal connectivity (light cones). Physical laws generally don’t privilege an intrinsic direction of time, but a consistent causal order emerges when one imposes conditions like the Second Law of Thermodynamics or quantum causality constraints (Causality (physics) - Wikipedia) (Arrow of time - Wikipedia). Modern quantum gravity theories suggest time might be emergent, potentially from causal or correlational structure (as in causal sets or entanglement) (Causal sets - Wikipedia) (Quantum Experiment Shows How Time ‘Emerges’ from Entanglement | by The Physics arXiv Blog | The Physics arXiv Blog | Medium), which hints that causality could be the more primitive ingredient in those frameworks. Yet, those causal structures are themselves “temporal” in the sense of ordering events – effectively putting the time into the theory by hand, albeit in discrete terms.
  • In metaphysics, if one views reality as a block (B-theory), then time is not an active flow but a dimension, and causality reduces to an ordered relationship within that block – suggesting time (as a whole) is the given backdrop and cause-effect is a secondary aspect. But if one views reality as an unfolding process (A-theory or process philosophy), then the ongoing act of causation is what creates time moment by moment – suggesting causality is the engine of temporal becoming. Each view highlights one of the pair as fundamental, yet each view has merits and problems. It may be that our intuitions here are guided by which aspect we consider more explanatory: the block view can explain time’s illusions but struggles with why we experience causation in one direction, while the process view matches experience of cause and effect but struggles with modern physics’ implications.
  • In cosmology and ultimate questions, if time had a beginning, the notion of a “prior cause” might break down, hinting that the origin of the universe may lie outside the normal cause-time framework (a timeless cause or no cause at all). On the other hand, if one posits a reason or cause for the universe (like a Creator or a quantum principle), that cause must operate in a novel way, not as an event in time but as a foundation of time. Here causality is invoked as a metaphysical principle more fundamental than physical time – the universe itself is seen as an effect of some cause, even if that cause is not temporally before. But this usage of causation is arguably a broader notion of “explanation” or “dependence.”

Given all this, one might lean to the conclusion that time and causality are so interdependent that neither can claim priority in any absolute sense. The existence of time (a sequence of moments) without any causal relations linking events would be physically inert and meaningless; likewise, causation without temporal order is incoherent in our usual understanding. The two arise together in our descriptions of reality. In many theories, causal order is time – to talk about what came before and after is literally to talk about time.

However, if pressed to choose which concept is more basic, one could argue the case for causality: The reason is that even the notion of time’s flow or direction seems to come from how events influence each other. We mark time by change, by the succession of causes and effects. In causal set theory, for example, the partial order (causality) is fundamental, and clock time is a derived concept (Causal sets - Wikipedia). Also, one can conceive (at least abstractly) of timeless causation (logical or existential dependence), whereas a completely causeless time is hard to make sense of (it would be just empty duration). Furthermore, some philosophers (and everyday reasoning) treat causal laws as what give time its significance – without lawful causation, time would be just empty form. We also find in human cognition that we infer the passage of time by observing causal processes (like the ticking of a clock or aging). In that psychological sense, change/causation is primary, time is inferred.

On the other hand, one could argue for time as more fundamental in that all causal statements implicitly assume a temporal framework in which they play out. Causation in physics is essentially operationalized by temporal conditions (cause in past light cone of effect) (Causality (physics) - Wikipedia). If there were no dimension along which to arrange events, the notion of influencing or producing would have no context. Even in discussing a causal set, we are assigning an order – effectively a primitive form of time. So perhaps time (as ordering) is the more primitive notion, and causality is a special kind of ordering (one that obeys certain rules or asymmetries).

In truth, separating the two is a bit artificial. Most likely, time and causality are complementary aspects of a deeper reality that our current understanding only partly captures. They could be emergent together from something more fundamental – be it the structure of quantum events, a timeless equation, or God’s creative act. Just as space and time turned out to be unified in relativity, perhaps in a Theory of Everything, time and causation will be seen as reflections of one underlying principle. For instance, some have suggested “causal structure” might be the bedrock, with time, space, and matter arising from it. Others suggest symmetry and information are bedrock, with time and causality emerging from the breaking of perfect symmetry into directed structures.

What we can say is that our universe manifests a tight linkage of time and causality: every cause precedes its effect in time, and the flow of time is marked by the unfolding of causes into effects. Whether one can exist meaningfully without the other remains doubtful in practice. The question of priority might ultimately be like asking whether the shape of a coin is more fundamental than the coin’s material – they are different aspects of one entity. Time provides the stage for causality; causality provides the script that makes the passage of time observable and meaningful.

In closing, as our knowledge stands in 2025, neither “time” nor “causality” has been proven to be the single fundamental element – both appear necessary to describe reality. As one encyclopedia on time notes, “a comprehensive and commonly accepted interpretation of time in natural sciences is neither at hand nor in sight” (Time: Physical and Biological Aspects | Encyclopedia.com), and the same could be said for a unified account of causation. It may be that future advances (in quantum gravity or in philosophy of physics) will illuminate a perspective in which the dichotomy dissolves – perhaps showing how time and causality emerge from a common substratum (like a network of quantum information, or a category of fundamental events). Until then, the debate remains open. We have deepened our understanding by exploring known ideas and even unknown unknowns, but the ultimate answer – what is truly fundamental – may lie outside our current conceptual framework, waiting for the next breakthrough in our understanding of reality’s structure.

Sources:

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Is Time or Causality More Fundamental?

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