Twenty billion years from now, Earth will be a frozen rock orbiting a dead star in total darkness—but only if it survives being swallowed by our dying Sun first.
The planet will bear no resemblance to the blue marble it is today, having been sterilized, scorched, and finally plunged into a deep freeze over a vast timeline.
Long before that 20-billion-year mark, the solar system will be violently reshaped. In about one billion years, the aging Sun will become roughly 10 percent brighter, increasing temperatures enough to boil Earth’s oceans and extinguish all life. Four billion years later, the Sun will exhaust the hydrogen fuel in its core and swell into a red giant. Its outer atmosphere will expand past Earth's current orbit, consuming Mercury and Venus. Earth’s fate during this phase is a coin toss: tidal forces might drag it inward to be vaporized, or the Sun’s loss of mass could push the planet into a slightly wider, safe orbit.
Assuming Earth escapes incineration, it will witness the Sun shed its outer layers into a glowing planetary nebula. What remains of the Sun will be a white dwarf—a hyper-dense sphere of carbon and oxygen about the size of Earth, holding roughly half the Sun's original mass.
Over the next 12 billion years, leading up to the 20-billion-year mark, this white dwarf will slowly radiate its residual heat into the void. It will cool from a brilliant white to a dull yellow, then to red, and finally into a dim infrared ember. Earth will be locked in a permanent, airless deep freeze, hovering just degrees above absolute zero. The night sky above this dead world will also look entirely different; the Milky Way and Andromeda galaxies will have long since merged into a single elliptical galaxy. Due to the accelerated expansion of the universe, almost all other galaxies will have receded past the cosmic horizon, leaving an immense, dark void beyond our immediate galactic neighborhood.