The Bitcoin community is facing one of the most momentous decisions in its six-year history. The Bitcoin network is running out of spare capacity, and two increasingly divided camps disagree about what, if anything, to do about the problem.

If these two sides fail to reach a consensus, the Bitcoin network could — according to one side, at least — slowly grind to a halt as the number of transactions exceeds the network's capacity to process them. Even worse, if a fix for this problem is forced through prematurely, it could split the Bitcoin network in two and permanently damage public trust in the network.

The argument is the closest thing the Bitcoin community has had to a constitutional crisis. Bitcoiners are trying to figure out who, if anyone, has the authority to make technical changes to the Bitcoin network's foundations. So far, neither side in the increasingly heated debate has shown much willingness to compromise.

The Bitcoin network is running out of capacity

The Bitcoin network processes transactions in units called "blocks," which are created about every 10 minutes. To prevent malicious parties from clogging up the system with spam, the original Bitcoin software limited the size of each block to one megabyte, which corresponds to a few thousand transactions. When Bitcoin was created in 2009, that left plenty of room for growth.

But Bitcoin usage has been growing, bringing the network closer and closer to its maximum capacity. Right now, the network is only 30 to 40 percent full on average, but it sometimes gets congested during periods of high demand, causing delays for users. And if current growth continues, things could get a lot worse in the next year or two, as the network gets closer to 100 percent capacity.

And if Bitcoin is going to become a mainstream payment platform, it's going to have to grow a lot more. Bitcoin handles tens of thousands of transactions per day. Visa handles tens of millions. To compete with Visa and other mainstream payment technologies, the network is going to need more capacity.

Changing the limit is easy — if everyone agrees

The limit is just a number in the Bitcoin software. If that number were changed to a higher value, the Bitcoin network would have more capacity.

The difficulty is that this only works if everyone agrees to raise the limit. The Bitcoin network is built on consensus. If some parts of the Bitcoin network raise the limit and others don't, the network would be split in two. Having two competing versions of the Bitcoin network running simultaneously would be catastrophic. It would destroy trust in the Bitcoin network, since users could never be sure which transactions were official. And it would likely cause the value of bitcoins — the unit of currency — to plunge, as people questioned whether the network had a future at all.

Having two competing versions of the Bitcoin network running simultaneously would be catastrophic

So this seemingly simple technical decision — whether to boost the Bitcoin network's capacity or not — has divided the Bitcoin community into warring camps. Two prominent Bitcoin developers, Mike Hearn and Gavin Andresen, lead the faction that wants to increase the capacity of the network, and they enjoy the support of well-funded Bitcoin startups such as Coinbase and Bitpay.

Their argument is simple: Bitcoin needs to grow if it's going to become a mainstream technology, and the current limit doesn't leave enough room for growth.

But not everyone agrees with them.

Changing the limit could undermine what makes Bitcoin unique

Opponents of the proposal make two major arguments. One is that increasing the capacity of the network will lead to centralization of the Bitcoin system.

Right now, Bitcoin transactions are processed in a parallel fashion by thousands of computers distributed around the internet. The Bitcoin network is designed in a clever way that prevents anyone from being able to control how it works — at least so long as no one controls a majority of the network's computing power.

But as the volume of transactions has gone up, the number of computers participating in this transaction-processing task has gone down. And some critics worry that boosting the network's capacity will make it more expensive to participate in the process, further reducing the number of computers that participate. That, in turn, could make the system less reliable, or more vulnerable to attempts by governments or others to seize control of the network.

When the Bitcoin network becomes congested, Bitcoin has a system of transaction fees that help bring supply and demand into balance.

Some people want to simply let this mechanism work. They hope this will spur people to develop technical workarounds that allow transactions to be processed in ways that don't burden the primary Bitcoin network.

The rules of the Bitcoin software act as a kind of constitution for the Bitcoin community

Lurking in the background is a larger philosophical disagreement. Bitcoin is built on the promise that many of its rules can never be changed. For example, the rules of Bitcoin say that there will never be more than 21 million bitcoins created. However, that's just a social convention — the people who write the Bitcoin software could decide to increase the rate at which new bitcoins are created so that many more wind up in circulation.

In short, the rules of the Bitcoin software act as a kind of constitution for the Bitcoin community. And critics of raising Bitcoin's transaction limit worry that a hasty increase — or, perhaps, any increase at all — could undermine the public's trust that other aspects of the system won't be modified in the future.

No one knows what will happen next

While increasing the capacity of the Bitcoin network might seem like a minor change, it would be the first change made to the core rules of the Bitcoin network since it was launched in 2009. (Developers quickly fixed a very minor bug that briefly broke the network in 2013.) And there are no established rules for making this kind of change.

As often happens, each side of the argument has developed its preferred talking points. Supporters of the higher limit present it as a matter of common sense. Opponents portray it as a power grab by a handful of prominent developers and deep-pocketed companies. There have been endless debates, proposals, and counterproposals about how to resolve the problem.

Each side accuses the other of endangering the Bitcoin network. Proponents worry that the network will grind to a halt if the limit isn't raised in time. Opponents counter that it's reckless to foist a change on the Bitcoin community before a consensus is reached.

Right now, the most popular Bitcoin software is an open-source project that's managed democratically by a five-person group of developers. Andresen is a member of this group, but he hasn't been able to convince his colleagues to increase the limit. So he and Hearn have created competing software, Bitcoin XT, that supports a higher limit.

Bitcoin XT is programmed so that it won't start supporting a higher transaction limit — breaking compatibility with the older software — until 75 percent of the Bitcoin network (as measured by computing power) adopts the new software. At that point, the other 25 percent of the network will risk being left behind if they don't switch. But we don't know if Hearn and Andresen can convince 75 percent of the network to switch. If they can't, we don't know what will happen next.

Ultimately, how the dispute is resolved may matter more than the specific decision that's reached. If Hearn and Andresen's gambit is successful, it could become a template for resolving future arguments. On the other hand, if Bitcoin XT falls short and the warring camps can't reach a consensus, it could do lasting damage to Bitcoin's reputation.