Basically, in physics, the arrow of time comes from entropy. The second law of thermodynamics states entropy only goes up, which means disorder in the Universe only goes up, which means concentrated free energy only goes down. If you look at living things (humans, plants, civilizations, what have you) these systems are locally reversing entropy. Humans locally reverse entropy because we have action.
In that death, there’s no concentrated energy, and everything is at the same energy level. Therefore, we’re all one thing. We’re essentially indistinguishable.
What we do as living systems accelerates getting to that state. The more complex system you create, whether it’s through computers, civilization, art, mathematics, or creating a family—you actually accelerate the heat death of the Universe. You’re pushing us towards this point where we end up as one thing.