There are numerous galaxies we can observe today, about 13.8 billion years after the massive Big Bang explosion, that in any previous point in the Universe‘s history. As time goes by, the number of potentially visible galaxies will enhance, and even they are receding at a faster pace, no galaxy will ever completely disappear from researchers’ sight.
Why? The Universe has been taking place in a terrific cosmic race: the initial expansion rate and the powerful force of gravitation. Based on this system, there are three possible outcomes.
The Expansion of the Universe
The first possible result is that the initial expansion is far too massive for the matter and energy we have, and the Universe continues to expand forever. The second outcome suggests that there could be too much matter and energy for the initial expansion rate, and the Universe magnifies to a maximum size and then shrinks, collapsing into an explosion. Finally, the Universe could exist right on edge between those two scenarios, where the expansion ratio asymptotes to zero, but it doesn’t re-collapse.
Rather than following these three concepts, the Universe does something different. For the first few billion years, it seems like the expansion ratio and the matter and energy density balance almost ideally, as the expansion ratio goes down together with the density, walking towards that state where the expansion rate asymptotes to zero.
Distant galaxies seem to recede from at a continual slower pace, even as they get bigger and bigger distances. As the expansion ratio diminishes, ultra-distant galaxies, whose light has been gleaming towards Earth for billions of years, start to catch up to us, ultimately becoming noticeable.
Then, about six billion years ago, these ultra-distant galaxies seem to distance themselves from us at an accelerated pace. All of a sudden, the presence of the dark energy gets noticed. The reason for this is rather simple.
As the Universe expands, its volume enhances, but the number of particles within it stays the same. With time, the matter density falls in portion to the level of the Universe cubed: the separation distance between any two places to the third power. The radiation then falls even more dramatically – to the fourth power – since the quantity of particles dilutes, and the expanding Universe also magnifies that radiation wavelength.
However, if there is a non-zero quantity of energy natural to space, the energy density doesn’t fall at all, although the Universe stretches. Rather, the dark energy density stays the same, which means that as the matter and radiation density lower by gigantic amounts, dark energy becomes more significant. Until now, it has become the main form of energy in the Universe.
Nothing Actually Disappears
However, what does that mean for the magnification of the Universe? Numerous mathematical equations might make it seem like the Universe is disappearing. As time passes, individual galaxies that are grouped in clusters will stay together in these individual clumps, but separate, standalone clumps will all recede away from one another, at an accelerated pace, as the Universe develops.
In another 100 billion years, researchers won’t be able to detect any galaxy that’s located beyond our group, formed of Andromeda,Triangulum, and about 60 other small galaxies.
Currently, there are about two trillion galaxies hosted by our observable Universe. Only around six percent of them are noticeable by researchers, which means that the other 94 percent will always appear as they were in the past: we will never get to see them because they exist 13.8 billion years after the Big Bang, and that light will never get to us.
However, with time, more galaxies will be detected, although we’ll only see them in their early cosmic years, making the total number of observable galaxies 4.7 trillion. In the end, nothing will really disappear as the photons will just get here more seldom and will less energy.