What is Time?

by Maggie Boyle

Our experience of being alive contains the experience of what we call time. We are prepared to say we were born; we are alive now and we will die. These are ‘tensed’ statements as defined in linguistic theory. In normal use they imply the passage of time. However, we can ask: Does time exist? Does it flow? Is it one dimensional? Does it loop? Does it have a beginning, an end? Is it a thing? How is it measured? What is the rate at which it passes? Is that rate a constant? Can time flow backwards? Is there a universal Now? What is our internal experience of time? How do we perceive time? Is the future open or closed? Does our human experience of time affect how we act? Does the timescale on which we tend to think affect our moral principles?

To attempt to answer these questions we need to look into 2000 years of philosophical and religious debates, developments in scientific measurement, physics theories of relativity, space-time, gravity, entropy and quantum mechanics, psychology, neuroscience and even theories of morals and prudential rationality. Are the answers to these questions consistent ‘across the board’?

Does time exist? Is it a thing? Does it flow?

Atomists: Time is continuous, infinite, no beginning, no end, the movement of atoms through the void of infinite space is seen as the fundamental mechanism driving the flow of time;

Anaximander: Time produces inherent order (one thing follows another), everything is subject to cycles of creation and destruction, balancing opposing forces;

Socrates: Time is real and essential to our existence and understanding of past, present and future;

Aristotle Time is not a thing in itself but a means of measuring change and ordering events as before and after, it requires a mind to perceive and count changes;

St Augustine: The present is the moving image of eternity. Neither the past nor the future exist, as the past is what has been and the future is what is yet to be. Time is the distension of the mind. It is the mind’s ability to remember the past and anticipate the future as it is subjected to the variations of the external world that constitute its temporal condition;

Newton: Time is absolute, independent of observer, flows uniformly through the universe at a constant rate regardless of events, it is a separate entity that passes even if there are no events within;

Kant: Time is not an inherent property of the world, rather a form of intuition our minds impose on our sensory experiences, time is a priori, not derived from experience;

McTaggart: A and B theories of time… A: There is a real past, present and future, there is an actual flow of time, time is tensed, the present moment is special, the truth about an event is always shifting… B: All moments exist equally, time is a tenseless block universe;

Einstein: Time is not absolute, its rate of flow depends on your frame of reference (speed, location), time is relative, space-time is four dimensional, a block;

Quantum Mechanics: At the quantum level systems can exist in multiple states simultaneously (superposition) until they are measured. This introduces a form of time that is non-linear and probabilistic, as the outcome of a measurement can affect the perceived flow of time.

How is it measured? What is the rate at which it passes? Is that rate a constant? Can time flow backwards? Is it one dimensional? Does it loop? Does it have a beginning, an end?

National Institute of Standards and Technology and etc.: Time has no physical property to measure, we measure time intervals, the duration separating two events. The most accurate clocks are atomic, Cesium atoms absorb microwaves with a frequency of 9,192,631,770 cycles per second, which then defines the international scientific unit for time, the second. Time dilates, clocks go slower relative to time on earth the higher they are above the earth, and the faster they travel. Ground stations adjust satellite clocks to ensure they synchronise with reference time on earth;

Sadi Carnot, Rudolf Clausius, Lord Kelvin, Boltzmann: The ‘arrow’ of time for physical systems points from the past into the future, as we experience it. This is accounted for by the second law of thermodynamics: the state of a system will evolve towards an increase in entropy. One way of understanding this is that heat flows from a hot substance to a cold substance and not the other way round. Thus, time does not loop.

Big Bang Theory and final entropic equilibrium of the universe: Physicists cannot calculate time effects before the big bang, it is a singularity. Therefore, at present, one can say, that time began with the Big Bang! One could also hazard a guess, given current theories, that eventually the whole universe will arrive at a state where there is no possibility for entropy to increase further. At that point nothing will be able to change and it could be said that time would come to an end.

Is there a universal Now?

Einstein: No! Your measurement of when an event happens depends on your frame of reference, your location and your speed and the finite, constant speed of light. One way to think about it is… the light reaching you from the sun left the sun 8 minutes ago. Hence in your now you can only witness what happened on the sun 8 minutes ago.

Neuroscience and Simultaneity: Two visual stimuli are considered simultaneous up to 5ms apart! Different sensory information is processed at different sensory speeds. Thus, we can speak to someone in Australia and feel as though we are in the same now! That is because the phone signals travel at the speed of light to reach you and you don’t perceive the very short time that has elapsed. So, fortunately for us, there is a bubble of Nowness that is about the size of the earth!

What is our internal experience of time? How do we perceive time?

Neuroscience: We have a perception of time, different parts of the brain contribute different aspects, the parietal cortex helps us perceive time in the present moment, the hippocampus is associated with memory and time perception of the past, basal ganglia contribute to timing mechanisms and motor control, cerebellum fine-tunes time perception. Time perception is influenced by emotions, attention and novelty. Athletes experience flow states.

Shadlen, neuroscientist: He reports experimental evidence that suggests that human and animal brains anticipate the timing of future events and neurons prepare to fire, e.g. when clapping a rhythm. He conjectures that it is possible that our brains create the experience of time itself! Weaving past experience, our attention in the present to an anticipation of the future;

Hegel: When we listen, we desire to beat time, music is a temporal art from; time is the dialectic motor, time is intuited becoming;

Bergson: Time is a continuous experience, duration is felt and experienced and requires intuition to grasp, for us it is not an objectively measured quantity;

Heidegger: Projections into the future create our present. Dasein: is inherently stretched out through time, relating to past, present and future, the future being most significant for our being in the world.

Is the future open or closed? Does our human experience of time affect how we act? Does the timescale on which we tend to think affect our moral principles?

Einstein: In the physics version of the block universe, at every point the space-time block there is a possible observer, relativity theory does not prioritise any observer, so the entire block exists! This would seem to imply that the future is closed.

Time Theory A: The future is open.

Computability (Boyle, M): Our brain makes as good a prediction of the future as it can, so we can act. However, in complex and chaotic systems (in which we live) it is impossible to calculate possible outcomes definitively, certainly at present, so in effect we never know how things will play out, our action is based on the best choice between the probabilities we can calculate. Therefore, we act as though the future is open and we can influence it. That is what I feel a future that is open means to me!

The Long Now Foundation: The founders hope they can encourage humans to think on a timescale that is much longer than our normal lifespan, to counteract short term thinking. We are already familiar with the idea that we should think not only of ourselves when taking action, but of the consequences of our actions on others. Thinking on very long timescales might stop us privileging ourselves over future generations in our decision-making.

Consistency across all the above approaches…

You would not be wrong in thinking that several of the entries above seem to contradict each other. Philosophers take positions with respect to A theories and B theories which each have many variants in the details. I currently have not found one that corresponds completely to the current fundamental physics proposed by Einstein, which at least has experimental measurements that tell us that its predictions have been verified so far (although block universe theories come closest). Furthermore, there are some philosophers (e.g. Bergson) who have strenuously argued that Physics does not explain our human experience. Quantum mechanics has developed models in which time can actually go backwards! How do we work out what matters for us? I have been particularly, pleasantly surprised at how well Carlo Rovelli explains how we can go from the quantum world to the scale of the Cosmos and embrace the various ways time needs to be considered at the various scales. I highly recommend his book. I also feel the appeal of the pragmatists, Charles Sanders Peirce, in particular:

Pragmatism is a philosophical tradition that views language and thought as tools for prediction, problem solving and action, rather than describing, representing, or mirroring reality.

- Wikipedia entry on Pragmatism.

I hope our discussion can encompass both ways of looking at Time.

Bibliography

My primary resource has been Carlo Rovelli, The Order of Time, Penguin Books, 2018.

Other

Stanford Encyclopedia of Philosophy, Entry on Time

NPL, SI Units, Second (s)

Pragmatism – Wikipedia