Archive for category thought experiment

Where do we live? Part 2

In Part 1 we tried to imagine just how huge our galaxy is, to show where we live in this universe of ours. To accurately describe the universe beyond our galaxy we’re going to have to shrink the scale we used last time a hell of a lot more. Let’s take our already shrunk 6 million kilometre wide Milky way and pull it all the way down to 1 metre across. At this scale the Sun is 1.5 billionths of a metre across (half the width of DNA) and the Earth is 13.5 trillionths of a metre across (half the size of the smallest atom!). The entire galaxy now comfortably fits between your outstretched hands; hundreds of billions of stars, perhaps trillions of planets all between your fingertips.

The Large Magellanic Cloud

But our galaxy doesn’t sail through the universe alone, dotted around us are a number of satellite galaxies, there are around 25 smaller galaxies clustered around our own! The largest is called the Large Magellanic Cloud, on our scale it is a metre and a half from our galaxy (off to the side and slightly below). Home to billions of stars this 14 thousand lightyear wide galaxy would be the size of a pineapple on our little scale. The other galaxies surround ours in all directions with the closest 1 foot from our model and the furthest over 13 metres away, a real-world distance of over 1 million light years!

Even the Milky Way and her satellites are not alone, they are part of what we call the Local Group. Comprised of three major galaxies and dozens of satellites on our scale the local group is the size of a football pitch. Within these 10 millions lightyears lie trillions of stars, the largest galaxy is our nearest neighbour called Andromeda which itself contains well over 1 trillion stars. I always think fondly of Andromeda, as a child I had a book about the universe and I remember becoming upset because it told me that in 4 to 5 billion years the Milky Way and Andromeda are going to crash. Count to five……I’ll give you time to do it……we are now 600 kilometres closer! We are on a collision course with each other, on our scale Andromeda is 25 metres from us (2 and a bit buses) and its racing towards us at a rate of 5 billionths of a metre every year. Granted that doesnt scare me any more, but it’s going to be a titanic display!

In billions of years to come somebody will be voiding their no claims bonus...

Our Local Group may seem huge but it is tiny compared to some of the other groups nearby. 65 million light years away the Virgo Cluster is home to over 1 thousand galaxies! When we look at the Virgo Cluster now we’re seeing it as it was when the dinosaurs were walking the Earth, from the entirety of that point until now those photons have been serenely flying through space until one day after aeons of travel they land in our telescopes to tell us a tale from the deep past. The Virgo Cluster is so huge that we use it to name our local supercluster. Yes our Local Group is just a small part of a bigger group. The Virgo Supercluster contains at least 100 galaxy clusters and on our scale where the Milky way is a metre across and the Earth just half an atom wide it is over a kilometre wide. That’s about the same scale as an ant standing next to a car

Now I know this is beginning to sound repetitive but even our supercluster is just a tiny dot. When we look out beyond our supercluster we see that there are many, many more. Superclusters litter our universe forming truly colossal structures. They bunch together forming filaments (chains billions of lightyears long) and Great Walls formed from giant webs. This is our home. This is our universe. At this size our scale collapses again, with the Milky Way 1 metre wide some of these filaments would be tens of kilometres long!

One of the universe's 'Great Walls' made from filaments of superclusters

This is the observable universe, countless stars in hundreds of billions of galaxies. We are but a tiny part of this but it’s all out there! The numbers are horrible and the distances incomprehensible but I hope my analogy has helped. I was planning on taking this further and explaining just how small things in our universe can be but I found this brilliant animation that paints a picture worth a thousand blog posts. Its awesome, its unimaginably big, and its where we live.

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Where do we live?

The answer to that question quite obviously relies on the reader, I’m in London for example. You could be in a town nearby, or across the country or for all I know thousands of miles away. But we can group together where we live, if you are reading this in Brighton or Dunstable then we could say we both live in the south of England. If you’re reading this in York or Leicester we could stretch it and say we both live in England. We can play this game for a little while before we inevitably come to the conclusion “we all live on Earth”, but where exactly is that?

Everyone you've ever known is somewhere down there

Our pale blue dot is flinging itself around the campfire we call the Sun at around 30km per second (London to New York in 3 minutes). We share this Sun with seven other planets; Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune along with five dwarf planets; Ceres, Pluto, Haumea, Makemake, and Eris. Along with a few score moons, a couple of asteroid belts and a sprinkling of comets we all make up the solar system together. It’s hard to get round just how big the solar system is, there isn’t even a definitive boundary with clouds of asteroids extending for trillions of kilometres around our Sun. But that number “trillions of kilometres” is meaningless, let’s face it, I could have said billions or zillions for all the connection it has with our lives. In light of this I’d like to share an analogy I often use…

Imagine the distance between the Earth and the Sun (some 150 million kilometres) and shrink it right down to just one metre. At this scale the Earth is just 80 millionths of a metre wide (about the size of ten red blood cells side by side). The Sun is little bigger than a marble at 9 thousandths of a metre. 40cm from the Sun we find Mercury and just 30cm beyond that we have Venus. Within our metre sized orbit the Moon is nearly 2mm from our bacteria sized Earth, about the size of two grains of sand. This is the furthest mankind has ever gone in our universe. It took years for thousands of geniuses and billions of dollars to take us just 2mm on our scale. With the solar system shrunk down like this Neptune, the furthest planet, is just 30 metres away from our marble sized Sun. Eris, the furthest dwarf planet doubles that distance at 62 metres. Taking this orbit as the boundary of our system on our scale a football pitch would fit within our entire solar system with a few metres either side to spare. This is our solar system, over 120 metres wide and the furthest we have travelled is just two measly millimetres. But our home doesn’t stop there.

Our Galaxy viewed from Earth

Our solar system is just one of hundreds of billions inside the galaxy we call the Milky Way. If you live in a place with low light pollution you can look up at night and see the disk of our galaxy cutting straight across the dark. Our spiral galaxy is so large that we have to measure it in lightyears, that’s the distance that light (the fastest possible thing, it travels at 299,792.4 kilometres every second) travels in an entire year! In kilometres that’s 9,450,000,000,000,000! In our scale one lightyear is 61km, nearly twice the length of the English channel at it’s smallest width. The nearest star system to us is four times that again! On our little scale where the Sun is a marble and the Earth just a collection of cells wide the Milky Way is 6 million kilometres wide. Even with our horrendously shrunk down scale the length of the Milky Way is equivalent to circling the equator 200 times. This is our home; our town, our country, Earth, every planet we’ve ever seen all of them are there in this galaxy. But if we are being honest, it’s not really our home. Oh no, we’ve barely begun to talk about that…to be continued.

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Who am I, who are you and who the hell is the guy I was?


We all use it, we all have a name and we all identify ourselves by some means. The question of “who am I” is multifaceted. Am “I” the meaty object standing in front of you? Am “I” the emergent property of a squidgy organ in the head of that meaty object? Am “I” the sum of all of the perceptions of me?

We tend to use all three (with an emphasis on the first two) but I propose that we can’t really pinpoint what is “us”. I’ve always been really fascinated with identity, practically it’s very useful. You can call me Ryan and point to somebody else and call them Brian and we would know who you were talking about, the interesting thing for me is that you can point to a picture I have from five years ago and call that “Ryan”. You could do it to a ten year old picture; you could even do it to a picture of my mother holding a baby that’s just been named “Ryan”. Therein lies the dilemma for me, I accept that “I” am this body in front of you (a body whose physical functions result in the expression of a mind) but am “I” the boy in those pictures?

To show why this is an issue I’m going to borrow an old question in philosophy called the Ship of Theseus (I may not relay the story faithfully but the premise is the same). Theseus goes off sailing in his ship; his ship is made from a set number of wooden components. Over time these wooden parts rot one by one. Every time they rot they are removed and replaced with a new peace made from fresh wood. Let’s posit that there are one thousand parts that make up the ship and by the time he comes home every component of the ship has had to have been replaced. In other words there is no part of that ship that was technically there the day the ship left. The big question is “is it still the same ship?”

Repaired piece by piece is this still Theseus's ship?

This is a hard question. Often the first response is that it isn’t the exact same ship, that the act of replacing bits of it over time has made the ship different. I have another version of this thought experiment, what happens if every time a wooden component is replaced it is replaced with a completely different part? Imagine a ship made from one thousand wooden planks and every time they rot they are replaced with metal, when the sail tears and the mast rots they are replaced with a propeller and when the navigator drinks too much and falls overboard he’s replaced with GPS. Is that the same ship? In this example I imagine most people would say it is not and there are justifiable reasons for believing that. But this is more than just a fun thought game.

Every second of every day we are dying, tens of thousands of cells die and are recycled or shed from our skin (a lot of house dust is dead skin). This is no big problem because we replace all these dying parts. We do this by eating food, digesting it and using it to rebuild parts of us. Over a large enough span of time all things in our body are replaced, cells die and are replaced and importantly every component in those cells are replaced too. I’ve heard various numbers of how long this takes but it doesn’t really matter exactly how long it is merely that at some point in your life there are no atoms in your body that were there at the start of your life. This is the Ship of Theseus acting in real life and it’s a very interesting thing to think about, the body that people identified as “Ryan” at the beginning of this identity has nothing left in the body that is now identified as “Ryan”.

This phenomenon applies to our personality too, over time we develop new behaviours and loose old ones to the point where if we were to place Ryan at ten years next to Ryan at twenty years next to Ryan at one hundred years and you will struggle to see that they used to be the same person. Am I really the same “Ryan” if I share no matter nor mind with this past Ryan? Are we not strangers? And am I accountable for this strangers actions? The point I am trying to press is what is “I”?

An Evil Genius stealing your atoms, one by one

Lastly there is one more thought experiment I would like to propose; imagine there are three identical hotel rooms next to each other (left, middle and right). You go to bed in the middle room and at some point in the night some Evil Genius sneaks in and freezes your body. Then he or she takes you apart atom by atom. They start by taking one atom from the bottom of your foot and take it from the middle room to the room on the left. In this identical room they place this atom in the corresponding place in the bed that it was in the middle room. This Evil Genius then does this again but this time places the second atom in the room on the right. This act continues with you being dismantled atom by atom with each atom going to the left or the right room until finally there are no atoms left in the middle room and exactly 50% in both the left and right. Where there is a gap between atoms in the left room there is an atom to be found in the right room and vice versa. As one last act the Evil Genius fills in the gaps of both these two bodies with atoms from stock and warms both bodies up before fleeing the scene.

As the alarm clock goes off in both rooms the two bodies wake up and stumble out of the room only to see another them down the corridor. Which one is you?

I’ve asked a lot of questions here and not provided any answers but I hope they are all questions that have got you thinking.

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