In about 100 billion years, astronomers will face a dull period when they will only be able to observe 1,000 galaxies, compared to the billions of galaxies we see today. This is a consequence of the universe’s extremely rapid expansion: stars at the edge will disappear beyond the “cosmic horizon,” meaning we will never see their light again.
Astronomer Abraham Loeb from the Harvard-Smithsonian Center for Astrophysics (USA) states that the farther an object is, the more likely it is to vanish from our view. Moreover, it may take only 50 billion years before the universe stops expanding.
The “Expanding Universe” theory posits that right after the Big Bang, the universe began to expand and continues to do so. However, most astronomers believe that this expansion is significantly slowed down by the gravitational pull between galaxies. In fact, gravity could even create a tendency to contract, leading to a Big Crunch that would return the universe to its original state.
Nonetheless, recent discoveries regarding the outburst of distant stars over the past few years have allowed for the assumption that this expansion is occurring at a very fast rate, pushing all objects further apart.
The farther away objects are, the faster the expansion of the universe occurs. At that point, changes in these objects will reach us more slowly (in relative terms: when an object is close, we see it change quickly. When it is far away, we perceive those changes more slowly). Eventually, we may hardly perceive any changes in the universe, meaning time will seem to stand still (we perceive time due to changes in surrounding objects).
At this stage, an object has reached the “cosmic horizon” (event horizon – also known as the boundary of the expansion process, beyond which lies the unknown). This phenomenon can be compared to an object being sucked into a black hole, causing us to never see its light again. Once an object disappears beyond the event horizon, physicists assert that it has transcended the boundaries of scientific inquiry and entered the realm of mysticism.
What causes the universe to expand? This question remains the greatest challenge in astrophysics. One hypothesis suggests that the vacuum of space is filled with a certain amount of dark matter, which is pushing celestial bodies apart. Another hypothesis proposes that there must be something that constantly changes over time, subtly influencing this process. However, to prove these hypotheses, evidence is needed, and the current evidence does not support either hypothesis.
B.H. – Minh Hy (according to Nature)
