Speaker 1: Hey, Daniel, is it true that everything gets stretched out
Speaker 1: as the universe expands?
Speaker 2: That's what the physics tells us so far.
Speaker 1: Yeah, so is that why I feel so tired all
Speaker 1: the time because I'm getting stretched thin?
Speaker 2: You know? I think physics is always your first scapegoat, isn't.
Speaker 1: It, But this time it's kind of true, right. I mean,
Speaker 1: each day my gym gets a little bit further from
Speaker 1: my house, right, so it is making it harder. It's
Speaker 1: stained shape.
Speaker 2: I mean, physics is telling you that the universe is
Speaker 2: getting stretched out, but it's not physics fault. Don't blame
Speaker 2: the messenger.
Speaker 1: Oh well, he could have kept quiet, maybe we wouldn't
Speaker 1: have noticed.
Speaker 2: And that's the end of the podcast. Physics keeps quiet.
Speaker 1: That's a bit of a stretch, though. Hi am for Hey.
Speaker 1: I'm a cartoonist and the author of Oliver's Great Big Universe.
Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor
Speaker 2: at UC Irvine, and I want to hear the message
Speaker 2: from physics, whether it's good news or bad news.
Speaker 1: Really, you want to know if like the Earth is
Speaker 1: about to blow up, or if a supernova is about
Speaker 1: to engulf us in flames.
Speaker 2: I definitely want to know that. But that's not bad news.
Speaker 1: Bad news for me and for the human race unless
Speaker 1: you know something we don't know, Daniel.
Speaker 2: No, I'm thinking much bigger.
Speaker 3: You know.
Speaker 2: Cosmic bad news is stuff like, oh, the universe is
Speaker 2: inaccessible to you, or there's lots of dimensions to the
Speaker 2: universe we can never see, or the universe will never
Speaker 2: be understood. That's the kind of philosophically cosmic bad news
Speaker 2: I'm afraid of.
Speaker 1: Oh my goodness, Really that keeps you up at night.
Speaker 2: Absolutely, Yeah. This whole project of physics is based on
Speaker 2: the assumption that the universe follows laws and then we
Speaker 2: can figure them out somehow with our tiny little brains.
Speaker 2: Who knows if that's even true.
Speaker 1: Well, so, what's the physics version of a horror movie?
Speaker 1: Just some scientists coming up and tell you you're never
Speaker 1: gonna know anything.
Speaker 2: No, Now, the physics horror movie is the aliens arrive,
Speaker 2: they explain the universe to us, and we just can't
Speaker 2: get it. We're like, huh, what try again and it
Speaker 2: just never works.
Speaker 1: Or the aliens come and then you ask them what
Speaker 1: are the secrets of the universe? And they go, I'm
Speaker 1: not gonna tell you see you later, No.
Speaker 2: Exactly they want serve man, but.
Speaker 1: Anyways, welcome to our podcast Daniel and Horra Explain the Universe,
Speaker 1: a production of iHeartRadio in.
Speaker 2: Which we die bravely into the task of explaining the universe,
Speaker 2: whether or not it is explainable or understandable, we think
Speaker 2: it's at least worth trying to make sense of everything
Speaker 2: that's happening out there in the cosmos, from tiny little
Speaker 2: particles screaming through space nearly the speed of light, to
Speaker 2: massive black holes gobbling up everything that they can, all
Speaker 2: the way from the tiniest particles to the largest phenomena.
Speaker 2: We try our best to understand the universe, to wrangle
Speaker 2: it into some mathematical sense, and to explain all of
Speaker 2: that to you.
Speaker 1: That's right. We ponder the entire universe, and we wonder
Speaker 1: what it would be like to be out there in space,
Speaker 1: traveling the far reaches of the cosmos, maybe getting stretched
Speaker 1: out by relativity or by the expansion of the universe,
Speaker 1: and hopefully expanding and stretching your mind in the process.
Speaker 2: The whole project of understanding the universe means fitting it
Speaker 2: into your skull, means making it makes sense. The first
Speaker 2: step of that is to figure out what the laws
Speaker 2: are of physics, what are the rules that everything is following,
Speaker 2: and then thinking about whether that clicks together, what happens
Speaker 2: when I apply those rules over here or over there?
Speaker 2: Are there really universal? How does that connect with this
Speaker 2: other idea? I have a lot of physics is just
Speaker 2: trying to stick these puzzle pieces together right right?
Speaker 1: So then the engineer is going to be like, hey,
Speaker 1: can we break that rule? Can we push push the
Speaker 1: limit there? What's going to happen if we try?
Speaker 2: The bridge is going to collapse. That's what's going to happen.
Speaker 2: And that's why I'm glad I'm not an engineer.
Speaker 1: MM, because you're not building bridges, you're just burning them.
Speaker 2: I'm burning mathematical bridges. But when I make a mistake,
Speaker 2: nobody dies.
Speaker 1: Oh really, it seems kind of dangerous to be near
Speaker 1: a particle collider. I mean there's a lot of security
Speaker 1: around those.
Speaker 2: Yeah, that's true, and that's why we rely on accelerator
Speaker 2: physicists to build and operate those things.
Speaker 1: That's why they don't allow me down there.
Speaker 2: Yeah, probably not, But we aren't doing our best to
Speaker 2: develop the most universal laws of physics, we can ones
Speaker 2: that apply to everything under the Sun, including all the
Speaker 2: different kinds of particles that come to us from the Sun.
Speaker 1: Yeah, because the Sun is constantly spewing out not just
Speaker 1: a lot of light and warmth and energy for us
Speaker 1: to joy and to use, but also it's also spewed
Speaker 1: out a ton of other things, particles and uh, lots
Speaker 1: of different kinds of radiation.
Speaker 2: Right, that's right. All the stars out there in the
Speaker 2: universe are pumping out photons, but also a solar wind
Speaker 2: made of all different kinds of particles protons, electrons, neutrinos.
Speaker 2: And we talk a lot about what happens to those
Speaker 2: photons as they move through an expanding universe from galaxies
Speaker 2: moving away from us at very high recession velocities, But
Speaker 2: we don't as often apply those same questions, those same
Speaker 2: rules to the other particles being emitted by those stars.
Speaker 1: So today on the podcast will be tagling the question
Speaker 1: ken neutrinos get red shifted? Now, Daniel, when you talk
Speaker 1: about the solar wind, do you say wind in the
Speaker 1: sense of like a nice breezy summer wind, or do
Speaker 1: you mean it like like a fart, like the sun
Speaker 1: breaks wind.
Speaker 2: Kind of neither of those? Are those the only two options?
Speaker 2: Can I get an option C? Please? Nobody's ever out
Speaker 2: there in space like hmm, I'd like some more solar wind, please.
Speaker 2: I'm overheating. That's never happened.
Speaker 1: Yeah, it's not refreshing out there in space.
Speaker 2: No, I guess it. Yeah, I guess if I have
Speaker 2: to pick between those two. Solar wind is more like
Speaker 2: a fart, because it's kind of unpleasant and dangerous and
Speaker 2: you want to be as far away from it as possible.
Speaker 1: Right, Yeah, it stinky as well.
Speaker 2: You know, people joke about what space smells like, and
Speaker 2: it is partially due to the solar wind, but it's
Speaker 2: also just due to trace other particles that are out
Speaker 2: there that like adhere to the outside of a space
Speaker 2: suit on a spacewalk, which then volatilize as you come
Speaker 2: back inside. People say it smells like barbecue out there
Speaker 2: in space.
Speaker 1: Whoa, and not just because they're cooking in that radiation.
Speaker 2: Yeah, that's right now. If your fart's smelled like barbecue,
Speaker 2: then I don't know. I guess you'd be more popular
Speaker 2: at parties.
Speaker 1: If you fart on the space station. You would not
Speaker 1: be popular up there. It's a pretty closed environment, but
Speaker 1: it must happen. Sounds like a podcast episodedan.
Speaker 2: Sounds like a question for Zach and Kelly, since they're
Speaker 2: an expert in everything unpleasant in space. I'll ask her
Speaker 2: next time she's on.
Speaker 1: There You Go, There you go. What are the physics
Speaker 1: of farts in space? Like how quickly would it dissipate?
Speaker 1: Or like if you're out there and you smell without
Speaker 1: a helmet, would you die first? Or would you smell
Speaker 1: the fart first?
Speaker 2: Or could a really stinky fart cause an international incident
Speaker 2: on the space station which leads to World War three?
Speaker 2: In the end of humanity. You've heard of the butterfly effect.
Speaker 2: Now we're talking about the space fart effect.
Speaker 1: Wow, jeez, it's a dangerous place space.
Speaker 2: Now bring this back to neutrinos.
Speaker 1: Is it like in space no one can hear you fart?
Speaker 2: Or what if your farts were all neutrinos? Here we go,
Speaker 2: I'm bringing this back to the topic.
Speaker 1: Oh you're trying to bring it all right? Right? Smell
Speaker 1: that also or do they have.
Speaker 2: A neutral smell? M?
Speaker 1: Yeah.
Speaker 2: Another question is whether neutrinos have a color and whether
Speaker 2: you could consider them being red shifted or blue shifted?
Speaker 1: All right?
Speaker 2: All right?
Speaker 1: I can tell you're trying to get us back on
Speaker 1: track here.
Speaker 2: This is a physics podcast, not a fart podcast.
Speaker 1: After all, But farts are physical. I dang it, sorry,
Speaker 1: are you trying to ignore part of the physical universe?
Speaker 2: I retract that comment, and I respectfully request we get
Speaker 2: back on track.
Speaker 1: So, yeah, are neutrino's parts of the sun.
Speaker 2: That's the question today, right, The question is whether neutrinos
Speaker 2: can get red shifted the way we know that photons.
Speaker 1: Can, right right, all right, all right, Yeah, it's an
Speaker 1: interesting question. Can I Natrina get red shifted? Because you know,
Speaker 1: the word red shifted we usually applied to light, not neutrinos.
Speaker 2: Yeah, that's right. But if these laws are universal, if
Speaker 2: the same rules apply to everything, then you can ask
Speaker 2: the question, and this is what some listeners have asked me,
Speaker 2: whether the same rules apply to neutrinos from distant stars
Speaker 2: as they do two photons from those stars?
Speaker 1: Well, does that mean that the rules also apply to farts?
Speaker 1: Can Farce get redshift? All right?
Speaker 2: All right?
Speaker 1: Well, as usually, when we're wondering how many people out
Speaker 1: there had thought about Nutrina's and whether or not they
Speaker 1: can get red shifted.
Speaker 2: Thanks very much to everybody who answers questions for this
Speaker 2: segment of the podcast. If you'd like to hear your
Speaker 2: voice for a future episode, please don't be shy. Write
Speaker 2: to me two questions at Danielandjorge dot com.
Speaker 1: So think about it for a minute. Do you think
Speaker 1: neutrinos can get red shifted? Here's what people had to say.
Speaker 2: No, they're not an electron back that spectrum.
Speaker 1: I think yes, neutrinos have la a proton away from
Speaker 1: and if there's an ext arting body coming from there,
Speaker 1: the camera just shifted, I think.
Speaker 4: I assume this is to do with quantum mechanics and
Speaker 4: how particles have a frequency.
Speaker 2: What rechhift.
Speaker 4: That just means like the frequency gets stretched, I think,
Speaker 4: So I guess yeah, it can happen. I don't know
Speaker 4: how or why.
Speaker 3: I don't see why not, but I know the problem
Speaker 3: with them is that they're just so hard to see.
Speaker 3: They seem to pass through just about everything, and I
Speaker 3: know there's a few different kinds. So I guess yes
Speaker 3: they could, But how would you detect that? I'm not sure?
Speaker 1: All right, Well, some pretty interesting answers sort of in
Speaker 1: the range of why not. Who knows?
Speaker 2: Yeah, some people saying yeah, they're a particle like everything else.
Speaker 2: Other people saying no, that only applies to photons and
Speaker 2: things in the electromagnetic spectrum.
Speaker 1: Hmmm, all right, well, let's dig into it, Daniel. Let's
Speaker 1: recap first of all, what is a neutrino.
Speaker 2: Neutrinos are some of the weirdest and most fascinating particles
Speaker 2: in the universe because they're sort of like an extreme
Speaker 2: example of what the universe can do. You know, most
Speaker 2: of the particles we're familiar with, quarks and electrons feel
Speaker 2: a bunch of forces. Quarks feel the strong force and
Speaker 2: the electromagnetic force and the weak force. Electrons feel only
Speaker 2: the electromagnetic force and the weak force. They don't feel
Speaker 2: the strong force. They're neutral in the strong force. Neutrinos
Speaker 2: are like one step further. They're saying, hey, I'm going
Speaker 2: to be neutral also in electromagnetism. I'm going to only
Speaker 2: feel the weak force. So we have examples of particles
Speaker 2: that feel all three quantum forces. The quarks an example
Speaker 2: of particles that feel two of the quantum forces. Electrons
Speaker 2: feel electromagnetism and the weak force, and then an example
Speaker 2: of a particle that feels only one of those forces,
Speaker 2: just the weakest one, the weak force. So neutrinos are
Speaker 2: particles that are out there in the universe that we
Speaker 2: can just baurreally sense, barely interact with, because the only
Speaker 2: way they interact with us is through the way weakest
Speaker 2: force we know about, right.
Speaker 1: Right, But they can still exist, right like, They're still
Speaker 1: made out of real energy in this universe, so you
Speaker 1: can make them. They just sort of ignore us and
Speaker 1: won't talk to us in the ways that most other
Speaker 1: particles talk to us.
Speaker 2: Yeah, exactly. And remember that all of these particles are
Speaker 2: just ripples in fields, and these fields are all on
Speaker 2: top of each other. The way to think about these
Speaker 2: interactions is whether the fields can transfer energy back and forth.
Speaker 2: Then neutrino fields couple very very weakly to all these
Speaker 2: other fields. So it's sort of like having another universe
Speaker 2: on top of us that we can just barely interact with.
Speaker 2: Even if all sorts of crazy stuff is going on,
Speaker 2: even if there's huge numbers of them and enormous amounts
Speaker 2: of mass and energy and velocity, we just barely sense it.
Speaker 2: So it's almost like having a parallel universe. Right on
Speaker 2: top of us. And you know, the even more extreme
Speaker 2: would be dark matter. Dark matter we think might be
Speaker 2: a particle that feels none of these forces, and so
Speaker 2: it's on top of us, but we only sense it gravitationally.
Speaker 2: So neutrino is like almost the extreme limit of that.
Speaker 3: Right.
Speaker 2: They are energy, they're part of our universe, and they
Speaker 2: even have mass. We know the neutrinos are not like
Speaker 2: photons and other massive particles. There is a little bit
Speaker 2: of stuff to them, an incredibly tiny amount of stuff
Speaker 2: to these neutrinos.
Speaker 1: And now, do neutrinos feel gravity? Do we know that.
Speaker 2: Everything with energy feels gravity? Absolutely? Gravity is universal. You
Speaker 2: can't have energy and not feel gravity because remember gravity.
Speaker 1: But have we seen it that we see neutrinos like
Speaker 1: bend by the path of the massive things.
Speaker 2: Oh yeah, great question. We can't observe neutrinos well enough
Speaker 2: to see their path bending, but we know something about
Speaker 2: the massive neutrinos and the number of neutrinos, and that
Speaker 2: affects the overall curvature of space and time, and we
Speaker 2: can see their impact in the early universe and its curvature.
Speaker 2: So we know the neutrinos have energy, and that energy
Speaker 2: does contribute to the curvature of space time. Yeah. M,
Speaker 2: but we haven't seen one bend to gravity, have we
Speaker 2: We have not seen them move in a curved path. No,
Speaker 2: but we know that their energy contributes to the curvature.
Speaker 1: Hmm. Interesting. And is there sort of a perspective on
Speaker 1: why some fields or why some particles interact with some
Speaker 1: forces and not others, or is just sort of how
Speaker 1: the universe was made or how these particles turn out
Speaker 1: to be, you know, like, is there is it like
Speaker 1: a parameter and the equations that is just kind of
Speaker 1: random or what.
Speaker 2: Yeah, it's a great question. Is there an explanation or
Speaker 2: is it just descriptive? Currently it's mostly descriptive. Like we
Speaker 2: say that quarks have a strong charge and electrons don't
Speaker 2: because we see that electrons ignore colored fields. We say
Speaker 2: that neutrinos don't have an electric charge because we see
Speaker 2: that they don't get accelerated by electric fields. So that's
Speaker 2: sort of what we mean by that. It's just a
Speaker 2: description of what we see in these particles. Do we
Speaker 2: do notice a bunch of patterns, like all the quarks
Speaker 2: have the same kinds of charges and electrons and muons
Speaker 2: and towels all have the same electric charge and this
Speaker 2: kind of stuff. So there definitely some patterns and some
Speaker 2: struct sure there, but we definitely do not understand it.
Speaker 2: It's just descriptive. It might be explained by some future
Speaker 2: theory physics that tells us what all these particles are
Speaker 2: made out of, some quiz bits and what knots that
Speaker 2: have fundamental pieces to them, and when you put them
Speaker 2: together in certain ways, or they interact or oscillate in
Speaker 2: certain ways, you get the particles that we see with
Speaker 2: their various properties. But currently we can't explain it. We're
Speaker 2: sort of at the stage of the periodic table one
Speaker 2: hundred and fifty years ago where we see all these
Speaker 2: elements with these different properties, but we don't understand why
Speaker 2: they have that nature.
Speaker 1: And you mentioned there's sort of like ghostly particles, but
Speaker 1: I feel like that maybe understates because there's a huge
Speaker 1: amount of neutrino's going through us right now. Right there's
Speaker 1: like bazillions of them going through our bodies as we speak.
Speaker 2: Yeah, that's right. Neutrinos hardly interact with us, but there's
Speaker 2: no shortage of them because the Sun produces an incredible
Speaker 2: number of neutrinos. Every fusion reaction produces neutrinos, and it
Speaker 2: also produces photons, but those photons are mostly absorbed by
Speaker 2: the Sun, Like the Sun is opaque to most of
Speaker 2: the photons it produces, so those photons are reabsorbed by
Speaker 2: the Sun and it generally heats it up. People talk
Speaker 2: about the photons we see on Earth as having been
Speaker 2: produced in fusion. Technically that's not really accurate. The photons
Speaker 2: produced infusion heat up the Sun and then the Sun
Speaker 2: glows as a black body or because its atmosphere is hot.
Speaker 2: Those are the photons we see, but the neutrinos are different.
Speaker 2: The Sun is transparent to neutrinos the way basically everything
Speaker 2: is transparent to neutrinos. So if a neutrino is made
Speaker 2: at the heart of the Sun, it flies out and
Speaker 2: goes through the Earth and we can observe it directly
Speaker 2: from that fusion process. And there's a huge number of
Speaker 2: them passing through our bodies instead of a billion neutrinos
Speaker 2: per square centimeter per second.
Speaker 1: Yeah, it's huge, and none of them are interacting with
Speaker 1: us or are they a little bit maybe a little
Speaker 1: bit dangerous, Like are some of them maybe knocking on
Speaker 1: some of my DNA.
Speaker 2: Maybe some of them are definitely interacting with you, but
Speaker 2: it's a tiny, tiny number. To give you a sense
Speaker 2: of it, like we have many fewer muons passing through
Speaker 2: our body every second, like one per square centimeter per minute,
Speaker 2: but every single one of those is interacting with your body.
Speaker 2: Like when a muon hits your body, it's like a
Speaker 2: tiny bullet. It's hitting those atoms and it's depositing energy.
Speaker 2: Mostly they're not doing damage, they don't hit anything important,
Speaker 2: and you're fine because they're just these tiny bullets. But
Speaker 2: every single muon does interact with your body. But for neutrinos,
Speaker 2: most of them do not interact with you. So for scale,
Speaker 2: the neutrinos were discovered in an enormous tank underground. We're
Speaker 2: talking about like thousands and thousands and thousands of liters
Speaker 2: of liquid run for a year to see like one
Speaker 2: neutrino bounce off of one of those particles. So neutrino
Speaker 2: interactions with our kind of matter are extraordinarily rare. So yes,
Speaker 2: they are interacting with us, because it's a huge number,
Speaker 2: but it's a tiny, tiny fraction of the neutrinos that
Speaker 2: are created and a tiny overall number of interactions compared
Speaker 2: to like the muons and other particles that are interacting
Speaker 2: with you.
Speaker 1: Now, are these the ones that you can see in
Speaker 1: some science museums where they have like a little chamber
Speaker 1: of water vapor and you see the traces. Are these
Speaker 1: neutrinos or am I thinking of something else?
Speaker 2: Those are mostly muons. Yeah, cloud chambers which you can
Speaker 2: see in science museums, and you can actually build at
Speaker 2: home in your garage without too much trouble. I got
Speaker 2: an email from a listener who was inspired by a
Speaker 2: comment I made a year ago, and she and her
Speaker 2: son built a cloud chamber in her garage and they
Speaker 2: saw muon tracks. So those are mostly muons. Neutrinos. You'd
Speaker 2: need to build an enormous underground chamber of like xenon
Speaker 2: or something in order to see one neutrino, and you
Speaker 2: wouldn't see a track. You'd see the neutrino bumping into
Speaker 2: a normal particle and you'd see the recoil of that particle.
Speaker 2: You can never really see a track of neutrinos because
Speaker 2: that would require multiple interactions of the same neutrino, which
Speaker 2: would be astronomically unlikely. You only ever see like one interaction,
Speaker 2: one push from a neutrino.
Speaker 1: Meons go through the roof of your garage.
Speaker 2: Oh yeah, muons can go through rock. Also, you can
Speaker 2: see muons when you're underground. That's why they build the
Speaker 2: neutrino detectors so deep underground to shield themselves from all
Speaker 2: the muons which can penetrate through meters and meters of rock.
Speaker 1: Mmm. Now, and neutrinos are not just ghostly, but they're
Speaker 1: super duper fast, right, Because they're so little mass, they're
Speaker 1: going almost at the speed of light all the time.
Speaker 2: Yeah. Neutrinos have a tiny, tiny mass, much smaller than
Speaker 2: even electrons, which means when they're produced, if they have
Speaker 2: even a tiny smidge of energy, they're basically going at
Speaker 2: the speed of light, very very close to the speed
Speaker 2: of light.
Speaker 1: Can you slow them down? Like, could you ever hold
Speaker 1: innutrino in your hand?
Speaker 2: Yeah, you could slow neutrinos down. Because they do have mass,
Speaker 2: they can exist at zero velocity. Unlike photons. Photons, there
Speaker 2: is nothing to them if they have no velocity because
Speaker 2: they are just velocity. But if you slow a neutrino down,
Speaker 2: it has mass, right, mass means rest energy, So you
Speaker 2: can be in the same reference frame as a neutrino.
Speaker 2: You could like catch up to a neutrino and look
Speaker 2: at it, or equivalently, you could slow a neutrino down
Speaker 2: and hold it in your hand.
Speaker 1: Yeah, m pretty cool. All right, Well, now the question
Speaker 1: is do neutrinos get red shifted as the universe expands?
Speaker 1: And so let's get into what red shifting is. Can
Speaker 1: it happen for neutrinas and does it make them smell
Speaker 1: like farts or maybe not? We maybe we won't get
Speaker 1: to that in time, but let's give it a try.
Speaker 1: We'll dig into that, but first let's take a quick break.
Speaker 1: All right, we're talking about nutrinas and whether they can
Speaker 1: get red shifted as the universe expands, So those are
Speaker 1: all pretty interesting concept there in one sentence, let's start
Speaker 1: with red shifting.
Speaker 2: What is red shifting and a sentence. Red shifting is
Speaker 2: when a wave gets a longer frequency because it's being
Speaker 2: omitted by something that's moving away from you. So all
Speaker 2: waves have frequency, like sound waves, the sounds you're hearing
Speaker 2: from us have certain frequencies, frequencies and higher frequencies and
Speaker 2: all that kind of stuff. We can describe sound as waves,
Speaker 2: and we can measure the number of times the wave
Speaker 2: waves per second. That's its frequency, just inversely proportional to
Speaker 2: its wavelength, So longer wavelengths lower frequency.
Speaker 1: It sounded like you're trying to hit like a high
Speaker 1: scene and a low S there, Daniel.
Speaker 2: That's sort of like a very low CE and a
Speaker 2: less low C. That's all I'm capable of.
Speaker 1: Low. You can't do falsetto.
Speaker 2: That was my false Oh that was you. I think
Speaker 2: I think you can do better. You're I'm gonna rely
Speaker 2: on our sound editor here, Corey. Can you make this
Speaker 2: sound like a high se.
Speaker 1: Just get a healum balloon there. You don't need.
Speaker 2: Special sects, Chipmunk. Daniel, Yeah, I.
Speaker 1: Think I've seen a video of Morgan Freeman red shifting
Speaker 1: his voice or blue shifting his voice with a healum balloon.
Speaker 2: That's amazing.
Speaker 1: So red shifting is and whenever any kind of wave
Speaker 1: gets stretched out basically right, it becomes a low lower frequency,
Speaker 1: which means bigger wavelengths.
Speaker 2: Yeah, and shift there just tells us that we're changing something.
Speaker 2: And red shift means we're changing it to be more red.
Speaker 2: And red is on the long wavelength low frequency end
Speaker 2: of the visible spectrum. So when we say we're getting
Speaker 2: longer wavelengths or lower frequency, we talk about red shifting,
Speaker 2: and the opposite is blue shifting. If you're making something
Speaker 2: higher frequency or shorter wavelengths, you're making it blue er.
Speaker 2: So red shifting just means you're extending the wavelength, you're
Speaker 2: lowering the frequency, right.
Speaker 1: Right, Although I have to say, I feel like you're
Speaker 1: kind of cheating a little bit here because I don't
Speaker 1: think I've ever heard anyone used to phrase red shifting
Speaker 1: or blue shifting when it comes to anything except light waves. Like,
Speaker 1: nobody ever says, can you give me a blue shifted
Speaker 1: C note or a red shifted D note? Do you
Speaker 1: know what I mean?
Speaker 2: Yeah, that's true. We apply red shifting mostly to astronomical objects,
Speaker 2: and mostly astronomical stuff we see with photon, so that's
Speaker 2: why it's applied there. But you know, if a police
Speaker 2: car is passing by you, as it's driving towards you,
Speaker 2: the wavelengths are shortened, and as it's driving away from you,
Speaker 2: the wavelengths are lengthened, and so you could call that
Speaker 2: blue shifting and red shifting in.
Speaker 1: That case we call it the Doppler effect.
Speaker 2: Right, yeah, exactly, the Doppler effect.
Speaker 1: No, he calls it the red shifting or blue shift.
Speaker 2: But police cars have red and blue lights, so maybe
Speaker 2: somehow I don't know.
Speaker 1: Yeah, yeah, yeah, I figure if I create a if
Speaker 1: you're cheating, Danieler, come on.
Speaker 2: I'm just trying to throw a bunch of random ideas
Speaker 2: at you to distract you from the fact that you're
Speaker 2: right about this.
Speaker 1: Well, I think what you're trying to get at is that,
Speaker 1: you know, anything with a wave, it can get stretched
Speaker 1: out or or it can get shortened, right like anything,
Speaker 1: sound wave, an ocean wave, anything like that can increase
Speaker 1: or decrease in frequency. And for light, that usually means
Speaker 1: that it's changing color, which is where the name red
Speaker 1: shifting and blue shifting come from.
Speaker 2: That's right, And because we're normally applying it to astronomical stuff,
Speaker 2: you know, light from distant galaxies. If that distant galaxy
Speaker 2: is moving away from us, for example, we say that
Speaker 2: it's red shifted and the light from that galaxy looks
Speaker 2: redder than if that galaxy had not been moving away
Speaker 2: from us. And if an object in the sky like
Speaker 2: Andromeda is moving towards us, its light gets blue shifted.
Speaker 2: And you're right that it applies to the wavelength of
Speaker 2: the light and also applies to the color of the
Speaker 2: light as we see it if it's in the visible spectrum,
Speaker 2: and it tells us something about the energy of that light,
Speaker 2: because for light, the wavelength is very closely connected to
Speaker 2: the energy, like red or light is lower energy and
Speaker 2: blue or light is higher energy.
Speaker 1: Right, And this red shifting and blue shifting of light
Speaker 1: out there in the universe happens not just because things
Speaker 1: are moving away from us or towards us, but also
Speaker 1: because the universe is expanding, right.
Speaker 2: Yeah, And these are actually two different ways to talk
Speaker 2: about the same phenomena. You can get confused and think, oh,
Speaker 2: there's two red shifts happening. One that the universe is
Speaker 2: expanding and it makes all waves links longer than the other.
Speaker 2: The galaxies are moving away from us faster and faster
Speaker 2: than the Doppler ship is making their light redder. Those
Speaker 2: are actually two different ways to think about the same phenomenon.
Speaker 2: What's happening there is that your description depends on your
Speaker 2: frame of reference. If you think about the whole universe
Speaker 2: in a single frame, like we're at the center and
Speaker 2: everything is moving away from us. You're measuring the velocity
Speaker 2: of those galaxies relative to us. Then you can use
Speaker 2: the Doppler story to describe what's happening, but instead, in
Speaker 2: a more general relativity sense, you say, well, you can't
Speaker 2: really put everything into a frame because the universe is
Speaker 2: expanding and space is curved between here and other galaxies.
Speaker 2: Which you really have to do is imagine every galaxy
Speaker 2: in its own frame and space increasing between them. And
Speaker 2: in that picture there is really no relative velocity because
Speaker 2: every galaxy has no velocity in its own frame. And
Speaker 2: so what happens to the photons as they go from
Speaker 2: galaxy to galaxy is the expanding space between them is
Speaker 2: doing the work of expansion. It's a good example of
Speaker 2: how you can build physics and lasts to different ways.
Speaker 2: You can start from a few different axioms and end
Speaker 2: up with a different description of the same physical process.
Speaker 1: Right, But it is two separate effects, isn't it, Like
Speaker 1: one is just from its motion and the other one
Speaker 1: is from the expanding of the universe.
Speaker 2: No, it's two descriptions of the same thing. Like in
Speaker 2: the expansion of the universe model, there is no relative velocity.
Speaker 2: In fact, that's more accurate because you can't really talk
Speaker 2: about relative velocity across the whole universe. That's also why
Speaker 2: you end up with sort of nonsense answers, like those
Speaker 2: galaxies are moving away from us faster than the speed
Speaker 2: of light because you're making measurements across two different frames
Speaker 2: where space is curved between them.
Speaker 1: Right, But I feel like there are sort of two
Speaker 1: effects there that can maybe add or subtract, Right, Like,
Speaker 1: if there's a galaxy really far away from us that's
Speaker 1: maybe spinning, for example, then some things they'll be moving
Speaker 1: away from us, and sometimes they'll be moving towards us,
Speaker 1: so they'll be shifting of the light because of that.
Speaker 1: But then also it's really far away, which means that
Speaker 1: on top of that, there's going to be some sort
Speaker 1: of wretch due to the long distances getting longer and longer.
Speaker 2: You can add more layers to it, certainly, like you
Speaker 2: can add not just the fact that these galaxies are
Speaker 2: moving away from us, or equivalently, that space is expanding
Speaker 2: between us, but that also within those frames there is
Speaker 2: some motion relative to the frame itself. So as you
Speaker 2: say galaxies are spinning, and that spinning is what we
Speaker 2: call peculiar motion relative to the frame of the galaxy,
Speaker 2: which is moving with the center of mass of the galaxy.
Speaker 2: And you're right that moving relative to the center mass
Speaker 2: of the galaxy can cause an additional red shift or
Speaker 2: blue shift, so that really is a separate effect. The
Speaker 2: rotation of the galaxy does add another contribution to red
Speaker 2: shifting and blue shifting, and we can see that in
Speaker 2: distant galaxies and we can use it to help measure
Speaker 2: their rotation.
Speaker 1: Right, So there are two effects, right.
Speaker 2: The expansion of the universe and the recession velocity of
Speaker 2: an entire galaxy are two equivalent ways of talking about
Speaker 2: one effect. The rotation of a galaxy does add another effect. Yes,
Speaker 2: you're right that there are multiple contributions to the red shift,
Speaker 2: the motion and the sin but if you're thinking in
Speaker 2: the relative velocity point of view, they're both just contributing
Speaker 2: to the relative velocity. So it's two contributions to one
Speaker 2: red shift effect, not two different effects.
Speaker 1: So how do we measure all this red shifting that's
Speaker 1: going on in the light of the universe.
Speaker 2: Yeah, it's really tricky because you can't stop the galaxies, right,
Speaker 2: or like go to the galaxy and measure like it's
Speaker 2: light that you would measure if you were right there
Speaker 2: next to it. So you have to sort of imagine
Speaker 2: what light you think the galaxy was emitting in its
Speaker 2: own frame and then compare that to what we're seeing. Fortunately,
Speaker 2: galaxies are filled with objects we pretty much understand, stars,
Speaker 2: et cetera, and those are following physics that we pretty
Speaker 2: much understand, so we have a pretty good way to
Speaker 2: predict the light we think a galaxy should be emitting,
Speaker 2: and then we can compare it to the light we're
Speaker 2: seeing from the galaxy and we can tell that it's shifted.
Speaker 2: And specifically, the frequency of the light from these galaxies
Speaker 2: has a few specific handles in it, like a fingerprint
Speaker 2: where we can tell that it's been shifted along Like
Speaker 2: we know that atoms tend to emit light at very
Speaker 2: specific narrow frequency ranges that correspond to the energy levels
Speaker 2: of the atoms. As an electron jumps down one energy
Speaker 2: level around hydrogen, for example, it tends to emit a
Speaker 2: photon with the specific energy of the gap between those
Speaker 2: energy levels. And so if we see light from a
Speaker 2: distant galaxy and it has a huge spike close to
Speaker 2: that energy level, but a little bit shifted. We can say, oh,
Speaker 2: that's probably from hydrogen. It's just shifted a certain amount
Speaker 2: in the red or in the blue. So these like
Speaker 2: standard candles help us understand how the light is shifted
Speaker 2: from these distant galaxies.
Speaker 1: Right. It kind of goes to that idea that stars
Speaker 1: have a sort of fingerprint to them, like the light
Speaker 1: they emit have a very specific pattern of them in
Speaker 1: the fregency spectrum that you can sort of identify what's
Speaker 1: in the star or what it's supposed to have. And
Speaker 1: so if you see that fingerprint kind of smearred, then
Speaker 1: you know that it's red shifted. Right. But then I
Speaker 1: think you can also just generally tell right, because most
Speaker 1: of the light from those things around us is mostly
Speaker 1: you know, a certain color. But I imagine as you
Speaker 1: look out into the universe and things are further away
Speaker 1: from us, things just look redder.
Speaker 2: Yeah, But that's how we can tell the distance to
Speaker 2: things by measuring the red shift. Because there's a correlation
Speaker 2: between how far away things are and how quickly away
Speaker 2: from us they're moving. Then you can use the red
Speaker 2: shift as a measure of distance. Now you have to
Speaker 2: calibrate that is we have a whole episode about the
Speaker 2: cosmic distance ladder to calibrate these things. But generally things
Speaker 2: that are farther away are moving away from us faster.
Speaker 2: So if you measure the red shift of an object,
Speaker 2: you can tell how far away it is or how
Speaker 2: old that light is. But there can also be a
Speaker 2: lot of uncertainty on those measurements because the wider the
Speaker 2: spectrum you measure, like the more of these fingerprints, the
Speaker 2: more of these atomic lines that these spikes that you identify,
Speaker 2: the more accurately you can measure this red shift. This
Speaker 2: is why, for example, when you point multiple telescopes at
Speaker 2: different frequencies at the same galaxy, you can get a
Speaker 2: better measurement for its red shift. Like James Webb recently
Speaker 2: saw some galaxies that were like crazy weird far away.
Speaker 2: Those numbers came from the red shift numbers which were
Speaker 2: pretty uncertain because James Webb didn't have a chance to
Speaker 2: do a broader spectrum and Hubble hadn't looked at it
Speaker 2: yet in a different spectrum. And so that's why sometimes
Speaker 2: when you follow up with more measurements, you can get
Speaker 2: more handles on the light from that galaxy, and that
Speaker 2: revises the red shift measurement, which tells you how far
Speaker 2: away this thing really is.
Speaker 1: Right, But I guess what I'm saying is that that's
Speaker 1: kind of if you want to get really granular and
Speaker 1: know exactly how much the red shifting is. But I wonder,
Speaker 1: and I'm asking if there's a kind of a general
Speaker 1: effect that anyone could affect with their naked eye. You know,
Speaker 1: as the star that we see at night are in
Speaker 1: our galaxy, so I imagine they're not very red shifted. So
Speaker 1: all the light we see from our stars look white
Speaker 1: or yellowish. But if you were to look at the
Speaker 1: rest of this guy, that things are not stars, and
Speaker 1: generally the light we'll see from that is redder.
Speaker 2: Yeah, that's exactly right. And that was Hubble's experience, right,
Speaker 2: you looked up in the night sky. He saw a
Speaker 2: bunch of stars, but he also saw these smudges that
Speaker 2: people thought, oh, those are just like clouds or nebula
Speaker 2: or whatever within our galaxy. But then by calculating the
Speaker 2: red shift and by understanding the relationship between red shift
Speaker 2: and distance, he was like, oh my gosh, look these
Speaker 2: things are redshift. That means they're super duperor far away.
Speaker 2: They're actually other galaxies. So the red shift gives us
Speaker 2: that like third dimension to the night sky rather than
Speaker 2: just seeing like a screen. He gives us the ability
Speaker 2: to project that into the third dimension and understand the
Speaker 2: depth of the night sky.
Speaker 1: Right. Or I wonder if you just put on like
Speaker 1: infrared glasses, right or use an infrared camera, you will
Speaker 1: sort of see more of the rest of the universe.
Speaker 2: Right, yeah, exactly. And that's why James Web, for example,
Speaker 2: is an infrared telescope. They're like, let's focus on the deepest,
Speaker 2: reddest light in the universe, because that's from the most
Speaker 2: distant objects that things were seeing from the early universe.
Speaker 2: That's why you build infrared telescopes exactly, right.
Speaker 1: Right, And if you get really mad, then you'll be
Speaker 1: seen red and so opening your eyes up to more
Speaker 1: of the universe. No, no, not a valid theory.
Speaker 2: Yeah. I mean, if somebody farts really badly at your
Speaker 2: astronomy party, that can make you sopid also yeah.
Speaker 1: Yeah yeah, or in your space station the universe the
Speaker 1: costumers will open up to you. All right. Well, now,
Speaker 1: the main question we're asking here today is whether neutrinos
Speaker 1: can be red shifted, which again I feel like it's
Speaker 1: a little bit of a cheat here because it depends
Speaker 1: on whether you only apply the word redshifting to light,
Speaker 1: which is kind of what some of our listeners brought up.
Speaker 1: So maybe let's settle that right now, Daniel, are you
Speaker 1: expanding the definition of red shifting to things that are
Speaker 1: not light?
Speaker 2: I see, that's a fair question. I hadn't even thought
Speaker 2: about that. To me, redshifting up lies to all sorts
Speaker 2: of waves, even the Doppler effect. Like when that police
Speaker 2: siren is coming at me, I think of that sound
Speaker 2: as blue shifted. I see how blue there implies something
Speaker 2: about visual light, But to me, it's a more general meaning,
Speaker 2: and just that it's changing the frequency.
Speaker 1: Right. But I mean like if a ocean wave got,
Speaker 1: you know, higher frequency, you wouldn't say it got red shifted,
Speaker 1: like nobody would understand you.
Speaker 2: If you got a higher frequency, I would say it
Speaker 2: got blue shifted. Yeah. I think that's pretty cool. Blue
Speaker 2: shifting ocean waves awesome. I'm gonna start saying that everywhere. Now.
Speaker 1: It wouldn't get bluer, right or like you know, a
Speaker 1: high C note, it isn't bluer than a low C note.
Speaker 1: It's sort of a subtle thing. But some of our
Speaker 1: listeners did say that the answer is that it cannot
Speaker 1: because nutrinos are not light, so therefore they can't be
Speaker 1: red shifted.
Speaker 2: I see that that's a fair point. I think blue
Speaker 2: to just mean it's changing in that direction of the frequency.
Speaker 2: You could extend that argument even further and say, like, well,
Speaker 2: that only applies to visible light, because invisible light isn't
Speaker 2: bluer or redder even if its frequency is shifting.
Speaker 1: So what's the answer here for the people who said
Speaker 1: nutinios can be red shifted because they're not light.
Speaker 2: I think we should consider red shifting blue shifting more
Speaker 2: generally to refer to changing the frequency of the waves.
Speaker 1: Okay, so just for today, we're gonna go against what
Speaker 1: most people consider the English language.
Speaker 2: I think that's the accepted meaning of red shifting and
Speaker 2: blue shifting, and I.
Speaker 1: Think we're just going to consider the question of whether
Speaker 1: the wavelength of a nutrinia can change as the universe expands.
Speaker 2: So, according to Wikipedia, which is just looked up and physics,
Speaker 2: a redshift is an increase in the wavelength and corresponding
Speaker 2: decrease in the frequency and energy of electromagnetic radiations. Such
Speaker 2: as light. That's interesting.
Speaker 1: So even Wikipedia disagrees with you.
Speaker 2: Dariel, Yeah, interesting, Yeah, some subtle wrinkles in the definitions here.
Speaker 1: Okay, So then officially, according to Wikipedia, and you know
Speaker 1: most humans who speaks English, the answer to our question
Speaker 1: is no, neutrinus can get red shifted.
Speaker 2: If you define red shifting to only apply to photons,
Speaker 2: then yes, yeah.
Speaker 1: If disregard language, then anything can be anything. But basically,
Speaker 1: I'm saying the listener who said the answer is no,
Speaker 1: because neutrinos are not light, then they're partly right.
Speaker 2: Yeah, they're partly right according to that definition. I'm surprised
Speaker 2: to have to make the argument to you that, like,
Speaker 2: you know, language can be evocative of broader themes and
Speaker 2: deeper ideas that we find patterns of across the universe
Speaker 2: and across phenomena. But you know, to me, I think
Speaker 2: the interesting part of the question is, like, you.
Speaker 1: Mean, you're surprised that you have to be clear about
Speaker 1: what you call things in physics. You're surprised. But at
Speaker 1: this point five years.
Speaker 2: In, yeah, I should learned that should have learned.
Speaker 1: Well, okay, so let's just say the answer is no,
Speaker 1: Nutritius cannot get red shifted because I think even Wikipedia
Speaker 1: agrees that it applies to light only. But it's still
Speaker 1: an interesting question to ask whether neutrinos that are traveling
Speaker 1: out there in space do their wavelengths get stretched out
Speaker 1: by the expansion of the universe.
Speaker 2: Do they get shifted to longer or shorter wavelengths?
Speaker 1: Yeah, do their wavelengths get stretched or squeeze as the
Speaker 1: universe expands? So let's tackle that question.
Speaker 2: So I agree that is right, interesting question.
Speaker 1: Yes, okay, So then so it happens to light because
Speaker 1: the universe is expanding, right, So as it's traveling, it's
Speaker 1: having to travel through more space as it goes along.
Speaker 1: Is that why it stretches, Just because it's sitting in
Speaker 1: space and space is being stretched, its frequency gets stretched.
Speaker 2: Yes, the second one, space itself is getting stretched out,
Speaker 2: and radiation gets stretched out differently than like matter. Does
Speaker 2: you know, electrons sitting in space, you stretch out the space.
Speaker 2: You still have one electron and now you have more space,
Speaker 2: so you have less matter per volume where things get
Speaker 2: diluted in a certain way. The same thing happens to radiation.
Speaker 2: You have one photon in that volume, but that photon's
Speaker 2: energy also decreases because the wavelength of that photon also changes.
Speaker 1: Right, So then the question is do neutrinos have a
Speaker 1: frequency or a wavelength?
Speaker 2: Yeah, So in this sense, you can think of all
Speaker 2: particles as ripples in some field, right, and those ripples
Speaker 2: have frequencies. Like we talked to Mats Dressler about this recently,
Speaker 2: and you can imagine electrons is having like a standing wave,
Speaker 2: which is an oscillation in that field, and a traveling wave,
Speaker 2: which is like the motion of the electron through that field.
Speaker 2: Photons only have a traveling wave because they have no mass.
Speaker 1: Where there's two kinds of waves, a traveling wave and
Speaker 1: a standing wave, what's the difference, Like, do electrons have
Speaker 1: both waves?
Speaker 2: Yeah, the electron field can do both, right. The electron
Speaker 2: field can just oscillate in place in a certain way,
Speaker 2: and that's what a stationary electron is. That's why electrons
Speaker 2: have mass. An electron field can also ripple in a direction. Right,
Speaker 2: that's a traveling wave. Don't think of it as two waves.
Speaker 2: It's the same wave. It's just that electrons you can
Speaker 2: see standing still in which case they're just doing the
Speaker 2: standing wave thing, or you can see them moving, in
Speaker 2: which case it's also a traveling wave, but that depends
Speaker 2: on your frame of reference. Right now, For photons, you
Speaker 2: can't see them standing still because there's no frame of
Speaker 2: reference in which they're at rest. They're always traveling waves.
Speaker 1: When things have a standing wave, are those waves actually
Speaker 1: rippling or are they more like probability waves.
Speaker 2: These are ripples in a field, which some people think
Speaker 2: is a physical thing, right, and so these are should
Speaker 2: and so these should be thought of as like actual
Speaker 2: oscillations in a physical quantity. People think the field is
Speaker 2: real and it's out there. That's sort of a question
Speaker 2: of philosophy. This is separate from like wave functions and probabilities,
Speaker 2: which are in an abstract probability space. These are ripples
Speaker 2: in real space what we think is a real physical thing,
Speaker 2: whether or not it's actually happening, whether you can observe it,
Speaker 2: and what happens when you take measurements, et cetera. There's
Speaker 2: a whole other question in philosophy. But we think these
Speaker 2: are physical ripples of a field.
Speaker 1: It's actually oscillating, and so they're different than the quantum
Speaker 1: probability waves. Right, yes, Okay, Now what does it mean
Speaker 1: that an electron is rippling? In place, like it's jiggling.
Speaker 1: Its energy is increasing and decreasing and pulsating, or what
Speaker 1: does it mean if it's standing still because it's not moving.
Speaker 2: Well, as we talked about with Matt Stresslo, you can
Speaker 2: think about the wave as sort of like the way
Speaker 2: you think about a string oscillating. Right, a guitar string
Speaker 2: can oscillate in place as a standing wave. What's happening
Speaker 2: there is it's oscillating between kinetic and potential energy. Right,
Speaker 2: it gets distorted, it has more potential energy, and then
Speaker 2: it comes back and has kinetic energy, then it slashes
Speaker 2: back into potential energy. So the same way the electron
Speaker 2: field can oscillate between having kinetic and potential energy. So
Speaker 2: the value of the field is changing. It's some values
Speaker 2: that has more potential energy, some values that has less
Speaker 2: potential energy but more kinetic energy, so that energy is
Speaker 2: conserved within the field. It's just oscillating back and forth
Speaker 2: between kinetic and potential energy, the way like a ball
Speaker 2: inside a glass can roll around if you ignore friction,
Speaker 2: it could roll around forever. It's like oscillating within them.
Speaker 1: Or I guess I'm imagining like a balloon sitting in
Speaker 1: space it's maybe squashing and stretching in different directions. Right.
Speaker 1: That means it energy is going between the potential energy
Speaker 1: and kinetic energy as it squeezes and compresses. But then,
Speaker 1: how is that different than traveling waves.
Speaker 2: In order to do this special trick of oscillating in place,
Speaker 2: you have to have mass. Mass is the thing that
Speaker 2: allows you to do that. That's really what mass is
Speaker 2: is the ability to store energy in one location within
Speaker 2: the field. Because remember that mass is just like a
Speaker 2: measurement of internal stored energy. But some fields can't do that,
Speaker 2: Like the photon field doesn't have any mass. There's something
Speaker 2: the electron field can do that the photon field cannot do.
Speaker 2: But the photon field and the electron fields can both
Speaker 2: have traveling waves, which is like a wave moving through space.
Speaker 2: You have an oscillation here, and then the oscillation is
Speaker 2: over there, and the oscillation is further along, So it's
Speaker 2: sort of like that energy is moving through the field
Speaker 2: rather than just staying in place.
Speaker 1: Okay, now, let's say for an electron. Doesn't mean that
Speaker 1: the electron is physically like going up and down as
Speaker 1: it moves or as it's moving in a straight line.
Speaker 1: It's somehow undulating. What exactly is a traveling wave for
Speaker 1: a particle like the electron.
Speaker 2: Yeah, well, it sounds like you're trying to hold in
Speaker 2: your mind simultaneously the picture of an electron is a
Speaker 2: little particle that has a definite location, and you're trying
Speaker 2: to marry that with the idea of a wave. But
Speaker 2: instead just think about the electron as a fluctuation in
Speaker 2: the wave. And as we talked about recently, when you
Speaker 2: think about like how photons ripple, photons are not undulating,
Speaker 2: they're not moving side to side. What's changing along a
Speaker 2: straight line is the value of the field along that line.
Speaker 2: A fields pointing in one direction, and then another direction,
Speaker 2: and then a third direction. Because the photon field is
Speaker 2: actually a vector, it's not just a number, it's a direction.
Speaker 2: So for the electron, again, moving along a straight line,
Speaker 2: as an electron moves, what's changing is the value of
Speaker 2: the electron field along that line. It isn't like wiggle
Speaker 2: sideways in any way, except sometimes when we draw this
Speaker 2: on paper, we draw sideways wiggles to indicate the value
Speaker 2: of the field. In a physical sense, there's no sideways undulation.
Speaker 2: It's just like the numbers of the electron field are changing.
Speaker 2: The electron field is not as complicated as the photon
Speaker 2: field because it's a fermion and not a spin one
Speaker 2: boson like the photon is, which is a full vector.
Speaker 1: Well, just following what you said, which is that you know,
Speaker 1: like an electron has a standing wave like a standing ribble,
Speaker 1: and then it has a traveling wave. But you can
Speaker 1: also imagine a standing wave that's moving in a constant
Speaker 1: speed in a straight line that doesn't need a traveling wave.
Speaker 1: Or is this traveling wave basically a moving standing wave.
Speaker 2: Yeah, that's what a traveling wave is, and it maintains
Speaker 2: its shape, right. One of the cool things about particles
Speaker 2: is as they move through the universe, they maintain their energy.
Speaker 2: They don't like diffuse and spread out, right, because it's
Speaker 2: a minimum oscillation of this quantum field, so it can't
Speaker 2: go down to a lower value. You can't have like
Speaker 2: a half an electron than a quarter electron. So this
Speaker 2: shape maintains itself as it moves through the electron field.
Speaker 1: So then I wonder if maybe the question you're really
Speaker 1: asking here today is whether the standing wave of nutrino
Speaker 1: gets stretched out as the universe expands, like you don't
Speaker 1: even need a natrina to be moving. You can just
Speaker 1: have anatrino standing in space out there. And as the
Speaker 1: universe expands, does the neutrinos standing wave also expand?
Speaker 2: Like?
Speaker 1: Are those do the same question?
Speaker 2: They're not quite the same question, because now you're talking
Speaker 2: about particles at rest, and because the neutrino field and
Speaker 2: the electron field and everything else that has mass has
Speaker 2: a specific frequency at which it can oscillate that isn't
Speaker 2: affected as the universe expands. What is directly affected by
Speaker 2: the expansion of the universe is not the frequency, but
Speaker 2: the wavelength that's always stretched out for all particles. For photons,
Speaker 2: which only have a traveling wave, the wavelength and the
Speaker 2: frequency have a very simple relationship. Longer wavelength, lower frequency.
Speaker 2: For electrons, which also have mass, it works in the
Speaker 2: same direction, but the relationship is more complicated because of
Speaker 2: the mass part. The mass part isn't affected directly by
Speaker 2: the wavelength, but the expansion still influences the overall frequency,
Speaker 2: and that frequency is also affected by the mass part.
Speaker 2: So as the universe expands, it stretches out the wavelength,
Speaker 2: which does in the end lower the electrons frequency. But
Speaker 2: the math is a little bit different. There's a minimum
Speaker 2: frequency for the electrons that they can't lose because they
Speaker 2: still have mass. This effect really only changes how particles
Speaker 2: move through the universe, not how much mass they have.
Speaker 1: All Right, So, then if we're asking the question, do
Speaker 1: neutrinos change wavelengths as the universe expands? What exactly does
Speaker 1: that mean? Does that mean that it's standing wave gets
Speaker 1: stretched or it's traveling wave gets thressed. But then you
Speaker 1: just said that the traveling wave is just as standing
Speaker 1: wave moving in a straight line, So I guess I'm confused.
Speaker 1: What do you mean by a neutrino's wavelength getting stretched
Speaker 1: by this expension.
Speaker 2: There's two different kinds of things that these fields can do, right.
Speaker 2: They can oscillate in place, some of them, and they
Speaker 2: can also oscillate in a traveling wave motion. And so
Speaker 2: for those of you who want to know more about
Speaker 2: the technicality details of that, go back and check out
Speaker 2: our episodes at Matt Strassler about exactly what that means.
Speaker 2: For the purposes of today's episode, we just need to
Speaker 2: think about the motion of those particles, the traveling waves,
Speaker 2: and the frequency of those particles as they're moving, and
Speaker 2: for photons, for example, we know that they get stretched
Speaker 2: out if you see something being emitted from a high
Speaker 2: velocity object, or if the universe is expanding between you
Speaker 2: and them. Really the same effect described in two ways.
Speaker 2: And so the question today is like, does that also
Speaker 2: apply to neutrinos, which we know are generated by stars
Speaker 2: far away and fly to us across space. Does the
Speaker 2: expansion of space also affect them? And the answer is yes, absolutely,
Speaker 2: Their wavelength is also shifted as they move through space
Speaker 2: because everything is just a ripple in these fields, and
Speaker 2: other than the mass ripple, which is controlled by some
Speaker 2: fundamental properties of the field, the velocity of it reflects
Speaker 2: the energy of that particle and that decreases as space expands.
Speaker 1: So what does that mean for a particle like the neutrino?
Speaker 1: Does it? Is it going to look different or is
Speaker 1: going to end up looking or being a different particle
Speaker 1: when it reaches the other side of the universe.
Speaker 2: Yeah, it means that it has less energy, right, It
Speaker 2: doesn't change its fundamental nature. It still has the same mass,
Speaker 2: just like an electron will always have the same mass.
Speaker 2: It still looks the same, It still looks the same,
Speaker 2: but it has less energy. The same way a photon does. Right,
Speaker 2: when a photon gets red shifted, it has less energy
Speaker 2: than it did before. When the universe expands, photons lose energy,
Speaker 2: which is sort of fascinating. Then violets our intuition that
Speaker 2: like energy should be conserved, but it isn't for photons, right,
Speaker 2: photons get lower energy. We have a great example of that,
Speaker 2: which is the cosmic microwave background radiation, which is very
Speaker 2: very red. Photons they're down in the microwave, but when
Speaker 2: they were emitted back in the very early universe, they
Speaker 2: were very high energy because they were emitted from a
Speaker 2: super duper hot, bright gas. And as the universe has expanded,
Speaker 2: they've been stretched out to very low energies. So the
Speaker 2: same thing happens to neutrinos and electrons and every other
Speaker 2: particle moving through the universe as the universe expands. Or equivalently, again,
Speaker 2: if you emitted from something moving at high speed away
Speaker 2: from you, and those particles are red shifted to lower energy,
Speaker 2: same mass, but lower kinetic energy.
Speaker 1: So wait, wait, are you just basically saying that the
Speaker 1: expansion of the universe slows down neutrinos.
Speaker 2: Yes, absolutely it does, and it's a really interesting point,
Speaker 2: because photons don't get slower, right, They just get lower
Speaker 2: energy at the same velocity, because photons are always moving
Speaker 2: at the speed of light. But neutrinos have mass, and
Speaker 2: so as they get lower energy, they do get slower.
Speaker 2: They're basically always traveling at almost the speed of light
Speaker 2: anyway because their mass is so small. But yes, technically
Speaker 2: they do get slower as their wavelength gets longer.
Speaker 1: Right, right, So then what's the difference between neutrino that
Speaker 1: I detegged from the Sun which is really close to us,
Speaker 1: and in neutrina that is emitted by the Sun really
Speaker 1: far away that gets to us after billions of years
Speaker 1: and it's been going through expanding space when it gets
Speaker 1: to me and I compare to the nutrina from our sun.
Speaker 1: Do they look the same? It's just that one of
Speaker 1: them is going faster than the other. Or are they
Speaker 1: going to look different?
Speaker 2: Well, each individual neutrino will not look different, but the
Speaker 2: spectrum of them will. So if you measure the energy
Speaker 2: of all the neutrinos from the Sun you make a
Speaker 2: graph of that, it's going to have some distribution. And
Speaker 2: then if you measure the energies of neutrinos from distant stars,
Speaker 2: stars that are really far away from us, where the
Speaker 2: universes expanded between us and them, those will have a
Speaker 2: lower energy distribution, exactly the same way is for photons.
Speaker 2: Photons from distant stars are shifted down lower in energy.
Speaker 2: Neutrino energy distribution should also be shifted down.
Speaker 1: Shoot, so they'll just be slower.
Speaker 2: Yeah.
Speaker 1: So I mean basically you can ask this question of anything.
Speaker 1: Any particle doesn't have to be neutrinos.
Speaker 2: Yeah.
Speaker 1: So, like an electron that is shot at us from
Speaker 1: really far away, by the time it gets us, it's
Speaker 1: going to be going at a slower speed.
Speaker 2: Yeah, or as we say, colder or redder. But yeah,
Speaker 2: fundamentally it's a lower velocity.
Speaker 1: Right. I mean you can say smeliar too, but I
Speaker 1: think the practical says you would just say it's slower.
Speaker 2: Yeah, it's definitely slower as less kinetic energy.
Speaker 1: Ah. Wait, so that means like if I was Superman,
Speaker 1: or if I was shot out of a cannon from
Speaker 1: a space station in orbit around Earth and I was
Speaker 1: flying through space, nothing gets in my way, no dust, nothing,
Speaker 1: I would still slow down eventually to a standstill.
Speaker 2: Depends on what you mean by standstill, because there's no
Speaker 2: absolute velocity in space, right, And I think that this
Speaker 2: slow down is a relative effect, so you would as
Speaker 2: symptotically approach zero velocity relative to some observer. But yes,
Speaker 2: things do get slowed down as the universe expands.
Speaker 1: Yeah, Like initially I would see planets whizzing by me,
Speaker 1: but then eventually at the end of the universe, planets
Speaker 1: would not be whizzing by me. That would be going
Speaker 1: slower relative to them.
Speaker 2: Yeah, I remember that this is a relative effect, right.
Speaker 2: One person will see a photon red shifted, somebody else
Speaker 2: see that same photon not red shifted. So this is
Speaker 2: a frame dependent effect.
Speaker 1: Right, But it's basically as I just describe. But initially
Speaker 1: things will whizzing by me, but eventually the things will
Speaker 1: be going by me slower.
Speaker 2: I'm not one hundred percent sure about the thrust of
Speaker 2: Superman here, but if he only has an initial velocity
Speaker 2: and that he's coasting.
Speaker 1: Forget I said, Superman. That's why I shipped it to
Speaker 1: a cannon, Like if I get shot out of a cannon. Now,
Speaker 1: does that mean that our whole episode here today? Instead
Speaker 1: of calling it can Neutrina's be red shifted if they
Speaker 1: we could have just called it. Do things in space
Speaker 1: get slowed down by the expansion of the universe?
Speaker 2: And the answer is yes, except for photons. Photons get
Speaker 2: red shifted, but they don't get slowed down because they
Speaker 2: have no mass. They're always traveling at the speed of light, right.
Speaker 1: But the light is not a thing. Basically, does anything
Speaker 1: with mass things matter gets slowed down as the universe expands,
Speaker 1: and it seems like answers yes.
Speaker 2: The answer is yes, but it's very difficult to see
Speaker 2: because in order to detect that, to do the experiment
Speaker 2: I mentioned, you'd need to have a source of neutrinos
Speaker 2: with very specific energies. And because we see so few
Speaker 2: neutrinos it's so difficult to pin them down to observe them.
Speaker 2: We can't actually do the experiment that I talked about earlier,
Speaker 2: like looking at the distribution of energies of neutrinos from
Speaker 2: a distant star. And also stars don't emit neutrinos a
Speaker 2: very specific energies the way they do photons, right, and
Speaker 2: so we don't have like spectral lines of neutrinos that
Speaker 2: we can use to measure these redshifts. But the only
Speaker 2: thing we can do is look for the cosmic neutrino background,
Speaker 2: which is similar to the cosmic microwave background. We think
Speaker 2: there were a bunch of neutrinos created in the early universe,
Speaker 2: very high speed, very high energy, and the expansion of
Speaker 2: space has cooled them all down to much slower moving neutrinos,
Speaker 2: still nearly the speed of light, but much slower moving.
Speaker 2: If we can measure the cosmic neutrino background and basically
Speaker 2: measure their velocity their energy distribution, that would be direct
Speaker 2: evidence of seeing particles slowed down by the expansion of
Speaker 2: the universe, or red shifted neutrinos. But we haven't seen
Speaker 2: them yet.
Speaker 1: But I wonder if there's maybe an easier experiment you
Speaker 1: can do. Can you look at other particles that are
Speaker 1: getting to us from far away. Can we just tell
Speaker 1: that they're somehow slower than the particles that are being
Speaker 1: sent to us from closer sources, or is there no
Speaker 1: such thing.
Speaker 2: It's difficult because we're talking about particles, and particles don't
Speaker 2: make it through the universe the same way photons do,
Speaker 2: so it's harder to attribute individual particles to like specific
Speaker 2: extragalactic sources and we're talking about like electrons or protons
Speaker 2: from another galaxy with a very small number of those.
Speaker 2: Those are very high energy cosmic rays, and we have
Speaker 2: lots of questions about what's even making those. So no,
Speaker 2: we don't have a good sample of electrons or protons
Speaker 2: from other galaxies to do that kind of.
Speaker 1: Experiment with, or would you even need to do the
Speaker 1: experiment just because that's what relativity says it's going to happen. Right,
Speaker 1: things are going to slow down as you move through
Speaker 1: expanding space, and we already know that a lot of
Speaker 1: relativity is true, So why wouldn't it work for this case.
Speaker 2: Yeah, we have no reason to think it wouldn't, but
Speaker 2: it's always a good idea to double check because there
Speaker 2: could be a surprise. It could be one of those
Speaker 2: things where we're like, yeah, that's totally going to be boring,
Speaker 2: go out and do it, yon yon yon, Oh my gosh,
Speaker 2: what and the universe tells us something new. So we
Speaker 2: strongly suspect and believe that this is what's happening. But
Speaker 2: you always got to check the stuff.
Speaker 1: Right, Right, you're saying it's a good idea to shoot
Speaker 1: Joorge out of a cannon, space.
Speaker 2: Good idea aboutity? I don't know, but we could learn
Speaker 2: a lot.
Speaker 1: Yeah, yeah, although it would be hard because you know,
Speaker 1: to make it a perfect experiment. As I'm flying through space,
Speaker 1: I can't eject any matter because it would ruin the experiment.
Speaker 2: Right, mm hmmm yeah.
Speaker 1: So if you I see where you're going with just
Speaker 1: trying to bring it back around or down, as the
Speaker 1: case may be. So if we do an experiment, uh no,
Speaker 1: the person can fart fart right.
Speaker 2: That's right. You got to hold it in, hold it in.
Speaker 1: Hold it in, hold it in for billions of years,
Speaker 1: hold it in for I think I feel like like
Speaker 1: that just describes my job here in the podcast, holding
Speaker 1: it in or not hold it in, hold it in.
Speaker 1: I don't think you've been holding it together.
Speaker 2: You've been letting it all out on this episode.
Speaker 1: Are you saying I've been I've been stinking it up?
Speaker 1: What you're saying with far jokes, you're like you said
Speaker 1: it or on me? All right? Well, I guess just
Speaker 1: to recap the question, we started asking, can Neutrino's get
Speaker 1: red shifted right off the gate? The answers no, because
Speaker 1: I think most people would agree redshifting only applies to
Speaker 1: electromagnetic light, as some of our listeners pointed out.
Speaker 2: Where most people notably doesn't include me. But yes, go ahead, Oh.
Speaker 1: That's why it's most But if you have a question,
Speaker 1: the wavelength of the neutrino get stretched out by explaining universe,
Speaker 1: and the answers yes, in fact, it happens to all
Speaker 1: particles with mass, right, And really what that means doesn't
Speaker 1: mean that it somehow changes the neutrina It just means
Speaker 1: that it slows down.
Speaker 2: Yeah.
Speaker 1: So really the question is do particles get slowed down
Speaker 1: by the expansion of the universe, And you're saying the
Speaker 1: answers yes, because that's what relativity tells us.
Speaker 2: Yeah, all particles have their wavelength extended when the universe expands.
Speaker 2: For photons, that doesn't mean a change in the velocity,
Speaker 2: but for particles with mass it does.
Speaker 1: All right, Well, it was a circuitous path, but we
Speaker 1: got here. Now, what happens to a fart with the
Speaker 1: expansion of the universe. It also slows down, right.
Speaker 2: It slows down, But the stink is invariant like mass.
Speaker 2: It's a fundamental quality of the fart. Something the fart
Speaker 2: field can do.
Speaker 1: Each individual particle. Its stinkiness does not decrease because its
Speaker 1: nature doesn't change.
Speaker 2: I prefer to think about farts it's waves as they
Speaker 2: sort of pass over you, rather than think about the
Speaker 2: individual fart particles than where they came.
Speaker 1: From sticking in your nose. Yeah, nobody wants to think
Speaker 1: about that exactly. Yeah, all right, well, I think another
Speaker 1: lesson about how crazy this universe is and how big
Speaker 1: it is, and how the effects of it getting even bigger.
Speaker 1: What's that going to do to everything in it?
Speaker 2: That's right, And our intuition for what happens to photons
Speaker 2: sometimes does apply to other particles. Because they have mass,
Speaker 2: they follow slightly different rules.
Speaker 1: All right, We hope you enjoyed that. Thanks for joining us.
Speaker 1: See you next time.
Speaker 2: For more science and curiosity, come find us on social media,
Speaker 2: where we answer questions and post videos. We're on Twitter, This, Org, Insta,
Speaker 2: and now TikTok. Thanks for listening, and remember that Daniel
Speaker 2: and Jorge Explain the Universe is a production of iHeartRadio.
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