Where can I read more about this? It seems fundamentally wrong to me that growth can continue unabated forever. Apparently I don't understand the system.
Growth forever is a bit of a hard pill to swallow. History shows us that countries don't grow forever. But, eskimospy's point is still correct: a country can deficit spend forever. You can do that even without growth.
Suppose that you had a mortgage for $182,760. Suppose your after tax income was $2517/month ($30,204/year post tax). Suppose you spent a total of $2922/month ($35,064/year post tax). Thus, you are deficit spending month after month because your total payments are more than your total income. You need to borrow another $405 month after month forever. What happens to your debt?
Most people will answer that if you are spending more than you make, then you can't continue it forever. They assume that if you keep borrowing another $405/month that your debt will keep going up and that something will eventually have to give. However, that answer is naive.
The real answer comes down to the type of debt payments you are making. Suppose your mortgage was a new 10-year mortgage and you were paying 2.26% interest. If that is the case, then you are paying $1706/month on your mortgage ($1362 in principal and $344 in interest). Since that $1362 in principal is essentially paying yourself, you actually aren't deficit spending. Lets try the math:
1) This month you owe: $182,760
2) Next month you reduce your debt by $1362 in principal, add $344 in interest, and have to borrow another $405. Now your debt becomes: $182760 - $1362 + $344 + $405 = $182147.
Notice how your total debt went down even though you had a deficit in your spending?
3) Repeat month after month, and your debt keeps going down even though you spend more than you earn each month.
Now multiply all numbers by 100,000,000 and you get exactly the federal government's picture. The US federal government owes $18,276 billion, brings in $2517 billion a month on average, spends $2922 billion, has a lot of 10-year treasuries at today's rate of 2.26%. Theoretically, the US could do this deficit spending forever and the debt would keep dropping. The real problem is that we just aren't spending our deficit on principal and are instead just charging more and more.
It isn't the deficit spending that is the problem, it is that we are deficit spending in a poor way.
Add in growth and the pictures get better for both the mortgage example and the US government. With raises the mortgage gets easier and easier to pay off. With growth and more taxes, the US debt gets easier and easier to pay off.