Lots of brilliant ideas from Albert Einstein have proved to be accurate in recent decades, but only for four years have we had proof that one of his most visionary intuitions is reality. September 14, 2015 we saw for the first time gravitational waves, the spacetime ripples predicted by general theory of relativity of the great German physicist.
But let's start from the beginning, from Einstein's revolution. In summary, we could explain it like this: the vacuum doesn't exist, because every particle of the cosmos is immersed in the gravitational field. The latter is not a normal field, like the electromagnetic one, because it is not immersed in space: it's space. Or better, spacetime, written in one word, because space and time are two faces of the same reality. With a legendary image, Einstein described the gravitational field (i.e. spacetime) as a "clam” which envelops all things, capable of flexing, bending, rippling.
This is why objects fall towards the center of the Earth and the Earth orbits the Sun. There is no invisible force, no magical fluid: are the masses that deform the space, bending it and attracting nearby objects with lower masses. To visualize the idea, let's imagine this scene: a group of people holds a cloth (the gravitational field, i.e. space) suspended in mid-air; in the center of the sheet we place a bowling ball (the Sun), which folds the sheet; after that, on the same cloth we place a marble (the Earth), which will inevitably fall towards the center.
In short, space has a physical and mobile consistency. It can undulate, just like the surface of a lake when we throw a stone into it. And it is precisely one of these ripples that we managed to see four years ago, when the Virgo interferometer (a gigantic hyper-technological measuring instrument) has captured for the first time a gravitational wave. Since then, 14/XNUMX has been renamed “Gravity Day”. The day when the most beautiful of theories – as the Russian physicist Lev Landau defined it – has finally shown itself to our eyes.
