Network hash must grow at least at the rate of Moore's Law. This is also known as Sweft's Law. If Bitcoin fails to satisfy this condition, then it will be prone to attack.
Why wouldn't hashrate grow according to Moore's law. If hardware performance increases in hashrate per $, everything else being equal, why wouldn't the bitcoin network hashrate increase accordingly and Sweft's Law be satisfied?
There will always be new miners entering the game with new up-to-date hardware (or existing miners upgrading) and old rigs will drop out, keeping bitcoin hashing equipment up-to-speed with moore's law.
An explanation of Sweft's Law for those having trouble understanding it.
Moore's Law states that the number of transistors doubles every two years.
This means two years from now, the cost of the network (hash / ($ / hash)), given equivalent hash, will be half.
And half in another two years. And half in another 4 years.
That means in 6 years it will take 1/8th the amount of capital to replicate the original hash.
Thus, the network must grow at the rate of Moore's Law to sustain the value of its hash so that the value to replicate the original hash does not decrease.
That means that the network must double its hash every two years.
Every two years there has to be a capital investment equivalent to the cost of network hash / 2 to double the hash in accordance with Sweft's Law.
But then we also have to calculate electricity costs, which i will do later.
I don't get it... bitcon network hashrate could just increase forever. what's the problem with that?