How far can we travel into space?

Is there any place where we cannot go? Are there borders that we cannot cross, no matter how hard we try? The answer is yes, even if we possess the technology of our science-fiction movies we will still be trapped in the pocket of our universe. I know! a lot of questions are popping inside your head. Just keep reading and you will get the answers to all your questions. And if still, any question is left then comment your question below.

We live in Milky Way which is a spiral galaxy of average size about 100 thousand light-years. It consists of billions of stars, gas clouds, dark matter, black holes neutron stars and planets with the supermassive black hole in the galactic center. From afar our Galaxy seems dense but in reality, it consists mostly of empty space. With our current technology sending a human to the closest star will take thousands of years, and hope this will give you a little idea about how big our galaxy is. The milky way is not alone, though along with the Andromeda Galaxy and more than 50 dwarf galaxies it's part of the Local Group. It is 10 million light-years in diameter. It is one of the hundreds of Galaxy groups in the Laniakea Supercluster which itself is only one of the millions of superclusters that make up the Observable Universe.

 Now let's do a bit of time travel, let's say after few centuries, humanity becomes a type 3 Civilization, does not get wiped out by aliens and develops interstellar travel based on our current understanding of physics in this best scenario how far will we go? Well, the answer is the Local Group. It is the biggest structure that humanity will ever be a part of while it certainly seems to be a large group but it accounts for only 0.00000000001%  of the observable universe. ok take your time and let this number sink in your brain. We are limited to a hundred billionth percent of the observable universe. The simple fact that there is actually a limit for us and that there is so much Universe that we will never be able to explore is kind of frightening! Why can't we go further? Well, it all has to do with the nature of nothing, nothing or empty space isn't empty but has energy intrinsic to itself so-called Quantum fluctuations on the smallest scale there is constant action particles and antiparticles appearing and annihilating themselves. We will talk about it later.

Now let's go back to 13.8 billion years when the fabric of space consisted of nothing at all. Right after the Big Bang in an event known as cosmic inflation the observable universe expanded from the size of a marble to trillions of kilometers in a fraction of a second. This sudden stretching of the universe was so fast and extreme that all those Quantum fluctuations were stretched as well and subatomic distances became Galactic distances with dense and less dense region. After inflation gravity began to pull everything back together. At the largest scale, inflation was too quick and powerful to overcome but, at smaller scale gravity emerged victorious. So, over time the denser regions or pockets got locked by the force of gravity, creating galaxies like the one in which we live today. 

But, wait 'what's the problem then, why can't we travel from our pocket (galaxy) to another pocket?' The problem is Dark energy It makes everything complicated. About 6 billion years ago dark energy took over and it started acting as a border between galaxies. It is an invisible force that causes and speeds up the expansion of universe. We don't know what is dark energy but, we can feel it's effect. Our local group is surrounded by a lot of stuff but, none of them are gravitationally bound to us. So, the more the universe expands, the larger the distance between us and other galaxies become. Overtime dark energy will push the rest of the universe away from us causing all the other clusters and galaxies unreachable for us. The nearest galaxy is already millions of light-years away from us but, all of them are moving away from us at such speed that we cannot ever hope to match. And at some point, the galaxies outside of the local group will move so far away that that would become almost invisible for us. Once this happens, no information outside the local group would be able to reach us. The universe will recede from view. It will appear to be dark and empty in all directions, forever. 

The beings that will come into existence in the local group after a few billion years and won't come into contact with human civilization for them this local group will only become the whole universe. It is because when they will try to explore the space, all they would see outside the local group will be more emptiness and darkness and they will come to the conclusion that the local group is the whole universe. They won't be able to see cosmic background radiation, and they won't be able to learn about the Big Bang. They will have no way to know what we know today- the nature of the expanding universe, when it began, and how it will end. They will think the universe is static and eternal. And the same scenario might happen in other galaxies.

Still, with its trillion stars, the Local Group is certainly large enough for humanity. After all, we still have not figured out how to leave our Solar System and we have billions of years to explore our galaxy. We have the incredible luck to not only see our future but also our mysterious past.

Hey, wait I have a question for you ' don't you think that the scenario which we are assuming for the other beings that will come into existence after billions of years in the Local Group is true, and might be we are those beings who don't know about the past of the universe and there are other civilizations which are much advanced than us' Well, I don't know. And if you know then please let me know.