Latest / Boring Science / We Can Reach Pluto... So Why Can_t We Fly Above the Solar System_

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We Can Reach Pluto... So Why Can_t We Fly Above the Solar System_ · Boring Science

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Speaker 1: Hello, and welcome to Boring Science to Sleep, a quiet
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Speaker 1: place where science becomes slow, soft and easy to drift through. Tonight,
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Speaker 1: you're going somewhere that sounds very simple, but becomes stranger
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Speaker 1: the longer you think about it. You're going to look
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Speaker 1: above the solar system, not toward another planet, not toward
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Speaker 1: another star, but simply upward, away from the broad plane
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Speaker 1: where the planets quietly travel around the sun. and you'll
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Speaker 1: discover why something that sounds so easy, just flying straight up,
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Speaker 1: is surprisingly difficult. But before you settle in, if you
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Speaker 1: truly enjoy these calm journeys through interesting facts about science,
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Speaker 1: you're welcome to like this video and subscribe, only if
0:47
Speaker 1: it feels right for you. And when you're ready, let
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Speaker 1: me know in the comments where you're listening from, and
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Speaker 1: what time it is right now. It's always a quiet
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Speaker 1: joy to see how many places and moments gather here together. Now,
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Speaker 1: dim the lights, maybe let a fan hum softly in
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Speaker 1: the background. Make yourself comfortable, and let your breathing become
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Speaker 1: a little slower. There's nothing to do, you are safe.
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Speaker 1: You can simply listen, and drift. And now, very gently,
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Speaker 1: let's begin by imagining that you are floating above Earth.
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Speaker 1: For a moment, imagine that you are no longer lying
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Speaker 1: in your room. You are floating quietly above the Earth.
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Speaker 1: Far enough away that the familiar blue surface has begun
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Speaker 1: to soften into a small sphere beneath you. There is
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Speaker 1: no ground beneath your feet, there is no ceiling above
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Speaker 1: your head. There is only space, dark and quiet, extending
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Speaker 1: in every direction. And somewhere in front of you, far
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Speaker 1: beyond the earth, is the sun. Around it, the planets
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Speaker 1: continue their long journeys. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune,
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Speaker 1: and countless smaller worlds move through the darkness, each following
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Speaker 1: its own enormous path, each carrying a little of the
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Speaker 1: ancient motion that shaped the solar system. From a great distance,
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Speaker 1: you might imagine all of those paths as lying on
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Speaker 1: a vast, almost invisible sheet. A broad plane of motion,
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Speaker 1: a quiet, geometric surface that you cannot touch, cannot see directly,
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Speaker 1: and cannot bump into. This is the planetary plane. It
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Speaker 1: is one of the most useful ways to picture our
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Speaker 1: solar system, because most of the planets travel around the
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Speaker 1: sun in roughly the same broad direction. But the strange
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Speaker 1: thing is that this plane is not really a floor.
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Speaker 1: You cannot stand on it, you cannot fall beneath it,
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Speaker 1: and there is nothing physically preventing you from moving away
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Speaker 1: from it. You could in principle be point a spacecraft
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Speaker 1: upward and leave it behind. The difficulty begins because you
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Speaker 1: are already moving. Even while you are lying completely still
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Speaker 1: in your bed, even while your body feels wonderfully motionless,
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Speaker 1: the Earth beneath you is travelling around the Sun at
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Speaker 1: roughly 30 kilometres every second. You do not feel this
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Speaker 1: motion because you, your room, the atmosphere, the oceans and
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Speaker 1: the entire Earth are moving together. It feels like stillness
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Speaker 1: because everything around you shares almost the same journey. But
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Speaker 1: in space, your spacecraft does not begin from rest. It
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Speaker 1: begins with the motion of Earth already inside it. Imagine
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Speaker 1: holding a small arrow in your hand. The arrow represents
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Speaker 1: your motion through space. At the moment you leave Earth,
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Speaker 1: that arrow is already pointing mostly sideways, along Earth's journey
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Speaker 1: around the Sun. If you want to travel toward another planet,
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Speaker 1: This existing motion is surprisingly helpful. Mars is moving around
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Speaker 1: the Sun in roughly the same broad planetary plane. Jupiter
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Speaker 1: is too. Saturn is too. Even Pluto, although its path
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Speaker 1: is somewhat more tilted, remains part of this enormous family
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Speaker 1: of orbital motion. So when you travel outward toward these worlds,
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Speaker 1: you are not starting by fighting against everything the Earth
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Speaker 1: is already doing, you are gently reshaping the motion you
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Speaker 1: already have. But now imagine something different. Imagine that instead
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Speaker 1: of travelling outward along the broad plane of the planets,
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Speaker 1: you want to turn your arrow upward. Not a little,
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Speaker 1: not gently. You want to point almost directly away from
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Speaker 1: the planetary plane. The farther you tilt your path, the
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Speaker 1: more you have to change the direction of that invisible arrow.
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Speaker 1: And this is where the simple word up begins to
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Speaker 1: hide a surprisingly large problem. You are not climbing a ladder.
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Speaker 1: You are not pushing against the floor. You are trying
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Speaker 1: to redirect motion that is already carrying you sideways through
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Speaker 1: the solar system. That is why the planetary plane can
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Speaker 1: feel like a strange kind of invisible road. Not because
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Speaker 1: it traps you. Not because space has walls, but because
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Speaker 1: your spacecraft arrives already travelling along it. The solar system
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Speaker 1: itself has no memory of a ceiling. It only has
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Speaker 1: a memory of motion, and that memory reaches much farther
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Speaker 1: back than the first spacecraft, much farther back than the
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Speaker 1: first planet, and even farther back than the Earth itself.
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Speaker 1: About four and a half billion years ago, the young
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Speaker 1: solar system began from a vast cloud of gas and dust.
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Speaker 1: The cloud was slowly rotating, gravity drew its material inward.
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Speaker 1: As it contracted, Its rotation became increasingly important, and the
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Speaker 1: material gradually settled into a broad, flattened disk. The sun
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Speaker 1: formed near the centre. The planets formed from material remaining
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Speaker 1: around it, and because those planets inherited much of the
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Speaker 1: motion of that original rotating material, they continued to travel
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Speaker 1: around the sun in roughly the same broad plane. So
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Speaker 1: when you look at the solar system today, you are
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Speaker 1: seeing the quiet remains of an ancient movement. The planetary
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Speaker 1: plane is almost like a memory, a memory of a
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Speaker 1: cloud that turned long before there was an Earth, long
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Speaker 1: before there was anyone here to wonder which way was up.
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Speaker 1: And now, floating far above our planet, you can begin
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Speaker 1: to see something important. There was never really a cosmic
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Speaker 1: floor beneath the planets. There was only motion, there was
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Speaker 1: only direction. There was only the particular arrangement created by
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Speaker 1: the way our small corner of the universe happened to form.
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Speaker 1: You can leave that plane, physics does not forbid it,
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Speaker 1: but leaving it is not the same as simply pointing
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Speaker 1: a rocket upward. You would need to change the direction
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Speaker 1: of your existing motion, and changing that direction can require
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Speaker 1: a remarkable amount of energy. So for now, you remain
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Speaker 1: quietly suspended above the earth, watching the planet continue its
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Speaker 1: invisible journey around the sun. Below you, the Earth keeps moving.
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Speaker 1: Far away, the other planets keep moving. Nothing is holding
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Speaker 1: them down. Nothing is holding you up. And perhaps that
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Speaker 1: is the first gentle surprise of this journey. The solar
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Speaker 1: system only looks flat because of the way it was born.
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Speaker 1: And if you could somehow turn your spacecraft and begin
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Speaker 1: changing that ancient direction of motion, you would slowly discover
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Speaker 1: that the hardest part of going up is not finding
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Speaker 1: what is above you, It is changing the motion that
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Speaker 1: brought you here. And somewhere ahead, beyond the quiet plane
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Speaker 1: of the planets, there is a different path waiting, one
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Speaker 1: that begins not with a wall, but with a turn.
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Speaker 1: You are still drifting above the earth, and beneath you,
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Speaker 1: the planet continues its slow journey around the sun. From here,
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Speaker 1: everything feels still. The earth looks calm, the sun looks calm,
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Speaker 1: Even the planets seem to hang quietly in the darkness,
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Speaker 1: like small lights placed across an enormous black room. But
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Speaker 1: nothing here is actually standing still. Everything is moving, and
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Speaker 1: your spacecraft is moving too. Before you even begin to
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Speaker 1: travel toward the outer solar system, you are already carrying
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Speaker 1: the motion of Earth around the Sun, roughly 30 kilometres
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Speaker 1: every second, a speed so large that it becomes difficult
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Speaker 1: to imagine as movement at all. You do not feel it.
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Speaker 1: There is no wind around you, no vibration, no sensation
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Speaker 1: of speed. You simply float, and yet your invisible arrow
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Speaker 1: of motion is already pointing mostly sideways. This is the
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Speaker 1: quiet problem hidden inside the simple idea of flying upward.
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Speaker 1: If you wanted to visit another planet, you could work
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Speaker 1: with that existing motion. You could gradually reshape your path.
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Speaker 1: allowing the gravity of the sun and planets to help
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Speaker 1: guide you. But if you wanted to turn almost completely
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Speaker 1: away from the planetary plane, you would need to do
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Speaker 1: something much more demanding. You would need to turn that
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Speaker 1: invisible arrow. Imagine again that you are holding a small
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Speaker 1: arrow in your hand. It points sideways. Now imagine slowly
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Speaker 1: rotating your hand until the arrow points upward. The arrow
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Speaker 1: itself is not difficult to turn when it is only
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Speaker 1: a drawing. But a spacecraft is carrying real momentum. Its
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Speaker 1: motion has direction. And changing that direction means changing its velocity.
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Speaker 1: This is an important distinction. You do not necessarily need
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Speaker 1: to stop the spacecraft completely and then begin again. That
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Speaker 1: would be an enormous waste of energy. Instead, you need
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Speaker 1: to redirect the motion you already have. and the closer
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Speaker 1: you want to come to a 90 degree change in direction,
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Speaker 1: the more difficult the maneuver becomes. For a simple illustration,
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Speaker 1: if you began with Earth's roughly 30 kilometers per second
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Speaker 1: orbital motion, and wanted to redirect that motion by nearly
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Speaker 1: 90 degrees, the required change in velocity would be on
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Speaker 1: the order of 42 kilometers per second. You do not
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Speaker 1: need to remember that number. It is enough to feel
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Speaker 1: what it means. The spacecraft is already moving very quickly,
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Speaker 1: and now you are asking it to turn that motion
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Speaker 1: almost completely sideways. That is a great deal to ask
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Speaker 1: from a rocket. A chemical rocket can only carry so
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Speaker 1: much fuel. The fuel must be lifted into space. The
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Speaker 1: fuel itself has mass. And carrying more fuel requires even
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Speaker 1: more energy. So a spacecraft cannot simply bring an enormous
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Speaker 1: tank of propellant and burn its way wherever it wants.
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Speaker 1: Every additional change in motion comes with a cost. This
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Speaker 1: is why travelling to Pluto, and travelling directly above the
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Speaker 1: planetary plane, are such different journeys. Pluto is far away,
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Speaker 1: unimaginably far by human standards, but its orbit still belongs
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Speaker 1: broadly to the same family of motion as the planets.
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Speaker 1: A spacecraft travelling toward Pluto is use the existing architecture
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Speaker 1: of the solar system. It can fall toward the sun
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Speaker 1: and climb away again. It can alter its path gradually.
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Speaker 1: It can allow gravity to do some of the work.
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Speaker 1: Flying directly upward is different. You are not merely asking
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Speaker 1: the spacecraft to go farther. You are asking it to turn.
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Speaker 1: And there is a beautiful trick hidden in the solar
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Speaker 1: system that allows spacecraft to do exactly this without carrying
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Speaker 1: all the energy themselves. You can let gravity help. Imagine
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Speaker 1: approaching a giant planet, perhaps Jupiter, not as a destination,
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Speaker 1: but as a quiet gravitational guide. As your spacecraft passes
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Speaker 1: around the planet, Jupiter's gravity bends its path. The planet
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Speaker 1: is moving through space as well, and during the encounter,
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Speaker 1: a tiny amount of that motion can be exchanged. The
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Speaker 1: spacecraft leaves on a new trajectory. It has not burned
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Speaker 1: a gigantic amount of fuel. Instead, it has borrowed a
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Speaker 1: little of the geometry of a much larger moving world.
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Speaker 1: This is called a gravity assist. The name sounds technical,
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Speaker 1: but the idea is gentle. You are allowing gravity to
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Speaker 1: turn your path for you. The spacecraft arrives moving in
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Speaker 1: one direction, passes through the gravitational field of a planet,
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Speaker 1: and leaves moving in another. Nothing pushes it with a hand.
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Speaker 1: Nothing pulls it along a visible rope. Gravity simply reshapes
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Speaker 1: the journey. And for changing the orientation of a spacecraft's orbit,
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Speaker 1: this can be enormously useful. There is another subtle idea here,
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Speaker 1: one that spacecraft engineers have learned to use when thinking
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Speaker 1: about energy. It is called the Oberth effect. The name
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Speaker 1: is less important than the basic picture. A rocket engine
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Speaker 1: burn can have a greater effect on a spacecraft's orbital
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Speaker 1: energy the spacecraft is moving very quickly, so in some
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Speaker 1: kinds of manoeuvres it is useful to make an engine
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Speaker 1: burn deep within a gravitational field where the spacecraft is
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Speaker 1: moving rapidly. But this does not magically solve the problem
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Speaker 1: of flying straight upward. The trick is especially helpful for
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Speaker 1: changing orbital energy, while changing the tilt of the orbital
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Speaker 1: path is a different problem. For a large change in
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Speaker 1: direction The geometry of the motion still matters. So even
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Speaker 1: clever orbital techniques cannot make the difficulty disappear. They simply
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Speaker 1: allow engineers to spend the available energy more carefully. And
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Speaker 1: perhaps this is one of the quietest lessons hidden inside
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Speaker 1: orbital mechanics. Space is not difficult because there is something
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Speaker 1: in the way. There is no invisible ceiling. There is
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Speaker 1: no thick layer of resistance above the planets. There is
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Speaker 1: nothing physically pressing the spacecraft back toward the solar system's
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Speaker 1: broad plane. The difficulty comes from motion itself. You are
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Speaker 1: already going somewhere. You are already carrying a direction. And
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Speaker 1: if you want to change that direction dramatically, you must
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Speaker 1: somehow provide the energy for the change. So imagine yourself
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Speaker 1: once again above Earth. Your spacecraft is quiet. Your instruments
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Speaker 1: are quiet. The planet below is turning slowly beneath you.
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Speaker 1: The sun is far ahead, and your invisible arrow of
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Speaker 1: motion still points sideways. You do not need to fight
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Speaker 1: the universe. You only need to understand how your motion
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Speaker 1: is already carrying you. Perhaps, in the darkness around you,
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Speaker 1: the planets no longer look like barriers. They look more
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Speaker 1: like companions in a great moving system. each one carrying
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Speaker 1: the memory of the same ancient disk from which they
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Speaker 1: were born. And if you could use one of those
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Speaker 1: worlds to gently bend your path, your arrow could begin
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Speaker 1: to turn, not suddenly, not violently, just gradually, quietly, patiently,
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Speaker 1: until one day you might find yourself looking down at
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Speaker 1: the planetary plane instead of looking across it. And humanity has,
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Speaker 1: in fact, done something remarkably close to this. A spacecraft
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Speaker 1: once used the gravity of Jupiter to leave the familiar
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Speaker 1: plane of the planets behind, and for a while it
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Speaker 1: travelled above and below the Sun in a path that
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Speaker 1: looked almost vertical from our usual perspective. It was called Ulysses.
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Speaker 1: You are still drifting quietly through the darkness, carrying with
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Speaker 1: you the simple question that began this journey. Can you
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Speaker 1: really fly above the solar system? By now, you know
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Speaker 1: that there is no invisible roof above the planets, and
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Speaker 1: no physical surface keeping spacecraft inside their broad orbital plane.
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Speaker 1: The difficulty is motion. Earth is already moving around the Sun.
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Speaker 1: Your spacecraft inherits that motion, and to turn that motion
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Speaker 1: almost completely upward requires a great deal of energy. But
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Speaker 1: there is something reassuring about knowing that difficult does not
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Speaker 1: mean impossible. Humanity has already found a way to rise
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Speaker 1: far above the familiar plane of the planets. And the
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Speaker 1: spacecraft that did it was called Ulysses. Imagine it quietly
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Speaker 1: leaving Earth, carrying instruments instead of passengers, moving outward through
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Speaker 1: the solar system without any need for a dramatic climb.
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Speaker 1: It does not simply point its engines upward and push. Instead,
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Speaker 1: it takes a longer, more patient route. It travels toward Jupiter.
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Speaker 1: and Jupiter, with its enormous gravity, becomes part of the journey.
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Speaker 1: As the spacecraft passes through Jupiter's gravitational field, its path
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Speaker 1: is gently reshaped. The planet does not behave like a
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Speaker 1: launch platform. It does not throw the spacecraft upward in
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Speaker 1: a single dramatic motion. Rather, its gravity bends the spacecraft's trajectory,
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Speaker 1: changing the direction of its journey from in a way
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Speaker 1: that would have been much more expensive to accomplish with
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Speaker 1: engines alone. It is almost as though the spacecraft has
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Speaker 1: found a quiet current in the solar system. The current
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Speaker 1: is gravity, and Jupiter is the enormous body creating it.
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Speaker 1: After the encounter, Ulysses is no longer following the familiar
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Speaker 1: paths that keep most planets close to their broad orbital plane.
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Speaker 1: Its new orbit is tilted dramatically. Eventually, The spacecraft reached
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Speaker 1: an inclination of almost 80 degrees relative to the planetary plane.
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Speaker 1: That number is easier to understand as an image. Imagine
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Speaker 1: the broad plane of the planets beneath you. Imagine it
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Speaker 1: stretching away in every direction. An almost invisible sheet of motion.
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Speaker 1: Now imagine your spacecraft rising far above it. The sheet
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Speaker 1: is no longer beneath you in the way a floor
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Speaker 1: is beneath a person. It has become something you can
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Speaker 1: simply look down upon. The Sun is still nearby. The
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Speaker 1: planets are still moving. But your path has changed. You
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Speaker 1: are seeing the solar system from an angle that most
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Speaker 1: spacecraft never experience. And eventually, Ulysses passed over the northern
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Speaker 1: and southern polar regions of the Sun. For a spacecraft
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Speaker 1: designed to study our star, this was an extraordinary viewpoint.
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Speaker 1: Most planets and spacecraft approached the Sun from near its
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Speaker 1: equatorial region, roughly following the broad architecture inherited from the
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Speaker 1: original solar system. Ulysses was different. It could look toward
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Speaker 1: the Sun from much higher above that familiar plane. It
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Speaker 1: could pass over one solar pole, continue along its enormous orbit,
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Speaker 1: and later pass over the other. And yet, there is
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Speaker 1: a small irony here. Ulysses did not return the kind
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Speaker 1: of spectacular photograph that you might imagine. It did not
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Speaker 1: carry an ordinary camera designed to photograph the solar system
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Speaker 1: from above. Its instruments were built for another purpose. It
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Speaker 1: studied the solar wind. It measured magnetic fields. It examined
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Speaker 1: charged particles moving through the space around the sun. Its
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Speaker 1: mission was about understanding the invisible environment surrounding our star,
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Speaker 1: not about taking a postcard. And this technology you something
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Speaker 1: important about how humanity has explored space. A spacecraft is
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Speaker 1: rarely built simply because a beautiful picture would be nice
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Speaker 1: to have. Every instrument has weight. Every kilogram must be launched.
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Speaker 1: Every system requires power. Every sensor has a purpose. And so,
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Speaker 1: sometimes the spacecraft that reaches the most unusual places is
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Speaker 1: carrying an instrument that cannot give you the photograph you
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Speaker 1: were hoping for. Still, you can imagine that photograph. You
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Speaker 1: can imagine yourself floating where Ulysses travelled, the sun below you,
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Speaker 1: its bright surface surrounded by darkness, the planets no longer
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Speaker 1: arranged in the familiar flat pattern from a textbook diagram.
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Speaker 1: Earth reduced to a tiny world somewhere far behind you.
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Speaker 1: And if you look toward the solar system from this
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Speaker 1: great height, something else would become clear. A true photograph
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Speaker 1: of the solar system from above would not look very
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Speaker 1: much like the diagrams you have seen. The sun would
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Speaker 1: be overwhelmingly bright. The planets would be tiny points of light.
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Speaker 1: Some would be difficult to distinguish from the background stars.
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Speaker 1: Their orbital paths would not appear as glowing lines. Space
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Speaker 1: does not draw those lines for us. The elegant circles
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Speaker 1: and ellipses in textbooks are maps of motion. They are
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Speaker 1: not visible roads painted across the darkness. This is why
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Speaker 1: the familiar picture of the solar system, with every planet
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Speaker 1: neatly placed along a bright orbit, is really a carefully
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Speaker 1: constructed representation. A photograph is different. A photograph shows light.
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Speaker 1: And most of the solar system is remarkably dark. From
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Speaker 1: far enough away, the planets become almost lost in that darkness.
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Speaker 1: The sun becomes the dominant object. The little worlds that
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Speaker 1: seem so large from Earth become almost impossibly small. To
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Speaker 1: create a recognisable portrait of the solar system, scientists would
21:55
Speaker 1: need to combine images taken with different exposures, enlarge the
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Speaker 1: faint planets, and often add the orbital paths afterward as information.
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Speaker 1: rather than as something that the camera actually saw. So
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Speaker 1: there is a strange difference between knowing where the planets
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Speaker 1: are and seeing them all together. You can calculate their positions.
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Speaker 1: You can draw their paths. You can construct a beautiful map.
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Speaker 1: But the universe itself does not provide the clean diagram.
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Speaker 1: It gives you darkness, scattered light, distant worlds and motion.
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Speaker 1: And perhaps this makes Ulysses even more beautiful. It did
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Speaker 1: not need to take a photograph for its journey to matter.
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Speaker 1: It simply changed our perspective. It showed that the solar
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Speaker 1: system is not a flat cage. It is a three-dimensional place.
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Speaker 1: The planets happen to travel mostly within one broad region,
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Speaker 1: but a spacecraft can leave that region. It can rise,
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Speaker 1: it can fall, it can pass over the sun. And yet,
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Speaker 1: even after travelling so far above the planetary plane... Ulysses
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Speaker 1: had not reached the edge of the solar system, not
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Speaker 1: even close, because the solar system is much larger than
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Speaker 1: the region occupied by its planets. Far beyond the familiar worlds,
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Speaker 1: the sun continues to send its influence outward. A quiet
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Speaker 1: stream of particles travels away from the solar surface, and
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Speaker 1: around the sun, this outward flow creates an enormous region,
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Speaker 1: much larger than the planetary system you usually picture. You
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Speaker 1: could imagine yourself drifting there now, high above the planets,
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Speaker 1: with the sun far below and behind you. The planets
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Speaker 1: have become small, their familiar arrangement has almost disappeared, and
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Speaker 1: ahead of you is something you cannot see directly, something
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Speaker 1: that is not a wall, not a shell, and not
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Speaker 1: a surface. It is simply the far-reaching influence of the
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Speaker 1: sun itself, expanding gently into the space between the stars.
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Speaker 1: The farther you drift, the less useful the old picture becomes.
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Speaker 1: There is no longer a neat row of planets beneath you.
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Speaker 1: There is only the sun, surrounded by an enormous, invisible environment.
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Speaker 1: And somewhere within that environment, the boundary of the sun's
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Speaker 1: outward wind waits quietly in the darkness, not as a
24:22
Speaker 1: solid edge, but as a gradual meeting between one cosmic
24:26
Speaker 1: neighbourhood and another. You can rest here for a moment.
24:30
Speaker 1: imagining that boundary far ahead. There is nothing to reach tonight,
24:35
Speaker 1: nothing to measure, nothing you need to understand perfectly. You
24:39
Speaker 1: are simply drifting above the familiar solar system, looking down
24:44
Speaker 1: at the worlds that once seemed enormous, while the sun's
24:47
Speaker 1: influence continues outward into a much larger and quieter space.
24:53
Speaker 1: And as your imagined journey carries you farther, the question
24:57
Speaker 1: slowly changes. It is no longer only about how to
25:00
Speaker 1: fly above the planets. It becomes a softer question. How
25:05
Speaker 1: far does the Sun itself reach? You are still drifting
25:11
Speaker 1: above the familiar plane of the planets, and far below you,
25:15
Speaker 1: the solar system continues its quiet motion. The Earth is
25:19
Speaker 1: somewhere behind you now, too small to see clearly. Jupiter, Saturn, Uranus, Neptune, Venus,
25:27
Speaker 1: and the distant path of Pluto have begun to lose
25:30
Speaker 1: their familiar importance. From this distance, they are no longer destinations.
25:36
Speaker 1: They are simply small worlds moving through a much larger space.
25:40
Speaker 1: And yet, even though you have travelled above the planetary plane,
25:44
Speaker 1: you have not really left the Sun behind. The Sun
25:47
Speaker 1: reaches much farther than the bright circle of its surface.
25:51
Speaker 1: Its influence stretches outward in every direction. carried by a
25:55
Speaker 1: continuous flow of tiny charged particles. This flow is called
25:59
Speaker 1: the solar wind. The name can sound almost poetic, because
26:04
Speaker 1: it is not wind in the ordinary sense. There is
26:08
Speaker 1: no air here for you to feel. No breeze touches
26:11
Speaker 1: the windows of your spacecraft. No sound travels through the darkness. Instead,
26:17
Speaker 1: the solar wind is a thin stream of particles leaving
26:20
Speaker 1: the sun and moving outward through space. You can imagine
26:24
Speaker 1: it as an almost invisible breath from the sun, expanding
26:29
Speaker 1: continuously into the darkness. The particles begin their journey near
26:33
Speaker 1: the solar surface, where the sun is unimaginably hot and active.
26:38
Speaker 1: From there, they move outward. Some travel quickly. Some follow
26:43
Speaker 1: magnetic structures. Some continue for enormous distances before encountering anything
26:49
Speaker 1: that changes their path. And because the Sun is constantly
26:52
Speaker 1: releasing this outward flow, it creates something much larger than
26:56
Speaker 1: the region occupied by the planets. Scientists call this enormous
27:01
Speaker 1: region the heliosphere. You can think of the heliosphere as
27:06
Speaker 1: the Sun's vast bubble of influence. But remember that it
27:10
Speaker 1: is not a soap bubble. There is no solid surface.
27:14
Speaker 1: There is no transparent shell that your spacecraft could touch.
27:18
Speaker 1: If you travelled toward its outer edge, you would not
27:21
Speaker 1: suddenly bump into anything. Instead, the character of the space
27:26
Speaker 1: around you would gradually change. Closer to the sun, the
27:30
Speaker 1: solar wind is more dominant. Farther away, the surrounding material
27:35
Speaker 1: between the stars becomes increasingly important. And somewhere in this
27:39
Speaker 1: broad transition is a boundary known as the heliopause. The
27:44
Speaker 1: word sounds precise, almost like the name of a wall,
27:48
Speaker 1: but the reality is much softer. The heliopause is the
27:51
Speaker 1: region where the outward flow of the sun finally meets
27:55
Speaker 1: the surrounding interstellar environment strongly enough that the solar wind
28:00
Speaker 1: no longer dominates in the same way. It is a
28:03
Speaker 1: boundary of influence, not a physical fence, not the end
28:07
Speaker 1: of space. Not even necessarily the end of everything we
28:11
Speaker 1: might call the solar system. That last distinction is important.
28:16
Speaker 1: When you hear that a spacecraft has crossed the heliopause,
28:19
Speaker 1: It is tempting to imagine that it has crossed the
28:22
Speaker 1: final edge of the solar system, but the solar system
28:25
Speaker 1: has more than one meaningful boundary. There is the region
28:29
Speaker 1: where the sun's particles dominate. There is the much larger
28:33
Speaker 1: region where the sun's gravity still influences distant objects. And
28:37
Speaker 1: far beyond the planets is the enormous population of icy
28:41
Speaker 1: bodies we call the Oort cloud. So crossing the heliopause
28:45
Speaker 1: is more like leaving one neighbourhood than leaving an entire city.
28:50
Speaker 1: You have entered a different kind of space, but you
28:53
Speaker 1: are still surrounded by the wider gravitational family of the Sun.
28:57
Speaker 1: As you drift farther outward, you can imagine the solar
29:01
Speaker 1: wind becoming thinner and thinner. The particles are more widely separated.
29:06
Speaker 1: The Sun becomes smaller behind you. The darkness becomes increasingly dominant.
29:11
Speaker 1: And somewhere around you is the quiet meeting place between
29:15
Speaker 1: the Sun's influence and the space between stars. This boundary
29:19
Speaker 1: is not perfectly simple. The heliosphere is affected by the
29:23
Speaker 1: Sun's changing activity, by magnetic fields, and by the properties
29:28
Speaker 1: of the surrounding interstellar environment. Its shape is therefore more
29:32
Speaker 1: complicated than the simple round bubble often used in illustrations.
29:36
Speaker 1: Some modern models suggest that the heliosphere may have a
29:39
Speaker 1: shape somewhat like a long, curved croissant, with different regions
29:44
Speaker 1: stretching and narrowing as the solar wind interacts with the
29:48
Speaker 1: material around it. It is a useful image, but it
29:52
Speaker 1: is still an image of a scientific model. The actual
29:55
Speaker 1: heliosphere is an enormous, changing region that we understand through
30:00
Speaker 1: spacecraft measurements, magnetic fields, particles, and computer models. You cannot
30:07
Speaker 1: simply look out of a window and see its outline.
30:11
Speaker 1: That is one of the strange things about space. Some
30:14
Speaker 1: of the most important boundaries are invisible. You know they
30:18
Speaker 1: are there because instruments detect changes, particles behave differently, magnetic
30:23
Speaker 1: fields shift, the environment changes, and gradually, a pattern appears.
30:30
Speaker 1: Voyager 2 is one of the spacecraft that helped us
30:33
Speaker 1: understand this distant region. After travelling outward for decades, it
30:38
Speaker 1: crossed the heliopause and entered interstellar space. But even then,
30:43
Speaker 1: the journey was nowhere near finished. The spacecraft had crossed
30:47
Speaker 1: the Sun's great bubble of particles. It had not crossed
30:51
Speaker 1: the Sun's entire gravitational neighbourhood. There is something peaceful about
30:56
Speaker 1: that distinction. The sun does not have a single obvious edge.
31:01
Speaker 1: Its light fades with distance. Its particles spread outward. Its
31:06
Speaker 1: magnetic influence changes. Its gravity reaches still farther. And beyond
31:12
Speaker 1: all of this, the sun's distant family of icy bodies
31:15
Speaker 1: may continue outward into an enormous, nearly spherical region. So
31:20
Speaker 1: perhaps the solar system is less like a room with
31:22
Speaker 1: walls and more like a collection of overlapping circles of influence.
31:27
Speaker 1: One fades into another. One becomes less important, while another
31:32
Speaker 1: becomes more noticeable. There is no single moment when the
31:36
Speaker 1: universe announces that you have finally left. You simply keep drifting,
31:41
Speaker 1: and the farther you go, the quieter the sun becomes.
31:45
Speaker 1: Imagine looking back now. The sun is still visible, but
31:49
Speaker 1: it is smaller. The planets are almost impossible to distinguish.
31:53
Speaker 1: The broad planetary plane has become only a memory of geometry.
31:58
Speaker 1: And yet, around you, the sun's influence continues. The heliosphere
32:04
Speaker 1: stretches behind you like an enormous invisible shelter. Beyond it
32:09
Speaker 1: lies the space between stars. But even there, the journey
32:14
Speaker 1: is not finished. Because the solar system contains a region
32:18
Speaker 1: so distant and so difficult to observe directly that scientists
32:22
Speaker 1: know it mostly through the paths of objects that occasionally
32:26
Speaker 1: return from its darkness. A vast reservoir of ancient ice.
32:31
Speaker 1: A nearly spherical cloud surrounding the sun. A region so
32:36
Speaker 1: large that even the fastest spacecraft humans have built would
32:40
Speaker 1: need thousands upon thousands of years to cross its broader reaches.
32:45
Speaker 1: You are approaching the Oort cloud now, at least in imagination.
32:49
Speaker 1: And as you drift toward it, the familiar solar system
32:53
Speaker 1: becomes quieter still. There are no bright planets waiting ahead.
32:58
Speaker 1: no rings. No moons, only darkness, scattered sunlight, and countless
33:04
Speaker 1: small pieces of frozen material moving slowly through an immense
33:08
Speaker 1: gravitational landscape. And somewhere in that darkness, the sun's distant
33:14
Speaker 1: family continues to orbit, almost unseen, almost forgotten, waiting patiently
33:20
Speaker 1: at the farthest edge of our familiar cosmic neighbourhood. you
33:27
Speaker 1: have drifted far beyond the familiar planets now, and behind you,
33:31
Speaker 1: the sun has become a smaller light in the darkness.
33:35
Speaker 1: The heliosphere, that enormous region shaped by the sun's outward
33:39
Speaker 1: stream of particles, stretches behind you like an invisible boundary
33:44
Speaker 1: of influence. But even after crossing that distant region, you
33:48
Speaker 1: have not reached a simple edge of the solar system.
33:51
Speaker 1: There is still more, much more, and this time, The
33:56
Speaker 1: thing waiting ahead is almost impossible to see. You are
34:00
Speaker 1: entering the realm of the Oort Cloud. The name sounds
34:04
Speaker 1: like something distant and complicated, but the basic idea is
34:08
Speaker 1: wonderfully simple. Far beyond the known planets, scientists think there
34:13
Speaker 1: may be an enormous population of icy objects surrounding the Sun,
34:18
Speaker 1: not in a thin, flat disk like the planets, not
34:21
Speaker 1: arranged in neat circular lanes. Instead, These distant objects are
34:26
Speaker 1: thought to be spread around the sun in something closer
34:30
Speaker 1: to a vast sphere. You can imagine yourself floating at
34:33
Speaker 1: its outer edge, although there would be no visible edge
34:37
Speaker 1: to stand upon. No glowing boundary. No sign saying that
34:41
Speaker 1: you have arrived. Only darkness. And scattered through that darkness, perhaps,
34:47
Speaker 1: tiny pieces of ancient ice. The Oort cloud has never
34:51
Speaker 1: been photographed directly. That is important. When you see an
34:55
Speaker 1: illustration of it, you are not looking at a photograph
34:58
Speaker 1: from a spacecraft. You are looking at a scientific representation,
35:03
Speaker 1: built from what we can infer about the distant objects
35:06
Speaker 1: that sometimes travel inward toward the sun. And one of
35:10
Speaker 1: the most beautiful clues comes from comets. Every so often,
35:14
Speaker 1: a comet appears in the inner solar system. It may
35:17
Speaker 1: travel inward from a tremendous distance, pass near the sun,
35:22
Speaker 1: brighten in the sunlight, and then begin the long journey
35:25
Speaker 1: outward again. Some of these comets follow very long, stretched-out paths.
35:31
Speaker 1: Their orbits can arrive from many different directions, and when
35:35
Speaker 1: astronomers study those paths they find patterns suggesting that many
35:39
Speaker 1: of these long-period comets may have originated in a distant,
35:43
Speaker 1: roughly spherical reservoir surrounding the Sun. That reservoir is what
35:48
Speaker 1: we call the Oort Cloud. So instead of seeing the
35:51
Speaker 1: cloud itself, You see its footprints. You see icy visitors
35:56
Speaker 1: arriving from the darkness. You watch their paths. You trace
36:00
Speaker 1: those paths backward. And slowly, from these faint clues, a
36:05
Speaker 1: picture begins to emerge. It is a quiet kind of astronomy.
36:10
Speaker 1: Nothing needs to flash. Nothing needs to announce itself. You
36:14
Speaker 1: simply notice where something has been travelling, and from that
36:18
Speaker 1: motion you begin to understand where it may have come from.
36:22
Speaker 1: This also changes the way you think about Pluto. Pluto
36:25
Speaker 1: feels extraordinarily far away from Earth. It takes sunlight hours
36:30
Speaker 1: to reach the outer planets, and the distances involved are
36:34
Speaker 1: enormous by human standards. Yet compared with the possible scale
36:39
Speaker 1: of the Oort cloud, Pluto is still relatively close to
36:42
Speaker 1: the Sun. The familiar planetary solar system is only a
36:46
Speaker 1: small inner region of a much larger gravitational neighbourhood. You
36:51
Speaker 1: could imagine the planets gathered near the centre, like a
36:54
Speaker 1: small collection of lights. Farther out, the heliosphere surrounds them.
36:59
Speaker 1: Farther still, the distant population of icy bodies may continue
37:03
Speaker 1: in every direction. And suddenly, the solar system stops looking
37:08
Speaker 1: like a little diagram. It becomes something enormous, something almost
37:13
Speaker 1: too large for the human mind to hold at once.
37:17
Speaker 1: Even the spacecraft that have travelled farther than any other
37:20
Speaker 1: human-made machines are still only beginning to cross these distances.
37:25
Speaker 1: Voyager 2, after decades of travel, reached interstellar space by
37:30
Speaker 1: crossing the heliopause. But reaching the heliopause is very different
37:35
Speaker 1: from crossing the Oort Cloud. The timescale changes completely. A
37:40
Speaker 1: spacecraft travelling outward could take centuries just to approach the
37:44
Speaker 1: inner regions associated with the Oort Cloud. and crossing the
37:48
Speaker 1: broader cloud could take tens of thousands of years. You
37:52
Speaker 1: do not need to picture yourself waiting that long. Instead,
37:57
Speaker 1: let the number become a feeling. A human lifetime is short.
38:01
Speaker 1: A civilisation is still short. A spacecraft mission lasting a
38:05
Speaker 1: few decades is almost nothing on this scale. The Oort
38:09
Speaker 1: cloud belongs to a different rhythm, a rhythm measured in thousands,
38:13
Speaker 1: perhaps millions of years. Objects can remain there for unimaginable
38:17
Speaker 1: stretches of time. They drift around the sun in the
38:20
Speaker 1: deep cold, receiving only a faint amount of sunlight. They wait,
38:25
Speaker 1: and sometimes something changes. A passing star can disturb the
38:30
Speaker 1: delicate balance of a distant icy body. The gravity of
38:34
Speaker 1: the Milky Way can slowly influence its path. A collection
38:38
Speaker 1: of distant objects can be gently rearranged. And occasionally... an
38:43
Speaker 1: object may begin falling inward toward the Sun. One example
38:47
Speaker 1: from the history of our stellar neighbourhood involves a small
38:50
Speaker 1: star system known as Schultz's star. Roughly 80,000 years ago,
38:56
Speaker 1: this nearby stellar system passed through or very close to
39:00
Speaker 1: the outer region of the Oort cloud. Its gravity may
39:03
Speaker 1: have disturbed some of the distant icy bodies there. Perhaps
39:07
Speaker 1: a few were nudged onto different paths. Perhaps some began
39:11
Speaker 1: journeys inward, But even then, nothing would have happened quickly.
39:16
Speaker 1: An object disturbed in the distant Oort cloud might take
39:20
Speaker 1: millions of years to reach the inner solar system. There
39:23
Speaker 1: is something deeply calming about that timescale. A tiny gravitational
39:28
Speaker 1: change happens. then silence. For thousands of years, for hundreds
39:33
Speaker 1: of thousands, for millions. The object continues drifting. No one
39:39
Speaker 1: is watching. No one is waiting. And yet gravity keeps
39:43
Speaker 1: quietly shaping its path. You can imagine one of those
39:47
Speaker 1: icy bodies moving through the darkness now, It does not
39:50
Speaker 1: shine brightly like a star. It does not announce its presence.
39:55
Speaker 1: It is simply a small, cold object travelling around a
39:58
Speaker 1: distant sun. Perhaps another star passes far away. Its gravity
40:04
Speaker 1: gently changes the orbit. The change is almost impossible to notice.
40:09
Speaker 1: But over immense stretches of time, a tiny change can
40:12
Speaker 1: become a completely different journey. This is one of the
40:16
Speaker 1: reasons the solar system cannot be understood simply by looking
40:19
Speaker 1: at the planets. The planets are only the bright, nearby
40:23
Speaker 1: portion of the story. Beyond them are distant objects. Beyond
40:28
Speaker 1: those objects is interstellar space. And beyond interstellar space is
40:34
Speaker 1: the larger structure of the Milky Way. You are slowly
40:37
Speaker 1: leaving behind the region that humans have explored directly. The
40:42
Speaker 1: spacecraft become fewer. The measurements become harder, the objects become fainter,
40:48
Speaker 1: but the gravitational connection remains. The sun is still the
40:53
Speaker 1: centre of this vast family. Even where its light is weak,
40:57
Speaker 1: its gravity can still matter. And as you drift farther away,
41:02
Speaker 1: you begin to understand why asking where the solar system
41:05
Speaker 1: ends is not as simple as drawing a circle around Pluto.
41:09
Speaker 1: There are several different meanings of edge. There is the
41:13
Speaker 1: region dominated by the solar wind. There is the region
41:17
Speaker 1: where the sun's gravity continues to influence distant objects. There
41:21
Speaker 1: is the possible reservoir of ancient icy bodies surrounding the sun.
41:26
Speaker 1: And beyond all of these, there is the space between stars.
41:30
Speaker 1: You are approaching that space now. The sun behind you
41:34
Speaker 1: is becoming quieter. The Oort cloud, if you could somehow
41:37
Speaker 1: see it, would not look like a glowing cloud. It
41:41
Speaker 1: would be mostly darkness. A vast, cold, almost invisible population
41:46
Speaker 1: of distant objects. And beyond it, the darkness becomes even
41:51
Speaker 1: more open. You are no longer simply above the planets.
41:55
Speaker 1: You are moving through the enormous space between stars. There
41:59
Speaker 1: are still atoms here. There is still dust. There are
42:03
Speaker 1: magnetic fields and faint traces of matter. But everything is
42:07
Speaker 1: spread so thinly that that the emptiness itself begins to
42:10
Speaker 1: feel like the dominant presence, and as you drift into
42:14
Speaker 1: that quiet region, the solar system becomes something very small
42:18
Speaker 1: behind you, not gone, not truly left behind, just smaller,
42:23
Speaker 1: a tiny stellar neighbourhood moving peacefully through something much larger,
42:28
Speaker 1: and somewhere ahead, beyond the sun's distant family of icy worlds,
42:33
Speaker 1: you are about to enter the space that belongs not
42:36
Speaker 1: to one star, but to the space between stars themselves.
42:43
Speaker 1: You have drifted farther now, beyond the familiar worlds, beyond
42:47
Speaker 1: the region where the sun's outward breath dominates the space
42:51
Speaker 1: around it, and beyond the distant realm where ancient icy
42:55
Speaker 1: bodies may quietly circle our star. Behind you, the solar
43:00
Speaker 1: system has become very small. The sun is still there,
43:04
Speaker 1: still shining, still carrying its warmth across the darkness. but
43:08
Speaker 1: from where you are now, its light feels softer, more distant,
43:12
Speaker 1: almost like a small lamp left glowing in another room.
43:16
Speaker 1: Ahead of you is something that sounds like emptiness, interstellar space,
43:20
Speaker 1: the space between stars. It is easy to imagine this
43:24
Speaker 1: region as absolutely nothing, a perfect blackness containing no matter
43:29
Speaker 1: at all. But the universe is rarely quite that simple.
43:34
Speaker 1: Even here, where enormous distances separate one star from another,
43:39
Speaker 1: there are still tiny traces of matter drifting through the darkness.
43:43
Speaker 1: There are atoms. There are charged particles. There are incredibly
43:48
Speaker 1: small grains of dust. There are magnetic fields. There is
43:52
Speaker 1: radiation passing quietly from one place to another. The difference
43:57
Speaker 1: is that everything is spread so thinly that the space
44:00
Speaker 1: around you still feels almost completely empty. You could drift
44:05
Speaker 1: for an enormous distance without coming close to another object.
44:09
Speaker 1: And that is one of the strange things about travelling
44:11
Speaker 1: through space. The farther you go, the less the universe
44:15
Speaker 1: resembles a crowded collection of objects. Instead, it becomes a
44:20
Speaker 1: landscape of enormous distances, with tiny amounts of matter scattered
44:25
Speaker 1: gently through them. Our solar system itself is moving through
44:29
Speaker 1: this thin environment. At the moment, the Sun and its
44:33
Speaker 1: planets are passing through a small region of interstellar material
44:37
Speaker 1: known as the Local Interstellar Cloud. The name sounds grand,
44:42
Speaker 1: but there is nothing like an ordinary cloud here. You
44:45
Speaker 1: would not see a pale mist surrounding your spacecraft. You
44:49
Speaker 1: would not feel moisture against the windows. It is simply
44:53
Speaker 1: a slightly denser patch of extremely thin gas and dust
44:57
Speaker 1: within the space between stars. Compared with the air around
45:01
Speaker 1: you on Earth, it is almost unimaginably sparse. And yet,
45:06
Speaker 1: compared with the surrounding regions of interstellar space, it is
45:09
Speaker 1: enough to give astronomers a way to describe our immediate
45:13
Speaker 1: stellar neighbourhood. So imagine yourself drifting through it now. The
45:17
Speaker 1: spacecraft is silent. The windows show almost nothing. A few
45:22
Speaker 1: particles pass through the surrounding space. Perhaps a tiny grain
45:26
Speaker 1: of dust is moving somewhere far away. There is no wind,
45:30
Speaker 1: there is no sound, only motion so slow and distances
45:35
Speaker 1: so large that the difference between movement and stillness becomes
45:38
Speaker 1: difficult to feel. And around this neighbourhood lies something much larger,
45:44
Speaker 1: the local bubble. You can think of it as an enormous,
45:47
Speaker 1: low-density cavity in our region of the Milky Way, extending
45:52
Speaker 1: across roughly a thousand light-years. Again, it is not a
45:56
Speaker 1: bubble like the ones you see floating through the air.
45:59
Speaker 1: There is no shiny surface, no shell that you could touch.
46:03
Speaker 1: It is simply a large region of space, where the
46:06
Speaker 1: gas is thinner than in many of the surrounding areas.
46:10
Speaker 1: And this great cavity appears to have a long history.
46:13
Speaker 1: Long before humans were here, long before Earth had the
46:17
Speaker 1: familiar landscapes you know today, massive stars lived and eventually
46:22
Speaker 1: died in our broader stellar neighbourhood. Some ended their lives
46:26
Speaker 1: in enormous explosions called supernovae. Those explosions released energy and
46:32
Speaker 1: material into surrounding space. Over immense periods of time, repeated
46:37
Speaker 1: stellar events could shape the gas around them, pushing material
46:41
Speaker 1: outward and creating large, complicated regions of lower and higher density.
46:47
Speaker 1: The quiet cavity around our solar system may be part
46:51
Speaker 1: of that ancient story. You can imagine the galaxy changing
46:55
Speaker 1: very slowly. Stars are born, stars live, stars disappear, their
47:01
Speaker 1: remains spread outward, the surrounding gas shifts. Then, after millions
47:07
Speaker 1: of years, the shapes created by those ancient events are
47:12
Speaker 1: still influencing the neighbourhood where the sun now travels. There
47:16
Speaker 1: is something strangely peaceful about this kind of history. You
47:20
Speaker 1: do not need to imagine the explosion itself. You do
47:23
Speaker 1: not need to hear it. By the time you arrive,
47:26
Speaker 1: there is no dramatic event left to witness. There is
47:30
Speaker 1: only the evidence. A faint trace. A changed environment. A
47:35
Speaker 1: chemical signature preserved in places where scientists can still find it.
47:40
Speaker 1: One of those clues is a radioactive form of iron
47:43
Speaker 1: known as iron-60. Scientists have found traces of iron-60 in
47:48
Speaker 1: deep-sea sediments on Earth. These deposits provide evidence that material
47:53
Speaker 1: from relatively nearby stellar explosions reached our solar system in
47:57
Speaker 1: the past. Think about that for a moment. Something happened
48:01
Speaker 1: far away. A massive star ended its life. Material travelled
48:06
Speaker 1: through interstellar space. And much later, tiny traces of that
48:11
Speaker 1: ancient stellar material became part of the sediments resting quietly
48:16
Speaker 1: beneath Earth's oceans. There is no need to imagine the
48:20
Speaker 1: material arriving as a dramatic wave. It was a slow,
48:24
Speaker 1: delicate process. Tiny particles settling, layers accumulating, years passing, then centuries,
48:34
Speaker 1: then thousands of years, then millions, and eventually, long after
48:39
Speaker 1: the original stars had vanished, humans came along and found
48:43
Speaker 1: the traces. You are still drifting, The earth is still
48:48
Speaker 1: far behind you. The sun is still moving through the
48:51
Speaker 1: local bubble, and the stars around you are participating in
48:55
Speaker 1: a much larger pattern that takes millions of years to change.
48:59
Speaker 1: This is another way of understanding why space can feel
49:03
Speaker 1: empty while still being full of history. The distances are enormous.
49:08
Speaker 1: The material is sparse. The events are slow, but nothing
49:13
Speaker 1: is entirely disconnected. a star can change the space around it.
49:17
Speaker 1: A passing star can gently disturb distant comets. Ancient explosions
49:22
Speaker 1: can leave traces in interstellar material. The sun can move
49:26
Speaker 1: through different clouds of gas and dust as it travels
49:30
Speaker 1: around the Milky Way. And Earth, quietly carried along with
49:34
Speaker 1: the sun, moves through all of it. You may have
49:38
Speaker 1: begun this journey by asking what lies above the solar system,
49:42
Speaker 1: but the farther you drift, the more that question begins
49:45
Speaker 1: to change. Above the solar system, you might find the
49:49
Speaker 1: heliosphere from a different angle. Farther away you might encounter
49:54
Speaker 1: the distant Oort cloud, and beyond that, there is not
49:58
Speaker 1: a simple above, there is simply the space between stars.
50:02
Speaker 1: The local interstellar cloud is not above us. The local
50:06
Speaker 1: bubble is not above us. They surround our region of space.
50:11
Speaker 1: Their boundaries and structures exist in three dimensions, extending in
50:16
Speaker 1: directions that do not fit neatly into a single vertical line.
50:20
Speaker 1: And this is where the idea of up becomes increasingly fragile.
50:25
Speaker 1: On Earth, up is easy. Your feet point toward the ground.
50:30
Speaker 1: Your head points toward the sky. Gravity gives you a
50:34
Speaker 1: natural reference. But once you are floating between stars, there
50:38
Speaker 1: is no floor beneath you. There is no ceiling above you.
50:42
Speaker 1: There is only a chosen direction. You can call one
50:46
Speaker 1: direction north. You can call another direction toward the centre
50:50
Speaker 1: of the Milky Way. You can call another direction away
50:53
Speaker 1: from the galactic disk. But these names are descriptions, not
50:58
Speaker 1: universal laws. The universe does not mark one direction as
51:02
Speaker 1: the correct one. And as you continue drifting, the solar
51:06
Speaker 1: system becomes smaller behind you, while the Milky Way slowly
51:10
Speaker 1: begins to reveal itself as the larger structure surrounding your journey.
51:15
Speaker 1: The Sun is only one star among hundreds of billions.
51:19
Speaker 1: Our planetary plane is only one small orientation inside that galaxy.
51:24
Speaker 1: And the galaxy itself extends far beyond what you can
51:27
Speaker 1: see from Earth. Somewhere farther away, above the broad disk
51:32
Speaker 1: of stars, There are enormous structures that have nothing to
51:35
Speaker 1: do with the simple plane of our planets. Long streams
51:39
Speaker 1: of stars, huge clouds of energetic particles, and an invisible
51:44
Speaker 1: gravitational halo surrounding the entire galaxy. You do not need
51:49
Speaker 1: to rush toward them. For now, you can simply remain here,
51:53
Speaker 1: suspended in the thin space between the stars, feeling how
51:57
Speaker 1: the word empty has slowly changed its meaning. It is
52:02
Speaker 1: not nothing. It is a quiet place filled with distance,
52:06
Speaker 1: faint matter, ancient traces, and very slow motion. And as
52:11
Speaker 1: the Milky Way begins to widen around you, the solar
52:14
Speaker 1: system becomes only one tiny part of a much larger landscape,
52:19
Speaker 1: waiting quietly beyond the darkness. You are drifting now far
52:25
Speaker 1: beyond the familiar neighbourhood of the sun, far beyond the planet's,
52:29
Speaker 1: beyond the distant region where the sun's particles slowly give
52:33
Speaker 1: way to the space between stars. The solar system is
52:36
Speaker 1: still with you, but it has become very small. Behind
52:40
Speaker 1: you there is a star, a collection of planets, moons, comets,
52:45
Speaker 1: and countless pieces of ancient material, all gathered together in
52:49
Speaker 1: one quiet corner of the Milky Way. And as you
52:52
Speaker 1: continue to drift, you begin to see that the solar
52:55
Speaker 1: system itself is not a separate universe. It is part
53:00
Speaker 1: of something much larger, the Milky Way. From Earth, you
53:05
Speaker 1: usually experience the galaxy from inside it. You see a
53:08
Speaker 1: pale band of light stretching across the night sky. You
53:12
Speaker 1: see individual stars scattered above you. But you do not
53:16
Speaker 1: see the entire structure. You cannot simply step outside the
53:20
Speaker 1: galaxy and look back. So, for a moment, imagine that
53:24
Speaker 1: you could. Imagine yourself rising far above the broad disk
53:28
Speaker 1: of stars. The Milky Way spreads beneath you. Its countless
53:32
Speaker 1: stars form a vast, slowly turning structure. There are clouds
53:37
Speaker 1: of gas and dust. There are regions where new stars
53:41
Speaker 1: are being born. There are older stars moving through the galaxy.
53:45
Speaker 1: And somewhere within that enormous disk is the small solar
53:49
Speaker 1: system you have been leaving behind. From this distant perspective,
53:54
Speaker 1: the word above begins to become even stranger. You might
53:58
Speaker 1: say that you are above the Milky Way. But what
54:01
Speaker 1: does that really mean? It simply means that you have
54:04
Speaker 1: chosen the plane of the galaxy as your reference. You
54:08
Speaker 1: have decided that the broad disk of stars is your
54:11
Speaker 1: horizontal surface, and that moving away from it is upward.
54:16
Speaker 1: But the universe has not made that decision for you.
54:19
Speaker 1: There is no universal ceiling above the Milky Way. There
54:23
Speaker 1: is no cosmic floor beneath it. There is only a
54:26
Speaker 1: direction you have chosen to describe your position. And the
54:29
Speaker 1: same thing was true much closer to home. The planetary
54:33
Speaker 1: plane was not a cosmic flaw. It was simply the
54:36
Speaker 1: broad plane inherited from the rotating cloud that formed our
54:40
Speaker 1: solar system. Now, from far above the galaxy, you can
54:44
Speaker 1: see another important structure. A long stream of stars stretches
54:48
Speaker 1: away from the Milky Way. It is called the Sagittarius Stream.
54:53
Speaker 1: It is associated with a small dwarf galaxy that has
54:56
Speaker 1: been gradually disrupted by the much larger gravitational presence of
55:00
Speaker 1: the Milky Way. You can imagine it as a long
55:03
Speaker 1: trail left behind as the smaller galaxy travels around its
55:07
Speaker 1: larger neighbour. Stars are pulled away. Their paths are stretched.
55:12
Speaker 1: The original small galaxy becomes increasingly difficult to recognise as
55:17
Speaker 1: a separate object. Over enormous periods of time, gravity slowly
55:22
Speaker 1: rearranges the system. Nothing needs to happen quickly. A star moves,
55:27
Speaker 1: another star moves, the galaxy turns. And after millions or
55:32
Speaker 1: billions of years, the shape becomes something very different from
55:36
Speaker 1: where it began. The Sagittarius stream is therefore not simply
55:40
Speaker 1: something sitting above the solar system. It belongs to the
55:45
Speaker 1: larger architecture of the galaxy. It reminds you that even
55:49
Speaker 1: the Milky Way is not a perfectly isolated, unchanging disk.
55:53
Speaker 1: It interacts with its surroundings. It pulls. It bends. It gathers.
55:59
Speaker 1: It reshapes. And if you continue drifting toward the region
56:03
Speaker 1: above the galactic centre, another enormous structure comes into view.
56:09
Speaker 1: Two vast regions of energetic material extend above and below
56:13
Speaker 1: the centre of the Milky Way. These are known as
56:16
Speaker 1: the Fermi bubbles. They stretch tens of thousands of light-years
56:20
Speaker 1: from the galactic centre. Try not to imagine them as
56:24
Speaker 1: ordinary bubbles floating through space. They are enormous regions filled
56:28
Speaker 1: with energetic gas and particles, detected through high-energy light. From
56:34
Speaker 1: your imagined viewpoint, they might look like two enormous lobes
56:38
Speaker 1: rising from the centre of the galaxy, one extending above
56:42
Speaker 1: the galactic plane and another extending below it. But even here,
56:47
Speaker 1: the word above is only relative. One lobe is above
56:52
Speaker 1: because we have chosen the galactic disk as our reference plane.
56:56
Speaker 1: The other is below for the same reason. The structures
56:59
Speaker 1: themselves do not know which one we have named up.
57:02
Speaker 1: Scientists are still studying how these enormous regions formed. One
57:07
Speaker 1: possibility is that they were created by past activity associated
57:11
Speaker 1: with the supermassive black hole at the centre of the
57:14
Speaker 1: Milky Way. known as Sagittarius, a star. Another possibility involves
57:20
Speaker 1: periods of intense star formation near the galactic centre. There
57:24
Speaker 1: may be more than one process involved, and you do
57:27
Speaker 1: not need to decide between them tonight. It is enough
57:30
Speaker 1: to imagine that something happened long ago near the centre
57:33
Speaker 1: of our galaxy, something energetic enough to leave a structure
57:38
Speaker 1: that can still be observed today. The universe is full
57:42
Speaker 1: of these old traces. Events happen, The light travels. Particles move.
57:48
Speaker 1: And long after the original event has faded, its consequences
57:52
Speaker 1: can remain visible. You continue drifting. The galactic disk grows
57:57
Speaker 1: smaller beneath you. And now, as you move farther away,
58:01
Speaker 1: another invisible structure begins to matter. You cannot see it.
58:05
Speaker 1: You cannot photograph it directly. But without it, the motions
58:09
Speaker 1: of galaxies would be difficult to understand. It is called
58:13
Speaker 1: dark matter. The name can make it sound mysterious, but
58:17
Speaker 1: the basic idea is quite gentle. Astronomers observe the way
58:22
Speaker 1: stars and galaxies move. They observe how galaxies rotate. They
58:27
Speaker 1: observe how groups of galaxies travel. They observe how gravity
58:31
Speaker 1: bends light from more distant objects. And again and again,
58:36
Speaker 1: the amount of visible matter does not seem sufficient to
58:39
Speaker 1: explain all of the gravitational behaviour. Something else appears to
58:44
Speaker 1: be contributing to the gravity. That unseen contribution is what
58:49
Speaker 1: scientists call dark matter. You can imagine a vast invisible
58:54
Speaker 1: halo surrounding the Milky Way. It is much larger than
58:58
Speaker 1: the bright disk of stars. The stars are what you
59:01
Speaker 1: can see. The dark matter is inferred from what gravity does.
59:06
Speaker 1: And this distinction matters. Dark matter has not been directly
59:10
Speaker 1: detected as a substance in the way that ordinary matter has.
59:15
Speaker 1: Scientists have strong evidence for its gravitational effects, but the
59:19
Speaker 1: physical nature of dark matter remains unknown. So, as you
59:23
Speaker 1: drift farther above the galaxy … you are moving into
59:27
Speaker 1: a region where much of the structure around you cannot
59:29
Speaker 1: be seen directly. The visible Milky Way becomes only one
59:33
Speaker 1: part of the picture. There are stars, there is gas,
59:37
Speaker 1: there is dust. There are energetic particles, and there appears
59:42
Speaker 1: to be a much larger invisible gravitational halo surrounding them.
59:46
Speaker 1: The galaxy itself is therefore not a flat island floating
59:50
Speaker 1: in an otherwise empty universe. It is a three-dimensional structure.
59:55
Speaker 1: It has depth, It has motion. It has streams and
59:59
Speaker 1: bubbles and invisible mass. And your solar system is somewhere
1:00:03
Speaker 1: inside all of it. Think back to where you began.
1:00:07
Speaker 1: You were lying on Earth. Earth was moving around the Sun.
1:00:11
Speaker 1: The planets were travelling in their broad orbital plane. You
1:00:15
Speaker 1: imagined yourself flying upward. At first, up seemed like a
1:00:19
Speaker 1: simple direction. Then you learned that changing direction is difficult
1:00:23
Speaker 1: because you were already moving sideways. Then you imagined Ulysses
1:00:27
Speaker 1: rising high above the Sun. Then you travelled beyond the heliosphere.
1:00:32
Speaker 1: Then toward the distant Oort cloud. Then into the space
1:00:36
Speaker 1: between stars. And now, from far above the Milky Way,
1:00:40
Speaker 1: you can see that every version of Up was created
1:00:43
Speaker 1: by choosing something as a reference. The planetary plane. The
1:00:48
Speaker 1: solar equator. The galactic disk. Each gives you a different
1:00:52
Speaker 1: way to describe direction. None is the universal one. You
1:00:57
Speaker 1: can choose to move above the galaxy. You can choose
1:01:01
Speaker 1: to move below it. You can turn toward the galactic centre.
1:01:05
Speaker 1: You can turn away. All of these are meaningful descriptions.
1:01:09
Speaker 1: But none is the cosmic direction of up. And perhaps
1:01:13
Speaker 1: this is why space feels so different from Earth. On Earth,
1:01:17
Speaker 1: gravity gives you a constant sense of orientation. Your body
1:01:21
Speaker 1: knows where the ground is. Your feet know which way
1:01:24
Speaker 1: to point. But in deep space, there is no ground
1:01:28
Speaker 1: waiting beneath you. You are not climbing. You are not falling.
1:01:33
Speaker 1: You are simply moving. And now, as you drift farther
1:01:36
Speaker 1: from the Milky Way, the galaxy slowly becomes another distant
1:01:41
Speaker 1: shape beneath you. The old question remains, what is above
1:01:45
Speaker 1: the solar system? The answer is becoming wonderfully simple. Whatever
1:01:50
Speaker 1: direction you choose, and somewhere beyond the direction you have
1:01:54
Speaker 1: called upward, The universe continues without a ceiling, without a floor,
1:02:00
Speaker 1: and without any need for you to decide which way
1:02:03
Speaker 1: is truly up. You are still drifting, very quietly, far
1:02:10
Speaker 1: from the earth, far from the planets, and now far
1:02:13
Speaker 1: enough from the Milky Way that even the enormous galaxy
1:02:17
Speaker 1: beneath you has begun to feel like a distant island
1:02:20
Speaker 1: of light. There is no floor here, there is no ceiling,
1:02:24
Speaker 1: There is no obvious direction in which you are supposed
1:02:27
Speaker 1: to travel. And perhaps, after everything you have seen, that
1:02:31
Speaker 1: feels less strange than it once did. You began this
1:02:35
Speaker 1: journey with a very human idea. You imagined yourself standing
1:02:39
Speaker 1: somewhere inside the solar system, looking upward and wondering what
1:02:43
Speaker 1: might be there. It seemed natural. Earth has a ground.
1:02:48
Speaker 1: Earth has a sky. So when you think about the
1:02:51
Speaker 1: solar system, you might instinctively imagine that it has a
1:02:55
Speaker 1: similar arrangement, with something below and something above. But space
1:03:00
Speaker 1: does not work that way. The solar system has a
1:03:03
Speaker 1: planetary plane because of the way it formed. The planets
1:03:07
Speaker 1: inherited much of the motion of the ancient cloud of
1:03:10
Speaker 1: gas and dust that surrounded the young sun. That original
1:03:14
Speaker 1: cloud rotated. Gravity drew it inward. As it became smaller,
1:03:19
Speaker 1: its material gradually settled into a broad disc. The sun
1:03:24
Speaker 1: formed at the centre. The planets grew from the material
1:03:27
Speaker 1: around it. And so, billions of years later, you still
1:03:31
Speaker 1: see the memory of that ancient rotation in the paths
1:03:34
Speaker 1: of the planets. But a memory is not a wall.
1:03:38
Speaker 1: The planetary plane is not a physical surface. You can
1:03:42
Speaker 1: cross it. You can rise above it. You can travel
1:03:45
Speaker 1: beneath it. You can turn almost any direction you like.
1:03:49
Speaker 1: The difficult part is not escaping a cage. The difficult
1:03:53
Speaker 1: part is changing your motion. Earth already carries you around
1:03:57
Speaker 1: the Sun. Your spacecraft begins with that sideways movement. To
1:04:02
Speaker 1: redirect it dramatically, you need energy. And so spacecraft engineers
1:04:07
Speaker 1: often use the natural movements of the solar system itself.
1:04:12
Speaker 1: Gravity assists can bend trajectories. Planets can become quiet gravitational partners.
1:04:19
Speaker 1: A spacecraft can borrow a little of the motion of
1:04:21
Speaker 1: a moving world, and leave along a very different path.
1:04:26
Speaker 1: Ulysses showed how powerful this idea could be. By using
1:04:30
Speaker 1: Jupiter's gravity, it reached an orbit tilted by almost 80
1:04:34
Speaker 1: degrees relative to the planetary plane. It passed over the
1:04:38
Speaker 1: northern and southern regions of the Sun. And yet, even
1:04:42
Speaker 1: that remarkable journey did not reveal a universal top or bottom.
1:04:48
Speaker 1: It simply gave us another viewpoint. Then you travelled farther.
1:04:53
Speaker 1: You crossed the region where the solar wind gives way
1:04:56
Speaker 1: to the surrounding interstellar environment. You imagined the heliopause, not
1:05:01
Speaker 1: as a solid shell, but as a gradual boundary where
1:05:05
Speaker 1: the sun's outward influence becomes less dominant. Beyond it, you
1:05:10
Speaker 1: entered the thin space between stars. You passed through the
1:05:13
Speaker 1: kind of sparse environment surrounding our solar system today. Within
1:05:18
Speaker 1: the broader region, astronomers call the local bubble. And eventually
1:05:23
Speaker 1: you looked farther still, toward the distant Oort cloud, where
1:05:28
Speaker 1: ancient icy objects may surround the sun in an enormous,
1:05:32
Speaker 1: almost spherical reservoir. Even there, the word above began to
1:05:38
Speaker 1: lose its meaning. Because a sphere does not have one top,
1:05:43
Speaker 1: the sun can be surrounded from every direction. And the
1:05:46
Speaker 1: same is true when you look at the Milky Way.
1:05:49
Speaker 1: The galaxy has a broad disc. It has streams of stars.
1:05:53
Speaker 1: It has enormous energetic structures extending above and below its
1:05:58
Speaker 1: central region. It appears to have a vast dark matter
1:06:01
Speaker 1: halo surrounding its visible structure. But once again, above and
1:06:06
Speaker 1: below are descriptions we create by choosing a reference. The
1:06:11
Speaker 1: Fermi bubbles appear above and below the galactic disk, because
1:06:16
Speaker 1: we have decided that the disk is our horizontal reference.
1:06:20
Speaker 1: If you rotated your imaginary viewpoint, the same universe would
1:06:24
Speaker 1: look different. The galaxy would not physically rotate itself simply
1:06:28
Speaker 1: because you changed your perspective. Only your description would change.
1:06:33
Speaker 1: This is one of the quiet freedoms of space. There
1:06:36
Speaker 1: is no privileged viewpoint. There is no universal camera position.
1:06:41
Speaker 1: There is no cosmic photograph taken from the one correct direction.
1:06:46
Speaker 1: Every perspective is local. Every direction is relative to something.
1:06:51
Speaker 1: You can say that the sun is above the galactic plane.
1:06:55
Speaker 1: You can say that it is below another chosen plane.
1:06:58
Speaker 1: You can describe a spacecraft as moving north, south, inward, outward,
1:07:04
Speaker 1: above or below. Each word can be useful. But none
1:07:08
Speaker 1: of those words belongs to the universe itself. They belong
1:07:12
Speaker 1: to you. And perhaps that is why the solar system
1:07:15
Speaker 1: can be so difficult to picture. The diagrams we use
1:07:19
Speaker 1: are wonderfully helpful. They give the planets names, they show
1:07:23
Speaker 1: their orbits, they place the sun in the centre. They
1:07:26
Speaker 1: allow you to imagine the system at a glance. But
1:07:29
Speaker 1: the real solar system is three-dimensional, constantly moving, and almost
1:07:34
Speaker 1: completely dark. If you could somehow float far above it
1:07:38
Speaker 1: and photograph everything at once, you would not see the
1:07:42
Speaker 1: neat glowing lines that appear in textbooks. The sun would
1:07:46
Speaker 1: be bright. The planets would be tiny. Many would be
1:07:49
Speaker 1: nearly invisible against the stars. The orbital paths would have
1:07:54
Speaker 1: to be added afterward as information. And even then, the
1:07:58
Speaker 1: picture would show only one moment from one chosen perspective.
1:08:03
Speaker 1: Change your position and the picture changes. Turn around and
1:08:07
Speaker 1: your sense of direction changes. Move farther away and the
1:08:12
Speaker 1: solar system becomes smaller. Move farther still and the Milky
1:08:16
Speaker 1: Way becomes the more important structure. Continue outward, and even
1:08:21
Speaker 1: the Milky Way becomes one galaxy among countless others. There
1:08:25
Speaker 1: is no final place from which you can stand outside
1:08:27
Speaker 1: everything and point toward the universal up. There is always
1:08:32
Speaker 1: something larger, something farther, another reference, another perspective, and eventually, perhaps,
1:08:40
Speaker 1: this is the most peaceful answer to the question. There
1:08:43
Speaker 1: is nothing wrong with asking what is above the solar system.
1:08:47
Speaker 1: It is a perfectly natural question. But the universe answers
1:08:51
Speaker 1: in a gentle way. Above the solar system there is space.
1:08:55
Speaker 1: There are stars. There are distant clouds of gas and dust.
1:09:00
Speaker 1: There are invisible gravitational structures. There are galaxies. There is darkness.
1:09:05
Speaker 1: And there is no single direction that the universe itself
1:09:09
Speaker 1: calls upward. You are free to choose one. You are
1:09:13
Speaker 1: free to turn. You are free to drift. And beneath you,
1:09:17
Speaker 1: or beside you, or behind you, Depending entirely on the
1:09:21
Speaker 1: direction you choose, the solar system continues its ancient journey
1:09:25
Speaker 1: through the Milky Way. Earth continues around the Sun. The
1:09:29
Speaker 1: planets continue along their broad paths. The Sun continues through
1:09:34
Speaker 1: its stellar neighbourhood. The Milky Way continues its slow movement.
1:09:38
Speaker 1: Nothing needs to stop for you. Nothing needs to wait.
1:09:42
Speaker 1: The universe does not become confused when you change direction.
1:09:46
Speaker 1: Only your description changes. So let yourself become still for
1:09:50
Speaker 1: a moment. Imagine the earth again, small, blue, quiet. Imagine
1:09:57
Speaker 1: the sun, a distant star carrying a family of worlds.
1:10:01
Speaker 1: Imagine the planetary plane stretching through the darkness, not as
1:10:05
Speaker 1: a flaw, but as a memory of ancient motion. And
1:10:10
Speaker 1: now let even that plane fade. Let the solar system
1:10:13
Speaker 1: become smaller. Let the Milky Way become smaller. Let the
1:10:18
Speaker 1: idea of above become softer. There is nothing to reach.
1:10:22
Speaker 1: There is nowhere you need to go. You are safe.
1:10:26
Speaker 1: There is nothing to do. You can simply listen and drift.
1:10:31
Speaker 1: Perhaps the universe is not a place arranged from bottom
1:10:34
Speaker 1: to top. Perhaps it is simply a vast collection of relationships, motions,
1:10:39
Speaker 1: distances and perspectives, with every direction becoming meaningful only when
1:10:45
Speaker 1: you choose something to measure it against. And as you
1:10:48
Speaker 1: rest there in the quiet, the question that began this
1:10:51
Speaker 1: journey no longer needs a complicated answer. You can reach
1:10:55
Speaker 1: Pluto because you can work with the motion already carrying
1:10:58
Speaker 1: you through the solar system. Flying far above the planetary
1:11:02
Speaker 1: plane is harder because changing that motion requires energy. But
1:11:07
Speaker 1: there is no forbidden region above the planets. There is
1:11:10
Speaker 1: no cosmic ceiling. There is only space. Endless space. Quiet space.
1:11:17
Speaker 1: space extending in every direction, and somewhere within that immense stillness,
1:11:22
Speaker 1: the sun continues to shine, the planets continue to turn,
1:11:26
Speaker 1: and you can simply let your thoughts become lighter, slower,
1:11:30
Speaker 1: and quieter. And perhaps, if you remain here a little longer,
1:11:35
Speaker 1: even the difference between above and below will begin to disappear.
1:11:41
Speaker 1: And so, our journey drifts quietly to its end. You
1:11:46
Speaker 1: have travelled above the familiar plane of the planets, beyond
1:11:49
Speaker 1: the sun's outward breath, through the thin space between stars,
1:11:54
Speaker 1: and into the much larger structure of the Milky Way.
1:11:57
Speaker 1: You have seen that the solar system is not a
1:11:59
Speaker 1: flat cage, and that the darkness above the planets is
1:12:03
Speaker 1: not an empty ceiling waiting at the edge of space.
1:12:06
Speaker 1: There is simply more space, more distance, more quiet, and
1:12:11
Speaker 1: more directions than any single word can contain. Whether you
1:12:16
Speaker 1: are still listening beneath the gentle glow of your screen,
1:12:19
Speaker 1: or already floating somewhere between waking and dreaming, you can
1:12:23
Speaker 1: let the solar system become smaller now, the planets becoming
1:12:27
Speaker 1: faint points of light, the sun becoming a distant star,
1:12:31
Speaker 1: the Milky Way becoming a soft band of brightness somewhere
1:12:35
Speaker 1: far away. There is nothing to do. You are safe.
1:12:39
Speaker 1: The universe does not need you to understand everything tonight.
1:12:43
Speaker 1: It will continue without effort. The planets will keep moving.
1:12:47
Speaker 1: The sun will keep shining. The stars will keep drifting
1:12:51
Speaker 1: through the galaxy. And you can simply rest. Perhaps tomorrow,
1:12:56
Speaker 1: you may look at the night sky and remember that
1:12:58
Speaker 1: there is no true top or bottom out there. No
1:13:02
Speaker 1: universal ceiling. No single direction waiting to be discovered. Only
1:13:07
Speaker 1: an enormous, quiet universe, extending gently in every direction. So
1:13:12
Speaker 1: let your breathing become slow. Let the room around you
1:13:16
Speaker 1: become quiet. Let the last few thoughts pass without needing
1:13:20
Speaker 1: to follow them. And while you sleep, the earth will
1:13:23
Speaker 1: continue its small journey around the sun, carried peacefully through
1:13:27
Speaker 1: the darkness, beneath no ceiling and above no floor, simply
1:13:31
Speaker 1: moving through space. Rest well. The stars will keep burning,
1:13:37
Speaker 1: the planets will keep turning, and the universe will carry
1:13:40
Speaker 1: on softly around you while you sleep.