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Warp schrieb:
> 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).)
I think #2 is just #1 taking into account the attractive forces working
simultaneously, so I see no difference there; so I'd say space is
appearing everywhere, but it's not noticeable at subatomic levels
because the attractive forces compensate for it.
In case the rate of "space growth" should be indeed increasing (as some
scientists claim it is), then it might be possible that (a) this
/acceleration of growth/ will cause the distance between subatomic
particles to increase (as there will be a new distance of equilibrium
between "space growth" and all the other forces), and (b) the rate of
"space growth" might some time in the future exceed the attractive
forces' ability to compensate, so that "space growth" itself (and not
just the acceleration thereof) might drive even subatomic structures apart.
> It also seems to be some kind of common misconception that the expansion
> of the Universe would somehow change units of measurements accordingly.
Well, obviously it cannot change units of measurements: Those are
/defined/. What it /can/ change is (a) practical realizations of
measurements, and (b) possibly the value of natural "constants" as
expressed in these units of measurement.
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