We only need to peek into a telescope to be dazzled by the beauty of the cosmos. We can look at billions and billions of explosions, halos and sparkles, pulsing like a single heart among all of the immensity of space. And yet, every moment, a new fraction of the universe disappears forever, at an ever growing rate.
Our universe is expanding: every part that constitutes it is irremediably moving away from the others at a growing rate, like dots on the surface of a balloon that is being inflated. The force that is causing this phenomenon is still unknown to scientists, who have gaven it the name of dark energy.
Light and matter have a maximum speed, however the very fabric of space-time itself is not constrained by these limitations. As the expansion continues, the galaxies around us are moving further and further away, and the further away they are, the faster they are moving away, faster than their light can travel in the opposite direction to reach us.
Overwhelmed by the unobservable universe
Thanks to astrophysicists' calculations, we can estimate that the radius of the observable universe (that is to say, whose light reaches us) is 46 billion light-years (380,000 years after the Big Bang, taking the expansion into account). Gradually, the galaxies in our vicinity ‘overflow’ over this horizon, like a liquid overflowing from a glass which one continues to fill at an ever faster rate.
Thus every year, a fraction of the universe disappears to be swallowed up by the unobservable universe: even if we can theoretically suppose that these galaxies still exist, their light will never be able to reach us because they are moving too fast away from us. Little by little, the cosmos will become darker, until only a handful of galaxies keep us company. But our universe still has a bright future ahead before that happens.
Check out the video above for more explanation of this fascinating phenomenon!