If you ever try and fail to get to sleep at night, worrying about the events of the day and wondering what new challenges await you in the morning, it can be useful to try and visualise our place in the universe, and to picture the utter triviality of our existence.
According to the scientists, who have the benefit of the finest instruments known to mankind, and have been looking for centuries for evidence to test their theories, our universe came into being 13.787Bnyrs ±20m years ago, following a Big Bang. In the first tiny fractions of the first second, all of the main forces in the universe were formed, as well as the basic components of the matter and anti-matter that make up the universe. All material in the universe expanded from a single point during a period of ‘inflation,’ during which our current understanding of physics cannot reach, but which involved expansion at higher than light-speed, and colossal temperatures and pressures. Microscopic variations in density in the initial expanding material were enough to later form the large-scale structure of the universe (of which more later). A few minutes after the Big Bang, with the temperature of the universe still at a billion degrees centigrade, neutrons and protons combined to form helium and deuterium, with the rest remaining as hydrogen (75% of the matter in the universe). While normal ‘baryonic’ matter came to dominate the observable universe (albeit making up only about 5% of the total matter/energy), invisible and mysterious ‘dark energy’ (73%) and cold ‘dark matter’ (23%) make up the rest - with physics struggling to tie down the properties of both. Nobel prizes await for success in these subject areas. However, dark energy is thought to be driving the current accelerating expansion of the universe.
So, back to those tiny fluctuations in density. At around 370,000 years after the Big Bang, the universe had cooled from plasma and expanded enough for it to be transparent to light. The remaining heat energy distribution of the cosmos dates back to this time and has been mapped as the Cosmic Microwave Background radiation - now at a temperature of 2.75 Kelvin above absolute zero. It varies by around 1 in 100,000 - a tiny amount, but enough in the early universe for those most dense areas to attract more matter through gravity, forming vast gas clouds. These became the first stars and the first galaxies, with the first galaxies having formed only 300Myrs after the Big Bang, making them nearly 13.5Bnyrs old.
Amazingly, and not a lot of people know this, there are huge structures in the universe - strings or filaments of galaxies, walls and clusters of galaxies and - in between them - huge voids that are nearly devoid of matter, with perhaps only one atom per cubic metre.
There are estimated to be somewhere between 100 billion and two trillion galaxies, and perhaps 200 billion trillion stars (that’s 200,000,000,000,000,000,000,000 stars in the universe). However, even on the darkest night, with the clearest view, you might only be able to see 9000 stars. And every single one of them is in our own galaxy - the Milky Way. The vast majority of the stars that you can see are in our own minor Orion-spur arm of the spiral Milky Way. For us to be able to see them, each one of those stars is vastly larger than our own sun. The space between stars means that when galaxies collide, they don’t. They just slip through each other, with a stellar collision being incredibly rare.
Sophisticated star maps have revealed that our galaxy already contains the remnants of around 40 smaller galaxies that have been captured over its life span, while there are other galaxies that are literally in orbit around the Milky Way - including the Large and Small Magellanic Clouds - visible in the southern hemisphere. Our galaxy - containing up to around 400 billion stars - is just one of around 50 in the Local Group of galaxies. The next closest major galaxy - the Andromeda Galaxy, the furthest thing you can see with your naked eye - is 2.537 million light years away and is also in the Local Group. Clusters of galaxies such as the Coma and Perseus Clusters contain hundreds to thousands of galaxies, while Superclusters are large collections of clusters: our Local Group sits on the edge of the Laniakea Supercluster. Superclusters can form walls or sheets, with the Coma Wall being 500 million light years long but only 16 million wide, and the Sloan Great Wall, extending 1.4 billion light years. These walls, strings, sheets and clusters form a Cosmic Web - which makes up the fabric of the universe - unimaginably large, unfathomably complex.
So, when sleep eludes you, it may be calming to try to place yourself in context of the universe, as a relatively tiny nearly inconsequential blob of protoplasm. It might not help with paying the bills, getting that promotion, overheating dryer bearings or problems with the kids, but you might get a better night’s sleep.
https://en.wikipedia.org/wiki/Big_Bang
https://science.nasa.gov/universe/galaxies/large-scale-structures/
