Latest / Daniel and Kelly’s Extraordinary Universe / How do we know quantum mechanics is really random?

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How do we know quantum mechanics is really random? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, do you have a pretty good routine? You
• 0:10
  Speaker 1: mean like a dance routine or like ten tight minutes
• 0:13
  Speaker 1: of stand up comedy? I mean like a schedule, Like
• 0:16
  Speaker 1: do you have the same day plant every day? Or
• 0:18
  Speaker 1: do you wing it every day? Yeah? I'm pretty into
• 0:20
  Speaker 1: my schedules. It's the only way I can really stay
• 0:23
  Speaker 1: on top of everything. Oh man, that is the opposite
• 0:25
  Speaker 1: of what I do. I like to wake up every
• 0:27
  Speaker 1: day not knowing what's gonna happen. Well, I like to
• 0:29
  Speaker 1: plan every day, but in the end, every day turns
• 0:32
  Speaker 1: out totally different because my well laid plans get blown
• 0:35
  Speaker 1: up by something that happens. See, so what's the point
• 0:38
  Speaker 1: of making plans. I like to live in a superposition
• 0:41
  Speaker 1: of organization and chaos. So you're both or neither depends
• 0:45
  Speaker 1: on which day you collapse my wave function and on
• 0:47
  Speaker 1: which day my schedule collapses. Sounds like you're the one
• 0:50
  Speaker 1: who collapses at the end of the day, though. That's
• 0:52
  Speaker 1: how you know him a true quantum mechanic. Hi am
• 1:09
  Speaker 1: or Him and Cartoonists, and the co author of Frequently
• 1:11
  Speaker 1: Asked Questions about the Universe. Hi, I'm Daniel. I'm a
• 1:15
  Speaker 1: particle physicist. And a professor at U C Irvine, And
• 1:18
  Speaker 1: I'm supposed to understand quantum mechanics. You're supposed to do that,
• 1:22
  Speaker 1: I guess because you're a physicist, right, that's right, it's
• 1:24
  Speaker 1: my official job. Particles are definitely quantum objects, and yet
• 1:28
  Speaker 1: it's still something that everybody in the field struggles with.
• 1:32
  Speaker 1: But didn't Richard Fine when famously said that nobody understands
• 1:35
  Speaker 1: quantum mechanics and if you do, then you don't really
• 1:38
  Speaker 1: understand it. And he was one of the top five
• 1:40
  Speaker 1: smartest physicists. So yeah, everybody below him on the ranking
• 1:43
  Speaker 1: can't understand it better than he does. With the top four, dude,
• 1:49
  Speaker 1: I think there are a few people out there that
• 1:50
  Speaker 1: might understand quantum mechanics better than Richard Fineman. Yeah. Do
• 1:53
  Speaker 1: you think it's maybe just a limitation of the human
• 1:56
  Speaker 1: brain or is the quantum mechanics use there not understandable.
• 1:59
  Speaker 1: I think we definitely can understand the mathematics of it,
• 2:02
  Speaker 1: but sometimes translating that mathematics into intuition is really complicated.
• 2:08
  Speaker 1: It's hard to understand things which are very unfamiliar to us.
• 2:13
  Speaker 1: Because in the end, physics is about trying to explain
• 2:16
  Speaker 1: the unfamiliar in terms of the familiar. But sometimes we
• 2:19
  Speaker 1: don't have a good intuitive analog to reach for. Sometimes
• 2:23
  Speaker 1: we find something which really is very different from anything
• 2:26
  Speaker 1: we've experienced before. That's why I don't believe in intuition,
• 2:29
  Speaker 1: either schedules and intuitions. I just leave him at home
• 2:33
  Speaker 1: every day. But anyways, welcome to our podcast Daniel and
• 2:36
  Speaker 1: Jorge Explained the Universe, a production of My Heart Radio
• 2:39
  Speaker 1: in which we attempt to apply our intuition to understanding
• 2:43
  Speaker 1: everything about the universe. For these little squishy brains that
• 2:46
  Speaker 1: evolved on this one rock around one planet. It's an
• 2:49
  Speaker 1: incredible task to try to understand everything that's out there,
• 2:53
  Speaker 1: including phenomena that our ancestors never saw, crazy black holes,
• 2:58
  Speaker 1: incredibly dense neutron stars, any buzzing particles. Is it even
• 3:01
  Speaker 1: possible to grop all of that, to import it somehow
• 3:04
  Speaker 1: into our minds so we can play with it, manipulated
• 3:07
  Speaker 1: and understand it. That's right, because it is a vast
• 3:10
  Speaker 1: and incredible universe full of amazing things that run counter
• 3:14
  Speaker 1: to our intuitions sometimes and that are very difficult to understand.
• 3:17
  Speaker 1: And so the only thing we can schedule on this
• 3:19
  Speaker 1: podcast is the idea that we're gonna talk about it
• 3:22
  Speaker 1: and try to understand it and ask questions about it.
• 3:25
  Speaker 1: Because on the podcast we try to do something which
• 3:27
  Speaker 1: may be impossible, which is to translate all of these ideas,
• 3:32
  Speaker 1: which in the end are expressed mathematically, into concepts that
• 3:36
  Speaker 1: we can deliver into your brain just with chit chat
• 3:39
  Speaker 1: and conversation. It's not always easy to know how to
• 3:42
  Speaker 1: transform these ideas from their essential mathematical principles into an
• 3:47
  Speaker 1: intuitive understanding, a stream of words which land in your
• 3:50
  Speaker 1: ear and build in your mind a little model that
• 3:53
  Speaker 1: makes you go, oh, I get it. But that's what
• 3:55
  Speaker 1: we're going for. Yeah, it's a pretty challenging problem if
• 3:58
  Speaker 1: you think about it, right, because we're trying to take
• 3:59
  Speaker 1: the higher universe, which is at least four dimensions, maybe more,
• 4:03
  Speaker 1: and we're trying to get it down to really one dimension, right,
• 4:06
  Speaker 1: because audio is just one one degree of freedom, right,
• 4:10
  Speaker 1: I suppose though, although in principle there are an infinite
• 4:13
  Speaker 1: number of frequencies along which to convey information. But yeah,
• 4:16
  Speaker 1: that's a good point. We're trying to like serialize the
• 4:19
  Speaker 1: universe into a stream of information which unpacks itself into
• 4:23
  Speaker 1: your mind to give you a mental model of the
• 4:25
  Speaker 1: universe that somehow works. I guess it would help if
• 4:28
  Speaker 1: maybe we're recording stereo, like I could be on people's
• 4:31
  Speaker 1: left ear and you could be on people's right ear,
• 4:33
  Speaker 1: and then we could maybe convey more information that way,
• 4:35
  Speaker 1: like a little angel and devils standing on your shoulders.
• 4:38
  Speaker 1: Or maybe we need to cartoonists and to physicists going simultaneously.
• 4:42
  Speaker 1: How does that help, and we're all talking at the
• 4:45
  Speaker 1: same time exactly, it would be two dimensional podcasting simultaneously.
• 4:50
  Speaker 1: I feel like you would still collapse right under the
• 4:52
  Speaker 1: amount of information. You're still collapsing the information down to
• 4:55
  Speaker 1: one dimensional audio. Yeah. I think probably it's best to
• 4:58
  Speaker 1: stick with one dimension and do best to project these
• 5:01
  Speaker 1: crazy ideas down into a one dimensional audio stream. It
• 5:05
  Speaker 1: is a complex universe, and sometimes it's a seemingly random universe.
• 5:09
  Speaker 1: It's a huge universe, and all kinds of things are
• 5:11
  Speaker 1: happening in it, and it's not quite clear where the
• 5:13
  Speaker 1: things are happening according to a plan or if they
• 5:16
  Speaker 1: are just randomly occurring in the universe. Yeah. One of
• 5:19
  Speaker 1: the most fundamental questions about the nature of the universe
• 5:23
  Speaker 1: is whether you can predict what's going to happen in
• 5:26
  Speaker 1: the future based on the past. Is the universe like
• 5:29
  Speaker 1: a big clock, where if you understood all of the
• 5:32
  Speaker 1: rules and had enough information, you could tell exactly what
• 5:35
  Speaker 1: was going to happen? Or fundamentally, is there something weird
• 5:38
  Speaker 1: going on at the heart of the machine that is
• 5:41
  Speaker 1: running the universe, something different from anything we have ever
• 5:44
  Speaker 1: experienced directly, something truly random? And well, I guess the
• 5:49
  Speaker 1: universe seems pretty random, right, Like if I flip a coin,
• 5:51
  Speaker 1: it's really hard to tell if it's going to be
• 5:53
  Speaker 1: heads or tails. Right, it does, And we often use
• 5:56
  Speaker 1: flipping a coin or rolling a dice as an approximation
• 5:59
  Speaker 1: for some random But those are not actually random processes.
• 6:03
  Speaker 1: Those are just very very complicated processes, things which are
• 6:07
  Speaker 1: hard to predict, but in principle possible to predict if
• 6:11
  Speaker 1: you had enough information and enough computer processing power. What
• 6:15
  Speaker 1: about whether we're going to explain something well or not?
• 6:17
  Speaker 1: Isn't that also kind of random? Hey, sometimes what we
• 6:21
  Speaker 1: talk about on the podcast feels a little random. You know,
• 6:23
  Speaker 1: I'll prepare a whole outline and we'll never get past
• 6:25
  Speaker 1: the first bit. Wait, are you saying I'm the random
• 6:27
  Speaker 1: filter here? I'm saying that Daniel Jorge interaction is a
• 6:31
  Speaker 1: little unpredictable. Sometimes what we end up talking about in
• 6:34
  Speaker 1: the best possible way. I love those episodes when you're
• 6:36
  Speaker 1: like a whole lot of second, slow down, what does
• 6:39
  Speaker 1: that actually mean? And then we spend forty five minutes
• 6:41
  Speaker 1: talking about the definition. We may we just need like
• 6:44
  Speaker 1: a parallel podcast or something. Maybe we need the multi
• 6:46
  Speaker 1: World's podcast where we take every possible branch and every
• 6:49
  Speaker 1: possible digression simultaneously. Well, this idea of whether the universe
• 6:53
  Speaker 1: is random or not with something that sort of came
• 6:55
  Speaker 1: up recently in the last hundred or two hundred years, right,
• 6:58
  Speaker 1: I mean, after Newton, people have figured that the universe
• 7:00
  Speaker 1: was pretty mechanical, pretty much like a machine where everything
• 7:04
  Speaker 1: followed F equals m A, and you could predict what
• 7:07
  Speaker 1: the path of a baseball or dropping a coin, what
• 7:10
  Speaker 1: was going to happen. You could predict that. But then
• 7:12
  Speaker 1: came quantum mechanics, who said, well, maybe things are not
• 7:15
  Speaker 1: that predictable. Yeah, And both of those really are revolutions
• 7:19
  Speaker 1: in our understanding of how the universe works. I mean,
• 7:22
  Speaker 1: before quantum mechanics, even just the idea that the universe
• 7:25
  Speaker 1: was deterministic, that it was like clockwork, that the whole
• 7:28
  Speaker 1: apparatus of reality was somehow following physical laws which you
• 7:33
  Speaker 1: could uncover and understand and used to predict the future.
• 7:36
  Speaker 1: This was a big idea, right. This flew in the
• 7:39
  Speaker 1: face of lots of people sort of spiritual sense that
• 7:42
  Speaker 1: there was somebody out there, unpredictable, in control of the universe.
• 7:46
  Speaker 1: To reduce it to a set of natural laws which
• 7:48
  Speaker 1: governed it, that was a big step forward. And so
• 7:51
  Speaker 1: then to pull the rug out from underneath that and say, actually, no,
• 7:55
  Speaker 1: at the heart of all of it, there might be
• 7:57
  Speaker 1: something unpredictable, some process which determines the outcome but isn't
• 8:02
  Speaker 1: determined by the past, is somehow fundamentally random. That was
• 8:06
  Speaker 1: a crazy, big new idea. Yeah, I guess it was
• 8:08
  Speaker 1: a double sweeping of the rug, right, because before Newton,
• 8:11
  Speaker 1: I guess, and before these fundamental laws of the universe,
• 8:15
  Speaker 1: people kind of thought the universe was random. Right. It
• 8:18
  Speaker 1: was random, or at least at the whim of some
• 8:20
  Speaker 1: gods or some deity that sort of randomly decided things.
• 8:23
  Speaker 1: And then we thought it was all ordered, and then
• 8:25
  Speaker 1: we realized, wait, it is sort of random. Yeah, exactly
• 8:28
  Speaker 1: though random in a very very different way. Right, quantum
• 8:31
  Speaker 1: mechanical randomness, as we'll dig into, it's not arbitrary or
• 8:34
  Speaker 1: at the whims of some god. Right, how do you know, Daniel?
• 8:37
  Speaker 1: You know, we might be at the whims of the
• 8:39
  Speaker 1: writers of the simulation. But whatever code they wrote is
• 8:42
  Speaker 1: what determines how the universe seems to work. What if
• 8:45
  Speaker 1: that code is at the whim of some other writers. Well,
• 8:47
  Speaker 1: maybe it is, but they don't seem to have been
• 8:49
  Speaker 1: changing the code recently. It seems like the code is
• 8:52
  Speaker 1: pretty stable over the fourteen billion years at the universe's history,
• 8:56
  Speaker 1: So there haven't been any updates. Well, it seems like
• 8:58
  Speaker 1: we've done a double take here on the random of
• 9:00
  Speaker 1: the universe. And the latest is that according to quantum mechanics,
• 9:03
  Speaker 1: things are random. But is that really true? And so
• 9:07
  Speaker 1: to be on the podcast we'll be tackling the question
• 9:14
  Speaker 1: how do we know quantum mechanics is really random as
• 9:18
  Speaker 1: opposed to just plane wacky or flaky or at the
• 9:22
  Speaker 1: whim of some quantum mechanical gods. Well, you know, quantum
• 9:26
  Speaker 1: mechanics has probabilities in it, and you can talk about
• 9:29
  Speaker 1: what probabilities means. Sometimes probability just means our lack of information.
• 9:34
  Speaker 1: Things we don't know, but in principle could predict. And
• 9:37
  Speaker 1: sometimes probability means fundamentally random, governed by our process outside
• 9:42
  Speaker 1: of our control. You're gonna bet on the outcome of
• 9:44
  Speaker 1: a Roulette wheel spin, for example, you might think that's random,
• 9:47
  Speaker 1: and in principle, if you knew how the ball bounced
• 9:50
  Speaker 1: and you spun it the same way twice, you should
• 9:52
  Speaker 1: get exactly the same answer, So it's not really random.
• 9:55
  Speaker 1: The probabilities, they're just come from your lack of understanding.
• 9:59
  Speaker 1: The question really is quantum mechanics the same way. Are
• 10:02
  Speaker 1: there details which actually do determine the outcome of these experiments,
• 10:06
  Speaker 1: which is not aware of them? Or is the universe
• 10:08
  Speaker 1: really actually at its core a random number generator? You're
• 10:12
  Speaker 1: asking is it really random or does it just seem random?
• 10:15
  Speaker 1: Because something can seem random, right like I can have
• 10:17
  Speaker 1: a computer code that spits out random numbers, which will
• 10:21
  Speaker 1: look pretty random to anyone, but actually there's sort of
• 10:24
  Speaker 1: card coded on the computer right exactly. Random number generators
• 10:27
  Speaker 1: follow a sequence where computers follow rules. They can't actually
• 10:31
  Speaker 1: generate random numbers. They can only have pseudo random number
• 10:35
  Speaker 1: sequences that sort of look random ish, right, And so
• 10:38
  Speaker 1: we're asking the same question about the entire universe. Is
• 10:41
  Speaker 1: the universe actually random at its core? Or does it
• 10:44
  Speaker 1: just seem random? And I guess we need to go
• 10:46
  Speaker 1: to quantum mechanics to find the answer. And we've been
• 10:48
  Speaker 1: talking around this topic and a few recent episodes and
• 10:52
  Speaker 1: listeners have responded and asked us to dig into the
• 10:55
  Speaker 1: heart of the matter. Yeah, and as usually, we were
• 10:57
  Speaker 1: wondering how many people out there I thought about whether
• 10:59
  Speaker 1: quantum mechanics really is random or not. So thanks to
• 11:02
  Speaker 1: everybody who answers these questions for us. It gives us
• 11:05
  Speaker 1: a great sense for what people know and what they're
• 11:07
  Speaker 1: wondering about, and what you might be thinking out there.
• 11:10
  Speaker 1: And if you would like to lend your voice for
• 11:12
  Speaker 1: a future episode, please don't be shy, all right to
• 11:14
  Speaker 1: us two questions at Daniel and Jorge dot com. So
• 11:17
  Speaker 1: think about it for a second. Do you think quantum
• 11:20
  Speaker 1: mechanics really is random? Here's what people had to say. Actually,
• 11:24
  Speaker 1: I then that's what Einstein thought. He thought there was
• 11:26
  Speaker 1: some hidden variables are controlled all the processes, and we
• 11:30
  Speaker 1: didn't know about that, and that's why we thought it
• 11:32
  Speaker 1: rest them, but I think there have been many experiments
• 11:36
  Speaker 1: where they redeed the same thing over in our work,
• 11:38
  Speaker 1: but in the same conditions, but there's a different result
• 11:42
  Speaker 1: each time, and that's what that's how we know that
• 11:45
  Speaker 1: it is truly random is such a question. We do
• 11:49
  Speaker 1: experiments thousands and thousands of times so that we can
• 11:53
  Speaker 1: get probability curves that show randomness. But he would only
• 11:57
  Speaker 1: know to a certain amount of certainty based on how
• 12:00
  Speaker 1: many experiments you do, and you can't do an infinite
• 12:03
  Speaker 1: number of experiments. So maybe we don't know that it's random,
• 12:06
  Speaker 1: but it's just random enough for purposes. Well, if it's
• 12:10
  Speaker 1: not random, I guess scientists would have figured out how
• 12:13
  Speaker 1: it's really working, and we would have really cool quantum
• 12:15
  Speaker 1: computers by now. We may not know it as an
• 12:19
  Speaker 1: absolute fact, but our models really suggest it is random
• 12:25
  Speaker 1: through many experiments and theories. That model of randomness holds
• 12:30
  Speaker 1: out really, really well. And that's about as good as
• 12:33
  Speaker 1: we can get if the model fits we accepted. I'm
• 12:37
  Speaker 1: a big fan of the idea that there's a hidden
• 12:39
  Speaker 1: variable that we don't understand, But at the same time
• 12:41
  Speaker 1: I realized that all the evidence says that it's really
• 12:44
  Speaker 1: really random. There's that whole thing where you send electrons
• 12:49
  Speaker 1: through a slit experiment, one electron at a time, and
• 12:53
  Speaker 1: they still interfere because, as I've heard you guys say,
• 12:57
  Speaker 1: it's a field, not a point. But I don't really
• 12:59
  Speaker 1: understand damn that um. As a computer programmer, I know
• 13:03
  Speaker 1: that quantum is the gold standard for truly random numbers,
• 13:08
  Speaker 1: but I guess I really don't understand that at all.
• 13:10
  Speaker 1: If you set up an experiment, well so they call
• 13:13
  Speaker 1: it an ensemble, if you set up multiple instances of
• 13:16
  Speaker 1: that experiment and everything is the same, and you produce
• 13:21
  Speaker 1: the electron, say you, I don't know if I were
• 13:23
  Speaker 1: it in a given direction, And then well, since you
• 13:26
  Speaker 1: know its position or the trajectory it's taking, if you
• 13:30
  Speaker 1: then try to measure its momentum while it's moving, even
• 13:34
  Speaker 1: though the experiments are set up in exactly the same way,
• 13:37
  Speaker 1: you get different answers for the momentum, and it doesn't
• 13:40
  Speaker 1: depend on how you've set up the experiment, because the
• 13:43
  Speaker 1: ensembles are exactly the same and there is no like
• 13:47
  Speaker 1: sort of external factor that you can change that somehow
• 13:50
  Speaker 1: correlates with the measured momentum and that's why we say
• 13:55
  Speaker 1: quantum mechanics is random. Well, I guess you could set
• 13:58
  Speaker 1: up the same experiment many many times and if you
• 14:01
  Speaker 1: get different outcomes um with the sort of random distribution,
• 14:06
  Speaker 1: you would know that it's very random. Otherwise I have
• 14:10
  Speaker 1: no idea. Interesting, I feel like some people don't want
• 14:14
  Speaker 1: to know, kind of. It is really hard to accept
• 14:16
  Speaker 1: this idea that the universe is so different from the
• 14:19
  Speaker 1: one you experience. So I think a lot of people resisted. Yeah,
• 14:23
  Speaker 1: and do you think quantum mechanics is random or maybe
• 14:27
  Speaker 1: it was just discovered randomly? It does seem like the
• 14:30
  Speaker 1: history of science is a little bit random, you know,
• 14:33
  Speaker 1: especially in the case of quantum mechanics, because we had
• 14:36
  Speaker 1: a few experiments that people had done and nobody really understood,
• 14:39
  Speaker 1: and then Einstein and Plank came along and sort of
• 14:41
  Speaker 1: put the pieces together years later. Makes you wonder if
• 14:44
  Speaker 1: it could have happened sooner, or maybe if it could
• 14:46
  Speaker 1: have happened decades later. It's fun to think about alternative
• 14:50
  Speaker 1: histories and what we might have discovered or not at all. Right,
• 14:53
  Speaker 1: Like what if Einstein had decided that he wanted to
• 14:55
  Speaker 1: play soccer for a living. Maybe we wouldn't be having
• 14:58
  Speaker 1: this conversation at all. Usually can't say that about historical figures,
• 15:02
  Speaker 1: but Eisen is one of those figures where if he
• 15:03
  Speaker 1: hadn't come along at the moment he did, things would
• 15:05
  Speaker 1: be super different. Things might be different. There are people
• 15:08
  Speaker 1: who say that a lot of the precursors to his
• 15:10
  Speaker 1: ideas came from other people, and so it was sort
• 15:13
  Speaker 1: of inevitable for them to click together. You know, a
• 15:15
  Speaker 1: lot of the math that underpins relativity was developed by
• 15:18
  Speaker 1: other folks. Rimon, for example, developed the rimanny and manifold,
• 15:22
  Speaker 1: which Einstein realized was a great way to describe the
• 15:25
  Speaker 1: curvature of space. Other folks were working on similar ideas
• 15:28
  Speaker 1: and may have brought it together even without Einstein, though
• 15:31
  Speaker 1: it could have taken a few years or decades longer. Well,
• 15:34
  Speaker 1: Eisen did what he did. And here we are talking
• 15:37
  Speaker 1: about quantum mechanics and randomness and whether or not it
• 15:40
  Speaker 1: is actually random at its core. And so I guess, Daniel,
• 15:43
  Speaker 1: let's start with the basics here. Uh, Well, first of all,
• 15:46
  Speaker 1: what do we mean by the word random? So by
• 15:48
  Speaker 1: random we really mean something which is not determined by
• 15:51
  Speaker 1: the experimental setup you'd build an experiment to shoot a ball,
• 15:55
  Speaker 1: or to flip a coin, or to roll a dice
• 15:57
  Speaker 1: or whatever. If it really is random, then you can
• 16:00
  Speaker 1: do the same experiment twice and get different outcomes, right
• 16:04
  Speaker 1: Like For example, a computer random number generator is not
• 16:07
  Speaker 1: really random because it uses a computer formula, right like that.
• 16:10
  Speaker 1: One works by taking a look at the current time,
• 16:13
  Speaker 1: grabbing a bunch of different variables that are changing all
• 16:16
  Speaker 1: the time, and then it processes those and then it
• 16:19
  Speaker 1: spits out what seems like a random number, but it's
• 16:21
  Speaker 1: not really random because venia what all the numbers that
• 16:24
  Speaker 1: went into the random number generator, you could generate the
• 16:26
  Speaker 1: exact same sequence, right yeah, and we do that all
• 16:28
  Speaker 1: the time. You have a random number seeds for example.
• 16:31
  Speaker 1: These are the parameters that control the random number generation.
• 16:34
  Speaker 1: And if you give a computer the same seeds, it
• 16:36
  Speaker 1: will generate the same sequence of random numbers every time.
• 16:39
  Speaker 1: So computer random number generators are deterministic. They can be
• 16:43
  Speaker 1: predicted from their inputs and reproduced. You run the same
• 16:47
  Speaker 1: random number generator with the same inputs get exactly the
• 16:50
  Speaker 1: same outputs, So that's deterministic. That's not random, But they
• 16:53
  Speaker 1: are chaotic. They are hard to predict. Their designed to
• 16:57
  Speaker 1: be complicated the way. For example, a die is designed
• 17:00
  Speaker 1: to be unpredictable, as all these sharp edges which bounce
• 17:04
  Speaker 1: unpredictably against surfaces and makes it really tricky to know
• 17:07
  Speaker 1: if a two or four is going to land upright,
• 17:10
  Speaker 1: It's very sensitive to exactly how you throw it, which
• 17:14
  Speaker 1: makes it hard to predict and appear random but not
• 17:17
  Speaker 1: actually be random, right, because a die with sharp edges
• 17:20
  Speaker 1: sort of like if you stand it on one corner,
• 17:23
  Speaker 1: I guess it might fall to the rider, It might
• 17:24
  Speaker 1: fault to the left, or it might bounce to the
• 17:26
  Speaker 1: right or left, just like a coin if you stand
• 17:28
  Speaker 1: it up on its side, it could maybe um flip
• 17:31
  Speaker 1: or land and either way. Yeah, imagine trying to learn,
• 17:34
  Speaker 1: for example, how to flip a coin so that it
• 17:36
  Speaker 1: always comes up heads. In principle, you could you could
• 17:40
  Speaker 1: learn how to spin it at just the right frequency
• 17:42
  Speaker 1: and toss it in the air just the right velocity,
• 17:44
  Speaker 1: so it has a certain number of flips before it
• 17:46
  Speaker 1: lands on your hand and it's always going to come
• 17:48
  Speaker 1: up heads. That would be a great skill, right, But
• 17:51
  Speaker 1: it's so hard to do because it's so sensitive to
• 17:54
  Speaker 1: all of those details. You'd have to be a master
• 17:56
  Speaker 1: coin flipper to be able to do that same with
• 17:59
  Speaker 1: a dive. Some many knew how to roll sevens every
• 18:01
  Speaker 1: single time. They would make zillions of dollars at casinos
• 18:05
  Speaker 1: every day. Right, The whole game of craps is built
• 18:07
  Speaker 1: on the assumption that nobody can really control what happens
• 18:10
  Speaker 1: to the diet even though they give them to you,
• 18:12
  Speaker 1: they let you roll them, right, And so the whole
• 18:14
  Speaker 1: assumption there is that you can't reproduce the same toss
• 18:18
  Speaker 1: over and over again. So I don't let you into
• 18:20
  Speaker 1: casinos anymore. It may they stop you at the door first,
• 18:23
  Speaker 1: they're like, are you Antonian physicists or a quantum mechanicis
• 18:26
  Speaker 1: may say quantum physicists. They'll let you in. They'll let
• 18:29
  Speaker 1: you in exactly because you've given up. You've allowed the
• 18:32
  Speaker 1: randomness to enter your life, all right. So that's the
• 18:34
  Speaker 1: kind of the difference between random and not random. Random
• 18:37
  Speaker 1: you can't predict given the initial conditions, and not random
• 18:41
  Speaker 1: you can't predict it even if it is really hard.
• 18:43
  Speaker 1: If you can't predict it, then it's possible that you
• 18:45
  Speaker 1: can't predict it, and so it's not random, and everything
• 18:48
  Speaker 1: in your everyday experience is not random. Whether you hit
• 18:52
  Speaker 1: a green light, or whether you trip on the steps,
• 18:55
  Speaker 1: or whether that bird poops on your shoulder or whatever.
• 18:58
  Speaker 1: These things can seem random, whether really just complex. They're
• 19:01
  Speaker 1: actually just chaotic. Even the weather, right, the weather is
• 19:04
  Speaker 1: not fundamentally quantum mechanically random. It's just difficult to predict
• 19:08
  Speaker 1: because it's so complicated. So in our experience, everything that
• 19:11
  Speaker 1: seems random is actually just deterministic and complicated, or at
• 19:15
  Speaker 1: least I think you mean, it's mostly deterministic and chaotic, right,
• 19:19
  Speaker 1: And it's it's just saying that Newtonian dynamics dominate our
• 19:22
  Speaker 1: everyday lives. But there is still a little bit of
• 19:24
  Speaker 1: a quantum at it's hard right at the microscopic level,
• 19:28
  Speaker 1: right like as the coin hits the table, there is
• 19:31
  Speaker 1: some sort of maybe quantum interaction there. They could determine
• 19:34
  Speaker 1: whether it flips to the right or to the left. Well,
• 19:36
  Speaker 1: we do know that microscopically everything we experience is made
• 19:39
  Speaker 1: of quantum objects, and so if quantum mechanics is random,
• 19:42
  Speaker 1: then you know, you might ask why aren't things made
• 19:45
  Speaker 1: of quantum objects also random. The answer is that that
• 19:48
  Speaker 1: randomness mostly averages out, and so even electron is going
• 19:52
  Speaker 1: to like quantum mechanically fluctuate to the left somewhere than
• 19:54
  Speaker 1: an electron quantum mechanically fluctuating to the right. So when
• 19:57
  Speaker 1: you have in big enough groups of quantum objects, these
• 20:00
  Speaker 1: things tend to wash out. It's very difficult to actually
• 20:04
  Speaker 1: pinpoint quantum mechanical impacts on everyday macroscopic classical objects. Otherwise
• 20:11
  Speaker 1: we would have discovered quantum mechanics sooner. You know, it
• 20:13
  Speaker 1: would have been more obvious if there were quantum mechanical
• 20:15
  Speaker 1: impacts on our everyday life. Right, But you just found
• 20:17
  Speaker 1: it a little bit absolute in But then you said
• 20:19
  Speaker 1: you mostly wash this out, right, not completely right. There
• 20:23
  Speaker 1: is still a little bit of tiny, little bit of
• 20:25
  Speaker 1: maybe quantum randomness in our everyday lives too. Yeah, there's
• 20:28
  Speaker 1: a little bit there. Right In the end, these things
• 20:30
  Speaker 1: are averages, so there are probabilities you could in principle
• 20:34
  Speaker 1: disappear and quantum tunnel to the other side of your house. Right,
• 20:37
  Speaker 1: It's not impossible. That's why you should never say things absolutely. Also,
• 20:41
  Speaker 1: this is not something that we a hundred understand, right,
• 20:45
  Speaker 1: How do quantum mechanical objects when they're all tiny, the
• 20:48
  Speaker 1: huge frothing mass of them, how did they come together
• 20:50
  Speaker 1: to make the classical picture that we understand that boundary
• 20:54
  Speaker 1: is kind of fuzzy and not super well understood. So
• 20:56
  Speaker 1: there might be places where quantum effects really do have
• 20:59
  Speaker 1: so of like cascading consequences which lead to macroscopic effects,
• 21:04
  Speaker 1: like the heart of the human brain. Are there quantum
• 21:07
  Speaker 1: effects inside your neurons which change the decisions that you make?
• 21:11
  Speaker 1: We don't really understand that in enough detail to be
• 21:13
  Speaker 1: absolutist about it, right, But I think what you're saying
• 21:15
  Speaker 1: that then, is that our everyday lives that things are
• 21:20
  Speaker 1: mostly deterministic because all the quantum mechanics sort of mostly
• 21:24
  Speaker 1: washes off. But although there's still a little bit of
• 21:27
  Speaker 1: room there for things to be random, but they're not
• 21:29
  Speaker 1: as random as they are at the microscopic level. If
• 21:32
  Speaker 1: you're looking at like one electron that has a as
• 21:35
  Speaker 1: a huge random as factor whether it goes right or
• 21:37
  Speaker 1: left exactly, we think that at the microscopic level, quantum
• 21:40
  Speaker 1: mechanics might be really truly random. Although there are a
• 21:43
  Speaker 1: lot of different interpretations for these weird experiments that we're
• 21:47
  Speaker 1: going to dig into, these bells experiment with entangled particles, right, So,
• 21:51
  Speaker 1: even at the macroscopic level, you can ask the question
• 21:54
  Speaker 1: if an electron is actually actually random or whether it
• 21:58
  Speaker 1: just seems random. Right, that's the question we're asking today.
• 22:01
  Speaker 1: That's the one at the heart of the matter. If
• 22:03
  Speaker 1: the tiniest little bits in the universe can be predicted
• 22:06
  Speaker 1: if you have not all the information, or if the
• 22:09
  Speaker 1: universe is like rolling a truly random die every time
• 22:13
  Speaker 1: an electron has to decide where it's going to go.
• 22:15
  Speaker 1: All right, well, let's dig into whether or not the
• 22:18
  Speaker 1: universe is random at the microscopic level or not, and
• 22:22
  Speaker 1: how we could maybe tell the difference using a famous experiment. First,
• 22:26
  Speaker 1: let's take a quick break. All right, we're asking the
• 22:40
  Speaker 1: question whether the universe really is random, and whether or
• 22:44
  Speaker 1: not Daniel can plan his day with any certainty at all,
• 22:47
  Speaker 1: or is it all a futile exercise. Just give up
• 22:51
  Speaker 1: like I do. Just embrace the chaos. Yeah, embrace the randomness.
• 22:56
  Speaker 1: It's different than kids. Well you should e'mbrace both. I
• 22:58
  Speaker 1: guess just let whatever have happened. Yeah, So that there's
• 23:02
  Speaker 1: a famous way to tell whether or not electrons and
• 23:05
  Speaker 1: things at the microscopic level are truly random, or whether
• 23:08
  Speaker 1: or not they just seem random. Right, And this is
• 23:11
  Speaker 1: the idea of Bell's experiment, And it goes actually back
• 23:14
  Speaker 1: to Einstein again. Einstein, though he had some of the
• 23:18
  Speaker 1: foundational ideas that led us to develop quantum mechanics, he
• 23:22
  Speaker 1: was fundamentally uncomfortable with the idea that the universe was
• 23:25
  Speaker 1: truly random. He thought that perhaps there were just details
• 23:29
  Speaker 1: there that we were not understanding, that when things seemed random,
• 23:32
  Speaker 1: it was just because there was missing information that we
• 23:35
  Speaker 1: didn't have that was actually controlling the outcome of the experiments.
• 23:39
  Speaker 1: So he and a couple of buddies of his came
• 23:41
  Speaker 1: up with a thought experiment because he was like a
• 23:43
  Speaker 1: champion of thought experiments, to demonstrate how weird it would
• 23:46
  Speaker 1: be if quantum mechanics was really random. Yeah, And I
• 23:50
  Speaker 1: think it all sort of goes back to this picture
• 23:52
  Speaker 1: of one electron, right, Like, if you shoot an electron
• 23:54
  Speaker 1: towards a magnet, it has kind of a random equal
• 23:57
  Speaker 1: probability of serving to the right, as does swerving to
• 24:01
  Speaker 1: the left. Right. That's kind of the fundamental random experiment
• 24:04
  Speaker 1: that people picture when they picture quantum mechanics. Right, It's
• 24:07
  Speaker 1: like it has a half a probablegy to go right.
• 24:09
  Speaker 1: Have a probability to go left, and it's totally randomly.
• 24:13
  Speaker 1: There's no way you could maybe predict whether it's going
• 24:15
  Speaker 1: to go right or left. Yeah, And just to clarify,
• 24:17
  Speaker 1: electrons always go the same direction when they hit like
• 24:20
  Speaker 1: a big macroscopic magnet, because magnetic fields turn electrons in
• 24:24
  Speaker 1: a way that we understand it. But electrons also have
• 24:26
  Speaker 1: another quantum mechanical component, the spin, which affects their little
• 24:30
  Speaker 1: magnetic field, and so that can affect whether they go
• 24:33
  Speaker 1: like left or right when they hit like a weird
• 24:35
  Speaker 1: magnetic field. And so you're right. Quantum mechanics says there's
• 24:38
  Speaker 1: an equal probability for it to be spin up or
• 24:40
  Speaker 1: spin down, which means that it goes left or it
• 24:42
  Speaker 1: goes right, and it says that that's not actually determined
• 24:45
  Speaker 1: until somebody measures it, that both possibilities are live simultaneously
• 24:50
  Speaker 1: until you actually measure it, whereas the other view says, no,
• 24:54
  Speaker 1: no, no no, there's some detail that determines whether it's spin
• 24:57
  Speaker 1: up or spin down, whether it's going to go left
• 24:59
  Speaker 1: or right, and it those left or it goes right
• 25:01
  Speaker 1: the whole time until you look at it. Right. That's
• 25:03
  Speaker 1: the idea of the hidden variable right, Like, maybe the
• 25:05
  Speaker 1: electron at its core knows whether it's spinning up or
• 25:08
  Speaker 1: spinning down. It's just that we don't know. And so
• 25:11
  Speaker 1: that's why you call it a hidden variable. And so
• 25:13
  Speaker 1: the question is, does the electron actually know if it's
• 25:15
  Speaker 1: spinning up or down? Or does even the electron not
• 25:18
  Speaker 1: know what's going to happen until somebody comes in and
• 25:21
  Speaker 1: ask it or puts it. Yeah, and you might imagine
• 25:23
  Speaker 1: it's impossible to tell the difference, like how can you
• 25:25
  Speaker 1: know if it's actually determined but you're just not aware
• 25:28
  Speaker 1: of it, or if it's chosen at the time you
• 25:30
  Speaker 1: poke it, because before that nobody's poking it, So how
• 25:32
  Speaker 1: can you tell? So Einstein's big idea was to add
• 25:35
  Speaker 1: another electron, which said, well, what if you have two
• 25:38
  Speaker 1: of these things and you know something about the pair
• 25:41
  Speaker 1: of them. You know that they have to have opposite spins,
• 25:44
  Speaker 1: maybe they come from the same source, so they're constrained somehow.
• 25:47
  Speaker 1: There's a connection between them, so that if one of
• 25:49
  Speaker 1: them is spin up, the other one has to be
• 25:51
  Speaker 1: spinned down. This is the idea of quantum entanglement. And
• 25:54
  Speaker 1: it's not so hard to I understand the general idea
• 25:57
  Speaker 1: For example, you have two bags, one with the red ball,
• 26:00
  Speaker 1: one with a blue ball in it, and you and
• 26:02
  Speaker 1: your friend each take one bag, but you don't know
• 26:04
  Speaker 1: which is which, and you travel like ten miles apart.
• 26:07
  Speaker 1: Now you look at the bag and you say, oh,
• 26:08
  Speaker 1: I have the blue ball. That means my friend has
• 26:11
  Speaker 1: the red ball. Or if your friend has the blue ball,
• 26:13
  Speaker 1: that means you have the red ball. Because you know
• 26:15
  Speaker 1: there's only one blue ball, then you know something about
• 26:18
  Speaker 1: what's happening with the other particle. That's the idea of
• 26:20
  Speaker 1: entanglement connecting these two electrons together, right, Because when you
• 26:24
  Speaker 1: separate the balls in the bags, you take one this
• 26:26
  Speaker 1: way and take the other one that way. They have
• 26:28
  Speaker 1: something that ties their history together, right, some sort of
• 26:32
  Speaker 1: constraint that says if one is blue, the olne spread
• 26:34
  Speaker 1: and if this one is red deal and has to
• 26:36
  Speaker 1: be blue. Right, it's something that ties their histories together exactly.
• 26:39
  Speaker 1: In Einstein's point was if things really aren't determined until
• 26:43
  Speaker 1: you look, that means something really weird. That means that
• 26:46
  Speaker 1: the electrons, which are now five miles apart from each other,
• 26:49
  Speaker 1: if you measure one of them and it determines to
• 26:51
  Speaker 1: be spin up if you're saying that they really weren't
• 26:54
  Speaker 1: determined until you're measured, that means that the other electron,
• 26:57
  Speaker 1: now ten miles apart, instantaneously is from undetermined to spin
• 27:01
  Speaker 1: down without anybody even looking at it. So this was
• 27:05
  Speaker 1: Einstein's complaint that if quantum mechanics really was random, then
• 27:09
  Speaker 1: it was somehow nonlocal. It is somehow instantaneous collapse of
• 27:13
  Speaker 1: the distant electron the other one the way you weren't
• 27:16
  Speaker 1: even looking at. Right. Yeah, you mentioned the idea of local,
• 27:19
  Speaker 1: because that's kind of a big part of it, right,
• 27:21
  Speaker 1: Like if I take one of the balls and I
• 27:23
  Speaker 1: go to New Mexico and you stay in Los Angeles,
• 27:26
  Speaker 1: and I opened my ball and I know and I
• 27:27
  Speaker 1: see that it's red, then I know that your ball
• 27:30
  Speaker 1: is blue. But you don't know that I opened my
• 27:32
  Speaker 1: bag and found a red ball right to you. It's
• 27:34
  Speaker 1: still uh, totally unpredictable what's in your bag. Unless I
• 27:39
  Speaker 1: go and I call you or I send you an
• 27:41
  Speaker 1: email saying, hey, my ball was a certain color, then
• 27:44
  Speaker 1: you would know what color your ball is exactly. But
• 27:47
  Speaker 1: according to quantum mechanics, it is at that point determined
• 27:50
  Speaker 1: once you've measured yours to be red, then mine is blue.
• 27:53
  Speaker 1: So Einstein's big point here was to say, this is ridiculous,
• 27:56
  Speaker 1: This idea that quantum mechanics is random, that there aren't
• 27:59
  Speaker 1: details determining which one is spin up and which one
• 28:02
  Speaker 1: has spin down, requires them to somehow conspire across great
• 28:05
  Speaker 1: distances faster than the speed of light. So we said,
• 28:08
  Speaker 1: obviously this can't be true, but it turned up that
• 28:12
  Speaker 1: it is true. I feel like you were leading me
• 28:14
  Speaker 1: into that, but I don't really know. That's what Einstein
• 28:17
  Speaker 1: I wanted everybody to think. But again you can ask
• 28:19
  Speaker 1: the question, how can you know? Maybe quantum mechanics really
• 28:22
  Speaker 1: is just weird that way and it doesn't sit well
• 28:25
  Speaker 1: in Einstein's brain, doesn't mean it isn't reality. Is there
• 28:28
  Speaker 1: some way we can enhance this experiment so we can
• 28:31
  Speaker 1: tell the difference. We can tell if it really is
• 28:33
  Speaker 1: random and decided at the last minute before you measure it,
• 28:36
  Speaker 1: or if it's all somehow decided in advance using information.
• 28:40
  Speaker 1: We just don't have access to some sort of weird
• 28:42
  Speaker 1: hidden details about these particles that determine which one is
• 28:46
  Speaker 1: spin up or spin down. So that was the great challenge.
• 28:48
  Speaker 1: Is there a way to come up with an experiment
• 28:50
  Speaker 1: to tell the difference. Right, you're saying that as soon
• 28:53
  Speaker 1: as I opened my bag in New Mexico and I
• 28:55
  Speaker 1: see that my ball is read, suddenly your ball goes
• 28:59
  Speaker 1: from being a quant mechanical object that could be anything
• 29:02
  Speaker 1: to a non quantum mechanical object which can only be blue.
• 29:06
  Speaker 1: That's the weird thing that kind of freak instain out.
• 29:09
  Speaker 1: As soon as I opened my bag in New Mexico,
• 29:11
  Speaker 1: So your bag in Los Angeles starts being quantum mechanical instantaneously. Yeah.
• 29:16
  Speaker 1: So people were chewing on this problem, and one other
• 29:18
  Speaker 1: very smart guy who might understand quantum mechanics better than
• 29:22
  Speaker 1: Richard Feynman, he came up with a really ingenious idea
• 29:25
  Speaker 1: for how to tell the difference, for how to know
• 29:28
  Speaker 1: if quantum mechanics was doing this at the last minute,
• 29:31
  Speaker 1: if it was really was left undecided and truly randomly
• 29:34
  Speaker 1: collapsed at the last moment, or if he was determined
• 29:37
  Speaker 1: by some information we just didn't have access to. He
• 29:40
  Speaker 1: actually came up with a way to test that, to
• 29:42
  Speaker 1: build an experiment which would tell you what the universe
• 29:45
  Speaker 1: was doing. Well, what's the alternative? Then, in the case
• 29:48
  Speaker 1: of the two balls, the one in New Mexico and
• 29:50
  Speaker 1: the one in Los Angeles. Like, if Einstein is right,
• 29:52
  Speaker 1: then what actually happened to the balls? You actually knew
• 29:54
  Speaker 1: which one was red and blue the whole time. Yeah,
• 29:57
  Speaker 1: if eine Stein is right, then one was red and
• 29:59
  Speaker 1: one was blue with whole time. We don't have access
• 30:01
  Speaker 1: to the information. We didn't know that until we opened
• 30:04
  Speaker 1: it up. But it actually was read the whole time.
• 30:07
  Speaker 1: And if quantum mechanics is right, then it wasn't read.
• 30:10
  Speaker 1: It was a possibility of being read and a possibility
• 30:13
  Speaker 1: being blue. Right in the quantum mechanical view, both were
• 30:16
  Speaker 1: possibilities until I open minding in Mexico, and in which
• 30:19
  Speaker 1: case both became non possibilities exactly. And if Einstein was right,
• 30:23
  Speaker 1: you get what he calls realism. He says, the universe
• 30:26
  Speaker 1: is a certain way, even if you aren't looking at it.
• 30:29
  Speaker 1: There is a fact of the matter, and the ball
• 30:31
  Speaker 1: is blue or is read regardless of whether we know
• 30:34
  Speaker 1: it or not. That's what Einstein believed. But the typical
• 30:37
  Speaker 1: description of quantum mechanics says that it really is undetermined
• 30:40
  Speaker 1: and there's a random process that chooses it at the
• 30:44
  Speaker 1: last moment, just before you measure it, or as you
• 30:46
  Speaker 1: measure it, or the act of you measuring it collapses
• 30:49
  Speaker 1: it and forces the universe to access its true random
• 30:52
  Speaker 1: number generator. And I think one the Einstein's point is
• 30:55
  Speaker 1: that it's hard to tell the difference between those two
• 30:57
  Speaker 1: scenarios whether they were red and blue the whole time
• 31:00
  Speaker 1: time or whether they decided only when I opened mining
• 31:02
  Speaker 1: New Mexico, because there's no way to tell a difference,
• 31:04
  Speaker 1: which is that simple experiment, So you need to sort
• 31:06
  Speaker 1: of do an experiment two point oh that maybe messages
• 31:10
  Speaker 1: with that to see if actually things were random or not. Yeah, exactly,
• 31:14
  Speaker 1: And that was Bell's big idea. Bell came up with
• 31:16
  Speaker 1: a way to test this, and at first, blush, it
• 31:19
  Speaker 1: feels impossible, right, like how could you tell whether it's
• 31:23
  Speaker 1: undetermined when you don't look without looking, and by looking
• 31:26
  Speaker 1: you collapse it. So it seems sort of like a paradox,
• 31:28
  Speaker 1: like impossible to probe. Bell's big idea was taking advantage
• 31:32
  Speaker 1: of another aspect of quantum mechanics that didn't exist in
• 31:35
  Speaker 1: the hidden variables picture, and that's the fact that it
• 31:37
  Speaker 1: matters along which direction you're measuring the spin. So we're
• 31:40
  Speaker 1: talking about a quantum mechanical property of these electrons. It's
• 31:43
  Speaker 1: called spin, and they can be spin up or spin down.
• 31:46
  Speaker 1: But it can be spin up or spin down along
• 31:48
  Speaker 1: with some direction. Right, if you have like an axis
• 31:51
  Speaker 1: you're defining as X, you can say, is my electron
• 31:54
  Speaker 1: spin up or spin down along this axis? You can
• 31:56
  Speaker 1: also measured along Y or measured along z. Asid anything
• 32:00
  Speaker 1: quantum mechanically is that these things are connected. Like in
• 32:04
  Speaker 1: quantum mechanics, you can't know the spin in X and
• 32:07
  Speaker 1: in Y and in Z simultaneously. They're all weirdly entangled
• 32:11
  Speaker 1: by the Heisenberg uncertainty principle, the same way that like
• 32:14
  Speaker 1: you can't know the position and momentum of an object
• 32:17
  Speaker 1: at the same time those two pieces of information are
• 32:20
  Speaker 1: really connected together. So Bell came up with this experiment
• 32:23
  Speaker 1: where people in different locations might use different axes, they
• 32:27
  Speaker 1: might be measuring the spin in different directions, and quantum
• 32:30
  Speaker 1: mechanics would make a different prediction for the correlations between
• 32:33
  Speaker 1: those measurements than the hidden variable theory would. Yeah, let
• 32:36
  Speaker 1: me just let me go back the little bit on
• 32:38
  Speaker 1: this idea of spin, because this is when I think
• 32:40
  Speaker 1: it's going to be hard to explain over audio. I
• 32:42
  Speaker 1: think maybe a way to picture it is that you know,
• 32:44
  Speaker 1: instead of a red and a blue ball that we
• 32:46
  Speaker 1: put in our and those hidden bags, instead of drawing
• 32:49
  Speaker 1: arrow on our balls, like an arrow pointing up or
• 32:51
  Speaker 1: an arrow pointing down right, or I guess the arrow
• 32:55
  Speaker 1: could be pointing in any direction. Really in the in
• 32:57
  Speaker 1: the ball right, it could be pointing up, down, left, right, diagonal,
• 33:01
  Speaker 1: diagonal down, diagonal up, So it can be pointing in
• 33:03
  Speaker 1: any of those directions. But one thing about quantum mechanics
• 33:08
  Speaker 1: is that you can't ask whether it's pointing up and
• 33:09
  Speaker 1: down and left and right at the same time. That's
• 33:12
  Speaker 1: a weird thing about quantum mechanics, right. The weird thing
• 33:14
  Speaker 1: about quantum mechanics there is that it matters the order
• 33:16
  Speaker 1: in which you do it. Just like if you measure position,
• 33:19
  Speaker 1: you get a number, and then you measure momentum, then
• 33:22
  Speaker 1: your position measurement is no longer valid. Once you measure momentum,
• 33:25
  Speaker 1: you scramble the position. In the same way here, if
• 33:28
  Speaker 1: you measure the spin along one axis, you look to
• 33:30
  Speaker 1: see if the arrow is pointing up or down according
• 33:33
  Speaker 1: to your imaginary Z axis, and then you do it
• 33:36
  Speaker 1: along y or X. It scrambles the first measurement, so
• 33:39
  Speaker 1: you can't know the spin in all three directions simultaneously
• 33:43
  Speaker 1: for a quantum object the way you can for a ball.
• 33:45
  Speaker 1: Right ball, you can just look at and say, oh,
• 33:47
  Speaker 1: it's kind of up in Z and kind of down
• 33:49
  Speaker 1: and X and kind of whatever. You can just know
• 33:51
  Speaker 1: it's determined as possible. These are sort of like orthogonal
• 33:54
  Speaker 1: directions in the hidden variable theory quantum mechanics. They're weirdly
• 33:58
  Speaker 1: connected to each other. Is like let information available. There's
• 34:01
  Speaker 1: like shared information between x, Y and Z and the
• 34:04
  Speaker 1: spin measurements. Right, Like, let's maybe explain it. Like let's
• 34:07
  Speaker 1: say I point an arrow on the face of my ball,
• 34:09
  Speaker 1: and it can be up, down, left, right, the daggon
• 34:12
  Speaker 1: or whatever. Maybe you can picture it as like the
• 34:14
  Speaker 1: hour hand in a clock, So it can be pointing
• 34:18
  Speaker 1: up at twelve o'clock or down at six o'clock, or
• 34:20
  Speaker 1: right at three o'clock or left at nine o'clock, or
• 34:22
  Speaker 1: it could put pointing at one o'clock, four o'clock, eight o'clock,
• 34:25
  Speaker 1: ten o'clock. And you can only sort of ask one
• 34:27
  Speaker 1: thing at a time, whether it's generally pointing up or
• 34:31
  Speaker 1: down or left or right, not both at the same time.
• 34:34
  Speaker 1: So like, if it's actually pointing at two o'clock, I
• 34:37
  Speaker 1: can as well as it pointing up or down, and
• 34:38
  Speaker 1: you would say, well, it's at two o'clock, so it's
• 34:40
  Speaker 1: pointing up. Where I can ask is the pointing left
• 34:43
  Speaker 1: or right? And you say, well, it's pointing right because
• 34:45
  Speaker 1: it's pointing at two o'clock. But I can't ask both
• 34:48
  Speaker 1: of them at the same time to really figure out
• 34:50
  Speaker 1: what the hour was like. Once you ask whether it's
• 34:52
  Speaker 1: up or down, the whole thing collapses and that's it.
• 34:55
  Speaker 1: I can't know anything else about it. Yeah, once you
• 34:57
  Speaker 1: make a measurement, all your previous measurements are now relevant,
• 35:00
  Speaker 1: so you can't like zero in on the exact details. Right,
• 35:04
  Speaker 1: Like you would maybe said your hour clock at a
• 35:06
  Speaker 1: point in your clock right, and then I would ask
• 35:08
  Speaker 1: you is it up or down? And you would see up.
• 35:12
  Speaker 1: And now I can't ask you whether it was right
• 35:14
  Speaker 1: or left because I would tell me exactly where the
• 35:16
  Speaker 1: hand was right, remember that there might not be any
• 35:20
  Speaker 1: where it really was. In the theory of local realism,
• 35:24
  Speaker 1: there is a true position, a total reality, and the
• 35:26
  Speaker 1: clock really is pointed in just one direction, but in
• 35:29
  Speaker 1: the quantum theory without hidden variables, measuring it along one
• 35:34
  Speaker 1: direction scrambles it any other directions, so they're not just
• 35:37
  Speaker 1: not known, they are not determined. And that's really the
• 35:41
  Speaker 1: issue we want to address. The question we want to answer,
• 35:43
  Speaker 1: can we tell if those measurements are undetermined or unknown?
• 35:47
  Speaker 1: And the fact that in quantum mechanics you can't know
• 35:50
  Speaker 1: more than one direction of spin at once is the
• 35:53
  Speaker 1: crucial concept in Bell's theory because it changes how measurements
• 35:58
  Speaker 1: in different directions are core lated measurements along different axes,
• 36:02
  Speaker 1: And this is the exact idea at the heart of
• 36:04
  Speaker 1: Bell's experiment. Bell says, let's take our balls and let's
• 36:08
  Speaker 1: pick three directions in advance. And the people who are
• 36:10
  Speaker 1: doing these measurements, they're gonna pick one of these three
• 36:13
  Speaker 1: directions to make their measurement. As you say, it's like
• 36:16
  Speaker 1: picking two o'clock or nine o'clock or six o'clock on
• 36:18
  Speaker 1: the clock right to make your measurement, to ask whether
• 36:20
  Speaker 1: the arrow is up or down. They're going to pick
• 36:22
  Speaker 1: one of those. And if things really are determined, then
• 36:25
  Speaker 1: the direction they pick doesn't matter, doesn't change the state
• 36:28
  Speaker 1: of the ball at all, it's a very simple relationship
• 36:31
  Speaker 1: between whether or not they're they're likely to see the
• 36:34
  Speaker 1: same answer. You know, if they both pick twelve o'clock,
• 36:36
  Speaker 1: they're going to see the same answer. One of them
• 36:37
  Speaker 1: picks twelve and the other one picks two o'clock, they're
• 36:39
  Speaker 1: almost always going to see the same answer. This kind
• 36:42
  Speaker 1: of stuff. So you can say, if things aren't messed
• 36:45
  Speaker 1: up in that way, measuring in one direction doesn't measure
• 36:48
  Speaker 1: and the other directions, then we understand exactly how often
• 36:51
  Speaker 1: people should get the same answer. But in the quantum
• 36:53
  Speaker 1: mechanics version, if these things are scrambled, if measuring one
• 36:56
  Speaker 1: direction messes up, the measurements in the other directions, get
• 37:00
  Speaker 1: a different relationship with people with the two balls or
• 37:02
  Speaker 1: the two electrons get the same answer sort of more
• 37:04
  Speaker 1: often than you would expect. If things really are determined
• 37:08
  Speaker 1: by hidden variables, these correlations between the different directions quantum
• 37:12
  Speaker 1: mechanically come into play and sort of mess up the
• 37:14
  Speaker 1: otherwise perfect picture, right. I think you're saying that, Like
• 37:17
  Speaker 1: in our original experiment where we have the tool balls
• 37:20
  Speaker 1: in Los Angeles, and I took one of the balls
• 37:22
  Speaker 1: to New Mexico. Now we're going to introduce something new
• 37:24
  Speaker 1: to eights experiment in order to test this quantum randomness,
• 37:28
  Speaker 1: and that is to put people in between Los Angeles
• 37:32
  Speaker 1: and New Mexico and have them asked questions about the
• 37:36
  Speaker 1: ball on the way as it's traveling from Los Angeles
• 37:39
  Speaker 1: to New Mexico, right, and somehow that's going to tell
• 37:41
  Speaker 1: you whether or not things are actually random or not.
• 37:44
  Speaker 1: You measure each ball one time, because once you've measured it,
• 37:48
  Speaker 1: there's no more entanglement with the other ball going in
• 37:50
  Speaker 1: the other direction, and you don't necessarily measure each ball
• 37:54
  Speaker 1: along the same spin axis. Each ball gets measured along
• 37:57
  Speaker 1: one of three directions. You can make the three directions
• 38:00
  Speaker 1: like a Mercedes symbol if you want. Both balls might
• 38:02
  Speaker 1: get measured along the same direction, which case one is
• 38:05
  Speaker 1: up and one and down. That happens a third at
• 38:07
  Speaker 1: the time, but two thirds of the time you don't
• 38:10
  Speaker 1: choose the same axes and bells and equalities all about
• 38:13
  Speaker 1: how often both balls that measured spin up or spin
• 38:16
  Speaker 1: down along the random access that's chosen for a hidden
• 38:20
  Speaker 1: variable model, you get the same answer from both balls
• 38:23
  Speaker 1: less than two thirds of the time, And so when
• 38:25
  Speaker 1: you compare the answers for one ball and the other ball.
• 38:28
  Speaker 1: It just depends on like what angle the ball actually
• 38:30
  Speaker 1: was at. Right, Maybe let's step people through that example
• 38:33
  Speaker 1: in our scenario here of l a Vers is New Mexico.
• 38:36
  Speaker 1: So like, let's say that things are not quantum mechanical,
• 38:39
  Speaker 1: and you actually drew on your ball, you know, an
• 38:42
  Speaker 1: arrow pointing at one o'clock right now. The first person's
• 38:45
  Speaker 1: going to ask is it generally pointing in the twelve
• 38:47
  Speaker 1: o'clock direction, and you would say yes, And when it
• 38:50
  Speaker 1: arrives in New Mexico, it's still going to be pointing
• 38:53
  Speaker 1: at one o'clock like you drew it right exactly. You
• 38:55
  Speaker 1: also have to have people asking the same questions of
• 38:57
  Speaker 1: the other ball and then comparing the answers. That's the
• 39:00
  Speaker 1: key to the experiment. Okay, now that's what it's going
• 39:03
  Speaker 1: to happen. If the universe is not random, if he
• 39:06
  Speaker 1: has hidden variables, if you actually drew the arrow on
• 39:09
  Speaker 1: the ball before putting it into the bag. But now
• 39:11
  Speaker 1: let's paint the quantum mechanical version where it's something. It's
• 39:15
  Speaker 1: not really drawn on the ball, it's just something. It
• 39:18
  Speaker 1: just has the probability of being something. Right, Yeah, So
• 39:21
  Speaker 1: as a probability in any random direction, And the only
• 39:24
  Speaker 1: thing we know is that whatever direction is in the
• 39:26
  Speaker 1: other ball going to the other city is pointing the
• 39:29
  Speaker 1: other way. And so in the quantum mechanical version, you
• 39:32
  Speaker 1: can really only ask one question. You can measure it
• 39:35
  Speaker 1: along one direction. You can say, is it pointing towards
• 39:38
  Speaker 1: two o'clock or is it pointing towards eleven o'clock. Once
• 39:41
  Speaker 1: you've done that, you sort of messed it up. You
• 39:42
  Speaker 1: can't really get any more information about the ball. So
• 39:45
  Speaker 1: you can make one measurement about your ball, and your
• 39:48
  Speaker 1: friend going the other direction you can make one measurement
• 39:50
  Speaker 1: about their ball. If you pick these three directions in advance,
• 39:52
  Speaker 1: then you can predict how often they will get the
• 39:55
  Speaker 1: same answer. Like both people say two o'clock, then you
• 39:57
  Speaker 1: know they're going to get opposite answers. Right, one ball
• 40:00
  Speaker 1: is going to be up with respect to two o'clock,
• 40:01
  Speaker 1: the other one is going to be down. But if
• 40:03
  Speaker 1: one person uses two o'clock and the other person uses
• 40:05
  Speaker 1: eleven am, then they might get different answers. And quantum
• 40:08
  Speaker 1: mechanics tells you how likely they are to get different answers. Well,
• 40:12
  Speaker 1: let's step people through it. What happens if it is
• 40:14
  Speaker 1: a quantum mechanical ball that goes through and gets the question.
• 40:17
  Speaker 1: So the first person says, is it generally pointing towards
• 40:20
  Speaker 1: twelve o'clock? And then that will sort of collapse the
• 40:23
  Speaker 1: ball a little bit, right. I think that's what you're saying,
• 40:26
  Speaker 1: is that now the ball cannot be pointing downwards if
• 40:29
  Speaker 1: I say yes, if you say yes, then the ball
• 40:32
  Speaker 1: cannot be pointing downwards. So that if the next person says, hey,
• 40:35
  Speaker 1: is it pointing three o'clock, they can't tell you. Right. Well,
• 40:38
  Speaker 1: what happens is you've destroyed the entanglement, so you can
• 40:40
  Speaker 1: make the measurement, but it's no longer constrained to be
• 40:43
  Speaker 1: the opposite of what the other ball is. And the
• 40:45
  Speaker 1: whole idea is that these things need to be entangled.
• 40:47
  Speaker 1: Once you've made a measurement, then the entanglement is broken.
• 40:50
  Speaker 1: You can only use up the entanglement sort of one time.
• 40:53
  Speaker 1: That's why you can only really make one interesting measurement.
• 40:56
  Speaker 1: You can make as many measurements as you like, but
• 40:57
  Speaker 1: they're not really as interesting because you no longer measure
• 41:00
  Speaker 1: ring an entangled system. Right. Once you interact with something,
• 41:03
  Speaker 1: you break the entanglement. But wait, is that really a
• 41:05
  Speaker 1: good analogy of Bell's theorem that somebody along the way
• 41:08
  Speaker 1: asks if it's pointing towards twelve o'clock. Sort of if
• 41:11
  Speaker 1: you take one more step. Bell's experiment says, pick three
• 41:14
  Speaker 1: directions in advance. Everybody decides in those three directions, and
• 41:18
  Speaker 1: then when you actually make your measurement, you pick one
• 41:20
  Speaker 1: of those three directions randomly. So you know, Jorge in
• 41:24
  Speaker 1: New Mexico is going to pick the two o'clock direction,
• 41:27
  Speaker 1: and Daniel in l A. Is maybe he's gonna pick
• 41:29
  Speaker 1: the two o'clock direction, maybe he's gonna pick the eleven o'clock.
• 41:31
  Speaker 1: There's a random element there. If we pick the same directions,
• 41:34
  Speaker 1: we're gonna get answers exactly opposite each other. Of course,
• 41:36
  Speaker 1: if we don't pick the same directions, then we might
• 41:39
  Speaker 1: get the same answers. We might not. And that's the
• 41:40
  Speaker 1: part that's predicted by quantum mechanics. Oh, I see, you
• 41:44
  Speaker 1: don't ask it the three times when it's going from
• 41:46
  Speaker 1: l A to New Mexico. You ask it one time,
• 41:49
  Speaker 1: like one of the three people ask their question. That's
• 41:52
  Speaker 1: what you're saying, and the person who gets to ask.
• 41:55
  Speaker 1: The question is decided at random exactly, and in the
• 41:58
  Speaker 1: hidden variables version, you can very easy calculate what are
• 42:00
  Speaker 1: the chances that the one ball is going to give
• 42:03
  Speaker 1: you the same answer as the other ball, And it's
• 42:05
  Speaker 1: all determined, and so you can just do the calculations.
• 42:07
  Speaker 1: You get a very crisp number of prediction. But quantum
• 42:10
  Speaker 1: mechanics adds more connections between these balls because it says
• 42:12
  Speaker 1: measurements in one direction are connected to measurements in another direction,
• 42:15
  Speaker 1: which doesn't exist for the hidden variables versions. So it
• 42:18
  Speaker 1: means you're more likely in the quantum mechanics to get
• 42:21
  Speaker 1: the same answer as the other person. Bell's experiment is
• 42:24
  Speaker 1: not a one off thing. You can't say from one experiment, Oh, definitely,
• 42:27
  Speaker 1: it was random. It's a statistical calculation. Across many iterations
• 42:31
  Speaker 1: of this experiment, you get a correlation between these things
• 42:33
  Speaker 1: which should be impossible. In the hidden variables version, your
• 42:37
  Speaker 1: measurements agree more often than if all the details were
• 42:41
  Speaker 1: specified in advance, and it's because of that quantum mechanical
• 42:43
  Speaker 1: connection between measuring in different directions. All right, Well, dig
• 42:48
  Speaker 1: into this a little bit more, because I feel like
• 42:50
  Speaker 1: maybe you're sort of waving your hand and saying, there's
• 42:52
  Speaker 1: a lot of complex math here that we can't understand
• 42:55
  Speaker 1: on the podcast. But I wonder if there are sort
• 42:57
  Speaker 1: of intuitive ways for us to figure out why they
• 42:59
  Speaker 1: would give you different results if there was there was
• 43:01
  Speaker 1: a hidden variable or not. Let's try to dig into that.
• 43:04
  Speaker 1: But first let's take another quick break. Alright, we're talking
• 43:19
  Speaker 1: about Bell's experiments, which, if it's true, confirms whether or
• 43:23
  Speaker 1: not quantum mechanics really is random or we just think
• 43:27
  Speaker 1: it's random, which would also confirm whether the universe is random.
• 43:31
  Speaker 1: And that's a pretty big deal, right. If the universe
• 43:33
  Speaker 1: is random, then it's totally unpredictable. If the universe is
• 43:36
  Speaker 1: not random, then everything that happens is kind of predetermined.
• 43:40
  Speaker 1: Although to this day there are very strenuous philosophical arguments
• 43:43
  Speaker 1: about what the results of Bell's experiment really means. Is
• 43:47
  Speaker 1: it actually ruling out local hidden variables? And one person
• 43:51
  Speaker 1: who argued very strongly that these experiments don't rule out
• 43:55
  Speaker 1: hidden variables was Bell. Bell was persuaded not that the
• 43:59
  Speaker 1: universe was random, but just that the universe was non local,
• 44:04
  Speaker 1: that it was somehow coordinating the results of these experiments
• 44:06
  Speaker 1: across space and time in a way that we didn't understand. Well,
• 44:10
  Speaker 1: we had this experiment setup where we had some balls
• 44:13
  Speaker 1: and we drew arrows on them, or had them quantum
• 44:15
  Speaker 1: mechanically drawn on the balls, and then we sent them
• 44:17
  Speaker 1: to New Mexico, and you had people asking questions alowing
• 44:20
  Speaker 1: the way. But it seems sort of like you're saying that, really,
• 44:22
  Speaker 1: to understand how Bill's experiment works, we sort of really
• 44:25
  Speaker 1: need to dig into the math, because that's where the
• 44:27
  Speaker 1: differences between a random universe and a non random universe
• 44:31
  Speaker 1: really are. Like, if it's really random, then the math
• 44:33
  Speaker 1: says that you should get one type of result from
• 44:36
  Speaker 1: this experiment, and if it's not random, then the math
• 44:38
  Speaker 1: has you should get another kind of results. Yeah, it
• 44:40
  Speaker 1: does come down to the math. And there are lots
• 44:42
  Speaker 1: of times in quantum mechanics where things don't make intuitive
• 44:45
  Speaker 1: sense to us, but the math is pretty clear and
• 44:48
  Speaker 1: it tells you exactly what's going to happen. And this
• 44:50
  Speaker 1: is one of those scenarios where you're like, well, that
• 44:52
  Speaker 1: would be really weird if that were true. The quantum
• 44:55
  Speaker 1: mechanic predicts it to happen, and then you go and
• 44:57
  Speaker 1: you do it in the experiment, and it does like
• 44:59
  Speaker 1: people have in these experiments starting in the seventies and
• 45:02
  Speaker 1: up till fairly recently, more and more sophisticated versions of them,
• 45:05
  Speaker 1: and the numbers they get agree with quantum mechanics. They
• 45:08
  Speaker 1: disagree with the local hidden variables picture of the universe.
• 45:11
  Speaker 1: And what you want is to, like have a deep
• 45:13
  Speaker 1: understanding of why that is. What is it about quantum
• 45:16
  Speaker 1: mechanics that makes it have a different prediction. So this
• 45:19
  Speaker 1: experiment predicts something different for quantum mechanics and the hidden
• 45:22
  Speaker 1: variables theory, and that's tricky. I mean, it's very clear
• 45:25
  Speaker 1: to just look at the math, like you write out
• 45:26
  Speaker 1: the probabilities, you do the calculation, the number comes out
• 45:29
  Speaker 1: of certain value. But we don't all think mathematically, and
• 45:31
  Speaker 1: so you want sometimes an intuitive understanding. And I think
• 45:34
  Speaker 1: the most intuitive understanding I have of it at least
• 45:37
  Speaker 1: is that quantum mechanics ties up these different measurements, if
• 45:40
  Speaker 1: you're thinking about measurements in one direction, how they're connected
• 45:42
  Speaker 1: to measurements in other directions than sort of in the
• 45:44
  Speaker 1: hidden variables version, everything is clean and crisp and they
• 45:47
  Speaker 1: don't mess up each other, whereas in the quantum mechanical version.
• 45:50
  Speaker 1: You make a measurement in one direction, it's more connected
• 45:53
  Speaker 1: to measurements in other directions. That's what gives you these
• 45:56
  Speaker 1: enhanced mathematical probabilities. All right, well, I think maybe the
• 45:59
  Speaker 1: next and then should be have people actually done this experiment?
• 46:02
  Speaker 1: I mean, we sort of talked about it, and we
• 46:04
  Speaker 1: know that if it comes out one way, it sort
• 46:06
  Speaker 1: of proves quantum mechanics is random or not. And have
• 46:09
  Speaker 1: people actually done this experiment? They have. The first test
• 46:12
  Speaker 1: was in nineteen seventy two, originally done with photons. You
• 46:16
  Speaker 1: can do this kind of experiment with any sort of
• 46:17
  Speaker 1: quantum object, where you can create entanglement, where you create
• 46:20
  Speaker 1: a connection between these two things so that they have
• 46:23
  Speaker 1: to like follow some overall constraint, want to spin up
• 46:26
  Speaker 1: or want to spin down. In the case of photons,
• 46:28
  Speaker 1: they're not spinning one half particles. They don't spin up
• 46:31
  Speaker 1: or down. They have three different states, including like a
• 46:33
  Speaker 1: circuit of polarization. But fundamentally the idea is the same.
• 46:37
  Speaker 1: And so the first test confirmed Bell's experiment in nineteen
• 46:40
  Speaker 1: seventy two. That was just a few years after his
• 46:43
  Speaker 1: original paper. It's actually a funny story about that because
• 46:46
  Speaker 1: Bell chose to publish his theorem in a really cheap
• 46:49
  Speaker 1: journal that didn't charge him to publish it, and it
• 46:51
  Speaker 1: meant that very few people actually read the paper when
• 46:54
  Speaker 1: it first came out. It was such a cheap journal
• 46:56
  Speaker 1: that if Bell wanted copies of his own paper, the
• 46:59
  Speaker 1: journal would even charge large him for his own copies. Usually,
• 47:02
  Speaker 1: if you write a paper, you get like a certain
• 47:03
  Speaker 1: number of free copies. So he published it in this cheap,
• 47:06
  Speaker 1: obscure journal, which meant that not many people saw it.
• 47:08
  Speaker 1: But one guy did and he was really intrigued, and
• 47:11
  Speaker 1: he set up the first experiment in the seventies to
• 47:13
  Speaker 1: test this idea. And it involves kind of pairing up
• 47:17
  Speaker 1: electrons or pairing up photons, and so maybe just to
• 47:19
  Speaker 1: paint us a picture. You know, you've sort of run
• 47:22
  Speaker 1: this bunch of times, right, not just once, and then
• 47:24
  Speaker 1: you can tell the universe is random or not. You
• 47:26
  Speaker 1: have to run it like a hundred times. And if
• 47:28
  Speaker 1: at the end you get you know a certain number
• 47:31
  Speaker 1: of times them both being spin up or spin down,
• 47:34
  Speaker 1: it means that the universe is random. But if at
• 47:37
  Speaker 1: the end you get that there was both spin up
• 47:39
  Speaker 1: or spin down, as a different percentage, then you know
• 47:42
  Speaker 1: that the universe is maybe not random. Right, that's kind
• 47:45
  Speaker 1: of what we're looking at. Yeah, you prepare these particles,
• 47:48
  Speaker 1: you send them off in different directions. Then you have
• 47:50
  Speaker 1: some process to randomly choose the axis along which you're
• 47:53
  Speaker 1: going to measure the spin. Remember, you have to have
• 47:55
  Speaker 1: like three different possibilities and you have to randomly choose
• 47:59
  Speaker 1: which one. Oh, how did they do it? Did they
• 48:02
  Speaker 1: flip a coin? I don't remember the details of the
• 48:04
  Speaker 1: first experiment, but they've become more and more elaborate as
• 48:07
  Speaker 1: time goes on. They use things like telescopes pointed to
• 48:10
  Speaker 1: distant stars, and like the flickering of that star helps
• 48:14
  Speaker 1: determine which when you pick. They've been really really careful
• 48:17
  Speaker 1: about how to determine these things. Sometimes they're linked to
• 48:20
  Speaker 1: cosmic rays, which people think might be fundamentally random. Is
• 48:23
  Speaker 1: there a mu on hitting my detector right now? So
• 48:26
  Speaker 1: they do a lot of work to try to make
• 48:27
  Speaker 1: sure these things are random. Remember in our episode about
• 48:30
  Speaker 1: super determinism, this was the heart of the matter. People
• 48:33
  Speaker 1: were worried about whether that choice really was random, or
• 48:36
  Speaker 1: whether it just appeared to be random, whether the whole
• 48:39
  Speaker 1: universe had been built to conspire to make these things
• 48:41
  Speaker 1: look random when really they weren't. Wait wait, I think
• 48:44
  Speaker 1: you're telling me that this experiment that humans have devised
• 48:47
  Speaker 1: to test whether the universe is random or not depends
• 48:50
  Speaker 1: on us doing something random. It's a little bit funny,
• 48:54
  Speaker 1: isn't it. Absolutely, and people have been digging into these
• 48:57
  Speaker 1: apparent loopholes and Bells experiment and that one of them like,
• 49:00
  Speaker 1: how do we know that the way we constructed the
• 49:02
  Speaker 1: experiment is actually random? Another one is, how do you
• 49:06
  Speaker 1: know these two things actually aren't communicating in some way?
• 49:10
  Speaker 1: The first experiment wasn't that big, you know, the photons,
• 49:12
  Speaker 1: They didn't send them very far apart. And so they've
• 49:14
  Speaker 1: been making these experiments more and more elaborate, trying to
• 49:17
  Speaker 1: make them more actually random in the way they choose
• 49:20
  Speaker 1: the axis, and making the particles further and further apart,
• 49:23
  Speaker 1: so there's no way to transmit information from one to
• 49:26
  Speaker 1: the other unless you do it faster than the speed
• 49:28
  Speaker 1: of light. So they've been slowly working to try to
• 49:30
  Speaker 1: close these loopholes. And every time somebody does want one
• 49:33
  Speaker 1: of these experiments, somebody goes, oh, wait, but what if
• 49:36
  Speaker 1: have you checked? How do you really know in one
• 49:38
  Speaker 1: of the core foundational loopholes that people are trying to
• 49:41
  Speaker 1: close is this one about the randomness. So they come
• 49:43
  Speaker 1: up with these more and more elaborate systems to try
• 49:46
  Speaker 1: to ensure that the construction of the experiment itself is
• 49:49
  Speaker 1: actually random, right, because if the experiment depends on you
• 49:52
  Speaker 1: doing something random, if you're if you're not really random
• 49:55
  Speaker 1: doing it, then the whole experiment sort of falls apart
• 49:57
  Speaker 1: a little bit, right. Yeah, absolutely, that's the base is
• 50:00
  Speaker 1: of super determinism, to say no, things really are determined.
• 50:04
  Speaker 1: It's just that even how you're choosing the apparently random
• 50:06
  Speaker 1: element of this experiment is not random, that itself is
• 50:10
  Speaker 1: determined by things that happened before. All Right. So then
• 50:13
  Speaker 1: people have been doing this experiment for fifty years, and
• 50:17
  Speaker 1: they've been trying harder and harder to make it more
• 50:19
  Speaker 1: and more pure and exact and full proof. And what's
• 50:23
  Speaker 1: the overall result that they've been getting. They've been getting
• 50:26
  Speaker 1: that the universe is really random at the quantum level.
• 50:28
  Speaker 1: They've been getting a result that says that there are
• 50:29
  Speaker 1: no local hidden variables, right, That says that there's no
• 50:33
  Speaker 1: information that's being passed along with these particles that somehow
• 50:37
  Speaker 1: determines whether the ball is red or blue, or you know,
• 50:40
  Speaker 1: what direction is pointed at. There's no information with the particles. Wait,
• 50:44
  Speaker 1: I feel like maybe you're using um sort of lawyers
• 50:47
  Speaker 1: speak here. Absolutely, I am right, Like I asked whether
• 50:50
  Speaker 1: the universe is random or not, and you said there
• 50:52
  Speaker 1: are no local hidden variables, which is not a yes
• 50:55
  Speaker 1: or no answer, not a yes or no answer. So
• 50:57
  Speaker 1: what are what are the lawyerly nuances here? Yeah, because
• 51:00
  Speaker 1: it's possible that there are global hidden variables, that there's
• 51:04
  Speaker 1: something controlling everything that happens in the universe that determines
• 51:08
  Speaker 1: the outcome of this experiment. Bell's experiment only rules out
• 51:12
  Speaker 1: local hidden variables, not global hidden variables. What's the difference, Well,
• 51:16
  Speaker 1: local hidden variables would mean information is being passed along
• 51:19
  Speaker 1: with the electron. Something about the electron itself in the
• 51:23
  Speaker 1: environment of the electron determines whether it goes spin up
• 51:26
  Speaker 1: or spin down. Something global would be coordinating across space
• 51:30
  Speaker 1: time faster than the speed of light. And so. For example,
• 51:32
  Speaker 1: there is an interpretation of quantum mechanics called Bomian mechanics
• 51:36
  Speaker 1: where quantum mechanics is not random. But there's this pilot wave.
• 51:40
  Speaker 1: This thing which controls the whole universe and arranges for
• 51:43
  Speaker 1: these things, coordinates and says, oh, if this one over
• 51:45
  Speaker 1: here spin up, I'm going to go make this one
• 51:48
  Speaker 1: be spin down. And so it's like coordinating globally faster
• 51:52
  Speaker 1: than the speed of light. Wait, so a local hidden
• 51:54
  Speaker 1: viroiable is when the ball you put in the bag
• 51:57
  Speaker 1: has a little pocket inside of it that knows whether
• 51:59
  Speaker 1: it is spinning up or down. That's the local hidden variable.
• 52:03
  Speaker 1: And the Bell's experiment proves that there is no such
• 52:05
  Speaker 1: pocket inside of the the electron or the ball, but
• 52:08
  Speaker 1: there might be a global hidden variable, meaning like there's
• 52:10
  Speaker 1: a giant universe size pocket out there hiding information and
• 52:15
  Speaker 1: coordinating information between here and alpha centric kind of right exactly,
• 52:20
  Speaker 1: And that seems really weird. So the more common interpretation
• 52:23
  Speaker 1: is equantum mechanics is really just random. If you don't
• 52:26
  Speaker 1: like nonlocality, if you don't like things being coordinated across
• 52:29
  Speaker 1: the universe, then the more common interpretation is, well, things
• 52:32
  Speaker 1: are just really random. But it's important to remember that
• 52:35
  Speaker 1: that's one possible interpretation of Bell's experiment. There are other
• 52:38
  Speaker 1: ones which involve non local hidden variables, So it doesn't
• 52:41
  Speaker 1: actually put a nail in the coffin of hidden variables completely,
• 52:45
  Speaker 1: just local hidden variables. Wait, you're saying that like a
• 52:47
  Speaker 1: global hidden viroiable, like the whole universe is coordinated somehow magically.
• 52:52
  Speaker 1: Is this looks the same as a totally random universe. Yes,
• 52:56
  Speaker 1: we cannot tell the difference. Nobody's come up with a
• 52:59
  Speaker 1: way to disting between that view, which is Bowmian mechanics,
• 53:02
  Speaker 1: which actually Bell himself is a huge proponent of and
• 53:06
  Speaker 1: sort of Copenhagen view where these things are not determined
• 53:10
  Speaker 1: and then they collapse when you make this measurement. I guess.
• 53:12
  Speaker 1: Then the next question is if there is a giant
• 53:15
  Speaker 1: universe size hidden pocket viable, you know, thing coordinating everything,
• 53:21
  Speaker 1: is that random or not? In that theory, it's not random,
• 53:24
  Speaker 1: it's deterministic. In that theory, everything that happens is determined
• 53:28
  Speaker 1: by the initial conditions. There's no randomness in it. I
• 53:31
  Speaker 1: feel like this confirms something I've sort of come to
• 53:34
  Speaker 1: believe it for a long time, which is that there's
• 53:36
  Speaker 1: really no difference between a totally random universe and a
• 53:39
  Speaker 1: universe run by all powerful God. Well, we can't tell
• 53:45
  Speaker 1: the difference. Philosophically, it's a very different statement about what's
• 53:48
  Speaker 1: out there, what's real, what's happening in the universe. But
• 53:51
  Speaker 1: it really goes to the heart of the question and
• 53:53
  Speaker 1: like what that means. What does it mean for things
• 53:55
  Speaker 1: to be happening if we can't know the difference, If
• 53:57
  Speaker 1: these particles really are undetermined, or if they were determined
• 54:00
  Speaker 1: the whole time by some crazy pilot function which is
• 54:03
  Speaker 1: controlling the fate of the universe, What really is the
• 54:05
  Speaker 1: difference to us if we can't ever devise an experiment
• 54:09
  Speaker 1: to tell the difference, is there really a difference? I
• 54:12
  Speaker 1: don't know. It's a really interesting question in philosophy, which
• 54:14
  Speaker 1: is one reason why philosophers still have jobs, because people
• 54:19
  Speaker 1: are confused. It sounds like we need to start a
• 54:21
  Speaker 1: new religion called pilotism, maybe pilotism or how would you
• 54:25
  Speaker 1: call it, global hidden vinableism. It's not a religion. It's
• 54:29
  Speaker 1: a totally respectable philosophy of quantum mechanics, and it's not
• 54:33
  Speaker 1: very mainstream because for a long time people thought that
• 54:36
  Speaker 1: Belle's experiment ruled it out, and there was actually a
• 54:39
  Speaker 1: proof by von Neumann that suggested that no hidden variables
• 54:42
  Speaker 1: were allowed, but there was a mistake in it. So
• 54:44
  Speaker 1: it's a sort of a historical accident that Bowman mechanics
• 54:47
  Speaker 1: was sort of cast aside for many years, even though
• 54:49
  Speaker 1: Bell himself was a proponent of it and people thought
• 54:53
  Speaker 1: that his experiments ruled out all hidden variables. And now
• 54:55
  Speaker 1: Bowmian mechanics is sort of like an afterthought. People don't
• 54:58
  Speaker 1: get taught it in schools, not mentioned very often, even
• 55:01
  Speaker 1: though it's totally consistent with our understanding of the universe.
• 55:04
  Speaker 1: It's just maybe even stranger than a random universe. Well,
• 55:08
  Speaker 1: it's interesting to think that maybe we'll never find out right, Like,
• 55:11
  Speaker 1: it's possible that it's impossible to tell the difference between
• 55:14
  Speaker 1: you know, all powerful God or pilot function or pilot
• 55:17
  Speaker 1: wave and a totally random, unpredictable universe. It's possible, or
• 55:22
  Speaker 1: maybe we just need next centuries and John Bell to
• 55:24
  Speaker 1: come up with an even more clever idea for an
• 55:27
  Speaker 1: experiment that can somehow tell the difference. I mean, I
• 55:30
  Speaker 1: remember learning about this experiment as an undergrad in quantum
• 55:33
  Speaker 1: mechanics and thinking, how could you possibly construct an experiment
• 55:36
  Speaker 1: to tell the difference. It's impossible, and then reading his
• 55:38
  Speaker 1: experiment going oh wow, that's clever. I never would have
• 55:41
  Speaker 1: thought of that. So it might just mean that we
• 55:43
  Speaker 1: need another generation of clever scientists. Maybe somebody out there
• 55:46
  Speaker 1: listening has actually understood our description of Bell's experiment and thought,
• 55:50
  Speaker 1: what if you add in this feature to it? What
• 55:52
  Speaker 1: if you did that? What have you changed in this
• 55:54
  Speaker 1: way to come up with a new experiment that might
• 55:56
  Speaker 1: tell us the difference? Well, what's the probability of that
• 56:00
  Speaker 1: somewhere between zero and one? As long as it's not zero,
• 56:02
  Speaker 1: I guess we just gotta keep doing it and eventually
• 56:04
  Speaker 1: somebody will come up with the answer. Right, that's how
• 56:07
  Speaker 1: statistics works. That's right. If we do an infinite number
• 56:10
  Speaker 1: of podcast we will eventually inspire the physical theory of
• 56:13
  Speaker 1: the universe. Yeah, we'll eventually get to take credit for
• 56:17
  Speaker 1: understanding the universe exactly monkeys on typewriters and cartoonists and
• 56:21
  Speaker 1: physicists on podcasts. Well, we're making pretty good progress, right,
• 56:24
  Speaker 1: we'ven We've got a couple of hundred episodes on Under
• 56:27
  Speaker 1: our Belt. Yeah, something north of four hundred. Yea, So
• 56:30
  Speaker 1: now we just need what infinity minus for hundred more exactly?
• 56:34
  Speaker 1: Let me do the calculation to do too. That's infinity
• 56:38
  Speaker 1: but getting close all right, Well, we hope you enjoyed
• 56:42
  Speaker 1: that attempt to try and explain Bell's theorem, which is
• 56:45
  Speaker 1: pretty complicated. It's pretty complicated even if you have the
• 56:48
  Speaker 1: math and the diagrams in front of you. So thanks
• 56:50
  Speaker 1: for bearing with us and this attempt to translate into
• 56:53
  Speaker 1: a one dimensional form for your audio stream. Hope you
• 56:56
  Speaker 1: enjoyed it. Yeah, and please join my new church of
• 56:59
  Speaker 1: pilot Is where Jorge is the God. Are you accepting donations?
• 57:03
  Speaker 1: There you go, that's right, I am the pilot Wave.
• 57:06
  Speaker 1: Thanks for joining us. See you next time. Thanks for listening,
• 57:17
  Speaker 1: and remember that Daniel and Jorge Explain the Universe is
• 57:20
  Speaker 1: a production of I Heart Radio. For more podcast for
• 57:23
  Speaker 1: my heart Radio, visit the I Heart Radio app, Apple Podcasts,
• 57:27
  Speaker 1: or wherever you listen to your favorite shows. Ye