The big Bang Theory It is a cosmological theory to explain the origin of the universe and the one that currently has more acceptance in the scientific community. It states that the universe began with a big bang, about 13.8 billion years ago, and has been continuously expanding ever since..
From this great explosion came matter, time and space, which later became galaxies and star systems, including our own Milky Way, the solar system and finally ourselves..
The theory originated in 1915, with Albert Einstein's equations of relativity, which among other things predict the expansion of the universe, a fact with which the German scientist was never comfortable..
However, the Belgian astronomer George Lemaitre, when studying relativity, suggested that if the expansion was true, obviously the universe must have a starting point. In 1927 Lemaitre published an article in which he presented his ideas about the origin of the universe, which he called "the primeval atom".
The American astronomer Edwin Hubble promoted the new theory, confirming in 1929 that galaxies are moving away from each other and also from us.
Going back in time, the galaxies must certainly have been much closer than they are today. And therefore there must have been an instant when all matter was incredibly compressed, occupying an infinitely small space: a singularity.
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The term "big bang" was coined by physicist Fred Hoyle in 1940, who was not sympathetic to the idea, so he referred to it derisively, calling it "that big bang." Hoyle was convinced that the universe was stationary.
Although its name leads us to think of some catastrophic event, physicists and cosmologists now believe that it was neither great nor a cataclysm from which galaxies flew in all directions..
But it was so powerful that the four fundamental interactions of Physics were unified during those first moments.
The entire universe was originally in an incredibly hot and dense state, and then it suddenly expanded as it slowly cooled. That expansion continues today.
The big bang does not explain how the original singularity arose, least of all what existed before it. What it explains is what happened to the universe during the early days when the singularity ceased to be..
Scientists estimate that the big bang happened 13.8 billion years ago and it is not possible to know what happened before, since time, together with space and matter, were created at that precise moment.
It was not a localized event. It turns out that the more distant the objects we see with the most powerful telescopes are, the further we go back to the time the big bang occurred, no matter which direction we look at it..
After the big bang, the temperature dropped and the subatomic particles that we know were formed: protons, neutrons and electrons, to give rise to atoms.
During the big bang, gravity emerged, the unifying force of attraction of matter, as well as the other fundamental interactions.
The first chemical elements formed were hydrogen, the simplest of all, and then helium and lithium, in a process called nucleosynthesis. Over time, huge clouds of these elements gave rise to the first galaxies.
The big bang is based on:
-The equations of the theory of relativity proposed by Einstein.
-The standard model of particles, which describes the structure of matter in terms of the fundamental particles and the interactions between them.
-The cosmological principle, which affirms that the universe is homogeneous and isotropic, when we see it on a larger scale. This means that its properties are identical in all directions and the laws of Physics are the same everywhere..
Of course we know that there are accumulations of matter, separated by spaces of much less density. From that point of view, the properties of the universe certainly differ. But the scale encompassed by the cosmological principle is much larger than that..
According to the cosmological principle, the universe does not have a center, nor does it have borders or limits, because preferential places simply do not exist..
It is therefore concluded that the universe has an origin in time and therefore a finite age, although it is not yet clear whether its extension is finite or infinite..
Scientists distinguish three major stages, the first of a universe very primal, the second of the primeval universe proper and the third the stage of the structure formation.
During the first two, the universe was dominated first by radiation and then by matter.
During this era, energy was in the form of photons, massless elementary particles that make up light. Thanks to them, the electron-positron pairs of matter and antimatter were created, which annihilate when they meet, emitting energy again in the form of photons..
However, at some point matter slightly predominated over antimatter, which later led to the appearance of the first subatomic particles..
Cosmologists believe that this stage lasted about 700,000 years, and in it the following periods are distinguished:
Starts from 10-43 seconds after the big bang occurred and includes:
-The Planck era, when the four fundamental interactions - electromagnetic, strong nuclear, weak nuclear, and gravity - constituted a single fundamental force.
-The era of unification, occurred 10-36 seconds later, when gravity is separated from the other forces, but the others remained fused in what is called GUT (grand unified theory) as the universe expanded and cooled.
From 10-36 up to 10-33 seconds, in which the universe underwent accelerated growth, cooled and its density rapidly decreased, as a consequence of the expansion.
This is how the universe grew from something less than the tip of a pin, to a sphere the size of several suns like ours, all at great speed.
The growth of the universe slowed without stopping and the first elementary particles emerged: protons, electrons and neutrons..
After three minutes, protons and neutrons collided to form the first nuclei. Then these nuclei met and the light atoms were formed.
Paradoxically, the high temperatures of the early universe did not allow light to appear until about 380,000 years after the big bang..
But then the universe had already cooled enough to allow the formation of neutral hydrogen, with which photons - light carriers - could move great distances without obstacles.
The universe, previously opaque due to its high density, became transparent to radiation and matter became predominant.
In this way the first conglomerates were formed, thanks to the action of gravity and the universe began to acquire its current shape. It is the stage of the formation of structures.
Gravity collapsed the gas clouds to form the first stars, which later associated into galaxies. Experts believe this happened about 400 million years after the big bang..
The expansion of the universe has not stopped, on the contrary it seems to have accelerated.
Now scientists believe that there is a matter different from the matter we can see, called dark matter, which is responsible for this accelerated expansion.
The big bang is still observable today, despite the elapsed time, through radiation that comes from the most distant places in the universe..
The cosmic microwave radiation background (cosmic microwave background) was discovered in the mid-1960s by two researchers at Bell Laboratories: Arno Penzias and Robert Wilson.
It is the glow that the big bang left behind, something that theory had already pointed out in advance, but that had not been detected until the experiments of Penzias and Wilson..
In 1929 Edwin Hubble affirmed that the universe is expanding, and for eight years he was in charge of collecting the data necessary to test it at the Mount Wilson Observatory, California..
In this way he enunciated the following law, in which the speed v with which galaxies are moving away from us, is proportional to the distance R, being H Hubble's constant:
v = HR
Where H = 22 x 10-3 m / (light year). This simple form of the law is valid when it comes to galaxies not too far away..
The Hubble Space Telescope confirms that distant galaxies are homogeneously distributed, in accordance with the cosmological principle.
The greater the redshift, the greater the apparent magnitude of a distant galaxy, which means that the wavelength of its light lengthens as it travels through an expanding universe..
In theory there are many points that remain obscure, for example scientists still do not know what triggered the great inflation.
On the other hand, many experts are not satisfied with the fact that before the big bang time, matter and space did not exist, since some think that time has always existed.
Of course, cosmological theories point to large-scale phenomena and are refined or discarded thanks to new discoveries. Scientists hope to resolve discrepancies such as the following:
Entropy was abnormally low during the first moments of the universe and cosmologists cannot explain the increase in entropy to current levels..
This problem refers to the fact that the speed of light is finite and nothing travels faster than it, however, regions that during the big bang could not be in contact due to their separation, it turns out that they were in thermal equilibrium..
It is believed that we live in a flat universe, however the big bang theory does not offer a physical mechanism that satisfactorily explains the reason.
The big bang theory predicts the existence of magnetic monopoles, but so far they have not been found. Every time we try, by sectioning a magnet, we always get smaller magnets with north and south poles, never separate magnetic poles (monopoles).
Other concerns about the theory are: where did the singularity originate from? And how did matter come to predominate over antimatter? Or how and why did the great inflation occur? There is still a long way to go.
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