The acute reader, having read the previous two posts in this series, must now be cautious about applying intuitive reasoning when thinking about the universe. I have given two examples of how intuition might fool us into treating the universe as a physical system and assuming that it has a beginning or that there could be something outside it.
In this post, I will attempt to crack another intuitive nut.
There are probably no concepts that we find easier to grasp than causality. An infant does not need to understand what causality is or be told that the universe is causal before crying for its mother’s attention. The assumption of a causal universe is made apriori, not just by human infants or by conscious beings but by all physical systems in existence.
Causality can be informally described as an implication relationship between two events in time. If the cause happens at a point in time then the effect happens at a later point. For example, if I press a light switch then the light bulb connected to it will turn on in a non-zero amount of time later. In this case, pressing the switch can be called the cause and the turning on of the light bulb the associated effect.
I will now bring back the snapshot notation that I used to examine the nature of time in the previous post. Here, I will use it to describe what causation really means.
For my light bulb example, I can capture the two universe state snapshots that contain pressing the switch (the cause event) and the turning on of the light bulb (the effect event). Causation can be described by saying that if the cause event happens at a snapshot k1 then the laws of physics mandate the occurrence of the effect event in a subsequent snapshot k2. The timing relationships between k1 and k2 and other specifics including whether the universe is truly deterministic or inherently stochastic do not concern us here. What is important to understand is that causality is a relationship between two universe state snapshots where the one containing the cause predates the one containing the effect.
You may already be seeing where am going with this. I am now going to spell out the argument starting with the conclusion of the previous post as a premise. There are no universe state snapshots that predate the big bang. In consequence, the big bang is not the effect of any cause!
But surely all events have causes and if you follow events back in time there are always “initial causes” that predate all chains of cause and effect, can’t it be the same for the universe?
If you’ve read the previous two posts then you may have a hunch at what the answer to this question might be. Perhaps the following figure will be of help …
This question commits the same intuitive mistake of treating the universe as a physical object within a universe. We have defined causation as a relationship between the contents of two universe state snapshots. To ask what causes snapshots themselves (the universe) to come into existence is to assume the existence of a container space-time in a master universe in which this form of hyper-causation can be defined. As I’ve already explained in the previous post, this gets us nowhere because it doesn’t solve the problem but shifts it elsewhere.
In conclusion, the phrase “the cause of the big bang” is actually no different from the phrases “before the big bang” and “outside the universe”. All three are meaningless concoctions that confuse the universe for a physical object that occupies a region of space-time and whose existence is attributed to other events in prior moments of its parent universe.