Today, the Universe has evolved into the complex, life-friendly place we know it to be because we were able to form neutral atoms early on in the Universe. Yet without just the right quantum properties, the formation of stable, neutral atoms would have been delayed significantly, or might not have even occurred at all, rendering life, and the Universe as we know it, an impossibility. (Credit: agsandrew / Adobe Stock and remotevfx / Adobe Stock)
There are a few small cosmic details that, if things were just a little different, wouldn’t have allowed our existence to be possible.
Our Universe has grown up impressively since the Big Bang.
At the start of the hot Big Bang, the Universe was rapidly expanding and filled with high-energy, very densely packed, ultra-relativistic quanta. An early stage of radiation domination gave way to several later stages where radiation was sub-dominant, but never went away completely, while matter then clumped into gas clouds, stars, star clusters, galaxies, and even richer structures over time, all while the Universe continues expanding. (Credit: Big Think / Ben Gibson / NASA / Pablo Carlos Budassi)
From a hot, dense, near-uniform initial state, stars, galaxies, and living planets emerged.
Our Universe, from the hot Big Bang until the present day, underwent a huge amount of growth and evolution, and continues to do so. Our entire observable Universe was approximately the size of a modest boulder some 13.8 billion years ago, but has expanded to be ~46 billion light-years in radius today. The complex structure that has arisen must have grown from seed imperfections of at least ~0.003% of the average density early on, and has gone through phases where atomic nuclei, neutral atoms, and stars first formed. (Credit: NASA/CXC/M. Weiss)
Without these five coincidences, our Universe would have inevitably been lifeless.
At the high temperatures achieved in the very young Universe, not only can particles and photons be spontaneously created, given enough energy, but also antiparticles and unstable particles as well, resulting in a primordial particle-and-antiparticle soup. Yet even with these conditions, only a few specific states, or particles, can emerge, and by the time a few seconds have passed, the Universe is much larger than it was in the earliest stages. As the Universe begins expanding, the density, temperature, and expansion rate of the Universe all rapidly drop as well. (Credit: Brookhaven National Laboratory)
1.) A photon-rich early Universe.
In the early Universe, it’s very easy for a free proton and a free neutron to form deuterium. But while energies are high enough, photons will come along and blast these deuterons apart, dissociating them back into individual protons and neutrons. This prevents heavier elements from forming at early times, dependent on a large photon abundance. (Credit: E. Siegel/Beyond the Galaxy)
Large photon abundances make forming stable atomic nuclei difficult early on.
