Saturday, May 7, 2022

Big Bang: the beginning we know!

We're still not sure why or even how this happened. We know nothing about what existed before the Big Bang. Theoretically, scientists believe that our  Primitive Universe was born from a very hot and dense point . That point expanded very fast in a fraction of a second, creating its own space and time.

In the beginning, our universe had no galaxies, stars, planets or even atoms. Everything had to be created from  very small fundamental particles  , smaller than anything we know. How these particles were generated is still an unanswered question. Quark,  gluon , electron and photon  are among the first fundamental particles formed in the Big Bang. From the combination of quark particles, even in the first seconds of the universe's life,  protons  and  neutrons were formed , the components of  atomic nuclei .

It takes a  strong force  to hold the atomic nuclei particles together, and the glue that holds them together is the gluon. The formation of nuclei was only possible because the universe was very hot and dense; that is, many fundamental particles concentrated in a very small space. The cooling of the universe associated with the expansion process allowed electrons to attach themselves to atomic nuclei; thus joined by an  electromagnetic force .

So, 380,000 years after the Big Bang, electrons began to lodge around atomic nuclei. From this union the first  atoms were born , components of all matter that we know. Photons are the mediators of this union, and when this union weakens, photon particles are emitted in the form of light.

The building blocks of all matter

An atom is very small, so small that it does not reflect light. Even with all our technology, we still haven't been able to see the inside of an atom. However, if an atom were the size of a large football stadium, the nucleus would be a fly in the center of that empty stadium. In this immense stadium a few seats would be occupied by electrons. It is the scattering of these electrons, ultimately, that defines the size of the atom. A single type of atom forms a  chemical element,  which is nothing more than a characteristic atom, that is, an individual.

The first chemical element formed was hydrogen (H). It is the simplest chemical element in our universe, it has 1 proton, 1 electron and no neutrons. Electrons are much smaller particles than protons and neutrons, their mass is almost negligible. Therefore, the  mass  of an atom depends on the sum of the particles it has in its atomic nucleus. In the case of H, its mass is 1. In the early universe, still very hot, nuclei of H merged to form a second chemical element, helium (He). Helium has 2 protons, 2 electrons and 2 neutrons; that is, its mass is 4.

Shortly after the Big Bang, fundamental particles morphed into all of the H and some of the He that exist, and this represents virtually all of the known mass of our universe. The process of transforming fundamental particles into H and He is called  primordial nucleosynthesis . This process took place in the first few minutes after the Big Bang, and it was a one-time event. All the H in the universe was generated there, and no more atoms of this element will be created in the future history of our universe. 

It is at this point that it all starts to happen, as the chemical elements are the basic building blocks for all  matter  as we know it .  When chemical elements are combined, held together by a force of attraction,  chemical bonding , they can form molecules . Molecules also combine, that is, simple atoms and together form more complex systems. OH likes to form  molecules, with two atoms, but on the other hand, He prefers to be alone. Both chemical elements occur naturally in the  gaseous state , that is, they occupy all the space they find. These elements were the first inhabitants of this space under construction that we now call the universe. At this point in its evolution, the universe is relatively empty space, filled with H and He gas.

the universe expands

In expansion, the universe is getting colder and less dense, that is, more space for the same number of individuals. The atoms and molecules of H and He were moving at great speeds in this expanding universe. Sometimes these building blocks would group together and form immense, dense clouds that rotated endlessly. These clouds, formed at different points in the universe, attracted even more particles, thickening, and increasing empty space. It's law, matter attracts matter due to a force of attraction called  gravity .  This clumped matter formed the first  nebulae ,  which are immense clouds of gas, sometimes over trillions of kilometers long. At this point the universe was quite boring.

Millions of years have passed. In some points of the nebulas the matter accumulates by the action of gravity. These points of accumulation of matter thicken and contract to a point where they collapse. From this collapse gigantic and dense spheres form. The temperature inside these spheres was very hot. This allowed nuclei of H atoms to fuse to form He atoms. That is, the H burned to form He. This  nuclear fusion  caused the spheres to "glow", in a process called  stellar nucleosynthesis . Thus, the first stars  were born  , hot spots in a cold universe. When stars come together, they form  galaxies .

Life and Death of the Stars

Stars, like living beings, are born, grow, age and die. Nebulae are considered nurseries of stars. The first stars took tens of millions of years to be born. And they are already dead. In  the course of their lives and during their sometimes violent deaths,  stars give rise to new chemical elements by nuclear fusion. We can compare a star to a furnace, where in its core H burns to form He. And then, when the H runs out, the He burns to form progressively heavier chemical elements such as carbon (C), oxygen (O), silicon (Si), iron (Fe) and nickel (Ni). In this process the star expands.

The initial size of the star defines which chemical elements can be formed in this process. Only very large stars will have enough energy and mass to form heavier nuclei, such as O, Si, Fe and Ni. When these very large stars run out of fuel, that is, are no longer capable of nuclear fusion, the star's core collapses and it explodes. This explosion is called a  supernova .  In this explosion, new chemical elements of greater mass are formed, such as gold (Au) and lead (Pb). The last and heaviest chemical element formed in the Supernova is uranium (U), which has 92 protons, 92 electrons and 146 neutrons. The mass of this element is 238.

Atomic nuclei launched into space can also collide with subatomic particles traveling at high speeds ( cosmic rays ). This collision can generate light chemical elements, such as lithium (Li) and beryllium (Be). Some of the Li and Be were also generated in primordial nucleosynthesis.

“In nature nothing is created, everything is transformed”

The atoms of a given element are identical and are different from the atoms of all other chemical elements. However, most elements undergo transformations during their lifetime. For example, any atom can capture neutrons and change its mass, transforming itself into a new version of itself, called an  isotope .  A single chemical element can have multiple versions, that is, multiple isotopes, depending on how many neutrons it captures.

Uranium, for example, has three most common isotopes, with masses of 238, 235, and 234. All of them are said to be natural isotopes. The most common of these is U 238. In addition, a more massive isotope can also lose fundamental particles, becoming lighter, in a process of  nuclear decay  or  radioactive decay .  The  weak force  is responsible for interactions that cause decays. In this process an element can become an isotope of itself or even another chemical element.

When an isotope decays it is called a  radioactive isotope .  For example, U 238 can transform into Pb, with mass 206. Pb, in this case, is considered a  child isotope  of U, and is also called a  radiogenic isotope .  In this context U 238 is the  parent isotope .  All the U 238 ever produced in supernovas will one day transform into Pb 206. In this transformation process, U 238 progressively decays, transforming itself into other isotopes or lighter elements along the way, until it reaches mass 206. The transformation of U 238 in Pb 206 takes 4.47 billion years. That is, the U 238 formed in the first supernovae no longer exists. This transformation time is the  half-life of the U; that is, the time it takes for half of the U 238 atoms to decay into Pb 206.

Some isotopes have very short half-lives, sometimes less than a second. When radioactive decay happens, it releases particles and energy. Some isotopes, however, never change, being called  stable isotopes .  Pb 206, for example, is a stable isotope. Lighter isotopes are more stable.

Where do we walk?

 118 different chemical elements have been identified  so far (2020). Of these 118, 94 are naturally occurring, especially related to the life and death of stars, and 24 were synthesized in the laboratory.

The heavier the chemical element, the smaller its quantity in the Universe. With the  periodic table  of the elements complete, matter became increasingly complex as different chemical elements combined to form different molecules.

When it all started, back in the Big Bang, the very high temperatures helped fundamental particles combine to form atomic nuclei and then the simplest atoms, H and He. These two elements make up about 98% of all elements in the Universe, being 75% H and 23% He. The Universe no longer produces H, as it no longer has the energy to combine the fundamental particles. And the H is gradually being burned in the hearths of the universe, the stars, turning into other elements. This process is making the universe increasingly complex. In this way, simple particles were transformed into different atoms, stars, planets and galaxies. Nebulae are no longer just clouds of gas, but a mixture of gas and dust, that is, tiny solid particles, especially the first minerals,  formed by the continuous transformation of matter. 

New nebulae are continuously formed by chemical elements generated by the death of stars, giving rise to more stars, in a continuous process of recycling of matter. The nebula that formed our star, the Sun, 4.56 billion years ago was seeded with chemical elements and dust generated by stars that no longer exist. Our existence, the Earth, rocks and minerals are linked to these chemical elements and to their  cosmic origin.  This is a story that began to be told a long time ago,  “with no traces of a beginning and no prospect of an end”

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