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What is a symmetron? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Hey, Jorge, are you a collector?
0:10
Speaker 2: What do you mean like a debt collector?
0:13
Speaker 1: I mean, like, do you have a room in your
0:15
Speaker 1: house full of original Transformers still in the packages?
0:19
Speaker 2: I wish, but no. Those might be worth a lot
0:21
Speaker 2: of money now, but no, I actually took them out
0:23
Speaker 2: and played with them, although I wish you had those also.
0:27
Speaker 1: So is that the source of your encyclopedic knowledge of
0:30
Speaker 1: Pokemon and Transformers?
0:31
Speaker 2: What do you mean?
0:32
Speaker 1: Well, you know, every time I describe some new hypothetical particle,
0:35
Speaker 1: you tell me that's actually the name of a Transformer.
0:39
Speaker 2: I don't think that's because I'm an expert. I think
0:40
Speaker 2: that's just because all physics names sound like Transformers.
0:44
Speaker 1: Or maybe because we actually stole them from Transformers.
0:47
Speaker 2: What do you have to give credit then, to Hasbro
0:50
Speaker 2: in your papers?
0:51
Speaker 1: Yeah, we give them a share of the zero dollars
0:53
Speaker 1: we make off of each particle.
0:55
Speaker 2: What do you mean you don't work for free?
0:57
Speaker 1: Do you the particles?
0:59
Speaker 3: Do?
0:59
Speaker 2: Did you tax dollars?
1:16
Speaker 4: Hi?
1:16
Speaker 2: I'm Hori mccartoonist and the author of All Our's Great
1:19
Speaker 2: Big Universe.
1:20
Speaker 1: Hi I'm Daniel. I'm a particle physicist and a professor
1:23
Speaker 1: at UC Irvine. And I hope you never have to
1:26
Speaker 1: name a particle. Wait, why not, doesn't it mean you
1:28
Speaker 1: discovered it. Oh I'd love to discover a particle. But
1:31
Speaker 1: then I'm given that huge responsibility of choosing a name.
1:34
Speaker 1: And frankly, after all our conversations, I'm terrified.
1:38
Speaker 2: You're terrified of cartoonis criticizing your name choices.
1:44
Speaker 1: I'm terrified of legacy history.
1:46
Speaker 5: Man.
1:46
Speaker 1: People who have given particles silly names. History doesn't look
1:49
Speaker 1: kindly on them. Oh.
1:50
Speaker 2: I see, so that's your excuse for not having discovered
1:52
Speaker 2: a particle.
1:53
Speaker 1: That's one of my many excuses.
1:55
Speaker 2: Yes, that sounds a little convenient.
1:58
Speaker 1: Know the truth is, I would love to discover particle.
2:01
Speaker 1: And in that case, you know, I just crowdsourced the
2:03
Speaker 1: name hmmm, to your kids, maybe to the internet. So
2:07
Speaker 1: it ended up with like particle face.
2:09
Speaker 2: Is it a website? Like? Is there a website for
2:11
Speaker 2: coming up with particle names?
2:13
Speaker 1: Not yet, but what a great idea.
2:15
Speaker 2: You can find anything on the Internet. I wonder what
2:18
Speaker 2: happened if you ask Chad Gpt to come up with
2:20
Speaker 2: a name for a new particle.
2:21
Speaker 1: Let's do it. Naming a new particle is a significant responsibility.
2:25
Speaker 1: It suggests we avoid personal or self referential names. We
2:28
Speaker 1: should consider its properties, we should go after historical figure,
2:32
Speaker 1: we should consult with the scientific community. See, this is
2:35
Speaker 1: serious stuff.
2:36
Speaker 2: I feel like maybe that chat GPT's trained on your neuroses.
2:40
Speaker 2: It seems to know your anxieties. Maybe maybe it's been
2:43
Speaker 2: learning all this time that you've been talking to it.
2:45
Speaker 1: No, I think chat GPT and I are both trained
2:48
Speaker 1: on the neurosis of the internet.
2:50
Speaker 2: Hmmm, well, now you have chat GPT, so you have
2:53
Speaker 2: no excuse for not discovering a new particle.
2:55
Speaker 1: All right, I'll get to work.
2:56
Speaker 2: But anyways, welcome to our podcast. Daniel and Jorge explain
2:59
Speaker 2: the universe production of iHeartRadio.
3:01
Speaker 1: In which we are absolutely desperate to understand the nature
3:05
Speaker 1: of the universe, to uncover new particles and forces, to
3:09
Speaker 1: reveal the fundamental nature of space and time, and to
3:13
Speaker 1: put it all together, to explain our experience in this
3:17
Speaker 1: crazy cosmos.
3:18
Speaker 2: WHOA, WHOA desperate. I don't know if we could go
3:20
Speaker 2: that far. It make us sound kind of thirsty.
3:24
Speaker 1: I am thirsty for knowledge. Absolutely, Yes, you're thirsty to
3:28
Speaker 1: get it on with the particles of the universe. I mean,
3:31
Speaker 1: I've said it before. I would invite aliens to Earth,
3:34
Speaker 1: even if I knew they were going to zap Us
3:35
Speaker 1: from orbit, if they would only tell us the truth
3:38
Speaker 1: of the universe.
3:38
Speaker 2: Boy, you would make that choice for the entire human race.
3:41
Speaker 1: I'm thirsty, man, I got a thirst, and it's got
3:45
Speaker 1: to be quenched.
3:45
Speaker 2: It sounds like a good excuse to put you in
3:47
Speaker 2: a rocket ship and shoot you out of here. You're
3:50
Speaker 2: clearly not on our side.
3:51
Speaker 1: I'm on the side of knowledge, man.
3:55
Speaker 2: You're on the side of dinner apparently. But yeah, it
3:58
Speaker 2: is an interesting universe and we are are really at
4:00
Speaker 2: a loss for understanding how it all works, what it's
4:03
Speaker 2: all made out of, and what are the rules that
4:05
Speaker 2: govern what can happen and what cannot happen in the universe.
4:08
Speaker 1: Though you might feel like the universe is pretty well
4:11
Speaker 1: understood scientifically speaking, and historically, we're just beginning our journey
4:16
Speaker 1: of understanding it. In one hundred years or in five
4:18
Speaker 1: hundred years, people will look back on this era of
4:21
Speaker 1: science and say, Wow, they were very clueless about how
4:24
Speaker 1: the universe worked.
4:26
Speaker 2: Do you think that's a very optimistic view of humanity.
4:28
Speaker 1: That will be around in five hundred years To look back.
4:30
Speaker 2: You mean, yeah, that we're not going to go into
4:32
Speaker 2: the post apocalyptic healthscape of humanity, and we'll look back
4:37
Speaker 2: at this time as maybe the peak of humanity.
4:41
Speaker 1: In our caves in a few hundred years, scratching out
4:43
Speaker 1: podcasts for our few listeners. We will look back to
4:47
Speaker 1: the golden age of science when Daniel didn't discover anything.
4:50
Speaker 2: We're going to look back and be like, what's a podcast?
4:54
Speaker 1: Was that a particle?
4:55
Speaker 2: Who had time for that?
4:57
Speaker 1: You're right, I'm implicitly being optimistic, assuming that scientific knowledge
5:01
Speaker 1: will continue to accumulate and the pace will continue to
5:04
Speaker 1: accelerate the way it has over the last decade, fifty years,
5:07
Speaker 1: even one hundred years. I'm hopeful. But that requires us
5:10
Speaker 1: to survive and maintain society and to make science a priority.
5:15
Speaker 2: Yeah, and not to sell us out to the hungry aliens.
5:18
Speaker 1: Hmm though that would fast forward us into the future
5:21
Speaker 1: of knowledge and dinner. But what if the aliens don't
5:25
Speaker 1: have all the answers? Well, what if they have the
5:27
Speaker 1: answers and we just can't grock them? Oof? So frustrating.
5:31
Speaker 1: I just sold the human race for nothing.
5:32
Speaker 2: Yeah, you might want to look at the menu first,
5:37
Speaker 2: figure it out. Before they sell us all out.
5:40
Speaker 1: But we can't rely on those aliens or even those
5:42
Speaker 1: future humans. We got to figure it out. We are
5:44
Speaker 1: working hard today to try to understand the nature of
5:47
Speaker 1: the universe on the largest scales, how big is it,
5:50
Speaker 1: how much bigger is it getting? And how quickly is
5:52
Speaker 1: it getting bigger.
5:53
Speaker 2: That's right. We're on our own trying to figure out
5:55
Speaker 2: the mysteries of the universe, and it all starts with
5:57
Speaker 2: asking questions and coming up with maybe sometimes crazy ideas
6:01
Speaker 2: to try to explain how it all works.
6:03
Speaker 1: We're pretty sure that most of our ideas about how
6:06
Speaker 1: the universe works and the largest scale, the size of it,
6:09
Speaker 1: the shape of it, the rate of its expansion, why
6:11
Speaker 1: it's expanding, why that expansion is accelerating, We're pretty sure
6:15
Speaker 1: those ideas are wrong. And what we looked back on
6:18
Speaker 1: is just sort of like initial explorations. But that's crucial.
6:21
Speaker 1: Science is not a straight line. It's a zigzag wandering
6:24
Speaker 1: through a dark forest hoping to find the clearing and.
6:27
Speaker 2: So sometimes you have to get creative about it and
6:29
Speaker 2: even come up with things that sound like transformers or pokemons,
6:33
Speaker 2: or maybe come up with transformers that would be pretty cool.
6:37
Speaker 2: They could help us find the answers to the universe.
6:39
Speaker 1: You think they'll be mad when they discovered to've been
6:41
Speaker 1: stealing their names for particles for a few decades.
6:44
Speaker 2: Or maybe they'd be honored to be named after certain particles.
6:47
Speaker 1: Now you're the one being optimistic.
6:48
Speaker 2: Yeah, I am an optimist prime And so today on
6:53
Speaker 2: the podcast, we'll be tackling the question what is a symtron.
7:03
Speaker 1: And what does it transform into?
7:05
Speaker 2: What does it not transform into?
7:08
Speaker 1: Maybe it transforms us into aliens that do understand the universe.
7:13
Speaker 2: What is a symmetron? I don't think I've heard that
7:15
Speaker 2: word before, but it sounds a little bit like symmetry
7:18
Speaker 2: and tron, so something electronic.
7:21
Speaker 1: You're not far from the truth. Yeah, boom podcast over.
7:24
Speaker 2: Do you know why the word tron or ending a
7:26
Speaker 2: word with tron somehow implies electricity or technology or particles.
7:31
Speaker 2: Do you know the origin of that? I'm asking if
7:33
Speaker 2: you know, because I don't know.
7:34
Speaker 1: I think the word ion comes from some Greek word,
7:38
Speaker 1: but I'm not an expert in the etymology of particles.
7:41
Speaker 2: Oh, you're saying like, maybe that's where the word electron
7:45
Speaker 2: comes from.
7:46
Speaker 1: Yeah, although you know the electron originally was named something else.
7:49
Speaker 1: The discoverer of it, JJ. Thompson called it a corpuscule,
7:52
Speaker 1: and then later it was renamed electron. But my guess
7:56
Speaker 1: is that all these ons come from ion, which is
7:59
Speaker 1: a Greek word.
8:00
Speaker 2: Well, I guess that was a good thing, because otherwise
8:02
Speaker 2: we'd be associating technology. But the word puscal with the
8:05
Speaker 2: ending puscol, and everything would be named pusicle. The bad
8:11
Speaker 2: guy in Transformers would be called megapuscal. But I'm guessing
8:14
Speaker 2: this is maybe one of those creative ideas that a
8:16
Speaker 2: scientists have come up with to try to explain some
8:19
Speaker 2: deep mystery of the universe.
8:21
Speaker 1: It is indeed well as usually.
8:23
Speaker 2: We were wondering how many people out there had heard
8:25
Speaker 2: of a symmetron or could guess what it is or
8:28
Speaker 2: what it transforms into. So Daniel went out there into
8:32
Speaker 2: the internet again to ask people what is a symmetron.
8:37
Speaker 1: Because this podcast is all about audience participation, you guys
8:40
Speaker 1: can write us questions and we'll answer. You can hear
8:43
Speaker 1: your voice on the podcast speculating about the topic of
8:46
Speaker 1: the day. If you'd like to join this group, please
8:48
Speaker 1: write to me two questions at Danielandhorge dot com.
8:51
Speaker 2: So think about it for a second. Is it a
8:53
Speaker 2: pokemon or is it a robot? Here's what people had
8:56
Speaker 2: to say.
8:57
Speaker 6: Well, it's either a transformer or a quantum particle or both. Symmetron,
9:05
Speaker 6: it obviously has something to do with symmetry. Other than that,
9:08
Speaker 6: I can't really hazard a guess.
9:10
Speaker 5: Guessing based on the on at the end of it
9:12
Speaker 5: that like a photon or a beryon, that it's some
9:15
Speaker 5: kind of particle that conveys a type of symmetry.
9:20
Speaker 3: Well, symmetron makes me think of cyclotron, and a cycloton
9:25
Speaker 3: I think is the old term for a well another
9:28
Speaker 3: term for a particle collider and symmetron symmetrical would be
9:34
Speaker 3: sort of means that it's the same in some way.
9:38
Speaker 3: Maybe is it a strait as opposed to a ring
9:41
Speaker 3: format particle collider?
9:43
Speaker 4: Well, I've never heard of a symotron. It sounds like
9:45
Speaker 4: a particle that exhibits some special symmetry, But lots of
9:48
Speaker 4: particles exhibit symmetry, which makes me think it's probably some
9:51
Speaker 4: theoretical symmetry we haven't seen yet that defines what this
9:55
Speaker 4: particle is.
9:55
Speaker 3: A symmetron, is a device that you can set on
9:58
Speaker 3: top of your piano to the pace it goes.
10:02
Speaker 2: No, I guess it's a.
10:03
Speaker 1: Particle and it communicates symmetry between other particles. I have
10:10
Speaker 1: no idea.
10:11
Speaker 7: Is that a particle wave it's identical to another particle?
10:20
Speaker 7: Cancels it out?
10:21
Speaker 5: Maybe?
10:22
Speaker 2: Or all right? Some creative answers here.
10:26
Speaker 1: Well, I mean you put this name on anything. You
10:28
Speaker 1: could name it your cat, right, The answer to the
10:30
Speaker 1: podcast could be like, Symmetron is my cat?
10:33
Speaker 2: Oh, there you go. You could name your cat Symmetron. Yes,
10:37
Speaker 2: but isn't that a big responsibility also to name your cat?
10:40
Speaker 1: Hmmm? That's true, although I don't think history will judge
10:43
Speaker 1: you as much because it's probably just between you and
10:45
Speaker 1: the cat, mostly unless the cat becomes famous.
10:49
Speaker 2: Yeah. Well, also, you don't mind your cat unhappy with you?
10:51
Speaker 2: I hear that's a bad thing. It would be a
10:54
Speaker 2: catastrophe in IIan.
10:55
Speaker 1: It's the cats who are in charge.
10:56
Speaker 2: But yeah, it's an interesting idea, and so let's dig
10:59
Speaker 2: into this, Uh, Daniel, what is a symotron?
11:02
Speaker 1: So, a symotron is a hypothetical new particle that of
11:06
Speaker 1: course also comes with a field that has really unusual properties,
11:11
Speaker 1: and physicists invent a new field and particles sometimes not
11:15
Speaker 1: just for fun. We don't just like line in the
11:16
Speaker 1: grass and be like, h what if there's this kind
11:18
Speaker 1: of particle. We do it to explain something we've seen
11:21
Speaker 1: in the universe. The whole process of physics is like
11:24
Speaker 1: go out there, see stuff that's happens, and then try
11:27
Speaker 1: to build a model that explains it. And when the
11:30
Speaker 1: model fails, we add new who's it's and what's it's
11:33
Speaker 1: to try to get it to describe the universe. So
11:35
Speaker 1: the symmetron is a new thing people are trying to
11:38
Speaker 1: add into our model of physics to explain some stuff
11:41
Speaker 1: that we otherwise can't explain.
11:43
Speaker 2: Although sometimes in the history of physics it has been
11:46
Speaker 2: the case that you just kind of like tool around
11:48
Speaker 2: in the lab and you discover stuff.
11:50
Speaker 1: Right. Oh, there was a golden era the particle Zoo,
11:52
Speaker 1: when every time you turned on the accelerator you saw
11:55
Speaker 1: a new particle and you could give it.
11:56
Speaker 2: A name every time.
11:58
Speaker 1: It was incredible, and they cranked up the energy boom
12:01
Speaker 1: new particles made. It was amazing. I missed those days, hmmm.
12:06
Speaker 1: They were decades before I was born, but I still
12:08
Speaker 1: miss them.
12:08
Speaker 2: But I think we're talking about a theoretical particle here,
12:12
Speaker 2: not one that we have discovered or seen or explored experimentally,
12:15
Speaker 2: just one that we have dreamed of to try to
12:18
Speaker 2: explain something that is happening that we can't explain.
12:22
Speaker 1: Yeah, and the same spirit that, like the Higgs boson,
12:24
Speaker 1: was conceived of theoretically. Peter Higgs saw this pattern in
12:28
Speaker 1: nature and he thought, hmm, this would be so much prettier.
12:31
Speaker 1: It would make much more sense if we added a
12:33
Speaker 1: new particle and feel to the story. And it all
12:35
Speaker 1: worked out mathematically and beautifully, and then we went out
12:37
Speaker 1: and looked for it. So you can add things theoretically,
12:40
Speaker 1: but if they don't actually describe what's happening in the universe,
12:43
Speaker 1: it's not very useful. So in this case, people are
12:46
Speaker 1: again adding a new theoretical particle to try to explain
12:49
Speaker 1: some stuff that otherwise doesn't make sense.
12:52
Speaker 2: Okay, So then what is the mystery that the symotron
12:55
Speaker 2: hopes to resolve?
12:56
Speaker 1: So the simitron is here to do battle with a
12:59
Speaker 1: really big question in physics, which is why is the
13:02
Speaker 1: universe expanding faster and faster every year? Like we know
13:06
Speaker 1: the universe is really big. We can look out there
13:09
Speaker 1: and see stuff that's really far away. We've known for
13:11
Speaker 1: like one hundred years that the universe is expanding. You
13:14
Speaker 1: look out in every direction and you see galaxies moving
13:17
Speaker 1: away from us. But a couple of decades ago we
13:19
Speaker 1: got precise enough measurements about how that expansion is changing
13:23
Speaker 1: over time that we learned something kind of shocking that
13:26
Speaker 1: the expansion is not slowing down like Einstein thought, but
13:30
Speaker 1: that it's actually speeding up. There's something out there accelerating
13:34
Speaker 1: the expansion of space.
13:36
Speaker 2: Meaning it's getting bigger, faster and faster each time.
13:39
Speaker 1: Yeah, space between galaxy clusters is getting bigger, and every
13:43
Speaker 1: year it's getting bigger at a higher rate. So we
13:46
Speaker 1: new space is being created faster.
13:48
Speaker 2: And faster, and they're not just running away from alias
13:52
Speaker 2: that want to eat them.
13:54
Speaker 1: They may be accomplishing that, but it's sort of the
13:56
Speaker 1: secondary thing. And in physics we give this a name
13:59
Speaker 1: dark energy, But just because we give it a name
14:02
Speaker 1: doesn't mean we understand what's going on or we can
14:05
Speaker 1: explain what's happening. So far, this is just observational. We've
14:09
Speaker 1: seen this in our telescopes and in our measurements and
14:11
Speaker 1: we've tried to grapple with it. We've like, what could
14:14
Speaker 1: explain this, What possible mechanism could we have that could
14:18
Speaker 1: generate this kind of crazy accelerating expansion.
14:21
Speaker 2: Because I guess the idea that it's accelerating is weird, right, Like,
14:26
Speaker 2: if it was expanding at a constant rate, then you
14:28
Speaker 2: might assume that, well, maybe you had some initial velocity
14:33
Speaker 2: from the beginning of the universe and so it's just
14:35
Speaker 2: coasting and getting bigger. But the idea that it's accelerating
14:37
Speaker 2: means there's something going on, right, something must be powering
14:40
Speaker 2: this acceleration.
14:42
Speaker 1: Yeah, exactly. It was really shocking in the context of
14:44
Speaker 1: Einstein's general relativity because in his model, if you have
14:48
Speaker 1: a universe with mass in it, that causes negative acceleration
14:52
Speaker 1: of the expansion basically pulls everything together. It curves the universe,
14:56
Speaker 1: and it pulls everything together. Basically just gravity should pull
14:59
Speaker 1: the whole universe together. But when Hubble and others discovered
15:02
Speaker 1: that the universe is expanding, then people thought, all right,
15:04
Speaker 1: so we have an expanding universe as you say, initial velocity,
15:08
Speaker 1: but still should be negative acceleration because all the gravity
15:11
Speaker 1: should be pulling everything together, and we didn't know if
15:13
Speaker 1: there's gonna be enough gravity to pull everything back together
15:16
Speaker 1: to like squeeze it down into a big crunch, or
15:19
Speaker 1: if there's gonna be so much velocity that it coast forever,
15:22
Speaker 1: slowing down but never actually come back. Then we discovered
15:25
Speaker 1: that neither of those are the case, and what actually
15:27
Speaker 1: happening is something else is giving us positive acceleration, is
15:31
Speaker 1: increasing the rate of expansion every year.
15:34
Speaker 2: Now, back then, do we know that it was space
15:36
Speaker 2: itself that was expanding or did we maybe think that
15:39
Speaker 2: all the galaxies were just moving through space and getting
15:42
Speaker 2: further apart from each other.
15:43
Speaker 1: How far back then are you talking Einstein and Hubble?
15:46
Speaker 1: Are you talking discovery dark energy twenty years ago?
15:50
Speaker 2: I mean before an hour ago before. I'm becoming familiar
15:57
Speaker 2: with this topic.
15:57
Speaker 1: Well, ever since we've had general relativity, we've understood that
16:02
Speaker 1: to describe the expanding universe is to describe the expansion
16:05
Speaker 1: of space itself, because general relativity tells us that the
16:08
Speaker 1: universe has a shape and it has curvature, and so
16:10
Speaker 1: you can't have like a single reference frame for the
16:13
Speaker 1: whole universe. Instead, you should think about it as like
16:16
Speaker 1: a reference frame for each galaxy, and then those reference
16:18
Speaker 1: frames are moving relative to each other in space is
16:21
Speaker 1: expanding between them, So you can't really answer the question
16:25
Speaker 1: like what is the velocity of that galaxy and measured
16:28
Speaker 1: in our frame? You really just have to say, they
16:31
Speaker 1: have a frame, we have a frame, and the space
16:33
Speaker 1: between them is expanding.
16:35
Speaker 2: But back then, did we know that, Like when we
16:38
Speaker 2: first noticed that the galaxies were moving away from us,
16:41
Speaker 2: did we know that it was space it's expanding, or
16:43
Speaker 2: did we maybe at first thought, oh, they're just moving
16:45
Speaker 2: away from us through space.
16:47
Speaker 1: Well, all this requires is general relativity, which we've had
16:49
Speaker 1: well before we knew the universe was expanding. So the
16:52
Speaker 1: answer is yes, we've described in terms of expanding space
16:55
Speaker 1: since the beginning. This might sound a little confusing to
16:57
Speaker 1: listeners because we often talk about the receipt eschen velocity
17:00
Speaker 1: of galaxies, and when you hear about the expansion of
17:03
Speaker 1: the universe, we talk about these velocities, and for stuff
17:06
Speaker 1: that's really really far away, you could even say that
17:08
Speaker 1: recession velocity is faster than the speed of light. That's
17:11
Speaker 1: just sort of a sloppy shorthand that's saying, well, look,
17:13
Speaker 1: we know it's space expanding but that's hard to think about.
17:16
Speaker 1: So let's just pretend we could measure the velocities of
17:19
Speaker 1: those galaxies. If we could do that, what would that
17:21
Speaker 1: velocity be? But those velocities aren't meaningful. We can't actually
17:25
Speaker 1: measure those things because we don't have a single frame
17:27
Speaker 1: that puts both galaxies in it. So the technical way
17:30
Speaker 1: to think about it accurately is to think about separate
17:32
Speaker 1: frames with space expanding between them.
17:35
Speaker 2: You're saying, like, these velocities are really just the expansion
17:39
Speaker 2: of space getting bigger.
17:40
Speaker 1: Yeah, exactly, And you know that because you can't measure
17:43
Speaker 1: that acceleration. Like, if you wanted to think about it
17:45
Speaker 1: in terms of acceleration, then all those galaxies should be
17:48
Speaker 1: accelerating away from us. You should be able to measure
17:50
Speaker 1: that acceleration. You like, have an accelerometer in that galaxy.
17:54
Speaker 1: You should be able to measure it. But you can't
17:56
Speaker 1: because there is no real acceleration there. It's just the
17:58
Speaker 1: expansion of space. If you put a ball in the
18:00
Speaker 1: back of a pickup truck, doesn't slant one side because
18:03
Speaker 1: space is expanding in some direction, right, it stays flat.
18:06
Speaker 1: Because we don't measure any local acceleration. Because we're not
18:09
Speaker 1: accelerating in our frame, even though the expansion of space
18:13
Speaker 1: between us and other galaxies is accelerating. And all of
18:16
Speaker 1: this happily lives within general relativity, but it requires an
18:19
Speaker 1: explanation the same way like you need mass to bend space,
18:23
Speaker 1: you need something to provide this negative pressure to expand space.
18:27
Speaker 1: And the big question about dark energy is what is that?
18:30
Speaker 1: What is doing this thing? What is providing the energy
18:33
Speaker 1: to accelerate the expansion of space.
18:35
Speaker 2: Okay, I think you're saying that space it's growing. It's
18:38
Speaker 2: not just growing, it's growing faster and faster so that
18:41
Speaker 2: the galaxies look like they're accelerating away from us. But
18:44
Speaker 2: really it's just the expansion of space that's like going
18:47
Speaker 2: a double time. And so the question now is what's
18:50
Speaker 2: powering all that creation of new space? And so that's
18:54
Speaker 2: kind of what dark energy is a placeholder for.
18:57
Speaker 1: Yeah, dark energy says something's doing it, we don't know what.
19:01
Speaker 1: And the cool thing is you don't have to throw
19:02
Speaker 1: away general relativity. General relativity has a knob in it.
19:05
Speaker 1: This is called Einstein's cosmological constant. You could just crank
19:08
Speaker 1: this knob up and say, what if there's energy in
19:11
Speaker 1: empty space. If all of empty space is filled with
19:14
Speaker 1: potential energy, then general relativity says, exactly this would happen.
19:18
Speaker 1: The question is is that what's happening is the universe
19:20
Speaker 1: filled with this potential energy? Where does it come from?
19:23
Speaker 1: What field would that be? So you can incorporate it
19:26
Speaker 1: into general relativity if you have like a field that
19:28
Speaker 1: has a lot of potential energy. But we don't and
19:31
Speaker 1: we can't explain that. So there's like a mechanism within
19:34
Speaker 1: gr to do this, but we don't know how to
19:36
Speaker 1: turn that mechanism on.
19:37
Speaker 2: Meaning like you have your equations and you put a
19:40
Speaker 2: number in if there's a term in the equations that
19:42
Speaker 2: explains or that would account for this acceleration of space growing.
19:48
Speaker 2: And so now the question is like what is that number?
19:50
Speaker 2: What's causing that number? Is it a field? Is there
19:53
Speaker 2: a particle associated with it? Are there pokemons hidden inside
19:56
Speaker 2: of there?
19:57
Speaker 1: Yeah, that's exactly right. General relativity says, if you have
20:00
Speaker 1: a field with high potential energy, then that translates into
20:03
Speaker 1: a number in these equations, and that creates accelerating expansion.
20:06
Speaker 1: But what is that field with potential energy? We look
20:09
Speaker 1: around to all the fields we know, like the Higgs field,
20:12
Speaker 1: which actually does have significant potential energy. And we try
20:15
Speaker 1: to calculate what number we should put into the equations,
20:18
Speaker 1: and we get some number, But the number we should
20:20
Speaker 1: put in from our calculations is different from the number
20:22
Speaker 1: we need to explain the acceleration by a huge amount,
20:26
Speaker 1: by ten to the one hundred. So if there's potential
20:29
Speaker 1: energy out there in the universe, it's not from a
20:31
Speaker 1: field we know about.
20:33
Speaker 2: Well, all right, well let's get into those discrepancies and
20:36
Speaker 2: let's go deeper into this mystery that might be solved
20:39
Speaker 2: by this simitron. So let's stick into that. But first
20:43
Speaker 2: let's take a quick break. All right, we're talking about
20:57
Speaker 2: the symitron, which is so far are an imaginary or
21:01
Speaker 2: imaginative particle that scientists have thought it to try to
21:04
Speaker 2: explain why the universe is getting bigger, faster and faster.
21:08
Speaker 2: And Danielie, we're saying that we have equations for the universe.
21:11
Speaker 2: There's a number there that maybe explains or that would
21:14
Speaker 2: give you a universe that's expanding faster and faster. But
21:17
Speaker 2: now the question is what is that number. Is it
21:20
Speaker 2: a field like our other fields, or is it just
21:22
Speaker 2: a fudge factor? Or is it just the finger of God.
21:29
Speaker 1: Yeah, we actually know what the number is, right, We
21:31
Speaker 1: know exactly what number you need in the equations to
21:34
Speaker 1: get the accelerating expansion that we see. The question is
21:37
Speaker 1: where does that number come from? And there's a bunch
21:40
Speaker 1: of possible explanations. One is like, look, every universe just
21:43
Speaker 1: sort of has a number, and ours is generated with
21:45
Speaker 1: this one. Let's just sort of like give it up,
21:47
Speaker 1: shrug it off anthropic explanation and say there is no answer.
21:51
Speaker 1: It just is what it is. Move on. Nothing to see.
21:54
Speaker 2: Here, meaning it doesn't correspond to anything physical. It's just
21:57
Speaker 2: that the equations of our universe don't balance out to zero.
22:00
Speaker 2: They balance out to some random number.
22:03
Speaker 1: Yeah, Einstein's cosmological constant can come from a field of
22:06
Speaker 1: potential energy. But you can also just put a number
22:07
Speaker 1: in and say, oh, these are the equations of our universe.
22:10
Speaker 1: They have this number in them. Why that number? Well,
22:13
Speaker 1: you know, every universe gets a random number, and there's
22:15
Speaker 1: an infant number of universes and this is the one
22:17
Speaker 1: that we're in. It's not a great explanation, but it's
22:20
Speaker 1: an explanation.
22:21
Speaker 2: I mean, like, why does the universe have to balance
22:23
Speaker 2: out to zero. You could ask that question too, right,
22:26
Speaker 2: why does the balance out to three point four or seven.
22:29
Speaker 1: Or forty two? Right, that's the best number anyway.
22:32
Speaker 2: Right, Yes, that's the answer.
22:34
Speaker 1: That's the answer exactly. And now we finally found the question.
22:38
Speaker 1: But those of us who are curious about the universe
22:41
Speaker 1: aren't satisfied with just being told I don't know it
22:43
Speaker 1: is what it is. Move on. We want to know
22:45
Speaker 1: if there is an explanation. And so many times in
22:47
Speaker 1: the history of science we found things that looked weird
22:50
Speaker 1: and we dug deeper and we have found explanations, reasons
22:52
Speaker 1: why it had to be this and not something else.
22:56
Speaker 1: And so some people have explored this idea of like,
22:58
Speaker 1: let's create new fields that have potential energy that maybe
23:01
Speaker 1: could explain why we have this number and not some
23:04
Speaker 1: other number that we need to put into Einstein's.
23:07
Speaker 2: Equation, meaning like we need this number to make the
23:09
Speaker 2: equations balance out or to match what we see out
23:11
Speaker 2: there in reality. And so let's pretend that this number
23:14
Speaker 2: actually represents or maybe comes from some kind of physical
23:18
Speaker 2: field of the universe.
23:20
Speaker 1: Yeah, exactly, because then we get to kick the can
23:22
Speaker 1: down the street and say, oh, the expansion is due
23:24
Speaker 1: to this potential energy from this field, and then we
23:25
Speaker 1: can ask what's this field all about? Why does it
23:28
Speaker 1: have to exist? How does it fit in with the
23:30
Speaker 1: other fields? And we get to, you know, keep asking questions. Yeah,
23:33
Speaker 1: stay employed, stay curious, stay curious, don't be so cynical.
23:38
Speaker 2: All right, Well, so then the idea is end that
23:41
Speaker 2: this constant, this number in the equations represents a field,
23:44
Speaker 2: and is this this symmetron field.
23:46
Speaker 1: Then no, so the cimitron field is a slightly weirder
23:49
Speaker 1: version of this. The simplest idea is to just use
23:52
Speaker 1: a constant, but there is no field out there that
23:54
Speaker 1: we know about that provides this constant. So instead people
23:57
Speaker 1: are trying another idea. Instead of having a constant, to
24:00
Speaker 1: add a different term.
24:01
Speaker 2: It wasn't the Higgs field a constant too.
24:03
Speaker 1: They put in a number which isn't constant. The Higgs
24:05
Speaker 1: field is a constant. It's just not enough, right. The
24:07
Speaker 1: Higgs field provides a tiny little bit, but doesn't provide
24:11
Speaker 1: enough to explain the accelerating expansion. So people thought, oh, well,
24:14
Speaker 1: let's try adding a different kind of term. Instead of
24:16
Speaker 1: just adding a number, let's add something which has a derivative, right,
24:20
Speaker 1: which doesn't disappear when you ask about the changes.
24:23
Speaker 2: Meaning something that's changing with respect to time for example, Yeah,
24:27
Speaker 2: like a variable, like a variable instead of a constant.
24:29
Speaker 1: Exactly, a variable instead of a constant. Now, for a
24:32
Speaker 1: long time, this has not been a very popular idea
24:35
Speaker 1: because that does more than just explain the expansion of
24:37
Speaker 1: the universe and its acceleration. It also creates new forces.
24:41
Speaker 1: It says, oh well, if you have something which it varies,
24:43
Speaker 1: it basically changes how gravity works in a way that
24:46
Speaker 1: creates a new force on things, so like a fifth force.
24:50
Speaker 1: So this has not been a very theoretically popular way
24:52
Speaker 1: to go because it creates a fifth force, and you
24:54
Speaker 1: know we don't see any fifth forces.
24:56
Speaker 2: But I guess the question is, if a constant explains
24:58
Speaker 2: the expansion of the universe, why do you need a
25:01
Speaker 2: viable Why don't you stay with a constant.
25:03
Speaker 1: Because we don't have an explanation for that constant.
25:05
Speaker 2: So then the idea is just make it more complicated.
25:08
Speaker 1: The idea is to make it more complicated. Say, maybe
25:11
Speaker 1: a constant is the wrong way to go. We couldn't
25:13
Speaker 1: make a work with a constant. We have no way
25:14
Speaker 1: to explain that constant. So instead, let's choose a different
25:17
Speaker 1: term that's not constant, that's variable. It's like, let's look
25:19
Speaker 1: under a different kind of rock because we ran out
25:21
Speaker 1: of the original kind of rock.
25:23
Speaker 2: I guess maybe explain to our listeners what does it
25:25
Speaker 2: mean to explain it? Like how does the constant fail
25:27
Speaker 2: to explain the expansion?
25:29
Speaker 1: The constant on its own wouldn't fail to explain it,
25:31
Speaker 1: Like we know what constant you would need to put
25:33
Speaker 1: in there to explain the accelerating expansion. We just don't
25:36
Speaker 1: know how to justify that content, like where did it
25:38
Speaker 1: come from? There's no field we know about that can
25:40
Speaker 1: explain that constant.
25:42
Speaker 2: But then if you put it viable, couldn't you also
25:45
Speaker 2: ask the same question like why is it there?
25:47
Speaker 1: Absolutely, if you put it in a variable, you also need
25:49
Speaker 1: to justify it. It's just another idea, and then you
25:52
Speaker 1: need to explain like where does that come from? The
25:54
Speaker 1: answer is, oh, comes from a new field that we
25:56
Speaker 1: haven't seen yet. Well, let's talk about what that field
25:59
Speaker 1: is and how we might see it and what it
26:00
Speaker 1: would look like.
26:01
Speaker 2: Oh, I see, No, actually don't see it. Sounds like
26:06
Speaker 2: maybe you're just making it more complicated, just to make
26:10
Speaker 2: it more complicated, to see if maybe the universe is
26:12
Speaker 2: actually more complicated. But it sounds like it's not, though,
26:15
Speaker 2: because it sounds like a constant, you know, matches what
26:18
Speaker 2: we see experimentally.
26:19
Speaker 1: You know, when you're in the early days of scientific ignorance,
26:22
Speaker 1: you try lots of things. You try the simplest thing
26:24
Speaker 1: first usually, and that's like just put in a constant
26:26
Speaker 1: that hasn't really worked because we don't have any way
26:29
Speaker 1: to explain those constants. So now we're trying the second
26:31
Speaker 1: simplest thing, like, well, let's put in something which changes
26:34
Speaker 1: a little bit, which has features and wiggles and is
26:36
Speaker 1: a little bit more complicated, and let's just see what
26:38
Speaker 1: that predicts. And if that's the universe we live in. Yeah,
26:41
Speaker 1: maybe we do live in a more complicated universe. Maybe
26:44
Speaker 1: there isn't a constant in this equation. Maybe there is
26:46
Speaker 1: something that changes. I see.
26:48
Speaker 2: You're just kind of exploring what these things can be. Like,
26:51
Speaker 2: maybe what you're measuring is more complicated than what you're
26:55
Speaker 2: actually see.
26:56
Speaker 1: Yeah, exactly. It's like if you notice cookies disappearing from
26:59
Speaker 1: your kit, encounter simplest explanation that your kids eat it.
27:02
Speaker 1: But you know, maybe there's some new animal out there
27:05
Speaker 1: you never discovered before that only eats kitchen cookies, and
27:08
Speaker 1: so you should consider the hypothesis and it might take
27:10
Speaker 1: you new places, like let's go look outside to find
27:12
Speaker 1: evidence for this new crazy cookie eating animal because maybe
27:15
Speaker 1: it does exist in your universe in the same way. Here,
27:19
Speaker 1: like the simplest explanation hasn't really panned out, So some
27:21
Speaker 1: people are like, well, let's look for a slightly more
27:23
Speaker 1: complicated cookie eating universe.
27:25
Speaker 2: But did you ask your kids if they took the
27:27
Speaker 2: cookie first.
27:30
Speaker 1: In this hypothetical scenario, I have somehow alibied them out
27:34
Speaker 1: of the cookie eating.
27:35
Speaker 2: Yes, I see, Well, why not even go further? It
27:40
Speaker 2: was aliens that ate the cookies?
27:41
Speaker 1: Yeah, exactly. You could go further and there are people
27:43
Speaker 1: doing that, right. There's no limit on what you can
27:45
Speaker 1: do in theoretical physics. It's just a question of like,
27:47
Speaker 1: is it a good idea, is it compelling, does it
27:50
Speaker 1: lead to something we can test? Is it an interesting
27:52
Speaker 1: thing to explore? And it's just up to the individual,
27:55
Speaker 1: Like I'm sure there's some theoretical physicist out there going like, oh, yeah,
27:58
Speaker 1: I have an even more complicated theory that you're really cool.
28:01
Speaker 2: I guess what I'm really asking is you're saying that
28:02
Speaker 2: you can't really explain a constant for that equation. So
28:06
Speaker 2: are you saying that maybe adding a variable will lead
28:08
Speaker 2: you to an explanation of that variable.
28:11
Speaker 1: Yeah, exactly. Let's put in a variable and see if
28:14
Speaker 1: we can explain it. Let's explore the consequences of that variable.
28:17
Speaker 1: What does it mean for other things in the universe.
28:20
Speaker 1: What predictions does it make? Can we go out and
28:21
Speaker 1: test those? If you predict that there's some new cookie
28:24
Speaker 1: eating lizard in your backyard, then you have something to
28:27
Speaker 1: go look for, you know, scratches on your window or something.
28:30
Speaker 1: So in the same way, we're like, let's add a
28:32
Speaker 1: slightly more complicated theory of the universe to explain this
28:35
Speaker 1: accelerating expansion and also see what else it predicts that
28:38
Speaker 1: maybe we could find.
28:40
Speaker 2: All right, So, then the cimotron field is a special
28:43
Speaker 2: new kind of field which has a variable and not
28:45
Speaker 2: a constant in the equations of the universe. Tell me
28:48
Speaker 2: about this field.
28:48
Speaker 1: So mostly these fields are really not mainstream theoretical physics
28:52
Speaker 1: for one important reason, which is that the variable nature
28:56
Speaker 1: of them produces this extra force, and people are like, well,
28:59
Speaker 1: we've never seen extra force, so that's out. So if
29:02
Speaker 1: you're going to build this kind of theory and you
29:04
Speaker 1: really want to make it work, you have to come
29:05
Speaker 1: up with an explanation for why we haven't seen it yet.
29:08
Speaker 2: Wait, why does it predict the force?
29:10
Speaker 1: Because when you put that number into Einstein's equation to
29:13
Speaker 1: figure out how things move, you end up having to
29:15
Speaker 1: take a derivative of it. If it's a constant, that
29:17
Speaker 1: goes away. If it's not a constant, if it's a variable,
29:20
Speaker 1: then it's derivative doesn't go away. Its rate of change
29:23
Speaker 1: with time is non zero, and that changes how things move,
29:26
Speaker 1: and effectively, that's like a force.
29:28
Speaker 2: It sticks around it like influences the acceleration of other
29:32
Speaker 2: things in the equation, and so therefore that's what you
29:34
Speaker 2: call a force.
29:35
Speaker 1: Yeah, Basically, it's like it changes how gravity works, as
29:38
Speaker 1: if there was another force out there, right, But.
29:40
Speaker 2: We haven't seen a force like that, And so now
29:42
Speaker 2: the question is like, how do you contort your theory
29:46
Speaker 2: so that it explains why we haven't seen its force?
29:48
Speaker 1: Yes, exactly, And so the symmetron is one of a
29:51
Speaker 1: category of theories like this, there's another that's called the
29:54
Speaker 1: chameleon theory, another that's called the galileon theory, and this
29:59
Speaker 1: one is called symotron theory, and it has a particular
30:02
Speaker 1: way to avoid being ruled out by all these experiments,
30:05
Speaker 1: as a symtron field. And this symotron field behaves differently
30:10
Speaker 1: when there's a lot of stuff around, when it's like
30:12
Speaker 1: high density materials, and when it's low density materials, So
30:16
Speaker 1: in high density regions like within galaxies and in our
30:18
Speaker 1: solar system, et cetera, et cetera, there's a symmetry in
30:21
Speaker 1: this field. There's like basically two parts of it that
30:24
Speaker 1: balance out and you get no force. So it basically
30:27
Speaker 1: doesn't exist within the galaxy, which is cool because it
30:30
Speaker 1: doesn't change how the solar system works, and we've measured
30:33
Speaker 1: that very precisely. We would have noticed if something was weird.
30:35
Speaker 1: But out past the edges of the galaxy where things
30:38
Speaker 1: are very very low density, the symmetry in this field breaks,
30:42
Speaker 1: and the broken symmetry there is what creates that force.
30:46
Speaker 1: So basically the symmetron field behaves differently. When there's a
30:48
Speaker 1: lot of mass around, it goes away, and when there's
30:51
Speaker 1: no mass around. That's when it really starts to take
30:54
Speaker 1: effect that.
30:55
Speaker 2: It seems very convenient.
30:57
Speaker 1: I think contrived is the way to think about it. Yeah, contorted,
31:02
Speaker 1: made up, and that's not something to be ashamed of. Like,
31:04
Speaker 1: this is how theoretical physics works. So like here, I
31:07
Speaker 1: have an idea that conflixs with what we know about
31:09
Speaker 1: the universe. Can I avoid that somehow? Can I add
31:12
Speaker 1: some bells and whistles to my theories to avoid this
31:14
Speaker 1: experimental measurement? I literally hear theorists doing that all day long.
31:18
Speaker 2: Mmm, and it has that How often does that work?
31:22
Speaker 1: Never so far?
31:23
Speaker 2: I guess never so far? Well why not keep doing it?
31:30
Speaker 1: Then? No? No, I mean you can go back to
31:32
Speaker 1: the Higgs theory, like Higgs have to come up with
31:34
Speaker 1: some new particle and new field which explained this puzzle
31:38
Speaker 1: and didn't violate any of the other experiments people had done.
31:41
Speaker 1: And so I'm sure that ruled out all sorts of
31:43
Speaker 1: other simpler explanations that people first considered.
31:46
Speaker 2: All right, So then the cymmetron field is a theoretical field,
31:50
Speaker 2: and it just so happens that you can see it
31:53
Speaker 2: around us, but maybe in between galaxies. You're saying, where
31:56
Speaker 2: there's less stuff. Maybe that's when you would see it.
31:59
Speaker 1: Yeah, exactly between galaxies is where you need to explain
32:02
Speaker 1: how it wakes up and accelerates the expansion of the universe,
32:05
Speaker 1: because really between galaxies and galaxy clusters is where the
32:09
Speaker 1: dark energy is happening.
32:11
Speaker 2: Oh so you're saying, like the cymatron field is a force,
32:14
Speaker 2: and maybe it's the force that's achilarating the expansion of
32:17
Speaker 2: the universe.
32:18
Speaker 1: Loosely speaking, that's accurate. We can't really think of it
32:20
Speaker 1: as a force because gravity isn't a force. It doesn't
32:23
Speaker 1: generate measurable acceleration in that way, so you can't do
32:26
Speaker 1: like f equals MA for things generated by gravity, and
32:30
Speaker 1: this is something generated by general relativity, and so it
32:33
Speaker 1: is sort of like a modification of gravity. But loosely speaking,
32:36
Speaker 1: you can think of it as like an effective force.
32:39
Speaker 1: We would see it as a force the way we
32:40
Speaker 1: see gravity as a force in our.
32:42
Speaker 2: Measurements, meaning it's not really pushing that the galaxies to
32:46
Speaker 2: move away from us. It's just kind of like acting
32:49
Speaker 2: there to create more space between us.
32:51
Speaker 1: Yeah, exactly right.
32:52
Speaker 2: So then how could we prove that whether the cymatron
32:55
Speaker 2: field exists or not.
32:57
Speaker 1: Yeah, it seems difficult because it's very conveniently impossible to
32:59
Speaker 1: detect this thing within the galaxy, which is where we live, right.
33:03
Speaker 1: But there's a recent paper where people were speculating about
33:07
Speaker 1: mimicking the environment outside the galaxy by creating very low
33:12
Speaker 1: density experiments. Essentially, try to do an experiment inside a
33:16
Speaker 1: vacuum low density where you could see this force in action,
33:19
Speaker 1: where you could detect the simitron field at work.
33:22
Speaker 2: WHOA, Well, so let me picture this experiment. You create
33:26
Speaker 2: a chamber like a box. You suck out all the
33:29
Speaker 2: air to create a vacuum, and if this cymtron field exists,
33:33
Speaker 2: it would maybe cause the space inside the box to
33:37
Speaker 2: expand we get bigger.
33:40
Speaker 1: And principle, yes, your box would get bigger, But remember
33:43
Speaker 1: that dark energy is really a tiny effect over short distances,
33:46
Speaker 1: like fractionally speaking, it's very very small. It's only really
33:50
Speaker 1: measurable over very very large distances, like between galaxies, So
33:53
Speaker 1: you'd never be able to measure the box getting bigger.
33:56
Speaker 1: Though I love that idea.
33:57
Speaker 2: Way would the box be bigger or would the space
34:00
Speaker 2: side of it get bigger? But then it will go
34:03
Speaker 2: through the box.
34:04
Speaker 1: M Well, then you have a philosophical question of what's
34:07
Speaker 1: the difference? Right? If there's more space inside the box,
34:10
Speaker 1: isn't the box bigger?
34:11
Speaker 4: No?
34:11
Speaker 2: I mean like the space that the boxes in gets bigger,
34:15
Speaker 2: but the box for me is the same.
34:17
Speaker 1: Well, I think the space inside the box would get bigger,
34:19
Speaker 1: though the box would remain the same. But what do
34:21
Speaker 1: you mean by the space inside the box gets bigger?
34:23
Speaker 1: You mean you measure the distance from one side of
34:25
Speaker 1: the box to the other. That would definitely grow. But
34:28
Speaker 1: this isn't the experiment they're proposing. That's impossible to measure.
34:31
Speaker 1: You could never measure that tiny growth of space.
34:34
Speaker 2: Yeah, let's thick to only things that are possible.
34:36
Speaker 1: Sure, go, they've come up with a way to detect
34:41
Speaker 1: the simotron field inside that vacuum.
34:44
Speaker 2: Okay, how do they do that or how do they
34:46
Speaker 2: propose to do that?
34:46
Speaker 1: They proposed to do it basically by doing very very
34:49
Speaker 1: precise tests of gravity. If this simtron field exists, it's
34:53
Speaker 1: like a distortion of how gravity works. And so do
34:55
Speaker 1: very precise tests of gravity. Take two masses, bring them
34:59
Speaker 1: closer together and further apart, measure the forces on them
35:02
Speaker 1: very precisely, and see if you see any deviation from
35:06
Speaker 1: general relativity without the symmetron field. That's very very tricky
35:10
Speaker 1: to do because gravity is very very weak, right, It's
35:13
Speaker 1: like ten to thirty times weaker than any other force.
35:16
Speaker 1: So these experiments have to be super duper precise. But
35:19
Speaker 1: we have some techniques to.
35:20
Speaker 2: Do them, so you can do this experiment.
35:22
Speaker 1: You can do this experiment. And people have been interested
35:25
Speaker 1: in deviations from gravitational predictions over small distances for a
35:29
Speaker 1: few decades because there are other theories that predict that also,
35:33
Speaker 1: like if there are extra dimensions to space and time
35:36
Speaker 1: more than just the three we know about, then gravity
35:39
Speaker 1: would work differently. But maybe those dimensions are really really small.
35:42
Speaker 1: So a lot of these experiments were motivated by looking
35:45
Speaker 1: to see if gravity changed when things got within like
35:47
Speaker 1: a millimeter or a centimeter apart. And until twenty or
35:51
Speaker 1: thirty years ago, nobody knew the answer to that because
35:53
Speaker 1: we could only really do gravitational measurements on like planets
35:56
Speaker 1: and stuff interacting with planets. Two rocks pull on each
35:59
Speaker 1: other with gravity, but it's very difficult to measure, so
36:02
Speaker 1: people came up with these ingenious devices to measure gravity
36:05
Speaker 1: on short distance scales. They're basically souped up versions of
36:08
Speaker 1: the original torsion pendulums that we talked about once in
36:11
Speaker 1: the podcast for how people would measure the gravitational constant.
36:14
Speaker 1: In this case, you have two rotating discs, and the
36:17
Speaker 1: discs have holes drilled inside of them, and you rotate
36:21
Speaker 1: one of the discs and let the other one free.
36:23
Speaker 1: Then you measure how the free disc is pulled by
36:26
Speaker 1: the rotating disc because if gravity is strong, and then
36:28
Speaker 1: they'll try to line up those two discs to line
36:31
Speaker 1: up the places where there's more mass and line up
36:34
Speaker 1: the places where there isn't this much mass. So if
36:36
Speaker 1: you slowly rotate one of these disks and measure the
36:39
Speaker 1: rotation of the other disc, you can measure the force
36:42
Speaker 1: of gravity between these two objects that are just like
36:45
Speaker 1: kilograms of mass.
36:46
Speaker 2: Sounds a bit complicated, so maybe let's dig into the
36:48
Speaker 2: details of this experiment and how it might or might
36:52
Speaker 2: not show the existence of the symtron field and what
36:55
Speaker 2: it could mean for our theory of the universe and
36:58
Speaker 2: the future employment of all physicists. So let's dig into that.
37:02
Speaker 2: But first let's take another quick break. All right, we
37:18
Speaker 2: are inventing fields left and right, here to try to
37:21
Speaker 2: explain the expansion of the universe, which is pretty inexplicable.
37:26
Speaker 2: The universe is getting bigger and bigger, faster and faster.
37:29
Speaker 2: We're trying to come up with an idea. A physicists
37:32
Speaker 2: have come up with the idea of a cymitron field
37:35
Speaker 2: to try to explain it. But Daniel, you're saying it
37:37
Speaker 2: requires us to measure gravity at a really really tiny
37:41
Speaker 2: small scale. Which I always thought, because you've said it
37:43
Speaker 2: several times, is that it's almost impossible.
37:46
Speaker 1: It's difficult. It requires real experimental bravado to figure out
37:50
Speaker 1: how to remove sources of vibration and anything else that
37:54
Speaker 1: might influence your experiment. In principle, these effects are happening
37:57
Speaker 1: all the time right in front of you. They're just
37:59
Speaker 1: drowned down by other, much bigger effects, and so in
38:02
Speaker 1: order to reveal them, you need to remove those effects.
38:04
Speaker 1: It's like if somebody's whispering the secrets of the universe
38:07
Speaker 1: but really really quietly, and you can't hear it because
38:09
Speaker 1: your neighbor is pumping some crazy death metal. In order
38:12
Speaker 1: to hear you have to isolate yourself from all that noise.
38:15
Speaker 1: So in the same way, these experiments are set up
38:17
Speaker 1: really cleverly, sort of stimilate to how ligo is done,
38:20
Speaker 1: to be isolated from everything else, so that you're measuring
38:23
Speaker 1: the right thing, this tiny little effect that you're looking for,
38:26
Speaker 1: and not being drowned out by the other much bigger
38:28
Speaker 1: effects that are more common.
38:30
Speaker 2: M Okay. So then you're saying that to maybe discover
38:33
Speaker 2: whether the cymmetron field exists or not, We're gonna take
38:36
Speaker 2: two discs. We're gonna place them facing each other, really
38:41
Speaker 2: close together but not touching. We're gonna spin one of them.
38:45
Speaker 2: And I guess these discs are not perfectly symmetrical, right,
38:49
Speaker 2: You're saying that maybe they have like a weight on
38:52
Speaker 2: either side.
38:52
Speaker 1: Or something for example.
38:54
Speaker 2: Yeah, and so if you twist one of them, does
38:55
Speaker 2: the gravity from that twisting disc make the other disc
38:59
Speaker 2: twist as well?
39:00
Speaker 1: Well? And the answer to that is definitely yes. And
39:02
Speaker 1: the question is by how much?
39:04
Speaker 2: Wait, what do you mean? It's definitely yes, but the
39:06
Speaker 2: other disc can't be symmetrical in there.
39:08
Speaker 1: Neither of them are totally symmetrical. You could think of
39:10
Speaker 1: them as like, you know, rods with masses on the ends.
39:13
Speaker 1: In practice, what they actually do is discs with holes
39:16
Speaker 1: drilled out of them. But either way, it's not totally symmetrical,
39:19
Speaker 1: and so gravity will pull on them to try to
39:22
Speaker 1: align them.
39:23
Speaker 2: Right, and you have to kind of rule out the
39:26
Speaker 2: effects and the other effects I might be like maybe
39:28
Speaker 2: the static electricity between the two plates, or maybe the
39:31
Speaker 2: vander wall forces maybe.
39:33
Speaker 1: Exactly, or the tides of the moon or anything. Right,
39:36
Speaker 1: everything else is basically bigger than this. You have to
39:39
Speaker 1: remove every possible other effect, and then you want to
39:42
Speaker 1: bring them closer and closer and closer, so you can
39:44
Speaker 1: see how gravity varies with distance, because one big clue
39:47
Speaker 1: is to see if we understand how gravity gets weaker
39:50
Speaker 1: and stronger as the distances get larger or smaller, because
39:53
Speaker 1: that's a crucial prediction of both Newton's and Einstein's theories
39:57
Speaker 1: of gravity.
39:58
Speaker 2: Right, there's like famously, like the the force of gravity
40:01
Speaker 2: between like the Earth and the Moon is equal to
40:03
Speaker 2: the mass of the Earth, sometimes the mass of the
40:05
Speaker 2: Moon divided by the square of the distance between the
40:08
Speaker 2: two things. Right, m M exactly the square of the distance,
40:12
Speaker 2: or is it maybe more like the square point two
40:15
Speaker 2: of the distance?
40:15
Speaker 1: Yeah, exactly? Or maybe does it change when you get
40:18
Speaker 1: down to really small scales exactly. Any deviation from the
40:22
Speaker 1: classical prediction means something new is happening, gravity works differently,
40:26
Speaker 1: which could be the symtron field. In this paper, they
40:28
Speaker 1: predict that if you get these two discs really really
40:31
Speaker 1: close to each other, like tens of microns apart from
40:33
Speaker 1: each other, then you could be able to detect the
40:36
Speaker 1: effect of the simitron field in.
40:39
Speaker 2: What way, Like how does the symtron field change gravity?
40:42
Speaker 1: The answer to that is very unsatisfying because there's actually
40:45
Speaker 1: lots of versions of the simtron field, and so you
40:48
Speaker 1: can get lots of different kind of deviations. So basically,
40:51
Speaker 1: any deviation from this you could explain using the symotron
40:55
Speaker 1: field the.
40:55
Speaker 2: Way, meaning like, if you find that the actually gravity
40:58
Speaker 2: works is the distance squared point two, then you're saying,
41:02
Speaker 2: like the point two that's the symmetron.
41:04
Speaker 1: Yeah, exactly. The semitron feels like a category of theories
41:08
Speaker 1: with a bunch of knobs and parameters, and if you
41:11
Speaker 1: find some deviation then you can explain it in terms
41:13
Speaker 1: of the symmetron field in almost every sense.
41:16
Speaker 2: Couldn't we just be wrong about gravity? Why does it
41:18
Speaker 2: have to be a symmetron?
41:19
Speaker 1: Yeah, we could just be wrong about gravity, and that's
41:22
Speaker 1: one thing people are looking at right And the answer
41:23
Speaker 1: could be that we're wrong in some other way, that
41:25
Speaker 1: we're wrong about the assumption that space has three dimensions,
41:28
Speaker 1: or we're wrong about how gravity works over short distances,
41:30
Speaker 1: general relativity breaks down, or this is just an effort
41:33
Speaker 1: to explain it in terms of general relativity, because if
41:36
Speaker 1: you find this and you measure a certain value, then
41:38
Speaker 1: it also explains the accelerating expansion of the universe. So
41:42
Speaker 1: that would be kind of.
41:43
Speaker 2: But it wouldn't improve or disprove the symmetron. I feel
41:46
Speaker 2: like you're saying it could be anything.
41:48
Speaker 1: Yeah, lots of theories in particle physics have that problem.
41:51
Speaker 1: Like supersymmetry can predict almost anything. So you find some
41:54
Speaker 1: new particle, can you explain it using supersymmetry? Yeah, does
41:58
Speaker 1: it mean it's supersymmetry, No, but it's still some new particle.
42:01
Speaker 1: So in this case, you find some deviation from gravity,
42:04
Speaker 1: if you've ruled out like experimental effects and you know
42:06
Speaker 1: gravity's working differently, then yeah, either space is different from
42:10
Speaker 1: what you expected, or general relativity is broken, or general
42:13
Speaker 1: relativity isn't broken and space has three dimensions, and there's
42:16
Speaker 1: some new bit added to it, like the symotron field.
42:19
Speaker 1: There's always going to be a variety of explanations. But hey,
42:22
Speaker 1: we'd be happy to be in that situation of trying
42:25
Speaker 1: to understand some weird deviation of gravity. I see.
42:28
Speaker 2: So like, if you find a deviation, maybe a cymotron
42:31
Speaker 2: is the reason, but maybe not. And so this is
42:34
Speaker 2: just this experiment you just described. It isn't to prove
42:37
Speaker 2: the cimitron. It's just to poke holes gravity.
42:39
Speaker 1: It's to poke holes of gravity. This experiment is interesting
42:42
Speaker 1: in the context of symmetrons because until recently, we haven't
42:45
Speaker 1: thought that any of these kinds of theories that have
42:48
Speaker 1: like variable additions to Linstein's equations could be tested at all,
42:52
Speaker 1: because all of them basically disappeared within the galaxy. So
42:55
Speaker 1: this is a cool way to say, oh, look, this
42:56
Speaker 1: is one we can actually test. You're right, it's not conclusive,
42:59
Speaker 1: but there are other ways we could also test the
43:01
Speaker 1: symmetron field, not just in these laboratory experiments of gravity.
43:04
Speaker 1: So there might be ways that we could discover it
43:06
Speaker 1: in different contexts. So it pulls together into a coherent idea.
43:10
Speaker 2: But I guess you know, if you put these discs
43:12
Speaker 2: closer and closer together, aren't you then violating this clues
43:17
Speaker 2: that you made about the cinmatron that it has to
43:19
Speaker 2: exist in it only exists in empty space.
43:22
Speaker 1: Yeah, that does get tricky. It gets tricky experimentally because
43:25
Speaker 1: having discs rotating really really close together, like fifty or
43:29
Speaker 1: ten microns is hard, and it also breaks down this
43:32
Speaker 1: assumption of load density. So then you have to make
43:35
Speaker 1: these things lighter. You have to make them smaller and smaller.
43:37
Speaker 1: So then you're playing this game of balance because you
43:39
Speaker 1: bring them closer together, which makes gravity stronger, and then
43:42
Speaker 1: you're removing mass to maintain the load density threshold, which
43:46
Speaker 1: makes gravity weaker.
43:47
Speaker 2: All right, so stay tuned, I guess is the answer here?
43:50
Speaker 2: Are they actually doing this experiment? Have they found anything yet?
43:54
Speaker 1: People are doing this experiment. It's a whole successive generations
43:57
Speaker 1: of these at the University of Washington, where people still
44:00
Speaker 1: now they could test gravity. It's centimeter scales and then
44:02
Speaker 1: millimeter scales. Now they're pushing down even further, just like
44:05
Speaker 1: a whole series of graduate students, each coming up with
44:08
Speaker 1: some new clever way to make it slightly more sensitive
44:11
Speaker 1: and over decades. It's really establishing the frontier.
44:14
Speaker 2: And what have they found so far? That gravity does
44:16
Speaker 2: work as a distance squared or maybe not?
44:18
Speaker 1: Oh yeah, so far they found exactly zero deviations from
44:21
Speaker 1: Einstein's gravity. Now we'd be talking about the Nobel Prize
44:24
Speaker 1: if somebody found a deviation from general relativity. So far
44:27
Speaker 1: it perfectly confirms.
44:28
Speaker 2: Gr So like the twenty years of PhD thesis, all
44:32
Speaker 2: with the same title, Einstein was right Einstein yeh, still right,
44:36
Speaker 2: Einstein was right side, Einstein's still going strong.
44:43
Speaker 1: Yeah, no, that's true. We keep confirming Einstein. We keep
44:46
Speaker 1: hoping to see a deviation, not because we don't like
44:48
Speaker 1: the guy, but because a deviation from the theory is
44:51
Speaker 1: an opportunity to learn something. It gives theorists an opening
44:54
Speaker 1: to add new bells and whistles to the theory that
44:56
Speaker 1: might also correspond to bells and whistles in the universe.
45:00
Speaker 2: Hmmm, all right, well let's talk about that then, Like,
45:02
Speaker 2: if we do this cover the symtron and the symtron field,
45:06
Speaker 2: what would that mean about our understanding of the universe.
45:09
Speaker 1: It would mean that general relativity is still right, Einstein
45:12
Speaker 1: was right, but that there's this term we have to
45:14
Speaker 1: add to these equations that the universe has more than
45:17
Speaker 1: just mass and energy density, that there's something else going on,
45:21
Speaker 1: this weird symtron field that changes how the universe grows.
45:25
Speaker 1: It's like a new conception of gravity.
45:27
Speaker 2: Wait, I thought you said gravity would stay the same.
45:29
Speaker 2: It's just that we have this new thing called the
45:31
Speaker 2: symmetron field.
45:32
Speaker 1: Yeah, you don't have to overthrow general relativity. The symmetron
45:35
Speaker 1: field plays nicely with general relativity, but it does change
45:38
Speaker 1: how the universe expands. It would explain basically why that
45:41
Speaker 1: expansion is.
45:42
Speaker 2: Accelerating, because the symotron is the force that would be
45:45
Speaker 2: pushing the universe to get bigger and bigger.
45:48
Speaker 1: Yeah, the symtron is that field which enters in Einstein's equations,
45:52
Speaker 1: which generates this accelerating expansion of the universe.
45:56
Speaker 2: And that's more satisfying than the constant explanation.
45:59
Speaker 1: That would be more satis fine than the constant because
46:01
Speaker 1: the constant is totally unexplained. The only explanation for the
46:03
Speaker 1: constant is that's just the number. Eat it. That's all.
46:07
Speaker 1: There's really nothing there.
46:09
Speaker 2: As opposed to that's just the simitron. Eat it.
46:13
Speaker 1: Well, the simitron gives us a handle. We could ask
46:16
Speaker 1: more questions about it, like why this symmetron field, why
46:19
Speaker 1: does it have these numbers in it? Where does it
46:21
Speaker 1: come from? How early in the universe did it appear?
46:23
Speaker 1: It gives us something to ask about, you know, it's
46:25
Speaker 1: more specific.
46:27
Speaker 2: Like who came up with that name? Come on, TSK
46:30
Speaker 2: not me, that's for sure. You wish it.
46:33
Speaker 1: I wish it had been me. Yes, okay, finally I
46:36
Speaker 1: admit it.
46:36
Speaker 2: Yes, yes, all right, Well what else does it say
46:41
Speaker 2: about the universe and how it's expanding.
46:43
Speaker 1: It could actually have impacts on the way that galaxies form.
46:46
Speaker 1: We see galaxies forming and ellipses and galaxies forming in
46:49
Speaker 1: spirals in the early universe. As the symmetron field was
46:52
Speaker 1: created and then cooled, it could have broken its symmetry
46:55
Speaker 1: in different ways between different galaxies, creating these like barriers
46:58
Speaker 1: between them, and those barriers might create like effectively walls
47:02
Speaker 1: between galaxies that are invisible that could affect how galaxies form.
47:06
Speaker 1: And so there's this other prediction that if a symmetron
47:08
Speaker 1: field is there, you could explain why we tend to
47:11
Speaker 1: see fewer satellite galaxies than we expect. So there are
47:13
Speaker 1: predictions we can make inside our laboratories and also how
47:16
Speaker 1: deep within galaxies, and it could just give us another
47:19
Speaker 1: insight into how the universe works, Like what else invisible
47:23
Speaker 1: is out there is shaping our universe?
47:25
Speaker 2: Who because the mysteries aren't just in the expansion of
47:28
Speaker 2: the universe, it's also sort of like how the universe
47:30
Speaker 2: ended up the way it is.
47:32
Speaker 1: Yeah, there's lots of open questions about the universe, and
47:34
Speaker 1: you know, physicists, just like listeners, like to tie them together. Ooh,
47:37
Speaker 1: what if this mystery is explained by that mystery and
47:39
Speaker 1: I can simultaneously solve a couple of open problems. That's
47:43
Speaker 1: really a juicy idea.
47:45
Speaker 2: Yeah, like, what if you're missing cookies we're taken by
47:48
Speaker 2: a new particle called the Pikachuu tron.
47:52
Speaker 1: Done Nobel prize, boom a cookie prize and give me
47:55
Speaker 1: ten here?
47:58
Speaker 2: All right, Well, another interesting idea in the field of
48:00
Speaker 2: physics and particle physics that has consequences not just at
48:03
Speaker 2: the microscopic level, but maybe at the biggest level of
48:06
Speaker 2: them all the entire universe. How it came to be
48:09
Speaker 2: and what keeps it growing bigger and bigger.
48:11
Speaker 1: And if this whole process of theoretical physicists inventing crazy
48:14
Speaker 1: emails and whistles staff to the universe seems a little
48:17
Speaker 1: out of hand or bonkers to you. Then, don't take
48:19
Speaker 1: that as criticism. Take it as inspiration to think of
48:22
Speaker 1: your own crazy ideas about the universe. You're in good company.
48:26
Speaker 2: Yeah, I mean, I'm a cartoonist. I think of crazy
48:29
Speaker 2: things all the time.
48:31
Speaker 1: Well, you have a PhD in podcast physics, so.
48:34
Speaker 2: Hey, yeah, that's right. It's not a PhD. It's a pod.
48:40
Speaker 2: I have a pod in podcast physics. All right, Well,
48:43
Speaker 2: we hope you enjoyed that. Thanks for joining us. See
48:46
Speaker 2: you next time.
48:51
Speaker 1: For more science and curiosity, come find us on social
48:54
Speaker 1: media where we answer questions and post videos. We're on Twitter, This, Org, Instant,
48:59
Speaker 1: and now TikTok. Thanks for listening, and remember that Daniel
49:03
Speaker 1: and Jorge explain The Universe is a production iHeartRadio. For
49:07
Speaker 1: more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,
49:12
Speaker 1: or wherever you listen to your favorite shows.