Two months ago I posted on how the theory of Special Relativity refutes the idea of a flow of time or a universal present moment. You can read that post here.
Today as promised I put forward the arguments from modern-day Theoretical Physics which seek to push back and restore our intuitive notion of an objective passage of time and a universal now.
Two of these arguments come from, no surprises here – Quantum Mechanics (quantum theories and relativity theories have always been bitter rivals) however an argument can also be produced from General Relativity – Special Relativity’s big brother. I will present these arguments as briefly and as concisely as possible, but as we all know the workings of theoretical physics are far from simple so I hope the advanced readers amongst will not seek to crucify me too much over my wording at times. If you are so inclined to hear such arguments more comprehensively and for some reason you miraculously aren’t bored of me already here is my full dissertation on the topic with the very verbose title:
“In light of the theory of Special Relativity is a Passage of Time and the argument of the Presentist untenable?”
Rescuing the present moment is all about finding a privileged reference frame. (A reference frame of an observer is just a system which constitutes of an observer who is considered to be at rest and the events around him.) In Special Relativity all reference frames are equal; an observer moving away from a platform at constant speed on a train is equally as justified to claim he is “at rest” as an observer standing still on the platform. Due to this differing of opinion and the measurement of events, Special Relativity highlights to us that no observer is more justified in claiming the events he measures as happening instantaneously around him are justified to constitute the ‘present moment’ than any other. Events happening in the present moment as perceived by one observer may be regarded as past or future for another and all reference frames are equal. If you’re confused I urge you to go back and read (or re-read) the first post – it is rather mind bending stuff. However if we can find a privileged reference frame we can claim that the moment that is considered to be the present in that frame is actually the true universal present moment and the state of affairs that this reference frames regards as happening instantaneously really are happening in the present moment.
Remember the image of the block universe we spoke of before?
Well you can still think of different slices through this block as representing the present state of affairs for different observers but what these two arguments are trying to say is there is one preferential slicing which represents the true present in the universe and with reference to this, all events can be distinctly divided into past and future. Some would argue that with this universal present the future side of the block no longer pre-exists and this is similar to idea of the growing block universe. But how do we find this preferential slicing? Well let’s discuss.
The first claim for the privileged reference frame is from Quantum Mechanics and the wave-function. If you need a refresher on what this is, check out this post. Taking a summary from my co-author: “The wave function is a complex valued probability amplitude; which in essence is a mathematical expression of all the things something may be with probabilities assigned to them. The wave function describes all the states a particle may occupy and the probabilities associated with being in each state.” Now during measurements these wave functions are understood to collapse to produce single outcomes as opposed to the messy previous state of affairs where many possibilities are represented with different associated probabilities.
Now the key point is that Quantum Mechanics insists that these collapses happens instantaneously but this conflicts directly Special Relativity. As the collapse of the wave function is an event like any other surely it cannot coincide with an overarching now across all reference frames as all observers are moving at different speeds relative to the wave function. Only those at rest with respect to the wave function, would regard it as instantaneous. Thus the plane of simultaneity which represents the true present moment in spacetime is the one in which is at rest with the wave function. As a wise man once said (my dissertation supervisor, Nicholas Maxwell) “Collapses of quantum states are all that there is in the constitutions of things that pick out ‘there reference frame at rest’ and thus ‘the associated cosmic now.'”
However, there is much speculation in this argument as the nature of the wave function is a highly controversial issue. If one adopts the deterministic interpretation of quantum mechanics such as the Bohm or Many Worlds Interpretation which we’ve talked about here the wave function goes off to realise all the different outcomes represented as different probabilities in alternative universes – we just assume the function is collapsing because it’s all we can “see” from the confines of our own universe. Furthermore perhaps the wave function does not actually correspond to anything physically real in reality, it could just be a product of the mathematics of Quantum Theory. If this is the case and the wave function is not actually tangible the collapse could be made reconcilable with Relativity Theory, preserving equivalence across all reference frames. However, this interpretation of the Quantum world where the wave function is physically real and we accept what is known as the ‘probabilistic interpretation’ of Quantum Mechanics, this instantaneous collapse poses a great problem to the equality of all reference frames as postulated by Special Relativity. And I should note this interpretation of the Quantum world is the most popular – a universal present might be back on the cards.
Now let’s take a look at an argument from a theory much closer to home for Special Relativity, its big brother General Relativity. Special Relativity, is as its name indicates, special as it is only valid in ‘inertial’ frames of reference, which move with constant velocity with respect to each other. General Relativity however applies to curved spacetime and can accommodate references frames moving at accelerating velocities. Although in Special Relativity there are no frames of reference that can be considered privileged, some believe that in General Relativity could produce a case for one. How so? Well certain theoretical physicists believe grounds for such privileged reference frames can be found on the astronomical scale. Lee Smolin in his book ‘Time Reborn’ writes ‘the universe is arranged in such way that it naturally picks out a preferred state of rest… the motion of the galaxies pick out a preferred observer, hence a preferred state of rest at each point in space.’ Godel agrees that time could regain its objective existence on this astronomical state when he says ‘the existence of matter, as well as the particular kind of curvature of space-time produced by it, largely destroy the equivalence of different observers and distinguish some of them conspicuously form the rest, namely those which follow in their notion of the mean motion of matter.’ (Godel: A Remark about the Relationship between Relativity Theory and Idealist Philosophy).
So it’s all about weighing up the overall matter distribution in the universe to find this preferential frame. Of course, on the local scale we have no detection of this and the principles of Special Relativity apply with sufficient accuracy. We cannot move fast and we cannot see big and therefore we have the illusion that all our reference frames are equivalent because we are only considering our local vicinity which can pretty much be modelled as flat spacetime. But… once we consider the matter on an astronomical scale and we think about curved spacetime we might be able to find the grounding to pick out a preferred reference frame in the universe and thus rescue a true passing of time.
So either the salvation for a universal present moment and the absolute flow of time comes from the world of the very tiny or the world of astronomically huge. When being stuck in our mediocre middle ground which can be modelled approximately as flat spacetime Special Relativity works very well – and it stubbornly tells us the present moment isn’t real. But if we keep experimenting and testing our theories in the other domains we may realise the present moment is indeed rescuable. After all, Special Relativity isn’t a theory of everything, it’s just a theory that works very well in certain applications when studying this vast mysterious universe. So, as far as theoretical physics stands today you have the choice in whether you believe an objective present does or doesn’t exist as both are academically respected. Which viewpoint I prefer, I’m not too sure.