As the mathematician De La Soul

Physicists know it as α, or the fine structure constant. “It has been a mystery ever since it was discovered,” Feynman *QED: The Strange Theory of Light and Matter*. “All good theoretical physicists put this number up on their wall and worry about it.”

It’s both incredibly mysterious and unbelievably important: a seemingly random, dimensionless number, which nevertheless holds the secret to life itself.

“It’s a measure of the strength of the interaction between charged particles and the electromagnetic force,” explained SUNY Stony Brook astrophysics professor Paul M Sutter in an article for

“If it had any other value, life as we know it would be impossible,” he wrote. “And yet we have no idea where it comes from.”

Normally, this would be the part where we give you some examples of where the value turns up – but the answer to that, quite literally, is “everywhere.” It was

“In our everyday world, everything is either gravity or electromagnetism,” Holger Müller, a physicist at the University of California, Berkeley, told

Of course, physics is no stranger to constants – there’s *c*, the speed of light; *G*, the gravitational constant; in quantum physics there’s both *h* and to describe the Planck constant; if you’re a real aficionado you may even know about *k*, the Boltzmann constant. But α has something none of those other constants have – or, to be more precise, it *doesn’t* have something they *do*.

“There are no dimensions or unit system that the value of the [fine structure constant] depends on,”

Take the speed of light, for example. Look it up in a search engine, and you’ll find it’s equal to 299,792,458 meters per second. Or is it 670,615,200 miles per hour? Our mistake: it’s actually 1,802,600,000,000 furlongs per fortnight. Screw it – let’s just say it’s one light-year per year.

Get the picture yet? The value of the constant isn’t actually, well, constant – it depends on the units you use. But the fine structure constant doesn’t have that property: it’s an entirely dimensionless constant.

“If you were to meet an alien from a distant star system, you’d have a pretty hard time communicating the value of the speed of light. Once you nailed down how we express our numbers, you would then have to define things like meters and seconds,” explained Sutter.

“But the fine structure constant? You could just spit it out, and they would understand it.”

But perhaps the weirdest thing about this seemingly most pure of constants is that it may, in fact, not be constant. Some physicists have suggested that today’s α is actually

As Feynman

“You might say the ‘hand of God’ wrote that number, and ‘we don’t know how He pushed his pencil.’”

*An earlier version of this article was published in June 2022.*