And they are all orbiting in different directions, which means that we are all moving in different directions.
Look around you. Where are you? Where is this place you are occupying? Somewhere in a room, maybe in a city on a continent on a planet orbiting a star in a galaxy among billions. But…where is all of that? While this may feel like a daft question, it turns out that the concept of an absolute position is something humans made up. In a nutshell, the universe is a big bag of space that has things in it. If someone removed all these things, the stars and planets and black holes and dust, there would just be empty space left. In empty space, the concept of having a position loses all meaning. Empty space is uniform, the same everywhere.
The space we occupy is not like a stage under our feet. We can’t mark specific points, or staple something to spacetime as an anchor. Without things there is no position. We are really ever only at a position in relation to something else. Which also means that things we take for granted, like up and down are actually relative too.
Ok, let us fill the universe up with things again and try to find out where you are, right now. Relative to everything else. Let us start this video at a familiar place and then get increasingly weird. From your perspective the world is seemingly flat and you can move in 3 dimensions. It’s what physicists call a ‘frame of reference’ - the perspective you have of the universe and how you see things moving around you. Where your up and down is. Your frame of reference is correct. For you – but not for the rest of the universe.
Around 5 kilometers from you, where the horizon begins, the ground noticeably curves away from you. If you could see through the ground, you’d see people from below or sideways. But they don’t fall ‘down’ off the planet because gravity doesn’t actually pull them down. ‘Down’ is an illusion of your reference frame. To earth’s reference frame, gravity just pulls in. But for humans there is an up and down because within our frame of reference that just makes sense. Which is also why we think that the planet itself has an up and down, north and south. And we made our maps accordingly.
But an observer looking at the solar system might disagree. Our maps make sense to us because we are used to them, not because they are correct. Ok. So this is step one – your position on what feels like a flat surface but is actually a sphere. But this sphere is always moving, never staying in one position. Earth is orbiting a star, the sun at the center of the solar system.
While we usually imagine this as pretty orderly, someone looking at us from the outside would see something pretty messy. To see this more clearly we’ll exaggerate all these movements, this is not to scale. First of all, our orbit really is an ellipse, so we spend half the year sinking a little bit closer to the sun speeding up, and half the year rising up a bit and slowing down. And the ellipsis itself changes its shape every 100,000 years too. And in another cycle of 112,000 years, the ellipse itself is drifting – which at least creates a beautiful shape. In the end, we get an orbital path that looks like a wobbly circle with wavy edges.
And it gets worse, as the moon now starts to screw things up too. As the moon is a pretty massive thing, it pulls on earth. Both objects orbit their common center of gravity, that lies around 4700 km off to the side of Earth’s core. In practice this means that as the moon orbits earth, it is jerking earth around a bit, enough to make it jiggle.
Ok so you are standing on the surface of a rotating planet, that is jiggling around the sun in an elliptical orbit that changes a bit every year. But who’s to say the earth is right? From the perspective of the sun the plane of the solar system is arbitrary, it’s defined as the plane the earth orbits in because that is convenient for us. In reality the other planets are just a little bit inclined with respect to our plane. And they are all orbiting in different directions, which means that we are all moving in different directions. We wouldn’t have been able to do this if we had focused on what we couldn’t do.
From their point of view, we’re the ones with a slightly bent orbit. However, the solar system as a whole is orbiting the center of the Milky Way galaxy, and the plane of the solar system is not aligned with the plane of the galaxy. This orientation in space means that sometimes the planets are sort of in front of the sun as it orbits around the galactic core. This is still not the whole story, as the mass of the galactic disk is constantly pulling on the solar system too, making it dive up and down through the plane of the galaxy. Further, the Milky Way is part of a galaxy group that appears to be part of greater structures like the Laniakea Supercluster, which itself is part of the gigantic Pisces–Cetus Supercluster Complex and finally a galactic filament that spans hundreds of millions of lightyears in all directions and orientations.
At this point, the frame of reference becomes a bit arbitrary and pointless because of the nature of the universe at this scale. Someone looking right at us from that far away will only see the End of Greatness, making everything appear homogeneous and the same everywhere. Just like with empty space, when everything looks the same, who’s to say anyone’s view is better than anyone else’s?
We have reached the end of our little exercise in cosmic humility, and it is clear that perspective really is everything. That is true for the universe we all inhabit, but even more so within our personal universes. The way our lives will unfold also depends on what we consider possible.
Let us make the journey backwards again - back to you, right now, watching this video. If this is all a bit much, don’t feel bad. It doesn’t really matter because it doesn’t change where you are. You’re already in the best spot you could possibly be - right here, right now. Nothing can stop you from being right at the center of your own little universe. We began to create our own lines of science posters, calendars and fun Kurzgesagt merch - pieces of Kurzgesagt - that you can take home and touch. To make this happen, we partnered with Shopify, who kindly sponsored this video. Shopify is an e-commerce platform that allows you to start and grow your business - from scratch. Whether you want to sell your handmade ceramic mugs out of your bedroom today or scale your one-man show to a sizeable team, Shopify has the tools to support you. To get started, check out Shopify.com/Kurzgesagt for a free 14 day trial.
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