00:00Many science fiction movies will make you believe that everything that happens in space is accompanied by a kind of sound effect.
00:07But it is absolutely false. In space, no one will hear you scream. There is no air. The void is almost perfect.
00:15And the sound waves do not spread in the void. They cannot reach your eardrums and make them vibrate.
00:21Nor send signals to your brain. But it's a good thing. Especially for astronauts out in space.
00:28Without the silence that reigns there, they would be completely deafened by the sound of solar storms.
00:34Is there anything more impressive than a gigantic explosion in space? Whether it is scientifically possible or not, that's another question.
00:42On our planet, explosions are what they are because of the air and gravity.
00:47You see, the air is a western agent. And the pressure makes everything fly in a spectacular way, and then collapse.
00:54But this process is very different in space. And it's even more formidable.
00:59If an explosion occurred in space, there would still be a little fire despite the lack of air.
01:05Because certain types of fuel can take the place of western agents.
01:09But it would not be the fire you are used to. This fire would look like an expanding ball of light.
01:16And the process would apparently be endless because of the microgravity and the lack of air resistance.
01:22Space shuttles in the vicinity would be in great danger.
01:26Because splinters would fly in all directions until something stopped them.
01:31All comets have beautiful and long tails. Here is another well-received idea.
01:36In reality, comets are celestial bodies very difficult to spot.
01:40They usually spend long periods far from the stars.
01:44There, in the darkness of space, they are rather inactive and completely frozen.
01:50The tails of comets only form when they approach a star.
01:54It is then that they begin to warm up.
01:57This process allows them to surround themselves with a kind of cloudy atmosphere, or hair, and to have a tail.
02:04The tail always points to the opposite of the star that influences the comet.
02:08The reason is that the tail is blown by radiation and solar winds.
02:13This is why the tail can often be in front of the comet, and not behind.
02:18The internal and external planets of the solar system are separated by an asteroid belt.
02:24A ring made up of various debris and space objects orbiting the sun.
02:29When they shoot a film in space, filmmakers often use this region as a setting.
02:34In general, they show us the asteroid belt as an extremely crowded place.
02:39With compact clouds of gigantic rocks through which the pilots must maneuver skillfully.
02:45In reality, if you took a look at this area when your ship crossed it,
02:49it would be a bit like when you look at the sky from Earth.
02:53Because in truth, the distances are immense in space.
02:57If you decided to cross this asteroid belt, you would have very little chance of coming across a space object.
03:03Asteroids are really very far from each other.
03:06Black holes are huge and frightening cosmic vacuum cleaners.
03:12But in reality, they look more like fly traps.
03:16They do not actively seek things they could devour.
03:20Instead, they wait, passively.
03:23It is only when a star, or any other object, approaches too close, that a black hole takes action.
03:30And even so, only the space bodies that cross a certain limit are torn apart.
03:37In fact, black holes are no different from any other celestial body.
03:42Their attraction is directly proportional to their mass.
03:46They only swallow what their size allows them to swallow.
03:49If our sun, for one reason or another, were to be replaced by a black hole,
03:54nothing would change for the Earth or any other planet in the solar system.
03:59From the point of view of gravity, of course.
04:02We often use lasers in space battles in the cinema.
04:06But if you watched such a fight up close, you would probably be disappointed.
04:11In fact, it would not look at all like what we see in the movies.
04:15A laser beam is a concentrated discharge of energy.
04:18And we could actually use it for many purposes during a fight.
04:22But a real laser beam would be totally invisible in space,
04:26since there would be no particles to diffuse the light and make it bright red, green or other.
04:32A human would be torn to pieces if he found himself in space without a special suit.
04:38Well, contrary to popular belief,
04:41removing his suit during an extravehicular exit would not be as dramatic as what is often illustrated in the movies.
04:49The timid astronaut would simply lose consciousness after 15 seconds due to lack of oxygen.
04:55But only if he exhaled as much air as possible.
04:59Otherwise, it is the oxygen itself that would damage his lungs from the inside, tearing them apart.
05:05After that, without the protection of the suit, the pressure inside his body would drop.
05:11And that would cause even more serious problems.
05:14So, although our astronaut would not explode in a spectacular way,
05:18he would very quickly have big, big troubles.
05:21People often believe that in space, we experience the absence of gravity.
05:25It is said that astronauts are in weightlessness in the International Space Station.
05:30But this is not entirely true.
05:32Gravity is one of the most important forces in the universe.
05:36Thanks to it, the Moon orbits around the Earth.
05:39And the Sun will not wander off our Milky Way.
05:43Astronauts from the International Space Station can feel the effects of gravity.
05:48But we are rather talking about microgravity.
05:51The gravity in the space station is only 10% lower than the gravity on the surface of the Earth.
05:58But astronauts are constantly in free fall.
06:01The spaceship, the people inside, and all the objects on board keep falling forward.
06:07Not down, but around our planet, following a specific orbit.
06:12And as everything falls at the same time, the crew and the objects inside seem to float.
06:17This is why astronauts are able to move objects weighing hundreds of kilos from the tip of their fingers.
06:23So, calling microgravity absenteeism is not entirely accurate.
06:28A light year translates a quantity of time, doesn't it?
06:31Not really.
06:32Light years actually measure distances.
06:35The definition of the NASA of a light year is as follows.
06:39The total distance that a beam of light, moving in a straight line, travels in a year.
06:45And since light travels at a speed of about 300,000 km per second,
06:50a light year is equivalent to about 9,460 and 11 billion kilometers.
06:55One might think that the sun is always on fire.
06:58This is at least what the photographs and films seem to show us.
07:02But in reality, our star is a gigantic gas ball.
07:06Permanent nuclear reactions in its core burn it.
07:10Every second, hundreds of millions of tons of hydrogen are converted into almost as much helium.
07:16During this process, huge amounts of energy are released in the form of gamma rays.
07:22Then, these rays turn into light.
07:25In other words, the sun actually emits dazzling light and incredible heat.
07:31But it is not really on fire, because there is no oxygen in the process.
07:36The speed of light is considered the ultimate barrier when it comes to space travel.
07:42And we often think that it is impassable.
07:45There are many theories about what it could be to reach this speed,
07:49but no equation evokes the possibility of surpassing it.
07:53And yet, we know that there is at least one thing in the universe that is faster than the speed of light.
07:59It is the rate of its expansion.
08:01Yes, the universe expands faster than the speed of light.
08:05And this disconcerts astronomers as much as simple physicists.
08:10But this limit applies to objects moving in space.
08:14Not to the universe itself, which expands independently.
08:18At present, this is not something that scientists understand well.
08:22The rate of expansion of the universe is also proportional to the distance of an object.
08:28The further away it is from us, the faster it moves away.
08:32But even if we do not grasp its mechanics yet, we have our proof.
08:37Even if it remains theoretical for the moment.
08:40That some particles could be able to move faster than the speed of light.
08:46Some scientists think that there could be certain things in space capable of defying this limit.
08:52We just have to find them.
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