In order to answer this question, we first need to define what we mean by up and down in space. And also acknowledge that the only reason ‘up and down’ exists as a binary is because we created them as humans.
What is up and what is down?
Since we are held to the surface of the earth thanks to its gravitational pull and the effects of that on our bodies, we have called the direction of gravitational pull ‘down’. The opposite direction is obviously ‘up’.
We have created this binary in accordance to the gravitational forces that affect our earth. So, it follows that we use this binary to measure things in space too.
So, is there an up or down in space?
Yes! If you adhere to the binary that humans have constructed anyway. And since we are adhering to that, there is an up and down in space.
If we apply the same rules to space as we do to earth, then ‘down’ would simply be the direction that gravity pulls your towards. If an astronaut were to be floating near a planet, and they are getting closer to the planet thanks to its gravitational pull, then they are falling down towards the planet.
Since gravity is centrally attractive, meaning that it attracts until the center of the object’s mass in question, you are falling down and being pulled towards the object. This can occur in any direction in relation to the object.
So, ‘up’ could be away from a planet in any direction as long as it is away from the gravitational pull.
What about the North and South poles?
Contrary to popular belief, the North Pole is not ‘up’, and the South Pole is not ‘down’. This is simply down to the fact that gravity is not any different at the North Pole than it is at the South Pole.
If you are travelling to the North Pole, you are not travelling ‘up’, you are simply travelling North. ‘Down’ would be towards the earth’s center and ‘up’ would be away from the earth’s center thanks to gravity.
What about astronauts in space?
Astronauts who are living on the International Space Station will appear to be floating, with absolutely no compliance with the laws of gravity and up and down. But this is wrong.
These astronauts are actually in free fall. Free fall is what astronauts can reach when they are orbiting earth and are at the sweet spot of falling towards earth but also having enough sideways trajectory to remain floating. ‘Down’ to these astronauts will still be towards earth, because that is the way that gravity would act on them.
The very fact that they are orbiting earth means that they are within earth’s gravitational field, and therefore falling towards earth.
What if you are nowhere near earth and its ‘up’ and ‘down’?
If you get far enough away from earth to not be affected by its gravitational pull, then you would simply be floating in space until you became close enough to another astronomical body that would exert its own gravitational force on you.
As we have found out, the concept of up and down is not considered exclusive to earth. This is because we are saying that up and down is reliant on the direction of gravitational pull.
This means that any astronomical body that has mass enough to have a gravitational pull will also create the same ‘up’ and ‘down’ binary.
So, even if you are far enough away from earth to no longer be affected by its gravitational pull, there will still be ‘up’ and ‘down’ in space, at least by human definitions anyway.
There will always be an ‘up’ and a ‘down’ in space because there will always be gravity and large bodies in space that will have gravitational pulls.
What if you aren’t close to a planet?
As stated, there is always a ‘down’ in space because there is always gravity. But if you are far enough away from all of the planets in our galaxy and find yourself floating in space, then the ‘down’ will become towards the sun. The sun has the strongest gravitational pull of our solar system.
Aside from that, the black hole at the center of our galaxy would be the constant ‘down’ into which all of the solar systems and stars are falling but orbiting.
If you found yourself floating outside of our Milky Way galaxy, ‘down’ would be towards the cluster of galaxies. If you were far enough away from the cluster of galaxies that our galaxy resides in, then you would fall ‘down’ towards another cluster.
What does this mean?
All this means is that all matter that is in space is constantly falling ‘down’. This is simply because all matter will be affected by gravity and the gravitational pull of large objects in space.
We cannot notice this very much because of the enormous scale that space and all of the astronomical bodies are on compared to us on earth. But the falling ‘down’ is definitely occurring.
Because of this slow movement thanks to the astronomical size of things in space, we don’t normally use the word ‘falling’, but instead use words like ‘orbit’, ‘trajectory’ and ‘path’.
But all of these are really just fancy science-y terms that mean that something is falling ‘down’ towards the gravitational center that is affecting the object at the time.