Which force(s) power the human senses?

Daniel and Katie talk about how we experience the Universe and what physics underlies our senses.

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Episode Transcript

Speaker 1 (00:08):
Hey, Katie, pain me a picture of where you are.
Tell me what you're seeing right now?

Speaker 2 (00:13):
Okay, Well, I'm seeing sort of the corner of my
microphone because it's very close to my face. I'm seeing
a wall, my computer, some plants. Shall I go on?

Speaker 1 (00:26):
No, now, let's add to the picture. Tell me what
sounds there are around you?

Speaker 2 (00:30):
Well, sort of a very faint humming sound, your voice
in my ear, and I think the little footsteps of
my dog pacing outside waiting for me to be done
with this podcast.

Speaker 1 (00:44):
And how about the smells in your sensorium?

Speaker 2 (00:47):
Well, I smell my microphone, which does have a smell.
It's not gross, it's just, you know, microphone smell. I
think my husband is cooking something chicken maybe, or a
chicken like protein.

Speaker 1 (01:00):
Does your microphone not smell like chicken? I thought everything
smells like chicken.

Speaker 2 (01:03):
Hang on, let me see. I mean, if I really
think about chicken while smelling my microphone, I can make
that connection. Sure, all right?

Speaker 1 (01:10):
And then the last sense is touch. What is your
sense of touch telling you?

Speaker 2 (01:15):
Well, the sense of touch in my butt is telling
me that I should have invested in a much more
expensive ergonomic podcasting chair.

Speaker 1 (01:26):
All right, So is that all I need to know
about what it's like to be you right now? To
pilot the meat machine that you call, Katie.

Speaker 2 (01:32):
Golden, Well, there's little grimlins in my ear whispering things
at me. But other than that, yeah.

Speaker 1 (01:39):
Those aren't gremlins, Katie, that's just me.

Speaker 2 (01:41):
It's just a physicist. I don't know what to be
more afraid of the grimlins or a physicist physics grimlins.

Speaker 3 (02:04):
Hi.

Speaker 1 (02:04):
I'm Daniel. I'm a particle physicist and a professor at
UC Irvine, and I wonder what the world beyond my
senses is really like.

Speaker 2 (02:12):
I'm Katie Golden. I host the podcast Creature Feature, which
is all about animal behavior and human behavior, and I
like to try to imagine what it's like to be
my dog by smelling other people's butts.

Speaker 1 (02:29):
And how does that go over? I mean, I've been
Italy in a while, but I imagine that's still not a
typical kind of activity for.

Speaker 2 (02:35):
Saying Hello, it's not I'm in jail.

Speaker 1 (02:41):
You're doing everything you can to improve the reputations of
Americans abroad, right exactly, and welcome to the podcast. Daniel
and Jorge explain the universe in which we explore everything
that's out there in the universe, what people's butts smell like,
what the night sky looks like, what's actually out there
in deep space, how all the particles between our toes

(03:02):
are working to weave themselves together into our reality, and
how we sense experience and maybe even understand all of it.
My friend and co host Jorge can't be with us today,
but I'm very excited to have Katie Golden, one of
our regular and favorite guest hosts, to be with us
here today. Thanks Katie for joining us.

Speaker 2 (03:19):
It feels good to be here.

Speaker 1 (03:23):
And now I'm wondering if I ever do meet you
in person, Katie, if you're going to do more than
just shake my hand, if you're gonna.

Speaker 2 (03:28):
Smell me up, like There's a lot you can tell
about a person just by huffing.

Speaker 1 (03:34):
In that sense, you'll probably tell that I have dogs
and I have kids based on the random hairs on
my body.

Speaker 2 (03:40):
The feel of the stickiness quotient is how I measure
whether someone has kids, Like, is there sticky patches on
your shirt? That's right, is in the shape of a
very small, curious little hand.

Speaker 1 (03:53):
Do you have dried cheerios stuck to the side of
your shorts. If so, you have a toddler. But we're
not just interested in sensing other people. We are interested
in sensing the world. Everything we do in physics in
the end relies on these little data streams that we
get from the external universe that in the end we're
just assuming exists. We have a model for what's out there,

(04:15):
how it bangs around and creates information that we can
then perceive filter down into our minds and unravel into
a mathematical model in our heads that tries to explain
everything that we think is out there. But it seems
like kind of a long, complicated chain of events from
supernova explodes to somebody on Earth goes ooh, I think

(04:36):
I understand it. So on this podcast we try to
unravel all of those tricky, complicated things and make sure
you understand all of them.

Speaker 2 (04:44):
It's so interesting to me that every sense we have
right is the direct result of physical interaction with the world,
because it feels strange since our mind seems very internal,
it seems very ice like, well, what I'm seeing is
kind of happening in my mind, But everything I'm seeing

(05:05):
like there's a direct sort of physics based interaction that's
happening between me and the world, and I don't know.
That makes me feel good. It makes me feel less
isolated in my own brain.

Speaker 1 (05:18):
It really does a great job of reminding you that
information is physical, and that all observation is active. There's
no like passive just looking at the world. You are
absorbing it, you are consuming it, you are interacting with it.
When you see something, it's because photons are hitting your eye.
You're not just like passively observing it. And that of
course changes the way you feel about the universe and

(05:39):
has big philosophical implications for like quantum mechanics and what
happens when we collapse wave functions. But it also has
real consequences for what it means to like smell something nasty.
I mean, you're walking down the street and you're like,
m somebody didn't clean up after their dog. You know
that means poop molecules are hitting your nose.

Speaker 2 (05:55):
When I have that realization, I think I was in
high school. It ruined my life world. I have never
gotten over that that like poopy smells, It's like, well,
the poopy particles are interacting with my nasal membranes in
some way. I don't like that and it is. Yeah,
it's a realization that ruined my life, and I'm glad
we can spread it to others.

Speaker 1 (06:16):
And as we're going to learn later on, the sense
of smell the sense of taste are very closely intertwined,
and most of your experience of taste really is smell,
which means you're not just smelling that dog poop, you're
really tasting it delicious And we are excited to understand
this entire, delicious and disgusting universe in all of its glory.

(06:37):
And so today on the podcast, we're going to be
digging into the physics of this mechanism, how exactly information
gets banged around and propagated through all these amazing systems
into your brain so that you can experience the wonderful
smells of chicken cooking and the less wonderful smells of
dog residue.

Speaker 2 (06:56):
I have smelled both today.

Speaker 1 (06:59):
And so today on the podcast, we'll be answering the
question which forces power the human senses?

Speaker 2 (07:11):
That sounds so cool. I'm imagining sort of my eyes
being powered by some kind of like futuristic technology.

Speaker 1 (07:21):
Yeah, I guess power there can be confusing. It's not
like you have little coal power plants in your eyeballs
that are like making it all work in some sort
of steampunk version of your senses.

Speaker 2 (07:30):
Now, I mean, as we all know, it's tiny grimlins
in there, running little projectors, the.

Speaker 1 (07:36):
Little physics grimlins all the way down. Now, the idea
I think is to understand everything from a physics point
of view. I mean, you can zoom out to biology
and say, oh, yeah, we understand this bit and that
sell and they send signals or whatever. But I always
wonder from a microphysics point of view, like, what's really
happening at the lowest level. If in the end reductionism works,
and we can understand the whole universe in terms of

(07:59):
a few partsarticles and their interactions, and we should be
able to explain everything from human consciousness to supernova to
black holes to the evolution of the entire universe with
those fundamental laws. Of course, most of that is beyond
our ability currently, and the complex nature of these interactions
requires too much chaos for us to be able to compute.

(08:20):
But in some cases we can actually complete the thread.
We can't drill down and understand what is happening when
that chicken dinner enters your nose. How are you actually
seeing those things? What is the mechanism by which you
feel pain? In terms of the fundamental physics that we
do understand in our universe. So that's what we want

(08:40):
to dig into today.

Speaker 2 (08:41):
I mean, it is really interesting because when you look
at biological processes like the smaller you get, you have
a very extensive, basically Rube Goldberg machine happening inside your
body on a tiny scale every time you sense something,
and then you zoom out and there's another Rube Goldberg
machine happening on a slightly larger scale. And I feel

(09:03):
like that's not too dissimilar to physics, although Goldberg machines
are operated by physics of force, which is not the
only kind of like physics we're talking about here, but
it's still it's still interesting that, you know, when you
have this whole complex process, domino effective physical phenomenon happening,

(09:25):
and then once it gets to your body and it
triggers an event, then you have a whole other complex
system of things that happens. There's so much just for
you to look at like a wadded up tissue. There's
so many things that have to happen so much.

Speaker 1 (09:40):
Glorious physics in that experience of the watered up tissue.
But you know, I'm wondering how biologists feel about these machines,
these Rube Goldberg machines, because that's not exactly a compliment.
Like if I designed the machine to do something and
you said, wow, Daniel, that's kind of a Rube Goldberg machine,
I take it as like that's broke and overly complicated,
likely to fail, and could be better engineered. On the

(10:03):
other hand, I often hear biologists exclaiming that the wonders
of nature and the amazing things that evolution has been
able to engineer. So do you feel some pride in
evolution as an engineer or do you feel like embarrassed, like,
oh my gosh, this is ridiculous.

Speaker 2 (10:17):
I think it could be both things, honestly. I mean,
I've heard of our immune systems being described as like
this amazing complicated ballet and dance, and that's true. But
then sometimes our immune system can act like an insane
traffic jam, just a horrible traffic snarl. And I think
these kinds of things happen in biold you or we

(10:39):
look at things like, you know, like the eyeball is incredible.
It's one of those things that make people question whether
evolution can be real. Of course, once you look at
the way in which ees develop over long periods of time,
you can see how it. You know, just after millions
of years you can get an eyeball. It's such an
elegant thing. And then on the other hand, we've got

(11:01):
some kind of weird uh things that happen in evolution,
you know, like these are called spandrels, where you have
an evolutionary trait that doesn't really have a purpose anymore,
or doesn't have any like a parent purpose, but it's
there because there's some other structural thing that occurred. And
then you just happen to have this thing because it

(11:23):
is a byproduct of other necessary structures. So it's not
meant to be necessarily elegant. It's just like what works works,
and sometimes it's elegant and sometimes it's not.

Speaker 1 (11:35):
That's what you get when you leave the job up
to biology gremlins. All right, well, let's hear about what
some other gremlins had to say on this topic. I
reached out to listeners of the podcast to hear what
their thoughts were on the question. So before you hear
these answers, think to yourself, do you know which forces
power of the human senses. Here's what people had to say.

Speaker 4 (11:56):
I'm going with the electromagnetic force, as I think all
of our sensors rely on that to send the signals
to our brain where we interpret them internally.

Speaker 5 (12:05):
I suppose this would be the same as the forces
driving other metabolic processes. So ultimately the breakdown of ATP
to power some protein or enzyme that's involved in the
sensing signal transaction pathway, and then externally there would be
the force of the thing itself that's being sensed. Particularly exposed,
with the light, you'd have the photons striking rods or cones,
or in the case of sound, you'd have the vibrational

(12:27):
energy being sensed by the hairs. I guess with chemical
sensing it would be slightly more subtle, but there might
be some analogous process.

Speaker 3 (12:35):
Well. I understand that the human senses are a collection
of receptors of very quantum phenomena such as light and
microscopic smell molecules. So I think that at the very end,
the fundamental forces such as electromagnetism and strong forces are
involved in somehow.

Speaker 4 (12:55):
If you count equilibrium as a sense, then gravity would
affect that. Then touch, smell, here, and taste are all
physical contact ultimately, which is the interaction of molecules held
together by electromagnetism. And then vision is directly sensing the
electromagnetic spectrum. Ultimately everything is nerve impulses, which are electrochemicals.
So it seems like electromagnetism is the big winner.

Speaker 1 (13:14):
I'd say the electromagnetic force is mostly responsible for powering
the human sensus.

Speaker 3 (13:19):
Our entire nervous system basically works out in elecricity and
says our senses.

Speaker 1 (13:24):
Are part of that. I'd say that's our usual suspect.
All right, We've got a lot of electromagnetism, but also
some gravity and chemistry and quantum mechanics mixed up in there.

Speaker 2 (13:35):
I mean, I can't really disagree with this if we
blend all these answers together in sort of a stew
because as far as I understand it, like there's a
lot of different elements in terms of our ability to
perceive things. It's not always electromagnetic force, but that is
a major force and a lot of our sort of

(13:58):
the chain of events that occur that allow us to
perceive things. It's just there's so many different elements that
are happening all at once, or not all at once,
but in a sort of very quick rapid succession of events.

Speaker 1 (14:13):
There are a lot of pieces at play. But one
of the things I love about the story we're telling
today is the eventual unity. How we achieve this sort
of physics goal of pulling everything together into one thing.
So I'm excited to get into that and take the
listeners on that saga and talk about what the fundamental
forces are that undergird the human senses.

Speaker 2 (14:34):
So I understand fairly well the human senses and non
human senses, but I feel like I could use a
refresher on the main forces that exist in the physical
world that we can perceive, or at least something could perceive,

(14:55):
even if it's not a human.

Speaker 1 (14:56):
Yeah, exactly. So we're going to map the human senses
to the fundamental forces. But are the fundamental forces? What
is the sort of target? What is the menu of options?
We have to describe stuff? So physics is all about
describing the universe, and humans have been observing stuff for
thousands of years and trying to describe it, And every
time we see something move in an unexplained way, get accelerated,

(15:18):
get a force applied to it, we come up with
a new force. We say, okay, well there must be
a new force that pushes things in this way. But
over thousands of years, we've worked to coalesce these things
into sort of the shortest list possible to say, oh,
the thing that does lightning is probably the same that
does that static electricity that zaps me. So we have
a list of the fundamental forces, the sort of basic

(15:39):
things that the universe can do, and that current list
has five things on it. So number one top of
the list is electricity, right, something humans have definitely known
about four thousands of years and a very important thing
in our lives. I mean, I drive an ev Electricity
is powering my entire life. You're listening to this device

(16:00):
using electricity. It's everywhere in our world. Hard to imagine
a universe without electricity.

Speaker 2 (16:05):
How did we know about electricity before we had socks
and carpet.

Speaker 1 (16:09):
Though Ben Franklin actually invented socks and carpets just to
do that experiment. Not a well known story, And we've
had sort of colloquial folk understanding of electricity for thousands
of years. But in the last couple of hundreds of years,
people doing experiments with literally like rags and glass rods
and all sorts of weird experiments have figured out that
we have charged particles, and those charge particles have these

(16:31):
electric fields that can push and pull on each other.
So you have two electrons, for example, they each have
an electric field and their electric fields can push on
other charged particles, and so that's the fundamental electrical force.

Speaker 2 (16:44):
So can electrons because I know that electrons are often
a part of an atom or an atomic structure. Can
electrons just be out by themselves?

Speaker 1 (16:55):
Oh? Yeah, Electrons do not have a curfew. They can
just be out there in the universe, and the Sun
produces a huge number of electrons shoots them out into
the universe. So if you take a spaceship through interstellar space,
you'll be swimming through a sea of electrons and protons
and all sorts of other particles. It's only when things
are cool, when these particles don't have enough velocity to escape,

(17:16):
that they're trapped into bonds. But the formation of the
atom is also electrical. Is the electrical force between the
proton and the electron that builds the atom. That's why
they bind together into hydrogen, and that's why atoms link
together into more complex molecules. So the structure of the
atom itself, and basically all of chemistry, the foundation of

(17:36):
that is electricity. It's all the forces of electrons on
each other and on nuclei.

Speaker 2 (17:41):
So can you use electricity to facilitate chemical reactions in chemistry?

Speaker 1 (17:46):
I mean, I think if you dig up a corpse
and lay them on a table and zap them with
lightning they come back to life, is that count as chemistry?
I think I saw that experiment somewhere.

Speaker 2 (17:56):
That's true. I have seen muscle tissue. If you pour
like soy sauce or salt on it, it reacts like
the sort of electrical activity resumes, even though it's clearly
a dead thing. It can be a chunk of flesh.
And I think it's because of the sodium in the
salt or in the soy sauce, kind of like activating

(18:17):
these sodium channels and creating some kind of difference in
electrical voltage that allows there to be sort of this
twitching that happens. So if you see a video of
a fish or some meat on a plate kind of
twitching after you apply like soy sauce. It's not undead.
It's just a be re animated by the soy sauce.

Speaker 3 (18:38):
Right.

Speaker 1 (18:38):
But to give a serious answer to your question, yes, absolutely,
if you apply electricity or voltage or current to something,
youur depositing energy and that can definitely catalyze chemical reactions.
But you bring up another really important point, which is
how signaling happens. We know, of course, we can use
electrical signals to send information. You're listening to this podcast
with electrical signals, digital signals from computer to computer, and they're

(19:01):
probably analog signals and the speakers that are actually making
the sound that get to your ear. But also inside
our body, our nervous system uses these ionic channels, uses
charged particles and electrical forces two senden signals up and
down your nerves, which is why they move at almost
the speed of light.

Speaker 2 (19:17):
Yeah, it's really fascinating because it's another thing is you
really can't chug soy sauce. It's bad for you. I'm
being silly, but it's also not a joke. If you
chug soy sauce, it's very dangerous because it interferes with
the ion channels in your brain, and it can actually
make it difficult for those electrical signals to occur in
your brain, and that's very dangerous. That can result in

(19:40):
coma or even death. So, you know, it's really interesting
how chemistry, right, like even basic chemistry, like the way
that sodium ions work and electricity, the tiny electrical impulses
in your brain work together and can be messed up
by soy sauce. Soy sauce is just so dangerous, you guys.

Speaker 1 (19:59):
It's brewed up by soy goblins. I think they're quite
so dangerous.

Speaker 2 (20:02):
I love soy sauce in moderation.

Speaker 1 (20:04):
But that gives you a really cool picture of the
sort of electrical map of your body. And it reminds
you that your body is not just mechanical structures, not
just like cells and membranes and bones, but there are
electrical structures. There are also things that can get messed
up if you pour the wrong number of positively or
negatively charged particles in the wrong place. Your body is

(20:24):
sort of like a computer. If you poured soy sauce
on your computer, you would not expect it to operate
very well either. And it makes you wonder sometimes philosophically,
like what is this thing we call electric charge? Where
does it come from? And that's a tricky rabbit hole
to fall down, because really, fundamentally, in physics, charge is
something we assign. We say that some particles react in

(20:44):
the presence of electric fields, and that means that they're charged.
That's what charge means. And as we'll talk about it
in a minute when we get to the other forces,
we have other kinds of charge. Also, if you feel
the other fundamental forces, you are charged for those forces.
So we're used to talking about charge for an electrical sense,
we don't really know philosophically what it means. Why the
electron has a charge, Why these other particles have charges.

(21:07):
Some particles don't have charges. It's just something we observe
and describe.

Speaker 2 (21:11):
So like all electrons have some kind of charge, but
we really like when do we feel that?

Speaker 3 (21:17):
Right?

Speaker 2 (21:18):
Like when can we observe that charge? Because like you know,
you have your door handle in your socks and somehow
by rubbing your socks on the carpet, now when you
touch the door handle, you have a charge that you
can actually sense a little zap. So what happens to
these charges to make us actually notice them, like lightning happens.

(21:39):
We can notice that even though this charge can be
all around us at this like sub atomic level without
us noticing.

Speaker 1 (21:46):
Yeah, great question. I mean fundamentally, we notice something is
charged when it's moved by an electrical field. And that's
the definition of charge. If you give me a new
particle I'd never seen before, one of the first things
I would do would be descended through an electric field
and see is it accelerated by the field? Is it
pushed around by the field. If so, then it has
an electric charge, because that's the definition of it. When

(22:07):
you rub a cloth onto a glass rod, you're stripping
some of those charged particles from one to the other.
You're creating an imbalance, which creates an electric field, which
is then can accelerate any charge particle across it, which
is why you get that zap when things come back
close enough for that field to break down the air
and let the electrons pass through the other direction and
create that spark. So in the end, really charge is

(22:29):
about being moved by an electric field, which feels a
little circular because we also define an electric field to
be something created by a charge, and so that gives
you a glimpse into how deeply we do and do
not understand the fundamental forces.

Speaker 2 (22:42):
It's very interesting. So it's like you have to have
some kind of imbalance in charge in order for us
to kind of sense that charge.

Speaker 1 (22:49):
Yeah, exactly. If everything is totally neutral, then there are
no forces.

Speaker 2 (22:53):
So I'm going to test this theory out by rubbing
my socks against the carpet and zap my husband while
he's trying to cook chicken. So I'm going to go
do that and I will report my experiment back when
we return. So the experiment was an unqualified success. I

(23:26):
did zat my husband. He said, ouch, what are you doing.
I'm just trying to cook some chicken. So we have
talked about electrical forces, that they exist in your body,
they exist outside of your body. It is something that
we see in lightning, in you know, static electricity, and

(23:48):
in our own bodies, in our synapses, in our brain
and in our along these long nerve fibers on our
spinal cord. So what other forces are there in the
world that can affect us?

Speaker 1 (24:01):
So we've seen other stuff, not just electricity to spark
our husbands and to fry trees in a lightning storm.
But like magnets, right, magnets are definitely a different thing
than electricity. These are things we've known about for thousands
of years, and a couple of hundred years ago, a
clever Scotsman helped us understand that magnetic fields, which are

(24:21):
very similar to electric fields, actually fit together with them
into a blended concept called electromagnetism. But that doesn't mean
that electricity and magnetism are the same thing. A lot
of people get confused and imagine that the union of
electricity and magnetism into one concept means that they are
the same thing. But it's more like how the union
of the front of an elephant and the back of

(24:42):
an elephant, and give you a whole elephant, doesn't mean
the front in the back are the same thing.

Speaker 2 (24:47):
Yes, and you will learn that if you're an elephant
keeper and you're behind an elephant.

Speaker 1 (24:51):
Go out and take some data. You will learn that
very quickly. Sort of how two sides of the coin
make more sense when you think of them together than
when you think about them separately. But heads does not
equal tails, So magnetism really is its own thing. It's
just like a different part of electromagnetism, and it's fascinating
because it's very similar to electricity, but it's also very different.
One way in which it's different is that there are

(25:14):
no particles out there with like magnetic charge. We have
particles like electrons that can give you electric fields, but
there are no particles that just sit there and give
you magnetic fields. Magnetic fields only come from the motion
of electric charges, like a current will give you a
magnetic field, or something rotating with a charge on it
will give you a magnetic field. There are no particles

(25:34):
out there with a pure magnetic charge, which makes it
pretty different from electricity.

Speaker 2 (25:38):
Now, hang on, Daniel, you say that magnetism is from
sort of the movement of charged particles. But I have
two magnets. They look pretty motionless, and then I put
them next to each other, and they still either stick
together or push each other apart. What's happening with magnet

(26:00):
If this is something that can be produced by an
electrical field, like something that is moving, the magnets themselves
do not, to my eyes, appear to be moving unless
I'm actually forcing them together through magnetism.

Speaker 1 (26:15):
And you probably are not running an electric current through it.
So you're wondering, like, where's the motion of the charges
that's giving me these magnetic fields, And it's the electrons spinning,
and these little quantum particles electrons and protons whatever, they
have a property called quantum spin, which is not physical spin.
It's not like they're actually little balls that are literally spinning.
It's a different kind of quantum mechanical property. Check out

(26:36):
our podcast episode about what is quantum spin. But it
is definitely a kind of spin. It carries angular momentum
for sure, and it does generate a magnetic field. So
a charged particle with quantum spin has also a little
magnetic field to it, and enough of these particles line
up in your little blob of metal and it becomes
a permanent magnet. So that's how a fridge magnet works.

(26:59):
There really is a kind of motion inside of it
that's creating a magnetic field. And you might think, hold on,
doesn't that contradict what Daniel just said about how there
are no like objects just that have magnetic fields. Well,
the fridge magnet doesn't just have a magnetic field the
way an electron has an electric field. It has a
dipole field. It has a north and a south. Overall,
there's no net magnetic field because it's a north and

(27:21):
a south. They cancel each other out. There's no particle
out there that just has like a north or just
has a south. That would be something we call a monopole. Though,
when an electron can just have like a negative field
and a proton can have a positive field. In magnetism,
you can only have the north and south together because
it's generated by the motion of an electric charge.

Speaker 2 (27:40):
It's interesting. So it's like if you're sort of in
a pool, like you're a little electron and you're moving
back and forth, there's always gonna be waves behind you
and in front of you. There's no such thing as
like if you're moving back and forth, it's not just
going to generate waves in front of you and not
behind you exactly.

Speaker 1 (27:57):
It's always in balance. There's no over a magnetic charge
in the universe. It's just fascinating because it's a stark asymmetry.
On one hand, magnetism works exactly the same way as electricity.
You write down the equations, they're all the same equations,
except for this one key difference that there are no
pure sources of magnetism in the universe that we know about.

(28:18):
Check out our podcast episode on magnetic monopoles and the
Hunt for them. But it means that magnetism is a
sort of weird shadow version of electricity, and together the
two can do this incredible dance. The electric fields and
the magnetic fields can oscillate together. The electromagnetic oscillation is
something we call light. Photons are oscillations in the electromagnetic

(28:42):
field as it slashes back and forth between electricity and magnetism.

Speaker 2 (28:46):
That's really interesting. I've never seen light occur just with magnets,
but I have seen light, you know, occur from electricity.
Natural sort of occurring plasma from a light is very bright,
So it's interesting that electromagnetism is like, is there like
a magnetic field around lightning?

Speaker 1 (29:09):
There are definitely magnetic fields around lightning, absolutely, because you
have lots of very highly charged particles moving at very
high speed. So you could definitely detect lightning using a compass.

Speaker 2 (29:19):
So is that a safe way to predict whether you're
gonna get hit by lightning? If you hold a compass
out and it starts going crazy.

Speaker 1 (29:26):
I think compasses will definitely go crazy in a lightning storm.
So if you see your compass going crazy, it means
either aliens are arriving or you might be about to
get zapped. Either way, you might get zapped.

Speaker 2 (29:37):
I'm gonna believe in the aliens option. Have you ever
wondered what would happen if you put like a giant
magnet next to your brain.

Speaker 1 (29:48):
I've done that. Actually, I've had an MRI that's basically
a giant magnet next to your brain.

Speaker 2 (29:52):
That is true. That's why you can't bring metal into
an MRI room, otherwise it's going to cause a big
problem problem.

Speaker 1 (30:00):
And for our particle accelerators, we have huge magnets in
these facilities underground to bend charge particles. And sometimes you
go down there when the magnet's on and they tell you,
like take off everything. You know, screwdrivers can become weapons.
I once saw a woman who forgot to take off
her earrings and her ear lobes were tugged very very stiffly.

Speaker 2 (30:19):
Ooh ah, that is that's like some final destination stuff
right there. So, like you can use electromagnetic forces to
impact the brain and actually kind of selectively shut off
parts of the brain. It's a reversible process. That's done
sometimes in research, sometimes in a clinical setting where you're

(30:42):
either stimulating or sort of shutting down parts of the
brain using electromagnetic forces. It is very creepy to me.
I'd be very interested to see what it feels like
to have like parts of your brain shut off, but
it's also scares me a little bit. I don't know
if I'd ever want to sign up for a study that.

Speaker 1 (31:02):
Is terrifying, especially if it's computer controlled, which means eventually
there'll be an app for that where you can like
shut off parts of your brain.

Speaker 2 (31:08):
This is how the AI win.

Speaker 1 (31:13):
The computer gremlins.

Speaker 2 (31:14):
So we've talked about electricity, We've talked about magnetism and
the way the two are like different sides of the
same coin. Are there other forces out there that you
know I could taste or touch or smell or know about.

Speaker 1 (31:30):
Yeah, there are. The sort of next natural one on
the list is the weak nuclear force. This is the
force that lets us see neutrinos, which for example, have
no electric charge, no magnetic field, cannot be seen at
all with electromagnetism, but neutrinos carry a weak charge, a
different kind of charge, not electrical charge, but a weak charge,

(31:50):
so they interact via the weak force, which is a
very different kind of force. It doesn't use photons to interact.
That has wn z bosons, and it's called the weak force.
It's not nearly as powerful as electromagnetism. It's much much weaker,
but it does have an impact on our life and universe.
For example, is the cause of most nuclear decay as

(32:11):
neutrons turn into protons, for example, via beta decay, which
is a weak process. So a lot of radioactivity is
due to the weak force.

Speaker 2 (32:20):
Now you say it is a weak force, and then you,
in the same sentence say radioactivity, which to me is
something that is powerful and scary. How can a weak
force be behind something like something being radioactive, which can
really mess with you.

Speaker 1 (32:37):
Yeah, it's a great question. By week, we really don't
mean that it's not capable of giving particles high speed.
That it doesn't mean that it can't give particles a kick.
It means that it's less likely to wake up and
do its thing, like if you shoot a nutrino through
a wall, it will mostly ignore those other particles because
it has a very low probability of interacting. So the

(32:58):
weakness is really about a chances of it happening, not
about the force that it can apply. That's why neutrinos
can pass through like a light year of lead without
kicking into any particle. But if they do, if one
of those particles rolls the right number on the many
billion sided die and actually does interact with that neutrino,
it can get a substantial kick. You can have fairly

(33:19):
high energy interactions using the weak force. It's more about
the chances of it happening than the power that it
can transmit.

Speaker 2 (33:26):
I feel like you guys should have named this the
shy forces then, because that neutrino is just shy, but
when you get to know it be pretty powerful.

Speaker 1 (33:36):
Yeah, exactly.

Speaker 2 (33:37):
So if there are weak forces, can I guess that
there are also strong forces.

Speaker 1 (33:43):
Yes, this is one place in which maybe particle physics
has done a good job, because there is the force.
We call these strong nuclear force. This affects particles that
have a strong nuclear charge, which we also call color.
To be extra confusing, so some particles like quarks, for example,
have color.

Speaker 2 (34:01):
Get your own word.

Speaker 1 (34:02):
Wait a minute, there's red, green, and blue quarks. Any
particle that has color will feel the strong nuclear force.
The strong nuclear force super duper powerful, lots of energy,
and very likely to interact. Basically, almost always does interact,
and so quarks are never seen by themselves. They are
always busy interacting with each other and forming bound states

(34:24):
like protons and neutrons, which are just collections of quarks
wrapped together into a blob. So the strong nuclear force
is very, very powerful and fundamental to the way our
whole universe works because it's built the proton, which is
really the building block of the atom, which is pretty
important when you're making a chicken dinner.

Speaker 2 (34:41):
All. Let my husband know to not forget the atoms
in the chicken dinner. So, because this is such a
strong force, is that why you know splitting an atom
causes such a huge effect?

Speaker 1 (34:54):
Yes, exactly. And this can be a little confusing because
we think of the strong force as holding a proton
together or holding a neutron together, and technically those objects
are color neutral, they don't have an overall strong charge
to them. But the strong force is also capable of
holding those protons and neutrons together into the nucleus because
while overall the proton is not charged and the neutron

(35:16):
is not charged, there is a little bit of residual charge,
because these quarks are not all on top of each other,
they're in different places inside the protons, So like one
side of a proton will have a little bit of
color charge and the other side will have a little
bit of color charge, and that's enough to stick the
protons and neutrons together. And then when you split the atom,
you're breaking those bonds and releasing energy. So even just

(35:38):
this little extra residual bit of the strong force is
powerful enough to power nuclear weapons and nuclear reactors and
all sorts of crazy stuff. It's a very strong force.

Speaker 2 (35:47):
It makes me think of two velcrow balls. Like the
balls themselves don't necessarily have any attraction to each other,
but the velcrow little individual hooks and tiny tiny loops
do have some attraction to each other. Well, it's not
a great metaphor because we're talking about velcrow versus quarks,

(36:08):
but like the quirks that make up the proton and
neutrons are attracted to each other, have a force pulling
them together. So they're like the parts are greater than
the sum of the parts, which is the opposite of
what it usually is.

Speaker 1 (36:22):
Yeah, exactly. It's fascinating and it's complicated. We don't really
understand how the nucleus holds together. In some cases, you
have all these protons which are being pushed apart by
their electrical charges but being held together by the nuclear force.
As you add more neutrons in there, it helps keep
the protons further apart, so it makes it more stable.
There's a whole field of nuclear physics about understanding how

(36:42):
big a nucleus you can make, and which ones are
stable and which ones are not. Not something we understand.
Because the strong force is also really really hard to
do calculations with because it's so powerful, little changes in
position can totally throw off your calculation.

Speaker 2 (36:56):
I mean that seems like it puts you in a
very difficult position as particle physicists and being able to
measure strong nuclear forces.

Speaker 1 (37:05):
It is indeed very difficult. It's difficult to do the
theoretical calculations and difficult to make the measurements, which is
why the strong force is an enduring mystery in particle physics.

Speaker 2 (37:13):
Well figure it out, you guys. What are we paying
you for? So is that it? Are there any other
forces that I should know about?

Speaker 1 (37:21):
There's one more force which may not even be a force,
and that's gravity. Gravity is something we often think about
as a force colloquially, though in relativity we describe it
instead as the impact of the curvature of space time
changing the way things move and changing the relative distances
between things. But in our daily life and our experience,

(37:41):
we still sort of see it as a force because
we can't see that curvature of space time directly. Instead,
we just experience it as if there was a force there.
And gravity is very powerful in terms of building the universe,
like the Earth is held together because of gravity. The
whole structure of the universe is because of gravity. But
it's also dooper weak, Like you can overcome the gravity

(38:03):
of the Earth using the power of your muscles. Right
every time you leap off the surface of the Earth,
you were defeating an entire planet size gravitational field with
just your impressive quads.

Speaker 2 (38:14):
Yeah, take that Earth.

Speaker 1 (38:17):
But we don't know fundamentally if gravity is just the
curvature of space time or if it's a quantum force
like the other ones. There's a whole group of people
working on quantum gravity try to understand how to unify
gravity with the other forces for which we have quantum theories.

Speaker 2 (38:31):
Yeah, and it's interesting because we can kind of feel gravity,
and I don't just mean like when you've impacted on
the ground, because you're just sort of feeling the ground
at that point, but like when you're weightless, if you've
ever been on a roller coaster or you feel kind
of weightless, it's not so much maybe that we're feeling
the gravity, but we're feeling acceleration or the lack thereof

(38:53):
when we're expecting it. But there's definitely sort of some
senses that we have that gravity definitely impacts.

Speaker 1 (39:00):
Yeah, and we'll dig into that in a minute. And then,
of course there are forces we don't yet know about.
These are the ones we've experienced and categorized and described,
but there could be other forces out there in the universe.
Remember that most of the matter in the universe is
not the kind of matter that makes us up and
that we experience. It's dark matter, and dark matter might
have some other kind of forces that it uses to

(39:21):
obeying against itself that we have never experienced.

Speaker 2 (39:25):
So you're saying there are like physics gremlins that we
just don't really know about.

Speaker 1 (39:31):
Maybe the aliens are physics gremlins.

Speaker 2 (39:34):
So we've talked about physics forces. Now I want to
talk about biology a little bit. I want to talk
about how physics interacts with our bodies.

Speaker 1 (39:42):
Absolutely, let's talk about what we can sense and how
that works, how we map that to these fundamental forces.
And I think we should start with vision because to me,
it's one of the most fundamental senses. You know, it's
the way that we sort of build our model of
the world out there by looking around us and imagining
where stuff is.

Speaker 2 (39:58):
Yeah, humans are interests because we are very vision focused,
I think. So vision is something that's very important to
us in terms of our socialization and our societies. And
you know, of course, like there are people who operate
without vision and they make it work, but sort of

(40:20):
evolutionarily speaking, vision is a very sort of fundamental sense
for human beings and how our socialization has developed, like
in terms of being able to see each other's faces,
understand each other's emotions, kind of these maps we have
in our brains of what a face should look like.

(40:41):
So it's really it's an interesting thing because there are
a lot of animals, There are a lot of creatures
in the world that are not as visually dependent as
humans are in terms of their sort of survival strategies.

Speaker 1 (40:52):
Yeah, it's incredible sort of how we build our mental
maps of the world and how that's informed by what
we see what we don't see. But let's break it
down and think about like the journey of a photon
in terms of the fundamental physics. Of course, the photon itself,
the thing that you're seeing is a little ripple in
an electromagnetic field. It's created by an electron maybe that's
jumped down an energy level or whizzed around in the

(41:14):
universe and gotten bent by a field and had to
change directions. So given off a photon, that photon is
now a little pulse of energy in the electromagnetic field
wiggling through the universe at the speed of light. And
that is in the end, what we're trying to sense, right,
And so that photon then hits your eyeball, and there's
a lot of Rube Goldberg like mechanical bits that happen there.

(41:34):
When the photon hits your eyeball, you might say like, okay,
photon is electromagnetics, so therefore that's the force that powers it.
But you also have to dig into like how we
actually see the photon, not just what the photon itself
is made out of.

Speaker 2 (41:47):
Yeah, exactly. So it's really interesting too, because our entire
eye is kind of one of the more elegant things
that evolution has produced, that there is all of these
structures that are specifically designed to be able to capture
and focus light. Of course, like we have the cornea,

(42:11):
which essentially like allows the light to pass through and
then it bends it and then it hits that lens
which can focus the light onto the back of the eye.
And the back of the eye is called the retina,
and the retina has all of these photoreceptors on it,
the rods and the cones. The iris is that colorful

(42:33):
ring around your pupil, and that focuses the constriction and
opening of the iris determines how much light is lit in.
And the pupil is not really a thing, it's the
absence of a thing. The pupil is just the hole
that leads into your eye.

Speaker 1 (42:52):
Yes, you have this sort of squishy muscular sack that
controls where those photons go and how they get back
to the receptor, which is the part that's really doing
the sensing. But you can't just ignore the eyeball because
also it's a filter, right, It controls the amount of light,
so it rejects some photons. It also filters them by frequency.
Not all frequencies of light. See, the eyeball is equally transparent.

(43:15):
Some of them don't make it to the back of
the eyeball, and some of them do, which is why
you can and cannot see some frequencies of light.

Speaker 2 (43:22):
That's right, Like, that's why we can't see UV light
generally because the cornea filters it out. That's why people
who have had surgery on their eyes where they're removing
a part of the cordia and replacing it with an
artificial cornea actually sometimes can see UV light because that
natural corneal filter is no longer there.

Speaker 1 (43:44):
Wow, that's crazy, like a whole new window onto the universe.
But the actual sensing motion itself is amazing to mean,
because it's like a tiny little machine. I mean, you
imagine this whole thing is going to be electrical. They
have a pulse of electromagnetism which is then received and
turned into an electrical pulse. The nerves, et cetera, et cetera.
The whole thing's got to be electrical, right, But at
the heart of it is a little machine. These proteins,

(44:06):
which are fundamental building blocks of biology in the end,
are little molecular machines they like. And what a photoreceptor
fundamentally is is a protein that when a photon hits
it undergoes a conformational change. It's like it flips a
switch on this protein. It's kind of incredible to me
that the whole thing is so mechanical.

Speaker 2 (44:24):
Yeah, it just kind of like snaps into place, and
that snapping is actually what causes the signal to be
sent to the nerve, and then that goes to the nerve.
Like all of these little smaller nerves collect into that
nerve bundle at the back of your eye. That's actually

(44:44):
where your blind spot is, and all of that goes
to the occipital lobe in your brain. But it all
starts with that snapping action of the photoreceptive cell.

Speaker 1 (44:55):
It's incredible how important it is that things really move right.
We're used to thinking about solve state technology and hard
drives that don't spin is lasting longer, But in order
for you to see, you have to have these proteins
in your eye that flip back and forth. Right, they
flip when they get hit by a photon, and they
flip back quickly so you can see a new picture.
It's like having all these little mechanical shutters worrying inside

(45:17):
your eyeball at all times.

Speaker 2 (45:19):
And depending on the type of cell, it responds to
the different wavelengths of light. So that's how we can
distinguish color, right, Like, if we didn't have that ability
to distinguish between wavelengths of light, we can only kind
of understand whether there's light or not. But because they
are specifically able to have that snapping movement to maybe

(45:41):
red light to green light, to blue light, or some
combination of that, like some sensitivity, it's usually on a spectrum.
That's how we are able to not only be able
to tell the difference between those types of wavelengths of light,
but to build a complex repertoire of a whole gray
of light, like we could in theory see like an

(46:04):
almost infinite combination of different types of wavelengths hitting our
eyes causing that reaction, and then our brain is the
thing that calculates like what we actually see, how we
actually interpret that color. But it's thanks to this mechanical
ability of those cells to respond differently to different wavelengths

(46:26):
of light. And so you'll have a cell that does
not respond to a longer wavelength of light, but that
same cell responds to a shorter wavelength of light, or
a different cell that only responds to longer wavelengths of light.
So it's that combination of those differentiated cells that allows
you to see complex color.

Speaker 1 (46:45):
Yeah, it's sort of like frequency triangulation. You can figure
out by understanding how much each of them was triggered
where the real frequency was, which gives you the ability
to sense the infinite spectrum of photons. But even though
it is mechanical, even though you have all these little
machines worrying inside your eyeball all the time, which if
you're really quiet, maybe you could listen to and hear,
in the end, it is still electro mechanical because all

(47:09):
these things are chemical, like the protein structures and the
way the protein moves, the way a respond to the
photon is in the end, all because of the atomic bonds.
The way these proteins are built, the way they can
settle into various states, all come down to how the
atoms inside those protons are bonded with each other where
they like to be, where the lowest energy states are.

(47:29):
And that's all due to the atomic bonds which comes
from the electron the whizzing around between these nuclei. So
in the end, the entire chain here really is just
due to electromagnetism.

Speaker 2 (47:41):
It's like an even tinier Roob Goldberg machine inside of
the tiny Roob Goldberg machine's Roob Goldberg machines all the
way down, which is a hard thing to say. The
words don't come out of my mouth very well.

Speaker 1 (47:53):
So it's a pulso electromagnetism which then gets converted via
a little machine which is built on electromagnetism, into an
electromagnetic pulse in your nerves. So it's sort of like
a Rube Goldberg zapping machine, right.

Speaker 2 (48:05):
And then once it hits your brain, of course, the
electromagnetic elements of the brain, it is the pattern of
the synapses firing. You have some kind of difference in
electrical potential between two neurons and then that causes firing
across the synapse of transfer neurotransmitters, and it's that pattern
of firing that gives you the conscious experience of the.

Speaker 1 (48:29):
Color exactly, and your whole visual experience of the world
rests on electromagnetism. Without those electrons and their little magnetic properties,
you couldn't see anything.

Speaker 2 (48:39):
I feel like this is a commercial for electromagnetism. Electromagnetism,
you couldn't do anything without it.

Speaker 1 (48:48):
I am indeed a shill for big electron.

Speaker 2 (48:50):
Well, we are going to take a quick break, but
you know what, we couldn't have taken a quick break
without electromagnetism. So here's a word from our sponsor, electromagnetism.

(49:14):
All right, so we are back. I hope you've all
purchased a big box of electromagnetism. I don't even know
what that would look like, a bunch of magnets and
light bulbs something. But yeah, let's talk about more senses
and how they work, how this complex dance between the
world of the physical and then our brains and our

(49:36):
sensory organs kind of interact.

Speaker 1 (49:39):
Yeah, let's see if we can escape the little electromagnetic
grimlins and find out if other forces play important roles
in our senses in the universe. And maybe next we
should talk about the one that you're experiencing right now,
the one you're using to hear our voices. Sound. What
sound is and how we experience it. Sound waves are
just molecules bumping into each other. Soundwaves are not fun

(50:00):
mental properties of the universe. The way a photon is
a photon is a ripple in the electromagnetic field, a
sound wave is a ripple in something else that already
exists in the universe, matter in the universe. So if
you imagine like a table filled with ping pong balls
and you push on the ping pong balls on your side,
they're gonna push on the next set of ping pong ball,
to push on the next set, and eventually they'll fall

(50:21):
off the other side of the table. So sound is
really just like that. It's pressure waves in air or
in metal, or in water, or in any kind of
matter that squeeze together as bonded enough together for one
bit to push on another bit.

Speaker 2 (50:35):
It's like a Newton's cradle and then the final ball
sor it's inside your ear, the little delicate organs that
help you experience sound.

Speaker 1 (50:44):
And that's why sound requires some kind of matter medium. Right,
you can't have sound in a perfect vacuum because there's
nothing to push whereas you could have photons because photons
are ripples in the fundamental electromagnetic fields, which are always there,
no matter how much stuff you suck out of your chamber.

Speaker 2 (51:01):
So when they say that there's no sound in space,
there's really no sound. Like It's not like if a
tree falls in a forest and no one's around, it's like, well,
it does make a sound because it is pushing the
air around it. So technically, if what we're calling sound
is the wave of molecules bonking into each other, it

(51:22):
does exist in a forest, but it really does not
exist in space.

Speaker 1 (51:26):
Yeah, physics would say that pressure waves are created in
the air when a tree falls in the forest, but
it doesn't impact anybody's sensors. Is it really a sound
or is it just pressure waves? I think that's the
philosophical question, but the physics question for space. Actually, the
answer is that sound does exist in outer space because
space is not a vacuum. There are particles out there,
electrons and protons constantly whizzing around. Now much much lower density,

(51:50):
of course than anything we experience on Earth, but there
are particles out there, and you can push on them,
and you can make pressure waves in the solar wind,
for example, So technically there is sound in outer space,
so feel free to scream if you're attacked by the
electromagnetic gremlins on your next space voyage.

Speaker 2 (52:07):
So did Star Wars lie to me or not?

Speaker 1 (52:10):
The question? The answer to that is definitely yes. No
matter what we're talking about. Star Wars is a big lie.
We've got the force, we've got lightsabers, I mean, the
whole thing is just magical realism. I love it, of course,
but it's a big lie. So in terms of how
we perceive sound, right, we know sound are pressure waves
through the air, and we've developed these biomechanical abilities to

(52:31):
sense this. And the ear is basically like a complex
instrument for focusing and transmitting that energy into a mechanism
that your brain can perceive. And there's various parts of
the ear. It's really incredibly complicated. The outer ear focuses
the sound waves towards the ear drum, which then vibrates. Right,
you have this like literal drum inside your ear that's

(52:51):
vibrating at the same frequency as these pressure waves. And
you might think, oh, well, that's it. You have an
ear drum and it's vibrating, You're done. But that's just
like step one.

Speaker 2 (52:59):
Right, And this is also why you do not use
Q tips in your ear, because it is a literal physical,
stretchy membrane, but it's very delicate, and it needs to
be very delicate to pick up on these very like
minute vibrations because we can hear soft sounds as well
as loud sounds, so it's got to be sensitive to that.

Speaker 1 (53:20):
So you should always clean your ear drum with a squeegee.

Speaker 2 (53:22):
Right exactly, you shove a cue tip in too far,
you'll actually puncture that ear drum.

Speaker 1 (53:29):
Oh please don't do that.

Speaker 2 (53:30):
Yeah, please don't do that. Don't I'm saying not to
do that, And.

Speaker 1 (53:35):
Yet you're giving me a mental image of it happening,
which is making me show.

Speaker 2 (53:40):
So we've shrunk down real tiny, and we're inside your ears.
We've found the ear drum, Like what else are we
going to find in here?

Speaker 1 (53:49):
So then in the middle ear, we have these three
tiny little bones which basically help transmit those vibrations from
the outer ear to the inner ear. And this is
a little bit of an engineering called impedance matching. If
you want a signal to get transmitted across different kinds
of materials without complicated reflections. Then you have to be
really careful about how that interface happens so you don't

(54:11):
get all sorts of lostiness and reflections which you can
echo back on each other. So these are engineered to
sort of transform the waves from the ear drum into
the inner ear, which has this little tube filled with
fluid which can then vibrate. So it's really complicated process
with these ear drum and then these three tiny bones,
and then finally in the end it's this little spiral,

(54:32):
fluid filled tube that you want to vibrate so that
you can actually hear something.

Speaker 2 (54:37):
That's so cool. I mean, in the complexity of the ear,
I think can also help us understand where a sound
is coming from, like is it coming from behind us?
Is it coming from right next to us. We have
not just a sense of sound, but a sense of
the location of the sound, which is really interesting. In fact,

(55:00):
in owls, they have a really unique thing where their
ear holes. They don't really have the external ears that
humans have, but they have ear holes and one ear
hole is actually lower than the other, so they're not symmetrical,
and that's to help them specifically be able to tell
where sound is coming from. When they are scanning for

(55:21):
a sound coming from the ground, because then the difference
in where the sound hits like their ear holes helps
them triangulate very specifically. Like if they hear a little
mouse in a field, they have to triangulate exactly where
that mouse is, and having that difference in locations of
the ear holes gives them yet another sort of mathematical

(55:43):
calculation that their brain can do of this difference of
the sound hitting each ear hole, and then they can
triangulate where the tasty mouse is and grab it.

Speaker 1 (55:52):
Yeah, the key is always having different sensors with different
capacities allows you to triangulate, and that's fascinating. But every
time you say ear holes, it makes me wonder if
that's like a big insult that owls use on each other,
like they call each other ear holes.

Speaker 2 (56:05):
You're a real ear hole, Frank.

Speaker 1 (56:07):
You ate that little mouse and I totally called it.
So you have this little spiral, fluid filled tube which
is vibrating with the sounds which were created when Katie
screamed in space. How do you actually experience that in
your brain? Well, there's one more step, which is that
there are these little hairs that wiggle and the hairs
are in different places in this tube, and the tube

(56:30):
is designed so that the sound frequencies will resonate in
different parts of the tube. So a certain frequency, like
the really highest sounds in Katie's scream, will land in
a different place than this tube than the lower frequencies.
When she's like mostly given up, the ghost will land
in a different spot. And so different hairs get wiggled
by different frequencies, and then that sends signals to your brain.

(56:52):
The different hairs send different signals, and your brain is like, oh,
that was a lower frequency scream or a higher frequency scream.

Speaker 2 (56:58):
Right, And the difference is ear structure based on what
animal you are determines whether you can hear higher or
lower frequency, Like elephants are really good at hearing really
low frequencies that we cannot hear with our dinky little
human ears, and dogs can hear higher frequencies that we
cannot hear with Like if you have a dog whistle

(57:20):
not talking about someone doing something naughty and pretending not
to it's like the very high frequency sound, your dog
will hear it and we won't. Younger people will hear
higher frequency than older people because older people after we
go to enough rock concerts, we start to become less
sensitive to high frequency sound because of damage we've actually

(57:43):
done to our ears.

Speaker 1 (57:44):
It's sort of the opposite of what happens in a band.
Like the bigger instruments like the tuba can make deeper
sounds because they physically have to be larger to contain
the longer wavelength resonance modes there, and the little piccolo
like the mini flute, is super duper kind, so it
can get to those really high sounds which have shorter wavelengths.
In the same way, bigger ears can hear deeper sounds

(58:07):
lower wavelengths, and tiny ears can hear higher sounds at
higher frequencies. So these hairs wiggle and then they're transmitted
into nerve pulses, which is like the fundamental language of
how your brain works. So now we have the whole chain, right.
The scream happens in outer space, It creates a pressure
wave which then gets transformed into different kinds of pressure
waves in different parts of your ear, which eventually wiggle

(58:27):
those hairs and send a nervous pulse up to your brain.
And so in the end, it's all mechanical. Right. Sound
is mechanical all to the very very end when it
gets transformed into a nervous pulse. But that mechanical interaction
in the end is still electromagnetic because how does the
machine work. It's no different than those photoreceptors in your eyes,
which are little machines. They're built out of electrons, out

(58:49):
of atoms. The way they push against each other are
electrical forces. Like we started off talking about pingpong balls
pushing on each other, how does that happen? How does
one air molecule push against another air molecule. Their electrons
are repelling each other when they get too close. How
does your chair hold you up when you sit on it.
It's the mesh of electrical forces holding it together. So

(59:10):
the atomic structure which is used to build all of
these machines is the fundamental force that allows sound to
be transmitted through the universe into your ear holes.

Speaker 2 (59:20):
So whether it's two ping pong balls hitting each other,
or molecules moving through the air and hitting this complex
structure inside of your ear, those are both things to
electromagnetic forces.

Speaker 1 (59:32):
Absolutely, it's all electromagnetic forces that constructs the world that
we live in and allows machines to have a physical
extent and transmit forces to each other. And that's really
what sound is. All of mechanical engineering really is electrical.

Speaker 2 (59:45):
Engineering, speaking of physical things bonking into each other. I
believe probably the same force might be behind what happens
in the inner ear in terms of your sense of
balance and acceleration and gravity. It's like why you get
motion sick, why you feel vertigo or a sense of

(01:00:08):
lack of balance, like when you feel slightly off balance.
Inside these fluid filled chambers in your ear, there's a liquid,
but suspended in the liquid are actually these tiny calcium
crystals that can When the movement of these crystals and
interaction with these tiny nerves, that information is sent to

(01:00:32):
your brain and it tells you like, hey, I'm moving,
I'm accelerating. I'm on a roller coaster. Oh no, i
hate roller coasters. So like, the ear not only is
a complex sound detector, it is also a movement kind
of like gravity and acceleration detector, which is really cool.

Speaker 1 (01:00:51):
Yes, absolutely, the ear is capable of measuring acceleration right
as these crystals move to the liquid, or as the
liquid slashes around inside your ear and touches different parts
of it. Your brain can tell that you're being accelerator
or you're upside down. It's sort of like if you
had a ball inside the back of a truck. When
you hit the acceleration on the truck, then the ball
gets left behind, it hits the back of the truck.

(01:01:12):
When you hit the brakes on the truck, the ball
will roll towards the front of the truck bed. If
you're inside the bed of the truck, you can tell
when the gas is being pressed and when the brake
is being pressed just by watching the ball. In the
inner part of your ear basically works like that, and
it allows you to measure acceleration and gravity and what's
up and what's down. And that raised an interesting question
like what's the fundamental force involved there. We know there

(01:01:33):
are electromagnetic signals, and we know that the structure of
the inner ear and all the things that it works
on our little machines that are built with electromagnetic forces.
But in the end, it's sensing gravity, right, It's sensing
acceleration and motion, and so that's an interesting combination like
gravity I think really does play a role there. We're
using electromagnetics based sensors to observe gravity and acceleration.

Speaker 2 (01:01:56):
Yeah, it's so interesting. It's that like, gravity is this
unique thing in the universe that may not even be
a force, and yet we still have an ability to
detect it with our ears. We've evolved this complex system
that is basically an accelerometer like inside of our heads.

Speaker 1 (01:02:16):
It's amazing and very useful. And if it ever gets
messed up while the world feels like an unpleasant.

Speaker 2 (01:02:21):
Place, yeah, that is like a dysfunction of those like
little ear crystals is thought to be behind disorders like vertigo.
I feel like we've covered the ears, not literally covered
the ears, because you still want to hear this podcast.
But let's talk a little bit about smell, because I'm
smelling that chicken. I do want to go to dinner,

(01:02:41):
but I first want to learn about how smell works.

Speaker 1 (01:02:45):
Smell is super fascinating because in some ways it's much
more mechanical than the other senses, but it's also much
more complicated. Like sound and vision in the ends can
be expressed as observing different frequencies of the same thing,
So you can boil it down to information, right, like
what frequencies of light are you seeing? What frequencies of
sound are you hearing. You can look at the equalizer

(01:03:06):
on your stereo see like the fundamental building blocks of
the song that you're hearing, and so it can be
digitized and it can be transmitted. You can have like
electronic vision and hearing right microphones and cameras and screens
and all that stuff. The same is not true for
smell because it's much more complex. It's not just a
single frequency spectrum along which every smell sits. It's a

(01:03:26):
super high dimensional space. Essentially, smell is detecting individual molecules
of different kinds. You know, you're smelling a poop molecule,
you're smelling a chicken molecule, you're smelling molecules from flowers. Really,
smell is detecting super dilute presence of specific molecules in
the air. It's really incredible that it works at all.

Speaker 2 (01:03:46):
This is one of the things that like, it's so
hard for me to understand, and I think it's also
just hard for experts to understand how smell works, because
it is one of these things where it's like we
have just a bunch of receptors and they kind there's
some sort of lock and key mechanism that happens with

(01:04:07):
these molecules and it sends a signal to the brain
and then we experience that smell and it can be
way more complicated, even in say like a dog, who
is able to distinguish massive amount of smells. In fact,
I would say like a dog's world is probably more

(01:04:27):
smell focused than it is vision focused. Of course they
can see, but smell is probably their primary way they
experience the world, which is very different from humans.

Speaker 1 (01:04:38):
Yeah, dogs can be blind and they're like whatever, no
big deal. As long as I can still smell, I
can tell who's there and what they're doing, what they
ate for dinner, like three weeks ago is incredible. And
it all comes down to these super powerful lock and
key mechanisms. Basically to detect which molecules are out there,
what you need is some way to say, like, okay,
here's a little chicken molecule, or here's a little molecule

(01:04:58):
of pasta or whatever. I always want to understand these
things from the microphysics point of view, like zoom in
what is really happening? How do you have a sensor
which reacts to only one kind of molecule and not
another kind of molecule. So I talked to my wife
about this, who's a biochemist. She has a pretty deep
understanding of the fundamental mechanism. And essentially, you have these
cells in your nose that have membranes in them, like
every cell does, but you have these proteins which go

(01:05:21):
across the membrane. They have some bits that stick out
on the outside of the cell, and some bits on
the stick on the inside of the cell, and the
bits that stick on the outside all have funny, weird shapes,
so they're basically like the lock that the molecule fits
into like a key, so they trigger it. So if
the right molecule comes along and fits into these little
bits of the protein that stick out past the edge

(01:05:42):
of the cell and interacts with it, it can then
transmit a signal through the cell membrane into the inside
of the cell and make something happen, and that's how
you detect it. And then of course you have like
hundreds or thousands or maybe even more kinds of receptors
in your nose, so you can smell different kinds of stuff,
just like a spectrum from red light to green light
to blue light. It's like a huge list of individual

(01:06:05):
different kinds of receptors that can all detect different kinds
of molecules.

Speaker 2 (01:06:09):
I mean, it actually kind of reminds me of how
the immune system works. It's a very similar lock and
key mechanism, where you have immune cells and they have
all sorts of surface receptors and they will be able
to fit with like different kinds of antigens. Like that's
like the key, and then the surface cell is like
the lock, and then they fit together. And then once

(01:06:30):
that happens, you have a basically chemical chain reaction that
happens across the membrane and into the cell. So like
that lock and key mechanism is so important in biology,
and it's found sort of in all sorts of biological processes,
including our sense of smell. Like those poop molecules are
getting real intimate with your cells.

Speaker 1 (01:06:51):
They're unlocking something deep inside you. But it's even more
complicated than just a lock and a key, which gives
you the sense of like a mechanical thing. You might
be wondering, like, well, who's turn earning the lock? Right,
It's more complicated than just having the piece fit into
the right slot. There are electric fields there, right, because
these atoms have electrons whizzing around. That all has to
fit in just perfectly so that the atoms like to

(01:07:12):
hang out with each other. And then you have to
have like the right hydrophobic properties. Maybe together the lock
and the key element like to dispel water, They like
to push water out, so they fit together really snugly.
And these bits of these things which are squishy and
have to have like the right squishiness to click together
in the right way. And the end, what you're doing
is transmitting some energy from the molecule into the receptor,

(01:07:33):
and that either happens by coming in and hitting it
or interacting it with it in some way. But it's
not a deep bond. It's not like the lock and
the key are forming some new macromolecule through covalent bonding.
It's more like they're pushing up against each other. But
as you say, Katy, it's not something we actually understand
very well. There are all sorts of theories about how
that energy gets transmitted. There's lock and key mechanism, where

(01:07:54):
sort of mechanical transmission of energy is one of them.
But there's another theory called vibration theory that the molecule
that comes along is actually emitting a low energy photon
like an infrared photon as it transitions from one state
to another, and then that triggers the change of state
by the receptor, which is moving from one state to
another by absorbing this photon and doing it through quantum tunneling.

(01:08:16):
There's two states. It couldn't otherwise get from one to
the other. It needs a little bit of boost of energy,
but doesn't actually have enough energy to go over the hump,
so it tunnels through that barrier. We have, of course,
have a whole podcast episode on quantum tunneling. But fundamentally
the physics involved in smell is not something that we understand,
which is incredible that it's still an open mystery, right,

(01:08:37):
such basic questions of the human experience still not understood
in terms of the fundamental physics.

Speaker 2 (01:08:42):
Well right, because I mean fundamental physics are not fully understood,
and fundamental physics are fundamental to understanding how it interacts
with biologies. I mean, I think it's just a humbling
thing to remember that, hey, biology, it is completely linked
with particle physics, like have a full understanding of biology,

(01:09:02):
like we would need to have a full understanding of
particle physics, so you know, hurry up, you guys figure
it out.

Speaker 1 (01:09:09):
And there's so many questions still open about how smell
works and how these receptors work. My wife Katrina was
telling me that they find these receptors not just in
your nose and of course in the back of your mouth,
but all over your body, like on the palms of
your hands, inside your body, like in your guts. There
are these same kinds of receptors, which is like, are
we smelling our own poop inside our body? Are you

(01:09:30):
can smell a flour with your palm when you're holding it.
These reactions are happening, we just don't always sense them.
They don't always get converted by our brain into the
smell sensation.

Speaker 2 (01:09:42):
Yeah, the gut thing is really interesting because there's definitely
a lot of information that's sent from your gut to
your brain and back and forth, and a lot of nerves,
a lot of neural activity that actually happens in your gut.
That's why things like ibs or like if you're anxious,
that can impact your guts functioning and vice versa. But yeah,
it's I mean, I don't think we know exactly what

(01:10:04):
those essentially like smell and taste receptors inside your gut does,
but it may have something to do with like how
our bodies regulate our guts, like how much blood are
we sending down to help speed up metabolism things like that.

Speaker 1 (01:10:18):
Yeah, it's sort of like a subconscious smelling, like it's
a sensation of the presence of these molecules in a
way you're not consciously experiencing.

Speaker 2 (01:10:26):
And thank goodness for that.

Speaker 1 (01:10:29):
And also a lot of these receptors trigger molecules we
don't know, but we don't understand. It's not easy to
look at a receptor and say, oh, this one obviously
senses ketchup and this one's sense is mustard. And there's
lots of receptors we like, well what is this one sense?
We don't know, and they're all over the place, so
we have a lot to learn. And then there's a
lot of fascinating wrinkles on like how you actually experience

(01:10:50):
that smell. And one of my favorite tidbits comes from rats.
It turns out that in rodents is a very close
connection between smell and sound, which means that like if
they smell something, they smell it differently. If certain sounds
are playing. So in rodent science, they call this neural
convergence a new kind of perception called smound, which is

(01:11:10):
a combination of smell and sound.

Speaker 2 (01:11:13):
Right, that is so interesting. I mean I think that
very rarely can happen in humans if you are affected
by something called synesthesia, which is when you're getting all
your sensory information as one typically would, but then in
your brain it is actually kind of mixing and matching

(01:11:35):
your sensory experience. So like you'll smell something and you
feel like that smell is a color, or you feel
like a number is a certain kind of color or feeling,
and it's very interesting. So like, I feel like this
is one of the things, like it's usually difficult to know,
like as humans, what it would be like to be

(01:11:56):
an animal. But I bet if you ask someone with
an esthesia, they could maybe give you something of an
idea of this experience of the rats where they have
this mound.

Speaker 1 (01:12:08):
Makes me wonder, like what music pairings we should be
playing in fine restaurants, you know, because maybe your food
smounds good with Mozart, but doesn't smeund good with Black
Sabbath or whatever.

Speaker 2 (01:12:20):
I feel like Mozart would be good with like a kianti,
whereas black Sabbath would be good with I don't know,
red bull.

Speaker 1 (01:12:28):
There you go. Well, there's all sorts of fascinating biology
and wrinkles. The experience of smell we don't have time
to get into. You know, how dogs have like hundreds
or tens of thousands of times more acute senses. The
grizzly bears have even stronger senses than the bloodhound. How
people can sometimes smell like whether they're related to somebody
based on their body odor. It's really incredible, it really is.

Speaker 2 (01:12:53):
The Only thing I'll say is that if you want
to make your dog happy, let them smell stuff like
that is, if you let your dogs smell, smell all
the smells, they'll be so happy. It's like them going
to the movies or to a museum. Smells are a
dog's whole world.

Speaker 1 (01:13:07):
And in the end, all of this smell, in terms
of the fundamental physics, is chemistry.

Speaker 3 (01:13:11):
Right.

Speaker 1 (01:13:11):
We're talking about the interactions of molecules with each other, mechanical, electrostatic,
but fundamentally it's all chemistry. It's all electromagnetic. Everything involved
in smell is electromagnetic interactions of big complex molecules with
other complex molecules, whether that's mechanical which again is built
on the electromagnetic force, or literal electrostatic interactions between these molecules.

(01:13:35):
It's all electromagnetism.

Speaker 2 (01:13:37):
So let me guess is touch also electromagnetism.

Speaker 1 (01:13:42):
Touch also seems to be electromagnetism. The way you sense
touch is through various kinds of sensors in your skin.
Some sense pressure, some sense temperature, some sense damage. Right,
each one has a special kind of mechano receptor to
tell like are you being squeezed or are you being
heat it up? And then they send their signals up

(01:14:02):
to your brain using of course electromagnetic pulses.

Speaker 2 (01:14:07):
That is so interesting. So like when I'm zamped with
some static electricity, I'm having electromagnetism zap me, but then
also electromagnetism telling my brain ouch I got zapped exactly.

Speaker 1 (01:14:22):
And then the last sense, taste is very closely connected
to the sense of smell, as we talked about. Of course,
of course your mouth is different from your nose, and
you have a tongue with taste receptors on it, but
taste receptors are not nearly as complicated or as varied
as smell receptors. You have a few thousand of them
on your tongue, which can sense basic things about classes

(01:14:42):
of molecules, so you have like sweet, sweet, sour, salt, bitter, savory,
or sometimes people call it umami. Each of these are
like receptors in your nose, except they're more coarse. They
like detect certain classes of molecules that they can trigger.
They're not like one of a kind molecule receptors the
way your nose, which is why most of your sense
of taste actually comes from your nose. Your mouth contributes

(01:15:05):
to it, and your tongue helps. But if you last
time you've had a cold, for example, and you couldn't
smell anything, you might notice that things sort of taste cardboardy.
And that's because the tongue can only distinguish like five
different senses, and your nose can distinguish like hundreds and
hundreds of different senses. It's much more complex.

Speaker 2 (01:15:23):
That's why you hold your nose when you're taking cough
medicine and makes it taste less bad.

Speaker 1 (01:15:28):
And I thought this was fascinating. It turns out that
most of smell's contribution to flavor occurs when you exhale,
as opposed to with smell. When you smell something, that's
during inhalation, right, you're breathing it in across those receptors.
But when you eat something, it's when you breathe out
that smell contributes to that sense of taste. It's really
sort of incredible how closely linked they are.

Speaker 2 (01:15:49):
I'm sorry to keep bringing it back to dogs, but
it reminds me of how like with thugs, when they exhale,
they're getting a ton more information from the smell, like
in their nose, like a specific channels in their nose
that allows them to experience more, which you know, you
always think that like when you're breathing in, you're breathing
in a smell like that's where you're getting the biggest experience.

(01:16:11):
But exhaling can give us, maybe not in terms of
identifying smells like with dogs, but for us it gives
us this much grander experience with flavor m M.

Speaker 1 (01:16:22):
And in the end, in terms of the fundamental physics,
all this again is chemistry. It's the interactions of molecules,
which is determined by their structure, which is based on
their atomic bonds, which is electromagnetism and their electrostatic propulsion
of each other. So in the end, this sense is
also electromagnetism.

Speaker 2 (01:16:40):
So has everything we've talked about been electromagnetism except for
that inner ear sort of accelerometer.

Speaker 1 (01:16:49):
Yes, it turns out that electromagnetism is really the fundamental
force we use to experience the universe, with the exception
of this sense of balance, which also is connected to electromagnetism.
Of course, because it's built out of these pieces that
use electromagnetic structures. Everything really is fundamentally due to electromagnetism.
We don't rely on the weak force or the strong

(01:17:09):
force in order to interact with the universe. Though of
course without the strong force you couldn't have these molecules,
and so you might argue that the core structure of
the atom is due to the strong force, but doesn't
really play a deep role in how those things interact.
That's really due to the electromagnetic interactions of the atoms,
how they bond together. So yeah, underlying everything is electromagnetism.

Speaker 2 (01:17:33):
It's kind of a particle chicken before the particle egg
kind of question one for philosophers.

Speaker 1 (01:17:38):
Yeah, although there's another side of the story, which is
that maybe all these forces are more closely connected than
we initially described. I told you about how electricity and
magnetism are really just two sides of the same coin.
About fifty years ago we discovered that the weak force
is actually linked to electricity and magnetism in a very
similar way. You put them together into something we call electroweak,

(01:18:00):
which is actually a much prettier and much more sensible object,
has more symmetries, it's linked together. It's really this coin
has three sides. It turns out.

Speaker 2 (01:18:08):
Wow, you just blew my mind. I can't picture a
coin with three sides. I guess it technical. Wait, a
coin does have three sides, because you got the head,
you got the tails, and then you got the little
rim around it.

Speaker 1 (01:18:19):
The weak force is the rim around the coin of
electricity and magnetism. So in the end, the weak force
is also playing a role in your sensus because it's
part of the electra weak force, which really fundamentally is
the thing that lets you interact with the universe. Lots
of people are working on grand unified theories which would
combine the strong force with the electroweek into one single

(01:18:39):
unified force to describe all of these quantum interactions. And
so if that is successful, maybe one day we will
say that there's just one force out there that lets
us experience the universe.

Speaker 2 (01:18:50):
Daniel, you told me Star Wars was lying to me
about the force.

Speaker 1 (01:18:56):
In the end, it's all midichlorians. Those are the fundamental
little gremlins of the universe.

Speaker 2 (01:19:02):
And we've done it. We've jumped the shark.

Speaker 1 (01:19:06):
So an important way that we see the universe is
literally by seeing photons. But it turns out that electromagnetism
is deeply rooted in every kind of sense we have
of the universe, which gives us a rich and very
picture of what's out there, but also limits us in
what we can do and what we can experience. There's
lots of stuff out there in the universe that doesn't
experience electromagnetism, like dark matter, and so our electromagnetic based

(01:19:28):
senses might be missing out on the bigger picture.

Speaker 2 (01:19:31):
Electromagnetism made me new friends and made me prettier too,
So get your electromagnetism today, call now.

Speaker 1 (01:19:42):
This podcast is sponsored by Big Electron. Thanks everybody for
listening and tune in next time. Thanks for listening, and
remember that Daniel and Jorge explain the Universe is a
production of I heart Radio. Or more podcasts from iHeartRadio,

(01:20:03):
visit the iHeartRadio app, Apple Podcasts, or wherever you listen
to your favorite shows.