January 7, 2021 • 44 mins
Daniel and Jorge talk about quantum decoherence and why big things don't act like quantum particles.
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Speaker 1 (00:08):
Hey, Daniel, can you pass through walls? No? Keep trying
and just keep getting more bumps on my head? How
about can you bean too pleased at the same time?
Sometimes it feels like I'm supposed to be but I've
never actually managed it. So I guess you're not a
quantum object. No. Actually, I'm quite classical. But you're a
particle physicists. Aren't you made of particles? And aren't those
particles quantum mechanical? I study particles and I'm made of particles,
(00:33):
but I follow the rules of classical physics. Classic. I
mean you're classic, Daniel. I'm not new Coke Daniel. I
(00:56):
am more hammad cartoonists and the creator of PhD comics.
I'm Daniel. I'm a particle physicist, but I'm quite classical
in my tastes. Are you a fan of classical music
and it's better than quantum music? Let me tell you
that's a new genre to mak a new category at
the Grammy. Oh I wish it was a new genre,
but I'm sure if we type it into Google we
will find something for quantum music. I feel like that's
(01:19):
all music these days. It's both good and bad. It's
kind of incoherent. It's both original and stale. Welcome to
our podcast, Daniel and Jorge Explain the Universe, a production
of My Heart Radio in which we explore everything in
the universe and try to make sense of it. We
try to understand how things move in our world and
how tiny particles move. We try to understand the rules
(01:41):
of the universe, whether they govern supernovas and black holes
or tiny little electrons, and we try to make sure
that you understand them. Yeah, because we try to make
this podcast a super position of both fun and real science,
physics and banana jokes. You often think those two can't
be in the same place. Said the same time, what
(02:01):
makes you say that you haven't met any fun physicists.
You mean the physicists is fun, or they know how
to have fun, or just doing physics is fun. Why
doesn't everybody see that? Come on, I think that's the
problems and that's the problem. But yeah, it's a weird
and strange universe out there, and so we like to
talk about all of the things and make it weird
and strange. It's pretty unintuitive the universe it is, and
(02:24):
physics has done a great job of building this edifice
to help us understand the way the universe really is,
not the way we think the universe should be or
might be, or the way that makes sense to us
based on our limited experience, but actually revealing to us
the true nature of reality. But sometimes what we learn
is pretty hard to swallow. Yeah, and specifically quantum mechanics.
(02:45):
I feel like that really trips people up. It trips
me up, for sure, And it's kind of hard to
wrap your head around all of the weird, kind of
unintuitive phenomenon that happens at the quantum level. Yeah, it
is pretty weird because quantum particles seem to be following
different rules. They seem to be able to break rules
that are hard and fast for things like baseballs and
(03:06):
basketballs and scoops of ice cream. And that's a hard
thing to understand because it's weird and it's new. It's
also hard to understand, like why are there different rules?
And you know, what's the difference between an electron and
a baseball? You know, where is the sort of threshold
between those two where the quantum rules take over or
the classical rules take over. Yeah, it is kind of
weird that, you know, things are so weird at that level,
(03:28):
at the microscopic level, but then once you scale up,
things feel more gosh normal, more solid, less uncertain, or
at least more familiar. Right. Science is all about delving
into the unknown, and typically we try to explain the
unknown in terms of the known, but that fails if
the unknown is something really new, something different, something that's
(03:51):
fundamentally can't be described by what we already know. We've
often talked about how physics is like exploring the universe,
but it's just been studying the tail of the elephant,
and when you look at the rest of the elephant,
it's not always true that what you learn from the
tail can help you understand the rest of the elephant.
Sometimes you really do discover something weird and different. Yeah,
but is that elephant quantum mechanical, Daniel, Is it really
(04:13):
there or not there? It's a theoretical thought experiment elephant.
So it's just totally not there. That's classically non existent.
Al Right. Well, that connection between the quantum world and
our regular, everyday world is what we'll be exploring today
on this episode to be on the podcast. We'll be
asking the question what is quantum decoherence? That's hopefully a
(04:41):
coherent question, yes, and quantum decoherence is the key concept
to understanding the answer to this question. Why do big
objects not seem to follow quantum rules? What is the
difference between quantum objects and big objects? Where is the threshold?
Why do we seem to have two sets of rules
or is it just that one set of rules sort
(05:02):
of morpse into the other. Right, it's an important concept,
and it seems to be sort of related to this
idea of quantum measurements. I think maybe that's something that
if you've heard of quantum mechanics or have talked about
it or seen any videos about it or read about it,
it's something that seems to be important that you know
things are quantum, but then when you poke at them
(05:23):
or measure them or try to look at them, things
collapse for some reason. Yeah, this is a big and
still totally unsolved problem in quantum mechanics. Quantum mechanical things
can have like multiple possibilities, but we don't observe multiple possibilities.
When you poke an electron, as you say, it picks
one of them, and we don't really understand how that happens,
how one of them gets picked, and actually when that
(05:45):
picking happens, you know, Does it happen when your finger
touches the electron? Does it happen when you look at
the results? That happens somewhere in between. That's a really
interesting and hard problem, and it's related to quantum decoherence,
but they're not quite the same thing. To today, we'll
try to explain what quantum decoherence is, how it helps
us understand the difference between quantum and classical objects. But
(06:06):
it's important to understand that it doesn't actually solve this
problem of the quantum measurement. Is that what happens when
you pull on the tail of the elephant, things get
real real quick. You get quantum stomped. It makes quantum
music out of you. All right, Well, this is an
interesting question what is quantum decoherence? And so as usual
we were wondering how many people out there in the
real world know what it means. So as usual, Daniel
(06:28):
went other into the wilds of the internet to ask
what is quantum decoherence? So thank you very much to
everybody who will volunteered your speculation for the podcast. If
you would like to volunteer for a future podcast, please
write to us. Two questions at Daniel and Jorge dot com.
Think about it for a second, soone ask you what
quantum decoherence is. What would you say it is, or
(06:50):
at least guess it is. Here's what people had to say.
I'm not sure if I recognized this right, but I
think decoherence is about how the quantum and the normal
little few collide, so how we can map quantum effects
into all reality. Since coherent means to make sense, I'm
(07:10):
thinking quantum decoherence is when quantum particles can't logically follow
the rules of the universe, of the constants of the universe,
or something of the nature. I'm not sure what quantum
decoherence is, but I think it might be wave function collapse,
which is how the wave function of a quantity and
(07:32):
a quantum system collapses when you measure that quantity. I
don't know what quantum decoherence is, but my guess would
be that it is the occurrence of something totally inconsistent
that disrupts the quantum realm. It's got me thinking of
something to do with quantum entanglement. All right, Some pre
(07:53):
coherent answers for the most part, or at least coherent
in there not knowing what it is. Nobody actually quite
nailed it. But you know, people are in the vicinity,
and they seem to understand that there's a concept of coherence,
at least in quantum mechanics. Somebody said that it is
sort of where the real world and the normal world collide.
(08:14):
I guess they do, maybe think it has something to
do with the connection between the quantum world and our
everyday experience. Yeah, and that one is the closest I
think to the right answer, to the right way of
thinking about it. Quantum to coherence, in brief is the
idea that explains how quantum objects look like classical objects
when they get really big and messy. All right, well,
let's jump into a Daniel and I guess let's start
(08:35):
with just a quick recap of quantum of a small
subject called quantum physics. You know, what is it that
we actually call quantum and how can we kind of
describe those effects? So the thing to understand is that
when you look at really small objects, things like electrons
or photons or individuals tiny particles, they seem to be
(08:57):
following rules that don't apply to bigger objects like baseballs
and Basketball's right, and the key concept to understand when
thinking about these tiny particles is that they're not just particles.
They're not like tiny versions of a baseball. They're not
just like miniaturize little blobs of stuff flying through space.
(09:17):
Right when people were first thinking about the atom, for example,
they were thinking about the electron like orbiting the nucleus
like a tiny planet around the star. But we pretty
quickly figured out that was impossible because if an electron
orbits and nucleus, then it's going to give off radiation
because it's accelerating, it's giving off radiation. And they did
the calculation and discovered, well, that would collapse in like
(09:38):
a hundred billions of a second because they would lose
all of his energy. And so instead they had to
have a new idea for what controls and electron, what
defines what an electron does and how it interacts, and
so instead they try to use like wave like properties
to describe it. So you've probably heard this phrase called
the wave function. The wave function is just a mathematical
(09:58):
tool that helps us under and what an electron is
likely to do. And the key concept is that the
wave function tells you where a particle is likely to
be and where it's not likely to be. Sean Carroll
says that the wave function is the dope ist name
in the world for one of the most profound things
in the universe, which really made me laugh. Well, dope
and profound go hand in hand. I think like physics
(10:21):
and fun, right, Yeah, well, yeah, I think that is
maybe the hardest thing to grasp about quantum mechanics and physics.
You know, I think everyone sort of grows up at
Leaston's early in school and definitely in popular culture. You know,
the depiction, like pictures of an atom always look like
little planetary systems, you know, like a bunch of little
balls in the middle cluster together, and then other little
(10:43):
balls kind of swinging around in large orbits and rings
around that. And that's the picture that we have about
the atom. But you're saying, at some point we figured
out that's not possible, like that that doesn't make sense. Yeah, exactly.
It's not like the electron has a trajectory, has a
path and we just don't know it. It doesn't actually
(11:04):
have a path that doesn't have like a position at
every moment in time. Instead, what it has is this
quantum wave that the quantum wave behaves all sorts of
normal wave like rules. But what it does is tell
us where the electron is likely to be, and so
the electron is likely to be here and it's likely
to be there now. Sometimes people say that means that
the electron is in two places at once, but that's
(11:27):
not actually correct. It means it has the probability to
be here or there, and those in both probabilities can
exist at the same time. It doesn't mean it's actually
in both places at once. If you ask the electron
where are you, then it collapses as we talked about earlier,
It picks one place or the other. But the wave
function describes what's likely to happen. Well, I guess you
(11:48):
mentioned before that it has a dopey name. Why do
you think it's a bad name, And what would you
have called it if not the wave function? And why
is it called the wave fund? Well, wave, I suppose
because it follows a wave equation. Shorting's equation is very
much like equations for other waves that we've seen before,
that electromagnetism, and it just waves in water. Right, there's
(12:10):
a certain differential equation which just looks like a wave equation,
like a wiggle like a like a like a rippling wiggle. Yeah,
it's like a rippling wiggle, but you know, it's not
a rippling wiggle in anything physical, right, Like sound waves
are a wiggle in air, like air pressure. Right yeah,
light waves are a wiggle in the electromagnetic field, which,
even if it's hard to imagine, is a physical thing.
(12:31):
The wave function is complex. It's imaginary values. It's like
you know, one plus three I and so it's not
a wiggle in a physical thing itself. So it's it's
hard to understand because it's like this sort of abstract
literally complex things in the sense that it exists in
the imaginary plane, but it controls something real. So I
(12:51):
wouldn't have called it the wave function, you know, I
like the word wave, but function to me is sort
of confusing. Which you have called it the imaginary function? Well,
I feel like alluding to the imaginary complex plane that
is not helping me here, I guess, And you just
brought up maybe a source of confusion, which is that
you know, you just said the light or a photon
(13:12):
is like a ripple in the electromagnetic field, right, It's
a ripple like kind of like a sound waving that
it's like, it's more intense here in this intense here
are you saying that? There's also like a photon would
also have another kind of waving, nous, which is imaginary. Absolutely,
the photon also has a wave function, right, and that
(13:34):
wave function determines where the photon is likely to go,
like which parts of the electromagnetic field are likely to ripple,
you know, for example, you know, the classical situation is,
imagine you shoot a photon at two slits in a screen.
You know which one is it going to go through.
It has a probability to go through one and a
probability to go through the other. The wave function controls
(13:54):
what those probabilities are, right, And if it collapses and
picks the one on the left, then you get an
electro magnetic wave through the one on the left. So
the probability wave and the electromagnetic wave are sort of
two different things to keep in your mind, and they
both spread differently. Like why did they call them waves
in the first place, Like do these like probabilities ripple
(14:14):
out into space also, or or do they just look
like a ripple that moves around. They do ripple, and
they do follow wave mechanics, and that's why they call
it a wave, and that's why they can do really
amazing and fascinating things. Because the location of electron is
controlled by something which is fundamentally a wave, it can
do things that waves can do. Like it can interfere, Right,
(14:36):
you can have probabilities interfering with themselves, probably being here
and there, can interfere with each other and create probabilities
in other places, just like actual waves can. Right, you
put two hands in a lake or in a bathtub
and you make two sources of waves. Those waves can
interfere with each other, meaning just that they can add
up or cancel out. So, for example, if I have
(14:57):
like an electron here, it has like a ripple of
probability kind of emanating from it, or is that kind
of static if the electron is static. Well, electrons can't
actually be totally static, right, because their quantum objects. So
you can't just like say, electron is here and it's
not moving. That would violate the Heisenberger in certainty principle,
would effectively be an electron at absolute zero. But if
(15:19):
you have an electron, you shoot it out of like
an electron gun or something, and you want to describe
what's it likely to do, where is it likely to go?
Then you have a probability for all those various outcomes, right,
And the key thing to understand is like, there's not
a real history that's happening between when you shoot the
electron and when it hits the wall, and you're just
learning about it. It's uncertain, right. It has both possibilities
(15:42):
existing simultaneously until you measure it. And that's the key
thing that's hard to understand about quantum mechanics is like
how this measurement changes it from like having two possibilities
to actually existing in one place, but doesn't exist between
the places you measure. It only exists where you measure
in between. They're just probabilities, all right. So you're saying
(16:03):
that maybe, like an electron is like a little tiny baseball,
but we just don't know where it is, and where
it is is determined by this ripple in probability. Yeah,
I'm saying an electron is like a little tiny baseball,
but it doesn't have a place where it is. It's
not like it is someplace and we don't know its
place is not determined the probability of it being in
(16:23):
one place or another is determined by the way functions
like probably to be there seventy one probability be here
or whatever, so they add up to one. But the
probabilities are determined by the way function but doesn't actually
have a location. It just has those probabilities again until
you measure it, which is the weird bit, and then
when you measure it then it then it feels like
(16:43):
you're hit by a baseball. It certainly does. And that's
why we see these weird quantum effects because these particles
like electrons can do things that waves can do, like
if you have two sources of them, you get these
interference effects, or they can like tunnel through walls. These
are things that waves can do. Probability waves can do,
and you get effects because you have these wave like
(17:03):
properties of the electrons wave function. These probabilities can go
through walls like the wall doesn't affect it, like it
just goes through them. The wall does affect that. We
have a whole fun podcast on quantum tunneling. And it's
possible to go through walls right because you can have
a probability to be on one side of the wall
and then a probability to be on the other side
of the wall, and you can do that without going
(17:24):
through the wall. The probability can leak through the wall,
giving you a chance to be on the other side
of the wall, even if you're never actually in the wall,
all right, And so that means that the baseball would
just appear on the other side, or that that it's
found a way through the wall. It just appears on
the other side. Remember that quantum particles don't have to
have paths between where you've seen them. You see it
(17:47):
at A and you see it at B doesn't mean
it went from A to B. Doesn't have like a
secret history how it got from A to B. It
was a A and then it was at B. Remember
they follow fundamentally different rules. It was A, then it
had lots of probabilities from maybe how it got to
be not like one of them is true and we
just don't know it. There are those probabilities. It's undetermined.
(18:08):
It's not unknown, it's undetermined, and then later it's aid B.
So it doesn't have to go from A to B
in order to be at A and then be at B.
And this is highlighted by the quantum tunneling experiment because
you can't go from A to B. There's a barrier there.
All right, Well, let's get into quantum coherence and how
that relates or how that ties this uncertainty and this
(18:29):
way function to real things like baseball. But first let's
take a quick break. All right, we're talking about quantum decoherence,
and hopefully Daniel will we're not. We're not breaking down
(18:53):
into de coherence, talking about is. But okay, So particles
have a way function which tells you it's like a
ripple in the imaginary space, that tells you the probability
where that little tiny baseball where you will find it.
Maybe you weren't to poke in, Yes, exactly right. So
then what does coherence and decoherence means? So quantum coherence
(19:14):
is when you have two possible outcomes for what's going
to happen to your particle, and those possibilities sort of
line up like the wave functions for those two possibilities
line up. Now, any solution to the wave equation, any
like quantum state, you can take it and added to
another quantum state to get a third quantum state, which
is a mixture of the two. So you can mix
(19:36):
two possible wave functions like if you have when it
says the electron is gonna arrive at point A, and
you have another one that says the electron's gonna arrive
at point B. You can have a mixture that like
mixes A and B with fifty fifty odds. So that's
a coherent combination. It just says you have two possibilities
and you've added them together, and they're coherent because their
wave functions are sort of syncd up. They start in
(19:57):
the same place and they sort of wiggle in time
aim together, right, but they don't end up in the
same place. Isn't there some kind of cancelation or some
kind of or are you saying coherence is when they
don't cancel. They can cancel, right. The fact that they
can cancel is because they are coherent. You only get
interference effects from coherence sources of waves. Like go back
to the example of like bathtubs. Right, so you put
(20:20):
your hand in the water and you slap it, You
make a rhythm, and you get waves in the water.
You do the same thing with your other hand if
you're doing it in the same way, right, if you're
like slapping the water in time, then you get these
waves which either add up or cancel out coherently. If
your second hand instead it's just like a random just
like randomly slapping it, then they're not going to add
up nicely. It's just going to be a big emotion.
(20:41):
It's going to spread out to nothing. So you only
get these interference effects when the quantum waves are in sync.
That's quantum coherence, and that's what allows quantum things to
be sort of quantumy, meaning that they're in sync in time.
So what you're saying or in time and space, Yeah,
they're in sync in time, and so at every point
in space they can interfere. At one point in space,
(21:05):
you might get cancelation because they're waving in opposite directions,
and at another point in space they might support each
other because they're waving in the same direction. But they
can only do that consistently if they're in sync in time.
So it sounds like, you know, particles have these wave
functions and they someone have to sync up in order
for them to interact with each other, because if they
(21:27):
don't sink up, then then what happens They just cancel
each other out or they can interact, or what happens
if they don't sink up. If they don't sink up,
then you don't get any of these interference effects. It's
like if your noise cancelation headphones, right, if those were
sort of just like randomly putting out sounds instead of
like sinking up to the sounds that are coming at
your ear and producing exactly the opposite sound to cancel
(21:50):
them out. Right, your noise canceling headphones only work because
they produce a coherent noise which cancels out the ambient noise. Otherwise,
if they put out just random, arbitrary noise, they wouldn't
cancel each other out, and you just get sort of
normal stuff you can have like A and B. You
wouldn't have like weird interference effects between the incoming noise
and the noise produced by the headphones, and all the
(22:12):
weird quantumness comes from those like interference effects, these effects
of the probability wave. And if you don't have coherence,
then you don't get those effects. Okay, so you need
coherence in order to have interference, just a little maybe
counter in Twitter. But it's not a frequency thing, right,
It's not like they have to be the same frequency
or fit the same number of wavelengths within the same space.
(22:35):
It's something a little bit more than that. It's more
than that they have to be linked up. They have
to like sync up in time. Otherwise you could have
like coherence just for a moment, right, but to sink
up in time to be like consistently giving up these
probability waves that interfere, then they have to be sort
of syncd up, which is linked in time that to
like start at the same place and go down the
same time or up at the same time. Either way,
(22:56):
they have to like match each other in phase, right,
But they can so cancel each other out and be coherent, right,
Like you can be coherent and destructive at the same time.
It's different than decoherent, just like noise canceling headphones. Right.
The cool thing about the quantum wave function is that
we actually have a lot of intuition for how waves work. Right,
All these effects, interference and cancelation, these are normal things.
(23:19):
It's just weird when you apply it to the probability
for something to happen. So we're very familiar and happy
to talk about waves and that none of that is weird,
Like noise canceling headphones are not quantum magic. It's just
weird when you apply to the probability for an experiment
to have a certain outcome. Right, And lasers are also coherent, right, Like,
that's kind of what a laser is, Yes, exactly, a
(23:40):
laser is a coherent source of light. All the photons
are like in phase and have the same frequency, so
they add up together. Right, So it's a very intense
source of coherent lights. Okay, So that's at the microscopic level,
like electrons and photons and quirks. They can have this coherence.
But then something happens when you go up to the
bigger things, like when we have to worry about coherence
(24:01):
at the baseball level. Right, Well, we don't have to
worry about interference of baseballs because they're not coherent quantum objects,
like all of their particles are not wiggling in phase.
They're all scrambled and random. It's like a huge choir
of children all singing different songs at different volumes and
different speeds. And so what we see is like a
big average gamush. We don't see any sort of like
(24:22):
interference effects when two baseballs bounce off each other because
they don't have coherent quantum waves, their faces are all scrambled.
All right, Well, let's talk about that scrambling, because I
think maybe that's the key of what makes things quantumy
or not, Like maybe step us through, Like, okay, we
start with one atom, and the particles inside the atom
(24:42):
do have this wave function, and presimably they're coherent. Like
are the protons and neutrons and quarks inside of an
atom coherent together? Or is there already some kind of
smushing at that level? They can be coherent. Absolutely. There's
no limit to how large a coherent system can be.
It just gets harder and harder to do because it
has to be isolated. The key is that anytime you
(25:03):
interact with something, then it becomes part of your system,
and so the system sort of grows and grows and grows,
so it's easier to start from like like a single particle.
Take a single electron or a single photon, right, it
has a certain way of function, and that way function
is coherent, has like two possibilities for what it can do,
and those possibilities are coherent, and so you get like
interesting interference effects. That's why, for example, a single photon
(25:27):
going through the famous double slid experiment can interfere with itself. Right,
It's two possibilities are interfering. So single photon with two
coherent possibilities can interfere with itself. Now things get messy
once that photon starts to interact with other stuff because
now the two possibilities for the photon interact differently with
the environment. You know this interact with the wall or
(25:49):
interact with the tool whatever you're using to measure it,
and they change the phases of those two different outcomes,
and now it's decoherent. So a particle can be coherent.
You can even have two particles coher but once you
touch it, once you interact with it, then you can
break that coherence. Right. But you know we're trying to
build up from like particles up to a baseball. And
so like if I assemble you know, three quarts together
(26:12):
into a proton, are they still coherent together or do
they start to kind of get out of sink? Once
I put them together into a proton, they can be
coherent together. And you can have a single wave function
that describes just those particles. And if you want to
have a wave function that describes just those particles, it
can't be interacting with anything else, because then you'd have
to include that in the wave function. If you want
(26:33):
to have a wave function for just your atom, you
have to keep it isolated, right, And that gets harder
and harder to do as things get bigger. Like it's
possible to imagine a photon in an experiment that doesn't
interact with anything you've built a special trap or whatever.
It's harder to imagine a baseball that doesn't interact with anything.
No air, molecules, no photons, know nothing. There's so many
(26:55):
particles in there, it becomes harder and harder to keep
it isolated. That's why decoherence appears as soon as things
get big, because it's really hard to keep larger, realistic
size things isolated and coherent. Right, I guess I'm trying
to understand when that comes in. So, like, if I
build a nucleus side of protons that are all in
(27:15):
sync inside, then are they all also together in sync?
Like you know, like carbon has twelve of them in
the nucleus and they're all content there together, held by
the strong nuclear force. Are they still coherent or are
they starting to kind of fuzz out? If you keep
it isolated, it can stay coherent absolutely. Okay, So then
I build an atom, I throw in some electrons, and
that also gets syncd up. And at what point do
(27:38):
things start to kind of go awry? At the point
where it becomes impossible to keep it isolated from the
rest of the universe. But then couldn't I be in
sync with the rest of the universe Daniel, Yes, exactly.
Some people think that there is a wave function for
the whole universe, right. The problem is that now we're
inside the wave function. Now the way function includes us,
(27:58):
and so it's hard to see these quantum effects now
because we are part of the experiment. All right, So
I got an atom and it's coherent and it's syncd up,
and now I add another atom. Is that a problem
or does it just get bigger. It's not a problem.
It gets bigger. It's just harder to keep a coherent
because you have to keep it isolated from the system.
Remember one time we talked about building macroscopic like big
(28:20):
stize stuff that behaves in a quantum mechanical way. This
has done in a special way using Bose. Einstein condensates
special form of matter that can be coherent that can
stay together and you can stay isolated from the rest
of the system. These things don't last very long. They
last like, you know, seconds or minutes because it's hard
to keep them isolated. So it's like real experimental bravado
(28:42):
if you can put more than a few atoms together
in a quantum coherent system and keep them coherent, keep
them from interacting with the rest of the universe and
getting their way functions sort of muddled up with the
rest of the universe. Yeah, well, I guess maybe a
big part of it seems to be this idea of
an experiment and like who's in on the know and
who's outside of the experiment, and what does it mean
(29:04):
for something to be kind of pristine or not pristine?
So maybe let's get a little bit into that, which
is I think basically the idea of decoherence. Right, all right,
let's get into that, but first let's take another quick break.
(29:27):
All right, we're talking about quantum decoherence, which is kind
of at the heart of this kind of headache that
people have about quantum mechanics and trying to understand it
at an intuitive level. So, you know, small particles can
have quantum effects and wave functions and weird probability existences.
(29:47):
But once you start piling them on together, it gets
harder to kind of keep pristine I guess, right, untouched
from to an observer from the outside or just to
the universe into the same because the universe, i imagine,
doesn't care, right, like the universe if there is a
quantum way function for the entire universe, like, it doesn't care,
(30:08):
Like it doesn't know the difference between something that you
you would think is inquirent or not. Yeah, that's right.
And the tricky thing here is that we want to
have a wave function just for our experiment because we
want to see quantum effects. If we become part of
the experiment, then we no longer see the quantum effects
because we only are like on one branch of that history.
What do you mean we don't see the effects like
(30:30):
we are also existing in multiple plays at the same
time to somebody outside of our universe. Somebody outside of
our universe sees a wave function for the whole universe,
and they see lots of different possible outcomes, right, and
those things can exist simultaneously until like if they observe
the universe. But we're on just sort of one branch
of that history the way we are existing, and so
(30:50):
we don't see those other branches necessarily. And so if
you want to see a quantum effect, you have to
be like outside of that quantum system and take some
measurements of it. Right now, as soon as you take
those measurements of it, you've sort of inserted yourself in
that quantum system and it becomes much muddier. I think
you just blew my mind here, because like, if we
(31:11):
are all part of the quantum function of the universe,
that means that there are like multiples of me out
there to some alien observer outside of the universe. Like
I I only think that I exist as one person
because what because I am observing myself? I guess. Yeah,
(31:31):
it's complicated. And this whole question of like who is
an observer? Who can collapse the wave function? When does
the wave function get collapsed? It's very complicated. It's a
whole other philosophical question that it hasn't been resolved. We
don't know the answer to it. It's like the biggest
problem in the foundations of quantum mechanics. We're not going
to figure it out today on the podcast, but it
is connected to this question of quantum decoherence and quantum
(31:54):
coherence because we're interested in observing quantum effects, like when
do things look quantumy and when do the not look quantity,
and if you are inside the experiment, things don't look quantity.
Like I've never talked to a photon. I don't know
what it's like to be a photon in a double
slit experiment that has experienced one path does it experienced
some weird combination of multiple paths? But I know what
(32:15):
it's like to be me, and I don't experience superpositions, right,
I don't live two lives at the same time. Sometimes
it feels like it. Yeah, okay, so it kind of
depends on who you're who you ask whether something feels
quantity or not. Like, you know, we can have a
little experiment here in front of us and looks and
feels quantity, but to the particles inside it doesn't feel quantity,
(32:36):
or to an observer outside of our universe, we feel
quantumy to them, oh absolutely, Like there's a very simple
thought experiment to think about that. Say I set up
a quantum experiment that can have you know, two outcomes
A or B, and I run the experiment. Now before
I read the outcome of the experiment, you could say,
there's two possibilities A or B. Cool. What if you're
running experiment and your experiment is me running that experiment.
(32:58):
So you put me in a box and I do
the experiment, and I know the outcome, but you don't
yet know the outcome, right, So I am your experiment.
Well you know, am I living in the outcomes of
both experiments until you ask me what's the outcome of
my experiment? Right? So absolutely, Like the quantumminess depends on
who's doing the asking and who's doing the observing and
(33:21):
who has collapsed the wave function. And that's like that
deep question of quantum mechanics that we don't know the
answer to, is like when do wave functions get collapsed
and how did they get collapsed? Right? Like if the
cat ensured the Inger's box was a physicist, like, the
cat knows whether or not it's dead or alive, or
you know, the radioactive particle click or not. But to
(33:42):
us the cat is dead analyzed, but to the cat
it's not. That's right. And so that's why I say
you can observe quantum effects if you're outside the experiment,
Like you observe a quantum effect on me because I'm
part of your experiment. I observe a quantum effect on
the little experiment that I'm running with the cat or whatever, Right,
I don't experience the quantum effect that you observe in me. Right,
(34:02):
So then how does that apply to our baseball? Like
is it? I think kind of like as you pile
on more particles that are interacting with more things, you're
sort of opening up those throwed a group boxes. Yeah, exactly.
There's two ways to think about it, sort of one
is intuitive and the other is mathematical. The intuitive way
is that as the baseball starts to interact with more stuff,
(34:22):
that stuff becomes part of the baseball's quantum wave function, right,
Like now you have a wave function for the bat
and the baseball together, and so the bat can no
longer do like quantum experiments on the baseball because it's
like entangled with the baseball the same way that like
I'm inside your experiment, And so the intuitive ways, like,
as a particle starts to interact with the system around it,
(34:44):
it gets sort of enmeshed quantum mechanically with the wave
function of the larger system. So that system is now
part of that you know, particle or baseball's quantum wave function,
and it can no longer see the quantum effects of
those things. That's decoherence. And so the mathematical way to
think about it is that when a particle interacts with something,
what happens is that its phase gets shifted a little bit,
(35:07):
and the phases of the different possibilities get shifted differently
based on how you're interacting. And so what happens is
that all the phases of the baseball when it hits
the bat gets shifted a tiny little bit and they
all get scrambled. And so now the phases are like
out of sync and they can't do quantum stuff together
because they have deco here because they're all like random phases. Wait,
(35:28):
so you know I was building this baseball from atoms,
and so it isn't impossible to build a baseball that
is still coherent, like all of the wave functions inside
are in sync and happy and quantumy, in which case
the whole baseball is quantumy. Theoretically possible, practically very very
difficult because you have to isolate it from the entire
(35:49):
university nobody could interact with or observe that baseball. Right,
Let's say I put it inside of a short finger's box.
It's there, it's not interacting. That baseball is quantumy. That
baseball is quantumy. Now, like, practically shortening this box is
impossible because you know, no box is impervious to heat
and all sorts of other interactions. But let's say theoretically
you've built some way to isolate the baseball completely. Then yes,
(36:12):
it is still quantumy. It has not interacted with anything else. Right,
But I think maybe a key limitation here is that
it's not that the baseball can be here or in mars.
The probability of where it is isn't that big, because
you know, you're just adding tiny little probabilities, right, Like
it can't be here or a meter away. That quantum
(36:32):
meanness of the isolated baseball is like it's here or
it's a few angst from to the right. It could
actually have quite different possible locations. It depends on how
you set it up inside the box. It could be
sensitive to one quantum fluctuation which sends it in one
direction or the other direction. I think what you're referring
to though, is more like the classical sense of the
decohered baseball. Baseball that's like that you're familiar with is
(36:55):
flying through the air in a normal baseball game. We
don't see those quantum effects because they all are bridge out,
because all the quantum effects of all those particles in
the baseball are not pulling like in the same directions.
You never see like weird interference effects or weird probability
distributions because they've all averaged out. They're all decoherent. If
they were coherent, then yes, the baseball could do quantum
(37:16):
things the way like Schruninger's cat can do quantum things
like be dead or alive. Have those possibilities at the
same time. Okay, so now you're saying that, like, if
I has this baseball on the box and I open it,
that's the same thing as hitting it with a bat, Yes,
because now photons are hitting it and you are seeing
those photons, and like the bat is connected to a batter,
(37:37):
and the batter is connected to the ground, and the
ground is connected to me, and there's air in between,
and there are photons flying back and forth, meaning like
like I am kind of inextricably tied to this baseball,
which means that I am now inside of a larger
box with the baseball exactly. Then that's why you don't
see quantum effects on big things, because big things are
always interacting, you know. Einstein famously asked somebody like, do
(38:00):
you believe the moon isn't there when you're not looking,
because he was thinking, like, it's silly to imagine that
the universe like is uncertain when you're not existing. And
the answer is like, of course the moon is there
because photons are hitting it and bouncing off of it,
and so the universe is always looking because the universe
is filled with particles and they're always sort of bouncing
off of things and gravity to right, it's interacting through
(38:22):
gravity with us. Oh, that's tricky because we don't know
if gravity is quantum mechanical and if there are gravitons
bouncing around through space. But in principle yes, and so
quantum de coherence is just like when an object no
longer becomes isolated and its wave function is now like
complicated lee mixed up with the rest of the environment
so that they don't like add up coherently anymore. Like
(38:42):
this little bit of the wave function is mixed up
with that part of the wave function from the bat,
and that part of the wave function from the ball
is mixed up with this other bit of the wave
function from the bat. And if you were outside the
baseball game, you could view the whole baseball games wave function.
Then you can say, oh, I still see quantum effects, right,
because I'm looking at the wave function of the whole
baseball game. But if you're inside, you are the batter, right,
then now you're only seeing one slice of it. All right.
(39:05):
Well it's weird because you know, I feel like the
word decoherence means that things get out of sink, but
really it means I got sucked into the box. Yeah,
you are entangled right and decoherent, right, Yeah, exactly. I
see how that's confusing. Yeah, it's more like I got
sucked into the box. But the word decoherence kind of,
(39:26):
you know, implies like some kind of like noise or
some kind of like breakdown of things. And I think
the key there is that, you know, just the ball
itself has not become decoherent. Are you no longer have
just a wave function that describes the ball. You have
to describe the ball and the bat or Jorge and
the cat. There's no way function by itself that now
describes the ball because the ball is entangled with the bat,
(39:48):
and so the balls isolated individual wave function is no
longer coherent. It's like a part of a larger wave function.
It can't be isolated. And so that's why you can't
get quantum effects on the ball anymore, because it's complicatedly
tied up with the things you want to use to
measure those quantum effects. Because we are the ball now, Daniel,
the ball on us are one. That's what decoherence means, right,
(40:09):
kind of like it. It gets so complicated. I guess
that's why we use the word decoherence, just because it
gets complicated beyond our ability to be outside the box.
It's like we're in the box now and we can't
make out what these quantumness effects are. Yeah, exactly, it's
too much for us to calculate, too much for us
to understand. And so what happens is that quantum mechanics
(40:32):
doesn't fail, doesn't go away. This is just what quantum
mechanics looks like at a big scale. Quantum mechanics over
zillions and zillions of objects. Looks different because you don't
see those coherent effects anymore. They only exist when you
have like one or two or three little things that
you can keep separated, so you can have a wave
function just for that. When you're part of the wave function,
(40:53):
quantum mechanics says that things look different. They look more
smeared and averaged out. So it's not like classical physics
is in agreement with quantum mechanics. It's what quantum mechanics
looks like, sort of from a high altitude, right, like,
to an alien observer outside of our universe, we are
still all coherent. We are you and I and this
podcast and that baseball. It still looks like a pristine
(41:15):
quantum universe. Yeah, and I hope that alien that has
that deep understanding quantum mechanics has a coherent understanding of
what we've been talking about today, because it's gotten pretty
tricky al right. Well, I think hopefully that gives people
a sense of kind of the issues involved. You know,
it's kind of about what you consider the box to be,
(41:36):
what's interacting with what, and how these kind of probabilities
add up or don't add up, And it's not just
like an academic question or a philosophical question. It's actually
really important for quantum computing. If you want to build
a quantum computer, you need cubits. You need weird particles
that follow quantum rules so you can have them do
quantum computations. And to do that, you need to keep
(41:58):
them isolated. And that's okay to do for one cubit,
two cubits, three cubits, But imagine having a really big
quantum computer with thousands and thousands of cubans or millions
or trillions, right, you gotta keep them all isolated and
all individually coherent. It becomes really difficult. So this is
something people are literally working on, is building larger coherent
(42:18):
quantum systems. Yeah. I can't wait for that quantum phone
so I can take quantum pictures of my kids playing
quantum So you can ignore that email and answer it
at the same time. Yeah, that's right, So I can
do everything at the same time, exactly. And this is
really closely connected to deep issues and the philosophy of
(42:39):
quantum mechanics. You know who's doing the observing, why does
it matter? When does the wave function collapse? And I
want to have another episode where we talk about wave
functional collapse in the measurement problem. But this is sort
of like a warm up to that because it helps
you understand, you know why sometimes the probabilities are more
classical instead of quantum mechanical. Quantum coherence tells you, like,
you know, it's likely to happen. It doesn't explain why
(43:02):
it collapses from two possibilities down to one actual thing.
That's the tricky part. That's one of the tricky parts.
That's the trickiest part. It's all tricky. But you just
have to get inside the box and then it's not tricky. Yeah, exactly,
Then you understand it. You don't understand just like the cat,
Yeah exactly. If you want quantum mechanics to go away,
just you know, only work on big, complicated systems where
(43:23):
those effects don't appear because they're all decoherent. All right, Well,
we hope you enjoyed dad and got a better sense
of quantum mechanics. Thanks for joining us, See you next time.
Thanks for listening, and remember that Daniel and Jorge Explain
(43:45):
the Universe is a production of I Heart Radio or
more podcast from my heart Radio. Visit the I heart
Radio app Apple podcasts or wherever you listen to your
favorite shows. No.
Hey, Daniel, can you pass through walls? No? Keep trying
and just keep getting more bumps on my head? How
about can you bean too pleased at the same time?
Sometimes it feels like I'm supposed to be but I've
never actually managed it. So I guess you're not a
quantum object. No. Actually, I'm quite classical. But you're a
particle physicists. Aren't you made of particles? And aren't those
particles quantum mechanical? I study particles and I'm made of particles,
(00:33):
but I follow the rules of classical physics. Classic. I
mean you're classic, Daniel. I'm not new Coke Daniel. I
(00:56):
am more hammad cartoonists and the creator of PhD comics.
I'm Daniel. I'm a particle physicist, but I'm quite classical
in my tastes. Are you a fan of classical music
and it's better than quantum music? Let me tell you
that's a new genre to mak a new category at
the Grammy. Oh I wish it was a new genre,
but I'm sure if we type it into Google we
will find something for quantum music. I feel like that's
(01:19):
all music these days. It's both good and bad. It's
kind of incoherent. It's both original and stale. Welcome to
our podcast, Daniel and Jorge Explain the Universe, a production
of My Heart Radio in which we explore everything in
the universe and try to make sense of it. We
try to understand how things move in our world and
how tiny particles move. We try to understand the rules
(01:41):
of the universe, whether they govern supernovas and black holes
or tiny little electrons, and we try to make sure
that you understand them. Yeah, because we try to make
this podcast a super position of both fun and real science,
physics and banana jokes. You often think those two can't
be in the same place. Said the same time, what
(02:01):
makes you say that you haven't met any fun physicists.
You mean the physicists is fun, or they know how
to have fun, or just doing physics is fun. Why
doesn't everybody see that? Come on, I think that's the
problems and that's the problem. But yeah, it's a weird
and strange universe out there, and so we like to
talk about all of the things and make it weird
and strange. It's pretty unintuitive the universe it is, and
(02:24):
physics has done a great job of building this edifice
to help us understand the way the universe really is,
not the way we think the universe should be or
might be, or the way that makes sense to us
based on our limited experience, but actually revealing to us
the true nature of reality. But sometimes what we learn
is pretty hard to swallow. Yeah, and specifically quantum mechanics.
(02:45):
I feel like that really trips people up. It trips
me up, for sure, And it's kind of hard to
wrap your head around all of the weird, kind of
unintuitive phenomenon that happens at the quantum level. Yeah, it
is pretty weird because quantum particles seem to be following
different rules. They seem to be able to break rules
that are hard and fast for things like baseballs and
(03:06):
basketballs and scoops of ice cream. And that's a hard
thing to understand because it's weird and it's new. It's
also hard to understand, like why are there different rules?
And you know, what's the difference between an electron and
a baseball? You know, where is the sort of threshold
between those two where the quantum rules take over or
the classical rules take over. Yeah, it is kind of
weird that, you know, things are so weird at that level,
(03:28):
at the microscopic level, but then once you scale up,
things feel more gosh normal, more solid, less uncertain, or
at least more familiar. Right. Science is all about delving
into the unknown, and typically we try to explain the
unknown in terms of the known, but that fails if
the unknown is something really new, something different, something that's
(03:51):
fundamentally can't be described by what we already know. We've
often talked about how physics is like exploring the universe,
but it's just been studying the tail of the elephant,
and when you look at the rest of the elephant,
it's not always true that what you learn from the
tail can help you understand the rest of the elephant.
Sometimes you really do discover something weird and different. Yeah,
but is that elephant quantum mechanical, Daniel, Is it really
(04:13):
there or not there? It's a theoretical thought experiment elephant.
So it's just totally not there. That's classically non existent.
Al Right. Well, that connection between the quantum world and
our regular, everyday world is what we'll be exploring today
on this episode to be on the podcast. We'll be
asking the question what is quantum decoherence? That's hopefully a
(04:41):
coherent question, yes, and quantum decoherence is the key concept
to understanding the answer to this question. Why do big
objects not seem to follow quantum rules? What is the
difference between quantum objects and big objects? Where is the threshold?
Why do we seem to have two sets of rules
or is it just that one set of rules sort
(05:02):
of morpse into the other. Right, it's an important concept,
and it seems to be sort of related to this
idea of quantum measurements. I think maybe that's something that
if you've heard of quantum mechanics or have talked about
it or seen any videos about it or read about it,
it's something that seems to be important that you know
things are quantum, but then when you poke at them
(05:23):
or measure them or try to look at them, things
collapse for some reason. Yeah, this is a big and
still totally unsolved problem in quantum mechanics. Quantum mechanical things
can have like multiple possibilities, but we don't observe multiple possibilities.
When you poke an electron, as you say, it picks
one of them, and we don't really understand how that happens,
how one of them gets picked, and actually when that
(05:45):
picking happens, you know, Does it happen when your finger
touches the electron? Does it happen when you look at
the results? That happens somewhere in between. That's a really
interesting and hard problem, and it's related to quantum decoherence,
but they're not quite the same thing. To today, we'll
try to explain what quantum decoherence is, how it helps
us understand the difference between quantum and classical objects. But
(06:06):
it's important to understand that it doesn't actually solve this
problem of the quantum measurement. Is that what happens when
you pull on the tail of the elephant, things get
real real quick. You get quantum stomped. It makes quantum
music out of you. All right, Well, this is an
interesting question what is quantum decoherence? And so as usual
we were wondering how many people out there in the
real world know what it means. So as usual, Daniel
(06:28):
went other into the wilds of the internet to ask
what is quantum decoherence? So thank you very much to
everybody who will volunteered your speculation for the podcast. If
you would like to volunteer for a future podcast, please
write to us. Two questions at Daniel and Jorge dot com.
Think about it for a second, soone ask you what
quantum decoherence is. What would you say it is, or
(06:50):
at least guess it is. Here's what people had to say.
I'm not sure if I recognized this right, but I
think decoherence is about how the quantum and the normal
little few collide, so how we can map quantum effects
into all reality. Since coherent means to make sense, I'm
(07:10):
thinking quantum decoherence is when quantum particles can't logically follow
the rules of the universe, of the constants of the universe,
or something of the nature. I'm not sure what quantum
decoherence is, but I think it might be wave function collapse,
which is how the wave function of a quantity and
(07:32):
a quantum system collapses when you measure that quantity. I
don't know what quantum decoherence is, but my guess would
be that it is the occurrence of something totally inconsistent
that disrupts the quantum realm. It's got me thinking of
something to do with quantum entanglement. All right, Some pre
(07:53):
coherent answers for the most part, or at least coherent
in there not knowing what it is. Nobody actually quite
nailed it. But you know, people are in the vicinity,
and they seem to understand that there's a concept of coherence,
at least in quantum mechanics. Somebody said that it is
sort of where the real world and the normal world collide.
(08:14):
I guess they do, maybe think it has something to
do with the connection between the quantum world and our
everyday experience. Yeah, and that one is the closest I
think to the right answer, to the right way of
thinking about it. Quantum to coherence, in brief is the
idea that explains how quantum objects look like classical objects
when they get really big and messy. All right, well,
let's jump into a Daniel and I guess let's start
(08:35):
with just a quick recap of quantum of a small
subject called quantum physics. You know, what is it that
we actually call quantum and how can we kind of
describe those effects? So the thing to understand is that
when you look at really small objects, things like electrons
or photons or individuals tiny particles, they seem to be
(08:57):
following rules that don't apply to bigger objects like baseballs
and Basketball's right, and the key concept to understand when
thinking about these tiny particles is that they're not just particles.
They're not like tiny versions of a baseball. They're not
just like miniaturize little blobs of stuff flying through space.
(09:17):
Right when people were first thinking about the atom, for example,
they were thinking about the electron like orbiting the nucleus
like a tiny planet around the star. But we pretty
quickly figured out that was impossible because if an electron
orbits and nucleus, then it's going to give off radiation
because it's accelerating, it's giving off radiation. And they did
the calculation and discovered, well, that would collapse in like
(09:38):
a hundred billions of a second because they would lose
all of his energy. And so instead they had to
have a new idea for what controls and electron, what
defines what an electron does and how it interacts, and
so instead they try to use like wave like properties
to describe it. So you've probably heard this phrase called
the wave function. The wave function is just a mathematical
(09:58):
tool that helps us under and what an electron is
likely to do. And the key concept is that the
wave function tells you where a particle is likely to
be and where it's not likely to be. Sean Carroll
says that the wave function is the dope ist name
in the world for one of the most profound things
in the universe, which really made me laugh. Well, dope
and profound go hand in hand. I think like physics
(10:21):
and fun, right, Yeah, well, yeah, I think that is
maybe the hardest thing to grasp about quantum mechanics and physics.
You know, I think everyone sort of grows up at
Leaston's early in school and definitely in popular culture. You know,
the depiction, like pictures of an atom always look like
little planetary systems, you know, like a bunch of little
balls in the middle cluster together, and then other little
(10:43):
balls kind of swinging around in large orbits and rings
around that. And that's the picture that we have about
the atom. But you're saying, at some point we figured
out that's not possible, like that that doesn't make sense. Yeah, exactly.
It's not like the electron has a trajectory, has a
path and we just don't know it. It doesn't actually
(11:04):
have a path that doesn't have like a position at
every moment in time. Instead, what it has is this
quantum wave that the quantum wave behaves all sorts of
normal wave like rules. But what it does is tell
us where the electron is likely to be, and so
the electron is likely to be here and it's likely
to be there now. Sometimes people say that means that
the electron is in two places at once, but that's
(11:27):
not actually correct. It means it has the probability to
be here or there, and those in both probabilities can
exist at the same time. It doesn't mean it's actually
in both places at once. If you ask the electron
where are you, then it collapses as we talked about earlier,
It picks one place or the other. But the wave
function describes what's likely to happen. Well, I guess you
(11:48):
mentioned before that it has a dopey name. Why do
you think it's a bad name, And what would you
have called it if not the wave function? And why
is it called the wave fund? Well, wave, I suppose
because it follows a wave equation. Shorting's equation is very
much like equations for other waves that we've seen before,
that electromagnetism, and it just waves in water. Right, there's
(12:10):
a certain differential equation which just looks like a wave equation,
like a wiggle like a like a like a rippling wiggle. Yeah,
it's like a rippling wiggle, but you know, it's not
a rippling wiggle in anything physical, right, Like sound waves
are a wiggle in air, like air pressure. Right yeah,
light waves are a wiggle in the electromagnetic field, which,
even if it's hard to imagine, is a physical thing.
(12:31):
The wave function is complex. It's imaginary values. It's like
you know, one plus three I and so it's not
a wiggle in a physical thing itself. So it's it's
hard to understand because it's like this sort of abstract
literally complex things in the sense that it exists in
the imaginary plane, but it controls something real. So I
(12:51):
wouldn't have called it the wave function, you know, I
like the word wave, but function to me is sort
of confusing. Which you have called it the imaginary function? Well,
I feel like alluding to the imaginary complex plane that
is not helping me here, I guess, And you just
brought up maybe a source of confusion, which is that
you know, you just said the light or a photon
(13:12):
is like a ripple in the electromagnetic field, right, It's
a ripple like kind of like a sound waving that
it's like, it's more intense here in this intense here
are you saying that? There's also like a photon would
also have another kind of waving, nous, which is imaginary. Absolutely,
the photon also has a wave function, right, and that
(13:34):
wave function determines where the photon is likely to go,
like which parts of the electromagnetic field are likely to ripple,
you know, for example, you know, the classical situation is,
imagine you shoot a photon at two slits in a screen.
You know which one is it going to go through.
It has a probability to go through one and a
probability to go through the other. The wave function controls
(13:54):
what those probabilities are, right, And if it collapses and
picks the one on the left, then you get an
electro magnetic wave through the one on the left. So
the probability wave and the electromagnetic wave are sort of
two different things to keep in your mind, and they
both spread differently. Like why did they call them waves
in the first place, Like do these like probabilities ripple
(14:14):
out into space also, or or do they just look
like a ripple that moves around. They do ripple, and
they do follow wave mechanics, and that's why they call
it a wave, and that's why they can do really
amazing and fascinating things. Because the location of electron is
controlled by something which is fundamentally a wave, it can
do things that waves can do. Like it can interfere, Right,
(14:36):
you can have probabilities interfering with themselves, probably being here
and there, can interfere with each other and create probabilities
in other places, just like actual waves can. Right, you
put two hands in a lake or in a bathtub
and you make two sources of waves. Those waves can
interfere with each other, meaning just that they can add
up or cancel out. So, for example, if I have
(14:57):
like an electron here, it has like a ripple of
probability kind of emanating from it, or is that kind
of static if the electron is static. Well, electrons can't
actually be totally static, right, because their quantum objects. So
you can't just like say, electron is here and it's
not moving. That would violate the Heisenberger in certainty principle,
would effectively be an electron at absolute zero. But if
(15:19):
you have an electron, you shoot it out of like
an electron gun or something, and you want to describe
what's it likely to do, where is it likely to go?
Then you have a probability for all those various outcomes, right,
And the key thing to understand is like, there's not
a real history that's happening between when you shoot the
electron and when it hits the wall, and you're just
learning about it. It's uncertain, right. It has both possibilities
(15:42):
existing simultaneously until you measure it. And that's the key
thing that's hard to understand about quantum mechanics is like
how this measurement changes it from like having two possibilities
to actually existing in one place, but doesn't exist between
the places you measure. It only exists where you measure
in between. They're just probabilities, all right. So you're saying
(16:03):
that maybe, like an electron is like a little tiny baseball,
but we just don't know where it is, and where
it is is determined by this ripple in probability. Yeah,
I'm saying an electron is like a little tiny baseball,
but it doesn't have a place where it is. It's
not like it is someplace and we don't know its
place is not determined the probability of it being in
(16:23):
one place or another is determined by the way functions
like probably to be there seventy one probability be here
or whatever, so they add up to one. But the
probabilities are determined by the way function but doesn't actually
have a location. It just has those probabilities again until
you measure it, which is the weird bit, and then
when you measure it then it then it feels like
(16:43):
you're hit by a baseball. It certainly does. And that's
why we see these weird quantum effects because these particles
like electrons can do things that waves can do, like
if you have two sources of them, you get these
interference effects, or they can like tunnel through walls. These
are things that waves can do. Probability waves can do,
and you get effects because you have these wave like
(17:03):
properties of the electrons wave function. These probabilities can go
through walls like the wall doesn't affect it, like it
just goes through them. The wall does affect that. We
have a whole fun podcast on quantum tunneling. And it's
possible to go through walls right because you can have
a probability to be on one side of the wall
and then a probability to be on the other side
of the wall, and you can do that without going
(17:24):
through the wall. The probability can leak through the wall,
giving you a chance to be on the other side
of the wall, even if you're never actually in the wall,
all right, And so that means that the baseball would
just appear on the other side, or that that it's
found a way through the wall. It just appears on
the other side. Remember that quantum particles don't have to
have paths between where you've seen them. You see it
(17:47):
at A and you see it at B doesn't mean
it went from A to B. Doesn't have like a
secret history how it got from A to B. It
was a A and then it was at B. Remember
they follow fundamentally different rules. It was A, then it
had lots of probabilities from maybe how it got to
be not like one of them is true and we
just don't know it. There are those probabilities. It's undetermined.
(18:08):
It's not unknown, it's undetermined, and then later it's aid B.
So it doesn't have to go from A to B
in order to be at A and then be at B.
And this is highlighted by the quantum tunneling experiment because
you can't go from A to B. There's a barrier there.
All right, Well, let's get into quantum coherence and how
that relates or how that ties this uncertainty and this
(18:29):
way function to real things like baseball. But first let's
take a quick break. All right, we're talking about quantum decoherence,
and hopefully Daniel will we're not. We're not breaking down
(18:53):
into de coherence, talking about is. But okay, So particles
have a way function which tells you it's like a
ripple in the imaginary space, that tells you the probability
where that little tiny baseball where you will find it.
Maybe you weren't to poke in, Yes, exactly right. So
then what does coherence and decoherence means? So quantum coherence
(19:14):
is when you have two possible outcomes for what's going
to happen to your particle, and those possibilities sort of
line up like the wave functions for those two possibilities
line up. Now, any solution to the wave equation, any
like quantum state, you can take it and added to
another quantum state to get a third quantum state, which
is a mixture of the two. So you can mix
(19:36):
two possible wave functions like if you have when it
says the electron is gonna arrive at point A, and
you have another one that says the electron's gonna arrive
at point B. You can have a mixture that like
mixes A and B with fifty fifty odds. So that's
a coherent combination. It just says you have two possibilities
and you've added them together, and they're coherent because their
wave functions are sort of syncd up. They start in
(19:57):
the same place and they sort of wiggle in time
aim together, right, but they don't end up in the
same place. Isn't there some kind of cancelation or some
kind of or are you saying coherence is when they
don't cancel. They can cancel, right. The fact that they
can cancel is because they are coherent. You only get
interference effects from coherence sources of waves. Like go back
to the example of like bathtubs. Right, so you put
(20:20):
your hand in the water and you slap it, You
make a rhythm, and you get waves in the water.
You do the same thing with your other hand if
you're doing it in the same way, right, if you're
like slapping the water in time, then you get these
waves which either add up or cancel out coherently. If
your second hand instead it's just like a random just
like randomly slapping it, then they're not going to add
up nicely. It's just going to be a big emotion.
(20:41):
It's going to spread out to nothing. So you only
get these interference effects when the quantum waves are in sync.
That's quantum coherence, and that's what allows quantum things to
be sort of quantumy, meaning that they're in sync in time.
So what you're saying or in time and space, Yeah,
they're in sync in time, and so at every point
in space they can interfere. At one point in space,
(21:05):
you might get cancelation because they're waving in opposite directions,
and at another point in space they might support each
other because they're waving in the same direction. But they
can only do that consistently if they're in sync in time.
So it sounds like, you know, particles have these wave
functions and they someone have to sync up in order
for them to interact with each other, because if they
(21:27):
don't sink up, then then what happens They just cancel
each other out or they can interact, or what happens
if they don't sink up. If they don't sink up,
then you don't get any of these interference effects. It's
like if your noise cancelation headphones, right, if those were
sort of just like randomly putting out sounds instead of
like sinking up to the sounds that are coming at
your ear and producing exactly the opposite sound to cancel
(21:50):
them out. Right, your noise canceling headphones only work because
they produce a coherent noise which cancels out the ambient noise. Otherwise,
if they put out just random, arbitrary noise, they wouldn't
cancel each other out, and you just get sort of
normal stuff you can have like A and B. You
wouldn't have like weird interference effects between the incoming noise
and the noise produced by the headphones, and all the
(22:12):
weird quantumness comes from those like interference effects, these effects
of the probability wave. And if you don't have coherence,
then you don't get those effects. Okay, so you need
coherence in order to have interference, just a little maybe
counter in Twitter. But it's not a frequency thing, right,
It's not like they have to be the same frequency
or fit the same number of wavelengths within the same space.
(22:35):
It's something a little bit more than that. It's more
than that they have to be linked up. They have
to like sync up in time. Otherwise you could have
like coherence just for a moment, right, but to sink
up in time to be like consistently giving up these
probability waves that interfere, then they have to be sort
of syncd up, which is linked in time that to
like start at the same place and go down the
same time or up at the same time. Either way,
(22:56):
they have to like match each other in phase, right,
But they can so cancel each other out and be coherent, right,
Like you can be coherent and destructive at the same time.
It's different than decoherent, just like noise canceling headphones. Right.
The cool thing about the quantum wave function is that
we actually have a lot of intuition for how waves work. Right,
All these effects, interference and cancelation, these are normal things.
(23:19):
It's just weird when you apply it to the probability
for something to happen. So we're very familiar and happy
to talk about waves and that none of that is weird,
Like noise canceling headphones are not quantum magic. It's just
weird when you apply to the probability for an experiment
to have a certain outcome. Right, And lasers are also coherent, right, Like,
that's kind of what a laser is, Yes, exactly, a
(23:40):
laser is a coherent source of light. All the photons
are like in phase and have the same frequency, so
they add up together. Right, So it's a very intense
source of coherent lights. Okay, So that's at the microscopic level,
like electrons and photons and quirks. They can have this coherence.
But then something happens when you go up to the
bigger things, like when we have to worry about coherence
(24:01):
at the baseball level. Right, Well, we don't have to
worry about interference of baseballs because they're not coherent quantum objects,
like all of their particles are not wiggling in phase.
They're all scrambled and random. It's like a huge choir
of children all singing different songs at different volumes and
different speeds. And so what we see is like a
big average gamush. We don't see any sort of like
(24:22):
interference effects when two baseballs bounce off each other because
they don't have coherent quantum waves, their faces are all scrambled.
All right, Well, let's talk about that scrambling, because I
think maybe that's the key of what makes things quantumy
or not, Like maybe step us through, Like, okay, we
start with one atom, and the particles inside the atom
(24:42):
do have this wave function, and presimably they're coherent. Like
are the protons and neutrons and quarks inside of an
atom coherent together? Or is there already some kind of
smushing at that level? They can be coherent. Absolutely. There's
no limit to how large a coherent system can be.
It just gets harder and harder to do because it
has to be isolated. The key is that anytime you
(25:03):
interact with something, then it becomes part of your system,
and so the system sort of grows and grows and grows,
so it's easier to start from like like a single particle.
Take a single electron or a single photon, right, it
has a certain way of function, and that way function
is coherent, has like two possibilities for what it can do,
and those possibilities are coherent, and so you get like
interesting interference effects. That's why, for example, a single photon
(25:27):
going through the famous double slid experiment can interfere with itself. Right,
It's two possibilities are interfering. So single photon with two
coherent possibilities can interfere with itself. Now things get messy
once that photon starts to interact with other stuff because
now the two possibilities for the photon interact differently with
the environment. You know this interact with the wall or
(25:49):
interact with the tool whatever you're using to measure it,
and they change the phases of those two different outcomes,
and now it's decoherent. So a particle can be coherent.
You can even have two particles coher but once you
touch it, once you interact with it, then you can
break that coherence. Right. But you know we're trying to
build up from like particles up to a baseball. And
so like if I assemble you know, three quarts together
(26:12):
into a proton, are they still coherent together or do
they start to kind of get out of sink? Once
I put them together into a proton, they can be
coherent together. And you can have a single wave function
that describes just those particles. And if you want to
have a wave function that describes just those particles, it
can't be interacting with anything else, because then you'd have
to include that in the wave function. If you want
(26:33):
to have a wave function for just your atom, you
have to keep it isolated, right, And that gets harder
and harder to do as things get bigger. Like it's
possible to imagine a photon in an experiment that doesn't
interact with anything you've built a special trap or whatever.
It's harder to imagine a baseball that doesn't interact with anything.
No air, molecules, no photons, know nothing. There's so many
(26:55):
particles in there, it becomes harder and harder to keep
it isolated. That's why decoherence appears as soon as things
get big, because it's really hard to keep larger, realistic
size things isolated and coherent. Right, I guess I'm trying
to understand when that comes in. So, like, if I
build a nucleus side of protons that are all in
(27:15):
sync inside, then are they all also together in sync?
Like you know, like carbon has twelve of them in
the nucleus and they're all content there together, held by
the strong nuclear force. Are they still coherent or are
they starting to kind of fuzz out? If you keep
it isolated, it can stay coherent absolutely. Okay, So then
I build an atom, I throw in some electrons, and
that also gets syncd up. And at what point do
(27:38):
things start to kind of go awry? At the point
where it becomes impossible to keep it isolated from the
rest of the universe. But then couldn't I be in
sync with the rest of the universe Daniel, Yes, exactly.
Some people think that there is a wave function for
the whole universe, right. The problem is that now we're
inside the wave function. Now the way function includes us,
(27:58):
and so it's hard to see these quantum effects now
because we are part of the experiment. All right, So
I got an atom and it's coherent and it's syncd up,
and now I add another atom. Is that a problem
or does it just get bigger. It's not a problem.
It gets bigger. It's just harder to keep a coherent
because you have to keep it isolated from the system.
Remember one time we talked about building macroscopic like big
(28:20):
stize stuff that behaves in a quantum mechanical way. This
has done in a special way using Bose. Einstein condensates
special form of matter that can be coherent that can
stay together and you can stay isolated from the rest
of the system. These things don't last very long. They
last like, you know, seconds or minutes because it's hard
to keep them isolated. So it's like real experimental bravado
(28:42):
if you can put more than a few atoms together
in a quantum coherent system and keep them coherent, keep
them from interacting with the rest of the universe and
getting their way functions sort of muddled up with the
rest of the universe. Yeah, well, I guess maybe a
big part of it seems to be this idea of
an experiment and like who's in on the know and
who's outside of the experiment, and what does it mean
(29:04):
for something to be kind of pristine or not pristine?
So maybe let's get a little bit into that, which
is I think basically the idea of decoherence. Right, all right,
let's get into that, but first let's take another quick break.
(29:27):
All right, we're talking about quantum decoherence, which is kind
of at the heart of this kind of headache that
people have about quantum mechanics and trying to understand it
at an intuitive level. So, you know, small particles can
have quantum effects and wave functions and weird probability existences.
(29:47):
But once you start piling them on together, it gets
harder to kind of keep pristine I guess, right, untouched
from to an observer from the outside or just to
the universe into the same because the universe, i imagine,
doesn't care, right, like the universe if there is a
quantum way function for the entire universe, like, it doesn't care,
(30:08):
Like it doesn't know the difference between something that you
you would think is inquirent or not. Yeah, that's right.
And the tricky thing here is that we want to
have a wave function just for our experiment because we
want to see quantum effects. If we become part of
the experiment, then we no longer see the quantum effects
because we only are like on one branch of that history.
What do you mean we don't see the effects like
(30:30):
we are also existing in multiple plays at the same
time to somebody outside of our universe. Somebody outside of
our universe sees a wave function for the whole universe,
and they see lots of different possible outcomes, right, and
those things can exist simultaneously until like if they observe
the universe. But we're on just sort of one branch
of that history the way we are existing, and so
(30:50):
we don't see those other branches necessarily. And so if
you want to see a quantum effect, you have to
be like outside of that quantum system and take some
measurements of it. Right now, as soon as you take
those measurements of it, you've sort of inserted yourself in
that quantum system and it becomes much muddier. I think
you just blew my mind here, because like, if we
(31:11):
are all part of the quantum function of the universe,
that means that there are like multiples of me out
there to some alien observer outside of the universe. Like
I I only think that I exist as one person
because what because I am observing myself? I guess. Yeah,
(31:31):
it's complicated. And this whole question of like who is
an observer? Who can collapse the wave function? When does
the wave function get collapsed? It's very complicated. It's a
whole other philosophical question that it hasn't been resolved. We
don't know the answer to it. It's like the biggest
problem in the foundations of quantum mechanics. We're not going
to figure it out today on the podcast, but it
is connected to this question of quantum decoherence and quantum
(31:54):
coherence because we're interested in observing quantum effects, like when
do things look quantumy and when do the not look quantity,
and if you are inside the experiment, things don't look quantity.
Like I've never talked to a photon. I don't know
what it's like to be a photon in a double
slit experiment that has experienced one path does it experienced
some weird combination of multiple paths? But I know what
(32:15):
it's like to be me, and I don't experience superpositions, right,
I don't live two lives at the same time. Sometimes
it feels like it. Yeah, okay, so it kind of
depends on who you're who you ask whether something feels
quantity or not. Like, you know, we can have a
little experiment here in front of us and looks and
feels quantity, but to the particles inside it doesn't feel quantity,
(32:36):
or to an observer outside of our universe, we feel
quantumy to them, oh absolutely, Like there's a very simple
thought experiment to think about that. Say I set up
a quantum experiment that can have you know, two outcomes
A or B, and I run the experiment. Now before
I read the outcome of the experiment, you could say,
there's two possibilities A or B. Cool. What if you're
running experiment and your experiment is me running that experiment.
(32:58):
So you put me in a box and I do
the experiment, and I know the outcome, but you don't
yet know the outcome, right, So I am your experiment.
Well you know, am I living in the outcomes of
both experiments until you ask me what's the outcome of
my experiment? Right? So absolutely, Like the quantumminess depends on
who's doing the asking and who's doing the observing and
(33:21):
who has collapsed the wave function. And that's like that
deep question of quantum mechanics that we don't know the
answer to, is like when do wave functions get collapsed
and how did they get collapsed? Right? Like if the
cat ensured the Inger's box was a physicist, like, the
cat knows whether or not it's dead or alive, or
you know, the radioactive particle click or not. But to
(33:42):
us the cat is dead analyzed, but to the cat
it's not. That's right. And so that's why I say
you can observe quantum effects if you're outside the experiment,
Like you observe a quantum effect on me because I'm
part of your experiment. I observe a quantum effect on
the little experiment that I'm running with the cat or whatever, Right,
I don't experience the quantum effect that you observe in me. Right,
(34:02):
So then how does that apply to our baseball? Like
is it? I think kind of like as you pile
on more particles that are interacting with more things, you're
sort of opening up those throwed a group boxes. Yeah, exactly.
There's two ways to think about it, sort of one
is intuitive and the other is mathematical. The intuitive way
is that as the baseball starts to interact with more stuff,
(34:22):
that stuff becomes part of the baseball's quantum wave function, right,
Like now you have a wave function for the bat
and the baseball together, and so the bat can no
longer do like quantum experiments on the baseball because it's
like entangled with the baseball the same way that like
I'm inside your experiment, And so the intuitive ways, like,
as a particle starts to interact with the system around it,
(34:44):
it gets sort of enmeshed quantum mechanically with the wave
function of the larger system. So that system is now
part of that you know, particle or baseball's quantum wave function,
and it can no longer see the quantum effects of
those things. That's decoherence. And so the mathematical way to
think about it is that when a particle interacts with something,
what happens is that its phase gets shifted a little bit,
(35:07):
and the phases of the different possibilities get shifted differently
based on how you're interacting. And so what happens is
that all the phases of the baseball when it hits
the bat gets shifted a tiny little bit and they
all get scrambled. And so now the phases are like
out of sync and they can't do quantum stuff together
because they have deco here because they're all like random phases. Wait,
(35:28):
so you know I was building this baseball from atoms,
and so it isn't impossible to build a baseball that
is still coherent, like all of the wave functions inside
are in sync and happy and quantumy, in which case
the whole baseball is quantumy. Theoretically possible, practically very very
difficult because you have to isolate it from the entire
(35:49):
university nobody could interact with or observe that baseball. Right,
Let's say I put it inside of a short finger's box.
It's there, it's not interacting. That baseball is quantumy. That
baseball is quantumy. Now, like, practically shortening this box is
impossible because you know, no box is impervious to heat
and all sorts of other interactions. But let's say theoretically
you've built some way to isolate the baseball completely. Then yes,
(36:12):
it is still quantumy. It has not interacted with anything else. Right,
But I think maybe a key limitation here is that
it's not that the baseball can be here or in mars.
The probability of where it is isn't that big, because
you know, you're just adding tiny little probabilities, right, Like
it can't be here or a meter away. That quantum
(36:32):
meanness of the isolated baseball is like it's here or
it's a few angst from to the right. It could
actually have quite different possible locations. It depends on how
you set it up inside the box. It could be
sensitive to one quantum fluctuation which sends it in one
direction or the other direction. I think what you're referring
to though, is more like the classical sense of the
decohered baseball. Baseball that's like that you're familiar with is
(36:55):
flying through the air in a normal baseball game. We
don't see those quantum effects because they all are bridge out,
because all the quantum effects of all those particles in
the baseball are not pulling like in the same directions.
You never see like weird interference effects or weird probability
distributions because they've all averaged out. They're all decoherent. If
they were coherent, then yes, the baseball could do quantum
(37:16):
things the way like Schruninger's cat can do quantum things
like be dead or alive. Have those possibilities at the
same time. Okay, so now you're saying that, like, if
I has this baseball on the box and I open it,
that's the same thing as hitting it with a bat, Yes,
because now photons are hitting it and you are seeing
those photons, and like the bat is connected to a batter,
(37:37):
and the batter is connected to the ground, and the
ground is connected to me, and there's air in between,
and there are photons flying back and forth, meaning like
like I am kind of inextricably tied to this baseball,
which means that I am now inside of a larger
box with the baseball exactly. Then that's why you don't
see quantum effects on big things, because big things are
always interacting, you know. Einstein famously asked somebody like, do
(38:00):
you believe the moon isn't there when you're not looking,
because he was thinking, like, it's silly to imagine that
the universe like is uncertain when you're not existing. And
the answer is like, of course the moon is there
because photons are hitting it and bouncing off of it,
and so the universe is always looking because the universe
is filled with particles and they're always sort of bouncing
off of things and gravity to right, it's interacting through
(38:22):
gravity with us. Oh, that's tricky because we don't know
if gravity is quantum mechanical and if there are gravitons
bouncing around through space. But in principle yes, and so
quantum de coherence is just like when an object no
longer becomes isolated and its wave function is now like
complicated lee mixed up with the rest of the environment
so that they don't like add up coherently anymore. Like
(38:42):
this little bit of the wave function is mixed up
with that part of the wave function from the bat,
and that part of the wave function from the ball
is mixed up with this other bit of the wave
function from the bat. And if you were outside the
baseball game, you could view the whole baseball games wave function.
Then you can say, oh, I still see quantum effects, right,
because I'm looking at the wave function of the whole
baseball game. But if you're inside, you are the batter, right,
then now you're only seeing one slice of it. All right.
(39:05):
Well it's weird because you know, I feel like the
word decoherence means that things get out of sink, but
really it means I got sucked into the box. Yeah,
you are entangled right and decoherent, right, Yeah, exactly. I
see how that's confusing. Yeah, it's more like I got
sucked into the box. But the word decoherence kind of,
(39:26):
you know, implies like some kind of like noise or
some kind of like breakdown of things. And I think
the key there is that, you know, just the ball
itself has not become decoherent. Are you no longer have
just a wave function that describes the ball. You have
to describe the ball and the bat or Jorge and
the cat. There's no way function by itself that now
describes the ball because the ball is entangled with the bat,
(39:48):
and so the balls isolated individual wave function is no
longer coherent. It's like a part of a larger wave function.
It can't be isolated. And so that's why you can't
get quantum effects on the ball anymore, because it's complicatedly
tied up with the things you want to use to
measure those quantum effects. Because we are the ball now, Daniel,
the ball on us are one. That's what decoherence means, right,
(40:09):
kind of like it. It gets so complicated. I guess
that's why we use the word decoherence, just because it
gets complicated beyond our ability to be outside the box.
It's like we're in the box now and we can't
make out what these quantumness effects are. Yeah, exactly, it's
too much for us to calculate, too much for us
to understand. And so what happens is that quantum mechanics
(40:32):
doesn't fail, doesn't go away. This is just what quantum
mechanics looks like at a big scale. Quantum mechanics over
zillions and zillions of objects. Looks different because you don't
see those coherent effects anymore. They only exist when you
have like one or two or three little things that
you can keep separated, so you can have a wave
function just for that. When you're part of the wave function,
(40:53):
quantum mechanics says that things look different. They look more
smeared and averaged out. So it's not like classical physics
is in agreement with quantum mechanics. It's what quantum mechanics
looks like, sort of from a high altitude, right, like,
to an alien observer outside of our universe, we are
still all coherent. We are you and I and this
podcast and that baseball. It still looks like a pristine
(41:15):
quantum universe. Yeah, and I hope that alien that has
that deep understanding quantum mechanics has a coherent understanding of
what we've been talking about today, because it's gotten pretty
tricky al right. Well, I think hopefully that gives people
a sense of kind of the issues involved. You know,
it's kind of about what you consider the box to be,
(41:36):
what's interacting with what, and how these kind of probabilities
add up or don't add up, And it's not just
like an academic question or a philosophical question. It's actually
really important for quantum computing. If you want to build
a quantum computer, you need cubits. You need weird particles
that follow quantum rules so you can have them do
quantum computations. And to do that, you need to keep
(41:58):
them isolated. And that's okay to do for one cubit,
two cubits, three cubits, But imagine having a really big
quantum computer with thousands and thousands of cubans or millions
or trillions, right, you gotta keep them all isolated and
all individually coherent. It becomes really difficult. So this is
something people are literally working on, is building larger coherent
(42:18):
quantum systems. Yeah. I can't wait for that quantum phone
so I can take quantum pictures of my kids playing
quantum So you can ignore that email and answer it
at the same time. Yeah, that's right, So I can
do everything at the same time, exactly. And this is
really closely connected to deep issues and the philosophy of
(42:39):
quantum mechanics. You know who's doing the observing, why does
it matter? When does the wave function collapse? And I
want to have another episode where we talk about wave
functional collapse in the measurement problem. But this is sort
of like a warm up to that because it helps
you understand, you know why sometimes the probabilities are more
classical instead of quantum mechanical. Quantum coherence tells you, like,
you know, it's likely to happen. It doesn't explain why
(43:02):
it collapses from two possibilities down to one actual thing.
That's the tricky part. That's one of the tricky parts.
That's the trickiest part. It's all tricky. But you just
have to get inside the box and then it's not tricky. Yeah, exactly,
Then you understand it. You don't understand just like the cat,
Yeah exactly. If you want quantum mechanics to go away,
just you know, only work on big, complicated systems where
(43:23):
those effects don't appear because they're all decoherent. All right, Well,
we hope you enjoyed dad and got a better sense
of quantum mechanics. Thanks for joining us, See you next time.
Thanks for listening, and remember that Daniel and Jorge Explain
(43:45):
the Universe is a production of I Heart Radio or
more podcast from my heart Radio. Visit the I heart
Radio app Apple podcasts or wherever you listen to your
favorite shows. No.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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