Somebody on Reddit proposed to solve overpopulation by shipping people to Mars. He reasoned that the cost for space transportation is expected to go down by a lot, with SpaceX pioneering reusability and novel concepts. While this is certainly true, I’m afraid overpopulation cannot be solved this way. Here’s why:

Ok, let’s say it’s the year 2050. We have  more than 10bn people on Earth. Maybe population growth is slowing down, going into reverse around the year 2100, which the UN seems to think will happen.

Let’s further say, we’d like to ship 5bn people to Mars, so that both planets have a population of 5bn each, which seems pretty reasonable.

For the sake of simplicity, let’s just assume that half of humankind would actually chose to go to Mars.

Now, let’s do the math to figure how many BFR/BFS flights, each carrying a 100 people, would be required to ship 5bn people to Mars. It’s 50 million. Fifty million BFR/BFS launches. Let that number sink in. Then try it with different values — maybe future BFR/BFS versions can carry a 1000 instead of a hundred people; and maybe it’s enough to ship 2bn people off planet to make an ecological impact. Run the numbers again. Let them sink in again.

I estimate that the whole of Earth would have to be turned into an operation that does nothing else but BFR/BFS launches for hundreds, if not thousands of years. I would furthermore estimate that the population on Mars, while constantly growing, would still be hard pressed to construct infrastructure accomodating 5bn people in a sensible timeframe. On that scale, with that many people coming, terraforming of Mars is inevitable; but we don’t have a plan for that yet, just some wild ideas. We don’t have a testcase or proof of concept. We just don’t know what will work, and won’t know until we’ve done it. Which may take thousands or even tens of thousands of years. We don’t know.

And I’ve not even talked about the ecological damage millions upon millions of rocket launches/landings during hundreds of years will do to both planets.

To maybe get around all those problems and make your plan work, we’d have to build two thousand space elevators: a thousand here, on Earth, another thousand on Mars. We don’t have a single one yet, don’t have the technology yet, and will very likely not get there anytime soon. Additionally, we’d need a large fleet of interplanetary vessels that don’t land on planetary surfaces at all.

I am not saying your idea is impossible in principle. What I’m saying is that it’s prohibitively impractical. And I’m saying that as someone who would do just about anything to live on Mars (but I won’t do that).

No. The overpopulation problem, if it is a problem at all, must be addressed right here, on Earth.