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How does this work relate to the work of Carlo Rovelli?
[Informal question, received verbally, 2021]
One early question was how these ideas relate to those of Italian theoretical physicist Carlo Rovelli. Rovelli's work was not included in this first book, but comparison is interesting so I'll present a synopsis here.
Since time is so intangible, and can only measured in terms of observable change, then it is often considered to be just a representation of change. There is no absolute time and so no special measure that all observers can agree upon, but an explicit dependence on time is also incompatible with the supposed space-time fluctuations of quantum mechanics.
Rovelli addresses this by removing the 't' variable from the equations of quantum mechanics, and rearranging them to relate changes in one observable to changes in another. This interpretation is described as 'relational quantum mechanics' (RQM). He rejects eternalism (i.e. the block universe viewpoint) and so his stance is clearly an experiential one that accepts dynamical change as real, at least at the macroscopic level.
A major difference is that the book does not consider dynamical change to be fundamental, or that each state is transient and evolving to the next state. It places the burden of this on conscious awareness, and equates 'now' with any point within a protracted consciousness. As such, there is a continuous static change of state over a dimension that we deem to be time, and the book posits that this overall state is finite and that its variation is addressable through mathematical relations, i.e. relations between the states at different times rather than specifically between observables.
It is worth mentioning that §5.4 of the book, in looking at the fundamental nature of measurement, explains that space and time are the only things directly measurable — through the relative separation of objects and/or events — and that all else (e.g. mass, energy, momentum) are all measurable only through observable changes over space-time. It is then the case that relating two different observables — or, more specifically, measurable quantities — is merely taking advantage of their individual relationships to space-time. In simpler terms, relating some observable change to, say, the sweeping hands of a clock is avoiding the fact that both phenomena have a variation over another dimension.
Are you saying that time does not exist?
[Question arose as part of general discussion of Rovelli, 2021]
No, time does exist, but there are two views on it. Whereas Rovelli tries to sidestep the many temporal issues by re-writing the equations of physics without a 't' variable, this work acknowledges that time exists but that those issues are part of our perception only.
In space-time, events (i.e. points in space-time) are separated by an interval that has four dimensions. We perceive three of these as space but there is clearly a fourth and that corresponds to the objective time: time as it is in the absence of conscious observers. This view will be familiar to anyone who has read about special relativity.
But subjective time is the one that we perceive, and it is intimately related to the phenomenon of consciousness. We observe it as the separation of changes in our environment, and we have to employ something with regular changes (such as a clock) because we cannot measure it accurately through thought alone. Along with subjective time comes the notion of 'now', which is merely a position in our private conscious stream and nothing fundamental to the universe. Associated with 'now' is the distinction between past and future, and the sensation that time is flowing (or that we're flowing through time). That our lives are completely dependent upon subjective time leads to notions of motion, general change, cause-and-effect, chance, choice, and probability, all of which are illusory.
In other words, whereas Rovelli tries to eliminate all time, this work separates the subjective from the objective aspects of time, and only eliminates the former.
How can causality not exist? What about an atomic explosion causing damage?
[Question from Alan Meehan, Ireland, April 2022]
You cannot have dynamical change without a preferred temporal reference point that appears to be progressing. This is our present moment, and we call it 'now'. It is afforded by our consciousness and there is no objective basis for it.
Causality is no more than our subjective rationalisation of the smooth (i.e. no discontinuities) dynamical change that we observe in our surroundings. It is not a fundamental phenomenon, and it has no strict definition. In other words, it is something that we invented to try and make sense of things; things that would appear entirely different to some super-observer able to look at the whole block universe together.
Physics applies reductionism to a causal connection in order to establish a causal chain (A caused B which then caused C, etc.), which is possible because all change appears to be statically connected, but the individual elements of that chain will lose their description as causation if taken to a low enough level. Applying reductive analysis to them will always reach a level where it no longer applies, and where we just have discrete particle interactions (which are symmetrical in time), or even quantum entanglement. In other words, there is no physical definition of causation that stands up to such scrutiny.
Furthermore, what we deem to be a cause is selected to give the most appropriate explanation under the circumstances. For instance, ‘I feel warm because the sun is shining’ versus ‘photons from the sun are impacting the molecules in my skin and increasing their kinetic energy’. The latter alternative is not the lowest level, but things would then become more abstract, very mathematical, and a long way from any notion of causation. This line of reasoning also applies to the many so-called mind-body problems, such as 'I move my arm because I wanted to' versus 'A signal from an area of the brain travelled down a nerve to the muscle, causing the cells to contract, which in turn moved a bone about a flexible joint', etc. Interestingly, in everyday life we more often look for the bigger causes: storms, weather patterns, conspiracies, or the supernatural.
How can the second law of thermodynamics not be connected with time when we see it in action?
[Question from Alan Meehan, Ireland, April 2022]
The book starts with the shuffling of a card deck to illustrate that randomisation — which lies at the heart of the second law of thermodynamics — is time-symmetric but irreversible. Hence, that the notion alone cannot be used to explain a preferred temporal direction, or an arrow of time. In fact, randomisation is not even a temporal phenomenon, and it can be demonstrated algorithmically, including by computer software (i.e. it is sequenced but not temporal).
As a visual analogy, consider a trough of water. If you put your hand into the water and try to push it to one side then it will quickly flow back and reach a steady state again. But if you pushed in the opposite direction then the same evolution to a steady state would occur; simply in the opposite direction.
The pertinent question is why things were not in equilibrium in previous time periods. What we observe is simply a natural progression from an unbalanced system to equilibrium.
In the Block Universe theory of time, has future already happened?
[Question appeared on quora.com way back in 2017, but is so representative of reader misunderstandings]
“Happened” is not the right word to use here as it implies the flowing subjective time that we live by, rather than the static dimensional time of the block universe. When you mix these two viewpoints up then you get into all manner of contradiction and paradoxes. The block universe (also known as a space-time continuum in relativity) treats time in the dimensional way, described as objective in the book, and as formal by Gödel. What we experience is the flowing time that has a distinct past and future separated by the present moment, described in the book as subjective, and by Gödel as intuitive.
All points in time would be extant in a block universe, but no time actually passes. Think of it more as a complete history of everything that ever did happen, or ever will happen, and you will be closer to an understanding.
A block universe is implied by relativity, and advocates of the block universe say that all dynamical change and movement, including the passage of time, is merely a psychological phenomenon.
When eternalists say "past, present, future co-exist, but don't happen "now"" I am confused. Eact instance is "now", so since they share the same feeling of "now", why not just call them all simultaneous, going on "now"?
[Question from Alexandrina G., France, May 2022]
You’re mixing two different views of reality: the objective dimensional one and the subjective dynamical one. That never works and you’ll tie yourself in knots.
There is a slight difference between eternalism and the block universe, although I’m not aware of any other eternalism model than the block universe and so I will answer on the basis of the latter.
To “happen” requires a present moment: a 'now'. Without that concept then you cannot have dynamical change or motion, and all you have is a static “history” of all events laid out in a block where their instant-to-instant changes are represented structurally.
For instance, with simple inertial motion, the representation in the block universe would be a fixed line, or pipe-like structure if the object has a size. There is no 'now' and so nothing is “happening”. It is an immutable structure representing the fact that it occupied various places in space for corresponding instants in time. There is no specific past/present/future, and all temporal instants co-exist.
I am arguing that this is the true nature in the absence of conscious observation and interpretation, but in your subjective reality — your everyday existence — you are aware of a specific 'now' that appears to progress, and this allows you to interpret that static change as a dynamical one.
That 'now' is part of your consciousness and does not exist outside of it, but any “happening” arises from a stream of such moments, not from any single one of them. Your 4-D self would extend across the corresponding instants of that object’s world-line, and your mental state would be present at each such instant, but the overall conscious awareness only emerges as a result of the whole stream of them.
If there is no genuine passage of time in the universe, what gives us the sensation that there is one?
[Question from Alexandrina G., France, May 2022]
From the premise of a block universe (aka space-time continuum) then there is no passage, flow, or otherwise objective progression of things in the temporal sense.
What we have, instead, is a static change that is arguably smooth and continuous (i.e. differentiable), finite, and deterministic; and hence fully susceptible to mathematical description and analysis.
Each of our 'now' moments are extant, and part of a protracted conscious stream. Together, as an inductive chain, they represent a conscious mind and yet no single moment is actually “conscious”.
Awareness of dynamical change arises as each such moment acquires a contextual record of information from prior moments (for reasons too complex to lay out here). The smooth static change allows this emergent consciousness to intuit a dynamical quality. A filmstrip analogy is often used to portray this, but it is weak without considering the acquired context.
No single moment is using this context, and hence conscious, just as velocity has no meaning for a single instant. You would have to look to things that emerge over a period of time. For instance, each point in the conscious stream has contextual information that allows it to recognise and understand dynamical change, and so it’s an ongoing phenomenon. Taking a very simple case, we could not say an object was physically moving unless we had a record of it being slightly displaced previously, and so on. Then when we look at the much larger picture, we can correlate movement with some other agent and infer what we call causality.
 Carlo Rovelli, The Order of Time, transl. Simon Carnell and Erica Segre (UK: Penguin Books, 2018), p.97.