To many, time is a way of telling us when to do things or expect things to be done: when to meet, when to eat, when to sleep, but what is the scientific definition of time? One source defines it as the “indefinite and continuous duration…in which events succeed one another“, meaning the past is the past and the future will always come after, a linear perception. However, what if time isn’t linear and our perception is wrong? Strap in.
During the pandemic my partner and I have had numerous discussions about the state of the world, but it has also made us ask more philosophical questions (because there’s only so many times I can talk about the government/policies/economics/employment and not want to cry): is our definition and perception of time real? An episode of the Infinite Monkey Cage with Prof Brian Cox addressed the question “Does Time Exist” earlier this year and it was the first time I had stopped to think about it. Time has always appeared to be a constant, something measurable, but physics questions whether time is a reality or a human construct. Some theories suggest that everything may in fact be happening all at once, and that time is just an illusion.
This in itself is a difficult concept to process especially when we’re used to seeing the past and not the future. For example, when you make a cake you go from eggs, flour etc. to a (hopefully) edible sponge; you can’t then reverse that process and get your ingredients back (nor would you want to, it’s cake). Scientists call this the “arrow of time“, the direction in which we perceive time to pass. Theoretical physicist, Sean Carroll, states that it comes down to entropy, whereby everything (that is not isolated) will move from an ordered to a disordered state (i.e. increasing entropy). For example, freshly cut grass would eventually grow into a messy meadow if left alone; that’s entropy in action. Observing entropy in this way (i.e. watching things get messier/more disordered) accounts for why we can see time in a linear way. For this reason, and others, plenty of physicists believe time is not an illusion, but is very real and exactly the way we perceive it.
However, many also believe our perception of time is not real. Whilst on the macroscopic scale (i.e. things visible without a microscope) we can perceive time to flow forwards (e.g. making a cake). The microscopic scale however doesn’t follow suit and the “difference between the past and future vanishes“, says physicist, Carlo Rovelli (who appeared on the podcast). To address whether time is real, we need to mention Einstein’s theory of general relativity; our best current scientific understanding of time. His theory states that time and space are not constant as we perceive them to be, but that only the speed of light is truly constant. In fact, general relativity teaches that there is no Global “now”, meaning there is no Global present moment only a local present moment which you yourself are able to experience. This brings us to the “block universe theory” which is a widely accepted concept amongst physicists who study general relativity. In the block universe, all events (whether we perceive them as the past, present or future) have the same status; they are all happening simultaneously and are fundamentally timeless. This belief stems from the general relativity theory being unable to account for our experiences of time. General relativity has correctly predicted an incredible number of things including the science we now use for GPS, as one example. However another predicted possibility, which we are yet to observe, is that you could take a trip and return to find your children are older than you, a concept explored in the 2014 film, Interstellar. For more on this concept check out this article HERE. Overall though, this arises from the notion that time works differently to how we perceive it (i.e. a block universe), and it is our perception that is wrong, not the theory. Physicists believe that to experience these scenarios, and thus stop perceiving time linearly, we need to reorganise our way of thinking about time.
Fay Dowker (a theoretical physicist who appeared on the aforementioned Infinite Monkey Cage episode), argues that whilst general relativity is currently our best theory for understanding time, the fact that it cannot account for our linear experience of time should point physics research towards finding a better theory, which can supersede general relativity and account for the arrow of time. Until then however, all we have is general relativity and what if there isn’t another theory; what does this mean for time? The whole theory relies on everything being relative and that nothing is absolute. I believe physicist Julian Barbour describes it well, saying that change is real, but time is not; time is merely a reflection of the change in a system which our brain uses to construct a perception that time passes. If absolutely nothing were to happen (and I mean nothing, no breathing, blinking, ticking clocks etc.), we would have absolutely no notion of time; it wouldn’t exist.
If this is the case, that time is a construct of our brains, not linear and that everything happens at once, would it be possible to access our whole “timeline” as fictional linguist Louise Banks (played by Amy Adams) does in the 2016 film Arrival? Could we rewire our perception of time? Unfortunately physicists still don’t have a definite answer to this. Prof. Dowker is researching causal set theory and says if this is proved right, it will be impossible to go back in time. Prof. Rovelli states that whilst the theory of general relativity theoretically allows for the movement along your timeline, he does not believe we will ever be able to have memories of our future as this would go against entropy (i.e. if you had memories of the future, entropy wouldn’t be increasing as it should). So the jury is still out, is time real, or is it a construct of our brains formed when we see change? If you want a break from the pandemic, consider if time is real…