It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn’t feel like a giant. I felt very, very small. - Neil Armstrong
There’s quite a lot of science fiction involving intergalactic space-faring civilizations. It’s something of interest to the adventurer residing in all our hearts, however to leave our galaxy the most important part of the equation isn’t time but rather speed.
To really wrap your mind around the idea of intergalactic travel understand first what it is to go into
orbit and how we travel space.
All an orbit is is you moving sideways so fast that the roundness of the Earth (it’s curvature)
falls away from you faster than you fall towards the ground. If you’re
above the atmosphere than the friction with air particles at this speed
won’t burn you up (you’re above the air particles in space obviously).
Therefore all it takes to stay in orbit (sort of) is your inertia once
you’re there: an object in motion stays in motion unless acted upon by external forces.
you’re moving at a speed so great that the ground falls away from you
just as fast as you fly sideways around the Earth this is called orbital velocity.
much faster and you’ll fly sideways at such speed that the Earth will
begin to recede into the distance faster than you fall towards it. This
is called escape velocity.
Reaching escape velocity is very hard. It takes a huge amount of fuel, money and ingenuity.
The fastest spacecraft to have ever left Earth is NASA’s New Horizons probe currently on its way to Pluto this year. It’s going so fast that it will escape the solar system, just like Voyager 1 did.
It’s orbit around the Sun is such that New Horizons is moving faster than the Sun’s gravity can pull it back. The speed of this probe is 16.26 km/s.
Now that you have an idea of human capacity at the moment, think about how much gravity and mass is in our entire galaxy.
Sun represents just one solar system that we’ve barely escaped from
with our very fastest probes. There are 400,000,000,000 other ‘Suns’ in
the Milky Way and to escape into another galaxy we’d have to basically
escape the average gravitational pull of all 400,000,000,000 other solar
systems at the same time (as well as the intervening dark matter).
Long story short: we’re far from being able to do this.
There is some promising technology however which could give an insight into where our research should go if we want to become a species capable of leaving the galaxy.
Ion propulsion is a candidate. It’s a very slow rate of acceleration, but the fuel efficiency is remarkable.
Another is the new technique of solar sailing. Using a highly reflecting material such as mylar groups like JAXA and NASA (and the Planetary Society will soon) have utilized the momentum of light to sail across space without needing to carry fuel. Both solar sails and ion propulsion could build incredible speeds over time.
Antimatter propellant would be a powerful and efficient accelerator as well, although right now antimatter is terrifically unstable and would be far too dangerous and expensive to try and turn into a propellant.
Even were we to have some sort of technology that could bridge the gap between galaxies, there’s the ultimate speed limit to consider: the speed of light. It seems like not only is this speed (300,000 km/s) far faster than anything we can attain but even were we able to go that fast just getting to the nearest star would take over 4 years.
The time we’d spend on our spaceship going to the nearest major galaxy (even if we could move at the speed of light) would be so long that we would evolve into a different species while we were on the ship.
So at the moment we have our limits. Although the universe seems to conspire to keep us here, humanity has always found a way to go further. In the span of one lifetime a girl, Gertrude Weaver, was born in Arkansas to a family of sharecroppers.
In her lifetime she’s seen us create airplanes. She’s seen the birth of computers, super computers and robots. She’s seen us land on the Moon. She’s seen five states brought into the United States. She watched both World Wars. She was around when atomic weapons were invented.
One of her parents had been a slave. It’s impossible to tell how far we will go, even in the span of a single lifetime. It’s exciting to think about what tomorrow will bring…