How Far Can We Go? Limits of Humanity (Old Version – Watch the New One)

Are There Places We Can Never Reach?#

Turns out, even with super advanced technology, we might be stuck in just a tiny corner of the universe. No matter how hard we try, there are borders we might never cross. How can this be, and just how far can we go?

Our Place in the Cosmos#

We live in a quiet spiral arm of the Milky Way galaxy.
The Milky Way is considered average size, about one hundred thousand light years across.
It’s made up of billions of stars, gas clouds, dark matter, black holes, neutron stars, and planets.
There’s a supermassive black hole right at the galactic center.
From far away, it looks dense, but most of it is actually empty space.
With our current technology, sending a human to the closest star would take thousands of years. So yeah, our galaxy is pretty darn big.

But the Milky Way isn’t alone.

It hangs out with the Andromeda galaxy and over fifty dwarf galaxies.
Together, these make up the “Local Group.”
This Local Group is a region of space about ten million light years in diameter.

The Local Group isn’t the end of the story either.

It’s just one of hundreds of galaxy groups inside the Laniakea Supercluster.
And the Laniakea Supercluster is only one of millions of superclusters that make up the observable universe.

A Glimpse into a Hypothetical Future#

Let’s imagine a super bright future for humanity.

We become a Type 3 civilization (that means we can use all the energy available in our galaxy).
We manage not to get wiped out by aliens (phew!).
We figure out interstellar travel based on what we currently understand about physics.

In this absolute best-case scenario, how far could we possibly travel?

The answer is: The Local Group.
It’s the biggest structure that humanity could ever realistically be a part of.

Now, the Local Group is huge, no doubt. But here’s the kicker:

The Local Group accounts for only 0.00000000001% of the observable universe.
Just let that sink in. We’re potentially limited to a hundred billionth of a percent of everything we can see.

The idea that there’s a hard limit for us, and that so much of the universe will forever be out of reach, is honestly a bit frightening.

Why Can’t We Go Further? It’s About “Nothing”#

Why are we seemingly trapped in our local neighborhood? It all boils down to the very nature of “nothing” – or what we think of as empty space.

Empty space isn’t actually empty! It has energy built into it.
This energy is tied to something called quantum fluctuations.
On the smallest scales, space is constantly buzzing with activity.
Particles and anti-particles are popping into existence and immediately wiping each other out.
You can picture this “quantum vacuum” like a pot of bubbling water, with some spots a bit denser than others.

The Big Bang and Cosmic Inflation#

Now, rewind about 13.8 billion years to the very beginning.

Right after the Big Bang, there was an event called cosmic inflation.
During inflation, the observable universe exploded from the size of something tiny, like a marble, to trillions of kilometers across in just fractions of a second.
This sudden, incredibly fast stretching of the universe did something wild: it stretched those tiny quantum fluctuations too.
What were once subatomic distances became galactic distances.
This created vast regions that were slightly denser and slightly less dense across the universe.

Gravity vs. Expansion: Forming Pockets#

After inflation finished, gravity started trying to pull everything back together.

On the larger scales, the universe’s expansion was just too quick and powerful for gravity to win.
But on smaller scales, gravity was victorious.
So, over long periods, the slightly denser regions – those “pockets” of the universe – grew into groups of galaxies, just like the one we live in today.

Only the stuff inside our pocket, the Local Group, is held together by gravity.

The Complication: Dark Energy#

So, if gravity holds our pocket together, what’s the problem? Why can’t we just hop from our pocket to the next one over? This is where dark energy steps in and makes everything complicated.

About six billion years ago, dark energy started dominating the universe’s expansion.
We don’t know exactly what dark energy is or why it exists, but we can see its effect clearly.
It’s basically an invisible force or effect that causes the universe to speed up its expansion.

Remember those larger, slightly colder spots around the Local Group from the early universe?

Those grew into huge clusters with thousands of galaxies. We are surrounded by a lot of stuff!
However, none of these structures or galaxies outside the Local Group are bound to us by gravity.

Growing Isolation#

As the universe expands, and dark energy makes that expansion accelerate, the distance between our gravitational pocket (the Local Group) and all the others gets bigger and bigger.

Over time, dark energy is going to push the rest of the universe further and further away from us.
Eventually, this will make all the other clusters, galaxies, and groups completely unreachable.

Consider this: the very next galaxy group is already millions of light years away. But they aren’t just sitting there; they are moving away from us at speeds we could never hope to match, no matter how fast we build our ships.

We could theoretically leave the Local Group and fly out into the intergalactic darkness.
But because of the expansion, we would fly forever and never actually arrive anywhere.

The Future of Our Pocket: Milkdromeda#

While we become more and more stranded in our pocket, the Local Group itself will become more tightly bound.

In a few billion years, the Milky Way and Andromeda, along with the dwarf galaxies, will merge together.
They’ll form one giant elliptical galaxy.
Its name? The rather unoriginal “Milkdromeda”.

The Universe Recedes from View#

But it gets even more melancholic.

At some point in the far future, the galaxies outside the Local Group will be so incredibly far away that they will be too faint for even advanced instruments to detect.
Any faint light (photons) that does make it to us will have its wavelength stretched so much by the expansion (called redshifting) that it will become completely undetectable.
Once this happens, no information from outside the Local Group will be able to reach us anymore.

The universe outside Milkdromeda will simply recede from view.

It will appear utterly dark and empty in all directions, seemingly forever.

A Future Without the Past#

Imagine a being born in Milkdromeda in the very distant future.

They will likely think their galaxy is the entire universe!
When they look out into space, they’ll see only endless emptiness and darkness.
They won’t be able to detect the cosmic background radiation (the afterglow of the Big Bang).
They won’t have any way to learn about the Big Bang or the early history of the universe.
They won’t know what we know today: about the expanding nature of the universe, when it began, or how it might end.
Based on what they see, they will likely believe the universe is static and eternal.

Milkdromeda will be an isolated island in the darkness, and that darkness will only deepen over time.

Our Fortunate Present#

Despite this potentially lonely future, there’s a bright side to our current situation.

The Local Group, even if it’s our ultimate boundary, is still gigantic! Milkdromeda will contain a trillion stars.
We haven’t even figured out how to leave our own Solar System yet, and we have billions of years to explore just our Milky Way galaxy.

We are incredibly lucky to be alive right now, at this particular moment in time.

We exist at a point where we can see not only glimpses of our future (like the Local Group merging) but also our most distant past (like the cosmic background radiation showing the Big Bang).
As isolated as the Local Group may eventually become, right now, we can perceive the entire universe – vast, grand, and spectacular – exactly as it is.

More Information#

Video URL: https://www.youtube.com/watch?v=ZL4yYHdDSWs
Huge thanks for the help with the video go to Ethan Seagal. You can check out his astronomy blog if you’re interested!
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Thanks for watching this far! We’ve put together a playlist about more universe-related topics for you to check out.