Darren New <dne### [at] sanrrcom> wrote:
> SharkD wrote:
> > I bet that the new unit will also be proven susceptible to "distortion" 
> > over very large amounts of time, like with the density of space changing 
> > over thousands of millennia or something. (Just a hunch.)

> I wonder if that counts, tho. If space gets twice as big over time, I'd be 
> worried if the measuring sticks didn't.

  There seems to be some confusion about what exact does it mean that the
universe is expanding. I have read two different explanations:

1) New space is appearing *everywhere*, making *all* distances larger over
time, including eg. distances between subatomic particles.

2) New space is appearing between galaxies, making only the distance between
galaxies grow larger over time. (The reason for this is that when you are
close enough to a galaxy, its gravitational pull is stronger than the
"outwards" movement caused by the expansion of the universe, which means
that gravity stops you from getting farther away from the galaxy due to
this expansion. In a way, you are "tied" to the galaxy and don't get farther
away from it (from the expansion phenomenon alone).)

  As far as I have understood, explanation #1 is a misconception. Distances
between subatomic particles is not growing because the forces keeping atoms
and molecules together is way stronger than any minuscule drift that the
expansion of the universe might cause.

  The same is true at macroscopic levels: The Earth is not expanding because
atomic bonds and gravity are strong enough to stop any expansive drift from
happening. The Sun's gravity is strong enough to stop planets from drifting
away due to the expansion of the Universe. All the way up to galactic sizes:
The gravity of a galaxy is strong enough to stop stars from drifting away
due to the expansion of the Universe.

  Only when we get to intergalactic space, very very far away from any
galaxy, is gravity so weak that it does not prevent galaxies from drifting
away from each other due to the expansion of the Universe.

  It also seems to be some kind of common misconception that the expansion
of the Universe would somehow change units of measurements accordingly.
Why would it? It simply means that distances between galaxies is growing.
It doesn't mean that units of distance are changing too. The diameter of
a proton will still be the same in 1 billion years than it is now. The
expansion of the universe only makes the universe bigger, it doesn't make
*everything* bigger, down to subatomic particles. It doesn't even make
galaxies bigger (AFAIK).

-- 
                                                          - Warp

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