Quote from: TheRealSteve on September 16, 2015, 10:20:18 AM

Quote from: speedt_ouch on September 16, 2015, 09:10:19 AM

Cant the difficulty go down?

Yes. The difficulty adjusts up or down depending on whether blocks are being found faster or slower than the intended rate (2016 blocks every 2 weeks). See: https://en.bitcoin.it/wiki/Target

It adjusts once every 2016 blocks.

If the hashrate is cut in half, this would mean up to 2016 blocks that would take 20 min to mine, so up to a month to the next diff, and this would effectively cut the daily profitability in half for miners, which could decide more miners to pull the (electric) plug, resulting in a cascade effect.

Also the bitcoin difficulty adjusts by no more than a factor four, in your hypothetical 330 PH to 330 MH case f.i., it would thus take 10 difficulty adjustments (4^10 approx equal to 1e6) for the difficulty to adjust back to 10 minutes blocks (without a hard fork), or 20160 blocks. If the block erupter is alone, it just would never be able to get through those 20160 blocks in any reasonable timeframe.

This is actually something that altcoins have been facing for a while (because of multipools jumping in & out), and the reason why fast difficulty adjustments have become standard in altcoins, with retargets every block.

Also since the mining hardware would still physically exist, a lower diff bitcoin would become easy prey to a 51% attack.

So it's far from a mental exercice.