[Karellen]

> at this rate the Earth will stop rotating in 50 billion years,

That's not what the link you posted says. It states that that's when the Earth-Moon system will be tidally locked, so that the Moon orbits the Earth at the same rate that the Earth rotates around its axis.

Kind of if the earth slowed so that one "day" took the equivalent of 28 days now. The earth would be locked with one side always facing the moon, so there would be no tides, but it would still be rotating. Except it will end up be a longer "day" than that, because as energy is transferred to the Moon its orbit is raised, which slows it down.

[piaste]

You're right, my mistake.

Ignoring for a second both the human factor and the Sun having gone red giant much earlier... I wonder what kind of ecosystem that would create. If the Earth were tidally locked to the Sun (which is what I was picturing in my confusion), it would clearly end up as two deserts with a tiny strip of life along the twilight circle. But how would complex life evolve to adapt to a 28*24h day/night cycle? We do have decently-sized ecosystems in caves so long nights aren't insurmountable, but being baked to really high temperatures for a month and then cooling down to freezing for another month sounds like quite a challenge.

[dylan604]

This is nice and all, but in 50 billion years, the moon's distance from the Earth will much greater which means it's gravitational effect on Earth will be much smaller.

[Karellen]

OK. Do you have any reason to suspect that the people making their calculation didn't take that into account? Of all the things that will vary over time, including the distance between the Earth and Moon, do you really think they'd have missed the fact that the Earth's gravity varies with distance?

If you've got what you think is a more accurate number, and can show your working, I'm sure the wikipedia editors would be willing to take a look at it.