I will wake you up from your dream, mining is totally no waste of energy and not useless. Mining is not just to solve mathematical problems, but to secure the network, this is called proof of work.

To explain it simple: miners are creating a password that is so strong that the network with all its computing power can crack it in about ten minutes. This means that to hack the Bitcoin network you need at least the same computing power as all the miners together, this is impossible for a single entity.

There is more behind Bitcoin than only a simple payment system. Because governments and banks have control over the money supply they can censor and exclude people and are able to make giant wars (through inflation).

Beside that 4 billion people on earth who could be productive can't make anything of their life because they are totally cut off from the financial system and when they manage to be productive they first have to work up to the inflation of the petro dollar before they can make any progress.
Billions of people every day are suffering from hunger and war.

The US dollar is the thing that enables all this suffering to enrich the less than 1%. Bitcoin will compete with the USD and give all these people a chance to involve in global trade and build up something without being knocked down by inflation.

How much energy you think is 'burned' every day by tanks and F16's in all the wars to protect the petro dollar (not even talking about the victims) and how much energy can get saved when all the centralized trust institutions disappear?

Also bitcoin miners are becoming extremely rich and alternative energy sources and energy efficiency will increase their profits. Miners will profit by better energy sources while current energy companies will lose on it (they are heavily invested in fossil energy sources. Miners will allocate their wealth to forse a break through!)

Humanity will be way better off with a decentralized payment system, all the sanctions, exclusions, inflation ect. will disappear. Beside that peace will come back because inflation the only way to mobilize a huge military as USA uses to terrorize the world. Every other payment system outside the control of govs and banks should be already be shut down, so proof of work is the only way to go.

BTW quantum computers are no problem, hundreds of devs are watching the network constantly. There is code already to make BTC resistant and when an attack occurs a hardfork will implement it immediately with full consensus.