Physicists say that the universe is expanding. However, they hotly debate (OK, pun intended as a foreshadowing device) if the rate of expansion is sufficient to overcome gravity—called escape velocity. It may seem like an arcane topic, but the consequences are dire either way. If the rate of expansion is too low, then it will get slower and slower until expansion stops entirely, then finally, begin collapsing again in a Big Crunch. That’s bad enough. But the other possible fate of the universe is even worse. If the expansion is fast enough, then the universe will keep expanding forever. Things will get colder and colder, until the state called the heat death occurs.

If only economics had similarly vigorous controversies. It faces its own existential problems. For example, there is an analogous concept to heat death in the economics universe. Will credit continue to grow, and with it the economy? Or will some force—or law of economics—prevent slow and stop it?

There is a force that can cause the heat death of the economic universe. It is not the moralizing argument that faults man for the sin of wanting more material comfort, and condemns his desire for growth as hubris.

Everyone needs growth. Even the environmentalists couch their anti-growth policies. They want us to stop using energy, but cannot openly promote energy poverty as an ideal. So they talk in terms of sustainability.

Sustainability is an interest concept. For a process or system to be sustainable, it means that there is no reason why it cannot continue indefinitely (well at least until the sun goes red giant and engulfs the Earth, which may not happen because before that our galaxy is on a collision course with the Andromeda galaxy…)

Well, is our economy and its monetary system sustainable? How do you even approach this question in a rigorous way?

We submit one fact for your consideration. To service debt, you must generate income. If you fail to pay at least the interest when due, then the creditors suffer big losses. This impairs their capacity and appetite to lend to others, which suffocates businesses who need capital to expand. So the key is generating enough income to pay interest. We would add on top of that the need to amortize the principal too.

The analogy to heat death of the universe is a pretty good fit. Physicists are not looking at one probe that is moving out of the solar system and will chill down to near absolute zero when its power supply runs out of juice. Nor one object, such as Pluto. They are looking at the universe and all entities in it including all stars and all life on all planets.

Similarly, we as economists must look at the economic universe and all business enterprises and people in it. If one business is stranded with, e.g. an obsolete product such as mobile phone that can only do voice calls, it will fail and default on its debts. That is not under question. The question is: can it happen to the entire economy? If it does, then the monetary system will fall and everyone will lose their savings.

If it can happen what are the circumstances?

So far, we said income (that is net income, after cost of goods sold and all other expenses) must exceed debt service. And, perhaps including debt amortization.