December 23, 2021 • 50 mins
Daniel talks to Prof. Valia Allori about the theory of Bohmian Mechanics, a deterministic alternative to traditional Quantum Mechanics.
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Speaker 1 (00:09):
Quantum mechanics just doesn't seem to make sense. It tells
us that the universe is fundamentally random, that some questions
just don't have answers, that there's a limit to what
can be known about reality, and that things change when
we look at them. More than that, it tells us
that reality is fundamentally different from what we have imagined.
(00:31):
But what if that's not true? What if that's wrong?
What if it were possible to build a theory of
quantum mechanics that doesn't describe the universe as bizarrely random,
that doesn't have any special role for observers, that doesn't
suffer from the famous measurement problem, and that lets us
think of the microscopic world as very similar to our
(00:54):
familiar intuitive world. And what if this theory actually worked
and was able to describe I've been predict experiments. That is,
what if there's an intuitive alternative to mainstream quantum mechanics.
If there were, why on Earth wouldn't it be embraced? Hi,
(01:28):
I'm Daniel. I'm a particle physicist and a professor of
physics that you see, Irvine, and I want to believe
that the world makes sense. We are all drawn to
basic questions about the nature of the universe. How does
it work, why is it this way and not some
other way? How did it all begin? And how will
it all end? Physics is supposed to be a way
to get answers to those questions, and so welcome to
(01:51):
the podcast Daniel and Jorge explained the Universe and production
of My Heart Radio, where this is precisely the kind
of question we ask and the kind of answer we
reach for. And the amazing thing is that physics kind
of seems to work. It offers explanations, explanations that not
only work because they could predict what happens in experiments,
but explanations that usually make some kind of sense. The
(02:15):
stories they tell us are mathematical and could be very
different from the stories we guessed at. It turns out
the Earth is billions of years old and not thousands,
that stars are massive balls of fusion in the sky
rather than tiny pin pricks in the screen. But in
the end, these mathematical stories that physics tells us about
the universe, they are coherent, they are sensible. We can
use them to understand how the universe really is. Except
(02:38):
in one area, quantum mechanics. While we do have a
working theory, we struggle to make sense of it. What
does it really mean? What is it telling us about
how the world really is? And while we have lots
of different interpretations, we struggle to accept the story that
they tell us. Is the universe really random? Is everything
(02:58):
really described by the wave function? Does it collapse when
you observe it? Or split into millions of meta universes?
Or do objects not really have any properties on their
own to observe or all properties relative to the observer.
None of these are easy to absorb, to click into
our minds and let you say, oh, yeah, I get it,
that's how the universe is. But what if there was
(03:21):
a version of quantum mechanics that was more intuitive, that
was deterministic, that didn't need some observer effect or multiple
universes or a redefinition of the nature of reality. Well,
today we will be exploring a less popular theory of
quantum mechanics that doesn't rely on randomness and uncertainty. It
tells us that what is happening to tiny particles is
(03:44):
much simpler and easier to swallow, and we'll talk about
why it's been overlooked by mainstream physics. So today on
the podcast, we'll be asking the question the quantum mechanics
have to be so random? My friend and co host
(04:05):
Orges on a break, so I'm continuing our series of
conversations with experts in quantum mechanics. We spoke to Adam
Becker about mainstream quantum mechanics, to Carlo Rovelli about his
theory of relational quantum mechanics, to Sean Carroll about the
many world interpretation, and today we are speaking to an
expert on pilot wave theory, also known as Boemian mechanics.
(04:31):
So it's my great pleasure today to introduce all of
you to Professor Valia Alori, who, if I understand correctly,
holds two pH d s, one in physics and one
in philosophy, so she's the perfect person for us to
talk to about the crazy philosophical consequences of quantum mechanics.
She's also a full professor in the Department of Philosophy
(04:51):
at Northern Illinois University and a fellow at the John
Bell Institute for Foundations of Physics. Professor A Lorii, welcome
the podcast. Thank you for having me, well, thank you
for coming here to talk to us about the mysteries
of quantum mechanics. Before we get into the details of
pilot wave theory, I thought we should take a step
back and remind ourselves why we have so many theories
(05:13):
of quantum mechanics and why there are still so many
questions about it. To me, the basic question we have
about quantum mechanics is what is going on? How do
we understand the story that it's telling us. Our intuition
is to think of particles as tiny dots of matter,
but quantum mechanics usually tells us that they are basically different,
that they are fundamentally different kinds of things because they
(05:36):
can maintain two contradictory possibilities at once. There's also this
wave function that seems to control what happens, but then
it collapses when you touch it, but it's not clear
what the rules of that collapse are. It's so hard
to get a mental picture of what's going on with
the little particles. So how do you approach this question
of trying to understand what quantum mechanics? So first of all,
(06:01):
let me just say that I'm not sure that we
should understand quantum mechanics philosophically there is a sense in
which we don't understand quantum mechanics even physically as a
physical theory, because I mean, the theory seems to be
talking about you know, electrons and protons and matter in
(06:22):
general and fields, but when you actually look at the formalism,
it's unclear exactly what plays the rollers of what. So
we do have a an equation, the Shouldinger equation, which
is a question of the evolution of the wave function.
Should we understand the way function as a physical object.
If the wave function is a physical object, what does
it represent? Does it represent particles, does it represent fields?
(06:45):
Since I was a student, just to put it bluntly,
I really had trouble relating to the theory as a
physics student. But even granting that the it's accurate to
talk about that as a theory about something. Let's put
it this way. The ory, I would say, is either
empirically inadequate or it's incomplete. Why is that? Well, because
(07:09):
I just said that, you do have this equation, which
is the shrining equation, which is a again equestion of
evolution of an objicle the wave function, and the wave
function is a called like that because it's a wave
so and wave can superimpose. You know, you throw a
rock in the pond, right, throw another rock in the pond.
(07:29):
Then you see waves from one rock and then you
see the other rock. They superimposed. You have interference and
the fraction of this kind of behavior that you would
attribute to waves. Okay, And so since there's two superimposed.
If you think of the wave functions are presenting objects
of physical objects right at the microscopic level, they could
be in a superposition state, right, and nucluse that adioactive
(07:52):
substance of subsort could be in the superposition of a
decade state or a non decade state. And by superposition
you mean that there's two possibilities for an object. It
could be spin up or spin down, or decade or
not decade. There's two options for the situation. It can
actually be in yes, in a sense, yes, more generally,
I mean mathematically, this is the mathematical property of the equation, right.
(08:14):
I mean the prototype example is the problem of the
shrilling a cat, right, in which you do have this
cat which is in a box. Right in the box
that is this vial of poison. De vial of poison
will break because it's connected to this radioactive substance, so
it will break if the substance will decay. If nothing happens,
(08:34):
it will not break. So what happens is that if
the nucleus decase, bile of poison breaks and the cat dies. Okay,
So that's a possible state of affairs. Otherwise nothing happens
in the cat stays alive, okay. And so what happens
is that, however, given the superposition state possibility, given the
fact that there is a possibility of having a superposition
(08:57):
state as a true physical state for this system, then
you could also have this microscopic superposition of decade and
not decayed, which actually spread out of the cat. And
so the theory predicts this microscopic superposition which we never
ever observed. They are not observable. That's not what we
have experienced. Off So there is a very strong sense
(09:20):
in which the theory as it is is empirically inadequate,
because when we open the box and we when we
check on the cat, the cat is either dad or alive.
So what I'm hearing you saying is that quantum mechanics
is useful as a description of these microscopic states. But
which I think you mean like quantum particles, electrons and photons, etcetera.
(09:41):
But that we don't really understand what it means and
we can't access it directly. We can't like see these things.
We have to interact with them using macroscopic objects like
detectors or our fingers or cats, etcetera, which don't have
the same quantum properties, And so it doesn't really answer
the question of like, what's actually going on in the
microscopic leve Is that a summary of the problem. Yes,
(10:02):
Actually it's more than that. So not only doesn't explain
what's going on intuitively at the microscopic level, but also
if you try to apply the theory to everything, including
cats and detectors and stuff like that, the theory doesn't
give you what you observe. So it's really bad for
the theory. The theory doesn't I mean, it is actually
falsified directly by the fact that the training Garry question
(10:25):
is it's a linear I think because you're saying that
they suggest that cats should also be in superpositions, and
fingers and detectors and everything should be in superpositions. But
that's not what we observe. That's what you mean by
experimentally falsifying, Yes, exactly, and of course, I mean, you know,
the family fathers were not naive and the newness okay,
and that's why they proposed, at least that's what for
(10:45):
Neuman did, right. He proposed that there is actually a
second evolution a question for the wave function. And so
they say, okay, right, you don't want macroscopy superposition. Okay,
So when do you get them again? Oh, when there
is a measurement. Uh huh. So when the measurement is performed,
then there is a different evolution equation. The wave function
randomly collapses in one of the terms a superpositional when
(11:08):
you open the door and you see the cat ha ha,
the wave function actually collapses. So you write in a
sense right as a detector, right, you collapse the wave function.
The issue there is that we don't have a clear
definition of what a measurement is and when it happens.
Because you can imagine, you know, if I'm poking something
with my finger, the tip of my finger is still
a microscopic particle, So why should it collapse the way
(11:30):
function and two particles on the tip of my fingers
should still be a quantum mechanical system. So there's no
like clear line when something becomes classical or microscopic when
the wave function should collapse. Yes, exactly. I mean we
don't know who does the collapsing, who kills the cat? Right?
So is it me when I open the door, or
is it my consciousness? We don't really want to enter
(11:51):
into that. So it is a problem that you're suggesting. Namely,
it's not a precise physical theory. It doesn't really define
what a measurement is. Because I mean, this is puzzling,
because we just would like measurement just to be physical
processes like anything else, right, I mean, they're made of particles,
quantum particles, and so why are they special? So there
(12:12):
is a sense in which started from this, which is
called the measurement problem, because I mean, we are actually
measuring what is the state of the cat, and the
cat is actually measuring what is the state of the particle.
Another way of putting this would be that measurements, when
you're performing a measurement. Quantum theory says that measurements do
not have a precise result. Okay, so like the cat
(12:35):
doesn't have a precise state, and so various people call
them interpretation. But I actually think that they are different theories,
but they have different solutions of these problem so to speak.
So bo mechanics is one of those. It does solve
this problem, even if I do think that's not the way.
The reason why it was proposed. So this theory was
(12:58):
proposed by I mean, the first version of this was
proposed by the Brody in ninety three as part of
his dissertation. So according to this theory, what happens is
that I just like very very some people like to
put it and romantic, right, something very plan and boring
in a sense obvious because it's according to this theory,
(13:20):
matter is made of particles, just liking classical mechanics, but
they do have a different evolution equation than quantum theories.
In this theory there is this object which is the
wave function, which is the same guy as ordinary quantum theory,
but it devolves according to Shrinninger equation. So you do
have this an evolution a question for the particles, which
(13:40):
is first to order, and then you have an object
which is the wave function, which evolves like in regular
quantum mechanics according to the Shrininger equation. So then in
the Copenhagen interpretation, the one most people are familiar with.
The wave function is supposed to be everything is supposed
to describe the whole system, and particles when we're not
looking at them, sort of operated according to this wave auction,
which you know evolves according to the Shortinger equation. But
(14:03):
then there's this weird second bit where things collapse to
particle like behavior that we observe when you look at them. So,
for example, you have a particle that's supposed to hit
the screen, the whole wave hits the whole screen, but
at some point when it interacts, when that measurement happens,
then it becomes a single point, a flash of light
on that screen. And so you're saying that Bomian mechanics
is different because not only do you have the wave function,
(14:24):
but you also have the particles. It's not like this.
There's sometimes waves and then sometimes particles. They're always particles,
but they're governed by this wave that sort of guides
them through their path. Yes, so there are always particles.
That's what matter is made off. Tables and chairs and
people and screens and detectors and whatever are all made
of particles. So what happens is that these particles their
(14:47):
trajectories is mathematically written down in terms of this wave function,
and this way function in itself evolves according to a
given equation. Okay, So usually what you said is kind
of important because some I mean, very common way of
describing the theory, which is also called because of this reason,
the pilot wave theory, is that this particle are pushed
(15:08):
around by this wave. Okay. So the user slogan is, oh,
it's not particle end waves or waves, it's particle end waves. Okay.
So there is a sense in which this is true,
in the sense that there are particles and there is
also this wave function. However, I think that it is
(15:28):
kind of misleading to think of that in these terms,
because if you think about what kind of entity the
wave function is, it is a wave, but not a
wave in three dimensional space. Okay. If you think of
how to represent the wave function, what the wave function
really is, It's a function of all the particles, right,
(15:49):
It is a function of the configuration in the case
of bow Mean mechanics, the function of the configuration about
the particles. So it has three dimensions for every particle.
So in total it has three n dimensions. If the
universe is composed of and particles, so it's not a
field into adimensional space. The way function, then, just to
be clear, talks about the trajectory of all of the
(16:10):
particles in the universe, and so they're all sort of
combined into this one grand object. The way function mechanics
talks about is the way function of the universe. So
the one that evolves according to the shooting their question
is the way function of the universe. So I do
have two things to clarify here. So the first thing is,
(16:32):
so how we should interpret this wave function physically. It's
an open question. I mean, philosophers and physicists are talking
about this all the time. But I do think if
you describe b My mechanics as I just did name
it is a theory of particles with the wave function
defining that trajectory, and you can understand that the way
function as pushing the particles just in the same way
(16:52):
as you understand gravity is pulling stuff right on the ground. Okay,
So it's I think that the best this is my
personal take on this, is that the best way of
understanding the way function in Bowman mechanics is to think
of that as law like right, It's part of the
ingredients of the law of nature, something that you need
(17:12):
right in order to specify the right trajectory, the one
that you observe. And so the other thing was about
the way function of the universe. So the fact that
the way function is a function of all these particles
is something that leads to a very important feature of
Bonan mechanics, which is it's no locality. And I want
to talk about non locality in a minute, but first
(17:32):
I just want to make sure that we have a
clear sense of what's going on here. So we talked
about how the problem with quantum mechanics was this measurement
problem that what happens when you measure this wave and
it collapses into a particle. So how exactly does bow
mean mechanics solve that problem? Is it because things are
always a particle and so when you look at them,
they were a particle and it's no big deal, and
this is where it was, and it has like a
(17:53):
well defined trajectory that in bow Mean mechanics you really
can think about like electrons as tiny little dots of
matter flying through the universe, the way planets fly through
the Solar system. Yes, I think that's right in the
case of the cat. The cats made of particles like
everything else, So it is either dead or alive. Okay.
The cat is either dead or alive at all times. Okay,
(18:17):
So the macroscopic superposition should not belong to the wave functions.
But the wave function is not what cat is made of.
The cat was made of particles and particulars a precise location,
which is what it is right, either in the dead
camp or a in the life camp. So this is
really different from the way people are sort of taught
to think about quantum mechanics. That information isn't there until
you measure it, that there's a fuzziness to the universe
(18:39):
that is fundamentally random, all these really alien elements of
quantum mechanics that make it so weird. Bo Mean mechanics
seems to sort of like chuck that out the window
and say, no, everything actually is determined. There is no
randomness or uncertainty. There's just some information you sometimes haven't
measured yet, but it's really there. That the cat really
is dead or is alive. It's never sort of uncertain.
(19:00):
Is that true? That there's really no randomness, no true
randomness In Boomian mechanics. It depends on what is meant
by that. So it is true that the cat is
either dead or alive. It is true that the particles
even passes through one sleet or the other sleet. It
is true that when you observe a flash on the screen,
that was coming from a particle that traveled all the
way from the source to the screen. And it is
(19:22):
true that there is no fuzziness. That's why I think
that Bomian mechanics is physically clear. And the question is okay,
so is there no randomness? Well, now there is randomness
because the prediction of Bomian mechanics are provable to be
the same as quantum mechanics. And quantum mechanics predicts probabilities. Right,
the traditional stories that you do get only the probabilities
(19:46):
of the results. Right, you obtain this, this or that
not with a definite outcome. For sure, you have a
probability distribution of the experimental results. So the legitimate question
is where is the probability is coming from in Bomia mechanics.
They come from the fact that So I mean, this
is more general question about how is it possible to
(20:09):
get probabilities if you have a deterministic theory. Deterministic theory,
you have one past, one future, right if you know
the law. If you not the initialis condition, you know everything, right,
everything is determined. If you have this laplacean demon knows
it at all and everything he knows everything. So this
is a deterministic theory. So where the probability is coming from.
They're coming from the initiative conditions. Okay, so there are
(20:30):
two elements here, right. In determinism is something like that,
given the initiative conditions and given the laws, you know everything.
So if you do know the laws and you do
know that, I mean principle, you can predict anything. I
want to talk more about this randomness and initial conditions,
but first let's take a quick break. All right, we're back,
(21:01):
and we are talking about Bomian mechanics, a really fascinating
quantum theory that describes the universe as filled with actual,
tiny little dots of matter moving on what are like
classical paths, but guided by a wave function that gives
them the appearance of wave like behavior. And the element
that we're talking about right now is this question of randomness.
(21:22):
In traditional quantum mechanics, we are told that the universe
is fundamentally random, that there aren't hidden variables that control
what actually happens. But Boian mechanics says the opposite. It
says that things are actually determined by the initial conditions,
and that if you do the same experiment multiple times
with exactly the same initial conditions, you should get the
same output. So I'm a particle physicist and at the
(21:43):
Large Hadron Collider we smash protons together multiple times, and
we often say that if we smash those protons together
with exactly the same initial conditions, we would still get
different outcomes every time. That is quantum mechanical, and that
it's drawn from some probability distribution that somewhere seriously, the
universe is like rolling the dye based on this probability
(22:03):
distribution and deciding what happens on the giving collision. But
you're saying that Bomian mechanics is deterministic, and that if
I get two different collisions giving me two different outcomes,
that's because the initial conditions were slightly different, the protons
that a slightly different energy or slightly different angle, and
that if it was actually able to repeat the same
exact experiment, I should get the same exact outcome, is
(22:24):
that right? So yes, so so so if you say
that you do have this distribution of the particles, the
particles of distributed according to quantum ecalibbon distribution, and it
is an equilibient distribution and nothing changes anymore, then that's
the most complete information that you may have about this particles.
And so we don't have more knowledge than this about
the particles. Then we have absolute tons certainty about the
(22:48):
precise positions of the particles. And so this plays out
into having a distribution of the outcomes at the end
of the experiment. I see. So we have particles which
go through the experiment using deterministic laws. So the entire
outcomes determined for each particle based on how it came
into the experiment. But we have some distribution of inputs
(23:10):
at the particles when they come into the experiment. They're
never all actually at the same angle or location or whatever.
There's some variation there and that gives a variation in
the output. So not a randomness, but you have sort
of variation and the inputs gets translated to a variation
on the outputs, sort of like you know that game
where you drop a ball and it goes left and right,
and left and right and left and right. It sort
of chaotic. It's very hard to predict exactly what slot
(23:32):
it's going to go into. But in theory, if you
did drop it exactly the same place twice, it should
end up in the same slot twice. So boomy and
mechanics describes the universe that way that you have some
like variation in how the balls start to drop, which
is how you get a variation in the output. But
each trajectory of each one really is like a tiny,
classical little baseball. That's crazy to me. I mean that
(23:53):
requires like a whole rethinking of the idea of quantum mechanics,
because I've spent twenty years getting used to this concept
of the universe being random and unavailable and fuzzy, and
this is now saying, oh, no, you actually don't have
to take that whole weird route after all. Yes, that's right,
so you don't have to and so why go for it?
So I I mean, there is this is uncertainty that
you have regarding the nition then the configuration, right, initial configuration,
(24:16):
But that's it, right, you don't have to transform that
into in the necessarily into somehow random trajectories or randomness
more radical levels. But where is the fuzziness come from
in the beginning? I mean, does the universe start with fuzziness?
Because the standard picture we have, like why the universe
is not totally smooth while we have galaxies here and
not over there, is that we had some like quantum
(24:38):
fluctuations in the early universe that gave us densities which
you know, dot dot dot. Billions of years later we
have galaxies. Where did those fluctuations in the density of
the early universe come from, If not from quantum randomness,
is it some pre pre initial condition before the Big Bang? Yeah, well,
I have no idea, I mean, but I mean this
is I think it's a very very important thing to notice. Right. So,
(25:00):
if you do have a theory, which is like moving mechanics,
is precise mathematically and physically, meaning you do have equations
right written there, they apply every time, right, it's not like, oh,
you use this or use that measurement or no measurement. No,
it's precise, okay, And it's precise physically gives you a
picture of what's going on, which is exactly how it
was in the classical you know, when we're thinking about
(25:21):
classical physics, and one of the you know, the marriage
is that you can visualize. Okay. So but if you
do have this theory and there are crazy things about it,
you know how to which questions are needed? Right? Which
questions are really the ones that we should focus on? Okay?
So one question is where is this absolute ansertainty coming from?
(25:43):
Another question, right, is what about the fact the way
function is a function of all the configuration. There is
a sense in which you may think that, you know,
bombing mechanics removes all the romance from from physics, and
that I think that's you know, a merriage romance. I
would say, removes all the headaches the head Oh yeah, exactly.
(26:04):
I mean to me, it removes all the headaches. But
some people, you know, they think of that, Oh yeah,
but I mean the observer, you know, gains again, right,
the center of the attention. I'm not sympathetic at all
about this kind of talk, but I mean some people
are attracted by the craziness, right, and so when they
hear about Bowman mechanics, they think, oh, what is the
(26:24):
all the fun? What is this? I mean, physics is fun,
but maybe in a different way. I'm sympathetic to that,
because I think we want physics to teach us the
truth of the universe, and we hope in our hearts
somehow the truth of the universe is not what we
imagine that we're gonna be learning something that requires some
sort of like mental revolution to be like, wow, the
universe is so weird and different from what we imagine.
(26:45):
And so if you're just telling me, know, the universe
at the tiny scale, it's just a tiny little bunch
of baseballs, the way it is sort of like at
the atomic scale and the macroscopic scale and the scale
of planets and stars, then yeah, I guess that does
remove a little bit of the mystery. But you know what,
I was struggling to learn quantum mechanics and absorb it
intuitively as a college student. The thing that really got
me over the hump were these bells, theorems, and these
(27:08):
bells and equalities that really seemed like definitive proof that
quantum mechanics was random. And we have these experiments and
very clever people have shown that there are these correlations
among entangled particles that simply cannot happen if quantum mechanics
was not fundamentally random that you can't like secretly hide
(27:28):
all the information that it can't be the things are
really just one way or not the other way that
you know before you look at the electronic always was
spin up in my mind. Those bells and equality really
sort of like killed that possibility. Said, no, you have
to accept fundamental randomness. Why don't these theorems, these bills
and equalities and those experiments, why don't they kill Bonian mechanics?
(27:50):
They did kill it for a long time. Actually, you
know the first theorem that was the theory which allegedly
proved that heat and variable something impossible. It was still
too for Neuman in nine five or something like that,
and so he basically wanted to put an end to
all uh for reasons that are you know, maybe historically interesting,
(28:13):
but I mean what he wanted to provide was a
proof and mathematical proof that you cannot do better than
quantum theory. So that was just like kind of you know, oh,
we all would like to have a pictorial view of
visualized visualize about theory, right, but we cannot. That's what
he wanted to prove, and so he went by contradiction. Okay,
so he said, Okay, let's pretend for a second that
(28:34):
we can complete quantum mechanics. Let's pretend for a second
that we can add these hidden variables right to the theory.
The theory is not complete, right, it is, there are
these even variables. At first, their hidden for them in
the sense that quantum theory doesn't specify what they are.
And so he said, okay, let's pretend let's start with
this theory, let's work it out, let's work the consequences out.
(28:54):
And what he obtained was that there is some sort
of a contradiction, like five is greater than seven. I mean,
it's not really the case, but I mean you can
imagine something like that. Okay. So he said, okay, what
are the assumptions? I mean the reasonable assumption. So the
only assumption that so we had reasonable assumption, we started
from this hidden variable theory, we get contradictions. So the
(29:15):
only way out is just to say there are no
hidden variables. The quantum world is weird. For those of
you who don't know of Annoyingment is one of the
great mathematical geniuses of the century and really credited with
like pulling together the mathematics of modern quantum theory, and
so when he said something, people tended to listen, and
you know, it was sort of difficult to stand up
to Vannyman. You know, back in the forties when he
(29:36):
was in his hey day, he was very influential exactly.
I mean, there is actually something normal. It's not like
you can charge these people to have listened and just
relied on the authority. It was just like kind of normous.
It's not for Noyman process theory. I mean, there's not
much of a reason to suspect that he was wrong.
But he was wrong because he assumed something, which is
(29:57):
the start that assumption of quantum theory. The experiment doesn't
really change the system, Okay, The interaction is small enough
that the property that you're trying to measure is left
the same. Okay, like I was talking about before, right,
I do believe I have a fever. Say, okay, I
want to measure my temperature and making an experiment, put
the thermometer under my arm. Wait a second, wait for
(30:19):
the interaction. Than the mercury or whatever, the gallium or
whatever it is, expands and it gives me the temperature. Okay,
So but the temperature that I read it's not really
my temperature before I actually put the thermometer under my army.
It's actually the equilibrium temperature between the thermometermy and me. Okay, so,
(30:41):
but what I read is we forget about this all
the time because we believe that, I mean, this is
the property of the thermometer, which was the thermometer in
such a way that it doesn't affect too much that
the equilibrium temperature is really close to my original temperature.
So you're saying that, for example, when you measure your temperature,
you actually measure slightly lower temperature than your actual temperature
because the thermometer is slightly cooler than you and you
(31:02):
guys have come into equilibrium, and it's sort of like
putting a tiny little piece of ice on you and
it's cooled you down a little bit. And in the
same way, you need to take that into account. And
van Neuman ignored the impact of the measurement on the
system when he was making all of his calculations and
proof that quantum mechanics had to be random, that you
couldn't have any hidden variables. Right, It's actually worse than that,
(31:24):
because I mean, this is a general assumption that we
all make when you're doing quantum theory, right, we do
assume that I mean the operators represent properties. The problem
is that most of the time the experiments are such
that they perturbed the system so much that they don't
measure anything about the system. They tell you something about
the interaction. Think about you want to know where the
(31:46):
table is, Okay, so you switch on the light. Basically
what happens you hit the table surface with photons, the
photos going to your retina, and the retina records the result. Right,
but I mean the photo world bounce back, but also
the table ricoisly to bit. You forget about that, okay,
because the mass and blah blah blah. Okay, it's much bigger. However, instead,
(32:07):
if you instead of willing to try and find the
position of the table, you want to try and find
the position of an electron. Okay, you switch on the light.
The photon hits the electron, and the electron goes. So
what you measure the electron is going to click somewhere
in some detectors somewhere, So the position what you're measuring
is not the position of the electron before, it's the
position afterwards, Okay, which is totally fine, but I mean
(32:29):
what is tricky and sometimes what you want is that
not What for no, Himan actually proved was not that
hidden variables are impossible, but that he proved that not
all experiments are actually measurement. So all these certain experiments
are able to measure, namely those experiments where the interaction
(32:50):
is not that high to destroy the system or perturbit
too much. And how does that connect with hidden variables?
Like I get that he's showing that you can only
make a measurement if you're making it very small, all
negligible interaction on the system, that you're extracting information from
what happened before he measured it. How does that connect
to the question of whether quantum mechanics is really random
or whether there's sort of hidden information in there that
(33:11):
controls what's happening. It doesn't have much to do with
him invariables. That for sure. His theorem was supposed to
be showing that he did invariables are impossible, Okay, But
he didn't show that because he had this assumption in it.
He came out with the contradiction because he was assuming
this and so he was assuming that there are properties
and these properties have actually weird behavior. So he set
(33:32):
out to prove that hidden variables couldn't exist, and he
did by contradiction, but instead of a false assumption into
his proof, which is the thing that led to the contradiction.
So his conclusion about hiddenvariables was therefore invalid because the
contradiction came from somewhere else. And then this stood for decades. Right,
people thought, oh no, him improved, the quantum mechanics must
be random, so this the burglary theory, This, this deterministic
(33:54):
idea of quantum mechanics, We shouldn't even think about that.
And then what happened? When did people realize, oh, hold,
the second pandomen was wrong and it's possible to have
determinist e quantum mechanics. Yeah, well, some people actually figured
this out immediately, but we're ignored either because they were
you know, not very well known figure, or because they
didn't really want to batter. I mean, according to some people,
(34:16):
did Einstein figured this out immediately, but he didn't bother
to reply. And it is also true that the original
proof of phen nomen had other issues, which, however, where
you know, taking care of in proofs that came later.
But the person who actually figured this out was Bell
John Bell, who actually came back to this for no
(34:37):
human proof and figure out where he was wrong, namely
the assumption that operators necessarily mean you can understand experiments
always as measurement, which is not necessarily the case. So
the same Bell who is responsible for most people thinking
that equantum mechanics has to be random because he showed
these crazy inequalities, is the one who also revealed that
(34:57):
no Eman was wrong improving the quantum exist random. So
this Bell guy had a pretty big role to play
in our understanding one of mechanics. Yes, yes, and I mean.
And also it is the case that he was often
misunderstood for many years, even if he clearly wrote down
what he was trying to prove. So I mean indeed
he was writing about for Annoyman's proven very shortly after
(35:18):
he came up with his own belt inequality. So he
did try to provide a didn't variable theory. So he
was trying to do the same as for Annoyman and say, okay,
so if we do have it, this is it an
a variable? Here? What do we get? There is a
sense in which you can take as you were doing
at the beginning, right, he's inequality, just like a different
(35:38):
variety of impossibility proof against the invariable. But actually, as
many people would say, even if there is a sense
in which is it's controversial, I mean it's it's controversial
whether he actually proved it. What it's not controversially is
what he thought, Namely, he thought to have proven that
at the end of the name, if you have a
theory which respects the prediction of quantum kind of extent,
(36:00):
this theory has to be non no com right, So
let's unpack what that means for a moment. Because bells
inequality tells us that the universe has to be random,
there can't be any hidden variables. But it turns out
there's a caveat. That's only true if you're talking about
so called local information, right, and information which is accessible
to somebody like in their immediate environment. You know, like
(36:20):
I can know what's near me, I can measure something nearby,
but I don't know anything about what's happening in Andromeda
right now because this sort of limited passage of information.
And I want to talk more about entanglement and locality,
but first let's take another quick break. Okay, we're back
(36:51):
and we are talking about whether quantum mechanics is what
we call local. We know that there's a limit on
how fast in formation can move, that there's this speed
limit of information in the universe, and that information cannot
move instantaneously. But this gets confusing when we talk about
entangled particles. You create two electrons so that they have
(37:14):
to have opposite spin, but you don't know which electron
has spin up and which one is spinned down. But
as soon as you measure one to be spin up,
for example, you know instantaneously that the other one has
to be spinned down. And that seems sort of nonlocal
because the particles can be entangled, but they can also
be really far apart. So all of a sudden, when
(37:35):
you measure the spin of one particle, the other one,
which is many many kilometers or maybe light years away,
instantaneously collapses to have the other possibility. So I would
put it slightly differently in the sense that I would
say that in general, what Bell proofed is that you
do have no locality. In general, at the beginning particle
(37:55):
one didn't have any spin property because of the entire state.
When it's measured. Instead, oh, it turns up up so
and the other immediately down. And the issue there, of course,
is that these things can be separated. Right, so if
these two particles, they have to have opposite spins, and
classical or in the traditional equantum mechanics tells us that
both of them have the possibility to be up and down.
(38:17):
And so when you measure one of them and it
becomes up, then the other one, now hundreds of miles
away or thousands of miles away, somehow instantaneously goes from
being up or down to only being down. And that's
this question of nonlocality, right, how does the information get
from one particle, you know, to the other particle faster
than the speed of light. Yes, that's a problem. That's
(38:39):
something that the scars and regarded as a non starter.
That was just like thinking about, I mean, that's one
possibility and the other possibilities instead that they really had
a property or spin since the beginning. Right, So you
measure spin up because the first guy always had spin
up from the start, okay, And so they don't actually talk, right,
(39:02):
they were prepared and up and down and you detect
them up and down. And that's this hidden variables interpretation
that they always are something. It's just you don't know
about it. It's sort of hidden from you until you
measure it. But that there's no like actual uncertainty. It's
not like there's the particles actually in up and down
until you measure it. And so that's this problem with nonlocality, right,
And you're saying, einstein collaborators were suggesting this is ridiculous
(39:24):
because it requires a theory that's nonlocal, that somehow these
things have to you know, coordinate to make sure that
they're always opposite spins. And so what did Bell showed?
Bell showed that every theory of quantum mechanics has to
be nonlocal, Yes, because I mean he started off with
a theory like that and he predicts inequality, and so
they eat in variables. You have to imagine something like this,
(39:47):
so you have quantum mechanics. Quantum mechanics implies that there
has to be eating variables. So one of the main
objections people might have to this theory of deterministic particles
being guided by the way function information is actually there,
it's just that we don't know it sometimes is that
we thought that quantum mechanics have to be random because
of these arguments by Bell and these experiments that showed
(40:09):
that you couldn't explain these experiments using some hidden variables.
But it turns out then you couldn't explain those experiments
using local hidden variables, but you can explain those experiments
using non local hidden variables. So Bonian mechanics works and
is consistent with experiments if you have nonlocality, this idea
that particles that are not in the same place, that
(40:30):
are not near each other, can somehow you know, communicate
or coordinate their arrangements. And you might think, well, that's crazy,
that it's bonkers, how could that be possible? And that
seems like a pretty big objection, But I think, as
you're saying, Bell showed that this is actually true and
required for all theories of quantum mechanics, not just Bomian mechanics,
And so it's not really a strike against Bomian mechanics
(40:52):
to say that requires non local information. Yes, that's true,
because I mean he did prove his inequality. And if
you if right, then down in the in the appropriate way,
you will see that the hidden variable is just a
passage in the deduction, but it's actually something that you
don't require so that arguably what's going on is that
(41:13):
every single theory that has the same predictions fantum mechanics
will turn out to be non local. But doesn't nonlocality
seems sort of crazy. I mean, special relativity tells us
that information takes time to propagate through the universe. That
what's happening in Andromeda can't influence me right now because
I'm outside of its light cone. So if you're telling
me that not only does Bonian mechanics, which seems like
(41:35):
a beautiful description of the universe and nicely deterministic, require nonlocality,
but all theories of econom mechanics require nonlocality, how do
I then accept that? How do I think about the
universe as nonlocal? Does it mean that every particle in
Andromeda potentially can influence me right now? Yeah? Okay, so
that's the craziness, right. So that's a good thing about
Bona mechanics because in this theory the non locality is obvious.
(41:57):
It's clear right there in the wave functions. So then
that thing that we need to do as physicist is
to investigate how it's possible for a theory like that
to be compatible with relativity theory, right, so we just
give access to the right questions again before I actually
talk a little bit about that. I mean, so you
don't really have to go into the interpretation and show
(42:19):
that all the other interpretation are no local. Just think
about the regular theory, okay, with the collapse. When you
do have the collapse, the collapse is no local, right,
I mean, think about the original EPR argument. Right, how
do you explain the compa relation over there? It's no local, right,
You measure one, the other has to tell the first
one has to tell the other one. Right, that's no
(42:40):
locality right there. It's not a problem of the hidden variables.
I mean the regular I mean, the textbook theory has
it right there. Indeed, Heisenberg accepted that, yes, there are
some lectures that I forgot the year the precise here
in which he talks about exactly this. Right, the collapse
is no local, But then he says it doesn't contradict relativity.
(43:03):
He did really take it seriously that much because he
thought that you kind of use the non locality of
the collapse transfer information. So if you think of relativity
as a theory of sicknals, there is not I mean,
you can't get around, there's no locality, right, And so
for our listeners who are curious, it does seem like
there's some weird nonlocal features of quantum mechanics, but it
(43:26):
is not possible to use that nonlocality to send information
faster than the speed of light. And Jorge and I
did a whole podcast on that, so check that out
in detail. We don't have time to get into all
of that today, but if you're curious about why you
can't send information fast in the speed of light using
quantum entanglement, we did cover that in the whole podcast episode.
All right, So this is really fascinating and I don't
want to use too much more of your time, so
(43:46):
I just want to ask you if Bowman mechanics, you know,
is a nice, beautiful picture of the universe and explains
all the experiments that we have and doesn't require us
to accept some strange, alien uncertainty and randomness that's counterintuited
and only requires the acceptance of this concept of nonlocality,
which already is present in all other quantum theories. Then
(44:08):
why isn't it the dominant quantum theory? What are the
objections against it? Is? It's still sort of like historical
inertia because von Neuman didn't like it, or there you know,
real philosophical objections to it. So I mean, I think
that part of the problem has to do with the
fact that historically it was blocked. I mean there is
all this, you know, historical accidents that happened one after
the other. I mean the first bomb was you know,
(44:30):
ostracized for various reasons, and then for Neuman contributed to this,
there seemed to be no real reason to reject this
theory from from a rational point of view. I mean,
it provides a clear mathematical picture. It's a clear physical
picture as well. You do have to accept no locality,
as you said, but I mean it's something that we
have to deal with. Some people sometimes mentioned that, oh,
(44:52):
it's not testable in the sense that probably the prediction
of the Boomian mechanics are the same as quantum theory.
That's not a good objection for a variety of reason. First,
because I mean, you have a piece of evidence. You
have two theories, right, and so which one of the
theories the evidence confirming, assuming that you can confirm a
theory the first? Okay, so who came first? The brawl
(45:14):
nine twenty three. Right, uh, and so because no, no, no, no,
but it's simpler, right, you come to mechanics is simpler,
that's just one equation, but the mechanics has two equations,
one equation with two evolution equation. Okay, so what about
time of light? You have particle physicists, right, you measure
time of flight, You measure where the particle how long
they take to go from here to there? But there
(45:35):
is no time open it. And so what are this
time of light results? Well, I mean the drugular quantum
theory have resorts to this kind of approximation. Right. If
you approximate the time measurement in one way or in
another way, you get different distribution of results. Booming mechanics
gives you uh, you know their particles, right, So you
don't need the operators, right, you just do you use
the particles trajectories and do the calculation that you would
(45:57):
do classically, but with quantum tra actorism. And so there
is the possibility of actually making an experiment. So there
are some cases in which you can put yourself in
a situation in which the prediction from quantum theory are
different from boom mechanics. This can happen because you know,
quantum mechanics is not precise, some bigues in disrespect, so
(46:20):
you can test out. So there is a strong sense
in which you can, you know, falsify quantum theory or
quantum mechanics. So even if your physicists are usually strong
about this undetectability business, but I mean, no, you can detect. So,
I mean, I really don't understand that much about the
reasons why quantum mechanics hasn't been taken more seriously by physicists.
(46:45):
And I hope the situation we've changed. Well, what it
might require for to change is maybe for us to
meet alien intelligence and talk to them about quantum mechanics
and you know, maybe their way in and will say, sorry, folks,
we think it's many worlds or no, what you call
booming mechanics is what makes most sense to us. So
on the topic, let me ask you are totally off
the wall question, what do you think are the chances
(47:06):
of that that if we meet alien intelligence that they
will have sort of similar concepts about the universe. I mean,
it's really another way to ask the question, do you
think what we're doing here are playing games inside our
own minds? To try to tell mathematical stories about the
universe it makes sense to us, or do you think
we're actually probing something deep and universal which we could
present without embarrassment at the first Interstellar Physics meeting after
(47:30):
we meet the aliens. I really do hope that we
can meaningfully talk about the universe, and it seems like
we are actually succeeding in that right. We explained so
many things since the beginning that we started doing science. No,
we've made many hypothesis and constructive many theories, and some
some of them were bad ideas, some of them are
(47:50):
better ideas. I think that the fact that we are
explaining so much is an indication that maybe we are
onto something, but I don't know. I hope that we
can contribute to the alien meeting in some way. Maybe
they have their own version of bondingment and they've made
their own mistakes along the way, so we can help
them understand some of the things that we have learned.
(48:13):
I hope also that when we meet the aliens, we
can talk physics with them, because I hope that they
are advanced and that millions of years ago they were
struggling with these questions and now to them. It's child's play.
But I fear honestly that everything we've learned is sort
of centered in the human mind. We're asking human questions,
we're telling human stories using mathematical tools that makes sense
to humans, and that it might be frankly impossible to
(48:34):
translate into this knowledge to any other intelligence. But it
remains to be seen, and the universe has filled with surprises.
So I look forward to having hard quantum mechanics conversations
with alien physicists. All right, And with that, I'll say
thank you very much for coming out a podcast and
talking to us about this crazy concept of boom and mechanics.
It seems to me like sort of a beautiful theory
that lets us recover the sense that the universe makes sense,
(48:56):
that these particles are flying through the air, and they
have victories, and they were here and then they're there,
which means that they were sort of in between in
the middle. That you can still think about the universe
in a way that's intuitive to you, and that you
can sort of get rid of a lot of this
quantum weirdness and uncertainty. In some ways, it even hangs
together better than other theories, and it's a sort of
unfortunate that it was cast aside for so many decades
(49:19):
because of the mistake of eminent physicists. But we'll see
what the future holds and how much progress we have
to make. So thanks again very much for coming on
the podcast. It was a pleasure. Thank you, Thank you
very much. Thanks for listening, and remember that Daniel and
(49:39):
Jorge explained. The Universe is a production of I Heart
Radio or more podcast. For my heart Radio, visit the
I heart Radio app, Apple Podcasts, or wherever you listen
to your favorite shows.
Quantum mechanics just doesn't seem to make sense. It tells
us that the universe is fundamentally random, that some questions
just don't have answers, that there's a limit to what
can be known about reality, and that things change when
we look at them. More than that, it tells us
that reality is fundamentally different from what we have imagined.
(00:31):
But what if that's not true? What if that's wrong?
What if it were possible to build a theory of
quantum mechanics that doesn't describe the universe as bizarrely random,
that doesn't have any special role for observers, that doesn't
suffer from the famous measurement problem, and that lets us
think of the microscopic world as very similar to our
(00:54):
familiar intuitive world. And what if this theory actually worked
and was able to describe I've been predict experiments. That is,
what if there's an intuitive alternative to mainstream quantum mechanics.
If there were, why on Earth wouldn't it be embraced? Hi,
(01:28):
I'm Daniel. I'm a particle physicist and a professor of
physics that you see, Irvine, and I want to believe
that the world makes sense. We are all drawn to
basic questions about the nature of the universe. How does
it work, why is it this way and not some
other way? How did it all begin? And how will
it all end? Physics is supposed to be a way
to get answers to those questions, and so welcome to
(01:51):
the podcast Daniel and Jorge explained the Universe and production
of My Heart Radio, where this is precisely the kind
of question we ask and the kind of answer we
reach for. And the amazing thing is that physics kind
of seems to work. It offers explanations, explanations that not
only work because they could predict what happens in experiments,
but explanations that usually make some kind of sense. The
(02:15):
stories they tell us are mathematical and could be very
different from the stories we guessed at. It turns out
the Earth is billions of years old and not thousands,
that stars are massive balls of fusion in the sky
rather than tiny pin pricks in the screen. But in
the end, these mathematical stories that physics tells us about
the universe, they are coherent, they are sensible. We can
use them to understand how the universe really is. Except
(02:38):
in one area, quantum mechanics. While we do have a
working theory, we struggle to make sense of it. What
does it really mean? What is it telling us about
how the world really is? And while we have lots
of different interpretations, we struggle to accept the story that
they tell us. Is the universe really random? Is everything
(02:58):
really described by the wave function? Does it collapse when
you observe it? Or split into millions of meta universes?
Or do objects not really have any properties on their
own to observe or all properties relative to the observer.
None of these are easy to absorb, to click into
our minds and let you say, oh, yeah, I get it,
that's how the universe is. But what if there was
(03:21):
a version of quantum mechanics that was more intuitive, that
was deterministic, that didn't need some observer effect or multiple
universes or a redefinition of the nature of reality. Well,
today we will be exploring a less popular theory of
quantum mechanics that doesn't rely on randomness and uncertainty. It
tells us that what is happening to tiny particles is
(03:44):
much simpler and easier to swallow, and we'll talk about
why it's been overlooked by mainstream physics. So today on
the podcast, we'll be asking the question the quantum mechanics
have to be so random? My friend and co host
(04:05):
Orges on a break, so I'm continuing our series of
conversations with experts in quantum mechanics. We spoke to Adam
Becker about mainstream quantum mechanics, to Carlo Rovelli about his
theory of relational quantum mechanics, to Sean Carroll about the
many world interpretation, and today we are speaking to an
expert on pilot wave theory, also known as Boemian mechanics.
(04:31):
So it's my great pleasure today to introduce all of
you to Professor Valia Alori, who, if I understand correctly,
holds two pH d s, one in physics and one
in philosophy, so she's the perfect person for us to
talk to about the crazy philosophical consequences of quantum mechanics.
She's also a full professor in the Department of Philosophy
(04:51):
at Northern Illinois University and a fellow at the John
Bell Institute for Foundations of Physics. Professor A Lorii, welcome
the podcast. Thank you for having me, well, thank you
for coming here to talk to us about the mysteries
of quantum mechanics. Before we get into the details of
pilot wave theory, I thought we should take a step
back and remind ourselves why we have so many theories
(05:13):
of quantum mechanics and why there are still so many
questions about it. To me, the basic question we have
about quantum mechanics is what is going on? How do
we understand the story that it's telling us. Our intuition
is to think of particles as tiny dots of matter,
but quantum mechanics usually tells us that they are basically different,
that they are fundamentally different kinds of things because they
(05:36):
can maintain two contradictory possibilities at once. There's also this
wave function that seems to control what happens, but then
it collapses when you touch it, but it's not clear
what the rules of that collapse are. It's so hard
to get a mental picture of what's going on with
the little particles. So how do you approach this question
of trying to understand what quantum mechanics? So first of all,
(06:01):
let me just say that I'm not sure that we
should understand quantum mechanics philosophically there is a sense in
which we don't understand quantum mechanics even physically as a
physical theory, because I mean, the theory seems to be
talking about you know, electrons and protons and matter in
(06:22):
general and fields, but when you actually look at the formalism,
it's unclear exactly what plays the rollers of what. So
we do have a an equation, the Shouldinger equation, which
is a question of the evolution of the wave function.
Should we understand the way function as a physical object.
If the wave function is a physical object, what does
it represent? Does it represent particles, does it represent fields?
(06:45):
Since I was a student, just to put it bluntly,
I really had trouble relating to the theory as a
physics student. But even granting that the it's accurate to
talk about that as a theory about something. Let's put
it this way. The ory, I would say, is either
empirically inadequate or it's incomplete. Why is that? Well, because
(07:09):
I just said that, you do have this equation, which
is the shrining equation, which is a again equestion of
evolution of an objicle the wave function, and the wave
function is a called like that because it's a wave
so and wave can superimpose. You know, you throw a
rock in the pond, right, throw another rock in the pond.
(07:29):
Then you see waves from one rock and then you
see the other rock. They superimposed. You have interference and
the fraction of this kind of behavior that you would
attribute to waves. Okay, And so since there's two superimposed.
If you think of the wave functions are presenting objects
of physical objects right at the microscopic level, they could
be in a superposition state, right, and nucluse that adioactive
(07:52):
substance of subsort could be in the superposition of a
decade state or a non decade state. And by superposition
you mean that there's two possibilities for an object. It
could be spin up or spin down, or decade or
not decade. There's two options for the situation. It can
actually be in yes, in a sense, yes, more generally,
I mean mathematically, this is the mathematical property of the equation, right.
(08:14):
I mean the prototype example is the problem of the
shrilling a cat, right, in which you do have this
cat which is in a box. Right in the box
that is this vial of poison. De vial of poison
will break because it's connected to this radioactive substance, so
it will break if the substance will decay. If nothing happens,
(08:34):
it will not break. So what happens is that if
the nucleus decase, bile of poison breaks and the cat dies. Okay,
So that's a possible state of affairs. Otherwise nothing happens
in the cat stays alive, okay. And so what happens
is that, however, given the superposition state possibility, given the
fact that there is a possibility of having a superposition
(08:57):
state as a true physical state for this system, then
you could also have this microscopic superposition of decade and
not decayed, which actually spread out of the cat. And
so the theory predicts this microscopic superposition which we never
ever observed. They are not observable. That's not what we
have experienced. Off So there is a very strong sense
(09:20):
in which the theory as it is is empirically inadequate,
because when we open the box and we when we
check on the cat, the cat is either dad or alive.
So what I'm hearing you saying is that quantum mechanics
is useful as a description of these microscopic states. But
which I think you mean like quantum particles, electrons and photons, etcetera.
(09:41):
But that we don't really understand what it means and
we can't access it directly. We can't like see these things.
We have to interact with them using macroscopic objects like
detectors or our fingers or cats, etcetera, which don't have
the same quantum properties, And so it doesn't really answer
the question of like, what's actually going on in the
microscopic leve Is that a summary of the problem. Yes,
(10:02):
Actually it's more than that. So not only doesn't explain
what's going on intuitively at the microscopic level, but also
if you try to apply the theory to everything, including
cats and detectors and stuff like that, the theory doesn't
give you what you observe. So it's really bad for
the theory. The theory doesn't I mean, it is actually
falsified directly by the fact that the training Garry question
(10:25):
is it's a linear I think because you're saying that
they suggest that cats should also be in superpositions, and
fingers and detectors and everything should be in superpositions. But
that's not what we observe. That's what you mean by
experimentally falsifying, Yes, exactly, and of course, I mean, you know,
the family fathers were not naive and the newness okay,
and that's why they proposed, at least that's what for
(10:45):
Neuman did, right. He proposed that there is actually a
second evolution a question for the wave function. And so
they say, okay, right, you don't want macroscopy superposition. Okay,
So when do you get them again? Oh, when there
is a measurement. Uh huh. So when the measurement is performed,
then there is a different evolution equation. The wave function
randomly collapses in one of the terms a superpositional when
(11:08):
you open the door and you see the cat ha ha,
the wave function actually collapses. So you write in a
sense right as a detector, right, you collapse the wave function.
The issue there is that we don't have a clear
definition of what a measurement is and when it happens.
Because you can imagine, you know, if I'm poking something
with my finger, the tip of my finger is still
a microscopic particle, So why should it collapse the way
(11:30):
function and two particles on the tip of my fingers
should still be a quantum mechanical system. So there's no
like clear line when something becomes classical or microscopic when
the wave function should collapse. Yes, exactly. I mean we
don't know who does the collapsing, who kills the cat? Right?
So is it me when I open the door, or
is it my consciousness? We don't really want to enter
(11:51):
into that. So it is a problem that you're suggesting. Namely,
it's not a precise physical theory. It doesn't really define
what a measurement is. Because I mean, this is puzzling,
because we just would like measurement just to be physical
processes like anything else, right, I mean, they're made of particles,
quantum particles, and so why are they special? So there
(12:12):
is a sense in which started from this, which is
called the measurement problem, because I mean, we are actually
measuring what is the state of the cat, and the
cat is actually measuring what is the state of the particle.
Another way of putting this would be that measurements, when
you're performing a measurement. Quantum theory says that measurements do
not have a precise result. Okay, so like the cat
(12:35):
doesn't have a precise state, and so various people call
them interpretation. But I actually think that they are different theories,
but they have different solutions of these problem so to speak.
So bo mechanics is one of those. It does solve
this problem, even if I do think that's not the way.
The reason why it was proposed. So this theory was
(12:58):
proposed by I mean, the first version of this was
proposed by the Brody in ninety three as part of
his dissertation. So according to this theory, what happens is
that I just like very very some people like to
put it and romantic, right, something very plan and boring
in a sense obvious because it's according to this theory,
(13:20):
matter is made of particles, just liking classical mechanics, but
they do have a different evolution equation than quantum theories.
In this theory there is this object which is the
wave function, which is the same guy as ordinary quantum theory,
but it devolves according to Shrinninger equation. So you do
have this an evolution a question for the particles, which
(13:40):
is first to order, and then you have an object
which is the wave function, which evolves like in regular
quantum mechanics according to the Shrininger equation. So then in
the Copenhagen interpretation, the one most people are familiar with.
The wave function is supposed to be everything is supposed
to describe the whole system, and particles when we're not
looking at them, sort of operated according to this wave auction,
which you know evolves according to the Shortinger equation. But
(14:03):
then there's this weird second bit where things collapse to
particle like behavior that we observe when you look at them. So,
for example, you have a particle that's supposed to hit
the screen, the whole wave hits the whole screen, but
at some point when it interacts, when that measurement happens,
then it becomes a single point, a flash of light
on that screen. And so you're saying that Bomian mechanics
is different because not only do you have the wave function,
(14:24):
but you also have the particles. It's not like this.
There's sometimes waves and then sometimes particles. They're always particles,
but they're governed by this wave that sort of guides
them through their path. Yes, so there are always particles.
That's what matter is made off. Tables and chairs and
people and screens and detectors and whatever are all made
of particles. So what happens is that these particles their
(14:47):
trajectories is mathematically written down in terms of this wave function,
and this way function in itself evolves according to a
given equation. Okay, So usually what you said is kind
of important because some I mean, very common way of
describing the theory, which is also called because of this reason,
the pilot wave theory, is that this particle are pushed
(15:08):
around by this wave. Okay. So the user slogan is, oh,
it's not particle end waves or waves, it's particle end waves. Okay.
So there is a sense in which this is true,
in the sense that there are particles and there is
also this wave function. However, I think that it is
(15:28):
kind of misleading to think of that in these terms,
because if you think about what kind of entity the
wave function is, it is a wave, but not a
wave in three dimensional space. Okay. If you think of
how to represent the wave function, what the wave function
really is, It's a function of all the particles, right,
(15:49):
It is a function of the configuration in the case
of bow Mean mechanics, the function of the configuration about
the particles. So it has three dimensions for every particle.
So in total it has three n dimensions. If the
universe is composed of and particles, so it's not a
field into adimensional space. The way function, then, just to
be clear, talks about the trajectory of all of the
(16:10):
particles in the universe, and so they're all sort of
combined into this one grand object. The way function mechanics
talks about is the way function of the universe. So
the one that evolves according to the shooting their question
is the way function of the universe. So I do
have two things to clarify here. So the first thing is,
(16:32):
so how we should interpret this wave function physically. It's
an open question. I mean, philosophers and physicists are talking
about this all the time. But I do think if
you describe b My mechanics as I just did name
it is a theory of particles with the wave function
defining that trajectory, and you can understand that the way
function as pushing the particles just in the same way
(16:52):
as you understand gravity is pulling stuff right on the ground. Okay,
So it's I think that the best this is my
personal take on this, is that the best way of
understanding the way function in Bowman mechanics is to think
of that as law like right, It's part of the
ingredients of the law of nature, something that you need
(17:12):
right in order to specify the right trajectory, the one
that you observe. And so the other thing was about
the way function of the universe. So the fact that
the way function is a function of all these particles
is something that leads to a very important feature of
Bonan mechanics, which is it's no locality. And I want
to talk about non locality in a minute, but first
(17:32):
I just want to make sure that we have a
clear sense of what's going on here. So we talked
about how the problem with quantum mechanics was this measurement
problem that what happens when you measure this wave and
it collapses into a particle. So how exactly does bow
mean mechanics solve that problem? Is it because things are
always a particle and so when you look at them,
they were a particle and it's no big deal, and
this is where it was, and it has like a
(17:53):
well defined trajectory that in bow Mean mechanics you really
can think about like electrons as tiny little dots of
matter flying through the universe, the way planets fly through
the Solar system. Yes, I think that's right in the
case of the cat. The cats made of particles like
everything else, So it is either dead or alive. Okay.
The cat is either dead or alive at all times. Okay,
(18:17):
So the macroscopic superposition should not belong to the wave functions.
But the wave function is not what cat is made of.
The cat was made of particles and particulars a precise location,
which is what it is right, either in the dead
camp or a in the life camp. So this is
really different from the way people are sort of taught
to think about quantum mechanics. That information isn't there until
you measure it, that there's a fuzziness to the universe
(18:39):
that is fundamentally random, all these really alien elements of
quantum mechanics that make it so weird. Bo Mean mechanics
seems to sort of like chuck that out the window
and say, no, everything actually is determined. There is no
randomness or uncertainty. There's just some information you sometimes haven't
measured yet, but it's really there. That the cat really
is dead or is alive. It's never sort of uncertain.
(19:00):
Is that true? That there's really no randomness, no true
randomness In Boomian mechanics. It depends on what is meant
by that. So it is true that the cat is
either dead or alive. It is true that the particles
even passes through one sleet or the other sleet. It
is true that when you observe a flash on the screen,
that was coming from a particle that traveled all the
way from the source to the screen. And it is
(19:22):
true that there is no fuzziness. That's why I think
that Bomian mechanics is physically clear. And the question is okay,
so is there no randomness? Well, now there is randomness
because the prediction of Bomian mechanics are provable to be
the same as quantum mechanics. And quantum mechanics predicts probabilities. Right,
the traditional stories that you do get only the probabilities
(19:46):
of the results. Right, you obtain this, this or that
not with a definite outcome. For sure, you have a
probability distribution of the experimental results. So the legitimate question
is where is the probability is coming from in Bomia mechanics.
They come from the fact that So I mean, this
is more general question about how is it possible to
(20:09):
get probabilities if you have a deterministic theory. Deterministic theory,
you have one past, one future, right if you know
the law. If you not the initialis condition, you know everything, right,
everything is determined. If you have this laplacean demon knows
it at all and everything he knows everything. So this
is a deterministic theory. So where the probability is coming from.
They're coming from the initiative conditions. Okay, so there are
(20:30):
two elements here, right. In determinism is something like that,
given the initiative conditions and given the laws, you know everything.
So if you do know the laws and you do
know that, I mean principle, you can predict anything. I
want to talk more about this randomness and initial conditions,
but first let's take a quick break. All right, we're back,
(21:01):
and we are talking about Bomian mechanics, a really fascinating
quantum theory that describes the universe as filled with actual,
tiny little dots of matter moving on what are like
classical paths, but guided by a wave function that gives
them the appearance of wave like behavior. And the element
that we're talking about right now is this question of randomness.
(21:22):
In traditional quantum mechanics, we are told that the universe
is fundamentally random, that there aren't hidden variables that control
what actually happens. But Boian mechanics says the opposite. It
says that things are actually determined by the initial conditions,
and that if you do the same experiment multiple times
with exactly the same initial conditions, you should get the
same output. So I'm a particle physicist and at the
(21:43):
Large Hadron Collider we smash protons together multiple times, and
we often say that if we smash those protons together
with exactly the same initial conditions, we would still get
different outcomes every time. That is quantum mechanical, and that
it's drawn from some probability distribution that somewhere seriously, the
universe is like rolling the dye based on this probability
(22:03):
distribution and deciding what happens on the giving collision. But
you're saying that Bomian mechanics is deterministic, and that if
I get two different collisions giving me two different outcomes,
that's because the initial conditions were slightly different, the protons
that a slightly different energy or slightly different angle, and
that if it was actually able to repeat the same
exact experiment, I should get the same exact outcome, is
(22:24):
that right? So yes, so so so if you say
that you do have this distribution of the particles, the
particles of distributed according to quantum ecalibbon distribution, and it
is an equilibient distribution and nothing changes anymore, then that's
the most complete information that you may have about this particles.
And so we don't have more knowledge than this about
the particles. Then we have absolute tons certainty about the
(22:48):
precise positions of the particles. And so this plays out
into having a distribution of the outcomes at the end
of the experiment. I see. So we have particles which
go through the experiment using deterministic laws. So the entire
outcomes determined for each particle based on how it came
into the experiment. But we have some distribution of inputs
(23:10):
at the particles when they come into the experiment. They're
never all actually at the same angle or location or whatever.
There's some variation there and that gives a variation in
the output. So not a randomness, but you have sort
of variation and the inputs gets translated to a variation
on the outputs, sort of like you know that game
where you drop a ball and it goes left and right,
and left and right and left and right. It sort
of chaotic. It's very hard to predict exactly what slot
(23:32):
it's going to go into. But in theory, if you
did drop it exactly the same place twice, it should
end up in the same slot twice. So boomy and
mechanics describes the universe that way that you have some
like variation in how the balls start to drop, which
is how you get a variation in the output. But
each trajectory of each one really is like a tiny,
classical little baseball. That's crazy to me. I mean that
(23:53):
requires like a whole rethinking of the idea of quantum mechanics,
because I've spent twenty years getting used to this concept
of the universe being random and unavailable and fuzzy, and
this is now saying, oh, no, you actually don't have
to take that whole weird route after all. Yes, that's right,
so you don't have to and so why go for it?
So I I mean, there is this is uncertainty that
you have regarding the nition then the configuration, right, initial configuration,
(24:16):
But that's it, right, you don't have to transform that
into in the necessarily into somehow random trajectories or randomness
more radical levels. But where is the fuzziness come from
in the beginning? I mean, does the universe start with fuzziness?
Because the standard picture we have, like why the universe
is not totally smooth while we have galaxies here and
not over there, is that we had some like quantum
(24:38):
fluctuations in the early universe that gave us densities which
you know, dot dot dot. Billions of years later we
have galaxies. Where did those fluctuations in the density of
the early universe come from, If not from quantum randomness,
is it some pre pre initial condition before the Big Bang? Yeah, well,
I have no idea, I mean, but I mean this
is I think it's a very very important thing to notice. Right. So,
(25:00):
if you do have a theory, which is like moving mechanics,
is precise mathematically and physically, meaning you do have equations
right written there, they apply every time, right, it's not like, oh,
you use this or use that measurement or no measurement. No,
it's precise, okay, And it's precise physically gives you a
picture of what's going on, which is exactly how it
was in the classical you know, when we're thinking about
(25:21):
classical physics, and one of the you know, the marriage
is that you can visualize. Okay. So but if you
do have this theory and there are crazy things about it,
you know how to which questions are needed? Right? Which
questions are really the ones that we should focus on? Okay?
So one question is where is this absolute ansertainty coming from?
(25:43):
Another question, right, is what about the fact the way
function is a function of all the configuration. There is
a sense in which you may think that, you know,
bombing mechanics removes all the romance from from physics, and
that I think that's you know, a merriage romance. I
would say, removes all the headaches the head Oh yeah, exactly.
(26:04):
I mean to me, it removes all the headaches. But
some people, you know, they think of that, Oh yeah,
but I mean the observer, you know, gains again, right,
the center of the attention. I'm not sympathetic at all
about this kind of talk, but I mean some people
are attracted by the craziness, right, and so when they
hear about Bowman mechanics, they think, oh, what is the
(26:24):
all the fun? What is this? I mean, physics is fun,
but maybe in a different way. I'm sympathetic to that,
because I think we want physics to teach us the
truth of the universe, and we hope in our hearts
somehow the truth of the universe is not what we
imagine that we're gonna be learning something that requires some
sort of like mental revolution to be like, wow, the
universe is so weird and different from what we imagine.
(26:45):
And so if you're just telling me, know, the universe
at the tiny scale, it's just a tiny little bunch
of baseballs, the way it is sort of like at
the atomic scale and the macroscopic scale and the scale
of planets and stars, then yeah, I guess that does
remove a little bit of the mystery. But you know what,
I was struggling to learn quantum mechanics and absorb it
intuitively as a college student. The thing that really got
me over the hump were these bells, theorems, and these
(27:08):
bells and equalities that really seemed like definitive proof that
quantum mechanics was random. And we have these experiments and
very clever people have shown that there are these correlations
among entangled particles that simply cannot happen if quantum mechanics
was not fundamentally random that you can't like secretly hide
(27:28):
all the information that it can't be the things are
really just one way or not the other way that
you know before you look at the electronic always was
spin up in my mind. Those bells and equality really
sort of like killed that possibility. Said, no, you have
to accept fundamental randomness. Why don't these theorems, these bills
and equalities and those experiments, why don't they kill Bonian mechanics?
(27:50):
They did kill it for a long time. Actually, you
know the first theorem that was the theory which allegedly
proved that heat and variable something impossible. It was still
too for Neuman in nine five or something like that,
and so he basically wanted to put an end to
all uh for reasons that are you know, maybe historically interesting,
(28:13):
but I mean what he wanted to provide was a
proof and mathematical proof that you cannot do better than
quantum theory. So that was just like kind of you know, oh,
we all would like to have a pictorial view of
visualized visualize about theory, right, but we cannot. That's what
he wanted to prove, and so he went by contradiction. Okay,
so he said, Okay, let's pretend for a second that
(28:34):
we can complete quantum mechanics. Let's pretend for a second
that we can add these hidden variables right to the theory.
The theory is not complete, right, it is, there are
these even variables. At first, their hidden for them in
the sense that quantum theory doesn't specify what they are.
And so he said, okay, let's pretend let's start with
this theory, let's work it out, let's work the consequences out.
(28:54):
And what he obtained was that there is some sort
of a contradiction, like five is greater than seven. I mean,
it's not really the case, but I mean you can
imagine something like that. Okay. So he said, okay, what
are the assumptions? I mean the reasonable assumption. So the
only assumption that so we had reasonable assumption, we started
from this hidden variable theory, we get contradictions. So the
(29:15):
only way out is just to say there are no
hidden variables. The quantum world is weird. For those of
you who don't know of Annoyingment is one of the
great mathematical geniuses of the century and really credited with
like pulling together the mathematics of modern quantum theory, and
so when he said something, people tended to listen, and
you know, it was sort of difficult to stand up
to Vannyman. You know, back in the forties when he
(29:36):
was in his hey day, he was very influential exactly.
I mean, there is actually something normal. It's not like
you can charge these people to have listened and just
relied on the authority. It was just like kind of normous.
It's not for Noyman process theory. I mean, there's not
much of a reason to suspect that he was wrong.
But he was wrong because he assumed something, which is
(29:57):
the start that assumption of quantum theory. The experiment doesn't
really change the system, Okay, The interaction is small enough
that the property that you're trying to measure is left
the same. Okay, like I was talking about before, right,
I do believe I have a fever. Say, okay, I
want to measure my temperature and making an experiment, put
the thermometer under my arm. Wait a second, wait for
(30:19):
the interaction. Than the mercury or whatever, the gallium or
whatever it is, expands and it gives me the temperature. Okay,
So but the temperature that I read it's not really
my temperature before I actually put the thermometer under my army.
It's actually the equilibrium temperature between the thermometermy and me. Okay, so,
(30:41):
but what I read is we forget about this all
the time because we believe that, I mean, this is
the property of the thermometer, which was the thermometer in
such a way that it doesn't affect too much that
the equilibrium temperature is really close to my original temperature.
So you're saying that, for example, when you measure your temperature,
you actually measure slightly lower temperature than your actual temperature
because the thermometer is slightly cooler than you and you
(31:02):
guys have come into equilibrium, and it's sort of like
putting a tiny little piece of ice on you and
it's cooled you down a little bit. And in the
same way, you need to take that into account. And
van Neuman ignored the impact of the measurement on the
system when he was making all of his calculations and
proof that quantum mechanics had to be random, that you
couldn't have any hidden variables. Right, It's actually worse than that,
(31:24):
because I mean, this is a general assumption that we
all make when you're doing quantum theory, right, we do
assume that I mean the operators represent properties. The problem
is that most of the time the experiments are such
that they perturbed the system so much that they don't
measure anything about the system. They tell you something about
the interaction. Think about you want to know where the
(31:46):
table is, Okay, so you switch on the light. Basically
what happens you hit the table surface with photons, the
photos going to your retina, and the retina records the result. Right,
but I mean the photo world bounce back, but also
the table ricoisly to bit. You forget about that, okay,
because the mass and blah blah blah. Okay, it's much bigger. However, instead,
(32:07):
if you instead of willing to try and find the
position of the table, you want to try and find
the position of an electron. Okay, you switch on the light.
The photon hits the electron, and the electron goes. So
what you measure the electron is going to click somewhere
in some detectors somewhere, So the position what you're measuring
is not the position of the electron before, it's the
position afterwards, Okay, which is totally fine, but I mean
(32:29):
what is tricky and sometimes what you want is that
not What for no, Himan actually proved was not that
hidden variables are impossible, but that he proved that not
all experiments are actually measurement. So all these certain experiments
are able to measure, namely those experiments where the interaction
(32:50):
is not that high to destroy the system or perturbit
too much. And how does that connect with hidden variables?
Like I get that he's showing that you can only
make a measurement if you're making it very small, all
negligible interaction on the system, that you're extracting information from
what happened before he measured it. How does that connect
to the question of whether quantum mechanics is really random
or whether there's sort of hidden information in there that
(33:11):
controls what's happening. It doesn't have much to do with
him invariables. That for sure. His theorem was supposed to
be showing that he did invariables are impossible, Okay, But
he didn't show that because he had this assumption in it.
He came out with the contradiction because he was assuming
this and so he was assuming that there are properties
and these properties have actually weird behavior. So he set
(33:32):
out to prove that hidden variables couldn't exist, and he
did by contradiction, but instead of a false assumption into
his proof, which is the thing that led to the contradiction.
So his conclusion about hiddenvariables was therefore invalid because the
contradiction came from somewhere else. And then this stood for decades. Right,
people thought, oh no, him improved, the quantum mechanics must
be random, so this the burglary theory, This, this deterministic
(33:54):
idea of quantum mechanics, We shouldn't even think about that.
And then what happened? When did people realize, oh, hold,
the second pandomen was wrong and it's possible to have
determinist e quantum mechanics. Yeah, well, some people actually figured
this out immediately, but we're ignored either because they were
you know, not very well known figure, or because they
didn't really want to batter. I mean, according to some people,
(34:16):
did Einstein figured this out immediately, but he didn't bother
to reply. And it is also true that the original
proof of phen nomen had other issues, which, however, where
you know, taking care of in proofs that came later.
But the person who actually figured this out was Bell
John Bell, who actually came back to this for no
(34:37):
human proof and figure out where he was wrong, namely
the assumption that operators necessarily mean you can understand experiments
always as measurement, which is not necessarily the case. So
the same Bell who is responsible for most people thinking
that equantum mechanics has to be random because he showed
these crazy inequalities, is the one who also revealed that
(34:57):
no Eman was wrong improving the quantum exist random. So
this Bell guy had a pretty big role to play
in our understanding one of mechanics. Yes, yes, and I mean.
And also it is the case that he was often
misunderstood for many years, even if he clearly wrote down
what he was trying to prove. So I mean indeed
he was writing about for Annoyman's proven very shortly after
(35:18):
he came up with his own belt inequality. So he
did try to provide a didn't variable theory. So he
was trying to do the same as for Annoyman and say, okay,
so if we do have it, this is it an
a variable? Here? What do we get? There is a
sense in which you can take as you were doing
at the beginning, right, he's inequality, just like a different
(35:38):
variety of impossibility proof against the invariable. But actually, as
many people would say, even if there is a sense
in which is it's controversial, I mean it's it's controversial
whether he actually proved it. What it's not controversially is
what he thought, Namely, he thought to have proven that
at the end of the name, if you have a
theory which respects the prediction of quantum kind of extent,
(36:00):
this theory has to be non no com right, So
let's unpack what that means for a moment. Because bells
inequality tells us that the universe has to be random,
there can't be any hidden variables. But it turns out
there's a caveat. That's only true if you're talking about
so called local information, right, and information which is accessible
to somebody like in their immediate environment. You know, like
(36:20):
I can know what's near me, I can measure something nearby,
but I don't know anything about what's happening in Andromeda
right now because this sort of limited passage of information.
And I want to talk more about entanglement and locality,
but first let's take another quick break. Okay, we're back
(36:51):
and we are talking about whether quantum mechanics is what
we call local. We know that there's a limit on
how fast in formation can move, that there's this speed
limit of information in the universe, and that information cannot
move instantaneously. But this gets confusing when we talk about
entangled particles. You create two electrons so that they have
(37:14):
to have opposite spin, but you don't know which electron
has spin up and which one is spinned down. But
as soon as you measure one to be spin up,
for example, you know instantaneously that the other one has
to be spinned down. And that seems sort of nonlocal
because the particles can be entangled, but they can also
be really far apart. So all of a sudden, when
(37:35):
you measure the spin of one particle, the other one,
which is many many kilometers or maybe light years away,
instantaneously collapses to have the other possibility. So I would
put it slightly differently in the sense that I would
say that in general, what Bell proofed is that you
do have no locality. In general, at the beginning particle
(37:55):
one didn't have any spin property because of the entire state.
When it's measured. Instead, oh, it turns up up so
and the other immediately down. And the issue there, of course,
is that these things can be separated. Right, so if
these two particles, they have to have opposite spins, and
classical or in the traditional equantum mechanics tells us that
both of them have the possibility to be up and down.
(38:17):
And so when you measure one of them and it
becomes up, then the other one, now hundreds of miles
away or thousands of miles away, somehow instantaneously goes from
being up or down to only being down. And that's
this question of nonlocality, right, how does the information get
from one particle, you know, to the other particle faster
than the speed of light. Yes, that's a problem. That's
(38:39):
something that the scars and regarded as a non starter.
That was just like thinking about, I mean, that's one
possibility and the other possibilities instead that they really had
a property or spin since the beginning. Right, So you
measure spin up because the first guy always had spin
up from the start, okay, And so they don't actually talk, right,
(39:02):
they were prepared and up and down and you detect
them up and down. And that's this hidden variables interpretation
that they always are something. It's just you don't know
about it. It's sort of hidden from you until you
measure it. But that there's no like actual uncertainty. It's
not like there's the particles actually in up and down
until you measure it. And so that's this problem with nonlocality, right,
And you're saying, einstein collaborators were suggesting this is ridiculous
(39:24):
because it requires a theory that's nonlocal, that somehow these
things have to you know, coordinate to make sure that
they're always opposite spins. And so what did Bell showed?
Bell showed that every theory of quantum mechanics has to
be nonlocal, Yes, because I mean he started off with
a theory like that and he predicts inequality, and so
they eat in variables. You have to imagine something like this,
(39:47):
so you have quantum mechanics. Quantum mechanics implies that there
has to be eating variables. So one of the main
objections people might have to this theory of deterministic particles
being guided by the way function information is actually there,
it's just that we don't know it sometimes is that
we thought that quantum mechanics have to be random because
of these arguments by Bell and these experiments that showed
(40:09):
that you couldn't explain these experiments using some hidden variables.
But it turns out then you couldn't explain those experiments
using local hidden variables, but you can explain those experiments
using non local hidden variables. So Bonian mechanics works and
is consistent with experiments if you have nonlocality, this idea
that particles that are not in the same place, that
(40:30):
are not near each other, can somehow you know, communicate
or coordinate their arrangements. And you might think, well, that's crazy,
that it's bonkers, how could that be possible? And that
seems like a pretty big objection, But I think, as
you're saying, Bell showed that this is actually true and
required for all theories of quantum mechanics, not just Bomian mechanics,
And so it's not really a strike against Bomian mechanics
(40:52):
to say that requires non local information. Yes, that's true,
because I mean he did prove his inequality. And if
you if right, then down in the in the appropriate way,
you will see that the hidden variable is just a
passage in the deduction, but it's actually something that you
don't require so that arguably what's going on is that
(41:13):
every single theory that has the same predictions fantum mechanics
will turn out to be non local. But doesn't nonlocality
seems sort of crazy. I mean, special relativity tells us
that information takes time to propagate through the universe. That
what's happening in Andromeda can't influence me right now because
I'm outside of its light cone. So if you're telling
me that not only does Bonian mechanics, which seems like
(41:35):
a beautiful description of the universe and nicely deterministic, require nonlocality,
but all theories of econom mechanics require nonlocality, how do
I then accept that? How do I think about the
universe as nonlocal? Does it mean that every particle in
Andromeda potentially can influence me right now? Yeah? Okay, so
that's the craziness, right. So that's a good thing about
Bona mechanics because in this theory the non locality is obvious.
(41:57):
It's clear right there in the wave functions. So then
that thing that we need to do as physicist is
to investigate how it's possible for a theory like that
to be compatible with relativity theory, right, so we just
give access to the right questions again before I actually
talk a little bit about that. I mean, so you
don't really have to go into the interpretation and show
(42:19):
that all the other interpretation are no local. Just think
about the regular theory, okay, with the collapse. When you
do have the collapse, the collapse is no local, right,
I mean, think about the original EPR argument. Right, how
do you explain the compa relation over there? It's no local, right,
You measure one, the other has to tell the first
one has to tell the other one. Right, that's no
(42:40):
locality right there. It's not a problem of the hidden variables.
I mean the regular I mean, the textbook theory has
it right there. Indeed, Heisenberg accepted that, yes, there are
some lectures that I forgot the year the precise here
in which he talks about exactly this. Right, the collapse
is no local, But then he says it doesn't contradict relativity.
(43:03):
He did really take it seriously that much because he
thought that you kind of use the non locality of
the collapse transfer information. So if you think of relativity
as a theory of sicknals, there is not I mean,
you can't get around, there's no locality, right, And so
for our listeners who are curious, it does seem like
there's some weird nonlocal features of quantum mechanics, but it
(43:26):
is not possible to use that nonlocality to send information
faster than the speed of light. And Jorge and I
did a whole podcast on that, so check that out
in detail. We don't have time to get into all
of that today, but if you're curious about why you
can't send information fast in the speed of light using
quantum entanglement, we did cover that in the whole podcast episode.
All right, So this is really fascinating and I don't
want to use too much more of your time, so
(43:46):
I just want to ask you if Bowman mechanics, you know,
is a nice, beautiful picture of the universe and explains
all the experiments that we have and doesn't require us
to accept some strange, alien uncertainty and randomness that's counterintuited
and only requires the acceptance of this concept of nonlocality,
which already is present in all other quantum theories. Then
(44:08):
why isn't it the dominant quantum theory? What are the
objections against it? Is? It's still sort of like historical
inertia because von Neuman didn't like it, or there you know,
real philosophical objections to it. So I mean, I think
that part of the problem has to do with the
fact that historically it was blocked. I mean there is
all this, you know, historical accidents that happened one after
the other. I mean the first bomb was you know,
(44:30):
ostracized for various reasons, and then for Neuman contributed to this,
there seemed to be no real reason to reject this
theory from from a rational point of view. I mean,
it provides a clear mathematical picture. It's a clear physical
picture as well. You do have to accept no locality,
as you said, but I mean it's something that we
have to deal with. Some people sometimes mentioned that, oh,
(44:52):
it's not testable in the sense that probably the prediction
of the Boomian mechanics are the same as quantum theory.
That's not a good objection for a variety of reason. First,
because I mean, you have a piece of evidence. You
have two theories, right, and so which one of the
theories the evidence confirming, assuming that you can confirm a
theory the first? Okay, so who came first? The brawl
(45:14):
nine twenty three. Right, uh, and so because no, no, no, no,
but it's simpler, right, you come to mechanics is simpler,
that's just one equation, but the mechanics has two equations,
one equation with two evolution equation. Okay, so what about
time of light? You have particle physicists, right, you measure
time of flight, You measure where the particle how long
they take to go from here to there? But there
(45:35):
is no time open it. And so what are this
time of light results? Well, I mean the drugular quantum
theory have resorts to this kind of approximation. Right. If
you approximate the time measurement in one way or in
another way, you get different distribution of results. Booming mechanics
gives you uh, you know their particles, right, So you
don't need the operators, right, you just do you use
the particles trajectories and do the calculation that you would
(45:57):
do classically, but with quantum tra actorism. And so there
is the possibility of actually making an experiment. So there
are some cases in which you can put yourself in
a situation in which the prediction from quantum theory are
different from boom mechanics. This can happen because you know,
quantum mechanics is not precise, some bigues in disrespect, so
(46:20):
you can test out. So there is a strong sense
in which you can, you know, falsify quantum theory or
quantum mechanics. So even if your physicists are usually strong
about this undetectability business, but I mean, no, you can detect. So,
I mean, I really don't understand that much about the
reasons why quantum mechanics hasn't been taken more seriously by physicists.
(46:45):
And I hope the situation we've changed. Well, what it
might require for to change is maybe for us to
meet alien intelligence and talk to them about quantum mechanics
and you know, maybe their way in and will say, sorry, folks,
we think it's many worlds or no, what you call
booming mechanics is what makes most sense to us. So
on the topic, let me ask you are totally off
the wall question, what do you think are the chances
(47:06):
of that that if we meet alien intelligence that they
will have sort of similar concepts about the universe. I mean,
it's really another way to ask the question, do you
think what we're doing here are playing games inside our
own minds? To try to tell mathematical stories about the
universe it makes sense to us, or do you think
we're actually probing something deep and universal which we could
present without embarrassment at the first Interstellar Physics meeting after
(47:30):
we meet the aliens. I really do hope that we
can meaningfully talk about the universe, and it seems like
we are actually succeeding in that right. We explained so
many things since the beginning that we started doing science. No,
we've made many hypothesis and constructive many theories, and some
some of them were bad ideas, some of them are
(47:50):
better ideas. I think that the fact that we are
explaining so much is an indication that maybe we are
onto something, but I don't know. I hope that we
can contribute to the alien meeting in some way. Maybe
they have their own version of bondingment and they've made
their own mistakes along the way, so we can help
them understand some of the things that we have learned.
(48:13):
I hope also that when we meet the aliens, we
can talk physics with them, because I hope that they
are advanced and that millions of years ago they were
struggling with these questions and now to them. It's child's play.
But I fear honestly that everything we've learned is sort
of centered in the human mind. We're asking human questions,
we're telling human stories using mathematical tools that makes sense
to humans, and that it might be frankly impossible to
(48:34):
translate into this knowledge to any other intelligence. But it
remains to be seen, and the universe has filled with surprises.
So I look forward to having hard quantum mechanics conversations
with alien physicists. All right, And with that, I'll say
thank you very much for coming out a podcast and
talking to us about this crazy concept of boom and mechanics.
It seems to me like sort of a beautiful theory
that lets us recover the sense that the universe makes sense,
(48:56):
that these particles are flying through the air, and they
have victories, and they were here and then they're there,
which means that they were sort of in between in
the middle. That you can still think about the universe
in a way that's intuitive to you, and that you
can sort of get rid of a lot of this
quantum weirdness and uncertainty. In some ways, it even hangs
together better than other theories, and it's a sort of
unfortunate that it was cast aside for so many decades
(49:19):
because of the mistake of eminent physicists. But we'll see
what the future holds and how much progress we have
to make. So thanks again very much for coming on
the podcast. It was a pleasure. Thank you, Thank you
very much. Thanks for listening, and remember that Daniel and
(49:39):
Jorge explained. The Universe is a production of I Heart
Radio or more podcast. For my heart Radio, visit the
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to your favorite shows.
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Daniel Whiteson
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