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Cosmoly for kids

Every tribe has its tale about how the universe was created. This is needed, for the children of the tribe to understand their place in the universe. The tale is sometimes adapted. For example if a new tribe is encountered, whose existence is not yet explained by the tale, the tale will be augmented and possibly modified. The tales of two tribes can be uncompatible and this leads to war, because of misunderstandings. One tribe believes that the Moon is a chump of cheese and another tribe that the Moon is the face of a god. What if the first tribe believes that every cheese in the world belongs to them and the second tribes believes that every place the Moon shines upon belongs to them? The modern world tries to base itself on a tale that can be verified. A modern Chinese and a modern Canadian, both know that the Moon is made of rock. Twelve people went there to confirm. Also, a tribe whose tale is inadequate, can make the wrong choices and disappear...

Then the question is how the universe was created. After countless observations, experiments, arguments, calculations, simulations and cross-verifications, it pretty much seems that the universe was created in a gigantic explosion: the Big Bang. Now, that Big Bang wasn't exactly an explosion like a cracker would.

Have you already seen the wind shield of car explode? It's not made of common glass. When a simple window breaks, it fractures in a few huge triangles, with sharp ends and cutting edges. Very dangerous. The wind shields of a car is different. When it fractures, it shatters in a swarm of little pieces, roughly the size of a bean. People can only be lightly wounded by those small pieces.

Balloons have a surface made of latex. You sure made many of them explode. The remains of the balloon are a few little pieces of latex with different shapes, folded on themselves.

Maybe at the start, the universe was pure energy. It had no shape, no dimension, even time did not exist.

Then the energy began to swell, like a balloon, with a surface made of energy instead of latex. There were no atoms, no electrons, no light... nothing but a surface of energy that was swelling. Hence space and time now existed; the space of the surface and the time of the swelling.

Then the surface shattered into small pieces, like an exploding wind shield. The pieces remained in the shape of a sphere, because they can only move on the surface of that sphere. Those pieces were mainly atoms of hydrogen and light, billion billion billion billions of them. They are the remnants of the initial sphere of energy.

All the pieces are identical. There are no big and little pieces like with the latex balloon. One atom of hydrogen is exchangeable with any other atom of hydrogen.

The membrane was made of energy but also the energy made the membrane. This keeps being true after the shattering. The atoms and the light are made of energy and they go on to constitute the surface of the sphere. If you would remove atoms, or light, from somewhere, there would be less surface there (less space). Conversely, if you pile atoms or light somewhere, there will be more space. Well just imagine that you have a balloon that's a bubble of melted latex. You pour a tad of melted latex somewhere on the surface and that supplement of latex will constitute a little swelling on the surface of the balloon, hence a place where there is a little more surface.

Yet there is a big difference between the liquid latex and the energy. The drop of latex that made the little swelling, will tend to spread and the balloon will become uniform again. On the contrary, a swelling in the universe will tend to make more matter and light flow towards it. So once a swelling starts, it tends to increase. You can check this by letting an apple fall. The Earth causes a very tiny swelling in the universe. That's why the apple goes towards the Earth. And the apple participates in the swelling caused by the Earth.

Everything has a price. In the universe, if something increases then something else decreases. The mass of the Earth creates a tiny little bit of space but then reciprocally the clocks tick slower close to Earth, because of the swelling. Now you cannot verify that by simply placing a digital clock aside a mechanical clock, because both clocks are slowed down exactly the same amount. What's more, the slowing down is so small that no common clock can be used to diagnose it. But, the astronauts that went to the Moon, when they came back, their onboard clocks were a tiny little bit in advance and one reason for this is that they were further from the Earth.

What if really a lot of matter piles up somewhere and creates more and more space? Well the matter will crunch itself down to what seems to be a single dot from the outside. That's a "black hole". The matter inside the black hole is maybe compressed towards something close to the pure energy at the start of the Big Bang... We don't know exactly... we really understand what happens around a black hole only till a given radius around it... Below that radius, we're not even sure if the very notion of a radius applies...

But let's get back to the moment when the universe was a swarm of hydrogen and light (there was also a little bit of helium and a lot of dark matter and black energy...) If those things had been very uniformly spread through the space, nothing would have happened. But, due to small irregularities in the Big Bang, there were places where things were a tiny little bit more concentrated than in other places. Hence those places started to attract the things from the places that contained less. That's how matter got concentrated where clouds of galaxies now exist. Inside those gigantic clouds, again there were places with slightly more things and that's where things coalesced to form the galaxies. Often with that much matter ultimately falling in the center of the galaxy that a giant black hole is formed. Everywhere in the galaxies, at billions of places, again matter coalesces and forms stars and planets, like our Sun, the Earth and our neighboring planets.

Of course the amount of matter that coalesces somewhere is each time different. That's why galaxies, stars and planets all come in different sizes and colors. But there are constraints. Stars with hugely more mass than our Sun cannot be formed, because that leads to a slow explosion that blows the extra matter way. On the other side, stars much littler than our Sun do exist, but they don't heat much so they are hardly visible.

Heating is the deal, when it comes to stars. You probably never tried it out but you were often told that when you compress air with your bicycle pump, it heats. When hydrogen falls to a place, in sufficient amount to form a star, and the slight swell of space hence formed pushes the hydrogen together really hard, the hydrogen will heat up. Don't try it at home, but if you take again the bicycle pump, with some air contained inside, and you heat it above a flame, you will see the piston be pushed outside by the air that expands because of the increase in temperature. So, the hydrogen tends to fall together to become a very little and concentrated sphere, but, the increase in temperature due to the pressure will prevent this. The compression will stabilize when the temperature becomes enough to get the hydrogen to tend to expand as much as it is compressed. That way you get something like the Sun, with a surface temperature of about 6,000 °C, that produces a tremendous quantity of light, simply because it is hot (put a wire of metal inside a flame, you will see it emit light too when it becomes hot).

By emitting light, which is energy, the Sun looses thermal energy. It cools down... Hence the hydrogen has less ability to expand. Hence the hydrogen can be pushed closer together. So the Sun would decrease radius constantly and cool down. More than a century ago, physicists assumed this and calculated that the Sun cannot give light for more than several hundred thousand years. This was a blow against those other scientists that pretended that fossil animals and tree leaves found in rocks dated from hundred of million years ago. It was a proof that the Sun could not have been lit that much time ago. Yet other people had pretended to calculate that, according to their religious believes, the Earth dated from merely a few tens of thousands of years ago. It seemed that the physics of the Sun was on their side...

But nowadays, we know why the Sun is lit since even more than a billion years... That's because of nuclear reactions. Inside the Sun, the pressure makes the temperature rise to about a million °C. This allows for hydrogen atoms to fuse together and form helium, which releases a tremendous amount of energy. This keeps the Sun hot and compensates for the losses of energy at the surface. Of course this will one day come to an end... but we still have billions of years ahead of us.

Some people are afraid because a "hydrogen" bomb, too, works by making atoms fuse together. Actually, the way the fusion happens inside such a bomb is quite different from what happens inside the Sun. First of all, the temperature inside the bomb during the explosion is ten times the temperature inside the Sun. Second, the bomb was assembled using an accurately computed combination of atoms, able to react together in a sudden. On the contrary, inside the Sun, the reaction that leads the atoms of hydrogen to fuse together is very, very slow. Each atom of hydrogen has to link itself to an atom of carbon and only when four atoms of hydrogen piled up and two of them transformed into neutrons, will the atom of carbon eject an atom of helium. So there is no danger at all that our Sun explodes. Countless astronomers look at the stars everyday, all over the planet, looking at billions of stars like our Sun, and never ever has one of them seen a star like our Sun explode...

The end of our Sun, in billions of years, will come when the hydrogen is almost up and has been transformed into helium. Then the core of the Sun will shrink further down, which will yield even higher temperatures and will start another fusion reaction, where helium fuses together. Meanwhile, because of the higher temperature of the core, the outside of the Sun will expand much further than the current radius. This will not last for long and the Sun will ultimately shrink down completely.

Anyway stars do explode, sometimes... For this, they must be heavier than our Sun. Then, during the last moments of their lives, they will either start to blow away huge amounts of their inside matter or they will literally and suddenly explode like an atom bomb would, here too blowing away much of their inside. This is of key importance for us, because during the last stages of its life, the nuclear fusion reactions inside the star create much of the matter that we are made of. Everything around us on Earth, and ourselves, is made of atoms that were fused together inside stars. Aluminum, chlorine, lead, mercury, gold, uranium, zinc, neon gas, whatever... is made of things that where fused together in dying stars. Then when the star exploded, that matter was swarmed all around in space and some of it could ultimately coalesce together around another young star in formation and form planets around that new star. That's how our solar system was created. It wouldn't harbor planets, and life on at least one of those planets, if the initial cloud of hydrogen that lead to our Sun didn't contain the ashes of previous stars.

Hydrogen, helium, tritium, beryllium, carbon, oxygen, nitrogen... are all different kinds of atoms, each one heavier than the previous. Amongst the heaviest ones are lead, gold, uranium and plutonium. Much heavier ones can be formed but they are unstable, they break apart immediately. It seems that a few very heavy and stable atoms can exist... but mankind has not yet managed to find or manufacture some. In the whole, a little more than a hundred different sorts of atoms exist. Away from the hot inside of stars, those atoms tend to assemble together to form compounds like water, methane, carbon dioxide, ammonia, all kinds of minerals that form dust and rocks... That's what the planets are made off, as well as the comets, the asteroids, down to shooting stars.

Those atoms cannot assemble at random. There are rules, like in the game of chess. Using the six different pieces of the game, many combinations can be formed that can be effective to protect an array or to attack your opponent's combinations. The way a combination works depends on the properties of each piece that's part of it. The thing is that if you put pieces on a chessboard at random, they highly probably won't form an efficient combination. They don't "glue" together to form an effective war machine. But atoms, with their own rules, tend to naturally form the combinations that glue together. Those are called molecules. That's what Chemistry is about. In common circumstances, the atoms will just clump together in quite little and simple molecules. The molecules found in space or on the other planets contain at most a few tens of atoms glued together, most often only two, three, four of five atoms glued together... forming the gases and the rocks.

About a billion years ago, on Earth, or maybe on another planet, something weird happened. There was a flux of energy, either coming from the inside volcanic activity of the planet or from the Sun. There were lightning strikes and reactive molecules... places were changing temperature back and forth... That flux of energy was constantly disturbing the molecules. They were broken apart and did recombine in every possible way, often quite unstable and short-lasting ways. Some of those molecules, called enzymes, had the effect of enhancing the impact of the flux on other molecules, and altogether this was leading to the creation of more of those enzyme molecules. Hence, it was so that slightly more of those enzyme molecules were constantly created than normally would. Also, if two kinds of enzyme molecules existed in a given place, the one kind that was more efficient at playing this game, would prevail on the other. Especially, if the winning one had the ability to dim down the reactions that are favorable to the other one. Things were boiling down that way on the planet... It happened that some kind of enzymes came to prevail significantly upon others, while being quite bigger than the others. You wouldn't think that a big enzyme molecule can prevail, because its size makes it more fragile. But, they were better at the enzyme reactions, thanks to their sizes and complexity, and this did compensate for their fragility. One of those super-enzymes came to control other enzymes. That would be the ancestor of our DNA... Its shape and size evolved and it got more and more efficient at influencing the other enzymes in its advantage. It started to create enzymes of its own... This capability allowed it to grow even further. Things went on that way for hundred of millions of year, till was constituted what we currently know as a living cell. The DNA is encapsulated inside the cell and rules the enzyme activity of the cell, protected by the outside membrane of the cell.

Then some of such cells came to assemble themselves together in clumps of cells. They would rather stay latched together than float away each alone... Then those clumps began to be such that different cells contributed in a different way to the survival of the clump. Those were the first plants. Then some of those plants became more like simplified animals; they developed exoskeletons or endoskeletons, muscles, nerves... then those nerves assembled in a brain... then those brains began to store and handle information... then some of those brains began to ponder about why they do exist...

Most items written here about are dealt with in Physics by General Relativity, Quantum Physics and Thermodynamics of Open Systems. In order to use and more or less understand those, you need an advanced knowledge of Mathematics, that builds upon the common Maths that you see in school.

By the way, I wrote, like many do, that the universe is a surface, of a sphere. Actually it is a volume, like you know. But that volume is constrained, like the surface of a sphere is. That's why it is often preferred to talk of the universe as being a surface. This allows to "feel" more easily the properties of the universe. But it's a volume...

Eric Brasseur  -  12 novembre 2009