Line 1. Let’s start with ‘typical’ humans. The average human adult male is 1.75 metres tall – that’s 3.83 cubits or 5.74 feet. The average female is 1.62 metres – that’s 5.4 light-nanoseconds or 0.008 furlongs.
You live on Earth (Sol d, perhaps?). This is an Earth-like planet in a Sun-like star system. The third planet of eight in a rich system, including a least one planet populated entirely by robots (Mars, perhaps?). Earth is 12,742 km in diameter and thus has a circumference of 40,000 km or roughly 25,000 miles. Humans live in a thin layer (~20km) around the surface called the troposphere. If the Earth was a beach ball then all life on Earth exists within just 1mm around the surface.
Through many years of international effort we have managed to keep a ‘space’ station in orbit – just above this troposphere – 1cm above the beach ball. But not high enough up that it can totally avoid the atmosphere – the ISS has to constantly boost itself back up because of air drag. We have sent just 24 people out into deep space, beyond the Earth’s atmosphere. All of then visited the Moon and the last ones returned in 1972: 42 years ago. They were all men, all white, and all American. We could do it again, we could do it better - but we chose not do so. (Mostly for political reasons IMHO.)
Those astronauts visited the nearest body in space: the Moon – the second brightest thing in the sky . They were kind enough to return some photos to show us how teeny tiny we are, and how delicate out world really is. The Moon sits about a quarter of a million miles away (384,000 km). You could fit all the Solar System’s other planets in that gap.
But that doesn’t include the Sun – the brightest thing in the sky. The Sun is truly huge. You can fit the Earth inside the Sun a million times. It has more than enough room for all the planets and then some. The Sun itself sits 93 million miles away – which means that light takes 8 minutes to reach us from the Sun. The Sun could have gone out 7.9 minutes ago and you’d only find out… now. Nope: we’re ok. For now.
And yet we have flung robots into space and downloaded the images they have recorded. Sometimes we take extremely long-range selfies of a sort. Images of the Earth, of humanity reduced to a pixel or two. Here’s one from Mars, one from Saturn and one from out near the edge of the Solar System – taken by Voyager. These images collectively earn us the moniker ‘pale blue dot’. Out by Pluto, the Sun itself is has dimmed to look like an other stars. From Saturn, we are just a couple of pixels as seen by the Cassini probe:
And truthfully, the Sun isn’t so special. In fact there are stars which make the Sun look even smaller than the Earth does here. VY Canis Major is staggeringly big – and could encompass the Sun 1,000,000,000 times. That’s a million trillion Earths. Oh and VY Canis Major isn’t even visible to the naked eye because it’s so far away that we can’t detect its photons without aid of telescopes or binoculars.
Which brings us to the Galaxy. The Sun is just one of hundred of billions of stars orbiting around the Milky Way. If the Sun was a blood cell then the Milky Way is the size of Europe. The Milky Way is staggeringly big also staggering diffuse – so much so that if you took two Milky Ways, and hit one with the other, then in all likelihood no two stars would collide. They would pass though each other like smoke.
In fact this will happen. The Andromeda galaxy – which is a lot like the Milky Way – is on a collision course with us. In about 4 billion years it will begin to merge with our galaxy in a spectacular collision. We see these happening elsewhere but the sheer scale of this vision in our own night sky makes me want to get a time machine and jump forward to see it happen. The Earth is unlikely to be affected by this, because of the lack of collisions – however our night sky will be spectacularly altered for hundred of billions of years. Makes you realise how dull it is right now. Just kidding!
But the Milky Way and Andromeda are just two out of hundred of billions of galaxies in the Universe. Gigantic stellar continents floating in a vast, void of almost nothing. Galaxies themselves form structures, and as we have looked deep into the cosmos we have seen one such structure: the Sloan Great Wall. A thick chain of galaxies, loosely bound to each other by gravity, stretching 1.4 billion light years across the Universe and about 1 billion light years from the Milky Way. It’s 1/60 of the Universe across. And yet there are even bigger thing out there.
The largest known structure in the Universe is the Hercules–Corona Borealis Great Wall. At 10 billion light years across, this huge filament of galaxies in 1/10 the size of the observable Universe. It’s 100,000 time the size of the Milky Way, and 70 million trillion times bigger than than the Sun. We don’t have a good picture of it, but we know it’s there. It’s 7,000,000,000,000,000,000,000 times bigger than the Earth, which is very much bigger than you. I refer you to line 1.