I post con tag "Onde Gravitazionali" archivio

Il Washington Post ripercorre la storia, la teoria e la fisica delle onde gravitazionali, la cui scoperta è valsa il Premio Nobel per la fisica a Rainer Weiss, Kip Thorne e Barry Barish.

Gravity is invisible, as you may have noticed, and a little bit spooky, because it seems to reach across space to cause actions at a distance without any obvious underlying mechanism. What goes up must come down, but why that is so has never been obvious.

Physicists tell us there are four fundamental forces in the universe: Gravity, electromagnetism, the strong nuclear force and the weak nuclear force. Of these, gravity is the most anemic, and yet over cosmic expanses it has shaped the universe. In our solar system, it governs the planets and moons in their orbits. On Earth, it motivates the apple to fall from the tree. You can feel it in your bones.

Aristotle believed that an object fell to Earth because it sought its natural place. Heavier objects, Aristotle believed, fell faster; weight was an inherent property of the object.

In the late 16th and early 17th centuries, Galileo brought scientific experiments into the conversation, and he discovered that a heavy object and a light object actually fall at the same speed. [...]

Galileo also discovered that objects always fall with constant acceleration and along a parabolic curve. [...]

Then came Isaac Newton. In the second half of the 17th century, he developed a universal law of gravity. He calculated that the attraction between two bodies was equal to the product of their masses divided by the square of the distance between them. This is true on Earth as well as in space. It explains the tides. It explains the motions of the planets around the sun. This is a basic law of nature, true anywhere in the universe.

But even Newton admitted that he didn’t understand the fundamental nature of this force. Newton could describe gravity mathematically, but he didn’t know how it achieved its effects.

In the early 20th century, Albert Einstein finally came up with an explanation, and it's rather astonishing. First he grasped that gravity and acceleration are the same thing. His General Theory of Relativity, formulated in 1915, describes gravity as a consequence of the way mass curves "spacetime," the fabric of the universe. It's all geometry. Objects in motion will move through space and time on the path of least resistance. A planet will orbit a star not because it is connected to the star by some kind of invisible tether, but because the space is warped around the star.

Il New Yorker racconta la storia della ricerca della onde gravitazionali.

In fisica le onde gravitazionali sono onde di deformazione della metrica dello spaziotempo. La loro esistenza fu prevista nel 1916 da Einstein, nelle basi della sua teoria della relatività generale.

La teoria della relatività generale, infatti, prevede che masse accelerate interagiscano con il campo gravitazionale provocando la propagazione di onde, così come avviene per il campo elettromagnetico in presenza di cariche elettriche accelerate. La radiazione causata dall'accelerazione delle masse nello spaziotempo non è però di tipo elettromagnetico, ma gravitazionale. Al passaggio di un'onda (radiazione) gravitazionale, lo spaziotempo si contrae ed espande ritmicamente: questo effetto è però difficile da rivelare perché gli stessi rilevatori si contraggono ed espandono, solidali con lo spaziotempo.

Fronti d'onda di particolare ampiezza possono essere generati da fenomeni cosmici in cui enormi masse variano la loro distribuzione in modo repentino (e con un momento di quadripolo non nullo), ad esempio nell'esplosione di supernove o nella collisione di oggetti massivi.

Un secolo di studi e rilevazioni da Einstein all'interferometro LIGO.

A hundred years ago, Albert Einstein, one of the more advanced members of the species, predicted the waves' existence, inspiring decades of speculation and fruitless searching. Twenty-two years ago, construction began on an enormous detector, the Laser Interferometer Gravitational-Wave Observatory (LIGO). Then, on September 14, 2015, at just before eleven in the morning, Central European Time, the waves reached Earth. Marco Drago, a thirty-two-year-old Italian postdoctoral student and a member of the LIGO Scientific Collaboration, was the first person to notice them. He was sitting in front of his computer at the Albert Einstein Institute, in Hannover, Germany, viewing the LIGO data remotely. The waves appeared on his screen as a compressed squiggle, but the most exquisite ears in the universe, attuned to vibrations of less than a trillionth of an inch, would have heard what astronomers call a chirp -- a faint whooping from low to high. This morning, in a press conference in Washington, D.C., the LIGO team announced that the signal constitutes the first direct observation of gravitational waves.