We know the universe of No Man's Sky is truly massive, thanks to its procedurally generated worlds. Even if developer Hello Games could share the exact number of worlds players can visit, it would be incomprehensibly big. What it can provide is a rough estimate of how long it would take to visit every planet in the game: five billion years.
That figure was shared with IGN by Hello's Sean Murray. It's an extraordinarily long time, but what makes it more impressive is the fact that it's merely how long it would take to visit each planet for a single second. What we've seen of the game so far suggests you'll need far longer than one minute, let alone one second, to fully explore any given world, so suffice it to say, you're never going to run out of new places to visit.
This is made possible because Hello opted to use 64-bit numbers to generate its worlds, rather than 32-bit numbers. When 32-bit numbers were being used at one point, it still would have meant taking several thousand years to visit each planet for one second. By moving to 64-bit numbers--which can store the astronomical sum of 2^64 total values, substantially more than the 2^32 total of 32-bit numbers--Hello was able to ensure it's even more difficult to fathom just how many planets No Man's Sky contains.
You can expect to hear more about the game before long, as Murray teased that Hello "will have something big to show soon."
The open-world game was first revealed last December and is expected out in 2015 for PlayStation 4. (A PC version is also in the works.) For more, check out our Next Big Game coverage from July, which dives into just how massive the game is and the tools Hello is using to make this all possible.