# If the Earth became tidally locked with the moon, would that last forever?

If the Earth and the moon became tidally locked, would this last theoretically forever (assuming no external gravitational force modifies their orbits, for example, ignoring the effects caused by the Sun)? Or would their orbits would change?

• "forever" is long time. The sun will turn into a red giant and the Earht and moon may be swallowed... But I feel that isn't what you are asking about. Apr 13, 2022 at 19:34
• @JamesK I feel like we'd have to relinquish such considerations for this question, especially since the sun will turn into a red giant before the Earth and Moon tidally lock... Apr 13, 2022 at 20:14
• @JamesK I am asking if it is theoretically possible, not practically possible, so in my scenario the Sun basically does not exist. So if we ignore the Sun effects, and no other body distorts the orbits (here we are only considering the Earth and the Moon) would this situation keep forever? Or would they change the orbits even without external influences? Apr 13, 2022 at 20:55
• @zephyr exactly. When I said "ignoring the effects caused by the Sun" I was basically saying that the Sun would not influence in any manner the Earth-Moon system in this exercise, as if it did not exist basically Apr 13, 2022 at 20:56
• I suspect the "will it last forever" the answer is almost always, no. But your scenario is a crazy-long timescale. How long will it take for gravitational waves to lead to the decay of an orbit . . . That would be many orders of magnitude. I wouldn't even want to try to calculate, but it would be shorter than forever. If the Earth and Moon orbit the white-dwarf our sun becomes, then the 3 body system could be stable for maybe trillions or hundreds of trillions of years, but given enough time, the tidal forces would probably destabilize it or another planet or rogue object could. Apr 17, 2022 at 21:07