What's the problem with the Standard Model?

Daniel and Jorge talk about the holes in the current theory of the Universe.

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Episode Transcript

Speaker 1 (00:08):
Hey, Daniel, are you guys done with physics yet? Done
with physics? I mean we're just getting started. Yeah, But
then you build that large hattern collider. Didn't that answer
all of your questions? Now there's always more stuff to
figure out? Man, What do you mean people paid ten
billion dollars for that and now you need more money.
That was just like the down payment on the project.
What was that a defined print? We missed that. Somehow

(00:30):
research is exploration. Man, They're never any guarantees about what
we're going to find. But I thought the Higgs Boson
completed the standard model. I mean it's called the standard model.
Aren't you done? It's the standard model. Now we want
to upgrade it to like the super standard model. Sounds
like you need to go work for Apple. It sounds
like we should work for f t X. Sounds like
we paid you ten billion dollars for the wrong model.

(00:52):
Can we have a hundred billion please? Hi am more
hammered cartoonist and the creator of PhD comics. Hi. I'm Daniel.

(01:13):
I'm a particle physicist and a professor at U C Irvine,
and I will never be done asking questions about the
nature of reality. But what if you get the final answer,
wouldn't you be done? Well? The lesson from that book
is that you're never done that even if you do
get the final answer. The next question is, well, why
this answer and not something else? Why do we live
in a universe where the answer is forty two and

(01:34):
not forty seven? What does it mean anyway? The questions multiply.
Maybe the ultimate answer is because that's a non answer.
It's an answer, it's not a very satisfying answer, and
in the end we're looking for explanations, not nonsense. But
welcome to our podcast. Daniel and Jorge Explained the Universe,
a production of I Heart Radio, in which we try

(01:55):
to satisfy your curiosity about the nature of the universe.
Why is the world made up of tiny little particles
frothing together to build up our reality? How far down
do you have to go before you can really understand
the universe at its most basic level? And is there
even a most basic level? Or is there an infinite
tower of questions all the way from galaxies down to

(02:18):
black holes, down to particles, down to strings, and then
down to whatever strings are made of. Yeah, it's an
incredible universe full of gigantic phenomenon like black holes and
galaxies and clusters of galaxies, but also with a lot
going on at the microscopic level, with atoms and particles
and tiny little quantum lips, and somehow it also needs

(02:38):
to be ruled by the same rules. The same rules
supplies from the tiniest levels to the most cosmic of
all levels. It really is incredible how many layers of
zoom we have for the universe. Like we can think
about the universe on the scale of super clusters of galaxies,
objects that are hundreds of millions of light years across,
and they follow gravity. We can make predictions about how

(03:01):
they swirl around each other, and then you can sort
of adjust your zoom knob and think about planets and stars,
and you can adjust your zoom knob again and think
about rocks and liquids, and you can do it again,
and think about atoms, and you can do it again.
You can think about protons. You can do it again
and think about corks. And we just don't know how
many layers of zoom are there, and we don't actually
even know the answer to the question of whether they

(03:23):
all follow the same rules. You know, our reductionist approach
assumes that there is a basic nature to the universe
with a certain set of laws from which everything else emerges.
But that's sort of a philosophical assumption. We're not even
sure that's true. Do you find yourself, Daniel, reading a
scientific paper that you print it out on paper and
then you're trying to zoom in with your fingers? Does

(03:44):
that work? I do sometimes click on blue links on
printed out papers, and I'm frustrated that they don't just
like print out the right paper for me. That would
be awesome if you could click on a link on
a paper and your printer would just print the next paper.
But it is pretty amazing that we know so much
about the universe, from the neest levels to the largest
of all stages the entire universe. And I guess the hypothesis,

(04:05):
like you said, it, is that there's one set of
rules that somehow rules at all. That's certainly one philosophical approach.
We call that reductionism, the idea that the tiny dominates
the huge. And it sort of makes sense to us
intuitively that things emerge from the smallest bits, But if
you dig down into it, there's not really a whole
lot of justification for it. I mean, why should the
small dominate the large? Why can't rules emerge at the

(04:29):
larger levels as well and dominate the small? Wait? Who
said the tiny dominate the large? I would say that
the particles here on Earth pretty much subject to whatever
the Sun wants to do. I think the sort of
standard philosophical approach to physics is to imagine that there
are basic rules at the smallest scale, and those rules
somehow weave themselves together to make our reality. And so

(04:49):
in order to understand the basic nature of the universe,
we should dig deep into the smallest particles to try
to find the smallest of the smallest of the small,
and a long way we have made a lot of progress,
a lot of encouraging results. We've understood the nature of
the periodic table based on how protons and neutrons and
electrons fit together to make all of those different atoms.
We've even understood how protons and neutrons are built out

(05:11):
of smaller pieces. So there are a lot of hints
that suggest that we should keep digging down into the
nature of reality to understand how the bigger things emerge.
It's kind of interesting how physics has some I've covered
both ends of the spectrum, but not the stuff in between.
Like you start on small with the particles and atoms,
but then that's when you're like, ah, that's chemistry, and

(05:31):
after that biology, and after that you know, political science.
We don't care about that. But then once you get
to like the size of the planet of the Solar System,
and you're like, Okay, now I'm back. Now I'm interested
in this again as a physicist will take over from
here until the end of the universe. Yeah, that's right.
And it's really fascinating sort of from a sociological point
of view, because for a long time, those communities, the

(05:54):
astrophysics community and the particle physics community were totally separate.
The people who worked on galaxies didn't they spent a
whole lot of time talking to the people who build
colliders and smashed particles together. Though they were in the
same department, they didn't really overlap very much. But more
recently those communities have come together because there is a
common mystery, for example, the mystery of dark matter. We

(06:14):
discovered it through astronomical observations that revealed that there's stuff
out there that is not made of our kinds of particles,
and now we have particle physicists searching for that dark matter.
So now we have a new kind of physicist, astro
particle physicists that work both on the biggest things and
the tiniest things in the universe. But you're right, skipping
everything in between. Yeah, I feel like you guys skip

(06:36):
over anything that's messy and complicated. I wonder if that
says something about your personalities. I do think that I
got into physics to avoid all the complications of chemistry
and biology. That's certainly true. We like approximating things as
simple objects, dots, spheres, circles whenever we can. Planets, right,
Planets are also just circles to you. So sons right,

(06:58):
basic kindergarten, She's as long as you stick with that
than your physicist. I think kindergarten is probably too advanced.
I mean, I wouldn't want a triangle shaped planet or anything.
Wouldn't that be interesting though, I'd be like that sounds
like chemistry to me. I'll focus on the spears. It
sounds like geometry. Forget about it exactly. We do have
a pretty interesting view of the universe now, and an
interesting model that describes how things work at the tiniest

(07:20):
levels and that we are hoping extends to the largest
of levels. But we do have a model about the universe,
and we've been building it over centuries. Right. Physics builds
our concepts of the universe sort of on these levels. Right.
We have like the atomic level where we think about
the elements, and then we zoom in and we think
about the nucleus, and then we zoom in and we
think about the quarks. And at the level of the

(07:42):
quarks and the electrons. You're right, we have a very
nice picture of all those particles, how they interact, what
they do. And that model also explains all the experiments
that we can do smashing particles together at very high
energies and all sorts of other very detailed, exhaustive experiments.
The picture we have of those particles we've been putting
together for about a hundred years. It's sort of all
clicks together very nicely. Now. Yeah, it's a pretty good

(08:04):
theory that describes what we can see and it works
pretty well. However, we sort of know it's not the
final theory or the ultimate theory of the universe. That's right.
Physics is never done asking questions. And even if we
have a beautiful concept which clicks together and explains experiments,
this is will always come up with ways to keep
the project going. Conveniently, you'll figure out a way to

(08:27):
keep your job going. You think being driven by curiosity,
staying up late at night wondering about the nature of
the universe is convenient. It's almost like an obsession. And
so to the end of program, we'll be asking the question,
what's the problem with the standard model? I think I

(08:48):
know the answer, Daniel, is it me? Am I the problem? Well,
that's one problem, yes, But maybe your main problem is
that you call it the wrong thing. I mean, you
call it the standard model. Not everyone thinks it's the
standard one. But now you're saying it's not standard. Yeah,
you'll be amazed to discover that we can't even actually
agree about what is the standard model. Some people think

(09:08):
the standard model is one thing, other people think it's
something else. So it turns out the standard is not
actually standard. It sounds like you guys have no standards
when it comes to naming things, especially models. It doesn't
surprise me that we didn't impress you on this one.
But really, maybe the question we are asking here today
is what are the problems with the standard model? Right,

(09:29):
because there's not just one problem with it, there are many.
There are many problems, There are unanswered questions, there are
cracks in it, there are missing pieces, there are things
we know the standard model cannot describe. All of these
things are vital hints and clues laying the path for
the next generation of physicists, who we hope will reveal
a deeper understanding into the nature of reality. So maybe

(09:50):
a better name would have been the model issue or
the sort of model, the non standard sort of model. Well,
usually were wondering how many people have thought about this
question and have wondered what are the missing pieces of
the standard model? What's wrong with it? So thank you
very much to everybody who answers these questions for this
segment of the podcast. We thoroughly enjoy hearing your thoughts

(10:13):
and we would love for everybody else to have a
chance to participate. If you would like to put your
voice on the podcast answering these questions, please write to
me two questions at Daniel and Jorge dot com. I
will set you up. So think about it for a second.
What do you think are the problems with the Standard Model.
Here's what people had to say. I feel like we're
confident about how gravity works, like on the microscope or

(10:35):
macroscopic level, and then we're confident about like quantum mechanics,
but we don't know how to relate the two. And
that's the problem. As I understand that the Standard Model
describes a proton and the nucleus and electrons, and the
problem with it is that it describes them as little
actual points in space as opposed to excitations of various

(10:58):
quantum fields. Uh. Therefore, I remember you saying actually in
the podcast that it's actually an incorrect interpretation to imagine
these little things as particles or a little discrete points
in space. Maybe the problem is that it doesn't have
anything for the dark matter and dark energy. But my
problem is that standard model has many things to remember

(11:19):
and it's too difficult for me. I think the main
bron with the Standard Model is that there's no room
for gravity, and I think, especially with the Higgs, it
kind of almost finalized. It snowork kind of stuck. Well.
I think that the problem with the Standard Model might
be that it is incomplete. It may not have the
particles to describe, for example, quantum gravity, so it can

(11:44):
be reconciled with general relativity. Well, I think the problem
with the standard model is that a people are unsure
about the missing pieces in the pattern, missing holes in
the periodic table type deal of the standard model. And

(12:05):
people are curious if there is on some sort of
emergent or if it's some sort of an emergent phenomena
of smaller particles, even smaller than those that we observe
in the standard model. All right, a lot of awesome
ideas here. There seemed to be a lot wrong with
the Standard model. I think this might be the first
time we can say that every single answer is correct. Wow,

(12:29):
that's amazing. So we're done. It turns out the listeners
are answering the questions for themselves. We have trained everybody
so well that we have worked ourselves out of a podcast. Sorry,
we have reached the singularity. Thank you everybody, it's been great.
What sounds like maybe you need some different standards or
the standard model, you know, like they have the Gold standard,

(12:50):
the Platinum Standard, Green Standard, the tin Can Standard. Well,
you know, I do think it's a strange name for
a theory, The Standard model it's like calling something modern physics.
You know, what we teach as modern physics these days
is physics as we knew it about a hundred years ago.
So when they started calling it modern physics, they sort

(13:10):
of painted themselves into a corner. And that happens every
time you give something a name like that. It's like
calling the draft of your paper final final, ready to submit.
You know, that's not the one you're going to submit.
It's going to be ready to submit virgin seven before
you actually turn that paper in. So then what do
you teach at the graduate level? Postmodern physics, deconstructive is physics,

(13:33):
impressionist physics. Yeah, now we have avoided giving an updated
name like supermodern physics or actually modern physics. We just
teach whatever it is we know. Now, well, I guess
there's a classical physics, so you've got to figure out
how to distinguish it from that, right, Yeah, Well, we
usually think about classical physics and quantum physics, and quantum
physics obviously more recent than classical physics. What do you

(13:57):
call this podcast physics? Light diet physics? No, this is
the juice man. This we are squeezing physics to extract
all of the core ideas and understanding. This is like
a shot of physics. This is like the frozen concentrate
kind of physics. This is like that protein powder man.

(14:19):
This will beef you up in your physics knowledge. Your
brain might not be great for your kidneys, but it
will make your mind strong. All right, Well, let's dig
into this, Daniel. I guess first of all, what is
the standard model and is it really standard? So the
standard model is our description of nature at the deepest
level that we have seen so far. You know, we

(14:40):
have six quarks, we have six leptons, we have forces
that tie them all together. The standard model is what
we call our theory of how all of that works.
And it really has emerged from a piece of work
that started like about a hundred and fifty years ago
with Maxwell, as he tied together electricity and magnetism into
a unified concept of electromagnetism. That was really like the

(15:03):
first step towards having any sort of holistic understanding of
various phenomena in physics and like one big idea. Right,
But then this sort of this was after Newton, right,
Like Newton had an idea of how forces and masses
and things interacted and worked. This is more about, like,
let's break it down and think about all the different
kinds of forces that are out there. Yeah, Newton was

(15:25):
thinking about how masses move and the effects of gravity,
but there are lots of other phenomena out there that
can't be explained by gravity, right, like electricity and magnets
and all sorts of other stuff. And Maxwell brought a
bunch of things together and put them sort of under
one umbrella. He developed sort of the standard model of electromagnetism,
and that's sort of like the founding kernel of today's

(15:46):
standard model. He explained how forces operate in terms of
fields and how a bunch of different forces really were
part of one bigger picture, right. And he was looking
at specifically at electrical things like you said, and magnetic things,
but not gravity. But it's still kind of using Newton's
equations to think about like, hey, if I put this
magnet in this field, how is it going to move

(16:08):
and why does it move? Like that? It's Newtonian in
the sense of F equals m A. He was calculating
the electric force, for example, on an electron, and you
can use F equals m A to deduce how the
electron accelerates. So it's part of mechanics in that sense,
but really he was digging deeper, was wondering just like,
what is the source of these forces? Why are there
forces in the universe? And can we explain all of

(16:30):
them in terms of a single idea rather than having
like a long list of different ones. And is that
where the name the standard model came in. The Standard
Model as a name didn't really appear until much much later,
like a hundred years later. So we have electromagnetism from Maxwell,
and then that was turned into a quantum theory when
we developed quantum mechanics, and it's sort of fine men

(16:51):
and a bunch of other folks that turned electromagnetism into
a quantum field theory, which is the more modern version
of it. That was about the nineteen fifties ish, and
he and some other folks won the Nobel Prize for that.
So then we had a quantum version of electromagnetism. But
we also have these other forces we had, like the
weak force, and Steve Weinberg, who won a Nobel prize,
figured out how to bring the weak force together with electromagnetism.

(17:15):
And that's the first time people really called this sort
of the standard model. And he wrote a paper called
a Theory of Leptons, which is what brought the weak
force together with electromagnetism. And around then is when people
started calling it the standard model. I see, I guess
what do you mean by the standard model. It's like, hey,
we have all these different ways that particles and things
can be pushed in, all these different forces that they

(17:37):
seem to experience. Can we put all of these forces
into like one umbrella or one you know, equation or theory,
and we can? And that's kind of standard because it
covers everything. Yeah, although of course the standard model doesn't
cover everything yet. Right, even the standard model we have
today does not describe everything, as we'll dig into in
a minute. So we should think of it as like
sort of our current best work in progress description of

(18:01):
all the particles that we can't explain so far. But
it's sort of like, you know, we're all building a
barn together. Let's all work on the same project at
least and try to put the whole thing together into
one edifice. But it's sort of like how far we've gotten.
It's like working draft underscore seven. Now, when you say
that you're putting all these different forces under one theory,

(18:22):
what does that mean. Does that mean that all these
forces are somehow related to each other, they somehow interact
with each other, or are they separate. It's just it's
just about, you know, putting them under the same grouping. Yeah,
that's a really great question. I think there's two ideas there.
One is putting the forces in the same mathematical language,
like can we describe these things in terms of the

(18:43):
same basic concepts? And the basic concept we have for
the standard model are these fields that fill space and
carry information and momentum around. And that's the basis for
why electromagnetism can push on things, and why the weak
force can push and pull on things, and also why
the wrong nuclear force can. So we have a mathematical
sort of formula for how that happens. And the Standard

(19:05):
model is cool because it puts all these things sort
of in the same mathematical language. For those of you
who know some physics and math, it means we can
describe everything as a quantum field theory just by specifying
its lagrangin, just by saying, here's where the fields are
here's how they wiggle, and also here's how they talk
to each other. That's sort of like the language we've
developed for the standard model. But there's another level to it,

(19:27):
which is deeper, which is that sometimes we can see
symmetries there. We can say, oh, look this piece of
the math over here and that piece of the math
over there. If you bring them together, they actually clicked
together into something simpler. So that's what we've done, for example,
with electromagnetism and the weak force, we've combined them into
one mathematical structure we called the electroweak force. So sort
of two levels to that. One is just writing it

(19:49):
in the same language, and the other is noticing patterns
and simplifying things by bringing them together. M Because I
guess it could have been that that wasn't the case, right,
It could have been that, you know, you study electromagnetism,
it's like, oh, it works in this way, and there's
this math to describe it. Then when you look at
how particles pull on each other through a different force,
like the strong force or the weak force, you know,

(20:10):
you study that and then it turns out that you
need a totally different kind of mas for that and
the tooth mass are not compatible. That could have been
the case. That could have been the case exactly, and
in fact, that is the case for gravity. We have
no way currently to bring gravity into this mathematical framework.
That's one of the problems we'll talk about later. And
so it hasn't succeeded in every single case, but it
has succeeded for these fundamental forces, the strong force, the

(20:33):
weak force, and electromagnetism. All right, so then that's the
standard model. It's something that describes all the known forces
except gravity, and all of the particles except a whole
bunch of parts. You make it sound like such an
amazing achievement, but really this is the accumulation of a
huge amount of knowledge and effort and ideas by so

(20:55):
many smart people over decades. You know. It really does
represent an incredible side into the nature of the universe.
But of course there's a lot of work left to
be done. Yeah, just the story is left. But let's
call it the standard model. Anyways. All right, well, let's
dig into the problems that we have with this standard model.

(21:16):
What are the missing pieces, what are the things it
can't describe, and what are the things that may never describe.
But first, let's take a quick break. All right, we're
having a standard conversation about the standard model, which is

(21:39):
to say that the standard model is not so standard.
You don't sound very impressed. I am a pressed. Yeah,
describing you know, four percent of the universe or less
is pretty good achievement. Yea, what great would you give
somebody if they got a four percent on their test?
You're the professor, Well, why would you give one of
your students of the four percent on a physics test? Yeah? Well,

(21:59):
you know, I have to say, what's the curve? Think
about all the other alien species out there that have
been working on physics for the same amount of time,
how far have they gotten? And really you've got the
greatest on that curve. I see. You're all about lowering
your standards. Is that what you're saying. I'm all about calibrating, man, Well,
calibrating this case, lower ring or standards. Maybe maybe it

(22:19):
could be that alien species out there basically figured it
all out in about twenty minutes and we've been struggling
with it for hundreds or thousands of years, depending how
you count, and we've hardly made any progress. Or maybe
there are aliens out there that have been working on
these problems for millions of years and having gotten as
far as we have, we just don't know. So then
what gray would you give us a for effort? I'd

(22:40):
have to go with incomplete, but that's gonna look bad
at my transcript. Then, Yeah, I don't think anybody should
hire us until we have a sensor whether we're good
at this or not. Are the human race all right? Well,
let's talk about the problems with the standard model, which
I guess is the shining achievement of physics. Right. It
described most of the forces that we know about, the

(23:02):
strong force, the electoral weak force, and it describes most
of the particles that we know about, including all of
the ones that were made out of it. Yeah, and
before we reveal all the chinks in its armor, let's
just spend a moment to appreciate it, because it means
something kind of cool about the human experience. It means
that basically everything you interact with, every event in your life,

(23:23):
everything that happens to you, is mostly explainable, Like there
isn't really any magic left in your experience of the universe.
Every experience you have, we can mostly explain in terms
of the fundamental physics that we do so far understand,
you know, lightning and stomach aches and all sorts of things.
We think we mostly understand the basic physics of that,

(23:45):
even if we can't always make it practical. We can't
predict the path of hurricanes that we don't think that.
There are mysteries in physics that actually affect your everyday life.
And that's a new experience for humanity, right, most humans
over the years have lived in a world that was
fundamentally not understood by them. Yeah, it's pretty amazing what
how much we can describe now although we were sort

(24:05):
of they're all already kind of like a hundred years ago, right,
Like stomach as we could have predicted the hundred years ago.
You don't need quantum physics for that. Yeah, I'm not
sure if doctors even now understand the stomaching. Maybe I
shouldn't give them too much credit. But you know, there
were lots of interesting puzzles about the way the world
worked and the particles that were out there that we
hadn't figured out yet until we brought them together into

(24:26):
this picture of the standard model. But now we mostly
understand the world that is around us. So as we
dig deeper, of course, there are lots of holes and
questions that come up. All right, well, let's dig into
some of these holes and and missing pieces of the
standard model. And let's start with the big one, the
heaviest one, the most massive one. Gravity. Gravity really is
the most missing piece of the standard model. Like all

(24:49):
the forces that we do experience in our everyday life,
the strong force, the weak force, electromagnetism, gravity is the
one that we cannot describe yet using the Standard Model,
which is in the end, a quantum mechanical description of
the nature of the universe. But gravity we have a
classical theory. We have general relativity, which ignores quantum mechanics

(25:09):
and describe spaces a bending place where particles can move smoothly. Yeah.
I know we've talked a lot in the on the
podcast about the problems with marrying quantum mechanics and gravity.
But maybe it gives a sense of why that's so
Hardlet like, I can calculate the gravity between the Sun
and the Earth. Why can't I calculate the gravity or
gravitational force between you know, an electron and a proton. Well,

(25:32):
if you knew exactly where the electron and the proton were,
then you could calculate them. You know the distance, you
know the masses, all that stuff, But you can write
it's possible to know the location of a particle. Electrons
are quantum objects, right, so they don't always have a
specific location. They have like a probability of being here
in a probability of being there. And one question about
gravity is like, well, how does that work? Is the

(25:54):
gravity of the electron also probabilistic, like the space bend
a little bit where the electron might be and a
little bit somewhere else with the electron might be. The
orders gravity collapse the electron's wave function, requiring it to
be in one place, so that it sort of it
knows how to bend space the right amount and exactly where.
I guess. Maybe the question is like, we can calculate
the force between an electron and a proton, right, and

(26:17):
as I understand it, it involves like exchanging a photon.
But when you can calculate that force and what happens
to those two particles, why can I do the same
with gravity? Think? If I have an electron a proton,
why can't I just calculate how much force they put
on each other. So if you're thinking about the electromagnetic
force between a proton and an electron, you're right. You
can calculate that force and you can think about in

(26:38):
terms of photons. And that's a quantum mechanical theory that
allows the electron to have a probability being here and
probability being there. That's all cool because electromagnetism is a
quantum theory. It allows all of that. It treats its
objects as quantum objects. But gravity, so far is not.
Gravity is a classical theory, and in order to know
how much space bends, you have to know where something

(26:59):
is and you have to know it's trajectory through space
and time, and that's not possible for quantum objects. So
people have tried what you suggested, like, well, let's build
a quantum theory of gravity and think about exchanging little
particles for those forces. They call them gravitons, and so
people certainly have worked on that. They have tried to
add gravity to the standard model to make it a
quantum theory. The problem is those calculations don't work, like,

(27:22):
we don't know how to do it yet. Gravity is
a different kind of force than electromagnetism is it requires
a slightly different sort of mathematical construction to describe it,
and those constructions sort of fail. When we try to
do those calculations, we get crazy numbers, we get infinities
and negative infinities. It just sort of hasn't worked out yet.
The crucial way that gravity is different is that it

(27:43):
couples to itself. Like a photon doesn't feel other photons
because photons only feel things that have electric charges and
photons don't have electric charges. But gravity feels everything because
gravity feels everything with energy, and so it's sort of
a much crazier system to try to describe using this
onto mechanical apparatus, and so far it just hasn't worked.
You mean, like maybe the idea of a graviton itself

(28:05):
feels gravity like gravity, graviton has energy, and therefore it
also affects the particles through its gravity exactly whereas a
photon doesn't feel the electromagnetic force, and so it's just
simpler to do those calculations. That doesn't mean it's impossible
to have a quantum theory of gravity, just means it's
going to need sort of new mathematical tools that we
just sort of haven't invented yet. The tools that we

(28:26):
have used so far haven't worked. Can you just invent
the graviton that doesn't feel its own gravity. You can
do that, And that's sort of actually the first step
in an approximate theory of gravity, you know, like a
perturbative theory. We say, let's try to describe part of
gravity and assume that the graviton has negligible effect on
the gravitational shape. Why can it have zero effect? Well,

(28:46):
that would be inconsistent with what we think about general
relativity and how gravity works. General relativity says that space
bends in response to energy density, and so if gravitons
carry that energy, then they should also bend space. Well,
maybe just don't apply general relativity at the quantum level. Yeah,
some people are building new theories of gravity. The tricky

(29:08):
thing is that we have a lot of measurements of
gravity already. So if you develop a new theory of gravity,
it has to also describe everything we've observed so far
about how planets orbit each other, and about black holes
and all these things that happened at the big scale,
you know, the scale of planets and stars and galaxies.
General relativity is past all of these tests with flying colors.
So if you develop a new theory has to reproduce

(29:30):
all of those calculations as well, and so far you
haven't been able to do that. So far, we haven't
been able to do that. All of our mathematical attempts
has sort of blown up in our hands. Sounds like
a heavy situation there, But let's get to some of
the other things missing in the standard model, because some
of them are pretty big. For example, the universe is
not covered by the Standard model. Yeah, the Standard Model

(29:50):
is really good at describing the kind of stuff that
we are made out of, atoms and molecules and quirks
and leptons and all these kinds of things. But in
the law asked a few decades, we've discovered that that's
not what most of the universe is made out of.
We know that if you take a random chunk of
space like a cubic light year, and you ask how
much energy is in there, it turns out that the

(30:11):
energy devoted to quarks and leptons and all the kind
of things that we do understand and they are described
by the Standard Model is only about five percent of
the energy in that cube, and then another like twenty
five percent is due to dark matter. So weird new
kind of matter that we know is out there. We
can see it's gravity and all sorts of other effects.

(30:32):
We just don't know what it is and what kind
of particle it's made out of, except that we're sure
it's not made of our kinds of particles, or at
least we know or we think it's not made out
of the particles that are currently tallied up by the
Standard Model. It's possible that is, it is made of
a particle, a different kind of particle or something that
then you could add to the Standard Model. That's right,

(30:53):
that would be the new Standard Model, Standard Model Underscore
Final or Update version two or whatever. But none of
the particles that are only in the Standard Model, the quarks,
the electrons and nuance, the towns of new trinos, none
of those can explain what dark matter is. And that's
a whole, really fascinating topic. People can dig into a
bunch of podcast episodes about why isn't dark matter neutrinos

(31:14):
or how do we know dark matter is not some
weird clump of quarks floating out there or primordial black
holes or something like that. But we're pretty sure that
dark matter is not made out of anything that's currently
described in the Standard Model, which means it's something new,
something weird, And you're right, if we figured out what
that was, we would have to add it to the
Standard Model, right. But it could also be the case
that maybe dark matter is made out of something that

(31:36):
is not described by the mathematics of the Standard Model, right,
just like gravity could be something not even compatible with
the Standard Model. Absolutely, And it's a sort of extraordinary
bit of extrapolation to even assume that it might be right,
because we've looked at a tiny fraction of the stuff
in the universe, and we developed mathematics that works to
describe mostly that, and then we imagine that, oh, maybe

(31:57):
the rest of it also, you know, even though we
know the rest of it is different and important and
fundamental ways from the bit we have studied. So it's
sort of a leap to say, maybe we can use
the same tools to describe the rest of the universe.
Maybe right, but also maybe not. It might be that
dark matters not made of particles at all. Their theories,
a matter that don't have a sort of scale that

(32:18):
as you zoom in, always look the same. Right, These
things are called unparticles. There's all sorts of other crazy
bonkers ideas that are not particle based dark matter. If
you ask me, that's what I would love for us
to discover because instead of just like adding a new
piece to the standard model and building on quantum field theory,
it would point to us a new way that the
universe operates, a completely different sort of foundational construct that

(32:41):
can describe reality. That would be pretty exciting. But also
the standard model doesn't describe dark energy, which is like
sixties seven of the universe. Right, two thirds of the
universe is also unexplainable by the standard model. Yeah, and
when we say two thirds again, we're thinking about a
sort of fictional chunk of the universe and accounting for
the action of the energy. Right, we don't know how

(33:02):
big the universe is, and we say two thirds of
the universe, some people might be confused about what are
you talking about? The universe is infinite. Two thirds is
also infinite. So that's why we think about in terms
of energy density, Like take a chunk of the universe
and ask how much energy is in that chunk, and
how is it apportioned. Well, two thirds of the energy
of any chunk of the universe we think is devoted

(33:22):
to this thing called dark energy, as you say, And
dark energy is just our description of the fact that
the universe is expanding, and that expansion is accelerating. That
every year, space is getting bigger, and it's getting bigger
faster every year, and that requires some energy. And as
space gets bigger, it makes new space, and that new
space has dark energy in it. And so dark energy

(33:44):
is a sort of runaway effect that keeps creating more
of itself, which creates more of itself to create more
of itself. And so actually the dark energy fraction in
the universe is growing. It's now the dominant fraction, and
unless something changes, we think it's going to forever dominate
our destiny. It seems like maybe the problem with the
standard model is that it doesn't talk about space itself right,

(34:06):
like it talks about particles and quantum fields, and it
assumes a fixed, non changing space. But there's all these
other theories like gravity and dark energy and the expansion
of the universe that assumes that space itself is changing.
Whereas in the Standard model it's it's it's almost like
a constant or an assumption. Yeah, I wouldn't say that
standard model doesn't talk about space, but you're right, it
certainly makes certain very crisp assumptions about space that are

(34:30):
in conflict with what we know to be true. Right. Usually,
quantum field theory operates on what we call like a
flat backdrop. We assume that space exists, and that it
always has existed, right, and that it always will exist.
The basic way the quantum field theory thinks about space
and time is not to think about them together the
way relativity does, but to think about them separately. And

(34:51):
space is something that exists in time is just how
things change in space, and so it thinks about space
and time quite separately. And turning there's a equation can
describe the universe all the way back infinitely in time
and all the way forwards infinitely in time. So quantum
field theory is consistent with the universe always having existed
and always existing into the future. Whereas when we look

(35:12):
at space, as you say, we see that it's changing
and that it's expanding, And if you think back far
enough in time, it's consistent with some crazy event that
we don't understand that might even be the beginning of space.
So you're right, there basic questions about the Standard model's
treatment of space itself that we don't know how to answer.
And that's really connected to this question of general relativity,
because general relativity is basically a description of what space is,

(35:35):
but we don't know how to unify that with our
understanding of quantum mechanics. Is there even a room in
the Standard Model for expanding space, Like, is there even
a lever you can pull there or a mechanism that
allows space to expand In the Standard Model. You can
do quantum field theory on curved space or on expanding space,
but what we don't know how to do is how
to have those fields themselves create that curved space, which

(35:59):
is what you sort of need for quantum gravity. So
it's possible to do quantum field theory on other funny
spaces or other dimensions or expanding spaces, that it gets
very very complicated. Can it even then explain the Big Bang?
Or not at all? So quantum field theory can't explain
the Big Bang as like a singularity, right, Quantum field
theory can describe what happens in space after that. But

(36:21):
it certainly cannot accommodate a singularity. Quantum mechanics that phoors
a singularity, right, because there's a fuzziness to information into
the universe. You can zoom everything down into a tiny,
dense little dot. You can't even have a singularity at
the heart of a black hole according to quantum mechanics.
So absolutely not. Our description of quantum field theory is
not consistent with a singularity at all. And so that's

(36:43):
why when we talk about the Big Bang, we talk
all the way back to very very early universe, and
we say, well, before that, we need some picture of
quantum gravity. Quantum effects and gravitational effects are both important,
and we just don't have that theory, and so we
don't even know how to think about what happened before
that time. Well, sort of sounds like maybe quantum mechanics
and the stand model will never maybe even be able

(37:04):
to explain why space expanded so fast during the Big Bang, right,
why the Big Bang happened at all? Yeah, the standard
model as we know it has no explanation for that
and may never write if it can handle space expanding
or ever explain space expanding. Yeah, well, we imagine that
there's some future theory, some quantum theory of gravity, which
can explain that. And then when you take the version

(37:24):
of that theory and ask what happens when space is
mostly flat and mostly cold, then you get the Standard
model sort of the same way that, like Newton's theory,
is a limiting case of Einstein's theory. Right. Einstein's theory
of relativity, we think, is a more accurate description of space.
But when gravity is weak and there aren't black holes nearby,
it reverts to Newton's theory, right, And so we think
that probably quantum gravity is a super version of the

(37:46):
Standard model, or the other way around, that the standard
model is like a limiting case of some deeper theory
of quantum gravity. All right, well, those are the two
big gaping holes in the Standard model gravity and also
dark matter and dark energy. But the holes don't stop there.
There are still other gaps in the Standard Model to
bring everything from antimatter to neutrinos. And so let's dig

(38:09):
into these mysteries. But first let's take another quick break.
All right, we're talking about the I guess it's not
so standard model or the standard lead incomplete model the

(38:32):
current best theory of physics so far that we're pretty
sure is wrong. It needs to be updated asap. That's
your standard star. No, it's wrong, but we will press on.
Standard really just means work in progress, like every theory
in science is always a work in progress. Oh, I
see you're using that definition of the word standard, like

(38:54):
the current model. It's really just the current model. It's
just the latest update Standard Model version six, as downloaded
onto your phone last night by Apple. We're still on data,
is that what you're saying, or and like we're always
beta testing science. All right, Well, as we heard, there
are still big things missing about the Standard Model, which
is exciting to physicists, And there are some big things missing,

(39:16):
but there are also other things that maybe people don't
think about are missing from the Standard Model. Even if
there weren't questions about dark matter and gravity just zooming
in on the particles that we do know about, there
are lots of questions that we don't have answers to.
So you can look at the Standard Model and you
can say, like, why is it this way not some
other way? And also does it actually explain everything we see?
One of the deepest mysteries that remain in explaining the

(39:38):
universe that we have is why it seems to be
made of matter and not anti matter. In the Standard Model,
we have all the particles we've been talking about, but
there's also a shadow particle for every single one. Every
quirk has an antiquark, every electron has an anti electron,
every tow has an anti tow. There's this beautiful symmetry
to all the particles. They have their anti part nticles.

(40:00):
And yet when we look out into the universe, we
see that I'm made of matter. You're made of matter.
Our solar systems made of matter, our galaxies made of matter.
We think the nearby galaxies are made of matter. It
seems like the universe is basically matter. So if the
theory of particles is symmetric, how do we get this
asymmetry in our universe? Where does that come from? This

(40:21):
sort of the big question. I think what you're saying
is that the Standard Model does have antimatter in it right,
like anti matter itself. It's not a mystery like that,
It's actually part of the Standard Model. Every particle in
the model has its antimatter particle. But I think maybe
what you're saying is that the model predicts that is,
there should be the same amounts of matter and anti matter,

(40:43):
right like, according to the theory, there's nothing in it
that says, oh, clearly matter is the best matter. Yeah,
and there's no reason we call one kind of matter
matter the other kind of antimatter except that we are
made of one kind, right, There really is no difference
between matter and antimatter. No, No, if you're not with us,
your anti us. If you're not made of us, you're
made of the anti us. Yeah. If you're not, if

(41:06):
you're not part of us, you're not us. There you go.
If you're not particles of us. Yeah, that's the interesting mystery.
And you imagine, for example, the very beginning of the universe.
We think probably matter and antimatter were made at the
same rates, because why not, Because the theory of particles
is basically symmetric with respectum matter and antimatter. There's antimatter

(41:26):
quantum fields for every matter quantum field. So then the
mystery is, how do you go from a universe that
has the same amount of matter and antimatter to our universe,
which is almost entirely matter. And that's the unanswered question.
We're looking for asymmetries. We're looking for ways the Standard
model prefers matter to antimatter, or like processes forces something
which produces matter preferentially over antimatter, and we have not

(41:50):
explained that yet. Well, there are some hints in the
Standard model, right, Like, according to the Standard Model, there
is a slight little preference for one kind of matter,
isn't there There are some process the seas that do
seem to prefer matter to antimatter in the Standard model. Yes,
in the Standard Model there are some. Right, it's not
perfectly symmetric, but these are pretty small. They're not nearly

(42:10):
big enough to explain the asymmetry that we see. It's
a hint because it's a crack in the perfect symmetry.
It says, maybe the universe prefers matter to antimatter, but
the effects that we have discovered cannot explain what we
see in the universe. Yet we're missing like a huge
chunk of it. Like most of the asymmetry is not explained.
But I guess if there was an effect that was

(42:31):
so large that it preferred a matter over antimatter to
the degree that we see in the universe today, wouldn't
they be, you know, kind of a big obvious hole
in the theory, or is it possible that what it
prefers matter or antimatter is external to the standard model
like gravity. Yeah, that's exactly the question. And we're looking
for those holes in the theory, and people are doing
searches for new processes that prefer matter to antimatter, and

(42:55):
recently they have some interesting hints for discoveries at CERN.
These are called the flavor anomalies, where like quarks change
from one flavor to another, and they tend to do
it to matter a little bit more often than antimatter.
And people are wondering if this is like the thread
we're going to pull on that reveals the universe's preference
for matter or antimatter. But nothing is certain yet. But
you're also right, it could be something else, something external

(43:17):
to the standard model. It could be that the universe
wasn't created symmetrically with matter and antimatter at the beginning
because of some theory of quantum gravity that prefers matter
to antimatter. We just don't know. It's a huge question. Mark. Well,
I am pro finding the answer to that. I'm not
anti that. Now, what are some of the other things
that are missing from the standard model. There are also
just a lot of missing explanations for the patterns that

(43:39):
we see. Like if you look at the patterns of
the particles, you see that there's a four basic particles,
the up, the down, and the electron and the neutrino.
But each one has two copies, right, The up has
the charm and the top, the electron has the muon
and the tow And this is sort of nice consistency
there where each of the four based particles has exactly
two copies. But the question, of course is why, right,

(44:02):
why should particles have any copies? You know, there's like
matter and antimatters, the particles have like a single reflection.
Why do these particles have these weird, heavier copies and
why two of them? That's totally unexplained. It's just sort
of like what we see, and to me, it's like
a hint. Is suggests that there's something happening underneath out
of which this emerges, but we just don't understand anything

(44:23):
about what that is. We do we know for sure
there are only two or three generations of particles, or
is that just what we've found, or it can find
with our colliders. Is it possible that there's an infinite
number of generations we just can never get to them
because they require too much energy. It's a really cool question.
We're pretty sure that there are only three kinds of
each of these particles, and the reason actually is the

(44:46):
Higgs boson, because the Higgs boson interacts with all of
these particles. So when we make the Higgs boson at
the large Hagon collider, we sort of make it out
of these particles. We throw corks and gluons together and
make a sort of a frothing mass of energy g
and the Higgs boson pops out of that frothing mass.
And it does so because it interacts with all of
those particles. And so the rate at which interacts with

(45:08):
those particles determines how often it's made. And if there
were more of these kinds of particles, if there was
like a super top cork, or like a heavier bottom
cork than the theory predicts, the Higgs boson would be
made much more often. So by measuring how often the
Higgs boson is made in our collisions, we can actually
measure how many generations of particles there are. Because the

(45:28):
number of generations determines how often we make the Higgs boson.
So we're really pretty sure there are three. But we
don't know is why there are three. What could there
be maybe uh, super higgs boson or heavier higgs boson,
or another generation of Higgs bosons that we don't know about.
There definitely could be We did a whole podcast about
other Higgs bosons and it might be there. And there

(45:51):
might also be other kinds of corks. They just would
be different, like they don't talk to our Higgs boson
or they're different in some way. So precisely, the statement
we can make is these kinds of corks, the quirks
we have found so far, we're pretty sure there are
only three of them. But there could be other kinds
of weird corks that don't talk to the Higgs the
same way and do other stuff that are out there.
And there's no limit on how many other weird heavy

(46:14):
particles could exist that we just haven't found yet. MM.
But I think what you're saying is if you look
at the math, if you look at the math of
the Standard model, it doesn't prevent you from having more
generations or have your cousins of the electron. It's just
that experimentally, you haven't seen any or seen any evidence
that more could be there. Yeah, directly, we haven't found
a name. We've looked, and indirectly we have some constraints

(46:36):
because we think if they exist, they would influence how
often the Higgs boson is made, the large Hagon collier.
But mathematically there's no limit, that's right. Mathematically there's no limit. Yeah,
there's no reason the Standard model couldn't have four or
seven generations or ninety thousand generations and particles. Mathematically there's
no reason why not. But it's an interesting clue, and
people wonder, like, what does it mean that there are

(46:57):
three is the universe? Like three? Ish? Is this just
what it is? Or is there a reason for it? All? Right?
What else is unexplained? Another really fund mystery is neutrinos. Right,
Neutrinos are part of this basic list, and we know
they exist and they're out there and that there are
three kinds of them, but we really don't understand their masses.
We know that they do have mass, and those masses

(47:19):
are very very small, but our theory, the Standard model,
actually doesn't allow them to have any mass. The theory
requires that they have zero mass, and we go out
there and we measure them and we see that they
do have mass. And so this is actually where people
disagree about what is the standard model. The sort of official,
official standard model has neutrinos with no mass, and now
people have like a new version of the standard model

(47:40):
where they've incorporated neutrino mass, and some people say that's
the standard model. Wait, what do you mean the standard
model doesn't allow the neutrino to have mass. What does
that mean? Well, this sort of old school standard model
has a bunch of rules for what these particles can do.
Like you have to keep track of the number of electrons.
You can't just create or destroy electrons. You have to
keep track of them and conserve number of electrons in

(48:01):
the universe. It's like a hard and fast rule in
the old school standard model. But if the electron neutrino
has a little bit of mass, then it can do
something tricky to sort of break this accounting. We had
a whole podcast episode recently about sterile neutrinos and and
all this kind of stuff, and so it breaks that
rule in the old school standard model. So if neutrinos
have mass, and that hard and fast rule, and the
old school standard model doesn't really hold up anymore as

(48:23):
a hard and fast rule. It's like approximate now. So
we have that sort of an updated version of the
standard model where you give neutrinos mass and it breaks
these rules a little bit. Some people consider that the
standard model, and some people consider that beyond the standard model.
What happens if you do allow mass in the standard
model for neutrinos? Are you're saying, other contradictions pop up? Yeah,

(48:44):
we don't really understand how that works yet. There's a
bunch of experiments to try to measure those neutrino masses
and they don't agree with each other. There's a question
about are there actually just three neutrinos or is there
like a sly fourth neutrino out there, the sterile neutrino
that's been messing up a few experiments that are out there.
We don't understand if neutrinos get mass the same way
the other particles do through the Higgs boson, or if

(49:05):
they're a really weird particle, like maybe they are their
own anti particle particle called a maorona. Particle which would
get mass in a completely different way, not from the
Higgs boson. So neutrinos are so of the next frontier,
like a part of the standard model that we've only
really just begun to explore and really haven't nailed down
very well. Interesting. Well, we don't have a lot of
time left, but there are still some interesting things missing

(49:27):
from the standard model. Maybe you want to step of
studies pretty quick. There's so many things we couldn't even
cover them all. One of my favorites is a question
of whether there are particles out there that have just
a north or just a south magnetic charge, Like there
are particles out there that have a positive or negative
electric charge, but so far, every particle we've seen in
the universe has a balanced magnetic charge, like you see

(49:50):
particles with north poles and south poles. You never see
particles with just a north pole or just a south pole.
That would be called a magnetic monopole. And actually the
theory prefers that they do exist, Like if they do
exist and the the theory is more symmetric, it's more balanced
than if they don't exist. So it's kind of a
mystery why we don't see them in the universe, and

(50:12):
a lot of physicists believes that they must exist somewhere
out there in the universe, but we've never found one.
But probably the deepest question that's open and remaining for
the standard model is what's next. We look at all
these particles and we wonder, like, is this the base
description of reality? It can't possibly be there all so
many weird patterns we don't understand. And you know, a

(50:32):
hundred years ago we looked at the periodic table, we
saw these weird patterns we didn't understand. Turns out all
those patterns were clues that said, oh, there's something deeper
going on. All these patterns are just complexity that arise
from how the little bits that things are made out
of fit together. So now we're looking at the periodic table,
the fundamental particles, and we're seeing all these patterns that
we don't understand, trying to explain them and wondering if

(50:54):
they're made out of some smaller bits that we haven't
yet seen, and maybe those bits are made of smaller bits,
and those bit are made of smaller bits, and maybe
this like a hundred levels between us and the base
layer of reality, or maybe just one or two, or
maybe there's no bottom. Yeah, I guess it's kind of
tricky because at some level you have the standard model
and you're seeing these patterns and maybe hinted something deeper.

(51:15):
But at the same time you also know that the
standard model is not correct, right, Like you know they
has hu mongous gaps in it and lots of things missing.
Kind of makes you wonder how much you should read
into these patterns, or whether even exploring those patterns is
going to be useful. Yeah, we don't know what the
best way forward is. When you read the history of physics,
it's written to sound kind of linear, like we did this,
and then we figure that out, and then we figure

(51:36):
this other thing out. But remember that at the same time,
there were lots of other branches. People were exploring other
crazy ideas which made sense to them at the time
when they were at the forefront of human knowledge. But
we mostly erased those other zigzags and those other branches
from our history of physics to give you a description
of sort of the theory we ended up at. But
now we're here at the forefront of human knowledge right now,

(51:58):
we just don't know what is the right way forward.
Should it be quantum gravity, Should it be anti matters,
Should it be magnetic monopoles? Should it be cracking open
the electron to see what's inside. We don't know what's
going to yield some inside, so we're all just sort
of like being curious and exploring and hoping to figure
something out. So the basic answer is that we've given
you all this money and still wide open question. It's

(52:20):
still a wide open question, which makes for a wonderful,
mysterious universe that we get to keep talking about on
the podcast. It sounds like maybe the answer to getting
are great as a species in the giant physics exam
of the universe is to ask for an extension. Daniel,
what's your policy and given students extensions. I'm pretty lenient. Actually, yeah,
I'm pretty lenient. What if they come to you say, hey,

(52:41):
instead of doing physics, I've been spending all my money
making Marvel movies and creating Netflix. Can I get an extension? Yeah? Sure?
Can I get some free tickets? I see you're open
to being bribed as a greater No. I think people
should go out there and explore their passions and discover
who they are, and everybody can contribute in some way

(53:04):
to this incredible journey we call life and the exploration
of the universe. It sounds like a standard answer, Danny, Well,
stay tuned as we keep exploring the universe and discovering
more about what we know and when we don't know
about this amazing cosmos. We hope you enjoyed that. Thanks
for joining us, See you next time. Thanks for listening,

(53:30):
and remember that Daniel and Jorge Explain the Universe is
a production of I Heart Radio. For more podcast from
my Heart Radio, visit the i heart Radio app, Apple Podcasts,
or wherever you listen to your favorite shows.