Yesterday announcement of the Harvard astronomy center about discovery gravitational waves and its confirmation theoryof cosmic inflation was one of the most important scientific discoveries of recent decades and came after a long and collaborative effort. But what was it that makes her so significant? In order to understand its meaning, it will be necessary to explain some concepts that are not in the everyday vocabulary.
The Big Bang
Our knowledge of cosmology has developed rapidly in the last century. It is indicative that at the beginning of 20th century we did not know that there were other galaxies beyond our own. In the first quarter of the last century it was known that not only are there many other galaxies but also that there is a phenomenon called the expansion of the Universe that overturned the image of a stable, eternal and unchanging universe.
Going backwards, one would reasonably assume that the Universe in the past was increasingly dense. According to astronomical observations as well as theoretical ones forecasts, πιστεύουμε πως πριν από περίπου 13.8 δισmillions years ago the Universe was condensed into a point of infinite density, from which arose what we call the Big Bang. Physical theories break down at the moment of the birth of the Universe, but scientists focus on the immediate moments that were decisive for the shape the Universe has today.
The cosmic inflation
The Big Bang model gives several answers to the universe, but leaves a series of unanswered questions: why the universe is so homogeneous and isotropic (it looks the same in whatever direction and if we look wherever we are), why the universe is so surprisingly set to be level (of all possible values, its density seems to balance with incredible precision at a certain value that involves a Universe described by Euclidean geometry) etc. These questions go rel elegantly the idea of cosmic inflation. According to this, shortly after the Big Bang (we do not know exactly when, but about 10-35 seconds later), the universe expands exponentially, for a short time, due to the presence of a field. The exact form of the inflation field is not known, as there are many different models that we can divide according to their projections, and scientific discoveries such as yesterday are therefore very useful.
General Relativity and gravitational waves
The "language" that describes modern cosmology is the theory of General Relativity, invented by Albert Einstein in the first quarter of 20th century. It is a gravitational theory, and since gravity, although the weakest of the forces, is predominant over long distances (matter is basically electrically neutral, while nuclear forces have a small range), through which the evolution of the universe is described.
Gravitational waves are a prediction of the theory, which, however, had not been confirmed until today. According to the General Theory of Relativity, gravity is related to the distortion of the geometry of spacetime which is caused by the presence of mass or energy -είναι στην ουσία το ίδιο πράγμα. Η παραμόρφωση αυτή διαδίδεται με τη μορφή κυμάτων τα οποία είναι πολύ δύσκολο να εντοπιστούν αφού προέρχονται από μία ασθενή δύναμη.
Background radiation and polarization
The main proof for Big Bang theory is the so-called background radiation, the light that continues to be emitted even today, as the echo of the birth of the Universe. As it is light (low frequency, since billion 13.8 billion years have been "frozen"), it shows the polarization property. Polarization of electromagnetic radiation can be of many kinds, they are called ways.
What scientists have spotted in the experiment VICEP (Background Imaging of Cosmic Extragalactic Polarization) was a particular way of polarizing the background radiation, called Mode B. This way is a "signature" of the effect of the gravitational waves of the early Universe, which happened because gravitational waves pressed space and time as they spread, and this compression creates a pattern for propagating radiation. Here is the concept of inflation, since discovery is a prediction of this theory. This point is particularly sensitive because it opens a window of compatibility between General Relativity (a classical theory) and quantum mechanics, which is one of the greatest problems of modern physics.
Today's discovery is important for a variety of reasons and is about to pave the way for new research. Firstly, it is the confirmation of one of the basic predictions of the theory of cosmic inflation and therefore of theory itself, while giving scientists the possibility of a new way of studying the Universe through gravitational waves.
