| 22954 | Newtonian mechanics does not distinguish negative from positive values of time [Newton, by Coveney/Highfield] |
| Full Idea: In Newton's laws of motion time is squared, so a negative value gives the same result as a positive value, which means Newtonian mechanics cannot distinguish between the two directions of time. | |
| From: report of Isaac Newton (Principia Mathematica [1687]) by P Coveney / R Highfield - The Arrow of Time 2 'anatomy' | |
| A reaction: Maybe Newton just forgot to mention that negative values were excluded. (Or was he unaware of the sequence of negative integers?). Too late now - he's done it. |
| 22908 | When one element contains the grounds of the other, the first one is prior in time [Leibniz] |
| Full Idea: When one of two non-contemporaneous elements contains the grounds for the other, the former is regarded as the antecedent, and the latter as the consequence | |
| From: Gottfried Leibniz (Metaphysical Foundations of Mathematics [1715], p.201) | |
| A reaction: Bardon cites this passage of Leibniz as the origin of the idea that time's arrow is explained by the direction of causation. Bardon prefers it to the psychological and entropy accounts. |
| 14935 | The direction of time is grounded in the direction of causation [Reichenbach, by Ladyman/Ross] |
| Full Idea: Reichenbach argued that temporal asymmetry is grounded in causal asymmetry. | |
| From: report of Hans Reichenbach (The Direction of Time [1956]) by J Ladyman / D Ross - Every Thing Must Go | |
| A reaction: I'm not sure that I can make sense of giving priority either to time or to causation when it comes to this asymmetry. How do you decide which one is boss? |
| 22947 | An ordered series can be undirected, but time favours moving from earlier to later [Le Poidevin] |
| Full Idea: A series can be ordered without being directed (such as the series of integers), …but the passage of time indicates a preferred direction, moving from earlier to later events, and never the other way around. | |
| From: Robin Le Poidevin (Travels in Four Dimensions [2003], 12 'Hidden') | |
| A reaction: I wonder what 'preferred' means here? It is not just memory versus anticipation. The saddest words in the English language are 'Too late!'. It is absurd to say that being too late is an illusion. |
| 22952 | If time's arrow is causal, how can there be non-simultaneous events that are causally unconnected? [Le Poidevin] |
| Full Idea: An objection to the Causal analysis of time's arrow is that it is surely possible for non-simultaneous events to be causally unconnected. | |
| From: Robin Le Poidevin (Travels in Four Dimensions [2003], 12 'Seeds') | |
| A reaction: I suppose the events could be linked causally by intermediaries. If reality is a vast causal nexus, everything leads to everything else, in some remote way. It's still a good objections, though. |
| 22953 | Time's arrow is not causal if there is no temporal gap between cause and effect [Le Poidevin] |
| Full Idea: If there is no temporal gap between cause and effect, then the causal analysis of time's arrow is doomed. | |
| From: Robin Le Poidevin (Travels in Four Dimensions [2003], 12 'simultaneous') | |
| A reaction: A number of recent commentators have rejected the sharp distinction between cause and effect, seeing it as a unified process (which takes time to occur). |
| 22951 | If time's arrow is psychological then different minds can impose different orders on events [Le Poidevin] |
| Full Idea: If the Psychological account of time's arrow is correct …then there is nothing to prevent different minds from imposing different orders on the world. | |
| From: Robin Le Poidevin (Travels in Four Dimensions [2003], 12 'The mind's') | |
| A reaction: All we need is for two people to disagree about the order of some past events. The idea that we are psychologically creating time's arrow when everyone feels they are its victims strikes me as a particularly silly theory. |
| 22948 | There are Thermodynamic, Psychological and Causal arrows of time [Le Poidevin] |
| Full Idea: The three most significant arrows of time are the Thermodynamic (the direction from order to disorder), the Psychological (from perceptions of events to memories), and the Causal (from cause to effect). | |
| From: Robin Le Poidevin (Travels in Four Dimensions [2003], 12 'Three') | |
| A reaction: It would be nice if one of these explained the other two. Le Poidevin rejects the Psychological arrow, and seems to favour the Causal. Since I favour taking time as a primitive, I'm inclined to think that the arrow is included in the deal. |
| 22949 | Presumably if time's arrow is thermodynamic then time ends when entropy is complete [Le Poidevin] |
| Full Idea: One consequence of the Thermodynamic analysis of time's arrow is that a universe in which things are as disordered as they could be would exhibit no direction of time at all, because there would be no more significant changes in entropy. | |
| From: Robin Le Poidevin (Travels in Four Dimensions [2003], 12 'Three') | |
| A reaction: And presumably time would gradually fizzle out, rather than ending abruptly. If entropy then went into reverse, there would be no time interval between the end and the new beginning. Entropy can vary locally, so it has to be universal. |
| 22950 | If time is thermodynamic then entropy is necessary - but the theory says it is probable [Le Poidevin] |
| Full Idea: The Second Law of Thermodynamics says it is overwhelmingly probable that entropy will increase. This leaves the door open for occasional isolated instances of decrease. But the thermodynamic arrow makes the increase a necessity. | |
| From: Robin Le Poidevin (Travels in Four Dimensions [2003], 12 'Three') | |
| A reaction: Le Poidevin sees this as a clincher against the thermodynamic explanation of the arrow. I'm now sure how the Second Law can even be stated without explicit or implicit reference to time. |
| 22975 | We must explain either the existence of a time direction, or our psychological sense of it [Price,H] |
| Full Idea: If the world comes equipped with a time orientation, where does it come from? If it doesn't, what explains our psychological feeling of a direction for time? | |
| From: Huw Price (The Flow of Time [2011], 3.5) | |
| A reaction: The chances of 'explaining' either one look slim to me. That is, the fact would explain our experience, but the experience without the fact looks ridiculous, and I cannot conceive of any time-free entity which could explain the fact. |
| 13440 | Causation is the power of one property to produce another, and this gives time its direction [Esfeld] |
| Full Idea: The metaphysics of causation in terms of powers is linked with an intrinsic direction of time. There is a causal connection if an F-property produces a G. One can argue that causation thus is the basis for the direction of time. | |
| From: Michael Esfeld (Humean metaphysics vs metaphysics of Powers [2010], 7.2) | |
| A reaction: I think this is my preferred metaphysic - that both time and causation are primitive, but the direction of time is the result of the causal process. Viewing some new world, we would just say that time went in whichever direction the causation went. |
| 22910 | To define time's arrow by causation, we need a timeless definition of causation [Bardon] |
| Full Idea: The problem for the causal analysis of temporal asymmetry is to come up with a definition of causation that does not itself rely on the concept of temporal asymmetry. | |
| From: Adrian Bardon (Brief History of the Philosophy of Time [2013], 5 'Causal') | |
| A reaction: This is the point at which my soul cries out 'time is a primitive concept!' Leibniz want to use dependency to define time's arrow, but how do you specify dependency if you don't know which one came first? |
| 22909 | We judge memories to be of the past because the events cause the memories [Bardon] |
| Full Idea: On the causal view of time's arrow, memories pertain to the 'past' just because they are caused by the events of which they are memories. | |
| From: Adrian Bardon (Brief History of the Philosophy of Time [2013], 5 'Causal') | |
| A reaction: How am I able to distinguish imagining the future from remembering the past? How do I tell which mental events have external causes, and which are generated by me? |
| 22904 | The psychological arrow of time is the direction from our memories to our anticipations [Bardon] |
| Full Idea: The psychological arrow of time refers to the familiar fact that that we remember (and never anticipate) the past, and anticipate (but never remember) the future. | |
| From: Adrian Bardon (Brief History of the Philosophy of Time [2013], 5 'Psychological') | |
| A reaction: Bardon rejects this on the grounds that the psychology is obviously the result of the actual order of events. Otherwise time's arrow would just result from the luck of how we individually experience things. |
| 22906 | The direction of entropy is probabilistic, not necessary, so cannot be identical to time's arrow [Bardon] |
| Full Idea: The coincidence of thermodynamic direction and the direction of time is striking, but they can't be one and the same because the thermodynamic law is merely probabilistic. Orderliness could increase, but it is highly improbable | |
| From: Adrian Bardon (Brief History of the Philosophy of Time [2013], 5 'Thermodynamic') | |
| A reaction: This seems to be persuasive grounds for rejecting thermodynamics as the explanation of time's arrow. |
| 22907 | It is arbitrary to reverse time in a more orderly universe, but not in a sub-system of it [Bardon] |
| Full Idea: It would seem arbitrary to say that the direction of time is reversed if the whole universe becomes more orderly, but it isn't reversed for any particular sub-system that becomes more orderly. | |
| From: Adrian Bardon (Brief History of the Philosophy of Time [2013], 5 'Thermodynamic') | |
| A reaction: The thought is that if time's arrow depends on entropy, then the arrow must reverse if entropy were to reverse (however unlikely). |
| 19951 | Entropy is puzzling, so we may need to build new laws which include time directionality [New Sci.] |
| Full Idea: Smolin observes that if entropy increases, the early universe must have been highly ordered, which we cannot explain. Maybe we need to build time directionality into the laws, instead of making time depend on entropy. | |
| From: New Scientist writers (New Scientist articles [2013], 2017.02.04) | |
| A reaction: [compressed] |
| 20470 | Only heat distinguishes past from future [Rovelli] |
| Full Idea: It is always heat and only heat that distinguishes the past from the future. | |
| From: Carlo Rovelli (Reality is Not What it Seems [2014], 12) | |
| A reaction: I can remember the past but not the future - so can that fact be reduced to facts about heat? |
| 23003 | Static theories cannot account for time's obvious asymmetry, so time must be dynamic [Baron/Miller] |
| Full Idea: One argument for the dynamic theory of time is that time is, obviously, asymmetric, and as static theories can't account for this asymmetry, we ought to posit temporal passage to explain it. | |
| From: Baron,S/Miller,K (Intro to the Philosophy of Time [2019], 5) | |
| A reaction: The B-series view (unlike the C-series) asserts that there is an order from past to future, but it offers no explanation of that fact. Physicists love to tell you the order could be in either direction, But why an 'order' at all? |
| 23004 | The direction of time is either primitive, or reducible to something else [Baron/Miller] |
| Full Idea: Primitivism is the view that time has a direction, and that its having that direction is intrinsic to time itself. Reductionism is the view that time has a direction, but its having that direction is reducible to something else. | |
| From: Baron,S/Miller,K (Intro to the Philosophy of Time [2019], 5.3.1) | |
| A reaction: The general suggestion for the second theory is that time's direction reduces to some aspect of the laws of nature. I strongly incline to the primitive view. Something's got to be primitive. |
| 23005 | The kaon does not seem to be time-reversal invariant, unlike the rest of nature [Baron/Miller] |
| Full Idea: The laws of nature are time-reversal invariant, with the small exception of the kaon (a type of sub-atomic particle) | |
| From: Baron,S/Miller,K (Intro to the Philosophy of Time [2019], 5.3.2) | |
| A reaction: If that fact about the kaon were very secure indeed, then that would mean the collapse of the claims about the time-invariance of the laws. Since time-invariance is still routinely asserted, I assume it is not secure. |
| 23006 | Maybe the past is just the direction of decreasing entropy [Baron/Miller] |
| Full Idea: We could say that what we call the past is just the direction towards (for instance) decreasing entropy, and the direction we call the future is the direction towards increasing entropy. | |
| From: Baron,S/Miller,K (Intro to the Philosophy of Time [2019], 5.3.3) | |
| A reaction: One problem is that locally entropy can sometimes go the other way, which would imply local pockets with a reversed time's arrow,. |
| 23010 | We could explain time's direction by causation: past is the direction of causes, future of effects [Baron/Miller] |
| Full Idea: An option for accounting for the direction of time would be to appeal to the direction of causation …to the future is the direction towards which there are effects, and the past is the direction towards which there are causes. | |
| From: Baron,S/Miller,K (Intro to the Philosophy of Time [2019], 5.6.2) | |
| A reaction: The obvious problem is that we can no longer pick out a cause by saying it 'precedes' its effect. It is not obvious what other criterion can be used to distinguish them (esp. given Hume's regularity account). |