In this scenario, since the lengths of the sides of the similar figure are twice the lengths of the corresponding sides of the original figure, the transformation that must occur is a dilation.
Dilation is a type of transformation that alters the size of a figure while maintaining its shape and proportionality. In this case, a dilation with a scale factor of 2 would increase the lengths of all sides of the original figure to twice their original lengths, resulting in a similar figure.
So the correct response is:
dilation