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
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