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What would happen if dark matter and dark energy disappeared? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Hey, or hey, let's do a physics thought experiment. Do
0:13
Speaker 1: I have to think about it? You have to have thoughts? Well,
0:17
Speaker 1: does it involve you know, Einstein on a moving train
0:21
Speaker 1: looking through a prison or something. No, No, we're going
0:23
Speaker 1: bigger than that, Bigger than like a supermassive black hole,
0:27
Speaker 1: even bigger. What could be bigger than billions of suns? Well,
0:30
Speaker 1: imagine that you could visit the universe's control room and
0:34
Speaker 1: just like turn something off. What would you remove from
0:38
Speaker 1: our universe? I imagine that all the time, Daniel waited,
0:43
Speaker 1: did you say what would I remove? Or who would
0:45
Speaker 1: I remove? Let's not make it personal. What would you
0:49
Speaker 1: remove from the universe? In that case? Probably Twitter? Twitter?
0:53
Speaker 1: I would probably remove immediately. I thought you were going
0:57
Speaker 1: to say, alarm clocks or emails? Yeah, those are pretty
1:01
Speaker 1: bad too, deadlines if I can flip multiple switches, yeah,
1:03
Speaker 1: they're all being flipped. Well, if that sounds good to you.
1:06
Speaker 1: The next time we have an election, vote for Jorge
1:08
Speaker 1: for Universe Control Room operating m Hi am Jorgemmay, cartoonists
1:28
Speaker 1: and the creator of PhD comics. Hi, I'm Daniel, I'm
1:31
Speaker 1: a particle of physicist, and I'm terrified to let Jorge
1:35
Speaker 1: into the control room of the universe. Are you worried
1:37
Speaker 1: I'm gonna do like a Homer Simpson and eat my
1:40
Speaker 1: doughnuts and excellently press the red switch. No, I'm terrified
1:44
Speaker 1: because you ask really good questions and so you'd be like, hmmm,
1:47
Speaker 1: what happens Is I pushed this all the way up?
1:50
Speaker 1: Or if I just flip all those knobs and the
1:52
Speaker 1: physicists would be like, what, don't even think about that?
1:54
Speaker 1: That's impossible. What if I flipped the switch on that
1:58
Speaker 1: everyone that gets a physics agree, I would love that.
2:02
Speaker 1: That is actually our goal, that's one of the missions
2:04
Speaker 1: of this podcast, in fact, is to educate everybody out
2:07
Speaker 1: there with a little bit of physics, to turn the
2:09
Speaker 1: switch on in your head, to make you think about
2:11
Speaker 1: the universe and to do a look out into the
2:13
Speaker 1: cosmos and maybe a whole different way. One of my
2:16
Speaker 1: proudest moments in this podcast was seeing somebody tweet that
2:19
Speaker 1: they had learned more physics from our podcast than in
2:21
Speaker 1: eight years as a PhD student in what But it
2:25
Speaker 1: was on Twitter, so who knows if it was really Also,
2:28
Speaker 1: could it have been one of your grad students or
2:33
Speaker 1: my stock puppet account on Twitter. One of your students
2:35
Speaker 1: is trying to tell you something, Daniel like, I hear
2:38
Speaker 1: more from my professor through this podcast than in actual life.
2:41
Speaker 1: I pay plenty of attention to my students, but thank
2:43
Speaker 1: you for standing up for them. Well. Yeah, so, welcome
2:46
Speaker 1: to our podcast, Daniel and Jorge Explained the Universe, a
2:48
Speaker 1: production of I Heart Radio, in which we talk about
2:51
Speaker 1: everything that's amazing in the universe, everything that's mysterious, everything
2:55
Speaker 1: that we do know, everything that we don't know, everything
2:58
Speaker 1: that we would like to know, and everything that Daniel
3:00
Speaker 1: students want to ask him but can't seem to find
3:03
Speaker 1: him in his office. For Yeah, I think they know
3:05
Speaker 1: by now to pretend to be somebody else and then
3:07
Speaker 1: send you a question. That's right because we think that
3:10
Speaker 1: everything that you wonder about, everything that we wonder about,
3:13
Speaker 1: everything that scientists are trying to figure out, We think
3:15
Speaker 1: that those questions belong to everybody, and then everybody deserves
3:19
Speaker 1: to know what's going on and what we know and
3:21
Speaker 1: what we don't know. So our goal is to transport
3:24
Speaker 1: you to the very forefront of human knowledge, and to
3:27
Speaker 1: do it without using any fancy words, because there are
3:30
Speaker 1: still a lot of questions out there in the universe.
3:33
Speaker 1: There are a lot of big mysteries that scientists are
3:35
Speaker 1: actively wondering about, and so scientists, for everyone, we should
3:39
Speaker 1: all be involved in this quest to understand where we
3:42
Speaker 1: are and how it is that we're here. Yeah, and
3:44
Speaker 1: one of the biggest questions we have about the universe
3:46
Speaker 1: is just why is it the way it is? Did
3:50
Speaker 1: it have to be this way? Is there some rule
3:52
Speaker 1: that tells us that the universe could only have been
3:55
Speaker 1: this way or could it have been totally different? So
3:58
Speaker 1: sometimes we look around with think, well, could the universe
4:01
Speaker 1: work without this bit or that bit? Or what if
4:04
Speaker 1: we flip these knobs with things still operate? Yeah, you mean, Daniel,
4:07
Speaker 1: we can't just say it is what it is. It
4:10
Speaker 1: definitely is what it is, But the question is why
4:13
Speaker 1: is it what it is and not something else? Yeah?
4:15
Speaker 1: Because I think you know, pondering these fundamental almost philosophical
4:19
Speaker 1: questions is also a big part of physics, you know,
4:22
Speaker 1: asking what if questions like why is it like that
4:25
Speaker 1: and not something else? What if the universe was totally different?
4:28
Speaker 1: Why isn't it what it Isn't that would be on
4:30
Speaker 1: my tombstone? Right? Why you just made me think they're Daniel,
4:37
Speaker 1: there's too many negatives in that one. Yeah, And we
4:40
Speaker 1: are curious about that, and so we play these mind
4:42
Speaker 1: games sometimes like do we need this bit or do
4:44
Speaker 1: we need that bit? Or how do these two things
4:46
Speaker 1: work together? And that's very helpful because it helps you
4:49
Speaker 1: understand why we have the various pieces of the universe
4:53
Speaker 1: that we have. We look out into the universe and
4:55
Speaker 1: we see the way it works, and we try to
4:58
Speaker 1: explain it, and we build up the minimal set of
5:00
Speaker 1: bits that we need to explain everything that we see
5:04
Speaker 1: in the universe. And so it's helpful to understand what
5:06
Speaker 1: would happen if you yanked at one part of the
5:08
Speaker 1: universe or yanked out another or turned something off. Ye.
5:11
Speaker 1: And you know, it's not just kind of a fun
5:13
Speaker 1: game to play, but it's also, you know, kind of
5:15
Speaker 1: a fundamental way in which science is done, right. I mean,
5:20
Speaker 1: when you ask yourself why something is like that, you
5:23
Speaker 1: in science, you kind of have to ask yourself, what
5:25
Speaker 1: if it wasn't like that? You know, I'm thinking about
5:28
Speaker 1: the null hypothesis, Yeah, exactly. Sometimes you have to ask,
5:31
Speaker 1: like do we really need this bit? Because the simpler
5:34
Speaker 1: explanation is always preferred, and so if you can explain
5:37
Speaker 1: the universe without some little extra you know, whiz bang
5:41
Speaker 1: bit in your theory, then great. Like if you have
5:44
Speaker 1: the current theory universe plus you have one with like
5:47
Speaker 1: invisible space kittens, well, you don't really need the invisible
5:50
Speaker 1: space kittens. They don't add anything to your theory. You
5:54
Speaker 1: like the invisible space kittens, you don't need the invisible
5:57
Speaker 1: space kitten. I would totally flip that swhich and that's
6:01
Speaker 1: why we're not letting you into the control room. But
6:04
Speaker 1: the point is we want the simplest theory, the one
6:06
Speaker 1: that explains everything we see with a minimal set of ideas,
6:10
Speaker 1: with the minimal set of numbers and details and complicated bits,
6:14
Speaker 1: because we think, we hope the universe is simple, and
6:17
Speaker 1: we can have long philosophical disagreements about whether the universe
6:20
Speaker 1: should be beautiful and should be pretty, but the goal
6:24
Speaker 1: of looking for simplicity has succeeded for a long time. Right,
6:27
Speaker 1: I'm thinking simple space kittens. Then then then you can't
6:31
Speaker 1: argue so single colors. For example, you don't have any
6:33
Speaker 1: calico invisible space kittens. Alright, Well, on today's episode, we'll
6:37
Speaker 1: be asking a really big what if question, maybe about
6:41
Speaker 1: as big as you can ask about the universe, right, yeah,
6:43
Speaker 1: I mean we're talking about the universe. What if it disappeared?
6:47
Speaker 1: That's right. We are gonna let Jorge delete of the
6:51
Speaker 1: universe Thanos could only do half the universe. Je has
6:55
Speaker 1: even more power. That's right. I am even more inevitable.
6:59
Speaker 1: I'm inevitably inevitable. Everybody out there, tremble in your headphones
7:04
Speaker 1: that I'll just snap my fingers limping on my infinity
7:07
Speaker 1: glove here, actually need to glove to get that's right. Yeah,
7:12
Speaker 1: that's right. That's a whole second arc of the Avenger sequence, right, Avengers,
7:16
Speaker 1: return of the Invisible Space Kittens, Jorges Army to destroy
7:20
Speaker 1: the universe or maybe destroyed our Avengers after game post game,
7:25
Speaker 1: still gaming anyways, So to be on the program, we'll
7:29
Speaker 1: be asking the question what if dark matter and dark
7:37
Speaker 1: energy disappear? Bom bom bomb or yes, the sound effect
7:41
Speaker 1: would be like yow, I like that. You should do
7:46
Speaker 1: that all the time here on the podcast. Due oh,
7:50
Speaker 1: I make those sound effects when I talked to my
7:52
Speaker 1: students in their meetings, and that's why they prefer to
7:55
Speaker 1: listen to the podcast No No, But it's a really
8:00
Speaker 1: fun question because, as you know, dark matter and dark
8:03
Speaker 1: energy are huge for actions of the universe. They play
8:06
Speaker 1: an enormous role, not just in how the universe look today,
8:09
Speaker 1: but how it looked in its early stages when it
8:12
Speaker 1: was a baby. Yeah, dark matter represents about of all
8:15
Speaker 1: the mass and energy in the universe, and dark energy
8:18
Speaker 1: represents about sixte right, Daniel, of all everything that there is. Yeah,
8:23
Speaker 1: that's right. And we often get questions from listeners about
8:26
Speaker 1: what that really means, like what's the denominator? You know,
8:29
Speaker 1: if you don't know how big the universe is, how
8:31
Speaker 1: can you say that dark matter is of what? And
8:37
Speaker 1: it's a great question of the whole thing. You don't
8:39
Speaker 1: need a denominate the whole thing. You don't need anominator
8:42
Speaker 1: because we usually think about it in terms of density,
8:44
Speaker 1: Like take any side blob of the universe. We're talking
8:48
Speaker 1: about of that and not just of the matter, but
8:51
Speaker 1: of the energy density, because remember that matter, that mass,
8:55
Speaker 1: the stuff that makes me and you, it's just another
8:58
Speaker 1: form of energy. And we talk go at the energy
9:00
Speaker 1: density because that's really what controls the curvature of space.
9:04
Speaker 1: In general, relativity it's not just stuff, but it's energy density.
9:08
Speaker 1: So when we talk about this pie that five of
9:11
Speaker 1: the universe is the kind of matter we're made out of,
9:13
Speaker 1: in twenty seven is dark matter and sixty is dark energy.
9:17
Speaker 1: We're really talking about the fractions of the energy density
9:21
Speaker 1: of any volume of the universe, right, And so the
9:23
Speaker 1: universe is really big or really small or infinite, it's
9:27
Speaker 1: kind of still means the same thing. Yeah, let's just
9:29
Speaker 1: talk about it without knowing the answer to that other
9:32
Speaker 1: super massive, incredibly important question that we're amazingly totally clueless about.
9:37
Speaker 1: And so we're asking the question, what would happen if
9:39
Speaker 1: you take it away, like if you went to the
9:41
Speaker 1: control room of the universe and just like flip the
9:43
Speaker 1: off switch on those two things, that's right, and made
9:46
Speaker 1: the dramatic sucking sound. And Daniel, do we mean like
9:50
Speaker 1: if we trend them off now, or if we like
9:53
Speaker 1: went back in time and took them out of the
9:55
Speaker 1: birth of the universe. Yeah, well, immediately when you ask
9:57
Speaker 1: that question, then I want to say, let's do all
9:59
Speaker 1: of them, because they're all really fascinating different experiments, and
10:04
Speaker 1: if you're going to understand the impact of these things
10:06
Speaker 1: on the universe. You want to play different games, and
10:09
Speaker 1: so yeah, we'll talk about if there had never been
10:11
Speaker 1: dark matter and dark energy in the universe, what would
10:13
Speaker 1: our universe look like? And also what would happen if
10:16
Speaker 1: you just deleted them from the universe, like instantaneously. Right now,
10:20
Speaker 1: we're going to cancel dark matter and dark energy. Right.
10:24
Speaker 1: Have you heard what dark matter dark energy said a
10:26
Speaker 1: hundred years ago? Boy, in modern context, it's embarrassing. We
10:30
Speaker 1: heard of their workplace policies, oh man, exactly, they were
10:35
Speaker 1: not very tolerant. But first, I was curious what our
10:38
Speaker 1: listeners knew about this subject, and so, as usual, Daniel
10:41
Speaker 1: went out there into the wilds of the Internet to
10:43
Speaker 1: ask people what they thought would happen if dark matter
10:47
Speaker 1: and dark energy disappear. So, if you're curious to play
10:50
Speaker 1: intellectual thought experiments for future episodes, please write to us
10:54
Speaker 1: two questions at Daniel and Jorge dot com. We'd love
10:57
Speaker 1: to get your voice on the podcast. So think about
11:00
Speaker 1: it for a second. What do you think would happen
11:02
Speaker 1: if both of those big things disappeared. Here's what people
11:06
Speaker 1: had to say if dark matter disappeared, assuming that it
11:10
Speaker 1: did exist before and now it disappeared, then I would
11:14
Speaker 1: assume that the galaxies would start to fall apart. The
11:18
Speaker 1: solar systems will probably be okay because the gravity there
11:21
Speaker 1: is enough to hold it together, but there wouldn't be
11:24
Speaker 1: enough matter to hold the galaxies together. If dark energy disappeared,
11:32
Speaker 1: then the universe would continue to expand it would stop accelerating.
11:36
Speaker 1: I believe I'm gonna go ahead and assume that the
11:38
Speaker 1: universe is is functioning the way it is now. I
11:41
Speaker 1: would imagine if dark energy disappeared, there'd be enough momentum
11:46
Speaker 1: of the expanding universe that it would continue expanding, and
11:50
Speaker 1: that if dark matter disappeared, I don't know if there
11:53
Speaker 1: would be enough regular matter to stop that expansion. Galaxies
11:58
Speaker 1: would start flying apart, and possibly even and solar systems
12:00
Speaker 1: might start flying apart. So would be kind of a
12:02
Speaker 1: chaotic experience there. If we're saying dark energy is somehow
12:05
Speaker 1: involved with the expansion of the universe, then I'm assuming
12:08
Speaker 1: that that's not going to happen anymore. Plus, listening to
12:12
Speaker 1: the latest episode on Black Holes, are not sure what's
12:17
Speaker 1: actually going to happen there. But I'm not sure that
12:20
Speaker 1: it actually interacts with us in any other way. That
12:23
Speaker 1: we know of right now, So that's a total unknown
12:26
Speaker 1: for me. Probably disaster. First of all, dark matter. Dark
12:30
Speaker 1: matter is between twenty of the universe. That would be
12:37
Speaker 1: pretty pretty bade. Everything would go crazy for sure if
12:42
Speaker 1: dark matter disappears. We know that that is the thing
12:45
Speaker 1: keeping us inside of our galaxy, and I did it,
12:49
Speaker 1: and that galaxy is spinning, all the planets and all
12:52
Speaker 1: the star starts with shootout and dark kind of is
12:55
Speaker 1: the thing that's expanding University, So maybe Huntin stops or
13:01
Speaker 1: maybe you know, to start to implode or something. All right,
13:05
Speaker 1: it sounds like the main message here is disaster. That's right.
13:09
Speaker 1: Nothing Good's right. The message is basically, keep Jorge out
13:12
Speaker 1: of the control room called the Avengers, called the Avengers back,
13:18
Speaker 1: knowing should have that much power, even the Avengers. I
13:21
Speaker 1: think that was not thinking big enough, right, Yeah, exactly,
13:24
Speaker 1: that was his problem. Yeah, he was not ambitious enough.
13:27
Speaker 1: It actually wasn't one of the infinity stones of dark
13:30
Speaker 1: matter or dark energy that they had, like a dark name.
13:32
Speaker 1: I don't remember the physics of it, but one of
13:35
Speaker 1: the cubes is supposed to be powered by dark energy,
13:38
Speaker 1: if I remember, isn't one of the infinity stones, the
13:41
Speaker 1: same cube that Thor was fighting over and that was
13:45
Speaker 1: powered by dark energy. You're getting me excited here, Daniel.
13:48
Speaker 1: We can spend the rest of the podcast going back
13:50
Speaker 1: through the test rack and the power that's it is
13:55
Speaker 1: powered by dark energy. That's the one. Yeah, but that
13:58
Speaker 1: turned out to have a stone inside of it. Woe. Anyways,
14:00
Speaker 1: back to physics. So not a lot of people have
14:02
Speaker 1: predicted good things would happen. Most people seem to think
14:05
Speaker 1: that the universe would sort of fall apart. Nobody is
14:07
Speaker 1: in favor of this proposal. Everyone wants to keep those
14:10
Speaker 1: things around as much as possible, which is why we're
14:12
Speaker 1: doing it as a thought experiment and not in reality
14:17
Speaker 1: that you know of, Daniel, And you know, there's a
14:19
Speaker 1: long and great history of thought experiments. Einstein's development of
14:22
Speaker 1: relativity was aided by thought experiments, just thinking what would
14:25
Speaker 1: happen if and sometimes they're just very useful to get
14:28
Speaker 1: you to think about the extreme situations. You know, you
14:31
Speaker 1: can't really do the experiment of flying in a spaceship
14:34
Speaker 1: at the speed of light and turning on a laser,
14:37
Speaker 1: but you can think about what the rules that we
14:39
Speaker 1: have suggest. You can think about what it would happen
14:42
Speaker 1: if you did that experiment. Now, we'd love to actually
14:45
Speaker 1: do it and to make those measurements, but even when
14:47
Speaker 1: we can't, we can still do the thought experiment to
14:49
Speaker 1: test the boundaries of the idea. Right, And you also
14:52
Speaker 1: kind of do thought experiments before you do actual experiment, hope.
14:55
Speaker 1: So like you probably work through all the possible ways
14:57
Speaker 1: that it could go and then you that's how you
14:59
Speaker 1: know to look for Yeah, we definitely thought about it
15:01
Speaker 1: before we built the large change on collider. For example,
15:05
Speaker 1: good will this destroy the world or not? We thought
15:08
Speaker 1: about that, and we also thought about what we could
15:09
Speaker 1: discover and how to build it, and so yeah, there's
15:12
Speaker 1: a lot of four planning involved in all of these experiments.
15:15
Speaker 1: All right, Well, just for those of you who might
15:16
Speaker 1: not be familiar, let's recap really quickly what dark matter
15:20
Speaker 1: and dark energy is. So let's start with dark matter.
15:23
Speaker 1: Explain dark matter in three minutes before we delete it
15:26
Speaker 1: from the universe. Let's remind people what it is. So
15:29
Speaker 1: dark matter we know is matter. It's some invisible stuff
15:33
Speaker 1: that's out there, and we know that it's matter and
15:35
Speaker 1: that it's out there because we see its gravitational effects.
15:38
Speaker 1: It's holding galaxies together that are otherwise spinning way too
15:42
Speaker 1: fast to be held together by the gravity of the
15:44
Speaker 1: stars that we can see. It controls the whole structure
15:48
Speaker 1: of the universe, seeding the formation of galaxies and all
15:51
Speaker 1: kinds of stuff. And we've measured that it's about twenty
15:54
Speaker 1: seven percent of the energy budget of the universe, which
15:58
Speaker 1: is about five times as as the normal matter, the
16:01
Speaker 1: stuff that makes up stars and gas and planets and
16:03
Speaker 1: bananas and all that good stuff, right and dark bananas obviously,
16:07
Speaker 1: But it's a big deal. I mean, it's not just
16:10
Speaker 1: like some small thing out there in space. It's it's
16:12
Speaker 1: literally five times more than the kind of stuff that
16:17
Speaker 1: we're made out of in stars and black and you know,
16:20
Speaker 1: black holes and galaxies. Yeah, we are literally the tip
16:23
Speaker 1: of the matter iceberg. And it's a wonderful lesson that
16:26
Speaker 1: there's so much going on out there that we weren't
16:28
Speaker 1: aware of until very recently, which means that there are
16:31
Speaker 1: big surprises coming around the bend in the future. And
16:35
Speaker 1: so we know that it's out there, we know that
16:37
Speaker 1: it's matter. It's definitely made of stuff because it has gravity.
16:40
Speaker 1: We don't know what it is. We don't know if
16:42
Speaker 1: it's a particle. We don't know if it's something else.
16:43
Speaker 1: We don't know, if it's seventies seven kinds of particles.
16:46
Speaker 1: I don't know a lot about it other than that
16:48
Speaker 1: it's dark and that it's matter. Hence the name dark matter, right,
16:51
Speaker 1: and so that's dark matter, and so dark energy also,
16:54
Speaker 1: how would you describe it? So dark energy is similar
16:57
Speaker 1: to dark matter in the sense that it's important, it's
16:59
Speaker 1: a big in the universe, and we don't know very
17:01
Speaker 1: much about it. Otherwise, that's about all it has in
17:04
Speaker 1: common with dark matter. Just basically the word dark dark
17:08
Speaker 1: because we can't see it with visual light, right, Yeah,
17:10
Speaker 1: we can't see it with visual light. And also we
17:12
Speaker 1: just don't really understand it. Dark energy is not really
17:16
Speaker 1: a thing. It's not something we understand, it's not something
17:19
Speaker 1: we have a theory about. It's just the observation that
17:21
Speaker 1: the universe is expanding and that that expansion is accelerating.
17:26
Speaker 1: So space is getting bigger and bigger, but it's getting bigger,
17:30
Speaker 1: faster and faster every year, and that takes energy. It
17:33
Speaker 1: takes a lot of energy. And we only recently, like
17:37
Speaker 1: years ago, discovered that this expansion is accelerating. So dark
17:40
Speaker 1: energy is a description of that acceleration of the expansion.
17:45
Speaker 1: We don't have a theory that describes that. We don't
17:47
Speaker 1: have a model that makes it work. We've just seen
17:50
Speaker 1: that this happens and we know that it's important. Right.
17:52
Speaker 1: It's kind of like you're five year old when they
17:54
Speaker 1: don't want to go to sleep and they're jumping in
17:55
Speaker 1: the bed. You're like, where do they get this energy? Like,
17:58
Speaker 1: it's not like they're glowing, they're just acting in a
18:01
Speaker 1: funny way. That's right. But they both contribute to this pie. Right.
18:04
Speaker 1: Dark energy takes a lot of energy. We can calculate
18:07
Speaker 1: how much energy it takes to expand the universe and
18:10
Speaker 1: to accelerate that expansion, and it's just under seventy percent
18:13
Speaker 1: of the energy density of the universe. And dark matter
18:17
Speaker 1: is and they fit together in this pie. And the
18:19
Speaker 1: pie is important because various elements of the pie work
18:22
Speaker 1: together to control whether the universe is expanding or contracting,
18:27
Speaker 1: and whether stuff is being formed like galaxies and stars,
18:30
Speaker 1: or whether everything is just sort of floating out their
18:32
Speaker 1: diffuse and so as we'll learn, these two elements are
18:36
Speaker 1: very important for the formation of our universe and to
18:39
Speaker 1: keep it blowing up, or to make a contract, or
18:41
Speaker 1: all of those things. So these are the most important
18:44
Speaker 1: parameters into like determining the whole structure and the shape
18:48
Speaker 1: and the size of the universe. Right, it's almost in
18:50
Speaker 1: a way like if you like the universe way, it
18:52
Speaker 1: is now like we are more expendable than dark matter
18:55
Speaker 1: or dark energy. It's like you can take away all
18:58
Speaker 1: the galaxies and stars and humans and bananas, and the
19:01
Speaker 1: universe would be less affective than if you took out
19:04
Speaker 1: one of these two things. That's right, If dark Corey
19:06
Speaker 1: gets into the universe control room, Dark Daniel will say, yeah, sure,
19:09
Speaker 1: turn off all the bananas another matter, It doesn't make
19:12
Speaker 1: any difference. Let's just delete ourselves. But then who built
19:17
Speaker 1: the control room Daniel? Well, you know, we don't know.
19:20
Speaker 1: But we are a tiny, maybe irrelevant fraction of the universe,
19:24
Speaker 1: and so we can't expect that everything is made in
19:27
Speaker 1: our image. Right, All right, let's get into what would
19:29
Speaker 1: happen to the universe if these two things suddenly disappeared.
19:34
Speaker 1: But first let's take a quick break. All right, Daniel,
19:48
Speaker 1: you've led me into the control room of the universe,
19:51
Speaker 1: and I see a big switch here that says dark
19:54
Speaker 1: matter with two options on or off. I'm gonna go
19:57
Speaker 1: with off. Here, I'm gonna flip the switch. Are you
19:59
Speaker 1: ready hold onto something? Click? All right, I've just made
20:05
Speaker 1: dark matters. I hear. What's gonna happen? All right? Well,
20:08
Speaker 1: it's important to know when we are in the universe simulation, like,
20:12
Speaker 1: are we going to remove dark matter from the very
20:14
Speaker 1: very beginning so there never was any, or are we
20:17
Speaker 1: going to delete it? We're going to cancel dark matter
20:19
Speaker 1: in the universe today. I guess that two different things
20:23
Speaker 1: might happen, right, all right, So let's let's start with
20:26
Speaker 1: the early universe. Let's say we pulled it back to
20:29
Speaker 1: the future, went back to the early universe, and then
20:32
Speaker 1: got rid of dark matter, but the universe be very different.
20:35
Speaker 1: The universe would be really different fourteen billion years later
20:39
Speaker 1: if there had never been any dark matter in it,
20:42
Speaker 1: because dark matter is really the thing that makes the
20:44
Speaker 1: universe interesting. Briefly, it's gravity is the reason that we
20:49
Speaker 1: have formed stars and galaxies and all sorts of interesting stuff.
20:53
Speaker 1: Like the gravity from our kind of matter is not
20:55
Speaker 1: sufficient to pull together into interesting structures this early in
21:00
Speaker 1: the universe. Without the gravitational assist of dark matter, because
21:05
Speaker 1: I guess without the gravity that dark matter brings, things
21:09
Speaker 1: wouldn't have clumped together as much or as interestingly, which
21:13
Speaker 1: one are you saying, yeah, both of them. I mean,
21:15
Speaker 1: the brief history of the universe is that you have
21:19
Speaker 1: very small over densities, little places where stuff is denser
21:23
Speaker 1: than other stuff that came out of quantum fluctuations in
21:26
Speaker 1: the very early universe, and then gravity takes over and
21:29
Speaker 1: stuff that's denser has more gravity attracts more stuff, which
21:32
Speaker 1: makes more gravity, which attracts more stuff. It's a feedback cycle,
21:36
Speaker 1: and what you need is stuff for that to happen.
21:38
Speaker 1: And so if you have dark matter and it's five
21:41
Speaker 1: times as much stuff as there is normal matter, then
21:45
Speaker 1: that happens a lot faster. And something that people don't
21:48
Speaker 1: typically understand is that dark matter is not just like
21:50
Speaker 1: everywhere in the universe. It's clumped, are big blobs of it,
21:54
Speaker 1: and those blobs are centered everywhere there is normal matter,
21:58
Speaker 1: and it's not coincidence. Right. Think about dark matters forming
22:02
Speaker 1: like depressions in the shape of the universe to collect
22:05
Speaker 1: normal matter, so that gas and hydrogen and helium falls
22:08
Speaker 1: into those depressions and then it squeezed together into stars
22:12
Speaker 1: and galaxies, etcetera. Without them, it would be much smoother.
22:15
Speaker 1: It take a lot longer for gravity to pull the
22:17
Speaker 1: hydrogen together and to form stars and galaxies. That was
22:21
Speaker 1: dark matter clumped initially, or was it out there in
22:25
Speaker 1: the Big Bang pretty smooth or were there quantum fluctuations
22:29
Speaker 1: in the dark matter as well? It was the quantum
22:31
Speaker 1: fluctuations that caused any structure at all, Like everything else,
22:35
Speaker 1: the universe would have started out perfectly smooth if not
22:38
Speaker 1: for these quantum fluctuations, and then we would have dark matter,
22:41
Speaker 1: even dark matter, Yeah, because dark matter and normal matter
22:44
Speaker 1: were made in the Big Bang, right when we went
22:47
Speaker 1: from really really hot and dense so that all the
22:49
Speaker 1: fields were crazy, and then they broke down and created
22:52
Speaker 1: the particles as the universe started to expand and cooled.
22:56
Speaker 1: So they were all made essentially during this initial expansion
22:59
Speaker 1: of the universe. But as you say, it would have
23:02
Speaker 1: been perfectly smooth without those quantum fluctuations, and so dark
23:05
Speaker 1: matter like accentuates it, like exaggerates the effect of these fluctuations,
23:09
Speaker 1: and it speeds things up. If you do a simulation
23:12
Speaker 1: of the universe without dark matter, we've literally done this.
23:15
Speaker 1: Then you just don't get stars and galaxies fourteen billion
23:18
Speaker 1: years into the universe, but you get them eventually, Like
23:21
Speaker 1: it's the effect of dark matter just speeding things up,
23:25
Speaker 1: or is it like we would never clump together as
23:28
Speaker 1: a galaxy. Well, it depends a little bit on what's
23:30
Speaker 1: going on with dark energy. It speeds things up, right,
23:33
Speaker 1: And so given enough time without dark energy expanding the universe,
23:37
Speaker 1: then yeah, it would form these gravitational structures and you
23:40
Speaker 1: would get stars and galaxies. But there's a bit of
23:42
Speaker 1: a race here, right. Dark energy is coming on the
23:45
Speaker 1: scene and it's pulling the universe apart. It's making it
23:48
Speaker 1: harder for gravity to form structures. So we got a
23:51
Speaker 1: little bit of a window there right before dark energy
23:53
Speaker 1: yanks the universe apart. It makes everything too far apart
23:56
Speaker 1: to do anything interesting. You've got a window there to
23:59
Speaker 1: form interest structures. So you don't have infinite time to
24:02
Speaker 1: get stuff done. You've got a deadline. I mean you
24:04
Speaker 1: have fourteen billion years, but you still got a deadline, right, Well,
24:07
Speaker 1: assuming that dark energy keeps going, that's right, Assuming that
24:10
Speaker 1: dark energy keeps going and that you know, you don't
24:12
Speaker 1: stumble into the control room and turn it off or
24:14
Speaker 1: accidentally double it or something. Stay tuned, Stay tuned. That's
24:18
Speaker 1: the last part of the podcast. So we wouldn't get
24:21
Speaker 1: interesting structures. So what would the universe look like today?
24:24
Speaker 1: It would just look sparser, like there wouldn't be like
24:28
Speaker 1: galaxies and stars will be more spread out apart, or
24:30
Speaker 1: there'll be less stars. Yeah, we would essentially just be
24:33
Speaker 1: earlier in the development of structure. And so whereas in
24:36
Speaker 1: our universe we had the first population of stars form
24:39
Speaker 1: in less than a billion years after the Big Bang,
24:41
Speaker 1: that would have happened much later, and galaxies formed, you know,
24:45
Speaker 1: in the first billion years or so. That would also
24:47
Speaker 1: happen much much later. And so at this point in
24:50
Speaker 1: the universe. It depends a little bit on the details
24:52
Speaker 1: of how are you modeling dark energy, But we would
24:54
Speaker 1: probably have some stars, but not big complicated galaxies like
24:58
Speaker 1: we have today. So dark matters like this, steroids kind
25:01
Speaker 1: of of the growth of the universe. All right, I
25:03
Speaker 1: thought the universe was organic and you know, hormone free,
25:07
Speaker 1: but I guess even the universe dopes a little. That's right.
25:10
Speaker 1: Market pressures, man, market pressures, alright, So then the other
25:13
Speaker 1: scenario that's interesting is like, what have you turned off
25:15
Speaker 1: dark matter? Now? Like we are where we are now,
25:18
Speaker 1: it is what it is, but then suddenly something happened
25:20
Speaker 1: to dark matter. That's right. Say you have had dark
25:23
Speaker 1: matter that super charged the acceleration of structure in the universe,
25:26
Speaker 1: gave us stars and galaxies, and then you deleted it
25:29
Speaker 1: Santos style from the universe. Well, you know, the structures
25:32
Speaker 1: that we have now depend on dark matter. It's not
25:36
Speaker 1: just like, well, we needed dark matter to get where
25:38
Speaker 1: we are, but now that we're rich and famous, we
25:40
Speaker 1: could forget about our friends from our hometown. We still
25:43
Speaker 1: need dark matter because it's holding our galaxy together. Like
25:47
Speaker 1: our galaxy is spinning, right, and things that are spinning
25:51
Speaker 1: tend to fly apart if there's not something holding them together.
25:54
Speaker 1: Like we say often in the podcast, you put ping
25:56
Speaker 1: pong balls on a merry go round and spin it,
25:58
Speaker 1: ping pong balls fly out. The reason that the stars
26:01
Speaker 1: in our galaxy, which is spinning, don't fly out into
26:05
Speaker 1: intergalactic space is because gravity is holding them together, and
26:08
Speaker 1: mostly that's dark matter. So if you deleted dark matter
26:13
Speaker 1: from the galaxy, then it'd be like as if you
26:16
Speaker 1: suddenly turned the merry go around on five times as fast,
26:19
Speaker 1: and you know, the stuff in the outer ring of
26:22
Speaker 1: the galaxy would get tossed out into intergalactic space. There
26:26
Speaker 1: wouldn't be enough gravity to hold it today. Would it
26:28
Speaker 1: just fly off or would it just you know, the
26:30
Speaker 1: galaxy would just get bigger in terms of things being
26:32
Speaker 1: more spread out. It would get bigger. But the stuff
26:34
Speaker 1: on the outside would essentially have escape velocity suddenly, so
26:38
Speaker 1: they would get tossed into intergalactic space. We would lose
26:41
Speaker 1: all those stars in the sort of exerbs of the galaxy. Well,
26:45
Speaker 1: we don't really need those stars to be there's a
26:49
Speaker 1: lot of crucial votes in those districts, man, so be careful.
26:51
Speaker 1: Which is it's a lot of politics here today, Daniel.
26:55
Speaker 1: But your fate depends sort of on your distance from
26:58
Speaker 1: the center of the galaxy. If you're the very edge
27:00
Speaker 1: of the galaxy, you're getting tossed out into space. You're
27:03
Speaker 1: becoming a rogue star, which is, hey, maybe not that bad. Like,
27:06
Speaker 1: what do you really need the galaxy for anyway? You know,
27:08
Speaker 1: if you believe in in limited galaxies, then maybe that's
27:11
Speaker 1: good for your philosophy. Well, what would happen to us
27:13
Speaker 1: in particular, like would our solar system be affected at all?
27:17
Speaker 1: Like would life go on the same for us, or
27:19
Speaker 1: would we also fall apart. Well, we're in so of
27:21
Speaker 1: that middle region and we would stay still gravitationally bound
27:25
Speaker 1: to the main galaxy. But we get a little further
27:27
Speaker 1: from the center, and probably what would happen is that
27:31
Speaker 1: all the stars in our vicinity would clump together to
27:33
Speaker 1: form basically like a little dwarf galaxy. You may not
27:36
Speaker 1: be aware, but our galaxy has little satellites, like you
27:40
Speaker 1: know our planet has a moon, right, our galaxy has
27:43
Speaker 1: its own satellites, things that orbited called dwarf galaxies, little
27:47
Speaker 1: clusters of stars that form many galaxies. So probably our
27:51
Speaker 1: son would end up in one of these little clumps
27:53
Speaker 1: that would be orbiting the old core of the Milky Way, really,
27:57
Speaker 1: but maybe further out or something further out, So instead
28:00
Speaker 1: of being like in the suburbs, would be a little
28:02
Speaker 1: town out deep in the wilderness. So you're saying, without
28:05
Speaker 1: dark matter, you would get more of these satellite galaxies.
28:08
Speaker 1: Why would we get more Well, because the middle part
28:10
Speaker 1: of the galaxy, this middle band where we live, wouldn't
28:13
Speaker 1: be held into the galaxy anymore sort of get spread
28:16
Speaker 1: out and instead of having being tossed all the way
28:19
Speaker 1: into space, we don't have enough velocity for that, We
28:21
Speaker 1: don't have escape velocity. We become gravitationally bound to the galaxy,
28:25
Speaker 1: but in sort of a clump, and so this middle
28:28
Speaker 1: part of the galaxy we sort of break up into
28:30
Speaker 1: a bunch of little galaxies that are then orbiting the
28:32
Speaker 1: old poor All right, Well, it sounds like if we
28:35
Speaker 1: took it out early in the universe, we wouldn't be here.
28:38
Speaker 1: The universe would look really different. But if he took
28:41
Speaker 1: it out today, you know, daily life, We mean, we
28:44
Speaker 1: we would sort of orbit around things differently, but it
28:46
Speaker 1: maybe wouldn't affect us in our daily lives. Yeah, we're
28:49
Speaker 1: almost not affected at all by the structure of the galaxy.
28:51
Speaker 1: Doesn't really matter to us at all whether those other
28:53
Speaker 1: stars are there. You know, we're dominated by the experience
28:57
Speaker 1: of the Sun, but whether there are other stellar n
29:00
Speaker 1: verse is not really a big deal. And you know,
29:02
Speaker 1: it affects maybe our prospects for galaxy spanning civilizations once
29:06
Speaker 1: in the future if we end up in a little
29:08
Speaker 1: dwarf galaxy further from the main core. But you know,
29:11
Speaker 1: if our ambitions are closer to home, then it doesn't
29:14
Speaker 1: really change our lives if dark matter is deleted today, right?
29:17
Speaker 1: Or I wonder how long before we would even notice
29:19
Speaker 1: dark matter was gone? Oh my gosh, are you Are
29:21
Speaker 1: you trying to admit? Are you trying to confess to
29:22
Speaker 1: having done something last night? Where are they going to notice?
29:26
Speaker 1: I'm like the bad guy and Watchman. It's like I
29:28
Speaker 1: flipped the switch twenty four hours ago, Daniel. This is
29:33
Speaker 1: the modern version of the tell tale heart, right, can
29:35
Speaker 1: anybody tell? They're all looking at me? Yeah, Like, like
29:39
Speaker 1: how long ago could I have flipped the switch before
29:42
Speaker 1: we even notice? And that's a good question, and it
29:44
Speaker 1: goes to like how well we know the structure of
29:46
Speaker 1: our galaxy, which is a whole fascinating podcast topic. We
29:49
Speaker 1: have schedules for a couple of weeks from now, but
29:52
Speaker 1: we know that the structure of the galaxy pretty well,
29:54
Speaker 1: and we can tell the distance to nearby stars, and
29:57
Speaker 1: so if that's suddenly changed, we we would be able
29:59
Speaker 1: to tell. But not for a few years, right, because
30:01
Speaker 1: the information we're getting is years old, because the closest
30:05
Speaker 1: stars are a few light years away and most of
30:07
Speaker 1: the rest of the galaxy is five ten a hundred
30:10
Speaker 1: thousand light years away, so it would be a while
30:12
Speaker 1: before we actually saw hundreds of years or something, right, Yeah,
30:15
Speaker 1: it could be hundreds or thousands of years before we
30:17
Speaker 1: figure that out. Before we're like, holl hey, what did
30:19
Speaker 1: you do? Or is great great great great great grandchildren
30:22
Speaker 1: or to be held to account? So what would it
30:24
Speaker 1: look like? Would we see less stars out in space
30:26
Speaker 1: when we looked at the nice guy? Yeah, we would
30:28
Speaker 1: see less stars out in space, and we'd be separated
30:31
Speaker 1: from the main core of the galaxy. Now, the core
30:33
Speaker 1: of the galaxy wouldn't change very much because it's got
30:36
Speaker 1: so much gravity already in the supermassive black hole would
30:39
Speaker 1: hang on to that. Instead of seeing the Milky Way
30:41
Speaker 1: as a band across the sky, we would see the
30:44
Speaker 1: core of the galaxy in our sky. Be pretty spectacular. Actually,
30:48
Speaker 1: it would get more intense. Maybe, yeah, I might get
30:50
Speaker 1: more intense. All right, Well that's um dark Matter. Thank
30:53
Speaker 1: you for playing dark Matter. We like what you're doing.
30:55
Speaker 1: We'll keep it. I guess I vote yes on dark
31:00
Speaker 1: You don't even know what it is, Daniel, I don't
31:02
Speaker 1: know what it is, but I want to keep it.
31:04
Speaker 1: Wrong I like it, I fear changed. Right, let's talk
31:07
Speaker 1: about what would happen if we took dark energy away?
31:09
Speaker 1: But first let's take another quick break. All right, Dan,
31:24
Speaker 1: we're talking about what would happen if we took out
31:26
Speaker 1: these big chunks with the universe way dark matter and
31:30
Speaker 1: dark energy, And so let's talk about what would happen
31:32
Speaker 1: if I made dark energy disappear? And again, I guess
31:36
Speaker 1: you can talk about taking it away at the beginning
31:39
Speaker 1: of the universe and today, So what would happen if
31:41
Speaker 1: I took it out when the universe started. It's fascinating
31:44
Speaker 1: because these two different components, dark matter and dark energy
31:48
Speaker 1: sort of dominate the stage at different part of the
31:50
Speaker 1: history of the universe, Like dark matter controls the structure
31:53
Speaker 1: of the universe from very early days, whereas dark energy
31:56
Speaker 1: really only takes over in the last few billion years,
32:00
Speaker 1: and so they really play a different role here, which
32:02
Speaker 1: is fast. Yeah. To understand this, we have to understand
32:06
Speaker 1: a little bit about the history of the expansion of
32:09
Speaker 1: the universe. So go all the way back to the
32:12
Speaker 1: very beginning and the universe somehow is created. We don't
32:16
Speaker 1: understand that at all. And then there's inflation when the
32:19
Speaker 1: universe goes from very hot and very dense to suddenly
32:22
Speaker 1: much larger, and again we don't really understand that at all.
32:26
Speaker 1: But from that going forward, we think we have an
32:28
Speaker 1: understanding of how the universe expands and how that expansion
32:32
Speaker 1: accelerates or decelerates, and it's controlled by how much matter
32:36
Speaker 1: and radiation there is, how much energy there is in
32:38
Speaker 1: the universe, and also in this dark energy, and the
32:41
Speaker 1: two forces are usually working at odds with each other,
32:44
Speaker 1: which so dark energy wasn't very instrumental in the Big Bang,
32:48
Speaker 1: like it was an inflation sort of partly due to
32:50
Speaker 1: dark energy, So we don't know. Inflation has a very
32:53
Speaker 1: similar effect to dark energy, and that expands the universe
32:56
Speaker 1: very rapidly, But we don't know if the mechanism of
32:59
Speaker 1: inflation is the same as the mechanism of dark energy,
33:02
Speaker 1: Like they both have the same effect, but we don't
33:04
Speaker 1: know if they're the same thing. They could be, and
33:07
Speaker 1: in some theories they are. In some theories they're totally different,
33:10
Speaker 1: but we're really just at the very beginning stages of
33:12
Speaker 1: understanding these things at all, and so we can't really
33:15
Speaker 1: say that inflation is the same as dark energy. So
33:17
Speaker 1: let's put inflation aside and think about what happens post inflation,
33:22
Speaker 1: right basically after the Big Bang, if there was no
33:25
Speaker 1: dark energy, I see, all right, So that the universe
33:27
Speaker 1: just exploded or expanded rapidly after inflation, and now everything's
33:33
Speaker 1: kind of hanging out there. So what would happen if
33:35
Speaker 1: I turned off dark energy? So really not very much
33:37
Speaker 1: like in the early universe, dark energy plays almost no role.
33:41
Speaker 1: And the reason is that things are still really very
33:43
Speaker 1: hot and dense. They have a lot of radiation. In
33:45
Speaker 1: the first thousand years of the universe. Mostly the universe
33:49
Speaker 1: is just radiation. We're talking like photons, like crazy, bouncing
33:52
Speaker 1: around everywhere for the first forty seven thousand years. And
33:56
Speaker 1: it's a little counterintuitive, but what happened in the very
33:58
Speaker 1: beginning of the universe is that you expansion of the universe,
34:01
Speaker 1: even though it's mostly just filled with stuff, right, And
34:04
Speaker 1: typically think of stuff causing gravity, which causes you know, contraction,
34:09
Speaker 1: But the matter in the radiation and the universe actually
34:11
Speaker 1: caused some expansion early on. It made the universe get bigger. Now,
34:16
Speaker 1: the effect of dark energy is to accelerate that expansion,
34:19
Speaker 1: is to make that expansion happen faster and faster and
34:22
Speaker 1: faster gravity works the other way, it makes the expansion
34:25
Speaker 1: happen slower. Are you saying that dark energy didn't play
34:30
Speaker 1: a role, Like it wasn't important or it was just
34:33
Speaker 1: turned down in the early moments of the universe. It
34:35
Speaker 1: didn't really play a role at all. Dark energy gets
34:38
Speaker 1: more important as the universe gets bigger because it has
34:41
Speaker 1: one really weird property is that it doesn't get diluted.
34:45
Speaker 1: Like every chunk of space has the same amount of
34:48
Speaker 1: dark energy, and if you double the space, you make
34:51
Speaker 1: space bigger, you get more dark energy, whereas with matter
34:55
Speaker 1: and radiation, like if you double the size of space,
34:58
Speaker 1: then the matter gets less dense because you have the
35:01
Speaker 1: same amount of matter, Like you have two protons in
35:04
Speaker 1: a cubic meter of space, and then you expand the
35:07
Speaker 1: universe to be twice as big. Now you have two
35:09
Speaker 1: protons in two cubic meters of space, so you have
35:13
Speaker 1: less matter density. But dark energy just doubles when you
35:17
Speaker 1: double the space. So as space gets bigger, dark energy
35:20
Speaker 1: gets more and more important. So dark energy, you could
35:22
Speaker 1: have deleted it from the very early universe, it would
35:25
Speaker 1: have had no role. But as the universe gets bigger
35:27
Speaker 1: and bigger, it starts to take over and become dominant. Right,
35:30
Speaker 1: I guess it's kind of like if you took it
35:31
Speaker 1: out before it grew, then it wouldn't make a difference.
35:34
Speaker 1: But now, in as the universe grew, dark energy also grew,
35:38
Speaker 1: and so it just became more consequence. That's right. And
35:40
Speaker 1: so if you had deleted it from the early universe
35:43
Speaker 1: and it never had happened, right, we never had dark energy,
35:46
Speaker 1: then the history of the universe would be like, you
35:48
Speaker 1: have the Big Bang, you have all this matter, you
35:50
Speaker 1: have all this radiation. You still have expansion of the
35:53
Speaker 1: universe in the very early universe. But then gravity is
35:56
Speaker 1: taking over. It's slowing down that expansion. Eventually it's stops
36:00
Speaker 1: the expansion and it turns things around. We have a
36:02
Speaker 1: contraction and the universe reverses and comes back into a
36:05
Speaker 1: big crunch. So dark energy is the reason we're still around.
36:09
Speaker 1: While we're still around, is the reason why we haven't
36:11
Speaker 1: had a big crunch. But you wouldn't have noticed it
36:13
Speaker 1: in the very early universe because it didn't really take
36:16
Speaker 1: over until a little bit later. So wait, so I
36:19
Speaker 1: took out dark energy at the beginning, the universe would
36:22
Speaker 1: have expanded. And are you saying that by now, like
36:24
Speaker 1: fourteen years into it, we wouldn't be here, like the
36:27
Speaker 1: universe would have crunched already. Absolutely. Yeah. Without dark energy
36:31
Speaker 1: in the universe, gravity would have won. It would have
36:34
Speaker 1: slowed down the expansion. It would have stopped and turned
36:36
Speaker 1: it around and crunched us. We wouldn't have this universe
36:39
Speaker 1: without dark energy, Like none of the starts would have formed,
36:42
Speaker 1: or they would have been starting to form. But then
36:45
Speaker 1: the universe would crunch. Because you still have dark matter,
36:47
Speaker 1: you would have formed stars and galaxies. But then without
36:51
Speaker 1: dark energy, all that gravity would have gone into a
36:54
Speaker 1: runaway effect and collapse the universe back into a very
36:57
Speaker 1: very dense state. Okay, so you took it out early.
37:01
Speaker 1: What have you waited a little bit before taking out
37:03
Speaker 1: dark energy? So there's a bit of a dial there, right.
37:05
Speaker 1: If you take it out too early, the universe crunches.
37:09
Speaker 1: If you leave it in a little bit longer, then
37:11
Speaker 1: allows the universe to expand more, It fights gravity longer,
37:14
Speaker 1: and it gives you a longer and longer window at
37:17
Speaker 1: some point. If you turn off dark energy late enough,
37:21
Speaker 1: it's too late, like gravity can no longer win Like
37:24
Speaker 1: in our universe today with dark energy, we have the
37:27
Speaker 1: acceleration of the universe happening right now, like space is expanding,
37:31
Speaker 1: and it's expanding faster and faster. So, for example, if
37:34
Speaker 1: he turns it off today, gravity could not pull the
37:38
Speaker 1: universe back into a dot. It's already too late for gravity.
37:41
Speaker 1: Really is, because if you take out dark energy, the
37:44
Speaker 1: universe stops expanding. It's like it's fixed in size. Wouldn't
37:48
Speaker 1: gravity eventually bring everything together? Yes, But if you take
37:52
Speaker 1: out dark energy, you don't stop the expansion. You stop
37:54
Speaker 1: the acceleration of the expansion. You stop adding to the velocity.
37:58
Speaker 1: Things still have a velocity. Remember Newton's lass tell us
38:02
Speaker 1: that things and motions stay in motion unless you apply
38:05
Speaker 1: a force to them, and so dark energy is that force.
38:07
Speaker 1: If you stop pushing on things, they're still flying out.
38:10
Speaker 1: Their space is still expanding. And so dark energy is
38:14
Speaker 1: the acceleration of the expansion, not the expansion itself. So
38:17
Speaker 1: if you take out dark energy, you stop the acceleration,
38:21
Speaker 1: but things are still expanding and gravity does not have
38:24
Speaker 1: the power to turn that around. Wait, what what is
38:26
Speaker 1: still expanding? Like the distance between stars and galaxies or
38:30
Speaker 1: with space itself still be you know, multiplying and growing both.
38:34
Speaker 1: We're talking about the expansion of space itself, right, and
38:38
Speaker 1: that expansion is accelerated by dark energy. But you still
38:41
Speaker 1: get expansion even without dark energy. Really, so if you
38:44
Speaker 1: take out dark energy, space would still be growing. What
38:47
Speaker 1: is making it grow? Don't you need energy for that? Well,
38:49
Speaker 1: the expansion can continue without dark energy. But matter itself
38:53
Speaker 1: causes the expansion of the universe, like we were talking
38:56
Speaker 1: about earlier in the very early university was just matter
39:00
Speaker 1: causes the universe to expand. Gravity gives you a negative
39:04
Speaker 1: derivative on that expansion. It slows down that expansion, and
39:08
Speaker 1: dark energy increases that expansion. So sort of two things
39:11
Speaker 1: to talk about there, like the velocity of space and
39:15
Speaker 1: its acceleration. So matter gives space velocity to expand outwards,
39:20
Speaker 1: gravity gives you a negative acceleration on that, and dark
39:25
Speaker 1: energy gives you positive accelerat Dark energy is kind of
39:27
Speaker 1: like the booster rocket or like the turbo yeah, and
39:30
Speaker 1: the universe. Yeah, So if you take away dark energy
39:33
Speaker 1: in the very very early universe, so it never happened,
39:36
Speaker 1: then gravity would win and things would crunch. If you
39:38
Speaker 1: take it away today, right then it's sort of too late.
39:41
Speaker 1: He's already won the game. And gravity can't turn things around,
39:45
Speaker 1: like things are moving out too fast and too far
39:47
Speaker 1: away for things to turn around. And there's like a
39:49
Speaker 1: middle time there where if you deleted dark energy just
39:52
Speaker 1: the right moment, you would find like a balance there.
39:55
Speaker 1: And there's some moment there there's a tipping point, and
39:58
Speaker 1: I'm not sure you could actually walk that and stay
40:00
Speaker 1: on that tipping point, but there's some point at which
40:03
Speaker 1: if you don't delete dark energy before that moment, it's
40:06
Speaker 1: gonna win. So I guess you're saying that dark energy
40:09
Speaker 1: could retire right now. It's done its job, it's put
40:12
Speaker 1: in its time, and now the universe will never crunch
40:15
Speaker 1: back down into right, I mean without even if you
40:19
Speaker 1: took out dark energy, that the universe will never crunch
40:22
Speaker 1: back down into an inverse big bang. That's right. To
40:25
Speaker 1: make an inverse big bang, now you need dark energy
40:27
Speaker 1: to reverse, not just to disappear. You needed to turn
40:31
Speaker 1: around and somehow cause the contraction of the universe. And
40:35
Speaker 1: you might think, well, but it's only ever caused the
40:37
Speaker 1: expansion of the universe. Why would it cause contraction, which
40:40
Speaker 1: is a great question. But remember that we don't know
40:43
Speaker 1: anything about dark energy. We have speculations that it might
40:46
Speaker 1: be the cosmological constant or something else, so the energy
40:48
Speaker 1: of empty space, but we really have no understanding of
40:51
Speaker 1: what it is, which means we can't predict its future.
40:54
Speaker 1: And it could do something bonkers like turn around and
40:58
Speaker 1: change direction and cause the contract of the universe, like
41:01
Speaker 1: it could start taking energy away from space almost and
41:04
Speaker 1: we don't understand it, so we can't predict its future.
41:07
Speaker 1: If dark energy disappeared today, then yes, there's already enough
41:11
Speaker 1: expansion that gravity can't win. And if you kept dark
41:13
Speaker 1: energy doing what it's doing, which is causing the acceleration,
41:16
Speaker 1: then you know it's already game over. And we're accelerating
41:19
Speaker 1: towards having more and more distance between galaxies, having these
41:23
Speaker 1: little blobs of stuff being more and more separated and
41:26
Speaker 1: more and more isolated, and each one gravity is strong
41:29
Speaker 1: enough to hold together. Right, dark energy is not going
41:32
Speaker 1: to rip you from the Earth or rip the Solar
41:34
Speaker 1: System apart, because gravity has won these little micro battles
41:37
Speaker 1: to hold these little structures together. More likely will collapse
41:41
Speaker 1: into a bunch of black holes than separated with vast
41:44
Speaker 1: distances between other black holes. Not a happy outlook black
41:50
Speaker 1: holes to the end of time. White's you have a
41:56
Speaker 1: dark choice here of people between lightness and dark that's right,
42:04
Speaker 1: reality or fantasy. All right, Well, I'm getting the sense
42:07
Speaker 1: of that dark energy and dark matter were super important
42:11
Speaker 1: for us to be here. We needed them to get
42:13
Speaker 1: to where we are. But now that the universe is
42:15
Speaker 1: kind of chugging along, we really don't kind of need
42:18
Speaker 1: either of them right now. Well, that's true, Like you
42:20
Speaker 1: could turn them off now and the humanity would probably
42:24
Speaker 1: go on the same trajectory as it would have been. Yeah, well,
42:26
Speaker 1: you know that's not very grateful. You know, it's just like,
42:29
Speaker 1: what can I remove from my life that I don't
42:30
Speaker 1: need anymore now that I've made it. That's a very
42:33
Speaker 1: generous attitude. We should remember how we got here and
42:36
Speaker 1: all the little people necessary along the way. But you know,
42:40
Speaker 1: as Mary consas is, you know, think about it and
42:43
Speaker 1: does it brings you joy? Daniel, And if not, just
42:45
Speaker 1: throw it out. Dark matter brings me joy. But you're right,
42:49
Speaker 1: we don't need it. We could delete dark matter from
42:51
Speaker 1: our universe and our solar system would be fine. We
42:54
Speaker 1: can delete dark energy from our universe, and it wouldn't
42:57
Speaker 1: really change the fate of our solar system all. So
43:00
Speaker 1: you're right, there were instrumental in getting us here, but
43:03
Speaker 1: we could cut them out of our enter. I guess.
43:06
Speaker 1: I mean like in a way almost like if you
43:07
Speaker 1: get rid of dark energy, it almost makes the universe
43:10
Speaker 1: more accessible, right, because if things aren't accelerating further apart,
43:14
Speaker 1: then it increases our chances of you know, reaching other
43:17
Speaker 1: places in the universe. Yeah, that's true. It's a bit
43:20
Speaker 1: of a grim picture to imagine that dark energy could
43:23
Speaker 1: be creating these vast distances between superclusters of galaxies, making
43:27
Speaker 1: it literally impossible to explore the universe. And so yeah,
43:31
Speaker 1: I would actually like to turn off dark energy or
43:33
Speaker 1: reverse it a little bit, bring some of that stuff
43:35
Speaker 1: a little closer. We have our human rocket engines a
43:37
Speaker 1: chance to explore that. You mean you would like me
43:39
Speaker 1: to go into the control room and fiddle with the knob,
43:43
Speaker 1: be like off on off sufficient adult supervision. Yes, so
43:49
Speaker 1: I'd be like flipping the switch and then just so
43:52
Speaker 1: that the eighties are close enough for you to say
43:54
Speaker 1: hi to them, and then switching it back on. That
43:57
Speaker 1: sounds great, Yeah, do that all right, let me, let
43:59
Speaker 1: me put on my infinity glossier and uh twiddle my thumbs.
44:04
Speaker 1: All right. Well, it sounds like these are a really
44:07
Speaker 1: super fun thought experiments, but I feel like they're also
44:11
Speaker 1: a big part of how you know that these things exist, meaning,
44:15
Speaker 1: like you know, you play these experiments in your head,
44:17
Speaker 1: like what if dark matter never existed, Well, the universe
44:20
Speaker 1: wouldn't be the way it is, which sort of tells
44:22
Speaker 1: you that dark matter does exist. Yeah, exactly. And it's
44:25
Speaker 1: not just these large scale structures the organization and the
44:28
Speaker 1: size the universe. There are a lot of other details
44:31
Speaker 1: that tell us how much dark matter there is, how
44:34
Speaker 1: much dark energy there is, how they interact, and that
44:37
Speaker 1: come from lots of different observations, you know, from looking
44:40
Speaker 1: at the early light of the universe at all sorts
44:42
Speaker 1: of other crazy detailed measurements. So it really seems like
44:45
Speaker 1: dark matter and dark energy are a thing and that
44:47
Speaker 1: they are necessary things to make the universe the way
44:50
Speaker 1: it is. And of course the next question is like
44:53
Speaker 1: why are they at those values? Could there have been
44:56
Speaker 1: more dark matter or more dark energy? Why these numbers
45:00
Speaker 1: and not other number? Right, But we almost kind of
45:02
Speaker 1: don't want to ask those questions, because then we wouldn't
45:04
Speaker 1: be here. I want to ask those questions because I
45:08
Speaker 1: want to know is it an accident that we're here?
45:11
Speaker 1: Or are we inevitable as the only possible universe one
45:15
Speaker 1: that has this kind of structure, or are we totally
45:17
Speaker 1: lucky one in a trillion chance. To me, those are
45:20
Speaker 1: the deepest questions of physics. Those are the reasons I
45:22
Speaker 1: got into physics, is to try to answer these massive
45:25
Speaker 1: philosophical questions about the context of our very lives. Right, yeah, See,
45:29
Speaker 1: it's not just Sanna's who's inevitable or wants to be inevitable,
45:34
Speaker 1: it's Daniel. It's questions. Really, it's wondering about the universe
45:39
Speaker 1: that's ineviable. All right, Well, I think we've reached the
45:42
Speaker 1: endgame here of our episode. We hope that you look
45:46
Speaker 1: out into the universe tonight or tomorrow or the next
45:49
Speaker 1: day and think about what are some of the things
45:51
Speaker 1: that led to us being here, and how important they are,
45:54
Speaker 1: and what would happen if things were totally different, and
45:57
Speaker 1: share with us you're wondering in your thoughts and your questions.
46:00
Speaker 1: Please write to us two questions at Daniel and Jorge
46:03
Speaker 1: dot com or interact with us on Twitter at Daniel
46:06
Speaker 1: and Jorge, where we make bad jokes and answer questions.
46:10
Speaker 1: Thanks for joining us, see you next time. Thanks for listening,
46:21
Speaker 1: and remember that Daniel and Jorge Explain the Universe is
46:23
Speaker 1: a production of I Heart Radio. For more podcast from
46:27
Speaker 1: my heart Radio, visit the i heart Radio app, Apple Podcasts,
46:31
Speaker 1: or wherever you listen to your favorite shows. Yea