I have just been reading (and enjoying) the chapter of your book that deals with tides. I believe that your explanation of the tidal bulge on the side of the Earth farthest from the Moon is unnecessarily complicated. All this talk about "astronauts in free-fall" and "relative to the centre of the Earth" is a distraction from the essential point: the Moon's gravity acts on all parts of the Earth, and tries to pull them towards the Moon. Because the water on the far side of the Earth is farthest from the Moon, it is pulled towards the Moon less than other parts of the Earth, and so is, as it were, "left behind" by the rest of the planet's lurch Moonwards. This accounts perfectly for there being a high tide on the side of the Earth farthest from the Moon.

One other point. In the same chapter, you write that one day the tidal effects of the Moon will slow the Earth's rotation down so that it will take the Earth one lunar month to rotate on its axis (and thus keep the same face turned towards the Moon). But that isn't what has happened to Mercury. The Sun's tidal effects on that diminutive body have slowed its rotation to just two thirds of its period. Surely the same will happen to the Earth?

Incidentally, I've never really understood why Mercury is locked into such a rotation. I'm guessing that for two thirds of its orbit the Sun's pull on its tidal bulge is slowing it down, while for the next two thirds of its orbit the Sun's pull is speeding it up, thus cancelling out the first effect. Is this correct?