14 DAY TRIAL // Geza Dyuk, the director of Astronomy at the Adler Planetarium, says that the universe is indeed expanding. Incredibly, even the great German physicist Albert Einstein didn't know for certain if the universe was expanding or contracting, at the time when he published his Theory of Relativity back in 1905. So, while working at the General Theory of Relativity, he considered the universe to be static, only to find out later that his own theory pointed towards a dynamic universe.
Not that a static universe would not be stable, but such a state would be possible only for short periods of time before it would either expand or contract. The breakthrough came in 1929 when the famous American astronomer Edwin Hubble concluded, while observing a series of galaxies, that the universe is inflating. Not only that, but its expansion speed is growing exponentially.
Ever since, all other observations confirmed that, except for a few galaxies in the Local Group, all other distant galaxies are receding away from us. The further a galaxy, the faster the speed. This is exactly what Einstein predicted in the Theory of General Relativity, the universe is continuously expanding, stretching matter, so that, in a distant future, there will be more space in relation to the matter in the universe.
Over time, other observations piled the evidence that the universe is expanding. However, what determines such a process is currently unknown, whether there is not enough matter to keep the universe together or dark matter exerts a repulsion force towards the normal matter. The inability to understand the exact nature of inflation is affecting our view of the whole universe. Astrophysicists are still struggling into comprehending the Big Bang, the nature of space-time, and the ultimate fate of the universe, whether that will be a Big Rip or a Big Crunch.