Questions: Causal Order and Temporal Order

Question 1

According to the causal theory of time, what does it mean for event A to occur 'before' event B?

• A. A has higher entropy than B, reflecting the thermodynamic arrow of time
• B. A and B are connected by a continuous chain of physical events
• C. A can causally influence B, but B cannot causally influence A
• D. A is closer in space to the observer's reference frame than B

Answer: (C)

The causal theory of time (associated with Reichenbach) identifies temporal order with the direction of causal influence: 'A is earlier than B' just means A is the kind of event that can affect B, while B cannot affect A. This reduces temporal order to causal structure, avoiding a primitive unexplained 'arrow of time.' The problem is that this threatens circularity: our best analyses of causation (especially counterfactual analyses) typically presuppose which event is 'earlier,' so defining temporal order in terms of causal order and causal order in terms of temporal order goes in circles.

Question 2

A physicist proposes a theory in which a measurement outcome can causally influence the earlier experimental setup via a retrocausal quantum mechanism. If such backward causation is coherent, this most directly suggests:

• A. The causal theory of time must be correct — backward causation confirms that causes always define temporal direction
• B. Causal order and temporal order are conceptually separable — an event can be a cause even if it is temporally later than its effect
• C. The second law of thermodynamics would necessarily be violated by any retrocausal process
• D. Counterfactual analyses of causation are refuted because they cannot accommodate backward causation

Answer: (B)

If backward causation is coherent — a later event causing an earlier one — then causal order and temporal order are not the same concept: 'cause' does not simply mean 'earlier.' The two asymmetries can come apart, showing they are conceptually independent. Fundamental physics is time-symmetric at the level of equations, so backward causation is not ruled out by physics. Whether it would violate the second law depends on the specific mechanism; the key philosophical point is the conceptual separability of the two asymmetries.

Question 3

If backward causation is genuinely possible, this demonstrates that causal order and temporal order cannot be identified with each other.

• T. True
• F. False

Answer: True

Backward causation means an effect temporally precedes its cause. If such cases are possible, then we have causes that are later than their effects in time — which means causal order and temporal order come apart. This undermines any simple identification of 'A causes B' with 'A is earlier than B,' since backward causation is precisely a counterexample to that identification. The possibility of backward causation shows the two concepts are logically distinct even if they typically align.

Question 4

The fundamental laws of classical mechanics and quantum mechanics are time-asymmetric — they describe processes that can unfold mainly in the forward temporal direction.

• T. True
• F. False

Answer: False

This is false, and it is central to the puzzle of causal-temporal order. Newton's laws, electrodynamics, and the Schrödinger equation are all time-symmetric: reversing the time variable (and, in quantum mechanics, taking the complex conjugate) yields equally valid solutions running backward. The apparent asymmetry of the world — causes preceding effects, entropy increasing — is not a direct consequence of the fundamental laws themselves. It requires additional statistical or initial-condition explanations (such as the entropic arrow of time) that are not built into the equations.

Question 5

Why does the causal theory of time — the view that temporal order is grounded in causal order — face a circularity problem?

Model answer: The causal theory wants to define 'A is earlier than B' in terms of 'A can causally affect B but not vice versa.' But our best analyses of causation — especially counterfactual analyses — themselves rely on temporal notions: they say something like 'if A hadn't occurred, B wouldn't have occurred,' and they typically restrict this to cases where A is earlier than B. If temporal order is defined using causal order, and causal order is defined using temporal order, neither concept is independently grounded. The circle is vicious if we want a reductive account.

The circularity problem shows that causal and temporal asymmetries cannot both be reduced to each other simultaneously. The alternative is to ground both in a third factor — most commonly the entropic arrow (the second law of thermodynamics) — which explains why causes precede effects and why entropy increases without deriving one from the other. This avoids circularity but treats both arrows as consequences of something deeper (statistical mechanics and initial conditions) rather than as one reducing to the other.