The title says it all. This episode is all about the Earth being stolen right out of orbit and out of the universe. Just imagine, if you were in a space above the planet, hearing "The Earth is gone!" and seeing nothing where your home planet used to be.
But how could that happen? How is that even possible?
In theory, it is possible but certainly not by human action (but then again it was not human action on the show). To occur naturally, an asteroid of large enough mass would need to pass by the Earth to pull just a small bit out of orbit and then the Earth would slowly move away from the Sun (if pulled in that direction).
But in this episode the entire planet is moved quite far, and quite quickly. Even though that itself is impossible, the Earth would never survive without the Sun and Moon.
Without the Sun, temperatures would plummet, daylight would cease to exist and humanity would only have a little while left to exist. All celestial objects in orbit around the Sun move fast enough to be in a constant state of free-fall towards it. That means that if the planets were to suddenly stop moving, they would immediately be pulled towards the Sun and fall into it. If the Sun were to disappear, anything orbiting it-planets,asteroids,comets,etc.- would retain its forward motion and, rather than fall towards the now nonexistent Sun, they would each fly off in a straight line into space. Think of it like a ball on string swung in a circular above your head. If let go of the string the ball flies off in a straight, tangent line from the last point it was at in the circular motion. That is essentially what anything orbiting the sun- if it disappeared- would do it as it they would all lack the central force holding them in orbit.
Well, that's all for now. Thanks for stopping by!