What are virtual particles?

Discover virtual particles with Daniel and Jorge

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Episode Transcript

Speaker 1 (00:00):
Hey, this is Daniel and Jorge from Daniel and Jorge
Explained the Universe. We interrupt this podcast for a special announcement.
This Friday March We're having our first ever Daniel and
Jorge Explained the Universe live stream event. So join us
as we record an episode in real time and take
questions from listeners like you. You can submit your questions

(00:20):
live on air, or send them to us ahead of
time at questions at Daniel and Jorghead dot com. To
tune in, just go to YouTube dot com slash PhD
Comics this Friday March at ten am Pacific. That's one
pm Eastern, six pm Europe. That's two am in Tokyo
and four am in Australia. What time it's out of Mars, Daniel,

(00:40):
You know in case aliens want to tune in? Do
you think aliens want to ask us questions? Um? May not,
you may they might have engineering questions. You know, well
I got questions for them. So tune in this Friday,
March twenty seven at ten am Pacific at YouTube dot
com slash PhD Comics and bring your question about the universe. Hey, Daniel,

(01:10):
are you a fan of virtual reality? I'm still trying
to get my head around this reality? What do I
need another one for? You know you can? You can
use it to walk on the surface of the Moon
without ever leaving your couch. That does actually sound pretty good.
But isn't it expensive? Here? It's virtually free. I think
that means it's expensive. Actually, I think it is. Can

(01:31):
I can I borrow some cash from you? Yeah? Sure,
I'll send you some virtual money. I am or had

(01:52):
any cartoon is and the creator of PhD comments, Hi,
I'm Daniel. I'm a particle physicist, and I'm the co
author of our book, We Have No Idea, A Guide
to the Unknown Universe. It's available in paperback, hardcover and
also virtual reality. You can put on goggles and experience
being inside our minds. Oh man, that sounds terrifying. Is

(02:15):
that a horror show? But welcome to our podcast Daniel
and Jorge Explain the Universe, a production of I Heart
Radio in which we take mental tours all over the
universe and talk about the biggest things, the smallest things,
the fastest things, the craziest things in the universe and
explain all of them to you in a way we
hope you find educational and entertaining. Yeah, that's hard. We

(02:36):
talked about all the real things out there in the
universe and the cosmos and the furthest reaches of the
galaxies and galaxy clusters, but we also like to talk
about things dad don't yet exist or may not even exists.
That's right. We want to take you inside the minds
of scientists and tell you how they think about the universe,
what models are going on in their head, and can

(02:57):
we distill those in a way that makes sense to you,
because we want you to understand sort of the forefront
of human thinking about how the universe works. Yeah, because
there are the things that are around us that we
can see and touch and feel and hold in our hands,
but there's sort of another universe out there that we
can't see, and that is maybe not quite as real

(03:20):
as you might imagine. Yeah. Well, we're always sort of
building a universe in our minds to map what's going
on outside. Like we can do experiments, we can make measurements,
We can see things, and then we try to understand them,
and that understanding requires building a model in our head
of what we think is happening. And some of those
things we can experience some of those things we wonder

(03:40):
are they real or are they just our imagination? Yeah,
So Daniel and I we wrote a book Daniel called
you know, We Have No Idea. I don't know if
you know we wrote a book by the way, I
had no Idea? Is that right? Yeah? Yeah, it's called
We Have No Idea? And uh. And then we talk
about all the things we don't know about the universe,
all the unanswered questions out there. Um of those of
you listening, please check it out if you are interested.

(04:03):
But I was sort of surprised to get today's topic
in an email for me this morning, because I don't
think we covered this topic in that book. No, this
is a really tricky topic, and it really has to
do with how physicists think about particles, what they mean,
and are they real? How do they talk to each other,
what happens when one electron pushes against another electron, and
how does that end? What happens inside the mind of

(04:25):
a physicist when she thinks about that. So this topic
that we're going to talk about today, was it just
too maybe extreme for our book? What did you think? What?
Why didn't we talk about it in our fun and
interesting book? Now? Available for purchase what we totally could have.
And you know, in the book, we have to make
some pretty hard choices about what topics to cover. We

(04:45):
talked about what is space and what is time? And
what is matter? And how will the universe end? And
we could have gone on forever and talked about all
the things we don't understand about the universe. It's a
pretty long list, but we had to make some choices.
I see, the book wasn't called we have lots of
no ideas. We have absolutely zero ideas about a lot

(05:06):
of things. But anyway, so today's talpic. It's pretty interesting
because I think everyone has heard of particles. I mean,
we all know that we are made out of molecules
and atoms, and atoms are made out of particles, and
they form the basis of for matter in all of
the universe. But I think maybe not not a lot
of people have heard about this particular type of particle. Yeah,

(05:28):
this is a concept that people talk about when they
think about you know, empty space and particles popping in
and out of the vacuum. And it's a topic that's
really important for thinking about forces and how things push
and pull against each other and how that actually works
at the microscopic level. So it's a really important concept
in particle physics, but it's sort of slipper and you

(05:49):
get your head around. But recently some listeners wrote in
and asked us to explain this to be on the podcast,
we'll be asking the question what is a virtual particle?
Is it a particle wearing virtual reality goggles? Is it
one particle imagining another particle? Is it a virtuous particle

(06:10):
who has a Stanza for its principles? These particles all
follow rules. Actually, that's a really good point because there's
a lot of sort of pop science misinformation about virtual particles.
People say, oh, virtual particles don't follow the laws of physics,
But they do. They follow the laws of physics absolutely,
just like all the other particles and as far as
we know, everything in our real universe. Interesting. I like

(06:33):
how you associate virtue with following the rules. Some deep
psychological things going on there. Daniel today on the podcast
Therapy of Daniel, How are you feeling steep virtually good?
Particularly virtual particular? Well, so it's an interesting topic. I

(06:54):
have to say, I've never heard of these virtual particles.
I guess because they're virtual. Is that part of what
we're gonna talk about today. Yeah, a little bit. They're
not real, Are they not real? Well, they are real,
they're just not really particles. There are a thing that's
out there in the universe. They're responsible for important physical
effects that we can see, but we can never see

(07:14):
them directly. So one way to think about them is
that they're sort of a calculational tool in our minds,
a way that we think about what's happening out there
in the universe, but not something that we can have
ever observed directly, sort of like we think about quantum
mechanical wave functions. We never observe the wave function itself.
We only observe its consequences, it's influence on things. But

(07:36):
it's important for us to predict those those experiments, to
predict those consequences, that we can use that in our calculations.
All right, well let's get let's get into it here today.
But first we were wondering, as usual, how many people
out there and you what a virtual particle was. So
I walked around campus that you see Irvine, and I
asked people this kind of crazy as a terror question.

(07:57):
So before you hear these answers, think about it for
a second. If someone asked you on this treet, what
is a virtual particle? What would you answer? Here's what
people had to say, not in the slowest an imaginary particle,
Houston light theories or something like that. Virtual state is
a state, kind of a transitory state where if you're

(08:18):
going to do like a two photon excitation, it's that
state in the middle that is a virtual state where
it's not really you can't describe I can't describe it
very well. I'm not into physics, but that's that's the
best I can do on that one. It's a particle
of matter. I don't know, something that's made up based

(08:40):
on technology. Maybe all right? Virtually no one said yes,
there was some creative answer, though. I really like the
person that said something that's made up based on technology.
That sounds pretty good. Like I was, I could use
technology to create new particles. That's sort of my job,
isn't that what you do? Did you create new particles?

(09:01):
That's what I'm supposed to be doing, and I'm using
a lot of technology and spending a lot of government money,
but instead you're here recording a podcast. Don't tell anybody
that's right, nobody knows about this, Daniel, don't worry. But
you know, an attempt only a few thousand people listen.
In my twenty years of searching for new particles, I've
never really found one. So I'm using technology to try

(09:24):
to find new particles. I just haven't been successful yet.
You're like, forget particles. I'm just gonna have a party.
It's a virtually easier But you know, this wasn't too surprising.
It's a sort of esoteric topic, and I think a
lot of people know why virtual particles are important without
knowing the concept itself. So I think you'll find that
the things we talk about the role virtual particles play

(09:47):
will be familiar to a lot more people than actually
know what virtual particles are and can explain. It's not
a crazy concept. It's just maybe kind of a naming
convention or sort of like how this is to see
some of these particles? Yeah, precisely. All right, Well let's
gett into it, Daniel. What is a virtual particle and
why is it called virtual? And is it not real? Well?

(10:08):
I think first let's get a clear picture for like
what is what do we mean by a particle in
a real particle? Because as you talked about earlier, like
we're made of stuff. I made of stuff, You're made
of stuff. We think when we are real, like I
imagine I'm real, and we think that we're made of particles,
and those particles have an existence. They're like stick around,
they have persistence, that can move through space, all this

(10:29):
kind of stuff, and we feel substantial, and so you
and I we are made of real particles. But those particles,
they're not like a little ball of stuff, and they're
not like a tiny dot, right, It's not like we're
built out of little tinker toys. As we've talked about
in the podcast several times, each of these particles should
be seen as like a ripple in a quantum field.

(10:49):
It's like you have this field that feels space and
at some points that has energy and it's vibrating, and
that's what each of these particles are. It's like a
little perturbation in in reality. Kind of yes, it's a
little perturbation in reality. And the key thing to know
is that real particles are special perturbations. There's not like
any perturbation in the quantum field is a part is

(11:10):
a real particle there if that perturbation follows certain rules
and has certain behaviors and has and obeys certain equations.
Then it's a real particle. You're saying, there are perturbations
that are not particles that or that don't form particles.
There aren't quantum fields. Yes, And that's uh, you just
gave away the ghosts. Because some perturbations are real particles

(11:32):
and some perturbations are virtual particles. So some small fraction
of the perturbations and quantum fields are what make up
real particles. That are you and me. I guess my
question is what makes a real particle real? What makes
that proturbation real? Well, it can do various things, Like
it can travel forever. Right, you shoot a real particle

(11:53):
through space, it will just keep going until it bounces
into something. It has this sort of self sustaining nature
to it. It doesn't just like spread out into nothing
or cancel itself out and and and it's propagating right
through the field. It's not like it's moving. It's like
it's I'm a perturbation here, and then I'm proturbing the
space next to me, and that's what we call moving.

(12:15):
That's right, And you need to keep two pictures in
your head. At once. One is sort of the quantum
field theory view, like think about the whole universe is
just space filled with quantum fields, and as you say,
a particle moving through them. Is the wiggle in the
field is here, and then the wiggle in the field
is there, So that wiggle is the thing that's propagating.
Is the energy moving At the same time, you like

(12:35):
to associate that will with a particle. You have maybe
this image in your head of like a little ball
that's moving from here to there. And in fact, if
you shoot an electron out of an electron gun, that's
sort of what you imagine. The most mathematically accurate way
to think about it is in terms of a little
ripple in the field that's moving through the field. But
you like to associate that with a real electron because

(12:58):
it has properties like mass and it can fly forever
um if it doesn't touch anything and that and that's
a real particle because it satisfies various rules like it
has a specific mass and it's kinetic energy. Makes sense,
you know, you can interpret that ripple as a particle.
Did you have to do with like the shape of
it or yes, it has What makes it special is

(13:21):
it just like a set of conditions that made it
is special, or there's something about the combination of things
that went into it that caused ripple to be special.
In a like the shape of it. It has a
lot to do with how it was made. And you
can imagine, for example, a guitar string. Take your guitar string.
If you plug it carefully, it has various modes that

(13:41):
it likes to wiggle at, right, and those are the
various notes of the guitar string. And you can, you know,
make the string shorter or longer to change those modes.
But just for like an open string, you play it,
it makes it. It likes to play it a certain
a certain frequency. But you could also do other things
on that string that aren't like a nice awcole shan.
You know, if your toddler comes in the room and

(14:02):
hits your guitar with with something crazy, it doesn't make
a nice sound. So you can imagine the difference between
like a careful, clean plucking of the string that sends
one well behaved wave propagating down the string, and a
sort of chaotic tumble of ripples that don't that can't
be interpreted the same way and because you're saying quantum
fields can be disturbed in any number of ways, but

(14:26):
like if you disturb it just right, it'll create this
kind of like perfect self sustaining um, you know, bumping it, yes,
and precisely. And the thing that it has it has
a definite mass. So an electron always has an electron's mass,
and it moves through the universe always having the same mass.
And so a real particle something that has a definite mass,

(14:47):
that has that stuff to it. That's the thing that
makes it real that it has a specific mass, and
you can interpret things about it that we're familiar with. Right,
You like to think, well, things have energy, like kinetic energy.
Are particle has a positive kinetic energy? That makes sense.
Later and we talk about virtual particles, you'll see that
they don't obey these same rules. They can't be interpreted

(15:08):
in the same way. There's still ribbles in the quantum field,
but they're not nice, clean ripples that follow these rules.
They're not that virtuous judgment. I'm a particle physicists. All
particles are welcome in my mind, except they want that
break rules. Apparently, well, they don't break. They don't break
the rules. It's a category, right, These are these that

(15:30):
you know satisfy some restrictions we call those. Really they
do certain things. It's just a label in our minds.
It's a distinction in our head Some of them have
a mass that sticks around forever and and and you know,
and follow these um these I guess they are rules. Yes,
I'm trying to I'm always saying that, But you're right,
m I do like rules for it. We'd be nothing

(15:52):
without rules. All right, Well, let's get into then, what
are virtual particles and whether or not they're real or
whether you can only see them on a VR headset.
But first let's take a quick break. All right, Daniel,

(16:20):
we're talking about virtual particles, and you're saying, a real
particle is like a perturbation in a quantum field which
surrounds us all around. And but it's like a perfect perturbation.
That's what a real particle is. It's like something that
somehow the field really likes and doesn't just kind of
like destroys or dissipates. Yeah, there are lots of different

(16:40):
kinds of perturbations, and some of them satisfy additional constraints.
Some of them satisfy a subset of them also satisfy
some equations, some wave equations that tell us about how
they move, and those real part of universe likes them.
They're like, hey, I like this sound, I like this note.
I'm just gonna let it keep on going. You're speaking
for the U niverse, now, do that's a bit presumptuous.

(17:02):
Maybe the universe likes the other kind of particles. It
thinks the real particles are like boring rule followers. Oh,
I see, well, somehow it allows the real particles to
to be a special right, yes, sort of like them. Well,
the real particles, real particles can do something that virtual
particles can't. But virtual particles can do lots of things
real particles can't. So what can real particles do that

(17:25):
virtuals can't. Well, real particles can propagate across the universe.
They have a fixed mass, and that carries them sort
of through space. You're saying forever nothing. They don't degrade.
They don't degrade. Like you look up at the sky
and a photon hit your I from a far away star.
That's a real photon. It's propagated through space and it
could have got another billion light years if your eye

(17:46):
hadn't blocked it. So, yeah, these things can travel forever.
But there are real particles also that don't last, like
don't we Are you telling me that some of the
higher energy particles, like the you know, some of these
heavy cords, they at some point they break apart. Yes, um,
higher mass particles are unstable, but they're still real. They're
real particles, but they can decay into lower mass particles.

(18:10):
So not every particle has an infinite lifetime like an
electron or a photon, but they are still real. You
can interact with them, you can see them, they can
propagate through space. All right. Well, then let's get into
what a virtual particle is. So I guess it means
it's not a real particle. Yeah, it's not a not
a clean ripple. It's like everything else, you know, it's
any other kind of disturbance in the quantum field, right,

(18:34):
And it's like a transfer of energy from one place
to another in the field. I mean, that's what the
disturbance is. But it's not something you can coalesce together
and say, oh, this is a nice little packet of
energy that moves in a tight way through the field
and we'll stay that way. It like diffuses out, it
spreads out, it fades away pretty quickly. Wait, so it's
possible for feels to be disturbed, not in particles. It's

(18:58):
possible for people feel to be disturbed in a way
that makes a real particle. It's also possible for fields
to be disturbed in a way that doesn't make a
real particle. What do we call that? We call that
a virtual particle. Do they break sort of the rule
of quantum mechanics, like the minimum amount of energy and
things like that, Like, is it possible to have a
ripple that's smaller than an electron? For example, you have

(19:18):
ripples in the electron field that don't have the mass
of an electron. Yes, but they're not breaking any of
the rules. This is a common misunderstanding. They follow the
rules of physics, but you know those rules have fuzziness
in them. So, for example, if you do something in
a very short amount of time, then the energy these
particles is very uncertain because there's an uncertainty relationship between

(19:39):
time and energy, like there is between momentum and space,
and so there are a lot of things they can
do that seem like they're breaking the rules, but isn't
actually Well, wait, so you can't have a ripple in
that's smaller than an electron. Then you can have a
ripple in the electron field that doesn't correspond to one

(19:59):
wheel of drown it's smaller, it's a smaller ripple than
one real electron. You might be thinking to hold on.
The field is supposed to be quantized, and that's true,
but that applies to real particles and in the case
of virtual part and you just broke over my head, Daniel.
All this time I thought it was like a fundamental
rule of the universe that that quantum fields can't ripple

(20:22):
with anything smaller than than than the quantum particles. But
you're saying they can't. They're just not real. Those are different,
not sustainable, they're not sustainable ripples. Yeah, and you know
the thing you're talking about are self sustaining. Real particles
create one, you can create two, you can create three.
You can't contain two and a half. Right, there's there's
no self sustaining mode. They can do that. But if

(20:45):
you're gonna have chaotic fluctuations of the field, then you
can have all sorts of crazy stuff. And so yeah,
that releases you from a lot of those requirements. Okay,
and these ripples you're saying, they don't propagate, or they
do propagate. They propagate, but they don't propagate as far.
They don't hold themselves to get other and so they
don't sustain themselves. They sort of just like spread out
and diffuse and eventually they sort of cancel themselves out.

(21:06):
When you mean what happens to them, They they like separate,
they become you know, inquirent or well, they're very short lived,
they're transient. And so for example, a virtual particle might
be like a little blob of energy that one electron
sends to another electron to push it away, Like two
electrons they push each other apart. Right, how does that happen, Well,

(21:27):
it happens through ripples in the electromagnetic field. And you
can that's not really a photon, Like it's not a
flash of light that goes between the electrons to push
them apart. But there is a transfer of energy, a
transfer of momentum, and that you can associate with a particle.
You say, oh, that's like a virtual photon. Wait, you're
saying that when an electron pushes another electron because they're

(21:49):
both negative charge. They I thought they always use photons.
You're saying that doesn't happen through photons. They do, but
it's a virtual photon. It's not a real photon. It's
not a photon that could like see you with your eye.
It's a virtual, short lived photon, not a photon that
could propagate across the universe and hit another star. That's
a special photon. But there's non special photons. Yes, real

(22:12):
photons are special photons. And Jorges universe though, I love
all particles equally, but there are two kinds of particles.
There's a real particles that can probably through the universe
forever without interacting, and then there are these transient, short
lived virtual particles that don't that you know, we could
argue about whether they really are particles, but we call

(22:32):
them virtual particles. I feel like it's be like telling
you your two kids. I think one of you is real,
one of you is not, but I think you're both
special to me. If one of your kids only lasts
or ten to the mine is twenty three seconds, you're
not even gonna be able to finish that sentence. Well, um, okay,
So so when an electron pushes another electron, they're not

(22:56):
interchanging photons. They're interchanging choosing the field that are like photons,
but not photons. They're not real photons. They are virtual photons.
And when we draw a little Feynman diagrams to describe
this between physicists, we draw a wiggly line just like
a photon. But that photon, you know, it is created

(23:17):
inside the interaction. It's emitted and then absorbed. It's never
seen externally, like you never see that. Nobody says, oh, look,
I will soft flash of light that only exists between
the two electrons. And so these virtual particles are not
ever directly observed. They just sort of used in our
calculation and inferred. Oh I see, But could someone intercept them?

(23:37):
Could you know, like let's say, when an electron is
pushing another electronic and suddenly another electron sweeps in in between,
would they be able to catch that photone and say, yes,
there was a photon here. Yeah, but that's going to
blow your mind because then the photon becomes real. Then
it becomes real. Then it becomes real, and you might ask, well,
how does it know? Right? Well, remembering quantum mechanics, there's
no like propagation. It's not like this is a thing

(24:00):
which goes somewhere. It goes from here to there. If
if you have an initial state and a final state,
your initial state is like an electron is flying off
and the final state is um some some photon from
that electron is now observed by your camera. All the
possible things that could explain that sort of can happen

(24:21):
all at once, right, and and only some of them survive.
And so if there's a camera there to observe it,
then the virtual options disappear. They can't exist anymore. But
if there's not a camera there to observe it, then
they can interact and sort of it's unobserved state with
other electrons and push them along and stay a virtual particle.

(24:41):
I totally understood that. Virtually my VR heads in here,
all right. It sort of sounds like, um, it's one
of these quantum mechanical things where there's sort of virtual
until you open the box. Kind Of, yes, they're virtual
until you open the box. And if you open the
box and interact with them, then only real particles can

(25:03):
satisfy that set of constraints since and then the virtual
particles sort of never happened. And if you're worried about
like you know causality there, you know, the whole interaction
is not like a flowing in time in that same way.
The whole interaction sort of understood is one thing. You know,
like there's this emission and absorption, and we're understanding this

(25:24):
whole sort of process in terms of one calculation, and
we think about all the ways that it can happen simultaneously.
Only some of those survive based on what the constraints
are when you open the box. When you open the box, Yeah,
all right, Well tell me you're saying that virtual particles
break rules. So what are some of the rules that
virtual particles can break? Right, So they don't violate like

(25:46):
deep laws of physics, but they can do things that
real particles can't do. For example, if you try to
interpret these wiggles in the quantum fields as a particle,
you get weird answers. Like you do the calculations to
get what's the kinetic energy of this thing? Well, it
can be negative negative kinetic energy. Negative kinetic energy, and
that's weird if you're used to think about kinetic energy

(26:07):
is like energy of motion, because like energy of motion,
no matter which direction you're going, is always positive, right,
there's a V squared in there, so any velocity gives
you positive energy. But in physics we calculate this energy,
you know, as a relationship between mass and momentum, and
it gets wonky because it's not like an individual, localized

(26:28):
little particle that's moving through space and the way you're
familiar with. It's like this weird disturbance and you're trying
to force this sort of particle view onto it and
doesn't quiet work. It's like a little void of energy almost.
It's sort of like you're asking an inappropriate question and
so you get a nonsense answer. Oh, I see, it's
like a it's like a wiggle, you know, and that
wiggle and can give you weird, weird answers when you

(26:52):
try to measure it. Yeah, and you're not measuring the energy.
You're like, well, here's the wiggle. If I sort of
trying to squeeze this into the particle a work, and
then ask what would be the energy if this was
a particle. You get sort of a nonsense answer, you know,
like if you asked how popular would Daniel be if
he was a famous movie star. But you're like, well,
that's nonsense. There's no way he'd be a famous movie star,
so he'd be like negative popular or something. And the

(27:15):
other thing is that these virtual particles aren't restricted to
have the same mass as the particles you're familiar with.
Like you know, the photon is no mass. Photons that
hate your eye from stars very very far away, they
have no mass because those are real photons. But virtual
photons can have mass. A special disturbance in the electromagnetic

(27:36):
field can have mass. Yes, yes, it can carry some
mass with it. And where does it carry it that
the other photons done? In its back pocket? Of course,
I mean where do you carry your masks? That's where
all minds these ago. It's sort of just another way
to interpret this in the light of a particle. It
sort of breaks one of those rules. And that's actually

(27:56):
the thing that distinguishes a virtual particle from a real particle.
A real particle is a little packet of energy that
has definite mass and propagates forever, and the virtual particle
doesn't have that definite mass. It can have high mass,
it can have low mass um for a photon, it
can have nonzero mass. You can do that mean that
the photon is going slower than the speed of light.

(28:17):
So virtual particles can go slower than the speed of light. Well,
all the information transfer in the electromagnetic field always happens
at the speed of light. But when you talk about
the speed of a particle, you usually want to define
in terms of like how fast is this packet moving,
And in terms of the virtual particle, it's like it's
more diffused, it's like spreading out everywhere, and so I'm

(28:37):
not even sure it makes sense to define the speed
of a virtual particle. Yeah, I feel I feel like
it's getting to this weird quantum realm. Yeah, And that's
exactly the problem is that we want to interpret things
happening on the microscopic scale in terms of things were
familiar with, in terms of things we know, and so
we ask these questions like what is its mass? What
is its kinetic energy? But those don't those are not

(28:59):
always appropriate questions, just like if you ask where is
the electron and where is it going? You know that
doesn't really always have a satisfactory answer, and so virtual
particles are less satisfactory than real particles. They have like
a fewer answers to cough up. All right, let's get
into then the question of whether or not they're actually real.

(29:19):
Can something be virtual and real at the same time?
But first, let's take a quick break, all right, Daniel,
So we we've defined virtual particles as being the wiggle

(29:41):
non particle wiggles in the quantum fields of the universe.
But are they actually real? Can we say that they're real?
If if it sounds like you're you're saying they're not real,
that's that's why you call them virtual. Yeah, Well, they're
not real in the sense that we define them, right.
Particle physicists have a very specific definition of what real is.
You know, when you say really, you mean like it

(30:02):
actually exists, is out there in that sense. Absolutely, virtual
particles are real. But you know, we took this word
real and we redefined it to mean it has a
specific mass, it can propagate infinitely through this quantum field. Oh,
I see, they exist, But they're just not real particles.
It's like a you have to keep the two words together. Yeah,
they're not really the capital R, I guess or if

(30:24):
they're not physics real you know, or like real or
whatever you would call it. But they but they have
real but they have actual effects on the universe. You know,
we talk about empty space, but we know that space
has energy in it, and that energy can be converted
into short lived virtual particles. You have energy. It's kind
of like saying like, um, it would be different if

(30:46):
I say Daniely is not real. Then if I said
Daniel is not a real movie star, that's kind of
perfect psychology. Daniel exists, but he's not a real movie star,
just like these wiggles exist, but they're not real particles.
That works perfectly, except I'm not even a virtual movie star,
so you can that's the whole point of virtual reality.

(31:09):
Then I'm gonna pop into your movie and then pop
right back out again. All right, So the um, they're
they're real, but they're not particles, And so why even
call them particles? Why even have they? Why why not
just call them, you know, squigglies or or ripples. Because
we like to categorize things, and we like to find
connections between things, and so we like to sort of say,

(31:32):
these real particles and the virtual particles are sort of
two sides of the same coin. And they are. You know,
real particles are very closely related to virtual particles. It's
not like a um, a hard wall you can put
between them. And say they're totally different. Real particles are
like a special case of virtual particles, and so we
call them particles because hey, we're particle busicists. Everything is

(31:53):
a particle and we just short sort of try to
categorize them together. M when when you have a hammer,
when have a sixteen dollar hammer, everything, let's take a particle.
Everything looks like a particle. And you know, we even
describe forces in terms of particles. We like to think
about electromagnetism and the strong force and the weak force

(32:15):
um operating in terms of particles, and that can be
confusing sometimes if you try to think about it like microscopically.
How can particles be responsible for forces? All forces are
done through virtual particles. All the forces that we can
describe quantum mechanically, like gravitation, we still don't know, but
all those quantum mechanical forces, yeah, they're described using virtual particles.

(32:37):
And the way you might have heard it described is
like one electron comes along and pushes on the other
electron by throwing a photon at it. But it's actually
throwing a virtual photon. It's a virtual wiggle in the field,
and it's not thrown from one to the other. Right,
it's not something that's moving and flying in a well
defined way through space. It's a little disturbance in the

(32:57):
field that's causing that's pushing on the they're electron. Yeah,
and that's a key thing to understand because fields can
do more than just push. Right, if you and I
are throwing a ball back and forth, all we can
do is push each other. I can't throw the ball
at you and then attract you somehow. That doesn't make
any sense. I'm transferring momentum to you and pushing you away,
So I can't throw a ball at you with negative momentum.

(33:19):
So that's why that analogy breaks down. Because real forces,
like electromagnetism, they're also responsible for you know, electrons attracting
to protons. Yeah, pulling, it's the same deal. So to
understand how that works in terms of virtual particles, you
have to let go of particles as these little balls
that were throwing back and forth and just think about
them in terms of like weird ripples. And the key

(33:41):
thing to think about there is like you are exchanging
a virtual photon if it has a certain amount of
energy to it. Heisenberg tells us, if you're well defined
in terms of momentum, you're not well defined in terms
of location. So that particle, that virtual photon that's being
passed back and forth, doesn't really exist any where. It
sort of exists everywhere. It's like if it's momentum is

(34:04):
very specific, then its location is flat. It's like you
can exist through the whole universe. So like if I
have a magnet, but let's say I'm holding too man
magnets here in the table in front of me, and
you know, I try to bring them together, and they're
pushing each other apart, these magnets. Um Before I was
thinking like maybe they're swapping photons so that they can

(34:26):
repel each other, but really they're they're not. They're just
sort of like just sort of like perturbing each other's fields. Yes,
they're perturbing each other's fields and transmitting energy back and forth,
but not in the sense of like little particles that
are actually flying back and forth like real particles. Like
you can't put a piece of cardboard between two magnets
to block the magnetism, right, and you'll be like, well, look,

(34:47):
photons can't get through my cardboard, so how can magnetism
get through right. The reason is that electromagnetic fields definitely
can get through your cardboard, or you can hear a
radio through cardboard. More like you're bending the fields or
on you, and that's what's pushing the other one. Yes, yes,
it's just not in a way that you can characterize
as a little ball is like a little self propagating,

(35:07):
nice package of field. And so that's how these things interact.
The interact with the fields, and you can, if you want,
interpret those in terms of virtual particles. It's sort of
like looser definition of what a particle is than just
the narrow definition of what real particles are. You sort
of expanded the definition to include more more of these
weird things. Yeah, by relaxing some of the rules, say,

(35:30):
you don't have to have the right mass, you don't
have to have a kinetic energy. That makes sense. It's
a ripple in the field. Let's have to be a
particle to be a particle, that's what you're saying. And
you could also just get rid of the particle picture entirely,
be like, you know what, that doesn't make any sense
to me. I'm just going to think about the fields
and you can do that. It's just it's really hard
because calculations and field theory are very, very complicated, and

(35:53):
so to simplify it, Fineman introduced this idea, said, well,
let's just think about it in terms of like the
simplest interaction, and drew these diagrams that showed like, well,
if it was exchanging one thing you would call a particle,
then it would look like this, And then let's think
about in terms of the second simplest and the third simplest,
and then they just ignore everything else. So he developed
this framework for approximating quantum field theory calculations by using

(36:17):
these like number of virtual particles. The most likely thing
to happen is one virtual particle, the second most likeliest two,
and then three, and as you go on, there's more
and more possibilities, but they get less and less likely,
so you can ignore them. It just lets you sort
of understand these complex field interactions. Yeah, lets you quickly
approximate and get mostly the right answer in a way

(36:39):
that sort of makes sense. And you know, physics is
all about like making sense. We know these are the
rules the universe, what do they mean to us? Like
this interpretation step is important, it's the physics part of it, right.
The rest of it's sort of mathematics, and it's like,
how do we use this to build up a picture
of the world that makes sense to us? And you're
always teasing me that I like rules, but like that's

(36:59):
what physics is, you know, we're trying to figure out
what the rules are and and uh and how they
limit us and whether they actually do limit us. M alright, cool, Well,
I feel feel my mind virtually blown a little bit
to learn that there are particles that are not particles.

(37:19):
They're very much real and they very much kind of
make everything work, right, because without virtual particles you can't
have forces, and without forces, nothing happens. The universe would
be pretty boring without any forces, So stay tuned for
Daniel's future virtual career in the movie about virtual particles.
It's sort of interesting to think that, you know, there's

(37:39):
more to the universe and what we can see and
feel in touch, that there's all this sort of you know,
underlying chaos happening in between what we imagine to be
matter and electrons and courts. Yeah, and that always our
descriptions of it are lacking, right, that we are limited
by the way our minds work and the way that

(38:00):
we think about the universe. We're trying to map that
onto this crazy, insane chaos that's going on at a
microscopic level, and it's never completely satisfactory. It's always running
into contradictions and seeming nonsense. And that's because the universe
at that scale is weird and alien and very difficult
to translate into sense for the human brain. But hey,

(38:20):
I think it's worth trying. So we hope that made
a little bit more sense to all of you. And
then now you know what a virtual particle is, or
what it's not, or what it what it is not
is virtually understand it. So thanks for listening. We hope
you enjoyed that. See you next time. Before you still

(38:46):
have a question after listening to all these explanations, please
drop us a line. We'd love to hear from you.
You can find us on Facebook, Twitter, and Instagram at
Daniel and Jorge That's one word, or email us at
Feedback at Daniel and Jorge dot com. Thanks for listening,
and remember that Daniel and Jorge Explain the Universe is
a production of I Heart Radio. For more podcast from

(39:08):
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podcasts or wherever you listen to your favorite shows. Yeah.