Why does bitcoin difficulty have to go up every 2 weeks?

[bitcoin talk]

Why does bitcoin difficulty have to go up a notch every 2 weeks?

[HCP]

It doesn't... The difficulty "adjustment" can go both ways... that is to say, it can actually go up OR it can go down.

The reason for this is to keep the "average" block time to 10 minutes. If more hashing power is brought online (ie. more miners), then chances are blocks will be found quicker and the average block time drops below 10 minutes... to counter this, the difficulty is increased.

However, if a chunk of the hashing power disappears (ie. some miners suddenly shift their hashing power to another chain because it is more profitable), then the average block time is likely to rise above 10 minutes... to counter this, the difficulty will be decreased.

It works on 14 day cycles because #reasons... I think 14 days was done as a "happy medium" whereby we can avoid miners trying to "game" the difficulty by taking hash power offline to lower the difficulty and then putting it all back online again so they can miner blocks faster and get more rewards etc... to do this on a 14 day cycle, miners would have to take their hash power offline for too long of a time to get the difficulty to drop... but 14 days is not tooo long to wait if the difficulty really is too high and needs to be lowered to get the block time back towards 10 minutes.

[chimcoin]

Your point is very correct and let me add that as the price of bitcoin increases, the number of people who can make a profit mining increases. That encourages more participation in securing the network, which results in the need for a difficulty increase. As these next generation of bitcoin miners come online, it is expected that the difficulty will continue to counteract the additional hash rate in the network.

[bitcoin talk]

The reason for this is to keep the "average" block time to 10 minutes. If more hashing power is brought online (ie. more miners), then chances are blocks will be found quicker and the average block time drops below 10 minutes... to counter this, the difficulty is increased.

Why does the block always need to hover around the 10 minute mark?Why not 5 minute or 15 minute etc?What is unique about the 10 minute mark that it must stay there?

[DannyHamilton]

Why does the block always need to hover around the 10 minute mark?Why not 5 minute or 15 minute etc?What is unique about the 10 minute mark that it must stay there?

That's the time that Satoshi chose when he created bitcoins.

It is fast enough that the currency is usable, but slow enough to reduce the orphan rate and give the blocks time to propagate to poorly connected nodes.

Once the time was chosen, any change to the time requires a hard fork.  People aren't going to want to accept a hard fork without a VERY good reason, and changing the average time between blocks is not a very good reason.

[slate_main]

Also supply and demand, the more demand, the less BTC there will be and thus price should increase... this is also a factor with Bitcoin 'halving', which is not actually a half, you can read more about that elsewhere if you should wish.