The Terrifying Truth About Our Size in the Universe

Welcome to the Science for Sleep channel, where we explore the wonders of the universe in a calm and relaxing way. Look around the room you're in right now. Take it in. The ceiling, the walls, the distance from where you are to the door. This space, whatever size it is, feels real and solid and comprehensible. Your body knows it. You could walk it in seconds. Hold on to that feeling.

because we are about to take it apart very slowly. We are going to start where you are and keep zooming out, your room, your city, your planet, your solar system, your galaxy, and then further, much further until the numbers stop feeling like numbers and start feeling like something else entirely. By the end of this video, the room you are sitting in will feel different, not because anything about it has changed, But because you will know, in a way you cannot unknow, exactly how much universe exists beyond its walls, this is not a comfortable video. It is an honest one.

Before we begin, drop a comment right now. Tell us where you are in the world, and what time it is where you are. We want to know who is watching this, from which corner of this pale blue dot, at what hour of the night or day. There is something quietly beautiful about the idea of people spread across this small planet, all looking up at the same darkness at the same time, all about to feel equally small together.

We will start gently, and then we will not. Start where you are. The room you are in right now, the ceiling above you, the walls around you, the floor beneath you. You know this space. You have a felt sense of its dimensions, how many steps it takes to cross it, how high the ceiling sits above your head, where the edges are. This is your immediate universe, the scale your body understands instinctively. Now step outside it, the human scale. The average human being is approximately 1.7 meters tall.

This is the unit of measurement your nervous system is calibrated to. distances that fit within a few multiples of your height feel comprehensible. A room, a street, a field, these are scales your body can walk, your eyes can survey, your mind can hold as a complete picture. A kilometer is already pushing the edge of intuitive understanding. You can walk it in about 12 minutes, which gives it a felt duration, but the distance itself 1,000 metres, 600 of your body lengths laid end to end, is already more abstract than concrete. 100 kilometres is a number, not a feeling.

The planet. The Earth has a circumference of approximately 40,000 kilometres at the equator. This number is so large relative to human experience that it resists intuition entirely. But consider it this way. Light, the fastest thing in the universe, travelling at 299,792 km per second, circles the Earth 7.5 times in a single second. In the time it takes you to blink, light has lapped the planet several times over.

The fastest aircraft ever built, the SR-71 Blackbird, travelled at approximately 3,000 500 km per hour. At that speed, faster than any human being has ever moved through the atmosphere, circumnavigating the Earth would take approximately 11 hours. The International Space Station, orbiting at 28,000 km per hour, completes a full orbit every 90 minutes. These numbers begin to convey something about the planet's size, but here is the comparison that tends to land most directly. If you shrank the earth to the size of a standard classroom globe, roughly 30 centimeters in diameter, a human being at the same scale would be approximately 0.01, five millimeters tall. Smaller than a grain of fine sand, invisible to the naked eye,

standing on the surface of that globe, you would not be able to see yourself. The atmosphere, Here is something that most people find genuinely surprising when they encounter it for the first time. The atmosphere, the layer of air that makes life on Earth possible, that contains every cloud and weather system, every bird and aircraft, every breath that every living thing on this planet has ever taken, extends to approximately 100 kilometers above the surface. This is the boundary called the Kármán line, where space is conventionally considered to begin. 100 kilometers sounds substantial, but relative to the Earth's diameter of nearly 13,000 kilometers, the atmosphere is vanishingly thin.

If you scale the Earth to the size of a standard classroom globe, the entire atmosphere, every cubic meter of breathable air on the planet, would be thinner than a coat of varnish applied to its surface. Everything that has ever lived, every ecosystem, every weather event in recorded history, contained in a layer so thin it is barely visible at planetary scale. What this means before we continue, we have not left the planet yet. We have not looked at the solar system, or the galaxy, or the universe.

We have simply tried to understand the size of the rock we live on. And already the numbers are beginning to resist ordinary comprehension. Already the scale is pulling away from anything your body has a felt sense of. This is just the beginning. The next step is the solar system. And the solar system will make everything we have just discussed feel very, very small. The sun is 150 million kilometres from Earth. Read that again. 150 million kilometers. In the context of everything we just established, the Earth's circumference of 40,000 kilometers, the atmosphere's depth of 100 kilometers. This number represents a scale increase so dramatic that the previous numbers effectively become zero by comparison. But the number alone

does not convey it. Let us try to make it real. The Sun. Begin with the Sun itself before we consider the distance to it. The Sun has a diameter of approximately 1.39 million kilometres. The Earth's diameter is approximately 12,700 kilometres. This means you could fit approximately 109 Earths side by side across the Sun's diameter. In terms of volume three-dimensional space, you could fit approximately 1.3 million Earths inside the Sunday. 1.3 million.

If the Sun were a hollow sphere and you began filling it with Earths, you would need to insert one Earth every single second, continuously, for 15 days before it was full. And the Sun is an average star. Not large, not small. a thoroughly unremarkable medium-sized star that would not attract particular attention from any astronomer surveying the galaxy. The distance.

Light travels from the Sun to the Earth in approximately 8 minutes and 20 seconds. This means that the sunlight warming your skin right now left the Sun more than 8 minutes ago. If the Sun disappeared at this exact moment, you would not know for 8 minutes. the light currently in transit would complete its journey. For eight minutes, the sky would remain bright while the source of that brightness had already ceased to exist. The furthest planet in our solar system, Neptune, orbits at a distance of approximately 4.5 billion kilometers from the Sunday light, takes approximately four hours to travel from the Sun to Neptune. A radio signal sent from Earth to Neptune and back takes approximately eight hours.

Voyager 1. In September 1977, NASA launched the Voyager 1 spacecraft on a trajectory that would take it out of the solar system. It is the most distant human-made object ever created. As of 2024, it has been traveling for 47 years, moving at approximately 61,000 kilometers per hour. faster than any other human-made object in history. It has covered approximately 24 billion kilometers and it has only just crossed the boundary of the heliosphere, the region of space dominated by the sun's solar wind entering what is called interstellar space.

The broader solar system, including the Oort cloud of comets that surrounds it, extends perhaps 100,000 times further than the Earth-Sun distance. At Voyager's current speed, crossing the full extent of the solar system would take approximately 30,000 years. We launched an object nearly five decades ago, It has been travelling continuously, faster than anything else we have ever built, every second of every day since 1977. It has barely left home, the scale model. Here is the exercise that tends to produce the most visceral understanding of the solar system's size. If you place the sun as a ball one metre in diameter at one end of a field, where would the planets be? Mercury would sit approximately 41

meters away, a marble-sized object at the far end of a small apartment. Earth would be approximately 107 meters away, slightly larger than a marble, located at the far end of a football field. Neptune, the outermost planet, would be approximately 3.2 kilometers away, a pea-sized object. more than three kilometers from the one meter Sunday. At this scale, the nearest star Proxima Centauri would be located approximately 28,000 kilometers away on the other side of the planet. The solar system is not a compact collection of worlds orbiting a central star in a region you could walk across. It is an almost incomprehensibly vast volume of mostly empty space in which the planets are tiny objects separated by distances

that make the gap between Earth and Moon feel intimate by comparison. And we have not yet left the solar system. The galaxy is next. The nearest star to our Sun is Proxima Centauri. It is 4.24 light-years away. This means that light travelling at 299,792 km per second The fastest speed the universe permits takes four years and three months to cross the distance between our sun and its nearest neighbour.

Four years. At the speed of light. What that actually means. The fastest spacecraft ever launched was NASA's New Horizons probe, which left Earth in 2006 travelling at approximately 58,000 km per hour. At that speed, the fastest we have ever propelled an object reaching Proxima Centauri would take approximately 78,000 years.

Not 78,000 days. Not 78,000 months. 78,000 years. Longer than modern human civilization has existed. Longer than the time since the last ice age. Travelling continuously, at the highest speed we have ever achieved. From the moment our species first began painting cave walls until today, we would not yet have arrived. And Proxima Centauri is our nearest neighbor, the galaxy.

The Milky Way is a barred spiral galaxy approximately 100,000 light years in diameter. It contains an estimated 200 to 400 billion stars. Our Sun sits roughly 26,000 light-years from the galactic centre, about two-thirds of the way, out toward the edge, in an unremarkable region of one of the spiral arms. If you wanted to cross the Milky Way at the speed of light, it would take 100,000 years.

At the speed of New Horizons, it would take approximately 2 billion years, roughly half the age of the Earth. The Milky Way contains up to 400 billion stars. If you counted one star per second, without stopping, it would take approximately 12,000 years to count them all. And every single one of those stars is, by human standards, incomprehensibly far from every other one. Our address. Here is what our location in the galaxy actually means. We are not at the centre. We are not at the edge. We are in a quiet, unremarkable region of a middling spiral arm, orbiting a thoroughly average star on a small rocky planet that would be completely invisible from even a modest distance within our own galaxy. From the centre of the Milky Way,

the Sun is one faint point of light among hundreds of billions of identical faint points of light, indistinguishable unremarkable, lost. We have not yet left the galaxy. The observable universe is next, and the observable universe will make the Milky Way feel like that grain of sand we discussed at the beginning. We have established that the nearest star is 78,000 years away at our fastest speed. We have established that that crossing our own galaxy would take 2 billion years.

We have established that our sun is one of 400 billion stars in the Milky Way, located in an unremarkable position in an unremarkable arm, indistinguishable from the hundreds of billions of stars surrounding it. Now we need to talk about how many galaxies there are. The number. For most of the 20th century, astronomers estimated the observable universe contained approximately 200 billion galaxies. This was already a number beyond meaningful comprehension, 200 billion collections of hundreds of billions of stars each, separated by distances that make the Milky Way feel intimate. In 2016, a more careful analysis of data from the Hubble Space Telescope revised that estimate dramatically upward, the observable universe contains approximately two trillion galaxies. Two trillion.

Two million million. A number so large that if you spent one second looking at each galaxy, examining it, acknowledging its existence, you would need 63,000 times the current age of the universe to finish. Each of those galaxies contains, on average, hundreds of billions of stars. Each of those stars is, by the standards we established in the previous section, an almost unreachable destination. The Milky Way, our galaxy, the one we could not cross in two billion years, is one of two trillion. The Hubble Deep Field. In December 1995...

NASA pointed the Hubble Space Telescope at a patch of sky near the Big Dipper that appeared to ground-based telescopes to be essentially empty. A dark, unremarkable region containing almost nothing of interest. They held the exposure for 10 consecutive days. What the image revealed has been described as one of the most important photographs ever taken. In that tiny patch of apparently empty sky, covering an area of the sky roughly equivalent to a grain of sand held at arm's length, Hubble detected approximately 10,000 galaxies. 10,000 galaxies in a piece of sky so small you could cover it with a grain of sand. The image was subsequently repeated in other directions, the Hubble Ultra Deep Field, the Hubble Extreme Deep Field,

and the result was consistent every time, every direction. Every apparently empty patch of darkness, thousands upon thousands of galaxies, each containing hundreds of billions of stars, each receding from us at speeds proportional to their distance. There is no empty sky. There is only sky we have not looked at carefully enough yet. The edge we cannot cross. The observable universe has a diameter of approximately 93 billion light years.

This number requires an explanation, because it seems to contradict the universe's age of 13.8 billion years. If the universe is only 13.8 billion years old, how can light from 46 billion light years away have reached us? The answer is that space itself has been expanding since the Big Bang. The light that is only now reaching us from the most distant galaxies was emitted when those galaxies were much closer, but in the billions of years that light has been travelling toward us. The space between us and its source has continued to expand. The galaxies that emitted that ancient light are now vastly further away than the distance the light has travelled. And beyond the observable universe, beyond the

sphere of space from which light has had time to reach us, the universe continues. How far it continues, nobody knows. Current measurements suggest the universe is either infinite or so large that the difference between finite and infinite is practically meaningless. Some of those distant galaxies are now so far away and receding so fast due to the expansion of space that light leaving them today will never reach us. The expansion of space between us and them is faster than light can travel across it. They are gone from us permanently not because of any barrier, but because space itself is growing too quickly for any signal to bridge the gap.

We are already... in a precise cosmological sense, permanently cut off from most of the universe. The pale blue dot revisited. In 1990, NASA commanded the Voyager 1 spacecraft, then approximately 6 billion kilometers from Earth, to turn its camera around and photograph the solar system it was leaving behind. Earth appeared in the image as a pale blue dot less than a pixel in size, suspended in a beam of scattered sunlight, surrounded by the absolute darkness of space. Carl Sagan, describing the image, wrote that every human being who ever lived, every king and peasant, every act of kindness and cruelty, every invention and discovery, every civilization and empire, had played out on that mote of dust suspended in a sunbeam.

That image was taken from within our own solar system. From the scale of the observable universe, our solar system is not visible. Our sun is not visible. The Milky Way is a faint smudge. The local group of galaxies is a barely distinguishable cluster. And the observable universe is, in all probability, only a small fraction of what actually exists.

Everything we have discussed so far, the two trillion galaxies, the 93 billion light-year diameter, the expanding space that has already permanently separated us from most of the cosmos, describes only the observable universe, the part we can see. What lies beyond it is a question that physics can approach but cannot yet answer. And the answers it approaches are, in their own way, more disorienting than anything the observable universe has produced. The edge of observation. The observable universe has a boundary not because the universe ends there, but because light has had only 13.8 billion years to travel.

Beyond a certain distance, the light that would tell us what exists has simply not had time to reach us yet. This boundary is not a wall. It is a horizon like the horizon at sea. which exists not because the ocean ends, but because the curvature of the Earth limits how far your eyes can reach. Beyond our cosmic horizon, space continues. Matter continues. Galaxies, stars and planets almost certainly continue, in patterns statistically similar to what we observe within our visible sphere. How far this continuation extends is unknown. Current cosmological measurements suggest that the total universe, the full extent of space, beyond the observable portion, is at least 250 times larger than the observable universe in diameter. Some models

suggest it is vastly larger than that. Some models suggest it is infinite. The Infinite Universe An infinite universe is not simply a very large universe. it is categorically different in its implications. In an infinite universe, every possible arrangement of matter that does not violate physical laws exists somewhere.

Given infinite space and finite combinations of particles, every configuration repeats infinitely many times. There is, in an infinite universe, an exact copy of you reading these exact words at this exact moment, somewhere beyond the observable horizon. Not a similar version, an exact duplicate, atom for atom, thought for thought.

There are also versions of you making every different decision you have ever made. Every road not taken exists in an infinite universe as a road taken somewhere else. This is not philosophy, it is mathematics. Infinity, applied to a finite set of particle configurations, produces exact repetition as a mathematical certainty. The multiverse, beyond the infinite universe hypothesis, lies something even less constrained. Inflationary cosmology, the leading theoretical framework for understanding the universe's earliest moments, predicts that the rapid expansion that followed the Big Bang may not have stopped everywhere simultaneously. Instead, it may be ongoing in regions beyond our observable horizon, with isolated pockets of slower expansion bubble

universes forming continuously within the larger inflating space. Our entire observable universe, in this framework, is one bubble among an effectively infinite number of bubbles, each with potentially different physical constants, different laws, different histories. Some bubbles may support structures like atoms and stars. Others may collapse immediately. Others may expand forever into featureless darkness. We cannot observe other bubbles. We cannot interact with them. We cannot confirm they exist. but the mathematics of inflation produces them as a near inevitable consequence, and the mathematics of inflation is otherwise extraordinarily well supported by observation. We may be one universe in an infinite

sea of universes, each unreachable, each unknowable, each as vast and as silent as the one we inhabit. The observable universe, two trillion galaxies, 93 billion light years across may be relative to what actually exists, essentially nothing, a single grain of sand on a beach that has no shoreline. We have come a long way from the room you started in, from the walls around you to the edge of the earth, from the earth to the solar system, from the solar system to the galaxy, from the galaxy to the observable universe, From the observable universe to whatever lies beyond it, infinite space, bubble universes, configurations of reality so vast that the word vast has long since stopped doing any useful work. And

now we have to decide what to do with all of that. Two ways to feel small. There are two responses to the scale of the universe, and they are almost opposites of each other. The first is insignificance. If the universe contains two trillion galaxies, each with hundreds of billions of stars, and we are one species on one planet, orbiting one star in one unremarkable arm of one galaxy, then nothing we do matters. Our wars, our art, our love, our grief, our civilizations that rise and fall across centuries, all of it is invisible at cosmic scales. A brief chemical accident on a pale blue dot, unnoticed and unremembered by a universe that will continue expanding long after the last star has burned out. This is one honest response.

It is not wrong. The second response is wonder. The same facts that produce insignificance can produce something else entirely, if you turn them slightly. In two trillion galaxies... Across 13.8 billion years of cosmic history, something happened here that may be extraordinarily rare. Matter arranged itself into structures capable of asking where it came from. The universe, through the specific chemistry of this specific planet orbiting this specific star, became aware of itself, capable of measuring its own size, capable of feeling small, Carl Sagan put it this way, We are a way for the cosmos to know itself. The universe is unimaginably vast, and almost certainly indifferent. But somewhere in it, on a pale blue dot in the outer

arm of an average galaxy, something looked up and noticed. That something is you. Whatever the universe is, however large, however old, however silent it produced, in at least one place, the capacity to look back at it and feel the weight of what it is, that is either the most insignificant fact in existence, or the most significant one. Perhaps it is both. Start where you are, the room you are in right now, The ceiling above you, the walls around you, the floor beneath you. You know this space.

You have a felt sense of its dimensions, how many steps it takes to cross it, how high the ceiling sits above your head, where the edges are. This is your immediate universe, the scale your body understands instinctively. Now step outside it, the human scale. The average human being is approximately 1.7 meters tall. This is the unit of measurement your nervous system is calibrated to. Distances that fit within a few multiples of your height feel comprehensible. A room, a street, a field, these are scales your body can walk, your eyes can survey, your mind can hold as a complete picture. A kilometre is already pushing the edge of intuitive understanding. You can walk it in about 12 minutes, which gives it a felt duration, but the distance itself, 1,000 metres,

600 of your body lengths laid end to end, is already more abstract than concrete. 100 kilometres is a number, not a feeling. The planet. The Earth has a circumference of approximately 40,000 kilometers at the equator. This number is so large relative to human experience that it resists intuition entirely.

But consider it this way. Like the fastest thing in the universe, traveling at 299,792 kilometers per second circles the Earth 7.5 times in a single second. In the time it takes you to blink, light has lapped the planet several times over. The fastest aircraft ever built, the SR-71 Blackbird, travelled at approximately 3,500 kilometres per hour. At that speed, faster than any human being has ever moved through the atmosphere, circumnavigating the Earth would take approximately 11 hours. The International Space Station said, orbiting at 28,000 km per hour, completes a full orbit every 90 minutes. These numbers begin to convey something about the planet's size, but here is the comparison that tends to land most directly. If you shrank

the Earth to the size of a standard classroom globe, roughly 30 cm in diameter, a human being at the same scale would be approximately 0.01 cm. five millimeters tall, smaller than a grain of fine sand, invisible to the naked eye, standing on the surface of that globe, you would not be able to see yourself. The atmosphere. Here is something that most people find genuinely surprising when they encounter it for the first time. The atmosphere, the layer of air that makes life on Earth possible, that contains every cloud and weather system, every bird and aircraft. Every breath that every living thing on this planet has ever taken extends to approximately 100 kilometres above the surface. This is the boundary called the Kármán line, where space is

conventionally considered to begin. 100 kilometres sounds substantial, but relative to the Earth's diameter of nearly 13,000 kilometres, the atmosphere is vanishingly thinned. If you scale the Earth to the size of a standard classroom globe, the entire atmosphere, every cubic metre of breathable air on the planet, would be thinner than a coat of varnish applied to its surface.

Everything that has ever lived, every ecosystem, every weather event in recorded history, contained in a layer so thin it is barely visible at planetary scale. What this means before we continue... We have not left the planet yet. We have not looked at the solar system, or the galaxy, or the universe. We have simply tried to understand the size of the rock we live on, and already the numbers are beginning to resist ordinary comprehension. Already the scale is pulling away from anything your body has a felt sense of. This is just the beginning. The next step is the solar system. And the solar system will make everything we have just discussed feel very, very small. The sun is 150 million kilometres from Earth. Read that again.

150 million kilometres. In the context of everything we just established. The Earth's circumference of 40,000 kilometres. The atmosphere's depth of 100 kilometres. This number represents a scale increase so dramatic that the previous numbers effectively become zero by comparison. But the number alone does not convey it. Let us try to make it real. The Sun. Begin with the Sun itself before we consider the distance to it. The Sun has a diameter of approximately 1.39 million kilometers. The Earth's diameter is approximately 12,700 kilometers. This means you could fit approximately 109 Earths side by side across the Sun's diameter.

In terms of volume three-dimensional space, you could fit approximately 1.3 million Earths inside the Sunday. 1.3 million. If the Sun were a hollow sphere and you began filling it with Earths, you would need to insert one Earth every single second, continuously, for 15 days before it was full. And the Sun is an average star. Not large, not small, a thoroughly unremarkable medium-sized star that would not attract particular attention from any astronomer surveying the galaxy. The distance. Light travels from the Sun to the Earth in approximately 8 minutes and 20 seconds. This means that the sunlight warming your skin right now left the sun more than eight minutes ago.

If the sun disappeared at this exact moment, you would not know for eight minutes. The light currently in transit would complete its journey. For eight minutes, the sky would remain bright while the source of that brightness had already ceased to exist. The furthest planet in our solar system, Neptune, orbits at a distance of approximately 4.5 billion kilometers from the Sunday light, takes approximately four hours to travel from the Sun to Neptune. A radio signal sent from Earth to Neptune and back takes approximately eight hours. Voyager 1.

In September 1977, NASA launched the Voyager 1 spacecraft on a trajectory that would take it out of the solar system. It is the most distant human-made object ever created. As of 2024, it has been traveling for 47 years, moving at approximately 61,000 kilometers per hour, faster than any other human-made object in history. It has covered approximately 24 billion kilometers, and it has only just crossed the boundary of the heliosphere.

the region of space dominated by the Sun's solar wind entering what is called interstellar space. The broader solar system, including the Oort cloud of comets that surrounds it, extends perhaps 100,000 times further than the Earth-Sun distance. At Voyager's current speed, crossing the full extent of the solar system would take approximately 30,000 years. We launched an object nearly five decades ago It has been travelling continuously, faster than anything else we have ever built, every second of every day since 1977. It has barely left home, the scale model.

Here is the exercise that tends to produce the most visceral understanding of the solar system's size. If you placed the sun as a ball one metre in diameter at one end of a field, where would the planets be? Mercury would sit approximately 41 meters away, a marble-sized object at the far end of a small apartment. Earth would be approximately 107 meters away, slightly larger than a marble, located at the far end of a football field. Neptune, the outermost planet, would be approximately 3.2 kilometers away, a pea-sized object. more than three kilometers from the one meter Sunday.

At this scale, the nearest star proximity Centauri would be located approximately 28,000 kilometers away on the other side of the planet. The solar system is not a compact collection of worlds orbiting a central star in a region you could walk across. It is an almost incomprehensibly vast volume of mostly empty space, in which the planets are tiny objects separated by distances that make the gap between Earth and Moon feel intimate by comparison. And we have not yet left the solar system. The galaxy is next. The nearest star to our Sun is Proxima Centauri. It is 4.24 light-years away. This means that light travelling at 299,792 kilometres per second, the fastest speed the universe permits, takes four

years and three months to cross the distance between our sun and its nearest neighbour. Four years. At the speed of light. What that actually means. The fastest spacecraft ever launched was NASA's New Horizons probe. which left Earth in 2006 travelling at approximately 58,000 km per hour. At that speed, the fastest we have ever propelled an object reaching Proxima Centauri would take approximately 78,000 years. Not 78,000 days. Not 78,000 months. 78,000 years.

Longer than modern human civilisation has existed. longer than the time since the last ice age, traveling continuously at the highest speed we have ever achieved. From the moment our species first began painting cave walls until today, we would not yet have arrived. And Proxima Centauri is our nearest neighbor, the galaxy. The Milky Way is a barred spiral galaxy, approximately 100,000 light years in diameter. It contains an estimated 200 to 400 billion stars. Our sun sits roughly 26,000 light years from the galactic center, about two thirds of the way out toward the edge in an unremarkable region of one of the spiral arms. If you wanted to cross the Milky Way at the speed of light, it would take 100,000 years. At the speed of new horizons,

it would take approximately 2 billion years, roughly half the age of the Earth. The Milky Way contains up to 400 billion stars. If you counted one star per second, without stopping, it would take approximately 12,000 years to count them all. And every single one of those stars is, by human standards, incomprehensibly far from every other one. Our address...

Here is what our location in the galaxy actually means. We are not at the centre. We are not at the edge. We are in a quiet, unremarkable region of a middling spiral arm, orbiting a thoroughly average star on a small rocky planet that would be completely invisible from even a modest distance within our own galaxy. From the centre of the Milky Way, The sun is one faint point of light among hundreds of billions of identical faint points of light, indistinguishable, unremarkable, lost. We have not yet left the galaxy. The observable universe is next, and the observable universe will make the Milky Way feel like that grain of sand we discussed at the beginning. We have established that the nearest star is 78,000 years away at

our fastest speed. We have established that crossing our own galaxy would take 2 billion years. We have established that our sun is one of 400 billion stars in the Milky Way, located in an unremarkable position in an unremarkable arm, indistinguishable from the hundreds of billions of stars surrounding it.

Now we need to talk about how many galaxies there are. The number. For most of the 20th century, astronomers estimated the observable universe contained approximately 200 billion galaxies. This was already a number beyond meaningful comprehension. 200 billion collections of hundreds of billions of stars each, separated by distances that make the Milky Way feel intimate. In 2016, A more careful analysis of data from the Hubble Space Telescope revised that estimate dramatically upward. The observable universe contains approximately two trillion galaxies. Two trillion. Two million million. A number so large that if you spent one second looking at each galaxy, examining it, acknowledging its existence, you would need 63,000 times

the current age of the universe to finish. Each of those galaxies contains, on average, hundreds of billions of stars. Each of those stars is, by the standards we established in the previous section, an almost unreachable destination. The Milky Way, our galaxy, the one we could not cross in two billion years, is one of two trillion. the Hubble Deep Field.

In December 1995, NASA pointed the Hubble Space Telescope at a patch of sky near the Big Dipper that appeared to ground-based telescopes to be essentially empty. A dark, unremarkable region containing almost nothing of interest. They held the exposure for 10 consecutive days. What the image revealed has been described as one of the most important photographs ever taken.

In that tiny patch of apparently empty sky, covering an area of the sky roughly equivalent to a grain of sand held at arm's length, Hubble detected approximately 10,000 galaxies. 10,000 galaxies in a piece of sky so small you could cover it with a grain of sand. The image was subsequently repeated in other directions, the Hubble Ultra Deep Field, the Hubble Extreme Deep Field, and the result was consistent every time, every direction. Every apparently empty patch of darkness, thousands upon thousands of galaxies, each containing hundreds of billions of stars, each receding from us at speeds proportional to their distance. There is no empty sky. There is only sky we have not looked at carefully enough yet. The

edge we cannot cross. The observable universe has a diameter of approximately 93 billion light years. This number requires an explanation, because it seems to contradict the universe's age of 13.8 billion years. If the universe is only 13.8 billion years old, How can light from 46 billion light years away have reached us? The answer is that space itself has been expanding since the Big Bang. The light that is only now reaching us from the most distant galaxies was emitted when those galaxies were much closer, but in the billions of years that light has been travelling toward us. The space between us and its source has continued to expand.

the galaxies that emitted that ancient light are now vastly further away than the distance the light has travelled. And beyond the observable universe, beyond the sphere of space from which light has had time to reach us, the universe continues. How far it continues, nobody knows. Current measurements suggest the universe is either infinite, or so large that the difference between finite and infinite is practically meaningless. Some of those distant galaxies are now so far away and receding so fast due to the expansion of space that light leaving them today will never reach us. The expansion of space between us and them is faster than light can travel across it. They are gone from us permanently not because

of any barrier but because space itself is growing too quickly for any signal to bridge the gap. We are already in a precise cosmological sense, permanently cut off from most of the universe. The pale blue dot revisited. In 1990, NASA commanded the Voyager 1 spacecraft, then approximately 6 billion kilometers from Earth, to turn its camera around and photograph the solar system it was leaving behind. Earth appeared in the image as a pale blue dot less than a pixel in size, suspended in a beam of scattered sunlight, surrounded by the absolute darkness of space. Carl Sagan describing the image, wrote that every human being who ever lived, every king and peasant, every act of kindness and cruelty,

every invention and discovery, every civilization and empire, had played out on that mote of dust suspended in a sunbeam, That image was taken from within our own solar system. From the scale of the observable universe, our solar system is not visible. Our sun is not visible. The Milky Way is a faint smudge. The local group of galaxies is a barely distinguishable cluster. And the observable universe is, in all probability, only a small fraction of what actually exists.

Beyond a certain distance, the light that would tell us what exists has simply not had time to reach us yet. This boundary is not a wall. It is a horizon like the horizon at sea, which exists not because the ocean ends, but because the curvature of the Earth limits how far your eyes can reach. Beyond our cosmic horizon, space continues. Matter continues. Galaxies, stars and planets almost certainly continue, in patterns statistically similar to what we observe within our visible sphere. How far this continuation extends is unknown. Current cosmological measurements suggest that the total universe, the full extent of space, beyond the observable portion, is at least 250 times larger than the observable universe in diameter. Some models

suggest it is vastly larger than that. Some models suggest it is infinite. The infinite universe. An infinite universe is not simply a very large universe. it is categorically different in its implications. In an infinite universe, every possible arrangement of matter that does not violate physical laws exists somewhere.

sea of universes, each unreachable, each unknowable, each as vast and as silent as the one we inhabit. The observable universe, two trillion galaxies... 93 billion light years across may be relative to what actually exists essentially nothing a single grain of sand on a beach that has no shoreline we have come a long way from the room you started in from the walls around you to the edge of the earth from the earth to the solar system from the solar system to the galaxy from the galaxy to the observable universe From the observable universe to whatever lies beyond it infinite space, bubble universes. Configurations of reality so vast that the word vast has long since stopped doing any useful work. And now we have to decide what

to do with all of that. Two ways to feel small. There are two responses to the scale of the universe, and they are almost opposites of each other. The first is insignificance. If the universe contains two trillion galaxies, each with hundreds of billions of stars, and we are one species on one planet, orbiting one star in one unremarkable arm of one galaxy, then nothing we do matters. Our wars, our art, our love, our grief, our civilizations that rise and fall across centuries, all of it is invisible at cosmic scale. A brief chemical accident on a pale blue dot, unnoticed and unremembered by a universe that will continue expanding long after the last star has burned out. This is one honest response. It is not wrong. The second response

is wonder. The same facts that produce insignificance can produce something else entirely if you turn them slightly. In two trillion galaxies... Across 13.8 billion years of cosmic history, something happened here that may be extraordinarily rare. Matter arranged itself into structures capable of asking where it came from. The universe, through the specific chemistry of this specific planet orbiting this specific star, became aware of itself, capable of measuring its own size, capable of feeling small, Carl Sagan put it this way, We are a way for the cosmos to know itself. The universe is unimaginably vast, and almost certainly indifferent.

But somewhere in it, on a pale blue dot in the outer arm of an average galaxy, something looked up and noticed. That something is you. Whatever the universe is, however large, however old, however silent it produced... in at least one place, the capacity to look back at it and feel the weight of what it is, that is either the most insignificant fact in existence, or the most significant one. Perhaps it is both. Thank you. Thank you for watching. Thank you. Thank you. Thank you for watching.

Thank you. Thank you. Thank you. Thank you. Thank you for watching. you

The Terrifying Truth About Our Size in the Universe _ Science for Sleep

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