Schrödinger's panties is derived from the term "Schrödinger's cat thought experiment" by physicist Erwin Schrödinger in 1935, the latter describes a hypothetical experiment that probes a parody in quantum physics.
The former term is coined in eastern Otaku culture which refers to situations where heroines wearing skirts in anime, video games or movies could never, under any circumstances (in the virtual world) reveal their underwear due to obvious moral reasons (in the real-world); resulting in almost impossible looking situations (in the virtual world) that are not probable even under the best luck of the heroine. Typical scenarios include heroine performing kung-fu style fighting moves (e.g. roundhorse kick, Butterfly kick), jumping and high wind situations (falling down).
As with "Schrödinger's cat thought experiment", the "Schrödinger's panties thought experiment", being a parody, states that as long as the bottom of the heroine is not observed, the statements that the heroine is and isn't wearing panties are both true and valid. Under physical terms, both situation are in a state of superposition. The reality only settles after observation.
While Schrödinger's panties refers the situation described above, the term iron curtain refers to the impenetrable skirt that makes the impossible possible.
(Watching an anime where a heroine with mini skirt jumps 50 metres down from high ground and perform a reverse somersault attack on a bad guy without any pantie flashing fan service)
Audience: Wow holy Schrödinger's panties! iron curtain! look at that, there's *%^$ no way the skirt will hold up.
An example is the character Athena in King of Fighters 12. Under any in-game frames and fighting moves, the following is true. The skirt of Athena is just long enough and moves of the heroine and the movement of the skirt are just right to not to reveal what is underneath.