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Discover the intriguing scientific theories that suggest the eventual evaporation of our universe, as postulated by the esteemed physicist Stephen Hawking.
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00:01There's this mysterious thing in space, an unusual spot that scientists haven't been able to explain for more than 15
00:08years.
00:09There are different theories, and one of them says that maybe this is an imprint from a collision with a
00:15parallel universe.
00:17Is this true? Well, let's see.
00:21Take a look at this map. This is the map of our universe.
00:25Well, not really. This is actually the map of Cosmic Microwave Background Radiation, or simply CMB.
00:33Many, many billions of years ago, there was a Big Bang.
00:37It was so powerful that it created our entire universe.
00:42And, of course, such an event couldn't occur without leaving some consequences.
00:47And these consequences are literally everywhere.
00:52The Big Bang left electromagnetic radiation, which we know as CMB.
00:58We don't notice it in our daily lives, but it's literally here, under our noses.
01:04And if you had some kind of superhuman vision, you would see how everything around you shines with this dim
01:10light.
01:12This radiation is very important.
01:14If we hadn't discovered the CMB, we would never have found out about the Big Bang.
01:20Previously, scientists believed that the universe had always existed.
01:24There was no beginning, and there was no end.
01:27It sounded pretty ridiculous to us now, but less than a century ago, people were absolutely sure of it.
01:34Stephen Hawking was one of the first scientists to guess that the universe did, in fact, have a beginning.
01:41The guy was so cool that he realized this as a student while working on his doctoral dissertation.
01:48But, unfortunately, he had no proof.
01:51If there was such a strong bang billions of years ago, then where are the traces?
01:56Where's the proof?
01:58Laughed people who believed in the eternal static universe theory.
02:02But don't worry.
02:03They had the proof rubbed in their faces real soon.
02:07In 1965, astronomers Arno Pienzas and Robert Wilson discovered CMB.
02:13And that was the first grandiose proof of the Big Bang.
02:17It turned out that radiation was everywhere.
02:21We just didn't notice it.
02:22In fact, at first, Pienzas and Wilson themselves mistook it for the noise of a big city, or pigeons, or
02:29something else.
02:31For their discovery, which turned the world of science upside down, they received the Nobel Prize.
02:38Alright, so people learned that they were surrounded by electromagnetic radiation.
02:43Then, they started collecting more data about it.
02:47They accumulated more and more info over the years until they made this very map.
02:52This is a map of CMB temperatures.
02:55But, while creating it, scientists discovered something unusual.
03:00Let's take a look at this map.
03:02It looks like a large and diverse pattern of cold and warm places.
03:07But, in reality, our universe is quite uniform.
03:10All temperatures on this map are close to negative 455 degrees Fahrenheit, with very little difference.
03:17All temperature fluctuations between these places are small.
03:21And each tiny speck actually spreads over millions of light years.
03:26So, everything in our world is pretty calm and stable, except for one point.
03:31This cold spot right here.
03:35Astronomers first discovered it in 2004.
03:38First, it looked like nothing unusual.
03:41It's just a region where the temperature is below average for a couple of microkelvins.
03:46But remember, we're not talking about a small area.
03:49This is a giant cold region.
03:51It's literally billions of light years in size.
03:55Wait, the scientists thought.
03:57This can't be true.
03:59The universe should be consistent everywhere.
04:01According to our standard model, this cold spot simply shouldn't exist.
04:06But it does exist, though.
04:08This isn't just some mathematical error.
04:10It's right there.
04:11So, what is this cold spot?
04:14And how did it appear?
04:16Astronomers have been trying to find the answers to these questions for years.
04:21Even now, we have only a few theories.
04:24So, let's discuss them all.
04:26Theory 1.
04:28Cosmic Texture
04:29This idea was brought up at the end of 2007.
04:33Then, scientists suggested that this cold spot could be the hills of space.
04:38In other words, it may be a bumpy region of the universe, just part of its texture.
04:44But that's a silly explanation.
04:46So, this theory was quickly discarded.
04:49Theory 2.
04:50The Supervoid
04:51This hypothesis was considered the most plausible for a while.
04:56It stated that the cold spot was actually the so-called Supervoid.
05:01It's a terrifying, dark place of our universe with almost no galaxies.
05:05And because it's an empty region with almost no stuff in there, it seems cold to us.
05:12However, this theory was refuted in May 2017.
05:16After carefully examining the cold spot, scientists found out that there were no signs of a Supervoid there.
05:23Moreover, voids and Supervoids, which actually exist, by the way, are still very small in size.
05:30The cold spot is literally thousands of times bigger than them.
05:34So, there must be some other explanation.
05:36And there is one.
05:38Perhaps the most bizarre of them all.
05:41Theory 3.
05:42A Parallel Universe
05:44This controversial idea was put forward by cosmologist and theoretical physicist Laura Mersini-Houghton.
05:52She suggested that the cold spot could be an imprint from the collision of our universe with a parallel one.
05:59Standard cosmology cannot explain such a giant cosmic hole, says Mersini-Houghton.
06:04This is the unmistakable imprint of another universe beyond the edge of our own.
06:10Her assumption is based on the theory of the multiverse.
06:14This theory says that there's actually an infinite number of universes like ours in the world.
06:21They constantly collide with each other, giving each other a push which creates a new Big Bang.
06:27So, maybe the cold spot is a bruise from such a collision.
06:30For quantum mechanics, such crazy theories are pretty common.
06:35But for standard physics and our simple understanding of the world, this is Earth-shattering.
06:41Of course, we need strong evidence.
06:44And Mersini-Houghton's team has begun to work on it.
06:48Professor Tom Shanks from the Center for Extragalactic Astronomy at Durham University also participates in this research.
06:57The craziest sounding of the exotic models for the explanation of the cold spot,
07:01the multiverse is actually the most standard in terms of our current model of the universe, he wrote in one
07:07of his works.
07:09So, what evidence do we need?
07:12Well, our cold spot is located in the southern hemisphere.
07:16According to Shanks, if there really was a collision between two universes,
07:20we should find another cold spot, and it should be in the opposite, northern hemisphere.
07:26If astronomers actually found it, this theory would be confirmed,
07:30and it'd become the first proof of the existence of a parallel universe.
07:35But it's not that easy.
07:36To find a second spot, we need the latest, highly sensitive telescopes.
07:41We also need to find out some info about the nature of dark energy,
07:46how it affects space, and, in other words, there's still a lot of work to do.
07:52Not so long ago, scientists actually believed they had discovered the second spot.
07:57Researchers from New Mexico thought they had found it in the northern hemisphere.
08:02But, unfortunately, this is likely to be a mistake.
08:05The map these researchers used had a high measure of randomness,
08:09so it's possible that their discovery is just an accident caused by other voids.
08:15So, basically, we haven't found another cold spot so far, despite careful analysis.
08:20But, again, even the best modern equipment is not perfect,
08:24and it doesn't mean that there's no second spot.
08:26It just means that we haven't found it yet.
08:29But if one day we did find it, it could change the world of science forever.
08:35We'd confirm not only the theory of parallel universes,
08:38but also the famous string theory.
08:40It could explain everything that occurs in our world.
08:44But if this happens, we'll get even more questions than we already have.
08:48How did these two universes collide?
08:50How does it all work?
08:52So far, it's all just guesswork.
08:55We can't claim that the cold spot is a print from the collision of parallel universes.
08:59But we can't refute this, either.
09:02Actually, we may never know the truth at all.
09:04But it's still interesting to strive for it.
09:08Empty space is not really empty.
09:10At least, that's what quantum field theory says.
09:13It's actually filled with tiny vibrations
09:15that can turn into virtual particles if they have enough energy.
09:19These virtual particles can produce packets of light with low energy called photons.
09:26Now, there's something every black hole has.
09:29An event horizon.
09:31It's a point of no return.
09:33That means once something crosses that point,
09:35it can never get away.
09:37Not even light.
09:38And there's an insanely strong gravitational force around the event horizon.
09:43Black holes survive by gobbling up gas and stars around them.
09:47In most cases, a black hole has a swirling disk of material that surrounds it,
09:52called an accretion disk.
09:54It glows brightly as all those things that come too close to an event horizon
09:58get heated up and torn apart before the black hole swallows them all.
10:02As material comes closer, it starts to travel and move faster and faster,
10:07going all around the black hole.
10:09This makes the accretion disk glow and at the same time,
10:13outlines the shadow of the black hole,
10:15which is basically the very event horizon we're talking about.
10:19Black holes might even want to hide,
10:22but they do so awfully badly.
10:24According to Einstein's theory of general relativity,
10:28gravity bends and warps space and time.
10:30It means that the closer you come to this extremely powerful gravitational pull
10:35around the black hole,
10:37the more twisted space and time around it become.
10:41That's what Stephen Hawking was talking about nearly 50 years ago,
10:44and it doesn't stop there.
10:46He also suggested that if these particles find a way to escape a black hole,
10:50they steal some of its energy.
10:52And because of these thieves,
10:53the black hole loses its energy as time goes by until it,
10:57at one point,
10:58completely disappears.
11:00He suggested that black holes release energy in the form of thermal energy or heat,
11:05which is called Hawking radiation.
11:07And this radiation doesn't carry any information.
11:10It means that when a black hole evaporates,
11:12it destroys all information it had about the star that created the black hole.
11:17That way,
11:18we can't know what really happened.
11:22And it's kind of confusing because the laws of quantum mechanics say the information can't be destroyed.
11:28This conflict is something we call the Hawking information paradox.
11:33According to Hawking,
11:34all this information isn't really lost,
11:37but is stored in a cloud of all those zero energy particles that surround the black hole.
11:41He called that soft hair.
11:44Now,
11:44there's this new study as a possible solution to this paradox.
11:49Maybe Hawking radiation is non-thermal.
11:52Instead of just releasing plain heat,
11:55it's possible the black hole sends out a message in the form of radiation.
12:00This message contains important information about the black hole's past,
12:04the stars that formed it,
12:06and other details we thought were lost forever.
12:09It's like a secret code that tells us all about the history of the black hole.
12:14But let's go back to Hawking's theory,
12:16where a black hole can eventually disappear.
12:19It says that not only black holes produce Hawking radiation,
12:22any object with enough mass can.
12:25Researchers actually studied a process called the Schwinger effect too.
12:29It's when an electromagnetic field creates strong distortions,
12:32and in that way,
12:33forms matter.
12:34They applied this idea to Hawking's theory of black hole radiation.
12:38What they found is that the radiation Hawking predicted can actually be created in places with different levels of gravity,
12:44not just around black holes.
12:47Here's the key.
12:48When there are massive objects,
12:50like stars or planets,
12:51they create a curving effect on space and time.
12:54This curving is there because of their strong gravity.
12:58Even if you're far away from a black hole,
13:00there's still some massive object somewhere around that creates the curving of space,
13:04which can make you feel like you're in that twisted space.
13:08It can create radiation,
13:10similar to what happens near black holes.
13:14It means that not only black holes can slowly evaporate,
13:17other massive objects in the universe can also lose their energy in the same way.
13:23If this is true,
13:24the energy of everything in the universe will slowly be drained away in the form of light particles.
13:30That means everything and everyone,
13:33including stars,
13:34planets,
13:35black holes,
13:36and us,
13:38share the same destiny,
13:39and will all eventually fade away.
13:43This sounds scary at first,
13:45but even if this theory is true,
13:47it's not going to happen anytime soon.
13:49It would take way longer than the current age of the universe
13:52for a supermassive black hole to completely disappear.
13:56So, in the way we measure time,
13:58black holes are basically eternal.
14:01And stars could last even longer since many black holes formed
14:04after some giant star collapsed upon itself.
14:09Some others belong to a group called
14:11primordial black holes.
14:13Hawking,
14:13who became famous for talking about black holes,
14:17mentioned those ones as well.
14:19And the theory says they probably formed spontaneously in the early universe,
14:23not long after the Big Bang happened.
14:27Hawking realized that primordial black holes could have different sizes,
14:31from very light to very heavy.
14:34Really small ones would have disappeared by now because of Hawking radiation.
14:38There's a pretty cool idea that these primordial black holes could be dark matter.
14:45It's a mysterious substance that scientists think exists in the universe.
14:49It doesn't give off or reflect light,
14:51so we can't see it directly.
14:53Scientists think dark matter might explain why stars and galaxies move in strange ways,
14:58but we still don't have the tools yet to confirm whether these black holes really exist,
15:02or if they're actually made up of dark matter or not.
15:06Hawking also explored the idea that our universe is just one of many universes.
15:12It's a concept called the multiverse.
15:15Some scientists believe it could be that any situation you can imagine in your life
15:19is happening somewhere in some other universe.
15:22Hawking didn't agree with that.
15:24So in his final paper, he proposed a new mathematical framework
15:28that made the multiverse finite instead of infinite.
15:31This means that there would be a limited number of universes
15:34rather than an infinite number.
15:37Another thing that's hard to test and prove,
15:39but at least he left us with something to think about.
15:44Believe it or not,
15:46time travel is not that impossible according to the laws of physics.
15:49Scientists have equations that suggest we could have something called
15:52closed time-like curves that might allow us to go back in time.
15:57Imagine going back to the most embarrassing moments of your life.
16:01Knowing what would happen, you could avoid them.
16:05But here's the tricky part.
16:06Going back in time could cause some big problems.
16:09It could create situations where things would happen in a way that doesn't make sense.
16:14Imagine you're walking down the street and meeting your younger or older self,
16:18or accidentally changing things that have already happened.
16:22Hawking was talking about this part too.
16:24And these are all things that made him concerned about time travel.
16:28He made a guess called the chronology protection conjecture.
16:32He suggested there might be a rule of nature that stops time travel from happening
16:37because it could create all these strange and confusing situations
16:40where we would just go back,
16:42fixing our wrong decisions rather than living in the present.
16:46Until we discover traveling through time without causing such disruptions,
16:50I guess all we're left with are life lessons and learning from our mistakes.
16:55In his last years, Hawking talked about the future of humanity,
16:58and we still don't know if he was totally serious.
17:01He mentioned a special particle called the Higgs boson
17:04that could cause a big bubble that could gobble up
17:07and eventually even destroy the universe.
17:11He also mentioned things like beings from other planets coming to Earth and conquering us,
17:15or robots becoming smart enough to take over the world.
17:19Some of his ideas turned out to be true,
17:21and time will tell if it will be the same with the others.
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