As those who know me and might well expect, I’m one of those people who actually read all the way through A Brief History of Time. It wasn’t quite what I was expecting and it took me ten years to get beyond the introduction. The sticking point in that case was the idea of atomic clocks recording time flowing at different rates the higher up we get from the planet. The implication, for me, was that, if time runs at different rates relative to gravity (i.e. the amount of stuff in the vicinity), then different parts of the universe are not the same age. If we say that the universe is around 14.5 billion years old: we have to specify where exactly we are talking about. The intervening ten years saw me reading lots of “popular science” and I eventually returned to A Brief History of Time with an attitude of suspension of disbelief.
While I understood most of what was said, I came away with a feeling of dislike for one of the things that was implied, if not directly said in the book: the idea that, if we live in a universe that has the critical mass to start contracting and eventually end up in a big crunch – the opposite of the big bang – then, at the point the universe starts contracting, everything starts running backwards. That would indicate that we could be in either the expansionary or contractionary stage of the universe right now and we wouldn’t really know the difference: our minds still perceive time as flowing in the same direction.
I’ve also never been a fan of the idea of multiple universes: they are currently non-disprovable and, therefore, unscientific: not to mention spawning far-too-many lazy and incoherent plot-lines in fiction.
It will take a little more travel to get to my point because at this point, I introduce the idea of causal determinism. In this instance, the idea runs that, because the universe is a chain of cause and effect: everything that happens is a result of what happened previously and, therefore, we have no choice. There is only one way that the universe can run and, if we could accurately quantify the present, we could accurately predict the future. The present is, of course, rather complicated and the ability to know everything about it would likely require a storage and processing system bigger than the universe itself so our ability to know it is limited, to say the least.
The final piece of this little puzzle is what’s known as the two-slit experiment. This one is something that most people will have been exposed to in basic science at school along with its companion: the pinhole camera experiment. In the two slit experiment, light is shone through two slits cut into a surface and an interference pattern of bright and dark lines can be seen on another surface behind the first. This shows that light travels as waves through the slits rather than in straight lines (in this case). On the contrary, when we do the pinhole camera experiment, we see an upside-down image at the back of our little home-made camera box which shows clearly that light travels as straight lines.
This idea: that light travels as both waves and in straight lines is a clear indication that the world is not as we perceive it. We accept it because we are told it but the investigation of this duality – called wave-particle duality – is a rabbit hole of no return.
How can a thing be a thing and also not a thing?
Fundamentally, it seems, matter is simply a condensed and structured form of energy and acts in different ways in different circumstances. So far, really, so mundane!
It is in pursuing the matter of the two-slit experiment that things start to get really weird. At some stage, some enterprising scientist decided to see what would happen if single photons – units of light – were sent through the experiment one by one. Given that we are sending single units of light, we would expect to see two dots on the second surface because single units of light won’t create an interference pattern in the same way that a continuous stream of light does. This was not the case. Sending single photons through the experiment produced an interference pattern.
Implication: the single photons were interfering with themselves!? Or perhaps there was some sort of temporal effect at play where the photons were interfering with each other across time?
The next step of investigation was to see if it could be determined which slit the individual photons passed through. A difficult job given that, in order to measure something, we often change it. However, by ingenuity that is not mine to understand, a way of registering which slit each photon passed through was found and the result was rather disconcerting. If we observe, for each photon that passes through the experiment, which slit it has passed through, the interference pattern collapses and we get a bright dot behind each slit: the light travels in straight lines.
It appears that the observation affects the experiment.
That could, of course, be due to the interference caused by the observation method: the method of registering which slit the photon passed through alters the trajectory of the photon: the experimenter interfering with the experiment and altering the outcome?
And this is where things become truly weird. It was somehow discovered that, if the apparatus is set up to measure which slit the photons pass through but the observer does not check on the outcome, the interference pattern does not collapse. It is the act of observation and not the mechanism of observation that causes the wave pattern to disappear and the photons to travel in straight lines. Deciding to look, or not, at the process changes the outcome.
At this point, it’s worth mentioning that photons are not the only things put through this experiment. Electrons, atoms and molecules have been shown to show this wave-particle duality. As of writing, molecules with up to 2,000 atoms have been shown to display this property so it applies to (relatively large chunks of) matter as well as light.
The final nail in the coffin of our normal reality comes with the delay of the decision whether to observe the trajectories of the particles until after the experiment has run its course: not deciding whether to look or not until after the particles have settled on where to land. Not looking: interference pattern = waves. Looking: two dots = no waves.
To me, the least weird explanation for this is that, as we generally think of it, the consequences of looking or not travel back in time and affect the outcome of the experiment. Or perhaps, the result of the delayed decision is inevitable because of the current state of the universe and the universe acts accordingly: deriving a future state from the previous state.
It is on the first option, I would like to dwell here and it relates to what I said earlier about causal determinism. If, as we think of it, the consequences of a decision can travel backwards in linear time, then it is likely, inevitable even, that such a chain of cause and effect travels all the way back to the beginning of the universe in the same way that we see current events as travelling in a chain of cause and effect into the unknown future. It would mean, in effect, that the idea of causal determinism can be true and yet the decisions we make along the way create the original circumstances that cause / allow those decisions to happen. Everything is both predetermined and yet our choices matter: they create the circumstances in which we choose.
I wouldn’t say that I believe this exactly but it creates a possible solution to the age-old discourse on whether we have free choice or not. In a social sense, we still seem to be very much the products of what has created us: our genes, our cells, our families, our culture and education and, in that milieu, there doesn’t seem to be any point at which we get to choose who we are where our choice isn’t the result of our biological and cultural circumstances but it does open up a possibility.
In the process, I have made my peace with Stephen Hawking’s reservable universe. Perhaps, as numerous scientists would say, our perception of linear time is just a matter of the perspective from which we observe. Just as a rainbow is the creation of perception derived from physical phenomena, so time may be equally a creation of perception. And in a universe where the chain of cause and effect runs in both directions, it makes more sense (to my little mind) that the expansion / contraction phases of the cosmos being identical makes a modicum of sense. We see a rainbow where there is just refraction of light: we see a flow of time where there is just … something that is not quite a flow of time.
Purely incidentally, it could also collapse the multiverse back into our little old universe. The multiverse idea exists as a result of “choice” at a quantum level: whenever two different options are available, both happen. However, if such “choice” creates the circumstances for the resolution of the choice into a single predetermined option, then there is no need for both to happen. We don’t sprout a new universe every time a subatomic particle decides to go this way and that.
Strange stuff but I think I have the principles right. If you fancy bending your mind on the matter, I suggest the works of John Gribbin, writer of much of the popular science that prepared my mind for the task of finally reading Stephen Hawking’s little treatise.