Even with the latest technologies at our hand, we have only been able to discover a very small part of this infinite universe. Ironically, we would never be able to witness it at all.
The universe as we now know was very different from the universe our ancestors have seen and likewise it would be different for future generations.
Another question that arises is since the universe is expanding, is there a border beyond which we cannot reach places? Yes, there is. We are trapped in a shell with some finite part of the universe.
There are galaxies near to us, galaxies far away from us, and some beyond our grasp.
When we look at the infinite universe from the earth, we are bound to assume that it would remain constant and as such forever and that the stars that we look at would be born and vanish endlessly at an exponential rate, but the reality is very different from this.
When we talk about the milky way which is 20,000 light-years wide and has about 100-400 billion stars, one might assume that every year millions of stars are born here, but in truth, only three stars are born every year.
The process of formation of stars is slowing down even more as we are at the tail end of the age of star formation and 95% of the stars that are known to exist in the universe have already been born.
Our galaxy is not the only galaxy in the universe as we know it, our galactic neighbourhood comprises the Andromeda galaxy and more than 50 dwarf galaxies, together they all form the local group of 10 million light-years in diameter.
Hundreds of these local groups further create the Laniakea Supercluster, which itself is one of the dense groups of superclusters. The universe we visualize is made up of two trillion galaxies.
Unfortunately, even if we would be able to travel by the speed of light, 94% of these galaxies are beyond our reach.
What we have to understand is that humanity has a limit, even though it is frightening but humans would never be able to discover a major part of the universe. All of this is because of the cause of its origin- The Big Bang.
After the Big Bang, through the process of cosmic inflation, the universe expanded from the size of a marble to trillions of kilometers in just a trillionth of a second.
The subatomic differences between the less dense and more dense regions in the universe turned into galactic distances.
Once the powerful inflation ended, gravity tried to pull everything back together and in the denser regions, it made a group of galaxies like the one we live in now.
Inside our Local Group galaxies are bound together through gravitational force. Our Local Group forms our local pocket.
At a larger scale outside the denser pocket, our Local Group is surrounded by a lot of stuff but none of it is gravitationally bound to us.
That simply reflects that everything outside our local pocket is becoming distant to us with the universal expansion.
Tragically, this expansion is exponential with an unknown cause. To describe this expansion the scientists came up with the concept of dark energy, an effect that speeds up the expansion.
The expansion signifies the occurrence of a cosmological horizon; a barrier between the observable and the non-observable universe.
Everything beyond this horizon is moving faster than the speed we can attain, so everything that passes the horizon will irretrievably be out of our reach forever with no possibility of interaction ever.
94% of the galaxies which we see at present have already passed the horizon.
Now the question that arises is, if we cannot interact with them, how can we still visualize them? The answer is simple, we aren’t observing the galaxies but the light they have emitted.
Although, speed of light is very fast it still needs time to travel through the infinite universe. Every second we observe light from trillions of galaxies, when the lights were emitted from the galaxies they were very near to us but now they have passed the horizon.
Even though we are still able to observe the galaxies through a telescope, we won’t ever be able to have an idea about how these galaxies look at present nor would we be able to establish any communication.
Everything that is beyond our Local Group would continue to expand and move out of the horizon, once they do, we won’t be able to observe them as their light won’t reach us.
From our perspective, they will fade into infinite darkness.
With every passing second, another 60,000 stars pass the horizon. Even though 94% of the universe is beyond our reach, the leftover 6% in our reach has a lot to explore too.
It comprises all the galaxy pockets that are 18-billion light-years away.
They too are moving away but at a comparatively slow speed enough for us to physically reach them, though the chances are shrinking with every passing second.
Even if we think to make a trip to Maffei, the nearest galaxy outside our Local Group, it would take 11 million years to do so.
The humans at present would not make this journey with the technologies available and soon even this galaxy will be beyond our reach.
Dark energy is known to push the rest of the universe far away from us, making the Local Group become more tightly bound in the near future.
In a few billion years, this will cause all the galaxies in our Local Group to fuse and form one giant elliptical galaxy with the unoriginal name, “Milkdromeda”.
The galaxies outside Milkdromeda will be so far away at some point that they’ll be too faint to detect.
Once this happens, there will be infinite darkness instead of the universe we know and no information of the space outside the Local Group will be known to us.
A being born in the distant Milkdromeda will only think that the universe consists of nothing but its galaxy, similar to the perception we had in the past.
When they would look into the far stretched space, they would only see ever-ending darkness and emptiness with no knowledge of the universe we know as of now.
They might think of the dynamic universe as static and eternal. But in reality, Milkdromeda would be similar to an island engulfed by the darkness.
Still, our Local Group with its trillions of stars is fascinating enough for humanity at present. We have been able to explore a lot and yet we still have a lot to comprehend.
We are fortunate enough to exist at a time where we can discern both the future and the past universe just by looking at our night sky.
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