(CNN) Sean Murray's brow furrows in concentration. He's trying to remember just how many planets players can explore in his latest game.

Finally satisfied, the founder of UK-based games maker Hello Games walks to a whiteboard to write out the number:

18,446,744,073,709,551,616.

That's 18 quintillion planets.

"If a new planet was discovered every second after the game comes out," says Murray, "it would take 584 billion years to visit every one just for a second."

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This unimaginably vast setting is the backdrop for "No Man's Sky," an ambitious, sci-fi adventure game that allows players to take on the galaxy as they wish.

Unique scope

"No Man's Sky" developer Sean Murray

The goal is to reach the center of the galaxy.

But "No Man's Sky" puts few restrictions on how to accomplish that. You're free to make your way as a trader, an explorer, or even as a fighter, preying on frigates to steal their precious freight.

Murray says he often compares the player to Han Solo in Star Wars. "He's whatever he needs to be to survive and that's what people are trying to do."

This vision enthralled gamers when it was unveiled at the VGX Awards in 2013.

Such scope is rare in games; even "Grand Theft Auto's" cities correspond to a small fraction of a real city. But "No Man's Sky" has real "planet-sized planets", each with its own unique environment and ecosystem of plants and creatures.

Herculean task

That led to a good degree of skepticism: Is the game really that big? How could a game like this come from just ten people at a small indie developer?

It feels real enough as Murray flies through the galaxy, whizzing past stars, then stopping to jump to the surface of unknown planets with a press of a button. It all happens virtually instantaneously, with no loading screens as he skips from planet to planet.

How did they pull it off? The answer is a technique called procedural generation.

Computer-created worlds

Instead of an artist drawing every single animal, plant or spaceship in "No Man's Sky", the computer creates it. It's given a set of rules for the world -- fish usually have fins, trees often have leaves, mountains look roughly like this -- and it is free to create within those boundaries.

That's not to say the artists at Hello Games is devoid of creative responsibility. Give the computer too many restrictions and everything looks the same. Too few, and you end up with creatures that are almost too alien.

Murray says at one point they had fish that looked so unlike fish, it tricked players into thinking they weren't underwater. One solution?

The most Earth-like creatures are found at the edge of the galaxy, where players will start the game; the closer you get to the center, the more alien the creatures become.

It also means that there's a good chance players will see things in No Man's Sky that no other human will ever see. The size of the galaxy, combined with the computer being responsible for creating its inhabitants, means players will undoubtedly see things that the team at Hello Games could never have anticipated.

"As a developer it's cool to feel that I don't know everything there is to see," says Murray.

Lonely journey?

One thing you'll rarely see are other players. "No Man's Sky" will support a limited form of multiplayer that may see explorers stumble across other gamers. But the size of the galaxy means players will likely be spread far apart, and meeting up with friends will take so long it'd be impractical. Still, there are other ways that players can make an impact on your game.

Players can scan planets as they explore them, cataloging their resources, finding new ships, even discovering new species. Uploading that information will send that information to everyone else's game, so if they stumble across that planet they'll know who discovered it and what they can expect. But they can also choose not to.

"There's a reward for every piece of information that you share, but you've got to judge whether it's as good as keeping it to yourself. You could be the only one to find a certain type of ship," says Murray. "It's an interesting experiment for when the game comes out."

When will the game come out? That's still to be decided. But it's a day Sean Murray is looking forward to.

"That's actually a big thing that drives us on, that one day the game's going to come out. I wonder what people will find."