The Universe

The Universe started with the Big Bang. There is a large amount of evidence for this. If the law of conservation of energy is correct and energy cannot be created or destroyed (it can only be transformed) then the Universe has always existed in one form or another.

It is said that in the beginning, the Universe was a very small, very dense and very hot "singularity". At this point, the laws of physics break down and the theory of relativity predicts infinities (infinite mass, infinite density, infinite temperature). The early Universe was governed by quantum physics, so we will probably know how the Universe started when there will be a quantum theory of everything.

A quantum fluctuation is the spontaneous creation of particle-antiparticle pairs. Physicists believe that this is how the Universe started, a big quantum fluctuation in which matter and antimatter were created and they annihilated each other but some matter remained by some strange process.

It may be that quantum fluctuations exist everywhere and that some quantum fluctuations give birth to Universes. Maybe the creation of a Universe is a local event, in a much larger picture. Maybe there are other universes, nobody really knows. I've heard that if a quantum fluctuation in our Universe gave birth to another Universe, it would look like a black hole to us, so, inside a black hole there might be another Universe.

The Universe may be an oscillating one, expanding and then contracting again, the final moments of contraction giving birth to the next expansion. The problem with the oscillating Universe is that it violates the second law of thermodynamics, which states that the entropy (disorder) must increase in a closed system, and the oscillating Universe does not have any proof, in fact, the current understanding suggests that the Universe will continue to expand forever.

I cannot believe that the singularity which created the Universe existed like that forever and just "decided" at one point to explode. I cannot believe that something appeared out of nothing. I believe that something has always existed, not a god, not an intelligent being, but something, I don't know what. It seems that nothingness cannot exist, it would violate the uncertainty principle, so, there is something everywhere.

The Universe does not have a center, as odd as it may seem. It can be compared with the surface of a balloon. A balloon does have a center but the surface of the balloon does not. It's difficult to imagine 3D space as the 2D surface of the balloon. The Universe is strange.

"The universe is not only stranger than we imagine, it is stranger than we can imagine." - J.B.S. Haldane

Before the formation of stars, the Universe was not very interesting, just scattered matter and energy. The first stars seem to have formed 400 million years after the Big Bang. Stars and galaxies exist because of irregularities in the distribution of matter. Where there was more matter, gravity caused it to collapse and form stars.

Those first stars were big and very hot and had short life spans, inside them fusion occurred, hydrogen fused into helium but, at the end of a star's life, helium fuses into heavier elements.

Stars attain an equilibrium between gravitational pull, which tends to compress the star and heat, which tends to expand the star. As a star compresses, it heats up, as it heats up, it expands. Most of the action happens in the core of the star, because there's the biggest pressure and the biggest temperature, atoms move very fast and they collide with each other and fuse into heavier atoms, releasing energy. As lighter atoms create heavier atoms, most heavier atoms remain in the core.

Of course, this process cannot go on forever and, at some point the core of the star cannot fuse anything anymore, so the heat stops abruptly, but heat was the only thing keeping gravity from compressing it. This is where the core collapses. The shock wave expels the outer layers into space and the core remains as an extremely dense body. The core can form a white dwarf, a neutron star or even a black hole if the star was massive enough. A teaspoon of material from a neutron star would weigh 10 million tons.

When a massive star explodes as a supernova, it ejects into space a lot of material, including heavy elements. These heavy elements can form planets like our own. Life is carbon based and this carbon was fused in the center of a star, we are made of stardust.

See this:
Supernova