Our understanding of the Universe has revealed that its existence, and indeed our own, relies on a particular set of rules. For example, the fundamental ‘constants of nature’, such as the charge of the electron, or the strength of the gravitational force, are set in stone.
We can measure them, but we don’t know why they have the values they do. But they also seem to be fine-tuned to allow galaxies, stars, planets and even life to exist. If any of these parameters were even slightly different, we wouldn’t exist and the Universe might not either!
So, are we the natural, even inevitable, result of an arbitrary set of numbers? Such an idea makes scientists uncomfortable.
Does it suggest intelligent design? Or are we, and the entire Universe, simply an astounding coincidence? Just how likely is the Universe? The fine-tuning of the fundamental constants suggests it is extremely unlikely.
We can overcome this problem if we allow for other universes. If there were an infinite number of universes, each with different sets of rules, it wouldn’t be surprising to find one in which we can exist. It would, in fact, be extremely likely.
We could also envisage a single but infinite universe that allows variations of the constants of nature. Then we’re just a likely ‘local’ phenomenon.
Of course, we have no evidence that we’re living in an infinite universe or that alternative universes exist. So, we can’t really say how likely our Universe is.
The Universe is fine-tuned in such a way that it allows random thermodynamic or quantum ‘fluctuations’. If the Universe exists for long enough, there’s a small chance that a conscious ‘brain’ can spontaneously form.
A so-called ‘Boltzmann brain’ (BB) could even contain false memories and perceive the Universe in exactly the same way as you. It’s an intelligent observer, just as you are. In fact, you may actually be a BB yourself!
The disturbing part of this strange idea is that, to the best of our knowledge, any sufficiently old universe would be overwhelmingly dominated by BBs over ‘normal’ observers. The only way to avoid this is to prevent the universe from existing forever.
Unfortunately, scientists are currently undecided whether the Universe is heading towards a definite end, so the BB problem remains. In effect, science is saying that you’re likely to exist, but not definitely!
This article is an answer to the question (asked by Russell Sparks, email) 'How unlikely is our Universe?'
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