WEBVTT - Do photons bump into each other? 0:00:08.600 --> 0:00:10.600 Hey, Daniel, I have a question for you, very important. 0:00:10.680 --> 0:00:12.719 All right, what is it? How close are we to 0:00:12.920 --> 0:00:16.880 having real life lightsabers? You're asking a physicist that question. 0:00:16.920 --> 0:00:19.560 I would ask the same question to my favorite engineer. Wait, 0:00:19.600 --> 0:00:21.920 do you think it's an engineering solution? Do we need 0:00:22.000 --> 0:00:24.759 like some kind of breakthrough in theoretical physics first? No, 0:00:25.000 --> 0:00:27.080 I mean the science fiction authors have done their job 0:00:27.080 --> 0:00:29.960 already and they passed it on to the physicists. Oh yeah, 0:00:30.000 --> 0:00:32.040 and the physicists I figured out how to do it. Well, 0:00:32.080 --> 0:00:34.960 you know, we've been smashing photons together to see what happens, 0:00:35.240 --> 0:00:38.199 and how does that do as a lightsaber? Well, so 0:00:38.320 --> 0:00:43.240 far it makes a really awesome sound, like but kind 0:00:43.240 --> 0:00:45.800 of cut through swords and deflect like guns. That's the 0:00:45.840 --> 0:01:04.160 engineering problem. Hi am or handy cartoonists and the creator 0:01:04.240 --> 0:01:07.440 of PhD comics. Hi. I'm Daniel. I'm a particle physicist 0:01:07.440 --> 0:01:10.280 and a professor at UC Irvine, and until a moment ago, 0:01:10.360 --> 0:01:13.360 I had never made a lightsaber sound with my mouth. Yeah, 0:01:13.640 --> 0:01:16.360 we could tell that was terrible, Daniel. All right, let's 0:01:16.360 --> 0:01:23.720 hear your lightsabers sound. Right, sounds a lot more accurate. Well, 0:01:23.760 --> 0:01:26.240 we'll let the listeners vote I think the coolest sound though, 0:01:26.240 --> 0:01:28.400 is when they clash, you know, because they're like woman, 0:01:28.560 --> 0:01:32.480 it's or something. When they hit that's even worse, Daniel, 0:01:32.560 --> 0:01:35.800 everyone knows it's oh, that was much better. All right, 0:01:35.840 --> 0:01:38.800 You're right, that's definitely better. And those movies are ingrained, 0:01:39.520 --> 0:01:41.880 are burned into my brain, for better or for worse, 0:01:42.200 --> 0:01:45.040 like somebody inscribed them with a lightsaber, like somebody was 0:01:45.280 --> 0:01:47.720 their hand and said I would only remember these movies 0:01:47.760 --> 0:01:50.880 for the rest of my life. It would be pretty 0:01:50.880 --> 0:01:54.080 awesome if the movies themselves were a Jedi mind trick, 0:01:54.280 --> 0:01:57.240 but I think they were. They certainly got a lot 0:01:57.240 --> 0:01:59.160 of my money out of my pocket. These are the 0:01:59.200 --> 0:02:01.720 movies you want to pay for. But anyways, welcome to 0:02:01.720 --> 0:02:04.640 our podcast. Daniel and Jorge explain the university production of 0:02:04.680 --> 0:02:07.240 My Heart Radio, in which we pull off the physics 0:02:07.280 --> 0:02:11.480 mind trick of attempting to understand the universe. We convince 0:02:11.520 --> 0:02:15.800 ourselves and hopefully convince you, that the crazy cosmic mysteries, 0:02:15.919 --> 0:02:19.440 the grandest questions of the existence of humanity, the things 0:02:19.440 --> 0:02:22.520 that philosophers have been wondering about for thousands of years, 0:02:22.560 --> 0:02:26.079 the very nature of our reality and its meaning, can 0:02:26.120 --> 0:02:29.760 be understood by tiny little squishy brains living on a 0:02:29.800 --> 0:02:33.000 little rock orbiting a very normal star. We talk about 0:02:33.040 --> 0:02:35.600 all of these questions and we explain all the answers 0:02:35.720 --> 0:02:38.480 to you. That's right. We used the force to understand 0:02:38.520 --> 0:02:41.079 the forces of the universe and to look out to 0:02:41.320 --> 0:02:44.359 galaxies far far away and actually also a long long 0:02:44.400 --> 0:02:46.840 time ago to understand how it's all put together and 0:02:46.919 --> 0:02:49.160 why it's all hanging there the way it is. Because 0:02:49.200 --> 0:02:52.560 everything around us presents mysteries. How do these things work? 0:02:52.639 --> 0:02:54.959 What happens when they bump into each other? And as 0:02:54.960 --> 0:02:58.040 a particle physicist, my favorite way to understand how things 0:02:58.040 --> 0:03:01.200 work is to do exactly that. Smash them into each other, 0:03:01.360 --> 0:03:03.639 or collide them into each other, or blow them up, 0:03:03.919 --> 0:03:07.000 whatever you prefer. Yeah, because the universe has a dark 0:03:07.040 --> 0:03:09.520 side and also a light side, and it seems to 0:03:09.560 --> 0:03:12.600 be in constant struggle with itself, bumping into each other, 0:03:12.760 --> 0:03:16.240 colliding fields, interacting with each other, all of it to 0:03:16.280 --> 0:03:19.040 create this amazing spectacle that we can see just by 0:03:19.080 --> 0:03:22.040 looking out into the night sky. And we've made remarkable 0:03:22.080 --> 0:03:25.919 progress in understanding the very nature of the universe by 0:03:26.040 --> 0:03:29.760 describing space itself and everything out there in terms of 0:03:29.880 --> 0:03:34.000 oscillating quantum fields, these things which fill the whole universe 0:03:34.240 --> 0:03:37.000 with their energy and slide and smush against each other 0:03:37.240 --> 0:03:40.280 to come together to describe the reality that you and 0:03:40.320 --> 0:03:43.119 I experience. Wait, Daniel, you mean it's not all made 0:03:43.120 --> 0:03:46.560 out of medic clorians, little tiny beings that you know, 0:03:46.960 --> 0:03:51.520 bind everything together. The medic Clorians were biological, not quantum mechanical. 0:03:51.680 --> 0:03:53.480 They never described it in Star Wars. Maybe they are 0:03:53.520 --> 0:04:00.000 quantum mechanical. Maybe they are quantum biology. Yeah, maybe right, Well, 0:03:59.720 --> 0:04:02.640 it seems almost the same. I mean, you're saying that 0:04:02.640 --> 0:04:06.120 the universe made of these fields that are bound together 0:04:06.440 --> 0:04:09.400 with these little tiny things that bump around each other 0:04:09.440 --> 0:04:11.920 and somehow direct the cosmos. That's kind of what George 0:04:12.000 --> 0:04:14.280 Lucas was saying. That's kind of what everybody was saying. 0:04:14.280 --> 0:04:16.159 If you're going to say kind of and be really 0:04:16.160 --> 0:04:20.000 generous about it, you know, yeah, kind of. But I 0:04:20.040 --> 0:04:22.679 love this picture of the universe as all these different 0:04:22.720 --> 0:04:25.120 quantum fields. You have like a field for the photon, 0:04:25.160 --> 0:04:26.560 you have a field for the electron, you have a 0:04:26.600 --> 0:04:28.640 field for the corks and you know those fields we 0:04:28.640 --> 0:04:31.120 can think about is having particles in them would slide 0:04:31.120 --> 0:04:34.120 around and keep a little discrete blob of energy. And 0:04:34.160 --> 0:04:36.520 we've talked to the podcast about how particles are these 0:04:36.560 --> 0:04:38.640 little ripples in the quantum fields. But one of the 0:04:38.640 --> 0:04:41.520 most interesting things that these fields can do is talk 0:04:41.600 --> 0:04:44.400 to each other. The photon field in the electron field 0:04:44.480 --> 0:04:47.040 don't just fill the space of the universe and ignore 0:04:47.080 --> 0:04:50.360 each other. They interact, They touch, they bind together, they 0:04:50.400 --> 0:04:54.120 transfer energy back and forth. Yeah, and thankfully, I guess right, 0:04:54.200 --> 0:04:57.120 because if all the fields ignored each other, like nothing 0:04:57.120 --> 0:04:59.599 would ever happen. We wouldn't be here. We're here because 0:04:59.600 --> 0:05:02.320 of those interactions. In a way, every interaction between two 0:05:02.360 --> 0:05:05.400 different kinds of particles, the way the electron is bound 0:05:05.440 --> 0:05:08.320 to the nucleus of the atom, the way chemical bonds form. 0:05:08.400 --> 0:05:10.440 The reason you don't fall through your chair is all 0:05:10.520 --> 0:05:13.960 because those quantum fields don't ignore each other. It's because 0:05:13.960 --> 0:05:17.480 they interact with each other, because they pass energy back 0:05:17.520 --> 0:05:19.240 and forth. In some sense, it's a bit of an 0:05:19.360 --> 0:05:22.600 artificial distinction to say we have two different fields. Might 0:05:22.640 --> 0:05:26.000 want to think of them holistically, is one bundle of fields, 0:05:26.720 --> 0:05:29.440 one force with the dark side and the light side, right, 0:05:29.800 --> 0:05:31.960 I think you're kind of saying the same thing, one 0:05:32.000 --> 0:05:34.680 force to rule them all. Now I'm mixing our mythologies. 0:05:35.520 --> 0:05:36.960 We need to have like a Lord of the Rings 0:05:36.960 --> 0:05:40.520 Star Wars crossover event. Who would win? Oh my goodness, 0:05:41.080 --> 0:05:44.280 fan fiction writers get on it? Are those owned by 0:05:44.320 --> 0:05:47.240 like different corporate conglomerates, in which case will never happen. 0:05:47.480 --> 0:05:49.680 Not on the internet. Anything can happened on the Internet. 0:05:52.040 --> 0:05:55.440 That's true until Disney's lawyers come after, you know, Disney 0:05:55.480 --> 0:05:57.400 buys Lord of the Rings. Then we might get like 0:05:57.440 --> 0:05:59.800 a Marvel Star Wars Lord of the Rings for a 0:06:00.160 --> 0:06:03.360 crossover right, Oh my goodness, would throw iron Men in there, 0:06:03.360 --> 0:06:08.560 And I'm all in Gandolf versus iron Man. Well, who 0:06:08.640 --> 0:06:13.760 would win? Doctor Strange or Gandalf or the Wizards. I 0:06:13.760 --> 0:06:16.880 don't know who's got a better grasp on the quantum fields, 0:06:16.920 --> 0:06:19.520 but it is interesting and things like Star Wars they 0:06:19.640 --> 0:06:22.120 use lasers, right, laser guns to shoot at each other, 0:06:22.240 --> 0:06:26.560 and also lightsabers to cut through appendages, and also doors 0:06:26.600 --> 0:06:28.960 and walls. And it's interesting to think that light can 0:06:29.040 --> 0:06:31.240 interact with matter, Like if you shoot a laser, it's 0:06:31.279 --> 0:06:33.400 gonna burn a hole through your wall, right, And you 0:06:33.400 --> 0:06:35.960 can even use light to push a solar sale, to 0:06:36.279 --> 0:06:39.680 push a spaceship off of the solar system. Exactly. Light 0:06:39.800 --> 0:06:42.359 is really weird. It has energy, it has a momentum, 0:06:42.360 --> 0:06:44.640 but it doesn't have any mass, and yet of course 0:06:44.680 --> 0:06:47.479 it can influence our world because of that energy. In 0:06:47.520 --> 0:06:50.120 that momentum, A laser will deposit a lot of energy 0:06:50.160 --> 0:06:52.400 in a very small spot and burn right through it. 0:06:52.520 --> 0:06:56.279 And that exactly happens because those photons can interact with 0:06:56.520 --> 0:06:59.560 charged particles. The quantum field of photon and the quantum 0:06:59.560 --> 0:07:03.520 field of those electrons or muns or quarks can interact 0:07:03.520 --> 0:07:06.560 and pass energy back and forth. I always wondered when 0:07:06.600 --> 0:07:09.640 I watched those lightsaber battles. I thought, how does that work? 0:07:10.080 --> 0:07:14.640 How do two lightsabers, two beams of light hit each other? Well, 0:07:14.720 --> 0:07:17.920 this is getting a little philosophical, Daniel. Our lightsabers beams 0:07:17.960 --> 0:07:21.400 of light actual like light that just stands there and 0:07:21.440 --> 0:07:24.720 sits there. Or are they like some kind of material, like, 0:07:25.120 --> 0:07:28.080 you know, like a plasma beam. Wouldn't they be called 0:07:28.120 --> 0:07:30.920 plasma sabers? Then? I mean they are called lightsabers, and 0:07:30.960 --> 0:07:33.920 I imagine George Lucas knows his quantum mechanics. Yeah, but 0:07:33.960 --> 0:07:36.400 maybe they're called lightsabers because they give off light. I 0:07:36.440 --> 0:07:38.120 guess that's a good point. You know, light bulbs are 0:07:38.160 --> 0:07:42.640 not made of light. As we're getting deep here, this 0:07:42.680 --> 0:07:48.480 is very stimulating, illuminating conversation here, well too, bright minds. 0:07:48.480 --> 0:07:50.760 You know, let's see what we can do. I guess 0:07:50.800 --> 0:07:53.480 we were talking about interacting things interacting, and you know, 0:07:53.520 --> 0:07:56.200 it's kind of interesting that electrons can definitely interact with 0:07:56.240 --> 0:07:59.520 other electrons, right, like an electron will repel another electron, 0:07:59.720 --> 0:08:02.640 and like a proton will repel no, the proton like 0:08:02.720 --> 0:08:05.240 things seem to be able to interact with it themselves, 0:08:05.280 --> 0:08:08.680 but not directly. Actually, electrons do not interact directly with 0:08:08.720 --> 0:08:14.000 other electrons. Electrons interact with photons, and photons interact with electrons, 0:08:14.000 --> 0:08:16.680 sort of like having an interpreter, and you can talk 0:08:16.720 --> 0:08:18.280 to the photon and the photon can talk to the 0:08:18.280 --> 0:08:21.640 other electron. But electrons don't interact with each other directly. 0:08:22.240 --> 0:08:24.760 I see, you gotta go through their agents, like talk 0:08:24.800 --> 0:08:27.840 to my people exactly. It's like electrons are celebrities. They 0:08:27.840 --> 0:08:30.840 don't just email you there people email your people. But 0:08:30.960 --> 0:08:34.480 I guess this brings up the an interesting question, which 0:08:34.600 --> 0:08:38.839 is what do photons interact with specifically? Yeah, exactly when 0:08:38.840 --> 0:08:41.079 these two lightsabers are about to cross, and to make 0:08:41.120 --> 0:08:44.120 that sound that I can't make what exactly is going 0:08:44.160 --> 0:08:47.360 on at the microscopic level in George Lucas's mind. Yea, 0:08:47.440 --> 0:08:49.200 so it's the On the podcast, we'll be asking the 0:08:49.280 --> 0:08:58.480 question do photons bump into each other? And Daniel this 0:08:58.520 --> 0:09:00.480 seemed a little risk a like, what do you mean 0:09:00.520 --> 0:09:04.760 bumping to each other? Like they bump and grind like casually, 0:09:04.800 --> 0:09:07.480 like oops, sorry, bumping to each other? Yeah. Well, you know, 0:09:07.480 --> 0:09:09.320 photons can do all sorts of things. They can be 0:09:09.360 --> 0:09:12.000 circularly polarized, so I guess they can do like spins 0:09:12.040 --> 0:09:13.960 on the dance floor. And you know, I'm not one 0:09:14.080 --> 0:09:16.240 to tell you what's appropriate and what's not appropriate. Talk 0:09:16.280 --> 0:09:18.280 to your parents about that. But this is more of 0:09:18.320 --> 0:09:21.079 a physics question. You know what happens when two beams 0:09:21.120 --> 0:09:23.920 of light cross each other? Do the photons ignore each other? 0:09:24.120 --> 0:09:27.680 Do they hit each other? Two photons push against each other? 0:09:27.960 --> 0:09:30.319 You know what happens when you cross the streams. Oh, 0:09:30.440 --> 0:09:33.680 and now we're getting to another mythology. Ghostbusters do not 0:09:33.800 --> 0:09:37.120 cross the streams exactly. I want to see bankman versus 0:09:37.120 --> 0:09:41.199 Gandolf versus a jedi. Now, oh, obviously Agreman would win. 0:09:41.240 --> 0:09:44.760 I mean, the smart engineer always wins. I don't know. 0:09:44.800 --> 0:09:47.120 I Bankman is quite the smart professor. Yeah, because I 0:09:47.120 --> 0:09:49.520 think this is something that I wondered about as a kid. 0:09:49.559 --> 0:09:52.000 Like if you take a flashlight and you take another 0:09:52.040 --> 0:09:54.839 flashlight and you point them not even at each other, 0:09:54.880 --> 0:09:56.719 but just like pointing them in the same direction, or 0:09:56.760 --> 0:09:59.679 cross their beams, Like, what's happening there? Like, what's happening 0:09:59.720 --> 0:10:02.440 to the Do the light beams ignore each other or 0:10:02.480 --> 0:10:06.080 do they kind of interfere or somehow scatter each other. 0:10:06.240 --> 0:10:08.400 So you're saying you wanted to understand light and so 0:10:08.520 --> 0:10:11.280 you make light collisions? Well, I don't know. Is it 0:10:11.320 --> 0:10:16.240 possible for light to collide? That's the question of today's episode. 0:10:17.000 --> 0:10:20.240 Can create a collite, a photon collider? So that's the 0:10:20.280 --> 0:10:23.320 big question we're asking today is can light bump into 0:10:23.320 --> 0:10:25.800 each other? Does light interact with itself? Because not every 0:10:25.800 --> 0:10:29.480 particle interact with other particles. Neutrinos, for example, ignore most 0:10:29.559 --> 0:10:31.920 of the matter in the universe, sliding right by as 0:10:32.000 --> 0:10:35.079 if it wasn't even there. Each particle, each ribble in 0:10:35.120 --> 0:10:37.840 the quantum field, can either see other fields or ignore 0:10:37.920 --> 0:10:39.760 the other fields. It's not like an option, it's not 0:10:39.800 --> 0:10:41.960 like it depends on its mood. Some of these fields 0:10:42.040 --> 0:10:44.520 couple with each other, and other fields just don't couple 0:10:44.559 --> 0:10:47.200 with each other at all. Well, it's kind of interesting 0:10:47.200 --> 0:10:49.240 because I know we've talked about this a lot before. 0:10:49.280 --> 0:10:52.440 How there are two kinds of particles. There are matter particles, 0:10:52.480 --> 0:10:54.360 like the stuff that we think of the stuff, and 0:10:54.360 --> 0:10:57.000 then there are force particles. And so a photon is 0:10:57.040 --> 0:10:59.360 a force particle. And so the question, I guess maybe 0:10:59.360 --> 0:11:02.960 a larger question is to force particles interact with themselves. 0:11:03.040 --> 0:11:05.400 It is a really interesting and deep question. Some of 0:11:05.400 --> 0:11:08.200 the force particles can actually interact directly with themselves, and 0:11:08.280 --> 0:11:11.760 others interact indirectly with themselves. But as we'll learn today, 0:11:11.960 --> 0:11:15.079 there's several layers of nuance to the answer. All right, well, 0:11:15.120 --> 0:11:17.000 we'll get right on it. But as usual, we were 0:11:17.000 --> 0:11:20.000 wondering how many people have thought about this like question, 0:11:20.120 --> 0:11:22.480 this question of whether light can interact with itself? And 0:11:22.480 --> 0:11:25.240 so as usual, Daniel went out there into the internet, Daniel, 0:11:25.360 --> 0:11:28.880 or to your campus. These are questions from our cadre 0:11:28.960 --> 0:11:32.280 of Internet volunteers. So thanks very much for everybody who 0:11:32.320 --> 0:11:35.800 continues to participate and fill my inbox with these really 0:11:35.840 --> 0:11:38.280 fun answers. I greatly appreciate it, and if you'd like 0:11:38.320 --> 0:11:40.520 to hear your voice on the podcast, please don't be 0:11:40.559 --> 0:11:43.439 shy right to us. Two questions at Daniel and Jorge 0:11:43.480 --> 0:11:46.559 dot com. Yeah, so we ask folks, do you think 0:11:46.920 --> 0:11:50.040 that photons bounce off of each other? Here's what people 0:11:50.040 --> 0:11:53.839 had to say. Since photons do not have electric charge 0:11:53.920 --> 0:11:57.720 and mass, I think they do not bounce off each other. 0:11:58.160 --> 0:12:01.800 I think that photons should bounce off each other because 0:12:02.920 --> 0:12:07.520 in physics we learned that photons are particles that act 0:12:07.559 --> 0:12:11.240 as waves because they have a particle wave kind of 0:12:11.679 --> 0:12:14.880 duality to them. So if their particles, they should be 0:12:14.880 --> 0:12:17.360 able to bounce off each other. But also at the 0:12:17.400 --> 0:12:20.839 same time, they're very small, so the rate that they 0:12:20.880 --> 0:12:23.840 do bounce off each other so small because it's very 0:12:23.880 --> 0:12:28.480 hard to hit two very small particles together. I would 0:12:28.520 --> 0:12:37.040 think not. I think they pass right on by each other. Yes, yes, yes, yes? 0:12:37.080 --> 0:12:41.880 Why or how? Wait? Pick up? Oh? Maybe they don't 0:12:43.040 --> 0:12:47.080 wait protons? Maybe they need neutrons. Do you know what 0:12:47.080 --> 0:12:50.600 a photon is? A photon? What's a photon? Way? A 0:12:50.840 --> 0:12:54.600 photon will need to stick to a proton what is 0:12:54.600 --> 0:12:59.960 a photon? Wait? Is it too protons? I would say 0:13:00.240 --> 0:13:03.840 the photons can bounce off each other, because I know 0:13:04.679 --> 0:13:09.360 my understanding is the photons don't have mass. But I 0:13:09.440 --> 0:13:13.319 know the idea of a light sale requires bouncing photons 0:13:13.360 --> 0:13:17.559 off of them. So it's something about the momentum or 0:13:17.679 --> 0:13:22.959 energy of a photon can actually impart some momentum into 0:13:22.960 --> 0:13:26.520 an object. So I would say because of that, photons 0:13:26.920 --> 0:13:30.720 probably can bounce off each other if shot at each other, 0:13:30.880 --> 0:13:34.000 just right, if I remember rightly, you've said on some 0:13:34.080 --> 0:13:38.480 prior episode that photons do not bounce off each other, 0:13:38.520 --> 0:13:42.120 but just pass right through. One might think they would 0:13:42.160 --> 0:13:46.400 bounce off because of their particle nature, but they also 0:13:46.480 --> 0:13:49.600 have wave nature, and I guess that's what lets them 0:13:50.000 --> 0:13:53.120 pass right through each other. I don't believe photons can 0:13:53.160 --> 0:13:58.559 directly interact with each other, being waves as well as particles. 0:13:59.200 --> 0:14:03.839 They just passed through, uh, interfering or not on their 0:14:03.880 --> 0:14:08.200 way through, but then continuing on their happy ways. I 0:14:08.280 --> 0:14:11.319 really don't know. I suppose they could. I know, if 0:14:11.320 --> 0:14:14.640 they hit hard enough, they'll break into other things, all right. 0:14:14.840 --> 0:14:18.640 I like that kid's answer. That was pretty funny. Yes, yes, 0:14:18.720 --> 0:14:23.120 of course, Wait what I love hearing people think about 0:14:23.120 --> 0:14:26.040 it on the fly, their initial reaction and then their 0:14:26.080 --> 0:14:28.560 physics brain engages and they're like, hold on a second, 0:14:28.640 --> 0:14:30.760 is that really the way this works? Really? They have 0:14:30.800 --> 0:14:33.680 two brains. I have lots of small brains all wrapped 0:14:33.760 --> 0:14:37.120 up together. To my, oh boy, that's a weird picture. 0:14:37.440 --> 0:14:39.960 Like if we open your skull, we wouldn't find a brain, 0:14:40.000 --> 0:14:42.200 We just find a whole bunch of little brains. Yeah, 0:14:42.240 --> 0:14:44.240 I'm like nineteen little brains in a trench coat, not 0:14:44.360 --> 0:14:49.160 actually a full person. Boy, that's a bit disturbing. I 0:14:49.240 --> 0:14:50.960 guess you know, you've got different parts of your life 0:14:50.960 --> 0:14:53.080 and so you gotta engage like, oh I need dad brain, 0:14:53.200 --> 0:14:56.240 or I need husband brain, or it's physics brain time. 0:14:57.960 --> 0:15:00.880 I find having split personalities is a bit of a problem. 0:15:00.920 --> 0:15:03.120 I see. So everybody's always just getting the same cartoon 0:15:03.160 --> 0:15:05.880 is braining all the time. Everyone's just getting the whole brain. 0:15:06.440 --> 0:15:10.800 There's no menu option. You get what you get and 0:15:10.880 --> 0:15:13.640 you don't get upset. But yeah, pretty interesting answers here 0:15:13.680 --> 0:15:16.640 from people. Some people think they yes, definitely they do, 0:15:16.720 --> 0:15:19.400 and some people think they definitely don't. And here's an 0:15:19.440 --> 0:15:23.040 interesting answer. Because they're waves. Can two waves interact with 0:15:23.280 --> 0:15:26.000 each other, yes, right, no reason why not. Like, two 0:15:26.040 --> 0:15:28.680 waves definitely can interact with each other. If you've seen 0:15:28.760 --> 0:15:31.240 waves in the ocean, you know they can add up together, 0:15:31.280 --> 0:15:34.200 they can even cancel each other out. So waves can 0:15:34.200 --> 0:15:36.520 definitely interact with each other. And photons can do that 0:15:36.560 --> 0:15:39.080 as well. You know, we've seen like the double slit experiment, 0:15:39.160 --> 0:15:43.320 is interference between photons, and so waves can definitely interact 0:15:43.360 --> 0:15:45.600 with each other. That's not an issue. But I guess 0:15:45.600 --> 0:15:48.080 in water in the ocean, if you get like one 0:15:48.120 --> 0:15:50.080 wave going one way and another way of going the 0:15:50.080 --> 0:15:52.000 other way, they do sort of mix in the middle, 0:15:52.040 --> 0:15:56.000 but afterwards they just keep going as if they hadn't interacted, right, Yeah. 0:15:56.040 --> 0:15:58.480 The effect that you see is a superposition of the 0:15:58.520 --> 0:16:02.200 two waves, and so there isn't necessarily direct coupling between 0:16:02.200 --> 0:16:04.640 the waves, but what you see is the addition of 0:16:04.680 --> 0:16:07.800 the two waves. In that sense, you experience the combination 0:16:07.840 --> 0:16:10.360 of them. But the individual waves can still be thought 0:16:10.400 --> 0:16:13.360 of as individual waves. Yeah, but then they keep going 0:16:13.560 --> 0:16:16.080 as if they hadn't interacted, right, Yeah. No, that's a 0:16:16.080 --> 0:16:18.120 good point. They don't interact with each other the way 0:16:18.120 --> 0:16:20.400 they would interact with for example, a boundary or a 0:16:20.440 --> 0:16:22.880 wall where they really would reflect. Yeah, they just sort 0:16:22.880 --> 0:16:25.160 of ignore each other. I mean in the moment, if 0:16:25.160 --> 0:16:27.760 you're setting in the middle, you would experience both waves 0:16:28.520 --> 0:16:31.400 and they would add or substract, but they eventually the 0:16:31.560 --> 0:16:33.920 waves keep going right. Yeah, that's true. And so the 0:16:34.000 --> 0:16:36.960 question is does the same happen to photons? That is 0:16:37.000 --> 0:16:39.400 indeed the question of the episode, And what happens when 0:16:39.400 --> 0:16:41.520 two photons getting near each other? Do they ignore each 0:16:41.560 --> 0:16:43.240 other or do they bounce off each other? Or do 0:16:43.280 --> 0:16:45.760 they do something else? All right, well, let's diget into it, Daniel, 0:16:45.800 --> 0:16:49.360 I guess, first of all, what does bouncing off actually mean? Like, 0:16:49.400 --> 0:16:51.320 what does it mean for one particle to bump into 0:16:51.360 --> 0:16:54.840 another particle? Do they actually bump? Yeah, so the microscopic 0:16:54.960 --> 0:16:58.000 view of bumping into things on the dance floor or 0:16:58.080 --> 0:17:00.480 sitting in your chair or whatever is sort of the 0:17:00.480 --> 0:17:03.520 conceptual view that you might have. You know, you probably 0:17:03.560 --> 0:17:05.960 imagine that the reason that you don't pass through a 0:17:05.960 --> 0:17:08.959 wall is that like the surface of your body is 0:17:09.040 --> 0:17:12.760 touching the surface of the wall and it's pushing back. Right, 0:17:13.040 --> 0:17:16.200 But what do we really mean by touching? Like microscopically? 0:17:16.600 --> 0:17:19.080 Zoom in? What's happening. Well, you know, the surface of 0:17:19.080 --> 0:17:20.840 your body is a bunch of atoms, and those have 0:17:20.880 --> 0:17:23.879 electrons around them. So really the tip of your finger, 0:17:23.960 --> 0:17:26.680 for example, is a bunch of electrons, and the edge 0:17:26.720 --> 0:17:28.680 of the wall, the surface of the wall, is also 0:17:28.800 --> 0:17:30.880 a bunch of electrons. And what happens when you push 0:17:30.960 --> 0:17:35.080 one against the other. The electrons themselves don't have to touch, right, 0:17:35.119 --> 0:17:38.679 They can repel each other without actually touching. So this 0:17:38.840 --> 0:17:42.240 microscopic view of the world from a physics point of view, 0:17:42.440 --> 0:17:46.080 there's no actual contact between these particles. It all happens 0:17:46.200 --> 0:17:49.639 via the fields between them, or equivalently, the particles that 0:17:49.640 --> 0:17:53.000 they're passing between each other. So when your finger pushes 0:17:53.000 --> 0:17:56.640 against the wall, it's ripples in the electromagnetic field or equivalently, 0:17:56.720 --> 0:17:59.960 photons that are transmitting that information that are pushing back 0:18:00.000 --> 0:18:02.080 back on you. Yeah, but you know, I think we 0:18:02.200 --> 0:18:05.960 have everyone has this intuitive feeling that things touch each 0:18:05.960 --> 0:18:09.320 other because like, my finger has a volume and the 0:18:09.359 --> 0:18:13.440 table has a volume, and that two objects can't sort 0:18:13.480 --> 0:18:16.800 of occupy the same space at the same time. And 0:18:16.880 --> 0:18:19.840 so if I press my finger against the table, like 0:18:19.920 --> 0:18:23.520 somehow the universe is resisting my finger being in the 0:18:23.560 --> 0:18:26.960 same place as the table, But two things can occupy 0:18:27.040 --> 0:18:29.520 the same place at the same time. Your body is 0:18:29.560 --> 0:18:32.240 full of neutrinos right now as well, and they're passing 0:18:32.359 --> 0:18:34.280 right through you and ignoring you. They are taking up 0:18:34.400 --> 0:18:37.720 your volume. The only reason you perceive a volume, the 0:18:37.760 --> 0:18:40.760 reason you think there's a boundary between your particles and 0:18:40.800 --> 0:18:43.280 the other particles is when there's a force between them. 0:18:43.640 --> 0:18:46.200 Neutrinos don't feel force, so they're just trapes right through 0:18:46.240 --> 0:18:48.160 the edge of Jorge and then out the other side, 0:18:48.280 --> 0:18:50.560 No big deal. The reason the table and the chair 0:18:50.640 --> 0:18:53.359 doesn't is because there's a force that prevents them. So 0:18:53.359 --> 0:18:55.960 it's really all about the force you can imagine things 0:18:55.960 --> 0:18:58.800 is sort of like with virtual springs between them, preventing 0:18:58.800 --> 0:19:02.119 them from getting too close, but there's no actual contact. 0:19:02.200 --> 0:19:05.639 Contact doesn't really mean anything. All there is is forced 0:19:05.680 --> 0:19:08.119 between particles, right. I think that's what you're saying, is 0:19:08.160 --> 0:19:11.000 that this idea that my finger can't occupy the same 0:19:11.040 --> 0:19:13.479 space as the table is really just kind of an illusion, right, 0:19:13.480 --> 0:19:16.840 because they could, I guess. But something is I'm not 0:19:16.960 --> 0:19:21.320 preventing my cluster of atoms in my finger from somehow 0:19:22.160 --> 0:19:26.240 being or you know, penetrating or infringing upon the volume 0:19:26.359 --> 0:19:29.240 of the atoms cluster together on the table. Yeah, and 0:19:29.240 --> 0:19:31.879 I wouldn't say the volume is an illusion. You know, 0:19:31.920 --> 0:19:35.560 people talk about like atoms being mostly empty space, and 0:19:35.600 --> 0:19:37.480 I think that's cool to give you the sense that 0:19:37.520 --> 0:19:39.840 like it's made of tiny particles, But it's also a 0:19:39.880 --> 0:19:42.840 little bit misleading that space isn't empty. It's filled with 0:19:42.960 --> 0:19:45.840 fields or with virtual photons that are zooming around and 0:19:45.920 --> 0:19:48.639 keeping everything in its position. You can define what your 0:19:48.720 --> 0:19:51.280 volume is, but that volume, the edge of it, is 0:19:51.280 --> 0:19:53.720 not defined by like the stuff that you're made out of, 0:19:53.960 --> 0:19:57.240 but the fields from that stuff, the forces of that stuff, 0:19:57.520 --> 0:20:01.040 And the volume also depends on what you're touching. Right, 0:20:01.119 --> 0:20:03.639 you want to touch a blob of neutrinos, then your 0:20:03.680 --> 0:20:06.000 volume is different. Then you want to touch something like 0:20:06.040 --> 0:20:09.359 a table or a chair. Right, So, because the volume 0:20:09.400 --> 0:20:12.240 depends on the fields, and not everything feels those fields, 0:20:12.480 --> 0:20:14.480 then the volume is a little bit dependent on what 0:20:14.520 --> 0:20:16.439 you're touching. Right. I think you're saying that, you know, 0:20:16.520 --> 0:20:18.600 instead of thinking of our fingers or at the table 0:20:18.720 --> 0:20:22.040 as collections of stuffy particles, maybe it's better to think 0:20:22.080 --> 0:20:25.639 of them as like clusters of ripples in the fields 0:20:25.640 --> 0:20:28.800 of the universe, Like my finger is not really a finger, 0:20:29.000 --> 0:20:31.800 is just a whole bunch of ripples kind of tightly 0:20:32.119 --> 0:20:35.520 cluster together. And so this whole bunch of ripples doesn't 0:20:35.640 --> 0:20:38.560 want to just um go through the bunch of ripples 0:20:38.560 --> 0:20:42.480 of the table. There's are forces that push my group 0:20:42.520 --> 0:20:46.720 of ripples against the tables group of ripples. That's right, 0:20:46.880 --> 0:20:49.640 And I like the sound of the word ripples, And yeah, 0:20:49.720 --> 0:20:52.480 you are made of little matter ripples, right, your particles, 0:20:52.600 --> 0:20:54.399 And you can think of as like little ripples in 0:20:54.480 --> 0:20:57.040 quantum fields of matter. And the way those things stay 0:20:57.040 --> 0:20:59.960 apart again is not that they are physically touching each 0:21:00.000 --> 0:21:02.760 each other, but that they exchange other kinds of ripples, 0:21:02.800 --> 0:21:05.359 these force ripples between them. So you can think of 0:21:05.400 --> 0:21:08.359 yourself as like a cloud of these little matter ripples 0:21:08.400 --> 0:21:12.040 that are maintaining their distance from each other by passing 0:21:12.080 --> 0:21:14.960 back and forth these other little ripples, and also maintaining 0:21:14.960 --> 0:21:18.400