Unemployment solved: 20-hour work week

While watching yet another presidential candidate promise how he would stimulate the economy to create more jobs, I found myself wondering why nobody is talking about an obvious solution: restricting the supply of labor by cutting the working hours.
 
Given the current productivity levels and 5 billion people of working age on the planet, it does not seem possible to give everyone a 40-hours/week job doing something useful.  There is a precedent for reducing working hours.  We went from 70 or more to 40 a while ago.  We also eliminated child labor.  Was it a coincidence that real wages went up and the middle class got created since then? 

Why is 20-hour work week a bad idea, or a good one?

>>37
So you want to give people more free time, but they can't enjoy it due to having no excess income?
So we can either have a 20 hour week and eliminate war or have a 40 hour week and stay at war? I propose reasonable solutions that have been tried before and haven't been repeatedly debunked like yours.
These liberal, economically illiterate shit stains are the same ones that believe in taking away people's guns. Hitler, Stalin and Mao were all leftists, so no I would not vote for them.
Warren Buffett does not want to pay more taxes, he makes all of his money via capital gains, he wants other people to pay more taxes. He's also old and has more money than he can possibly spend before he dies. There are plenty of rich people that I'm sure would disagree with him, yet you only reference him? He can be wrong you know.