 How the fuck does live work? That's it. That's the question we will answer in this video. And I know that most of you are waiting for QFT Episode 2. And that episode is recorded and edited. But some of the explanations in that video need quality animations to make sense. And that part of the process is taking longer than expected, but it is going. Anyway, recently I was watching this podcast I like called Trash Taste. You should check it out. The three hosts are very likable. And one reason for this is their insanely bad opinions on everything. From food to anime to video games. It's called Trash Taste for a reason. But this time they discussed the nature of light. And well... Like shadow should be like an honor of things. Light is both a particle and a wave. Light is the only thing that acts like that. Half our understanding of the universe would be solved if we just understand how light actually fucking works, but it's all guesswork. Light doesn't exist. It's just something we made up to answer all the questions. Light is also affected by gravity, which waves are not. But light does not have mass. Yes it does. How is it affected by gravity? Basically the universe just doesn't make sense. They got a lot of things wrong, which is fine. I mean it's normal to be wrong because no one is born knowing science. But since this is a topic that they are clearly interested about, I thought that maybe I could help them out by clearing out a few misconceptions. Let's begin with the nature of light. This light is just fucking weird to me. Is it like a particle? Or is it a wave? Or is it both? Or is it neither? For a long time scientists like Newton thought that light was made of tiny particles that our eyes could somehow detect. But this idea was destroyed. It was Isekai in 1807, when the double slit experiment was performed. And this started a new arc in the history of physics, the light wave arc. Conveniently I was working on an animation of this experiment for QFT Episode 2. It's not finished, but it'll do. Imagine this is water. As you can see, when the wave of water reaches this wall, it is mostly stopped. But there are these two slits in the wall. And so the water in those places begins oscillating. This creates two new waves that then interfere with each other, creating what we know as an interference pattern. But here's the thing. If you have the right tools, you can do the same with light. If you make light pass between two slits that are very, very close together, you will see an interference pattern proving that light is a wave. And if you want to see someone doing this experiment, I recommend this video by Looking Glass Universe. And also check out the rest of her channel. It's great. However, this begs the question. If light is a wave, what is waving? What is oscillating? If you think about what a wave is, it is usually just made of atoms bumping into other atoms who then bump into other atoms and so on. If this happens with a certain rhythm, with a certain frequency, then it will create a wave. For example, if I press this key on this machine, it makes the air molecules bump into each other 440 times every second, which we perceive as an A-flat. So in summary, a wave is just kinetic energy propagating through a medium. In this case, air. And now this brings us to some of your misconceptions, Joey, because you mentioned that only waves can move through the vacuum of space. Because people used to argue that, oh, it's a wave, right? Because it can pass through a vacuum like in space, right? And while it is true that light can move through the vacuum of space, now you can see that most waves cannot move through the vacuum. For example, sound cannot. In fact, famously in space, no one can hear you scream, because there are no air molecules that can bump into each other. At this point, scientists knew that light was a wave, and that it was moving through some medium, but they didn't know what it was. But they knew it had to be something really weird, because it filled the vacuum between the stars, but it was also mixed with the air, and the water, and inside transparent stones, like diamonds, and inside glass, and talking about glass, you could take a glass box and extract all the air from it using a vacuum pump, but light would still pass through it. To explain this, many scientists proposed that maybe the entire universe was full of some kind of substance which they called the ether, and that light was a wave propagating through this substance. But they also proposed that ether could sort of pass through matter, much like Mirio in My Hero Academia, although I guess you guys dropped the show before he was introduced. You guys get the idea. The point is that it was impossible to extract the ether with a vacuum pump. In fact, it was impossible to manipulate the ether with our tools because they are all made of matter. The ether also seemed to explain another unusual property of light. It always has the same speed. Scientists have noticed that the speed of a wave usually depends on the medium in which it is moving. For example, air can move faster through water than through air because the water molecules are much closer together than the air molecules. But if ether was made of some kind of particles, and the overall density of these particles was pretty much constant all over the universe, that would explain why the speed of light was always constant. At this point, scientists were in a real conundrum, because they had good reason to believe that ether existed, but it seemed impossible to do science with it because it passed through all their measuring devices made of matter. But people can be really clever sometimes, and so two guys, Michelson and Morley, figured out that if they wanted to detect the ether, they just needed to create a measuring device made of light. It would take me a while to explain this experiment in detail, but here's the gist of it. They took one beam of light and then they split it in two, sending it in two opposite directions, and then they recombined those two beams of light to create a single interference pattern, because remember that light is a wave. Okay, so now here's the thing. If at one point the light moving in one of these two directions moved faster than the light moving in the other direction, that would create changes in the interference pattern. And these changes would be really small, like millimeters shifted to one side or the other, but it would be measurable, it would be noticeable. But how could this happen? How could light move faster in one direction than the other? Imagine these blue dots were the ether particles. Light would be a wave moving through this medium, and in fact, here we can see a light wave. Well, if the medium itself was moving, then it would carry the light with it, making it move faster in one particular direction. This reminds me to the moving walkways you can find in airports. When you walk through these moving walkways, you move very fast as if you were running, but you are only walking. Well, if there was either wind, it would be like a moving walkway, but for light. And talking about moving walkways, they were very common in the legend of the galactic heroes. That's not relevant for this video, but I just wanted to mention it because I really like that show. But of course, the fact that the speed of light is constant means that if the ether particles exist, they must not be moving a whole lot. But you know who is moving? The earth. The earth is moving through the ether, and this should create ether wind. If this seems confusing, just move your hands very fast through the air. You will feel the air around your hands, even though the air is not moving a whole lot. Because when you think about it, there isn't much of a difference if you move towards the particles, or if the particles move towards you. They are different situations, but in both cases the result is wind, and wind is a moving walkway for light. Or well, ether wind, not just regular wind. Yeah, you know what I mean. But even better, earth moves in circles, which means that the direction of the ether wind should change over the course of the year. And this should create slight changes in the interference pattern that Michelson and Morley should have been able to measure. Michelson and Morley constructed this machine, and they measured the interference pattern every day, hoping to see anything that would reveal a change in the direction of the ether wind. But nothing happened. The interference pattern remained exactly the same every single day. Michelson and Morley were extremely disappointed, because they thought they had messed up the experiments somehow. But they didn't. They did everything right, and they had just proved that the ether didn't exist, and they didn't even realize it. This was a very interesting season finale in the history of physics, because it's all about the importance of being wrong. Michelson and Morley wrongly believed that the ether existed, and so they set out to prove it, and in doing so they did everything right, and they got the correct answer that it didn't exist. And yet they were so convinced that it did exist that they didn't realize they were right. The lesson for all of us in here is that sometimes, when the evidence contradicts everything we know, sometimes we should abandon what we know and accept what the evidence tells us. In the next season, it took scientists a couple of decades to understand what was happening, but today we know that light is an electromagnetic wave, and to understand this, first we need to understand the concept of a field. Take for example gravity. Here, near the surface of Earth, the value of gravity is roughly 9.81 meters per second square, and but then, if you start going away from Earth, you will feel weaker and weaker gravity, until at some point you will feel no gravity at all. But then, if you continue moving, and you get close to the Sun or Jupiter, you will feel gravity again and much stronger this time. So it's not like Earth has its own gravitational field, which is separate from the gravitational field of the Sun and Jupiter and the Moon. No, no, no, in a sense, there is a single gravitational field across all of space, and this field takes different values near certain objects. And well, the same happens with electromagnetism. All of space has a single electromagnetic field that just happens to be zero pretty much everywhere, except when you get close to objects with electric charge, like protons or neutrons. Near those objects, this field has a positive or negative value. This is important, because if you take an object with electric charge, and you make it oscillate at a certain frequency, these will create changes in the electromagnetic field that will propagate across space far away from the oscillating charge. Mathematically, this looks like taking Maxwell's equations and combining them in just the right way to get the equation for a wave. And this is what light is. The electrons in atoms are vibrating, and that creates the light we see. Instead of having atoms bumping into other atoms, we have the value of the electromagnetic force affecting the value at another point. The mechanism is different, but the result is the same. This also explains why light can move through the vacuum, because even if there are no atoms, the electromagnetic field is still there. That's the medium light is moving through. Except this is also wrong, because as Garnt correctly pointed out, light is treated like a particle which is called photons, which is what Einstein proved. Einstein discovered that light was made of particles, and he did this by studying the photoelectric effect. There are a ton of demonstrations of the photoelectric effect in YouTube, links in the description, but the summary of all of this is that Einstein discovered that the energy of light is transmitted by individual units, and these units are the particles we call photons. And in case you have any doubt that light is indeed a particle, Arthur Compton made an experiment in which he analyzed what happened when highly energetic photons interacted with electrons. And what he found was that the electrons were being launched away, they were being scattered in a way that could only be explained if they were being hit by individual particles. In fact, this is the experiment that finally convinced a ton of scientists that had been doubting Einstein's ideas for years. This brings us to something Conor mentioned, that light can push objects around. Like intense light can cause like small movements somehow. And this confused the boys because if light is an electromagnetic wave, then it has no mass, and if it has no mass, how can it push anything? And well, the answer is deceptively simple. A push is just a transfer of energy, and light has energy. So you don't need mass to transfer energy, all you need is the energy itself. Now Garnt, in case you're asking, but how can light have energy if it has no mass, the answer is simple. When you have an electron and you make it oscillate to generate light, creating this oscillation took energy, and that energy is carried away by the light. In a way, the process of creating light transforms this kinetic energy into light energy. And that light energy can be transformed into kinetic energy again if another electron absorbs that light. This explains why we can see. The sun makes its electrons vibrate a lot because they are very hot, and so they create a lot of photons. Some of those photons reach Earth, and they are absorbed by many different atoms and molecules. And then the electrons in those atoms and molecules vibrate again, creating new light. But because these electrons vibrate at different frequencies, they create the light of different colors that we can see. But anyway, let's look at what we've learned so far. We have evidence to believe that light is a wave, like interference patterns and Maxwell's equations. But we also have evidence to believe that light is a particle, like the photoelectric effect and Compton scattering. Now I ask you, should we be like Michelson and Morley and assume that our observations are wrong unless they match our worldview? Of course not, right? We should change our worldview to match our observations. That's what science is. The solution is that light is neither a particle nor a wave. It is a new kind of object with some of the properties of the two. This is what Joey correctly called the particle wave duality. Light is both a particle and a wave. It is called the particle wave duality. That's fucking stupid. That is that is stupid. No guard. It's not stupid. It might be confusing. It might be unexpected, but all the evidence indicate that this is how nature works. Or you know what? Maybe nature is stupid. But still, as far as we know, this is the truth. And in fact, scientists spent the last 100 years developing the mathematics to understand this. And this is what we know today as quantum mechanics. So Joey, you should give scientists a bit more credit instead of saying that we have no idea how this works. And scientists to this day do not know how that works. I have some understanding, but not quite the full picture. Thank you, Connor. Exactly. We have a fairly good understanding. It's not perfect, but it has been continuously improved for the past 100 years. In a sense, humanity has been going through a century-long training arc in quantum mechanics. Does that mean we are the strongest? Does that mean we can be dbaki? Of course not. We are not there yet. And perhaps we'll never be. But we are certainly much stronger than we were before. And in fact, I am on my own training arc because I'm trying to become self-sufficient with my YouTube channel. And if you want to help me, you can send me money through Wagner Coffee, or Kofi, or PayPal, or my Patreon. You can join for just one dollar per month, but then you can change the amount to whatever it is you want to give me each month. And if you cannot help me with money, you can still subscribe. You can like this video. You can share it with your friends. And if you cannot do any of that, you can still send me your energy so that I can do the Genki Dama. Yeah, yeah, I can feel it. It's working. Yeah, my power level is rising. We are almost there. But in the meantime, we should move on because there are still a few more misconceptions to clarify. Another thing you mentioned, Joey, is that only light presents the particle wave duality. Light is the only thing that acts like that. And to be fair to you, that's what Einstein thought. In fact, that's what most scientists thought for like 20 years, until a guy called Luis de Brugli came along. The story of de Brugli is very interesting. And I will review it more in depth in future episodes of Understanding QFT. Yes, I'm plugging my channel in my own channel. Shut up. But the most important part is this. People knew that when electrons orbit around the nucleus of atoms, they can only hold some very specific amounts of energy. And this creates the energy levels, which are very important in chemistry. But no one knew why these energy levels existed. Luis de Brugli mistakenly thought that photons had mass. And he was developing a theory around this when he suddenly had an idea that if photons could have mass and get the particles and waves, then maybe other particles with mass, like the electron, could also be waves. And this was right. And it's really interesting because de Brugli had to be wrong about photons having mass to arrive at the correct idea that electrons are also waves. And then de Brugli thought that if the electron was a wave, maybe the different energy levels were like different vibrations of this wave, like different musical notes. And then using this idea, he worked out the correct radios for the hydrogen atom. Later on, other scientists took de Brugli's ideas and improved upon them and tested them. And today we know that all the particles are both particles and waves. Photons, electrons, quarks and their combinations, all the protons, neutrons, and all the other variants and mesons. But this begs the question. If particles are waves, what is oscillating? You see the value of the electromagnetic force again? Well, that's what Schrodinger thought at first. But he was wrong. And it's really funny because he found the equation to describe these waves. And yet he was still wrong about what they were. And he needed the help from other scientists, like Max Born, to realize that what they really are is what was really is changing. Is the value of the probability of finding the particle at different points in the orbit? Particles are waves of probabilities. And once again, this is an idea that I'm gonna explore way more in depth in the second episode of Understanding QFT, as in two hours of in-depth explanation of how we reached that conclusion and what it means. Another topic the boys discussed was whether light was affected by gravity and how that relates to its lack of mass. Light does not have mass. Yes, it does. How is it affected by gravity? First of all, gravity is a distortion of space and time created by mass and energy. Because mass and energy are the same thing. In fact, a hot coffee waits more than a cold coffee. Anyway, the point is that mass and energy distort space and time, which are also the same thing. So we call them spacetime, not to be confused with PBS spacetime, which is the best educational YouTube science channel out there. What matters is that this distortion makes it so that if you are moving forwards in time, and you are, you are accelerated towards the center of this distortion. And sure, something can block you from moving in that direction, like the surface of the planet, but you are still being accelerated in that direction all the time, and you perceive this as a force pulling you down. But if there's nothing to stop you, you can also move fast enough to compensate for the strength of that force. And this is what being in orbit means. Now notice how we didn't mention the mass of the object being pulled down. That's because it doesn't matter. This is a distortion of space and time. If you exist, it will affect you. It doesn't matter if your mass is very large, or very small, or non-existent. There's another way to think about this. We often imagine that if you were in a spaceship and you wanted to move around the star, you would have to be constantly turning to one side, right? But no, if you moved perfectly straight, eventually you would reach the point where you started, because the mass of the star has distorted space so that a straight line is a circle. This sounds bizarre, but something similar already happens with air. If you move in a straight line in any direction in this planet, you will eventually reach the same spot again, because Earth is a sphere. In summary, gravity is a distortion of space and time, and if you exist, you will be affected by it, regardless of whether you are a wave, a particle, or something in between. However, I should mention that the mass of the object does matter for one thing. It changes the speed that you need in order to be in orbit around another object, and in the case of light, since it has a constant speed and no mass, it turns out that it is impossible for light to be in orbit around an object. And this is why you don't see rings of light around stars or very massive planets like Jupiter. And this brings me to my last point of confusion for the boys, specifically Gaurant. Shadows, how do they work? So what is a shadow? In my mind, like shadows should be like an on or off thing. There is either a shadow or not. What do you mean by that? And you know what? Too long scientists have been worrying about like the elements of nature or the fundamental laws of the universe. And no one has bothered, nay, no one has dared to ask the question how do shadows work until today? Today we fixed that historic mistake. Gaurant actually has a point. In fact, let's go back to the green screen and let me turn off some of my lights so that you can see. Okay, look, we have a shadow here. In fact, I don't know if you can notice that there's a shadow here and another here because I have two light bulbs. That's going to become relevant in a moment. But okay, I have a shadow here. And when we see a shadow, well, we can still see something, right? You can still see that this is green. It just looks darker than the green here. And so, yeah, shadows are not an absence of light. What they are is all about energy. When something is bright, it means that your eyes are detecting a lot of energy coming from that object. And when something is dim, it means your eyes are detecting a lot less light coming from that object. Now, here is important to distinguish between total energy and energy density. If you take a prism to make a rainbow and you put thermometers at every color, you will realize that the thermometer in blue light heats faster than the thermometer in red light. That's because blue photons have more energy than red photons. They have a higher energy density. And yet it is possible for a red object to be brighter than a blue object. All you need is to have enough red photons that their total energy is higher than the total energy of the blue photons. For this reason, we have the concept of light intensity, which refers to how much energy a beam of light is shining onto a surface every second. And it is measured in watts over a meter square. Now we can understand how shadows work. You are blocking most of the light reaching a certain surface, but you are not blocking all of it because light is bouncing all around us. So you reduce the intensity, but you didn't bring it down to zero. In the case of the shadow within a shadow you saw in your house garden, I assume it was something like this. In my room, I have two light bulbs. So when I sit here, my head blocks the light coming from one of the light bulbs, but Tabibito, the autobiography of Hideki Yukawa, blocks the light coming from the other light bulb. And so where these shadows meet, it creates a double shadow. The light reaching this surface is being blocked by two different objects in two different ways. And that's it. That should give you guys a decent amount of understanding of how light works. Thank you for watching. And thank you to all the people who have supported me so that I can continue making these videos, especially to Ivo Danihelka, Carlo Facioli, Manuel Marques, Lana Mantegasa, Otimo Tiosun, Valerie Hyde, T. Hyethil, Alec Luma, Daniel H. Manchilibrae, Robert Wigman, Richard Allen Park, Metarus 208, Ryan Roberts, Jadon Hansel, Azuria Salia, Edward Hof, Mattia Scherding, Cookies of Tea, Sinos Fan 2, Marlo Brown, Eds Dos, Matt Zweig, Ed Cossack, Martin Mait, Dan Babbage, Pedro Almeida, Josh Stein, and Tataker. All of you guys, thanks a thousand times, thanks a million times.