INFLATING BALLOON is a good analogy for understanding the expansion of the universe. The galaxies on the surface of the balloon are effectively at rest, and yet as the universe expands, the distance between any two galaxies increases. The galaxies themselves do not increase in size.
What Is Expansion, Anyway?
When some familiar object
expands, such as a sprained ankle
or the Roman Empire
or a bomb, it gets bigger
by expanding into the space
around it. Ankles, empires and bombs
have centers and
edges. Outside the edges,
there is room to expand into.
The universe does not seem to have an edge
or a center or an
outside, so how can it expand?
You are an ant living
on the surface of an inflating
balloon. Your world is two-dimensional;
the only directions you know are left,
right, forward and backward.
You have no idea what "up"
and "down" mean. One day
you realize that your walk to milk your aphids
is taking longer than it used to:
five minutes one day, six minutes the next day,
seven minutes the next. The time it takes
to walk to other familiar places is also
increasing. You are sure that you are not
walking more slowly and that
the aphids are milling around
randomly in groups, not systematically crawling
away from you.
This is the important point: the distances to the aphids
are increasing even though the aphids are not walking
away. They are just standing there,
at rest with respect to the rubber of the balloon,
yet the distances to them and between them are increasing.
Noticing these facts, you conclude that the ground
beneath your feet is expanding. That is very strange
because you have walked around your world and found no
edge or "outside" for it to expand into.
In Our Universe
as on the surface of the balloon, everything
from everything else. Thus, the big
was not an explosion
it was more
like an explosion
It did not go off at a particular
location and spread
out from there
imagined preexisting void.
everywhere at once.
If one imagines running
the clock backward
any given region
of the universe
and all galaxies in it
get closer and closer until they smash together
in a cosmic traffic jam--the big bang.
It was like having the surface
of Earth and all its highways shrink
while cars remained the same size. Eventually
the cars will be bumper to bumper
on every road.
No radio broadcast is going to help you
around that kind of traffic jam.
The congestion is everywhere.
The totality of space
The totality of space could be infinite.
Shrink an infinite space by an arbitrary amount,
and it is still infinite.
- sentences and phrases rearranged from Misconceptions about the Big Bang Baffled by the expansion of the universe? You're not alone. Even astronomers frequently get it wrong By Charles H. Lineweaver and Tamara M. Davis, in the March issue of Scientific American.
There is a moment after you move your eye away
when you forget where you are
because you've been living, it seems,
somewhere else, in the silence of the night sky.
You've stopped being here in the world.
You're in a different place,
a place where human life has no meaning.
You're not a creature in a body.
You exist as the stars exist,
participating in their stillness, their immensity.
Then you're in the world again.
At night, on a cold hill,
taking the telescope apart.
You realize afterward
not that the image is false
but the relation is false.
You see again how far away
each thing is from every other thing.
From the New Yorker, Jan 17, 2005.