Take a massive explosion to create plenty of stardust and a raging heat. Simmer for an eternity in a background of cosmic microwaves. Let the ingredients congeal and leave to cool and serve cold with cultures of tiny organisms 13.7 billion years later.
To understand the basic ingredients and the ‘cooking conditions’ of the cosmos, from the beginning of time to the present day, particle physicists have to try and reverse-engineer the ‘dish’ of the Universe. Within the complex concoction, cryptic clues hide the instructions for the cosmic recipe.
Space, time, matter... everything originated in the Big Bang, an incommensurably huge explosion that happened 13.7 billion years ago. The Universe was then incredibly hot and dense but only a few moments after, as it started to cool down, the conditions were just right to give rise to the building blocks of matter – in particular, the quarks and electrons of which we are all made. A few millionths of a second later, quarks aggregated to produce protons and neutrons, which in turn were bundled into nuclei three minutes later.
Then, as the Universe continued to expand and cool, things began to happen more slowly. It took 380,000 years for the electrons to be trapped in orbits around nuclei, forming the first atoms. These were mainly helium and hydrogen, which are still by far the most abundant elements in the Universe.
Another 1.6 million years later, gravity began to take control as clouds of gas began to form stars and galaxies. Since then, the heavier atoms of which we are all made (such as carbon, oxygen, and iron) have been continuously ‘cooked’ in the hearts of the stars. They are stirred in with the rest of the Universe each time a star comes to a spectacular end as a supernova.
The mystery ingredient
So far so good, but there is one small detail left out: cosmological and astrophysical observations have now shown that all of the above accounts for only a tiny 4% of the entire Universe. In a way, it is not so much the visible things, such as planets and galaxies, that define the Universe, but rather the void around them!
Most of the Universe is made up of invisible substances known as 'dark matter' (26%) and 'dark energy' (70%). These do not emit electromagnetic radiation, and we detect them only through their gravitational effects. What they are and what role they played in the evolution of the Universe are mysteries, but within this darkness lie intriguing possibilities of hitherto undiscovered physics beyond the established Standard Model.
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