Three is the magic number, as mathematician De La Soul famously noted. But, according to physicist Richard Feynman, the value is incorrect by a factor of 400. The “magic number” for Feynman, you see, is roughly 1/137 – exactly, 1/137.03599913. It’s also known as the fine structure constant by physicists. In his 1985 book QED: The Strange Theory of Light and Matter, Feynman remarked, “It has remained a mystery ever since it was found.” “Every competent theoretical physicist scribbles this number on their wall and obsesses over it.”

It’s both enigmatic and crucial: an apparently insignificant, dimensionless number that, despite its appearance, carries the key to existence itself. In an article for Space, SUNY Stony Brook astrophysics professor Paul M Sutter noted, “It’s a measure of the intensity of the interaction between charged particles and the electromagnetic field.” “Life as we know it would be inconceivable if it had any other worth,” he wrote. “However, we have no notion where it originates.”

Normally, this would be the point where we offer you some instances of where the value may be found, but the answer is “everywhere.” It was discovered by physicist Arnold Sommerfeld in 1916, but it had been appearing in equations for decades before that. It’s hidden in light and matter formulae, and it controls everything from the tiniest hydrogen atom to the birth of stars. “Everything in our everyday environment is either gravity or electromagnetic,” said Holger Müller, a physicist at the University of California, Berkeley. “That’s why alpha is so critical.”

Of course, constants are common in physics: there’s c, the speed of light; G, the gravitational constant; in quantum physics, there’s both h and to represent the Planck constant; and if you’re a true physicist, you might even know about k, the Boltzmann constant. But possesses a property that none of the other constants possess – or, to be more exact, possesses a property that none of the other constants possess. “The value of the [fine structure constant] is independent of any dimensions or unit system,” Sutter noted. “In physics, the other constants aren’t like this.”

Take, for example, the speed of light. If you look it up in a search engine, it equals 299,792,458 meters per second. Is it 670,615,200 mph (1,079,250,548 km/h) or 670,615,200 mph (1,079,250,548 km/h)? It is 1,802,600,000,000 furlongs per fortnight, not 1,802,600,000,000. Let’s just assume it is one light-year each year for now. Have you gotten the image yet? The value of the constant isn’t quite constant; it varies depending on the units used. The fine structure constant, on the other hand, lacks this property: it is a dimensionless constant.

“If you met an extraterrestrial from another solar system, you’d have a hard time explaining the worth of the speed of light.” “Once you’ve figured out how we represent our numbers, you’ll need to define things like meters and seconds,” Sutter stated. “But what about the fine structure?” You could simply spit it out and they’d understand.” The strangest thing about this seemingly pure of constants is that it could not be constant at all.

Some scientists believe that today’s is somewhat larger than it once was — just by one part in 100,000 over six billion years, but that’s enough to have far-reaching consequences in the long term. If you change 137 to 138, for example, you reduce the value of by 0.00005, which some scientists say is enough to stop stars from producing carbon and so stop the evolution of life as we know it. “It’s one of the biggest darn mysteries of physics,” Feynman said, “a magic number that comes to us with no human explanation.” “You might argue the number was written by the ‘hand of God,’ and we have no idea how He moved his pencil.”