Daniel and Kelly’s Extraordinary Universe - Which force(s) power the human senses?

Episode Date: October 26, 2023

Daniel and Katie talk about how we experience the Universe and what physics underlies our senses.See omnystudio.com/listener for privacy information.

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good stuff listen to the good stuff podcast on the iheart radio app apple podcasts or wherever you get your podcast every case that is a cold case that has DNA right now in a backlog will be identified in our lifetime on the new podcast america's crime lab every case has a story to tell and the DNA holds the truth he never thought he was going to get caught and i just looked at my computer screen, I was just like, ah, gotcha. This technology is already solving so many cases. Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Hey, Katie, paint me a picture of where you're seeing right now.

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? No, now let's add to the picture. Tell me what sounds there are around you. 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. And how about the smells in your Sensorium. 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. Does your microphone not smell like chicken? I thought everything smells like chicken.

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. And then the last sentence is touch. What is your sense of touch telling you? Well, the sense of touch in my butt is telling me that I should have invested in a much more expensive ergonomic podcasting chair. 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 Golden?

Well, there's little grimlins in my ear whispering things at me. But other than that, yeah. Those aren't gremlins, Katie. That's just me. It's just a physicist. I don't know what to be more afraid of. The Gremlins or a physicist. Hi, 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. 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. And how does that go over? I mean, I haven't been Italy in a while, but I imagine that's still not a typical kind of activity for saying hello. It's not. I'm in jail. 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 butt smell like what the night sky looks like

what's actually out there in deep space how all the particles between our toes 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. It feels good to be here. 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 going to smell me up. Like, there's a lot you can tell about a person just by huffing in that sense. You'll probably tell that I have dogs and I have kids. It's based on the random hairs on my body. The feel of the stickiness quotient is how I measure whether someone has kids. Like, is there sticky patches on your shirt that is in the shape of a very small, curious little hand. 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, 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 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. 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 isolated, like, well, what I'm seeing is kind of happening in my mind. But everything I'm seeing, like there's a direct sort of physical. 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.

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 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, hmm, somebody didn't clean up after their dog. You know that means poop molecules are hitting your nose. When I had that realization, I think I was in high school, it ruined my 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. 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. 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. I have smelled both today. And so today on the podcast, we'll be answering the question. Which forces power the human senses.

That sounds so cool. I'm imagining sort of my eyes being powered by some kind of like futuristic technology. 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. No, I mean, as we all know, it's tiny gremlins in there. Tiny business. Running little projectors. Little physics gremlins all the way down.

No, 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 cell 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 a few particles 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.

But in some cases, we can actually complete the thread. We can 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 to dig into today. 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 slight.

larger scale. And I feel like that's not too dissimilar to physics, although Rube 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 effect of physical phenomenon happening. 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 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 a 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 other hand, I often hear biologists exclaiming at 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. 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 biology where we look at things like you know like the eyeball is incredible it's 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 eyes 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 some kind of weird 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 apparent 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 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. 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 the human

senses. Here's what people had to say. I'm going with the electromagnetic force as I think all of our senses rely on that to send the signals to our brain where we interpret them. Internally, 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 as opposed with the light. You'd have the photo. or in the case of sound, you'd have the vibrational energy being sensed by the hairs. I guess with chemical sensing, it would be slightly more subtle, but there might be some analogous

process. 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 somehow. If you count equilibrium as a sense, then gravity would affect that. Then touch, smell, hearing, 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. I'd say the electromagnetic force is mostly responsible for powering the human senses. our entire nervous system basically works on electricity. And since our senses 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. I mean, I can't really disagree with this if we blend all these answers together and 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 in a lot of our sort of 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. 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. 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, even if it's not a human. Yeah, exactly. So we're going to map the human senses to the fundamental forces. What 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, 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 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 for 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 using electricity.

It's everywhere in our world. Hard to imagine a universe without electricity. How did we know about electricity before we had socks and carpet, 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 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 charged particles have these 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. 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? 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, that they're trapped into bonds. But the formation of the atom is also electrical. It's 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 that is electricity. It's all the forces of electrons on each other and on nuclei. So can you use electricity to facilitate chemical reactions in chemistry? 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. Does that count as chemistry?

I think I saw that experiment somewhere. 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 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 being reanimated by the soy sauce. Right. But to give a serious answer to your question, yes, absolutely. if you apply electricity or voltage or current to something, you're 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 there are probably analog signals in 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 to send signals up and down your nerves, which is why they move at almost the speed of light. 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 coma or even deaths. 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. It's brewed up by little soy goblins, I think. That's why it's so dangerous. I love soy sauce in moderation.

But that gives you a really cool picture of the sort of electrical map of your body and reminds you that your body is not just mechanical structures, not just like cells and membranes and bones, but there are electrical structures there 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 sort of like a computer. If you pour 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 the presence of electric fields, and that means that they're charged. That's what charge means. And as we'll talk about 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. some particles don't have charges. It's just something we observe and describe. So like all electrons have some kind of charge, but we really, like when do we feel that, right? Like when can we observe that charge? Because like, you know, you have your door handle and 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 we can notice that even though this charge can be all around us at this like subatomic level without us noticing yeah great question i mean fundamentally we notice something is charged when it's moved by an electrical field again that's the definition of charge if you give me a new particle i've never seen before one of the first things i would do would be to send it 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 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 going to accelerate any charged 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 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. 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. Yeah, exactly. If everything is totally neutral, then there are no forces. So I'm going to test this theory out by rubbing my socks against the carpet and zapping 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. I had this overwhelming sensation that I had to call her right then, and I just hit call. I said, you know, hey, I'm Jacob Schick. I'm the CEO of One Tribe Foundation, and I just wanted to call on and let her know there's a lot of people battling some of the very same things you're

battling and there is help out there. The Good Stuff podcast, season two, takes a deep look into One Tribe Foundation, a non-profit fighting suicide in the veteran community. September is National Suicide Prevention Month, so join host Jacob and Ashley Schick as they bring you to the front lines of One Tribe's mission. I was married to a combat army veteran, and he actually took his own life to suicide. One Tribe saved my life twice. There's a lot of love that flows through this place, and it's sincere.

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college superstar A. Z. Fudd. I mean, seriously, y'all. The guest list is absolutely stacked for season two. And, you know, we're always going to keep you up to speed on all the news and happenings around the women's sports world as well. So make sure you listen to Good Game with Sarah Spain on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Presented by Capital One, founding partner of IHeart Women's Sports. So the experiment was an unqualified success. I did zap 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 and static electricity and in our own bodies, 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? 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 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 an elephant and give you a whole elephant doesn't

mean the front and the back are the same thing. Yes. And you will learn that if you're an elephant Keeper and you're behind an elephant. 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 no particles out there with like magnetic charge. We have particles like electrons. they 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 out there with a pure magnetic charge, which makes it pretty

different from electricity. 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 magnets 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 and you probably are not running an electric current through it so you're wondering like where is the motion of the

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 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.

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 there's a north and a south that 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 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. 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 going to 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. It's always in balance. There's no overall 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. 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 oscillating. in the electromagnetic field as it sloshes back and forth between electricity and magnetism. 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 lightning is very bright. So it's interesting that electromagnetism is like, is there like a magnetic field around lightning? 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. So is that a safe way to predict whether you're going to get hit by lightning if you hold a compass out and it starts going crazy? 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. I'm going to believe in the aliens option. Have you ever wondered what would happen if you put like a giant magnet next to your brain? I've done that actually. I've had an MRI that's basically a giant magnet next to your brain. That is true. That's why you can't bring metal into an MRI room. Otherwise, it's going to cause a big problem.

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 take off everything, you know, screwdrivers can become weapons. I once saw a woman who forgot to take off her earrings and her earlobes were tugged very, very stiffly. Ooh, 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 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 also scares me a little bit. I don't know if I'd ever want to sign up for a study. That 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. This is how the AI win.

The computer gremlins. 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? Yeah, there are. The sort of next natural one in the lift 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 an electrical charge, but a weak charge.

So they interact via the weak force, which is a very different kind of force. It doesn't use photons to interact. It has WNZ bosons. And it's called the weak force because 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 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.

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. Yeah, it's a great question. By weak, we really don't mean that it's not capable of giving particles high speed. 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 neutrino through a wall, it will mostly ignore those other particles because it has a very low probability of interacting. So the weakness is really about the chances of it happening, not about the force.

that it can apply. That's why neutrinos can pass through like a light ear 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 high energy interactions

using the weak force. It's more about the chances of it happening than the power that it can transmit. 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, it'd be pretty powerful. Yeah, exactly.

So if there are weak forces, can I guess that there are also strong forces? Yes, this is one place in which maybe particle physics has done a good job because there is the force we call the 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. Get your own word. Wait a minute.

There's red, green, and blue corks. 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're always busy interacting with each other and forming bound states 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.

I'll 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? Yes, exactly. And this can be a little confusing because we think of the strong forces holding a proton together or holding a, you know, 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 is not charged, there is a little bit of residual charge because these corks are not all on top of each other.

They're in different places inside the proton. 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 then 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 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. It makes me think of two Velcro balls, like the balls themselves don't necessarily have any attraction to each other, but the Velcro 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 Velcro versus quarks, but like the quarks 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 like the sum of the parts, which is the opposite of what it usually is. 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 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 a strong force.

so powerful. Little changes in position can totally throw off your calculation. I mean, that seems like it puts you in a very difficult position as particle physicists and being able to measure strong nuclear forces. 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. Well, uh, 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? 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, in our experience, 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 super duper weak.

Like you can overcome the gravity 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-sized gravitational field with just your impressive quads. Yeah, take that earth. 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.

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're. 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 when we're expecting it. But there's definitely sort of some senses that we have that gravity definitely impacts. 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 obeying against itself that we have never experienced. So you're saying there are like physics gremlins that we just don't really know about. Maybe the aliens are physics gremlins. 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. Absolutely. Let's talk about what we can sense and how. 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 we sort of build our model of the world out there by looking around us and imagining where stuff is. Yeah, humans are interesting 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 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. 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. 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 universe and gotten bent by a field and had to change direction. 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 when the photon hits your eyeball. You might say like, okay, photon is electromagnetic. 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. 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, 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 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. Yes, you have this sort of squishy muscular sack that controls

where those photons go and how they get back to the receptors, 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. 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. 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 part of the cornea and replacing it with an artificial cornea actually sometimes can see UV light because that

natural corneal filter is no longer there. Wow, that's crazy, like a whole new window onto the universe. But the actual sensing motion itself is amazing to me 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 and 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, 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. 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 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. It's incredible how important it is that things really move, right? We're used to thinking about solid 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 whirring inside your eyeball at all times. 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 could only kind of understand whether there's light or not. but because they are specifically able to have that snapping movement to maybe 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 gradient of light like we could in theory see like an almost infinite combination of different types of wavelengths coming 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 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. 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 were really quiet, maybe you could listen to and hear. In the end, it is still electromechanical because all these things are chemical, like the protein structures and the way the protein moves and way it responds 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, and that's all due to the atomic bonds, which comes from the electrons whizzing around between these nuclei. So in the end, the entire chain here really is just due to electromagnetism. It's like an even tinier Rube Goldberg machine inside of the tiny Rube Goldberg machine. It's Rube Goldberg machines all the way down, which is a hard thing to say. The words don't come out of my mouth very well. So it's a pulse of 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. And then once it hits your brain, of course, the electromagnetic elements of the brain, like 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, a transfer of neurotransmitters. And it's that pattern of firing that gives you the conscious, experience of the 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. I feel like this is a commercial for electromagnetism. Electromagnetism. You couldn't do anything without it. I am indeed a shill for big electron. Well, we are going to take a quick break.

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Presented by Capital One, founding partner of IHeart Women's Sports. All right, so we are back. We'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 sensory organs kind of interact. Yeah.

Let's see if we can escape the little electromagnetic gremlins 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 sound waves are not fundamental 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 going to push on the next set of ping pong ball, push on the next set,

and eventually they'll fall 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's squeezed together that's bonded enough together for one bit to push on another bit. It's like a Newton's cradle and then the final ball sort of hits inside your ear, the little delicate organs that help you experience sound. 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. So when they say that there's no sound in space, there's really no sound. 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 bonging into each other, it does exist in a forest, but it really does not exist in space. 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, 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. And 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.

Did it Star Wars lie to me or not? It's a 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 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 eardrum, which then vibrates, right?

You have this like literal drum inside your ear that's 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, 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. So you should always clean your ear drum with a squeegee, right? Exactly. You shove a Q-tip in too far. You'll actually puncture that ear drum.

Ooh, please don't do that. Yeah, please don't do that. Don't. I'm saying not to do that. And yet you're giving me a mental image of it happening, which is making me show. So we've shrunk down a real tiny and we're inside your ears.

We found the eardrum. Like, what else are we going to find in here? 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 engineering called impedance matching.

If you want a signal to get transmitted across different kinds of materials without complicated reflections. You have to be really careful about how that interface happens so you don't get all sorts of lossiness and reflections, which can echo back on each other. So these are engineered to sort of transform the waves from the eardrum into the inner ear,

which has this little tube filled with fluid, which can then vibrate. So it's a really complicated process with these eardrum and then these three tiny bones. And then finally, in the end, it's this little spiral fluid-filled tube that you want to vibrate so that you can actually hear something. That's so cool. I mean, and the complexity of the ear, I think, can also help us

understand, like, 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, 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 earhole 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 a sound coming from the ground, because then like 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 calculation that their brain can do of this difference of the sound hitting each earhole. And then they can triangulate where the tasty mouse is and grab it. 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 earholes. You're a real earhole, Frank. 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 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 at a different place in this tube than the lower frequencies when she's like mostly giving 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. The different hairs send different signals. And your brain is like, oh, that was a lower frequency scream or a higher

frequency scream. Right. And the difference in 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, I'm not talking about someone doing something naughty and pretending not to. It's like a 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 done to our ears.

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 tiny, so it can get to those really high sounds, which have shorter wavelengths. In the same way, bigger ears can hear deeper sounds, 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 and different parts of your ear, which eventually wiggle 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 a machine work? It's no different than those photoreceptors in your eyes, which are little machines. They're built out of electrons, out of atoms.

The way they push against each other are electrical. forces. Like we started off talking about ping pong 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 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. 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? 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 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 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 in interaction with these tiny nerves, that information is sent to 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. 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 accelerated or you're upside down. 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. 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 raises an interesting question, like what's the fundamental force involved there? We know there are electromagnetic signals And we know that the structure of the inner ear and all the things that it works on are 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 electromagnetic-based sensors to observe gravity and acceleration. 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.

It's amazing and very useful. And if you ever gets messed up, wow, the world feels like an unpleasant 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, but I first want to learn about how smell works. 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 end 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 on your stereo to 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 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. 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 of there's some sort of locking key mechanism that happens with these molecules and then 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 smell focused than it is vision focused of course they can see but smell is probably their primary way they experienced the world, which is very different from humans. 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.

It's 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 of pasta or whatever. And 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 across

the membrane. They have some bits that stick out on the outside of the cell and some bits that 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 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. 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. So it's not just like a spectrum,

from red light to green light to blue light. It's like a huge list of individual different kinds of receptors that can all detect different kinds of molecules. 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 one, Once 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. 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 turning the lock? 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 the atoms like to 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 squishness to click together in the right way. In the end, what you're doing is transmitting some energy.

from the molecule into the receptor. And that either happens by coming in and hitting it or interacting it with in some way, but it's not a deep bond. It's not like the lock and the key are forming some new macro molecule through covalent bonding. It's more like they're pushing up against each other.

But as you say, Kate, 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 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. 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 physically, involved in smell is not something that we understand, which is incredible that it's still an open

mystery, right? Such basic questions of a human experience still not understood in terms of the fundamental physics. Well, right, because, I mean, fundamental physics are not fully understood and fundamental physics are fundamental to understanding how it interacts with biology. I mean, I think it's just a humbling thing to remember that, hey, biology, it is completely linked with particle physics. Like to have a full understanding of biology, like we would need to have a full understanding of particle physics. So, you know, hurry up, you guys. Figure it out. 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 smell a flower 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 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 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. 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. And thank goodness for that. And also a lot of these receptors trigger molecules we don't know about.

We don't understand. It's not easy to look at a reception and say, oh, this one obviously senses ketchup and this one senses mustard. And there's lots of receptors we're 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 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 a combination of smell and sound, 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 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 an animal.

But I bet if you ask someone with synesthesia, they could maybe give you something of an idea of this experience of the rats where they have a sign of this smound. 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. smell good with Black Sabbath or whatever. I feel like Mozart would be good with like a Kianti whereas Black Sabbath would be good with, I don't know, Red Bull. Red Bull. There you go. Well, there's all sorts of fascinating biology and wrinkles of 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. The only thing I'll say is that if you want to make your dog happy, let them smell stuff. If you let your dog 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. And in the end, all of this smell in terms of fundamental physics is chemistry, right?

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 electro-static interactions between these molecules. It's all electromagnetism. So let me guess is touch also electromagnetism? Touch also seems to be electromagnetism.

The way you sense touch is through very, very much. various kinds of sensors in your skin, some sense pressure, some sense temperature, some sense damage, right? Each one has a special kind of mechanoreceptor to tell, like, are you being squeezed or are you being heated up? And then they send their signals up to your brain using, of course, electro-magnetic pulses. That is so interesting. So like when I'm zapped with some static electricity, I'm having electromagnetism zap me, but then also electromagnetism telling my brain, ouch, I got zapped. Exactly.

And then the last sense taste is very closely connected to the sense of smell, as we talked about. You, 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 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're like detect certain classes of molecules that they can trigger.

They're not like one of a kind molecule receptors the way your nose is, which is why most of your sense of taste actually comes from your nose. Your mouth contributes 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. That's why you hold your nose when you're taking cough medicine and makes it taste less bad.

And I thought this was fascinating. It turns out that most of smells contribution to flavor occurs when you exhale as opposed to with smell. When you smell something is during inhalation, right? You're breathing it in across those receptions. 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. I'm sorry to keep bringing it back to dogs, but it reminds me of how like with dogs, when they exhale, they're getting a ton more information from the smell, like in their nose. Like there are 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, 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. 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.

So has everything we've talked about been electromagnetism except for that inner ear sort of accelerometer? Yes, and 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 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 it 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. It's kind of a particle chicken before the particle egg kind of question. and one for philosophers. 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 50 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 electro-week, which is actually a much prettier and much more sensible object. It has more symmetries. It's linked together. It's really this coin has three. Three sides, it turns out. Wow, you just blew my mind.

I can't picture a coin with three sides. I guess it's technically... 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. 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 senses because it's part of the electrow 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 Electra Week into one single 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. Daniel, you told me Star Wars was lying to me about the force. In the end, it's all Middichlorians. Those are the fundamental little gremlins of the universe. And we've done it. We've jumped the shark. 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 varied 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 senses might be missing out on the bigger picture. Electromagnetism made me new friends and made me prettier too. So get your electromagnetism today. Call now. 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 IHeart Radio. more podcast from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.

didn't have to audition? No, I didn't audition. I haven't auditioned in like over 25 years. Oh, wow. That's a real G-talk right there. Oh, yeah. We'll talk about all that's viral and trending, with a little bit of cheesement and a whole lot of laughs. And of course, the great Vibras you've come to expect. Listen to the new season of Dacia's Come Again on the IHeartRadio app, Apple Podcast, or wherever you get your podcast. It's important that we just reassure people that they're not alone, and there is help out there. The Good Stuff Podcast Season 2 takes a deep look into One Tribe Foundation, a non-profit fighting suicide in the veteran community.

September is National Suicide Prevention Month, so join host Jacob and Ashley Schick as they bring you to the front lines of One Tribe's mission. One Tribe, save my life twice. Welcome to Season 2 of the Good Stuff. Listen to the Good Stuff podcast on the IHeart Radio app, Apple Podcast, or wherever you get your podcast. I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about how to be a better you. When you think about emotion regulation, you're not going to choose an adaptive strategy which is more effortful to use unless you think there's a good outcome.

Avoidance is easier. Ignoring is easier. Denials easier. Complex problem solving. Takes effort. Listen to the psychology podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. This is an IHeart podcast. Thank you.