Approximately 18,000,000,000 years ago an event took place which marked the beginning of our universe. We call this event the Big Bang. All matter and energy now present in the cosmos were compressed into an ultimately dense concentration, perhaps even a dimensionless point. This must not be understood as if all matter and energy were compressed in one corner of the current cosmos but rather that the entire cosmos, matter and energy and space they fill occupied a very small volume of space. There was not much room for events to occur. After the titanic explosion, the cosmos began to expand and has not stopped since. As space expanded, matter and energy expanded as well, leading to rapid cooling. The radiation of that cosmic fireball which filled the cosmos then as it does today, moved through the spectrum from gamma rays and X-rays to ultraviolet light. Shifting further through the rainbow colours of the visible spectrum toward infrared radiation it finally reached the radio waves that we register now as background radiation coming from all directions in the sky. In its early stages, the cosmos was brightly illuminated. Over time, due to the expansion the radiation cooled, and for the first time space became dark as it is today, when observed in ordinary visible light.
The early cosmos was filled with radiation and abundance of matter. At the very beginning, there were only elementary particles of matter from which Hydrogen (H) and Helium (He) were built soon. Then, small pockets of gas were beginning to grow, hardly different. Those were the beginnings of enormous, slowly rotating clouds of gas. In this manner the largest structures of matter in the cosmos – galaxies – were created.
About 1,000,000,000 years after the Big Bang clusters of galaxies were created. Gravitational attraction caused galaxies to rotate faster around their axes, as required by the natural law of conservation of angular momentum. Within the newly born galaxies, much smaller clouds also experienced gravitational collapse. Inside such compressed gas clouds, extremely high temperatures developed and the first thermonuclear reactions began. The first stars ignited. Extremely hot, massive young stars quickly consumed the hydrogen fuel and soon ended their “lives” in bright explosions we call supernovae, thus sending back the material to interstellar gas for the creation of new stars. Within stars, prior to the explosion fusion takes place – the merging of the nuclei of gas atoms and the creation of atoms of higher atomic weight. This was how the composition of matter in the interstellar space was changing.
Supernovae explosions created successive hitting waves that collided in the surrounding gas and compressed the intergalactic environment thus accelerating the formation of galaxy clusters. After that, gravitation intensified the compression of matter. The hitting waves after stellar explosions most likely contributed to the contraction of matter of all sizes. The condensation of matter from the gas produced after the Big Bang had the following sequence: clusters of galaxies, galaxies, stars, planets, and finally life and reason.
The cosmos contains about 100,000,000,000 galaxies. Clusters of galaxies contain from several to tens of thousands of galaxies. The interior of the galaxy rotates as a solid body, while the outer parts rotate more slowly as the distance from the center increases, similar to the rotation of planets around the Sun. Both galaxies and galaxy clusters rotate around a central point. Force holding together the material of stars, galaxies, and galaxy clusters is called gravitational force. The amount of rotation and gravity must be in balance for celestial bodies to maintain a constant shape.
Scientists easily obtain data on the rotation speed of a galaxy or galaxy clusters. Based on the speed they determine the required amount of matter that would counteract the centrifugal force by means of its gravitational forces. In this manner, it was discovered that visible matter is only a part of the existing matter. Where exactly within the galaxies is the missing matter and in which form it exists, scientists do not know. What they do know is that to account for the effects of gravitational force, as much as ten times more matter is required than what they have so far observed in any way. That is a major problem indeed. It is even greater when it comes to galaxy clusters because the manner in which they rotate required the presence of missing, “invisible” matter uniformly distributed between the galaxies, rather than somewhere within the galaxies themselves. If we observe the very center of a galaxy which rotates as a solid body we will see that there is also a “shortage” of matter inside it, since it rotates too fast and has an excessive density of the stars it is formed of, which the visible mass cannot provide.
Modern cosmologists see the cosmos as a vast arena in which all galaxies spread out in all directions but in such a manner that each galaxy can consider itself the center of the cosmos. One might think that there had to be one real center, one point where the original explosion took place. There is no such center. When we deal with the cosmos it seems that we need to “leave our common sense at the door” to a certain extent, as was done in the research of microscopic worlds. We must rely on mathematical theories that seem strange at first but which, contrary to common sense, align with the experiments and observation. These theories state that the cosmos was not created simply in one explosion at one point in space, like an explosion of shrapnel that launched galaxies. The very space expands carrying galaxy clusters with it. Gravitational attraction within a galaxy holds the stars together in one unique whole, while the galaxies grouped in clusters create “local” gravitational force that holds the cluster together. However, neighbouring clusters, although being large concentrations of mass have no significant interactive gravitational attraction. The empty space between them continuously expands and clusters drift apart. The idea of “expanding empty space” can be stunning for the mind but in Einstein’s theory, space actually exists. Our glance toward the sky will confirm this expansion. The most distant points visible in the sky represent the light created during the formation of galaxies.
According to Einstein’s relativity, there is a finite speed in the cosmos. We call that speed – the speed of light. The wave of energy moves at this speed. Matter as we know it can never reach this speed. The mass of a body increases with its velocity. At speeds close to the speed of light, the mass of a body becomes infinitely large. This means that a body, regardless of the force it is driven by, cannot increase its speed. Likewise, Einstein’s relativity claims that depending on the velocity of motion, changes occur in the speed of time passage and lengths of objects and distances. The closer the speed is to the speed of light, the slower time passes, and lengths and distances in the direction of motion become shorter.
If we were to travel at the speed of light, objects that are behind us would start to appear in our field of vision, even though we are looking straight ahead. The world as seen through the eyes of someone traveling at that speed would seem strange. Everything ultimately compresses in a small round space located immediately before the person in motion. The mass of this person would increase, and the time he experiences would run slower. These astonishing facts, as the results of motion at speeds close to the speed of light, we call time and space dilation. Another paradox is the following fact: if several people were traveling in a spaceship at a speed close to the speed of light, inside the spaceship no one would experience any change. They would experience time the same way we do.
These unusual and at a first sight confusing predictions of the Special Theory of Relativity are true in the deepest sense in which anything in science can be true. These predictions depend on relative motion, but they are real and certainly not optical illusions, and most importantly, they are in concordance with numerous experiments that have been carried out and are mathematically verifiable.