Fission, the breaking apart of molecules, however, can be caused without heat. The process of freezing fractures and randomizes. When the sun dies, the earth's core will cool until there is no more lava to patch the cracks and earth will fracture into smaller pieces. Gravity, however, will become more powerful as the universe cools and matter fragments into the fine layer of energy predicted by randomization. We don't worry about the moon's orbit degrading into the earth, or the earth's into the sun, because there is sufficient mass from the smaller opposing body to keep its orbit in space.
Gravity holds together a universe whose size boggles the mind.
It is might be possible for gravity, when the suns die and matter freezes, fractures and becomes fine enough, to slowly wind everything back into a cold dense ball of matter and start the process of creation all over again. The inevitable question at this point, does all the matter in the universe have to freeze and fracture in order to create the Big Crunch that starts the universe burning and fusing again. In 1965 two American physicists, Arno Penzias and Robert Wilson were testing a very sensitive microwave detector when they discovered there are microwaves that bombard the earth that do not appear to be coming from any particular centered direction. These microwaves come in from the edges of the universe as well as from the center. Penzias and Wilson were awarded the Nobel Prize in 1978.