In an unimaginably distant future, approximately 1 sextillion years from now, the Earth's orbit, if it could possibly still exist within the remnants of our Solar System, would ultimately decay due to gravitational radiation, causing it to collide with what remains of the Sun.
The Vastness of Time: 1 Sextillion Years
To grasp the scale of 1 sextillion years (10^21 years) is challenging. It is a timescale so immense that it extends far beyond the projected lifespan of our universe's current stellar activity and even the eventual cooling of stellar remnants. For perspective:
- The current age of the universe is about 13.8 billion years (1.38 x 10^10 years).
- The Sun is expected to remain a main-sequence star for another 5 billion years.
- Even white dwarfs, the dense remnants of stars like our Sun, are predicted to take quadrillions of years to cool down to "black dwarfs" (a hypothetical state, as the universe might not be old enough for this to happen yet).
Therefore, the scenario where Earth still orbits the Sun (or its remnant) in 1 sextillion years is highly theoretical.
The Mechanism: Gravitational Radiation and Orbital Decay
The primary mechanism leading to the Earth's hypothetical collision with the Sun at such a remote time is the emission of gravitational radiation.
- Gravitational Radiation Explained: Just as accelerating electric charges produce electromagnetic waves (light), accelerating massive objects produce gravitational waves, which are ripples in spacetime. Orbiting bodies, like planets around a star, continuously lose a tiny amount of energy through these waves.
- Orbital Decay: This continuous loss of energy, however minuscule, causes orbits to slowly shrink over astronomical timescales. For a body like Earth orbiting the Sun, the rate of energy loss via gravitational radiation is extremely small. The time it would take for Earth to spiral into the Sun due to this effect alone is vastly longer than the Sun's expected lifespan.
- The Hypothetical Collision: After a staggering 1 sextillion years, this cumulative effect of gravitational radiation would theoretically lead to the complete deterioration of Earth's orbit, culminating in its impact with the Sun's remnant. This event assumes the Earth somehow avoids being consumed or ejected during the Sun's red giant phase (in about 5 billion years) and subsequent evolution into a white dwarf.
Earth and Sun's True Fates Long Before
Long before the 1 sextillion year mark, both the Earth and the Sun will have undergone dramatic transformations:
- Sun's Red Giant Phase: In approximately 5 billion years, the Sun will expand into a red giant, potentially engulfing Earth's orbit. Even if Earth isn't fully consumed, its atmosphere would be stripped away, and its surface sterilized.
- Sun's White Dwarf Phase: Following the red giant phase, the Sun will shed its outer layers, forming a planetary nebula, and its core will shrink into a white dwarf – a very dense, hot remnant about the size of Earth.
- Earth's Survival: It is highly unlikely that Earth would persist in a stable orbit around the white dwarf for trillions of years, let alone a sextillion. It would either be consumed by the red giant, ejected from the Solar System due to gravitational perturbations, or cease to be a habitable world.
Therefore, while gravitational radiation is a real phenomenon that causes orbital decay, the collision of Earth with the Sun in 1 sextillion years is a theoretical end-state under the extraordinary assumption that the Earth could survive in orbit around the Sun's remnant for such an immense duration.
