Each galaxy lives within its own three-dimensional halo of dark matter whose gravitational field corrals the stars within it. Without the stars, the halo would still be there, albeit invisible to our eyes; but if the halo vanished, the stars would scatter into the depths of the universe – just as a Christmas tree remains a tree with or without the pretty lights. Whereas without the tree, the lights would merely be a puddle of colour on the snowy ground.
As you can guess from the title, The First Three Minutes tells the story of the moments following the Big Bang. The early universe sets the stage for the development of the cosmos we observe today, and the Cosmic Microwave Background is a key link between the distant past and the present day.
One of the commonest questions about the Big Bang is "If the universe is expanding, is everything in it getting bigger? The solar system, the sun, the earth, our bodies and the atoms we are made of?"
Books could and probably will be written about this saga (science writers, call your agents): there is ambition, drama, excitement, Nobel fever, science-by-media, a telescope at the South Pole, and astrophysicists so hungry for data that they analysed images lifted from in Powerpoint slides when the originals were unreleased.
In 1915, Berlin was at the centre of an empire locked into a global war. But at least one resident of that city had his mind elsewhere: Albert