What would happen to the earth if it suddenly doubles in size? Would the opposite happen if it suddenly shrinks to half it size too? Would it fly out of orbit? The climate would be thrown out of order, but would anything still be able to survive?

Double in size? It'd take twice as long to get anywhere but, at least, there'd be plenty of room for the population.

Halve in size? Instant global war while the mega-nations sought to grab whatever land was available for their people. Those people who weren't killed off in the war would probably find they'd gained very little because much of Mini-Earth would by then be a nuclear wasteland.