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Hey, Daniel, do you think going to space will make you older or younger?
I think it's going to be a rough trip, so you probably come back to the pretty warned and older.
Yeah, but it's probably pretty exhilerating. So why don't you come back younger? In spirit?
I mean you might feel wiser, which is just going to make you feel older.
Wiser is good, But what does physics say? What does relativity say? If you go to space? Are you going to get older or younger?
Physics says, you're going to be a tiny bit younger, probably not enough to compensate for the decades of wear and tear.
But you're in space and you're floating. What wears you down the danger of dying at any moment. Perhaps that's the same here on Earth.
The lack of gravity, the intense radiation, and yes, the danger of dying, which is much higher up in space.
But if you can gain a second, I mean, isn't time priceless? It's all we have.
You gain one second and you lose ten years.
But what of you? Hi?
I'm Hoory. I'm a cartoonist and the author of Oliver's Great Big Universe.
Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, And I'm gonna enjoy every second of life here on Earth.
Yeah, presumably hopefully even these seconds where we are recording this podcast.
Oh these are some of my favorite seconds. Absolutely.
Would you rather be like floating off an island in the Pacific drinking some drinks? I mean, this is really cool, But how does that compare sitting in a private island.
That would be so selfish, you know, just thinking about my needs. We're here to talk about physics with everybody and help everybody understand the universe better. That's so much more valuable.
Well, actually, I am sitting in a pool in my private island right now recording this, So I think I think that means I win.
Is your garage a private island or is it just like a mental island.
I'm not even I am floating around somehow, You're floating in cyberspace. But anyways, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we float your brain through an ocean of crazy physics ideas. We try to take you through the private island of understanding, hoping to marinate your brain in these ideas and percolate some of them down into your consciousness. We think that the deepest questions in the universe, how it started, how big is it, how it all works, are things that can be understood and deserved to be understood, or at the very least, we can explain to you what we do and do not yet understand.
That's right, because it is an amazing universe, and we like to take your sense of wonder on a vacation siteeing through the universe and the cosmos, looking at things that are already understood by humankind and things that are still a huge mystery.
Because science is a never ending list of questions, We're always going to be curious about the way the world works and why it is the way that it is. And it's those questions that power science. Questions asked by people working in the very forefront of human knowledge, and questions asked by everybody looking up at the night sky or looking down between their toes wanting to understand how everything works.
Don't you ever want to take a vacation, Daniel from asking questions? Well, I guess this podcast is sort of your vacation because you're answering questions.
Vacations are just more questions. Where should we go, how should we organize it, how should we get there? What should we eat tonight? There's no end of questions.
What should we not do? That's my favorite question on a vacation. But yeah, the universe is full of questions. Things we can ask about it, things we can wonder about it, things we can try to find the answers to, and sometimes on the podcast we like to answer these questions.
If you have questions about the nature of the universe, how things work, or if ideas are just not clicking in your mind right to us, we would love to help you understand it. We answer all of our emails to questions at Danielandjorge dot com. And sometimes I get a question, I think, ooh, I bet other people want to hear the answer to this, or I want to hear what Jorge has to think or joke about this topic. So then we answer them here on the podcast.
On the program, we'll be tackling listener questions. Number fifty five. Fifty five doesn't seem like a very big number, but we are pretty deep into our production run.
Fifty five is a pretty big number. There are lots of podcasts out there that don't even have fifty five episodes.
Fifty five seventy five.
Time to take a vacation.
But yeah, we'd like to ask our listener questions. And so we have three great questions here about space travel, but the nature of light, and about quasi particles, not queasy particles, those are particularly uneasy.
We will not be talking about burbonds today.
Yeah, or bar fonds. But yeah, we have three awesome questions, and so let's dive into our first one. This one comes from Dan.
I'm Dan, and I have a question about space travel and time. If we're able to send a spaceh to Mars and back, wouldn't the astronauts be a different age than the rest of us when they returned, and would the difference be caused by how fast they traveled or how long they were gone?
Interesting question from Dan. I guess the main thing is is that a lot of people maybe associate space travel with differences in time, like the famous twin Paradix.
Yeah, it sounds like Dan is planning a vacation in Mars and he's wondering how many shirts he's got a pack? How long will that trip be for him?
Yeah? I guess if he's not aging, he won't need as many shirts, or he does it need to go to that rejuvenating spot on Mars.
Or maybe he's wondering about renting his place out while he's gone. If he's gone for one year, does he need to AIRBNBA for two years? Or how does that all work?
It's confusing here on Earth if you're changing time zones.
That's right exactly. But Dan is right to worry about this because clocks do run differently out in space and on space travel, but for two reasons, both of which will affect the answer.
M interesting. There are multiple factors here that the universe throws at you.
Yeah, there's two different ways that time can flow differently. One is based on relative velocity moving clocks run slow, and the other is an absolute one. It's just based on space curvature. When space is bent, time is also bended, so clocks tend to run more slowly when space is more curved. These are two separate effects with different causes and importantly different behaviors, but both of them will cause clocks to run more slowly.
I meaning the time depends not just on how fast you're moving, which is maybe the one people are more familiar with, but also just how close you are to heavy things things that bend space and time, including the Earth.
Including the Earth, and including the Sun. This is why, for example, if somebody is near a black hole, distant observers will see their time running super duper slowly, not because they're moving at some high speed, but just because they are in place of high curvature. They are near a big massive object, and time will run more slowly. That's called gravitation time dilation. So there's velocity based time dilation and gravitational time dilation.
Well, so then when you're leaving Earth, you're basically experiencing both at different degrees and at different times, right, because you're leaving the Earth, which is has a gravitational fuel, but you're also going potentially really fast out there in space.
Yeah, exactly, And so it depends a little bit on the details, but we can do some approximate calculations to give Dan a rough answer.
All right, well let's start with I guess the first factor velocity. How fast do you think Dan is going to Mars?
This is a good question. It depends a lot on what you assume. But I thought, let's crank it to the extreme. Let's think about like the fastest possible trip you could make to Mars to have the most dramatic impact on time.
You mean, like to calculate the speed, We're just going to draw a straight line from here to Mars.
Yeah, and we're also going to assume that we have super heavy duty engines and excellent power, because you could get to Mars really slowly, Like you could go to Mars at like walking speed. It would take you a zillion years and you'd have no time dilation effects. Or you can get to Mars super duper fast. If you have really powerful engines that push you up above a tiny fraction of the speed of light, then you'd have more time dilation effects. So the time dilation effects depend on your top speed in the journey, which depends a little bit on the technology you have to get to that top speed.
But in reality, I guess when we send things to Mars, they usually take this a roundabout way, right, Like you try to use orbital dynamics and you try to use maybe the gravity of other planets to assist you and push you along, and so it takes a while. But even though you're going pretty fast, yeah, it takes a while. It can take like six months to get to Mars. And you are going pretty fast relative to like the speed of a Lamborghini on Earth, but you're not going very fast relative to the speed of light. And that's the issue. The speed of light is crazy, super duper fast, and to see real time dilation effects, you've got to get somewhere near the speed of light, and that's pretty challenging. So I thought, how fast can we get to Mars to maximize this effect. I see you thought that it was not an interesting answer, So let's crank it up. Yeah, let's crak it Up's crack it up and make it more fun.
Yeah. Let's assume Elon Musk or somebody else develops like a really powerful engine, one that uses like antimatter fuel, that uses like antiprotons or anti electrons that totally annihilate perfectly efficiently into energy and can pour that directly into the acceleration of your spacecraft.
It doesn't have to be an antimatter engine. It just has to be a powerful engine, right.
Just has to be a powerful engine. But you want an efficient fuel source so that you minimize the amount of fuel you have to bring along, so the fuel is mostly pushing the spaceship and not the other fuel.
I feel like you're worrying about a real life consequences in an imaginary scenario. Like I guess maybe you calculated the distance to Mars.
What's that distance at the closest approach The Earth to Mars distance is about half of the Earth to the Sun distance, So it's like forty five million miles.
So we have a distance, and so how did you calculate how fast we need to go to get there in a reasonable scenario.
Well, I imagine that we could build an engine out of anti matter, and I thought, what are the practical limitations for launching that kind of ship? But how much engine power could it produce? And you know, if you spent like a few years generating antimatter, you'd have enough engine power at launch that's like more than a thousand times the electrical power output of the United States, which would require like five tons or so of antimatter, which is totally unrealistic. But if you did that, then you would be able to get to Mars in just a couple of days. Like that kind of super powerful engine would get you up to like a third of one percent of the speed of light for a pretty zippy trip to Mars.
Would that run into like acceleration limits, Like our bodies can only tolerate so many g's.
That's right, humans can only tolerate like eight to ten g's, And even that's pretty extreme. So I was assuming we have like super robust astronauts that can tolerate about eight to ten g's.
Okay, So then you calculated the trip for Dan and you get up to about point to eight c's.
Yeah, exactly. Then that's at the halfway point, because you've got to speed up and then you're going to turn around and slow down so that when you get to Mars, you're not just zipping by it at half a percent of the speed of light, because that's kind of beside the point. So the top speed is at the halfway point.
Now, this is a very small percentage of the speed of light, less than a third of a percent. So I'm guessing maybe time didn't move that much slower for than because of the speed.
Yeah, exactly. And relativity is very nonlinear, so if you're still at very low velocities, there's basically no effect. The effect gets stronger as you get closer to the speed of light. As you get very close to the speed of light, it gets much more dramatic. So when you're going at this pretty respectable speed compared to Lamborghinians on Earth, but still very very slow compared to photons.
How fast are we going relative to a Lamborghini.
Yeah, so that's about eight hundred and forty thousand meters per second, which is something like one point eight million miles per hour, so a lot faster than a Lamborghini.
Yeah, by a large amount. But even though you're going over a million miles per hour, the time dilation is not that much.
The time dollation factor is one point zero zero zero zero zero four, meaning like every million seconds somebody traveling at that speed experiences four seconds fewer at the peak speed at the peak speed.
Yeah, but Dan is not going at the peak speed the whole time. So like, if he goes there and back, how much time is a younger relative to his twin who was born at the same time here on Earth and that didn't go.
If he goes there in forty eight hours and back in forty eight hours, that's like roughly one hundred hours, which is not even a million seconds. So the difference is going to be less than a second overall.
But he's also had to accelerate up to the speed and accelerate down to zero, so it's probably even less than that, maybe maybe like a tenth of that.
Yeah, it's going to be less than a second for sure.
So Dan is gonna go to Mars come back. He's going to be at eight to ten g's the whole time, and he'll only be younger by about less than a second.
Yeah, less than a second, exactly. That's only considering the velocity effects.
Right right, like starting from orbit or something.
Mm hmm, exactly, that's not considering the gravitational time dilation.
All right, Well, let's get into that. What are the gravitational effects of a time due to gravity?
So there's two effects here to think about. One is that you're leaving Earth's gravity and time passes more slowly when you're close to earth gravity. We know this because like satellites in orbit that keep our GPS systems in sync, their clocks run faster than clocks on Earth. This is something we've measured, so we know this very very well.
They've measured this in with mountains too, right, Like you can tell the difference between someone at the bottom of a mountain and a clock running at the top of the mountain.
Yeah, exactly. They have atomic clocks that are like two meters apart in altitude, and they can tell the difference in how they run. It's very very precise. It's super awesome.
Yeah, which means like your feet are moving through time slower than your head if you're standing up.
Yes, But the size of this effect is tiny, Like time passes on Earth more slowly than out in deep space, by like points seven parts per billion. That means in a billion seconds, time on Earth will have ticked by point seven seconds more slowly.
So if Dan just went up to orbit Earth's orbit, we would be a little bit younger, but not by much. Like I have a part per billion.
Yeah, exactly a billion seconds is like thirty two years. So if you spend thirty two years, like in deep deep orbit, then your clock will have run faster by one second.
So it's a very negligible effect.
It's not I don't know if it's negligible, and you can measure it with very precise devices, but it's real. And the interesting thing is that Mars has lower gravity than Earth. Right, it's a smaller planet, so on the surface the gravity is not as intense, and so this same effect on Earth that's like zero point seven parts per billion is only point one four parts per billion on Mars. So if you go to Mars and spend a lot of time there, your clock will run faster than clocks on Earth because you're not as deep in a gravity.
Well, well you're aging faster in Mars.
You're aging faster on Mars exactly, but that's actually not even the biggest gravitational effect. Mars is further away from the Sun, so the Sun's gravity is weaker at Mars than it is on Earth. This is actually a bigger effect than the difference between Earth and Mars. Sun's gravity causes a seven parts per billion effect on Mars and a ten parts per billion effect on Earth.
Meaning from the Sun's gravity you're aging faster in Mars.
Also, yeah, that's right, you're aging faster on Mars because its gravity is weaker and because you're further from the Sun's gravity. Overall, this effect is like six parts per billion on Mars.
Okay, so then what's the grand total for that. It seems like he's gonna gain a little bit of time due to velocity going to Mars and back, but he's going to lose a little bit of time by being further away from the Sun and by being around a planet that's smaller. What's the grand total.
Well, it depends on how much time he spends there. Right, If he just goes there and back, there's basically no effect from gravitational curvature. But if he goes there and lives there for like a thousand years and he's going to accumulate some effect from the curvature. So it depends on how much time he spends there on.
Mars, depends on how long he books that Airbnb exactly.
But the overall story is that these are tiny, tiny effects. You'd be a challenge to measure these things. You'd need very precise devices. But in the assumption that we could build crazy powerful engines that get us to Mars in two days, then the time dilation effects are going to be the most dramatic. But even those are parts per million.
Yeah, they're super tiny, But what's interesting is that they're there, right, they're measurable. Like if we synchronize our clocks and you went out there and came back, like our clocks would be off.
Yeah, and it really reveals that we live in an unusual set of circumstances. You know, we're not living near very strong gravity, we're not traveling at very high speeds, and so our clocks are mostly just synchronized. But there are places in our universe with extreme gravity and where things are traveling at very high speeds relative to each other and their clocks are much creasier.
All right, Well, I guess then the answer for Dan is that he's much better off vacationing here with me my private island floating at the pool, than by going to Mars. I think my mojito will probably take more time off with his overall age than then going to space and then with an antimatter engine.
Yeah, that's right, His mojito will melt one second slower after a million mohidos.
Well, it'd be hard to drink and going at eight to ten g's. So again, come join me, Dan. This is much more comfortable.
Here, Dan, you just scored an invitation. Wow.
Yeah, of course I don't know your last name, Dan, so I'm just gonna ignore all emails from Dan's. I don't I know which one asked the question where's this Dan? Daniel? Did I just invite you to my island?
Yes? This is my alter ego, Dan.
This is your twin, the twin that wanted to go to space.
When I take off my glasses, I'm Dan.
Oh no, it's the twin parad doctor. All right, Well, let's get to our two other questions. We have an awesome question here about the nature of light and one about quasi particles and crossword puzzles. So we'll get to that clue, but first let's take a quick break.
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All right, we're asking listener questions here today and inviting people toward private island. Apparently. All right, we have a great question here from John Lopez about the reality and nature of light.
Hi, Daniel len Jorge. My question is what is the physical reality of a wavelength of light? Like, what does it look like to have a wavelength of nanometers versus wavelength of tens of meters long? On the graph? I know we represent it as the peaks and valleys all stretched out, but what does this mean in real life. For example, in microwaves, mesh holes block microwaves because their wavelength is longer than the size of the holes. The visible light passes through because the wavelength is so much smaller. So in reality, in wavelength must be something different than stretched out peaks and valleys, because otherwise it seems like both could pass through the holes.
Just fine, All right, great question. Basically, what exactly is light? Is the question? Can you shed some light on this topic?
I love this question because it's clear to me that John is trying to like build a mental picture in his mind, trying to think about what happens in the universe and trying to describe it mentally, thinking about like are the photon zigging and zagging is like really wiggling sideways? What is actually going on? How to think about this stuff? It's really important that you build this mental model in your head. That's what physics is. So I love hearing him doing physics in his mind, trying to link it all together to get a coherent picture. It's perfect.
Yeah, I guess he's trying to get it like an intuitive sense of what light is like like if you were shrunk down to the small level quantum level, What would it be like to experience light?
Yeah, that's a great question, and you know, fundamentally we don't know what light is. Quantum mechanical things are very hard to visualize and to think about. But John's question actually is more about like classical physics, like thinking about light in terms of electromagnetic waves, you know, the peaks and the valley and the wiggles, and why that means your microwave is not frying your brain even if you stick your nose against it while you're cooking your popcorn. That do you know, maybe that's why my brain is fried.
Oh my gosh, Yeah, you're too impatient. I'm the popcorn. There. She go to Mars, take a vacation, come back. You'll be ready for you.
And I think there's a lot to learn in terms of how to think about light as wiggles in the electromagnetic field, because I hear a lot of misconceptions out there and actually a lot of mistakes in popular descriptions of how light works. So I think we can clear up a lot of those misunderstandings, even just in the classical picture, ignoring quantum effects, not thinking about photons, just thinking about light as an oscillation in the electromagnetic field.
WHOA, Okay, So this is confusing me a little bit because I think maybe what I know, what a lot of people know, is that light is both a particle and a wave, right, Like, that's kind of one of the dualities that physics found out at some point. So you're saying, let's ignore the fact that it's a particle, or are we just going back in time and forgetting quantum physics.
We're going back in time and forgetting quantum physics because we don't need quantum physics to explain this effect. The reason you're microwave war work and the reason that Dessin fry your brain can be explained using purely classical physics.
So when you're talking about the wavelength of light as a wave in classical physics, is that the same wave as when you're talking about quantum physics and things having a wave function for example?
There's an evolution there from one idea to the other idea. Absolutely, But we don't need to go into quantum physics for this answer. And that's all diggression. And you might think, hold on a second, but you know the world is quantum. How can you do that? But you know, physics is all about making approximations. None of our theories of the universe are exact and perfect. They ignore quantum gravity because we don't understand it. But you only need to apply the physics. You need to answer the question. Like if somebody asks, is this canniball going to make it over that castle wall? You don't need to do quantum calculations. You just need F equals MA. So part of doing physics is applying physics judiciously. In this case, we can just think about like Maxwell's understanding of photons and light as waves in the electromagnetic field.
Well, I imagine John is curious and it seems like from his question he is about the nature of light. Yeah, so, like, is light a wave? Is light a not a wave? We can think of it as non a wave or as a wave or only a wave. What is the classical picture of light?
Yeah? So the classical picture of light. Maxwell's idea from like one hundred and fifty years ago, before quantum mechanics is that light is just wiggles in the electromagnetic field. Like an electron has an electric field, right, and if you wiggle an electron, the field wiggles with it. That's why wiggling electrons in an antenna will generate waves like radio waves, which are electromagnetic waves and other charged particles. Wiggling more quickly with higher frequency will generate waves in the electromagnetic field that have higher frequency. Some of those are visible light or even ultraviolet light. So all kinds of light and radio waves, all the electromagnetic radiation are just wiggles in the electromagnetic field. That's the classical picture.
And the electromagnetic field in this case is not the same as the electromagnetic quantum field that we've talked about before.
Well, you can quantize this whole theory, right. You can say the electromagninic field follows rules of quantum mechanics and so only some solutions are valid and there's minimum oscillations. But in classical physics, it just follows standard wave equations, and it's just the electromagneic field oscillating. It's the same field. It's just like which equations are using to describe it, and are those quant mechanical or not. And here we don't need to get into the quantum mechanics, but it is important to understand what that field is right, Sometimes we imagine a field is this like weird physical thing that fills space, But really what it is is a set of numbers at every point in space. Like if you think about an electric field, you think, well's strongest near the electron. It's weaker further from the electron. Right, there's values to the field, and those values vary across space. That's how you can have a wave propagating through it. It's like stronger here and weaker there, and stronger here, and those values are moving through the field.
Sort of I guess, like a sound wave kind of. But instead of there being like a physical air particles, imagine they're just being nothing there, just mad.
Yeah, exactly, just numbers. Imagine those numbers then moving through space. Like this location is a zero and the next location is a two, and that two is moving through space, and now a different location has that too. That's like a pulse moving through a field.
But is it two moving through space or is it two somehow like exciting the number besides it making it sort of like the wave in a stadium when you're watching a game or something.
Yeah, it's more like the wave in a stadium. Right. The energy is moving from one spot in space to another spot in space. It's a different place in the field that now has that energy.
Okay, so then before quantum physics, we thought all light is just like the wave in a stadium. It propagates that way. And I guess that makes sense for like a light bulb, which is emanating light in all directions. But then how do you think about it as a for a laser. Is it just like one row the stadium is carrying the wave.
Yeah, just like one row the stadium exactly. And there's an important point here. When you're visualizing that laser beam, that photon flying through space, you probably have in your mind some sort of like sidewave, like it's wiggling sideways as it moves through space, right, So what is actually wiggling sideways there? Does the laser actually have like a sideways extent? The answer is no. The light moves in a straight, perfect line. If you make a laser beam that has like zero width and it's perfectly parallel, then the light moves in a narrow line. It doesn't wiggle sideways. What's wiggling are the values of the field, right, Because electromagnetic fields are slightly more complicated than just numbers in space, there are vectors in space. So now at every point in the field, you don't just have a number like a two. You have a number and a direction, and so that's what's oscillating. As the light beam moves through space, you have like an arrow, a vector from that point, and that vector can change directions and magnitude. So when they depict a photon like wiggling sideways, it's not physically moving to other points of space. It's just that the arrow of the electro or magnetic field is now pointing in a different direction.
Like its value as a direction sort of perpendicular to the direction of the travel. Yeah, exactly is that direction changing? Like for a regular pulse of light, that direction doesn't really change, does it.
Absolutely it does, And that's what the wavelength is, right. The wavelength is how far the light travels before the arrow comes back to where it was before.
Wait, as it's going, as the pulse is going, it's changing in both the value and it's rotating.
That's right, because it's shifting between its electrical and magnetic components. At one point it's purely electrical in one direction, and then that electrical component is shrinking as the magnetic component is growing in a perpendicular direction. Those two fields are always perpendicular to each other. Which direction does it rotate and that depends on the polarization of the light, like can be polarized in lots of different directions, so it could not rotate, or it could rotate left, or it could rotate right. That's a whole other issue. We talked about that in another podcast, the polarization of light. But here we can just imagine the simplest scenario. Imagine it's not polarized. The electric fields is pointing in one direction, then it shrinks to zero as the magnetic field is created and it goes negative, so it points in the opposite direction and then it comes back. The wavelength of the light is how far it's traveled between those peaks of the electric field, all right.
So then John's question was like, what does it mean to have a nanometer wavelength and a wavelength that's maybe tens of meters long. Does that mean that the wiggles are just shorter.
Yeah, it just means the wiggles are shorter. So if you generate microwave radiation, you know with microwave wavelength that means like the light travels a very short distance between those peaks and the electric field. If it's like radio waves with tens of meters of wavelength, then it means that you can start off with like your electric field peaking at one place and then it's literally tens of meters before it osclates down and then back so that it has the electric field pointing in the same direction. Again, that really is something physical.
But in both cases, it's going at the speed of light. It's going at the same speed. Is just that's right, Spiraling or wiggling or changing at a different scale.
That's right. The frequency is different, but the overall speed of the wave is the same. It's still moving at the speed of light. Just how many wavelengths happen when you go one hundred meters.
But again, I feel like this is kind of the classical view. You preface this as being the classical view. Is this actually what's going on? And does this actually tell us what light is? Or is this just some mathematics that we came up with that helps explain what's going on with light?
You know, some mathematics that we came up with that helps explain what we see. Could describe all the physics. You know, we don't know what's really going on at any level philosophically. All of our theories are just some mathematics that help us explain what's going on. We don't know what's true. We think that none of our theories are true.
Well, there's a little bit of a difference, right, Like for example, like if you're dealing with waves in the ocean, you can use wave equations describe those ways, but really you know that underneath there's you know, little particles of water bumping against each other and propagating energy and pulling on each other. Right, So it's like the wave equations work and they start telling what's going on, but they may we don't tell you about the nature of what's going on underneath.
That's right, But sometimes they're actually better at answering questions. Depends on the question you're asking. If you're asking questions about waves and why they reflect or why they break, then the answer is better described in terms of the macroscopic why the waves break. It's because as they approach the shore, part of them get dragged. You can't really answer that question using the microscopic picture of waves as tiny particles, you get lost in the details. So the answer depends on the question you're asking. Which theory of physics you want to use, which approximation, which details you want to swep under the rug, depends on the question you're asking. Because fundamentally we don't know the deepest theory of the universe. So in that sense, we can't answer any questions. We always got to zoom out to some level and give the appropriate answer based on the question.
Right right, But I feel like John's question here is trying to get us to, like, what is the nature of things? Right? Like? I feel like we've just repeated his question thus far, which is like, yeah, life has different wavelengths, and some of them are shorter, somewhere them are longer. Like then, what would you say then, is the relationship between these oscillating electromagnetic fields and arrows? And maybe what we know now about the quantum particle nature of things?
I mean, I think maybe you're more curious about the quantum nature John wanted to know about microwaves, But you know, in terms of the quantum nature, quantum theory of electrodynamics is a natural successor of classical electrodynamics, like you take Maxwell's equations for electromagnetic fields and you quantize them, you say, well, they can't just have any value, they have to have limited values, and you end up with photons, packets, minimum bundles of energy in the field instead of arbitrary size energies. In classical theory, you can have as dim light as you want, but in quantum theory you can't. There's a minimum there. It's because it's additional mathematics. So there's definitely a relationship between like the wave function of a photon and the classical wave length of a beam of light. And we're actually going to talk about that in an episode coming up soon where we talk about like how long is a photon? But I think the answer John's question here about like why can mesh holes block microwaves? We only need to use classical physics.
All right, Well, let's answer that question then, because he asked that directly, like why is it that some waves can pass their holes and others not?
This is a really cool question, and actually a very difficult one. A simpler version of the question is much more simple, like why does a metal box at all block radiation? The microwave is encased in a metal box to protect you from the radiation. But you might wonder, like, how do the metal box block radiation? Like when you get into an elevator, why you have no cell phone signal? It's the same question, and this is a simple process called a Faraday cage. Anything that's a conductor that has electrons roaming around in it. If you try to pass an electrical signal through that conductor, the electrons inside the conductor are going to rearrange themselves to basically cancel out that electromagnetic radiation. Because there are electrons free to move. The radiation creates electric fields that pushes the electrons to counteract that electric field. So you basely can't have an electric field inside a conductor. So in sed you build a metal box, you can put your phone inside, for example, it'll get no signal and also nobody can spy on you. So that's how a Faraday cage works if it has.
No holes in it, because the box, i guess, is made out of stuff, and that stuff blocks the light trying to get in.
Yeah, exactly. And it's not just that it blocks light, right, you know, materials can block light, but metal can also block invisible radio waves. That could pass through walls, they just can't pass through metal.
So for a given metal box, there's no wave of light that can penetrate it.
It depends on the wavelength and the thickness of the box, Like there is a depth that electromagnetic radiation can penetrate into various conductors. So like a super high intensity beam or the right wavelength might be able to penetrate some metal boxes depending on their thickness. But for a perfect conductor, then yes, you have to have zero electromagnetic field inside of it.
Okay, So then what happens in like in my microwave that if you punch holes in this box?
Yeah, so you might wonder, Okay, there's holes in the box. Why can't light go through the holes and be blocked by the mesh? Right? Am I just getting like patchy radiation through the holes? Amazingly, You're not. Even though there are holes in that mesh, none of the light gets through.
Well, some light gets through, because I can see inside my microwave.
That's right, None of the microwaves get through. The light actually does get through. And so now it depends on the frequency of the light. And I think in John's question, he's wondering, like, is that because the light is like oscillating sideways and so it can't fit through the mesh. And the answer to that is no, that's misleading. Right, light is not oscillating sideways. Microwaves or visible light aimed right through the center of one of those holes. They can both fit through the holes. It's not a physical issue. They're not like bumping up against the size of the hole. It's a different effect that's filtering out the microwaves and not the visible light.
So then what is that effect?
Yeah, so what's going on there is a little bit more subtle. What has to happen is you have to have zero electric field inside the mesh. Like everywhere you have metal, you have conductor, you have electrons. That's going to zero out the field. Now you need to think of the light not as a particle, not like as one little thing that's like a tennis ball flying through the hole, but like a wave. And when a wave meets a new kind of material, like when light hits glass or when light hits water, right, then you have to find a solution that satisfies all the wave equations at the boundaries. What that really means is that the waves have to line up. Remember we talked about the waves as wiggles in the field, Well, you can't have weird discontinuities in the field. They have to match up at that boundary. This is why, for example, light bends when it goes from air to glass or water, because the different medium means a different index of refraction, which means a different wavelength. So for two fields to match at the boundary when they have a different wavelength, one of them has to be bent relative to the other at a different angle. The same principle applies here with the case of the mesh, but it's much harder to find solutions on both sides of the mesh because the mesh requi whires the field to be zero at so many places on it, and in this case, requiring that the electromagnetic field is zero inside the mesh creates these interference effects that cancel out any electromagnetic fields below a certain wavelength on the other side of the mesh.
Okay, you lost me a little bit there. I wonder if we've lost our listeners. So maybe let's maybe a more simple scenario. Let's say I'm a markwave and I'm flying through space. And I see a big metal sheet in front of me with a little tiny hole in it. Now earlier saying that I should be able to go through it because I don't really have any width to me right, Like the wavelength of my light is not sideways to me. It's more like how often I'm pulsing right A, Technically I could still go through that hole.
You have no width to you.
Yes, yeah, I'm a beam of light. If I'm a microwave, why can't I go through that little hole?
Yeah? It sounds like you should be able to. But you're actually using a particle picture, right. You're thinking of yourself as having one location and flying through space. But we're talking about waves, and waves have to have solutions everywhere in space. So you have to find a solution that satisfies all the equations everywhere in space. It's not about an individual particle flying through space. It's like a steady state. You have like waves in this box and they're bouncing around. Can any of them escape?
But didn't we talk about like a single beam of light being like one row in a stadium that's doing the wave like it's super thin. Couldn't that wave go through a little hole.
Yeah, it's one row, but you have to think about the whole row, right, You have to think about the equations of the whole row, and whether the equations work on one side of the mesh and the other side of the mesh. It's a little bit unsatisfactory because it's all about these interference terms satisfying the equations. It's hard to get a physical intuition on it. The best I can do is to remind you that when you approach that mesh, you're not just flying through it, right, You're inducing electromagnetic fields in nearby, and so you need a solution on both sides, and that effectively induces light in lots of different directions. And there's the requirement that the electric field be zero inside the meash means that you can't have wavelengths that are longer than that because it will hit that zero requirement and get canceled out. This is the same issue with like thinking about how like gets bent at an interface? Like, how does that actually happen? How does an individual photon get bent? How all the photons bent the same way? It's the photon picture that's the problem. It is really there's a wave description here and it's the solutions to the wave equations that dictate what happens. So the problem is thinking about it in terms of like a little particle flying through.
You're right, that is a very unsatisfied It's hard to tackle in a podcast. But I think what you're saying is that instead of thinking about this in a time sequential way, like I'm in one side of the wall with the hole in it, and then later I'm on the other side of the wall with the hole in it. You, because you're talking about waves, you kind of have to think about it all at the same time, Like the before and the after all have to be part of the same physical consistency. And somehow my wavelength is too big. I just can't go through that hole, Like there's no solution that puts me in both sides of the whole in the timeline of the universe.
Yeah, exactly. And you can actually escape this requirement a tiny bit if you send little pulses, like if you send individual tiny little pulses or microwaves, some of them will get through. But it's when you have a consistent source of the microwaves. It's like the previous ones are canceling out the future ones, and they're all interfering with each other in just the right way to cancel any waves that make it through. Individual pulses actually can get through a little bit. So you're exactly right. You have to think about, like the steady state solution, all the waves working together, can any of them make it through? So it's really it's an interference effect, like.
The before and the after at the same time. So I think to answer John's question, I mean he is asking, I think about the physical reality of wavelength and what's really the nature of these things. Maybe the answer is that the you know, light has this wave nature, and this wavelength nature is not just in space, it's also in time. And so for whatever reason, the nature of light means that you have to take into account the pass and the future all at the same time, and it all has to work together with the effects of the electromagnetic interactions with the wall exactly.
And this wave picture of light really can't explain all these kinds of effects. Light bouncing off of water, light refracting in water, and also light being trapped by Faraday cages.
Well, I feel like it's a bit of an unsatisfied answer for John. Here Basically, the answer is because you can't.
The answer is that, like the mental picture of light moving as a little particle isn't really the right way to think about this problem. And unfortunately you need different mental models to solve different problems. There's no single unifying understanding of physics that we can use in every situation.
All right, well, thank you John for that question. Now let's get to our last question of the day, and this one is about quasi particles and crossword puzzles. So let's dig into that. But first, let's take another quick break.
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All right, we're asking questions here today and our last question comes from Peter.
Hi, Daniel, and Jorge. This is Peter from Winchester, Massachusetts. My question comes from a crossword puzzle. The clue was type of quasi particle and had to be seven letters. The answer turned out to be plasmon p L A S M O N.
Could you explain what that is?
Thank you?
All right, interesting question here Peter was doing a crossword puzzle and he came across an interesting solution, which is a plast and so he's wondering what is that? Or maybe Peter just made a mistake on this crossword puzzle.
No, I think he's exactly right. A plasmon is a quasi particle and it has seven letters. So boom boom boom.
Oh all right, well I would have to look at the whole crossword puzzle to double check that answer. Sometimes crossword puzzles have multiple answers.
Hmm, that's true. Yeah, there might be many quasi particles that satisfy this.
Yeah. No, they actually design I think they even call them like quantum crossword puzzles, where there's like multiple solutions that can fit.
Oh my gosh, like crosswands interfering crosswands.
Yeah. Yeah, and they have wavelengths and time moves slower. It's the whole thing. All right. Well, it sounds like plasmon is a real thing.
What is it?
Daniel? And just to spell it out. Peter spells it out p L A s M M.
A plasmon is a quasi particle. It's like an oscillation in plasmas that we can describe using the mathematics of particles. Usually when we talk about particles, we're talking about oscillations in fields like the electromagnetic field or an electron. Is the oscillation in the electron field, and we have wave equations that describe how those fields oscillate and how they vibrate, and how the Higgs boson affects them to give them mass and all the kind of stuff you can imagine, like a little standing wave in the electron field. That's what an electron is. So when we talk about particles, we have math that describes the oscillation of these fundamental fields. We don't know what these fields are, what really is doing the oscillating, but that's the math we have. We can take that same mathematics and we can apply it to things that are not fundamental fields, like you can apply it to sound waves in air, or you can apply it to electrons moving through materials. You can apply in lots of situations, and those are quasi particles. Particles are these particular kinds of oscillations in fundamental fields. Quasi particles are the same kind of mathematics, the same kind of oscillations, but in something that isn't a fundamental field.
But then you can apply that to real things that are made out of things like water and air. Right, you can sort of apply those wave functions to media.
Yeah, exactly. And the cool thing about a particle is that it's persistent, right, It's that quantized, you can count it. It's discrete, and it like moves through the universe. An electron as it moves to the universe doesn't like dissipate down into little mini electron ripples, right. It's persistent in this way, And so sometimes you can see the same thing happening in other media, right, Like if you can make a smoke ring that's really persistent, right, it like flows thro the universe and holds itself together somehow. I mean, I'm not an expert in how smoke rings work, but imagine that. Then you could maybe describe that using the same kind of mathematics you could use to describe electrons. So you might call that a smoke on or whatever.
But maybe just even more typical like a wave in the ocean. You can use wave equations to describe them mm hm. And they're just ripples in the body of water. So in a way, they're sort of just like water ons, right.
Yes, not every wave phenomenon can describe a particle like a particle's a special kind of persistent discrete wave phenomenon. But yeah, in the end, it's all rooted in wave descriptions of how a medium is moving. And we talk about sound waves as like phonons. It's like a basic unit of the sound wave. Can you describe all sound in terms of these like sound quasi particles. That's what a phonon is.
Where I guess if we're following the same convention here, it would be airons perhaps depending on what the or gasons.
Yeah, if you want to reinvent stuff that already has names for it so that everybody gets totally confused, then perfect.
Yes, Yeah, to make it clearer, perhaps there is.
A thing called phonons, And there's lots of these quasi particles. People are discovering new ones all the time, you know. There's things called enions and plasmons are an example of a quasi particle. There are particular kinds of oscillations. But in plasma, so plasma is just gas that's really really hot. Like take hydrogen. It's got a proton and an electron. The electron is bound to the proton because it doesn't have the energy to fly away. Well, if you give that electron more energy so that it's moving like too fast to be bound by the proton, then it's free. And now you have a gas of protons and electrons instead of a gas of hydrogen. That's a plasma.
Now it is a plasma. Then basically a phonon in plasma.
Well, the phonon is like a density wave, and that's ignoring the charge distribution. Plasmon is a little bit more than that because it also has to do with the charge distribution, because once you have a gas that has charges in it, there's more kinds of forces that it can feel like hydrogen pressure passes through it because the particles are bumping up against each other. But in a plasma, pressure can move through it because the charges are repelling and attracting each other. So you have it's sort of like two gases on top of each other. You have a positive and a negative gas on top of each other. And they're pushing and pulling on each other. If everything has infinite time to sit around, it'll equilibrate, but that's not usually what happens. You form these things in high intensity situations, you have pulses in them, et cetera. And so plasma is a description of the oscillation of mostly the electrons, but also a little bit of protons due to the charges of these things.
So you have this plasma of electrons and protons floating around, flying around, and sometimes because of the dynamics between the different particles, you get these weird little effects that move around like there were particles inside of the plasma. And that's what you call a plasma exactly.
And that's actually related to the previous question because the reason these electrons are moving is because there's an electric field. Often the electric field is because the electrons are separated from the protons, so they've created an electric field between them. So now the electrons move to try to balance out that electric field that they had a part in making. But sometimes they overshoot, and so they oscillate back and forth and back and forth. So you get all these sort of like oscillations of the electrons because of their charge differential and those oscillations we can call plasmads. This is like people trying to make connections between different fields of physics. They're like, oh, people have all these cool mathematical tools they can use to describe waves as particles. Maybe if we apply that to our situation, we'll try to gain some understanding. This is all about like emergent physics, Like should we take a step up from the microphysics and try to understand the bigger picture immersion phenomenon. Should you think about the water particles or should you think about the waves? Right? It depends again on the questions you're asking and which tools you want to bring to bear. We don't have a fundamental theory of physics that can answer every question we can ask, so we have to sort of choose like how to zoom in, how to zoom out, what approximations to make, what things to focus on, what things to ignore. So plasmas can be useful for some kind of questions in plasma physics, like.
What kinds of questions? Like what are these useful for?
Like how do keep plasma stable? You know, in magnetic confinement fusion, when you get plasmas really really hot, and you hope that the protons will fuse sometimes and then create more fusion. You're really interested in these kinds of oscillations. The thing that makes magnetic confinement and fusion difficult is that plasmas are really hard to keep stable. They're very turbulent and very chaotic. So understanding the oscillations and a plasma, how to keep those stable, how to keep those from spiraling out of control and creating chaos that breaks up the plasma and ruins the fusion conditions can really help you build like a long lasting fusion reaction, which is the whole idea of magnetic confinement fusion.
That's kind of the holy grail of fusion, right, it was super clean energy that will last as forever, Like we can control plasma and then we can basically replicate what's going on inside the sun.
Yeah, that's exactly right. We need to understand plasma oscillations if we have any hope of keeping plasma stable and getting fusion, which is the energy source of the universe in the end. So plasmas can be really helpful for answering some questions about plasmas.
And crossword puzzles. Apparently, I wonder which one is more useful to humanity.
I don't know, but maybe you and Peter can answer these crossword puzzles as you drink mohedos on your private islands.
That sounds wonderful. It's going to be me, Dan, John and Peter drinking mojitos solving crossword puzzles in my private island while we get wiser and older.
That sounds good to me.
Wait, wait, are you Dan or not?
We?
Are you? Just happy for us?
I'm the quantum interference between Dan and Daniel.
Yeah, I need to know which one we're getting here? All right, Well, those are three awesome questions we've answered today. Thank you to all of our question askers.
And thanks to everybody who writes in with questions about the universe. Keep thinking deeply, keep asking questions, and don't give up until it makes sense to you.
And or you get an answer from Daniel or Us on the podcast that's right, or maybe shows up in a crossword puzzle. Either way to thrill.
And if you don't hear from me, feel free to look up poor his address and take him up on his invitation to the private island.
Yeah, there you go. All right, Well we hope you enjoyed that. Thanks for joining us. See you next time.
For more science and curiosity, come find us on social media where we answer questions and post videos. We're on Twitter, Discorg, Instant and now TikTok. Thanks for listening and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digesters to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's last sustainability to learn more.
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