“Ladies and gentlemen, please fasten your seat belts, we are going to start our voyage in the space-time!”
The captain powered the engines and in an enormous row, the rocket rushed forward the sky.
After few seconds this one turned black and the melody of Swan Lake waked up the several passengers who lost consciousness due to the pounding acceleration. The lift-off was very successful.
The captain waited a moment that the travellers accustom to weightlessness then he made an introduction explaining the aim of the voyage and said: “So let’s begin at the beginning!” and pointing the finger toward the large window he started:
“Here is the Earth, I think you recognize it ahahah, you can see its blue colour of oceans which is the mark of the life! Perhaps we are lucky ahahah because in this day and age it’s the only place in the Universe that we know with this mark! So we are interest well advised to take care!”
The voyagers were happy that the captain had sense of humour because humour wouldn’t hurt a fly.
“Ok, watch to your right, there is an artificial satellite, these satellites turn around the Earth and allow to recover many information on our planet. For the record, the first satellite was sent in 1957 and its name was Sputnik which means in Russian fellow traveller.”
The spaceship moved away more and more to the planet. The captain spoke again:
“Ok we have just passed a Lagrange point, that is the centre of the gravitational field between the Earth and the Moon, so only another 60 000 km to go!”
A child, who was anyway the alone, wanted to ask how the captain could know that, but all things considered, he kept silent.
Ten seconds later…
“Well there it’s already, here’s the Moon, it’s the only natural satellite of the Earth, its gravity is six times lower to the one of the Earth. Therefore there is no atmosphere to protect it of radiations and the presence of life, even the smallest bacterium, isn’t possible. Furthermore you can see the surface which is drilled by many craters due to meteorites. On the Earth there isn’t all of these because most meteorites disintegrate in atmosphere.”
The child thought the captain should have spoken of shooting stars. And as if the captain guessed his thoughts, he added:
“Also these disintegrations can create nice traces in the sky notably in august.... then don’t forget to make a vow ahahah.“
And he continued: “The darker vast regions gave the name of maria because Galileo, in the 17th century, thought they contained water.”
The captain had a bit of a cough and said:
“The first astronaut who landed on the Moon was Neil Armstrong on 07/20/1969 with Apollo missions, all televisions broadcasted his famous phrase: That's one small step for a man, one giant leap for mankind! I remember it as if it was yesterday, and yet I was a child at those days.”
He looked at the only child…”Yes, I was a child even younger than you, my boy.” He closed his eyes.
“Ok, now we are going to visit Venus named too Evening star.”
The spaceship changed its course.
“Venus is completely different to the beauty and the woman’s charms ahahah, because behind its name is hiding a terrific planet, consider that: its atmospheric pressure is 90 times higher than on the Earth, thus anybody humans would be crushed by this heavy mass. Furthermore it rains not water… but sulphuric acid! So I don’t recommend nobody to live on this planet ahahah. We won’t see Mercury because its planetary layout prevents us. Anyway its landscape isn’t particularly interesting.“
The heat began to be sultry and the captain stopped the spaceship.
“Now you can see the outside radiance which increases, in fact we are approaching to the Sun. We are going to halt at this distance because beyond this limit this could be very dangerous. Why ? The Sun, you probably remarked that, is a very hot star, in vague approximation the temperature of the surface is 6000° but the nucleus reaches 15 millions of degrees! Later we will see there are many other types of stars.
With this high temperature, the Sun is the location of thermonuclear reactions which convert several atoms of hydrogen in an atom of helium. Whereas in 1905, Albert Einstein showed the equivalence between mass and energy according to the law E=MC²…”
The captain looked at the voyagers, they were frightened, he apologized: ”Oh I’m sorry! But don’t worry ahahah because it will be the only formula of the voyage!”
He continued: “So according to the Einstein's law, this fusion processes free a huge quantity of energy in form of radiations. These photons are very harmful but no need to panic because the spaceship is equipped of a heavy armour! For finishing, not only radiations are created, but another charged particles are thrown out in the solar system. It’s the solar wind. When it meets the Earth magnetic field, that creates beautiful polar lights. We are going to start off again in the direction of the great Jupiter.”
The spaceship increased its speed and during the trip the captain was bombarded of questions. The child didn’t hesitate this time and tossed out:
“Captain, why all heaven’s bodies are spherical…? “
“Oh it’s a very interesting question, to do simple, the gravitation forces the objects to have a spherical symmetry and to be the most possible compact.”
The child looked at him incredulous “Ah… but why we haven’t the shape of a sphere ?”
The captain laughed “Ahahah well my boy you have an inquiring mind! That’s good! So in the Universe there are fortunately three other fundamental forces, whereas the gravitation is a force which acts on the great distances, the others on the other hand -nuclear forces and electromagnetic force- act on the shorter distances and…” He broke off his phrase.
“I will talk about that again later because here the computer calculated that we have the time to see Mars, so we are going to go for a trip round Mars!”
After three minutes they faced to the red planet.
“There was only one century, astronomers thought that the immense and deep canyons, which you can see, were dug out by Martians to transport water… And in 1938, the writer Orson Welles played a trick in an US radio emission where he announced, on an idea of the H.G.Wells science-fiction novel -The war of the worlds-, that by now the Earth was invaded by bellicose Martians. It was panic stations and it caused many accidents and suicides! Of course, today we know that there is no advanced life… but perhaps there was a primitive life there is some millions years…”
The captain had a break and the child took advantage of that, for saying to his mother that he had read this book. The captain looked at the lady, she was really splendid…
“Its colour is due to the iron oxide and an another thing to comment is the extraordinary extinct volcano, the great Mount Olympus, it measures up 26 km!” The spectators were delighted.
“In conclusion, man will walk upon this planet without doubt in the near future because some properties resemble to ones on the Earth and so the adaptation of human should be simplified. Ok, now go to Jupiter!”
The voyage continued quietly until…
“Boooom!”…Panic…
“What is this enormous bang ?” asked simultaneously the voyagers.
Immediately the captain took control of the spaceship and with his monitor screen he tried to avoid projectiles.
“Look!, there are boulders by hundreds!” cried out the child.
“Hum… yes we entered into the asteroids field earlier than expected!”
He was talking while manoeuvring skilfully.
“The calculator made a mistake, I don’t know if it’s a bug but it’s a stroke of luck that the collision wasn’t with a big stone of space… I will have to verify if there is a hole in the hull because the oxygen could volatilize in the vacuum… Ah là là, stupid computer!” which, in a robotics voice, replied at the great surprise of passengers:
“Sorry captain, I’m only a HAL model 8000 computer, my next version should be released only in one or two years.” For few, the name of HAL rings a bell…
After a moment, the spaceship was sheltered.
“Whew! That had a near miss! This asteroids field is located between Mars and Jupiter. There are 5 billions years there was only an interstellar cloud makes of many small particles. With the gravitation, the small particles are themselves accreted and thus the Sun then the planets could be produced. Of course it’s a great simplification of the reality… but if some of you would like more explanations I will give you my email at the end of the journey, just remind me about that because sometimes I have the head in the clouds ahahah.” The passengers smiled.
“A theory was that this belt of asteroids was an ancient planet, it’s wrong. In fact it’s only a vestige of accretion of solar system. It was discovered with the Titius-Bode’s empirical formula.
Now that we are approaching Jupiter, I ‘m going to tell you the structure of planets. This belt separates the telluric planets and giant planets. The first, e.g. the Earth, have a rock structure and have a modest size. The seconds, e.g. Jupiter, are principally compounded with gas and are gigantic. So the first have a great density and the others have a very little density, so much that these planets could float on water! Both types have a metallic nucleus, which creates the magnetic field of planets.”
He just ended when they were arriving at Jupiter.
“This his the giant Jupiter! It’s the biggest planet in the solar system. While the Earth has a radius of 6300 km, whereas Jupiter has a 70 000-km radius! Shined by the Sun, the most planets don’t radiate but Jupiter emits a lot of energy. In fact it’s possible that this planet is a failed sun. I think you have heard about its giant red spot ? It’s an immense storm where the speed of wind reaches 600 km/h!”
The child exclaimed: “This planet is very amazing! It’s like an arabesque with its orangey colours which become interlaced!”
“You can seen in front of the planet many natural satellites. Four are important -Io, Ganymede, Callisto, and Europe- because Galileo demonstrated in the 17th century they orbited around Jupiter. It was an essential observation because at that time, the Church thought that the Earth was the centre of the Universe and that all celestial bodies turned round the Earth… So it was a great anthropic advanced idea and thank god there was Galileo ahahah!”
After three minutes, the captain powered again the motors and the spaceship took the direction of Saturn.
“Oh look!!!! A comet!” cried out the child.
“Yes you can admire the bit of frozen rocks in fusion. Due to the solar wind, ice particles are ejected in the opposite direction of the Sun and that creates this beautiful tail. These objects come from the depths of the solar system.”
The spaceship already arrived at destination and the spectators were speechless at the magnificence of the scene.
“Isn’t it superb ?” asked the captain.
“This pretty planet, named Saturn, is the lord of the rings ahahah. Its rings are very fabulous, they are made up in fact by million and million small chucks of ice. Into the bargain, consider that: the width spread out over 100 000 kilometres for a thickness of… 1 km! In the same way, if a 10-cm necklace had the same proportion in thickness, this last would be measured 0.001 mm… so the rings are really very very thin. As Jupiter, Saturn is compounded with liquid and gaseous helium and hydrogen, and it has too many satellites. One, Titan, is very interesting because it could have life in the future. In fact there are three essential requirements for the appearance of the life. Who has an idea on this subject ?” asked the captain to the voyagers.
And the child answered:
“Well, there is life on the Earth consequently I think firstly the planet needs an atmosphere of nitrogen… secondly liquid water must be present…”
The child took time to reflect and finished:
“And thirdly a carbon synthesis method must be possible because… the whole of organic chemistry is based on carbon.”
The captain was astounded and applauded “Well done my boy!” and he continued:
“Whereas Titan has these three conditions. The science which studies the life in the Universe is named exobiology. There is a NASA research program, SETI, which analysis microwaves in order to find extraterrestrial intelligence signals. Ok, now we arrive to the frontier of the solar system. The last planets -Uranus, Neptune and Pluto- are practically unobservable from the Earth with a telescope and that’s normal! Watch the Earth…”
It was now nothing but a spot on the space. The odometer indicated a first number which was 3500 000 000 km and a second number which was 23 ua. The intrigued child asked:
“I suppose the huge first number is our distance to the Sun but what corresponds the second number ?”
“It’s the kilometres conversion into the unit of astronomy, this unit is equal to the distance between the Earth and the Sun, that is to say: 149 000 000 km. It’s allowed to simplify calculus. So now we are at 23 times the Sun-Earth’s distance, we did a long way… and it isn’t finished! Neptune is my favourite, she’s really lovely with her azure blue.” He did a pause.
“In fact the red’s radiation is absorbed by its atmosphere. From a such distance, temperature is only 20 degrees above the first limit in the Universe, that’s to say the absolute zero! And in addition, children would be very unhappy on this planet because they should celebrate Christmas and the New Year only every 60 000 days… ahahah, I don’t know if you should understand this joke because I admit that is far-fetched…”
The child smiled, but the other passengers stayed silent.
The captain made it clear:
“Because Neptune has a sidereal revolution period -which means period for a planet to revolve round the Sun- of 164 years… e.g. a Neptune year equals 164 Earth’s years.”
He was rewarded by his efforts because this time, on the whole, the passengers finally understood and smiled. And the child agreed with the captain: “Yes it’s really far-fetched!”
“In the science history, the discovery of Neptune is important. In the 19th century astronomers and mathematicians calculated, with the Newton’s law of gravitation, that the orbit of Uranus was perturbed by an unknown celestial body. Many calculations and observations were made and thus that permitted Le Verrier and Adams (respectively French and English citizens) to discover the 8th planet. In other words this discovery represents the triumph of the Newton’s classical mechanics.”
Now they went through Pluto and on the route, they met an another spaceship.
“There is no occupant.. Is it a phantom ship?” asked the child for a joke.
“Ahahah, in fact in the 70s/80s, many space probes were thrown in the solar system for exploring it. They were automatic and used gravitation of planets for modifying their trajectories. Two sent further information about the far planets and sent too superb photographs with a high resolution which showed many details. Their names was Voyager I and II and this probe you see is Voyager II. It goes out the solar system and it has an audio disc in gold which contains some information of our planet -various sounds, position of the Earth in the solar system, man’s behaviour, DNA structure- Hum... excuse me for this last I’m not sure, I think rather than it’s connected with the message sent by the radiotelescope of Arecibo… In short, perhaps in thousands years, the disc will be collected by an extraterrestrial civilization.”
He took a bottle of water and shook it. Some water bubbles escaped and he swallowed them. The child remembered seeing this scene and he didn’t do it on purpose but he talked in a loud voice:
“Ah oui, it’s in the adventures of Tintin: Explorers on the Moon…!” The other passengers laughed. And the captain continued: “... with that cursed Captain Haddock ahahah!”
“Now we are beyond the solar system.”
The voyagers looked at behind, the planets were now very far and a myriad of stars took place in the sky. It was a fantastic sight.
“You can rest because the travel to the next objective will be long, and the next part will be more technical. Sweet dreams!” concluded the captain.
A new background music with a very sad tune, whose the name was Amacord, began and the passengers went to sleep seeing stars. The child tried to stand up to fatigue but he finally fell asleep too.

After a long while, the captain who had rings under one’s eyes due to he didn’t sleep, waked gently up the passengers and they were surprised to find face to face with not one but with 7 blue suns.
As if the captain saw into the thought of voyagers, he said:
“Ahahah you didn’t imagine that they are blue stars! In fact, this is a young stellar cluster, that is to say several stars was formed at the same time there is some million years. Its name is Pleiades and its distance from the Earth is 410 light years. This is an incredible distance because if the spaceship could go at the speed of light, we would have took 410 years to do the travel, and I believe we should have at least white hairs ahahah… so thanks the author that we are in a story of fiction ahahah!”
The child wanted to ask a question but he refrained.
“The temperature of surface of these stars rises 30 000 degrees! Be careful, I’m talking only about the surface, their inside temperatures are far and away hotter.”
The child asked:
“How do you know that ?”
“In fact, it’s dead easy to say because the temperature of an incandescent body depends on the colour of its surface, for example if the star was red therefore its temperature of surface would be near 2000°, etc. If you glance at a sky atlas, you will see many information on stars, and yet they are at billion of billion kilometres from the Earth. So how find the astrophysicists these information ? Actually there are several methods, one is to refer to the Hertzsprung-Russell diagram…”
Immediately:
“And what is this Hert... what is this Hertzsprung-Russell diagram ?” The child had trouble to pronounce this name and he had to do two attempts.
“This diagram connects several parameters of a star. Thus for example if we know the distance of a reference star, its colour and its luminosity, which is established by spectroscopy, we can find its radius, its mass… and above all we can find these information for other stars with their apparent magnitudes. We will see that these parameters change in the course of ages and consequently, this diagram describes evolution of stars to the birth up to the death. So it’s very important. For instance, we know that the Sun is a standard star, what the astronomers call the main sequence, and we know it has completed half one’s lifespan, but don’t worry… because it has still 5 billion years to live ahahah!”
Now the child reminded of this diagram and exclaimed:
“Oh, be a fine girl, kiss me!” His mother scowled at him and he went red. After the mother looked hard at the captain and in his turn, he went red. He turned one’s eyes away and answered:
“Ahahah, yes this phrase is a memo technique way to remember the order of the spectral series, e.g. OBAFGKM.”
The spaceship arrived to two new stars. This time, one was red and enormous, and the other was white and very very small, and they were very close to each other.
“Here we are facing of a physical couple of stars, more exactly, it’s a binary system of x-rays. The biggest star is a red giant. Its radius can reach 10 000 times the one of the Sun! In fact when a star in the main sequence burnt almost all its hydrogen, it expands as if we blow up a balloon, and its radius is multiplied by 100 or more. In addition its temperature gets cold and consequently the colour of the surface becomes red." The captain broke off.
"Afterwards, its helium will be burning in its turn in heavier elements, in other words it will be the beginning of the nucleosynthesis. Then according to its mass, they are several possible deaths. One is precisely represented by the second star. When the red giant is burning a part of its helium, its radius is going to this once decrease and decrease for not to be more a minuscule star. Also its density and its temperature will be enormous…”
The child, who listened with passion the captain, said:
“Well of course! Its colour will be white because its temperature is high and it’s a tiny star… Now I understand why these bodies are named white-dwarves! Thanks captain!”
“You are welcome! An other important thing to say is the… Careful!!!”
A huge purple lightning was emitted not far from there. There was a second and besides a third. The captain just had time to push a button and in front of the wide window, a new translucent window, which seemed many thicker, took place. A warning indicated “Shield activated”.
“It came in the nick of time! These radiations are produced by the swap of matter between the two stars which forms an accretion disc, and they are x-rays which are a very penetrating radiation and can cause the destruction and lesion of cells of the human’s body. So it’s very dangerous… and we will not stay here a longer time.” The child knew that the lesion of cells could caused cancers.
No sooner said than done, the spaceship went away from the death flashes.
“I had not finished my phrase, the other thing to specify is the density of the little star, it can attain one ton by cm3… which amounts to saying that a thimble should have the mass of a car! So you must realize that a such density isn’t explainable by the classic mechanic any more. Consequently, a new theory was invented by physicians in the beginning of the last century, it’s the henceforth famous… quantum mechanics but that's outside our talk! Do you remember when I spoke about forces in the Universe ? The gravitation is an attractive force and so, if you consider it, all matter must be attracted to become a single point…”
He looked at the boy, he took notes on a sheet which seemed filled.
“But there is a second force, the electromagnetic force. According as the charges of two particles are in the same polarization -for example: positive/positive- or a different polarization -positive/negative- the two particles will be respectively repulsed and attracted. In a white-dwarf the state of matter is called quantum degenerate state, that is to say the star is made up of a free electrons gas. Therefore the electrons, which have a negative charge, are repealed each other and thus compensate the effect of gravitation. Hum... do you understand ?”
The child nodded his approval but he was the alone, the other passengers already lost the thread of the conversation.
“Mind you, an another force which is the pressure of radiation helps also the electromagnetic force… Here is the last objective in our galaxy.”
The passengers were filled with wonder at the sight: a multiple colour gas stretched as far as the eye could see. They cried out all “Wow!” except the child, who he didn’t always want to do nothing as nobody else, cried out “Wahou!”.
“This object is interesting for several things... but in the first time, who knows this object ?”
All voyagers gazed vacantly about one because they were afraid that the captain test them. A little voice said “Perhaps it’s a supernova…”
“Exactly my boy! In fact rigorously it’s a residue of a supernova and what is it ?”
Once again the same child jumped at the opportunity “It’s a star which exploded… “
“Great! I said a short while ago that a red giant can die of several manners. The first was a decrease in a white-dwarf. The second will be much more radical ahahah because… it will be the explosion pure and simple of the star! However It always left a residue of the star. It’s a neutron star but here we are luckily because moreover this star have another propriety, it spins round and round and thus creates a high magnetic field, which then is going to accelerate particles and consequently that is going to emit electromagnetic waves with the synchrotron effect. It’s called a pulsar -or a space lighthouse- because, like a lighthouse, it pulses a beam in a certain direction. Perhaps you ask yourself why sometimes the star dies in a supernova and other times it dies in a white-dwarf… No ?”
“Of course!” said the child.
“In fact that depends simply on the original mass of the star! There is a third possible case but which is only suggested theoretically by the theory of Einstein’s general relativity... they are the black holes but in my opinion it’s a pure invention of spirit... Now go back to supernovae. When the giant star explodes, its envelope is expulsed with a speed close to 10% of the speed of light and the luminosity can increase ten billion the one of the Sun! So when a star explodes… it’s preferable to not be in the vicinity ahahah. This cataclysm is going to entail the creation of new elements -for example: silicon, oxygen and sulphur- and will be logically the next step of the nucleosynthesis. So the beautiful gas you see, is precisely the ejected matter, we call it a nebula and here its name is Crab nebula. This supernova was observed in 1054 by the Chinese. They related in ancient text that it was visible in broad daylight! In few millions years, this matter will combine anew and then, if the gravitational contraction is sufficient, the temperature will be enough high to start the combustion of the core and then will appear a new star and later perhaps new planets. Ok now we know practically everything about stars, we are going to change distances scale. So I'm switching the speed to high.”
The stars passed to a stupefying speed and everything seemed tranquil till…
“There is a problem... we have gone off course... HAL, could you show the nearest stars ?”
“No sooner said that done dear captain, the nearest star is AOe 17416-6 and its distance is 1.3 parsec.”
“Strange… very strange…”
The child asked: “What ‘s going on ???”
“We are veered off course…” The captain looked very anxious.
Suddenly the spaceship was tossed from all sides.
“There are gravitational waves… Strange…Oh no! I understood… we are attracted by a… black hole.”
The passengers didn’t really know what was a black hole.
“Quick! HAL, active the front propulsion. It‘s a very stroke of luck because we don’t overstep the Schwarzschild horizon of the black hole… If we were on the contrary case, then we could say goodbye to our dear Earth! ahahah”
As a result all passengers quaked while the captain was streaming with sweat and fought against this mysterious object. He battled, battled and battled… and finally won the fight. He let out a “phew!” of relief and the voyagers done likewise. There was a lengthy hush because the crew knew that they had been face to face with the death.
“It’s unbelievable! It’s the first time a black hole is detected, so they truly exist… my colleagues won’t never believe me ahahah! I assume now you would like that I make a speech about black holes… So these objects are the third possibility when a star is in end of life. In fact, in theory, when a star has about ten times the Sun mass, neither the electromagnetic force, nor even nuclear forces, can’t counterbalance the gravitational attraction, the physicists will said that the star is in a gravitational collapse. Then the star becomes irrevocably increasingly small and consequently its density increases increasingly. That creates a spatiotemporal singularity, e.g. a mathematic point where the density is infinite, which is going to curve so much the space that nothing won’t be able to escape... not even the light! So this object is worthy of its name ahahah."
“I thought the light has no mass ?” asked the child.
The captain looked at the mum.
“Are you his mother ?”
“Yes, I’m sorry, he always wants to know the whys and wherefores!”
“Ok… but it’s not a fault ahahah!” This time that was absolutely certain, he fell in love…
“In a way, in the beginning of the last century, Einstein him again, demonstrated that mass warps the space-time, the result is the gravitation. In an another way he demonstrated that the light follows, that we call, the geodesics of space-time. This phenomenon was observed by Eddington in 1919 and partly proved that the general relativity wasn’t a simple invention and simple equations but, on the contrary, it was real. Therefore if the warping is sufficient, the geodesics will curve up and the light won’t be able to escape.”
“In fact it’s a sort of trap!” said the boy.
“Yes, and we very nearly fell into the trap ahahah but finally, all’s well that ends well! Ok, we reach last one’s destination…”

An abstract painting stretched away as far as the infinite. It had a black background composed artistically by many different shades and patterns. It was fine, very fine. The child felt that the painter had to have the cult of beauty.
“Here are the great structures of the Universe, that is to say the galaxies. What is a galaxy ? A galaxy is a group of stars, attention it’s not a star cluster because if a star cluster is a group of thousand stars, as regards a galaxy, it’s a group of about one hundred… of billion of stars! In this gigantic celestial object, stars and interstellar matter, are bounded by the gravitation... This is our Galaxy!” The captain pointed the finger to a spiral shape.
“Our Sun is in this spiral branch, you can see too the central bulb of the galaxy which shows that it’s a densely stars area. As for the exterior luminous halo is formed by old stars. There, this is M31 Andromeda… There is only since 80 years, scientists thought that the other galaxies were in fact dust nebulae included in our Galaxy. However, the philosopher Kant in the 18th century already made the assumption that these nebulae were other galaxies, he called them the universes-isles. In 1923, Edwin Hubble observed a variable star, more exactly a Cepheid, in M31, which allowed him to measure its distance, and he concluded that M31 was outside our Galaxy. So our Galaxy was in fact a galaxy among many. But the major year was in 1929, Hubble calculated the distances, but too the speeds of many galaxies. He put down on a graph his measures according to the two scales. Then appeared the one of the greatest discovery of 20th century, the law of Hubble: the more galaxy is far, the more speed of galaxy is high, and it’s important, as he was measuring the red-shift of galaxies, he proved that all galaxies, except some galaxies near our, moved away our Galaxy. In fact, all galaxies moved away each other, so the space -the Universe- is in expansion!”
The child explained:
“But if we think about it, if we could go back in time, we could see the galaxies squeeze increasingly!”
The captain continued:
“Ahahah, but don’t you know that the speed of light has a finite speed -and it’s the second limit in the Universe- which is about 300 000 km/s ? For example, when we observe simply the Sun, the light takes 8 minutes to arrive to the Earth, and, in other words, we see the Sun 8 minutes in the past, consequently we will say that the sun is at 8 light minutes. The oldest galaxies are at 13 billion light years, so when we watch these galaxies we observe them how they were there are 13 billion years. So on the contrary we can go back in time! With the spatial Hubble telescope we can observe the formation of galaxies and the beginning of the life of the Universe, that is to say, according to the latest theories, there are 15 billion years. So you understand now why it’s a voyage in the space and time!”
The child who didn’t miss a single word of the conversation said:
“If the Universe has a commencement, what has it passed before that ?”
“Ah, it’s a philosophical question so opinion is divided, but in fact I think we must take the start of time and so the start of reality, here. In any case, unfortunately there is an observation limit in the past, it’s easy to understand if you make the analogy with…”
The child broke:
“…With a black hole! Because Lavoisier said in Nature, nothing is lost, nothing is created, everything is transformed, so the mass -or the energy- of whole matter nowadays must be equal to the mass in the beginning of the Universe.”
In spite of his quotation the boy wasn’t haughty.
“That’s exactly, continue your idea…” encouraged the captain.
“In the past the Universe had to be little, perhaps even, it was a single elementary particle and then all matter was in this particle. So the density had to tend towards infinity, and as a black hole, there had to have a spatiotemporal singularity!”
“Very well my boy! This third limit in the Universe is called the time of Planck and all the laws of physics stop here because the results haven't any meaning any more and… that’s another story ahahah. Astrophysicists think that the beginning started with a big explosion which the astrophysicist Fred Hoyle named the big bang to make fun of this idea. But this idea was approved by many concrete facts, and the most important was the discovery of the cosmological radiation by Penzias & Wilson, which proved that the temperature in the beginning was very high. You could think that as the blast of an explosion ejects matter, here the ejected matter would be galaxies… Not correctly because don’t forget that the explosion created time but, and it’s important, the space too. So the galaxies recession is due to the expansion of the space itself. Mind you, the Universe is in a perpetual movement and evolution, if we will be able to accelerate time, we will see an absolute cosmic ballet! We would see the galaxies turn on as a merry-go-round, we would see stars lighting on then lighting out as tinsel garlands, we would see galaxies colliding with others and there would be then creation and explosion of many stars as a fireworks…”
To listen the captain, the passengers were in the seventh heaven.
“… But this cosmic ballet would be played in a great silence because there is no sound in space.”
The child dared:
“But captain, you spoke us of the commencement… but what will be the end of the Universe?”
“You always have good questions and that’s the big question. There are two possibilities, whether the density is sufficiently high then the Universe will be contracted until it becomes a new spatiotemporal singularity -that is to say it will reverse- or whether the density isn’t enough and then the Universe will continue increasingly to increase its volume and to increase the distances between galaxies, and a day will come when, with the radioactive disintegration, all elements will be transformed in the most stable nucleus -e.g. in iron-. So in any case, it will be a tragic death ahahah. Note that the second is the selected choice…for the moment!”
The child shout:
“…As long as the dark matter isn’t found!”
The only reply of the captain which was: “Yes” showed that the captain was tired, very tired. But he wasn't alone, because all passengers had travel worn and the eyestrains. The captain had strength left to finish: “I’m really sorry but the voyage stops here, I would have liked to talk of quasars, local group, types of galaxies, a short word on the theory of all, cosmologic constant, paradoxes, time travel… and many other things but precisely time prevents me from doing ahahah.”
Then the child said: “Ah time, again time, always time…”
The captain looked at him fondly and concluded:
“If you must remember only one thing of this voyage, that’s the Universe has a great variety of constituents and has several rung levels. But I hope you will remember more things ahahah. As for me, I learnt that the women are even more beautiful in space ahahah.”
He switched the automatic navigation and reclined his sear to sleep. All passenger did the same… all excepted one person, the child who preferred looking at a last time the Universe. And then he fell asleep during a lullaby and dreamed marvellously.

After a long while, HAL, which didn’t never sleep, announced: “We arrive safe and sound!”
It was already the end, all passengers went out the spaceship and said to one’s heart’s content:
“Thanks captain for this lovely voyage!!!”
The captain took his leave and is going to close the door when the child rushed to him and asked:
“You are going to forget to give me your email!”
Which the captain answered:
”Ahahah, no, I was sure that you would come to request me before I have to close this door. Take that, that’s for you and that’s for your mother…”
He waved a last sign of farewell and left the captain, this one gave him his email… and a bunch of flowers where was noted: “I love you”.

The End