Time travel is a tricky thing to implement in a video game, especially when it fundamentally affects the title's play mechanics. What if time travel is not only an active part of play, but its use constantly changes the game's experience? Independent game developer Hazardous Software is figuring out the answer to this question with Achron, a real-time strategy game that requires players to think in four dimensions instead of three.

Hazardous Software's president and founder, Chris Hazard, took some time to sit down with Ars and talk to us about Achron, also giving us access to the alpha build that is available to anyone who preorders the game. The bottom line: this is a game made by some very dedicated people, and it has a ton of potential.

The story

Humanity begins to settle across the stars and learns teleportation from studying ancient alien ruins. Colonization, for the obvious reasons, speeds up. Trade is revolutionized. Then, after a few decades, colonies start disappearing, turned to nothing more than shadows and dust. When humanity tries to combat this unknown alien threat, it finds itself outmaneuvered and out-thought at every turn. The game itself will begin after this staggering defeat, with players trying to figure out what happened and how they'll survive, cut off from humanity and surrounded by hostile alien forces.

This is a very smart game, involving some extremely advanced concepts based on real theoretical physics. Case in point: aside from incorporating time travel into the strategy, players will also have to account for the paradoxes that result from sending units through the fourth dimension.

Let's say you decide to take the sneaky route and destroy an enemy's factories in the past, thereby nullifying the armies they have in the present. However, before a time wave (explained later) reflects the changes in the present continuity, your opponent manages to pull the same move with you. This creates a paradox: both players' units shouldn't be around in the present, but each result will periodically dominate the present timeline when a time wave hits the present timeline, canceling out the other; the outcome oscillates between each player's favor.

If you're advanced enough, you can time out the time waves' patterns so the events work out for you. Paradoxes in Achron are resolved when an event falls off the observable Timeline, thereby locking them into the level's permanent continuity.

Hazard wanted to make time travel seem as realistic as possible. "I've always been annoyed with Hollywood-style 'science'," said Hazard, "so I put the constraint on Achron that, besides time travel and the related effect of teleportation, we were going to be as accurate as reasonably possible with respect to the science when creating Achron's units, alien races, and story, as long as it doesn't adversely affect gameplay. We've had countless interesting discussions figuring out how things should look and behave, what the motivations of characters and organizations in the story are, and how to make sure that the story and gameplay give a cohesive feel."

While Achron features innovative ideas, the game started out as a joke between college students. According to Hazard, "Late one night in undergrad I was talking with a friend of mine about the game Homeworld. It was one of the first RTS games to fully use three-dimensional space strategically. My friend asked, half-jokingly, what a four-dimensional RTS would look like. The concept of time waves seemed like an elegant way to solve [the] issues at the same time. I spent many months designing the algorithms and thinking about how the game mechanics would work, and once I was satisfied, I began coding."

A longer development time than most games

Achron may be an indie game, made by a small team, but Hazard has been working on the game since the late 1990s. When he began development, he was limited by the era's technology. "I started planning Achron's development back in the fall of 1999 and began implementation in 2001. I knew it would take a lot of CPU throughput to accomplish. Based on my initial estimations, I didn't think personal computers would even be fast enough to run it until at least 2004, so I began creating it looking as far in the future as I could. There wasn't any other game engine out there that could even support the types of things needed for the free-form time travel in Achron, and I began coding it from scratch.

"The problem with estimating the future of computing in 1999 was that back then it was easy to be overly optimistic. Memory latency increasingly became a bottleneck, and with the economic recession, people didn't upgrade their computers as much. Despite significant time optimizing Achron's Resequence engine, it wasn't until about 2008 that common home computers really became fast enough."

One factor in the lengthy development time is a consistently small team. At the moment, there is a six-person team of people working on the game full-time, with another dozen or so working part-time. This, however, is far more than the number of people who were initially working on Achron.

"Early on, I wasn't completely sure whether or not time travel would be feasible with respect to performance," Hazard explained. "I was cautious bringing people on board until it became stable."

Yes, but how does it play?

At the moment, the game is still in the alpha stage of development. That said, it's far along in terms of play mechanics. The basic elements of strategy games are all there, and they're well-implemented. There are three races in the game: the Vecgir, the Grekim, and Humanity. Each group has a specific strength: Vecgir specialize in teleportation, Grekim can shuffle time around like a pack of cards, and good old Humanity has the homefield advantage when it comes to firepower.

On the bottom of the screen is the Timeline, which lets you move between the immediate past, present, and future during play. The Timeline registers attacks from different players as graphs during different points, so if you suddenly see a graph showing up in the past, you can move the cursor on the Timeline back to that period and then counter it by moving some units around so that the battle then turns out in your favor.

One of the neatest elements is stylistic: the further back into the past, the more sepia-toned everything becomes. Eventually, after a couple of minutes back on the Timeline, you can barely make out any details. It's a very simple idea, but it shows how effective a simple style element can be when used well.

In order to issue commands in the past, you use up "chronoenergy," which is shown in a bar atop the Timeline. The further back into the past you go, the more chronoenergy is used each time you issue a command. Things get increasingly expensive when you are commanding multiple units further back in the timeline.

The use of chronoenergy came about—according to Hazard—as a way "to prevent players from continually undoing the past, and [we] have developed some balancing techniques to prevent players from using the grandfather paradox to obtain strong units with little expenditure. The most difficult challenge was to get the mechanics right to disincentivize the 'chronoclone grief' where a player takes advantage of the edge of the timeline to permanently clone a unit by time traveling. We've largely resolved this by a combination of adding delays between time travels, adjusting costs, and changing the chronoenergy consumption model slightly."

When you change an event in the past, its repercussions won't immediately register in the present/future. Instead, "time waves" scroll across the Timeline; when they hit the present point of the Timeline, changes will register on the game map. I'm not going to lie: it takes a while to get used to watching units/buildings that were wiped out pop back into existence after you take steps to ensure their protection in the past.

One of my favorite levels in the single-player campaign began with my base under attack, with my tanks and mechs not close enough to put a stop to the invasion. The solution? Go back in time and send my units to the base before the enemy arrived. This became my ongoing strategy: keep an eye on the Timeline, look for the graph indicating an enemy attack, jump to a point shortly before that and then counter the enemy forces with my own.

For an alpha release, this is great

For an indie game that's in an alpha release, Achron looks pretty good, albeit a little simple. At the same time, it's incredibly stable and the gameplay is very solid. As I worked my way through the demo levels that are available, I found myself replaying many of them so I could understand how to use teleportation nodes and time travel better. It was somewhat difficult to grasp at first, but it was interesting and became a ton of fun to play with once I got the hang of it.

Unsurprisingly, a strong community has built up around the game itself, with a little over a thousand users actually helping to fund the game's development by investing with Hazardous Software and getting access to the game's alpha build.

While Hazard admits the funding is nice to have—especially since the game is self-funded by its development team while they work from home—it isn't the real reason his company established the preorder program: "The primary purpose of our preorder program is to get feedback. Our community has been invaluable to us in this regard, and we've made and planned some gameplay changes based on feedback. The preorder program also gives people an opportunity to start modding and even contribute to Achron. We'll be releasing more mod tools in the next couple months."

As for the game's development schedule, the team is hoping to release the game soon. "We are aiming for a release early in 2011," said Hazard. "The story is finalized, the units for all three races and heroes are nearly all designed, and the engine is very stable. The majority of the remaining work can be worked on in parallel, and mainly includes art production, level implementation, balancing, and some UI improvements."

Based on what we've gotten to play of Achron so far, there isn't much like this on the market. Head over to the official site to learn some more.