What is the limit of Space travel? Is there a boundary we will never cross? Turns out there are places we will never reach, no matter how hard we try.
How Far Can We Go?
We live in the Milky Way Galaxy – a spiral galaxy about 100,000 light years across. It consists of billions of stars, gas clouds, dark matter, black holes, neutron stars, and planets, with a supermassive black hole in the galactic center.
From afar, our galaxy seems dense, but in reality, the average distance between stars is 47 trillion kilometers. With our current technology, sending a human to the closest star, would take thousands of years.
And the Milky Way is not alone, though. Along with the Andromeda galaxy, and more than fifty dwarf galaxies, it’s a part of “The Local Group“. That is a region of space about ten million light years in diameter.
It is one of the hundreds of galaxy groups in the “Laniakea Supercluster“, which, itself is only one of millions of super clusters, that make up the observable universe. So now we have pretty good idea how big the universe it.
Now, let’s assume, that we becomes a type three civilization, and develop interstellar travel based on our current understanding of physics. In this best case scenario, how far can we go?
Well, the simple answer is: The Local Group.
The Local Group is the biggest structure that humanity will ever be a part of. While it’s certainly huge, it accounts for only 0.00000000001% of the observable universe.
Yes, you read that right. We are limited to a hundred billionth of a percent of the observable universe.
The simple fact that there is actually a limit for us as to how far can we go, and that there is so much universe that we will never be able to touch, is kind of frightening.
Why Can’t We Go Further?
Well, it all has to do with the nature of empty space. Space has energy intrinsic to itself, so-called “quantum fluctuations”. On the smaller scale, there is constant action, particles and antiparticles appearing and annihilating themselves.
Now, let’s go back 13.8 billion years, right at the beginning of everything. After the big bang, in an event known as cosmic inflation, the observable universe expanded from the size of a small ball to billions of kilometers, all in fractions 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 regions.
After inflation, gravity began to pull everything back together. At the largest scale, the expansion was too quick and powerful to overcome but in smaller scales, gravity emerged victorious.
So, over time, the denser regions, or pockets, of the universe, grew into groups of galaxies, like the one we live in today. Only stuff inside our pocket – The Local Group – is bound to us gravitationally.
So What Is The Problem Then?
Why can’t we travel from our pocket, to the next one? And how far can we go? Here, dark energy makes everything complicated. It’s basically an invisible force or effect, which causes, and speeds up the expansion of the universe.
We don’t know what dark energy is, but we can see its effect clearly. In the early universe, there were larger, cold spots around the local group that grew into clusters with thousands of galaxies.
None of those structures and galaxies outside of the local group are gravitationally bound to us. So the more the universe expands, the larger the distance between us and other gravitational pockets becomes.
Over time, dark energy will push the rest of the universe away from us, causing all the other clusters, galaxies, and groups to eventually become unreachable. The next galaxy group is already millions of light years away, but all of them are moving away from us, at speeds we can’t, ever, hope to match.
We could leave the local group, and then fly through intergalactic space, into the darkness, but we would never arrive anywhere. While we will become more and more stranded in our quest to see how far can we go, the local group will become more tightly bound, and merge together to form one giant elliptical galaxy in a few billion years.
But Wait There’s More:
At some point, the galaxies outside the local group, will be so far away, that they will be too faint to detect. The few photons that do make it to us, will be shifted to such long wavelengths, that they will be undetectable.
Once this happens, no information outside of the local group will be able to reach us. The universe will recede from view. It will appear to be dark and empty in all directions, forever.
A being born in the far future in our galaxy, will think there is nothing but its own galaxy in the entire universe. The question of how far can we go will not even apply to them. When they look far into empty space, they will only see more emptiness and darkness; they won’t be able to see the cosmic background radiation, and they won’t be able to learn about the Big Bang.
They will have no way of knowing what we know today; the nature of the expanding universe, where it began, and how it will end. They will think the universe is static and eternal.
In The End:
We may be trapped in our pocket of the Universe. But with its trillions of stars, the local group is certainly large enough for humanity. After all, we still haven’t figured out how to leave our solar system, and we have billions of years to explore our galaxy.
We have the incredible luck to exist at the perfect moment in time to see, not only our future but also our most distant past. As isolated and remote as the local group is, we can perceive the entire universe, grand and spectacular as it is right now.
So what do you think? Let us know your thoughts in the comments below. And be sure to link, share, and subscribe to our website for more awesome posts like this.