I’m reading a fascinating book by Paul Halpern on the Edge of the Universe, where he says that astronomers can now give reasonable approximations to its age (about 13.75 billion years) and its observable size (approximately 93 billion light years in diameter). They also estimate that less than 5% of the observable universe is made of ordinary matter, the rest being dark matter (23%) and dark energy (72%). There is also strong scientific evidence that it began from an incredibly hot and unbelievably dense Big Bang and that it is expanding at a rate faster than previously anticipated.
This is what hard scientific evidence can tell us. Beyond this we can only speculate or join the realm of science fiction. Since I am not a Cosmologist I can only speculate about the many unanswered questions raised by the universe. Let me select three of them to speculate about – how much universe lies beyond the visible universe, how will the current expansion terminate and whether there are more universes beyond ours?
To help with my speculation I shall use an analogy with a child blowing soap bubbles as depicted in the following picture.
To answer the first two questions let us assume that our universe is the bubble that she is still blowing. The question then becomes how will it end? One possibility is that she will stop blowing and instead begin sucking in the air to deflate the bubble. This is the favourite forecast by those astronomers who believe in the so-called Big Crunch.
This possibility raises two correlated questions and answers. When will she decide to reverse the blowing and how many times can she use the same water and soap to inflate and deflate the bubble. Some astronomers who believe in the Big Crunch usually estimate that she will blow for about 100 billion years but do not venture an answer if or how often the process can be repeated.
As an economist I am inclined to accept that such cycles can repeat themselves indefinitely. But I have some difficulty to understand the existence of infinity outside mathematics and as something external to the human mind. So let me return to the other alternatives.
She may either continue blowing or stop blowing. In the latter case she could release the bubble or try to keep it. If she continues blowing, the bubble may release itself or simply bust. Whenever the bubble is released it can fly in space isolated or merge with other bubbles until eventually they implode or vanish from our sight.
It is easy to understand that the outcome is highly unpredictable in the absence of statistical history. Unfortunately, when it comes to forecasting the future expansion path of our universe(s) we do not have the luxury of statistical analysis. So we can only speculate on how large is the share of the observable universe. Is it 99% or just an infinitesimal part of it? This remains an open question.
Turning now to the third question – the possible existence of many universes – the picture seems to suggest that we can have many bubbles (universes) all originating from the same source. But we can equally admit that there more boys and girls blowing soap bubbles. Indeed, why not admit the possibility that there an infinity of universes? This multiverse idea about a collection of universes is gaining ground among many cosmologists but so far it can only be a speculation of the kind any layperson like me can make.
Even if the existence of one or two more universes is proved we are still left with the problem of deciding if their number is finite.
So, until we have tackled satisfactorily the notions of finite and infinity, scientific pronouncements must be separated from speculative hypothesis. That is, just like investors, cosmologists must separate facts from speculations.