Latest / Daniel and Kelly’s Extraordinary Universe / Listener Questions 47: Gravity, Time, Photons

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Listener Questions 47: Gravity, Time, Photons · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, We've been answering listener questions for years.
• 0:11
  Speaker 2: Right, yeah, more than five years actually.
• 0:14
  Speaker 1: M wow, that's wild. But do you think it's making
• 0:17
  Speaker 1: a difference? Like, are we making a dent in humanity's
• 0:20
  Speaker 1: understanding of the universe?
• 0:22
  Speaker 2: You know? I think every time we answer one person's question,
• 0:26
  Speaker 2: we move all of humanity forward, a tiny little bit
• 0:29
  Speaker 2: forward towards what towards the forefront of human knowledge? And
• 0:33
  Speaker 2: what's there the vast abyss of our confusion?
• 0:38
  Speaker 1: I was gonna say, I there are treats there, like
• 0:41
  Speaker 1: do you get a lollipop?
• 0:42
  Speaker 2: No, it's mostly just a bunch of scientists scratching their
• 0:44
  Speaker 2: head eating lollipops. Sometimes that's all you can do.
• 0:49
  Speaker 1: But can you sense humanity moving forward a little bit
• 0:52
  Speaker 1: each time you answer a question?
• 0:53
  Speaker 2: I guess so. I mean the nature of questions we
• 0:55
  Speaker 2: get has been changing. Sometimes people ask follow up questions
• 0:59
  Speaker 2: to answers to other people's questions.
• 1:01
  Speaker 1: Wow, so we're moving forward. That's pretty cool. But what
• 1:04
  Speaker 1: happens when we reach the edge of your understanding and
• 1:08
  Speaker 1: humanity's understanding?
• 1:09
  Speaker 2: Then we declare success and I retire as a physicist
• 1:12
  Speaker 2: or as a podcaster. Yes and yes, but.
• 1:17
  Speaker 1: Wait, if we reach that point, don't we need more physicists.
• 1:20
  Speaker 2: If we reach that point, then everybody's a physicist.
• 1:22
  Speaker 1: And then everyone gets to Lollipop and the podcast.
• 1:40
  Speaker 3: Hi.
• 1:40
  Speaker 1: I am jem, a cartoonists and the author of Oliver's
• 1:42
  Speaker 1: Great Big Universe.
• 1:44
  Speaker 2: Hi, I'm Daniel. I'm a physicist and a professor at
• 1:46
  Speaker 2: u C Irvine, and I'm a full time questions answerer.
• 1:50
  Speaker 1: Oh I thought you were a full time question asker.
• 1:52
  Speaker 1: Isn't that what physicists do? Do you feel like you
• 1:55
  Speaker 1: get paid to answer questions or to ask questions about
• 1:58
  Speaker 1: the universe? Which one pays more?
• 2:01
  Speaker 2: I feel like that's just two sides of the same coin.
• 2:04
  Speaker 2: But when I'm at work, I'm asking questions, and then
• 2:06
  Speaker 2: as soon as I get home, I'm answering them who
• 2:08
  Speaker 2: emptied the dishwasher? Who's turn is it to take out
• 2:11
  Speaker 2: the dog? I feel like I'm the answer repository.
• 2:13
  Speaker 1: Of the family Interesting and the dog walker. Apparently Well,
• 2:18
  Speaker 1: there's a quote in one of the PhD movies where
• 2:20
  Speaker 1: someone says, in academia, you're either known as the person
• 2:23
  Speaker 1: who came up with a question or the person who
• 2:25
  Speaker 1: answered the question. Everyone in between gets sort of forgotten about.
• 2:29
  Speaker 2: Like all those bricks don't matter. It is just the
• 2:30
  Speaker 2: person who puts the cap on the pyramid.
• 2:32
  Speaker 1: Yeah, the person who designs the pyramid and the person
• 2:35
  Speaker 1: who puts the last down gets all the fame.
• 2:38
  Speaker 2: Yeah, that might be true, but there's a lot of
• 2:40
  Speaker 2: things we learn along the way.
• 2:42
  Speaker 1: I guess you can still have fun doing the questions,
• 2:45
  Speaker 1: trying to answer the questions, and that's kind of what
• 2:47
  Speaker 1: science is all about, right, trying and failing.
• 2:50
  Speaker 2: Yeah, and it's also fundamentally exploring. You don't always know
• 2:52
  Speaker 2: where your research is going to end up. Might start
• 2:55
  Speaker 2: out asking one question and answering somebody else's question or
• 2:58
  Speaker 2: a completely different question. That's some of the joy of it.
• 3:01
  Speaker 1: The surprise, right right, Like what's going to be inside
• 3:03
  Speaker 1: this lollipop? Who knows? It could be a scorpion, it
• 3:06
  Speaker 1: could be chewing gum. Let's find out.
• 3:08
  Speaker 2: Let's give it to the dog and they'll find out.
• 3:11
  Speaker 1: Well, what if it has chocolate inside?
• 3:13
  Speaker 2: Oh no, mmm, oh no, I hope it's a chicken
• 3:15
  Speaker 2: flavored lollipop.
• 3:16
  Speaker 1: But anyways, welcome for our podcast Daniel and Jorge Explain
• 3:19
  Speaker 1: the Universe, a production of iHeartRadio.
• 3:21
  Speaker 2: In which we ask all sorts of questions about the
• 3:24
  Speaker 2: nature of the universe, how it works in the tiniest level,
• 3:26
  Speaker 2: how it comes together to make our incredible reality, and
• 3:29
  Speaker 2: how it exists on the grandest scale, expanding and accelerating
• 3:33
  Speaker 2: and zooming photons all through the universe. And we do
• 3:36
  Speaker 2: our best to try to answer some of the questions
• 3:38
  Speaker 2: that we have and that you have about how it
• 3:40
  Speaker 2: all works.
• 3:41
  Speaker 1: That's right, because it is a giant universe full of
• 3:44
  Speaker 1: mystery and unanswered questions, and so in this podcast we
• 3:47
  Speaker 1: try to think about those questions, figure out where they
• 3:50
  Speaker 1: came from, what those questions are, and sometimes how to
• 3:53
  Speaker 1: avoid them if we don't know the answer.
• 3:55
  Speaker 2: Boyd them. No, we embrace the questions we don't know
• 3:59
  Speaker 2: the answer to.
• 4:00
  Speaker 1: Actually, and you avoid questions sometimes like if you don't
• 4:03
  Speaker 1: know the answer, you pulled this kind of like politician
• 4:07
  Speaker 1: thing where you very cleverly circumvent the question.
• 4:11
  Speaker 2: I don't know what you're talking about.
• 4:13
  Speaker 1: Some there you go, if you're doing it right now.
• 4:16
  Speaker 2: But my daughter has been helping us a little bit
• 4:18
  Speaker 2: with our new TikTok account where I walk around campus
• 4:20
  Speaker 2: at UCI and ask people questions, and she's been commenting
• 4:24
  Speaker 2: that the answer of the question is almost always, well,
• 4:26
  Speaker 2: we don't know.
• 4:29
  Speaker 1: Unfortunately, that is the answer still for a lot of physics,
• 4:32
  Speaker 1: but also maybe kind of the fortunate thing. I guess
• 4:34
  Speaker 1: if you're a physicist because it means a job security.
• 4:38
  Speaker 2: Yeah, or if you're an aspiring physicist. There's still so
• 4:41
  Speaker 2: much left to figure out about the universe, and not
• 4:44
  Speaker 2: just heiny loose ends about how to do eleven dimensional
• 4:47
  Speaker 2: integrals over quantum brains, but really basic stuff about how
• 4:50
  Speaker 2: the universe works. So we encourage you all out there
• 4:54
  Speaker 2: to think about the universe, to try to understand it.
• 4:57
  Speaker 2: And when those ideas don't quite come together, when and
• 5:00
  Speaker 2: it doesn't weave itself together into a whole concept in
• 5:02
  Speaker 2: your mind, reach out to us. Ask us questions. We
• 5:05
  Speaker 2: will answer, We will help you understand. Write to us
• 5:08
  Speaker 2: two questions at Danielandhorge dot com.
• 5:11
  Speaker 1: Maybe what you need to do on TikTok is do
• 5:13
  Speaker 1: what of those dances that they do on TikTok And
• 5:15
  Speaker 1: then maybe that will distract people from the fact that
• 5:18
  Speaker 1: you don't know the answer.
• 5:19
  Speaker 2: It'll show them that I don't know the dance either.
• 5:22
  Speaker 2: I guess we'll be testing the theory that any publicity
• 5:25
  Speaker 2: is good publicity.
• 5:26
  Speaker 1: There you go, Or that maybe there's an intricate dance
• 5:29
  Speaker 1: of the universe in terms of math and physics and
• 5:33
  Speaker 1: the particles that make up reality.
• 5:36
  Speaker 2: I'm going to do two moves at the same time
• 5:38
  Speaker 2: to show you how an electron can be in superposition
• 5:41
  Speaker 2: of two quantum states.
• 5:42
  Speaker 1: That's right, And how does that run where it looks
• 5:44
  Speaker 1: like you're floating on the air work. That's what I
• 5:47
  Speaker 1: want to know.
• 5:48
  Speaker 2: That's not physics, that's dance engineering.
• 5:51
  Speaker 1: All right. But questions is sort of the name of
• 5:53
  Speaker 1: the game here. We talk about questions, and sometimes we
• 5:55
  Speaker 1: answer questions from listeners.
• 5:57
  Speaker 2: We absolutely do any question that comes in or inbox,
• 6:00
  Speaker 2: we will answer it. And some of those questions we
• 6:03
  Speaker 2: feature here on the podcast because we think lots of
• 6:05
  Speaker 2: people want to know the answer, or I just think
• 6:07
  Speaker 2: could be a great opportunity for Jorge to make fun
• 6:09
  Speaker 2: of physicists.
• 6:11
  Speaker 1: Yeah, I got to earn my keep here, but yeah,
• 6:13
  Speaker 1: do they own the podcast. We'll be tackling listener questions
• 6:21
  Speaker 1: number forty seven. We're getting close to fifty, but both
• 6:25
  Speaker 1: in Questions episodes and in Age Daniel.
• 6:29
  Speaker 2: You know, I'm forty eight, but once I passed forty five,
• 6:31
  Speaker 2: I just decided to round it up to fifty. And
• 6:33
  Speaker 2: then my wife recently turned forty five, and I said
• 6:36
  Speaker 2: to her, welcome to the rounded up to fifty club.
• 6:38
  Speaker 2: And she was not very happy with that invitation.
• 6:41
  Speaker 1: She's like, nope, I'd like to use more numbers of precision.
• 6:44
  Speaker 2: Please Exactly, She asked me, if when I get to
• 6:47
  Speaker 2: fifty one, if I was going to round it up
• 6:49
  Speaker 2: to one hundred, there you go. And I said, bring
• 6:51
  Speaker 2: it on.
• 6:51
  Speaker 1: Maybe you'll gain the wisdom by then of never commenting
• 6:54
  Speaker 1: on your wife's age.
• 6:58
  Speaker 2: See, there are always things to learn.
• 7:00
  Speaker 1: Yeah, there. It is a mysterious universe full of answers
• 7:03
  Speaker 1: to be had. But yeah, we like to answer listener
• 7:05
  Speaker 1: questions here on the podcast, and so today we have
• 7:08
  Speaker 1: three pretty intense questions. I feel like they're intense, not
• 7:12
  Speaker 1: just in the sense of how complicated the concepts are,
• 7:14
  Speaker 1: but also intense in the sense that it's all about
• 7:17
  Speaker 1: sort of atoms right and things at the smallest of levels.
• 7:21
  Speaker 2: Yeah. Absolutely, these folks are really digging in the details
• 7:24
  Speaker 2: of how the universe works and trying to make it
• 7:26
  Speaker 2: click together in their minds.
• 7:28
  Speaker 1: I love it, And so let's jump right in the
• 7:30
  Speaker 1: first question comes from knowl from Perth, Australia.
• 7:34
  Speaker 4: Hi Daniel and Juahai. This is not from Perth, Western Australia.
• 7:38
  Speaker 4: What question is how many atoms does it tyke before
• 7:41
  Speaker 4: you can measure its gravity? Thank you and Cape the
• 7:45
  Speaker 4: excellent content coming.
• 7:47
  Speaker 1: All right, awesome question here, pretty intense. It has something
• 7:51
  Speaker 1: to do with both the smallest things in the universe
• 7:54
  Speaker 1: and also maybe one of the most significant forces in
• 7:57
  Speaker 1: the universe.
• 7:58
  Speaker 2: Yeah, it's a great question because it leans in the
• 8:01
  Speaker 2: direction of understanding gravity for little particles, which is so important.
• 8:05
  Speaker 2: It's one of the biggest open questions in the universe
• 8:08
  Speaker 2: is how does gravity work for quantum particles? Can we
• 8:10
  Speaker 2: unify all the forces into a theory of quantum gravity?
• 8:14
  Speaker 2: And one of the reasons that it's difficult is that
• 8:16
  Speaker 2: it's even hard to see gravity happening on particles because
• 8:20
  Speaker 2: gravity is so weak, it's so much weaker than all
• 8:24
  Speaker 2: the other forces, and particles have tiny, tiny masses, so
• 8:28
  Speaker 2: it's almost impossible to see the gravitational effects of little particles.
• 8:32
  Speaker 1: Well, I guess it's not hard to see it. Like
• 8:34
  Speaker 1: if you hold up a rock, right, you know it's
• 8:37
  Speaker 1: made out of particles, and you like, go the rock,
• 8:39
  Speaker 1: the rock will fall down to the ground, so you
• 8:41
  Speaker 1: can see gravity acting on all the particles of that rock.
• 8:44
  Speaker 2: Yeah. Absolutely, the whole universe is made out of particles,
• 8:47
  Speaker 2: and we see gravity happening. But all those objects we
• 8:50
  Speaker 2: see gravity happening for these are classical objects where all
• 8:53
  Speaker 2: the quantum effects have averaged out right. The rock can
• 8:56
  Speaker 2: be described using purely classical physics ethicals MA even and
• 9:00
  Speaker 2: you don't even need relativity, and so we can describe
• 9:03
  Speaker 2: gravity there. I think Noel's question is, like how small
• 9:06
  Speaker 2: an object can you see gravity happening on? How many
• 9:09
  Speaker 2: atoms do you have to put together before you can
• 9:12
  Speaker 2: measure the gravity of an object? What's the tiniest thing.
• 9:15
  Speaker 1: I see you're talking about, like how to measure the
• 9:17
  Speaker 1: gravity or like how much gravity is being exerted on
• 9:21
  Speaker 1: a small clump of particles or atoms? Right, Because like
• 9:25
  Speaker 1: you can take a small clump of atoms and you
• 9:27
  Speaker 1: let it go, and it is going to fall to
• 9:28
  Speaker 1: the floor, isn't it. You're going to see it.
• 9:30
  Speaker 2: A small clump of atoms, if you let them go,
• 9:32
  Speaker 2: will feel gravity, we think, but we'll also feel a
• 9:34
  Speaker 2: bunch of other stuff. If there's any electromagnetic forces that
• 9:38
  Speaker 2: are residual, it'll feel that. That's why, for example, you
• 9:41
  Speaker 2: can use a magnet to overcome the gravity of the Earth,
• 9:45
  Speaker 2: or static electricity can hold something to your head defying gravity.
• 9:50
  Speaker 2: Gravity is so weak that any other force, if it's
• 9:52
  Speaker 2: an all in play, is going to overwhelm it. So
• 9:55
  Speaker 2: that's why you mostly see gravity happening on really really
• 9:59
  Speaker 2: big stuff where there's a lot of it in the
• 10:01
  Speaker 2: Earth and the Moon for.
• 10:02
  Speaker 1: Example, or a rock, yeah, or a lollipop or your dog.
• 10:06
  Speaker 2: The dogs and lollipops are lots and lots of particles, right,
• 10:10
  Speaker 2: You're not seeing gravity happen on individual particles there.
• 10:13
  Speaker 1: But I guess I'm thinking of like a gas. If
• 10:15
  Speaker 1: you fill up a room or even the gas in
• 10:18
  Speaker 1: our atmosphere, you can see the effects of gravity on
• 10:21
  Speaker 1: each one of those air particles, right, Like the air
• 10:24
  Speaker 1: is dens is near the surface than it is up
• 10:26
  Speaker 1: in the sky.
• 10:27
  Speaker 2: Mm hm. And if you want to think about like
• 10:28
  Speaker 2: where have we seen gravity in action, then thinking about
• 10:32
  Speaker 2: the atmosphere is a great way to do that, because
• 10:34
  Speaker 2: the reason we have an atmosphere is because of gravity.
• 10:37
  Speaker 2: Like the moon has no atmosphere has an exosphere, but
• 10:40
  Speaker 2: it has no atmosphere because it doesn't have enough gravity
• 10:43
  Speaker 2: to hold gas to it. If you turned off the
• 10:45
  Speaker 2: Earth's gravity, we would lose all of our particles of
• 10:48
  Speaker 2: atmosphere when we're actually already losing particles of atmosphere all
• 10:52
  Speaker 2: the time. They boil off the top of the atmosphere
• 10:55
  Speaker 2: if they have enough velocity, and that's something we've studied
• 10:58
  Speaker 2: in great detail. We know that like lighter atoms like
• 11:01
  Speaker 2: helium hygen boil off at faster rates and heavier atoms don't.
• 11:05
  Speaker 2: We can calculate the escape velocity for a particle to
• 11:08
  Speaker 2: leave the Earth's atmosphere. We do all these calculations and
• 11:11
  Speaker 2: we can even check them against things we've observed. So
• 11:14
  Speaker 2: that's an example of gravity acting on particles in a
• 11:17
  Speaker 2: way that we can calculate and that we can observe.
• 11:20
  Speaker 1: Right, so you can see the macro effects. But I
• 11:22
  Speaker 1: think maybe what you're talking about is like if we
• 11:25
  Speaker 1: want to measure the gravity on an atom. For example,
• 11:29
  Speaker 1: you might be able to see an atom and keep
• 11:30
  Speaker 1: track of it, but you can't maybe ascribe all of
• 11:34
  Speaker 1: its emotion or what it does to gravity, like it
• 11:36
  Speaker 1: might be affected by other forces which are stronger than gravity,
• 11:40
  Speaker 1: which might confuse your measurement of its gravity.
• 11:43
  Speaker 2: Yeah. I think there's a few things going on here.
• 11:44
  Speaker 2: One is what you just said, that it's hard to
• 11:46
  Speaker 2: get rid of everything else. So we can focus just
• 11:48
  Speaker 2: on the gravity, though people have done that, and we
• 11:51
  Speaker 2: can talk about experiments where people look at the gravitational
• 11:53
  Speaker 2: effects on just pure neutrons which have no electric charge.
• 11:57
  Speaker 2: But the real issue is that all of this is
• 11:59
  Speaker 2: probing still the gravity of the Earth, not the gravity
• 12:03
  Speaker 2: of that particle or that neutron. Right, we're pulling on
• 12:06
  Speaker 2: that object using the Earth's gravity. We're not like seeing
• 12:09
  Speaker 2: two neutrons attract each other gravitationally.
• 12:11
  Speaker 1: Oh I see. Now you're talking about measuring the gravity
• 12:14
  Speaker 1: between two small the objects like atoms. But was that
• 12:18
  Speaker 1: Nole's question?
• 12:19
  Speaker 2: Well, Nole says, how many atoms does it take before
• 12:21
  Speaker 2: you can measure its gravity? And so on one hand
• 12:25
  Speaker 2: you can say, well, the Earth is acting with gravity
• 12:27
  Speaker 2: on that object, and so by Newton's laws, therefore the
• 12:31
  Speaker 2: object is also acting on the Earth. There's a symmetry there,
• 12:34
  Speaker 2: But actually seeing the gravitational effect of a tiny little
• 12:38
  Speaker 2: clump of stuff, not the effect on it, but the
• 12:40
  Speaker 2: effect of it, I think would be really fascinating.
• 12:43
  Speaker 1: Oh, I see, you think that the Nole's question is like,
• 12:47
  Speaker 1: what's the smallest the bit of stuff that we can
• 12:49
  Speaker 1: measure how much it attracts other things?
• 12:52
  Speaker 2: Yes, exactly, because you have a neutron or a helium
• 12:55
  Speaker 2: atom in the atmosphere is being pulled on by the Earth.
• 12:57
  Speaker 2: We already know the Earth has gravity, No big deal.
• 13:00
  Speaker 2: How many atoms do you have to clump together before
• 13:02
  Speaker 2: you can feel something having its own gravity pulling on
• 13:05
  Speaker 2: other stuff?
• 13:06
  Speaker 1: All right? Because I think what he's maybe trying to
• 13:08
  Speaker 1: get at is that it's really hard to do it
• 13:10
  Speaker 1: with one atom, and so maybe even possible. But maybe
• 13:14
  Speaker 1: he's thinking, what if I take two atoms, or three
• 13:16
  Speaker 1: atoms or four atoms, Can I measure the gravity of
• 13:19
  Speaker 1: a small clump of atoms and then just divided by
• 13:21
  Speaker 1: the number of atoms, would that let me measure the
• 13:25
  Speaker 1: gravity of one atom?
• 13:26
  Speaker 2: Yeah? Exactly, And I think his question is how small
• 13:29
  Speaker 2: can that go? Technologically, like, in principle, any tiny amount
• 13:33
  Speaker 2: of matter has gravity to it, but in practice it's
• 13:37
  Speaker 2: very difficult to measure this gravity, And so how many
• 13:40
  Speaker 2: atoms do you have to put together before we can
• 13:42
  Speaker 2: register the effects of gravity, before we can actually see
• 13:45
  Speaker 2: the needle go above zero.
• 13:48
  Speaker 1: And I guess maybe this is more of a technical question,
• 13:50
  Speaker 1: like more of an engineering question, right, like what's the
• 13:53
  Speaker 1: best instrument that we've made to measure gravity? Or maybe
• 13:56
  Speaker 1: he's talking about a theoretical limit.
• 13:58
  Speaker 2: The theoretical limit is one two atoms near each other.
• 14:02
  Speaker 2: In theory, they have gravity, and we don't know what
• 14:04
  Speaker 2: the quantum mechanical description of their gravity is. But if
• 14:07
  Speaker 2: we assume they act classically, though of course they don't,
• 14:10
  Speaker 2: then we know how to calculate their gravity and how
• 14:12
  Speaker 2: they bend space and all sorts of stuff treat them
• 14:15
  Speaker 2: like tiny planets. We know how to do that theoretically,
• 14:17
  Speaker 2: and we think theoretically that there is gravity. There really
• 14:20
  Speaker 2: just a practical question of measuring it. It's essentially impossible
• 14:24
  Speaker 2: to measure the gravity of an individual atom because it's
• 14:26
  Speaker 2: so tiny and gravity is so weak. So I think
• 14:29
  Speaker 2: Noel's question is an engineering one, which is like, how
• 14:32
  Speaker 2: good have we gotten at measuring the gravity of tiny
• 14:35
  Speaker 2: bits of stuff?
• 14:36
  Speaker 1: Well, let's start maybe with something large and then try
• 14:39
  Speaker 1: to go down in size. Okay, so what do we
• 14:42
  Speaker 1: start with a bowling ball. Can we measure the gravity
• 14:45
  Speaker 1: inherent in a bowling ball? Have we done this important
• 14:49
  Speaker 1: measurement in the history of science?
• 14:52
  Speaker 2: Well, I know, bowling ball's weigh about what ten to
• 14:55
  Speaker 2: fifteen pounds?
• 14:56
  Speaker 1: How do you know?
• 14:56
  Speaker 2: They have numbers on the sides to tell you how
• 14:58
  Speaker 2: they are.
• 15:01
  Speaker 1: What if but not if they would drill the holes
• 15:05
  Speaker 1: in them, then it changes.
• 15:06
  Speaker 2: Oh no, oh, my gosh, they're totally inaccurate.
• 15:09
  Speaker 1: And now we're getting to a theoretical limit here.
• 15:11
  Speaker 2: But that's about six or eight kilos and that's the
• 15:14
  Speaker 2: kind of thing that we can measure. It's gravity, absolutely.
• 15:17
  Speaker 1: How would you measure that?
• 15:18
  Speaker 2: We have these torsion experiments where essentially you put like
• 15:21
  Speaker 2: two bowling balls and the ends of a long rod
• 15:24
  Speaker 2: and then you suspend it from a wire so it's
• 15:26
  Speaker 2: balanced really really well, and a tiny push sideways and
• 15:29
  Speaker 2: the bowling ball will make it spin. Then you bring
• 15:32
  Speaker 2: other bowling balls near it, like next to this torsion pendulum,
• 15:36
  Speaker 2: and you see if it spins a little bit. It
• 15:38
  Speaker 2: spins a little bit. That tells you there's a tiny
• 15:41
  Speaker 2: little force there between the bowling balls. So this is
• 15:44
  Speaker 2: like the Cavendish experiments. It's the most precise way we
• 15:47
  Speaker 2: know to measure the gravitational constant without knowing, for example,
• 15:50
  Speaker 2: already the mass of the Earth.
• 15:52
  Speaker 1: Okay, so if you do this for a couple of
• 15:54
  Speaker 1: bowling balls, then you can measure it's gravity. You can
• 15:57
  Speaker 1: see like the force and one bowling ball exerts on
• 16:00
  Speaker 1: the other bowling ball through gravity, and you're pretty sure
• 16:04
  Speaker 1: it's not like, you know, the electromagnetic attraction or vendor
• 16:08
  Speaker 1: wible forces between the two bowling balls exactly.
• 16:10
  Speaker 2: And this is really just pure experimental science, like isolating this,
• 16:14
  Speaker 2: keeping it stable, making sure you're not getting shaken by
• 16:16
  Speaker 2: trucks rolling down the highway or affected by astatic electricity,
• 16:20
  Speaker 2: or even by like the force of light on these
• 16:23
  Speaker 2: bowling balls. Remember, photons have momentum, so you have to
• 16:26
  Speaker 2: do this experiment like in the dark. And so yeah,
• 16:29
  Speaker 2: it's a real experimental accomplishment to make this work.
• 16:33
  Speaker 1: Also, you have to make sure your boiling lane is
• 16:36
  Speaker 1: like oiled evenly.
• 16:37
  Speaker 2: Right, that's bowling engineering. That's out of my field of expertise. Yeah,
• 16:43
  Speaker 2: I don't know.
• 16:45
  Speaker 1: Sorry, Yeah, that's not a physics experiment. So we can
• 16:48
  Speaker 1: measure the gravity of a bowling ball. We have done it,
• 16:51
  Speaker 1: you're saying, and like, how well do we know this
• 16:54
  Speaker 1: down to what precision? Like are we barely getting it?
• 16:57
  Speaker 1: Or are we pretty comfortable we know the gravity of
• 16:59
  Speaker 1: our of a buling ball.
• 17:00
  Speaker 2: We're pretty comfortable that we can measure the gravity of
• 17:03
  Speaker 2: six kilo objects and do it pretty precisely. These are
• 17:06
  Speaker 2: still the same kind of experiments we use to measure
• 17:09
  Speaker 2: big g although we have a whole podcast episode about
• 17:12
  Speaker 2: how we measure the gravitational constant, and these days we
• 17:15
  Speaker 2: can measure it using really really tiny twists of that
• 17:18
  Speaker 2: torsion pendulum. You do it by putting a mirror on
• 17:20
  Speaker 2: the wire and then you shine a laser on the
• 17:23
  Speaker 2: mirror so that even if the wire turns the tiniest
• 17:25
  Speaker 2: little bit, you can see the laser spot move. It's
• 17:28
  Speaker 2: really clever.
• 17:29
  Speaker 1: Okay, So we've tried it with bowling balls, and you're saying,
• 17:32
  Speaker 1: we've gone smaller like billiard balls, down to maybe even
• 17:36
  Speaker 1: smaller objects. What's the smallest object we've done.
• 17:38
  Speaker 2: The smallest experiment I could find used three quarters of
• 17:42
  Speaker 2: a kilogram lead weights, so basically billiard balls.
• 17:46
  Speaker 1: Billiard balls, So that's not that small. I mean, that's
• 17:48
  Speaker 1: only like a tenth of a bulling ball. It's a
• 17:51
  Speaker 1: billiard ball. That's the smallest we've done an experiment on where.
• 17:54
  Speaker 2: The objects are symmetric. We have the same mass, and
• 17:57
  Speaker 2: that seems pretty small. But remember that's still a lot
• 17:59
  Speaker 2: of atoms.
• 18:00
  Speaker 1: That's what was gonna say. It seems like it's huge.
• 18:02
  Speaker 1: I thought maybe we had measured thinks smaller.
• 18:05
  Speaker 2: Well, it's a pretty huge number of atoms. You know,
• 18:07
  Speaker 2: if you use Avagado's constant, it's like still two times
• 18:09
  Speaker 2: ten to the twenty four atoms. It's a lot of atoms.
• 18:12
  Speaker 2: There was another experiment where the sizes weren't symmetric. You
• 18:16
  Speaker 2: had like one bigger and one smaller, and that one
• 18:18
  Speaker 2: the smaller mass is down to fifty nine milligrams, So
• 18:22
  Speaker 2: that's a whole lot smaller, but it's still a pretty
• 18:25
  Speaker 2: big number of atoms.
• 18:26
  Speaker 1: Well, and in this case, you're measuring the gravity of
• 18:29
  Speaker 1: the fifty nine milligram mass, or you're measuring the gravity
• 18:32
  Speaker 1: on the fifty nine milligram mass.
• 18:35
  Speaker 2: So here the small mass is the one on the
• 18:37
  Speaker 2: torsion pendulum, so it's the one being.
• 18:39
  Speaker 1: Moved, so you're not measuring really it's gravity you're measuring
• 18:43
  Speaker 1: the effect of gravity on it.
• 18:44
  Speaker 2: Yeah, so that's a good point. And so the smallest
• 18:46
  Speaker 2: experiment where the things really are the same size, where
• 18:49
  Speaker 2: they're having the gravitational effect on each other, is three
• 18:52
  Speaker 2: quarters of a kilogram or a billiard.
• 18:54
  Speaker 1: Ball, which, as you said, it's like ten to the
• 18:58
  Speaker 1: twenty four atoms.
• 19:00
  Speaker 2: Yeah. I don't even know what the prefix is for
• 19:01
  Speaker 2: that number. It's a really really big number.
• 19:04
  Speaker 1: A bazillion, a gajillion, a ton exactly.
• 19:10
  Speaker 2: So engineers have a lot of work to do to
• 19:12
  Speaker 2: get us down to measuring the gravity of one atom.
• 19:15
  Speaker 1: Well, to tell me what happens if you try to
• 19:16
  Speaker 1: go smaller, like what if you put marbles there? What
• 19:19
  Speaker 1: do you get? You just get pure noise or you know,
• 19:23
  Speaker 1: it starts to go wonky. What happens if you go smaller?
• 19:26
  Speaker 2: So the limitations here really are experimental. It's sort of
• 19:29
  Speaker 2: like ligo. You're trying to measure a really small effect
• 19:32
  Speaker 2: and there are other effects that are trying to drown
• 19:34
  Speaker 2: it out. So it's like trying to listen to something
• 19:36
  Speaker 2: really really quiet. You need a super quiet room. And
• 19:40
  Speaker 2: so in this case, just the shaking of the building,
• 19:43
  Speaker 2: like the seismic noise of the Earth will shake your
• 19:46
  Speaker 2: apparatus in a way that's more dramatic than the gravity
• 19:49
  Speaker 2: of two marbles or the gravity of two tiny pebbles,
• 19:52
  Speaker 2: for example. So you need to isolate your room, you
• 19:55
  Speaker 2: need to remove from all other effects.
• 19:57
  Speaker 1: Well, maybe the problem is they keep doing these experiment
• 20:00
  Speaker 1: in like a bowling.
• 20:01
  Speaker 2: Alley next to a freeway.
• 20:03
  Speaker 1: Yeah, I think that's the problem at a poolhule. So
• 20:10
  Speaker 1: you're saying, like, if you try to measure anything smaller,
• 20:12
  Speaker 1: it just we don't have the instruments needed to get
• 20:15
  Speaker 1: past just the general noise of the universe to try
• 20:18
  Speaker 1: to measure something that weak.
• 20:20
  Speaker 2: Exactly. They keep inventing new instruments to suppress the noise,
• 20:24
  Speaker 2: to be insensitive to the noise. There's been like a
• 20:26
  Speaker 2: whole thirty or forty year system of these experiments, each
• 20:29
  Speaker 2: one more precise and more accurate than the last because
• 20:32
  Speaker 2: they figured out some clever way to prevent a source
• 20:35
  Speaker 2: of noise from infecting their experiment, which gives them new sensitivity.
• 20:39
  Speaker 2: And so they keep working on it, and they're going
• 20:41
  Speaker 2: to keep pushing it down, and I can see them
• 20:43
  Speaker 2: making progress steadily, but they're nowhere close to measuring it
• 20:46
  Speaker 2: for like one.
• 20:47
  Speaker 1: Atom, right right, right now, we're like ten to the
• 20:49
  Speaker 1: twenty four orders of magnitude away from order being able
• 20:53
  Speaker 1: to measure that.
• 20:54
  Speaker 2: Yeah, well that's twenty four orders of magnitude. Ten to
• 20:56
  Speaker 2: the twenty four orders of magnitude would be ten with
• 20:59
  Speaker 2: ten twenty four zero.
• 21:00
  Speaker 1: Oh sorry, yeah, you know what I mean. But I
• 21:03
  Speaker 1: think we've answered Nol's question, which is that he has
• 21:07
  Speaker 1: how many atoms does it take to before you can
• 21:09
  Speaker 1: measure it to gravity? And it seems like the right now,
• 21:11
  Speaker 1: the best state of the art is ten to the
• 21:13
  Speaker 1: twenty four atoms.
• 21:15
  Speaker 2: Yeah, though in theory the answer is one, and maybe
• 21:17
  Speaker 2: one day we'll get there.
• 21:19
  Speaker 1: Oh, I see theoretically. Yes, all right, well, let's get
• 21:22
  Speaker 1: to these other questions about the nature of matter and
• 21:25
  Speaker 1: reality and quantum mechanics. But first let's take a quick
• 21:29
  Speaker 1: break or we're answering listener questions here today we just
• 21:45
  Speaker 1: answer one about bowling, right and gravity?
• 21:49
  Speaker 2: Yeah, pebbles and lasers and pool balls and bowling.
• 21:52
  Speaker 1: Yeah, and I think we struck out or got to
• 21:56
  Speaker 1: go to a ball. I don't know. I don't know
• 21:58
  Speaker 1: sports enough to know what the rightlog here is. Maybe
• 22:01
  Speaker 1: we've got to split on it.
• 22:02
  Speaker 2: I think in bowling they call that a touchdown.
• 22:04
  Speaker 1: Yeah, there you go. All right, Well let's get to
• 22:07
  Speaker 1: our next question, and this one comes from anik who
• 22:10
  Speaker 1: has a question about the energy levels of an electron.
• 22:14
  Speaker 3: Hi, my name is aniic Eshner, and I have a
• 22:16
  Speaker 3: question about time and energy levels for an electron. Does
• 22:21
  Speaker 3: it take time or is it instantaneous when an electron
• 22:24
  Speaker 3: jumps between energy levels? Thank you, bye bye?
• 22:29
  Speaker 1: All right, interesting question. First of all, I guess maybe
• 22:33
  Speaker 1: we should talk about the energy levels of an electron,
• 22:35
  Speaker 1: Like what is that? What is this question he's asking
• 22:38
  Speaker 1: in the first place?
• 22:38
  Speaker 2: YEA, So an electron flying around the universe can have
• 22:41
  Speaker 2: any energy. But if you put an electron in a
• 22:44
  Speaker 2: box or like trap it around a proton in a
• 22:47
  Speaker 2: hydrogen atom, then there's only a few solutions to the
• 22:50
  Speaker 2: quantum mechanical equations we call those different energy levels. The
• 22:55
  Speaker 2: electron can't just have like any arbitrary energy as it's
• 22:58
  Speaker 2: hanging around the proton. There's like a ladder of energy
• 23:01
  Speaker 2: levels it can exist on.
• 23:03
  Speaker 1: Right. They usually do this visually by kind of going
• 23:05
  Speaker 1: back to the old model of the atom, where which
• 23:08
  Speaker 1: had electrons kind of going around the nucleus of an
• 23:11
  Speaker 1: atom in an orbit like a circular orbit.
• 23:14
  Speaker 2: They do, they have to do that.
• 23:16
  Speaker 1: They don't, But I think that maybe helps people understand it.
• 23:19
  Speaker 1: Like maybe if the atom worked the way people thought
• 23:23
  Speaker 1: it did, which was just like a kind of like
• 23:25
  Speaker 1: a planet going around the Sun. If the electron was
• 23:27
  Speaker 1: going around the nucleus of an atom, then an energy
• 23:30
  Speaker 1: level was kind of like the size of that orbit,
• 23:33
  Speaker 1: kind of right, because maybe a bigger orbit has more
• 23:35
  Speaker 1: energy to it.
• 23:36
  Speaker 2: It's definitely true that bigger orbits have more energy, and
• 23:39
  Speaker 2: like planets going around the Sun, have to move faster
• 23:42
  Speaker 2: to have a larger radius. The difference is that orbits
• 23:45
  Speaker 2: can have any radius. There's literally an infinite number any
• 23:49
  Speaker 2: velocity you pick for your planet, there's a radius where
• 23:51
  Speaker 2: it can sit happily. For electrons, that's not true. There's
• 23:54
  Speaker 2: only a few energy levels where all the mathematics works
• 23:58
  Speaker 2: out right.
• 23:58
  Speaker 1: They're discrete or quantize, which is kind of where the
• 24:01
  Speaker 1: idea of a quantum mechanics customer or at least a night.
• 24:06
  Speaker 2: Yeah, that's exactly right. And something I think is really
• 24:08
  Speaker 2: cool that not enough people appreciate is that the quantized
• 24:12
  Speaker 2: energy levels comes from putting the electron in confinement. An
• 24:16
  Speaker 2: electron out there in free space can have any energy.
• 24:18
  Speaker 2: It's putting it in a box, like trapping it around
• 24:20
  Speaker 2: the proton or sticking it in a square well or
• 24:23
  Speaker 2: something that generates the quantized solutions to the Shirtinger equation.
• 24:28
  Speaker 1: Right, It's maybe kind of analogous to like a guitar string.
• 24:31
  Speaker 1: Right when you start to get into quantum wave functions,
• 24:34
  Speaker 1: like when you can strain a string from two ends
• 24:38
  Speaker 1: of a guitar, then there are sort of like main
• 24:41
  Speaker 1: ways that it can vibrate.
• 24:42
  Speaker 2: Right, mm hm, yeah, that's exactly right. A string on
• 24:45
  Speaker 2: its own can vibrate in any way, but once you
• 24:47
  Speaker 2: put it in your guitar it has a fixed length.
• 24:49
  Speaker 2: You can post boundary conditions like it can't vibrate at
• 24:52
  Speaker 2: the points where it's tied down, and that limits the
• 24:55
  Speaker 2: solutions to the wave equation, and quantum particles are governed
• 24:59
  Speaker 2: by a different wave equation, the Schrodinger equation that tells
• 25:02
  Speaker 2: us where its quantum wave function can exist and what
• 25:04
  Speaker 2: solutions are allowed. And because you've put it essentially in
• 25:08
  Speaker 2: a box, you've created boundary conditions those limit the energy
• 25:12
  Speaker 2: levels that it can be.
• 25:13
  Speaker 1: At right, So, like an electron trapped kind of orbiting
• 25:17
  Speaker 1: around a proton like in the hydrogen atom, can only
• 25:20
  Speaker 1: do it in certain ways or configurations, and each one
• 25:24
  Speaker 1: of those has a different energy level.
• 25:26
  Speaker 2: Yeah, exactly. And something that's fascinating is that you just
• 25:29
  Speaker 2: can't exist between those energy levels. Like if the Earth
• 25:32
  Speaker 2: wanted to move into Mars' orbit, it could, you'd have
• 25:35
  Speaker 2: to put a rocket on it and speed it up
• 25:37
  Speaker 2: and do all sorts of stuff, and along the way
• 25:38
  Speaker 2: it would be sort of halfway between Earth's orbit and
• 25:41
  Speaker 2: Mars's orbit. But electrons can't do that. They can't be
• 25:44
  Speaker 2: in between. And yet they can be in one energy
• 25:46
  Speaker 2: level at one moment and be in another energy level
• 25:49
  Speaker 2: later on.
• 25:50
  Speaker 1: Well, I think that's what ANX question is asking. Is
• 25:54
  Speaker 1: like you're saying, like an electron can only fit around
• 25:58
  Speaker 1: a nucleus or a proton in certain modes or configurations,
• 26:02
  Speaker 1: but surely there might be some sort of transcision period
• 26:06
  Speaker 1: before it clicks into one of these. Like if I
• 26:08
  Speaker 1: just throw an electron at a proton, you know, you're
• 26:13
  Speaker 1: telling me there are some stable configurations, but as I
• 26:16
  Speaker 1: throw it, doesn't it sort of exist in between these configurations.
• 26:19
  Speaker 2: I think, ooh, that adds some complications. I think the
• 26:21
  Speaker 2: simpler way to think about it is taken at in
• 26:24
  Speaker 2: with an electron. A photon comes in with extra energy,
• 26:27
  Speaker 2: the electron absorbs that photon, and now it's in a
• 26:30
  Speaker 2: higher energy level. Does it take time to go from
• 26:33
  Speaker 2: the lower energy level to the higher energy level.
• 26:35
  Speaker 1: That's the question, and it has, right.
• 26:37
  Speaker 2: Yeah, that's the question, and it has exactly.
• 26:39
  Speaker 1: But it's sort of the same question as what I'm asking,
• 26:41
  Speaker 1: which is, like, you know, if I throw in an
• 26:44
  Speaker 1: electron out of proton or it switches levels, doesn't it
• 26:48
  Speaker 1: technically might take some time to go between the configurations.
• 26:52
  Speaker 2: So the electron doesn't have to go from one configuration
• 26:55
  Speaker 2: to another. Because remember, an electron doesn't have like a
• 26:58
  Speaker 2: location at every moment the way the Earth does. The
• 27:01
  Speaker 2: Earth is a classical object, so it has a path, right,
• 27:03
  Speaker 2: It has a location at every moment, and we think
• 27:06
  Speaker 2: that that path is smooth, it's continuous, there's no instantaneous
• 27:10
  Speaker 2: jumps in it. But electrons are not like that. They
• 27:12
  Speaker 2: don't have a defined location at every moment. They don't
• 27:16
  Speaker 2: have to go from one place to another to be
• 27:19
  Speaker 2: at one place and later be at another place. You
• 27:22
  Speaker 2: don't have to be able to track its location at
• 27:24
  Speaker 2: every intermediate spot for it to be somewhere and later
• 27:28
  Speaker 2: be somewhere else.
• 27:29
  Speaker 1: Right, because it's quantum mechanical, right.
• 27:30
  Speaker 2: It's fuzzy, Yeah, exactly.
• 27:32
  Speaker 1: But just because it's fuzzy doesn't mean it can't, like
• 27:34
  Speaker 1: be a weirdly shaped fuzzy in between the ones that
• 27:38
  Speaker 1: click around the proton, can it.
• 27:40
  Speaker 2: It can't be weirdly shaped fuzzy. Those solutions do not
• 27:43
  Speaker 2: satisfy the mathematics, right, so they just cannot be in between.
• 27:47
  Speaker 1: They don't satisfy the mathematics for them to be stable orbits.
• 27:51
  Speaker 1: But can it exist in an unstable orbit or a
• 27:54
  Speaker 1: configuration for a moment.
• 27:57
  Speaker 2: No, you really just can't do that as long as
• 27:59
  Speaker 2: it stays bound. Right, as long as it's still within
• 28:01
  Speaker 2: the atom, it's moving from one energy level the atom
• 28:04
  Speaker 2: to another, then there's no intermediate solutions. The way to
• 28:08
  Speaker 2: think about it is not that the electron is in
• 28:10
  Speaker 2: this state and then the electron is in that state.
• 28:12
  Speaker 2: What happens is that the electron has a probability to
• 28:15
  Speaker 2: be in the first state, call it one hundred percent,
• 28:17
  Speaker 2: and no probability to be in the higher state, so
• 28:19
  Speaker 2: zero percent, and then that probability can change. That probably
• 28:23
  Speaker 2: changes smoothly, so that like at some moment, the electron
• 28:26
  Speaker 2: has a fifty percent chance of being in the lower
• 28:28
  Speaker 2: state and fifty percent chance of being in the higher state,
• 28:31
  Speaker 2: and then later on it'll have one hundred percent chance
• 28:33
  Speaker 2: of being in the higher state and a zero percent
• 28:35
  Speaker 2: chance of being in the lower state. So it's probability changes,
• 28:39
  Speaker 2: and that actually changes smoothly. But which state is actually
• 28:42
  Speaker 2: in You can only ever measure it in one state
• 28:44
  Speaker 2: or another.
• 28:45
  Speaker 1: Right, because those are the stable solutions. But maybe I guess,
• 28:49
  Speaker 1: maybe I wonder if what Onik is asking is, you know,
• 28:52
  Speaker 1: as does probabilities transition and does take time? Maybe?
• 28:56
  Speaker 2: Yeah, so the probability transition does take time, absolutely, though
• 29:00
  Speaker 2: you can only ever measure it in one state or another.
• 29:03
  Speaker 1: So it does maybe take time for an electron to
• 29:06
  Speaker 1: switch energy levels.
• 29:07
  Speaker 2: Yes, absolutely, it takes time for that quantum state to transition.
• 29:11
  Speaker 2: Nothing happens instantaneously in a relativistic world. But you'll never
• 29:15
  Speaker 2: see the electron in between, right, what's happening is that
• 29:18
  Speaker 2: probability to be in a lower state or the higher state.
• 29:20
  Speaker 2: Those things are changing. It's sort of like if you
• 29:22
  Speaker 2: have a coin at coin you can flip it and
• 29:24
  Speaker 2: get heads or tails. And what if I have like
• 29:26
  Speaker 2: a little dial that changes the probability of heads or tails.
• 29:29
  Speaker 2: So I start out with only going to flip heads,
• 29:31
  Speaker 2: and then I can turn that knob, so now it's
• 29:33
  Speaker 2: fifty to fifty, and then later on it'll only retails
• 29:36
  Speaker 2: when you flip it. You'll always get heads or tails.
• 29:39
  Speaker 2: Just the probability of heads or tails will change over time.
• 29:42
  Speaker 1: But I guess maybe it depends on what you call
• 29:44
  Speaker 1: like an energy an electron being in a certain energy state, right,
• 29:48
  Speaker 1: Like what you call it in an energy state is
• 29:50
  Speaker 1: the probability of it being in an energy state. And
• 29:52
  Speaker 1: you're saying that the transition between probabilities is smooth and
• 29:55
  Speaker 1: takes time, then it does sort of typically take time
• 29:58
  Speaker 1: for an electron tow which between energy states.
• 30:01
  Speaker 2: Yes, absolutely, there's like a moment where you can describe
• 30:04
  Speaker 2: it as fifty percent in the lower state and fifty
• 30:06
  Speaker 2: percent in the higher state. That doesn't mean that it's
• 30:09
  Speaker 2: like physical location is in between the two, or that
• 30:12
  Speaker 2: you could ever measure it in any intermediate state, right,
• 30:15
  Speaker 2: But there is a moment when it has a probability
• 30:18
  Speaker 2: of being in the lower state or the higher state.
• 30:20
  Speaker 1: Well, at the particle quantum level, my understanding is that
• 30:24
  Speaker 1: things aren't really there anyways. There's just the probability of
• 30:27
  Speaker 1: things to be there.
• 30:28
  Speaker 2: Yeah exactly.
• 30:29
  Speaker 1: So the changing of its fuzziness from one shape to
• 30:32
  Speaker 1: the other, you're saying does take time.
• 30:34
  Speaker 2: Yeah, exactly, And so if you're thinking about it in
• 30:36
  Speaker 2: that quantum mechanical way, it all makes sense. I wonder
• 30:38
  Speaker 2: about Aix's question because I wonder if Onick is wondering
• 30:41
  Speaker 2: if the electron like teleports from one place to another instantaneously,
• 30:46
  Speaker 2: And so I just want to make sure that Onik
• 30:47
  Speaker 2: and averybody listening understands that the electron doesn't have like
• 30:50
  Speaker 2: an existing location has an energy level, which is a
• 30:53
  Speaker 2: probability distribution, and that transitions to a new probability distribution.
• 30:57
  Speaker 2: It's not like the electron is here and then it
• 31:00
  Speaker 2: appears instantaneously in another orbit.
• 31:02
  Speaker 1: Right. Well, I think maybe the way that most physicists
• 31:06
  Speaker 1: like to draw these orbits is is clouds, right, like
• 31:09
  Speaker 1: probability clouds, And you're saying, like a cloud can't just
• 31:13
  Speaker 1: convert from one shape to another. Cloud there has to
• 31:16
  Speaker 1: be this transition period where it's like maybe a little
• 31:18
  Speaker 1: bit of both, in which case the blob looks a
• 31:20
  Speaker 1: different shape.
• 31:21
  Speaker 2: Yeah, exactly, one blob is decreasing while another blob is increasing.
• 31:25
  Speaker 2: There's no intermediate blob.
• 31:27
  Speaker 1: Right, Well, if you add up to two, don't doesn't
• 31:29
  Speaker 1: that happen?
• 31:30
  Speaker 2: Yeah exactly. The intermediate blob is just different mixtures of.
• 31:32
  Speaker 1: The two, right, which would have its own shape.
• 31:35
  Speaker 2: Yeah, which has its own shape.
• 31:36
  Speaker 1: Okay, So yeah, so maybe like, don't think of it
• 31:38
  Speaker 1: as the electron jumping from one orbit to another. Think
• 31:41
  Speaker 1: of it just as like one electron changing from being
• 31:44
  Speaker 1: a blobby shape that looks like this to a different
• 31:46
  Speaker 1: blobby shape in the quantum world that looks like that,
• 31:49
  Speaker 1: and that does take time. You're saying, like how much time?
• 31:53
  Speaker 2: It depends on the energy. And it's actually a fascinating
• 31:55
  Speaker 2: a little wrinkle in quantum mechanics because the Schrodinger equation
• 31:58
  Speaker 2: is not relativistic. It doesn't like respect special relativity and
• 32:02
  Speaker 2: have the speed of light built into it. You have
• 32:04
  Speaker 2: to add that in when you get to like relativistic
• 32:06
  Speaker 2: quantum mechanics or quantum field theory. But there are still
• 32:09
  Speaker 2: some guardrails there that prevent things from happening instantaneously. Like
• 32:13
  Speaker 2: it's a wave function and waves evolve smoothly with time,
• 32:17
  Speaker 2: and because it's a wave, it's wave nature is what
• 32:19
  Speaker 2: generates the Heisenberg uncertainty relationships. So in this case, for example,
• 32:24
  Speaker 2: there's a relationship between energy and time. If you want
• 32:27
  Speaker 2: something to happen really really fast, like almost instantaneously, then
• 32:31
  Speaker 2: the energy of that process is very uncertain. If you
• 32:35
  Speaker 2: want something to be really specific about energy, then the
• 32:38
  Speaker 2: time is uncertain. Essentially, it can take a very long time.
• 32:41
  Speaker 2: So you can have something that happened really fast, but
• 32:44
  Speaker 2: then you can't be certain about the energy of it.
• 32:46
  Speaker 2: Or you can have something happen with really specific energy,
• 32:49
  Speaker 2: but then you can't really be sure it's going to
• 32:50
  Speaker 2: be fast, So you can't have something happen really fast
• 32:54
  Speaker 2: and to a very specific energy at the same time.
• 32:57
  Speaker 1: Yeah, it seems like it's maybe one of those things
• 32:59
  Speaker 1: we talked about in a pret podcasts about what the
• 33:01
  Speaker 1: uncertainty and quantum mechanics actually means. M Yeah, okay, so
• 33:07
  Speaker 1: well then what's the answer. How fast is it changing
• 33:10
  Speaker 1: or can it change? You're saying it they can change
• 33:12
  Speaker 1: instantaneously if you put infinite amount of energy into it.
• 33:14
  Speaker 2: If you have an infinite uncertainty in your energy, then yes,
• 33:18
  Speaker 2: you're going to approach an instantaneous transition. But then you
• 33:22
  Speaker 2: have no idea what transition you're going to. You're going
• 33:24
  Speaker 2: from energy level one two, energy level unknown.
• 33:28
  Speaker 1: Well, maybe give us a second, since you're a particle physicist.
• 33:30
  Speaker 1: When you smash these particles together and they're interacting at
• 33:33
  Speaker 1: the quantum level, like how fast are these reactions happening
• 33:37
  Speaker 1: or these transformations or these you know, breaking up of particles,
• 33:41
  Speaker 1: it's like nanoseconds, right or less?
• 33:44
  Speaker 2: Oh yeah, much faster than that. Yeah, we're talking about
• 33:46
  Speaker 2: events that like ten to the minus twenty three seconds,
• 33:49
  Speaker 2: so super short periods of time.
• 33:51
  Speaker 1: Hmmm. And in this case, you can measure those things
• 33:55
  Speaker 1: or is it kind of theoretical? Can you see? Can
• 33:58
  Speaker 1: you measure can you clock some thing happening that fast
• 34:01
  Speaker 1: or you just think it's happening that fast.
• 34:02
  Speaker 2: We can make those measurements, but it's sort of indirect.
• 34:05
  Speaker 2: Like the time that a particle survives depends on its
• 34:09
  Speaker 2: energy and its mass and the uncertainty in its mass.
• 34:12
  Speaker 2: So by measuring like the uncertainty in the mass of
• 34:15
  Speaker 2: a bunch of particles, we can measure how long effectively
• 34:18
  Speaker 2: those particles are living. So, for example, we measure the
• 34:21
  Speaker 2: top quark mass really really precisely, and we know the
• 34:24
  Speaker 2: variation from top quark to top quark, and that tells us
• 34:27
  Speaker 2: how long the top quarks live. But it's one or
• 34:29
  Speaker 2: two steps indirect from like actually looking at a clock
• 34:33
  Speaker 2: and seeing it tick by.
• 34:34
  Speaker 1: But you do seem to have some numbers for it.
• 34:36
  Speaker 1: So in the case of the electron, what kind of
• 34:38
  Speaker 1: number would you put on it? Like in our everyday lies,
• 34:40
  Speaker 1: you know, a ray of light hits my skin, how
• 34:44
  Speaker 1: long are the my electrons and my skin changing energy states?
• 34:48
  Speaker 2: So the energy levels of the hygien atom I happen
• 34:50
  Speaker 2: to know because my son is doing chemistry are like
• 34:53
  Speaker 2: thirteen point six ev so call it like ten electron volts.
• 34:57
  Speaker 2: And the uncertain relationship is dominated by Plank's con which
• 35:00
  Speaker 2: is like ten to the minus fifteen ev seconds. And
• 35:04
  Speaker 2: so put that together and it tells you that we're
• 35:06
  Speaker 2: talking about transitions of the order of like ten to
• 35:08
  Speaker 2: the minus fifteen seconds.
• 35:10
  Speaker 1: Whoa which seems slower than the ones when you smash.
• 35:14
  Speaker 2: Particles, yeap, but still pretty fast.
• 35:16
  Speaker 1: All right, well, I think that answers an next question.
• 35:18
  Speaker 1: It does take some time for the electronic jump between
• 35:21
  Speaker 1: energy levels, maybe to the order of ten to the
• 35:24
  Speaker 1: minus fifteen seconds. All right, let's get to our last question,
• 35:27
  Speaker 1: but first let's take a quick break. All right. We're
• 35:42
  Speaker 1: answering listener questions, and our last question here today has
• 35:46
  Speaker 1: to do with polarization, not of our country, but of
• 35:50
  Speaker 1: light exactly.
• 35:53
  Speaker 5: Hi, Daniel and George, I'm way from Brisbane. If you
• 35:58
  Speaker 5: would answer my question on polarization at quantum level, that
• 36:04
  Speaker 5: would be really good. You have a great podcast. What
• 36:10
  Speaker 5: the polarition is at photon level? Does a photon vibrate
• 36:16
  Speaker 5: in all planes and polarization allows only in a specific plane?
• 36:22
  Speaker 5: Or a photon vibrants only in one plane and polarization
• 36:26
  Speaker 5: allows photons which align with that polarization plane. Thank you?
• 36:32
  Speaker 1: All right. I think Vivek's question in general is basically like,
• 36:37
  Speaker 1: what is polarization, what's going on at the photon level?
• 36:40
  Speaker 1: What does it mean for a photon or a LightWave
• 36:43
  Speaker 1: to have polarization, because polarization is sort of all around
• 36:47
  Speaker 1: this right, as sunglasses are polarized, some of them. Definitely,
• 36:50
  Speaker 1: the screen on your phones are polarized, and so it's
• 36:54
  Speaker 1: something that actually affects us every day.
• 36:56
  Speaker 2: Yeah, and polarization is really fascinating and tricky to think about.
• 36:59
  Speaker 2: And I final a lot of listeners are confused on
• 37:02
  Speaker 2: some basic concept of the mental picture they have of
• 37:05
  Speaker 2: what a photon looks like is usually wrong. So I
• 37:08
  Speaker 2: thought it'd be fun to talk first about what is
• 37:10
  Speaker 2: polarization for classical electrodynamics, and then we can talk about
• 37:13
  Speaker 2: what it looks like for a photon.
• 37:14
  Speaker 1: Okay, Now this is a property that light has, right, Like,
• 37:17
  Speaker 1: light can be polarized.
• 37:19
  Speaker 2: Yeah, exactly, light can be polarized.
• 37:21
  Speaker 1: So what is it?
• 37:21
  Speaker 2: So if you think of light as just like a
• 37:23
  Speaker 2: wiggle in the electromagnetic field, and let's just ignore quantum
• 37:26
  Speaker 2: effects for now. Let's pretend that we're maxwell and we're
• 37:29
  Speaker 2: just thinking about light, is like oscillations and electric and
• 37:32
  Speaker 2: magnetic fields, right.
• 37:34
  Speaker 1: Meaning like basically all around us is an electromagnetic field,
• 37:37
  Speaker 1: Like we're all surrounded by this field exactly, and a
• 37:40
  Speaker 1: light ray is just kind of like a wiggle in
• 37:42
  Speaker 1: that field that zooms across the room exactly.
• 37:45
  Speaker 2: And there's an electric field and there's a magnetic field,
• 37:47
  Speaker 2: and they're sort of on top of each other. A
• 37:48
  Speaker 2: field is something that exists in all of space, right,
• 37:52
  Speaker 2: So there's an electric field and there's magnetic fields all
• 37:55
  Speaker 2: through space, and a light wave.
• 37:57
  Speaker 1: They're different.
• 37:58
  Speaker 2: They are different. There are two components of something larger
• 38:00
  Speaker 2: we call the electromagnetic field, but they're different, like the
• 38:03
  Speaker 2: way two sides of a coin are different but connected.
• 38:06
  Speaker 2: And a light wave is an oscillation in these two
• 38:09
  Speaker 2: fields that are linked. This is like Maxwell's greatest insight
• 38:12
  Speaker 2: to show that electric fields and magnetic fields are really
• 38:15
  Speaker 2: tightly coupled. One can generate the other.
• 38:18
  Speaker 1: So like a light ray is a wiggle in one
• 38:21
  Speaker 1: of these fields. But it's actually the two fields you're
• 38:23
  Speaker 1: saying are sort of like connected to each other. So
• 38:25
  Speaker 1: you can't just have a wiggle in one field. It
• 38:29
  Speaker 1: has to come with a wiggle in the other.
• 38:30
  Speaker 2: Field exactly, because changing electric fields will give you magnetic fields,
• 38:34
  Speaker 2: and changing magnetic fields will give electric fields. So it's
• 38:36
  Speaker 2: a coupled oscillation. It's like sloshing back and forth between them.
• 38:40
  Speaker 1: Okay, so we're surrounded by fields. A light ray is
• 38:42
  Speaker 1: a wiggle in that field, So what's its polarization.
• 38:45
  Speaker 2: So the crucial thing to understand is that these fields
• 38:48
  Speaker 2: are not just numbers. They're a vector, which means that
• 38:51
  Speaker 2: at every point in space, these fields don't just have
• 38:54
  Speaker 2: a value, they have a direction, like a tiny little arrow.
• 38:57
  Speaker 2: That's what's really interesting about the electromagnetic field. It's not
• 39:00
  Speaker 2: just like a number through space. It's a little arrow.
• 39:03
  Speaker 1: Meaning it's not just like an intensity at any given point,
• 39:07
  Speaker 1: or like a brightness to it. It's also like a
• 39:09
  Speaker 1: it has a directional component to it.
• 39:11
  Speaker 2: Exactly, it has a directional component to it.
• 39:13
  Speaker 1: Like you can have a wiggle that's pointing up or
• 39:15
  Speaker 1: a wiggle that's pointing down or to the sides.
• 39:17
  Speaker 2: And light is an oscillation of those little arrows. And
• 39:21
  Speaker 2: people often think that, oh, a light wave is like
• 39:23
  Speaker 2: literally moving side to side as it moves through the universe,
• 39:27
  Speaker 2: it's wiggling sideways, but it's not. A light wave is
• 39:30
  Speaker 2: moving along a straight line. What's wiggling sideways is the
• 39:34
  Speaker 2: vector of the electric field and the vector of the
• 39:37
  Speaker 2: magnetic field. So along a straight line, you have like
• 39:40
  Speaker 2: an arrow that's growing and shrinking and growing and shrinking.
• 39:43
  Speaker 2: Point a what direction those arrows are pointed perpendicular to
• 39:46
  Speaker 2: the motion of this wave, because light is a transverse wave.
• 39:50
  Speaker 3: Mm.
• 39:51
  Speaker 1: So you're saying a photon is like you can imagine
• 39:53
  Speaker 1: it like a little bead going along a string from
• 39:56
  Speaker 1: here to Like if I shoot a laser, I do
• 39:58
  Speaker 1: we can trace. It's like a little beat that's going
• 40:01
  Speaker 1: on a string from me to you. But as it's
• 40:03
  Speaker 1: going down the string, it has kind of like arrows
• 40:05
  Speaker 1: shooting out of it exactly to the sides and up
• 40:07
  Speaker 1: and down.
• 40:08
  Speaker 2: But it never moves sideways, right, It's always along that bead.
• 40:12
  Speaker 2: What's moving sideways is the strength of these little arrows.
• 40:15
  Speaker 2: The electric field and the magnetic field, and polarization is
• 40:19
  Speaker 2: telling you where those fields are pointing. So the electric
• 40:22
  Speaker 2: field is pointing perpendicular to the motion of photon, but
• 40:25
  Speaker 2: there's still lots of ways that it could point. Right,
• 40:27
  Speaker 2: there's a whole circle of directions it could point. Polarization
• 40:30
  Speaker 2: is telling you which direction is the electric field pointing
• 40:34
  Speaker 2: as the photon moves along that line.
• 40:36
  Speaker 1: So as it moves it maybe maybe you can have
• 40:37
  Speaker 1: an electric field that's pointing up and it wiggles by
• 40:41
  Speaker 1: shrinking and growing in the updirection.
• 40:43
  Speaker 2: Yeah, exactly, or sideways now.
• 40:45
  Speaker 1: Does a photon have to have a direction. Can you
• 40:48
  Speaker 1: have a photon that's like what what does it mean
• 40:51
  Speaker 1: to have a photon that's not polarized?
• 40:53
  Speaker 2: So an individual photon has to have a direction. You
• 40:56
  Speaker 2: can have a beam of light that's unpolarized. That means
• 40:59
  Speaker 2: that it's a big mixture of photons of lots of
• 41:01
  Speaker 2: different polarizations.
• 41:03
  Speaker 1: So you can't have an unpolarized photon. Each photon by definition,
• 41:08
  Speaker 1: is polarized exactly.
• 41:09
  Speaker 2: And now we're mixing sort of the classical and the
• 41:11
  Speaker 2: quantum version. The classical version is that these are just
• 41:14
  Speaker 2: waves in the field. There are no photons. Brighter light
• 41:18
  Speaker 2: means just like bigger wiggles in the field. The quantum
• 41:21
  Speaker 2: version says no, no, no, it comes in discrete packets. Each
• 41:24
  Speaker 2: one is its own photon. Brighter light is more photons,
• 41:28
  Speaker 2: And so in the quantum version this still happens, but
• 41:30
  Speaker 2: now you have quantum spin instead of like the direction
• 41:33
  Speaker 2: of the electric field. But still you can't have an
• 41:36
  Speaker 2: individual photon that's unpolarized. Every photon has a direction either
• 41:40
  Speaker 2: to its quantum spin or to its classical electric field,
• 41:43
  Speaker 2: and the polarization tells you what direction that's in right.
• 41:46
  Speaker 1: Like each photon you're kind of saying, has it like
• 41:48
  Speaker 1: a kind of like an up and down and a
• 41:50
  Speaker 1: left and right, and so its polarization is kind of like, uh,
• 41:54
  Speaker 1: in what direction is its up and down pointing?
• 41:56
  Speaker 2: Yeah, exactly, Like firefighters sliding down a pole, right, they
• 41:59
  Speaker 2: can slide down in lots of different angles. They're moving
• 42:02
  Speaker 2: down the pole always, but they can slide down facing
• 42:05
  Speaker 2: left or facing right or facing any angles. It's like
• 42:07
  Speaker 2: the polarization of the firefighter. So the same way, photons
• 42:10
  Speaker 2: moving in the same direction can have a different polarization
• 42:13
  Speaker 2: and still be moving in the same direction.
• 42:16
  Speaker 1: So then that's basically what polarization is. It's like the
• 42:19
  Speaker 1: direction in which its electric field is pointing it as
• 42:22
  Speaker 1: it wiggles.
• 42:23
  Speaker 2: Exactly. For classical electro dynamics, it's the direction of the
• 42:26
  Speaker 2: electric field. For quantum photon, it's the direction of its
• 42:30
  Speaker 2: quantum spin.
• 42:32
  Speaker 1: Interesting, now, when it comes to sort of like our
• 42:34
  Speaker 1: everyday experience, you're saying that polarized light is one in
• 42:38
  Speaker 1: which all the photons are basically pointing in the same direction,
• 42:41
  Speaker 1: and unpolarized light is where all the photons are like
• 42:45
  Speaker 1: they're all pointing in random directions exactly.
• 42:47
  Speaker 2: It's not really unpolarized. It's a sum of different polarizations.
• 42:51
  Speaker 2: It's like you have a bunch of people with different
• 42:52
  Speaker 2: political opinions. It's not like you have no politics. You
• 42:56
  Speaker 2: just have lots of different politics.
• 42:57
  Speaker 1: It's like multi polarized. Saying unpolarizes, you're really saying multipolarize, exactly.
• 43:04
  Speaker 2: And you can have polarization filters, for example, that only
• 43:06
  Speaker 2: allow a certain polarization through where you can only allows
• 43:09
  Speaker 2: light through. That's like going up and down, or only
• 43:11
  Speaker 2: allows light through that's going side to side with this polarization.
• 43:15
  Speaker 1: Now, the light from my cell phone, like the screen,
• 43:19
  Speaker 1: I know that light is like coming from the screen
• 43:21
  Speaker 1: is polarized. Now is that polarized because there's a filter
• 43:25
  Speaker 1: in the glass of my cell phone or because the
• 43:28
  Speaker 1: you know, whatever diodes or something that's generating the light
• 43:31
  Speaker 1: somehow only produce a certain kind of photon.
• 43:34
  Speaker 2: Yeah, I have no idea.
• 43:38
  Speaker 1: You're not even going to try to circumvent the question.
• 43:41
  Speaker 1: Let's see, let's see your crafted work. If I asked
• 43:44
  Speaker 1: you why my cellphone has polarized light, Daniel, what would
• 43:48
  Speaker 1: you say? And you can't cut this out later I
• 43:50
  Speaker 1: don't know.
• 43:51
  Speaker 2: I don't know. I don't know the answers. I don't know.
• 43:54
  Speaker 1: Maybe you wikipedia this sleep.
• 43:56
  Speaker 2: It's possible that your phone screen filters it out, or
• 43:58
  Speaker 2: it's possible that it's generated in such a way to
• 44:00
  Speaker 2: only be polarized. I think they do that because it's
• 44:04
  Speaker 2: easier to look at, but I'm not sure.
• 44:06
  Speaker 1: Interesting. All right, well, maybe we'll leave this as homework
• 44:10
  Speaker 1: for listeners to try to look it up. All right,
• 44:12
  Speaker 1: But the answer the basic question, that's kind of what
• 44:14
  Speaker 1: polarization is. You're saying, it's a direction of the wiggles
• 44:16
  Speaker 1: of a photon in the electric field and magnetic field.
• 44:20
  Speaker 2: Yeah, exactly. And remember that the photon itself is not
• 44:22
  Speaker 2: wiggling in space, never deviates from the line of its motion.
• 44:27
  Speaker 2: What's wiggling there are the electric and magnetic fields for
• 44:30
  Speaker 2: the classical picture and the quantum picture. The photon is
• 44:33
  Speaker 2: still moving just along that line, and now the polarization
• 44:36
  Speaker 2: is describing the direction of its quantum spin.
• 44:39
  Speaker 1: Right, although it's sort of like these are quantum objects, right,
• 44:42
  Speaker 1: so you can't really say that it's staying in the middle.
• 44:45
  Speaker 1: You're just mathematically that's where you assume that it's staying
• 44:49
  Speaker 1: on you exactly.
• 44:50
  Speaker 2: They have no path and no definitive location. But if
• 44:52
  Speaker 2: you're solving the equation for where it's likely to be,
• 44:55
  Speaker 2: then that's along a line, right.
• 44:56
  Speaker 1: So it is sort of maybe wiggling and in nactuality
• 45:00
  Speaker 1: you just mathematically it doesn't deviate on average.
• 45:03
  Speaker 2: Yeah, there's definitely a fuzziness to a photon's location, but
• 45:06
  Speaker 2: not in an oscillatory way. Yeah.
• 45:07
  Speaker 1: All right, Well those have been three awesome questions. Do
• 45:10
  Speaker 1: you think everyone deserves a lollipop? I feel like I
• 45:13
  Speaker 1: deserve one.
• 45:14
  Speaker 2: Yeah. I think a bowling ball flavored lollipop would really
• 45:17
  Speaker 2: finish this off. Oh my gosh.
• 45:20
  Speaker 1: Yeah, yeah, yeah, but you have to be careful though.
• 45:23
  Speaker 1: You have to make sure it is a lollipop. You
• 45:25
  Speaker 1: don't want to be licking any random bowling balls you
• 45:28
  Speaker 1: don't know where those have been, or a billion balls,
• 45:32
  Speaker 1: maybe a billion bars would be even worse.
• 45:35
  Speaker 2: Just don't lick stuff. That's the health advice from your physics.
• 45:37
  Speaker 1: Podcast unless you're absolutely sure. Yeah, I guess you could
• 45:43
  Speaker 1: test it on your dog maybe, or on a physicist.
• 45:45
  Speaker 2: And if you do lick stuff, don't sue us over it, please, Yeah,
• 45:51
  Speaker 2: unless you liked it that's a whole different kind of podcast,
• 45:56
  Speaker 2: or here.
• 45:57
  Speaker 1: Well as usual. Another reminder that we can still ask
• 46:00
  Speaker 1: a lot of questions about the universe. There's still a
• 46:02
  Speaker 1: lot of mysteries to think about, to explore, and sometimes
• 46:06
  Speaker 1: you can even stump physicists to the point where they say,
• 46:08
  Speaker 1: I don't know.
• 46:10
  Speaker 2: We say that all the time.
• 46:11
  Speaker 1: How often do you say it, Daniel, I don't know.
• 46:16
  Speaker 1: There you go, there you go. That's that's what That's
• 46:18
  Speaker 1: the exact answer I was looking for.
• 46:21
  Speaker 2: And if there's things that make you go I don't know,
• 46:23
  Speaker 2: then write to me and I'll talk to you about it.
• 46:25
  Speaker 2: I'll tell you everything I do and don't know about
• 46:28
  Speaker 2: the subject. The email address says questions at Danielandjorge dot
• 46:32
  Speaker 2: com and we love to hear from you.
• 46:33
  Speaker 1: We hope you enjoyed that. Thanks for joining us, See
• 46:37
  Speaker 1: you next time.
• 46:42
  Speaker 2: For more science and curiosity, come find us on social
• 46:45
  Speaker 2: media where we answer questions and post videos. We're on Twitter, Discord, Instant,
• 46:50
  Speaker 2: and now TikTok. Thanks for listening, and remember that Daniel
• 46:53
  Speaker 2: and Jorge Explain the Universe is a production of iHeartRadio.
• 46:57
  Speaker 2: For more podcasts from my Heart Radio, visit the iHeartRadio, app,
• 47:01
  Speaker 2: Apple podcasts, or wherever you listen to your favorite shows.