Some mad lad out there claims to have built "probably the biggest map in video game history," purportedly containing an incomprehensible 2,048 full-scale universes and spanning a number of miles my brain simply cannot compute.
The 1:1 Multiverse Garry's Mod creation, from modder Alexandrovich, is said to house 2,048 universes each containing "8.8e29km of star/galaxy clusters," which, according to PC Gamer's math, is 880 octillion kilometers. So, multiply whatever that number is by 2,048, and apparently you'll have the total size of this absurd map. Like our own real-life universe itself, this map is literally too big for the human brain to comprehend, if it's really as big as it claims.
It's worth noting that the mod was built using an existing mod called Infmap Base Creator, from Mee. That "truly infinite map," in the absolute simplest terms, uses a creative design illusion to simulate never-endingness. In the oversimplified terms my mind will only accept, it works by teleporting you back to the other side of the screen when you hit a boundary wall, a bit like the original Mario Bros. arcade game. When that happens, the mod is programmed to make objects on the screen invisible and un-collidable when you're looking ahead, but retain the same properties as before when looking behind, giving the illusion of infinite forward movement.
I will admit, that explanation made very little sense to me, and I'm the one that wrote it! But alas, it's the best way I've come up with to summarize the much more detailed explanation of how this all works from the original modder:
It's using this foundation that Alexandrovich can assure, "You will NEVER reach the end of this map no matter how hard you try." And the first part of trying, it turns out, is having a PC that can run the dang thing. In yet another testament to its behemothic size, the developer recommends you install the mod on a PC with 128 GB of RAM for best performance. Although the minimum required is a much more modest 12 GB, it says a lot about the mod that it can chew through 128 gigs, which is frankly unheard of for gaming applications.
Right now, it looks like the mod is populated solely by stars and star clusters, making the trip through infinity entirely not worth the time for all but the most dedicated virtual space explorers, but Alexandrovich promises the next update will bring 2048 solar systems - presumably one for each universe.
The same developer has a mod that lets you explore our own solar system, complete with "accurate" planet sizes and "approximate" distances between each celestial body (don't worry, there's a teleport option so you don't have to achieve immortality to travel between them).
In the meantime, here are the best space games to let you explore the unknown.
