Heat death of the universe
According to secular physicists, the heat death of the universe is one possible scenario for the final fate of the universe. It speculates that, over time, all energy in the universe will eventually be converted to heat energy, which will then be spread more or less evenly over all space as entropy increases in accordance with the second law of thermodynamics. With all energy so widely distributed, the universe will revert to an extremely cold state, and nowhere will there be a sufficient concentration of energy to sustain any physical activity or movement.
However, the second law of thermodynamics is statistical, so although entropy tends to increase, it can decrease. The reason entropy decrease is not seen in everyday life is because it is much more likely to increase, rather than decrease. Supposing the lifespan universe was infinite, then eventually there would be a point where entropy would decrease to its minimum possible value, and then the universe would effectively start again.