Some facts are bigger than numbers – a story

Some facts are just boring, like 1 + 1 = 2. You already knew them before they were presented as such, and now that you do, it’s hard to know what to do with them. Some facts are clearly important, even if you don’t know how you can use them, like the spark plug fires after there’s fuel in the chamber. These two kinds of facts may seem far apart but you also know on some level that by repeatedly applying the first kind of fact in different combinations, to different materials in different circumstances, you get the second (and it’s fun to make this journey).

Then there are some other facts that, while seemingly simple, provoke in your mind profound realisations – not something new as much as a way to understand something deeply, so well, that it’s easy for you to believe that that single neural pathway among the multitude in your head has forever changed. It’s an epiphany.

I came across such a fact this morning when reading an article about a star that may have gone supernova. The author packs the fact into one throwaway sentence.

Roughly every second, one of the observable Universe’s stars dies in a fiery explosion.

The observable universe is 90-something billion lightyears wide. The universe was born only 13.8 billion years ago but it has been expanding since, pushed faster and faster apart by dark energy. This is a vast, vast space – too vast for the human mind to comprehend. I’m not just saying that. Scientists must regularly come up against numbers like 8E50 (8 followed by 50 zeroes), but they don’t have to be concerned about comprehending the full magnitude of those numbers. They don’t need to know how big it is in some dimension. They have the tools – formulae, laws, equations, etc. – to tame those numbers into submission, to beat them into discoveries and predictions that can be put to human use. (Then again, they do need to deal with monstrous moonshine.)

But for the rest of us, the untameability can be terrifying. How big is a number like 8E50? In kilograms, it’s about a 100-times lower than the mass of the observable universe. It’s the estimated volume of the galaxy NGC 1705 in cubic metres. It’s approximately the lifespan of a black hole with the mass of the Sun. You know these facts, yet you don’t know them. They’re true but they’re also very, very big, so big that they’re well past the point of true comprehension, into the realm of the I’d-rather-not-know. Yet the sentence above affords a way to bring these numbers back.

The author writes that every second or so, a star goes supernova. According to one estimate, 0.1% of stars have enough mass to eventually become a black hole. The observable universe has 200 billion trillion stars. This means there are 2E20 stars in the universe that could become a black hole, if they’re not already. Considering the universe has lived around 38% of its life and assuming a uniform rate of black hole formation (a big assumption but should suffice to illustrate my point), the universe should be visibly darkening by now, considering photons of light shouldn’t have to travel much before encountering a black hole.

But it isn’t. The simple reason is that that’s how big the universe is. We learn about stars, other plants, black holes, nebulae, galaxies and so forth. There are lots and lots of them, sure, but you know what there is the most of? The things we often discuss the least: the interstellar medium, the space between stars, and the intergalactic medium, the space between galaxies. Places where there isn’t anything big enough, ironically, to be able to catch the popular imagination. One calculation, based on three assumptions, suggests matter occupies an incomprehensibly low fraction of the observable universe (1. 85% of this is supposed to be dark matter; 2. please don’t assume atoms are also mostly empty).

In numbers, the bigness of all this transcends comprehension – but knowing that billions upon billions of black holes still only trap a tiny amount of the light going around can be… sobering. And enlivening. Why, in the time you’ve taken to read this article, 300 more black holes will have formed. Pfft.