Science for Sleep I How Big Is the Universe... Really

Welcome back to Science for Sleep channel. Tonight we explore something almost impossible to imagine, the true size of the universe. How big is it? Does it have an edge? Or does it stretch on forever? Slowly and gently we'll travel from Earth, beyond our galaxy and into the observable universe. Take a deep breath. Let your mind expand with the cosmos.

And as the universe grows larger, let your thoughts grow quieter. Let's begin. Now pause for a moment. Look around you. The room you're sitting in. The building. The street. The city. They all feel big to you, don't they? Now, let's expand the scale a little. The planet we live on is called Earth. Its diameter is about 12,742 kilometres. That number might sound technical, but what does it actually mean?

If you boarded a plane and tried to travel all the way around Earth without stopping, you would need to cover roughly 40,000 kilometres. That's like flying from Istanbul to New York four or five times round trip. And that's just one lap Now, let's simplify it. Shrink Earth down to the size of a basketball. At that scale, what would a human be? Not even the size of a bacterium.

More like a barely visible speck of dust. The cities that seem enormous to you right now would be like microscopic bumps. On the surface of that basketball, mountains? Barely noticeable tiny ridges. Oceans, a thin layer of moisture. Here's the interesting part. Earth is actually big, truly big. Throughout most of human history, it wasn't even possible to see the whole planet. For centuries, people believed Earth was flat. Gradually, it became clear that we live on a massive sphere.

And that sphere is floating in space, attached to nothing. held by nothing, simply moving. Imagine this for a moment. Right now, you are rotating with Earth at about 1,670 km per hour at the equator. At the same time, you are orbiting the Sun at roughly 107,000 km per hour. Yet, you feel nothing, because everything moves together. We, the oceans, the atmosphere, the mountains, all traveling with this enormous sphere.

Let's look deeper. About 71% of Earth's surface is covered by water. The continents are actually a small portion of the surface. Because we live on land, we barely see most of the planet. In some places, the oceans exceed 11 kilometers in depth. At the deepest point, the Mariana Trench Even if you placed Mount Everest inside it, its peak would still remain underwater. So even Earth itself has not been fully explored. Now let's return to scale. If Earth were a basketball, how far away would the moon be?

About 7 metres. Not in the same room. Almost at the other end of a basketball court. And that's only the distance between Earth and the moon. We're not even thinking about the universe yet. The human mind struggles with distances because our daily lives are limited to meters and kilometers. But even Earth is far beyond our intuitive sense of scale.

Walking from one side of Earth to the other is nearly impossible. Even airplanes need hours, sometimes more than a full day, to complete long journeys. And yet... This massive sphere is considered small on a cosmic scale, but we're not there yet. For now, just notice this. The planet you live on is far bigger than you imagine. And you, on the surface of this vast sphere, exist beneath a very thin layer of atmosphere. Compared to Earth's diameter, that atmosphere is thinner than the skin of an apple. The layer protecting all life is astonishingly fragile. On such a large planet, we exist in such a small zone. And perhaps the most striking thought is this. Earth feels infinite to us, but it is finite, measurable, calculable. Compared to

the rest of the universe, it is only a starting point. In the next section, we'll expand the scale even further. We'll leave Earth and look at the solar system. And then we will realize that in the previous section, we realized how large Earth truly is. Now let's take a step back. Imagine watching Earth from space. A blue sphere, silently rotating. But that sphere is not alone. It is a small part of a much larger structure. That structure is called the solar system. At the centre, there is a star, the Sunday. The Sun makes up about 99.8% of the total mass of the solar system. Without it, almost everything else would be negligible. Now let's try to understand the scale. If we imagine the Sun as a

large beach ball, Earth would be the size of a pea, and the distance between them? About 25 metres, not on the same table. almost the length of a building apart. That might not sound extreme, but remember this is just Earth. What about the other planets? Mercury, our closest neighbour to the Sun, orbits much nearer than Earth does. Mars, on the other hand, is millions of kilometres away from us.

Here's the striking part. The planets are far more distant from each other than movies make them seem. They are not lined up side by side. Between them are enormous gaps. Mostly nothing. Now let's move even farther out. One of the most distant planets is Neptune. Neptune lies about 4.5 billion kilometres from the Sun. It is impossible to imagine walking that distance. Even at the speed of light, it takes about four hours to travel from the Sun to Neptune. Remember, light moves at 300,000 kilometers per second, and still it takes hours, but the story does not end there. Neptune is not the edge of the solar system. Beyond the planets lies the Kuiper belt. Farther still is the Oort cloud, a vast region of icy bodies and comets. Reaching the

outer boundary of the Oort cloud would take about a year, even at the speed of light, The solar system is far larger than most of us imagine. Now, build a model in your mind. The sun is a beach ball. Earth is a tiny pea. Neptune is hundreds of meters away. And between them, almost entirely empty space. Space is not filled with objects. It is filled with emptiness. That may be one of the most astonishing truths. Now, here is something even more striking. If we place the Sun at your doorstep, the nearest star, Proxima Centauri, at this same scale, would be thousands of kilometres away. The solar system is enormous, but compared to the distances between stars, it is still small.

And us? We are on the surface of a small planet, orbiting the Sun. at about 30 kilometers per second. Yet we feel nothing. Everything is balanced. Everything is quiet. When you think of the solar system, don't imagine the planets first. Imagine the emptiness. The true vastness lies there. The planets are like tiny islands. Between them is not an ocean, but near infinite void. And now, slowly realize this. In the previous section, Earth felt enormous. Now, beside the sun, it feels tiny. In the next section, we will expand the scale even further, because even the solar system is only the beginning of the story. Next, the light year.

So far, we've been talking in kilometers. The diameter of Earth, the distance to the sun day, the gaps between planets. But at a certain point, kilometers are no longer enough because space is too vast that's why we use a new unit of measurement the light year first think about how fast light travels light moves at about 300 000 kilometers per second that means in a single second It can circle Earth about 7.5 times. In one second. Now think about a minute. An hour. A day. A year.

A light year is the distance light travels in one year. That's about 9.5 trillion kilometres. Trillion. Your mind wants to pause there. Because that number is far beyond everyday experience. Let's try to feel it. Light. leaving the Sun takes about eight minutes to reach Earth. So the Sun you see in the sky right now is actually the Sun from eight minutes ago. If the Sun suddenly disappeared we wouldn't know for eight minutes because light takes time to arrive.

Now what about the nearest star after the Sun? That would be Proxima Centauri. It is about 4.24 light years away. The light we see from it today began its journey more than four years ago. When we look into space, we are looking into the past. A light year is not just a distance, it is also a kind of time machine. The farther we look, the older what we see becomes. When we look at the moon, we see it as it was 1.3 seconds ago. When we look at the sun, eight minutes ago. When we look at the nearest star, more than four years ago, look farther still, and we see thousands, millions of years into the past.

Let's build a sense of scale. If the distance between the Sun and Earth were just one metre, the nearest star would be about 270 kilometres away, not in the same city. In another city entirely, that's how enormous the space between stars truly is. The solar system felt large, but interstellar space is far greater. The concept of the light year teaches us this distances in space are so vast that ordinary units lose meaning. Kilometers are not enough.

Even billions of kilometers are not enough. So we use time because light is the fastest thing in the universe. And even for light, Journeys take years. Imagine this for a moment. If you boarded a spacecraft today and could travel at the speed of light, reaching the nearest star would still take over four years. But in reality, we cannot reach light speed. With today's technology, that journey would take tens of thousands of years. Travelling to the stars may sound romantic, But the distances are almost unimaginable. And this is only the beginning. We haven't yet spoken about galaxies.

We haven't yet looked at structures millions of light years away. For now, just notice this. When you look at the night sky, you are not looking at distance. You are looking at time. Every star is a message from the past. And we are. on the surface of a small planet, are watching the stories carried by light. In the next section, we will expand the scale once more. We will no longer speak of individual stars, but of an ocean of stars.

Until now, we've spoken about a single star, the sun day, but the sun is not alone. It is a small member of a vast collection of stars. That collection is called The Milky Way. The Milky Way is a galaxy, an enormous system made of billions of stars, clouds of gas, and invisible dark matter. Scientists estimate that the Milky Way contains between 100 and 400 billion stars. Pause for a moment.

400 billion. It's almost impossible to truly imagine that number. Think of all the grains of sand on every beach on Earth. There could be that many stars, and the sun is just one of them. Now try to feel the scale. The Milky Way is about 100,000 light years across. That means if you tried to cross it at the speed of light, it would take 100,000 years. A long journey, even for light. We are not at the center of the galaxy. We are located in one of its outer regions on a spiral arm. We are not at the center of the universe, not even at the center of our own galaxy. Our position is fairly ordinary. Many of the stars you see in the night sky belong to this same galaxy, that faint milky band stretching across the darkness.

that is a view from inside our own galaxy we are within it looking outward from the inside that's why we cannot see it as a whole now shrink again earth was small the solar system was vast but beside the milky way the solar system would be almost invisible if the galaxy were the size of a continent the solar system would be like a speck of dust And on that speck of dust, we exist. Perhaps the most striking truth is this. Our galaxy is not special. It is just one among many. In the next section, we will see that even this galaxy is not alone. Because the universe is not just an ocean of stars. In the previous section, we saw the scale of the Milky Way. 100,000 light years across, hundreds of billions of stars, it already

felt immense. But now let's step back once more. The Milky Way is not the only galaxy in the universe. When we look at the night sky, the sea of stars we see belongs mostly to our own galaxy. But when we look farther with powerful telescopes, we see other galaxies Our nearest large neighbor is the Andromeda Galaxy. It lies about 2.5 million light years away. What does that mean?

But in the observable universe, there may be hundreds of billions of galaxies. Each one potentially containing hundreds of billions of stars. Pause for a moment. It was already difficult. to grasp a single galaxy. Now imagine hundreds of billions of them, each with countless stars, perhaps trillions of planets, perhaps other forms of life, perhaps complete silence. Think about the scale again. If the Milky Way were a single grain of sand, the universe would be a vast beach, and we would be a microscopic speck inside that grain, here is something even more fascinating. Galaxies are not scattered randomly.

They form clusters. Galaxy clusters. Super clusters. Vast cosmic webs stretching across space. The universe is more structured than we once imagined. Yet at the same time, it is unimaginably large. And we are still only at the beginning. We haven't yet spoken about the edge, about what we call the observable universe. In the next section, we will step into that concept. So far, we left the Milky Way, saw other galaxies and realized that distances stretch across millions of light years. Now we arrive at a bigger question. Can we see the entire universe? The answer is no. We can only see the observable universe. The reason is simple, yet profound. The universe has an age. It is about 13.8 billion years old, and nothing travels faster than light. This

means light needs time to reach us. If light from a distant region hasn't had enough time to arrive, we simply cannot see it. The most distant light we can detect comes from the very early universe. It is known as the cosmic microwave background this radiation is the afterglow of the moment when light first moved freely through space it is in a way the universe's baby picture now let's try to grasp the scale the observable universe has a diameter of about 93 billion light years wait isn't the universe 13.8 billion years old yes But the universe is expanding. When the light we now observe first began traveling toward us, its source was much closer. While that light was on its journey, space itself expanded. So today,

the distance to those regions has grown to about 93 billion light years. That number challenges the mind. 93 billion light years. Even at the speed of light, crossing it from one side to the other would take 93 billion years. And that is only the part we can see. The entire universe. Maybe far larger. Perhaps infinite. Perhaps not. We don't know. Think again about scale. Earth was small. The solar system was larger. Galaxies felt enormous. Yet all of them exist within this 9-3 billion light-year sphere, and we are not at its centre. For every observer, the observable universe appears centred around them, from any location. It looks as though the universe is expanding outward, in all directions.

It feels strange, yet it is beautiful. Perhaps the most calming thought is this. Everything we can see has a boundary, but beyond that boundary, we do not yet know what exists, and the unknown may be the largest part of all. In the next section, we will talk about expansion itself. Is the universe truly growing? What is it expanding into? And, most importantly, will it ever stop? So far, we've seen that the universe is unimaginably vast. But here is something even more astonishing. The universe is not static. The universe is expanding. In the 1920s, astronomers studying distant galaxies noticed something strange. Their light was shifted toward red wavelengths. The astronomer who systematically demonstrated this was Edwin Hubble. The conclusion

was remarkable. Galaxies were moving away from us. All of them. What does that mean? The very fabric of the universe is stretching. Space itself is expanding. This is not like an explosion from a central point. It is not debris flying outward into empty space. It is more like this. Imagine a balloon with dots drawn on its surface. As the balloon inflates... The dots move farther apart, but no dot is the center. The universe expands in a similar way.

The beginning of this expansion is called the Big Bang. About 13.8 billion years ago, the universe was extremely hot and dense. Then it began to expand, and it is still expanding today. Now, picture something important. Galaxies are not just moving through space. Space itself is growing. The distance between two galaxies increases, because the space between them expands.

This is why very distant galaxies appear to recede from us, at speeds close to that of light. Not because they are racing through space in the usual sense, but because space itself is stretching. Will this expansion stop? We don't know. And here is something even more surprising. Observations in the 1990s showed that the expansion is not slowing down. It is accelerating. To explain this, scientists propose something called dark energy.

We don't fully understand what it is. In fact, most of the universe remains unknown. Pause and think. We are on a small planet orbiting a star. That star is inside a galaxy. That galaxy is drifting away from others. And all of this is happening within expanding space. Every second, the distance between galaxies increases slightly, silently, unnoticed. Perhaps the most striking realization is this. The universe is not a static stage. It is an ongoing process. A dynamic, changing, expanding reality. And we, small yet conscious beings, exist in the midst of that expansion. In the next section, we will try to truly feel the age of the universe.

What does 13.8 billion years really mean? And within that immense span of time, where are we? We said that the universe is about 13.8 billion years old. But what does that number really mean? 13.8 billion years is not a span of time the human mind easily grasps. So let's shrink it down. Let's compress the entire history of the universe into a single calendar year. January 1st. The Big Bang. The universe is born. During the first months, galaxies form. Stars ignite. But we do not exist yet.

By September, the Sun forms. A few days later, the Earth appears. Most of the universe's history has already passed before we arrive. Until December, life on Earth is only microscopic. Dinosaurs? The last week of December. Humans? December 31st, around 11.59 and 46 seconds p.m. All of human history fits into the final 14 seconds of the year. Pause for a moment.

The invention of writing? The last few seconds. The Industrial Revolution? Not even a full second. Your life? Too brief to appear on the calendar. This compression reveals something profound. we emerged in the very last moments of cosmic history. For billions of years, stars were born and died, galaxies collided, space expanded, and after all that immense time, consciousness appeared, beings capable of looking up at the sky and asking, how big is it? Perhaps the most powerful realization is this, the atoms in your body were once inside stars. Those stars exploded. Their elements scattered into space. New stars and planets formed. And eventually, you. The universe is not only vast, it is ancient. And we are a very late chapter

in its long story. In the next section, we will face an even harder question. Is there something beyond the universe? Or is everything we see all that exists? Now we are facing a very difficult question. We said that the observable universe has a diameter of about 93 billion light years. So what lies beyond that? The honest answer is, we don't know. We call it observable for a reason. We can only see as far as light has had time to reach us. But that does not mean the universe ends It only means we cannot see beyond that boundary.

Imagine a small sphere of light in the middle of an ocean. The light reaches only a certain distance. The part that remains in darkness is not invisible because it doesn't exist. But because the light hasn't reached it, the universe may be like that. Scientists consider several possibilities. The universe could be infinite. No matter how far you travel, it would continue, or it could be extremely large but finite, like the surface of a sphere, no edge yet limited.

These ideas arise largely from the general theory of relativity developed by program, Albert Einstein. Einstein. Space does not have to be flat. It can be curved. It can be bent. Even more intriguing, perhaps our universe is not the only one. Some theories suggest the possibility of multiple universes. A multiverse.

For now, however... This remains a hypothesis. We have no direct evidence. Now pause and think calmly. We are inside a 9.3 billion light year bubble. And about what lies beyond it, we have no direct knowledge. Perhaps endless darkness. Perhaps more galaxies. Perhaps entirely different laws of physics. Or perhaps nothing at all. The universe is vast, but its unknown is just as vast. And maybe the true greatness lies here. We do not know everything, yet we continue to ask. In the final section, we will reflect on humanity's place within all this immensity. In such an enormous universe, what does it mean to be small? Now let's return to the beginning. The earth turned out to be small.

the solar system even smaller. The Milky Way is enormous yet ordinary in the universe and the observable universe 93 billion light years across. On this scale, where is the human being? Almost invisible. If we imagine the universe as an ocean, we are not even a drop. We are closer to a single molecule. At first, That thought can feel unsettling. We are small. We live briefly. The universe existed for billions of years without us. But now let's look from a different angle. The universe may be vast.

But it does not know itself. Stars burn. Galaxies collide. Space expands. Yet none of them are aware of it. We are. The atoms in our bodies... were once inside stars. In a way, the universe produced consciousness from stardust. And that consciousness lifts its head, looks at the sky, and asks, how big is it? Perhaps the issue is not size.

Perhaps the issue is awareness. Yes, physically we are small, but we have the capacity to create meaning. We have curiosity. We have imagination in the final seconds of a 13, 8 billion year history. We appeared, and into that vast timeline, we introduced the question of meaning. That alone is extraordinary.

The universe is immense, silent, cold. Yet within it, there are beings who think. And perhaps that is the rarest thing of all. Pause gently and reflect. Maybe being small does not mean being insignificant. Maybe being small means being able to notice something vast. And right now, we are capable of contemplating the immensity of the universe. That alone is something immense. Now pause for a moment. Look around you the room you're sitting in, the building, the street, the city, they all feel big to you, don't they? Now, let's expand the scale a little. The planet we live on is called Earth. Its diameter is about 12,742 kilometres.

That number might sound technical, but what does it actually mean? If you boarded a plane... and tried to travel all the way around Earth without stopping, you would need to cover roughly 40,000 kilometres. That's like flying from Istanbul to New York, four or five times round trip. And that's just one lap. Now, let's simplify it. Shrink Earth down to the size of a basketball. At that scale, what would a human be? Not even the size of a bacterium.

more like a barely visible speck of dust. The cities that seem enormous to you right now would be like microscopic bumps. On the surface of that basketball, mountains, barely noticeable tiny ridges, oceans, a thin layer of moisture. Here's the interesting part. Earth is actually big, truly big. Throughout most of human history, It wasn't even possible to see the whole planet. For centuries, people believed Earth was flat. Gradually, it became clear that we live on a massive sphere.

And that sphere is floating in space, attached to nothing, held by nothing, simply moving. Imagine this for a moment. Right now, you are rotating with Earth. at about 1,670 km per hour at the equator. At the same time, you are orbiting the Sun at roughly 107,000 km per hour. Yet, you feel nothing, because everything moves together. We, the oceans, the atmosphere, the mountains, all travelling with this enormous sphere.

Let's look deeper. About 71% of Earth's surface is covered by water. The continents are actually a small portion of the surface. Because we live on land, we barely see most of the planet. In some places, the oceans exceed 11km in depth. At the deepest point, the Mariana Trench, even if you placed Mount Everest inside it, its peak would still remain underwater, so even Earth itself has not been fully explored. Now let's return to scale. If Earth were a basketball, how far away would the moon be?

About seven meters. Not in the same room. Almost at the other end of a basketball court. And that's only the distance between Earth and the moon. We're not even thinking about the universe yet. The human mind struggles with distances. Because our daily lives are limited to meters and kilometers, but even Earth is far beyond our intuitive sense of scale.

Walking from one side of Earth to the other is nearly impossible. Even airplanes need hours, sometimes more than a full day, to complete long journeys. And yet, this massive sphere is considered small on a cosmic scale. But we're not there yet. For now, just notice this. The planet you live on is far bigger than you imagine. And you, on the surface of this vast sphere, exist beneath a very thin layer of atmosphere. Compared to Earth's diameter, that atmosphere is thinner than the skin of an apple. The layer protecting all life is astonishingly fragile. On such a large planet, We exist in such a small zone. And perhaps the most striking thought is this. Earth feels infinite to us, but it is finite, measurable, calculable. Compared to

the rest of the universe, it is only a starting point. In the next section, we'll expand the scale even further. We'll leave Earth and look at the solar system. And then we will realize that in the previous section, we realised how large Earth truly is. Now let's take a step back. Imagine watching Earth from space. A blue sphere, silently rotating. But that sphere is not alone. It is a small part of a much larger structure. That structure is called the solar system. At the centre, there is a star, the sundae. The Sun makes up about 99.8% of the total mass of the solar system. Without it, almost everything else would be negligible. Now let's try to understand the scale. If we imagine the Sun as a

large beach ball, Earth would be the size of a pea, and the distance between them? About 25 meters. Not on the same table. Almost the length of a building apart. That might not sound extreme, but remember this is just Earth. What about the other planets? Mercury, our closest neighbour to the Sun, orbits much nearer than Earth does. Mars, on the other hand, is millions of kilometres away from us.

Here's the stratosphere. part. The planets are far more distant from each other than movies make them seem. They are not lined up side by side. Between them are enormous gaps. Mostly nothing. Now let's move even farther out. One of the most distant planets is Neptune. Neptune lies about 4.5 billion kilometres from the Sun day. It is impossible to imagine walking that distance. Even at the speed of light, it takes about four hours to travel from the Sun to Neptune. Remember, light moves at 300,000 kilometres per second, and still it takes hours, but the story does not end there. Neptune is not the edge of the solar system.

Beyond the planets lies the Kuiper Belt. Farther still is the Oort Cloud, a vast region of icy bodies and comets. Reaching the outer boundary of the Oort Cloud would take about a year, even at the speed of light. The solar system is far larger than most of us imagine. Now, build a model in your mind. The sun is a beach ball. Earth is a tiny pea. Neptune is hundreds of meters away. And between them, almost entirely empty space.

Space is not filled with objects. It is filled with emptiness. That may be one of the most astonishing truths. Now, here is something even more striking. If we place the sun at your doorstep, the nearest star, Proxima Centauri, at this same scale, would be thousands of kilometers away. The solar system is enormous, but compared to the distances between stars, it is still small. And us? We are on the surface of a small planet, orbiting the Sun at about 30 kilometers per second. Yet we feel nothing. Everything is balanced.

Everything is quiet. When you think of the solar system, don't imagine the planets first. Imagine the emptiness. The true vastness lies there. The planets are like tiny islands. Between them is not an ocean, but near infinite void. And now, slowly realize this. In the previous section, Earth felt enormous. Now, beside the Sun, it feels tiny. In the next section, we will expand the scale even further because even the solar system is only the beginning of the story. Next, the light year. So far, we've been talking in kilometers, the diameter of Earth, the distance to the Sunday, the gaps between planets. But at a certain point, kilometers are no longer enough because space is too vast. That's why

we use a new unit of measurement, the light year. First, think about how fast light travels. Light moves at about 300,000 kilometers per second. That means in a single second, it can circle Earth about 7.5 times in one second. Now think about a minute, an hour, a day, a year. A light year is the distance light travels in one year.

That's about 9.5 trillion kilometres. Trillion. Your mind wants to pause there, because that number is far beyond everyday experience. Let's try to feel it. Light leaving the sun takes about 8 minutes to reach Earth. So the sun you see in the sky right now is actually the sun from 8 minutes ago. If the sun suddenly disappeared, we wouldn't know for eight minutes because light takes time to arrive.

Now what about the nearest star after the sun? That would be Proxima Centauri. It is about 4.24 light years away. The light we see from it today began its journey more than four years ago. When we look into space, we are looking into the past. A light year is not just a distance. It is also a kind of time machine. The farther we look, the older what we see becomes. When we look at the moon, we see it as it was 1.3 seconds ago. When we look at the sun, eight minutes ago. When we look at the nearest star, more than four years ago, look farther still, and we see thousands, millions of years into the past.

Let's build a sense of scale If the distance between the Sun and Earth were just one metre, the nearest star would be about 270 kilometres away, not in the same city. In another city entirely, that's how enormous the space between stars truly is. The solar system felt large, but interstellar space is far greater. The concept of the light year teaches us this. Distances in space are so vast that ordinary units lose meaning. Kilometers are not enough.

Even billions of kilometers are not enough. So we use time because light is the fastest thing in the universe. And even for light journeys take years. Imagine this for a moment. If you boarded a spacecraft today and could travel at the speed of light, reaching the nearest star would still take over four years. But in reality, we cannot reach light speed. With today's technology, that journey would take tens of thousands of years. Travelling to the stars may sound romantic, but the distances are almost unimaginable. And this is only the beginning. We haven't yet spoken about galaxies, We haven't yet looked at structures millions of light years away.

For now, just notice this. When you look at the night sky, you are not looking at distance. You are looking at time. Every star is a message from the past, and we, on the surface of a small planet, are watching the stories carried by light. In the next section, we will expand the scale once more We will no longer speak of individual stars, but of an ocean of stars.

Until now, we've spoken about a single star, the Sunday, but the Sun is not alone. It is a small member of a vast collection of stars. That collection is called the Milky Way. The Milky Way is a galaxy, an enormous system made of billions of stars, clouds of gas, An invisible dark matter. Scientists estimate that the Milky Way contains between 100 and 400 billion stars. Pause for a moment.

400 billion. It's almost impossible to truly imagine that number. Think of all the grains of sand on every beach on Earth. There could be that many stars. And the sun is just one of them. Now try to feel the scale. The Milky Way is about 100,000 light years across. That means if you tried to cross it, at the speed of light, it would take 100,000 years. A long journey, even for light. We are not at the centre of the galaxy. We are located in one of its outer regions, on a spiral arm. We are not at the centre of the universe. not even at the center of our own galaxy our position is fairly ordinary many of the stars you see in the night sky belong to this same galaxy that faint milky band stretching across the darkness

that is a view from inside our own galaxy we are within it looking outward from the inside that's why we cannot see it as a whole now shrink again Earth was small, the solar system was vast. But beside the Milky Way, the solar system would be almost invisible. If the galaxy were the size of a continent, the solar system would be like a speck of dust. And on that speck of dust, we exist. Perhaps the most striking truth is this. Our galaxy is not special. It is just one among many. In the next section, we will see that even this galaxy is not alone, because the universe is not just an ocean of stars. In the previous section, we saw the scale of the Milky Way, 100,000 light years across, hundreds of billions of stars. It already

felt immense. But now let's step back once more. The Milky Way is not the only galaxy in the universe. When we look at the night sky, the sea of stars we see, belongs mostly to our own galaxy. But when we look farther with powerful telescopes, we see other galaxies. Our nearest large neighbor is the Andromeda Galaxy. It lies about 2.5 million light years away. What does that mean?

When we look at Andromeda today, we are seeing it as it was 2.5 million years ago. The light reaching us now began its journey long before modern humans existed. Andromeda is enormous, similar in size to the Milky Way, hundreds of billions of stars, and it is only the closest major one. How many galaxies are there? Estimates vary, but in the observable universe, there may be hundreds of billions of galaxies, each one potentially containing hundreds of billions of stars. Pause for a moment. It was already difficult to grasp a single galaxy. Now imagine hundreds of billions of them, each with countless stars, perhaps trillions of planets, perhaps other forms of life, perhaps complete silence. Think about

the scale again. If the Milky Way were a single grain of sand, the universe would be a vast beach, and we would be a microscopic speck inside that grain. Here is something even more fascinating. Galaxies are not scattered randomly. They form clusters. Galaxy clusters. Superclusters. Vast cosmic webs stretching across space. The universe... is more structured than we once imagined, yet at the same time, it is unimaginably large, and we are still only at the beginning. We haven't yet spoken about the edge, about what we call the observable universe.

In the next section, we will step into that concept. So far, we left the Milky Way, saw other galaxies, and realize that distances stretch across millions of light years, now we arrive at a bigger question. Can we see the entire universe? The answer is no. We can only see the observable universe. The reason is simple, yet profound.

The universe has an age. It is about 13.8 billion years old, and nothing travels faster than light. This means light needs time to reach us. If light from a distant region hasn't had enough time to arrive, we simply cannot see it. The most distant light we can detect comes from the very early universe. It is known as the cosmic microwave background. This radiation is the afterglow of the moment, when light first moved freely through space. It is, in a way, the universe's baby picture. Now let's try to grasp the scale. The observable universe has a diameter of about 93 billion light years. Wait, isn't the universe 13.8 billion years old? Yes, but the universe is expanding. When the light we now observe first began traveling toward us,

its source was much closer. While that light was on its journey, space itself expanded. So today, the distance to those regions has grown to about 93 billion light years. That number challenges the mind. 93 billion light years, even at the speed of light, crossing it from one side to the other, would take 93 billion years. And that is only the part we can see the entire universe may be far larger. Perhaps infinite. Perhaps not. We don't know.

Think again about scale. Earth was small. The solar system was larger. Galaxies felt enormous. Yet all of them exist within this 9, 3 billion light year sphere. And we are not at its centre. For every observer The observable universe appears centered around them, from any location. It looks as though the universe is expanding outward, in all directions.

It feels strange, yet it is beautiful. Perhaps the most calming thought is this. Everything we can see has a boundary, but beyond that boundary, we do not yet know what exists, and the unknown remains. may be the largest part of all. In the next section, we will talk about expansion itself. Is the universe truly growing? What is it expanding into? And, most importantly, will it ever stop? So far, we've seen that the universe is unimaginably vast. But here is something even more astonishing. The universe is not static. The universe is expanding. In the 1920s, astronomers studying distant galaxies noticed something strange. Their light was shifted toward red wavelengths. The astronomer who systematically demonstrated this was Edwin Hubble. The conclusion

was remarkable. Galaxies were moving away from us. All of them. What does that mean? The very fabric of the universe is stretching. Space itself is expanding. This is not like an explosion from a central point. It is not debris flying outward into empty space. It is more like this. Imagine a balloon with dots drawn on its surface. As the balloon inflates, the dots move farther apart, but no dot is the center. The universe expands in a similar way.

The beginning of this expansion is called the Big Bang. about 13.8 billion years ago, the universe was extremely hot and dense. Then it began to expand, and it is still expanding today. Now, picture something important. Galaxies are not just moving through space. Space itself is growing. The distance between two galaxies increases because the space between them expands.

We don't fully understand what it is. In fact, most of the universe remains unknown. Pause and think. We are on a small planet orbiting a star. That star is inside a galaxy. That galaxy is drifting away from others. And all of this is happening within expanding space. every second the distance between galaxies increases slightly silently unnoticed perhaps the most striking realization is this the universe is not a static stage it is an ongoing process a dynamic changing expanding reality and we small yet conscious beings exist in the midst of that expansion In the next section, we will try to truly feel the age of the universe.

What does 13.8 billion years really mean? And within that immense span of time, where are we? We said that the universe is about 13.8 billion years old. But what does that number really mean? 13.8 billion years is not a span of time the human mind easily grasps. So let's shrink it down. Let's compress the entire history of the universe into a single calendar year. January 1st, the Big Bang. The universe is born. During the first months, galaxies form. Stars ignite. But we do not exist yet.

By September, the Sun forms. A few days later, the Earth appears. Most of the universe's history has already passed before we arrive. Until December, Life on Earth is only microscopic. Dinosaurs? The last week of December. Humans? December 31st. Around 11.59 and 46 seconds PM. All of human history fits into the final 14 seconds of the year. Pause for a moment.

The atoms in your body were once inside stars. Those stars exploded. Their elements scattered into space. New stars and planets formed. And eventually, you, the universe is not only vast, it is ancient. And we are a very late chapter. in its long story. In the next section, we will face an even harder question. Is there something beyond the universe?

Or is everything we see all that exists? Now we are facing a very difficult question. We said that the observable universe has a diameter of about 93 billion light years. So what lies beyond that? The honest answer is, we don't know. We call it observable for a reason. We can only see as far as light has had time to reach us, but that does not mean the universe ends there. It only means we cannot see beyond that boundary.

Imagine a small sphere of light in the middle of an ocean. The light reaches only a certain distance. The part that remains in darkness is not invisible because it doesn't exist, but because the light hasn't reached it The universe may be like that. Scientists consider several possibilities. The universe could be infinite. No matter how far you travel, it would continue. Or it could be extremely large but finite, like the surface of a sphere, no edge yet limited.

These ideas arise largely from the general theory of relativity developed by program, Albert Einstein. Space does not have to be flat. It can be curved. It can be bent. Even more intriguing, perhaps our universe is not the only one. Some theories suggest the possibility of multiple universes. A multiverse.

For now, however, this remains a hypothesis. We have no direct evidence. Now pause and think calmly. We are inside a 9.3 billion universe. light year bubble and about what lies beyond it we have no direct knowledge perhaps endless darkness perhaps more galaxies perhaps entirely different laws of physics or perhaps nothing at all the universe is vast but its unknown is just as vast and maybe the true greatness lies here we do not know everything yet we continue to ask In the final section, we will reflect on humanity's place within all this immensity. In such an enormous universe, what does it mean to be small? Now let's return to the beginning. The Earth turned out to be small, the solar system even smaller. The Milky Way

is enormous yet ordinary in the universe, and the observable universe 93 billion light years across. On this scale, where is the human being? Almost invisible. If we imagine the universe as an ocean, we are not even a drop. We are closer to a single molecule. At first, that thought can feel unsettling. We are small. We live briefly.

The universe existed for billions of years without us. But now let's look from a different angle. The universe may be vast, but it does not know itself. Stars burn, galaxies collide, space expands, yet none of them are aware of it. We are. The atoms in our bodies were once inside stars. In a way, the universe produced consciousness from stardust, and that consciousness lifts its head, looks at the sky and asks, how big is it? Perhaps the issue is not size. Perhaps the issue is awareness. Yes, physically we are small, but we have the capacity to create meaning. We have curiosity. We have imagination. In the final seconds of a 13, 8, billion, year, history we appeared and into that vast timeline we introduced the question

of meaning that alone is extraordinary the universe is immense silent cold yet within it there are beings who think and perhaps that is the rarest thing of all pause gently and reflect maybe being small does not mean being insignificant Maybe being small means being able to notice something vast. And right now, we are capable of contemplating the immensity of the universe. That alone is something immense. Thank you.

Thanks for watching!

Science for Sleep I How Big Is the Universe... Really_

Kapitelklicken springt direkt hin

Shownotes

Transkriptvom Podcast bereitgestellt · Zeitmarken springen hin