What is the origin of everything?
Each mythology has a perspective that proposes a different response. Aristotle proposed that the universe did not have a beginning, that is, that it has always existed.
The Aristotelian cosmos was stable, immutable, eternally immobile. It was a universe where humanity could feel important, because it was located at the center of all things.
Source Image credit: NASA
According to science, the stars seem so permanent in the sky that until 1920 it was believed that the universe did not change, but then the astronomer Edwin Hubble made two great discoveries, in one of them he saw that some of the stars, were not stars but groups of millions of stars called "galaxies", as well as ours; the milky way.
The second discovery that is made is even more surprising.
Have you ever listened to a vehicle when it passed by very quickly, like an ambulance, or a train that, when approaching, emits a high-pitched sound and when a low sound disappears?
This happens because as the sound source goes so fast, the waves compress in front of the vehicle and move further behind it. This is called "Doppler Effect".
- How does this relate to galaxies?
For something similar happens with light, which also behaves like a wave. If an object moves away quickly its electromagnetic spectrum will run to red (waves of lower frequency), while if it approaches it will run to blue (waves of greater frequency). Hubble expected some galaxies to keep their distance, others to move away and others to approach us. However, what he discovered by analyzing his light discovered that the vast majority was redshifted, that is, they were moving away from us and faster when they were further away, this is Hubble's law. Source of the image
The obvious conclusion is that if the galaxies move away from each other, it means that in the past they were closer and perhaps at a given moment all the matter in the universe was occupying the same place in space. The universe had a beginning about 14 billion years ago.
Some scientists like Fred Hoyle, this sounded arbitrary, so they devised a theory called "Steady State", in which to explain the expansion, they assumed that matter is constantly being created in the universe, which maintains its constant density and there is no need to have a beginning or end. Hoyle mocked the contrary theory (Big Bang).
But Robert Penrose and Stephen Hawking, using the theory of relativity and direct observations, proved in 1965 that the universe, time and space, had had a beginning. At that point of space - time it is called "singularity", a zone of infinite energy density. The sudden expansion that came right after is the famous "Big Bang" ... but you wonder, what was before the singularity?
Source Image credit: NASA/WMAP Science Team
You see, that is exactly what makes it unique. Imagine that on earth you walk to the north, if you walk long enough you will reach the North Pole. If I ask you to walk further north, where would you go? ... it is not possible, in this sense the north pole is singular. In the same way, it is not possible to ask what was before the beginning: time itself began there.
Thanks to Einstein's theory of relativity We know that space and time are not absolute. They are dynamic and relative to each other, they are deformed by matter and energy. They are defined by the universe, they are not independent of it. That's why it does not make sense to talk about a time before the universe started. Time began with the universe.
The universe was so small at the moment of its inception (even smaller than an atom) that general relativity is not enough to understand it and we must incorporate quantum mechanics. The theory that explains the functioning of matter on a super-microscopic scale.
The reason why galaxies, stars and planets were formed is because the primordial quantum universe was irregular, as shown by the cosmic background radiation maps of the current universe. If there is the sun, the earth, human beings, it is due to the probabilistic irregularities of the quantum microuniverse.
Map of cosmic microwave background anisotropy Image credit: NASA/Goddard/WMAP Science Team
Although the theory I have just mentioned is the most accepted and answers many questions, there are still many questions to be answered.
Why do the farthest galaxies move away even faster?
Is there something that pushes them, the dark energy?
Will the expansion be eternal or will the universe collapse?
Why does the universe have these laws and not others?
By the way, before Hubble made his observations, the Belgian Georges Lemaître had already made calculations that pointed towards the singularity that I call "cosmic egg" and the Big Bang. Source of image
Georges Lemaître was a Catholic priest.
"He's not just the father of the Big Bang, I think he's the father of modern cosmology," said John Farrell, Lemaitre's biographer.
I invite you to read this article about Stephen Hawking
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