And G‑d said to Moses: "Stretch out your hand towards heaven, that there shall be darkness over the land of Egypt; palpable darkness"

Exodus 10:21

Darkness, by definition, is merely an absence of light. But darkness can be so heavy that it is palpable. In Egypt, the darkness grew "thick as a coin" so that "no man could move from his place for three days."

"There are three types of darkness," writes Rabbeinu Bachayei in his commentary on Torah. "There is the obscuring darkness (alatah) of the Covenant Between the Pieces (in which the exile of Israel was foretold to Abraham — see Genesis 15:17); there is the palpable darkness (afeila) of the ninth plague in Egypt; and there is the shimmering darkness (araphel) at the Giving of the Torah, where it is written 'And Moses drew near to the darkness, where G‑d was' (Exodus 20:18)."

Darkness is nothing. But darkness is a force. It is the force of nothingness, the most powerful force in nature. Existence, as G‑d created it, has an insatiable lust for being, for presence, for life. Create an absence, and the vacuum will fill itself with a ferociousness that no "active" force can match.

In 1977, the Lubavitcher Rebbe suffered a heart attack in the midst of the joyous celebration of the Shemini Atzeret festival. For the first time in decades, his chassidim danced with the Torah scrolls on Simchat Torah without their Rebbe. The glaring absence wrenched every chassid's heart: we danced and wept, wept and danced. The Rebbe, who was being treated in his study, watched one of the attending physicians draw a blood sample with a syringe, and sent the following message to his disciples: a syringe creates a vacuum, which forces the emptied space to fill with blood; so, too, every absence is but a force to draw greater vigor and life into the emptied space.

Darkness is nothing. Its nothingness is what makes it so alien, so paralyzing, and — ultimately — a place of infinite potential and the force to bring it to fruition.