The poem begins as a list, and the list keeps growing. It starts with humans, notes that our relatives the Neanderthals are already gone, and then widens to all life on Earth, then to life in the galaxy, and eventually to every star, every black hole, and every universe. Each step makes the loss bigger, until the poem reaches the largest scale it can imagine.
Then the form changes. The list stops, and the speaker asks a question about when the "clock of entropy" will freeze in the "cold of heat death." The question keeps breaking apart and repeating, as if the speaker is stalling or struggling to say it. The answer, when it comes, is a plain loop: the clock stops when it stops.
The mood is calm but chilling. The speaker doesn't panic or mourn loudly. Instead, the flat, matter-of-fact tone, along with small touches like the "(2?)" that admits uncertainty about the multiverse, makes the scale of the ending feel even more overwhelming.