...the theory of relativity permits space and time to possess a variety of boundaries or edges, technically known as singularities. One type of singularity exists in the centre of a black hole. Another corresponds to a past boundary of space and time at the big bang. The idea is that, as you move backwards in time, the universe becomes more and more compressed and the warping of space-time escalates without limit, until it becomes infinite at a singularity. Very roughly, it resembles the apex of a cone, where the fabric of the cone tapers to an infinitely sharp point and ceases. It is here that space and time begin.
Once this idea is accepted, it is immediately obvious that the question "What happened before the big bang?" is meaningless. There was no such epoch as "before the big bang", because time began with the big bang. Unfortunately, the question is often answered with the bald statement "There was nothing before the big bang", and this has caused yet more misunderstandings. Many people interpret "nothing" in this concept to mean empty space, but let's be clear: space did not exist either prior to the big bang.
Perhaps "nothing" here means something more subtle, like pre-space, or some abstract state from which space emerges? But again, this is not what is intended by the word. As Stephen Hawking has remarked, the question "What lies North of the North Pole?" can also be answered by "nothing", not because there is some mysterious Land of Nothing there, but because the region referred to simply does not exist. It is not merely physically, but also logically, non-existent. So too with the epoch before the big bang.
People tend to get very upset when told about this. They think they have been tricked, verbally or logically. They suspect that scientists can't explain the ultimate origin of the universe and are resorting to obscure and dubious concepts like the origin of time merely to befuddle their detractors. The mindset behind such outraged objection is understandable: our brains are hard-wired for us to think in terms of cause and effect. Because normal physical causation takes place within time, with effect following cause, there is a natural tendency to envisage a chain of causation stretching back in time either without any beginning, or else terminating in a metaphysical First Cause, or Uncaused Cause or Prime Mover.
