Expert: Tom Whiting - 1/19/2009

Question
with the available facts of the Big coming up sometimes in the future, what do you think will be the speed of Moon if it were to leave it's orbit to crashing into the Sun's orbital circle? And is it likely possible that Moon will be pulled by the gravitational pull of the Sun to itself?

Answer
Hi Sauti,
The Big Crunch is out. With the knowledge gained in 1998 and beyond
with results from Type Ia supernovae, we now know that the Universe
(the space itself, not the matter) is not only expanding, the
expansion rate is accelerating faster and faster. This eliminates
the "Big Crunch" (where the Universe eventually collapses back into
a pinpoint)....in favor of either a total heat death or the
"Big Rip" where everything will eventually be torn apart by the
rapid expansion, hundreds of billions or trillions of years from now.

Speed of the moon, relative to what? All velocities are relative
to some other body. If the Earth were the only body in the Universe,
we could not determine a velocity. If say there were one other
object in addition to the Earth, then we could only give the velocity of the Earth relative to that one other body.

The moon is ALREADY in orbit around the sun, along with the Earth,
in addition to it's orbit around the Earth. So the moon is already
"crashing" into the orbital circle around the sun. (Why do you use
the word "crash" in that context?)  The word crash implies something
catastrophic happens, whereas orbits around the sun are not
catastrophic...in fact, they are the norm.

And the Big Crunch (or Big Rip) has nothing to do with the orbital
velocity of the moon. The moon is on the local scale whereas the
other topics are on the super-large Universal scale. It's like
comparing the orbit of Neptune to a waterspout over Key West, Florida....there is no correlation between the two topics.  Furthermore, all that BIG stuff is hundreds of billions, perhaps hundreds of trillions of years in the future, whereas the entire Solar System is only a "temporary" event on that same timescale, the sun going into the Red Giant phase in "only" a few more billion years, so we, the Solar System, won't be around....at the very end of the Universe, so our 'lifespan' is very short, by comparison.

The moon is gravitationally locked into the Earth's gravitational
well, and both are gravitationally locked into the Sun's gravitational well, and nothing short of a very massive 'other' body
moving through the inner Solar System, will ever change that.

Also, gravity doesn't "pull"....under Einstein's concept of gravity
(General Relativity, circa 1917) gravity simply bends the spacetime
continuum to make it act like a force, but it's really not a force,
there is no 'pulling'...just a curved amount of space which all
the planets and bodies orbit their parent star, and in which the
moon orbits the Earth. (Actually, they both orbit a common barycenter
with is located well within the Earth's mantle.)

Now that you know the scientific facts, perhaps you may want to
re-word the question more appropriately, because under the current
laws and observations of physics, your question has no relative
meaning or logical interpretation. We can't logically compare snowfalls in northern India to butterfly movements in Maine.
Clear Skies,
Tom Whiting
Erie, PA