In article ,
stargene writes:

Is there an overarching link between the fact that, on the one hand: (1)
plate tectonic motions range typically between a few mm/year to about
100 mm/year, & (2) mantle convection speeds average roughly around
"..20 mm/yr.." (wikipedia entry)...and on the other hand: (3) the Moon,
due to tidal effects, is "..spiraling away from Earth at a rate of 3.8 cm/yr
[or about 38 mm/yr...me] per year (wikipedia entry) ?

Ie: Can these very similar values all have a common origin--perhaps in the
mutual spin and tidal interactions of the Earth-Moon-Sun system? The usual
driver for mantle (and plate) motion is said to be due to the heat flow and
the local geochemistry of the Earth's interior, and of course the decay of
several radionuclides. Ie: Is this similarity between (1, 2) and (3)
merely a quirky coincidence? Or, over billions of years, have all three
processes achieved some mutual energetics 'partitioning' balance?

[[Mod. note -- It's a coincidence. -- jt]]

I agree with jt here. In cosmology, some people make much of apparently
unrelated quantities, for example the age of the universe and the Hubble
time (which means that, essentially, the decelerating and accelerating
phases cancel---more interestingly, they do so only now), or the energy
density due to matter and the cosmological constant. Coincidence or
something deeper?

Essentially, this means that two quantities are roughly equal, or that
their ratio is a very small (or, if the other way around, very large)
number. Other people claim that it is extremely small (or large)
dimensionless numbers which need explanation, not the other way around
(cue "naturalness"). (I tend to think that an equality needs an
explanation; if two things are unrelated, chances are that their ratio
will be a small (or large) number.)

The literature here is confusing, to say the least.

The angular size of the Sun and the Moon---which allows the corona to be
seen during a total solar eclipse---is also such an equality, but for
some reason most don't see it as significant (and, as noted above, the
Moon is receding from the Earth, so this equality holds only now).

What determines whether such an equality (or near equality) is
"interesting"?

The brightest stars, planets, and meteors are all about 0 mag. As far
as I know, this is just a coincidence. (At other locations in the
universe, this would not hold.) As Yogi Berra said, one can find a lot
of things by looking.

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Well, the trouble with coincidences is that sometimes they tell you something
and sometimes they don't.

---Mike Turner