WEBVTT - Listener Questions 6 0:00:08.960 --> 0:00:11.280 Are you the kind of person that wonders if black 0:00:11.320 --> 0:00:14.200 holes have air on them? Do you ever think about 0:00:14.280 --> 0:00:16.880 what it's like to be in a fighter jet and 0:00:17.120 --> 0:00:20.520 roll down the windows. Do you ever wonder if light gets, 0:00:20.840 --> 0:00:23.960 you know, tired, on its way across the universe from 0:00:24.120 --> 0:00:27.720 distant stars all the way to Earth. If so, then 0:00:27.920 --> 0:00:30.400 you're the right person to be listening to this podcast, 0:00:30.480 --> 0:00:32.560 because that's exactly the kind of stuff we're gonna be 0:00:32.640 --> 0:00:53.560 talking about today. Hi. I'm Daniel. I'm a particle physicist, 0:00:53.640 --> 0:00:55.640 and I'm the co author of the book We Have 0:00:55.720 --> 0:00:59.640 No Idea, A Guide to the Unknown Universe. My co author, 0:01:00.040 --> 0:01:02.920 Jorge him is usually the co host of this podcast, 0:01:03.240 --> 0:01:06.720 Daniel and Jorge Explain the Universe, brought to you by 0:01:06.720 --> 0:01:10.360 I Heart Radio. Today, Jorge has to be away, so 0:01:10.520 --> 0:01:13.279 I'm going to do the podcast by myself, and today 0:01:13.280 --> 0:01:16.440 we're doing something which is absolutely my favorite, which is 0:01:16.959 --> 0:01:21.319 answering listener questions. I love listener questions because they give 0:01:21.360 --> 0:01:24.080 me feedback and help me understand what people out there 0:01:24.080 --> 0:01:27.480 are thinking, what they're understanding, and what they're confused about. 0:01:28.000 --> 0:01:30.720 When Jorge and I do lectures live, we talk about 0:01:30.720 --> 0:01:33.959 all the amazing mysteries of the universe, and then people 0:01:34.000 --> 0:01:37.920 ask questions, and those questions are so valuable because they 0:01:37.920 --> 0:01:41.479 show me exactly what people have misunderstood. If I said 0:01:41.520 --> 0:01:43.640 something and I thought I was super clear and then 0:01:43.640 --> 0:01:46.240 somebody asked the question, it helps me see how to 0:01:46.400 --> 0:01:50.640 better explain something. So I really value listener questions. Thank 0:01:50.680 --> 0:01:53.640 you to everybody who has written in, either with a 0:01:53.680 --> 0:01:55.760 point of confusion about something that we said on the 0:01:55.760 --> 0:01:59.240 podcast or something totally crazy that they were thinking about 0:01:59.480 --> 0:02:02.240 and they wanted us to explain. And for all of 0:02:02.280 --> 0:02:05.040 you who have not written into the podcast, what are 0:02:05.040 --> 0:02:07.440 you waiting for? We want to hear your questions. When 0:02:07.480 --> 0:02:10.080 I say I answer every email, I mean it. And 0:02:10.080 --> 0:02:12.920 when I say I love getting questions from listeners, I 0:02:13.000 --> 0:02:16.480 am being totally serious. So please send us your questions 0:02:16.480 --> 0:02:19.799 two questions at Daniel and Jorge dot com. You might 0:02:19.840 --> 0:02:22.760 even hear yourself on the podcast. So today we'll be 0:02:22.800 --> 0:02:26.720 answering listener questions. Questions about lights, questions about black holes, 0:02:26.919 --> 0:02:29.360 questions about flying at the speed of sound with the 0:02:29.360 --> 0:02:32.400 windows open, and all these questions have something in common, 0:02:32.440 --> 0:02:34.840 which is they're sort of like what if questions, like 0:02:35.080 --> 0:02:36.799 how could you do this? Or how could you make 0:02:36.840 --> 0:02:39.400 this work? Or what would happen if you did this thing? 0:02:39.919 --> 0:02:43.080 And all of these reveal people's just desire to understand 0:02:43.080 --> 0:02:45.519 what happens in the universe, to reveal secrets of the 0:02:45.600 --> 0:02:49.760 universe by cooking up crazy scenarios, scenarios where Nature has 0:02:49.800 --> 0:02:52.639 to reveal the truth. And in the end, that's really 0:02:52.760 --> 0:02:56.120 what experimental physics is. We want to know the answer 0:02:56.160 --> 0:02:58.680 to a question, you know, does the universe work this 0:02:58.720 --> 0:03:00.880 way or that way? And so we come up with 0:03:00.919 --> 0:03:04.360 some scenario where nature has to reveal to us the answer. 0:03:04.560 --> 0:03:07.520 We corner nature and say, well, show us you know, 0:03:07.560 --> 0:03:09.480 it is light a particle or is it a wave? 0:03:10.080 --> 0:03:12.400 Does the Higgs boson have this much mass or that 0:03:12.480 --> 0:03:16.680 much mass? Really, all experimental physics is is constructing physical 0:03:16.720 --> 0:03:20.000 scenarios where Nature has to show us her cards. And 0:03:20.080 --> 0:03:22.000 so a lot of the questions you'll hear about today 0:03:22.240 --> 0:03:25.200 are exactly that kind of question. So today we have 0:03:25.240 --> 0:03:29.359 three questions. Let's dive in. Hey, guys, my question is 0:03:29.680 --> 0:03:35.120 what would happen if we quantum entangled two particles and 0:03:35.200 --> 0:03:38.320 took particle one and shot it into a black hole? 0:03:39.320 --> 0:03:42.200 Could we learn anything? And what do you think we 0:03:42.320 --> 0:03:47.160 could learn if we can from particle two. Shout out 0:03:47.200 --> 0:03:50.520 to South Dakota and LEXI. All right, I got this 0:03:50.600 --> 0:03:52.600 question and it blew my mind. And it blew my 0:03:52.640 --> 0:03:55.800 mind because it combines so many different things that I love. 0:03:55.960 --> 0:03:59.200 You've got black holes, you've got quantum mechanics, you got 0:03:59.240 --> 0:04:02.240 inventing new ways to explore the universe. Right, So I 0:04:02.320 --> 0:04:05.400 love when listeners think up new ideas for how we 0:04:05.440 --> 0:04:08.440 could solve ancient questions. All right, so first let's talk 0:04:08.480 --> 0:04:11.280 about why would we want to know what's going on 0:04:11.320 --> 0:04:13.680 inside a black hole? Like, why does anybody care? Isn't 0:04:13.720 --> 0:04:16.560 it just basically the garbage disposal of the universe, jammed 0:04:16.600 --> 0:04:20.080 filled with rejected matter that's got swashed down the toilet 0:04:20.080 --> 0:04:22.400 bowl and into the black hole. Well, that's what we 0:04:22.440 --> 0:04:26.280 don't know. General relativity tells us that black holes might 0:04:26.320 --> 0:04:29.159 have a singularity in the center of them, right, a 0:04:29.200 --> 0:04:33.600 tiny dot of matter with infinite density something, which is, 0:04:33.640 --> 0:04:35.760 you know, hard for us to imagine. What does infinite 0:04:35.839 --> 0:04:40.240 density mean? And but according to Einstein's equations, that's exactly 0:04:40.320 --> 0:04:43.640 the conditions you need to create a black hole. Fine, 0:04:43.680 --> 0:04:46.880 And we know that Einstein's equations have been validated many, 0:04:46.920 --> 0:04:49.840 many times, and nobody's ever found flaw on them. They 0:04:49.839 --> 0:04:53.520 predicted gravitational waves, we've seen them. They predicted all sorts 0:04:53.520 --> 0:04:57.680 of other crazy gravitational phenomena, and they've been verified and checked. So, 0:04:57.720 --> 0:05:01.320 as far as we know, Einstein's equations are correc except 0:05:01.920 --> 0:05:05.480 quantum mechanics tells us that you can't have a singularity 0:05:05.480 --> 0:05:08.080 at the center of a black hole. Remember, quantum mechanics 0:05:08.080 --> 0:05:11.760 tells us the universe is not smooth and continuous, instead 0:05:11.800 --> 0:05:15.839 of the universe is discrete. Space itself is probably pixelated 0:05:16.000 --> 0:05:20.279 into tiny little units. Right, Mass is probably pixelated, time 0:05:20.440 --> 0:05:23.719 is probably pixelated. All these things are probably discreete and 0:05:23.720 --> 0:05:27.000 not continuous, And that means you can't have an infinitely 0:05:27.040 --> 0:05:30.040 small dot, certainly not one with an infinite mass inside 0:05:30.040 --> 0:05:32.120 of it. In addition, there's all sorts of issues about 0:05:32.120 --> 0:05:35.240 the Heisenberg uncertainty principle. Can you have so much matter 0:05:35.400 --> 0:05:39.240 localized in one spot for such a long time. Quantum 0:05:39.279 --> 0:05:42.400 mechanics says that that you should not find a singularity 0:05:42.440 --> 0:05:45.039 inside a black hole. The problem, of course, is it's 0:05:45.120 --> 0:05:47.919 awfully difficult to look inside a black hole. So I 0:05:47.920 --> 0:05:50.839 think that's probably what motivates this question the desire to 0:05:50.880 --> 0:05:53.200 see what's inside a black hole. And I'll be honest, 0:05:53.560 --> 0:05:55.479 if I could see inside a black hole, I would 0:05:55.520 --> 0:05:57.240 do it in a second. I would love to know 0:05:57.800 --> 0:06:00.320 what is going on inside there, all right, it So 0:06:00.640 --> 0:06:04.400 the idea from this question is to quantum entangle two 0:06:04.440 --> 0:06:07.680 particles and shoot one into a black hole, and I 0:06:07.720 --> 0:06:09.960 guess use the other one to sort of learn something 0:06:10.040 --> 0:06:13.120 about what's going on inside the black hole. Right, well, 0:06:13.240 --> 0:06:17.200 let's talk about quantum entanglement. Quantum entanglement is a very 0:06:17.200 --> 0:06:19.800 tricky topic, and we discussed in some depth on our 0:06:19.880 --> 0:06:23.479 quantum Computing episode. The short version is that it links 0:06:23.680 --> 0:06:29.000 two particles potentially across gray distances or great barriers like 0:06:29.080 --> 0:06:31.280 the edge of a black hole. The link is a 0:06:31.360 --> 0:06:34.600 kind of constraint. If one particle spins up, the other 0:06:34.600 --> 0:06:37.679 one has to spin down. So by knowing something about 0:06:37.760 --> 0:06:40.839 one of the particles discovering that it's spin up, for example, 0:06:41.120 --> 0:06:43.839 you can learn something about the other, such as knowing 0:06:43.839 --> 0:06:46.719 that it's spin down, even if you never see it 0:06:46.839 --> 0:06:50.359 or can't possibly see it because it's hidden. So you 0:06:50.400 --> 0:06:54.320 see the attraction for potentially probing a black hole using 0:06:54.440 --> 0:06:58.720 pairs of entangled particles to sort of extract some information 0:06:59.040 --> 0:07:02.440 from one particle by looking at the other one. All right, Well, 0:07:02.440 --> 0:07:05.279 the short answer is we would learn nothing, And the 0:07:05.320 --> 0:07:08.240 reason is that there are pretty solid theorems about getting 0:07:08.279 --> 0:07:11.440 information out of the black hole. All right, So the 0:07:11.640 --> 0:07:14.960 no hair theorem, I'm not joking. It's literally called the 0:07:15.000 --> 0:07:17.280 no hair theorem, and I don't know if it was 0:07:17.320 --> 0:07:20.520 invented by a business without hair, but the no hair 0:07:20.600 --> 0:07:23.679 theorem says that the only information you can get about 0:07:23.680 --> 0:07:27.720 a black hole is its mass, it's total electric charge, 0:07:28.000 --> 0:07:31.640 and its momentum. That's it, right. You can't get any 0:07:31.680 --> 0:07:35.320 other information. Nothing that's going on inside the black hole 0:07:35.360 --> 0:07:38.560 can never leave, right, certainly can't see things escaping the 0:07:38.600 --> 0:07:41.240 black hole. Nothing can escape, so no light can come 0:07:41.280 --> 0:07:43.600 out to reveal to you what's inside the black hole. 0:07:43.840 --> 0:07:46.360 But more than that, you cannot get any information, no 0:07:46.400 --> 0:07:49.800 matter how clever you are, other than those three pieces 0:07:49.800 --> 0:07:53.360 of information. And this raises all sorts of fascinating questions, 0:07:53.400 --> 0:07:57.080 Like um, the listener was asking about quantum entangled particles 0:07:57.080 --> 0:07:59.320 where one is inside and one is outside the black hole. 0:07:59.560 --> 0:08:03.480 That act really happens already. There's something called hawking radiation 0:08:03.920 --> 0:08:06.960 or a photon inside the black hole will decay to 0:08:07.120 --> 0:08:10.520 two quantum entangled particles, and the decay will happen so 0:08:10.640 --> 0:08:13.560 close to the event horizon that one of the particles 0:08:13.600 --> 0:08:16.320 slips out of the event horizon and gets to leave. 0:08:16.560 --> 0:08:20.800 That's Hawking radiation and requires this quantum fluctuation right right 0:08:20.840 --> 0:08:22.840 at the edge of the event horizon. And so you 0:08:22.920 --> 0:08:26.520 might ask, can we learn something about the side of 0:08:26.600 --> 0:08:29.680 the Hawking radiation that got slurred into the black hole 0:08:29.960 --> 0:08:32.800 by looking at what happens outside the black hole by 0:08:32.840 --> 0:08:36.360 measuring that Hawking radiation. Well, the answer is no, right, 0:08:36.480 --> 0:08:39.280 no information can leave the black hole. Is just impossible 0:08:39.320 --> 0:08:42.360 to extract any information. Even though that electron and that 0:08:42.400 --> 0:08:45.520 positron are entangled with each other, right, they do not 0:08:45.640 --> 0:08:49.480 contain any information about what's going on inside the black hole. 0:08:49.720 --> 0:08:51.640 And the shorter answer is, as soon as you're trying 0:08:51.640 --> 0:08:55.199 to interact with the electron impositron, you will anyway break 0:08:55.240 --> 0:08:58.680 that entanglement. Right. The entanglement only exists when those particles 0:08:58.679 --> 0:09:01.480 are isolated from the to the system. So as soon 0:09:01.520 --> 0:09:03.920 as you trying to measure something about that electron, you're 0:09:03.960 --> 0:09:07.040 probably going to break that entanglement anyway, which is usually 0:09:07.480 --> 0:09:10.400 usually the problem with entanglement is that you can't really 0:09:10.440 --> 0:09:13.520 use it to convey information because interacting with the particles 0:09:13.760 --> 0:09:17.680 breaks that entanglement. All Right, This brings us to another 0:09:17.840 --> 0:09:21.080 fascinating and current topic in black hole physics, which is 0:09:21.360 --> 0:09:25.960 people are wondering where the information goes. Like, according to 0:09:26.080 --> 0:09:29.600 black hole theories, no information can leave the black hole, right, 0:09:30.040 --> 0:09:34.880 But according to Hawking, radiation particles do escape the black hole, 0:09:34.920 --> 0:09:37.040 which means the black hole can shrink. In fact, for 0:09:37.120 --> 0:09:40.800 small black holes, black holes could even evaporate and disappear. 0:09:41.559 --> 0:09:44.839 So what happens to the information that went into the 0:09:44.880 --> 0:09:48.079 black hole? What happened to all that quant those quantum 0:09:48.080 --> 0:09:50.079 states and all that stuff that went into the black 0:09:50.080 --> 0:09:53.920 hole and then the black hole disappeared? Because there's another 0:09:54.040 --> 0:09:56.800 law of quantum mechanics that says It says that all 0:09:56.840 --> 0:09:59.520 the information about past states in the universe is contained 0:09:59.559 --> 0:10:02.880 in the ragement of the current universe, right, no information 0:10:02.920 --> 0:10:06.760 should be lost. For those mathematically inclined, this means essentially 0:10:06.920 --> 0:10:09.840 that the wave function is unitary, right. The transformations through 0:10:09.880 --> 0:10:13.559 times do not change the overall normalization of the wave function. 0:10:14.280 --> 0:10:18.200 So if black holes can evaporate and disappear, but no 0:10:18.280 --> 0:10:22.360 information can leave the black hole. That suggests that information 0:10:22.440 --> 0:10:25.600 is destroyed, and that particular puzzle goes by the name 0:10:25.640 --> 0:10:29.240 of the black hole information paradox. And people have proposed 0:10:29.280 --> 0:10:32.400 all sorts of crazy solutions to this, including firewalls and 0:10:32.440 --> 0:10:35.480 all sorts of crazy stuff that we might actually see 0:10:35.520 --> 0:10:38.360 at the edges of black holes one day. So thank 0:10:38.400 --> 0:10:41.560 you for this wonderful question about black holes and quantum 0:10:41.559 --> 0:10:45.360 mechanics and entanglement and information and all sorts of crazy, 0:10:45.360 --> 0:10:47.760 amazing stuff. One of my favorite things about these kinds 0:10:47.760 --> 0:10:51.480 of questions is that they seem theoretical, they seem crazy abstract, 0:10:51.720 --> 0:10:54.840 but these are real, like black holes, they're real objects. 0:10:54.920 --> 0:10:57.559 They are out there, and one day, if we build 0:10:57.600 --> 0:10:59.520 the right kind of spaceship and the right kind of probes, 0:10:59.600 --> 0:11:01.080 we could go when we could observe them, and we 0:11:01.160 --> 0:11:04.120 might learn the answers to some of these questions. So 0:11:04.200 --> 0:11:07.120 thanks for sending in that question, and keep writing. Well, 0:11:07.280 --> 0:11:09.280 this is a perfect spot to take a break. We'll 0:11:09.280 --> 0:11:24.959 be right back. This is a wonderful question that we 0:11:25.040 --> 0:11:28.959 got recently from a listener and from that listener's dad. Hi, 0:11:29.120 --> 0:11:32.360 my name is Phineas, and I'm in fourth grade and 0:11:32.400 --> 0:11:35.440 I live in Sico, Alaska. I was wondering, if you 0:11:35.440 --> 0:11:37.640 were in an airplane going faster on the speed of 0:11:37.679 --> 0:11:40.480 sound and you said something to the person next to you, 0:11:40.800 --> 0:11:43.079 would they actually be able to hear what you said. 0:11:44.000 --> 0:11:47.080 This is Phineas's dad. Phineas asked me this question a 0:11:47.080 --> 0:11:50.520 while ago, and it got me wondering if one was 0:11:50.600 --> 0:11:54.439 traveling at or above the speed of light, would they 0:11:54.480 --> 0:11:57.480 be able to see the person next to them? So 0:11:57.559 --> 0:12:00.440 I love this question for so many reasons. I love 0:12:00.480 --> 0:12:03.040 that that young boys imagining what it's like to be 0:12:03.080 --> 0:12:05.240 on a spaceship or what it's like to be on 0:12:05.280 --> 0:12:08.319 a plane traveling past the speed of sound. And it's 0:12:08.320 --> 0:12:12.200 a great question. He's wondering about how this information is processed, 0:12:12.200 --> 0:12:15.360 how this information is transmitted. Essentially, are you leaving that 0:12:15.480 --> 0:12:18.719 information behind right? Well, first of all, I want to 0:12:18.720 --> 0:12:21.120 break his bubble and say, if you're on a fighter 0:12:21.200 --> 0:12:24.480 jet that's traveling faster than the speed of sound, probably 0:12:24.559 --> 0:12:27.320 you don't have the windows open, right, which means that 0:12:27.360 --> 0:12:29.800 you're in a little air bubble. That air bubble is 0:12:29.840 --> 0:12:32.960 moving with you fast in the speed of sound. If 0:12:33.000 --> 0:12:35.680 you had the windows open and the air was rushing 0:12:35.720 --> 0:12:38.760 past you fasten the speed of sound, it would probably 0:12:38.800 --> 0:12:42.120 tear you to shreds. And that's why fighter jets, for example, 0:12:42.240 --> 0:12:45.360 have that little bubble right the window that protects them 0:12:45.600 --> 0:12:48.520 from what's going on outside. All right, so they have 0:12:48.559 --> 0:12:51.240 a little bubble of air. And that's the key, because 0:12:51.320 --> 0:12:55.640 sound is a wave, right, Sound is just vibrations of 0:12:55.679 --> 0:12:58.360 the air, and so what it does is it moves 0:12:58.880 --> 0:13:01.480 relative to the air. Right. It's like if you have 0:13:01.520 --> 0:13:04.560 a bathtub of water and you're slapping it to make 0:13:04.760 --> 0:13:07.640 to make waves, the waves move relative to the water. 0:13:08.280 --> 0:13:11.040 If that water, if that bathtub was on a train 0:13:11.400 --> 0:13:14.880 traveling a super duper fast, it wouldn't make any difference, Right, 0:13:14.920 --> 0:13:16.880 You could still have a bath and you can still 0:13:16.880 --> 0:13:19.680 make splashes and they wouldn't be any different. In the 0:13:19.760 --> 0:13:22.320 same way, if you're on a fighter jet and you're 0:13:22.320 --> 0:13:24.880 in a little bubble of air inside the fighter jet, 0:13:25.240 --> 0:13:26.920 you can turn to the person next to you, can 0:13:26.960 --> 0:13:30.079 say hello, would you please pass the peanuts or whatever 0:13:30.120 --> 0:13:32.080 you say to somebody in a fighter jet, and the 0:13:32.240 --> 0:13:35.560 air between you is not moving relative to you, so 0:13:35.600 --> 0:13:38.480 you can send waves through it normally, just as you 0:13:38.520 --> 0:13:40.719 would if you were sitting on your couch in your 0:13:40.720 --> 0:13:43.280 living room. So the sort of cheap answer to the 0:13:43.360 --> 0:13:46.480 question is that there's no difference if you're in a 0:13:46.480 --> 0:13:49.120 little bubble of air that's moving with you, all right, 0:13:49.240 --> 0:13:52.440 So that's no fun. Let's imagine what happens when you 0:13:52.480 --> 0:13:56.200 open the windows, right, You're going mocked too, You're zooming 0:13:56.240 --> 0:13:58.960 through the atmosphere. You open the windows, all of a sudden, 0:13:59.000 --> 0:14:01.520 the wind is screaming past you with two thousand miles 0:14:01.559 --> 0:14:04.920 per hour. Right now, that's an interesting question. What happens 0:14:04.920 --> 0:14:06.839 if you turn to your friend and you say, past 0:14:06.880 --> 0:14:10.040 the bananas? Right? Can they hear you? The key thing 0:14:10.080 --> 0:14:13.360 to remember is that sound moves at a fixed speed 0:14:13.720 --> 0:14:16.840 relative to the air. So if you shout into a 0:14:16.920 --> 0:14:20.080 wind blowing at your back, then your show gets carried 0:14:20.120 --> 0:14:22.760 away from you by the wind more quickly than if 0:14:22.760 --> 0:14:26.480 there had been no wind. Similarly, if the wind is 0:14:26.520 --> 0:14:29.640 blowing in your face, it can slow down your shout. 0:14:30.120 --> 0:14:32.120 If the wind blows in your face at the speed 0:14:32.120 --> 0:14:36.360 of sound, ouch, then when you scream, your scream doesn't 0:14:36.440 --> 0:14:39.640 actually go anywhere. It stays right there on top of you. 0:14:40.360 --> 0:14:43.320 So in the fighter jet, if the windshield is down 0:14:43.400 --> 0:14:45.320 or whatever they call it in a fighter jet, then 0:14:45.360 --> 0:14:47.480 they can just talk normally right there in a bubble 0:14:47.520 --> 0:14:49.560 of air. Just like if you're in a bathtub and 0:14:49.560 --> 0:14:51.640 you make waves. It doesn't matter if you're on a 0:14:51.680 --> 0:14:54.160 train at the time, because the water is moving with you. 0:14:54.760 --> 0:14:57.960 But if they open the windshield, the wind is whipping 0:14:58.000 --> 0:15:00.200 by them at faster than the speed of so sound, 0:15:00.440 --> 0:15:04.280 and so they will leave their words behind. There's no 0:15:04.360 --> 0:15:07.120 way that they can talk, even if they shout straightforwards. 0:15:07.360 --> 0:15:10.240 This is also why planes make sonic booms. If a 0:15:10.240 --> 0:15:13.240 plane is traveling faster than the sound it's making, then 0:15:13.280 --> 0:15:16.680 it's catching up to his own sound, and the sound 0:15:16.680 --> 0:15:18.960 from two seconds ago gets piled up on top of 0:15:18.960 --> 0:15:21.240 the sound from one second ago and the sound from 0:15:21.360 --> 0:15:24.520 right now. It's the same amount of sound total, doesn't 0:15:24.560 --> 0:15:28.360 generate more sound, but it gets concentrated in certain places 0:15:28.560 --> 0:15:31.240 because the plane is out racing the sound it's making. 0:15:31.760 --> 0:15:33.840 Just like with a boat in the water, if it 0:15:33.920 --> 0:15:37.080 travels faster than the waves in water, then those waves 0:15:37.120 --> 0:15:39.480 pile up and you get a wake. A sonic boom 0:15:39.520 --> 0:15:43.920 is just a plane's wake. Alright, awesome question, and my 0:15:44.000 --> 0:15:46.680 favorite part I think of this is that his dad 0:15:46.760 --> 0:15:51.160 couldn't help but jump in and ask even more physics equestion, right, 0:15:51.240 --> 0:15:54.320 a question about traveling at or faster than the speed 0:15:54.360 --> 0:15:57.840 of light. Wonderful and I love this because it allows 0:15:57.920 --> 0:16:00.400 us to draw this contrast between the speed of sound 0:16:00.440 --> 0:16:02.600 and the speed of light. Now, first of all, of course, 0:16:03.040 --> 0:16:06.040 you can't travel at the speed of light, right, Nothing 0:16:06.080 --> 0:16:08.600 that has mass can travel at the speed of light. 0:16:09.240 --> 0:16:12.160 Only things that are massless travel at the speed of light, 0:16:12.520 --> 0:16:17.920 and everything that's massless travels at the speed of light. Photons, gravitons, 0:16:18.000 --> 0:16:21.360 if they exist, anything that does not have mass has 0:16:21.400 --> 0:16:24.080 to travel at the speed of light, and always at 0:16:24.120 --> 0:16:28.119 the speed of light. Can't go any slower. The amazing 0:16:28.160 --> 0:16:31.040 thing about photons is not only that they travel at 0:16:31.040 --> 0:16:33.000 the speed of light, which is super dup or fast, 0:16:33.480 --> 0:16:37.160 but that they don't travel relative to some medium. Sound 0:16:37.200 --> 0:16:40.360 and water waves travel it's fixed speeds relative to their 0:16:40.440 --> 0:16:44.200 medium air or water, but the rules are totally different. 0:16:44.240 --> 0:16:47.240 For light. It's a wave, but it always moves at 0:16:47.280 --> 0:16:50.040 the speed of light relative to the person measuring it, 0:16:50.520 --> 0:16:55.120 not relative to the medium, because it doesn't have a medium. Now, 0:16:55.160 --> 0:16:57.600 for a while people thought that there has to be 0:16:57.680 --> 0:16:59.840 some medium that light traveled through, and they called it 0:17:00.080 --> 0:17:02.800 ether and searched for it. But now we know that 0:17:02.840 --> 0:17:06.160 there is no ether, no medium that's doing the waving 0:17:06.280 --> 0:17:09.520 for light like air does for sound. The Michaelson Morley 0:17:09.600 --> 0:17:12.359 experiments showed us that because they measured the speed of 0:17:12.440 --> 0:17:15.920 light in two different directions and found them to be identical, 0:17:16.240 --> 0:17:18.880 even though the Earth is obviously moving in one direction 0:17:18.960 --> 0:17:21.240 or the other as it goes around the Sun. The 0:17:21.280 --> 0:17:24.159 reason is because light doesn't have a medium. It's the 0:17:24.200 --> 0:17:27.800 waving of quantum fields that are the properties of space itself. 0:17:28.119 --> 0:17:31.120 So space can be empty and still have light in it. 0:17:31.280 --> 0:17:33.080 And the way we showed it is that we discovered 0:17:33.119 --> 0:17:37.000 that light moves at the speed of light relative to everybody, 0:17:37.040 --> 0:17:40.000 no matter how fast you're going. So if you are 0:17:40.080 --> 0:17:43.240 standing on Earth and you turn on a flashlight, those 0:17:43.280 --> 0:17:48.120 photons leave your flashlight at the speed of light. Right cool. Now, 0:17:48.160 --> 0:17:51.640 what happens if you jump into Lamborghini and you turn 0:17:51.680 --> 0:17:54.760 on a flashlight. Lamborghini is going to two miles per hour. 0:17:55.440 --> 0:17:58.760 You're in the Lamborghini, you turn on the flashlight. What happens, Well, 0:17:58.920 --> 0:18:01.240 the light leaves your fly light at the speed of 0:18:01.320 --> 0:18:05.240 light relative to you, No big deal. What about somebody 0:18:05.240 --> 0:18:07.439 on the ground, right, the person you left behind who 0:18:07.520 --> 0:18:10.920 you didn't offer a ride in your Lamborghini too? When 0:18:11.000 --> 0:18:13.280 they when you turn on the flashlight in your Lamborghini, 0:18:13.560 --> 0:18:16.119 how fast did they see the light going? Well, you 0:18:16.160 --> 0:18:18.600 might think, well, it's the speed of light plus the 0:18:18.640 --> 0:18:21.800 speed of the Lamborghini, right, because the flashlight itself is 0:18:21.840 --> 0:18:25.800 moving at two hundred miles. But that's where you'd be wrong. Right, 0:18:25.880 --> 0:18:28.880 That's whyw light is weird. That's how our whole universe 0:18:28.960 --> 0:18:32.480 is super bizarre. Frankly, it's bonkers. But we know that 0:18:32.600 --> 0:18:35.440 light always travels at the speed of light, no matter 0:18:35.560 --> 0:18:38.040 what the speed of the thing making it is, right, 0:18:38.080 --> 0:18:41.480 And everybody who measures the speed of light always sees 0:18:41.560 --> 0:18:44.440 it moving at the speed of light relative to them. 0:18:44.480 --> 0:18:47.359 And that's different from sound, right. Sound travels relative to 0:18:47.400 --> 0:18:50.280 a medium like air, and that's sort of an absolute 0:18:50.320 --> 0:18:53.159 reference frame. And sound always moves at the same speed 0:18:53.200 --> 0:18:55.639 relative to the air. And so if you're moving with 0:18:55.680 --> 0:18:57.520 respect of the air, like you're in a fighter jet, 0:18:57.640 --> 0:18:59.520 and you're moving at the speed of sound, if you 0:18:59.640 --> 0:19:02.760 screen sam, then you're moving with that sound. Right. So 0:19:02.800 --> 0:19:05.480 if you scream in a fighter jet and you're moving 0:19:05.480 --> 0:19:07.280 at the speed of sound, you can basically just like 0:19:07.440 --> 0:19:10.760 stay inside your scream. You can fly along through the 0:19:10.840 --> 0:19:14.160 air with your scream. That's not true with light, right, 0:19:14.240 --> 0:19:16.640 Light will always move at the speed of light relative 0:19:16.680 --> 0:19:19.520 to you. You turn on that flashlight, even if you 0:19:19.560 --> 0:19:21.720 were traveling very close to the speed of light, you 0:19:21.760 --> 0:19:24.880 couldn't stay with those photons. It would leave you at 0:19:24.920 --> 0:19:27.800 the speed of light. And so if you're traveling very 0:19:27.800 --> 0:19:29.560 close to the speed of light, because you can't travel 0:19:29.720 --> 0:19:32.840 at the speed of light, and you look next to you, right, 0:19:33.080 --> 0:19:35.720 and the person next to you has a flashlight, it's 0:19:35.720 --> 0:19:39.080 going to act totally normally for you, right, It doesn't 0:19:39.119 --> 0:19:42.680 matter what's happening outside. Light always travels at the speed 0:19:42.720 --> 0:19:45.200 of light relative to you. So the short I answer 0:19:45.200 --> 0:19:48.639 to your question is, if you're traveling nearly at the 0:19:48.640 --> 0:19:52.320 speed of light, then everything will feel normal inside your spaceship. 0:19:52.560 --> 0:19:55.280 Clocks will run normally. Everything will seem normal. Now if 0:19:55.280 --> 0:19:57.440 you look outside your spaceship, but things that are not 0:19:57.560 --> 0:20:00.520 traveling at that high speed, that's when relative he kicks in. 0:20:01.000 --> 0:20:04.040 Things seem to run slow and they seem to get shrunk. Right, 0:20:04.359 --> 0:20:07.840 But light always travels at the same speed no matter what. 0:20:09.520 --> 0:20:11.520 I hope that was an answer to your question. Thank 0:20:11.560 --> 0:20:14.040 you so much for writing in, Thank you for wondering 0:20:14.080 --> 0:20:16.280 about the universe, and thank you to all the parents 0:20:16.280 --> 0:20:19.680 out there who are sharing their wonderings about the universe 0:20:19.720 --> 0:20:22.399 with their kids and sharing this podcast with their kids 0:20:22.760 --> 0:20:26.479 and letting their kids ask us crazy, awesome, amazing, super 0:20:26.560 --> 0:20:30.800 fun questions about the universe that we totally love to answer. 0:20:31.000 --> 0:20:33.720 Let's get to our last question, but first, let's take 0:20:33.720 --> 0:20:49.879 a break. Okay, we're back and we're answering listener questions. 0:20:49.920 --> 0:20:52.359 Today we talked about zooming around at the speed of 0:20:52.400 --> 0:20:54.840 sound with the speed of light, and we talked about 0:20:54.960 --> 0:20:58.199 quantum entanglement and black holes, and our last question is 0:20:58.240 --> 0:21:01.720 also related to light and zoom across the universe. Here 0:21:01.720 --> 0:21:04.600 it is Hello, Daniel and Jorge. Hey, my name is 0:21:04.640 --> 0:21:07.760 Marcella and I'm forming a Jeanette Brazil. I'm a big 0:21:07.800 --> 0:21:10.840 fan of your podcast and your book. So my question 0:21:10.880 --> 0:21:14.960 is about how does light carry information or how exactly 0:21:15.040 --> 0:21:19.520 does a photon transmit or carry within itself a pixel 0:21:19.600 --> 0:21:21.879 so that we are able to see the images we 0:21:21.960 --> 0:21:25.800 see on our telescopes. How does it not disintegrate after 0:21:25.840 --> 0:21:30.120 traveling so far. Thank you so much. All right, that's 0:21:30.160 --> 0:21:32.920 not really one question. That's like a bunch of questions 0:21:32.920 --> 0:21:36.240 I'll stuck together but totally fair will answer all of them. 0:21:36.280 --> 0:21:39.320 The first part of the question was essentially what information 0:21:39.359 --> 0:21:41.800 does light carry? And I think the question is trying 0:21:41.840 --> 0:21:44.480 to ask, like, when you see a picture of like 0:21:44.520 --> 0:21:47.840 a distant star, what is it that the photon is carrying? 0:21:47.840 --> 0:21:50.159 How does it how does that picture come from the 0:21:50.200 --> 0:21:53.840 star and end up in my eyeballs or in my telescope. First, 0:21:53.880 --> 0:21:57.160