"BluMax" wrote in message
news:2004112913055116807%alsimcoe@alsimcoecom...
I have always wanted an answer that I can understand to the following
question.

Simply asked, "What is our Universe expannning into"?

Please explain it assuming I am an *ordinary* 13 years old.

I finally found this question and its answer, in a FAQ called
"Frequently Asked Questions in Cosmology":

http://www.astro.ucla.edu/~wright/cosmology_faq.html

It is all "%^$@^$%@^" to me. :-(

Thanks in advance to "anyone/everyone" who can explain it to
me so that I understand.

BluMax

Hi BluMax,

It's hard to get your head around this, because we tend to think of
things in terms we already understand and changing our understanding
involves thinking in the abstract.

The best way I can get to understand it is to think in the *wrong* way,
and then work out how to change the way I'm thinking to get the *right*
mental image.

First the *wrong* way . . .
Think of it as if we took a movie of a firework going off at the in the
middle of a large room like a school hall. The space is filled with
sparkles and streamers. As the movie plays, fast moving objects are
quicker to get to the walls while the slower ones are nearer the centre.
In this case, as time progresses, the explosion moves into the empty
space of the concert hall. This empty space is already there, and we
see the fastest moving sparks fill this space.
But that is the *wrong* way to view it.

Now let's modify this to get closer to the *right* idea.
To change the mental image in your head, imagine that you are looking at
the movie frame where the firework has just filled the hall - everywhere
is filled with something. Now mentally play the movie backwards, but
imagine that the walls of the hall itself are moving back with the
firework. Instead of the explosion getting smaller inside the hall; the
whole hall and explosion are getting smaller at the same time. Mentally
play the movie forwards and backwards in your head seeing how the whole
thing is expanding/contracting as a single item. There is no need to
think about what the universe is expanding 'into', because there is
nothing 'outside' - the whole universe is 'inside' the model, it's just
getting bigger all the time.

It's not a complete answer, and it's not perfect, but I hope you can see
how the two mental images differ. Don't expect to understand it straight
away, but keep plugging away with it .

Hope this helps.