The Tiferes Shlomo wonders how G-d can instruct Moshe to bring about the plague of darkness by raising his hands above the sky, “Netei es yadcha al ha’shamayim”. Obviously, one cannot lift one’s hands above the sky - the text must be a metaphor; what does it mean to convey?
The Radomker begins his answer by analyzing a perek in Tehillim which we include in Pesukei d’Zimra each morning: “Halilu es Hashem min hashamayim… v’hamayim asher m’al l’shamayim…” What are these “waters above the Heavens” which sing to G-d? The Radmonsker has a beautiful approach, but perhaps the question can be addressed using the Koidenover’s shalosh seudos torah. Recall that the Igra d’Kallah taught that “hamayim” is a contraction of two questions: “mi” and “mah”, the questions of “who am I” and “what is my obligation in the world”, which allow man to pierce the veil of nature and recognize that Havaya, the boundless light of G-d, is one and the same as teva, the laws of nature which seem to have their own independent reign. The praises of G-d are sung by all of nature, up to the greatest heights of the Heavens and the Angels which inhabit it. But there is an even higher praise of G-d we can sing. This is “hamayim”, when we see creation using “mi” and “mah”, which stands "m'al hashamayim", transcending even the physical heavens.
Darkness and light represent the forces of good and evil which are all mixed up in our topsy-turvy world. Hashem disperses hashpa'ah to all because there are no pure tzadikim who deserve it to the exclusion of pure reshaim who do not. It's is up to us to straighten things out so the good can get what they deserve and l'havdil, evil gets its downfall. If we extend our hand and reach “al hashamayim”, above the constraints of teva, by asking "mi" and "mah", meaning we rise above our own selfish constraining nature, then we will have exclusive rights to enjoy the ohr Hashem while Mitzrayim remain in darkness.
It's still a bit of a strange expression - why place the focus on raising one's hand, "yadcha"? Perhaps more to say on this down the road...