
click to enlarge
There are two major assumptions that the scenario of heat death is based upon.
1. Arrow of Time
To physicists, time is a four-dimensional block with three components in space and one in time. Time has one direction that always points from past to present, like an arrow. To see more on this and learn about the philosophical and physical implications involved, you may wish to read Bright Hub's What is Time?.
2. The Universe is Finite and Isolated
The universe is not infinite. It is closed in space and time, and is an isolated system. This means there will be no energy

click to enlarge
exchanges with other systems and there will be no new sources of energy, ever. There will never be any outside intervention from anything or anyone that will share energy with us. Not from aliens, not from
wormholes, not from
white holes, and certainly not from a Supreme Being.