Is time a psychological illusion or a parameter of the Universe?

I’ve recently read Paul Davies latest book, The Demon in the Machine (released in Feb) and I would highly recommend it.

We have reached a stage in politics and media generally that you are either for or against a person, an idea or an ideology. Anyone who studies philosophy in any depth realises that there are many points of view on a single topic. There are many voices that I admire yet there is not one that I completely agree with on everything they announce or proclaim or theorise about.

Paul Davies new book is a case in point. This book is very intellectually stimulating, even provocative, which is what I expect and is what makes it worth reading. Within its 200 plus pages, there was one short, well-written and erudite passage where I found myself in serious disagreement. It was his discussion on time and its relation to our perceptions.

He starts with Einstein’s well known quote: ‘The past, present and future is only a stubbornly persistent illusion.’ It’s important to put this into its proper context. Einstein wrote this in a letter to a mother of a friend who had recently died. It was written, of course, not only to console her, but to reveal his own conclusions arising from his theories of relativity and their inherent effect on time.

A consequence of Einstein’s theory was that simultaneity was dependent on the observer, so it was possible that 2 observers could disagree on the sequence of events occurring (depending on their respective frames of reference). Note that this is only true if there is no causal relationship between these events.

Also, Einstein believed in what’s now called a ‘block universe’ whereby the future is as fixed as the past. Some physicists still argue this, in the same way that some (if not many) argue that we live in a computer simulation (Davies, it should be pointed out, definitely does not).

I’m getting off the track, because what Davies argues is that the so-called ‘arrow of time’ is an ‘illusion’, as is the ‘flow of time’. He goes so far as to contentiously claim that time can’t be measured. His argument is simple: if time was to ‘slow down’ or ‘speed up’ everything, from your heart rate to atomic clocks would do so as well, so there is no way to perceive it or measure it. He argues that you can’t measure time against time: “It has to be ‘One second per second’ – a tautology!” However, as Davies well knows, Einstein’s theory of relativity tells us that you can measure the ‘rate of time’ of one clock against another, and this is done and allowed for in GPS calculations. See my post on the special theory of relativity where I describe this very phenomenon.

Davies argues that there is no ‘backwards or forwards in time’ and the arrow of time is a ‘misnomer’, a metaphor we use to describe a psychological phenomenon. According to him, it’s our persistent belief in a continuity of self that creates the illusion of ‘time passing’. But I think he has it back-to-front. (I’ll return to this later.)

So, if there is no direction of time and no flow of time, how do we describe it? Well, one way is to talk about whether phenomena are symmetrical or asymmetrical in time. In other words, if you were to reverse a sequence of events would you get back to where you started, or is that even possible? Davies argues that entropy or the second law of thermodynamics accounts for this perception. But here’s the thing: without time, motion would not exist and causation would not exist; both of which we witness all the time. And if time does not ‘pass’ or ‘flow’, then what does it do?

Mathematically, time is a dimension, which even has a smallest unit, called ‘Planck time’. Davies says it’s not measurable, but we do, even to the extent that we derive an age of the Universe. John Barrow, in his The Book of Universes, even provides an estimate in ‘Planck units’. Mathematically, we provide 4 co-ordinates for any event in the Universe – 3 of space and 1 of time. And, obviously, they can all change, but time is unique in that it appears to change continuously.*

And time is ‘fluid’ for want of a better word. Its ‘rate’ can change in gravity and relativistically because the speed of light is constant. The speed of light is the only thing that stops everything from happening at once, and for a photon, time is zero. A photon traverses the entire universe in zero time (from the photon’s perspective).

But for the rest of us, time is a constraint created by light. Everything you observe has already happened because it always takes a finite amount of time (from your perspective) for the photon to reach you and nothing can travel faster than light (because it travels in zero time). This is the paradox, but it’s the relationship between light and time that governs our understanding of the Universe. If something speeds up relative to something else (you), then the light it emits increases in frequency if it’s coming towards you and decreases if it’s moving away. Obviously, the very fact that you can measure its frequency means you can measure its velocity (relative to you), which is meaningless without the dimension of time.

So note that all observations (involving light) mean that everything you perceive is in the past – it’s impossible to see into the future. So the ‘arrow of time’, that Davies specifically calls a ‘misnomer’, is a pertinent description of this everyday perception – we can only observe time in one direction, which is the past.

Davies explains our perception of time as a neurological effect:

It is incontestable that we possess a very strong psychological impression that our awareness is being swept along on an unstoppable current of time, and it is perfectly legitimate to seek a scientific explanation for the feeling that time passes. The explanation of this familiar psychological flux is, in my view, to be found in neuroscience, not physics. (emphasis in the original.)

I’ve argued previously that perhaps it is only consciousness that exists in a constant present. It is certainly true that only consciousness can perceive time as a dynamic entity. Everything around us becomes instantly the past like we are standing in a river where we can’t see upstream. It is for this reason that the concepts of past, present and future are uniquely perceived by a conscious mind. Davies effectively argues that this is the sole representation of time: that ‘time passing’ only exists in our minds and not in reality. But if our minds exist in a constant present (relative to everything else) then time does pass us by; and past, present and future is not an illusion, but a consequence of consciousness interacting with reality.

There are causal events that occur around us all the time, but, like a photographic image, they become past events as soon as they happen. I believe there is a universal ‘now’, otherwise the idea of the age of the Universe makes no sense. But, possibly, only conscious entities ride this constant now, which is why everything else is dynamically going past us in a literal, not just a psychological, sense. This is where Davies and I disagree.

Meanwhile, the future exists in light beams yet to be seen. Quantum mechanically, a photon is a wave function (ψ) that’s in the future of whatever it interacts with. A photon is only observed in retrospect, along with its path, and that’s true for all quantum events, including the famous double slit experiment. As Freeman Dyson points out, QM gives us probabilities which are in the future. To paraphrase: ‘quantum mechanics describes the future and classical physics describes the past’. Most physicists (including Davies, I suspect) would disagree. The orthodox view is that classical physics is a special case of quantum mechanics and, in quantum cosmology, time mathematically disappears.

 Footnote: I should point out that Paul Davies is someone I’ve greatly admired and respected for many years.

*Paradoxically, at the event horizon of a black hole, time stops and we enter the world of quantum gravity. The evidence for black holes are accretion disks where the matter from a companion star forms a ring at the event horizon and emits high energy radiation as a result, which can be observed. However, from everything I've read, we need new physics to understand what happens beyond the event horizon of a black hole.

Addendum: I've since resolved this paradox to my satisfaction: it's space that crosses the event horizon at c. Then I learned that Kip Thorne effectively provided the same explanation, demonstrated with graphics, in Scientific American in 1967. He cited David Finkelstein who demonstrated it mathematically in 1958.