Bad Astronomy: Misconceptions and Misuses Revealed, from ...

252 BEAM ME UP
are mostly composed of water ice. And if that’s no good, there are
trillions of chunks of ice prowling the cold vastness of the Oort
cloud, the cometary halo of the Sun that is almost a light-year
across. Why expend all that energy to get to Earth when you can
mine the ice out of all those comets, a trillion kilometers from the
heat and fierce gravity of the Sun? And ice is a very convenient form
of water. It may take up slightly more room than liquid water, but
it doesn’t need a container. Simply chisel it into the shape you
want, strap it to the outside of your ship, and off you go.
Of course, in V, besides stealing our water, the aliens also came
here to eat us. In that case, they did have a good reason to come
to the Earth. Tough luck for us. Still, if I were some ravenous alien
with a taste for human flesh, I’d simply gather up a bunch of cells
and clone them to my heart’s (or whatever) content. Why travel
hundreds of light-years to eat out when staying home is so much
easier?
7. The Dreaded Enemy tries to escape Earth’s gravity, but is
caught like a fly in amber.
How many times have you heard the phrase, “escape from
Earth’s gravity”? Technically it’s impossible. According to Einstein,
the mass of the Earth bends space, and the farther away you get,
the less space gets bent. We feel that bending as gravity. But even
Albert would agree with Isaac Newton that in general terms, the
force you feel from gravity weakens proportionally as the square
of the distance. So, if you double your distance from the Earth,
you feel a force one-quarter what you did before. If you go 10
times farther away, that force drops by a factor of 100. You’ll note
that gravity drops off fast, but not infinitely fast. In other words,
even if you go a billion times farther away, you will still feel some
(extraordinarily small) force. Gravity never goes away, and if you
forget that for an instant you’ll be sorry. Toddlers tend to learn it
pretty quickly.
So if gravity is always around, it’s not like you are floating carefree
one instant and suddenly feeling a strong gravitational force
the next. It’s a gradual change as you approach an object. Star