Mining: what is the lowest possible target? Could it be a block hash of all zeros?
The retargeting every 2016 blocks is computed as follows:


previous_target * (T2-T1) / (20160 minutes)


Where:


T2: timestamp of previous block
T1: timestamp of block at current height - 2016
Target adjustment bounded to factor 4


Ignoring the target adjustment limit: For the resulting target to be zero, T2-T1 would need to equal zero. That would require an infinite amount of hash-rate. Therefore we can approach your scenario, but never reach it.