Latest / Daniel and Kelly’s Extraordinary Universe / Daniel answers Listener Questions about energy conservation, inflation and space dust!

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Daniel answers Listener Questions about energy conservation, inflation and space dust! · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Isaac Newton was very clearly a smart guy. He made
• 0:12
  Speaker 1: huge leaps and understanding of optics and gravity and calculus.
• 0:16
  Speaker 1: But one of the biggest mental steps he took was
• 0:19
  Speaker 1: applying the laws that we have down here on Earth
• 0:22
  Speaker 1: to what's going on up there in space. His biggest
• 0:27
  Speaker 1: idea was probably that there should only be one idea,
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  Speaker 1: one set of physical laws, but that it should cover everything.
• 0:36
  Speaker 1: And here we sit on a tiny, isolated rocking space
• 0:40
  Speaker 1: trying to make rules that explain the whole universe, only
• 0:44
  Speaker 1: able to see a tiny little bit of it and
• 0:47
  Speaker 1: study with our hands and our tools an even smaller bit.
• 0:51
  Speaker 1: It's sort of like visiting the zoo and only seeing
• 0:55
  Speaker 1: the insect exhibit, but then making laws that are supposed
• 0:58
  Speaker 1: to describe how elephants and amphibian's work. So ask yourself,
• 1:02
  Speaker 1: how likely is it that our ideas are actually universal? Hi?
• 1:22
  Speaker 1: I'm Daniel. I'm a particle physicist, and I have an
• 1:25
  Speaker 1: infinite list of questions about our probably infinite universe. And
• 1:30
  Speaker 1: welcome to the podcast. Daniel and Jorge explain the universe
• 1:34
  Speaker 1: of production of My Heart Radio. We talk about things
• 1:37
  Speaker 1: happening far far away, and we talk about things happening
• 1:40
  Speaker 1: under your feet. We ask questions about the very beginning
• 1:43
  Speaker 1: of time, and we ask questions about the very nature
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  Speaker 1: of time and the end of time. We ask questions
• 1:49
  Speaker 1: about the entire universe because we think that curiosity and
• 1:53
  Speaker 1: asking questions is universal. We think everybody out there has questions,
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  Speaker 1: and everybody deserves to have their question is explored, if
• 2:01
  Speaker 1: not answered, because not every question has an answer to
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  Speaker 1: it so far, but questions really are at the heart
• 2:08
  Speaker 1: of science, and that's why on today's program, while my
• 2:11
  Speaker 1: friend collaborator and co host Jorge can't be here today,
• 2:15
  Speaker 1: I'm gonna take the opportunity to gather up a bunch
• 2:18
  Speaker 1: of questions asked from listeners and try to answer them.
• 2:22
  Speaker 1: We're always asking people please send us your questions. If
• 2:25
  Speaker 1: there's something you don't understand about the universe, something you've
• 2:29
  Speaker 1: read and didn't quite follow, something you've thought through that
• 2:32
  Speaker 1: didn't quite make sense to you, please send it to
• 2:34
  Speaker 1: us because we cherish those questions. Those questions are our
• 2:38
  Speaker 1: opportunity to help people understand what we do and what
• 2:42
  Speaker 1: we don't know about the universe. And remember that everybody
• 2:46
  Speaker 1: out there who was asking questions is basically an armchair physicist.
• 2:50
  Speaker 1: If you are trying to wrap your mind around the universe,
• 2:53
  Speaker 1: you're trying to make one holistic sense of understanding of
• 2:56
  Speaker 1: how things work. If you've read something somewhere and you're
• 2:59
  Speaker 1: trying to make it agree with something else you used
• 3:01
  Speaker 1: to think, or something you read somewhere else, or something
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  Speaker 1: your friend told you, that's doing physics. You're trying to
• 3:07
  Speaker 1: unify your understanding. You're saying, I need to have one
• 3:11
  Speaker 1: set of ideas that describes the entire universe that explains everything. Now,
• 3:17
  Speaker 1: of course, we don't know if it's possible to describe
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  Speaker 1: the entire universities in one set of laws. We don't
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  Speaker 1: know if it's possible for humans to do it, or
• 3:25
  Speaker 1: maybe take some super alien intelligence or some artificial intelligence
• 3:30
  Speaker 1: with super incredible powers. But that doesn't stop us from trying,
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  Speaker 1: because it's our dream that we could encapsulate the entire
• 3:37
  Speaker 1: workings of the universe somehow inside the puny human mind.
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  Speaker 1: So please, if we haven't answered a question that's in
• 3:43
  Speaker 1: your mind, send it to us two questions at Daniel
• 3:47
  Speaker 1: and Jorge dot com. We answer all of our emails
• 3:50
  Speaker 1: and sometimes we put those questions here on the podcast.
• 3:54
  Speaker 1: But If you don't like writing emails or you don't
• 3:56
  Speaker 1: want to engage with us on Twitter, we have other
• 3:58
  Speaker 1: ways to get your questions answered. You can check out
• 4:02
  Speaker 1: Daniel's public office hours, look at the website for the podcast,
• 4:05
  Speaker 1: or go to sites dot you see I dot E,
• 4:09
  Speaker 1: d U slash Daniel, you'll see a link. Therefore, when
• 4:12
  Speaker 1: Daniel has public office hours, he hangs out on Zoom
• 4:15
  Speaker 1: and answers questions about physics and life and the universe
• 4:19
  Speaker 1: and everything from people like you, people who have thought
• 4:22
  Speaker 1: about stuff and have a nagging little question that they
• 4:25
  Speaker 1: can't find the answer to using Google and they just
• 4:28
  Speaker 1: have to know how it works, all right, And today
• 4:30
  Speaker 1: on the podcast will be answering questions from listeners from
• 4:34
  Speaker 1: all over the world. Our first question comes to us
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  Speaker 1: from Germany. I have a question concerning doc energy. Does
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  Speaker 1: it violate the law of energy conservation? It seems to
• 4:46
  Speaker 1: come out of nothing and getting bigger and bigger. Thanks
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  Speaker 1: a lot, all right, Thank you and Juras from Germany.
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  Speaker 1: This is a beautiful example of what I was just
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  Speaker 1: talking about about applying our ideas about how things work
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  Speaker 1: in the universe and taking them to the extreme and
• 5:01
  Speaker 1: saying does this really work everywhere. Is this a universal law?
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  Speaker 1: Is there some part of the universe that seemed to
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  Speaker 1: break this rule which would make it not universal? And
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  Speaker 1: one of the most fundamental things we thought we understood
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  Speaker 1: about the universe was this idea of energy conservation. Of course,
• 5:18
  Speaker 1: a hundred years ago, we thought other things were conserved,
• 5:21
  Speaker 1: like mass. We thought that stuff was conserved, that you
• 5:24
  Speaker 1: could move it around, you could switch it up, you
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  Speaker 1: could rearrange it like lego bricks, but you couldn't create
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  Speaker 1: or destroy mass. Now, of course we know that's not true.
• 5:34
  Speaker 1: And the lesson we learned from that, from the lack
• 5:36
  Speaker 1: of mass conservation, is that mass is not a fundamental
• 5:40
  Speaker 1: element of the universe. It can be created, it can
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  Speaker 1: be destroyed. You can have more mass, you can have
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  Speaker 1: less mass. It's not something which we should consider sort
• 5:48
  Speaker 1: of on the list of fundamental descriptors of the universe.
• 5:52
  Speaker 1: And that's important because what we're doing with physics is
• 5:56
  Speaker 1: trying to drill down to the most fundamental, the simplest description,
• 6:00
  Speaker 1: Because we imagine if one day we are looking at
• 6:03
  Speaker 1: a list of the fundamental elements of the universe, of
• 6:05
  Speaker 1: things that define the universe and completely explain the universe
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  Speaker 1: that we will somehow be revealing the nature of the universe.
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  Speaker 1: So we don't want anything on that list which isn't fundamental.
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  Speaker 1: You don't want that list to have like strings and
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  Speaker 1: energy and then ice cream, right because ice cream can
• 6:21
  Speaker 1: be described by all the other elements already on the list.
• 6:24
  Speaker 1: So we want to strip it down to a sort
• 6:26
  Speaker 1: of most minimal set of rules, most minimal set of
• 6:30
  Speaker 1: things you need to describe the universe. Having left our
• 6:33
  Speaker 1: list of things that describe how the universe works tells
• 6:36
  Speaker 1: us something about what the universe isn't. It isn't a
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  Speaker 1: place that cares so much about mass. However, energy seems
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  Speaker 1: to have retained its exalted stature as a quantity which
• 6:48
  Speaker 1: is conserved. And you know what is energy conservation anyway.
• 6:52
  Speaker 1: Energy conservation is the statement that you can calculate this
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  Speaker 1: thing about nature. You add up all the energy in
• 6:58
  Speaker 1: a system, all the ways that things can move or
• 7:00
  Speaker 1: wiggle or store energy, and then you let a bunch
• 7:03
  Speaker 1: of stuff happen. Things collide, things explode, things slash around, whatever,
• 7:08
  Speaker 1: and you add up all the energy again and it
• 7:10
  Speaker 1: should be the same. So it's sort of a statement
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  Speaker 1: that energy is fundamental to the universe. You can move
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  Speaker 1: it around, that you can change it from one thing
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  Speaker 1: to another, but that you can't get rid of it,
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  Speaker 1: that it's inherent, that it's fundamental, that it's a deep
• 7:23
  Speaker 1: part of what makes the universe the universe. So if
• 7:28
  Speaker 1: energy is not conserved, then that tells you what It
• 7:31
  Speaker 1: tells you that maybe energy isn't actually important to the universe.
• 7:35
  Speaker 1: Maybe energy isn't on that list of fundamental elements we
• 7:39
  Speaker 1: think are needed to define and describe the universe. So
• 7:42
  Speaker 1: Andreas is doing exactly what a physicists should be doing,
• 7:45
  Speaker 1: thinking about ways energy conservation might be violated. We know,
• 7:50
  Speaker 1: for example, that if you roll a boulder up a hill,
• 7:53
  Speaker 1: you're spending energy in your muscles, and that energy then
• 7:56
  Speaker 1: goes into the position of the boulder. It's gravitation in
• 8:00
  Speaker 1: a location is more distant from the Earth, And if
• 8:02
  Speaker 1: you let go of the boulder and run it back
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  Speaker 1: down the hill, the energy goes from that potential energy
• 8:07
  Speaker 1: of the boulder into its motion, into its kinetic energy.
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  Speaker 1: So we have lots of examples of where energy is conserved,
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  Speaker 1: and people probably expect to hear that energy is conserved
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  Speaker 1: everywhere in the universe and there's some way you can
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  Speaker 1: do the calculation to figure out that energy is actually
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  Speaker 1: conserved in the case of dark energy. So what is
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  Speaker 1: he talking about. Remember that dark energy is not something
• 8:29
  Speaker 1: that's very well understood. It's not a theoretically well formulated idea.
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  Speaker 1: It's more an observation. It's an observation that the universe
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  Speaker 1: is expanding and that that expansion is accelerating. So we
• 8:42
  Speaker 1: look out into the universe and we see that the
• 8:44
  Speaker 1: universe is expanding, and not only are things moving away
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  Speaker 1: from us, but the speed at which they're moving away
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  Speaker 1: from us is increasing. You might expect the opposite to
• 8:54
  Speaker 1: be happening. In fact, physicists expected the opposite to be
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  Speaker 1: happening for a long time, that things were moving away
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  Speaker 1: from us, but that speed might be decreasing as gravity
• 9:03
  Speaker 1: very slowly pulls on things and tugs them back together.
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  Speaker 1: After the Big Bang, what we actually found about years
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  Speaker 1: ago now is that things are moving away from us
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  Speaker 1: faster and faster, and we don't have an explanation for
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  Speaker 1: why this is. All we have is the observation that
• 9:20
  Speaker 1: it is happening. There are a few sort of proto explanations.
• 9:24
  Speaker 1: There are ideas for what might describe it, but none
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  Speaker 1: of those ideas really work so far. One of those
• 9:30
  Speaker 1: ideas is that there is energy in empty space, that
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  Speaker 1: all of space has energy in it. For example, the
• 9:37
  Speaker 1: Higgs Boson field is a quantum field that's in all
• 9:40
  Speaker 1: of space, and even when it's at its most relaxed,
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  Speaker 1: at its lowest level, it doesn't have zero energy in it.
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  Speaker 1: That means that when you create a piece of space,
• 9:50
  Speaker 1: you're creating a Higgs Boson field that has energy in it.
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  Speaker 1: And this is what Andreas is talking about. That dark
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  Speaker 1: energy creates more space because it's not just moving things
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  Speaker 1: through space. It's creating new space between galaxies. It's stretching
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  Speaker 1: that space. It's making new space. And when you make
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  Speaker 1: new space, it comes with new energy. So it seems
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  Speaker 1: an awful law like dark energy is in fact violating
• 10:17
  Speaker 1: conservation of energy because as you make more space, you
• 10:21
  Speaker 1: are increasing the total volume of the universe. And if
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  Speaker 1: every cubic meter of space has a certain energy, then
• 10:28
  Speaker 1: by increasing the volume of space, you're increasing the total
• 10:31
  Speaker 1: energy in the universe. How does that not violate conservation
• 10:35
  Speaker 1: of energy? Well, in fact it does, and as energy
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  Speaker 1: conservation is not guaranteed in our universe, and this is
• 10:43
  Speaker 1: one example. As space expands, the energy increases because you
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  Speaker 1: get more dark energy, which means overall more energy. There's
• 10:51
  Speaker 1: also another example, which is that energy can decrease when
• 10:55
  Speaker 1: space expands. If you have a photon flying through space,
• 10:59
  Speaker 1: for example, from the cosmic microwave background radiation, then what
• 11:03
  Speaker 1: happens when space expands. When space stretches, Well, that photon
• 11:07
  Speaker 1: gets red shifted. Its wavelength gets longer because space has
• 11:11
  Speaker 1: gotten stretched. Right, Imagine you draw a wiggle on a
• 11:15
  Speaker 1: sheet of paper and then you stretch that paper, the
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  Speaker 1: wavelength gets longer. But for photons, the energy and the
• 11:21
  Speaker 1: wavelength are very closely connected. One defines the other. Higher
• 11:26
  Speaker 1: energy photons are those with shorter wavelengths, and so if
• 11:29
  Speaker 1: you stretch the wavelength of a photon, then you decrease
• 11:32
  Speaker 1: its energy. Where does that energy go. It doesn't go anywhere.
• 11:37
  Speaker 1: It just goes away. So we have two examples of
• 11:40
  Speaker 1: the violation of the conservation of energy, both coming from
• 11:45
  Speaker 1: space expanding. And that's the clue as the clue that
• 11:48
  Speaker 1: tells us why energy might not be conserved, and most
• 11:52
  Speaker 1: of the conservation laws in physics, most of the things
• 11:54
  Speaker 1: that are conserved that are not changed when you let
• 11:57
  Speaker 1: things bang around and smash into each other come from
• 12:00
  Speaker 1: some kind of symmetry. This is very deep result in
• 12:04
  Speaker 1: physics called Noether's theorem from Emily Norther, who developed it
• 12:08
  Speaker 1: more than a hundred years ago, and she discovered that
• 12:11
  Speaker 1: every time you have a symmetry, like every time you
• 12:13
  Speaker 1: can take space and rotate it and still get the
• 12:16
  Speaker 1: same laws of physics, or move your coordinate system over
• 12:20
  Speaker 1: by ten kilometers and still expect the same law of physics,
• 12:23
  Speaker 1: or fast forward things by a hundred years and still
• 12:26
  Speaker 1: expect the same laws of physics. Every time you can
• 12:28
  Speaker 1: apply some sort of translation or rotation to the universe
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  Speaker 1: and not see any change in the law of physics.
• 12:35
  Speaker 1: That's a symmetry, and every symmetry has some kind of
• 12:38
  Speaker 1: conservation law that comes from it. So, for example, the
• 12:42
  Speaker 1: fact that space is the same everywhere, that the laws
• 12:45
  Speaker 1: of physics apply here and somewhere else, that gives you
• 12:48
  Speaker 1: the law of conservation of momentum, and the fact that
• 12:51
  Speaker 1: you can rotate space, that there's no preferred direction, that
• 12:54
  Speaker 1: physics should work the same in every direction. That's why
• 12:57
  Speaker 1: we have conservation of angular moment them and it's the
• 13:00
  Speaker 1: symmetry of the universe with respect to time is what
• 13:04
  Speaker 1: gives us conservation of energy. The fact that it seems
• 13:07
  Speaker 1: like the universe should work the same now as it
• 13:09
  Speaker 1: does in a hundred years and a thousand years ago
• 13:12
  Speaker 1: is what gives us conservation of energy. But that only
• 13:17
  Speaker 1: works if we expect the same rules to apply now
• 13:20
  Speaker 1: and in a hundred years and in a thousand years.
• 13:23
  Speaker 1: That only works if space is essentially static, if it's
• 13:26
  Speaker 1: not changing, if space is the same now and in
• 13:29
  Speaker 1: a hundred years and a thousand years ago. But we
• 13:32
  Speaker 1: know that it's not because we know that space is expanding.
• 13:37
  Speaker 1: So conservation of energy is something we expect to apply
• 13:39
  Speaker 1: in a static universe where space is not changing. In
• 13:43
  Speaker 1: our universe, however, space is expanding, and it's expanding quite rapidly.
• 13:48
  Speaker 1: Expansion is not a small thing in our universe. Seventy
• 13:51
  Speaker 1: percent of the energy budget of the universe goes towards
• 13:55
  Speaker 1: the expansion of space time, so when space is expanding,
• 13:59
  Speaker 1: energy is not concerned. Now, we did a whole podcast
• 14:02
  Speaker 1: episode about this conservation of energy, and there is one
• 14:05
  Speaker 1: way that you can sort of rig up a calculation
• 14:08
  Speaker 1: in which you get negative energy from gravity that might
• 14:11
  Speaker 1: account for some of this, but most cosmologists think it's
• 14:15
  Speaker 1: sort of a band aid and theoretically doesn't hold together.
• 14:17
  Speaker 1: And you're interested in more details and not check on
• 14:19
  Speaker 1: our whole podcast episode about conservation of energy. But congrats
• 14:24
  Speaker 1: to you Andrea's for figuring this out, for applying your
• 14:27
  Speaker 1: understanding of physics to crazy scenarios far beyond your living
• 14:32
  Speaker 1: room and coming up with a contradiction. And those contradictions
• 14:35
  Speaker 1: are what leads to questions, and those questions are would
• 14:38
  Speaker 1: lead us to deeper understandings about the universe. So keep
• 14:42
  Speaker 1: asking questions. Thanks very much for sending that in. All right,
• 14:45
  Speaker 1: I have more questions from listeners I want to get
• 14:48
  Speaker 1: to but first let's take a quick break. All right,
• 15:04
  Speaker 1: we're back, and this is Daniel and I'm here today
• 15:07
  Speaker 1: on my own answering questions from listeners. I love when
• 15:11
  Speaker 1: people write to us. They send us amazing questions, things
• 15:14
  Speaker 1: that they have been thinking about the universe and that
• 15:16
  Speaker 1: they can't figure out via Google, and they don't happen
• 15:19
  Speaker 1: to know a physicists they can ask these questions of,
• 15:22
  Speaker 1: so they send them to us. And I have a
• 15:24
  Speaker 1: bit of an embarrassing backlog of questions from listeners that
• 15:28
  Speaker 1: I really want to get to, and so while Jorge
• 15:30
  Speaker 1: isn't here, I'm gonna plow through a bunch of these
• 15:33
  Speaker 1: and try to catch up to our backlog. So thanks
• 15:35
  Speaker 1: very much to everybody who's senting questions. Here's the next
• 15:38
  Speaker 1: question we're gonna answer today. Hey guys, this is Jeff
• 15:41
  Speaker 1: from Los Angeles. My question relates to the period of
• 15:44
  Speaker 1: inflation after the Big Bang. I know you said the
• 15:48
  Speaker 1: universe expanded by a factor of ten to the thirty
• 15:51
  Speaker 1: in the small amount of time of ten to the
• 15:53
  Speaker 1: minus thirty. How do you explain that if nothing can
• 15:56
  Speaker 1: travel faster than the speed of light. I also want
• 15:59
  Speaker 1: to know if the edges of the universe were expanding
• 16:02
  Speaker 1: at this crazy fast speed, and it was expanding through nothing,
• 16:07
  Speaker 1: then what's slowing it down? Why isn't the universe still
• 16:11
  Speaker 1: expanding at that crazy rate of inflation? I look forward
• 16:14
  Speaker 1: to the answer. Thanks a lot, all right, Jeff from
• 16:16
  Speaker 1: l A who's basically an amateur cosmologist. Thank you for
• 16:19
  Speaker 1: thinking deeply about the universe and for trying to reconcile
• 16:22
  Speaker 1: what you've heard about the early days of the universe
• 16:25
  Speaker 1: with what you understand about how the universe works. Again,
• 16:29
  Speaker 1: that's exactly what doing physics means, so let's get to it.
• 16:33
  Speaker 1: The first part of your question was if the universe
• 16:36
  Speaker 1: expanded by a factor ten to the thirty intended to
• 16:39
  Speaker 1: minus thirty questions, how is that possible? Given that we
• 16:43
  Speaker 1: know that there's a very hard limit on how fast
• 16:46
  Speaker 1: things can move through space, which is the speed of light.
• 16:50
  Speaker 1: It's a great question. Another way to think about this
• 16:52
  Speaker 1: question is how did the universe get so big? I mean,
• 16:56
  Speaker 1: the universe is about fourteen billion years old, but the
• 17:00
  Speaker 1: size of the observable universe, the distance to the furthest
• 17:04
  Speaker 1: things that we can see, you might expect to be
• 17:07
  Speaker 1: fourteen billion years times the speed of light, which would
• 17:11
  Speaker 1: be fourteen billion light years, but it's not. It's much
• 17:15
  Speaker 1: much further than that. We can see things that are
• 17:17
  Speaker 1: about forty five billion light years away, So the size
• 17:22
  Speaker 1: of the observable universe is about ninety billion light years wide.
• 17:26
  Speaker 1: How is that possible? How is it possible to see
• 17:29
  Speaker 1: things which are further away than the speed of light
• 17:33
  Speaker 1: times the age of the universe. How did that stuff
• 17:35
  Speaker 1: get there so far? How did the universe expand faster
• 17:39
  Speaker 1: than the speed of light. So it's a wonderful question.
• 17:42
  Speaker 1: And the key concept you need to know to understand
• 17:45
  Speaker 1: this is that there's a difference between moving through space
• 17:49
  Speaker 1: and expansion of space. So moving through space is the
• 17:53
  Speaker 1: kind of thing you're familiar with. You move through space
• 17:55
  Speaker 1: every day. When you get out of your bed and
• 17:58
  Speaker 1: you go for a glass of water in the middle
• 17:59
  Speaker 1: of the night, you are moving through space. When you
• 18:02
  Speaker 1: throw a baseball really really fast. When you get on
• 18:04
  Speaker 1: your spaceship and you try to travel to a nearby star,
• 18:07
  Speaker 1: you are moving through space. When you turn on your
• 18:10
  Speaker 1: flashlight and you shine it at the moon, you are
• 18:12
  Speaker 1: sending photons through space to the moon. And there is
• 18:16
  Speaker 1: in fact a very hard limit on the speed at
• 18:19
  Speaker 1: which things can move through space, and that's the speed
• 18:22
  Speaker 1: of light. In a vacuum. Nothing, no information at all,
• 18:25
  Speaker 1: can move through space faster than the speed of light.
• 18:29
  Speaker 1: That includes neutrinos, that includes everything, that includes quantum information.
• 18:33
  Speaker 1: It's a very tough rule, and breaking it when undermine
• 18:36
  Speaker 1: special relativity, which we're pretty sure as an accurate description
• 18:40
  Speaker 1: of space time in our universe. All right, So that's
• 18:44
  Speaker 1: moving through space, but that's different from the expansion of space.
• 18:49
  Speaker 1: The expansion of space means stretching space itself. So imagine,
• 18:53
  Speaker 1: for example, you are one meter apart from your friend.
• 18:57
  Speaker 1: You have a meter stick, and you measure exactly how
• 18:59
  Speaker 1: far apart you are. You could take a step back.
• 19:01
  Speaker 1: That would be moving through space. But you could also
• 19:05
  Speaker 1: expand the space between you. You could take the very
• 19:09
  Speaker 1: universe and stretch it so that now you guys are
• 19:12
  Speaker 1: two meters apart without having moved through space at all. Right, Remember,
• 19:18
  Speaker 1: space is not just the backdrop on which things happen.
• 19:21
  Speaker 1: It's not the stage on which the acts of the
• 19:24
  Speaker 1: universe are played out on. It's a dynamical thing. It's stretchy,
• 19:28
  Speaker 1: it's like goo. It responds to the presence of mass
• 19:32
  Speaker 1: and energy. It bends, it twists, it can expand, and
• 19:37
  Speaker 1: it tells things how to move. So space is really
• 19:40
  Speaker 1: part of the universe. It's not just like some fuzzy
• 19:43
  Speaker 1: abstract concept, some set of glowing axes in our mind
• 19:47
  Speaker 1: that we just impose on the universe to try to
• 19:50
  Speaker 1: make sense of it. Space really can do a bunch
• 19:52
  Speaker 1: of weird things. You already know this because you know
• 19:55
  Speaker 1: that gravity is not just a force. It's actually the
• 19:58
  Speaker 1: curving of space. Right, The reason that the Earth goes
• 20:01
  Speaker 1: around the Sun is not because gravity is a force
• 20:04
  Speaker 1: which is tugging on it, but because the presence of
• 20:07
  Speaker 1: the Sun changes the shape of space in its vicinity,
• 20:11
  Speaker 1: so that an object moving in a straight up inertial
• 20:14
  Speaker 1: path will move in a circle around the Sun. That's
• 20:17
  Speaker 1: because space can bend and twist, changing the relative distances
• 20:21
  Speaker 1: between things. So, for example, a photon a beam of
• 20:25
  Speaker 1: light always takes the shortest path between two things, But
• 20:28
  Speaker 1: the shortest path between two things isn't always what you
• 20:31
  Speaker 1: imagine to be a straight line, because the shape of
• 20:34
  Speaker 1: space can be complicated between two points. The same way
• 20:37
  Speaker 1: an airplane going from l A to London takes the
• 20:39
  Speaker 1: Great Circle route right, which seems like a curve, is
• 20:42
  Speaker 1: actually the shortest distance between two places on a curved surface,
• 20:47
  Speaker 1: which is why gravity can influence even things that don't
• 20:50
  Speaker 1: have mass. All right, So that tells us that space
• 20:53
  Speaker 1: can do things, and it can stretch, and it can expand,
• 20:57
  Speaker 1: and so that's exactly what happened in the very early universe.
• 21:00
  Speaker 1: It wasn't an explosion like a tiny dot of stuff
• 21:04
  Speaker 1: and then everything exploded out from the center. Instead, it
• 21:07
  Speaker 1: was an expansion of space itself. Huge amounts of new
• 21:12
  Speaker 1: space were made everywhere all over the universe simultaneously. So
• 21:17
  Speaker 1: that doesn't make it easier to understand the fact. It
• 21:19
  Speaker 1: makes it even more buying boggling that this happened, That
• 21:23
  Speaker 1: every unit of space was blown up by a factor
• 21:25
  Speaker 1: of ten to the thirty intend to the minus thirty seconds.
• 21:30
  Speaker 1: It's an incredible moment in the history of the universe.
• 21:32
  Speaker 1: It's an incredible idea to even have in your mind.
• 21:36
  Speaker 1: Imagine coming up with this Bonker's notion and then realizing
• 21:39
  Speaker 1: that actually it's the story that makes the most sense
• 21:42
  Speaker 1: in the universe. And you might ask, well, how do
• 21:45
  Speaker 1: we know. How do we know that the universe expanded
• 21:48
  Speaker 1: in this way, that it didn't just explode from a
• 21:50
  Speaker 1: tiny dot and spread out through the universe. Well, answer
• 21:54
  Speaker 1: number one is that it would be impossible. As you say,
• 21:57
  Speaker 1: it's not possible for things to travel that are in
• 22:00
  Speaker 1: that short distance because of the limitation of the speed
• 22:04
  Speaker 1: of light. It's against the rules. The only way to
• 22:07
  Speaker 1: get things that far apart in that short amount of
• 22:09
  Speaker 1: time is to create space between them, is to expand
• 22:13
  Speaker 1: the space between everything. But it's more than that, because
• 22:17
  Speaker 1: Explosions and expansion look different. Explosions are like a bomb.
• 22:23
  Speaker 1: You push everything out from one central location and send
• 22:26
  Speaker 1: it flying in every direction. And if there is an explosion,
• 22:29
  Speaker 1: you could look at the direction things are flying and
• 22:31
  Speaker 1: you could track them backwards, and you could point back
• 22:34
  Speaker 1: to the center. Right. If you come upon an explosion,
• 22:37
  Speaker 1: you can look at the path of the debris and
• 22:39
  Speaker 1: you can figure out where the bomb was. That's not
• 22:42
  Speaker 1: true for an expansion, and expansion is more like a
• 22:46
  Speaker 1: loaf of bread rising in the oven, where everything is
• 22:48
  Speaker 1: growing at every point simultaneously, assuming you're not a terrible baker, right,
• 22:53
  Speaker 1: and that your loaf is expanding smoothly. And that's what
• 22:56
  Speaker 1: we see when we look out into the universe. We
• 22:58
  Speaker 1: see these galaxies and they are rushing away from us.
• 23:01
  Speaker 1: They are moving away from us, and they're moving away
• 23:03
  Speaker 1: from us faster and faster every year. So either we
• 23:07
  Speaker 1: are at the exact center of the universe by some
• 23:11
  Speaker 1: incredible cosmic coincidence there was an explosion and we happen
• 23:15
  Speaker 1: to be right at the center of it, or it
• 23:18
  Speaker 1: looks this way because it's an expansion, and it would
• 23:21
  Speaker 1: look this way at any point in the universe. See.
• 23:24
  Speaker 1: The way an expansion looks is that it always looks
• 23:27
  Speaker 1: like you're at the center of it. No matter where
• 23:29
  Speaker 1: you are in a loaf of bread, if you look
• 23:31
  Speaker 1: around you, everything is growing away from you. Imagine putting
• 23:34
  Speaker 1: a bunch of chocolate chips into your loaf of bread
• 23:37
  Speaker 1: and tracking their emotion everywhere inside the loaf of bread,
• 23:40
  Speaker 1: of course, except for the crust. You would see this
• 23:43
  Speaker 1: chocolate chips moving away from you. So that's what we see.
• 23:46
  Speaker 1: We see that the universe is expanding, not that it's
• 23:49
  Speaker 1: exploding out from a tiny dot. And this expansion is
• 23:52
  Speaker 1: actually really important to sort of the state of the
• 23:55
  Speaker 1: universe as we know it, because when the universe began,
• 23:58
  Speaker 1: we think it began very very smooth, like totally homogeneous.
• 24:02
  Speaker 1: Everywhere was exactly like everywhere else. And why wouldn't it
• 24:06
  Speaker 1: be right when the universe is created, Why would you
• 24:08
  Speaker 1: have one spot that's like denser than another spot. The
• 24:11
  Speaker 1: problem is, however, a universe like that that's created perfectly smoothly,
• 24:15
  Speaker 1: nothing very interesting ever happens in that universe. There's nothing
• 24:19
  Speaker 1: for gravity to do in that universe because there's no
• 24:22
  Speaker 1: spots that are heavier or denser than anything else, which
• 24:25
  Speaker 1: is what gravity needs to sort of like seed the
• 24:28
  Speaker 1: structure to start coalescing things together into stars and planets
• 24:32
  Speaker 1: and galaxies and all that good stuff. So how did
• 24:35
  Speaker 1: the universe get any structure? Well, it was perfectly smooth,
• 24:38
  Speaker 1: except down to the quantum level. Of the quantum level,
• 24:41
  Speaker 1: there are always random fluctuations. Every point in the universe
• 24:45
  Speaker 1: gets a different random fluctuation, so you get these really
• 24:48
  Speaker 1: super duper tiny little variations in the density of the
• 24:52
  Speaker 1: universe due to quantum mechanics, and then inflation steps in.
• 24:56
  Speaker 1: Inflation takes those tiny little quantum fluctuations and it blows
• 25:00
  Speaker 1: them up to the macroscopic scale, makes things which were
• 25:04
  Speaker 1: invisibly small somehow suddenly now huge. Right, takes a meter
• 25:09
  Speaker 1: stick sized thing and it blows it up to a
• 25:11
  Speaker 1: trillion light years. It takes something which was sub atomic
• 25:15
  Speaker 1: and it makes it macroscopic. So now those random quantum
• 25:18
  Speaker 1: fluctuations are not small. They're pretty big, and they're big
• 25:21
  Speaker 1: enough to see the structure of the universe. So the
• 25:25
  Speaker 1: reason that we have a galaxy over here and then
• 25:28
  Speaker 1: over there it's empty space is because of a random
• 25:31
  Speaker 1: quantum fluctuation in the very early universe, which was expanded
• 25:35
  Speaker 1: out into something macroscopic that see to the structure of
• 25:38
  Speaker 1: that galaxy and allow gravity to pull stuff together to
• 25:42
  Speaker 1: make something interesting, to make me and to make you,
• 25:45
  Speaker 1: and to make the sun that warms our toes. Now,
• 25:48
  Speaker 1: the second part of Jeff's awesome question is that if
• 25:50
  Speaker 1: the edges of the universe were expanding through nothing, what's
• 25:53
  Speaker 1: slowing it down? Why isn't it still expanding at that
• 25:57
  Speaker 1: crazy rate? So lots of really good angles on the question.
• 26:00
  Speaker 1: First of all, we don't know if there is an
• 26:02
  Speaker 1: edge to the universe. I think in his mind Jeff
• 26:05
  Speaker 1: might be imagining an explosion, an explosion which has a
• 26:08
  Speaker 1: wavefront which is moving through the universe and then slowing down.
• 26:11
  Speaker 1: But we don't know that there was an edge. We
• 26:13
  Speaker 1: don't know if there is an edge. I think the
• 26:15
  Speaker 1: cleanest way to think about these things is to think
• 26:18
  Speaker 1: that the universe is infinite. We don't know that's true,
• 26:21
  Speaker 1: but it seems somehow more natural to have an infinite
• 26:24
  Speaker 1: universe than to have an edge. And then you can grapple.
• 26:27
  Speaker 1: Instead of thinking about the whole universe, just think about
• 26:30
  Speaker 1: a chunk of it and think about sort of the
• 26:32
  Speaker 1: density of that part of the universe. So I imagine
• 26:34
  Speaker 1: the whole universe created infinite at its birth as a
• 26:38
  Speaker 1: very very dense place, and then expanded suddenly, very rapidly,
• 26:43
  Speaker 1: using inflation. So there's no edge there. Everything is moving
• 26:47
  Speaker 1: away from everything else. He also asks, if there's no edge,
• 26:51
  Speaker 1: what's slowing it down? Why isn't it still expanding at
• 26:55
  Speaker 1: that crazy rate? Awesome question. I wish I knew the answer.
• 26:58
  Speaker 1: There was this incredible moment of inflation in the very
• 27:01
  Speaker 1: early universe, this rapid expansion in a very short amount
• 27:04
  Speaker 1: of time. We don't know what caused it. We have
• 27:07
  Speaker 1: ideas about ideas were sort of proto ideas for what
• 27:11
  Speaker 1: might have caused it, crazy particles and field called the
• 27:14
  Speaker 1: infloton field, but those are sort of placeholders to have ideas.
• 27:17
  Speaker 1: We don't really have any well worked out, super well
• 27:20
  Speaker 1: formulated ideas that actually come together mathematically to explain inflation.
• 27:26
  Speaker 1: So because we don't know what started it and what
• 27:28
  Speaker 1: sustained it, we also don't know why it stopped. We
• 27:30
  Speaker 1: just know that it started and we know that it stopped,
• 27:33
  Speaker 1: but the expansion itself has not stopped. It was very
• 27:36
  Speaker 1: rapid in the very beginning, and then it was very
• 27:38
  Speaker 1: slow for a while, but about five billion years ago
• 27:41
  Speaker 1: it started to pick up again. Dark energy took over
• 27:44
  Speaker 1: and it started to accelerate the expansion of the universe
• 27:47
  Speaker 1: once again. And this expansion is very similar to what
• 27:51
  Speaker 1: happened in the inflationary period of the universe. It's not
• 27:54
  Speaker 1: nearly as rapid, but the sort of stretching of space
• 27:57
  Speaker 1: is the same concept. We don't know if there's a
• 28:00
  Speaker 1: relationship between the mechanism or the reason for why space
• 28:04
  Speaker 1: is expanding now and why space expanded in the very beginning.
• 28:08
  Speaker 1: We're pretty clueless about what dark energy is. Again. We
• 28:11
  Speaker 1: have a few basic ideas for what might explain it,
• 28:14
  Speaker 1: but none of them hold together mathematically, so most of
• 28:16
  Speaker 1: this is just an observation. We see that this happened,
• 28:19
  Speaker 1: we can't explain why. So it is still expanding at
• 28:23
  Speaker 1: a crazy rate, not as crazy, but we don't know
• 28:26
  Speaker 1: the answer to the question why the universe stopped inflating
• 28:29
  Speaker 1: and why it's not inflating at that crazy rate today. So, Jeff,
• 28:33
  Speaker 1: the answer to your question is that the universe expanded
• 28:36
  Speaker 1: so rapidly, not by things moving through space, but by
• 28:39
  Speaker 1: expanding the nature of space itself, by creating new space
• 28:43
  Speaker 1: between stuff and why did that stop. We don't know
• 28:46
  Speaker 1: why inflation itself stopped, but the expansion has not stopped.
• 28:50
  Speaker 1: The universe is still expanding, and it's expanding faster and
• 28:53
  Speaker 1: faster every day. All right, Thanks for that super awesome question.
• 28:57
  Speaker 1: I love all of these ideas. I have one more
• 28:59
  Speaker 1: question I'm an get to today, but first let's take
• 29:01
  Speaker 1: another quick break. Okay, we're back and this is Daniel
• 29:17
  Speaker 1: and I'm answering questions about the nature of the universe
• 29:20
  Speaker 1: and how it expanded and whether it violates conservation of energy.
• 29:25
  Speaker 1: And our next question is a tiny bit more concrete. Hi,
• 29:28
  Speaker 1: Daniel and JOI I'm Tristan from Melbourne, Australia. Congratulations on
• 29:33
  Speaker 1: the awesome podcast. My question is about spice dust. We
• 29:37
  Speaker 1: hear about it all the time, but what exactly is
• 29:40
  Speaker 1: spice dust? Is it tiny gas molecules or really minute
• 29:44
  Speaker 1: dust particles like here on Earth or is spice dust
• 29:48
  Speaker 1: just a relative term? And they'm all like basketball sized
• 29:51
  Speaker 1: or cast sized or bigger? All right, Thanks very much
• 29:54
  Speaker 1: for that fun question. This is actually a surprisingly fascinating
• 29:57
  Speaker 1: topic when you think about do you think it's like
• 30:00
  Speaker 1: dirt and something you want to get rid of. It's
• 30:02
  Speaker 1: an annoyance. It gets in your way. If you zoom
• 30:05
  Speaker 1: in on it, you discover that, like a lot of
• 30:07
  Speaker 1: the dust in your house is actually left over dried
• 30:10
  Speaker 1: bits of human skin that makes you want to throw
• 30:12
  Speaker 1: up a little bit. So space dust is sort of similar.
• 30:15
  Speaker 1: For a long time, people thought space dust was just
• 30:18
  Speaker 1: like an annoyance. It was this stuff floating in space
• 30:21
  Speaker 1: which like blocked your view. I mean, if you look
• 30:24
  Speaker 1: out into space, it's incredible how far we can see.
• 30:28
  Speaker 1: You're standing on the top of a rock in space
• 30:30
  Speaker 1: and you're peering out in your eyeballs are absorbing photons
• 30:33
  Speaker 1: that have traveled billions of light years, mostly unimpeded to
• 30:37
  Speaker 1: get to you. It's incredible that space is as clear
• 30:40
  Speaker 1: as it is, so we shouldn't be complaining. We have
• 30:43
  Speaker 1: the best view in the universe. The kind of things
• 30:46
  Speaker 1: we see with hubble are just eye dropping the gorgeous.
• 30:50
  Speaker 1: But sometimes there are things that are obscured by space dust.
• 30:54
  Speaker 1: If you look at the center of the galaxy, for example,
• 30:56
  Speaker 1: they're huge clouds of dust to make it harder to
• 30:58
  Speaker 1: see what's going on there. And for a long time
• 31:01
  Speaker 1: astronomers treated space dust that way, like an annoyance, like, oh,
• 31:06
  Speaker 1: these things are shrouded in dust, so we can't see
• 31:09
  Speaker 1: them what's going on inside there? And if you're like me,
• 31:12
  Speaker 1: your curiosity is only heightened when something is hidden, something
• 31:15
  Speaker 1: is behind a veil, like things inside a black hole.
• 31:19
  Speaker 1: It just makes me want to know even more what's there.
• 31:22
  Speaker 1: So for a long time space dust was treated that way.
• 31:25
  Speaker 1: It's just something that gets in our way, something to
• 31:27
  Speaker 1: be annoyed about. However, now we see that space dust
• 31:31
  Speaker 1: is just sort of part of the dynamics of space,
• 31:33
  Speaker 1: part of the astrophysical soup that's constantly churning, making new
• 31:38
  Speaker 1: stars and all their crazy things, and it can actually
• 31:41
  Speaker 1: help us understand the structure of the galaxies and how
• 31:44
  Speaker 1: things work. For example, we can see space dust. It
• 31:47
  Speaker 1: doesn't just blocklight, it actually gives off its own light.
• 31:52
  Speaker 1: This is something I think is not widely enough understood
• 31:55
  Speaker 1: that everything in the universe glows. Everything in the universe
• 31:59
  Speaker 1: that's made that of our kind of stuff atoms, that's
• 32:02
  Speaker 1: only five of the universe, but all that stuff glows,
• 32:06
  Speaker 1: and it glows based on its temperature. The hotter you are,
• 32:09
  Speaker 1: the more energetic photons you give off, which is why.
• 32:12
  Speaker 1: For example, if you heat up metal, it starts to
• 32:15
  Speaker 1: glow and it glows at different frequencies, different colors as
• 32:19
  Speaker 1: it gets hotter. Everything is actually like that. Even you glow,
• 32:23
  Speaker 1: and if you put on infrared goggles then you can
• 32:26
  Speaker 1: see your body heat because of your temperature. But it's
• 32:29
  Speaker 1: not just living things. Even rocks glow, even if they're
• 32:33
  Speaker 1: very very cold. They glow at some wavelength. And space
• 32:37
  Speaker 1: dust is out there and it glows as well, so
• 32:40
  Speaker 1: you can see it. It's not giving off visible light.
• 32:43
  Speaker 1: But if you have a special camera like night vision
• 32:46
  Speaker 1: goggles for the universe and what we call an infrared telescope,
• 32:49
  Speaker 1: then you can see it. And if you point an
• 32:51
  Speaker 1: infrared telescope, for example, at the Andromeda galaxy, you can
• 32:55
  Speaker 1: see where in Andromeda there is this space dust. The
• 33:00
  Speaker 1: space does glows at different frequencies than the stars. The
• 33:04
  Speaker 1: stars admitted visible light and you can see them. That's
• 33:06
  Speaker 1: super fascinating. But then if you turn on your night
• 33:09
  Speaker 1: vision goggles for space, you can see the other stuff,
• 33:12
  Speaker 1: the colder stuff, which is glowing at longer wavelengths in
• 33:16
  Speaker 1: the infrared, and you can see it totally differently, and
• 33:19
  Speaker 1: Dromeda looks different in the infrared, you can see where
• 33:23
  Speaker 1: the space dust is, and that helps us understand like
• 33:26
  Speaker 1: how did and Drameda form, what's going on over there,
• 33:29
  Speaker 1: what are the dynamics, what things are moving against the
• 33:31
  Speaker 1: other stuff. So these days space dust isn't just like
• 33:34
  Speaker 1: an annoyance. It isn't just a cloud that gets in
• 33:37
  Speaker 1: your way. It's another thing out there that we can study.
• 33:41
  Speaker 1: And it turns out that there's a lot of different
• 33:42
  Speaker 1: kinds of space dust. Most generally, what is space dust.
• 33:46
  Speaker 1: It's basically anything that's out there in space that's very,
• 33:50
  Speaker 1: very small, right, So you wouldn't call Earth a big
• 33:53
  Speaker 1: speck of space dust. This is one of those arbitrary
• 33:56
  Speaker 1: categorizations in astronomy and astrophysics. Space does is basically anything
• 34:00
  Speaker 1: that's out there that's smaller than like a millimeter, and
• 34:03
  Speaker 1: it can go down all the way to like a
• 34:05
  Speaker 1: few molecules, but the upper edge is generally agreed to
• 34:09
  Speaker 1: be like a millimeter or half a millimeter, maybe a
• 34:11
  Speaker 1: tenth of a millimeter. Anything that size or smaller that's
• 34:15
  Speaker 1: floating out in space, we call it space dust. Bigger
• 34:18
  Speaker 1: than that, like a basketball or car sized thing, we
• 34:21
  Speaker 1: would call that an asteroid. Or a comet, or even
• 34:24
  Speaker 1: a proto planet or a moon or right a sun
• 34:27
  Speaker 1: if it gets big enough. So there's this whole spectrum
• 34:30
  Speaker 1: of sizes of stuff in space and things on the
• 34:33
  Speaker 1: smaller edge we call space and dust. And you might wonder, like, well,
• 34:37
  Speaker 1: why is there space dust? After all, you have these
• 34:40
  Speaker 1: huge clouds of things formed after the Big Bang, and
• 34:43
  Speaker 1: some of it gathered together to make stars, and some
• 34:46
  Speaker 1: of it gathered together to make planets, but not everything
• 34:49
  Speaker 1: instantly gets clean together. Right. Gravity is very patient, but
• 34:53
  Speaker 1: it's also very very weak, And the gravity on very
• 34:57
  Speaker 1: small objects, tiny little specks of up floating out in space,
• 35:01
  Speaker 1: is very weak. And other things I'm much more powerful.
• 35:04
  Speaker 1: One thing that prevents gravity from gathering stuff together is
• 35:08
  Speaker 1: angular momentum. If something is moving in a circle around
• 35:11
  Speaker 1: something with gravity, then it doesn't necessarily fall in the
• 35:15
  Speaker 1: same way the Earth orbits the Sun without falling in,
• 35:18
  Speaker 1: even though there is gravity tugging on the Earth from
• 35:21
  Speaker 1: the Sun. The reason we don't fall in immediately is
• 35:24
  Speaker 1: because we're moving in a circle. The same reason the
• 35:26
  Speaker 1: whole galaxy doesn't collapse into the central black hole is
• 35:30
  Speaker 1: because of angular momentum. That's just one example and so
• 35:33
  Speaker 1: that keeps some space dust from collapsing into larger objects,
• 35:38
  Speaker 1: and so you end up with this whole spectrum of
• 35:39
  Speaker 1: really dense stuff that's sort of cleared out the space
• 35:42
  Speaker 1: around them than a whole distribution of smaller bits, which
• 35:45
  Speaker 1: we call space dust. And we can study this stuff.
• 35:49
  Speaker 1: NASA actually sends planes up into the high atmosphere to
• 35:52
  Speaker 1: gather space dust and these big collectors under the wings
• 35:56
  Speaker 1: to pull it together and say like, well, what's in there.
• 35:59
  Speaker 1: And actually there's a huge amount of space dust out there.
• 36:01
  Speaker 1: It's not very rare. The Earth is traveling through a
• 36:05
  Speaker 1: cloud of this stuff is like one particle per million
• 36:09
  Speaker 1: cubic meters, but there's a lot of cubic meters out there,
• 36:13
  Speaker 1: and there's a lot of square meters on the surface
• 36:15
  Speaker 1: of the Earth, and so a lot of space dust
• 36:17
  Speaker 1: actually falls onto the Earth every year. Some of the
• 36:21
  Speaker 1: stuff that's lying around your house might be dead bits
• 36:23
  Speaker 1: of skin, but some of it might be space dust,
• 36:26
  Speaker 1: because there are thousands of tons of space dust that
• 36:30
  Speaker 1: reached the surface of the Earth every year. Yeah. I
• 36:33
  Speaker 1: just about fell out of my chair when I read
• 36:35
  Speaker 1: that tidbit that fact thousands of tons of the stuff
• 36:39
  Speaker 1: if you could like sweep up all the space dust
• 36:42
  Speaker 1: that hits the Earth and make a pile of it,
• 36:44
  Speaker 1: it would be a huge, huge mountain of space dust,
• 36:48
  Speaker 1: all right. So then what is this stuff? Right? What
• 36:51
  Speaker 1: is this stuff that's out there, that's floating through the
• 36:53
  Speaker 1: universe that didn't get gathered together into planets and rocks
• 36:57
  Speaker 1: and other kinds of stuff. Well, it's a big mix, right.
• 37:00
  Speaker 1: It's basically a big soup of leftover stuff either from
• 37:03
  Speaker 1: the very early universe that never got gathered together into
• 37:07
  Speaker 1: something else, or that has had a chance to be
• 37:10
  Speaker 1: part of a star or a planet and then got
• 37:12
  Speaker 1: blown into little smithereens. So one category of stuff is
• 37:16
  Speaker 1: star dust. Star dust are little pellets made on the
• 37:20
  Speaker 1: outside of stars, a little grains, for example, of oxygen
• 37:24
  Speaker 1: or carbon rich elements that are floating out near the
• 37:27
  Speaker 1: outside of stars, and that gets blown out away from
• 37:30
  Speaker 1: the star and so they get frozen into these little pellets.
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  Speaker 1: Remember that in the first population of stars, we had
• 37:35
  Speaker 1: only hydrogen, but those hydrogen stars burned helium, and in
• 37:39
  Speaker 1: later generations of stars fuse that helium into heavier and
• 37:43
  Speaker 1: heavier stuff. So stars are the engines to make these
• 37:46
  Speaker 1: heavier elements, and eventually they can gather together. A lot
• 37:50
  Speaker 1: of this we call it ash because it's the product
• 37:52
  Speaker 1: of fusion. A lot of it falls to the center
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  Speaker 1: of the star, makes a denser and denser core, which
• 37:57
  Speaker 1: eventually leaves the star to collapse, not all of it,
• 38:00
  Speaker 1: so if it gets blown out into the outer edges
• 38:03
  Speaker 1: of the star, and then it can get pushed even
• 38:05
  Speaker 1: further out and float out into space. So these little
• 38:08
  Speaker 1: grains of stuff produced inside stars, this is called star dust,
• 38:13
  Speaker 1: and this is floating out there, and a good amount
• 38:15
  Speaker 1: of the space dust are actually these kinds of grains,
• 38:18
  Speaker 1: and a lot of them came together to form our
• 38:21
  Speaker 1: star and our planet. So a lot of what makes
• 38:24
  Speaker 1: me and you and the Sun are actually these bits
• 38:27
  Speaker 1: of other stars. Now, of course, inside the Earth and
• 38:30
  Speaker 1: inside the Sun, they've all been melted down to their
• 38:33
  Speaker 1: basic elements and maybe even fused into other stuff. But
• 38:36
  Speaker 1: space dust hasn't. It's frozen. It's like a little time
• 38:39
  Speaker 1: capsule that tells you where it came from. And if
• 38:42
  Speaker 1: you can capture one of these grains of star dust,
• 38:44
  Speaker 1: and you can look at the relative fractions of stuff,
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  Speaker 1: like how much iron is there, how much carbon is there?
• 38:50
  Speaker 1: Then you can get an idea from what kind of
• 38:52
  Speaker 1: star came from. You can read like it's ancient history
• 38:56
  Speaker 1: just by looking at what's inside of it. So each
• 38:59
  Speaker 1: of these is like a little time capsule that tells
• 39:01
  Speaker 1: us what happened. And these events are billions of years old.
• 39:05
  Speaker 1: You know the star dusk grains that helped form our sun,
• 39:08
  Speaker 1: well that was five billion years ago, So they were
• 39:10
  Speaker 1: produced more than five billion years ago, and they're still
• 39:14
  Speaker 1: floating around. Some of them coalesced into like micro meteorites,
• 39:18
  Speaker 1: but they don't necessarily lose their elemental structure. They just
• 39:21
  Speaker 1: sort of got like get stuck together like a big
• 39:23
  Speaker 1: pile of rice grains. And so if you're careful, you
• 39:26
  Speaker 1: can tear them apart and look at the individual grains
• 39:29
  Speaker 1: and still study these little time capsule from other stars. Now,
• 39:33
  Speaker 1: sometimes you look at these space dust capsules and you
• 39:35
  Speaker 1: see something really strange, and people actually predicted that you
• 39:38
  Speaker 1: would see this. You see things produced in supernovas. Supernovas, remember,
• 39:43
  Speaker 1: are these very special occasions. When it starts, gravity overcomes
• 39:47
  Speaker 1: its pressure and it collapses very very rapidly, this implosion,
• 39:51
  Speaker 1: which then leads to an explosion where it throws crazy
• 39:54
  Speaker 1: stuff through space. Well, in those moments of implosion are
• 39:59
  Speaker 1: intense moments of fusion, and these are situations that allow
• 40:02
  Speaker 1: for the creation of other kinds of elements and different
• 40:04
  Speaker 1: mixtures of elements than what you would expect from the
• 40:07
  Speaker 1: normal production you get in a star. And sometimes these
• 40:11
  Speaker 1: things get thrown out during the supernova and they're like
• 40:13
  Speaker 1: little time capsules, a little like samples from what's going
• 40:16
  Speaker 1: on deep inside is supernova. So these supernova grains are
• 40:21
  Speaker 1: super awesome vines because they're not created nearly as often,
• 40:25
  Speaker 1: and they're this little time capsule from this incredible moment
• 40:28
  Speaker 1: during one of the most violent acts in our universe,
• 40:32
  Speaker 1: so they're super fun. And then a lot of the
• 40:34
  Speaker 1: other space dust is just floating tiny rocks. Basically. Some
• 40:38
  Speaker 1: of them are carbonaceous, you know, other ones have iron
• 40:41
  Speaker 1: or sulfur or nickel. Some of them are silicates, which
• 40:43
  Speaker 1: means they're basically bits of sand, and they have all
• 40:46
  Speaker 1: sorts of irregular shapes, you know, just like any random rocks.
• 40:49
  Speaker 1: Some of them are kind of fluffy, loose amalgams. Some
• 40:52
  Speaker 1: of them are very compact. Some of them accumulate little
• 40:55
  Speaker 1: layers of ice around them, so you might expect them
• 40:57
  Speaker 1: to be like super mini comets, and and the sizes
• 41:00
  Speaker 1: of them differ. Right, they go all the way down
• 41:02
  Speaker 1: from the tiny, tiny little grains up to you know,
• 41:05
  Speaker 1: less than a millimeter or so. And this is important
• 41:08
  Speaker 1: because the size determines how you can see them. Like
• 41:12
  Speaker 1: pretty big grains actually reflect light, so if the sun
• 41:16
  Speaker 1: is behind you, you could see them the way you
• 41:18
  Speaker 1: see the moon, like comes from the sun bounces off
• 41:21
  Speaker 1: of them and then back to you. But if they're
• 41:23
  Speaker 1: really really small, then they don't reflect light. They just
• 41:26
  Speaker 1: sort of deflected a little bit, which means it's only
• 41:29
  Speaker 1: easy to see them if the light is behind them.
• 41:32
  Speaker 1: They have to be back lit, and this is why,
• 41:34
  Speaker 1: for example, we didn't really know that Jupiter had rings
• 41:38
  Speaker 1: and had rings made of dust until we got cameras
• 41:41
  Speaker 1: out past Jupiter and you could look back and you
• 41:45
  Speaker 1: could see those rings of dust back lit by the
• 41:48
  Speaker 1: sun because they only deflect the light a little bit.
• 41:51
  Speaker 1: So it's important how big they are, and it's also
• 41:54
  Speaker 1: important their shape. We think this space dust is not
• 41:57
  Speaker 1: just around the Solar System, and not just in the galaxy,
• 42:01
  Speaker 1: but also between the galaxies. It's basically spread out everywhere,
• 42:05
  Speaker 1: and it's actually really valuable because these grains are not spheres.
• 42:09
  Speaker 1: They're like weird, all blong shapes. So what they do
• 42:12
  Speaker 1: is they tend to align with magnetic fields. They're like
• 42:15
  Speaker 1: tiny little needles and they tend to line up with
• 42:18
  Speaker 1: magnetic fields. And people have been studying magnetic fields through space,
• 42:21
  Speaker 1: wondering like, is their magnetic fields all through the galaxy?
• 42:25
  Speaker 1: Are there magnetic fields between galaxies? Are there magnetic fields
• 42:29
  Speaker 1: in deep space that were created during the Big Bang?
• 42:32
  Speaker 1: This is called the primordial magnetic field. We have a
• 42:35
  Speaker 1: whole podcast episode about it. If you listen to that.
• 42:38
  Speaker 1: What you learn is that these dust grains line up
• 42:41
  Speaker 1: with magnetic fields, which is important because it changes how
• 42:44
  Speaker 1: light moves through it because these dust greens are now polarized,
• 42:48
  Speaker 1: and so we can use space duft to sort of
• 42:51
  Speaker 1: track the magnetic fields in otherwise empty portions of space,
• 42:56
  Speaker 1: sort of like sprinkling magnetic filings on a sheet to
• 42:59
  Speaker 1: see if the the magnetic field there. It's actually good
• 43:02
  Speaker 1: that space dust is sort of everywhere, because if space
• 43:05
  Speaker 1: was truly empty, it would be much much harder to
• 43:07
  Speaker 1: study it. Alright, So I hope that answers your question,
• 43:11
  Speaker 1: what is space dust? It's tiny little grains of stuff,
• 43:14
  Speaker 1: some of them created within stars, some within supernovas, some
• 43:18
  Speaker 1: of them aligning with magnetic meals to tell us where
• 43:20
  Speaker 1: things are. We don't know what their future is. Maybe
• 43:23
  Speaker 1: one day some of them will gather together to make
• 43:25
  Speaker 1: a new star, a new planet, even a new race
• 43:28
  Speaker 1: of intelligent aliens that make a podcast even better than ours.
• 43:32
  Speaker 1: All right, so thank you very much everybody who's sent
• 43:35
  Speaker 1: in questions, and thanks also to those of you who
• 43:37
  Speaker 1: have sent in listener questions audio and not yet had
• 43:40
  Speaker 1: your questions answer. I promise we will get through our
• 43:43
  Speaker 1: backlog and we will answer all of your questions, because
• 43:47
  Speaker 1: I think that everybody out there should be asking questions
• 43:49
  Speaker 1: about the universe, should be tapped into their innate curiosity.
• 43:53
  Speaker 1: Discovering how the world works. Asking these questions and knowing
• 43:56
  Speaker 1: that there's an answer is one of the most satisfying experience.
• 44:00
  Speaker 1: Is it tells you that maybe the human mind is
• 44:02
  Speaker 1: capable of gaining not a full understanding, but at least
• 44:05
  Speaker 1: a foothold into our universe of ignorance, cracking that open
• 44:09
  Speaker 1: a little bit and revealing a tiny slice of how
• 44:12
  Speaker 1: the universe works. It's certainly we're doing, even if it
• 44:15
  Speaker 1: doesn't immediately lead to applications and better lasers and pants
• 44:19
  Speaker 1: with better zippers and stuff like that. I view the
• 44:22
  Speaker 1: deep exploration of the nature in the universe to be
• 44:24
  Speaker 1: on par with the creation of art. It's part of
• 44:27
  Speaker 1: what makes life worth living. So thanks everyone for lending
• 44:31
  Speaker 1: us your questions and your curiosity. It's been a wonderful ride,
• 44:34
  Speaker 1: and tune in next time for more questions from listeners.
• 44:45
  Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain
• 44:48
  Speaker 1: the Universe is a production of I Heart Radio or
• 44:51
  Speaker 1: more podcast from my Heart Radio. Visit the I Heart
• 44:54
  Speaker 1: Radio Apple Apple Podcasts, or wherever you listen to your
• 44:58
  Speaker 1: favorite shows.