It almost always takes less energy to build on something that already exists than to create something new. We'll need to create new systems to solve these problems, but we can take inspiration from what has worked in the past. If you have an idea, look to the past for when it has been tried before.
It helps that systems in the past often carried fewer inherent externalities and were more efficient in energetic terms.
A homeless man comes into a greasy diner. He's hungry. Hamburger? $5. He doesn't have $5 dollars.
It's a time-honored legend that those who can't pay for food may -- at the establishment's prerogative -- work for their food. In some cultures and even in some establishments in the US, this is still the case. He gets the hamburger, the establishment gets clean floors or peeled potatoes.
The trouble with this model is that letting random people into the kitchen may violent health and safety standards, and there may not actually be any work for someone to do. Furthermore, this doesn't really hold up if a significant proportion of your customers are asking to wash the floors in exchange for hamburgers.
The equation changes significantly if the food in the restaurant is coming from close nearby. There might be a significant amount of work for a very large number of people, depending on how much food is being grown and consumed.
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