Ahhh ok, so the diff doesn't always increase then?
The reason I ask is because back in the early days (as I've read) you could mine a block with a laptop. The difficulty has increased to a point now which has made that impossible. But what you're saying is that in theory it could go right down at some point in the future?
No, difficultly only increases if the miners add more hashing power to the network.
So for example, if a miner adds new tech that increases their hashing ability so that they
can do 2x more work than previously, then they will potentially find blocks 2x faster than
prior. When this happens, blocks will be found faster than the 10 minute average, maybe
every 8 to 9 minutes for example. When the next difficultly adjustment arrives (every 2016
blocks) the network will see that blocks are found faster than the 10 minute average and will
increase the difficultly for the next 2016 blocks. Likewise, if miners turn off their hashing
power during this difficultly term, at the next adjustment the difficultly may go down.
Yes, in theory, difficultly could go down to such a point that home PCs could mine again.
It is not very likely since many people will push the difficultly back up and they will form
pools again, and be back to where we are now over time, but yes in theory it could happen.