I. How the model of the Universe is created
Once I read about a doctor in ancient China who examined the Caesar’s wife behind a curtain. The wife put one end of a thread to different parts of her body and the doctor by holding in his hand the other end of the thread observed only vibrations. He gave his diagnosis under the observations of the vibrating thread. I thought then that giving good diagnosis in such conditions was almost impossible.
When examining Cosmos we are, however, in a similar situation like the Chinese doctor. We cannot come closer to examine it. The only thing we can do is to observe various waves that reach us and strain our brains.
Usually, we do not realise that our model of the Universe is based on a specific mixture of observations and theoretical assumptions. The only observations as such are not enough. They may be even misleading. If we erase everything we learnt at school and we try to create our own perception of the Universe only on the basis of our direct observations, what will we receive? The Earth seems to be static and more or less flat, during the day the Sun travels across the sky from the East to the West, and at night the celestial sphere with stars turns over our heads. Even when we want to explain why the Sun in the morning reappears in the East, some assumptions need to be made, because it is not a direct result of observations. We have to formulate a theory on the basis of which our observations will be interpreted. It is a confusing situation which may move us towards a wrong direction for a longer period of time, making us to believe that we are right. New observations may be explained somehow as part of the current model, by adding new concepts or, by searching for a new model.
Before creating a new model it is worth reminding ourselves how the perception of the Universe appeared and changed throughout years starting from the ancient times. Which observations and arguments influenced people to change their opinions about the world and to create further models.
A long time ago on the basis of direct observations people thought that the Earth was static and the sky with stars was moving around, and the mutual distances between the stars did not change. It seemed to be logical that the stars were placed in a rotating sphere. The Sun and Moon could have been placed in separate spheres, a problem occurred when the planetary circulation had to be explained. Various attempts were made, finally Ptolemais offered a model, in which planets additionally move in circles called epicycles. It was rather a complicated structure and Ptolemaist himself probably was not satisfied with such model, however, the model so trustworthy reflected the observations that it survived over a thousand years.
Were there any other postulates? When everybody believed that the Earth is static, which was proved by the experience, it was difficult for them to believe it might have been different. Although, a few hundred years BC, Aristarchus of Samos had already offered a heliocentric model of the Solar system. It was a genus idea, but it did not reflect the observations. The positions of the planets were different than the calculations indicted.
As you can see you do not have to reject the model which does not reflect observations. Sometimes a minor modification or change in interpreting the results appears to be sufficient. Why the results did not corelate with the observations? Because no one at that time thought that planets could move by taking different paths than the circle, moreover, with variable speed. What was not also detected was the parallactic shift of stars, which was supposed to appear when the Earth travels around the Sun. Still in 16th century Tycho Brahe, after conducting thorough observations, overturned for that reason the heliocentric theory published by Nicolaus Copernicus. It was a result of other erroneous assumption. Tycho Brahe did not assume that the distances to stars might be so big that the parallactic shifts are beyond reach even for the most precise measurement instruments used at that time. It seems that the results of observations might be misleading. When we interpret them incorrectly, we may draw wrong conclusions.
The heliocentric model started to be treated seriously only when Johannes Kepler after the analysis of a great amount of data, came to the conclusion that the planets move around in elliptical orbits with variable speed, and the observations commenced to correspond with the computations.
The origins of seemingly strange movement of planets were not known. It was the only theory of gravity given first by Isaac Newton that gave an explanation to it.
Since people believed that the celestial sphere rotates around the Earth, it seemed obvious that the distances between us and all stars must be identical. When it appeared that motion of the stars in the sky is only apparent, immediately the identical distance between the stars and the Earth ceased to be essential. On the contrary, different brightness of stars that was observed indicated different distances. However, how to determine the distances and how big the entire Universe is? To rely only on the observations is proven to be insufficient. Again, some additional theoretical assumptions are required. Newton proved that the same laws apply to the celestial bodies as to the Earth. However, when it comes to stars, a new problem arose. When all bodies attract each other why all stars do not fall into each other?
Again, we see that the observations may lead us to the misleading conclusions. We find stars static only because the distances between them are very long. However, the Universe is not static at all. There were attempts to find a solution to that problem and that is how the concept of the endless Universe was developed.
According to the principles of Euclidean geometry which we were taught, an endless, non-curved space seems to be something natural. However, infinity can be proved neither by observations nor by experiment and it is in fact only a product of our imagination. Moreover, it appeared that an endless space is not the case when it comes to the stability of the Universe. In order to ensure stability of an infinite, static Universe, the theory of gravity needs to be modified in relation to the very distant objects. As will be seen later, the modification of Newton’s theory of gravity is required in case of the finite Universe, because it was formulated for the infinite, non-curved space.
There was another argument which was also against the concept of the infinite Universe. An infinite number of stars more or less equally deployed in the endless space should result in a bright sky also at night. It should have been explained somehow why it is dark. One of the possible explanations was the assumption that the stars do not generate light from the beginning. In this context there is the question when and how they start to generate light?
It seemed before that the topic could be only speculated about. The stars believed to be at such a long distance and so unreachable that they were only perceived as a pale light in the sky. It became clear, however, that such a feeble light we see may be a great source of information. By conducting research on the spectrum of stars, their chemical composition can be determined and by comparing various stadia of stars it can be concluded what processes and chemical reactions occur in them.
However, continuous analyses and examinations should be conducted to discriminate the direct observations and the theoretical models and therefore to determine how conclusions can be made regarding the real Universe. When a shift towards redness in the spectra of distant objects was observed and the bigger it is, the more distant is the object, it may be interpreted as an expansion of the Universe. It is not, however, the observation of expanding the Universe, therefore, it may be interpreted in a different way.
When we assume that the Universe expands, it seems to be logical that it was smaller and it was also created from a small area. A “beginning” called the “Big Bang” was assumed. It cannot be proved by direct observations, however, relic radiation was detected, which may be interpreted as the remaining of the Big Bang. There is also a mathematical model which describes the Universe in accordance with the already said assumptions. Does it mean that our current image of the Universe is the right one? We know that it is not. The fact that it is in contrary to the quantum theory indicates that something is wrong. More and more precise observations require more eccentric structures to give explanations for such observations. As for better correlation between the observations and the theory, cosmic inflation was conceived (expanding the Universe billions of billion times in a fraction of a second), dark matter and dark energy (no one knows anything about but the fact that they are necessary as part of the existing model). Yet another observations will occur which cannot be explained by the modern theory, for example, giant black holes in the early Universe.
Now it is time to stop and think which of our assumptions may be erroneous, and time to build the model of the Universe once again.