[rollo]

This graphic helps with understanding the metric expansion of space: https://upload.wikimedia.org/wikipedia/commons/b/b0/Expansio...

The Big Bang is better understood as a Big Stretch, which is still ongoing. As time progresses there just happens to be more space added between things. The balloon analogy breaks down because the galaxies themselves, or the dots on the balloon don't get bigger due to gravity. The expansion of space is only relevant on huuuge distances, not interstellar or even intergalactic, only when one gets to galaxy clusters and superclusters.