I’m writing a short story where a species of aliens wipe out all life they encounter because they see life as a threat since it accelerates entropy. However, many of the methods used for destruction, like atom bombs, lasers, etc, are horribly inefficient entropy wise. What would be the best way to wipe out all life on earth in an entropy friendly way?
Turn down the sun
Your aliens add material to the sun intended to quench fusion. Less fusion slows down entropy. It has the added benefit of chilling the planets and stopping life processes.
If the aliens do not have the tech to quench a star, they could just insert an object to shade the earth, perhaps at the L1 Lagrange point or in a tight interior orbit around the star. Large flat sheets would work. Shade will cool the earth down. Possibly deep Earth life might still persist, warmed by the Earths inner heat. Surface life will freeze.
Make a virus that kills all living organisms.
An advanced, interstellar civilization probably has powerful enough computers to quickly build a virus that can kill everyone they want dead.
Have it lie dormant for a few months of years while it spreads, and then trigger at a particular time.
Just drop it down, and a few kilos of package can quickly spread to kill everyone.