Welcome to another installment of our LBS physics deep dive.
After exploring the world of experimental physics at CERN in our first video
documentary in episode 93, we'll stay in Geneva for this one, but this time we'll
dive into theoretical physics.
We'll explore mysterious components of the universe, like dark matter and dark
energy.
We'll also see how the study of gravity intersects.
with the study of particle physics, especially when considering black holes
and the early universe.
Even crazier, we'll see that there are actual experiments and observational
projects going on to answer these fundamental questions.
Our guide for this episode is Valérie Dormcke, permanent research staff member
at CERN who did her PhD in Hamburg, Germany, and postdocs in Trieste and
Paris.
When she's not trying to decipher the mysteries of the universe, Valérie can be
found on
she's a big sailing fan.
This is Learning Vagin Statistics, episode 95, recorded September 6, 2023.
Hello my dear Vagins!
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If you go to
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Each week, we'll get on a one-to-one call and we'll walk through any questions,
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Again, that's topmate.io slash Alex underscore and Dora.
And now, let's talk theoretical physics with Valerie Donka.
I'll show you how to be a good peasy and change your predictions.
Valérie Damke, welcome to Learning Asian Statistics.
Glad to be here.
Yeah.
Thank you for taking the time.
I am really happy to have you on the show.
Again, a physics-packed episode.
I'm really, really happy about that and I have a lot of questions for you.
I think you're the first theoretical physicist to come on the show.
That's cool.
We're going to talk about topics.
a bit different than those we talk about when we have experimental physicists on
the show.
So that's cool, more diversity for the listeners.
And also, when that episode is going to air, by the magic of time travel, episode
93 will have been published.
So that's the one at CERN.
So the very special video documentary I did at CERN with Kevin Kaif.
So if listeners haven't checked it out yet, I highly recommend it.
And that one, of course, I recommend mainly watching the YouTube video because
I recorded and edited it firstly for video format.
You have access to the audio format also, but I'm telling you, it's going to be
funnier in video.
So now to actually complete what we talked about in episode 93.
where Kevin does a lot of fun experiments at CERN, today we are going to talk about
another part of physics that's done at CERN, thanks to you, Valerie.
But first, before doing that, let's start with your origin story.
How did you come to the world of theoretical physics, and how sinuous of a
path was it?
It was, it was more of a path that I kind of ended up on without honestly thinking
about it too much.
It's kind of been a topic that has fascinated me since I was quite young,
reading science fiction books and the like.
And I basically, we just kind of following my interests, taking the course of the
university that interests me most without thinking too much about where that would
lead me in the end.
And it was basically only when I was doing my PhD that I realized, wow, I'm actually
working on cosmology and kind of these big open questions of the universe, which is
something I was dreaming about as a kid.
And somehow I got there without, somehow without too much planning, but just
following what I thought was kind of the most interesting thing for me to do at
every step.
Oh yeah, so it's really like the call of passion for you.
In a sense, in a sense.
Yeah, that's really cool.
I mean, and that's also one of the cool things of this kind of job, right?
In physics or I don't know, airplane pilots or firefighters.
You can dream about them already as you're a kid and then make that your job.
I personally love my job, but...
I'm afraid I cannot say that I dreamed about patient statistics when I was a kid.
Like I never told when I was five years old, oh, I want to be a patient
statistician.
You know, that's not how it works, unfortunately.
Really?
Yeah, no, I know, I know that must be quite disappointing to a lot of people,
but I had to burst that bubble because I get a lot of questions about that, yeah.
So.
I would also say that you kind of have to really...
dream about or be enthusiastic about it, because doing science, you always
encounter moments when nothing works.
Yeah.
And if you're not passionate about actually solving the problem, it's, you're
just going to get stuck.
Yeah.
No, definitely.
That's a very good point.
And that's where actually statistics get back in the, in the mix, because that's, I
would say that's the same for
programming and the kind of statistics at least I do where you are going to get a
lot of bumps along the way.
And I always say to beginners that models never work, only the last iteration of a
model is going to work.
And even then, you just have to be satisfied with good enough.
So that's a field where you have to become comfortable failing all the time.
First, be comfortable with making mistakes and failing.
And also where you need to be driven by passion because if you don't have that
inherent passion, you're not going to still be driven to solve those numerous
data analysis issues and bugs and stuff like that.
So now, I'd like to talk about what you do actually, what you're doing nowadays,
because we know you dreamt about doing that since you were a child.
But how would you define the work you're doing nowadays and what are the topics
that you are particularly interested in?
Right, I think there's probably two parts to that question, right?
One is kind of how does an everyday day actually look like?
And the other one is, okay, what are the big topics I'm interested in?
Yeah.
So to start with the format, so what my day does not look like is that I kind of
sit in my office all by myself, waiting for the fantastic idea that is going to
win me a Nobel Prize.
That's kind of the image I had maybe as a kid of how a theoretical thesis would
work.
But that's not at all what my day looks like.
Right.
So I'm it's a lot discussing with people, listening to talks, going to conferences,
reading papers, discussing over coffee on a blackboard over lunch.
And then progress comes bit by bit.
But it does kind of, there's never a lack of things to work on.
There's never a lack of interesting questions.
There's only always a lack of time to decide what is the most interesting
question of all the questions to work on.
Because there's really a lot of things that we don't understand.
And that brings me a bit to the overarching team of my research.
So I work on the intersection of particle physics and cosmology.
So
meaning kind of the physics of the very, very smallest particles, the fundamental
building blocks of nature.
And at the same time, the physics of the very largest scales, so the largest scales
we can observe in our universe, and how the latter can teach us something about
the former.
So how kind of from astrophysical or cosmological observations, we can learn
something about what is really the nature of the fundamental building blocks of
nature.
Yeah, so small topics, fundamental building blocks of nature.
Yeah, thanks.
That's interesting.
I'm actually curious.
So of course, we're going to talk about the projects you work on a day to day a
bit more.
But also I'm curious now that you brought up basically what your days look like
concretely.
Yeah.
What's the part of basically solitary work with pen and paper?
What's the proportion of that in comparison to, as you were saying,
collaboration with people, exchange of ideas and things like that?
Because I think when you tell people you're a theoretical physicist, and that's
definitely the case when you tell people you're a statistician, most of the people
doing math on a blackboard.
So most of the time, which is not true if you're a statistician.
So yeah, I'm curious how it is on your slide.
Yeah, it's probably similar.
I mean, if I get one or two hours on block to actually sit down and do a calculation,
that's rather the exception than the rule.
So it is, of course, part of my job, and I enjoy it a lot.
Sometimes just to have time just to think.
really thoroughly about a problem, either analytically, so pen and paper, or coding.
But it's usually not like very long stretches at a time because then you
either you hit a problem, right?
Or you hit a solution.
And in either case, that's the point to reach out to your collaborators and
discuss the next steps.
Yeah.
I mean, that's interesting because for me, now I'm using more and more the
excuse of teaching to dive deep in a topic and a project because, well, I have to be
able to explain it properly to students.
So that's actually, these are actually the good occasions and rare, quite rare
occasions where I can just be myself working on the computer or sometimes with
a pen and paper and really understand deeply.
a topic that I need and want to understand because otherwise, yeah, you have so many
other projects and solicitations that can be hard to actually take the time just for
yourself and focus on these.
So I'm the same.
I do appreciate these solitary moments, although I'm happy that they are not 90%
of the work, I have to say.
Yeah, same here.
And actually, Sue, you...
You're a very math savvy person.
So of course you know about patient stats, but I'm curious if you were introduced to
Bayesian methods actually, you know, in your graduate studies or before, and if
you use them from time to time in your own work.
No, so I never received any.
any type of formal or informal training.
So it's, of course, it's something we need to know in the sense that we deal with
empirical data.
Even if I myself don't usually deal directly with the empirical data, but I
kind of deal with the processed empirical data, or I deal with the publications that
people have written on the data, and then I need to evaluate, interpret, and kind of
continue to work from there.
But for that, of course, I need to kind of understand the significance of certain
experimental results.
So I would say, okay, I mean, I have a fundamental understanding of them, right.
But it's, it's not something that actually kind of on a on a day to day basis, I
really am like deep in the in the details of it.
Yeah, because I'm more work at the kind of one level.
away, right?
So kind of that I that I kind of take, I need to understand what is the
significance of that result, right?
But once I've understood that, I can basically work directly with the result
without having going to back to the data at every step.
Which is quite a luxury, I have to say.
I'm a bit jealous.
I'm very, very happy that there's people who do the work that I don't need to do.
Yeah, that's, that's a very good point.
I like that.
And if you go listen to episode 93, you'll see the difference between basically that
kind of work that Valery does and the experimental physics work where statistics
is way more present and of course, patient statistics is extremely helpful.
So I find that super interesting to notice.
Just because you don't use patient stats, Valery doesn't mean that your work is not
interesting.
I have to put that out there.
On the contrary, I find it fascinating.
So let's dive in because one of your areas of interest is to go beyond the standard
model phenomenology to kind of probe it, if I understood correctly.
So can you tell us what that means and maybe first define the standard model for
us?
Right.
So the standard model basically reflects our current understanding of these
fundamental building blocks of nature.
So it kind of contains what we think are kind of elementary particles, which are no
longer further dividable into even smaller particles.
And there's not many of them.
There's basically a handful of them, depending how you count.
And we think that these...
fundamental particles together with the interactions between these particles that
they explain all of kind of nature, the way it surrounds us, right?
So all, all everything that we can, we can grasp, grasp or experience here on earth.
And the standard model describes basically this.
So it describes kind of which building blocks are there and how do they interact
with each other.
And now going beyond the standard model, because a model is always a model, right?
So it means that it describes kind of nature to the best of our knowledge.
But most models are incomplete at some level, right?
Because because it's kind of only a way that we describe nature, not actually the
fundamental theory of nature.
And for this, the standard model of particle physics, in particular, it, it
does extremely well in many respects, one could even say,
frustratingly well, because like in all our searches of looking for new
interactions, looking for new particles here at CERN at the Large Hadron Collider,
we always keep confirming the predictions that the standard model makes with
incredible accuracy.
But we still know the model is not complete.
And the reason we know that the model is not complete basically comes from
cosmology.
So there's observations that we make about the dynamics of the universe.
or properties of the universe, which are simply in contradiction with this model,
which tells us that there's ingredients missing.
And we have a rough idea of what these ingredients are.
Or rather, maybe, instead of one rough idea, we have 100 rough ideas.
And the big question is, which one of these is correct?
Is any one of these correct?
And how can we make progress in understanding these missing parts better?
So to give you some keywords, things like dark energy, dark matter, those are some
of the open questions.
Yeah, because we know basically you say they are open because first we cannot
really explain them fully for now, as we said in episode 93, but also we know that
the standard model breaks down at those points and cannot explain them.
So that's basically what you're trying to understand.
Why does the standard model fail here and how can we actually explain these
phenomena?
Correct.
I see.
So concretely, what does that research look like?
Maybe could you share an example of a discovery or theoretical development in
this field that has the potential to reshape our understanding of particle
physics?
You mean like a discovery in the past that did that or a discovery, potential
discovery in the future that...
I would say both.
Yeah, both if you can.
Let's start with the past.
So one observation, for example, was rotation curves of galaxies.
So people were looking at galaxies in the sky.
And they were they were looking at kind of how fast the stars were rotating, which
you can do by measuring the redshift of the stars.
Because as they move away from us, the light gets slightly red as they move
towards us, the light gets slightly bluer.
And if you know, like if you have an object on a stationary orbit, and you
know, you know, the orbit, you know, the velocity.
I mean, actually, even knowing the orbit and the mass of stars enough.
Then you can estimate how much mass you need in a center in order to make that a
stable orbit.
And so that's just Newton dynamics, high school physics.
And what people observed is that the mass that you needed in the center in order to
put these stars on the orbits that were being observed was much, much bigger than
the mass you would have inferred just by counting stars.
And now you can say, OK, well, counting stars is obviously not enough, right?
Because there's going to be planets.
Planets are not luminous.
So there's going to be a bit of an offset, but you would have expected that counting
stars would give you a good estimate.
And it turned out it was completely off.
So it turned out it was kind of a big amount of something that has an attractive
gravitational force in the center of the galaxies, or like in a halo around the
galaxies, which was invisible to our telescopes.
And that is basically what I'm coined the term dark matter.
because it kind of has a gravitational pull of matter, just like everything else.
But it's dark, meaning we can't see it.
And not seeing it means like not only kind of we don't pick it up with telescopes,
but kind of also all other type of experiment that we've performed to date,
trying to find this stuff.
And this stuff should be around everywhere, right?
So it's not that there's none of it on Earth.
It's just that it's so incredibly weakly interacting with...
Yeah.
all the instruments that we build, that it's very difficult to see.
And then observations, I mean, more observations, particularly cosmological
observations, reveal that there's actually five times more of this dark matter than
there is of what we call ordinary matter.
So ordinary matter is everything that we know of on Earth and everything that we
can describe with our standard model of part of the physics.
Meaning that there's really a lot of stuff out there that we don't know.
That's just one example.
And that kind of gave very clear indication that the Sonop model of
particle physics is incomplete.
And that we're not only missing a little bit, but that we're actually missing a
very big bit of the picture.
And along the same line of thought, you know, what would really be a
groundbreaking discovery if one of the many experiments looking for such a dark
matter particle, if they would actually find something.
I mean, even if they don't find anything, if a particular experiment doesn't find
anything, then okay, you still learn something because you can probably exclude
some class of models.
But if one of them actually made a discovery, and we would have kind of a
very clear indication of which direction to go in when we're kind of trying to
describe these dark matter particles, that would be a complete game changer.
Yeah, for sure.
And so these kinds of experiments are underway at CERN in particular, right?
Yeah, at CERN and across the world.
I mean, it's something you can look for when in a collider because you can always
hope that as your collider reaches higher and higher energy, or you have just more
and more particles that you're colliding, you'll eventually kind of reach the
threshold for producing these particles.
And then you can find indirect traces of them.
in the K channels, or you basically have some sort of, not a collider, but
basically just a very big detector volume somewhere.
So a very big amount of an noble gas, for example, even water.
And then you wait basically for a dark, you like have to shield it very well
against everything else.
And then you wait for some dark matter particle.
to have one of these very rare interactions with one of the atoms of your
detector.
And you're looking for that interaction.
And there's a there's a range of experiments underway, looking for very
different types of these dark matter candidates.
Yeah, so but we've been we've been hoping that we'll find it any day now.
Basically, since I don't know, I mean, basically, since I do physics.
So we don't know.
It could be around the corner or it could be very well hidden.
Yeah.
I mean, these kinds of experiments, I think I would not be able to work on them
at least full time, you know, that's awful.
Like you're just waiting for something and you cannot control anything.
Oh, there's plenty of stuff to do.
You're not just waiting, right?
I mean, because you're basically constantly fighting to reduce noise,
reduce background, understand noise.
understand background, argue with somebody who's making noise in the building next
door, right?
And disrupting your experiments.
So, Yeah, yeah, no, for sure.
That's, yeah, that's something you have to deal with all the time, I guess.
But yeah, I mean, I would be also, you know, incredibly stressed out.
Like, so did the, I think a lot of them are helium pools, right?
Or something like that.
Did the helium pool move tonight or not?
I would be incredibly stressed out.
Yeah, so thanks a lot.
That's actually very interesting to hear about that because I find this kind of
experiment absolutely fascinating.
And where does your work come into that picture?
So you're part of these big teams, right, in physics.
Like you see a physics paper, it's like most of the time a lot of people, because
a lot of you are very, like many of you are very specialized in what they do.
And so you bring one of the brick to the paper.
So you in this kind of work, what do you do?
What do you bring?
So the papers really with like the many hundreds of authors, they're usually the
experimental collaborations.
So.
As a theorist, you know, I usually have whatever, two, three, four, co-authors on
a paper.
That's a lot.
Right.
So we build, of course, very heavily on the results of these big collaboration
papers.
But largely, the work that I concretely do is with much smaller groups of people.
So, yeah, I basically have two...
two main approaches to this.
One is kind of starting from really standard model of particle physics, and
trying to come up with possible extensions of that, which kind of makes sense within
the framework that the standard model is written in.
So it makes sense within the symmetries that they are, makes sense within the
framework of quantum field theory, and address some of these open problems that
we have in cosmology.
And then the question is, okay, once you've kind of constructed
such an inherently consistent model, what sort of implications might that have in
various types of experiments?
Right.
So that can be experiments like the chart Hadron Collider.
It can also be some astrophysical observations, or it can be some
cosmological observations.
So that's kind of one approach, and coming kind of more from the fundamental
mathematical theory of it.
My other approach is more the lamppost approach, meaning, well, you, you look
where you can look right, and you hope that nature is kind.
And they're kind of the my approach is to say, okay, what types of probes do we have
of the universe of astrophysical processes?
Try and understand as much as possible about those, and then see what type of
models or what kind of types of building blocks of models.
you could test with these types of observations.
And there, for example, the new big player in the game are gravitational waves.
Because now since the first discovery with LIGO and now a tentative discovery in a
different frequency range this year with the pulse of timing arrays, that's kind of
opening up a completely new way of observing our universe.
And so there's the potential for...
for big excitement in that field.
So I'm also just involved in trying to understand as much as possible about how
gravitational waves can reveal something about the universe.
Oh, yeah.
So that's actually fascinating.
So yeah, talk to us a bit more about that, basically.
What can gravitational waves tell us about the universe?
And maybe redefine quickly what gravitational waves
waves are for listeners?
Right, so gravitational waves are, we think of them as perturbations of the
metric, so perturbations of space-time.
So the type of gravitational waves that we've already seen with LIGO and Virgo,
which are big Michelson interferometers, so the type of
which are circling each other and then finally merging.
So these are like extremely massive objects.
And as you might know, a massive object kind of creates if you want a dent in
space-time.
And if you have two of them, just kind of their dance around each other really like
sends out ripples of this kind of space-time perturbations out into the
universe.
If you're very close to a black hole, right, these ripples will be quite
significant.
But then you'd also have all sorts of other problems, right?
Because if you're really close to black hole, I mean, then you have a lot of
problems.
So, by the time these gravitational waves reach us, they've kind of spread out very
far, meaning the amplitude is very much decreased.
So, by the time they reach us, these are typically very, very small, like tiny
perturbations in space time.
So it's not something we have to worry about in everyday life, rather we need to
build an extremely sensitive detector to even pick them up.
And so, so far, the observations that we've made are this type of observation.
So observations of these black holes merging, which happened, I mean, still at
the distance of megaparsecs or gigaparsecs from here, right?
So it kind of...
Yeah, quite far away on cosmological scales.
But nevertheless, compared to the lifespan of the universe, these are still fairly
recent events.
So at the moment, we're using this to learn, as a new way to learn about the
universe surrounding us or the more recent universe or the relatively recent
universe.
Because these gravitational waves are so weakly interacting with everything, in
principle, even gravitational waves generated in the very, very early
universe, when the universe was not yet transparent to photons, when kind of no
other messenger could escape this primordial soup.
Gravitational waves could.
So in principle, if we detected them today, they could reveal information about
extremely early times in the universe, when the temperatures in the universe were
extremely high, when all the fundamental particles.
kind of existed as fundamental particles.
And when we can really kind of probe these constituents of the standard model or of
any model beyond the standard model.
So that's the ultimate hope.
But it's challenging because we don't know what is the amplitude of these gravitation
waves from the very early universe.
And so we first need to understand the gravitation waves generated in the late
universe.
Make sure we fully understand that before we kind of look for a fainter signal.
Very similar to with photons, right?
You basically first need to kind of understand all the light kind of coming
from the nearby universe, coming from the galaxy.
And only when you have a very good understanding of your foregrounds, can you
go and can you look for fainter light that is coming from earlier times.
Yeah, yeah, that makes sense.
Because also those waves are like so much weaker that...
Also, I'm guessing you have to be a bit more aware of what you're looking for,
because otherwise it's even harder.
And to understand, do we know if...
Just one black hole, for instance?
So for instance, the back hole at the center of our galaxy, is it emitting also
gravitational waves, but since it's not orbiting another one, at least that we
know of,
the gravitational waves are weaker so we cannot see them?
Or do we know that, no, you have to have the collision of two massive objects to
get those gravitational waves?
Yeah, so a single black hole won't do it because anything that is perfect spherical
symmetry won't do it.
That has to do with the fact that these gravitational waves are tensor modes,
right?
So they have two Lorentz indices and something that's spherical symmetric.
is a scalar quantity.
So a single black hole won't do it.
So you need two, or you need a black hole and another massive object, so you have a
black hole and a neutron star.
Okay.
Or anything else that breaks spherical symmetry, right?
So kind of, I don't know, you dancing around, right?
That will in principle generate gravitational waves.
They're just very, very small.
Thank you.
I'm flattered.
Yeah, I see.
Okay.
Yeah, so it's very like, it's really the density of the objects that count.
Yeah, again, you can imagine that.
A large concentration of mass and in some asymmetric way.
So some sort of violent process, which is condensing a lot of energy, a lot of mass.
Yeah.
But in some way that is moving in a bit of a non-trivial way.
Yeah, that makes sense.
Even though I...
I like thinking about these things because it's so hard to imagine.
Like the power of these collisions must be just incredibly devastating.
I would love to see that in a way, but that's so like, it's really impressive and
at the same time, really frightening.
Yeah.
So the, the gravitational waves that we saw.
with LIGO, there we think it's something like two black holes, roughly after the
mass, like roughly 10 solar masses each colliding, a bit more.
And the energy that is just the energy that is released into gravitational waves
corresponds roughly to the mass of our sun.
So it's a huge amount of energy.
And now the gravitational waves that we think we might have seen with these pulsar
timing arrays.
These are even more massive objects.
These are really the large black holes, right, like the one in the center of a
galaxy that we think we see colliding.
So this is two far away galaxies, each with their big, massive 10 to the 6 solar
mass black hole in the center.
And when they collide, that's the signal that we expect.
So that's a massive event, right?
I mean, two galaxies colliding.
Yeah, you don't want to be close to witness that.
Yeah, no, that's for sure.
These are absolutely fascinating topics and I'm wondering what are the main
challenges in understanding these topics right now and how do you folks as
researchers in this field...
address them.
That's, that's a broad question, right?
I mean, there's different levels of challenges, right?
So when it comes down, for example, to let's say something, something concrete,
like understanding these signals that we think might be from gravitational waves,
then I mean, a lot of the problems boil down to, you know, making sure this is a
signal and not a background or a noise source.
So
That means, of course, building experiments that are extremely precise
measurement devices.
It also means a lot of modeling of the various components that go in, and kind of
both on from the theoretical side and also from the experimental side.
And then when you get the data, again, to cross-check, is this really the type of
signal that we have kind of...
Do we have a way, a robust way to distinguish what we call a signal from
something that we call a background?
Take it into account that we might not have thought of every possible background,
right?
So do we kind of really have a telltale signal of what we think the signal would
look like, right?
And typically all these analysis are done as blind analysis, right?
So you think about what signal you need to see in order to be convinced that this is
what you're looking for before you open the box and look at your data.
So that's one challenge.
more kind of on the data analysis or experimental side.
The other challenge may be more on the theory side.
So when you're kind of building models, which extend to standard model of particle
physics, there's many, many options, and you need some sort of guiding principle.
And I mean, if you're lucky, you have data to guide you, you have some sort of
anomaly, something you feel like, okay, here's the weak point, right?
Here's kind of where you need to poke, where you need to extend.
Sometimes you have things like simplicity, right?
Which you kind of hope is a good principle, though, of course, you never
know that that's a good principle.
Yeah.
And recently, that's really been a bit of a challenge, precisely because the
standout model works as well as it does.
There's no...
I mean, sure, we know we need to explain dark matter, right?
But there's many, many possible options how that dark matter could or could not
tie into the standard model.
And there's no very obvious way, like, there's no obvious weak point at the
standard model.
It is not precise weak point.
I mean, there's a global weakness, things that cannot explain, but it's kind of not
quite clear where exactly it needs to be refined or extended.
And that I think for
In the past, it was more clear, or people had pretty clear ideas, right?
And then there was pretty obvious things that needed to be checked, right?
So we needed to find the Higgs particle, right?
So the last missing particle of this then our model.
And then we also thought, because the, I mean, the Higgs particle has certain
properties, which kind of led us to believe that we thought, okay, once we
find the Higgs particle, we should also be finding other particles somehow related to
this particle that would naturally explain certain open challenges.
But the fact that we haven't found them and that we're just kind of testing with
higher and higher accuracy, and we're just kind of getting the prediction of the
standard model or confirming the prediction of the standard model without
finding any small deviations is making it very hard to kind of decide a bit.
What's yeah, how, how should the extension work?
Right?
And how should the extension like is, is the extension in such a way that we can
actually test it with.
with the tools that we have, right?
Or do we need to think differently?
I mean, either different types of experiments, but also maybe different
theoretical concepts, because so far, most extensions of the standard model kind of
rely on the same theoretical framework point of view theory.
And then they kind of within that framework, you try different things.
But the fact that kind of we haven't had a real breakthrough there.
maybe indicating, okay, whatever, you know, it's just at higher energies, which
we can't reach, what may be indicating the framework we're thinking in is maybe not
the best.
So yeah, there's many, many questions, many levels of questions that can be
addressed.
Yeah, that's really interesting.
I'm curious, basically, what would you like to be true?
something that at some point nature will tell you, what would you like to see and
to observe and the kind of consequences it would have on our understanding of how the
universe works?
Well, I would mainly like nature to produce something that we can, like give
us something to work with.
I would like nature to be kind enough to produce some sort of signal, be it in dark
matter, be it in gravitational waves, be it at a collider.
that actually gives us something which is accessible with the two worlds, the
experiments that we have at the moment.
Because it could simply be that all these completions of the standard model live at
an extremely high energy scale, which is simply inaccessible to any type of
collider we can build on Earth.
And that'll make it not impossible, but very, very much harder to actually unravel
these questions.
Yeah, yeah, for sure.
And that, I mean, so that's one part of the work you're doing.
I told that work around gravitational waves, which are of course related to
gravity, in case people didn't understand.
Oh, and by the way, on the podcast, I had another researcher called Laura Mansfield
and she's working on gravity waves.
which are not the same as gravitational waves.
That's quite confusing, but yeah, that's also actually very interesting field of
research, basically gravity waves and the relationship with climate.
That's all here on Earth.
But that's also related to gravitational waves in a way, in the sense that it's big
objects basically on Earth.
Like the Everest or the Mont Blanc or all these big
massive mountains which actually distort a bit the gravitational field around them
and that has impact on the climate.
How do you model that?
Basian modeling gets here because that's really useful because you don't have a lot
of sample size.
I recommend listening to Episode 64.
I put that in the show notes.
Yeah, I was fascinated by the fact that gravity, you can study it here on Earth,
but also it has incredible effects in the universe and at masses that we cannot even
imagine, right, with the collisions of black holes and collisions of neuron
stars, so that's really something I find fascinating.
And actually, can you make the distinction between a neuron star and a black hole
listeners and yeah, so that they understand a bit the difference between
both.
Right.
So a neutron star is made of neutrons, meaning kind of it's a very, very densely
packed environment of nuclear matter.
And a black hole is even more denser, right?
So a black hole is really the densest object that we can imagine.
where kind of matter has really any type of matter has really just collapsed into
this object, and you don't care any much anymore kind of what it was initially made
out of, right?
If we just has one property.
Of course, it can also spin, but basically, it only has one property, which
has which is its mass, right?
And then it may also have spin if it's if it's rotating.
But it doesn't it doesn't matter anymore what it was made out of.
So one, one consequence of that is that if you have two
neutron stars merging as they get very close to each other, their gravitational
force will slightly distort them.
So they can be a little bit deformed because despite that they are very, very
compact, and very dense, they can still be kind of slightly deformed as they get very
close to each other, whereas two black holes will really stay perfectly spherical
as they as they approach each other.
So you can tell the difference between the two by looking at
details of the gravitational wave signal as you approach this merger event.
Okay.
I didn't know that black hole stayed spherical even as they approach each
other.
Is that because they are so dense that they cannot be deformed?
Yeah, it's basically because they are so dense.
And because they, I mean, in some sense, despite that they are physical objects in
our universe, in some sense, they kind of become a rather mathematical object.
Yeah, like a perfect sphere that you cannot deform or do anything on.
It's really weird.
Yeah.
And it's crazy that we're actually seeing them, right?
I mean, both in these gravitation wave signals as also then with direct
observations with optical telescopes.
That's like this first picture of the black hole in our galaxy and the
neighboring galaxy.
Yeah.
And so your work on gravity, I'm curious to understand it because here, obviously
when we talk about gravity, gravity is so weak that you have to have so massive
objects to really see its effects and also it needs a lot of time.
So obviously here we're dealing with the largest scales of the universe.
But you also work on particle physics, as you were saying, and you work at CERN,
where particle physics is one of the biggest fields.
So I'm curious, how does that study of gravity intersect with the study of
particle physics, especially when we consider the phenomena you work on, so
especially black holes and or the early universe?
Right.
Well, I mean, anybody, you know, who's, I don't know, fallen down the stairs, right,
will not say gravity is a weak force.
But indeed, right on Earth, right, when we compare the force of gravity to the other
forces that we have, so the forces that bind atoms together, things like that,
gravity is extremely weak.
So when we perform any particle physics experiment on Earth, we just completely
neglect gravity, and we're not introducing any error in our estimations.
Now, gravity can become important, as you say, either if you have some very massive
objects like black holes, or if you have very far distances, because here on Earth,
kind of, okay, we have so much matter interacting so strongly that we don't care
about gravity.
But the universe as a whole is actually pretty empty.
So in most of the universe, there's just nothing.
What leading order, there's nothing.
And that means that on those scales, because there's no matter which
has any interactions that are stronger on those large scales, it's really gravity
that is describing the dynamics of the universe.
And so if we want to understand both kind of the dynamics of the universe today, but
also extrapolating back in past, if we want to understand the evolution of the
universe, the birth of the universe, then we need to understand gravity.
And one of the big puzzles, for example, is
that at the moment observations tell us that we are in a phase of the universe
where the universe is not only expanding, but expanding in an accelerated way.
And that's pretty weird because normally you think if you just have a bunch of
matter, right, a bunch of galaxies, you think, well, they're going to have
gravitational interactions between each other.
So even if you somehow gave them some initial velocity, you would think, okay,
well, they're going to kind of slow down.
and eventually crunch back together again, because on those large scales, it's only
gravity that is important.
So on those large scales, you think you can you can either have things collapsing,
or you can have kind of things, at least if they're expanding, they should be
slowing down.
What we observe is the opposite, right?
What we observe is really, things are deferred, things are away from us, the
faster they are moving away.
So we're in a universe which is expanding faster and faster.
And that is also gravity driving that.
It's just not the usual form of gravity that we know on Earth, that gravity is
attractive.
But in some sense, you can call it a repulsive force of gravity, or it's a part
of gravity that acts as a pressure that drives the universe apart.
And that is what we call in dark energy.
So again, the term dark just implies we don't really understand and we can't see
it.
And energy basically comes from observations that it has this effect of
driving the energy of driving the universe apart.
So it acts as a type of energy in the expansion history of our universe and
concretely today.
But we don't really so we can model it, but we can't we don't really fundamentally
understand what it is.
So understanding that and understanding kind of.
how the universe evolved, not only today, but in the past.
That then immediately ties back into particle physics, because going back in
time in an expanding universe means you go to a smaller universe where everything was
much more dense, much more hot.
You end up in this primordial soup of particles.
So you're looking at particles at high temperatures, particles when they're
really kind of not bound in atoms and molecules, but when they exist really in
their fundamental
basically a lab to study particle physics.
So that's how the connection works between these very large scales of the universe
and then the very smallest particles that we study in that way.
I see.
Yeah, it's because then it's because you're going back to the early universe
where basically the structure that we have today of the universe didn't apply because
it didn't exist yet.
Correct.
We go back to when everything was really kind of just this hot primordial soup of
fundamental particles.
We tried to understand kind of how different properties of the soup, meaning
different possible extensions of the standard model, would kind of leave traces
in the evolution of the universe.
So would leave traces in kind of astrophysical and cosmological
observations that we can make today.
I see.
And...
these days, what's a specific experiment or project that you're involved in, in
this film, and what would be the main question that this project is trying to
answer?
Right.
So a big, big project I'm involved in, right?
So this is a, you know, many hundreds, thousands of people working together is
the LISA project.
So that's a future space-based gravitational wave observatory.
It's going to be an ESA mission.
The idea is to have three satellites circling around the sun on an orbit
similar to the Earth.
So following Earth.
on an orbit around the sun.
The satellites will be two and a half million kilometers apart.
They will exchange laser links.
So they will be shooting, there will be lasers going between all combinations of
the satellites.
And using these lasers, the idea is to measure very precisely distance between
these satellites as they orbit the sun.
And the idea is that if a gravitational wave comes, since it's a
little ripple in space-time, it will change very slightly the distance between
the satellites.
And so by kind of looking for this, looking for these little variations in the
distance between the satellites, the goal is to look for gravitational waves.
And being in space has the big advantage that a lot of the noise that you have to
deal with on Earth is not there.
So the idea is that you can
much better sensitivities than you could on Earth.
Yeah, that makes sense.
Also, although I'm guessing the sun can be noisier at times.
Right, but it's all a question of frequency, right?
So you need to kind of find a frequency band which is clean.
But yeah, I mean, there's obviously huge technological challenges in implementing a
mission like this and many things that can go wrong.
This is why you need a lot of people with a lot of different expertise coming
together and also a lot of money to build an instrument like that.
Yeah.
I mean, just the engineering part of it is you have to launch three satellites.
First, that's already hard.
And then you have to put them in orbit around the sun and that they still can
communicate with each other.
It's just, and they are extremely far apart from each other.
So just that part is...
absolutely incredible that we can do that.
Knock, knock, right?
I mean, we hope we can do it.
Yeah, I mean, that's just incredibly fascinating.
And so what's the ETA on this mission?
When will the satellites go up theoretically?
Right.
So the hope is to launch in the early 2030s, which seems a long way from now,
but it's really not.
Because, yeah, I mean, it takes a while to build a satellite.
And also to develop all the kind of the data analysis pipelines that you need.
Make sure you have all the sensors on board that you might need to perform
whatever type of cross checks.
Yeah, make sure you didn't put anything on board, which generates a bunch of noise.
Because once it's up there, it's up there, right?
You can't.
Yeah.
Yeah, I mean, it's not in the orbit, right?
Exactly.
You cannot find it, send anybody to repair it, right?
So once it's up there, it's up there.
So you really have to think of every possible complication beforehand.
Yeah, which is quite daunting.
I have to do that for my own statistical model, you know, where I probe them and
I'm like, okay, where can the model fail?
What could be the potential issues?
It's already...
stressing me out, but then if you have to do that for something you cannot go back
to, that's just incredibly daunting.
If you think a code release is stressful, then imagine this.
Oh, yeah.
Oh my God.
But so fascinating.
Personally, what's your part in this project, for instance, in the Lisa
project?
Right.
I'm in charge of coordinating research on what we call
the stochastic backgrounds.
So the signals we've talked about so far, and predicted the ones we see by LIGO, are
what we call transient signals, meaning most of the time the detector actually
sees nothing, just noise.
And then from time to time, you have a rather relatively strong signal.
You see it, then it's gone.
So if that's your data analysis challenge, then you can calibrate your detector in
the signal-free moments.
You can learn all about your properties of the noise and you can have a good noise
model.
And then when you get a signal, you can kind of do a pretty good signal to noise
discrimination.
Now with Lisa, the situation is going to be very different because we're going to
have, because it's such a sensitive instrument, we're going to have lots and
lots of stuff going on all the time.
So we're basically not going to have signal free time.
So we're kind of.
dealing with kind of measuring all these different signals and the noise at the
same time.
And at the same time, the idea is that we might have stochastic backgrounds.
So stochastic backgrounds could, they're not transient signals, but there's kind of
more like a white noise, which is there at all times.
They could be coming from unresolved astrophysical sources, so unresolved black
or black or merges that are kind of out of the range of our detector.
So we can't individually detect them, but they just kind of contribute to some
confusion noise.
Or they could be these signals from the very early universe, which is, of course,
the ones that I'm actually after.
But so you have to kind of dig them out between all these loud transient signals,
between these possible astrophysical noise like signals, which look very, very
similar to the kind of cosmological noise like signal that you will be looking for.
And of course, the words are very, very similar to instrument noise that you might
have mismodeled or misunderstood.
So.
And what I'm working on is okay, a on on, okay, understanding the possible models
for these for these different components, in particular for the cosmological
sources, but also trying to understand how could we if we you know, actually get some
actual data, how can we actually disentangle all of these components?
And how can we really kind of make the most of the of the mission, extract as
much information as possible?
which with all these kind of overlapping signals and challenges.
Yeah, yeah.
And I'm guessing that having to do that, not in a few months is something you
appreciate.
Yes.
Yes, yes, yes.
Yeah, so there's many challenges out there.
Obviously, many people working on it.
And I mean, luckily, as you say, luckily, we don't have to solve this in a couple of
months, right?
Because we're basically also counting on things like computing power, and so on,
increasing new methods becoming available.
But, but yeah, so it's, but still, I mean, the development has to happen now.
Because if we kind of figure, okay, we need a certain type of
sensor or some certain type of output data that would help us to discriminate these
different signals.
We can't come along with that when the mission is already built or even worse,
already launched.
So you can't wait till you see the data to decide how you're going to do the
analysis.
You at least have to have a very good idea of how you're going to do the analysis
before you see the data.
And then maybe you can refine once you see the data.
Yeah, definitely.
Actually, this kind of work that you do in theoretical physics or that kind of
project you just described, it really involves the development of models, of
hypotheses, and I'm curious if you have some favorite hypotheses or models or the
most intriguing theoretical ideas.
that you've encountered in your field and that you'd like to see tested.
And if we could actually test them right now with our current technology.
Good question.
I must say, I don't have a particularly favorite model.
I don't feel, I don't know, protective ownership of any particular idea.
I'm more the type of person who I start working on something because I find it
interesting.
And then once I've understood it to a certain degree, I move on to the next
topic.
But I think there are a couple of kind of big overarching...
questions, right?
So kind of, yeah, understanding, getting some experimental input on what on what
dark matter is, would really help a lot on the on the theory development side.
As I mentioned, when we also have issues understanding the Higgs particle,
understanding in particular mass of the Higgs particle, which is potentially
indicating there's something we don't understand properly about quantum field
theory about
that I find is incredibly exciting, because it would really mean kind of,
okay, not an add on, you know, not a small extension of our existing model, but
really, completely revolution and how we think about things.
Yeah, of course, it also makes it much more difficult, right?
Because you don't even have the framework.
Maybe we don't even have the mathematical framework to think about this.
It's a huge step to take.
So I would, I mean, that's what would be a big step, right?
So I'm not sure if and how that's going to happen.
If it's even necessary, right?
Maybe the current framework is totally fine, but that would definitely be a
development that on just on the pure theory side, that would be very exciting
to see happening.
Yeah.
Yeah, for sure.
Definitely.
I kind of, I'm also really curious about that.
Actually, is there one big question that you would like to see answered before you
die?
Your one big question that you'd really like the answer to.
I think I really would like to know the answer to Dark Matter.
Just because that-
It's well, there's this we have many, we have many very reasonable models, which
can be tested and which are being tested.
So we could still be unlucky and nature could choose not one of these nice and
reasonable models, right, but something completely different.
But that that's a field where there are some very good suggestions and they can be
tested.
Now, unfortunately, there was one excellent suggestion, right, which was
supersymmetry and the dark matter particle that comes with supersymmetry would have
solved, was mathematically beautiful, would have solved a ton of questions, was
in many ways the perfect theory, right?
Unfortunately, we didn't find it.
So it could still be out there, but kind of not as a solution to all of the
problems that we hoped it would solve.
Because if that were the case, we should already have seen it.
Yeah, so something kind of being the ideal theory from our point of view, doesn't
mean nature actually cares, right?
Yeah, for sure.
And does it that way.
But yeah, so Dark Matter, I think it really has the potential that we could
actually find it.
And if we find it, that could really be a starting point of a whole new exploration
of questions.
Yeah, definitely.
And that's interesting that you mentioned dark matter too, because Kevin Clive, I
asked him the same question and he answered dark matter too.
So that's interesting to see that it's really something that's picking up in the
physics space these days where it seems like we're less, let's say we're more
hopeful that we can actually start making sense of it and probing
the universe in a way that will give us some answers, at least to this mystery.
Whereas dark energy, from what I understand, we understand way less about
dark energy than we understand about dark matter for now, right?
Yeah.
That's correct.
And also there we have much less, I mean, we see what it does on large scales,
right?
But we have also much less of an idea how to make progress.
Both on the theory side, there's kind of not these kind of clear cut models that
kind of say, okay, here's a good theory of why it is how it is, and here's how you go
test it, right?
For Dark Energy, we have neither.
Neither a clear cut theory that kind of says, okay, here's a good explanation, nor
any way of probing them really.
So it's a much, it's much more in the blur.
Yeah.
So hopefully.
In 10 days, you'll come back to the show and we'll talk about Dark Energy and the
latest progresses.
Valerie, I think I have so many more questions, but you've been already very
generous with your time.
Before closing up, is there any topic I didn't ask you about and that you'd like
to mention?
I think we covered a lot, but nothing particular comes to my mind.
Okay.
Well, then I think we can call it a show, but as usual, before I think you go, I'm
going to ask you the last two questions I ask every guest at the end of the show.
First one, if you had unlimited time and resources, which problem would you try to
solve?
Yeah, that's as I said, that's actually a really tricky question because we are in
this in this situation that I find it very hard to pinpoint.
where is the weak point of the standard model?
Where should we poke it?
Right?
So from the pure theory side, without any experimental input, I feel like if I had
unlimited time and resources, I wouldn't engage on a single project right now.
But I would basically just try and, you know, gather as broad as possible
understanding of
as many concepts as possible and hope that we will eventually get some sort of data,
which points us in the direction we need to explore.
I don't at the moment really have a clear cut avenue where I say this is where I
would put all my money.
Yeah.
So wise answer where you don't put your eggs in the same basket.
And second question, if you could have dinner.
with any great scientific mind, dead, alive or fictional, who would it be?
Yeah, I think, well, we'd go for somebody dead, right?
Just because that's a chance you don't get on a regular conference dinner.
So I'd be really curious to talk with some of the people involved in the discovery of
quantum mechanics.
So say Heisenberg or somebody like that.
Because I feel like they were kind of...
at the core of the field, when the field was also in a situation where it was kind
of not so clear cut, at that time, not even clear cut that it was a need to kind
of extend the current understanding because classical physics was well
understood, right?
And nearly all phenomena were very well understood.
And people were thinking, okay, you know, physics, it's done, you know, we
understand nature.
And it was just kind of very small.
tweaks here and there, right, that kind of were a bit confusing.
So one could have easily believed everything is done and understood, go
study something else.
But they kind of opened the door to the world of quantum physics.
And with that then came quantum field theory, with that came kind of elementary
particle physics, with that came kind of all the questions that we have today.
So actually, from today's point of view,
we would say, well, they understood very little, right?
It was a whole bunch of new physics that was kind of not known to them, but they
didn't even know that it was not known to them, because there was kind of no glaring
open question.
So I'd really be curious to know how they perceived that situation and how they got
to the point of opening the door to the quantum world and taking up that
challenge.
Yeah, yeah, yeah.
Yeah, definitely sounds like a very fine dinner.
Please invite me.
So, well, awesome.
Thanks a lot, Varyry.
That was absolutely fascinating.
We didn't talk a lot about stats, but I love doing these episodes from time to
time, you know, where we de-zoom a bit from stats and just talk about fascinating
science in general.
I think it's very interesting and also quite important to put more rigorous
pedagogical scientific content out there in the world.
We've seen that in the recent years.
So thanks a lot for doing this for us, Valérie.
I will put a link to your website in the show notes for those who want to dig
deeper.
Also feel free to add any link to cool papers or experiments or videos that you
think listeners will appreciate.
And thank you again, Valérie, for taking the time and being on this show.
Thank you.
And rest assured that stats is still at the basis of all this, despite that we
took a more high-level approach in this discussion.
Yeah, for sure.
Well, thanks a lot, Valerie, and see you soon on the show.