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 Valerie Domcke, 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, Valerie can be found on boats, as she’s a big sailing fan.
Our theme music is « Good Bayesian », by Baba Brinkman (feat MC Lars and Mega Ran). Check out his awesome work at https://bababrinkman.com/ !
Thank you to my Patrons for making this episode possible!
Yusuke Saito, Avi Bryant, Ero Carrera, Giuliano Cruz, Tim Gasser, James Wade, Tradd Salvo, William Benton, James Ahloy, Robin Taylor,, Chad Scherrer, Zwelithini Tunyiswa, Bertrand Wilden, James Thompson, Stephen Oates, Gian Luca Di Tanna, Jack Wells, Matthew Maldonado, Ian Costley, Ally Salim, Larry Gill, Ian Moran, Paul Oreto, Colin Caprani, Colin Carroll, Nathaniel Burbank, Michael Osthege, Rémi Louf, Clive Edelsten, Henri Wallen, Hugo Botha, Vinh Nguyen, Marcin Elantkowski, Adam C. Smith, Will Kurt, Andrew Moskowitz, Hector Munoz, Marco Gorelli, Simon Kessell, Bradley Rode, Patrick Kelley, Rick Anderson, Casper de Bruin, Philippe Labonde, Michael Hankin, Cameron Smith, Tomáš Frýda, Ryan Wesslen, Andreas Netti, Riley King, Yoshiyuki Hamajima, Sven De Maeyer, Michael DeCrescenzo, Fergal M, Mason Yahr, Naoya Kanai, Steven Rowland, Aubrey Clayton, Jeannine Sue, Omri Har Shemesh, Scott Anthony Robson, Robert Yolken, Or Duek, Pavel Dusek, Paul Cox, Andreas Kröpelin, Raphaël R, Nicolas Rode, Gabriel Stechschulte, Arkady, Kurt TeKolste, Gergely Juhasz, Marcus Nölke, Maggi Mackintosh, Grant Pezzolesi, Avram Aelony, Joshua Meehl, Javier Sabio, Kristian Higgins, Alex Jones, Gregorio Aguilar, Matt Rosinski, Bart Trudeau, Luis Fonseca, Dante Gates, Matt Niccolls and Maksim Kuznecov.
Visit https://www.patreon.com/learnbayesstats to unlock exclusive Bayesian swag 😉
Links from the show:
- Valerie’s webpage: https://theory.cern/roster/domcke-valerie
- Valerie on Google Scholar: https://scholar.google.com/citations?user=E3g0tn4AAAAJ
- LBS #93 A CERN Odyssey, with Kevin Greiff: https://www.youtube.com/watch?v=rOaqIIEtdpI
- LBS #64, Modeling the Climate & Gravity Waves, with Laura Mansfield: https://learnbayesstats.com/episode/64-modeling-climate-gravity-waves-laura-mansfield/
- LBS Physics Playlist: https://learnbayesstats.com/physics-astrophysics/
Episode 95 is another instalment of our Deep Dive into Physics series. And this time we move away from the empirical side of this topic towards more theoretical questions.
There is no one better for this topic than Dr. Valerie Domcke. Valerie is the second researcher from the CERN we have on our show. She is located at the Department of Theoretical Physics there.
We mainly focus on the Standard Model of Physics, where it fails to explain observations, what proposals are discussed to update or replace it and what kind of evidence would be needed to make such a decision.
Valerie is particularly interested in situations in which the Standard Model brakes down, such as when trying to explain the excess gravitational pull observed that cannot be accounted for by visible stars.
Of course, we cover fascinating topics like dark matter, dark energy, black holes and gravitational waves that are places to look for evidence against the Standard Model.
Looking more at the practical side of things, we discuss the challenges in disentangling signal from noise, especially in such complex fields as astro- and quantum-physics.
We also touch upon the challenges Valerie is currently tackling in working on a new observatory for gravitational waves, the Laser Interferometer Space Antenna, LISA.
This is an automatic transcript and may therefore contain errors. Please get in touch if you’re willing to correct them.
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
We'll also see how the study of gravity
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
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
When she's not trying to decipher the
mysteries of the universe, Valérie can be
she's a big sailing fan.
This is Learning Vagin Statistics, episode
95, recorded September 6, 2023.
Hello my dear Vagins!
Some of you have reached out for advice
and coaching in parallel to my online
courses on intuitivevagin.com.
So, to help you, I have started something
If you go to
You can pair your online course with my
15-hour or 20-hour coaching packages to
get a fully premium learning path.
Each week, we'll get on a one-to-one call
and we'll walk through any questions,
difficulties, or roadblocks that you may
have to jumpstart your learning even more.
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
Glad to be here.
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.
We're going to talk about topics.
a bit different than those we talk about
when we have experimental physicists on
So that's cool, more diversity for the
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
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
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
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
You know, that's not how it works,
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.
I would also say that you kind of have to
dream about or be enthusiastic about it,
because doing science, you always
encounter moments when nothing works.
And if you're not passionate about
actually solving the problem, it's, you're
just going to get stuck.
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 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
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?
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
But that's not at all what my day looks
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
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.
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
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
Yeah, so small topics, fundamental
building blocks of nature.
I'm actually curious.
So of course, we're going to talk about
the projects you work on a day to day a
But also I'm curious now that you brought
up basically what your days look like
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
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.
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
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
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
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
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
Yeah, because I'm more work at the kind of
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
Just because you don't use patient stats,
Valery doesn't mean that your work is not
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
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
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
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
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
But we still know the model is not
And the reason we know that the model is
not complete basically comes from
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
And we have a rough idea of what these
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
Why does the standard model fail here and
how can we actually explain these
So concretely, what does that research
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
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
And they were they were looking at kind of
how fast the stars were rotating, which
you can do by measuring the redshift of
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
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
And so that's just Newton dynamics, high
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
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
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
So it's not that there's none of it on
It's just that it's so incredibly weakly
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
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
in the K channels, or you basically have
some sort of, not a collider, but
basically just a very big detector volume
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
to have one of these very rare
interactions with one of the atoms of your
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
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.
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
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
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
So you're part of these big teams, right,
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
So you in this kind of work, what do you
What do you bring?
So the papers really with like the many
hundreds of authors, they're usually the
As a theorist, you know, I usually have
whatever, two, three, four, co-authors on
That's a lot.
So we build, of course, very heavily on
the results of these big collaboration
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
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?
So that can be experiments like the chart
It can also be some astrophysical
observations, or it can be some
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
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
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.
So that's actually fascinating.
So yeah, talk to us a bit more about that,
What can gravitational waves tell us about
And maybe redefine quickly what
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
So these are like extremely massive
And as you might know, a massive object
kind of creates if you want a dent in
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
If you're very close to a black hole,
right, these ripples will be quite
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
So, by the time these gravitational waves
reach us, they've kind of spread out very
far, meaning the amplitude is very much
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
But nevertheless, compared to the lifespan
of the universe, these are still fairly
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
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
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
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
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
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
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
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,
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.
Or anything else that breaks spherical
So kind of, I don't know, you dancing
That will in principle generate
They're just very, very small.
Yeah, I see.
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
So some sort of violent process, which is
condensing a lot of energy, a lot of mass.
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.
So the, the gravitational waves that we
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
So it's a huge amount of energy.
And now the gravitational waves that we
think we might have seen with these pulsar
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
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...
That's, that's a broad question, right?
I mean, there's different levels of
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
That means, of course, building
experiments that are extremely precise
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,
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
The other challenge may be more on the
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,
Which you kind of hope is a good
principle, though, of course, you never
know that that's a good principle.
And recently, that's really been a bit of
a challenge, precisely because the
standout model works as well as it does.
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
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,
So the last missing particle of this then
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
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
So yeah, there's many, many questions,
many levels of questions that can be
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
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
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
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
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
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
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,
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
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.
I didn't know that black hole stayed
spherical even as they approach each
Is that because they are so dense that
they cannot be deformed?
Yeah, it's basically because they are so
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.
And it's crazy that we're actually seeing
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
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
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
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
But the universe as a whole is actually
So in most of the universe, there's just
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
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,
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
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
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
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
And energy basically comes from
observations that it has this effect of
driving the energy of driving the universe
So it acts as a type of energy in the
expansion history of our universe and
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
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
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
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.
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.
We go back to when everything was really
kind of just this hot primordial soup of
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.
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
So a big, big project I'm involved in,
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
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
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
Yeah, that makes sense.
Also, although I'm guessing the sun can be
noisier at times.
Right, but it's all a question of
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
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.
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
And so what's the ETA on this mission?
When will the satellites go up
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,
Yeah, I mean, it's not in the orbit,
You cannot find it, send anybody to repair
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?
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 my God.
But so fascinating.
Personally, what's your part in this
project, for instance, in the Lisa
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
And then when you get a signal, you can
kind of do a pretty good signal to noise
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
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
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
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.
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.
And I'm guessing that having to do that,
not in a few months is something you
Yes, yes, yes.
Yeah, so there's many challenges out
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
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
We can't come along with that when the
mission is already built or even worse,
So you can't wait till you see the data to
decide how you're going to do the
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
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.
I must say, I don't have a particularly
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
And then once I've understood it to a
certain degree, I move on to the next
But I think there are a couple of kind of
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
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
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, for sure.
I kind of, I'm also really curious about
Actually, is there one big question that
you would like to see answered before you
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
But that that's a field where there are
some very good suggestions and they can be
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
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?
And also there we have much less, I mean,
we see what it does on large scales,
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
In 10 days, you'll come back to the show
and we'll talk about Dark Energy and the
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
I think we covered a lot, but nothing
particular comes to my mind.
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
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
Where should we poke it?
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
as many concepts as possible and hope that
we will eventually get some sort of data,
which points us in the direction we need
I don't at the moment really have a clear
cut avenue where I say this is where I
would put all my money.
So wise answer where you don't put your
eggs in the same basket.
And second question, if you could have
with any great scientific mind, dead,
alive or fictional, who would it be?
Yeah, I think, well, we'd go for somebody
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
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
And nearly all phenomena were very well
And people were thinking, okay, you know,
physics, it's done, you know, we
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
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
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
Yeah, yeah, yeah.
Yeah, definitely sounds like a very fine
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,
I will put a link to your website in the
show notes for those who want to dig
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.
And rest assured that stats is still at
the basis of all this, despite that we
took a more high-level approach in this
Yeah, for sure.
Well, thanks a lot, Valerie, and see you
soon on the show.