What is the ideal population level? Please include statistical analysis to back up your conclusion based on sustainable resource use contrasted with an aging population and medical expenses related to increased lifespan.
It all theories now, but I read 9 billion. So without scientific advancements that is 2050 for 1/3rd of pop with a shortage of food. Scientists are working on solutions though. If you what stats google is your friend, many scientific papers and reports out there.