Raph Koster's career spans the evolution of the modern MMO. Creative lead on MUDs, Ultima Online, Star Wars Galaxies, and EverQuest 2, the systems and mechanics his teams developed live on in every active MMO today and many games besides. "People made fun of me for having dancing in Galaxies," Koster tells me. "Fortnite ought to give me royalties."

But the promise of his new game, Stars Reach is a scale bigger than everything he's made before. A sci-fi MMO set in a procedurally generated universe, where every world is a sandbox composed of material that behaves according to real-world physics. Feeling playful? Freeze a lake to create an ice rink. Feeling industrious? Boil it to become steam to power machines you've constructed. Looking for something a little deadlier? Electrify a salt deposit to create chlorine gas.

While Stars Reach has an overriding story about invading aliens that will appear on planets through emergent events, forcing players to band together to save one of their instanced, procedurally generated worlds before it falls to the mysterious Cornucopia, my discussion with Koster focused on the sandbox underpinning developer Playable Worlds' MMO.

Most immediately, why bother?

Stars Reach Early Access Trailer 2026

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"All of the game gets richer, the more the simulation underneath is present," Koster says. "That's not weird or unusual – shooters got better as the physics got better. We just think of this as an extension of that."

The main aim for the team is building a physics simulation that is consistent across all of Stars Reach's planets, Koster explains. It should "just do what you expect". The physics won't be faked in set pieces and specific places, or, as in some games, just apply to the avatar while the rest of the environment is "a cardboard stage". Achieve that and you make a coherent world that players just get because "now," Koster says, "the environment is real".

Once that consistency and reality is achieved, Koster says that players can both experiment and learn lessons that apply throughout its worlds, but it also means you can take what you know from outside Stars Reach and use it in the MMO's sandbox. Using farming as an example, Koster says "players can do things like affect the climate, set up heaters, chillers, and irrigation. You can literally reroute a river into a desert and cause the desert to bloom. Plants will grow there because the climate and the environment is different and the humidity levels and so on, and the sand will gradually turn into fertile soil."

In our demo, I watch as a player drills a hole in the bank of a mountaintop lake. As the earth gives way, the water pours out, creating an impromptu waterfall. The ground below the new cascade quickly turns to mud. While the impact here is limited, Koster recalls a time when players were trying to build a city on a planet called Gaiamar. He thought he'd add a nice pond and fountain to the centre of town, but the water features got out of hand and flooded the fledgling city – "many players didn't have reinforced basements on their home," Koster explains, "They relied on packed earth." When the water pressed up against the packed earth it turned back into mud and the walls collapsed under the weight of the houses above. Players and devs had to work overtime to dig out and rebuild the basements.

Koster compares what I'm seeing to other games where the physics are applied inconsistently, and the moment when you realise "you're able to knock a hole in the dam over here because the designer said so but can't knock a hole in the dam over there." That moment takes you out of the world because you clock that the first experience "wasn't simulated, it was a stagecraft moment. It was a set piece."

As well as heat rays, mining lasers, and cannons that shoot bolts of electricity, the simulation allows for more unusual tools, like a time gun. (Actual less-good name: Chronophaser.) Point this at anything in the world and you can rapidly age it. Marble turns to limestone, limestone to chalk, chalk to sand. Apparently, Stars Reach players use it when tunneling through mountains to lithify soft rock walls into harder materials that don't collapse under the weight of the mountains above. I would use it to rapidly age one of the space rabbits hopping about the world and study to see how it copes with the pressure of suddenly becoming the oldest bunny in the warren.

Now, I hope this isn't taken the wrong way by anyone working on Stars Reach, but for all the clever tech working away under the hood, the surface has the appearance of an MMO released in the early 2010s. So, while the game features events that sound dramatic, like a meteorite storm leaving the surface of a planet pockmarked with craters, the result might not look all that impressive. The way Koster tells it, I'm not the first one to point this out: "We've had folks see our videos and say 'What's the big deal with that crater? I dropped a nuke and Helldivers 2'". But, he explains they're "not realising the difference between a single set piece that's just an animation and actually having the power and the control to change things." When a nuke goes off in Helldivers 2, the effect is always the same, when a meteorite lands in Stars Reach it could tear a hole in the side of a reservoir, causing a flood and a crisis in the nearby town.

I realise most examples I've used so far involve water and mud, which reveals I am a simple soul whose architectural and geological learning effectively started and ended when, age eight, I spent a day building sandcastles on the beach at Eastbourne. However, the elemental interactions in Stars Reach are much, much more complex than that.

The logic underpinning Stars Reach, as with much procedural generation technology, is an early computer program called Conway's Game of Life. Developed back in 1970, the program is a turn-based simulation in which you set up the initial state of a world then sit back and watch as it plays out. The world is a simple grid and each cell in that grid can either be alive or dead, and, using four simple rules, at the end of each turn the program determines whether a cell is born, survives, or dies.

Lifted from the (actually very good) Wikipedia article on Conway's Game of Life:

1. Any live cell with fewer than two live neighbours dies, as if by underpopulation.
2. Any live cell with two or three live neighbours lives on to the next generation.
3. Any live cell with more than three live neighbours dies, as if by overpopulation.
4. Any dead cell with exactly three live neighbours becomes a live cell, as if by reproduction

If you've not seen Conway's Game of Life in action before, it's hard to imagine how that simple set up can form worlds that blossom with animated life. A small pattern of living cells can bloom into larger organisms within a few turns of the simulation beginning, or in some cases, they could lie almost dormant for hundreds of turns before colliding with another set of cells, reshaping the whole board. Go give it a play.

This all relates back to procedural generation, because by changing those four rules and randomly assigning which cells in the grid begin either alive or dead, you can create unique grids of cells that are either 'on' or 'off'. Grids that can then be read by a game engine as, for instance, rooms and corridors in a dungeon. But the main thing to take away from this is that with a stable system and a robust set of rules, you can build a self-perpetuating world.

This little diversion into computing history has a purpose, I swear. The fundamentals of Conway's simulation are behind the interaction of every cell in Stars Reach's world. As Koster sums it up: "Take Conway's Game of Life. Do it in 3D."

It's more complex than that, of course. Whereas in Conway's games, cells can only be alive or dead. Here cells can be different elements, and each element can be in a different state, and each element behaves differently in different circumstances. "Where Game of Life says, 'Oh well if I have neighbours like this I turn on, if I have neighbours like that, I turn off', we say 'Okay, we know the temperature and the humidity for each of these cells that determines which ruleset you use," Koster explains. If one cell is titanium and the other is iron, their melting points will be different, the speed at which they flow once they become liquids will be different, whether they blend with other liquids and become a new material will be different.

"The whole world is actually running one algorithm," Koster says. "The technical term for this is a cellular automata simulation. This is the stuff that Stephen Wolfram is always on about in his New Kind Of Science book, he's actually chasing after the idea that the real world, our world, works using cellular automata computation principle."

While Minecraft shares some of the same principles, there are far fewer interactions between the blocks being calculated. A more similar game, Koster says, is Nolla Games's Noita, the 2D roguelike where you're playing a wizard travelling deeper and deeper into a world where every single pixel is physically simulated. Fires burn and dry, ice forms and melts, water drowns and douses, and you must learn to use the physical properties of them all to survive in the dungeon. "That reactivity of the world is probably the closest analogy," Koster says.

Getting every element to interact correctly has taken years of work and experimentation. And when there are bugs, the procedural nature of the world can lead to a cascade of unusual problems. "We currently have a bug where silt is acting like mud," Koster says. "We're used to thinking of the word silt, as meaning loose silt at the bottom of a river. But our technical sense is that silt is actually what happens when mud is left behind and dries out." Long story short, they applied mud stats to dry soil and now there are certain biomes across Stars Reach where the ground won't stop moving – "Which is a problem," Koster says, perhaps picturing that time he collapsed an entire city's worth of basements with one water feature.

Koster has been building MMOs for decades, and he's dreamed of making a world like this before, but the physics simulation of Stars Reach wasn't possible to achieve in the past. "The CPU that we have available for simulation is something that just wasn't around back then," Koster explains. "Ultima Online ran on a computer less powerful than my Apple watch. We've had a lot of headroom open up in computing and cloud computing in particular." He says in the instanced zone we're exploring there are 270 million individual AI agents making up the landscape. Also, just to clarify, because AI is a loaded topic, we're not talking about generative AI or LLMs here, and the term agent simply means a program applying the physics rules to the chunk of world it oversees.

"Each cubic metre is inhabited by those individual agents and we're processing all of them multiple times per second in order to pull this off," Koster continues. "Then we build the environment on the fly. That required the ability to stream content over the internet fast enough. That kind of thing is what really enabled this from a technological point of view."

Though, possibly realising how technical our conversation had become, Koster ended saying "The other thing is the will, the desire to see worlds that are realer, more immersive, that offer that sense of wonder that can't just be boiled down to a strategy guide on a web page, but instead are constantly changing, and offering novelty. When you look at fictional portrayals of online worlds they take this for granted, they assume that this is what we will have. They're not about 'Let's just gather loot and level up'. Having responsive worlds that react predictably, that immersive dream is a huge part of the dream in video games."

Certainly, what I saw in that demo and the players' streams I've watched of Stars Reach since, this MMO is more than extended physics lesson. Yes, they're working together to carve up the base of giant mushroom trees just to see what will happen, but they're also building towns and transit systems, and communities. We recently updated our list of the Best MMOs on PC and we didn't add or remove a single game because the space has stagnated, so it's exciting to see a new game and one that's trying to do something decidedly different.