Speaker 1: Hey or hey, I have a physics version of would
Speaker 1: you rather?
Speaker 2: Well, oh, I'd rather not play?
Speaker 1: Not an option today? So would you rather be blown
Speaker 1: up in a supernova or crushed in a black hole?
Speaker 2: Well, if I fell into a black hole, there would
Speaker 2: be time dilation, so it sounds like it would take forever.
Speaker 2: So maybe I'll go with a supernova, nice and quick.
Speaker 1: All right? Next one, would you rather be eaten by
Speaker 1: aliens or live your life never knowing if aliens exist?
Speaker 2: I would pick live my life over and being eaten
Speaker 2: by anything, aliens or otherwise.
Speaker 1: Wrong answer, wrong answer. Next one, would you rather keep
Speaker 1: playing this game or start the podcast?
Speaker 2: I'll pick the supernova again. Please, I'm crushed just trying
Speaker 2: to blow this up.
Speaker 1: Hi.
Speaker 2: I'm hoorhamy cartoonist and the creator of PhD comics.
Speaker 1: Hi I'm Daniel. I'm a particle physicist and a professor
Speaker 1: at UC Irvine, and I would rather be eaten by
Speaker 1: aliens than never know if they exist for real.
Speaker 2: Well, I guess if you get do you get to
Speaker 2: choose when you get eaten by aliens? You know, if
Speaker 2: you can choose to get it done right before you're
Speaker 2: gonna die of natural causes. Maybe that's okay, but like
Speaker 2: right now, you would make that choice right now.
Speaker 1: I think this game is all about those loopholes, like
Speaker 1: when people are planning for end of life, like do
Speaker 1: you want to get buried or do you want to
Speaker 1: get cremated. I'm going to fill out a box that
Speaker 1: says I want to get eaten by aliens. But yeah,
Speaker 1: it'd be nice if they waited till after I already
Speaker 1: died of natural causes. Then you know, hey, barbecue me
Speaker 1: for the alien pot luck. That's fine.
Speaker 2: You gotta be careful, though, do you mean like extraterrestrial
Speaker 2: aliens or people who are you know, alien alien to
Speaker 2: your life or to your city?
Speaker 1: You know what, I'm not gonna be around, so I
Speaker 1: guess it doesn't really matter.
Speaker 2: Oh you're gonna be around as you're getting in.
Speaker 1: As long as I get to learn about the aliens
Speaker 1: while I'm still alive, nothing else really matters.
Speaker 2: Oh boy. Anyways, Welcome to our podcast Daniel and Jorge
Speaker 2: Explain the Universe, a production of iHeartRadio in which.
Speaker 1: We take great pains and great sacrifices to try to
Speaker 1: explain the nature of the universe to you. We cast
Speaker 1: our minds out into that dark cosmic mystery and wonder
Speaker 1: what's out there, who's out there, what's going on out there,
Speaker 1: how big is it? Is it still sloshing around, and
Speaker 1: what will be its final fate. We want to understand
Speaker 1: the cosmic context of our very existence because it drives
Speaker 1: the choices we make every day about whether or not
Speaker 1: we sign ourselves up to be part of an alien barbecue.
Speaker 2: That's right. It is a humongous universe full of amazing
Speaker 2: and awesome things out there that may kill you or
Speaker 2: eat you, and or inspire you to learn more about
Speaker 2: the universe and the cosmos and how everything works in it.
Speaker 1: And it's part of this sort of incredible mental history,
Speaker 1: the trajectory of our sort of mental map of the cosmos.
Speaker 1: You know, it started out pretty small, your little village,
Speaker 1: your neighborhood, eventually expanded to be a larger and larger region.
Speaker 1: Finally people started incorporating the cosmos into it, this mental
Speaker 1: picture of the whole universe that we were in. But
Speaker 1: it just gets bigger and bigger as we understand where
Speaker 1: our solar system sits and where our galaxy sits, and
Speaker 1: as our telescopes get more and more powerful, we can
Speaker 1: now understand even further the context of our cosmic neighborhood.
Speaker 2: Yeah, it used to be there. Our context was pretty
Speaker 2: much like the Earth, and people thought that the Sun
Speaker 2: and the moon and the stars all revolved around the Earth.
Speaker 2: People thought that the entire universe was just us.
Speaker 1: Yeah. I was reading about ancient Chinese astronomy and they
Speaker 1: even calculated like how far away the stars were. They
Speaker 1: thought it was something like twenty seven thousand miles above
Speaker 1: the Earth.
Speaker 2: Oh, that's pretty close.
Speaker 1: And the Greeks thought that everything moved in like literal
Speaker 1: crystal spheres around the Earth. That was the original ether.
Speaker 2: Interesting, now, Daniel, do we know for sure that's not true?
Speaker 2: Do you know for sure that's not true.
Speaker 1: I mean, we've sent probes out there to visit these things,
Speaker 1: so we're pretty sure there are no crystal spheres out
Speaker 1: there moving the planets.
Speaker 2: By we mean the perverurial we but have you gone
Speaker 2: up there and touched these that made sure there's no
Speaker 2: crystal spheres.
Speaker 1: I'm going to take NASA's word for it, you know,
Speaker 1: for sure. I'm not part of the conspiracy community that
Speaker 1: thinks NASA's been lying to us all these years.
Speaker 2: You know, part of the crystal sphere conspiracy.
Speaker 1: I'm sure there's a group of crystal truthists out there.
Speaker 2: You know, part of the China was right theory.
Speaker 1: No, but the Chinese did make a lot of really
Speaker 1: amazing observations. You know, we have like records of eclipses
Speaker 1: dating back foulands of years from China and observations is
Speaker 1: like super nova from almost a thousand years ago. So
Speaker 1: it's a really rich history of astronomical observations, some of
Speaker 1: which are still relevant to our studies today. Is incredible.
Speaker 2: Oh, it's pretty cool. Yeah, because, as you were saying,
Speaker 2: our understanding of where or and how we fit in
Speaker 2: this universe keeps growing and growing, and it seems like
Speaker 2: each time we just get more and more insignificant with
Speaker 2: each step.
Speaker 1: But we become more and more aware of that significance,
Speaker 1: which makes us sort of like philosophically more important. Right,
Speaker 1: We're like incorporating more of the universe into our minds.
Speaker 2: No, that makes no sense. We're insignificant specs in this
Speaker 2: giant universe.
Speaker 1: But it's better to know about your insignificance because then
Speaker 1: you've gained some philosophical stature.
Speaker 2: Like being know where you're being in by aliens doesn't help.
Speaker 2: The fact that you're being eaten by.
Speaker 1: Eight still makes it worth. It still makes it worth.
Speaker 2: In fact, that makes it worse. But it does seem
Speaker 2: like we are getting smaller and smaller in the sumer
Speaker 2: And literally that's true, right because every year, every second
Speaker 2: of the day, the universe, or our understanding of how
Speaker 2: big it is, keeps getting bigger.
Speaker 1: Right, it does. And even though we cannot explore the
Speaker 1: far flung edges of the observable universe, we can build
Speaker 1: this mental model, this sort of map of our neighborhood
Speaker 1: that tells us where we are in this glittering cosmos.
Speaker 1: And so even though no human will probably visit those
Speaker 1: planets or visit those stars, we can still tell you
Speaker 1: something about what's going on out there. And to me
Speaker 1: that's incredible. Yes, we are probably trapped on this rock
Speaker 1: or our neighboring rocks, but still we can build this
Speaker 1: map of the cosmos, we can understand something about it.
Speaker 1: And to me, that's a great achievement sort of intellectually
Speaker 1: and scientifically, and what I'm pretty proud of.
Speaker 2: Yeah, again, I think you're using the proverbial we there,
Speaker 2: you're proud of the work of others. Let's be honest here.
Speaker 1: No, I'm standing on the shoulders of many, many giants,
Speaker 1: and I'm proud of their work. Absolutely, I'm not personally
Speaker 1: taking credit for our understanding of the universe in case
Speaker 1: anybody misunderstood, But.
Speaker 2: At least we're helping, I guess talk about what they've
Speaker 2: done and disseminate this information out to others. And it's
Speaker 2: interesting when you say like that we might never reach
Speaker 2: those places that we're seeing far far away. I'm wonder
Speaker 2: if that's really true. I guess that's true because our
Speaker 2: view of the universe expanding at the speed of light,
Speaker 2: and there's no way that humans could outpacete that. Right.
Speaker 1: Yeah, it's amazing we can see things that are moving
Speaker 1: away from us faster than the speed of light. A
Speaker 1: bunch of listeners wrote in and asked, like, how does
Speaker 1: that work? We have a whole episode covering it, but briefly,
Speaker 1: the thing to understand when you're looking at an object
Speaker 1: and they tell you, oh, this thing is thirty billion
Speaker 1: years away and it's moving away from us faster than
Speaker 1: the speed of light, is that you're not seeing it
Speaker 1: where it is now. They're telling you where it is now.
Speaker 1: But you're seeing the light that was emitted from it
Speaker 1: when it was much much closer. So it used to
Speaker 1: be much closer, and it's sent a photon our way.
Speaker 1: In the meantime, it's moved really really far away. When
Speaker 1: they say here, we're looking at a galaxy that's really
Speaker 1: really far away, we're not seeing light that came to
Speaker 1: us from it when it was that far away. Were
Speaker 1: seeing light that came to us when it was much
Speaker 1: much closer. Light that leaves it now we will never see,
Speaker 1: which means also we will never visit it.
Speaker 2: Mmm. Yeah, Because the universe is expanding faster and faster
Speaker 2: every time, every second of the day. Although we don't
Speaker 2: know what's going to happen in the future right, it
Speaker 2: could be that in the far distant future or maybe tomorrow,
Speaker 2: the universe might decide, Hey, I think I'm going to
Speaker 2: stop growing and I'm going to collapse back on myself,
Speaker 2: and in which case, we're going to basically visit every
Speaker 2: place in the universe at some point.
Speaker 1: Yeah, or they're going to come visit us and they're
Speaker 1: going to bring with them all their aliens, with all
Speaker 1: their barbecue.
Speaker 2: Tools, all their appetites. Well, maybe the big joke is
Speaker 2: that in the end, the universe eats us.
Speaker 3: All.
Speaker 1: Well, we are the universe, so I guess the universe
Speaker 1: eats itself. I'm not sure how that works.
Speaker 2: Whoa dude.
Speaker 1: And even though we are learning that we are a
Speaker 1: tiny speck in a vast, vast cosmos, I think it
Speaker 1: does make us sort of like philosophically or intellectually more
Speaker 1: powerful to have grappled with that vast cosmos. It's better
Speaker 1: at least than being ignorant of what's going on right right?
Speaker 2: But don't they say ignorance is bliss Sometimes?
Speaker 1: Who's looking for bliss? Man, I'm looking for knowledge.
Speaker 2: Maybe that's the difference between you and me and Daniel.
Speaker 2: I'll go for bliss any day.
Speaker 1: Okay, Well, I'm glad we can split the tasks. But
Speaker 1: it's also fun to think about that far future you
Speaker 1: were talking about and wondering, like, what does the future hold?
Speaker 1: Will our solar system survive for our billion years? Will
Speaker 1: our galaxy survive for ten billion years? What exactly is
Speaker 1: going to happen to our cosmic neighborhood over cosmic deep time? Yeah?
Speaker 2: Because, as we mentioned, the universe is expanding faster and
Speaker 2: faster and faster and that has some pretty dramatic consequences
Speaker 2: for some of the bigger structures in the universe. And
Speaker 2: so today on the podcast we'll be tackling the question
Speaker 2: will our super cluster be torn apart? Sounds kind of sad.
Speaker 1: Like a chunk of juicy barbecue.
Speaker 2: Well, wow, who would eat a giant supercluster galaxies.
Speaker 1: Some giant super space crab? I suppose, Oh boy?
Speaker 2: And how big does the barbecue sauce bottle need to be? Well,
Speaker 2: this is an interesting question and so we'll dig into
Speaker 2: it of what a supercluster is, what does it mean
Speaker 2: for it to be torn apart? And what could be
Speaker 2: causing it to be torn apart? But as usual, we
Speaker 2: were wondering how many people had considered these words together
Speaker 2: as a question out there in the internet.
Speaker 1: So thanks very much to everybody who participates in this
Speaker 1: segment of our podcast. It's super fun for us to
Speaker 1: hear what you're thinking about the topic of the day.
Speaker 1: Please don't be shy. If you'd like to participate in
Speaker 1: the future, just write to me to Questions at Danielandjorge
Speaker 1: dot com.
Speaker 2: So think about it for a second. Do you think
Speaker 2: our supercluster will be torn apart. Here's what people have
Speaker 2: to say. I say no, I believe that dark matter
Speaker 2: and dark energy will keep it together, just like it
Speaker 2: build the supercluster that we see today.
Speaker 4: Well, our supercluster, if I believe right, is a collection
Speaker 4: of galaxy that we're in kind of grouped up. So
Speaker 4: if anything, I feel like it would get larger just
Speaker 4: by gravitationally attracting other galaxies that are just floating out there.
Speaker 3: If I get it right, the galaxies of our supercluster
Speaker 3: won't drift apart due to the expansion of the universe,
Speaker 3: but they might dive into each other.
Speaker 5: A supercluster is a group of galaxy dark energy. Obviously
Speaker 5: he's moving things apart. But I think the galaxy would
Speaker 5: stay together, but that galaxies would separate from each other.
Speaker 5: So I reckon our supercluster will be torn apart.
Speaker 2: All right, Some people are feeling optimistic about our supercluster.
Speaker 1: It looks like three to one for our superclusters sticking together.
Speaker 1: We got some optimists out there.
Speaker 2: Yeah. Yeah, everyone wants to remain I guess in the cluster.
Speaker 1: They want to stay cozy. No one wants to blow
Speaker 1: up our spot.
Speaker 2: Yeah, but I guess some people mentioned gravity us together
Speaker 2: instead of letting the supercluster get torn apart, and some
Speaker 2: people mention dark matter as a way to keep things together.
Speaker 1: Yeah, and the overall theme here is pretty much spot
Speaker 1: on that the universe is in a tug of war
Speaker 1: between gravity and dark energy and those things play out
Speaker 1: very differently on different distances and different scales. And so
Speaker 1: the fascinating question is like, at what point does dark
Speaker 1: energy win? And where will gravity win?
Speaker 2: Who will eat who? Gravity versus dark energy.
Speaker 1: That's like Godzilla versus King Kong.
Speaker 2: That's like slow roasted ribs versus grilled chicken.
Speaker 1: I'll just eat them both.
Speaker 2: Mane sounds good. Well, let's dive into this tasty topic here,
Speaker 2: step us through Daniel. What is a supercluster of galaxies?
Speaker 1: So a supercluster is the biggest thing in the universe.
Speaker 1: It's the largest structure we think can exist in the universe.
Speaker 1: And this episode is going to hinge closely on what
Speaker 1: we mean by a structure. What is a thing in
Speaker 1: the universe? Because you could just look out in space
Speaker 1: and say I'm going to group all this stuff together
Speaker 1: and call it a thing and give it a name,
Speaker 1: the way we sort of do for constellations, But astronomers
Speaker 1: like to think about things in the universe structures as
Speaker 1: things that sort of hold themselves together, that have enough
Speaker 1: gravity to be tied together to be an equilibrium. So
Speaker 1: in our immediate neighborhood, for example, we think of the
Speaker 1: Solar System as a thing. The Earth is going around
Speaker 1: the Sun and it's going to keep doing that. Gravity
Speaker 1: is holding the Earth around the Sun and all the
Speaker 1: other planets, So we think of the Solar System as
Speaker 1: a structure, as this gravitationally bound kind of object.
Speaker 2: Yeah, because I guess if you think about just the
Speaker 2: word structure and what it means in our everyday lives,
Speaker 2: it basically just means like things that are clumped together, right,
Speaker 2: or that move together, or that can be separated from
Speaker 2: each other. And you sort of drill down into it,
Speaker 2: like even the house you're sitting on, or the building
Speaker 2: you're sitting on, or maybe even the car you're sitting on,
Speaker 2: it's just a collection of loose parts being held together
Speaker 2: by a force in the universe. Like they're not part
Speaker 2: of the same thing. They're individual particles, but there's just
Speaker 2: some force that keeps them all moving together.
Speaker 1: Yeah, and it feels like a really natural thing. Right
Speaker 1: to say I'm held together, I'm a thing. You're held together,
Speaker 1: you're another thing. Even if we're standing next to each other,
Speaker 1: it's easy to draw the line between us and say,
Speaker 1: like where I end and you begin. That's sort of philosophically,
Speaker 1: very straightforward, and so we imagine maybe that's possible to
Speaker 1: do for other stuff too, Right to say, well, here's
Speaker 1: one planet and there's another planet, to draw these lines
Speaker 1: and say this thing holds itself together, and that thing
Speaker 1: holds itself together. So that's sort of the idea of
Speaker 1: a structure, But it can also get kind of fuzzy,
Speaker 1: Like when you look up at the sky and you
Speaker 1: see a cloud. It's this big blob of vapor. It's
Speaker 1: not really holding itself together. I mean, it looks like
Speaker 1: a thing sort of localized and clumped, but it's definitely
Speaker 1: not gravitationally holding itself together. It just sort of happens
Speaker 1: to be all in the same place at the same time,
Speaker 1: or like a crowd in a park at lunchtime. Right,
Speaker 1: they all happen to be near each other. They're clumped,
Speaker 1: but they're not holding themselves together. So there can be
Speaker 1: sometimes things that are like near each other. There are
Speaker 1: clumps but not structures.
Speaker 2: Interesting, Yeah, crowd is a good example, right, because it
Speaker 2: may look like a cluster, or like from a farm,
Speaker 2: might look like a clump of things, but really there's
Speaker 2: nothing keeping those individual people or structures together.
Speaker 3: Right.
Speaker 2: They could at any moment just leave the group.
Speaker 1: Yeah. Every kindergarten teacher knows that when you try to
Speaker 1: take them out on a field trip, right, they can
Speaker 1: all just suddenly run in any random direction.
Speaker 2: Yeah, Whereas maybe like for the planet Earth, all the
Speaker 2: rocks on planet Earth are being kept from flying away
Speaker 2: by gravity, by a force.
Speaker 1: And it's really fascinating to think about the sort of
Speaker 1: levels of structure, right, Like a rock is a structure,
Speaker 1: but it's also part of a larger structure the Earth,
Speaker 1: and the Earth of course is a structure, but again
Speaker 1: it's part of a larger structure. So we have this
Speaker 1: incredible nested hierarchy of structures, which is really fascinating to
Speaker 1: think about, like the scale of those things, right, Like
Speaker 1: an atom is a structure, You're made of so many
Speaker 1: structures on so many levels. Incredible to think about, like
Speaker 1: how organized the universe is, and as a whole group
Speaker 1: of philosophers who study this kind of thing and wonder like,
Speaker 1: why do we have structure of these distances and not
Speaker 1: other distances? And does it bubble up from the fundamental
Speaker 1: laws of the universe and all sorts of fascinating philosophical
Speaker 1: rabbit holes. But it's also just kind of fun to
Speaker 1: figure out, like what is the structure? What is our
Speaker 1: cosmic neighborhood, and so we can like zoom out step
Speaker 1: by step and understand how we fit in to this
Speaker 1: sort of larger cosmic set of like Russian nesting dolls.
Speaker 2: Yeah, because I guess you know, sort of like you
Speaker 2: were saying, the atoms in my body make up my structure,
Speaker 2: but they're all also kind of being pulled by the
Speaker 2: gravity of the earth, right, so like is it more
Speaker 2: part of my structure or are all the atoms in
Speaker 2: my body more part of the earth structure? And even
Speaker 2: like the atoms in my body are being pulled by
Speaker 2: the gravity of the sun. But we wouldn't say, like, hey,
Speaker 2: I'm just me and the sun are one, even though
Speaker 2: if you sort of follow the chain of forces that
Speaker 2: we are sort of in the same structure as the Sun.
Speaker 1: Yeah, And so you're part of many structures or you
Speaker 1: could say that there's substructure, right, You could just look
Speaker 1: at the whole galaxy and say the galaxy is a blob,
Speaker 1: but obviously it has substructure. It's not just a smooth
Speaker 1: distribution of atoms. There are stars and solar systems and
Speaker 1: even clumps to those stars. They are like these groups
Speaker 1: of stars are all formed together that are still moving together,
Speaker 1: like that Kindergarten group. So there's sort of lots of
Speaker 1: layers of structure, and it's fascinating to ask, like how
Speaker 1: many layers are there? How many layers can we zoom
Speaker 1: out and still see things that seem to be holding
Speaker 1: themselves together. So we start with ourselves, and then of
Speaker 1: course we have the Earth, and then there's the solar system,
Speaker 1: and then we zoom out. The next sort of big
Speaker 1: layer of structure would either be like a group of
Speaker 1: stars that we all form together with or you would
Speaker 1: zoom all the way out to the galaxy. Because those
Speaker 1: groups of stars that form together, they don't really hold
Speaker 1: themselves together for very long. They tend to disperse into
Speaker 1: the galaxy.
Speaker 2: M do we know that's for sure? Or I mean, like,
Speaker 2: do we know which stars are near us? And would
Speaker 2: you say maybe they're too far away for their gravity
Speaker 2: to really affect us.
Speaker 1: Yeah, other stars are too far away for the gravity
Speaker 1: to really affect us. And we all have velocity through
Speaker 1: the galaxy, and so we know a lot about actually
Speaker 1: how stars dissipate from their original cluster. It can take
Speaker 1: tens or hundreds of millions of years, but we definitely
Speaker 1: see evidence of that when we look out at the
Speaker 1: pattern of the stars in our galaxy. It also helps
Speaker 1: us understand how the stars are moving. For example, like
Speaker 1: the Big Dipper is a group of stars that were
Speaker 1: all formed together, and they're moving together, but they're also
Speaker 1: moving really fast and they're kind of close by, which
Speaker 1: means that the Big Dipper is changing. You don't think
Speaker 1: about the constellations as changing very much, but they actually
Speaker 1: are all moving. We're not all moving at the same
Speaker 1: relative velocity. So like the galaxy is a big, slashing
Speaker 1: bathtub of stars. So the Big Dipper changes, and over
Speaker 1: like one hundred thousand years or a few hundred thousand years,
Speaker 1: the Big Dipper will no longer look like the Big Dipper.
Speaker 2: Now are they would you say they're a structure or
Speaker 2: are they just moving together like a crowd, or like
Speaker 2: a wisp of clouds.
Speaker 1: They are not a structure because they're not going to
Speaker 1: hold themselves together. They're not like tight enough to be
Speaker 1: a structure. They're definitely going to dissolve into the larger
Speaker 1: sort of bathtub of the galaxy. There are sometimes substructures
Speaker 1: to the galaxy, but those tend to be like little
Speaker 1: dwarf galaxies that orbit the Milky Way and that have
Speaker 1: their own gravitational hold on themselves that haven't gotten pulled
Speaker 1: apart by the Milky Way. But within the Milky Way,
Speaker 1: there aren't really those kinds of structures.
Speaker 2: So you would say, like after our solar system, the
Speaker 2: next structure is a galaxy. You wouldn't maybe call the
Speaker 2: arms of a galaxy a structure.
Speaker 1: Well, those are density waves, right. Even the arms of
Speaker 1: the galaxy are not physical structures. It's not like the
Speaker 1: same stars are moving through those arms. The arms are
Speaker 1: a wave through the stars. Like when you go to
Speaker 1: a football game and people do the wave. That wave
Speaker 1: itself is not a structure. It's just an arrangement of
Speaker 1: the people as they move up and down. Galaxy arms
Speaker 1: are the same way. They're not physical structures. They're just
Speaker 1: density waves. So they're not actually whole themselves together, just
Speaker 1: like waves in the ocean are not really structures that
Speaker 1: I'm bound together.
Speaker 2: And so our solar system, our star is not part
Speaker 2: of a like a mini dwarf galaxy. We're just out
Speaker 2: in the larger Milky Way galaxy.
Speaker 1: Yep, we're just floating in the bathtub of the Milky Way,
Speaker 1: along with hundreds of billions of other stars.
Speaker 2: And potentially aliens that might eat us one of us. Right,
Speaker 2: it sounds like a dangerous hot tub. Well, let's dig
Speaker 2: into the next level of structure in the universe, and
Speaker 2: let's see how big we can go. How far can
Speaker 2: we add or recognize structure in the universe, and what's
Speaker 2: going to happen to all that structure at the end
Speaker 2: of time. So let's dig into that. But first let's
Speaker 2: take a quick break. All right, we're asking the question
Speaker 2: will our supercluster be torn apart? Which kind of sounds
Speaker 2: like an oxymoron question or a contradictory question. Well, something
Speaker 2: that's clustered together and not be clustered together.
Speaker 1: Yeah, in the end, we're going to learn that astronomers
Speaker 1: are arguing about how to define a supercluster, and some
Speaker 1: definitions make the answer obvious, and some definitions make the
Speaker 1: answer to this question very fuzzy.
Speaker 2: But we were talking about how you know things, how
Speaker 2: do you define structures? And it seems like sometimes, like
Speaker 2: in a cloud or in a crowd, things might look
Speaker 2: like they're together, but really they can fall apart at
Speaker 2: any point, so you wouldn't call that a structure. But
Speaker 2: like the atoms in your body or the atoms in
Speaker 2: the building or car you're sitting on, they're held together
Speaker 2: pretty tightly by forces, and they basically sort of ignore
Speaker 2: other forces in favor of the forces that are holding
Speaker 2: them together. And so maybe that's why we call them
Speaker 2: a structure.
Speaker 1: That's right, And it can be gravitational, or it can
Speaker 1: be electromagnetic, or can be the strong force that forms
Speaker 1: these structures, like the proton is a structure of the
Speaker 1: strong force, and the atom is a structure of electromagnetism.
Speaker 1: But at larger distances, basically anything bigger than a few meters,
Speaker 1: it's mostly gravity that takes over because the other forces
Speaker 1: are so powerful that they tend to neutralize themselves. Anything
Speaker 1: that has a large positive or negative charge is going
Speaker 1: to attract the opposite charge and end up neutralizing itself,
Speaker 1: but over the large distances, it's gravity that forms structure
Speaker 1: because gravity cannot be neutralized. Essentially, it's only attractive. There
Speaker 1: are a few scenarios we can talk about with like
Speaker 1: repulsive gravity, and dark energy might be an example of that,
Speaker 1: but on the whole, gravity is attractive, and so it's
Speaker 1: the force that's responsible for most of the structure we
Speaker 1: think about in the universe.
Speaker 5: Mmm.
Speaker 2: Yeah, Like after about the size of a planet, there's
Speaker 2: no other forces really at play in the universe that
Speaker 2: we know of. Maybe there's something hitting out there. Could
Speaker 2: dark matter be some kind of new force?
Speaker 1: It could in dark energy is definitely in that category.
Speaker 1: We don't know if it's a manifestation of gravity due
Speaker 1: to the quantum energy of space or something totally else
Speaker 1: and weird.
Speaker 2: All right, Well, we talked about how we're part of
Speaker 2: a solar system, and the Solar system is part of
Speaker 2: a bigger structure called the Milky Way galaxy.
Speaker 1: After that, so the galaxies aren't just like floating out
Speaker 1: in space sprinkled evenly through the universe. They tend to
Speaker 1: clump together, and they can clump together into something that
Speaker 1: we call a galactic group or a group of galaxies
Speaker 1: in our galaxy, the Milky Way is part of a
Speaker 1: group we call the Local Group very cleverly, and it
Speaker 1: has about fifty ish galaxies in it. The biggest one
Speaker 1: is Andromeda, which is also the nearest one to us.
Speaker 2: And so these are galaxies that are not just neros
Speaker 2: out of convenience. We're actually sort of locked together with
Speaker 2: them in some sort of gravitational dance. Right.
Speaker 1: Yeah. We think that these galaxies are holding themselves together.
Speaker 1: They're like a single gravitational object. They are orbiting the
Speaker 1: center of mass of all of these galaxies. And people
Speaker 1: hear a lot that the universe is expanding and everything
Speaker 1: is getting farther and farther away. And that's true sort
Speaker 1: of on the whole when you look at vast distances,
Speaker 1: but nearby gravity is powerful enough to hold us together,
Speaker 1: and that's happening also with these galaxies. That's why, for example,
Speaker 1: we are towards the Andromeda galaxy and in a few
Speaker 1: billion years our galaxy and Andromeda will collide and will
Speaker 1: merge because gravity is winning the battle over the expansion
Speaker 1: of space. So this local group, we think, is a thing.
Speaker 1: It's a structure that gravity is powerful enough to hold together.
Speaker 2: And now what kind of shape does this local group have?
Speaker 2: Is it like a disk like our solar system or
Speaker 2: the galaxy, or is it still kind of like a
Speaker 2: fuzzy cloud of things moving in all directions.
Speaker 1: It doesn't really have a great shape because it's sort
Speaker 1: of weirdly distributed, like there's Andromeda, then there's the Milky Way,
Speaker 1: there's another galaxy called the Triangular Galaxy, and the rest
Speaker 1: of it is like a sprinkle of little tiny galaxies.
Speaker 1: So they're not like nicely organized into a flat disc
Speaker 1: or anything like that. It's just sort of like a blob.
Speaker 2: Or at least not yet. Right, Like, maybe if you
Speaker 2: fast forward a few billion years, things will even out
Speaker 2: into a disk, because that's what things do in space,
Speaker 2: they organize themselves into discs, right.
Speaker 1: They do tend to do that if you give them
Speaker 1: enough time, because they're spinning and gravity will collapse everything
Speaker 1: down eventually, except along the plane of their spin they
Speaker 1: can resist gravity a little bit, which is why they
Speaker 1: end up as disks. So in sort of one direction
Speaker 1: they can collapse, and along the other two dimensions on
Speaker 1: that plane they end up sort of spinning around, which
Speaker 1: is how you get a flat solar system and a
Speaker 1: flat galaxy. Eventually, though, we think that gravity will win,
Speaker 1: that those things will bump against each other and lose
Speaker 1: angular momentum, or they will radiate gravitational waves and lose
Speaker 1: that energy. And eventually we think that gravitationally bound objects
Speaker 1: will all collapse together, first into one big galaxy and
Speaker 1: then eventually just into one big black hole.
Speaker 3: Yit.
Speaker 2: But before that happens, we can see other kinds of structures, right,
Speaker 2: bigger structures, So like a group of galaxies can be
Speaker 2: part of a larger kind of thing.
Speaker 1: Yeah, so we call this either a group or a
Speaker 1: cluster of galaxies. And depending on the size, like if
Speaker 1: there aren't that many galaxies in it, like in hours,
Speaker 1: we call it a group. If there are more galaxies
Speaker 1: in it, you can call it a cluster. And so nearby,
Speaker 1: for example, is the Virgo cluster. It has more than
Speaker 1: a thousand galaxies that are like the Milky Way, so
Speaker 1: it's much much bigger than the local group, and we
Speaker 1: think that is also like an object that has structure,
Speaker 1: we think it's going to hold itself together, that there's
Speaker 1: enough gravity to keep itself together.
Speaker 2: Yeah, isn't it pretty amazing to think even at these numbers,
Speaker 2: like a thousand. A thousand doesn't sound like a lot,
Speaker 2: But if you imagine a thousand galaxies like the Milky Way,
Speaker 2: that is sort of mind blowing. Right, Like, we think
Speaker 2: our galaxy is pretty huge and we'll probably never get
Speaker 2: to the other side of it, and has billions of stars.
Speaker 2: Now imagine there are thousands of these things out there
Speaker 2: in space.
Speaker 1: And the thing that blows my mind is the planets. Right,
Speaker 1: even in our galaxy, we know there are hundreds of
Speaker 1: billions of stars, and a significant fraction of those have
Speaker 1: Earth like planets. You know, planets about the same size
Speaker 1: with about the same surface temperature. We don't really know
Speaker 1: that much more about them, but like, that's a lot
Speaker 1: of Earth like planets. We're talking about tens of billions
Speaker 1: just in our galaxy, and now multiply that by a
Speaker 1: thousand for all the galaxies in the Virgo clusters hard
Speaker 1: to keep track of, like all the places aliens could
Speaker 1: be sharpening their barbecue tools.
Speaker 2: Yeah, so let's not think about that. Yeah, I agree with.
Speaker 1: You, But the Virgo cluster is like the biggest thing around.
Speaker 1: There are other little galaxy groups nearby, Like there's the
Speaker 1: M eighty one group, and the Sculptor group other little
Speaker 1: groups of galaxies that are sort of in this sort
Speaker 1: of the same size as our group. But the Virgo
Speaker 1: cluster is like the big Papa and Mama galaxy cluster nearby.
Speaker 1: It's like the most massive thing in the nearby universe.
Speaker 2: Well, it's interesting with gravity, I feel, because gravity doesn't
Speaker 2: have a limit, right, Like there's no distance limit for gravity,
Speaker 2: Like this Virgo cluster is super dup or duper far
Speaker 2: away from us. But technically speaking, like the atoms in
Speaker 2: my body and in your body and everybody's bodies is
Speaker 2: being tugged pulled by the gravity of that cluster super
Speaker 2: far away.
Speaker 1: That's right, Everything in the universe technically is pulling on
Speaker 1: you gravitationally. Gravity does have this weakness though, which is
Speaker 1: that its power drops as the dist is squared. So
Speaker 1: if you're twice as far away from something, it's gravity
Speaker 1: goes down by a factor of four. If you're ten
Speaker 1: times further away, then the gravity goes down by a
Speaker 1: factor of one hundred. And this gets to be a
Speaker 1: very powerful obstacle to gravity as distances grow large, and
Speaker 1: so the Virgo cluster, even though it's the most massive
Speaker 1: thing in the nearby universe. It's like fifty or sixty
Speaker 1: million light years away. That's a big distance to square, right,
Speaker 1: So its gravity is really tiny, which is why it's
Speaker 1: not obvious whether our little group, the local group, and
Speaker 1: the Virgo cluster should be considered as part of some
Speaker 1: larger object.
Speaker 3: Right.
Speaker 2: It gets attenuated a lot, it weakened a lot by distance,
Speaker 2: but it's still there, right, Like I feel like like
Speaker 2: I'm sensing I have this feeling of like a small
Speaker 2: tendril of force that pulls me from the atoms in
Speaker 2: my body to the Virgo cluster, right, And it also
Speaker 2: kind of depends like what if the Virgo cluster was
Speaker 2: super duper massive, right, we would eventually feel their gravity.
Speaker 1: Yeah, that's true, and we do feel it's gravity. You're
Speaker 1: absolutely right. I feel like you're just sort of preparing
Speaker 1: an argument for when the aliens come and you're like,
Speaker 1: hey man, we're all part of the same thing, and
Speaker 1: we can feel your gravity, and we do, and we
Speaker 1: can feel that gravity. And there's another way in which
Speaker 1: we are connected to those objects. Right now, we're just
Speaker 1: thinking mostly about the stars, the things that shine brightly,
Speaker 1: but there are these filaments that connect us to the
Speaker 1: other galaxies. Like between US and ANDRAMA is not empty space.
Speaker 1: There's this filament, this string of both matter like hydrogen atoms,
Speaker 1: et cetera, and also dark matter. So it's not like
Speaker 1: a bunch of dots out in space. These galaxies they're
Speaker 1: connected to each other. It's part of some huge cosmic
Speaker 1: web where the other parts are more invisible because they're
Speaker 1: not glowing.
Speaker 2: Yeah, it's sort of like a spider's web right the universe.
Speaker 2: Like if you look at a picture of the universe
Speaker 2: and all the stars in it, the stars, even though
Speaker 2: they're pinpoints, they sort of don't look like a random
Speaker 2: white noise. They sort of look like a spider's web kind.
Speaker 1: Of mm hmm. Between those dots there really is stuff.
Speaker 1: You know, galaxies form in certain locations because that happens
Speaker 1: to me where there was a little bit more dark matter.
Speaker 1: So there's like a blob of dark matter there that's
Speaker 1: gathered together enough light to start fusion going in those stars.
Speaker 1: But between them there are these filaments of gas and
Speaker 1: dark matter still flowing into those halos. So you could
Speaker 1: think about it like a network of lakes with rivers
Speaker 1: flowing into them, still filling them up, So galaxies are
Speaker 1: still gathering dark matter and gas from these filaments. Structure
Speaker 1: there is still sort of forming. Even though fourteen billion
Speaker 1: years have gone by, things are still happening out there
Speaker 1: in the universe.
Speaker 2: I guess if there's a big cloud of something like
Speaker 2: hydrogen out there in the middle of empty space, gravity
Speaker 2: would be pulling it together, that cloud together into a
Speaker 2: smaller cloud, and then our gravity would be and the
Speaker 2: gravity of other clusters would be trying to stuck that
Speaker 2: gas towards them. And so that's why maybe you get
Speaker 2: these tendrils, these sort of like tentacles of gas out
Speaker 2: there in space because they're being straight out and sucked
Speaker 2: and do the different galaxies.
Speaker 1: Exactly, And mostly it's the dark matter doing that. Remember,
Speaker 1: we only see the visible matter, but that's twenty percent
Speaker 1: of the matter that's out there, most of the gravity
Speaker 1: in the universe. Most of those tendrils you feel from
Speaker 1: the other cluster are actually from the dark matter in
Speaker 1: that cluster, because that's most of the matter, and so
Speaker 1: most of the gravity in the universe. Like, the reason
Speaker 1: we have a galaxy here and not somewhere else is
Speaker 1: because there was dark matter to form this structure. It
Speaker 1: created this like gravitational well, the sort of lake to
Speaker 1: pull all the other rivers of matter into it.
Speaker 2: Cool. Well, after a cluster of galaxies, what's next?
Speaker 1: So what's next is a little bit controversial, and in
Speaker 1: the last ten years or so there's been a lot
Speaker 1: of arguments about it. But there's a group of astronomers
Speaker 1: out there that say that all these clusters, in these
Speaker 1: little groups can be gathered together into something bigger called
Speaker 1: a supercluster. The supercluster would take like the Virgo cluster
Speaker 1: and our little group, and a bunch of other things,
Speaker 1: including like the Great Attractor and them a cluster, and
Speaker 1: the Centauris cluster and many others, into some huge object
Speaker 1: that has like one hundred thousand galaxies in it.
Speaker 2: Right, And this supercluster is called the Lenni Kiak supercluster. Right.
Speaker 1: Yeah, it's a Hawaiian word that means immense heaven, and
Speaker 1: it were defined in like twenty fourteen when a bunch
Speaker 1: of astronomers looked at the velocity of all these things
Speaker 1: and said, you know what, all these things are sort
Speaker 1: of like falling towards themselves, and there's another blob of
Speaker 1: stuff over there that's falling towards themselves, and so they
Speaker 1: figure out how to sort of like draw a line
Speaker 1: between one set of blobs and another set of blobs,
Speaker 1: and they said, we're in this blob over here.
Speaker 2: M I see. But can you make the mathematical calculation,
Speaker 2: like if you compute the gravity that we're feeling between
Speaker 2: these clusters, and does it really work out that you
Speaker 2: can group these superclusters as one or is it more
Speaker 2: like an illusion like a wisp of cloud or a
Speaker 2: crowd of people in a park.
Speaker 1: Yeah, that's exactly the question, and that's really what we're
Speaker 1: in entering today is what is the future of this supercluster?
Speaker 1: Is it going to hold itself together or is it
Speaker 1: going to get torn apart? Because we've been talking about
Speaker 1: gravity so far, but there's another force at play here,
Speaker 1: and that's dark energy. If it was only gravity, then
Speaker 1: this thing would collapse. Landi Ko would definitely fall into
Speaker 1: one big object and maybe form one super galaxy and
Speaker 1: one super black hole. There is enough gravity if the
Speaker 1: universe wasn't expanding to pull this thing together, like it's
Speaker 1: already right now falling inwards. Everything in the Lanti Kia
Speaker 1: supercluster has an overall in falling velocity. But there's another
Speaker 1: player on this stage, right, which is the expansion of
Speaker 1: the universe, and this has a very different behavior as
Speaker 1: distances grow large, like gravity gets weaker and weaker as
Speaker 1: distances grow large, but dark energy, this accelerating expansion of
Speaker 1: the universe, gets more powerful as distances grow large. So
Speaker 1: at some point it takes over. There's like a crossover
Speaker 1: point where dark energy starts to win.
Speaker 2: Well, let's stick into that to gives that is the
Speaker 2: question of the episode. Now we are in the Lenni
Speaker 2: Kia supercluster, and so the question is is something tearing
Speaker 2: it apart. It's the biggest structure in the universe, and
Speaker 2: so Danny, you're saying that maybe dark energy is tearing
Speaker 2: it apart, or maybe at least fraying it at the edges.
Speaker 1: Yeah, dark energy is definitely working to tear it apart.
Speaker 1: And listeners right in all the time and ask about
Speaker 1: dark energy and have this idea sometimes that dark energy
Speaker 1: is something happening at the edges of the universe, that
Speaker 1: there's something pulling on us from the outside, or that
Speaker 1: maybe the expansion is only happening out there between galaxies,
Speaker 1: but the expansion is happening everywhere. Every chunk of space
Speaker 1: is expanding. Like the Hubble constant is a measure of
Speaker 1: how fast things are expanding, and it's like seventy kilometers
Speaker 1: per second per megaparsek, which is sort of a hard
Speaker 1: thing to get your mind around, but really it just
Speaker 1: means that, like every megaparsec, which is like three light years,
Speaker 1: grows by about seventy kilometers every second, and that happens
Speaker 1: everywhere in space. If you have a smaller distance, like
Speaker 1: the distance between Earth in the Sun, which is only
Speaker 1: a few tens of millions of miles, it would grow
Speaker 1: by a much smaller amount than seventy kilometers every second.
Speaker 1: So that expansion is happening everywhere, but it's sort of
Speaker 1: faint and weak. It's not very strong over short distances,
Speaker 1: and gravity is strong enough to hold us together against
Speaker 1: this like very weak breeze of dark energy. But then
Speaker 1: at large distances, when gravity is weak, dark energy is
Speaker 1: more powerful. It sort of adds up as you get
Speaker 1: to these bigger distances, and so for the supercluster, it
Speaker 1: really is an interesting question of whether that's the crossover point.
Speaker 2: Yeah, it's interesting to think about. Like even here in
Speaker 2: the room where I'm at, and the room where you are,
Speaker 2: and where our listeners are. If you just stare at
Speaker 2: your hand, like the space that your hand is occupying
Speaker 2: is expanding, it's getting trying to like pull your hand
Speaker 2: apart in a way, except that your hand is being
Speaker 2: held together by the bonds of the atoms in it.
Speaker 2: But if it wasn't your hand, which is kind of
Speaker 2: dissipate eventually.
Speaker 1: Right, Yeah, exactly, if there wasn't gravity and there weren't
Speaker 1: those forces, than dark energy would pull your hand apart,
Speaker 1: and it would pull the Earth from the Sun. So
Speaker 1: there's a bunch of really interesting things all happening at
Speaker 1: the same time. Like gravity needs time to form structure.
Speaker 1: You start from like a fuzzy universe, and it gradually
Speaker 1: pulls things together, and so as time goes on, gravity
Speaker 1: makes bigger and bigger and bigger structures. So one reason
Speaker 1: we don't have bigger structures than superclusters, or even if
Speaker 1: superclusters counter structure is just time. Like without dark energy,
Speaker 1: if you ran the universe forward, it would form larger
Speaker 1: and larger and larger structures. But dark energy turned on
Speaker 1: a few billion years ago and it started accelerating the
Speaker 1: expansion of the universe. So gravity is sort of running
Speaker 1: out of time, which means something kind of fascinating. It
Speaker 1: means that we are living maybe at the moment of
Speaker 1: the largest structures in the universe.
Speaker 2: Well, I think that's kind of the point of discussion,
Speaker 2: is like, is dark energy eventually going to tear our
Speaker 2: supercluster apart? Or is maybe that expansion not strong enough
Speaker 2: to really tear apart and keep things the way they
Speaker 2: are forever, Right, that's kind of the question we're asking today.
Speaker 1: Yeah, that's right. But whether or not our supercluster survives,
Speaker 1: there will never be anything bigger in the universe because
Speaker 1: dark energy is getting more and more powerful, and so
Speaker 1: gravity will never have time to make anything bigger. Like
Speaker 1: if a structure hasn't formed by now in the universe,
Speaker 1: it will not because dark energy is just growing in power.
Speaker 1: So whether or not our supercluster survives, nothing bigger than
Speaker 1: anything that's been made already will ever be made.
Speaker 2: Well, let's dig into that and what it might mean
Speaker 2: for our local structure or superstructure of galaxies. Does that
Speaker 2: reduce our chances of getting eaten by aliens? We'll see. First,
Speaker 2: let's take another quick break all right, we're talking about
Speaker 2: getting eaten by aliens. Now, Daniel, are you sort of prepared?
Speaker 2: It sounds like you look forward to it. Now are
Speaker 2: you preparing yourself? Are you staying in shape? Or are
Speaker 2: you trying to fan yourself like like your goose so
Speaker 2: that you're tastier to the aliens? You know, tag on
Speaker 2: those calories.
Speaker 1: I just don't even know, Like what do aliens like?
Speaker 1: How am I supposed to anticipate what they're gonna find? Yummy? Like?
Speaker 1: So I'm just living my life, you know, and hoping
Speaker 1: and hoping that they.
Speaker 2: Put I'm hoping they pick you two over me.
Speaker 1: Hey, something we can agree on. Awesome.
Speaker 2: Well, we're talking about whether we're actually talking about whether
Speaker 2: our supercluster, which is called lanny Kia, which is a
Speaker 2: cluster of galaxy clusters, will one day be torn apart
Speaker 2: because of dark energy. Now, dark energy is expanding all
Speaker 2: space as far as we know, and the question is
Speaker 2: is it expanding space faster than lanny Kiya can hold
Speaker 2: itself together? And it sounds like you have the answer
Speaker 2: to that.
Speaker 3: I do.
Speaker 1: Yeah. So originally they defined a supercluster to be this
Speaker 1: object because everything was sort of falling in towards it.
Speaker 1: That like delineated a blob of stuff that was moving
Speaker 1: towards itself, and the next supercluster is a blob that's
Speaker 1: moving towards itself. But then astronomers thought, hm, that's not
Speaker 1: really enough. Like what we want is something that's gonna survive.
Speaker 1: We wanted to find a supercluster to be something that
Speaker 1: is going to manage to hold itself together against dark energy.
Speaker 1: So they did a bunch of calculations and it looks
Speaker 1: like it's probably not gonna make it. It looks like
Speaker 1: the supercluster is very loosely organized. It's just more like
Speaker 1: a cloud or like a crowd. You know, it happens
Speaker 1: to be nearby, but it's not really like in equilibrium.
Speaker 1: You know, like the Earth and the Sun had a
Speaker 1: lot of time to sort of get in balance and
Speaker 1: find a place where they're happy together, and the Earth
Speaker 1: can orbit forever and be here. But the supercluster, like
Speaker 1: we said earlier, hasn't really had a lot of time
Speaker 1: to gather together and to form something solid. It's just
Speaker 1: sort of like a big blob of stuff that happened
Speaker 1: to be near each other and are starting to fall
Speaker 1: in a little bit but dark energy is powerful enough
Speaker 1: that they're pretty sure it's going to tear it apart.
Speaker 2: Now you mentioned one one of the reasons is that
Speaker 2: dark energy is getting stronger. Now, is it getting stronger
Speaker 2: at the local level or is it just or you're
Speaker 2: saying it's getting stronger because the universe is getting bigger
Speaker 2: and so therefore there's more dark energy. Is it getting
Speaker 2: stronger measureably like inside of my hand, Is this dark
Speaker 2: energy that I would feel over the course of my
Speaker 2: life getting stronger or is it going to be constant?
Speaker 1: Dark energy is everywhere at the same level, so it's
Speaker 1: a constant in space here and there and in other galaxies.
Speaker 1: Every chunk of space has the same amount of dark energy.
Speaker 1: So when the universe expands, it's making more space, which
Speaker 1: means more dark energy doesn't get diluted. It's a constant
Speaker 1: in space. That's not true for other stuff like matter
Speaker 1: or radiation. As the universe expands, matter gets more dilute
Speaker 1: because more space doesn't mean more matter. So as time
Speaker 1: goes on, the expansion of the universe means dark energy
Speaker 1: is constant, But then it's an increasing fraction of the
Speaker 1: energy of the universe because it doesn't get diluted, and
Speaker 1: other stuff does. And when dark energy is an increasing fraction,
Speaker 1: that triggers more expansion, which only tells the balance further
Speaker 1: towards dark energy. So it's like a runaway effect. Once
Speaker 1: dark energy starts to win, which happened about six billion
Speaker 1: years ago, it will zoom ahead and be impossible to
Speaker 1: catch up to. But about seeing it change, we live
Speaker 1: such short lives that we can't really notice it changing
Speaker 1: on our time scales, but we can look back into
Speaker 1: the past by looking out into deep space and seeing
Speaker 1: how things used to be. And of course there's a
Speaker 1: huge asterisk to all of this because we don't really
Speaker 1: understand dark energy and what's going on and what's making
Speaker 1: this happen, and so the rules could be very different
Speaker 1: from this very simple model that honestly we're pretty sure
Speaker 1: is wrong.
Speaker 2: Right, Well, I guess what I mean is that, you know,
Speaker 2: we've always talked about dark energy as being kind of
Speaker 2: the force that's expanding the Universe's expanding space, and I
Speaker 2: always think of it as sort of like the foot
Speaker 2: in the accelerator. Like when I'm driving, I press the
Speaker 2: accelerator and I usually leave it at a certain level
Speaker 2: to keep going at a certain speed, and if I
Speaker 2: want to accelerate go faster, I press it harder, and
Speaker 2: if I want to go slower, I let go of
Speaker 2: the pedal. Now, it sort of seems from what we've
Speaker 2: talked about before that is that, you know, the pedal
Speaker 2: of dark energy is sort of pretty constant. And for example,
Speaker 2: our Solar system is never going to be torn apart
Speaker 2: by dark energy because the gravitational bonds between us and
Speaker 2: the Sun is strong enough that even if the space
Speaker 2: between us gets bigger and bigger and bigger, we're always
Speaker 2: going to hang on to the Sun.
Speaker 1: Dark energy is expanding the space in our Solar system,
Speaker 1: but it doesn't have much effect over those short distances.
Speaker 1: And short distances is when gravity is the most powerful.
Speaker 1: So gravity is always going to be powerful enough to
Speaker 1: hold the Solar system together if dark energy is a
Speaker 1: constant in space. Remember, a constant in space can still
Speaker 1: be an increasing fraction of the universe's energy budget, which
Speaker 1: leads to accelerating expansion even if the dark energy in
Speaker 1: any given chunk of space isn't changing. Except for the
Speaker 1: scenario of the Big Rip, where dark energy gets more
Speaker 1: powerful and even tears our solar system apart and even
Speaker 1: our atoms. But you're right, in our current projection of
Speaker 1: dark energy, it will not tear apart our solar system.
Speaker 2: Right, and so it's because it's not being accelerated enough.
Speaker 2: Now at the level of a galaxy, do we currently
Speaker 2: think that our galaxy is going to be torn apart
Speaker 2: or not?
Speaker 1: We think our galaxy is going to survive, and we
Speaker 1: think our group is going to survive. So everything below
Speaker 1: a supercluster, we're pretty sure gravity is already won and
Speaker 1: it's going to continue to win again, assuming this naive
Speaker 1: projection of dark energy continuing at the same rate that
Speaker 1: it's been continuing, that it's not going to ramp up
Speaker 1: into the big rip or turn around into the big crunch.
Speaker 1: So our solar system will survive, Our galaxy will survive,
Speaker 1: our local group will survive, The Virgo cluster nearby will survive.
Speaker 1: But the question is will our supercluster survive? And that's
Speaker 1: where dark energy starts to win, and dark energy will
Speaker 1: tear these groups of galaxies apart and basically pull apart leni.
Speaker 2: Ka because the things that make up Lenikia, you know,
Speaker 2: our cluster, the Virgo cluster, the Great Attractor, they are
Speaker 2: being attracted to each other, but not more than the
Speaker 2: expansion of the huge amount of space in between them.
Speaker 2: That's kind of what you're saying.
Speaker 1: Yeah, it's just too big, right. Gravity gets weak over
Speaker 1: those huge distances. It does not have the strength to
Speaker 1: overcome dark energy, and as the distances get bigger, dark
Speaker 1: energy becomes harder and harder to surmount. Like, it doesn't
Speaker 1: take that much mass and that much gravity to overcome
Speaker 1: dark energy in our solar system. It takes more mass
Speaker 1: to overcome the dark energy in the galaxy, and even
Speaker 1: more to overcome the dark energy of the group. But
Speaker 1: to overcome the dark energy of the supercluster, we need
Speaker 1: an incredible amount of mass because of the vast distances involved.
Speaker 2: So you're saying that lani Ka, the supercluster of galaxies,
Speaker 2: it's really more like a visual cluster, right, It's more
Speaker 2: of a visual structure. It looks like it's holding together.
Speaker 2: It looks like a wisp of cloud or a crowd
Speaker 2: of people in the park, But really there's nothing that
Speaker 2: much holding it together, or at least proportionally to the
Speaker 2: dark energy in the universe.
Speaker 1: Yeah, our supercluster seems to be right about that turnover
Speaker 1: point where things that are smaller or more massive either
Speaker 1: one would survive, and things that are bigger definitely would not.
Speaker 1: So sort of fascinating. It's like the biggest kind of
Speaker 1: blog we can identify, but it's not really technically a structure.
Speaker 1: So there were some papers a few years ago suggesting
Speaker 1: we shouldn't be calling Lenika a supercluster because it's not
Speaker 1: a structure, And they said, maybe we should redefine what
Speaker 1: a structure is as something that will survive in the future, right,
Speaker 1: things that will hold themselves together in the long term
Speaker 1: after dark energy has played itself out. So by that definition,
Speaker 1: the lani Kaya supercluster is not actually a structure and
Speaker 1: we shouldn't even be calling it a supercluster.
Speaker 2: Well, I mean, as long as you're playing with definitions,
Speaker 2: you can get either way. I feel like, right like
Speaker 2: you could just read a find what a super cluster means.
Speaker 2: A supercluster could just mean like a cloud or a
Speaker 2: crowd in a park. Right, Maybe you can just define
Speaker 2: a supercluster as not necessarily a structure, but you can
Speaker 2: still call it a super cluster, right because a cluster,
Speaker 2: the word cluster just means like, hey, hanging out together.
Speaker 2: M hmm.
Speaker 1: I suppose you could call it a banana if you wanted. Yeah,
Speaker 1: we want these words to have some meaning to them,
Speaker 1: and so these papers suggest that we shouldn't, and they
Speaker 1: actually suggest another name because there are some other superclusters
Speaker 1: that they do think will hold themselves together. So some
Speaker 1: superclusters are more massive or a little bit closer together,
Speaker 1: and they think they will overcome dark energy, and they
Speaker 1: suggest calling these things supersties clusters. Super So what it's
Speaker 1: a word in Latin that means survivor probably not pronouncing
Speaker 1: it correctly, but I think it's superstese clusters. It's the
Speaker 1: new name for superclusters that will survive dark energy.
Speaker 2: It sounds like we're really rather about way for what
Speaker 2: did you say? What did you just call them structures
Speaker 2: like superstructures? Why do we have to go Laddin?
Speaker 1: Well, because you know, not all superclusters are structures. They
Speaker 1: don't hold themselves together. And you're right, we could just
Speaker 1: put a name on things. But we like this hierarchy
Speaker 1: of structures. We like thinking about the universe in terms
Speaker 1: of the structures all the way down from the proton
Speaker 1: zooming out to the biggest structures in the universe. And
Speaker 1: we want a consistency there. We want it to mean something,
Speaker 1: for there to be a structure you don't want just
Speaker 1: like an arbitrary definition at every level.
Speaker 2: Well, I feel like maybe you're only having to adjust
Speaker 2: this definition because of dark energy, right, Like, if it
Speaker 2: wasn't for dark energy, yeah, lenning Care would be a
Speaker 2: structure and it would be gravitational bound and it would
Speaker 2: last until the end of time. But you have dark energy,
Speaker 2: which will make it fuzzy up in the future, except
Speaker 2: that you don't know what dark energy is going to do, right,
Speaker 2: So it seems a little bit like you're rushing ahead
Speaker 2: to redefine everything based on something you don't know what's
Speaker 2: going to happen.
Speaker 1: Well, you know, astronomers love fights over names and definition
Speaker 1: and who gets to name something, so this is one
Speaker 1: of the hot topics these days. But you're right that
Speaker 1: the definition of depends a little bit on what happens
Speaker 1: in the future. In that sense, it's sort of like
Speaker 1: the way you think about an event horizon for a
Speaker 1: black hole, Like the event horizon isn't a physical structure,
Speaker 1: it's just like a delineation that says anything passed here
Speaker 1: in the infinite future will never escape. To really know that,
Speaker 1: you have to see the infinite future. We just sort
Speaker 1: of project it and in the same way, we like
Speaker 1: group this stuff together and say, hey, is this going
Speaker 1: to survive if so that we can call it a
Speaker 1: cluster or a structure or a supercluster or a superstes
Speaker 1: cluster or whatever the astronomers finally settle on. But the
Speaker 1: basic story is that if dark energy continues the way
Speaker 1: it has been, probably Lanikea will just dissolve into a
Speaker 1: bunch of islands of mass.
Speaker 2: It sounds more like you're saying that we shouldn't call
Speaker 2: anything anything until the end of time.
Speaker 1: You go, that's exactly right. We want to be totally
Speaker 1: accurate about everything. We've got to wait to the end
Speaker 1: of the universe. Then we'll know what was going on.
Speaker 2: Well, let's spend the minute here because if we still
Speaker 2: have like a few minutes left here talking about the
Speaker 2: dark energy, right, because it seems like it all depends
Speaker 2: on what dark energy is going to do, whether the
Speaker 2: universe is going to press harder on the accelerator or
Speaker 2: press lower on the accelerator. What's been the history of that,
Speaker 2: Like since the beginning of the universe, there was a
Speaker 2: huge expansion, and then it slowed down and now it's
Speaker 2: picking back up again.
Speaker 1: Right, Yeah, that's true. And there's sort of a bunch
Speaker 1: of different time periods to talk about there, Like there
Speaker 1: was inflation very very early on, huge expansion and very
Speaker 1: short time scales. We don't understand what caused that at all.
Speaker 1: There's a few theories, the insuloton field, whatever, but it's
Speaker 1: a big question mark. And then after that, you know
Speaker 1: what we call the Big Bang, the sort of like
Speaker 1: more gradual expansion of the universe as it cools. We
Speaker 1: have pretty good models of that. We have gravity, and
Speaker 1: we have dark energy, we have all the other forces
Speaker 1: that come into play, and in that period we can
Speaker 1: model dark energy as constant, saying like a chunk of
Speaker 1: space has the same amount of potential energy, and that
Speaker 1: creates this repulsive field in general relative which drives the
Speaker 1: expansion of the universe. Remember that dark energy can be
Speaker 1: a constant in space, every chunk has the same amount,
Speaker 1: but still be a growing fraction of the universe's energy
Speaker 1: because other stuff is getting diluted as things expand, So
Speaker 1: dark energy is both constant and taking over as other
Speaker 1: things get more dilute. It's not exactly true, because we
Speaker 1: make these measurements over time we get slightly different answers,
Speaker 1: so nobody really knows if that's true or it needs
Speaker 1: a little bit of adjusting. We had a whole episode
Speaker 1: about early dark energy, whether dark energy was more powerful
Speaker 1: early on, this kind of stuff. But mostly we can
Speaker 1: explain the history of the universe after that first inflationary period.
Speaker 1: We can explain it assuming dark energy is constant, So
Speaker 1: that seems to be a reasonable assumption.
Speaker 2: Meaning that the universe is not pressing the accelerator faster,
Speaker 2: it's just kind of leaving it on.
Speaker 1: That's right. It's pressing the accelerator at the same level,
Speaker 1: meaning every part of space has the same amount of
Speaker 1: dark energy. But eventually that does take over. When you
Speaker 1: press the accelerator on your car. There are other things
Speaker 1: keeping you from going faster and faster, right, there's friction
Speaker 1: and this AerR, resistance whatever. That doesn't quite apply to
Speaker 1: this model because in this model, the level that the
Speaker 1: accelerator is at ends up speeding us up. It's like
Speaker 1: winning against the other forces. So it really is accelerating
Speaker 1: the expansion of the universe. So sort of two different
Speaker 1: ideas there. One is the amount of dark energy in
Speaker 1: space is constant, but because it overcomes the other things,
Speaker 1: it ends up accelerating the expansion of the universe.
Speaker 2: Meaning that the space is growing at an accelerated rate.
Speaker 2: But is that acceleration getting faster or is it slowing down?
Speaker 2: Or is it pretty constant.
Speaker 1: We think that acceleration itself is pretty constant, yes, and
Speaker 1: we can track that back through the history of the
Speaker 1: universe and see if that explains our history, and it
Speaker 1: mostly does. Again, there's some questions there about their early
Speaker 1: first few bits you might have read about, like different
Speaker 1: measurements of the Hubble constant that we can't quite reconcile.
Speaker 1: And that's what that's about. Is that level of acceleration
Speaker 1: the same all the way through time or.
Speaker 2: Not it is it or not?
Speaker 1: We think that it is, but we don't quite know
Speaker 1: that these measurements that we can't quite reconcile.
Speaker 2: I guess it's kind of the difference of whether dark
Speaker 2: energy is a constant, like a number in your equations
Speaker 2: of the universe, or is it a variable that somehow
Speaker 2: feeds in it itself or that maybe has a little
Speaker 2: button that you know, the makers of the universe are
Speaker 2: increasing exactly.
Speaker 1: Yeah, right, now, we can describe it just using a number.
Speaker 1: It's a cosmological constant. We don't know where that number
Speaker 1: comes from or why it is what it is. We
Speaker 1: have really no explanation for it. But we can mostly
Speaker 1: describe the history of the universe using just a number
Speaker 1: for dark energy.
Speaker 2: All right, Well, it sounds like the answer to the
Speaker 2: question of the episode is yes. It sounds like, as
Speaker 2: far as we know, if things stay the same with
Speaker 2: dark energy, are super cluster of galaxies that we live
Speaker 2: in will be torn apart sometime in the future.
Speaker 1: That's right. So our more immedia cosmic neighborhood is safe
Speaker 1: and probably will eventually collapse into a black hole, but
Speaker 1: the cluster will not be in our neighborhood forever. Dark
Speaker 1: energy will take over and pull us apart from it.
Speaker 2: It's going to be declustered, but we won't know, I
Speaker 2: guess until the end of time.
Speaker 1: That's right. So we'll do our five millionth episode at
Speaker 1: the end of time, and we'll answer this question definitively.
Speaker 2: So maybe I shouldn't call you a person, Daniel, because eventually,
Speaker 2: who knows, maybe aliens will come and tear you apart.
Speaker 2: We just have to wait and see before we call
Speaker 2: you a person.
Speaker 1: That's true. From that point of view, none of us
Speaker 1: are structured.
Speaker 2: We could all be lunch in our future, hey, fellow,
Speaker 2: lunch meat.
Speaker 1: Ashes to ashes, dust to lunch.
Speaker 2: And lunch to something else once the aliens digest us.
Speaker 2: All right, well, pretty interesting lesson to think about, not
Speaker 2: just like our place in the universe and how small
Speaker 2: we are compared to these enormous clusters of galaxies, but
Speaker 2: also about the permanence of the universe. Like even something
Speaker 2: as huge as a super cluster Lenni Kia, it may
Speaker 2: not be around for the entire life of the universe.
Speaker 1: That's right. Think about these incredibly powerful, vast forces at play,
Speaker 1: tugging on these galaxies with millions and billions of stars,
Speaker 1: all in a battle against dark energy. It's really a
Speaker 1: very dynamical place. If you think about the universe and
Speaker 1: sort of fast forward, it's slashing, it's frothen it's doing
Speaker 1: a lot.
Speaker 2: All right. We hope you enjoyed that. Thanks for joining us,
Speaker 2: See you next time.
Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain
Speaker 1: the Universe is a production of iHeart Radio. For more
Speaker 1: podcasts from iHeartRadio, visit the iHeartRadio, ap Apple podcasts, or
Speaker 1: wherever you listen to your favorite shows.