July 2, 2019 • 37 mins
Hint: It's not tunnels in switzerland.
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Speaker 1 (00:00):
Yeah, okay, are you any good at bowling? By any chance?
I am either the world's best or worst bull? All right?
But when you go bowling, do you ever get any
like gutter balls? I can't deny that I get gutter balls,
all right? But are you so off the mark that
(00:22):
sometimes your bowling ball ends up like in the next lane.
I also can't deny that that's ever happened to me.
Oh man, Well, in that case, you might have a
special physics distinction. Oh how's that? You might be the
world's first quantum bowler? Is that another TV show? Like
Quantum Leap, but about quantum bowling? That's right, it's the
(00:43):
Big Lebowski meets Quantum Leap. It's my new pitch. Hi.
I'm Jorge. I'm a cartoonists and the creator of PhD Comments.
(01:06):
And I'm Daniel. I'm a particle physicist, a terrible bowler,
and the co author of a book with Jorge called
We Have No Idea About All the Mysteries of the Universe.
So welcome to our podcast Daniel and Jorge Explain the Universe,
a production of I Heart Radio. That's Right, in which
we take things around us in the universe that we
find amazing or crazy, or wet and sticky, or just
(01:28):
weird and interesting, and we try to explain them to you. Right,
all the strikes, all the gutter balls, and all those
spars out there in the universe, that's right, even the splits,
We'll roll it right down the middle for you and
into your brain. Right. Sometimes there's even quantum spin on
the ball. Right. I have no idea how to do
spin on the ball. I see people do that. I've
(01:48):
tried to do that. It's failed miserably. I'm all about
the straight and Grandma rule. It's been actually helped you.
Do you think, as a particle physicist would be all
pro spinning balls and all that stuff. But I found
an impossible My wistomost breaks every time I try to
do it well. On the program, we usually talk about
topics that people have questions about or people are really
curious about about the universe. But physics about how the
(02:10):
world and the how reality really works. And so today
we're tackling a pretty interesting topic, right, Daniel, that's right.
This is a topic people wrote in and asked us
to explain. And I think it's because they here talked
about in physics podcasts, and you read about it in
physics books. There's a bunch of online videos talking about it,
but frankly, there are very few actually satisfying explanations, and
(02:32):
I think people wanted us to dig into it and
see if you can explain to them what's going on.
It's definitely one of those topics that sound cool for sure,
Like just those two words put together, Well, anything after
quantum sounds cool, right, Quantum banana, quantum bowling, even that
sounds interesting. An evening of quantum bowling with Daniel and Jorge.
That sounds like an event you pay twenty bucks to
(02:54):
go to. Right. Well, Today, on the program, we'll be
tackling a subject that is almost seems like maybe and
that a lot of people associate with perhaps teleportation, the
idea that maybe you can move from one spot to
another spot kind of instantly or through a wall or
something like that, so they On the podcast, we'll be
talking about quantum tunneling. Quantum tunneling is one of my
(03:21):
favorite topics because it's one of those really weird effects
you see in quantum mechanics. You know, when you zoom
in on the world and you discover it's microscopic nature.
You try to understand it in terms of things we
know and understand, and your brain is trying to use
particles and waves and all this stuff. This is one
of those effects that really just stumps us when it
when we try to explain it in terms of macroscopic things.
(03:43):
We try to get intuitive handle on it, and so
it just shows us that the world is so different
from the world that we actually understand. I guess my
question annially, is am I going to spend this episode
complaining about the naming of this effect? Like is this
really like a tunnel like every other episode, like every
other episode out of this podcast? Um? Probably? Yes, Probably, UM,
(04:04):
spend most of the time you complenty with the name
and me trying to argue that the physics version is
different from the cultural version or whatever, and that there's
poetry in physics. There is some poetry and physics there's
also plenty of clumsiness. Now, this is a fascinating topic
because it's the kind of thing that's really impossible to
explain in terms of classical analogs. You know, things that
(04:26):
you have intuition for particles and waves and bowling balls.
It's just something that those things can't do, and so
it opens the door in our minds. It says the
universe is weirder than you will ever understand, right, And
that's the kind of thing that got me into physics,
you know, the revealing that the universe operates under rules,
but rules that are weird and in some ways alien
(04:48):
to the to the world that we know. So, yeah,
it's got two cool words, quantum and tunneling, and so
I don't know, that makes me think of like a
something that drills deep down into the quantum realm or
you know, something that um lets me like travel to
the quantum realm or something. What is the what is
the quantum realm? Where is it? How do you get there?
That's a whole other podcast episode. It's on the Admin
(05:11):
Movies obviously. All right, well, we'll have to have Paul
Rudd on as a guest, and uh and Michael Douglas
since he's professor PIM. I mean, they can explain to
us all about the PM particles in the quantum realm.
But you're at quantum tunneling does have a really cool
sound to it, and so, as usual, I was wondering, like,
what do people know about quantum tunneling to people. Does
everybody already understand this and we don't need to explain it?
(05:32):
Or is it a huge mystery to people have misconceptions?
And so I walked around campus a you see Irvine,
and it costed friendly strangers to ask them. So before
you listen to these answers, think about it for a second.
If somebody asked you randomly on the street and didn't
give you the option of googling it, would you know
what quantum tunneling is? That's right, no googling allowed. Here's
(05:53):
what people had to say. Do you know what quantum
tunneling is? Um? I don't know what makes me think
of like the mountain since Wwitzerland and how they have
to like build tunnels underneath them and then that's where
certain is. So there's probably some quantum tunneling down there.
I have Can you explain it? No? I have not?
No um not really probably not. Well, I've heard, I've
(06:15):
heard of it, but I'm not sure what the concept is.
I don't know what's that mean? No, I have not,
I do not. I have not heard of that. I
have not. Something has to do with light and like hell,
the transflor on something like that alright, not a popular
or familiar topic, but half the people had never heard
of it. That's right. Um, people were pretty clueless, though
some people were pretty creative. I love the answer about
(06:38):
tunnels near certain that was very creative. Yeah, they said
that made them think of the tunnels underneath the mountains
of Switzerland, because Switzerland has tunnels and they do physics experiments.
So therefore two and two together. Obviously that's what a
quantum tunnel is. It's not a terrible answer, like, you know,
what kind of tunnel do you need to build a
(06:59):
large age uncle it? You know, hey, a quantum tunnel, right,
a tunnel in which you do quantum experiments. That's not
a terrible answer. Maybe that's more of a quantum ingunnel.
And the truth is the Swiss are awesome in building tunnels,
and they could sort of have to be because they're
surrounded by mountains, but they really are world class in
building these tunneling machines. And so it's still surprised that
the large Hadron collider is in Switzerland because that really
(07:21):
is the best place to build tunnels for your quantum experiments. Yea,
they have to dig all those tunnels to burial, that
money that they keep for rich people. Oh, that illicitly
elicitly gotten gold. You know, hey, what do you mean
I have a Swiss bank account in my dream? Well,
you know, true story. I discovered, um by opening her mail,
that my wife has a Swiss bank account. She has
(07:44):
a retirement plan in Switzerland. All right, what what other
secrets have you covered by opening her mail? The best
part of the story is that she didn't know she
had a Swiss bank account until I told her. Feels
like a Born movie here. No, it has actually pretty
mundate explanation. When we were in Switzerland so I could
work on the large age on collider, she had a
(08:05):
job working in research in Switzerland, and unbeknownst to her,
they opened an account in her name and deposited some
retirement funds there and uh, and then we discovered it
later and like, oh my gosh, look, Katrina has a
Swiss Bank acount with money in it. That's how banking
work in Switzerland. They just give it away. Yeah exactly. So, um, yeah,
she has a Swiss Bank account, but I don't. Well anyway,
so people were not very familiar with quantum tunneling, which
(08:28):
means that hey, we can. We can talk about it
on the podcast. That's right, It's an awesome topic to demystify.
First we'll explain what it is, and then we'll explain
how it works and how it's not teleportation. Right, That's
my big question is is it like teleportation? Is it
associated with teleportation? Can we teleport with quantum tunneling? All right?
Start us off, Daniel, What how would you describe what
(08:49):
quantum tunneling is? So I think the best place to
start is to sort of warm up our intuition, Like,
let's think about this problem using things were familiar with,
and then we can make the analogy to the quantum
version and we can understand where that breaks down, like
where our intuition goes wrong. So let's start with our
intuition and the sort of the problem. The kind of
problem we're trying to describe is sort of like playing
(09:11):
with a bowling ball inside an empty swimming pool. This
is still for the bowling ball and swimming pool. Yeah,
I mean, isn't that a familiar thing when you see
a swimming, empty swimming pool and you think, I wonder
what would happen if I threw a bowling ball in there? Well,
let's give our listeners just a quick idea of what
we're talking about. So, quantum tunneling is kind of this
idea that a particle or or in the usual case
(09:35):
it's an electron, it consider be on one side of
a barrier in one moment and then the next moment
it's on the other side of the barrier. Right. The
generally they have quantum tunneling is that it's really hard
to keep electrons in a little trap or in a
little hole. That they really they're hard to pin down.
And people are probably familiar with that because the Heisenberg
and certainty principle, like, you know, you can't really isolate
(09:56):
a quantum particle in one little spot in space very long,
but you know if you try to do it, then
you know eventually it's going to leak out. And and
the point of quantum tunneling is that electrons can build
these tunnels or burrow through these barriers to to you know,
adjacent little holes or adjacent little wells. So that's the
idea is that it's like you have a particle, there's
(10:17):
a barer in front of it, and at some point
it just moves to the other side of the barrier. Yeah, exactly.
You can see it on one side of the barrier,
and even if it doesn't have enough energy to get
over the barrier, sometimes you see it on the other
side and you have to ask, like, how did it
get here? Right, right, like spontaneously just appears on the
other side or what. Yeah, well, sometimes on one side
(10:37):
and then it's on the other side, and then it
goes back right, And there's a lot of interesting stuff
there about like, um, you know, if the particle was
here and then later it's there, how did it get
from one place from the first place to the next place.
Right In your mind, you're used to things. If it's
in one spot and then later it's in another spot,
you imagine it took a path from one spot to
the other spot. Right, That's the way classical things work,
(10:59):
based balls, hamsters, whatever. But that's not true for quantum objects.
Quantum bologists are here and then later they're there, and
there iss not necessarily any path between those places that
the particle took. It didn't move, It just was here
and then it was there. Yeah, it's frustrating because quantum
particles don't have this underlying hidden truth, right, it's not
(11:20):
like there is a true story about where the particle
was at every moment and we just don't know it.
It doesn't have that story. That story doesn't exist. You know,
it's it's it's in a location only when you ask
where is it? And then it's in a location later
when you ask where is it? You're saying it particles
don't really have a here or there. It's like they're
around here. Well, they have a here, Like at some
(11:42):
moment you can say it's here, and another moment you
can say it's there. But you can't connect the dots, right,
You can't say that there must be a line between
those two dots and the particle took that line or there.
There doesn't have to necessarily be aligned. It's just here
and then later it's there. It's you know, it's like
um frames in a movie, but without the intervening um connections.
(12:04):
Like if you're watching a movie, you know, the person
would be standing here, and then suddenly they'd be standing
over there, and then they'll be studying this other part
of the frame, right, almost like they were teleporting between spots.
I was just going to say that that's not teleportation.
Right when you're watching a movie, and you know, and
you watch this frame by frame, you don't imagine they're
(12:25):
teleporting from frame to frame. Right, you're just saying, well,
I know he's here in this frame and he's there
at that frame. Right. That's not teleportation. You're saying. A
quantum particle doesn't have a path between these two things.
It's like, if you ask you where it is, it'll
just kind of pop around all over the place. Yeah,
you can ask a particle where it is and it
will answer, right, and then later you can ask it
where it is and it will answer, But you don't
(12:46):
necessarily know anything about where it is in the intervening time,
and you can't assume that there's some classical path. You know,
if you if you ask where's my baseball and what's
his velocity? Right, then you can actually predict exactly where
it's going to go any moment. And so it has
this thing we call the classical path. It's position and
velocity at any point in time, and when you're looking
(13:07):
at it, you're just sort of sampling that. Right. But
for a quantum particle that doesn't exist, you can ask
where is it? And you're gonna ask where is it later? Right?
But you can't connect the dots between those two and
assume that there's a path that it's following. Well, this
is a perfect point to take a break, Okay. So
(13:35):
then the idea of quantum tunneling is that a particle
is on one side of a wall or a barrier,
and then the next instant it's in the other side
of the barrier. And so that what we want to
do here today is sort of explain how that happens
and why it's not teleportation. Exactly how does that happened
and what does it mean and why it's not teleportation.
And so you you think a great way to think
(13:57):
get into this topic is to think about bowling balls.
And yeah, well, I mean, what is a barrier after all? Right,
Like I think people think about electrons is tiny little balls.
So I was thinking about let's use a bowling ball
because that's macroscopic and what is really a barrier? Right,
I mean people might be thinking like, what kind of
barriers are we talking about? And so let's imagine a
macroscopic barrier, like a familiar one. Right, You're the bottom
(14:19):
of swimming pool with a bowling ball. By the way,
this is amazing video of a guy. This what inspired
me is this amazing video online of a guy with
the bowling ball in a swimming pool and he can
do these hilarious tricks where he puts like the pins
behind him and he rolls the bowling ball and it
does these crazy moves and he knocks off all the pins. Anyway,
so you're the bottom of the swimming pool with the
bowling ball, right, and what happens you just put it down.
(14:41):
Let's make it clear the pool is empty. I'm not
drowning here, I'm not empty swimming pool. I'm not holding
onto his heavy ball. And and then sitting at the
bar of gear does not make this anymore complicated. Yeah,
it's an empty swimming pool with a bowling ball. But
let's also make it clear it's one of these swimming
pool is that it has a curved floor, right, like
(15:02):
a bowl shaped floor, right like if if it's a
swimming pool with straight edges at the bottom, this is
not going to work, that's right. Also, there's no like
chain saws or you know, traps or you know, rabbit
hamsters or anything else in the swimming pool. Just you know,
to be clear, just just the bowling ball in an
empty curved pool, you know, or if it's easier for you,
(15:23):
imagine a grape in the bottom of a bowl or whatever.
But the point is what happens when you put the
bowling ball at the bottom of the swimming pool. It
just sits there, right, It doesn't leave. You're never going
to find it in your neighbor's empty swimming pool, right,
It's always going to be in that pool. And the
barrier in this case is the edge of the swimming pool.
You mean, like, if you don't touch it, if you
don't push it, if the wind doesn't blow, it is
(15:44):
just going to stay there. That's right exactly. And you
expected to stay there. You don't expect to come by
one day and find it in your neighbor's swimming pool. Right.
It is that if something does disturb it, like a
raccoon comes by and pushes it, it's just going to
roll back down to the bottom of the pool again. Right,
that's kind of the idea. That's right exactly, because the
walls of the pool are the barrier, right, That's where
we talk about. It's a potential barrier. And if a
(16:06):
raccoon comes and pushes it, you know, and he pushes it,
you know, as hard as a raccoon can. Then it's
gonna roll up, and then it's gonna roll back down,
and it might roll back up the other side, but
it's never gonna roll higher than it then it went originally, Right,
It's just gonna eventually relax down to the bottom of
the swimming pool. And so if you don't give it
enough energy to go over the lip, then it's trapped
(16:28):
in the pool. Right, It's never going to get out
of the pool unless it has enough energy to go
up and over the edge of the swimming pool, right,
And so that's the barrier, like that's the wall, yeah, exactly,
And your intuition says it's trapped, right, if you don't
give enough energy, it's never ever, ever, ever, ever, ever
ever ever going to end up in your neighbor swimming pool, right,
that's where your intuition says, right, unless there are some
(16:50):
really strong raccoons. But that's what different. I don't know
what kind of neighborhood this is with all these empty
swimming pools and like tough gangs of raccoons pushing bowling balls.
But we're to get out quite the science fiction dystopia here.
But Yeah, you don't expect it to ever be able
to get out of the pool by itself. That's right,
exactly that barrier you can consider it to be perfect. Right.
(17:10):
The only way um to the next swimming pools to
go over the barrier. Right, You can never go through
the barrier. These raccoons are not tough enough to throw
the bowling ball like and crush the ground and get
through it. Right. Wait, what are their Swiss raccoons and
they dig a tunnel? Yeah, or they're like superhero raccoons
(17:31):
like um in one of those Marvel movies system, isn't
there some super raccoon or is he just look like
a raccoon and he's not actually a raccoon and never
actually in genetically modified raccoon aliens that look like human
like Earth raccoons And never quite figured that one out.
But we digress, we do, we do digress. That's the analogy.
Right now, Think instead of the bowling ball, think of
(17:53):
an electron. And then when we talk about barriers, we're
talking about you know, barriers to that electron. So maybe
made by other particles, you know, protons or something that
would repel it, right, something that would you would build
to try to keep the electron localized like a little trap,
like a like a little magnetic field. Maybe he is
keeping it trapped or something. Yeah, a little magnetic field
(18:16):
or electrostatic potential or something anything you can do to
trap an electron. And people do this, right, they want
to study individual electrons or individual ions. They build atom
traps the pretty cool um and so people actually do this.
But it's also a good case study for quantum mechanics
because it helps us think about how these things work
and don't work. So it's a it's a very popular
sort of junior level quantum mechanics problem in college. So
(18:39):
what happens. You put the electron in this little well, right,
and it's like a barry. It's like a swimming pool,
and you think, if the electron doesn't have enough energy
to go over the edge, then it's trapped, right, just
like the bowling ball. If it doesn't have enough energy,
how could it ever get into the neighboring swimming pool. Well,
the thing you find is that even though it doesn't
have enough energy, sometimes it appears is in your neighbor's
(19:01):
swimming pool. Like it gets through that barrier. It appears
in the adjacent well. Like if you have a series
of these um potential wells, you know, these these little
traps made for electrons, and you put it in one,
you come back the next day and find it in
the next one. Even though it didn't have enough energy
to go over that barrier, even though it was trapped
(19:21):
by a magnetic field, it somehow slipped out, yes, exactly,
And so that's the that's what we call quantum tunneling. Right,
how did it get through the barrier? In principle, the
barrier should be should bar it, right, that's what barriers do.
It should borrow it from passing, just the way you're
the ground does, the end of the swimming pool does.
So the question is why does an electron not get stuck, right,
(19:44):
because if it tried to move, the field would push
it back into the trap. But somehow it's able to
live out or create a tunnel exactly exactly. And your
instinct might be to say, well, maybe like momentarily goes
over the barrier, like you know, I don't know Heisenberg
Uncertainty blog blog. You know, maybe it borrows a little energy,
(20:04):
momentarily gets over the barrier. Right. That's tempting because you
want to think of the barrier as working, and so
do you want to think that if it's going to
go to the other well, is somehow has to go over.
But it doesn't, right, it can't. It's a conservation of energy,
so that that explanation doesn't work. The electron doesn't get
more energy momentarily magically, it um it's just on one
side of the barrier and then it's on the next.
(20:25):
Like zoos didn't come down and touch the bowling ball
and push it into the other swimming pool. That's impossible,
that's right. We're assuming that there's no other source of energy, right,
and and it never has enough energy to go over
the edge of the swimming pool and into the next one.
So the only way to the other swimming pool is
to tunnel, is to go through the barrier. And then
once it's out and on the other side of the barrier,
(20:49):
does it stay there or does it sometimes pop back
in or does it fly off? At that point it
pop it pops back in. Yeah, it can pop back
in and it can go to the next one. Right.
The point it is that you can never really trap
an electron. And the reason is not that it goes
over the edge, and the reason is not really teleportation, right,
And the reason is that these these barriers and a
(21:12):
quantum level are just different than the barriers we have
here at the macroscopic level, and electrons are different from
bowling balls. Right. We like to think of them that
way because it's useful, because the way we understand the
unknown is to do it in terms of the known.
But in the end, these things can do things, These
quantum mechanical things can do things that the classical things,
(21:32):
the macroscopic things that we're familiar with, just can't do.
And one of those things is the electron. It has
a chance to just ignore the barrier. It's like every
time it goes up against the barrier, a die is
rolled and if it comes up you know, all sixes,
it's like, haja barrier, I get to ignore you. You
said every time it goes up against the barrier, Meaning
is it like it's always pushing against the barrier or
(21:54):
is it like a continual roll to die or what? No,
that's a good point, And the way I was speaking
about it, it's wrong because I was talking about it
like having a classical path, like it has a position
and a velocity at every moment. In reality, it's motion
is governed by this wave equation, right, the wave function
that we used to describe where it is, and that
tells us where it's more likely to be and where
(22:16):
it's less likely to be. And we know that for
it to get from one side of the barrier to
the other, it has to go through the barrier. We
know this because it can be inside the barrier. Like
in principle that should be impossible, right, like, how do
you how can you be inside the barrier? You're not
breaking the bearer, The bear is not destroyed, but it
can sort of like defy the barrier, can sort of
(22:36):
ignore the barrier. It has a probability to just sort
of like shrug off the barrier the way a teenager
shrugs off a curfew. You know. So the trap, the
magnetic field that trap is traveling the electron doesn't affect
the probability of where the electron can be, or it
does doesn't. It doesn't it like squeeze the probability cloud
(22:56):
of the electron or something like that. It totally does.
It affects it, but it can't trap it completely. It's
just impossible to trap it completely unless the barrier is
infinitely high, the barrier is infinitely strong, then the electron
is totally trapped. But as long as the barrier is
not infinite, right, imagine the swimming pool. It's infinitely deep,
(23:16):
then the quantum mechanical bowling ball can't get out. But
if the if it's even if it's super high, it's
a billion miles high, but not infinite, then the quantum
mechanical one can get to the other side. It just
has a chance. But you're right, it does affect that
it squeezes those probabilities. The probabilities are shaped by the barrier.
But you're saying there's still a little tiny probability that
it's going to jump over, not jump over, but go through, right,
(23:40):
And the probability is smaller if as the barrier gets wider,
and it's smaller as the barrier gets taller, So that
that all makes sense. The thing that's confusing is like,
how do you explain what it's doing in the barrier?
Is it just like ignoring the barrier and you just
have a chance to avoid the barrier. It's it's hard
to come up with a sort of like an intuitive
under standing of what it's doing there you know, it's
(24:02):
like it's in the Noman's land. It's in the place
where nothing should be, but there it is, right is it?
Because the bowling ball is not really a bowling ball, right,
it's more like a cloud, kind of like a like
a fog. And you're saying, sometimes the fog can sort
of extend and kind of appear on the other side
of the swimming pool. If you measure an electron, you say, okay,
it's in my trap, and then you ask where is
(24:24):
my electron likely to be in one second? Then most
likely it's to be it's going to be in the trap.
There's a little bit of probability it's going to be
in the barrier, and there's a little bit of probability
it's going to be in the next one. Right, it's
going to be in the next trap. So you know,
after you know where electron is, that doesn't tell you
where it is necessarily a second later. It's just you
(24:44):
have a probability distribution of where you're going to find it,
and we can candulate those probabilities using the Shortinger equation.
But that's again, that's just a description of what we
have observed. Right, the exhorting equation itself is not an explanation.
It's just like a mathematical formulation the success He describes
what we've observed. Oh, I see, it's a probability of
where it's going to be if you measure it. So
(25:06):
if you measure it, there's a tiny little probability you're
going to measure it in your neighbor's pool. Yes, exactly.
And it's tempting to think, oh, well, that's just particles. Right,
particles are here, and then particles are their. Right, that's
not the property that allows the electron to quantum tunnel. Right.
You can have that property in an infinitely deep swimming
pool where electrons can't tunnel, right, an infinitely deep potential well, right,
(25:31):
the electrons can't get out. That's the only one that
can completely hold them. But in now well, electrons can
still be here and then later be over there, and
then later be over here, as long as you're still
within the well. But if the wall is not infinitely high,
then there there's a probability that randomly it's gonna ignore
or jump over the barrier and be on the other side.
(25:53):
If you measure that's right, not jump over, but go through, right,
jumping over means why not jump over? Well, jumping over
means don't really know, right, you do not like he
was hit inside and then it was outside, and you
don't know. You don't really know what the path it
took to get outside, right. Well, to get over, it
would need to have enough energy to go over the barrier, right,
and that energy has to come from somewhere, and we
(26:14):
have energy conservation in our universe, and so it can't
go over the barrier, right. It's like the raccoon pushing
the bowling ball. If it doesn't have enough energy to
push it over the lip, it's just never going to
go over the lip. Um. And the reason this works,
we can do the calculations, and the reason it works
is because the electron is in the barrier. Like bear,
quantum barriers are just different from classical barriers. They're sort
(26:36):
of optional. You just always have a chance to ignore them,
you know. It's like a speed traps. Sometimes the copsies
you and sometimes he doesn't. But if you find it
inside the barrier, doesn't it mean it gained a whole
bunch of energy. No, it can be inside the barrier,
meaning that it doesn't have enough energy to be there.
But it's there anyway, where does the probability come from?
(26:57):
You know what I mean? Like for it to be probable,
He's who have some sort of physical explanation, doesn't it. Yeah,
And the explanation is that the bowling ball analogy is
wrong because this is not a bowling ball and these
are not a swimming pool. It's a weird, lobby, wavy,
fuzzy thing that can do this thing that no bowling
ball or swimming pool can do. And the barrier also
(27:20):
is a little fuzzy, right that you can't build a
perfectly strong barrier unless it's infinitely high um. In quantum mechanics,
barriers are not the same as swimming pools, right, that
they're different. And so the analogy breaks down, and these
things can do things that that the things were familiar
with can't do, and one of them is that sometimes
they sort of ignore each other. With that, let's take
(27:42):
a break. We'll be back in just a short minute.
(28:02):
But um, and the interesting thing is that it's not
just electrons, right, like you're talking about all particles. Oh yeah,
electrons are just the simplest case, But any quantum mechanical particle,
any particle that's motion is primarily described by like the
shortening air equation. So single particles or ions or nuclei,
whatever these things can do this also we see it
all over the place. It's actually an important part of
(28:24):
loss of physical processes that we know and love. Well.
I think it's interesting to think about the idea that,
you know, these walls in the room that I'm in
um are sort of just barriers to right, Like they're like,
what's preventing my hand from going through the wall. It's
not just my inner peace, but uh, it's it's like
the electromagnetic forces between my hand and the wall exactly.
(28:47):
And that, as you say, is a quantum mechanical barrier.
Like the very tip of your finger. Imagine that's an electron.
When it approaches the wall, it meets a barrier, a
barrier made by the electrons in the wall, and that's
what doing the repulsion. And so you're right, there's a
tiny chance so that first electron is just going to
go right through the barrier instead of bouncing off of it,
and I might lose that one electron from my finger,
(29:11):
you might, Or there's an even tinier chance that the
next set of particles will will quantum tunnel through, and
an even tinier chance that also the next ones will.
So there's some non zero chance that you'll put your
hand through the wall without breaking the wall. That's crazy.
It's it's non zero chance that I can walk through,
or do I walk through the wall or appear on
(29:31):
the other side or both. I know this would be
a horge quantum tunneling through the wall. Yeah, there's totally
a non zero chance. Now you could stand there all day,
your whole life, walking into walls and not successfully go
through it. And I'm pretty sure that would be your
experience because the probabilities we're talking about are ridiculously tiny, Like,
for these barriers are pretty tall, and there's lots of
(29:53):
particles and have to happen for all of them, and
so it's basically impossible, but not technically exactly zero. So
there is a possibility, Daniel, that you're sitting right there
where you are will suddenly find yourself on the other
side of the wall that's in front of you, right exactly.
There is a possibility I could quantum tunnel into the
bathroom or whatever. Let's say it happens right now. Proof
(30:14):
would you say you teleported to a battle. I mean,
what's what's the difference between that and actually teleporting. Well,
we did a whole episode about teleportition, remember, and we
decided that teleportition is impossible while this is possible. And
you know, it's really tempting to connect this this um
idea of tunneling with the concept that part of quantum
(30:36):
particles can sort of skip their way through life, right,
they don't need to exist at every moment, sort of
they're here and then they're there and the other thing.
And so if you want to call this telepartition, then
every particle is teleporting all the time, right, So that's
my problem with it. It's like this is a natural
thing that particles are always doing, even without barriers, Like
even a particle in an infinite box is doing this
(30:56):
sort of skipping thing because it doesn't exist between the
moments you're observing it. So if this is teleprotation, then
that's teleprotation also, and everything is constantly teleporting. You're saying
that you don't want to call it teleprotation, not because
it's not teleprotation, which I would argue maybe it is experientially,
but it's just that if you call it teleprot teleportation,
(31:17):
it would sort of the dilute or or break the
definition of teleprotation. Yeah, if this is teleprotation, then we're
all teleporting all the time. So if everyone is nice,
then nobody's nice. It's kind of right, like it's the
teleporters quantum dilemma exactly, all right, So that that that
that makes a bit more sense. And quantum tunneling is
(31:40):
really important, like it happens in the sun. If you
want nuclear fusion to happen, the kind of thing that
powers the sun, that generates all that light that you
know makes you look so nice and tan and grows
all that food that you eat, then you need these
particles to be able to quantum tunnel through some of
the potential barriers that they face. You know, particles infusion
don't like to touch each other, right because nuclei are
(32:03):
both positively charged because of all the protons. So to
get them to fuse, you have to push them together,
and they're repelling each other, and that's a barrier. So
you've got to get them sometimes through that barrier in
order to do the fusion. And you're saying sometimes they
tunnel to that, but mostly do they mostly get pushed
together or do they actually tunneled together. I think it's
some of both. I mean, the center of the sun
(32:24):
is so hot and so dense that these particles can
just sort of overcome the cool embarrier like they have
enough energy. But definitely, um tunneling is an important part
of it, Like fusion wouldn't be the fusion we know
and love without quantum tunneling. If everything is fusion, then
nothing is fusion. That's what you're saying. That's right, that's
the theme today, right, label everything um. And there are
(32:44):
other effects, like you know, back to electrons. Electrons don't
like to stay in little traps, but if you're building
chips for computers, then you'd like your electrons to be
in certain places you want to know, like hey, this
transistor is all on or this transistor is off or whatever.
And and it gets harder and harder to make transistors
be reliable as they get smaller and smaller, because you
(33:06):
get dominated by these quantum effects, and these little traps
get smaller and smaller, and electrons like to jump out
of them, and you don't want your ones in your
computer to suddenly switch into zeros. And so this actually
is a big effect in miniaturizing transistors, which is a
big effect in speeding up your iPhone. At some point,
if you make electronics small enough, the quantum effects are
(33:27):
gonna totally miss everything up. Yeah, exactly. Quantum mechanics messes
it up again, bummer, Why can't they just be elect
strikes out. Quantum mechanics strikes out again. Why can't we
just use little bowling balls and tiny little swimming pools
instead of electrons? Sorry, and bowling striking is good, so
it wins. Yeah, it strikes out, exactly. You brought a
(33:51):
full circle. They're very nice, all right. So that's that's
pretty much quantum tunneling. It's this idea that particles are
all quantum, and as such, they have these weird fuzzy
uh location right, They're not in any particular place, and
so it's impossible to trap a particle because it's fuzzy
and it might slip out. That's right. Quantum barriers are
(34:12):
just different from the ones you're familiar with, the work
under different rules, and those rules have little random exceptions
to them, so sometimes they can just be ignored and
it's weird and it's confusing, and your intuition breaks down.
But it's also wonderful because it shows you how the
world works at a smaller level. Right, it reveals to
you where your intuition is wrong, and that that means
(34:33):
that it's showing you the truth of the universe. Yeah,
and the and the truth is bowling. Exactly. The truth
is quantum bowling. This episode brought to you by the
American Bowling Association. Yeah, exactly. But so that's what happens
at the microscopic level, but on the larger level, we
(34:53):
we can't do that because you know, there's a lot
of lactrons in my hand, and the chance that all
of them are going to quantum tunnel at this time
it's just almost zero. Yeah, exactly. Like if there's a
chance for you to roll a one million sided die
and get zero, you know that's probably can happen. But
if you have to do that for a million die
all at once um and get the same answer, then
(35:15):
it's basically very improbable, almost impossible. So you the macroscopic
stuff sort of gets averaged out, but still possible. It's
still possible. Absolutely, you could quantum tunnel through the walls
and not counted as teleportation. All right, It's just what
quantum stuff does Yeah, yeah, drives them physicists crazy. No,
(35:39):
it excites us. Is it's wonderful. We're always looking for
weird quantum effects that show us how the universe works.
It's you know, it's a it's a it's what we
what we live for, these little moments. All right, Well,
we hope you enjoyed that discussion and hope that answered
all of the questions that listeners had about what is
quantum tunneling. Thanks for sending in your questions. They're inspiring
(35:59):
and if you have of questions about things you'd like
to see explained, please send them to us at questions
at Daniel and Jorge dot com. We love your messages,
that's right. And if you are Swiss one would like
to tunnel some money over to us, we are also
available at feedback at Daniel and Jorge dot com or
just dump it right into Katrina's bank account if that's
more convenient you go, all right, thanks for listening. If
(36:33):
you still have a question after listening to all these explanations,
please drop us a line. We'd love to hear from you.
You can find us at Facebook, Twitter, and Instagram at
Daniel and Jorge. That's one word or email us at
feedback at Daniel and Jorge dot com. Thanks for listening
and remember that Daniel and Jorge Explain the Universe is
a production of I Heart Radio. For more podcast for
(36:55):
my heart Radio, visit the I heart Radio app, Apple Podcasts,
or wherever you listen to your favorite ships. H
Yeah, okay, are you any good at bowling? By any chance?
I am either the world's best or worst bull? All right?
But when you go bowling, do you ever get any
like gutter balls? I can't deny that I get gutter balls,
all right? But are you so off the mark that
(00:22):
sometimes your bowling ball ends up like in the next lane.
I also can't deny that that's ever happened to me.
Oh man, Well, in that case, you might have a
special physics distinction. Oh how's that? You might be the
world's first quantum bowler? Is that another TV show? Like
Quantum Leap, but about quantum bowling? That's right, it's the
(00:43):
Big Lebowski meets Quantum Leap. It's my new pitch. Hi.
I'm Jorge. I'm a cartoonists and the creator of PhD Comments.
(01:06):
And I'm Daniel. I'm a particle physicist, a terrible bowler,
and the co author of a book with Jorge called
We Have No Idea About All the Mysteries of the Universe.
So welcome to our podcast Daniel and Jorge Explain the Universe,
a production of I Heart Radio. That's Right, in which
we take things around us in the universe that we
find amazing or crazy, or wet and sticky, or just
(01:28):
weird and interesting, and we try to explain them to you. Right,
all the strikes, all the gutter balls, and all those
spars out there in the universe, that's right, even the splits,
We'll roll it right down the middle for you and
into your brain. Right. Sometimes there's even quantum spin on
the ball. Right. I have no idea how to do
spin on the ball. I see people do that. I've
(01:48):
tried to do that. It's failed miserably. I'm all about
the straight and Grandma rule. It's been actually helped you.
Do you think, as a particle physicist would be all
pro spinning balls and all that stuff. But I found
an impossible My wistomost breaks every time I try to
do it well. On the program, we usually talk about
topics that people have questions about or people are really
curious about about the universe. But physics about how the
(02:10):
world and the how reality really works. And so today
we're tackling a pretty interesting topic, right, Daniel, that's right.
This is a topic people wrote in and asked us
to explain. And I think it's because they here talked
about in physics podcasts, and you read about it in
physics books. There's a bunch of online videos talking about it,
but frankly, there are very few actually satisfying explanations, and
(02:32):
I think people wanted us to dig into it and
see if you can explain to them what's going on.
It's definitely one of those topics that sound cool for sure,
Like just those two words put together, Well, anything after
quantum sounds cool, right, Quantum banana, quantum bowling, even that
sounds interesting. An evening of quantum bowling with Daniel and Jorge.
That sounds like an event you pay twenty bucks to
(02:54):
go to. Right. Well, Today, on the program, we'll be
tackling a subject that is almost seems like maybe and
that a lot of people associate with perhaps teleportation, the
idea that maybe you can move from one spot to
another spot kind of instantly or through a wall or
something like that, so they On the podcast, we'll be
talking about quantum tunneling. Quantum tunneling is one of my
(03:21):
favorite topics because it's one of those really weird effects
you see in quantum mechanics. You know, when you zoom
in on the world and you discover it's microscopic nature.
You try to understand it in terms of things we
know and understand, and your brain is trying to use
particles and waves and all this stuff. This is one
of those effects that really just stumps us when it
when we try to explain it in terms of macroscopic things.
(03:43):
We try to get intuitive handle on it, and so
it just shows us that the world is so different
from the world that we actually understand. I guess my
question annially, is am I going to spend this episode
complaining about the naming of this effect? Like is this
really like a tunnel like every other episode, like every
other episode out of this podcast? Um? Probably? Yes, Probably, UM,
(04:04):
spend most of the time you complenty with the name
and me trying to argue that the physics version is
different from the cultural version or whatever, and that there's
poetry in physics. There is some poetry and physics there's
also plenty of clumsiness. Now, this is a fascinating topic
because it's the kind of thing that's really impossible to
explain in terms of classical analogs. You know, things that
(04:26):
you have intuition for particles and waves and bowling balls.
It's just something that those things can't do, and so
it opens the door in our minds. It says the
universe is weirder than you will ever understand, right, And
that's the kind of thing that got me into physics,
you know, the revealing that the universe operates under rules,
but rules that are weird and in some ways alien
(04:48):
to the to the world that we know. So, yeah,
it's got two cool words, quantum and tunneling, and so
I don't know, that makes me think of like a
something that drills deep down into the quantum realm or
you know, something that um lets me like travel to
the quantum realm or something. What is the what is
the quantum realm? Where is it? How do you get there?
That's a whole other podcast episode. It's on the Admin
(05:11):
Movies obviously. All right, well, we'll have to have Paul
Rudd on as a guest, and uh and Michael Douglas
since he's professor PIM. I mean, they can explain to
us all about the PM particles in the quantum realm.
But you're at quantum tunneling does have a really cool
sound to it, and so, as usual, I was wondering, like,
what do people know about quantum tunneling to people. Does
everybody already understand this and we don't need to explain it?
(05:32):
Or is it a huge mystery to people have misconceptions?
And so I walked around campus a you see Irvine,
and it costed friendly strangers to ask them. So before
you listen to these answers, think about it for a second.
If somebody asked you randomly on the street and didn't
give you the option of googling it, would you know
what quantum tunneling is? That's right, no googling allowed. Here's
(05:53):
what people had to say. Do you know what quantum
tunneling is? Um? I don't know what makes me think
of like the mountain since Wwitzerland and how they have
to like build tunnels underneath them and then that's where
certain is. So there's probably some quantum tunneling down there.
I have Can you explain it? No? I have not?
No um not really probably not. Well, I've heard, I've
(06:15):
heard of it, but I'm not sure what the concept is.
I don't know what's that mean? No, I have not,
I do not. I have not heard of that. I
have not. Something has to do with light and like hell,
the transflor on something like that alright, not a popular
or familiar topic, but half the people had never heard
of it. That's right. Um, people were pretty clueless, though
some people were pretty creative. I love the answer about
(06:38):
tunnels near certain that was very creative. Yeah, they said
that made them think of the tunnels underneath the mountains
of Switzerland, because Switzerland has tunnels and they do physics experiments.
So therefore two and two together. Obviously that's what a
quantum tunnel is. It's not a terrible answer, like, you know,
what kind of tunnel do you need to build a
(06:59):
large age uncle it? You know, hey, a quantum tunnel, right,
a tunnel in which you do quantum experiments. That's not
a terrible answer. Maybe that's more of a quantum ingunnel.
And the truth is the Swiss are awesome in building tunnels,
and they could sort of have to be because they're
surrounded by mountains, but they really are world class in
building these tunneling machines. And so it's still surprised that
the large Hadron collider is in Switzerland because that really
(07:21):
is the best place to build tunnels for your quantum experiments. Yea,
they have to dig all those tunnels to burial, that
money that they keep for rich people. Oh, that illicitly
elicitly gotten gold. You know, hey, what do you mean
I have a Swiss bank account in my dream? Well,
you know, true story. I discovered, um by opening her mail,
that my wife has a Swiss bank account. She has
(07:44):
a retirement plan in Switzerland. All right, what what other
secrets have you covered by opening her mail? The best
part of the story is that she didn't know she
had a Swiss bank account until I told her. Feels
like a Born movie here. No, it has actually pretty
mundate explanation. When we were in Switzerland so I could
work on the large age on collider, she had a
(08:05):
job working in research in Switzerland, and unbeknownst to her,
they opened an account in her name and deposited some
retirement funds there and uh, and then we discovered it
later and like, oh my gosh, look, Katrina has a
Swiss Bank acount with money in it. That's how banking
work in Switzerland. They just give it away. Yeah exactly. So, um, yeah,
she has a Swiss Bank account, but I don't. Well anyway,
so people were not very familiar with quantum tunneling, which
(08:28):
means that hey, we can. We can talk about it
on the podcast. That's right, It's an awesome topic to demystify.
First we'll explain what it is, and then we'll explain
how it works and how it's not teleportation. Right, That's
my big question is is it like teleportation? Is it
associated with teleportation? Can we teleport with quantum tunneling? All right?
Start us off, Daniel, What how would you describe what
(08:49):
quantum tunneling is? So I think the best place to
start is to sort of warm up our intuition, Like,
let's think about this problem using things were familiar with,
and then we can make the analogy to the quantum
version and we can understand where that breaks down, like
where our intuition goes wrong. So let's start with our
intuition and the sort of the problem. The kind of
problem we're trying to describe is sort of like playing
(09:11):
with a bowling ball inside an empty swimming pool. This
is still for the bowling ball and swimming pool. Yeah,
I mean, isn't that a familiar thing when you see
a swimming, empty swimming pool and you think, I wonder
what would happen if I threw a bowling ball in there? Well,
let's give our listeners just a quick idea of what
we're talking about. So, quantum tunneling is kind of this
idea that a particle or or in the usual case
(09:35):
it's an electron, it consider be on one side of
a barrier in one moment and then the next moment
it's on the other side of the barrier. Right. The
generally they have quantum tunneling is that it's really hard
to keep electrons in a little trap or in a
little hole. That they really they're hard to pin down.
And people are probably familiar with that because the Heisenberg
and certainty principle, like, you know, you can't really isolate
(09:56):
a quantum particle in one little spot in space very long,
but you know if you try to do it, then
you know eventually it's going to leak out. And and
the point of quantum tunneling is that electrons can build
these tunnels or burrow through these barriers to to you know,
adjacent little holes or adjacent little wells. So that's the
idea is that it's like you have a particle, there's
(10:17):
a barer in front of it, and at some point
it just moves to the other side of the barrier. Yeah, exactly.
You can see it on one side of the barrier,
and even if it doesn't have enough energy to get
over the barrier, sometimes you see it on the other
side and you have to ask, like, how did it
get here? Right, right, like spontaneously just appears on the
other side or what. Yeah, well, sometimes on one side
(10:37):
and then it's on the other side, and then it
goes back right, And there's a lot of interesting stuff
there about like, um, you know, if the particle was
here and then later it's there, how did it get
from one place from the first place to the next place.
Right In your mind, you're used to things. If it's
in one spot and then later it's in another spot,
you imagine it took a path from one spot to
the other spot. Right, That's the way classical things work,
(10:59):
based balls, hamsters, whatever. But that's not true for quantum objects.
Quantum bologists are here and then later they're there, and
there iss not necessarily any path between those places that
the particle took. It didn't move, It just was here
and then it was there. Yeah, it's frustrating because quantum
particles don't have this underlying hidden truth, right, it's not
(11:20):
like there is a true story about where the particle
was at every moment and we just don't know it.
It doesn't have that story. That story doesn't exist. You know,
it's it's it's in a location only when you ask
where is it? And then it's in a location later
when you ask where is it? You're saying it particles
don't really have a here or there. It's like they're
around here. Well, they have a here, Like at some
(11:42):
moment you can say it's here, and another moment you
can say it's there. But you can't connect the dots, right,
You can't say that there must be a line between
those two dots and the particle took that line or there.
There doesn't have to necessarily be aligned. It's just here
and then later it's there. It's you know, it's like
um frames in a movie, but without the intervening um connections.
(12:04):
Like if you're watching a movie, you know, the person
would be standing here, and then suddenly they'd be standing
over there, and then they'll be studying this other part
of the frame, right, almost like they were teleporting between spots.
I was just going to say that that's not teleportation.
Right when you're watching a movie, and you know, and
you watch this frame by frame, you don't imagine they're
(12:25):
teleporting from frame to frame. Right, you're just saying, well,
I know he's here in this frame and he's there
at that frame. Right. That's not teleportation. You're saying. A
quantum particle doesn't have a path between these two things.
It's like, if you ask you where it is, it'll
just kind of pop around all over the place. Yeah,
you can ask a particle where it is and it
will answer, right, and then later you can ask it
where it is and it will answer, But you don't
(12:46):
necessarily know anything about where it is in the intervening time,
and you can't assume that there's some classical path. You know,
if you if you ask where's my baseball and what's
his velocity? Right, then you can actually predict exactly where
it's going to go any moment. And so it has
this thing we call the classical path. It's position and
velocity at any point in time, and when you're looking
(13:07):
at it, you're just sort of sampling that. Right. But
for a quantum particle that doesn't exist, you can ask
where is it? And you're gonna ask where is it later? Right?
But you can't connect the dots between those two and
assume that there's a path that it's following. Well, this
is a perfect point to take a break, Okay. So
(13:35):
then the idea of quantum tunneling is that a particle
is on one side of a wall or a barrier,
and then the next instant it's in the other side
of the barrier. And so that what we want to
do here today is sort of explain how that happens
and why it's not teleportation. Exactly how does that happened
and what does it mean and why it's not teleportation.
And so you you think a great way to think
(13:57):
get into this topic is to think about bowling balls.
And yeah, well, I mean, what is a barrier after all? Right,
Like I think people think about electrons is tiny little balls.
So I was thinking about let's use a bowling ball
because that's macroscopic and what is really a barrier? Right,
I mean people might be thinking like, what kind of
barriers are we talking about? And so let's imagine a
macroscopic barrier, like a familiar one. Right, You're the bottom
(14:19):
of swimming pool with a bowling ball. By the way,
this is amazing video of a guy. This what inspired
me is this amazing video online of a guy with
the bowling ball in a swimming pool and he can
do these hilarious tricks where he puts like the pins
behind him and he rolls the bowling ball and it
does these crazy moves and he knocks off all the pins. Anyway,
so you're the bottom of the swimming pool with the
bowling ball, right, and what happens you just put it down.
(14:41):
Let's make it clear the pool is empty. I'm not
drowning here, I'm not empty swimming pool. I'm not holding
onto his heavy ball. And and then sitting at the
bar of gear does not make this anymore complicated. Yeah,
it's an empty swimming pool with a bowling ball. But
let's also make it clear it's one of these swimming
pool is that it has a curved floor, right, like
(15:02):
a bowl shaped floor, right like if if it's a
swimming pool with straight edges at the bottom, this is
not going to work, that's right. Also, there's no like
chain saws or you know, traps or you know, rabbit
hamsters or anything else in the swimming pool. Just you know,
to be clear, just just the bowling ball in an
empty curved pool, you know, or if it's easier for you,
(15:23):
imagine a grape in the bottom of a bowl or whatever.
But the point is what happens when you put the
bowling ball at the bottom of the swimming pool. It
just sits there, right, It doesn't leave. You're never going
to find it in your neighbor's empty swimming pool, right,
It's always going to be in that pool. And the
barrier in this case is the edge of the swimming pool.
You mean, like, if you don't touch it, if you
don't push it, if the wind doesn't blow, it is
(15:44):
just going to stay there. That's right exactly. And you
expected to stay there. You don't expect to come by
one day and find it in your neighbor's swimming pool. Right.
It is that if something does disturb it, like a
raccoon comes by and pushes it, it's just going to
roll back down to the bottom of the pool again. Right,
that's kind of the idea. That's right exactly, because the
walls of the pool are the barrier, right, That's where
we talk about. It's a potential barrier. And if a
(16:06):
raccoon comes and pushes it, you know, and he pushes it,
you know, as hard as a raccoon can. Then it's
gonna roll up, and then it's gonna roll back down,
and it might roll back up the other side, but
it's never gonna roll higher than it then it went originally, Right,
It's just gonna eventually relax down to the bottom of
the swimming pool. And so if you don't give it
enough energy to go over the lip, then it's trapped
(16:28):
in the pool. Right, It's never going to get out
of the pool unless it has enough energy to go
up and over the edge of the swimming pool, right,
And so that's the barrier, like that's the wall, yeah, exactly,
And your intuition says it's trapped, right, if you don't
give enough energy, it's never ever, ever, ever, ever, ever
ever ever going to end up in your neighbor swimming pool, right,
that's where your intuition says, right, unless there are some
(16:50):
really strong raccoons. But that's what different. I don't know
what kind of neighborhood this is with all these empty
swimming pools and like tough gangs of raccoons pushing bowling balls.
But we're to get out quite the science fiction dystopia here.
But Yeah, you don't expect it to ever be able
to get out of the pool by itself. That's right,
exactly that barrier you can consider it to be perfect. Right.
(17:10):
The only way um to the next swimming pools to
go over the barrier. Right, You can never go through
the barrier. These raccoons are not tough enough to throw
the bowling ball like and crush the ground and get
through it. Right. Wait, what are their Swiss raccoons and
they dig a tunnel? Yeah, or they're like superhero raccoons
(17:31):
like um in one of those Marvel movies system, isn't
there some super raccoon or is he just look like
a raccoon and he's not actually a raccoon and never
actually in genetically modified raccoon aliens that look like human
like Earth raccoons And never quite figured that one out.
But we digress, we do, we do digress. That's the analogy.
Right now, Think instead of the bowling ball, think of
(17:53):
an electron. And then when we talk about barriers, we're
talking about you know, barriers to that electron. So maybe
made by other particles, you know, protons or something that
would repel it, right, something that would you would build
to try to keep the electron localized like a little trap,
like a like a little magnetic field. Maybe he is
keeping it trapped or something. Yeah, a little magnetic field
(18:16):
or electrostatic potential or something anything you can do to
trap an electron. And people do this, right, they want
to study individual electrons or individual ions. They build atom
traps the pretty cool um and so people actually do this.
But it's also a good case study for quantum mechanics
because it helps us think about how these things work
and don't work. So it's a it's a very popular
sort of junior level quantum mechanics problem in college. So
(18:39):
what happens. You put the electron in this little well, right,
and it's like a barry. It's like a swimming pool,
and you think, if the electron doesn't have enough energy
to go over the edge, then it's trapped, right, just
like the bowling ball. If it doesn't have enough energy,
how could it ever get into the neighboring swimming pool. Well,
the thing you find is that even though it doesn't
have enough energy, sometimes it appears is in your neighbor's
(19:01):
swimming pool. Like it gets through that barrier. It appears
in the adjacent well. Like if you have a series
of these um potential wells, you know, these these little
traps made for electrons, and you put it in one,
you come back the next day and find it in
the next one. Even though it didn't have enough energy
to go over that barrier, even though it was trapped
(19:21):
by a magnetic field, it somehow slipped out, yes, exactly,
And so that's the that's what we call quantum tunneling. Right,
how did it get through the barrier? In principle, the
barrier should be should bar it, right, that's what barriers do.
It should borrow it from passing, just the way you're
the ground does, the end of the swimming pool does.
So the question is why does an electron not get stuck, right,
(19:44):
because if it tried to move, the field would push
it back into the trap. But somehow it's able to
live out or create a tunnel exactly exactly. And your
instinct might be to say, well, maybe like momentarily goes
over the barrier, like you know, I don't know Heisenberg
Uncertainty blog blog. You know, maybe it borrows a little energy,
(20:04):
momentarily gets over the barrier. Right. That's tempting because you
want to think of the barrier as working, and so
do you want to think that if it's going to
go to the other well, is somehow has to go over.
But it doesn't, right, it can't. It's a conservation of energy,
so that that explanation doesn't work. The electron doesn't get
more energy momentarily magically, it um it's just on one
side of the barrier and then it's on the next.
(20:25):
Like zoos didn't come down and touch the bowling ball
and push it into the other swimming pool. That's impossible,
that's right. We're assuming that there's no other source of energy, right,
and and it never has enough energy to go over
the edge of the swimming pool and into the next one.
So the only way to the other swimming pool is
to tunnel, is to go through the barrier. And then
once it's out and on the other side of the barrier,
(20:49):
does it stay there or does it sometimes pop back
in or does it fly off? At that point it
pop it pops back in. Yeah, it can pop back
in and it can go to the next one. Right.
The point it is that you can never really trap
an electron. And the reason is not that it goes
over the edge, and the reason is not really teleportation, right,
And the reason is that these these barriers and a
(21:12):
quantum level are just different than the barriers we have
here at the macroscopic level, and electrons are different from
bowling balls. Right. We like to think of them that
way because it's useful, because the way we understand the
unknown is to do it in terms of the known.
But in the end, these things can do things, These
quantum mechanical things can do things that the classical things,
(21:32):
the macroscopic things that we're familiar with, just can't do.
And one of those things is the electron. It has
a chance to just ignore the barrier. It's like every
time it goes up against the barrier, a die is
rolled and if it comes up you know, all sixes,
it's like, haja barrier, I get to ignore you. You
said every time it goes up against the barrier, Meaning
is it like it's always pushing against the barrier or
(21:54):
is it like a continual roll to die or what? No,
that's a good point, And the way I was speaking
about it, it's wrong because I was talking about it
like having a classical path, like it has a position
and a velocity at every moment. In reality, it's motion
is governed by this wave equation, right, the wave function
that we used to describe where it is, and that
tells us where it's more likely to be and where
(22:16):
it's less likely to be. And we know that for
it to get from one side of the barrier to
the other, it has to go through the barrier. We
know this because it can be inside the barrier. Like
in principle that should be impossible, right, like, how do
you how can you be inside the barrier? You're not
breaking the bearer, The bear is not destroyed, but it
can sort of like defy the barrier, can sort of
(22:36):
ignore the barrier. It has a probability to just sort
of like shrug off the barrier the way a teenager
shrugs off a curfew. You know. So the trap, the
magnetic field that trap is traveling the electron doesn't affect
the probability of where the electron can be, or it
does doesn't. It doesn't it like squeeze the probability cloud
(22:56):
of the electron or something like that. It totally does.
It affects it, but it can't trap it completely. It's
just impossible to trap it completely unless the barrier is
infinitely high, the barrier is infinitely strong, then the electron
is totally trapped. But as long as the barrier is
not infinite, right, imagine the swimming pool. It's infinitely deep,
(23:16):
then the quantum mechanical bowling ball can't get out. But
if the if it's even if it's super high, it's
a billion miles high, but not infinite, then the quantum
mechanical one can get to the other side. It just
has a chance. But you're right, it does affect that
it squeezes those probabilities. The probabilities are shaped by the barrier.
But you're saying there's still a little tiny probability that
it's going to jump over, not jump over, but go through, right,
(23:40):
And the probability is smaller if as the barrier gets wider,
and it's smaller as the barrier gets taller, So that
that all makes sense. The thing that's confusing is like,
how do you explain what it's doing in the barrier?
Is it just like ignoring the barrier and you just
have a chance to avoid the barrier. It's it's hard
to come up with a sort of like an intuitive
under standing of what it's doing there you know, it's
(24:02):
like it's in the Noman's land. It's in the place
where nothing should be, but there it is, right is it?
Because the bowling ball is not really a bowling ball, right,
it's more like a cloud, kind of like a like
a fog. And you're saying, sometimes the fog can sort
of extend and kind of appear on the other side
of the swimming pool. If you measure an electron, you say, okay,
it's in my trap, and then you ask where is
(24:24):
my electron likely to be in one second? Then most
likely it's to be it's going to be in the trap.
There's a little bit of probability it's going to be
in the barrier, and there's a little bit of probability
it's going to be in the next one. Right, it's
going to be in the next trap. So you know,
after you know where electron is, that doesn't tell you
where it is necessarily a second later. It's just you
(24:44):
have a probability distribution of where you're going to find it,
and we can candulate those probabilities using the Shortinger equation.
But that's again, that's just a description of what we
have observed. Right, the exhorting equation itself is not an explanation.
It's just like a mathematical formulation the success He describes
what we've observed. Oh, I see, it's a probability of
where it's going to be if you measure it. So
(25:06):
if you measure it, there's a tiny little probability you're
going to measure it in your neighbor's pool. Yes, exactly.
And it's tempting to think, oh, well, that's just particles. Right,
particles are here, and then particles are their. Right, that's
not the property that allows the electron to quantum tunnel. Right.
You can have that property in an infinitely deep swimming
pool where electrons can't tunnel, right, an infinitely deep potential well, right,
(25:31):
the electrons can't get out. That's the only one that
can completely hold them. But in now well, electrons can
still be here and then later be over there, and
then later be over here, as long as you're still
within the well. But if the wall is not infinitely high,
then there there's a probability that randomly it's gonna ignore
or jump over the barrier and be on the other side.
(25:53):
If you measure that's right, not jump over, but go through, right,
jumping over means why not jump over? Well, jumping over
means don't really know, right, you do not like he
was hit inside and then it was outside, and you
don't know. You don't really know what the path it
took to get outside, right. Well, to get over, it
would need to have enough energy to go over the barrier, right,
and that energy has to come from somewhere, and we
(26:14):
have energy conservation in our universe, and so it can't
go over the barrier, right. It's like the raccoon pushing
the bowling ball. If it doesn't have enough energy to
push it over the lip, it's just never going to
go over the lip. Um. And the reason this works,
we can do the calculations, and the reason it works
is because the electron is in the barrier. Like bear,
quantum barriers are just different from classical barriers. They're sort
(26:36):
of optional. You just always have a chance to ignore them,
you know. It's like a speed traps. Sometimes the copsies
you and sometimes he doesn't. But if you find it
inside the barrier, doesn't it mean it gained a whole
bunch of energy. No, it can be inside the barrier,
meaning that it doesn't have enough energy to be there.
But it's there anyway, where does the probability come from?
(26:57):
You know what I mean? Like for it to be probable,
He's who have some sort of physical explanation, doesn't it. Yeah,
And the explanation is that the bowling ball analogy is
wrong because this is not a bowling ball and these
are not a swimming pool. It's a weird, lobby, wavy,
fuzzy thing that can do this thing that no bowling
ball or swimming pool can do. And the barrier also
(27:20):
is a little fuzzy, right that you can't build a
perfectly strong barrier unless it's infinitely high um. In quantum mechanics,
barriers are not the same as swimming pools, right, that
they're different. And so the analogy breaks down, and these
things can do things that that the things were familiar
with can't do, and one of them is that sometimes
they sort of ignore each other. With that, let's take
(27:42):
a break. We'll be back in just a short minute.
(28:02):
But um, and the interesting thing is that it's not
just electrons, right, like you're talking about all particles. Oh yeah,
electrons are just the simplest case, But any quantum mechanical particle,
any particle that's motion is primarily described by like the
shortening air equation. So single particles or ions or nuclei,
whatever these things can do this also we see it
all over the place. It's actually an important part of
(28:24):
loss of physical processes that we know and love. Well.
I think it's interesting to think about the idea that,
you know, these walls in the room that I'm in
um are sort of just barriers to right, Like they're like,
what's preventing my hand from going through the wall. It's
not just my inner peace, but uh, it's it's like
the electromagnetic forces between my hand and the wall exactly.
(28:47):
And that, as you say, is a quantum mechanical barrier.
Like the very tip of your finger. Imagine that's an electron.
When it approaches the wall, it meets a barrier, a
barrier made by the electrons in the wall, and that's
what doing the repulsion. And so you're right, there's a
tiny chance so that first electron is just going to
go right through the barrier instead of bouncing off of it,
and I might lose that one electron from my finger,
(29:11):
you might, Or there's an even tinier chance that the
next set of particles will will quantum tunnel through, and
an even tinier chance that also the next ones will.
So there's some non zero chance that you'll put your
hand through the wall without breaking the wall. That's crazy.
It's it's non zero chance that I can walk through,
or do I walk through the wall or appear on
(29:31):
the other side or both. I know this would be
a horge quantum tunneling through the wall. Yeah, there's totally
a non zero chance. Now you could stand there all day,
your whole life, walking into walls and not successfully go
through it. And I'm pretty sure that would be your
experience because the probabilities we're talking about are ridiculously tiny, Like,
for these barriers are pretty tall, and there's lots of
(29:53):
particles and have to happen for all of them, and
so it's basically impossible, but not technically exactly zero. So
there is a possibility, Daniel, that you're sitting right there
where you are will suddenly find yourself on the other
side of the wall that's in front of you, right exactly.
There is a possibility I could quantum tunnel into the
bathroom or whatever. Let's say it happens right now. Proof
(30:14):
would you say you teleported to a battle. I mean,
what's what's the difference between that and actually teleporting. Well,
we did a whole episode about teleportition, remember, and we
decided that teleportition is impossible while this is possible. And
you know, it's really tempting to connect this this um
idea of tunneling with the concept that part of quantum
(30:36):
particles can sort of skip their way through life, right,
they don't need to exist at every moment, sort of
they're here and then they're there and the other thing.
And so if you want to call this telepartition, then
every particle is teleporting all the time, right, So that's
my problem with it. It's like this is a natural
thing that particles are always doing, even without barriers, Like
even a particle in an infinite box is doing this
(30:56):
sort of skipping thing because it doesn't exist between the
moments you're observing it. So if this is teleprotation, then
that's teleprotation also, and everything is constantly teleporting. You're saying
that you don't want to call it teleprotation, not because
it's not teleprotation, which I would argue maybe it is experientially,
but it's just that if you call it teleprot teleportation,
(31:17):
it would sort of the dilute or or break the
definition of teleprotation. Yeah, if this is teleprotation, then we're
all teleporting all the time. So if everyone is nice,
then nobody's nice. It's kind of right, like it's the
teleporters quantum dilemma exactly, all right, So that that that
that makes a bit more sense. And quantum tunneling is
(31:40):
really important, like it happens in the sun. If you
want nuclear fusion to happen, the kind of thing that
powers the sun, that generates all that light that you
know makes you look so nice and tan and grows
all that food that you eat, then you need these
particles to be able to quantum tunnel through some of
the potential barriers that they face. You know, particles infusion
don't like to touch each other, right because nuclei are
(32:03):
both positively charged because of all the protons. So to
get them to fuse, you have to push them together,
and they're repelling each other, and that's a barrier. So
you've got to get them sometimes through that barrier in
order to do the fusion. And you're saying sometimes they
tunnel to that, but mostly do they mostly get pushed
together or do they actually tunneled together. I think it's
some of both. I mean, the center of the sun
(32:24):
is so hot and so dense that these particles can
just sort of overcome the cool embarrier like they have
enough energy. But definitely, um tunneling is an important part
of it, Like fusion wouldn't be the fusion we know
and love without quantum tunneling. If everything is fusion, then
nothing is fusion. That's what you're saying. That's right, that's
the theme today, right, label everything um. And there are
(32:44):
other effects, like you know, back to electrons. Electrons don't
like to stay in little traps, but if you're building
chips for computers, then you'd like your electrons to be
in certain places you want to know, like hey, this
transistor is all on or this transistor is off or whatever.
And and it gets harder and harder to make transistors
be reliable as they get smaller and smaller, because you
(33:06):
get dominated by these quantum effects, and these little traps
get smaller and smaller, and electrons like to jump out
of them, and you don't want your ones in your
computer to suddenly switch into zeros. And so this actually
is a big effect in miniaturizing transistors, which is a
big effect in speeding up your iPhone. At some point,
if you make electronics small enough, the quantum effects are
(33:27):
gonna totally miss everything up. Yeah, exactly. Quantum mechanics messes
it up again, bummer, Why can't they just be elect
strikes out. Quantum mechanics strikes out again. Why can't we
just use little bowling balls and tiny little swimming pools
instead of electrons? Sorry, and bowling striking is good, so
it wins. Yeah, it strikes out, exactly. You brought a
(33:51):
full circle. They're very nice, all right. So that's that's
pretty much quantum tunneling. It's this idea that particles are
all quantum, and as such, they have these weird fuzzy
uh location right, They're not in any particular place, and
so it's impossible to trap a particle because it's fuzzy
and it might slip out. That's right. Quantum barriers are
(34:12):
just different from the ones you're familiar with, the work
under different rules, and those rules have little random exceptions
to them, so sometimes they can just be ignored and
it's weird and it's confusing, and your intuition breaks down.
But it's also wonderful because it shows you how the
world works at a smaller level. Right, it reveals to
you where your intuition is wrong, and that that means
(34:33):
that it's showing you the truth of the universe. Yeah,
and the and the truth is bowling. Exactly. The truth
is quantum bowling. This episode brought to you by the
American Bowling Association. Yeah, exactly. But so that's what happens
at the microscopic level, but on the larger level, we
(34:53):
we can't do that because you know, there's a lot
of lactrons in my hand, and the chance that all
of them are going to quantum tunnel at this time
it's just almost zero. Yeah, exactly. Like if there's a
chance for you to roll a one million sided die
and get zero, you know that's probably can happen. But
if you have to do that for a million die
all at once um and get the same answer, then
(35:15):
it's basically very improbable, almost impossible. So you the macroscopic
stuff sort of gets averaged out, but still possible. It's
still possible. Absolutely, you could quantum tunnel through the walls
and not counted as teleportation. All right, It's just what
quantum stuff does Yeah, yeah, drives them physicists crazy. No,
(35:39):
it excites us. Is it's wonderful. We're always looking for
weird quantum effects that show us how the universe works.
It's you know, it's a it's a it's what we
what we live for, these little moments. All right, Well,
we hope you enjoyed that discussion and hope that answered
all of the questions that listeners had about what is
quantum tunneling. Thanks for sending in your questions. They're inspiring
(35:59):
and if you have of questions about things you'd like
to see explained, please send them to us at questions
at Daniel and Jorge dot com. We love your messages,
that's right. And if you are Swiss one would like
to tunnel some money over to us, we are also
available at feedback at Daniel and Jorge dot com or
just dump it right into Katrina's bank account if that's
more convenient you go, all right, thanks for listening. If
(36:33):
you still have a question after listening to all these explanations,
please drop us a line. We'd love to hear from you.
You can find us at Facebook, Twitter, and Instagram at
Daniel and Jorge. That's one word or email us at
feedback at Daniel and Jorge dot com. Thanks for listening
and remember that Daniel and Jorge Explain the Universe is
a production of I Heart Radio. For more podcast for
(36:55):
my heart Radio, visit the I heart Radio app, Apple Podcasts,
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