Question: do you beleive in the big bang theory??

Ian Cade answered on 19 Nov 2014:

I would avoid using the word ‘believe’ when assessing particular theories (though I understand it makes sense in the common use of this word)

Instead, when assessing theories there are essentially only three considerations:

1) Is your theory descriptive? – is it consistent with your observations

2) Is it predictive? – by plugging in initial variables (from observations now) is the theory able to predict the evolution of the system it is supposed to describe (the way it changes in time)

3) Is the theory the simplest possible model that describes the system?

Beyond this any other concerns are (scientifically) meaningless. These ‘irrelevant concerns’ include ‘is the theory true?’. Quite simply you cannot measure the truth of a model, you can however measure its descriptiveness, predictiveness and simplicity.

So how well formulated is the Big Bang theory? (I’ll just run through one or two examples to illustrate my point)

Observations of the universe seem to indicate that, on the whole, everything is moving away from everything else… This surely means that in the past that everything was closer than today. If you run time backwards it looks like everything (including the fabric of space) starts at a single point of extremely high density.

One of the predictions of this theory is that at some point soon after the Big Bang, the universe is full of plasma and opaque to light… but a little later everything cools enough for electrons and protons to form atoms of hydrogen at which point the universe becomes transparent to light. This means that wherever you look in the night sky there should be a dim glow of that first flash of light… and indeed there is, this is ‘the microwave background’.

And its simplicity, at least when it comes to describing the nature of the theory it is fairly straightforward (the particular mathematical details are more complicated, but you can get a feel for the broad implications of the theory just from a simple description).

Now to evaluate whether the big bang is a better theory than others just repeat this process of looking at the descriptiveness, predictiveness and simplicity of other theories.

For me, the ‘Big Bang’ theory seems to work perfectly well, though it is almost certain to be modified and improved in future.