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I have been reading a lot about this 10 minute block in the Bitcoin network. I'm slightly confused because I thought mining was a somewhat random process, mostly based on how powerful your mining facilities are. So if I had a quantum computer and could really churn through calculations, couldn't I mine a block faster than 10 minutes? Or is there something in the network taht would prevent me from submitting my mined block until 10 minutes had passed since the last mined block?

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Nope, nothing prevents it. The actual time from one block to the next is random, and it very often happens to be less than ten minutes, just by chance.

Ten minutes is the target time. The block difficulty adjusts with the goal of having ten minutes be the average time between blocks. Of course if the average is ten minutes, then you would expect some blocks to be faster and others slower.

  • Can you please share the statistical assumptions of that time? I guess the 10 minutes is a mean right? What is the rule to update the difficulty? – user_Lee Jan 6 '18 at 0:18
  • The time between blocks follows a negative exponential distribution, with mean 10 minutes. – Pieter Wuille Jan 6 '18 at 7:38
  • Where does the difficulty target come from? Is that set by the Bitcoin algorithm, kind of like how the number of Bitcoins given as a reward halves every so often? – Dave Jan 7 '18 at 18:30
  • @Dave: Yes, it's set by the algorithm. It is calculated by a prescribed formula from the timestamps of previous blocks, which provide an estimate on the hash rate of the entire network. – Nate Eldredge Jan 7 '18 at 18:35
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I have been reading a lot about this 10 minute block in the Bitcoin network. I'm slightly confused because I thought mining was a somewhat random process, mostly based on how powerful your mining facilities are.

Correct, and because its random, its theoretically possible to mine the next block within seconds, it could even be the first hash you try. Its just probability, the 10 minutes is the average block time.

So if I had a quantum computer and could really churn through calculations, couldn't I mine a block faster than 10 minutes? Or is there something in the network taht would prevent me from submitting my mined block until 10 minutes had passed since the last mined block?

This is somewhat unrelated to the randomness, because a more powerful computer can try more hashes anyway so is more likely to find a valid block sooner, yes. But this is the purpose of the mining difficulty. The difficulty changes once every 2016 blocks to keep the time roughly 10 minutes average. If blocks are mined too quickly, the difficulty will increase so it again takes 10 minutes on average.

Also note that quantum computers are a very unlikely threat to bitcoin mining. Quantum computers aren't just better at everything, there is quite a lot of hype around them without foundation :)

  • I shoudl have read your answer before I asked my other question to Nate, but I'll ask a follow-up here. You said, "The difficulty changes once every 2016 blocks to keep the time roughly 10 minutes average." So does that mean if the previous 2016 blocks were mined really quickly the difficulty target of the next 2016 blocks would be adjusted to try adn make teh average time of the 4032 (the quickly mined 2016 and the as yet unmined next 2016) most recent blocks mined 10 minutes? – Dave Jan 7 '18 at 18:33
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    @Dave not quite, it would be adjusted so that the next 2016 are mined at 10 minutes average, it wouldn't try and compensate for the quick 2016 – MeshCollider Jan 7 '18 at 20:23
  • But having said that, it is still possible that the next 2016 blocks may be mined in less than 10 minutes on average. Who knows, all the miners got lucky and found the right has quicker. – Suhas Jan 19 '18 at 10:32
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Yes (temporarily), but doing so would require a 51% attack, preferably just after the difficulty has been adjusted (at 51% the mining time for you would be an average of ~9:30 (9 minutes and 30 seconds) until the difficulty change which would happen in about a week in this case or another miner with a relatively small amount of control (2% would be fine, but let's say they have 5%) stops you from centralizing the network like Libra. If you want to do this PERMANENTLY, then (purely theoretically) mine 2^257 (or something like that) hashes per block. That particular number would decrease avg. time to 5 minutes.

  • Mining a block faster than 10 minutes has nothing to do with a 51% attack - blocks are mined faster than 10 minutes all the time – Raghav Sood Jun 26 at 14:09
  • I mean by “block time” average block time over a longer period (like a day in this case), not individual block times. – Number File Jun 26 at 14:11
  • Again, that has happened several times in the past, usually when someone brings a large chunk of mining power online quickly, before a difficulty adjustment period has completed - it does not require a single entity to have more than 51% of the hashrate, only for the average hashrate to be greater than the previous difficulty adjustment period had estimated – Raghav Sood Jun 26 at 14:13
  • I mean by my answer not just the entire network, but a single entity and the network. – Number File Jun 26 at 14:15

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