Darkness. Total and complete. Few of us get to experience it.

At the bottom of a cave, perhaps; or in a basement when the power shuts off. But there’s usually some faint glow coming from somewhere. Even the night sky never seems truly black, not least because there’s usually a star or two twinkling in the distance.

So it’s hard to imagine a time when all that existed was darkness, when you could travel in any direction for millions of years and still see absolutely nothing.

But this is the story that scientists tell us, of the “dark ages” that gripped the Universe before the first stars ignited. And very shortly, they intend to show us that time, or rather how it ended – how the cosmos ultimately became filled with light.

Launching in the coming days, JWST is on a mission to look deeper into the Universe – and therefore further back in time – than even the legendary Hubble Space Telescope, which it succeeds.

Equipped with a 6.5m-wide (21ft) mirror and four super-sensitive instruments, Webb will stare for days at a very narrow spot on the sky to detect light that has been travelling through the immensity of space for more than 13.5 billion years.

“They will be just little red specks,” says JWST senior project scientist and Nobel Prize winner John Mather.

“We think there should be stars, or galaxies, or black holes maybe beginning at 100 million years after the Big Bang. There won’t be many of them to find at that time but the Webb telescope can see them if they’re there, and we’re lucky,” the US space agency (Nasa) researcher tells a special edition of Discovery on the BBC World Service.

It’s an astounding idea that you might still be able to witness such a thing. But that’s the consequence of light having a finite speed in a vast and expanding cosmos. If you keep probing deeper and deeper, you should eventually get to retrieve the light from the pioneer stars as they group together into the first galaxies.

For what purpose, though? Why spend 10 years conceiving, and another 20 years building, a $10bn machine to detect some faint, red blobs on the sky?

Well, essentially it comes down to the most fundamental of questions: Where do we come from?

When the Universe was formed in the Big Bang, it contained only hydrogen, helium and a smattering of lithium. Nothing else.

All the chemical elements in the Periodic Table heavier than these three had to be forged in stars. All the carbon that makes up living things; all the nitrogen in Earth’s atmosphere; all the silicon in rocks – all these atoms had to be “manufactured” in the nuclear reactions that make stars shine, and in the mighty explosions that end their existence.

We’re only here because the first stars and their descendants seeded the Universe with the material to make stuff.

“Webb’s mission is about the formation of all likeness; it’s the ‘we’re all made of stardust’ argument,” ponders Rebecca Bowler, a University of Oxford astronomer who’s a team-member on Webb’s NIRSpec instrument.

“It’s about the formation of the first carbon atom ever. It’s absolutely amazing to me that we could actually observe that process in progress.”

We don’t know much about the first stars. We can put the laws of physics into computer models and run them to get a sense of what might be possible. And it sounds fantastical.

“Estimates range from anywhere of order 100 to 1,000 times the mass of our Sun,” says Marcia Rieke, the principal investigator on Webb’s NIRCam instrument. “And, in fact, all stars follow the rule that the length of time they can exist as a star is inversely proportional to their mass – meaning, the more massive a star, the faster it uses up its fuel. And so these early stars might have only lasted at most a million years or so.”

Live fast, die young. Our own Sun seems so timid in comparison. It’s already burned for nearly five billion years and will probably keep on burning for another five.

The emphasis on the search for the first starlight makes Webb sound like a “one note flute”. It’s actually anything but.

It’ll observe just about everything there is to see out there beyond Earth – from the icy moons and comets in our own Solar System to the colossal black holes that seem to reside at the core of all galaxies. It should be particularly adept at studying planets around other suns.

Webb has, however, been tuned to look at all its targets in a very particular way… in the infrared.

Hubble was designed to be sensitive to light predominantly at optical, or visible, wavelengths. That’s the same type of light we detect with our eyes.

Webb, on the other hand, is set up specifically to detect longer wavelengths, which, although invisible to our eyes, are exactly in the regime where the glow from the most distant objects in the Universe will show up.

“Distant starlight gets stretched by the expansion of the Universe and shifts into the infrared region of the spectrum. We call it redshift,” explains Richard Ellis, a University College London astronomer who’s impatient to explore the end of the dark ages.

“The limiting factor we have with Hubble, for example, is that it doesn’t reach far enough into the infrared to detect the starlight signal we want. It’s also not a particularly large telescope. It’s been a pioneering facility, for sure. Amazing pictures. But the diameter of its mirror is only 2.4m, and the power of a telescope scales with the square of the diameter of the mirror. And that’s where JWST comes in.”

It was the 18th-Century astronomer Will