Stephen Hawking,a few years ago, was asked his opinion on the future of mankind. His answer was he felt human existence on this earth had 100 to 150 years and we’re done because the planet’s resources are already strained. Population was 4 billion fifty years ago and is approaching DOUBLE that now. No way this earth can handle 30 billion people
Certainly not impossible, and I'm not as smart as Stephen Hawking, but 100-150 years seems VERY short to me.
Malthus famously predicted this 200+ years ago but he's been spectacularly wrong... so far. Population has grown fast, but production has grown even faster. Maybe that can't continue forever and we'll eventually hit diminishing returns, but I don't see any obvious technological or logistical reasons why that should be imminent.