Do neutrinos get redshifted?

Daniel and Jorge talk about what happens to neutrinos as the Universe expands.

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Episode Transcript

Speaker 1 (00:08):
Hey, Daniel, is it true that everything gets stretched out
as the universe expands?

Speaker 2 (00:13):
That's what the physics tells us so far.

Speaker 1 (00:15):
Yeah, so is that why I feel so tired all
the time because I'm getting stretched thin?

Speaker 2 (00:21):
You know? I think physics is always your first scapegoat, isn't.

Speaker 1 (00:24):
It, But this time it's kind of true, right. I mean,
each day my gym gets a little bit further from
my house, right, so it is making it harder. It's
stained shape.

Speaker 2 (00:35):
I mean, physics is telling you that the universe is
getting stretched out, but it's not physics fault. Don't blame
the messenger.

Speaker 1 (00:41):
Oh well, he could have kept quiet, maybe we wouldn't
have noticed.

Speaker 2 (00:46):
And that's the end of the podcast. Physics keeps quiet.

Speaker 1 (00:51):
That's a bit of a stretch, though. Hi am for Hey.
I'm a cartoonist and the author of Oliver's Great Big Universe.

Speaker 2 (01:11):
Hi, I'm Daniel. I'm a particle physicist and a professor
at UC Irvine, and I want to hear the message
from physics, whether it's good news or bad news.

Speaker 1 (01:19):
Really, you want to know if like the Earth is
about to blow up, or if a supernova is about
to engulf us in flames.

Speaker 2 (01:26):
I definitely want to know that. But that's not bad news.

Speaker 1 (01:30):
Bad news for me and for the human race unless
you know something we don't know, Daniel.

Speaker 2 (01:37):
No, I'm thinking much bigger.

Speaker 3 (01:38):
You know.

Speaker 2 (01:38):
Cosmic bad news is stuff like, oh, the universe is
inaccessible to you, or there's lots of dimensions to the
universe we can never see, or the universe will never
be understood. That's the kind of philosophically cosmic bad news
I'm afraid of.

Speaker 1 (01:52):
Oh my goodness, Really that keeps you up at night.

Speaker 2 (01:55):
Absolutely, Yeah. This whole project of physics is based on
the assumption that the universe follows laws and then we
can figure them out somehow with our tiny little brains.
Who knows if that's even true.

Speaker 1 (02:06):
Well, so, what's the physics version of a horror movie?
Just some scientists coming up and tell you you're never
gonna know anything.

Speaker 2 (02:17):
No, Now, the physics horror movie is the aliens arrive,
they explain the universe to us, and we just can't
get it. We're like, huh, what try again and it
just never works.

Speaker 1 (02:29):
Or the aliens come and then you ask them what
are the secrets of the universe? And they go, I'm
not gonna tell you see you later, No.

Speaker 2 (02:41):
Exactly they want serve man, but.

Speaker 1 (02:44):
Anyways, welcome to our podcast Daniel and Horra Explain the Universe,
a production of iHeartRadio in.

Speaker 2 (02:49):
Which we die bravely into the task of explaining the universe,
whether or not it is explainable or understandable, we think
it's at least worth trying to make sense of everything
that's happening out there in the cosmos, from tiny little
particles screaming through space nearly the speed of light, to
massive black holes gobbling up everything that they can, all

(03:11):
the way from the tiniest particles to the largest phenomena.
We try our best to understand the universe, to wrangle
it into some mathematical sense, and to explain all of
that to you.

Speaker 1 (03:21):
That's right. We ponder the entire universe, and we wonder
what it would be like to be out there in space,
traveling the far reaches of the cosmos, maybe getting stretched
out by relativity or by the expansion of the universe,
and hopefully expanding and stretching your mind in the process.

Speaker 2 (03:38):
The whole project of understanding the universe means fitting it
into your skull, means making it makes sense. The first
step of that is to figure out what the laws
are of physics, what are the rules that everything is following,
and then thinking about whether that clicks together, what happens
when I apply those rules over here or over there?
Are there really universal? How does that connect with this
other idea? I have a lot of physics is just

(04:01):
trying to stick these puzzle pieces together right right?

Speaker 1 (04:04):
So then the engineer is going to be like, hey,
can we break that rule? Can we push push the
limit there? What's going to happen if we try?

Speaker 2 (04:12):
The bridge is going to collapse. That's what's going to happen.
And that's why I'm glad I'm not an engineer.

Speaker 1 (04:19):
MM, because you're not building bridges, you're just burning them.

Speaker 2 (04:23):
I'm burning mathematical bridges. But when I make a mistake,
nobody dies.

Speaker 1 (04:27):
Oh really, it seems kind of dangerous to be near
a particle collider. I mean there's a lot of security
around those.

Speaker 2 (04:35):
Yeah, that's true, and that's why we rely on accelerator
physicists to build and operate those things.

Speaker 1 (04:41):
That's why they don't allow me down there.

Speaker 2 (04:43):
Yeah, probably not, But we aren't doing our best to
develop the most universal laws of physics, we can ones
that apply to everything under the Sun, including all the
different kinds of particles that come to us from the Sun.

Speaker 1 (04:55):
Yeah, because the Sun is constantly spewing out not just
a lot of light and warmth and energy for us
to joy and to use, but also it's also spewed
out a ton of other things, particles and uh, lots
of different kinds of radiation.

Speaker 2 (05:07):
Right, that's right. All the stars out there in the
universe are pumping out photons, but also a solar wind
made of all different kinds of particles protons, electrons, neutrinos.
And we talk a lot about what happens to those
photons as they move through an expanding universe from galaxies
moving away from us at very high recession velocities, But
we don't as often apply those same questions, those same

(05:30):
rules to the other particles being emitted by those stars.

Speaker 1 (05:34):
So today on the podcast will be tagling the question
ken neutrinos get red shifted? Now, Daniel, when you talk
about the solar wind, do you say wind in the
sense of like a nice breezy summer wind, or do
you mean it like like a fart, like the sun

(05:55):
breaks wind.

Speaker 2 (05:58):
Kind of neither of those? Are those the only two options?
Can I get an option C? Please? Nobody's ever out
there in space like hmm, I'd like some more solar wind, please.
I'm overheating. That's never happened.

Speaker 1 (06:13):
Yeah, it's not refreshing out there in space.

Speaker 2 (06:15):
No, I guess it. Yeah, I guess if I have
to pick between those two. Solar wind is more like
a fart, because it's kind of unpleasant and dangerous and
you want to be as far away from it as possible.

Speaker 1 (06:25):
Right, Yeah, it stinky as well.

Speaker 2 (06:31):
You know, people joke about what space smells like, and
it is partially due to the solar wind, but it's
also just due to trace other particles that are out
there that like adhere to the outside of a space
suit on a spacewalk, which then volatilize as you come
back inside. People say it smells like barbecue out there
in space.

Speaker 1 (06:49):
Whoa, and not just because they're cooking in that radiation.

Speaker 2 (06:53):
Yeah, that's right now. If your fart's smelled like barbecue,
then I don't know. I guess you'd be more popular
at parties.

Speaker 1 (07:00):
If you fart on the space station. You would not
be popular up there. It's a pretty closed environment, but
it must happen. Sounds like a podcast episodedan.

Speaker 2 (07:10):
Sounds like a question for Zach and Kelly, since they're
an expert in everything unpleasant in space. I'll ask her
next time she's on.

Speaker 1 (07:17):
There You Go, There you go. What are the physics
of farts in space? Like how quickly would it dissipate?
Or like if you're out there and you smell without
a helmet, would you die first? Or would you smell
the fart first?

Speaker 2 (07:30):
Or could a really stinky fart cause an international incident
on the space station which leads to World War three?
In the end of humanity. You've heard of the butterfly effect.
Now we're talking about the space fart effect.

Speaker 1 (07:40):
Wow, jeez, it's a dangerous place space.

Speaker 2 (07:46):
Now bring this back to neutrinos.

Speaker 1 (07:49):
Is it like in space no one can hear you fart?

Speaker 2 (07:51):
Or what if your farts were all neutrinos? Here we go,
I'm bringing this back to the topic.

Speaker 1 (07:57):
Oh you're trying to bring it all right? Right? Smell
that also or do they have.

Speaker 2 (08:02):
A neutral smell? M?

Speaker 1 (08:04):
Yeah.

Speaker 2 (08:04):
Another question is whether neutrinos have a color and whether
you could consider them being red shifted or blue shifted?

Speaker 1 (08:11):
All right?

Speaker 2 (08:12):
All right?

Speaker 1 (08:12):
I can tell you're trying to get us back on
track here.

Speaker 2 (08:15):
This is a physics podcast, not a fart podcast.

Speaker 1 (08:18):
After all, But farts are physical. I dang it, sorry,
are you trying to ignore part of the physical universe?

Speaker 2 (08:26):
I retract that comment, and I respectfully request we get
back on track.

Speaker 1 (08:32):
So, yeah, are neutrino's parts of the sun.

Speaker 2 (08:36):
That's the question today, right, The question is whether neutrinos
can get red shifted the way we know that photons.

Speaker 1 (08:42):
Can, right right, all right, all right, Yeah, it's an
interesting question. Can I Natrina get red shifted? Because you know,
the word red shifted we usually applied to light, not neutrinos.

Speaker 2 (08:56):
Yeah, that's right. But if these laws are universal, if
the same rules apply to everything, then you can ask
the question, and this is what some listeners have asked me,
whether the same rules apply to neutrinos from distant stars
as they do two photons from those stars?

Speaker 1 (09:12):
Well, does that mean that the rules also apply to farts?
Can Farce get redshift? All right?

Speaker 2 (09:23):
All right?

Speaker 1 (09:25):
Well, as usually, when we're wondering how many people out
there had thought about Nutrina's and whether or not they
can get red shifted.

Speaker 2 (09:33):
Thanks very much to everybody who answers questions for this
segment of the podcast. If you'd like to hear your
voice for a future episode, please don't be shy. Write
to me two questions at Danielandjorge dot com.

Speaker 1 (09:43):
So think about it for a minute. Do you think
neutrinos can get red shifted? Here's what people had to say.

Speaker 2 (09:50):
No, they're not an electron back that spectrum.

Speaker 1 (09:53):
I think yes, neutrinos have la a proton away from
and if there's an ext arting body coming from there,
the camera just shifted, I think.

Speaker 4 (10:03):
I assume this is to do with quantum mechanics and
how particles have a frequency.

Speaker 2 (10:11):
What rechhift.

Speaker 4 (10:12):
That just means like the frequency gets stretched, I think,
So I guess yeah, it can happen. I don't know
how or why.

Speaker 3 (10:19):
I don't see why not, but I know the problem
with them is that they're just so hard to see.
They seem to pass through just about everything, and I
know there's a few different kinds. So I guess yes
they could, But how would you detect that? I'm not sure?

Speaker 1 (10:37):
All right, Well, some pretty interesting answers sort of in
the range of why not. Who knows?

Speaker 2 (10:45):
Yeah, some people saying yeah, they're a particle like everything else.
Other people saying no, that only applies to photons and
things in the electromagnetic spectrum.

Speaker 1 (10:53):
Hmmm, all right, well, let's dig into it, Daniel. Let's
recap first of all, what is a neutrino.

Speaker 2 (11:00):
Neutrinos are some of the weirdest and most fascinating particles
in the universe because they're sort of like an extreme
example of what the universe can do. You know, most
of the particles we're familiar with, quarks and electrons feel
a bunch of forces. Quarks feel the strong force and
the electromagnetic force and the weak force. Electrons feel only

(11:20):
the electromagnetic force and the weak force. They don't feel
the strong force. They're neutral in the strong force. Neutrinos
are like one step further. They're saying, hey, I'm going
to be neutral also in electromagnetism. I'm going to only
feel the weak force. So we have examples of particles
that feel all three quantum forces. The quarks an example
of particles that feel two of the quantum forces. Electrons

(11:42):
feel electromagnetism and the weak force, and then an example
of a particle that feels only one of those forces,
just the weakest one, the weak force. So neutrinos are
particles that are out there in the universe that we
can just baurreally sense, barely interact with, because the only
way they interact with us is through the way weakest
force we know about, right.

Speaker 1 (12:02):
Right, But they can still exist, right like, They're still
made out of real energy in this universe, so you
can make them. They just sort of ignore us and
won't talk to us in the ways that most other
particles talk to us.

Speaker 2 (12:13):
Yeah, exactly. And remember that all of these particles are
just ripples in fields, and these fields are all on
top of each other. The way to think about these
interactions is whether the fields can transfer energy back and forth.
Then neutrino fields couple very very weakly to all these
other fields. So it's sort of like having another universe
on top of us that we can just barely interact with.
Even if all sorts of crazy stuff is going on,

(12:35):
even if there's huge numbers of them and enormous amounts
of mass and energy and velocity, we just barely sense it.
So it's almost like having a parallel universe. Right on
top of us. And you know, the even more extreme
would be dark matter. Dark matter we think might be
a particle that feels none of these forces, and so
it's on top of us, but we only sense it gravitationally.

(12:56):
So neutrino is like almost the extreme limit of that.

Speaker 3 (12:59):
Right.

Speaker 2 (13:00):
They are energy, they're part of our universe, and they
even have mass. We know the neutrinos are not like
photons and other massive particles. There is a little bit
of stuff to them, an incredibly tiny amount of stuff
to these neutrinos.

Speaker 1 (13:13):
And now, do neutrinos feel gravity? Do we know that.

Speaker 2 (13:17):
Everything with energy feels gravity? Absolutely? Gravity is universal. You
can't have energy and not feel gravity because remember gravity.

Speaker 1 (13:25):
But have we seen it that we see neutrinos like
bend by the path of the massive things.

Speaker 2 (13:32):
Oh yeah, great question. We can't observe neutrinos well enough
to see their path bending, but we know something about
the massive neutrinos and the number of neutrinos, and that
affects the overall curvature of space and time, and we
can see their impact in the early universe and its curvature.
So we know the neutrinos have energy, and that energy
does contribute to the curvature of space time. Yeah. M,

(13:54):
but we haven't seen one bend to gravity, have we
We have not seen them move in a curved path. No,
but we know that their energy contributes to the curvature.

Speaker 1 (14:03):
Hmm. Interesting. And is there sort of a perspective on
why some fields or why some particles interact with some
forces and not others, or is just sort of how
the universe was made or how these particles turn out
to be, you know, like, is there is it like
a parameter and the equations that is just kind of
random or what.

Speaker 2 (14:23):
Yeah, it's a great question. Is there an explanation or
is it just descriptive? Currently it's mostly descriptive. Like we
say that quarks have a strong charge and electrons don't
because we see that electrons ignore colored fields. We say
that neutrinos don't have an electric charge because we see
that they don't get accelerated by electric fields. So that's

(14:45):
sort of what we mean by that. It's just a
description of what we see in these particles. Do we
do notice a bunch of patterns, like all the quarks
have the same kinds of charges and electrons and muons
and towels all have the same electric charge and this
kind of stuff. So there definitely some patterns and some
struct sure there, but we definitely do not understand it.
It's just descriptive. It might be explained by some future

(15:06):
theory physics that tells us what all these particles are
made out of, some quiz bits and what knots that
have fundamental pieces to them, and when you put them
together in certain ways, or they interact or oscillate in
certain ways, you get the particles that we see with
their various properties. But currently we can't explain it. We're
sort of at the stage of the periodic table one
hundred and fifty years ago where we see all these

(15:26):
elements with these different properties, but we don't understand why
they have that nature.

Speaker 1 (15:32):
And you mentioned there's sort of like ghostly particles, but
I feel like that maybe understates because there's a huge
amount of neutrino's going through us right now. Right there's
like bazillions of them going through our bodies as we speak.

Speaker 2 (15:46):
Yeah, that's right. Neutrinos hardly interact with us, but there's
no shortage of them because the Sun produces an incredible
number of neutrinos. Every fusion reaction produces neutrinos, and it
also produces photons, but those photons are mostly absorbed by
the Sun, Like the Sun is opaque to most of
the photons it produces, so those photons are reabsorbed by

(16:07):
the Sun and it generally heats it up. People talk
about the photons we see on Earth as having been
produced in fusion. Technically that's not really accurate. The photons
produced infusion heat up the Sun and then the Sun
glows as a black body or because its atmosphere is hot.
Those are the photons we see, but the neutrinos are different.
The Sun is transparent to neutrinos the way basically everything

(16:29):
is transparent to neutrinos. So if a neutrino is made
at the heart of the Sun, it flies out and
goes through the Earth and we can observe it directly
from that fusion process. And there's a huge number of
them passing through our bodies instead of a billion neutrinos
per square centimeter per second.

Speaker 1 (16:46):
Yeah, it's huge, and none of them are interacting with
us or are they a little bit maybe a little
bit dangerous, Like are some of them maybe knocking on
some of my DNA.

Speaker 2 (16:55):
Maybe some of them are definitely interacting with you, but
it's a tiny, tiny number. To give you a sense
of it, like we have many fewer muons passing through
our body every second, like one per square centimeter per minute,
but every single one of those is interacting with your body.
Like when a muon hits your body, it's like a
tiny bullet. It's hitting those atoms and it's depositing energy.

(17:16):
Mostly they're not doing damage, they don't hit anything important,
and you're fine because they're just these tiny bullets. But
every single muon does interact with your body. But for neutrinos,
most of them do not interact with you. So for scale,
the neutrinos were discovered in an enormous tank underground. We're
talking about like thousands and thousands and thousands of liters
of liquid run for a year to see like one

(17:39):
neutrino bounce off of one of those particles. So neutrino
interactions with our kind of matter are extraordinarily rare. So yes,
they are interacting with us, because it's a huge number,
but it's a tiny, tiny fraction of the neutrinos that
are created and a tiny overall number of interactions compared
to like the muons and other particles that are interacting
with you.

Speaker 1 (18:00):
Now, are these the ones that you can see in
some science museums where they have like a little chamber
of water vapor and you see the traces. Are these
neutrinos or am I thinking of something else?

Speaker 2 (18:08):
Those are mostly muons. Yeah, cloud chambers which you can
see in science museums, and you can actually build at
home in your garage without too much trouble. I got
an email from a listener who was inspired by a
comment I made a year ago, and she and her
son built a cloud chamber in her garage and they
saw muon tracks. So those are mostly muons. Neutrinos. You'd
need to build an enormous underground chamber of like xenon

(18:30):
or something in order to see one neutrino, and you
wouldn't see a track. You'd see the neutrino bumping into
a normal particle and you'd see the recoil of that particle.
You can never really see a track of neutrinos because
that would require multiple interactions of the same neutrino, which
would be astronomically unlikely. You only ever see like one interaction,
one push from a neutrino.

Speaker 1 (18:51):
Meons go through the roof of your garage.

Speaker 2 (18:53):
Oh yeah, muons can go through rock. Also, you can
see muons when you're underground. That's why they build the
neutrino detectors so deep underground to shield themselves from all
the muons which can penetrate through meters and meters of rock.

Speaker 1 (19:06):
Mmm. Now, and neutrinos are not just ghostly, but they're
super duper fast, right, Because they're so little mass, they're
going almost at the speed of light all the time.

Speaker 2 (19:16):
Yeah. Neutrinos have a tiny, tiny mass, much smaller than
even electrons, which means when they're produced, if they have
even a tiny smidge of energy, they're basically going at
the speed of light, very very close to the speed
of light.

Speaker 1 (19:28):
Can you slow them down? Like, could you ever hold
innutrino in your hand?

Speaker 2 (19:32):
Yeah, you could slow neutrinos down. Because they do have mass,
they can exist at zero velocity. Unlike photons. Photons, there
is nothing to them if they have no velocity because
they are just velocity. But if you slow a neutrino down,
it has mass, right, mass means rest energy, So you
can be in the same reference frame as a neutrino.
You could like catch up to a neutrino and look

(19:53):
at it, or equivalently, you could slow a neutrino down
and hold it in your hand.

Speaker 1 (19:57):
Yeah, m pretty cool. All right, Well, now the question
is do neutrinos get red shifted as the universe expands?
And so let's get into what red shifting is. Can
it happen for neutrinas and does it make them smell
like farts or maybe not? We maybe we won't get
to that in time, but let's give it a try.
We'll dig into that, but first let's take a quick break.

(20:31):
All right, we're talking about nutrinas and whether they can
get red shifted as the universe expands, So those are
all pretty interesting concept there in one sentence, let's start
with red shifting.

Speaker 2 (20:43):
What is red shifting and a sentence. Red shifting is
when a wave gets a longer frequency because it's being
omitted by something that's moving away from you. So all
waves have frequency, like sound waves, the sounds you're hearing
from us have certain frequencies, frequencies and higher frequencies and
all that kind of stuff. We can describe sound as waves,

(21:04):
and we can measure the number of times the wave
waves per second. That's its frequency, just inversely proportional to
its wavelength, So longer wavelengths lower frequency.

Speaker 1 (21:16):
It sounded like you're trying to hit like a high
scene and a low S there, Daniel.

Speaker 2 (21:20):
That's sort of like a very low CE and a
less low C. That's all I'm capable of.

Speaker 1 (21:26):
Low. You can't do falsetto.

Speaker 2 (21:28):
That was my false Oh that was you. I think
I think you can do better. You're I'm gonna rely
on our sound editor here, Corey. Can you make this
sound like a high se.

Speaker 1 (21:41):
Just get a healum balloon there. You don't need.

Speaker 2 (21:43):
Special sects, Chipmunk. Daniel, Yeah, I.

Speaker 1 (21:46):
Think I've seen a video of Morgan Freeman red shifting
his voice or blue shifting his voice with a healum balloon.

Speaker 2 (21:53):
That's amazing.

Speaker 1 (21:54):
So red shifting is and whenever any kind of wave
gets stretched out basically right, it becomes a low lower frequency,
which means bigger wavelengths.

Speaker 2 (22:02):
Yeah, and shift there just tells us that we're changing something.
And red shift means we're changing it to be more red.
And red is on the long wavelength low frequency end
of the visible spectrum. So when we say we're getting
longer wavelengths or lower frequency, we talk about red shifting,
and the opposite is blue shifting. If you're making something

(22:22):
higher frequency or shorter wavelengths, you're making it blue er.
So red shifting just means you're extending the wavelength, you're
lowering the frequency, right.

Speaker 1 (22:31):
Right, Although I have to say, I feel like you're
kind of cheating a little bit here because I don't
think I've ever heard anyone used to phrase red shifting
or blue shifting when it comes to anything except light waves. Like,
nobody ever says, can you give me a blue shifted
C note or a red shifted D note? Do you

(22:52):
know what I mean?

Speaker 2 (22:53):
Yeah, that's true. We apply red shifting mostly to astronomical objects,
and mostly astronomical stuff we see with photon, so that's
why it's applied there. But you know, if a police
car is passing by you, as it's driving towards you,
the wavelengths are shortened, and as it's driving away from you,
the wavelengths are lengthened, and so you could call that
blue shifting and red shifting in.

Speaker 1 (23:14):
That case we call it the Doppler effect.

Speaker 2 (23:15):
Right, yeah, exactly, the Doppler effect.

Speaker 1 (23:18):
No, he calls it the red shifting or blue shift.

Speaker 2 (23:20):
But police cars have red and blue lights, so maybe
somehow I don't know.

Speaker 1 (23:25):
Yeah, yeah, yeah, I figure if I create a if
you're cheating, Danieler, come on.

Speaker 2 (23:30):
I'm just trying to throw a bunch of random ideas
at you to distract you from the fact that you're
right about this.

Speaker 1 (23:37):
Well, I think what you're trying to get at is that,
you know, anything with a wave, it can get stretched
out or or it can get shortened, right like anything,
sound wave, an ocean wave, anything like that can increase
or decrease in frequency. And for light, that usually means
that it's changing color, which is where the name red
shifting and blue shifting come from.

Speaker 2 (23:58):
That's right, And because we're normally applying it to astronomical stuff,
you know, light from distant galaxies. If that distant galaxy
is moving away from us, for example, we say that
it's red shifted and the light from that galaxy looks
redder than if that galaxy had not been moving away
from us. And if an object in the sky like
Andromeda is moving towards us, its light gets blue shifted.

(24:20):
And you're right that it applies to the wavelength of
the light and also applies to the color of the
light as we see it if it's in the visible spectrum,
and it tells us something about the energy of that light,
because for light, the wavelength is very closely connected to
the energy, like red or light is lower energy and
blue or light is higher energy.

Speaker 1 (24:39):
Right, And this red shifting and blue shifting of light
out there in the universe happens not just because things
are moving away from us or towards us, but also
because the universe is expanding, right.

Speaker 2 (24:50):
Yeah, And these are actually two different ways to talk
about the same phenomena. You can get confused and think, oh,
there's two red shifts happening. One that the universe is
expanding and it makes all waves links longer than the other.
The galaxies are moving away from us faster and faster
than the Doppler ship is making their light redder. Those
are actually two different ways to think about the same phenomenon.

(25:10):
What's happening there is that your description depends on your
frame of reference. If you think about the whole universe
in a single frame, like we're at the center and
everything is moving away from us. You're measuring the velocity
of those galaxies relative to us. Then you can use
the Doppler story to describe what's happening, but instead, in
a more general relativity sense, you say, well, you can't

(25:31):
really put everything into a frame because the universe is
expanding and space is curved between here and other galaxies.
Which you really have to do is imagine every galaxy
in its own frame and space increasing between them. And
in that picture there is really no relative velocity because
every galaxy has no velocity in its own frame. And
so what happens to the photons as they go from

(25:52):
galaxy to galaxy is the expanding space between them is
doing the work of expansion. It's a good example of
how you can build physics and lasts to different ways.
You can start from a few different axioms and end
up with a different description of the same physical process.

Speaker 1 (26:07):
Right, But it is two separate effects, isn't it, Like
one is just from its motion and the other one
is from the expanding of the universe.

Speaker 2 (26:14):
No, it's two descriptions of the same thing. Like in
the expansion of the universe model, there is no relative velocity.
In fact, that's more accurate because you can't really talk
about relative velocity across the whole universe. That's also why
you end up with sort of nonsense answers, like those
galaxies are moving away from us faster than the speed
of light because you're making measurements across two different frames

(26:34):
where space is curved between them.

Speaker 1 (26:36):
Right, But I feel like there are sort of two
effects there that can maybe add or subtract, Right, Like,
if there's a galaxy really far away from us that's
maybe spinning, for example, then some things they'll be moving
away from us, and sometimes they'll be moving towards us,
so they'll be shifting of the light because of that.
But then also it's really far away, which means that

(26:57):
on top of that, there's going to be some sort
of wretch due to the long distances getting longer and longer.

Speaker 2 (27:03):
You can add more layers to it, certainly, like you
can add not just the fact that these galaxies are
moving away from us, or equivalently, that space is expanding
between us, but that also within those frames there is
some motion relative to the frame itself. So as you
say galaxies are spinning, and that spinning is what we
call peculiar motion relative to the frame of the galaxy,

(27:23):
which is moving with the center of mass of the galaxy.
And you're right that moving relative to the center mass
of the galaxy can cause an additional red shift or
blue shift, so that really is a separate effect. The
rotation of the galaxy does add another contribution to red
shifting and blue shifting, and we can see that in
distant galaxies and we can use it to help measure
their rotation.

Speaker 1 (27:43):
Right, So there are two effects, right.

Speaker 2 (27:45):
The expansion of the universe and the recession velocity of
an entire galaxy are two equivalent ways of talking about
one effect. The rotation of a galaxy does add another effect. Yes,
you're right that there are multiple contributions to the red shift,
the motion and the sin but if you're thinking in
the relative velocity point of view, they're both just contributing
to the relative velocity. So it's two contributions to one

(28:09):
red shift effect, not two different effects.

Speaker 1 (28:12):
So how do we measure all this red shifting that's
going on in the light of the universe.

Speaker 2 (28:16):
Yeah, it's really tricky because you can't stop the galaxies, right,
or like go to the galaxy and measure like it's
light that you would measure if you were right there
next to it. So you have to sort of imagine
what light you think the galaxy was emitting in its
own frame and then compare that to what we're seeing. Fortunately,
galaxies are filled with objects we pretty much understand, stars,

(28:37):
et cetera, and those are following physics that we pretty
much understand, so we have a pretty good way to
predict the light we think a galaxy should be emitting,
and then we can compare it to the light we're
seeing from the galaxy and we can tell that it's shifted.
And specifically, the frequency of the light from these galaxies
has a few specific handles in it, like a fingerprint
where we can tell that it's been shifted along Like

(28:59):
we know that atoms tend to emit light at very
specific narrow frequency ranges that correspond to the energy levels
of the atoms. As an electron jumps down one energy
level around hydrogen, for example, it tends to emit a
photon with the specific energy of the gap between those
energy levels. And so if we see light from a
distant galaxy and it has a huge spike close to

(29:22):
that energy level, but a little bit shifted. We can say, oh,
that's probably from hydrogen. It's just shifted a certain amount
in the red or in the blue. So these like
standard candles help us understand how the light is shifted
from these distant galaxies.

Speaker 1 (29:35):
Right. It kind of goes to that idea that stars
have a sort of fingerprint to them, like the light
they emit have a very specific pattern of them in
the fregency spectrum that you can sort of identify what's
in the star or what it's supposed to have. And
so if you see that fingerprint kind of smearred, then
you know that it's red shifted. Right. But then I
think you can also just generally tell right, because most

(29:58):
of the light from those things around us is mostly
you know, a certain color. But I imagine as you
look out into the universe and things are further away
from us, things just look redder.

Speaker 2 (30:10):
Yeah, But that's how we can tell the distance to
things by measuring the red shift. Because there's a correlation
between how far away things are and how quickly away
from us they're moving. Then you can use the red
shift as a measure of distance. Now you have to
calibrate that is we have a whole episode about the
cosmic distance ladder to calibrate these things. But generally things
that are farther away are moving away from us faster.

(30:32):
So if you measure the red shift of an object,
you can tell how far away it is or how
old that light is. But there can also be a
lot of uncertainty on those measurements because the wider the
spectrum you measure, like the more of these fingerprints, the
more of these atomic lines that these spikes that you identify,
the more accurately you can measure this red shift. This
is why, for example, when you point multiple telescopes at

(30:55):
different frequencies at the same galaxy, you can get a
better measurement for its red shift. Like James Webb recently
saw some galaxies that were like crazy weird far away.
Those numbers came from the red shift numbers which were
pretty uncertain because James Webb didn't have a chance to
do a broader spectrum and Hubble hadn't looked at it
yet in a different spectrum. And so that's why sometimes

(31:15):
when you follow up with more measurements, you can get
more handles on the light from that galaxy, and that
revises the red shift measurement, which tells you how far
away this thing really is.

Speaker 1 (31:25):
Right, But I guess what I'm saying is that that's
kind of if you want to get really granular and
know exactly how much the red shifting is. But I wonder,
and I'm asking if there's a kind of a general
effect that anyone could affect with their naked eye. You know,
as the star that we see at night are in
our galaxy, so I imagine they're not very red shifted. So
all the light we see from our stars look white
or yellowish. But if you were to look at the

(31:49):
rest of this guy, that things are not stars, and
generally the light we'll see from that is redder.

Speaker 2 (31:55):
Yeah, that's exactly right. And that was Hubble's experience, right,
you looked up in the night sky. He saw a
bunch of stars, but he also saw these smudges that
people thought, oh, those are just like clouds or nebula
or whatever within our galaxy. But then by calculating the
red shift and by understanding the relationship between red shift
and distance, he was like, oh my gosh, look these
things are redshift. That means they're super duperor far away.

(32:17):
They're actually other galaxies. So the red shift gives us
that like third dimension to the night sky rather than
just seeing like a screen. He gives us the ability
to project that into the third dimension and understand the
depth of the night sky.

Speaker 1 (32:30):
Right. Or I wonder if you just put on like
infrared glasses, right or use an infrared camera, you will
sort of see more of the rest of the universe.

Speaker 2 (32:39):
Right, yeah, exactly. And that's why James Web, for example,
is an infrared telescope. They're like, let's focus on the deepest,
reddest light in the universe, because that's from the most
distant objects that things were seeing from the early universe.
That's why you build infrared telescopes exactly, right.

Speaker 1 (32:56):
Right, And if you get really mad, then you'll be
seen red and so opening your eyes up to more
of the universe. No, no, not a valid theory.

Speaker 2 (33:07):
Yeah. I mean, if somebody farts really badly at your
astronomy party, that can make you sopid also yeah.

Speaker 1 (33:12):
Yeah yeah, or in your space station the universe the
costumers will open up to you. All right. Well, now,

(33:33):
the main question we're asking here today is whether neutrinos
can be red shifted, which again I feel like it's
a little bit of a cheat here because it depends
on whether you only apply the word redshifting to light,
which is kind of what some of our listeners brought up.
So maybe let's settle that right now, Daniel, are you
expanding the definition of red shifting to things that are

(33:55):
not light?

Speaker 2 (33:56):
I see, that's a fair question. I hadn't even thought
about that. To me, redshifting up lies to all sorts
of waves, even the Doppler effect. Like when that police
siren is coming at me, I think of that sound
as blue shifted. I see how blue there implies something
about visual light, But to me, it's a more general meaning,
and just that it's changing the frequency.

Speaker 1 (34:15):
Right. But I mean like if a ocean wave got,
you know, higher frequency, you wouldn't say it got red shifted,
like nobody would understand you.

Speaker 2 (34:24):
If you got a higher frequency, I would say it
got blue shifted. Yeah. I think that's pretty cool. Blue
shifting ocean waves awesome. I'm gonna start saying that everywhere. Now.

Speaker 1 (34:32):
It wouldn't get bluer, right or like you know, a
high C note, it isn't bluer than a low C note.
It's sort of a subtle thing. But some of our
listeners did say that the answer is that it cannot
because nutrinos are not light, so therefore they can't be
red shifted.

Speaker 2 (34:48):
I see that that's a fair point. I think blue
to just mean it's changing in that direction of the frequency.
You could extend that argument even further and say, like, well,
that only applies to visible light, because invisible light isn't
bluer or redder even if its frequency is shifting.

Speaker 1 (35:03):
So what's the answer here for the people who said
nutinios can be red shifted because they're not light.

Speaker 2 (35:07):
I think we should consider red shifting blue shifting more
generally to refer to changing the frequency of the waves.

Speaker 1 (35:13):
Okay, so just for today, we're gonna go against what
most people consider the English language.

Speaker 2 (35:19):
I think that's the accepted meaning of red shifting and
blue shifting, and I.

Speaker 1 (35:24):
Think we're just going to consider the question of whether
the wavelength of a nutrinia can change as the universe expands.

Speaker 2 (35:30):
So, according to Wikipedia, which is just looked up and physics,
a redshift is an increase in the wavelength and corresponding
decrease in the frequency and energy of electromagnetic radiations. Such
as light. That's interesting.

Speaker 1 (35:46):
So even Wikipedia disagrees with you.

Speaker 2 (35:48):
Dariel, Yeah, interesting, Yeah, some subtle wrinkles in the definitions here.

Speaker 1 (35:54):
Okay, So then officially, according to Wikipedia, and you know
most humans who speaks English, the answer to our question
is no, neutrinus can get red shifted.

Speaker 2 (36:06):
If you define red shifting to only apply to photons,
then yes, yeah.

Speaker 1 (36:10):
If disregard language, then anything can be anything. But basically,
I'm saying the listener who said the answer is no,
because neutrinos are not light, then they're partly right.

Speaker 2 (36:23):
Yeah, they're partly right according to that definition. I'm surprised
to have to make the argument to you that, like,
you know, language can be evocative of broader themes and
deeper ideas that we find patterns of across the universe
and across phenomena. But you know, to me, I think
the interesting part of the question is, like, you.

Speaker 1 (36:40):
Mean, you're surprised that you have to be clear about
what you call things in physics. You're surprised. But at
this point five years.

Speaker 2 (36:47):
In, yeah, I should learned that should have learned.

Speaker 1 (36:51):
Well, okay, so let's just say the answer is no,
Nutritius cannot get red shifted because I think even Wikipedia
agrees that it applies to light only. But it's still
an interesting question to ask whether neutrinos that are traveling
out there in space do their wavelengths get stretched out
by the expansion of the universe.

Speaker 2 (37:10):
Do they get shifted to longer or shorter wavelengths?

Speaker 1 (37:14):
Yeah, do their wavelengths get stretched or squeeze as the
universe expands? So let's tackle that question.

Speaker 2 (37:20):
So I agree that is right, interesting question.

Speaker 1 (37:23):
Yes, okay, So then so it happens to light because
the universe is expanding, right, So as it's traveling, it's
having to travel through more space as it goes along.
Is that why it stretches, Just because it's sitting in
space and space is being stretched, its frequency gets stretched.

Speaker 2 (37:39):
Yes, the second one, space itself is getting stretched out,
and radiation gets stretched out differently than like matter. Does
you know, electrons sitting in space, you stretch out the space.
You still have one electron and now you have more space,
so you have less matter per volume where things get
diluted in a certain way. The same thing happens to radiation.
You have one photon in that volume, but that photon's

(38:01):
energy also decreases because the wavelength of that photon also changes.

Speaker 1 (38:06):
Right, So then the question is do neutrinos have a
frequency or a wavelength?

Speaker 2 (38:11):
Yeah, So in this sense, you can think of all
particles as ripples in some field, right, and those ripples
have frequencies. Like we talked to Mats Dressler about this recently,
and you can imagine electrons is having like a standing wave,
which is an oscillation in that field, and a traveling wave,
which is like the motion of the electron through that field.
Photons only have a traveling wave because they have no mass.

Speaker 1 (38:33):
Where there's two kinds of waves, a traveling wave and
a standing wave, what's the difference, Like, do electrons have
both waves?

Speaker 2 (38:41):
Yeah, the electron field can do both, right. The electron
field can just oscillate in place in a certain way,
and that's what a stationary electron is. That's why electrons
have mass. An electron field can also ripple in a direction. Right,
that's a traveling wave. Don't think of it as two waves.
It's the same wave. It's just that electrons you can
see standing still in which case they're just doing the
standing wave thing, or you can see them moving, in

(39:04):
which case it's also a traveling wave, but that depends
on your frame of reference. Right now, For photons, you
can't see them standing still because there's no frame of
reference in which they're at rest. They're always traveling waves.

Speaker 1 (39:16):
When things have a standing wave, are those waves actually
rippling or are they more like probability waves.

Speaker 2 (39:22):
These are ripples in a field, which some people think
is a physical thing, right, and so these are should
and so these should be thought of as like actual
oscillations in a physical quantity. People think the field is
real and it's out there. That's sort of a question
of philosophy. This is separate from like wave functions and probabilities,
which are in an abstract probability space. These are ripples

(39:44):
in real space what we think is a real physical thing,
whether or not it's actually happening, whether you can observe it,
and what happens when you take measurements, et cetera. There's
a whole other question in philosophy. But we think these
are physical ripples of a field.

Speaker 1 (39:56):
It's actually oscillating, and so they're different than the quantum
probability waves. Right, yes, Okay, Now what does it mean
that an electron is rippling? In place, like it's jiggling.
Its energy is increasing and decreasing and pulsating, or what
does it mean if it's standing still because it's not moving.

Speaker 2 (40:15):
Well, as we talked about with Matt Stresslo, you can
think about the wave as sort of like the way
you think about a string oscillating. Right, a guitar string
can oscillate in place as a standing wave. What's happening
there is it's oscillating between kinetic and potential energy. Right,
it gets distorted, it has more potential energy, and then
it comes back and has kinetic energy, then it slashes
back into potential energy. So the same way the electron

(40:36):
field can oscillate between having kinetic and potential energy. So
the value of the field is changing. It's some values
that has more potential energy, some values that has less
potential energy but more kinetic energy, so that energy is
conserved within the field. It's just oscillating back and forth
between kinetic and potential energy, the way like a ball
inside a glass can roll around if you ignore friction,

(40:57):
it could roll around forever. It's like oscillating within them.

Speaker 1 (41:00):
Or I guess I'm imagining like a balloon sitting in
space it's maybe squashing and stretching in different directions. Right.
That means it energy is going between the potential energy
and kinetic energy as it squeezes and compresses. But then,
how is that different than traveling waves.

Speaker 2 (41:18):
In order to do this special trick of oscillating in place,
you have to have mass. Mass is the thing that
allows you to do that. That's really what mass is
is the ability to store energy in one location within
the field. Because remember that mass is just like a
measurement of internal stored energy. But some fields can't do that,
Like the photon field doesn't have any mass. There's something

(41:39):
the electron field can do that the photon field cannot do.
But the photon field and the electron fields can both
have traveling waves, which is like a wave moving through space.
You have an oscillation here, and then the oscillation is
over there, and the oscillation is further along, So it's
sort of like that energy is moving through the field
rather than just staying in place.

Speaker 1 (41:57):
Okay, now, let's say for an electron. Doesn't mean that
the electron is physically like going up and down as
it moves or as it's moving in a straight line.
It's somehow undulating. What exactly is a traveling wave for
a particle like the electron.

Speaker 2 (42:10):
Yeah, well, it sounds like you're trying to hold in
your mind simultaneously the picture of an electron is a
little particle that has a definite location, and you're trying
to marry that with the idea of a wave. But
instead just think about the electron as a fluctuation in
the wave. And as we talked about recently, when you
think about like how photons ripple, photons are not undulating,
they're not moving side to side. What's changing along a

(42:31):
straight line is the value of the field along that line.
A fields pointing in one direction, and then another direction,
and then a third direction. Because the photon field is
actually a vector, it's not just a number, it's a direction.
So for the electron, again, moving along a straight line,
as an electron moves, what's changing is the value of
the electron field along that line. It isn't like wiggle

(42:52):
sideways in any way, except sometimes when we draw this
on paper, we draw sideways wiggles to indicate the value
of the field. In a physical sense, there's no sideways undulation.
It's just like the numbers of the electron field are changing.
The electron field is not as complicated as the photon
field because it's a fermion and not a spin one
boson like the photon is, which is a full vector.

Speaker 1 (43:15):
Well, just following what you said, which is that you know,
like an electron has a standing wave like a standing ribble,
and then it has a traveling wave. But you can
also imagine a standing wave that's moving in a constant
speed in a straight line that doesn't need a traveling wave.
Or is this traveling wave basically a moving standing wave.

Speaker 2 (43:33):
Yeah, that's what a traveling wave is, and it maintains
its shape, right. One of the cool things about particles
is as they move through the universe, they maintain their energy.
They don't like diffuse and spread out, right, because it's
a minimum oscillation of this quantum field, so it can't
go down to a lower value. You can't have like
a half an electron than a quarter electron. So this

(43:53):
shape maintains itself as it moves through the electron field.

Speaker 1 (43:58):
So then I wonder if maybe the question you're really
asking here today is whether the standing wave of nutrino
gets stretched out as the universe expands, like you don't
even need a natrina to be moving. You can just
have anatrino standing in space out there. And as the
universe expands, does the neutrinos standing wave also expand?

Speaker 2 (44:17):
Like?

Speaker 1 (44:17):
Are those do the same question?

Speaker 2 (44:19):
They're not quite the same question, because now you're talking
about particles at rest, and because the neutrino field and
the electron field and everything else that has mass has
a specific frequency at which it can oscillate that isn't
affected as the universe expands. What is directly affected by
the expansion of the universe is not the frequency, but
the wavelength that's always stretched out for all particles. For photons,

(44:41):
which only have a traveling wave, the wavelength and the
frequency have a very simple relationship. Longer wavelength, lower frequency.
For electrons, which also have mass, it works in the
same direction, but the relationship is more complicated because of
the mass part. The mass part isn't affected directly by
the wavelength, but the expansion still influences the overall frequency,

(45:04):
and that frequency is also affected by the mass part.
So as the universe expands, it stretches out the wavelength,
which does in the end lower the electrons frequency. But
the math is a little bit different. There's a minimum
frequency for the electrons that they can't lose because they
still have mass. This effect really only changes how particles
move through the universe, not how much mass they have.

Speaker 1 (45:26):
All Right, So, then if we're asking the question, do
neutrinos change wavelengths as the universe expands? What exactly does
that mean? Does that mean that it's standing wave gets
stretched or it's traveling wave gets thressed. But then you
just said that the traveling wave is just as standing
wave moving in a straight line, So I guess I'm confused.
What do you mean by a neutrino's wavelength getting stretched

(45:47):
by this expension.

Speaker 2 (45:49):
There's two different kinds of things that these fields can do, right.
They can oscillate in place, some of them, and they
can also oscillate in a traveling wave motion. And so
for those of you who want to know more about
the technicality details of that, go back and check out
our episodes at Matt Strassler about exactly what that means.
For the purposes of today's episode, we just need to
think about the motion of those particles, the traveling waves,

(46:10):
and the frequency of those particles as they're moving, and
for photons, for example, we know that they get stretched
out if you see something being emitted from a high
velocity object, or if the universe is expanding between you
and them. Really the same effect described in two ways.
And so the question today is like, does that also
apply to neutrinos, which we know are generated by stars
far away and fly to us across space. Does the

(46:32):
expansion of space also affect them? And the answer is yes, absolutely,
Their wavelength is also shifted as they move through space
because everything is just a ripple in these fields, and
other than the mass ripple, which is controlled by some
fundamental properties of the field, the velocity of it reflects
the energy of that particle and that decreases as space expands.

Speaker 1 (46:54):
So what does that mean for a particle like the neutrino?
Does it? Is it going to look different or is
going to end up looking or being a different particle
when it reaches the other side of the universe.

Speaker 2 (47:05):
Yeah, it means that it has less energy, right, It
doesn't change its fundamental nature. It still has the same mass,
just like an electron will always have the same mass.
It still looks the same, It still looks the same,
but it has less energy. The same way a photon does. Right,
when a photon gets red shifted, it has less energy
than it did before. When the universe expands, photons lose energy,
which is sort of fascinating. Then violets our intuition that

(47:27):
like energy should be conserved, but it isn't for photons, right,
photons get lower energy. We have a great example of that,
which is the cosmic microwave background radiation, which is very
very red. Photons they're down in the microwave, but when
they were emitted back in the very early universe, they
were very high energy because they were emitted from a
super duper hot, bright gas. And as the universe has expanded,

(47:48):
they've been stretched out to very low energies. So the
same thing happens to neutrinos and electrons and every other
particle moving through the universe as the universe expands. Or equivalently, again,
if you emitted from something moving at high speed away
from you, and those particles are red shifted to lower energy,
same mass, but lower kinetic energy.

Speaker 1 (48:07):
So wait, wait, are you just basically saying that the
expansion of the universe slows down neutrinos.

Speaker 2 (48:13):
Yes, absolutely it does, and it's a really interesting point,
because photons don't get slower, right, They just get lower
energy at the same velocity, because photons are always moving
at the speed of light. But neutrinos have mass, and
so as they get lower energy, they do get slower.
They're basically always traveling at almost the speed of light
anyway because their mass is so small. But yes, technically

(48:33):
they do get slower as their wavelength gets longer.

Speaker 1 (48:36):
Right, right, So then what's the difference between neutrino that
I detegged from the Sun which is really close to us,
and in neutrina that is emitted by the Sun really
far away that gets to us after billions of years
and it's been going through expanding space when it gets
to me and I compare to the nutrina from our sun.
Do they look the same? It's just that one of

(48:57):
them is going faster than the other. Or are they
going to look different?

Speaker 2 (49:01):
Well, each individual neutrino will not look different, but the
spectrum of them will. So if you measure the energy
of all the neutrinos from the Sun you make a
graph of that, it's going to have some distribution. And
then if you measure the energies of neutrinos from distant stars,
stars that are really far away from us, where the
universes expanded between us and them, those will have a
lower energy distribution, exactly the same way is for photons.

(49:24):
Photons from distant stars are shifted down lower in energy.
Neutrino energy distribution should also be shifted down.

Speaker 1 (49:30):
Shoot, so they'll just be slower.

Speaker 2 (49:33):
Yeah.

Speaker 1 (49:34):
So I mean basically you can ask this question of anything.
Any particle doesn't have to be neutrinos.

Speaker 2 (49:39):
Yeah.

Speaker 1 (49:39):
So, like an electron that is shot at us from
really far away, by the time it gets us, it's
going to be going at a slower speed.

Speaker 2 (49:47):
Yeah, or as we say, colder or redder. But yeah,
fundamentally it's a lower velocity.

Speaker 1 (49:52):
Right. I mean you can say smeliar too, but I
think the practical says you would just say it's slower.

Speaker 2 (49:59):
Yeah, it's definitely slower as less kinetic energy.

Speaker 1 (50:02):
Ah. Wait, so that means like if I was Superman,
or if I was shot out of a cannon from
a space station in orbit around Earth and I was
flying through space, nothing gets in my way, no dust, nothing,
I would still slow down eventually to a standstill.

Speaker 2 (50:19):
Depends on what you mean by standstill, because there's no
absolute velocity in space, right, And I think that this
slow down is a relative effect, so you would as
symptotically approach zero velocity relative to some observer. But yes,
things do get slowed down as the universe expands.

Speaker 1 (50:35):
Yeah, Like initially I would see planets whizzing by me,
but then eventually at the end of the universe, planets
would not be whizzing by me. That would be going
slower relative to them.

Speaker 2 (50:45):
Yeah, I remember that this is a relative effect, right.
One person will see a photon red shifted, somebody else
see that same photon not red shifted. So this is
a frame dependent effect.

Speaker 1 (50:56):
Right, But it's basically as I just describe. But initially
things will whizzing by me, but eventually the things will
be going by me slower.

Speaker 2 (51:03):
I'm not one hundred percent sure about the thrust of
Superman here, but if he only has an initial velocity
and that he's coasting.

Speaker 1 (51:09):
Forget I said, Superman. That's why I shipped it to
a cannon, Like if I get shot out of a cannon. Now,
does that mean that our whole episode here today? Instead
of calling it can Neutrina's be red shifted if they
we could have just called it. Do things in space
get slowed down by the expansion of the universe?

Speaker 2 (51:25):
And the answer is yes, except for photons. Photons get
red shifted, but they don't get slowed down because they
have no mass. They're always traveling at the speed of light, right.

Speaker 1 (51:35):
But the light is not a thing. Basically, does anything
with mass things matter gets slowed down as the universe expands,
and it seems like answers yes.

Speaker 2 (51:44):
The answer is yes, but it's very difficult to see
because in order to detect that, to do the experiment
I mentioned, you'd need to have a source of neutrinos
with very specific energies. And because we see so few
neutrinos it's so difficult to pin them down to observe them.
We can't actually do the experiment that I talked about earlier,
like looking at the distribution of energies of neutrinos from

(52:04):
a distant star. And also stars don't emit neutrinos a
very specific energies the way they do photons, right, and
so we don't have like spectral lines of neutrinos that
we can use to measure these redshifts. But the only
thing we can do is look for the cosmic neutrino background,
which is similar to the cosmic microwave background. We think

(52:24):
there were a bunch of neutrinos created in the early universe,
very high speed, very high energy, and the expansion of
space has cooled them all down to much slower moving neutrinos,
still nearly the speed of light, but much slower moving.
If we can measure the cosmic neutrino background and basically
measure their velocity their energy distribution, that would be direct
evidence of seeing particles slowed down by the expansion of

(52:47):
the universe, or red shifted neutrinos. But we haven't seen
them yet.

Speaker 1 (52:51):
But I wonder if there's maybe an easier experiment you
can do. Can you look at other particles that are
getting to us from far away. Can we just tell
that they're somehow slower than the particles that are being
sent to us from closer sources, or is there no
such thing.

Speaker 2 (53:04):
It's difficult because we're talking about particles, and particles don't
make it through the universe the same way photons do,
so it's harder to attribute individual particles to like specific
extragalactic sources and we're talking about like electrons or protons
from another galaxy with a very small number of those.
Those are very high energy cosmic rays, and we have
lots of questions about what's even making those. So no,

(53:27):
we don't have a good sample of electrons or protons
from other galaxies to do that kind of.

Speaker 1 (53:31):
Experiment with, or would you even need to do the
experiment just because that's what relativity says it's going to happen. Right,
things are going to slow down as you move through
expanding space, and we already know that a lot of
relativity is true, So why wouldn't it work for this case.

Speaker 2 (53:45):
Yeah, we have no reason to think it wouldn't, but
it's always a good idea to double check because there
could be a surprise. It could be one of those
things where we're like, yeah, that's totally going to be boring,
go out and do it, yon yon yon, Oh my gosh,
what and the universe tells us something new. So we
strongly suspect and believe that this is what's happening. But
you always got to check the stuff.

Speaker 1 (54:05):
Right, Right, you're saying it's a good idea to shoot
Joorge out of a cannon, space.

Speaker 2 (54:10):
Good idea aboutity? I don't know, but we could learn
a lot.

Speaker 1 (54:13):
Yeah, yeah, although it would be hard because you know,
to make it a perfect experiment. As I'm flying through space,
I can't eject any matter because it would ruin the experiment.

Speaker 2 (54:23):
Right, mm hmmm yeah.

Speaker 1 (54:24):
So if you I see where you're going with just
trying to bring it back around or down, as the
case may be. So if we do an experiment, uh no,
the person can fart fart right.

Speaker 2 (54:40):
That's right. You got to hold it in, hold it in.

Speaker 1 (54:43):
Hold it in, hold it in for billions of years,
hold it in for I think I feel like like
that just describes my job here in the podcast, holding
it in or not hold it in, hold it in.
I don't think you've been holding it together.

Speaker 2 (55:00):
You've been letting it all out on this episode.

Speaker 1 (55:04):
Are you saying I've been I've been stinking it up?
What you're saying with far jokes, you're like you said
it or on me? All right? Well, I guess just
to recap the question, we started asking, can Neutrino's get
red shifted right off the gate? The answers no, because
I think most people would agree redshifting only applies to

(55:27):
electromagnetic light, as some of our listeners pointed out.

Speaker 2 (55:30):
Where most people notably doesn't include me. But yes, go ahead, Oh.

Speaker 1 (55:33):
That's why it's most But if you have a question,
the wavelength of the neutrino get stretched out by explaining universe,
and the answers yes, in fact, it happens to all
particles with mass, right, And really what that means doesn't
mean that it somehow changes the neutrina It just means
that it slows down.

Speaker 2 (55:50):
Yeah.

Speaker 1 (55:51):
So really the question is do particles get slowed down
by the expansion of the universe, And you're saying the
answers yes, because that's what relativity tells us.

Speaker 2 (56:00):
Yeah, all particles have their wavelength extended when the universe expands.
For photons, that doesn't mean a change in the velocity,
but for particles with mass it does.

Speaker 1 (56:08):
All right, Well, it was a circuitous path, but we
got here. Now, what happens to a fart with the
expansion of the universe. It also slows down, right.

Speaker 2 (56:20):
It slows down, But the stink is invariant like mass.
It's a fundamental quality of the fart. Something the fart
field can do.

Speaker 1 (56:25):
Each individual particle. Its stinkiness does not decrease because its
nature doesn't change.

Speaker 2 (56:31):
I prefer to think about farts it's waves as they
sort of pass over you, rather than think about the
individual fart particles than where they came.

Speaker 1 (56:37):
From sticking in your nose. Yeah, nobody wants to think
about that exactly. Yeah, all right, well, I think another
lesson about how crazy this universe is and how big
it is, and how the effects of it getting even bigger.
What's that going to do to everything in it?

Speaker 2 (56:55):
That's right, And our intuition for what happens to photons
sometimes does apply to other particles. Because they have mass,
they follow slightly different rules.

Speaker 1 (57:03):
All right, We hope you enjoyed that. Thanks for joining us.
See you next time.

Speaker 2 (57:12):
For more science and curiosity, come find us on social media,
where we answer questions and post videos. We're on Twitter, This, Org, Insta,
and now TikTok. Thanks for listening, and remember that Daniel
and Jorge Explain the Universe is a production of iHeartRadio.
For more podcasts from iHeartRadio, visit the iHeartRadio Apple Apple Podcasts,

(57:33):
or wherever you listen to your favorite shows.