Xandra draws beautiful pictures of animals, but she never draws her friend SpaceBoy.
SpaceBoy arrived when Xandra was three. He is slightly shorter than Xandra. Every year as Xandra grows, SpaceBoy does too, just not as much as Xandra. That is all we know about what he looks like. If you ask for details she says "he is just a boy". That is why he is not in the picture. We can't draw him.
All that Xandra tells us is that SpaceBoy is her imaginary friend and that he is real.
SpaceBoy and Xandra explore the universe in his spaceship. They are very interested in Space and the Universe.
"Dad," she asked one day, "where did the moon and stars come from?"
"Billions of years ago there was a Big Bang" Dad said, "and that is when everything started."
"What's a Big Bang" Xandra asked.
Dad told her that near the beginning of the Universe rhere was a "Big Bang". To understand the beginning of the universe she would have to know about cosmology, which is a branch of science that studies the Universe. Luckily enough she already knew enough science, so Dad would explain.
"You need to know about MASS, VOLUME, DENSITY and GRAVITY" Dad said. "We'll start with GRAVITY."
Xandra looked worried. Anything with a "Big Bang" sounded interesting: but would Science be hard?
