Sabine Hossenfelder, a theoretical physicist (she did a doctoral thesis on black hole production) and a prolific science popularizer, discussed in her blog recently whether physicists have any good reason to posit the existence of "dark energy." About the turn of the millennium, physicists determined that the expansion of the universe is accelerating. They didn't know why, so they proposed a "dark (otherwise unobservable) energy" that was driving this acceleration. There is a key paper by Chevalier and Polarski in the International Journal of Modern Physics from 2001. But the simple idea, once postulated, didn't stay simple. Theorists were soon explaining why dark energy has to be understood to be "evolving," and competing scenarios for that evolution themselves evolved. Now quite recently, a group of mathematicians have looked at the numbers and have decided that this work may all have been a wild goose chase. There need be no dark energy ...
The Parthians were the folks who ran a large part of what we now call Iran as the Hellenistic kingdom in the region, the Seleucids, was fading away. The Parthians were known for a trick they perfected in heated battles, when it was necessary for some part of their line to make a retreat. They learned to fire a terrible volley of arrows in one direction while moving in the other -- creating what later writers would call a "covering fire" that kept their foes at bay while they could re-organize. This sort of volley became known for a long time as a "Parthian shot," although in English that got simplified and dumbed down over time into ... "parting shot."