Latest / Daniel and Kelly’s Extraordinary Universe / Why does measuring a quantum object change it?

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Why does measuring a quantum object change it? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Once upon a time, physicists seemed to have the world
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Speaker 1: figured out almost There were one or two loose threads
0:15
Speaker 1: to be tidied up, but a solid idea about how
0:18
Speaker 1: the universe worked had emerged, and it made sense. At
0:21
Speaker 1: a particle level, physicist thought the universe worked basically the
0:25
Speaker 1: same way it did at the human level and at
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Speaker 1: the planetary level little balls moving around, orbiting each other,
0:32
Speaker 1: occasionally even careening off of each other. How wonderful and
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Speaker 1: symmetric and symbol it seemed that the same concepts worked
0:39
Speaker 1: from the very small to the very large. What a deep,
0:43
Speaker 1: satisfying truth about the universe we had revealed that explained
0:47
Speaker 1: almost everything other than a few pesky experimental results, And
0:52
Speaker 1: then those remaining loose threads unraveled the whole picture. To
0:56
Speaker 1: explain those weird experiments, we needed to break that symmetry
1:00
Speaker 1: and come up with a new vision for how the
1:02
Speaker 1: microscopic world works. At the smallest level, the world wasn't
1:06
Speaker 1: made of little spinning balls, but of something new and
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Speaker 1: quite alien, quantum objects that followed a weird set of
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Speaker 1: rules that gave headaches to even the geniuses of the
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Speaker 1: twentieth century. So then, what is real. Is the world
1:19
Speaker 1: made of stuff that moves through space like basketballs and planets?
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Speaker 1: Or does it follow some crazy new, weird quantum rules.
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Speaker 1: And if the quantum rules are real, does that mean
1:28
Speaker 1: that the universe doesn't make any sense deep down? Hi?
1:47
Speaker 1: I'm Daniel. I'm a particle physicist and I'm desperate to
1:50
Speaker 1: know what is real about the universe. And with me
1:54
Speaker 1: today is a special guest astrophysicist Adam Becker, and an
1:58
Speaker 1: expert on reality, given that he's written a wonderful book
2:01
Speaker 1: about quantum mechanics titled What Is Real? Adam, Welcome to
2:05
Speaker 1: the program. Say hello, Hi, Yeah, thanks for having me Daniel.
2:08
Speaker 1: This is a lot of fun. Well, I'm especially pleased
2:10
Speaker 1: to have you on today because when listeners right in
2:13
Speaker 1: and ask me what they can read to get a
2:15
Speaker 1: better understanding of the thorny problems of quantum mechanics, I
2:18
Speaker 1: always recommend your book. So thanks for joining us and
2:21
Speaker 1: for helping us unravel a little bit about what we
2:24
Speaker 1: know and what we don't know about the universe. Well
2:27
Speaker 1: that's great. I'm really glad to hear that you're plugging
2:29
Speaker 1: my book And welcome everybody to the podcast. Daniel and
2:34
Speaker 1: Jorhigg explain in the universe where we try to do
2:37
Speaker 1: just that, embrace our knowledge and admit our ignorance. We
2:40
Speaker 1: do a deep dive into what things really mean and
2:42
Speaker 1: admit when words and science are being used to describe
2:45
Speaker 1: our lack of knowledge rather than our actual understanding. We're
2:48
Speaker 1: here to explain all of it to you, and on
2:50
Speaker 1: today's program, we're gonna attempt to do something very hard,
2:54
Speaker 1: to tackle one of the trickiest topics in modern physics,
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Speaker 1: the meaning of quantum mechanics. But our goal is to
3:01
Speaker 1: find the solution today, but instead to help guide you
3:04
Speaker 1: through the current situation, the status of our knowledge and ignorance,
3:08
Speaker 1: to show you where the tricky bits are, why they
3:10
Speaker 1: have been so persistently tricky, and what the various ideas
3:14
Speaker 1: are for making progress. I mean, we know that quantum
3:17
Speaker 1: mechanics works right, the math is correct, it can predict
3:19
Speaker 1: the results of experiments with incredible precision. It seems like
3:22
Speaker 1: our universe is quantum mechanical. But we want to know
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Speaker 1: what that means about the universe. We want to know
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Speaker 1: what is real to me. That's what physics is is
3:32
Speaker 1: explaining the unknown in terms of the known. Is grappling
3:35
Speaker 1: with it and getting our intuition around it. So my
3:38
Speaker 1: first question to you, Adam, is do you think that's possible?
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Speaker 1: Do we even have the tools, the mental tools to
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Speaker 1: explain and understand something this alien, to understand what is real?
3:48
Speaker 1: I mean, hopefully, because that's the short answer. The longer
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Speaker 1: answer is, you know, so far we seem to be
3:55
Speaker 1: doing a pretty okay job. I am certainly open to
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Speaker 1: the possibility that the human mind is just not capable
4:02
Speaker 1: of comprehending some basic features of reality. On the other hand,
4:06
Speaker 1: you know, throughout the history of science, we've got a
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Speaker 1: pretty good track record of you know, banging our heads
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Speaker 1: against a problem and eventually coming up with a pretty
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Speaker 1: good theory of what's going on in a pretty good mathematical,
4:17
Speaker 1: you know, description to go along with that theory. Quantum mechanics,
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Speaker 1: of course, is deeply strange, but there's no rule against
4:26
Speaker 1: reality being strange. Right. In fact, it be kind of
4:29
Speaker 1: weird if the world we're not weird, be disappointing, yeah, exactly. Yeah,
4:33
Speaker 1: And also, come on, have you been here? Have you
4:35
Speaker 1: seen this place? Of course it's weird, but you're toutings
4:37
Speaker 1: are the history of our accomplishments, and those are wonderful,
4:40
Speaker 1: but a lot of those are limited to sort of
4:42
Speaker 1: the the narrow regime in which our intuition works, right,
4:46
Speaker 1: because we grew up experiencing at things, These are familiar
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Speaker 1: questions we have. Why does the thing roll down the hill?
4:52
Speaker 1: What are these stars moving around us? Does that necessarily
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Speaker 1: mean it's possible to like extrapolate to other weird realms
4:59
Speaker 1: where just have not grown up with any sort of
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Speaker 1: natural experience. Yeah, I mean not necessarily. It's possible that
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Speaker 1: we'll hit some sort of limit. I'm just not convinced
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Speaker 1: that quantum mechanics represents that limit. I mean, first of all,
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Speaker 1: we have this phenomenally accurate and precise theory in quantum
5:15
Speaker 1: mechanics and quantum physics more generally, you know, arguably the
5:18
Speaker 1: most accurate scientific theory ever in terms of, you know,
5:22
Speaker 1: how well it matches experiment. And it's not as if
5:27
Speaker 1: we've looked at the theory and thrown up our hands
5:29
Speaker 1: and said, you know, this is impossible to understand. We have,
5:32
Speaker 1: you know, mathematical tools, but there's no way that the
5:34
Speaker 1: human mind can comprehend the reality behind the math. If anything,
5:38
Speaker 1: it's the opposite. We have too many ideas about how
5:42
Speaker 1: to understand the reality behind the math. So that doesn't
5:44
Speaker 1: sound like a failure of human intuition to me, at
5:49
Speaker 1: least not yet. You know. Yeah, I'm totally open to
5:52
Speaker 1: the idea that we'll get there at some point. All right, Well,
5:54
Speaker 1: you sound like a supporter of quantum mechanics. In fact,
5:56
Speaker 1: it sounds like you're a shill for Big Quantum. You know.
6:00
Speaker 1: I don't think anyone has ever accused me of being
6:02
Speaker 1: a shill for a big quantum before. But I can't
6:05
Speaker 1: say that you're wrong. I'm just not exactly a paid shill.
6:09
Speaker 1: There's no money in it. Oh you're not getting your checks?
6:11
Speaker 1: Oh man? Yeah, well I not from big Quantum, just
6:13
Speaker 1: from the publisher. Well, we can't tagle all of qualum
6:18
Speaker 1: mechanics in a single episode, so today I want to
6:20
Speaker 1: focus on one issue in particular, which is I think
6:23
Speaker 1: at the heart of it all and sometimes known as
6:26
Speaker 1: the measurement problem. So on today's program, we're asking the
6:29
Speaker 1: question what makes the wave function collapse? What is measurement
6:39
Speaker 1: in quantum mechanics? And Adam, before we dig into it,
6:43
Speaker 1: we do something fun on the program, which is that
6:45
Speaker 1: I ask our listeners to answer this question just to
6:47
Speaker 1: get a sense for like what out there are people thinking,
6:50
Speaker 1: How much of a grass to people have on this question.
6:52
Speaker 1: It helps orient us to know where to aim our answer.
6:55
Speaker 1: So I have for us some clips from listeners, and
6:59
Speaker 1: if you they're listening, would like to participate for future
7:02
Speaker 1: episodes to answer really hard physics questions with no preparation.
7:06
Speaker 1: Please write to me two questions at Daniel and Jorge
7:09
Speaker 1: dot com. It's a lot more fun than it's outs.
7:11
Speaker 1: Here's what our listeners had to say. Okay, I have
7:16
Speaker 1: I've been learning about wave functions and quantum physics and
7:21
Speaker 1: I think I know that's a really important part of
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Speaker 1: measuring something, and I have heard about it collapsing, but
7:28
Speaker 1: I'm not sure what makes the collapse. I'm going to
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Speaker 1: guess that what makes a wave function collapse is when
7:34
Speaker 1: um something's measured. I would say, once the energy in
7:38
Speaker 1: the wave is reduced to a certain point, the wave
7:42
Speaker 1: can no longer support itself and it collapses. I'm just
7:47
Speaker 1: going to guess here, probably something that intervenes from outside
7:57
Speaker 1: so on outside interaction. Alright, So those the answers from
8:05
Speaker 1: our awesome listeners Adam, what do you think about those speculations.
8:09
Speaker 1: I mean, they mostly sound like the kinds of things
8:12
Speaker 1: that you would see in a quantum mechanics textbook actually,
8:16
Speaker 1: which is to say kind of fake. Right. There's a
8:19
Speaker 1: lot of talking there about like, well, I'm not sure
8:22
Speaker 1: something about measurement, but I don't really know what that means,
8:25
Speaker 1: and like that's really the heart of the problem, right,
8:28
Speaker 1: Like nobody really knows what we mean by measurement or
8:31
Speaker 1: by observation. So we like have a word for it,
8:34
Speaker 1: we have a phrase for but we don't really know
8:36
Speaker 1: exactly what that means is happening deep down. Yeah, that's
8:39
Speaker 1: exactly right, all right, So I think maybe we should
8:42
Speaker 1: start just by orienting ourselves, just by getting sort of
8:45
Speaker 1: like using the same vocabulary and making sure everybody out
8:48
Speaker 1: there knows what we're talking about when we say the
8:51
Speaker 1: wave function, Can you give us a short definition of
8:54
Speaker 1: what the wave function is and why it's so important
8:56
Speaker 1: to this question. I mean, there's a sense in which
8:58
Speaker 1: the question of what the wave function is kind of
9:00
Speaker 1: what's at the heart of all this too. But yeah,
9:02
Speaker 1: I can take a stab of that's so in sort
9:05
Speaker 1: of classical physics, the physics of Isaac Newton, the physics
9:09
Speaker 1: of everyday life, the physics of you know, billiard balls
9:12
Speaker 1: and car crashes. The way that we describe where things are.
9:18
Speaker 1: We usually use three numbers to describe where something is,
9:21
Speaker 1: or at least where the center of mass of something is.
9:23
Speaker 1: You know, we say, okay, well, here's where it is
9:25
Speaker 1: in the X, y and z. Here's how high off
9:27
Speaker 1: the ground it is. Here's how far in front of
9:29
Speaker 1: me it is, and here's how far it is off
9:31
Speaker 1: to one side. And that's all you really need to
9:34
Speaker 1: describe where something is, because we live in a three
9:36
Speaker 1: dimensional world exactly right. But in quantum mechanics, if you
9:41
Speaker 1: want to do the same thing, if you want to
9:43
Speaker 1: take all the information we have about where something is,
9:46
Speaker 1: like if you want to talk about where an electron is,
9:49
Speaker 1: you need more than three numbers. You actually need on
9:52
Speaker 1: infinity of numbers spread out across all of space. And
9:57
Speaker 1: that's the wave function. So the numbers are higher in
10:00
Speaker 1: some spots and lower in others. And usually what we
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Speaker 1: say the wave function represents is that it's to do
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Speaker 1: with the probability of finding the electron in a particular
10:12
Speaker 1: spot when we look, which makes it sound like the
10:16
Speaker 1: wave function isn't really a thing in nature, and it's
10:20
Speaker 1: just a lot more about our information. Yeah, so hold
10:23
Speaker 1: on it. Let me ask you about that, because you're
10:25
Speaker 1: making an analogy to a classical particle where we're talking
10:28
Speaker 1: about like where it actually is, and you're saying that
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Speaker 1: you need more information to talk about where an electron is.
10:34
Speaker 1: But now you're describing the wave function in terms not
10:37
Speaker 1: of where the object is or what it is, but
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Speaker 1: about our measurements of it already, sort of like we've
10:42
Speaker 1: already sort of snuck into the electron. That's exactly right.
10:45
Speaker 1: I mean, there's there are I wasn't kidding when I
10:48
Speaker 1: said that, you know, the question of what the wave
10:50
Speaker 1: function is it's sort of part of the controversy here
10:53
Speaker 1: and part of what's at stake. We'll see if we
10:55
Speaker 1: get past this one question and the whole thing exactly. Yeah.
10:58
Speaker 1: I'm not convinced succeed, but yeah, I mean the reason
11:01
Speaker 1: I say, oh, this is sort of the quantum analog
11:07
Speaker 1: of you know, the three numbers describing where something is
11:10
Speaker 1: in Newton's physics is that, you know, it sort of
11:13
Speaker 1: plays the same role in the same sorts of physical
11:17
Speaker 1: laws in quantum physics. So the question of whether the
11:21
Speaker 1: wave function is a thing out in the world or
11:24
Speaker 1: if it's just something about our information about stuff out
11:27
Speaker 1: in the world is you know, a live question and
11:32
Speaker 1: a subject of active debate. But it's not just as
11:35
Speaker 1: simple as saying, oh, it's just our information about what's
11:39
Speaker 1: out there. It's just that in the most simple way
11:41
Speaker 1: imaginable because wave functions, I mean, like the name sort
11:46
Speaker 1: of implies the wave functions. Wave they behave in ways
11:50
Speaker 1: that we actually tend to associate with physical objects. They
11:54
Speaker 1: undulate smoothly, the numbers change smoothly from one place to another,
11:59
Speaker 1: they change over time, and they can even perform some
12:02
Speaker 1: of the same tricks that waves perform. You can send
12:05
Speaker 1: them through a narrow slit and they'll defract outward on
12:09
Speaker 1: the other side. They can interfere with themselves and cause
12:13
Speaker 1: you know, patterns of light and darkness on a photographic plate,
12:16
Speaker 1: that sort of thing. So we call it a wave
12:18
Speaker 1: function because mathematically it's described by similar equations to describe
12:21
Speaker 1: other kind of classical waves were familiar with, that's right, yeah,
12:24
Speaker 1: And it also performs some of the same tricks as
12:27
Speaker 1: classical waves that were familiar with physically, so you know,
12:30
Speaker 1: we don't tend to think of our information about a
12:34
Speaker 1: thing as doing that. And it doesn't mean that it can't.
12:38
Speaker 1: It just means that if we want an account of
12:41
Speaker 1: wave functions in terms of our information about the world,
12:43
Speaker 1: as opposed to saying, you know, the wave functions actually
12:46
Speaker 1: a wave that's out there, we need to do some
12:47
Speaker 1: extra work. So you're saying the wave function tells us
12:51
Speaker 1: how to predict the outcomes of our experiments, like if
12:53
Speaker 1: I'm going to find the electron over here, or if
12:55
Speaker 1: I'm gonna find it over there, or if I'm gonna
12:57
Speaker 1: find it's been up or going to find it's been down.
12:59
Speaker 1: It tells me what I'm likely to observe, but we're
13:01
Speaker 1: not sure whether it's like actually real and distinct separate
13:05
Speaker 1: from our ability to measure it and interact with it.
13:08
Speaker 1: We don't know sort of philosophically, whether we can take
13:10
Speaker 1: that step. Yeah, yeah, I mean, there are theorems that
13:13
Speaker 1: suggests that there's something like the way function out in
13:15
Speaker 1: the world, but it's not. You know, this is an
13:18
Speaker 1: open question and has been since the beginning of quantum
13:22
Speaker 1: physics almost addrey years ago. And I think that's sort
13:24
Speaker 1: of one of the most fascinating points. I mean, you
13:26
Speaker 1: talk about classical physics, there's no distinction there between the
13:30
Speaker 1: thing exists and we measure it to exist there. It's
13:34
Speaker 1: just like those two things are just part of the
13:35
Speaker 1: same idea. You see the ball there because it is there, right,
13:39
Speaker 1: and it would be there if you weren't here to
13:41
Speaker 1: look at it as all this kind of stuff. So
13:43
Speaker 1: I love these discoveries and physics that make us sort
13:46
Speaker 1: of crack open two ideas we thought were so naturally entangled,
13:50
Speaker 1: so like deeply connected, and now we realize there's a
13:53
Speaker 1: possibility for these two things to be actually separate and distinct.
13:56
Speaker 1: Observing something is there doesn't mean that it is there
14:00
Speaker 1: some deeper sense. It's like totally crazy. Yeah, no, it's
14:03
Speaker 1: it's absolutely true. And one of the strange things about
14:09
Speaker 1: wave functions and measurement is just the idea that, you know,
14:12
Speaker 1: measurement and observation are coming into what's supposed to be
14:16
Speaker 1: a fundamental theory at all, because you know, measurement is
14:18
Speaker 1: not a well defined thing. What do we mean when
14:22
Speaker 1: we say measurement? Right? And I think that a key
14:24
Speaker 1: concept we need to tackle before we get into measurement
14:27
Speaker 1: is this question of superposition, right, because quantum mechanical objects
14:31
Speaker 1: can do something that like our baseballs can't do, which
14:35
Speaker 1: is that they can for a long time, have two
14:37
Speaker 1: possible outcomes and maintain those two possibilities simultaneously. Right, So
14:41
Speaker 1: the wave function can incorporate various possible outcomes inside of itself. Yeah,
14:46
Speaker 1: now that that's exactly right. If you send uh ping
14:49
Speaker 1: pong ball into a maze, it's just gonna go down
14:53
Speaker 1: one path in that maze and you can watch it
14:55
Speaker 1: take one path. But if you send an electron or
14:58
Speaker 1: a photon or some other you know, tinique wantum object
15:00
Speaker 1: into you know, some sort of maze, like send a
15:03
Speaker 1: photon into a set of mirrors and prisms on an
15:06
Speaker 1: optical bench, you know, in the basement of a physics
15:08
Speaker 1: department somewhere. It's not going to take just one path.
15:11
Speaker 1: Quantum mechanics says, no, it's it's going to take a
15:13
Speaker 1: superposition of all of those paths. It's going to go
15:16
Speaker 1: down two or three or four different paths at the
15:19
Speaker 1: same time, or as wave function will. But then when
15:21
Speaker 1: we measure it at the end, right, we say, all right,
15:24
Speaker 1: I'm going to put a device in here. I'm going
15:26
Speaker 1: to ask the question, which one did it actually go down?
15:29
Speaker 1: I can't measure all those paths, right, I get one answer.
15:33
Speaker 1: That's right, you get one answer. If you put a
15:35
Speaker 1: detector on one of the paths, then you'll get an
15:37
Speaker 1: answer saying you know, yes it went down this path
15:40
Speaker 1: or no it didn't. But if instead you set up
15:44
Speaker 1: your optical bench, your maze, whatever you want to call it,
15:47
Speaker 1: or your double slit experiment so that there's an interference
15:50
Speaker 1: pattern on the other side, you will get interference. So
15:53
Speaker 1: when you're not asking the question of which way the
15:58
Speaker 1: photon went and when it went into your setup, it
16:02
Speaker 1: sort of goes down all of those paths and then
16:05
Speaker 1: interferes with itself. But if you ask weight which way
16:08
Speaker 1: did you go, well, then it says, oh, no, I
16:10
Speaker 1: went this way, and then it doesn't interfere with itself.
16:13
Speaker 1: And so we know that the wave function does this
16:16
Speaker 1: superposition thing having two possible outcomes at the same time
16:20
Speaker 1: because we see the interference, that's proof of superposition. But
16:24
Speaker 1: then when we try to measure the photon, the superposition
16:27
Speaker 1: sneaks away. And for you, is that like the clearest
16:30
Speaker 1: encapsulation of this question, this measurement problem, like how the
16:34
Speaker 1: wave function goes from having like various quantum mechanical possibilities
16:38
Speaker 1: for the paths of a photon to basically picking one.
16:41
Speaker 1: How the universe like ends up rolling that die choosing
16:44
Speaker 1: this path or that path or the other path. I
16:46
Speaker 1: think it's a very clear example of that. The way
16:48
Speaker 1: that I usually talk about it is a little different,
16:51
Speaker 1: you know, I I say, Okay, this is one example
16:53
Speaker 1: of the measurement problem, But in general, the measurement problem
16:57
Speaker 1: is more about that sort of undulating property of the
17:01
Speaker 1: wave functions that I was talking about before. Right, we
17:04
Speaker 1: have this very nice equation, the shroding Er equation. It's
17:08
Speaker 1: a law of physics. Right, we think of it as
17:10
Speaker 1: a law of nature, and that describes how wave functions wave. Right,
17:15
Speaker 1: it says that they always wave sort of smoothly and evenly,
17:21
Speaker 1: and you know, they don't make any abrupt transitions. But
17:25
Speaker 1: sometimes the shroding Er equation is temporarily suspended. What you
17:30
Speaker 1: can't do that you can just pause the laws of physics.
17:33
Speaker 1: Sometimes it says, if someone just hits pause on the
17:35
Speaker 1: shrodding Er equation and instead you have to use this
17:39
Speaker 1: other thing called the Born rule, which says, okay, take
17:43
Speaker 1: the wave function and look at all the different possibilities.
17:47
Speaker 1: It gives you for the way that your experiment is
17:50
Speaker 1: going to turn out, and that gives you the probabilities
17:54
Speaker 1: for the different outcomes. That's what the wave function does.
17:56
Speaker 1: When you use the Born rule, And then whichever one
17:59
Speaker 1: you actually serve, cut out all the other parts of
18:02
Speaker 1: the wave function, that's the only one that's left. All
18:04
Speaker 1: the others just instantly go to zero and then violates
18:08
Speaker 1: the shorting your equation, and that violates the shroting your equation.
18:11
Speaker 1: The shrodding your equation doesn't have anything in it like that.
18:13
Speaker 1: And then when you stop looking, that's what happens when
18:17
Speaker 1: you make a measurement. And then when you stop looking,
18:19
Speaker 1: the shorting your equation applies again. And so then the
18:23
Speaker 1: question is, okay, well, so if you have these two
18:25
Speaker 1: different rules and they contradict each other, then first of all,
18:30
Speaker 1: why And second we better be really, really really clear
18:36
Speaker 1: about when to use one and when to use the other.
18:39
Speaker 1: And this is the collapse of the wave function. And
18:42
Speaker 1: so the usual answer to the question when do we
18:44
Speaker 1: use one and when do we use the other? When
18:46
Speaker 1: does the wave function collapse. The usual answer that is,
18:50
Speaker 1: when we make a measurement. And so now the fact
18:53
Speaker 1: that the word measurement is kind of vague goes from
18:59
Speaker 1: you know, a little troublesome or annoying to a really
19:03
Speaker 1: serious problem. Right, So that's a great encapsulation of the
19:07
Speaker 1: question we're facing. Like, we have this beautiful equation, the
19:10
Speaker 1: shortening your equation that tells us how this wave function
19:14
Speaker 1: moves and changes and squishes through the world, and we
19:17
Speaker 1: verified it to zillions of degrees of accuracy, except that,
19:21
Speaker 1: as you say, sometimes it seems to be ignored and
19:24
Speaker 1: sometimes it doesn't seem to apply. And so we have
19:27
Speaker 1: this question of like how a wave function goes from
19:29
Speaker 1: this smooth under lending property to like collapsing into just
19:32
Speaker 1: a point when we make a measurement, what that measurement
19:35
Speaker 1: even means. So I want to dig into that in
19:37
Speaker 1: much more detail, but first let's take a quick break.
19:53
Speaker 1: All right, we're back and we're talking to ask ify
19:55
Speaker 1: is this Adam Becker, author of What is real about
19:58
Speaker 1: the nature of the quantum a function and what happens
20:01
Speaker 1: to it when we look at it? And I have
20:04
Speaker 1: this quote that I love from Bell who says either
20:07
Speaker 1: the way function as given by the Shorting your equation
20:09
Speaker 1: is everything, or it's not right. What do you make
20:13
Speaker 1: of that? I see what he's getting that there, and
20:15
Speaker 1: I think he's kind of right. I mean, there's got
20:17
Speaker 1: to be something more that tells us, Okay, when do
20:22
Speaker 1: we apply the shorting our equation and when don't we
20:25
Speaker 1: because otherwise, you know, uh, And I think Bell said
20:28
Speaker 1: something along these lines as well. We're stuck in this
20:30
Speaker 1: situation where these laws of physics that are supposed to
20:33
Speaker 1: be fundamental or just kind of hopelessly vague. So we
20:36
Speaker 1: have to take the Shortinger equation and the wave function,
20:38
Speaker 1: all of which seems wonderful and perfect and beautiful, and
20:40
Speaker 1: we love it, and we need to add something else.
20:43
Speaker 1: We need to say. Plus, there's this other mechanism that
20:46
Speaker 1: makes things collapse. And this, I think is where people
20:49
Speaker 1: disagree how to describe this weird combination of ideas and
20:54
Speaker 1: sort of a holistic concept. And so first let's talk
20:57
Speaker 1: about maybe the most mainstream way to a hack, this
21:00
Speaker 1: the most common, the one that people most read about
21:03
Speaker 1: in their textbooks. And then I think a lot of
21:05
Speaker 1: our listeners referred to which is basically the Copenhagen interpretation,
21:09
Speaker 1: where you add something to the shorting your equation that
21:12
Speaker 1: makes the wave function collapse when you look at it.
21:14
Speaker 1: So how does that actually happen? Like, what do you
21:16
Speaker 1: add to your system, you know, mathematically to make that happen.
21:20
Speaker 1: You can't just have like a thing that says and
21:22
Speaker 1: by the way, if there's a measurement, I mean, doesn't
21:24
Speaker 1: everything have to be like you know, written down in
21:26
Speaker 1: some sort of equation. The thing is it is just
21:29
Speaker 1: kind of added on. They do basically just say, yeah,
21:32
Speaker 1: use the shorting your equation, except when a measurement occurs,
21:35
Speaker 1: and what a measurement occurs, use this other thing instead.
21:38
Speaker 1: Use this collapse roule called the Born rule, named after
21:41
Speaker 1: Backs Born, you know, one of the architects of quantum physics.
21:44
Speaker 1: And it's just got a completely different mathematical form and
21:46
Speaker 1: it's said, you know, it says, okay, you know, like
21:49
Speaker 1: I said before, it lets you use the wave function
21:51
Speaker 1: to calculate probabilities, and then says, and then the rest
21:56
Speaker 1: of the wave function other than the part that you
21:58
Speaker 1: saw collapse. So if you're looking for an electron somewhere
22:03
Speaker 1: and you've got the wave function of the electron, which is,
22:06
Speaker 1: you know, this sort of nice smooth thing that's maybe
22:08
Speaker 1: got three or four different peaks. You look for the electron,
22:11
Speaker 1: you find it near one of the peaks. The Born
22:15
Speaker 1: rule says, okay, well, then what happens to the electron's
22:18
Speaker 1: wave function is you know, now it just has one
22:21
Speaker 1: extremely narrow peak exactly where you found it, and it
22:24
Speaker 1: goes to zero everywhere else. And then when you stop
22:28
Speaker 1: looking the shroudding, your equation just applies again, which is
22:32
Speaker 1: kind of incredible. And it requires us to sort of
22:34
Speaker 1: insert our selves into the equation, right, it needs like
22:38
Speaker 1: the measurement part is when we are interacting with this thing.
22:41
Speaker 1: And I think the most common question is what counts
22:44
Speaker 1: as a measurement? If I put a particle detector in
22:47
Speaker 1: there but don't turn it on, does it count? If
22:49
Speaker 1: I turn it on but don't connect it to my computer?
22:52
Speaker 1: Does it count? If I hook it all up but
22:54
Speaker 1: then don't look at the computer screen? Does it count
22:56
Speaker 1: as a measurement? And what's special about my part goal detector?
23:00
Speaker 1: Isn't that particle constantly interacting with other things? Doesn't that
23:04
Speaker 1: count as a measurement? So can we tackle it by
23:07
Speaker 1: thinking about so the quantum particles we're using to make
23:10
Speaker 1: the measurement, you know, because we don't just like look
23:12
Speaker 1: at an electron, right, we like bounce a photon off
23:15
Speaker 1: of it or something like that. Yeah, yeah, I mean
23:17
Speaker 1: the Copenhagen interpretation sort of lives or dies on on
23:20
Speaker 1: what you mean by measurement, right, And so it is
23:22
Speaker 1: tempting to say, okay, well, maybe we can get around
23:24
Speaker 1: this problem by saying that, you know, the measurement devices
23:28
Speaker 1: itself also quantum. But the problem is that if you
23:31
Speaker 1: use the shrouding your equation, you know, wave functions and
23:34
Speaker 1: the mathematical machinery of quantum mechanics to describe the measurement
23:38
Speaker 1: device as well, then all that happens when you make
23:40
Speaker 1: a measurement is you go from your measured system in
23:44
Speaker 1: a superposition and you're measuring device sort of ready to
23:48
Speaker 1: make a measurement, to a state where both the measured
23:53
Speaker 1: system and the measuring device are in a superposition. And
23:57
Speaker 1: so you know, if you wanted to say, okay, did
23:59
Speaker 1: the electron go left or did it go right, and
24:03
Speaker 1: then you use your measuring device to answer that question,
24:06
Speaker 1: then the shrodding your equation says at the end of
24:08
Speaker 1: that measurement. What you're gonna end up with is a
24:11
Speaker 1: superposition of the electron went left and the measuring device
24:14
Speaker 1: says left, and the electron went right and the measuring
24:17
Speaker 1: device says right. So the measuring device has become sort
24:20
Speaker 1: of part of the experiment exactly. Yeah, And so that's
24:23
Speaker 1: not gonna get you out of it. Eventually, you have to,
24:27
Speaker 1: according to the Copenhagen interpretation, you have to say, well,
24:30
Speaker 1: then a measurement occurs, and so the shrodding your equation
24:32
Speaker 1: doesn't apply anymore, and we have to use the collapse rule,
24:35
Speaker 1: the born rule, and so you really need to get
24:39
Speaker 1: comfortable with whatever it is that a measurement means, which
24:44
Speaker 1: the Copenhagen interpretation is kind of famously vague about. So
24:48
Speaker 1: let's break that down a little bit more. So. We
24:50
Speaker 1: have our electron and we probe it with the tip
24:53
Speaker 1: of some very very narrow tool, and the tip is
24:56
Speaker 1: just like a single particle that's interacting with the electron.
24:59
Speaker 1: Now we might say, okay, the tools touching the electron,
25:02
Speaker 1: so it's being measured, it should collapse. It should just
25:04
Speaker 1: collapse right there. But somebody else coming in and looking
25:07
Speaker 1: to the experiment. The same way could say no, no no, no,
25:10
Speaker 1: I think the system is the electron plus the tip
25:12
Speaker 1: of the tool, and the rest of the tool is
25:14
Speaker 1: the measuring device. So the tip of the tool plus
25:17
Speaker 1: the electron, that's your experiment. That's what you're probing. The
25:20
Speaker 1: measurement happens when like the next particle over reads off
25:24
Speaker 1: the information from the tip of the tool, And somebody
25:26
Speaker 1: else could come along and say no, no, no, I
25:28
Speaker 1: think the original electron plus the first two things on
25:31
Speaker 1: the tip of the tool are part of the experiment,
25:34
Speaker 1: and the rest of it is the measurement. And you
25:35
Speaker 1: can just basically do this forever, right all the way
25:38
Speaker 1: down the tool, including as many particles as you like,
25:41
Speaker 1: or even including the experiment or him or herself. Yeah,
25:44
Speaker 1: I mean, quantum mechanics says this weird propensity to just
25:47
Speaker 1: sort of generate these sorts of thought experiments like the
25:50
Speaker 1: one that you're talking about that sounds like something out
25:52
Speaker 1: of like ancient Greek philosophical dialogue or something Zeno's quantum
25:56
Speaker 1: experiment exactly. Yeah, I mean there even is a Zene experiment,
26:00
Speaker 1: though not that one. But yeah, the problem here is,
26:04
Speaker 1: you know, it'd be easy to say, when a measurement occurs.
26:07
Speaker 1: If we could say, well, there's a quantum world, and
26:09
Speaker 1: then there's a non quantum world, and when a non
26:13
Speaker 1: quantum thing interacts with a quantum thing, that's a measurement thing.
26:16
Speaker 1: Is nobody believes that anymore because all non quantum things
26:19
Speaker 1: are made of quantum things, right exactly. Yeah, we believe
26:22
Speaker 1: that the world is made of everything in the world
26:26
Speaker 1: is made of molecules, which are made of atoms, which
26:29
Speaker 1: are made of sub atomic particles, all of which are
26:31
Speaker 1: subject to the loss of quantum mechanics. And quantum mechanics
26:34
Speaker 1: doesn't have a real size limit. I mean, certainly there
26:38
Speaker 1: are you know, sizes at which some of its features
26:42
Speaker 1: are more obvious than others. But in principle, there's no
26:46
Speaker 1: limit to the size of a system that you can
26:48
Speaker 1: use quantum mechanics to describe. And we believe that the
26:51
Speaker 1: whole world is made of particles subject to the laws
26:54
Speaker 1: of quantum physics. So yeah, the question becomes if there's
26:59
Speaker 1: no border between the quantum world in the non quantum world,
27:01
Speaker 1: because the whole world is quantum, then when does a
27:05
Speaker 1: measurement occur? Is it when the measurement device touches the object. Well,
27:09
Speaker 1: in that case, does that mean that quantum mechanics doesn't
27:11
Speaker 1: apply to the measurement device? Okay, Well, maybe it's when
27:14
Speaker 1: somebody looks at the measurement device. Maybe it's when I
27:17
Speaker 1: look at the measurement device. Okay, But does that mean
27:19
Speaker 1: that quantum mechanics doesn't apply to me. I'm made of
27:21
Speaker 1: quantum stuff, you know. I'm made of cells, which are
27:24
Speaker 1: made of molecules, which are made of sub atomic particles
27:26
Speaker 1: and so on. You know, there's no reason to think
27:28
Speaker 1: that quantum mechanics doesn't apply to all of the stuff
27:32
Speaker 1: in my body and brain. In fact, every time we've
27:35
Speaker 1: checked on something like that, we've found that, you know,
27:38
Speaker 1: every biochemical process is fully explained by quantum mechanics. All right,
27:42
Speaker 1: but there is one wrinkle there, right, Like you are
27:45
Speaker 1: different from you know, the ascilloscope or the probe using
27:49
Speaker 1: to touch the electron. We think in that you are conscious, right,
27:52
Speaker 1: you are a self aware, you're living, thinking, breathing person.
27:56
Speaker 1: I don't know about the ascilloscope. I didn't invite the
27:58
Speaker 1: acilloscope to be a guest on the podcast to speak
28:00
Speaker 1: up for itself. But you know, I think a lot
28:02
Speaker 1: of people. Imagine that that might be the moment when
28:05
Speaker 1: the measurement happens, when the information like goes through the
28:08
Speaker 1: tool and up the computer and into your brain and
28:10
Speaker 1: it's like known by a conscious observer. What about that?
28:14
Speaker 1: Why can't we use that as a distinction. Well, so
28:16
Speaker 1: there's a few issues there, right. One is, you know,
28:19
Speaker 1: consciousness is something that we don't understand. Well, what do
28:22
Speaker 1: we mean by consciousness? You know, you were sort of
28:25
Speaker 1: getting at that before when you were bringing in this
28:27
Speaker 1: thought experiment of you know, okay, well, when I look,
28:29
Speaker 1: is that the measurement? No? Well, then when you come
28:32
Speaker 1: in the room and you look at me, is that
28:33
Speaker 1: the measurement. This was put together by this famous physicist
28:37
Speaker 1: Eugene Vigner, and it's called the Vigner's friend experiment. And
28:41
Speaker 1: I'm conscious, right, my friend is conscious. So maybe the
28:45
Speaker 1: measurement happens where I look, or is it when my
28:47
Speaker 1: friend looks at me? Or you know, does it have
28:49
Speaker 1: to be a human? What if we put a chimp
28:52
Speaker 1: in there? Right? What about a dog or a crow? Right?
28:55
Speaker 1: Crows are really smart. Hold on, let's break down the
28:57
Speaker 1: Vigner's friend experiment, because I think this is where it
28:59
Speaker 1: described having like essentially, the idea is, you are doing
29:02
Speaker 1: this experiment, you are measuring this electron. You're using a tool,
29:06
Speaker 1: and you do the evaluation and you get a number.
29:09
Speaker 1: Now I don't know the answer yet, and so in
29:12
Speaker 1: some sense I can look at you and say, well,
29:14
Speaker 1: you are a part of my tool. Adam, I haven't
29:16
Speaker 1: asked you yet what happened, So I don't know the answer.
29:19
Speaker 1: So you are still in a quantum superposition of the
29:23
Speaker 1: electron went left and the electron went right. So in
29:26
Speaker 1: that sense, like a conscious person can be in a
29:29
Speaker 1: quantum state, Right, you can have like the wave function
29:32
Speaker 1: of Adam Becker having two different possibilities. Yeah, I mean
29:36
Speaker 1: that's a problem, right, because that that's the sort of
29:38
Speaker 1: thing that feels like you could lead to an infinite regress,
29:41
Speaker 1: right you know, Okay, but then you're in a superposition
29:44
Speaker 1: until your friend talks to you, and then we start
29:46
Speaker 1: having problems like okay, but then, why does everybody agree
29:49
Speaker 1: about the outcome of the experiment? And right, what was
29:53
Speaker 1: it like to be in a superposition? What did it
29:55
Speaker 1: feels What was it like to be in a superposition? Exactly?
29:57
Speaker 1: What does it feel like? I don't think that I've
29:59
Speaker 1: ever been in two places at once, so that I've
30:01
Speaker 1: ever believed that an experiment I felt like I needed
30:04
Speaker 1: to be into businesses but exactly and never achieved. Yeah,
30:07
Speaker 1: And I certainly don't think that I've ever like, you know,
30:10
Speaker 1: looked at the outcome of an experiment and thought, oh,
30:13
Speaker 1: that went both of the two mutually contradictory ways that
30:16
Speaker 1: it could go. You know, the electron went left and
30:19
Speaker 1: it also went right. And I saw the measurement device
30:22
Speaker 1: say left and also say right at the same time.
30:25
Speaker 1: That's not an experience I remember having. And that kind
30:28
Speaker 1: of rules out this notion of consciousness being the threshold,
30:32
Speaker 1: because you can put a conscious observer into your experiment
30:35
Speaker 1: and still have the wave function not collapse until after
30:38
Speaker 1: the conscious observer reports their results. Right, Just at a
30:41
Speaker 1: conscious observer observing something doesn't necessarily make the wave function collapse,
30:46
Speaker 1: isn't that right? Yeah? With an asterisk tell us about
30:50
Speaker 1: the asterisk. Yeah, So, I mean you can set up
30:53
Speaker 1: a system where you've got a quantum wave function and superposition,
30:58
Speaker 1: and you can sort of verify that it's in a superposition,
31:02
Speaker 1: and that verification does not itself lead to the collapse
31:06
Speaker 1: of the wave function. Wait, how do you do that?
31:08
Speaker 1: How do you verify that? Is that by observing interference? Yeah,
31:11
Speaker 1: that's by observing interference. You can see that there's interference.
31:14
Speaker 1: But what you can't do, at least what we don't
31:17
Speaker 1: have the ability to do right now, is put a
31:20
Speaker 1: human in there as part of the system that is
31:24
Speaker 1: exhibiting interference. Right, I see, I can't see the various
31:29
Speaker 1: modes of Adam interfering with themselves exactly. Yeah, but there
31:33
Speaker 1: are other reasons to think that consciousness is probably not
31:36
Speaker 1: what's going on here, or if it is, you need
31:38
Speaker 1: a really good account of how that's possible. Right, Because
31:42
Speaker 1: one of the things that we want to be able
31:45
Speaker 1: to use quantum physics to do, and you know, as
31:48
Speaker 1: a cosmologists by training, this is near and dear to
31:50
Speaker 1: my heart. We want to use quantum physics to describe
31:52
Speaker 1: the very early universe. Who want to do quantum cosmology,
31:56
Speaker 1: and you know that means talking about things like the
31:59
Speaker 1: wave function of universe. And indeed, you know we talk
32:03
Speaker 1: about that when we talk about things like, you know,
32:06
Speaker 1: patterns in the cosmic microwave background radiation, the oldest light
32:11
Speaker 1: in the universe, and echo of the Big Bang. We
32:14
Speaker 1: see the imprint of quantum mechanics in the sky. And
32:17
Speaker 1: now I am going to almost directly quote John Bell.
32:20
Speaker 1: Was the wave function of the universe waiting for billions
32:24
Speaker 1: and billions of years for you know, a paramesium to
32:29
Speaker 1: arrive and collapse the wave function? Or did it need
32:32
Speaker 1: a better qualified observer, you know, someone with a PhD.
32:36
Speaker 1: The first PhD collapse, the universe's waiting exactly. Yeah, I
32:40
Speaker 1: don't think that that's how that works. I don't think
32:43
Speaker 1: that conscious beings are necessary in order for quantum mechanics
32:48
Speaker 1: to work. So if the wave function collapses, and we've
32:51
Speaker 1: really know the wave function is real and exists outside
32:55
Speaker 1: the mind of humans. But if it is real and
32:57
Speaker 1: it does collapse, it seems like it must have been
32:59
Speaker 1: collapsing for billions of years before we showed up. That's right.
33:02
Speaker 1: And if it doesn't collapse, we need to figure out
33:04
Speaker 1: why it looks like it does seem important And I
33:07
Speaker 1: think that you mentioned something really interesting about how we
33:10
Speaker 1: know that asymmetries do exist, right, Like, this question is
33:14
Speaker 1: important not just for philosophers, but for like quantum cosmologists.
33:18
Speaker 1: How do you go from the beginning of a universe
33:21
Speaker 1: where you assume I have a symmetric wave function because
33:25
Speaker 1: anything else would be bonkers, and somehow get asymmetries, right,
33:28
Speaker 1: how do you get a universe that's not exactly the
33:30
Speaker 1: same in every direction? Where do those things come from?
33:33
Speaker 1: Those come from quantum fluctuations, which are quantum collapses, right, Yeah,
33:38
Speaker 1: that's right. Quantum fluctuations happen when you might have equal
33:41
Speaker 1: probabilities to go left or right, but like one of
33:43
Speaker 1: them is chosen. The universe does roll a die. And
33:46
Speaker 1: so the fact that we exist here and not a
33:48
Speaker 1: billion light years to the left is evidence that quantum
33:51
Speaker 1: mechanics does fluctuate, that there are these collapses, that these
33:54
Speaker 1: things are real somehow, Yeah, exactly, or at least that's
33:57
Speaker 1: something like collapse or something that in tates collapse or
34:00
Speaker 1: gives the appearance of collapse happens all right, So it
34:03
Speaker 1: seems like this Copenhagen interpretation is pretty problematic, right, Like
34:07
Speaker 1: there's a basic fundamental unknown in it, like what this
34:11
Speaker 1: even means by measurement. We need measurement to get the
34:13
Speaker 1: way function to collapse, or to get it to look
34:15
Speaker 1: like it collapses, but we don't even really know what
34:18
Speaker 1: that means and what triggers it. So how could this
34:20
Speaker 1: possibly be the most mainstream, core idea in the most
34:25
Speaker 1: fundamental concept in physics. That's a great question, and it
34:29
Speaker 1: unfortunately has a very simple answer. The answer is when
34:32
Speaker 1: people ask these sorts of questions, they were just sort
34:36
Speaker 1: of waved away. It's more complex than that. I wrote
34:39
Speaker 1: a whole book about how this happened. Before I did,
34:42
Speaker 1: I used to say, well, I could write a book
34:44
Speaker 1: about it, and then it turns out that I made
34:46
Speaker 1: good onto that way. Function did collapse into a book,
34:49
Speaker 1: Yes it did. But yeah, the answer is, you know,
34:53
Speaker 1: people ask, well, what do we mean by measurement? We
34:56
Speaker 1: have to get more specific about this. How could this
34:59
Speaker 1: possly be this vague and ill defined and contradictory And
35:05
Speaker 1: the answer that was usually given was it works, so
35:09
Speaker 1: don't worry about it. This was sort of summed up
35:11
Speaker 1: famously by the physicist David Merman as shut up and calculate.
35:16
Speaker 1: That's basically like, don't worry about what it means. It works,
35:19
Speaker 1: it predicts our experiments. Who cares. Yeah, don't pay any
35:23
Speaker 1: attention to the man behind the curtain, just you know,
35:26
Speaker 1: do the calculations, and you'll be able to build most
35:30
Speaker 1: of the technology that the modern world is based on,
35:32
Speaker 1: which is you know, absolutely true. You know you don't
35:35
Speaker 1: need to answer this question in order to do things
35:37
Speaker 1: like design semiconductor transistors and build computer chips and lasers
35:44
Speaker 1: and l ed s and you know, nuclear power and
35:47
Speaker 1: all of the other incredible and you know, awesome in
35:52
Speaker 1: the most literal sense technologies that quantum physics has enabled
35:57
Speaker 1: over the last century. But science and physics is not
36:00
Speaker 1: just about delivering technological improvements for humanity, right, Like, I
36:05
Speaker 1: love that all our listeners can hear this podcast on
36:08
Speaker 1: various devices enabled by quantum mechanics. But I didn't go
36:11
Speaker 1: into physics to like make a better iPhone. I went
36:14
Speaker 1: into physics to understand the universe? Right, So doesn't that
36:18
Speaker 1: really fly in the face of sort of the core
36:20
Speaker 1: mission of the entire discipline to gain some understanding. I
36:25
Speaker 1: completely agree with you, but apparently not everyone does. Alright, Well,
36:31
Speaker 1: I'm glad we agree on that, and I want to
36:33
Speaker 1: dig into some other possibilities, some other ways people have
36:36
Speaker 1: attacked this problem, some crazy, totally different ways of thinking
36:40
Speaker 1: about what might be real about the universe. But first,
36:42
Speaker 1: let's take another break. All right, we're back and we're
36:57
Speaker 1: talking to Adam Becker about what is real and if
37:00
Speaker 1: anything is real and if the universe can possibly make
37:02
Speaker 1: sense at all, and are we even here? And we've
37:05
Speaker 1: been talking about the wave function and how the Copenhagen
37:08
Speaker 1: the mainstream interpretation of quantum mechanics has a basic problem
37:12
Speaker 1: in it and that it can't define what a measurement is.
37:15
Speaker 1: But a measurement is essential to making the theory work,
37:18
Speaker 1: so it can't be the only idea that's out there.
37:21
Speaker 1: Surely people have thought of some other approaches. And so
37:25
Speaker 1: if you're a listener to Sean Carroll, for example, you
37:27
Speaker 1: probably heard him as a big proponent of this ever
37:30
Speaker 1: already in many worlds interpretation. So how does a many
37:34
Speaker 1: worlds interpretation, How does manufacturing billions and billions of branching
37:38
Speaker 1: universes solve this measurement problem? Or does it? That's a
37:42
Speaker 1: great question I want to say before I answer that
37:45
Speaker 1: this is something that I get a lot of email
37:49
Speaker 1: and people asking me about it. Back when you know,
37:52
Speaker 1: in person, back when you know we could do things
37:55
Speaker 1: in person. For whatever reason, a lot of people came
37:58
Speaker 1: away from my book thinking that I agree with Sean Carroll,
38:02
Speaker 1: and I like Sean Shan is a great guy. Yeah,
38:07
Speaker 1: but I think that his position is a reasonable one.
38:11
Speaker 1: But I don't think that it's the only reasonable one.
38:14
Speaker 1: And I think that I am not here as a
38:18
Speaker 1: shill of big many worlds, just a shill of big quantum.
38:23
Speaker 1: Many world is already big. You don't say big in front.
38:26
Speaker 1: Yeah that's true. Now, many worlds, I think is pretty
38:29
Speaker 1: clearly the next most popular interpretation after this sort of jumble.
38:34
Speaker 1: That is the Copenhagen interpretation. All right, to breakdown for us,
38:37
Speaker 1: what is the many worlds interpretation? So the many world's
38:40
Speaker 1: interpretation gets out of the measurement problem by saying, oh, yeah,
38:43
Speaker 1: collapse doesn't happen. It just sort of looks like it does.
38:46
Speaker 1: It takes the sort of infectious property of superposition, where
38:51
Speaker 1: you know, if a measurement device measures something that's in superposition,
38:55
Speaker 1: then it will go into superposition. It takes that property
38:58
Speaker 1: and sort of embraces it wholeheartedly and turns it into
39:01
Speaker 1: a strength. It says, okay, well, collapse never happens. The
39:05
Speaker 1: Born rule is, you know, not a fundamental thing in
39:10
Speaker 1: nature that describes what's actually happening in the world. It's
39:13
Speaker 1: just something we need to make predictions. And in reality,
39:17
Speaker 1: the Schrodinger equation or you know, the relativistic extensions thereof
39:21
Speaker 1: always apply, and so wave functions always just evolved smoothly,
39:26
Speaker 1: which means that when you make a measurement of an
39:30
Speaker 1: electron or something in a superposition. You know, the classic
39:33
Speaker 1: example here is Schrodinger's cat. You set it up with
39:36
Speaker 1: a quantum device where you know, if it goes one way,
39:39
Speaker 1: the cat lives, and if it goes the other way,
39:41
Speaker 1: the cat dies. So when you open the box, you
39:45
Speaker 1: find a cat that is both dead and alive. It's
39:49
Speaker 1: in a superposition of dead and alive. And then you know,
39:52
Speaker 1: in the process of opening the box, you enter into
39:55
Speaker 1: a superposition yourself of seeing a dead cat and seeing
40:00
Speaker 1: a living cat. And then someone else comes in the
40:02
Speaker 1: room and they enter a superposition of you know, seeing
40:05
Speaker 1: you crying over this dead cat and seeing you, you know,
40:09
Speaker 1: playing with the living cat and so on, and this
40:12
Speaker 1: just sort of spreads out into the universe. So you're saying,
40:16
Speaker 1: the way function never actually collapses and picks one of
40:19
Speaker 1: these branches. It just keep branching, and we are only
40:23
Speaker 1: in one of those branches, which is why it looks
40:25
Speaker 1: like it collapses sort of. The question of where we
40:29
Speaker 1: are in the theory is definitely something that's contentious, But
40:33
Speaker 1: I think that what Sean would say, Well, I don't
40:36
Speaker 1: want to put words into Sean's mouth. If I put
40:38
Speaker 1: on my many world's hat and say, Okay, I'm gonna
40:40
Speaker 1: pretend to be a real advocate of many worlds, I
40:42
Speaker 1: would say, no, we're in both branches. But once we split,
40:47
Speaker 1: a quantum process called decoherence ensures that the two branches,
40:52
Speaker 1: you know, once they involve large objects made of many
40:55
Speaker 1: quantum particles, can't interfere or communicate with each other in
40:59
Speaker 1: any way a very very quickly, and so we split.
41:04
Speaker 1: And so you know, if you ask one of the
41:09
Speaker 1: copies of you that is in either branch, hey, how
41:13
Speaker 1: many cats do you see? How many outcomes do you
41:16
Speaker 1: see for this cat? Both of them would say, oh,
41:18
Speaker 1: I only see one outcome. They just disagree about what
41:22
Speaker 1: that outcome is. And so this is why it's called
41:25
Speaker 1: many worlds, because it imagines that multiple versions of the
41:29
Speaker 1: universe are existing decoherently, that they've decohere from each other,
41:34
Speaker 1: and they're all out there. They're real, but they're sort
41:36
Speaker 1: of like not accessible to us anymore because we're only
41:40
Speaker 1: in one branch of the way of function. Yeah, we're
41:43
Speaker 1: this copy of ourselves is only in this branch, but
41:45
Speaker 1: there are other near identical copies in all of the
41:48
Speaker 1: other branches. And so I was trying to lead you
41:50
Speaker 1: down the garden path there, I think to my major
41:52
Speaker 1: objection to the many worlds interpretation, which is like, why
41:55
Speaker 1: are we in this one? Because, as you say, like
41:59
Speaker 1: there's a copy of me in all of those universes
42:02
Speaker 1: that have observed every possible outcome of the Schrodinger's box experiment.
42:05
Speaker 1: But still I'm this one, and I know that in
42:08
Speaker 1: the other universe, the other me thinks that it's that one,
42:11
Speaker 1: and that's fine, But why is it in that universe?
42:13
Speaker 1: And I'm in this universe? Like there is still something
42:16
Speaker 1: special about this universe because I'm in it, right, Well,
42:20
Speaker 1: you know, your copy in the other universe where the
42:24
Speaker 1: cat died would say the same thing. I know, but
42:27
Speaker 1: it also has a reasonable objection, Right, there is still
42:30
Speaker 1: something different about this universe because I'm in it, And
42:33
Speaker 1: there's something different about that universe because it's in that one.
42:36
Speaker 1: It seems to me like does not really avoid this
42:38
Speaker 1: problem because it still takes one universe to be special
42:42
Speaker 1: in some sense, because this is the only one that
42:44
Speaker 1: I'm experiencing anyway. What are your concerns about the many
42:47
Speaker 1: world interpretation. Well, the classic concern about it is that
42:51
Speaker 1: you still actually need the Born rule, right, because quantum
42:54
Speaker 1: mechanics doesn't issue forth certain predictions. It doesn't say this
42:58
Speaker 1: is you know, definitely what's going to happen. It says
43:03
Speaker 1: that sometimes, But most of the time, the predictions of
43:05
Speaker 1: quantum mechanics come in the form of probabilities that says, well,
43:08
Speaker 1: there's a twenty percent chance that this is going to happen,
43:10
Speaker 1: in a thirty percent chance that's gonna happen, a fifty
43:12
Speaker 1: percent chance that that's going to happen, and you know,
43:14
Speaker 1: those are the possible outcomes. But in a world where
43:17
Speaker 1: the shroting Your equation always applies, well, the shroting Your
43:20
Speaker 1: equation has no probability in it. The Shrotinger equation is
43:24
Speaker 1: actually like Newton's physics, and that it's completely deterministic. You know,
43:29
Speaker 1: when you ask, uh, many worlds person, well, what's going
43:32
Speaker 1: to happen? When you open the box. They'd say, well,
43:35
Speaker 1: with one d percent probability, I will split into two copies,
43:39
Speaker 1: one of which we'll see a living cat and the
43:41
Speaker 1: other we'll see a dead cat. That's definitely what's going
43:44
Speaker 1: to happen. And so then you know the next question,
43:47
Speaker 1: which is, you know, what's the probability that you're going
43:49
Speaker 1: to see a living cat because I don't want to
43:51
Speaker 1: get a cat. The answer to that has to be, well,
43:55
Speaker 1: you need to use the Born rule. You need to
43:57
Speaker 1: use this collapse rule, because that collapse rule is how
44:00
Speaker 1: we get predictions out of quantum physics. It's what makes
44:02
Speaker 1: it so phenomenally accurate and powerful. And so you need
44:07
Speaker 1: to figure out, Okay, how do we introduce probability into
44:11
Speaker 1: a theory in which literally anything that can happen does happen.
44:15
Speaker 1: That's a little thorny and one way of going about it.
44:19
Speaker 1: And this is actually a position that I know for
44:22
Speaker 1: sure Sean holds. So now I am gonna like do
44:25
Speaker 1: my best Sean Carroll impression. Sean says that, well, the
44:29
Speaker 1: probability comes from basically exactly your concern that we don't
44:34
Speaker 1: know where in this branching multiverse of worlds we are located,
44:41
Speaker 1: and so we have uncertainty about where we are, and
44:45
Speaker 1: that uncertainty is where the probabilities come from. When we
44:48
Speaker 1: do the experiment and we see an outcome, what we're
44:50
Speaker 1: actually doing is learning where in the many worlds we are.
44:56
Speaker 1: And then you can look at the structure of this
45:02
Speaker 1: multiverse and sort of derive the Born rule from it.
45:06
Speaker 1: You can say, okay, well, this is the right way
45:08
Speaker 1: to answer questions about probabilities. So the problem with the
45:12
Speaker 1: many worlds interpretation, then, is that it keeps the wave
45:15
Speaker 1: functions sort of too long. The wave function itself doesn't
45:18
Speaker 1: actually make predictions, as you say, it can be used
45:21
Speaker 1: to make predictions, but if you just keep the wave
45:24
Speaker 1: function going forever, then how do you actually predict the
45:27
Speaker 1: outcome of an experiment? All right, that's fascinating. Yeah, you
45:30
Speaker 1: need to answer that. And I want to be clear
45:33
Speaker 1: the many advocates of many worlds generally have answers to that,
45:36
Speaker 1: although I don't think that there's consensus around one single
45:41
Speaker 1: answer to that among all of the many advocates of
45:44
Speaker 1: you know, this kind of interpretation. They're aware of this
45:47
Speaker 1: problem and they've addressed it, and they have answers to it.
45:50
Speaker 1: So the question isn't you know how do you answer it?
45:53
Speaker 1: The question is does one or several of the answers
45:56
Speaker 1: that have been provided work? And that is an open question. Awesome,
46:01
Speaker 1: And so before we wrap up, I want to touch
46:03
Speaker 1: on a couple of other ideas. So those totally different
46:06
Speaker 1: directions people are taking about attacking this deep question about
46:10
Speaker 1: the meaning of the wave function and what measurement means.
46:13
Speaker 1: And one of my favorites is this hidden variable theory
46:16
Speaker 1: or the categories of theories called hidden variable theories, because
46:19
Speaker 1: when I was learning about quantum mechanics, I remember thinking like, well, sure,
46:23
Speaker 1: but how do we know it's not like just actually
46:25
Speaker 1: determined by something we're not aware of? You know? It
46:28
Speaker 1: feels like maybe our lack of information, this uncertainty in
46:32
Speaker 1: the universe doesn't just come from inherent uncertainty, but it
46:36
Speaker 1: just comes from like our not seeing the full picture.
46:38
Speaker 1: So maybe there's like something going on behind the scenes
46:41
Speaker 1: that's controlling everything. How do we know that's not the case?
46:44
Speaker 1: How do we know that it's not just like more
46:46
Speaker 1: to the universe that makes it actually deterministic. That's a
46:49
Speaker 1: great question, and you're a really good company there as
46:52
Speaker 1: I'm sure you know. You know, Albert Einstein basically had
46:55
Speaker 1: exactly the same question. You know, it's a myth that
46:57
Speaker 1: he never accepted quantum physics. He knew that it worked,
47:00
Speaker 1: and he he fully accepted that it worked. He just
47:03
Speaker 1: thought it couldn't be the whole story for basically the
47:06
Speaker 1: same reason that you're giving. And in particular, he was
47:11
Speaker 1: very unhappy about the idea that things depended on observation
47:16
Speaker 1: and that you couldn't talk about what was happening when
47:19
Speaker 1: you weren't looking. He thought that this was, you know,
47:22
Speaker 1: as you were saying, just kind of avoiding the whole
47:25
Speaker 1: point of science. Science is about figuring out what's in
47:28
Speaker 1: the world and how it works. And he was also
47:30
Speaker 1: really concerned about the possibility introduced in quantum physics for
47:35
Speaker 1: what he called spooky action at a distance, these long
47:38
Speaker 1: distance connections between objects, and that is actually directly related,
47:45
Speaker 1: as it turns out, to the answer to your question.
47:48
Speaker 1: You know, the question, is there's something going on that
47:51
Speaker 1: we don't know about some you know, hidden properties what
47:55
Speaker 1: we usually call hidden variables of these particles that you
47:59
Speaker 1: know to termine their behavior, and we just don't know
48:01
Speaker 1: what they are. And that's where the uncertainty comes from.
48:04
Speaker 1: The answer to that that we know is yes, it's possible,
48:10
Speaker 1: but you have to pay a price. The price is
48:14
Speaker 1: spooky action at a distance, and that was proven by
48:18
Speaker 1: experiments that were done to test a theorem by John Bell.
48:23
Speaker 1: So we can have a super deterministic universe, but it
48:27
Speaker 1: can't be local. We can't also have like everything we
48:30
Speaker 1: determined about what's happening right here. So yeah, I gotta
48:33
Speaker 1: be like really pedantic and nitpicky. There is actually a
48:37
Speaker 1: class of interpretations called super determinism, and that's something else.
48:44
Speaker 1: But yes, we can have a deterministic universe. We can
48:49
Speaker 1: have hidden variables that determine everything that's going on. But
48:52
Speaker 1: the price we have to pay is that, you know,
48:55
Speaker 1: things that happen right here can instantaneously influenced stuff that
48:59
Speaker 1: happens arbitrarily far away, and do so in a way
49:04
Speaker 1: that provably can't be used to send anything information or
49:09
Speaker 1: material faster than the speed of light. All right, So
49:12
Speaker 1: that's super deterministic with a lower case as and two words, Yes,
49:16
Speaker 1: what's super determinism single where where the capital as is
49:20
Speaker 1: that superman is determining the outcome of all these quantum experiments.
49:23
Speaker 1: Super Determinism is the idea of like a hardcore clockwork universe.
49:28
Speaker 1: It's this idea that, oh, we can explain the outcome
49:32
Speaker 1: of these Bell experiments without sacrificing locality and without you know,
49:37
Speaker 1: without sacrificing the idea that you know, instantaneous action at
49:40
Speaker 1: a distance can't happen. We can also do it without
49:43
Speaker 1: sacrificing the idea of determinism. But to do that instead,
49:49
Speaker 1: we have to say, oh, at the beginning of time,
49:53
Speaker 1: in the Big Bang, a whole bunch of really fine
49:58
Speaker 1: grained information was encoded into every particle in the universe
50:03
Speaker 1: about the outcomes of those experiments, those Bell experiments that
50:07
Speaker 1: would be conducted, you know, thirteen point eight billion years
50:11
Speaker 1: later um, that would arrange for them to turn out
50:16
Speaker 1: in a way that would trick us into thinking that,
50:20
Speaker 1: you know, the universe was nonlocal. So we do these
50:22
Speaker 1: experiments and they seem to suggest the universe is nonlocal,
50:26
Speaker 1: but that's just because they've been cleverly arranged fourteen billion
50:29
Speaker 1: years ago to look that way. Yeah, that's super determinism. Yeah,
50:33
Speaker 1: that's super nuts. Yeah, I'm not super sympathetic to supers,
50:39
Speaker 1: but you know, all these ideas are kind of crazy.
50:41
Speaker 1: All of them have things you might object to. I guess.
50:43
Speaker 1: In the end, the question I have for you is
50:46
Speaker 1: are we going to figure this out? Or how could
50:48
Speaker 1: we figure this out? Are there experiments we can do
50:52
Speaker 1: to figure out which of these things are real? Or
50:54
Speaker 1: is it just going to rely on philosophers smoking bananappeals
50:58
Speaker 1: and organism in their minds? Yeah? I know this is
51:01
Speaker 1: a great question. So the answer depends on what you
51:05
Speaker 1: mean by is there an experiment that we can do? Right? So,
51:08
Speaker 1: if you're asking, is there an experiment that we can
51:12
Speaker 1: do to figure out which of these different interpretations of
51:17
Speaker 1: quantum physics is the right way to think about quantum
51:21
Speaker 1: physics right now? The answer to that is no, because
51:28
Speaker 1: they all give the same or almost all give almost
51:32
Speaker 1: all the same outcomes for all experiments provably. I mean,
51:36
Speaker 1: there are some proposals for solving the measurement problem that
51:39
Speaker 1: aren't just new interpretations but are actually completely different theories.
51:43
Speaker 1: There's a class of theories called objective collapse theories that
51:46
Speaker 1: modify the shrouding R equation. Those can be tested, so yes,
51:49
Speaker 1: some of them can just be directly tested, and those
51:52
Speaker 1: tests are sort of ongoing. But for most of these,
51:54
Speaker 1: like many worlds, interpretation or the best known and most
51:58
Speaker 1: developed of the hidden ables interpretations called Bonian mechanics or
52:02
Speaker 1: depoid bone theory or pilot wave theory, has a few
52:04
Speaker 1: different names, which is, you know, nonlocal. And they think
52:07
Speaker 1: that that's like a good thing about the theory, and
52:09
Speaker 1: that's a whole other story. I'm not saying that to
52:11
Speaker 1: disparage them. I understand why they say that, and I
52:14
Speaker 1: think that that's also a reasonable position. But the point
52:16
Speaker 1: is those two and you know, many of the other
52:19
Speaker 1: interpretations of quantum mechanics are just that their interpretations, they
52:23
Speaker 1: all provably give rise to exactly the same outcomes in
52:27
Speaker 1: all of these experiments. And so if you ask them, well,
52:29
Speaker 1: what's the experimental evidence, they'd say, all experimental evidence for
52:32
Speaker 1: quantum physics, you know, is experimental evidence for this interpretation
52:36
Speaker 1: as well. So in that sense, no, there's no experimental
52:39
Speaker 1: way to distinguish between them. Doesn't that mean we just
52:42
Speaker 1: haven't been clever enough. I mean, if we have seven
52:44
Speaker 1: theories that all fit the data, it just means we
52:47
Speaker 1: need to come up with a more clever experiment that
52:49
Speaker 1: can distinguish between those seven theories right. Otherwise you have
52:53
Speaker 1: to accept the possibility that there could be multiple theories
52:56
Speaker 1: of physics that work perfectly to describe our universe, in
53:00
Speaker 1: which case, like the whole project of physics of coming
53:03
Speaker 1: up with a unique idea to describe the universe and
53:05
Speaker 1: then interpreting what that idea means is sort of cast
53:08
Speaker 1: into doubt. I have some good news and some bad news.
53:14
Speaker 1: Let's start with the bad news. The bad news is
53:17
Speaker 1: all of these theories provably give rise to exactly the
53:21
Speaker 1: same mathematics and provably you know, spit out the same
53:26
Speaker 1: results for the same experiments. And in fact, you can
53:32
Speaker 1: even prove that given the mathematical structure of any scientific
53:37
Speaker 1: theory you could ever devise, there is an infinite number
53:42
Speaker 1: of interpretations that you could come up with to you know,
53:46
Speaker 1: explain what's going on in that theory. So that does
53:49
Speaker 1: sound bad from the perspective of you know, physics and
53:53
Speaker 1: the project of trying to understand what's going on in
53:55
Speaker 1: the world. The good news is that's not at actually
54:00
Speaker 1: how physics works. You know, we don't sit down and say, okay, well,
54:03
Speaker 1: there's an infinite space of possible theories for the mathematical
54:06
Speaker 1: structure that we devised, and so now we need to
54:09
Speaker 1: try to narrow that infinite space. That's not how we
54:12
Speaker 1: do physics. How we do physics and how we do
54:14
Speaker 1: science more generally, as we say, okay, well, look, we
54:17
Speaker 1: have these ideas about how nature works. And these ideas
54:19
Speaker 1: come from a variety of places. They come from the
54:21
Speaker 1: results of experiments. They come from older theories that we
54:25
Speaker 1: have that worked and now seem to be breaking down.
54:28
Speaker 1: They come from new theoretical ideas that we've been kicking
54:32
Speaker 1: around because we like them. And they come from you know,
54:36
Speaker 1: preconceived cultural and social norms, and you know, mythology and
54:41
Speaker 1: and storytelling and whatnot. You know, just ideas that we
54:44
Speaker 1: have about the world. And all of that goes into
54:47
Speaker 1: the process of judgment that is made when new theories
54:52
Speaker 1: are developed and choices are made about how to interpret
54:55
Speaker 1: those theories. It sounds like you're talking about a neta
54:57
Speaker 1: level of measurement where we're like measuring the ability and
55:01
Speaker 1: experiment to satisfy our need to understand the universe exactly. Yeah,
55:05
Speaker 1: that's not wrong. But the thing is that's actually good
55:09
Speaker 1: news when it comes to the question of interpreting quantum
55:14
Speaker 1: physics and finding out which, if any of these, is
55:16
Speaker 1: the best way to think about quantum physics, because we
55:20
Speaker 1: know we're not done. You know, the one thing aside
55:24
Speaker 1: from the success of quantum physics that I think that
55:26
Speaker 1: you could get everyone in you know, the world of
55:30
Speaker 1: quantum foundations, in the world of physics more generally to
55:32
Speaker 1: agree upon, is that we are not done in our
55:38
Speaker 1: search for the fundamental laws of the universe. We know,
55:41
Speaker 1: if nothing else, that we have not found a way
55:45
Speaker 1: to get our best theory of gravity general relativity to
55:48
Speaker 1: work with our best theories of you know, quantum physics,
55:53
Speaker 1: you know, quantum field theory and the standard model of
55:55
Speaker 1: particle physics. And we also know that that standard model
55:58
Speaker 1: is not just missing gravity, but is also missing things
56:01
Speaker 1: like dark energy and dark matter. So we know that
56:04
Speaker 1: we're not done, and so that means we're still on
56:07
Speaker 1: the hunt for new theories. And one of the things
56:11
Speaker 1: that goes into the mix when coming up with new
56:14
Speaker 1: theories is the interpretations of old theories. So the way
56:19
Speaker 1: we think about quantum physics now can influence the hunt
56:24
Speaker 1: for the next theory that will go beyond our current
56:27
Speaker 1: understanding of physics, and it also goes backwards. If and
56:31
Speaker 1: when we come up with that theory, it will probably
56:36
Speaker 1: suggest to us an experiment that can be conducted that
56:40
Speaker 1: would distinguish between some or all of the existing options
56:44
Speaker 1: on the table for interpreting quantum mechanics. Yeah. I have
56:48
Speaker 1: faith in the future of experimental physics to get us
56:51
Speaker 1: out of this jam by coming up with a clever
56:53
Speaker 1: new experiment. Yeah, we should all right. Well, that's wonderful.
56:58
Speaker 1: Thank you very much, Adam. I think it's been a
57:00
Speaker 1: delightful journey through the problems and possible solutions to the
57:04
Speaker 1: questions at the heart of quantum mechanics. And I'm glad
57:07
Speaker 1: that there's still a lot of work to do because
57:09
Speaker 1: us quantum physicists will still have a job. So thanks
57:13
Speaker 1: Adam very much for joining us and for explaining these
57:15
Speaker 1: things so clearly. Before we go, do you want to
57:17
Speaker 1: tell our listeners about any upcoming projects you have or
57:20
Speaker 1: at places they can find you other than your excellent
57:22
Speaker 1: book What Is Real? First, I just want to encourage
57:25
Speaker 1: people go find my book if you like hearing about
57:30
Speaker 1: these things. I like talking about them, but I like
57:33
Speaker 1: writing about them even more. And there's you know, three
57:35
Speaker 1: hundred pages of it available wherever fine books are sold.
57:39
Speaker 1: If you want to find me on Twitter or really
57:41
Speaker 1: almost anywhere else, my Twitter name and online handle is
57:46
Speaker 1: freelance Astro, so i'm you know, on most social media
57:50
Speaker 1: under that name, and my website is freelance astro dot
57:54
Speaker 1: com and you can find links to my latest work there.
57:57
Speaker 1: And yeah, aside from that, I am working on another
58:00
Speaker 1: book about science and Silicon Valley, but it will not
58:04
Speaker 1: be out for another couple of years, still in the
58:07
Speaker 1: very early stages. But yeah, if this sort of thing
58:10
Speaker 1: is interesting to you, please have a look at my book.
58:13
Speaker 1: All right, Well, thanks again for coming on, and I
58:15
Speaker 1: hope your next book collapses into a very readable pile
58:18
Speaker 1: just like the first one. Thank you best of luck
58:20
Speaker 1: with that, and thanks again for coming on. Thanks thanks
58:23
Speaker 1: for having me. This was a lot of fun, and
58:24
Speaker 1: thanks to all your listeners for coming along on another
58:27
Speaker 1: ride of curiosity where we investigate what the universe actually
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Speaker 1: means and try to explain it all to you. Tune
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Speaker 1: in next time. Thanks for listening, and remember that Daniel
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Speaker 1: and Jorge explained the universe. Is a production of I
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Speaker 1: Heart Radio or more podcast for my Heart Radio, visit
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Speaker 1: the I Heart radio, app, Apple podcasts, or wherever you
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Speaker 1: listen to your favorite shows. No.