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00:00When you stand on the seashore and look far away, you can see a clear line.
00:05It seems like the world is ending right there, but as you move forward, that line
00:11It also keeps moving forward if you look at it.
00:14You can stay but you cannot touch and from here a very strange question arises about the universe.
00:20Is it so, what we consider to be its edge, is it really its edge or just ours?
00:25The cosmic horizon is the limit up to which we can see.
00:43Common sense says that by now we should have seen some edge of it.
00:47After all, there is a limit to everything.
00:49Everything has a beginning and an end,
00:52Then why is this not happening in the case of the universe?
00:54And this is where our most basic thinking begins to shake,
00:58Because we may be looking at the universe in the wrong way,
01:02We may be mistaking the horizon for the edge.
01:05And it may be that the problem is not in the universe, but in our thinking.
01:09In today's video, we will understand this secret step by step in easy language.
01:13We will see if the universe has an edge after all.
01:17Why expansion doesn't always mean no boundaries
01:20And why does modern cosmology remind us again and again,
01:23that the universe is much stranger than we imagined,
01:26And if you also like to understand such space mysteries in easy language,
01:30So please like the video,
01:32Because it shows that you like such deep but simple videos.
01:37And subscribe to the channel,
01:39Because in the future, we are going to unravel such biggest questions of the universe one by one.
01:44Now let's start with that simple thought,
01:47Which forced us to believe that the universe must also have some edge.
01:54Look, if a person hears the question for the first time whether the universe has an edge,
01:59The first answer will almost always be yes, it should be,
02:03And to be honest, this thinking doesn't seem wrong either.
02:06Because our whole lives are spent amidst things like this,
02:10Every road ends somewhere,
02:12Every river has an mouth,
02:14Every room, every city, every country, everything has some limit,
02:18The world we live in,
02:20There is practically no such thing as no end,
02:23So when we think about the universe,
02:25So our brain automatically applies the same rule to that as well,
02:29Now you might be wondering what is wrong in this.
02:31The mistake is not that we think so,
02:34The mistake is that we apply our everyday experience to the entire universe,
02:39And this is where the confusion begins.
02:41We naturally assume that if there is a universe,
02:44So he must have someone outside too,
02:46If its size is
02:47So there will be a boundary too.
02:49If he's expanding,
02:51So he must be reaching somewhere.
02:53And if it started with Big Bank,
02:55So common sense says that matter must have emerged from some starting point, must have moved outwards.
03:01And after so much time, there must be some distance, some limit, some edge.
03:05At first glance, this seems very logical.
03:08Imagine if there was an explosion in the middle of a room and pieces flew in every direction.
03:12So after some time they will spread in a limited area
03:15You can stand outside them and say that the debris has reached till here, not beyond this point.
03:20Our mind creates the same image for the Big Bang.
03:23There was an initial blast, everything rushed outside.
03:26And now the universe is expanding
03:28Therefore, it must have an outer region somewhere.
03:31But this is where the first big problem begins.
03:34The expansion of the universe is not like a bomb blast.
03:37And this is the twist that turns the whole topic upside down.
03:41Because what happens in a bomb blast
03:43The explosion occurs within a pre-existing space.
03:46That means the place is already there.
03:48And something stirs inside him
03:50Then its pieces spread in that area.
03:52But in the case of the universe the story is different.
03:55Here galaxies are not things flying in empty space.
03:58Here space itself is expanding.
04:00This difference is not small
04:02This changes the whole game.
04:04Understand it in an easy way
04:06Suppose there is a balloon
04:07And you made small dots on its surface.
04:11Now that the balloon is inflated
04:12So the dots are not running away from their place.
04:14They are on the surface of the balloon.
04:16But due to surface stretch
04:18The distance between the dots increases
04:20Now if one of those dots starts thinking
04:23Everyone else is moving away from me
04:24So he will think that maybe I am at some center
04:27But the truth will not be
04:29The truth would be that the entire surface is expanding.
04:31Meaning, galaxies are not spheres floating in space.
04:35that escapes from a central blast
04:37But the distance between them is increasing.
04:39Because space itself is stretching.
04:42And now a dangerous question arises here.
04:45If space itself is expanding
04:47So where is it spreading?
04:48Is there anything outside of that?
04:50And if there's nothing outside
04:52So what does spreading mean?
04:54This is where common sense begins to break down for the first time.
04:58Because our mind always wants expansion
05:00understands it as spreading into an empty space
05:03But cosmology tells us
05:05that the expansion of the universe is not like that
05:07As we see in the everyday world
05:09So the first thing we need to understand is
05:12That is, it is not necessary to be the edge of the universe
05:15Just because we are used to seeing the edge of everything
05:18Maybe our intuition is failing here.
05:21The universe may not behave like a room, a field, or explosion debris.
05:25And if that's the case, then the next question becomes even bigger.
05:29if galaxies just keep going away
05:31So has any scientist ever understood how this entire system actually works?
05:36From here we have to take the story towards Einstein and Hubble.
05:39Because understanding the real meaning of expansion begins from there.
05:44Now, from here, the story goes back a bit.
05:47At a time when scientists were first trying to understand
05:51How the entire universe actually behaves
05:53Because today it seems normal to us that the universe is expanding.
05:57But there was a time when almost all scientists believed
06:01that the universe has always been the same
06:04Neither getting bigger nor smaller
06:06It has always existed and will always be so.
06:09But in the year 1915, a scientist shook this thinking.
06:13His name was Albert Einstein
06:16Einstein gave a theory which we know today as general relativity.
06:21This theory changed the way we understand gravity.
06:24Earlier people thought that gravity was just a force.
06:27that pulls objects towards each other
06:29But Einstein said that gravity actually modulates the structure of space and time.
06:34That is, where there is mass
06:36Space time bends a little there.
06:38Now you might be wondering what this has to do with the universe.
06:42This is where the most interesting thing comes in.
06:44Einstein's equations indicated this
06:47that if the entire universe is filled with matter
06:49So space time cannot be completely stable.
06:51He will either expand
06:53or will contract
06:55That means the universe cannot remain static
06:58But at that time, Einstein himself believed that the universe was static.
07:02So they added an extra term to their equations.
07:05which he called the cosmological constant
07:08Its job was to balance the effect of gravity
07:10so that the universe appears static
07:12For many years, scientists believed this was the correct picture.
07:15But then a discovery happened in the year 1929.
07:18that changed the whole story
07:20was an astronomer
07:21Edwin Hubble
07:22He observed distant galaxies.
07:25And we found that almost every galaxy is moving away from us.
07:28And the most surprising thing was this
07:31That's how far away the galaxy was
07:32She seemed to be moving away just as quickly.
07:35Now stop and think
07:37If galaxies are moving away in every direction of the universe
07:40So at first glance it seems like
07:42It's as if we're standing at the center of a long-ago explosion.
07:45It's like there's been a blast and the pieces are flying in every direction.
07:49This is where many people imagine the Big Bang as a bomb blast.
07:54But scientists soon realized
07:56This picture is not completely accurate
07:58Because if that were really the case
08:00So, we should have seen the center of that blast in some direction in the universe.
08:05A place where everything began
08:08But till date no such centre is visible.
08:10Hubble's discovery did not actually mean this.
08:13that galaxies are flying from some central point
08:16What it really meant was
08:17that the distance between galaxies is increasing
08:20That means the entire space is stretching.
08:22Understand it like this
08:24Imagine you are standing in a large field.
08:26And there are thousands of people around you standing in different directions.
08:30Suddenly, for some reason, the entire field began to expand.
08:33People are not running away
08:35But due to the pull of the earth, the distance between them increases.
08:39Every person will feel that everyone else is moving away from him.
08:42But the truth is that no one is at the center.
08:45In fact, the entire land is expanding.
08:47The same thing is happening in the universe.
08:49Galaxies are not objects floating in empty space.
08:53Rather, space itself is expanding.
08:55And because of this the distance between galaxies is increasing.
09:00Now here we have to understand a very important concept.
09:02Because the question we've asked so far is where is the edge of the universe?
09:06The question itself may be a bit wrong.
09:08And the reason for this is something called science.
09:12Observable Universe
09:13Look, the universe is as big as it gets.
09:16We can only see that part of it.
09:18from where the light has had time to reach us
09:21The speed of light is limited
09:23And the age of the universe is about 13.8 billion years.
09:26The meaning is clear
09:28We can't see things that far away.
09:31whose light has not yet reached us
09:34That means we are not seeing the entire universe.
09:36We are only seeing the observable part of it.
09:38And that's the point.
09:40that completely changed cosmology
09:43The universe is not static
09:44The universe is expanding
09:46But this discovery also created a new mystery.
09:49If the universe is expanding
09:51If the galaxy keeps moving away
09:54If it all started with Big Bank
09:56Then why don't we see his edge?
09:58Why no telescope has ever seen this
10:01That there is a galaxy up to this point and nothing beyond that.
10:03This is the question where the real mystery of the universe begins.
10:07Because it might be what we're looking for.
10:11He's not really an age
10:12And to understand this, we need to understand another concept.
10:16Cosmic Horizon
10:17Now you might be wondering if we are seeing only one part of the universe.
10:21So the boundary that we see will be its edge.
10:24This is where the real twist lies
10:26The boundary we see is not actually the edge of the universe.
10:30Rather, this is the limit of our observation.
10:32This is called the cosmic horizon.
10:34That is, the distance beyond which light has not yet reached us.
10:39Understand this with a very simple example
10:41Suppose you are standing in a large field at night.
10:45And you have a flashlight
10:46How far can your flashlight reach?
10:49You can only see as much
10:51There is still ground ahead of him.
10:53But you can't see it because of the darkness.
10:56This does not mean that the field ends there.
10:58It just means that your viewing limit is limited to that extent.
11:02Something similar is happening in the universe.
11:04The extent to which we see galaxies
11:07That's probably not the end of the universe
11:09It's simply the distance that the light has had enough time to travel to reach us.
11:13And now here comes another interesting point.
11:16Humans have made similar mistakes in history before.
11:19For a long time, people thought the Earth was flat.
11:22Because whenever they looked far away they could not see any curvature
11:27Only flat land was visible all around.
11:29At that time, it was perfectly logical to believe that the Earth was flat.
11:33But the real problem was that the scale was too big.
11:36The Earth is so vast that its curvature is not easily visible to us.
11:40Later, when observations and calculations improved
11:43Then we found out that Earth is actually the goal
11:46Now just think about it
11:47If humans can misunderstand a planet like Earth for thousands of years
11:52So how reliable can our intuition be about the entire universe?
11:56This is where cosmology introduces another big twist.
12:00What if the universe isn't actually flat or endless, but rather has a curved geometry?
12:05This means that if you theoretically keep traveling in the same direction in the universe
12:10So after a long time you can end up back where you started.
12:15Just like it happens on the surface of the Earth
12:18You keep going straight and then make a complete circle and come back to the starting point.
12:23In this situation, there will be no traditional edge of the universe.
12:27Because if space itself is curved, then it will not end like a wall.
12:31He'll just keep moving forward and probably end up connecting with himself.
12:35Now the story gets more interesting from here.
12:38Because if the universe has no straight edges
12:41If the only boundary we see is the cosmic horizon
12:45So how do we understand the whole story of the Big Bang?
12:48And this is where another mystery in modern cosmology comes into play.
12:55So far we have understood one thing that the limit is visible to us
12:59That's not necessarily the true edge of the universe.
13:01It could just be the distance up to which light has reached us.
13:05But this is where another big question arises.
13:08If the universe is expanding and this expansion began with the big bang
13:13So is the story of Big Bang completely clear?
13:15The truth is that the big bang model is one of the strongest theories of cosmology today.
13:20It is supported by several strong observations.
13:23The movement of galaxies, the expansion of the universe, and most importantly, the cosmic microwave background.
13:29This radiation appears very similar in almost every direction.
13:33No matter where you point the telescope in the sky
13:36The difference in temperature is very small
13:38Now you might be wondering what the problem is with this.
13:41The problem is if the universe really began with a violent event.
13:46So how is the heat distributed so perfectly?
13:49How did energy spread so smoothly over such vast distances?
13:52that today we see almost the same pattern in every direction
13:56This is the puzzle that forced scientists to think.
13:59And then came another twist in the tale.
14:01In 1998, astronomers were observing distant supernovae.
14:06Their aim was to understand whether the expansion of the universe is slowing down with time.
14:11Because common sense dictated that gravity would gradually slow down the expansion.
14:16But the result surprised everyone.
14:20The expansion of the universe was not slowing down, but rather accelerating.
14:23This means that the galaxy was not only moving away, but was also moving away faster with time.
14:29This clearly meant that there was something in the universe that was working against gravity.
14:34And is constantly pushing space to expand
14:37Scientists named this mysterious thing
14:41dark energy
14:41According to today's observations
14:43About 70% of the universe is made up of dark energy
14:47But the problem is that we still don't know exactly what this thing is.
14:52We can see its effect
14:54But its true nature is still a mystery.
14:56And now here's something to think about.
14:58If dark energy is causing space to expand rapidly
15:02So this also means that distant parts of the universe will move away from us faster.
15:07That means, over time, some regions may become like this.
15:10whose light can never reach us
15:12It simply means the part of the universe that we can see.
15:16That's probably just a small part of the entire universe.
15:19And this is where the question becomes even more profound.
15:22If the universe continues to expand rapidly
15:25If dark energy is further increasing this expansion
15:28So will we ever really be able to see the edge of the universe?
15:32Or it could be that the universe has no traditional edge at all.
15:36And perhaps this is why some scientists are now starting to think that
15:40that we are asking the wrong questions about the universe
15:43Because the real story of Brahman may not be found by searching for edges.
15:46Rather, it starts with understanding its structure.
15:49And that leads us to the next and final question.
15:52Does the universe really have no edge?
15:56The entire story so far leads us to a strange conclusion.
16:00We have always believed that the universe must end somewhere.
16:04But the more we try to understand it
16:07It becomes increasingly clear that this assumption itself may be wrong.
16:11The first possibility is that the universe has no traditional edge.
16:16The only boundary we can see is the observable horizon.
16:20That is, the distance up to which light has been able to reach us till date.
16:24There may be galaxies and stars beyond that, and perhaps a similar universe continues to exist.
16:29But their light has not yet reached us.
16:32So it seems to us as if the universe ended there.
16:36The second possibility is related to geometry.
16:39If space is actually curved
16:41So the structure of the universe may be completely different from our everyday intuition.
16:45In this situation you will never see any wall, any boundary or any end edge.
16:51Because you can move forward continuously while moving in curved space
16:55But still you will never hit any final edge
16:58Just like there is no edge on the surface of the Earth
17:02You keep going and travelling but in the end you just take a complete round and come back to the same place where you were.
17:08had left from
17:09Now the third possibility is even more interesting.
17:12It is also possible that the Big Bang itself may not be the absolute beginning of the universe.
17:16Some cosmological models suggest that the Big Bang may have been just one phase of a larger process.
17:22yes
17:22That means there must have been some state before that or some such condition in which the behaviour of space and time was different.
17:28yes
17:29Some theories also say that the universe can expand and contract repeatedly.
17:33Or our universe may be just one part of a larger cosmic structure.
17:38These ideas don't have final answers yet.
17:41But one thing is certainly clear
17:43As the observations get better
17:46The universe is turning out to be much more complex than we imagined.
17:49And this is where the most interesting aspect of this whole discussion comes to light.
17:53Perhaps the biggest mystery of the universe isn't its size.
17:57Perhaps the real secret is what questions we ask to understand it.
18:01Because we always ask where the universe ends.
18:04But maybe the right question is something else.
18:07Perhaps the right question is
18:09Does the universe even need to end?
18:11And if it really is so
18:13Then maybe that's the edge we're looking for
18:16He will never meet
18:19Sometimes the Universe gives us a very simple but profound lesson.
18:23When we stand by the sea and look into the distance
18:26So Horizon feels like the world ends there.
18:30But as you move in that direction
18:32The same horizon moves forward again
18:35You keep looking at it but never catch it.
18:38Perhaps something similar is happening with the universe.
18:41what we consider its edge
18:43It's probably just our vision.
18:46Maybe we're still making the same mistake.
18:49Like ancient civilizations did with Earth
18:52When they thought the world was flat
18:54And it ends somewhere
18:57But as knowledge increased
18:59We discovered the truth was much more strange and beautiful.
19:03And we may be at the same stage today regarding the universe.
19:07Where we think we understand a lot
19:10But the real picture is still not completely clear.
19:13Now the real question is this
19:15Do you think the universe really has an age?
19:18Or are we simply mistaking the cosmic horizon for its end?
19:22Please write your opinion
19:24I really want to know what you think about this mystery.
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