The curiosity about the nature and the structure of our universe has been an important topic for thought and wonder since the time immemorial. The philosophical inquiry by Empedocles, one of the prominent pre-socratic philosophers, on the basic constituent of the universe as being earth, air, fire and water was remarkable. Aristotle’s view on motion of the celestial bodies around the earth and prediction of eclipses was significant though inefficient to fulfill the requirements of a scientific theory. This period should be regarded as the birth of cosmology in a sense that what remained beyond the Earth was the topic of inquiry. Aristotle’s works led to the development of geo-centric (geo meaning ‘earth’) model of the universe by Ptolemy at around 100 A.D. This makes evident as to what degree, the universe was a major topic for skepticism and thought inquiry in ancient time.
Followed by the Copernican revolution around the mid-16th century by proposing the helio-centric (helios meaning ‘sun) model of the solar system, the pioneering work by Johannes Kepler on the motion of planetary bodies and other related investigations by Galileo in 17th century, the knowledge of cosmos was systematized in the domain of classical physics developed much by Newton in 17th century. Based on a radically new idea of space-time fabric (the notion of 3 space dimensions viz. length, breadth and height and one dimension of time, were united to a single entity called space-time having 4 dimensions) the general theory of relativity was developed by Einstein in 1917. The General Theory of Relativity marked the beginning of modern cosmology. This framework based on space-time fabric modified the concept of gravity from force to the effect of the curvature of space-time. Under this framework, new insights about the origin, evolution and the large scale structure of the universe were formulated by a number of scientists. A significant work by Penrose and Hawking in early 1960s established the idea of origin of universe from a single point known as the Big Bang, wronging the notion of steady state eternal universe as conceived earlier 1). In 1970s the development in particle physics and field theories led to the idea of unification of all laws of physics into a single framework. This led to the development of string theory and other quantum field theories, under which cosmology governed by gravity, is only a specific case. On the other hand, the advancement in our observational and detection technologies brought a major upheaval in our understanding of the universe. The accelerated expansion of the universe as theorized earlier was confirmed by the observation of distant supernovae (by analyzing the spectrum of light of such supernovae) in 1998.
The accelerated expansion of the universe gives us an idea that the universe must have been at a single point in the past like what was shown by Penrose and Hawking. When traced backward, this point known as Big Bang was found to be 13.78 billion years away in time. But for the universe to start spontaneously from a single point and produce the present universe, things are extremely unlikely. So, at least in order to explain different properties of present universe, an accelerated expansion in the early universe has to be incorporated in the standard Big Bang scenario. This period of accelerated expansion lasted from 10-36 to 10-32 seconds after the Big Bang and is known as Inflation. Inflation expanded the universe by, well over, 30 orders of magnitude: meaning that, the universe expanded, in those tiny fractions of a second by an amount more than the distance covered by light since the beginning of the time (though the velocity of light is fastest speed attainable by any object in the universe. Inflation is an expansion due to a sort of vacuum energy so there is no causal relation to velocity of light). In cosmology, things are enormous in scale.
Theory of everything (TOE), the most ambitious framework of theoretical physics so far, can be expected to be developed in a couple of decades . TOE can be defined as a model of four fundamental forces that is elegant, theoretically plausible in its own right and consistent with observation and experimentation (unless the scientific method is the criteria: 2). It is expected that a TOE would enable us to know literally everything about the four fundamental forces and but not anything that sentient beings like us would choose to invoke.
The shape and size of universe still remains a mystery but to hide our ignorance, there is a common trend to infer such questions being non-sensical. There is nothing other than “universe is terribly complicated and incredibly large” -type of opinion. Our level of comprehension is tiny as we are an insignificant creature from cosmological standpoint. Strictly speaking, the universe was not made to accommodate futile creatures like us. But to provide substantial evidence to support my statement would require a new article. We are simple primates having a limited sensorial perceptions and there is no physiological mechanism to understand anything apart from subjective biases that we inherently possess. But the idea that an objective sense of the physical world can be developed, irrespective and independent of anything else, is the program behind the whole scientific enterprise and we have to be optimistic about it.
The direction to which we are heading in science is sure to provide further insights about the universe and emanate our understanding as intelligent creatures further. The thing to be glad is that a small species of creatures like us whose existence was possible simply by a fleeting chance event, have managed to know a lot about the universe and upon sustained efforts, there is no limit to where we could go.