[quote="Garyjohn2, post:10, topic:234358"]
This is a tough one to counter! However, it doesn't take into account technological advances, with can reduce the amount of resources required to live, increase the amount of resources we have, or change the resources we use entirely. Genius inventors, engineers, and scientists are the ones that can make these changes. The more people that are born, the greater the chance a genius will be created and invent something great.
Also, there are 8 billion people in the world now. What if the limit is 20 billion? What if it is 500 billion? By the time we reach 500 billion people, we could be colonizing other planets. It would take a long, long time, and a lot could change by then.
Also, populations don't always grow at the same rate. In the animal kingdom, once a species reaches a certain population density, the growth of population tapers off. This can happen (and is happening) in many ways. This last point can be discussed a lot, and might require a whole different thread! (for example, as women become more educated, they have less children on average (for better or worse), also as food becomes more scarce, less people can live, meaning we don't have to manage our own population because it will manage itself (for better or worse) among other things!) This last point doesn't seem to desireable...but the catch is we don't know the population limit, or if there is one. Artificially limiting human population growth before we hit our true population potential could handicap the human race, in effect.
There definitely is a limit, assuming human life remains uniplanetary.
The Earth has a finite mass, and only a very small part of that mass is available to biological life, and only a very small fraction of THAT can be converted into human bodies. Also, only a small proportion of its energy flow can be channeled into that conversion.
Now, if human life gets serious about space expansion, all bets MIGHT be off. But it might still prove impossible for the human body to live full-time in space, in which case, we would face a final limit in numbers, though it might not be discovered for centuries.