Physics is not only in laboratories
Today is a memorable day for Science and for human kind as well. Today, LIGO and VIRGO collaborations have announced the first direct observation and, so the discovery, of the gravitational waves. Exactly 100 years ago, one of the most famous scientist ever lived in our wonderful planet, Albert Einstein, postulated their existence. In Einstein's theory of general relativity, gravity is treated as a phenomenon resulting from the curvature of spacetime. This curvature is caused by the presence of mass. Generally, the more mass that is contained within a given volume of space, the greater the curvature of spacetime will be at the boundary of this volume. As objects with mass move around in spacetime, the curvature changes to reflect the changed locations of those objects. In certain circumstances, accelerating objects generate changes in this curvature, which propagate outwards at the speed of light in a wave-like manner. These propagating phenomena are known as gravitational waves. The waves detected by the two collaborations are due to two black holes moving around each other, spinning faster and faster and then collapsed in a unique more massive black hole.
It took a century to really see them, because, in a nutshell, it's an extremely rare and difficult to detect phenomenon. The experiment which is supposed to detect them must be extremely precise and accurate, and the scientists who are supposed to be the observer must be extremely patient.
The discovery of this phenomenon strengthens the Einstein's theory of general relativity and opens a wide field of research for Physics and Astrophysics. Being there in the main auditorium, at CERN, seeing and hearing proud scientists talking about their experiment, their amazing tecnology, their wonderful capability to build something so accurate; all of this makes me feel so proud of my choice and an extremely lucky witness of the moving forward of the human kind.
For this reason, I decided it's time for my second photo of my project. And which topic better than BLACK HOLES?
Despite its name, a black hole is anything but empty space. Rather, it is a great amount of matter packed into a very small area: think of a star ten times more massive than the Sun squeezed into a sphere approximately the diameter of New York City. The result is a gravitational field so strong that nothing, not even light, can escape.
The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although crossing the event horizon has enormous effect on the fate of the object crossing it, it appears to have no locally detectable features. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is on the order of billionths of a kelvin for black holes of stellar mass, making it essentially impossible to observe. The Hawking radiation is one of the possible solution of the paradox of the loss of information. Think about something, like light, falling into the black hole: it's violating some important and fundamental conservation laws in our universe, like the energy conservation. It's like something simply disappears, puf!, it doesn't exist anymore. It's not possible and scientists, during this century, argued a lot about that. The Hawking radiation could explain this paradow, assuming that the black hole emits a radiation, it's more or less an evaporation.
Of course, many theories were conjectured and all are possible, in the limits of the general relativity equations solutions.
One of the most curious and interesting theory, accordin to me, is the one which speculates that a black hole is actually a tunnel between universes, a type of "wormhole", the so-called Einstein-Rosen bridge. The matter the black hole attracts doesn’t collapse into a single point, as has been predicted, but rather gushes out a “white hole” at the other end of the black one. Einstein’s theory suggests singularities are infinitely dense, and are infinitely hot, a concept supported by numerous lines of indirect evidence but still so outlandish that many scientists find it hard to accept. Instead, according to the new equations, the matter black holes absorb and seemingly destroy is actually expelled and becomes the building blocks for galaxies, stars, and planets in another reality.
This theory is not demonstrated yet and frankly I don't know if it will never be demonstrated, but I like thinking it could be possible. Another universe, another possible reality, at the end of a black hole.
