Because we still have not the slightest idea of how to “create gravity” aside from a planet-sized mass. You can spin your spaceship to get some sort of force, but that’s impractical.

Scientists thought of this idea over 70 years ago. Generally, if you ask some question like, “Why haven’t scientists thought of X?” then the answer is, “You are the most brilliant human, have a Nobel Prize,” but “They did, generations ago.”

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