Yearning for Certainty

Yearning for Certainty September 11, 2020

Oh, how we yearn for certainty! Doubt is confidence destroying and can even lead to suicidal depression, but is it reasonable to expect certainty? Well, I’ve got some bad news: there is no certainty in Science. 

OK, we can speculate about possible certainties, build hypotheses based on the idea of certainty, but we have never observed it or succeeded in making it. The trouble is, certainty requires absoluteness, and that probably doesn’t exist, which is why we can never prove anything in Science. The best we can do is gather repeatable, shareable observations and say, “This proposition is highly probable and hasn’t been falsified yet.”

It’s not for lack of trying! Scientists have investigated proposed certainties for centuries, I mentioned two hypothetical ‘absolutes’ in my article about Proof, ( but here’s a couple more examples of our failure to find absoluteness…

Thanks to Einstein, we know that, counter-intuitively, time is not absolute; it depends on the speed of the observer. This is beautifully explained by Professor Brian Cox and Professor Jim Al Khalili here

Of course, that relies on our understanding that the speed of light in a vacuum is absolute – nerdy schoolboys will know the figure – 186,000 miles per second! That is a phenomenal speed and very difficult to measure so it’s unsurprising that we have not been able to attempt it until recently. We’ve been getting better at it as you can see from this table:

We can even do it as a demonstration today

But, notice that the lecturer says, ‘about one foot per nano second’. This is because we cannot be sure that we have a perfectly accurate value. A better measurement can always be obtained – by increasing the distance of the far mirror, for example. And, don’t forget, this was done in air, not a vacuum, which is something we have never achieved or observed! Consequently, the speed of light is calculated, not observed, and, here’s the thing, all our other supposed certainties depend on that one being true!

In science we have to make do with ‘highly probable and currently unfalsified’ as good enough, and as close as we can get to certain, in practice. 

Some people will say that there are other ‘magisteria’ in which we can have certainty, but those fields are always open to contest. One person’s account of an incident may be challenged by someone who has a different viewpoint. Very few convicts admit guilt…

This is why Voltaire said “Doubt is not a pleasant condition, but certainty is absurd.”


Image: Portrait of Voltaire by Nicolas de Largillière, c. 1724 (public domain)

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