It doesn’t exist in real life. In science fiction, it’s often used to hand wave how a spaceship can speed up significantly in seconds without everyone and everything inside being splattered against the back wall.
In real life, astronauts train to survive up to around 10 g’s of force due to inertia. The space craft can’t reasonably accelerate any faster without endangering the astronauts inside. And while it may seem fast, it would take a very long time to reach a significant portion of light speed.
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