00:00Scientists are advancing a fascinating theory.
00:03What if the whole of our universe was actually inside a black hole?
00:07This concept, called black hole cosmology, suggests that the observable universe,
00:13everything around us, could be housed inside a black hole,
00:17itself located in a parent universe, or even in a multiverse.
00:21This multiverse could in turn belong to an even larger set,
00:26and so on, like a Russian doll.
00:29It seems to be science fiction, but this hypothesis is based on intriguing facts.
00:35By retracing the history of our world,
00:37scientists explain that everything would have started with a singularity.
00:41Imagine gradually reducing a gigantic sphere.
00:45At some point, it would become extremely dense before collapsing.
00:50Although it is difficult to imagine this,
00:52space allows to compress unimaginable quantities of mass into a tiny point.
00:58This point, called singularity, contains the compressed matter in an infinitely reduced space,
01:04smaller than an atom, while retaining the entirety of its mass,
01:08that of the whole universe, while occupying almost no volume.
01:12Inside this singularity, the conditions are so extreme
01:16that the classical laws of physics cease to apply.
01:18Everything we know, time, space, matter,
01:23collapses, making any process beyond this point totally incomprehensible for our current logic.
01:29Thus, scientists estimate that this was the starting point of our universe.
01:33When the Big Bang occurred, this tiny point containing everything that exists expanded,
01:39until it covered the entire space.
01:41It is from there that the universe as we know it began to form.
01:46However, according to researchers, a similar singularity would also exist at the heart of black holes.
01:52General relativity affirms that a black hole is formed when a very large object, like a star,
01:57collapses under the effect of its own weight.
02:00The more the mass is important, the more the gravity intensifies.
02:04In the case of a colossal star, tens of times more massive than our sun,
02:08this tiny point develops a phenomenal gravity.
02:12It is this force that attracts everything around it and deforms so deeply the structure of space-time
02:17that it creates the appearance of a hole in the universe.
02:20It would be the center of a black hole.
02:22A point where all these things come together and are crushed into an infinitely dense singularity.
02:28So, could our universe be a simple singularity point,
02:33nestled inside a huge black hole, itself located in another universe?
02:38It would be truly amazing.
02:40But it is not so easy to compress an object to the point of literally deforming space-time.
02:44It would take extreme pressure.
02:47If you wanted to create a small black hole on a human scale,
02:50you would have to reduce this object to the size of an atomic nucleus.
02:53To obtain a black hole the size of a chickpea,
02:56you would have to compress the entirety of our planet.
02:59But our universe is made up of 99% empty space,
03:03with billions of kilometers of void between the stars.
03:06If you grouped the entire matter of the universe,
03:08the result would be surprisingly compact.
03:11Everything around us, including galaxies, stars, planets and dust,
03:16would be held in a cube of only 1 billion light-years apart.
03:20For comparison, the Milky Way alone measures 100,000 light-years.
03:24That is to say, if the matter is rare in the universe.
03:27However, at such a density, this whole would be of an absolutely colossal mass.
03:33This mass would probably collapse into a black hole.
03:36And here is the surprising part.
03:38This black hole would have about the same size as the universe itself,
03:42with an equivalent mass and energy.
03:45In addition, it would have the same average density.
03:48The radius of a black hole increases with its mass.
03:51The more it swallows, the more it grows.
03:54But paradoxically, its density decreases as it develops.
03:58For a size as large as that of the universe,
04:01it would actually be rather clear.
04:04And this is not the only coincidence.
04:06We have a concept called the Hubble ray,
04:09or horizon of cosmological events.
04:12If we imagine our observable universe as a gigantic bubble,
04:16its edge would represent the most distant area of the universe that we can perceive.
04:20It's a bit like when you stand in a field and try to see in the distance.
04:24Your eyes describe a circle, it's the same idea.
04:27There could be more beyond this point, but it will remain a mystery forever.
04:32Beyond this horizon, the light coming from distant regions of the universe
04:36will never be able to reach our world.
04:39This is due to the limited speed of light
04:41and the too fast expansion of space between us and these regions.
04:45It's like running towards something while being pushed back,
04:48by a wind of an immeasurable force.
04:51As long as we stay on Earth,
04:53we will never be cut off from these distant borders of the universe.
04:56Black holes have something terribly similar,
04:59called the horizon of events, or the Schwarzschild ray.
05:03It is the point of no return.
05:05It is this imaginary line that is often represented
05:08in the form of luminous contours around black holes.
05:11Everything that crosses this horizon of events,
05:14falling inside, is irrevocably lost.
05:17Neither light, nor matter, nor information can get out of it.
05:21The gravity of black holes is far too powerful,
05:24which makes them perfect cosmic vacuum cleaners.
05:27As we mentioned earlier,
05:29if we created a black hole the size of the universe,
05:32it would have the same mass and the same horizon of events.
05:35Although some scientists think that this is a simple coincidence,
05:39others believe that this could be a clue
05:42suggesting that our universe is inside a black hole.
05:45This theory also suggests that our universe would not be the only one.
05:49It could exist in one of the many black holes
05:52distributed in an even larger multiverse.
05:55In this nonsensical model, each of these universes,
05:58as much ours as that of our parent world,
06:01could be the cradle of its own universe,
06:04governed by a distinct set of physical laws and structures.
06:08It would be a strange chain.
06:10There is a theory that suggests that universes
06:13could be born inside black holes, in a way.
06:16It is known as the Einstein-Cartan theory.
06:20This theory also addresses the question of singularity,
06:23but from a different angle.
06:26It suggests that, instead of condensing into an infinitely dense point,
06:30matter could generate a glass hole.
06:33The latter would be a kind of tunnel through space and time.
06:36This glass hole, also known as Einstein-Cartan bridge,
06:40could link two distinct regions of the universe.
06:43In this scenario, one side of the tunnel would correspond to the black hole,
06:46while on the other side,
06:48a whole new universe could be being formed.
06:51Thus, it could function as a teleportation.
06:54As soon as you cross the event horizon,
06:57you would be transported to this new world.
07:00But in this case, there should be a kind of opening.
07:03Some researchers have imagined this and called it a white hole.
07:07Although it does not really exist, at least to our knowledge,
07:11it could be possible somewhere on the other side.
07:15This white hole would function as the exit of a glass hole,
07:18an area where matter is constantly expelled instead of being sucked.
07:22This means that you could not throw anything there.
07:25Everything would be immediately rejected.
07:27All of this remains purely theoretical, of course.
07:30These ideas are well integrated into the Big Bounce concept.
07:33This theory suggests that, instead of our universe starting with a single Big Bang,
07:37it would have rebounded from a previous state of contraction.
07:41Do you remember the analogy of the compressed ball?
07:44Maybe there was another universe ball,
07:47compressed to a tiny size, before bouncing and expanding again.
07:52Thus, instead of a universe made of nothing,
07:55we could live in a universe that would be the cosmic recycling of another.
08:00There is also another version of this theory,
08:03sometimes called shock wave cosmology.
08:06This idea supports that the Big Bang could have been caused by an explosion
08:10inside a black hole.
08:13This would have given birth to the expanding universe we see today.
08:17As the universe expands and the density of matter decreases,
08:20the black hole could end up turning into a white hole.
08:23The opposite of a black hole,
08:25where matter is expelled instead of being sucked.
08:28But even if these connections are fascinating,
08:30they are not evidence.
08:32There is no experience or observation
08:35that could validate or invalidate these bold theories.
08:39They remain, for the moment, mere speculations.
08:42But at least, it's fun to speculate.
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