<deleted> you. I'm a scientist. Why do you want to murder me? Halving the population is simplistic. Which part of the population has to die or not get to live? Addressing population size through birthrates will kill your society in about 3 generations, ie China. The main challenge of population growth is food, or energy demand. Between 0 and 15 years, a child requires 26 million kcal. We can further model that by age; a baby has a lower calorific requirement than a 15 year old. But both are nothing but consumers. But they will both become producers. Assuming death at 90 years, a 65 year old will consume 19 million kcal. They will always be a consumer. Adulthood has a cost of 44 million kcal. Assuming arable agriculture, then about 9 quadrillion kcal is produced each year. Based on the current global population mix, annual demand is about 6.6 quadrillion kcal. There is not that much slack. If we address population size by reducing the number of young people, through birth control, then eventually you will see falls in agricultural outputs because there are less farmers. Countries get away with that right now because there is always another country with more farmers, hence China massively imports soy from predominantly catholic, and fecking like bunnies, Brazil. Otherwise, you get away with it for a while by artificially boosting yields through fertilisers (but blokes like you want to murder the scientists, so you're going to run out of new fertilizers, pesticides, genetically improved crops). Eventually you won't be able to innovate through mechanisations, because your best engineers are all retired and your pool of would be engineers (kids) has declined. So the alternative is that other part of the non-productive population, the old. We only keep them alive out of sentimentality, and all they do is cost us money and food. And they feel entitled to do that. If you have to murder anyone to solve demands due to population growth, kill the old, not the scientists. Soylent Green was right. Here's a thought experiment. Assume improvement to crop yields is elastic; that there is no upper constraint due to technological innovation, and that all the innovation is carried out by 15-65 year olds. In this version of Logan's Run, you get to live to 70 years, before being topped (solving worries about pensions etc, eliminating the vast majority of chronic healthcare). Then the population is not constrained by food supply. We won't starve. But water becomes the next limiter. If we consider water' we can make it, using extraterrestrial material, but probably the planet could sustain 30-40 billion before things become problematic again, maybe even 50 billion. By then, we will collectively ascend to the next energy plain. If technological progress is allowed to remain indefinitely elastic, population itself may cease to have a conventional "carrying capacity". The limiting factor becomes the amount of energy and technology available to manufacture an increasingly artificial environment. In other words, the question has moved from "How many people can Earth feed?" to "How many people can an industrial civilisation maintain?" But don't kill the scientists, so you can live a life of religious fanaticism, ISIS style.
