The definition of space is ambiguous in itself. In one sense, it refers to the physical room in which anything exists but studies in Astronomy has changed the way we generally understand it. Now, space refers to the totality of all creation and the vastness of the universe. The pale yellow/red dots like stars that appear to be scattered in the night sky, other strange objects that seem only occasionally and the planetary systems that these stars monitor, are all the elements of space science.
In primitive days of our civilization though proper knowledge couldn’t be developed as a result of not being acquainted with science in a way it was necessary, there were ideas among the philosophers that the universe must be endless and eternal. Aristotle in the ancient Greece thought that the earth, where we live must have unique natural laws, different than the rest of the world. But when Galileo in the 17th century built telescope and saw the Jupiter and its moons orbiting each other –with the little aid of astronomy– the notion of unique world was abandoned. With continued progress in science, we became able to analyze light emitted by stars in far space and understand in some ways the dynamics they exhibit 1). The light is emitted due to the nuclear fusion reactions that take place in such stars in which the energy radiated in such nuclear processes is emitted as an electromagnetic wave which can travel even in empty space and thus reach everywhere. The visible light that we see (because of our evolutionary adaptation) belongs only to a specific range of wavelength in the vast electromagnetic spectrum.
Light approaching towards us grows in intensity and the one receding away from us grows dimmer. Using this idea of everyday experience, scientists then, were able to estimate the distance to stars by analyzing the light emitted by them. Cepheid variable stars (a class of pulsating stars whose intensity changes in a fixed pattern in a cycle) were first used for distance approximation in Astronomy 2). The result was astonishing as the distance to them was found to be many order of magnitude greater than we expected, meaning that those stars are much farther from us and that the world is much larger than we thought. With the progress in molecular chemistry and spectroscopy, this analysis of light turned into a new direction. We became able to predict different elements present in the stars and the interstellar medium by looking at the emission spectra of stars. The energy is governed by the laws of quantization (meaning that it is absorbed and released in packets), but when radiated, it is in a range of continuous wavelength. Absence of a line from the emission spectra hints the prediction of an element in the star or the interstellar medium which would absorb light of that characteristic wavelength. In this way, higher resolution spectroscopy helped to predict a number of elements marking the success of Astronomy.
In the 1950s and 60s, a number of rocketry feats were achieved especially by the USSR and the US. Artificial satellites were sent to the space to orbit the Earth for precise weather prediction; Marnier mission was sent to Venus and finally, the dream of human landing on moon was achieved in 1969.
Today a lot of artificial satellites (each designed for a specific purpose) orbit the earth which has facilitated a lot of human technologies easing the life we live. A place called International Space Station, the size of a football court has been made in space which orbits the earth 15 times a day and acts as a space research laboratory. 3)
We soon realized that there are more than 100 billion galaxies like our Milky Way in the universe, each of which consists of billions of suns each with its own planetary system. That’s like a total of billions and billions of stars in the universe. Now, the probability that any intelligent life could develop like our own in any of these star systems is non-trivial. Thus, the doubt of we being alone amidst of this vast creation turns out to be pseudo-scientific backed up by rational presumption (which ought to be taken seriously).
The question ‘why no extraterrestrial communication has been maintained or why there is not even a slightest hint of any intelligent life sustaining elsewhere’ can be answered simply as ‘because of the problem of acquisition’. Neither we nor our intelligent partners, whom we hope to communicate with, know where to look for. This is the problem with aliens of extragalactic origin but there could be an intelligent life in the Milky Way itself in so called exo-planets which orbit different star system (other than the sun). Many exo-planets with remarkable similarity to earth have been found in astronomical studies and this probe is continuing with special efforts as well. Search for Extra-terrestrial Intelligence (SETI) is a collective name for all such probes 4). We can certainly be optimistic for extra-terrestrial communication in the near future.