I would argue that the exponential increase in population in the 20th century was a "bubble", explained by the discovery of antibiotics and other advances in me

I would argue that the exponential increase in population in the 20th century was a "bubble", explained by the discovery of antibiotics and other advances in medicine. People that were not expected to live past the life expectancy (which was 40 years or so) lived on, thus overlapping with the next generations. If there won't be any other similar breakthroughs in medicine, I don't think the exponential growth can last much longer, people will be born and die in a more predictable pattern.