Stine and Teit, your average urban middle-class artists and intellectuals, leave Copenhagen for the wilds of neighbouring Sweden’s forest. Soon, they find out that something is strange there – most disturbingly – when their son Nemo suddenly thinks his mother isn’t really his mother anymore. It becomes clear once Stine and Teit discover that they have neighbours who look exactly like them – mirror images made flesh and blood.
The subject of reflections and doubles is introduced in the film’s first shot: a view of a lake landscape turned 90° so that the water’s surface runs vertically through the image’s centre. Only once the shot gets tilted is it revealed which side mirrors which. Later, a mother and child are reflected in a glass door.
However, this is not your doppelganger thriller of the gothic variety. Note the title: in physics, superposition means (per Merriam-Webster) "the combination of two distinct physical phenomena of the same type (such as spin or wavelength) so that they coexist as part of the same event". This is more a metaphysical meditation towards the realisation that none of us is ever alone, but also never unique.