San Francisco: Tesla and SpaceX CEO Elon Musk has slammed the United Nations (UN) once again, saying that there are "not enough people" in the world and one should be more worried about population collapse. In a latest tweet, Musk posted, "UN projections are utter nonsense. Just multiply last year's births by life expectancy. Given downward trend in birth rate, that is best case unless reversed." https:\/\/twitter.com\/elonmusk\/status\/1483485798548840450?s21 "We should be much more worried about population collapse," Musk wrote. https:\/\/twitter.com\/elonmusk\/status\/1483484932961972227?s21 Musk said that if there aren't enough people for Earth, "then there definitely won't be enough for Mars." The SpaceX CEO's theory believes that when an increasingly-elderly global population clashes with declining birth rates around the world in the near future a 'population bomb' would go off. Musk first broached the topic back in 2017 when Musk replied to a publication saying, "The world's population is accelerating towards collapse, but few seem to notice or care." Tim Peake, a British astronaut earlier said that Musk's prestigious SpaceX project could accelerate time to help man walk on Mars in just another 20 years or so by 2040.