Someone once asked me:
“what is the opposite of now ?”
Just a moment…
Time is fundamentally mysterious. In many ways it is the most intimate and omnipresent feature of our existence – what could be more readily apparent than duration, lived experience, memory or the ever-ticking memento of personal mortality which the clock represents ? However, attempts to pin down time, to nail down a concrete definition that applies in all contexts is quite difficult. Does time pass ? Is time something that we move through ? Is there one time or many ? What is the actual reality and agreeable consensus definition of the present, the past, the future ? As our essential definitions of logic and reality probably rely upon the sensible and sequential or procedural flow of time as an extension or container within which logical relations and operations can exist and occur, what certainty can we have in anything we believe to be truth or fact when we are so fundamentally uncertain about what time actually is ? Definitions of time vary dependent upon person, place, culture, historical epoch and current scientific consensus. It may be an irony that the definition of time is itself subject to change and that the definitions of time may appear to fluctuate from moment to moment and in different contexts, social situations or under differing metrics and paradigms of rational analysis.
Most mysteries do not avail themselves of simple or brief analysis but it can help to take just one aspect of an enigma and analyse it more deeply. The thread of analysis we will examine initally (and before extending the depth of speculative temporal investigations) is the present moment, the “now”.
Generally speaking, we perceive (and experience) time in a purely linear sense. What is the current moment moves into the past. The future similarly moves into the current moment. This is the arrow of time. We measure this in seconds, minutes, hours, days and years. The future is becoming the past, passing through the nexus and filter of this current moment, the now.
The current moment can be visualised as being t=0 on an extended one-dimensional line:
Negative numbers here represent temporal extension into the past, measured as decreasing away from the present moment; positive numbers represent temporal extension as measured into the future:
Time is of course a process. The present moment is moving into the past at a speed of 1 second per second. This present moment is becoming the future at the same rate:
Curiously, only now seems to be real as the past has already happened and is immutable and the future is yet to happen. This would appear to be a fundamental differentiation between what has happened and been irrevocably determined and what is potential and still pregnant with possibility. Barring the possibility of time-travel (to try and keep things here as intelligible as possible), the past is immutable and the future is a matter of probability. Some things may be more likely to happen than others but anything which has happened, remains a historical or temporal fact.
As time is a process moving forward (or at least moving in what appears to be a single direction) and is here represented on a 1 second metric, any specific instance of now (t2) is +1 to the second before (t1) it and -1 to the second which occurs later (t3):
The successive sedimentation of layers of time (measured here in a depth dimension of seconds) can be represented as a stack.
This stack is also the basis of the block spacetime considerations of relativistic physics. In this block spacetime, time T is considered to be a (temporal) dimension of extension in just the same way that X, Y or Z axes are considered to be (spatial) dimensions of extension. Extension in one dimension is a line, in two dimensions is a plane and in three is a volume. Suppressing one of the spatial dimensions allows us to illustrate a block structure to time:
The four-dimensional spacetime that this represents is mathematically well-understood and brings with it a whole suite of fascinating interpretations and problems. Some of the interpretations include Presentism (the view that neither the future nor the past exist, that the present moment is the only reality), Possibilism (the idea that there are real possibilities available in an open future, that the past is locked in place) and Eternalism (the view that all points in time are equally real, that all of time exists in some sense already). In the diagram below (3 METAPHYSICS OF TIME), we see an illustration of these views of time. The pink volume represents the time which has been “laid down” or sedimented as the past.
In Presentism, only now is real and it is moving constantly into the future – this is to me the most problematic of the three views as the present moment is only “present” in relation to something else which by logical extension must be the past or the future but it is also possible to consider that the present moment (or now) is all that there is because it is all that we ever actually experience. I find Presentism at first look to be far too problematic and requiring of too much intricate philosophical trickery to deal with past and future to be of much significant use but then again, the now is all that we do (appear to) experience so there is certainly something worthwhile in the concept. Presentism seems to accurately define the existential experience of time but does not assist us to precisely visualise or understand the dimensional depth (of past and future) that we require to be able to contextualise and fully understand or locate the present moment.
Possibilism allows for the existence of a past defined concretely as an immutable volume or extension in the temporal dimension. In this view, although the past is concretely defined – the future is still wide open and this at least aligns with the fundamental uncertainty and probabilistic realities characteristic of the quantum world. In possibilism, the past is being sedimented 1 second per second and after having “happened” it remains as a historical fact in the past. Time has extension but only in the intelligible direction of the past, from whence all truth and facts can be reliably extracted (although the attributed interpretations of facts can be thoroughly unreliable and are subject to cognitive bias). Possibilism appeals to me a little more than Presentism as it at least allows for a coherent account of the past but the future remains something of a problem as it is completely open and undetermined – this is a philosophical (as much as a physics) problem because considerations of relativistic spacetime appear to mandate an all-at-once or block spacetime). Possibilism manages to place the present moment of now at the collapsing wavefront defined by the present moment but does not contain sufficient explanation for the temporal extension which the future represents.
Eternalism is the form of block spacetime most closely reflecting the 4-dimensional manifold that relativistic physics. In this view – time is already in some sense “all there”, with past and future laid out in a continuous dimension of extension. This form of time aligns most closely with physics and mathematical understanding of the macroscopic world but causes significant issues with our understanding of concepts such as free will, freedom and liberty. If everything which is ever going to happen has already been predetermined, then no one ever chooses anything – it is already always decided, predestined, fated. If there is no free will, then concepts such a personal freedom or political liberty also take significant hits as the justification for personal freedom seems to rely a capacity to choose between available options (or indeed to construct further options which previously did not exist).
Another significant problem of Eternalism is that of the sub-microscopic quantum world. Quantum mechanics relies in a fundamental way on the description of probabilities of events occurring. There are different interpretations of quantum theory. One of these interpretations, the Many-Worlds Interpretation, implies that at every possible branching of probabilities in reality, the universe splits and follows all of the possible branches which occur. If you throw a dice in the air, when it lands on one side – you just happen to be in the copy of the Universe that this option is was what happened. All of the other options exist in their own versions of reality and each with an identical past up until the bifurcation point at which the probability of which side landed upright was selected. This makes reality seem to be a bit more like the Possibilist model, with a solid and immutable past but this extension into the past becomes not a matter of one past, but uncountably many to account for all the possible bifurcations which occurred in all the possible worlds which were each defined by the multitude of different possibilities that have been selected for. Not only this, but if spacetime is laid out all-at-once as in the Eternalist block model – then every single possible variation, every possible branching of reality at every place where one thing may have happened instead of another – they all exist and each in their own copy of reality.
Regardless of the trending towards infinity of the Many-Worlds Interpretation, another troubling feature of quantum theory is the role of the observer (or – observer-like events) in collapsing the probabilistic waveforms into an actualised reality. I am not so much here interested in the observer or observer-like event as to note that we can loop this back into the issue of the present moment as it is an observation or event at a specific moment. That specific moment is again the present or now which, regardless of whatever else may be going on (infinitely many copies of all possible worlds, observers in some sense building realities out of collapsing probabilities, etc.) the lived and existential boundary of our intellect and moving now is where we find ourselves located.
The majority of problems that come to us from General Relativistic interpretations of spacetime are not so much problems as likely limitations of a mammalian brain which has not evolved to comprehend the intricacies of high energy/velocity physics and cosmological scales and time-frames. Reality is whatever it is, regardless of human conceptual difficulty in comprehending what the mathematics and observations tells us about it. I find that after you have been thinking about the strange, plastic and ultimately flexible spacetime we live in for a while – it starts to become slightly more intuitive but remains no less bizarre. The best advice in trying to understand this is to read as widely as possible and to aggregate as many perspectives and mental points of view as possible so that you can start to construct your own conceptual vocabulary around this issue.
Relativity of Simultaneity
The Relativity of Simultaneity is one of the more at first confusing aspects of physics. The gist of this is that what we consider to “now” is actually not necessarily the same for different observers in different places and moving at different velocities. If all three observers are (notionally) in the same place and at rest, what is happening “now” appears to be the same:
However, if those observers are moving relative to one another at sufficiently high velocity tending towards the speed of light or at sufficient (i.e. cosmological) distances from one another, what appears to be now for one can also include what appears to past or future for another. If we are at t=0 for Location B below, our motion relative to other Locations (A and C) may cause us to move into the past or future of those other locations as experienced by observers there. “Now” is a conundrum but still here appears to depend on the existential pivot of the observer.
This means that, among other things, if you were to walk a short distance in any direction – you may be travelling into the past or the future of some distant galaxy by thousand or millions of years. This is all quite counter-intuitive and difficult to accept when you first come across it but I assure you that it is real, in fact – the GPS satellites that orbit our planet have to take into account relativistic concerns to maintain precise measurements and be able to assist you finding your way to wherever you may be navigating.
Time is much stranger than just these apparent anomalies. In the Hafele–Keating experiment, two planes carrying extremely sensitive synchronised atomic clocks were flown around the world (at the eq in opposite directions and it was found that time actually passes faster in one direction that the other. The Earth drags time (or more correctly, spacetime) along with it in its daily rotation. The relationship of time to gravitation and spacetime curvature is another kettle of fish which I have no time (!) for here.
Are we there yet ?
The main take-away from all of this is that time is actually very complex and fundamentally counter-intuitive. By a happy accident of biological evolution and the pure serendipity of our location on the cosmic ladder of energy and scale, we are equipped to experience a more or less linear and steady-flowing time within which our lives are able to make some degree of logical sense.
The block time model of Possibilism or Eternalism seems to be more intuitive to lived experience. Eternalism has more claim to authenticity in that the time it portrays, in which the past, present and future are all laid out in one slab of spacetime and this also allows for the rationalisation of the simultaneity of relativity.
A fundamental problem of all these models of time in regards to the actual lived experience of time is that we experience time at all. The current moment, relentlessly moving forwards as it is at 1 second per second, is what we experience – it is in some fundamental sense the totality of reality. What has previously happened or occurred is indelibly (?) inked in the linearly-defined past or negative dimension (receding from us at 300,000 kilometres per second into the 4th dimension) and becomes apparent as its consequences are in some sense recorded or stored in the present. In this sense we can almost see the present moment as the data store for previous events. The positive (future direction) dimension of time becomes the realm of possibility, probability and (significantly for us) the future locus for the exercise of choice.
The primordial enigma here is, again, in that we experience this particular moment at all. I am not sure that an appeal to this being merely a happy accident of biological circumstances (as previously discussed briefly here) is sufficient to explain all problems It may be that for some reason conscious sentience in the sense that we understand it can only develop at the energy, velocity and size scales of our macroscopic, anthropomorphically-defined world. This is of course completely unverifiable as in a potentially infinite Universe, there are uncountably many opportunities for self-organising complexity (as sentient life) to emerge and the experience of time at the human scale may not be the same as the experience of time at a sub-microscopic scale, at a stellar or galactic scale or in any possible sense of the words “intelligence as developing in and measured on a multidimensional platform”. For reference on the associated issue of technologically advanced civilisations, consider the Kardashev Scale.
The relationship of the time of physics to the time of psychology and neurobiology is another extended tapestry of complexity and mystery. It appears to me that memory may have been the kind of thing that might develop for any organism that was required to (i.e. needed to) store information or energy obtained from its environment for later use. Information is structured or patterned energy, so the process by which an organism stores it for later use is likely very similar to the thermodynamic two-way exchange of energy with its environment. The structuring or patterning of energy as information may be a way of compressing it, of maximising storage potential. In a systems-theoretical conceptualisation of this we can understand the internalisation of environmental information or energy as being in some sense the internalisation of the environment, the copying of an environment which is then replicated in some respect as a sub-system of the organism. Where the sense-data, environmental input or energy being received becomes too much to use immediately but is still of use for survival (and benefits the natural selection of the organism), it can be stored, compressed and reorganised for later use. This model of memory or energy has the storage of memory as appearing late on the spectrum from (for instance) the immune response of antibody expression by relatively primitive cells (copying, simulating and storing their environmental input in ways which will benefit their survival) through to the memories we accumulate on a daily basis and which allow us to for the most part successfully navigate our environment. This is all fairly speculative and for all the compelling points I see here, there is no explanation of why time passes; there is merely an indication that our experience of time and reality is facilitated by a memory function which has evolved to assist us manage energy and information flows with our non-corporeal environment, to help us survive.
The feeling that there is some collapsing waveform or material, ontological essence and transition or change occurring which defines the present moment seems (intuitively, subjectively) inescapable to me. I do not doubt that those who fought in the Battle of Hastings (1066) or the discovery of Radium by Marie and Pierre (1898) are any less real moments for those who experienced them, merely that these are all not the moment that is being experienced currently as I write (or later – as you read). What we experience as real time passing is actually happening but there is no sense in which it should be distinguishable from any other moment other than its position at the apogee in the dimensional extension of the past which we call this present moving moment of now. The mathematics of time may not necessarily privilege any specific moment but there is a genuine subjective sense in which this current moving moment appears to be in some way pivotal or axiomatic to physical reality.
The collapsing wavefront of something inexplicable is insufficient to posit as a definition of now. That the smallest measurable unit of time (the Planck Time) is definable does not actually assist explanation either – the experience of motion through a medium is not dramatically effected or made explicable by an awareness of the metric upon which that vector of motion is measured. Time, in any case, has been shown to be interchangeable with space and the measurement of temporal extension for one observer might be the measurement of spatial extension for another observer in a different inertial frame of reference.
I have a suspicion that there is a deep connection between the observation of time and the sense that it passes, flows, moves or any other applicable verb – that the position of the observer is the existential pivot in all of this. It remains a truth that the current moment is mathematically comprehensible but remains existentially ineffable. It is clear that there are no complete answers, only further questions. I should probably leave it at that for now as I could very easily continue extrapolating this topic indefinitely into the distant future.