So I'm going to...
I play around with the titles of my talks a lot and so maybe
I'm a little too
old for the crowd, but I decided I wanted to make a field of dreams reference because I'm a big baseball fan and
What I really want to do is give people a sense of why cosmology is exciting rather than focus on the very specific details
Exactly the thing that I do but I do want to encourage people if I say anything that catches your interest feel free to
Come talk to me afterwards or even you know send me an email. I'm if you would like to
So first of all, what do I mean by
Cosmology? So I think of cosmology as storytelling
I think that humans are natural storytellers and so what we really like to do is figure out.
Sequences of events, and I think that whether you're a novelist, or you're a theoretical physicist or you're a condensed matter
Experimentalist what you're doing is creating stories and so in particular
I think is the best story in the universe and I am biased this is an okay bias to have
is the cosmological story and so what you're looking at here is a
Timeline from what we might call the big bang
And I say might because there's now a lot of debate about whether we live in an eternally inflating universe
so what we might call the big bang all the way up until
about here
So this is obviously not to scale
And so along the way the questions that we were asking are things like how did particles come into existence
How did space-time come into existence? What is the dynamic between particles and space-time?
I would say if you could pick one thing that perimeter institute does it's think about what's the dynamic between particles and space-time?
Um and then how do we get from whatever weird particle soup singh to this room today?
To me that's all cosmology. I don't really see the same distinctions.
of disciplined that other people do
So to put this in very basic terms, what are a few things
We think we knew about the universe?
And I'm going to hedge and say we think we know because our
Paradigms are always ready to be blown at by someone who has a better one right and so this is for example. What Einstein did
I'm so we think that we knew that we live in an expanding universe and so that's one of the reasons that the previous slide
Is not to scale and when we say expanding universe so probably all of you have heard I'm some kind of like race car analogy
That galaxies are racing away from each other
so I actually think this is not a great analogy and we have a much better one and
Because actually what's happening is way cooler than that
So if you imagine a balloon, and you think about putting little Magic dots on the balloon
So it hasn't been blown up or anything, and then you blow up the balloon and the dots all stay the same size
But the balloon keeps getting bigger, so the space between the dots is larger. That's really what's happening?
It's not so much that galaxies are flying away from each other, but rather that the space time between galaxies is continuously growing
So we live in this extraordinary universe
Where space time continues to grow between these objects that we live in?
So a couple of other things that we know we think we know about the universe and this is kind of known as the cosmological
Principle is that we live in a homogeneous and isotropic universe
And so what homogeny really means is that you can go anywhere in the universe, and it will essentially look basically the same
So obviously we're in this room. It's pretty diverse
So that's not true to all scale, but it's true what we would call cosmological scales
And isopotry means that you can stand in any spot in the universe and no matter what direction
You look in things will look about the same
So this is these are kind of two operating principles and frameworks that we work in with cut in cosmology, but of course
The question is how does the universe get this way?
It's one thing to say is this way but in physics were always interested in why and in particular
How do you get such a large universe to look the same no matter? Where you stand?
And what's the same in all directions?
So just to talk about one thing that I have worked on so we have something called inflation
So I like this this slide in particular for kind of a dorky reason
But I think it's particularly important for the students
I hated freshman physics like Super Super super hated it and
If I didn't already want to be a cosmologists totally would have dropped out of the physics major like big time cuz I hated
Freshman Physics
I'm and what I really wish someone had told me is that when you think about things rolling down on ink lines and you're plotting
Your potentials and all of the things that seem really like like how is this relevant to my life or anything cool in physics?
That actually you're going to spend the rest of your career pushing things down potentials
And so actually the reason freshman physics is really important is because it really lays the conceptual foundation
So I just want to plug that for anybody who was thinking like God mechanics really suck I agree
I'm also now a phd holder in physics. It's worth sticking it out
I'm so the idea behind inflation. Is that we have an era of rapid expansion
Driven by a particle that we creatively call the inflaton
We're not that creative sometimes, and after inflation ends this inflaton oscillates on its potential and so
What you can think about is that you can really think of this particle?
It's kind of like a ball rolling down an incline right and the potential energy is changing the kinetic
Energy is changing and that this causes the universe to expand very rapidly and this rapid expansion
Allows the universe to become homogeneous and isotropic
So this is the general picture that we think we have and then after inflation ends
We often don't talk about this and I realized I had my phd and had never thought about what happens to be in inflaton after
the end of inflation
Right so I just want to point out that if you've never asked this question. I had a phd in neither had I
So I started working on an era called re-heating. Where you think about
What is the particle?
Production afterwards what happens to this whole ball rolling down in incline does it just stop when it gets to the bottom um?
Is there an incline on the other side is it rolling back and forth and what does that mean for the structure of the universe?
So another way I like to reframe the question and the idea
Working on a storyline in physics another version of that first slide that I showed you about cosmology is this timeline
So you have time running forward here in seconds you have temperature going up here
and you have energy going up here and
So essentially what you're looking at is the thermal one way of thinking about
Cosmology is that we're trying to fill in the thermal history of the universe and so you can imagine
the universe might start very very hot because things are very condensed and
whatever your favorite big bang analogy is and then you think about space-time expanding very very rapidly and
You imagine it must cool down right and so this is the era of inflation that I was just talking about
but we know from
observational Data that in order for Big bang nucleosynthesis
and
early Hydrogen formations you occur but the temperature actually has to be warmer than what you might expect at the end of inflation and
so this is the era of reheating and I have
For the last couple of years been working on the era of preheating which is a very early
Time period Where energy is transferred from the input onto other particle field
so I like to highlight this because
Preheating is a problem. That's basically completely unsolved reheating is completely unsolved
We don't know how to calculate how you get from here to here
So this is an open question that I hope some of the students in the room will consider working on
So what is another way to think about this cosmological storytelling that we're doing and what we're trying to accomplish
well
this is the planck map, so this might look familiar to a lot of people because
It's pretty much ubiquitous and in PR for cosmology astronomy and physics
So this is a map at the universe when it was about
380,000 years old so this was like. I don't know
I am the universe is like learning to walk and maybe still puking on you when you burp it
I'm and so you notice that there are some blue
There's some orange still with the color differential for you, so basically this map is
Isotropic it's homogeneous
The differences in color are one part in 10 to the 5 these are very small differences
And we're looking at temperature, so these are small small small very small variations in temperature
But these variations in temperature are also where we begin
These are the seeds of structure formation in the universe
So I said earlier that you could think about your question being what is the thermal history of the universe?
But you can also think that your question is
Where do what are the seeds of structure formation and how does that get us, but where do we begin?
So I
Have spent my entire career being kind of a fence sitter between astronomy and physics
So in fact I started a phd in astronomy at UC
Santa Cruz, and then was lured away by Lee Smolin to come to the perimeter institute
To move I'm to do theoretical physics and I have to say like that
I went to him because I wanted to be lured away, so I'm that's not entirely on him
I am but with that what I find interesting
Continuously living in that world between physics and astronomy is how astronomers and physicists can ask the same questions
But in completely different ways and that provides and exciting, but also sometimes extraordinarily
Frustrating challenge for cosmologists, so this map is really like astronomers wonder ok, how do I make this map?
How do I interpret this map?
So these are those who work in theoretical physics and in particle physics think about that map completely differently?
So this is the theoretical physics version of this map
Which is to ask where do particles come from because that's really what we're trying to understand. So again I mentioned that
one of the driving questions at PI
is are they inextricably tied to space-time at the quantum
Gravitational level and this is something that I thought about quite a bit as a phd student
So we also think about things that you might have heard about fields
So I just kind of wanted to mention if I slip and I'm say field instead of particle
What do I mean by that so they mean as there are quantum fields? They're everywhere and when they get excited
You can think of a particle as an excitation of one of these fields
So another way of asking that question of where do these thermal variations come from where did these speeds of structure formation?
Come from is to ask
How did you get so excited that it led to structure formation?
But it eventually produces
stars and galaxies which and stars which have solar systems and solar systems with planets
That are right in the correct ziran for water formation and carbon life to arise so again for me
This is still a question of how do you make this room even though?
I'm mostly interested in the very very early stages of that process
So another way of asking this question is to just say, what is the universe made of right?
And I think that this is you know, maybe the more popular science version that were used to hearing so let me start by
Talking about this slide by telling a story
so the summer after my freshman year of college, this was back in 2000
I Went to see a talk by the esteemed cosmologists Rocky Kolb while I was doing research
I'm at the university of Chicago and at fermilab and Rocky said we live in a very exciting time for cosmology
because we basically figured out what the universe is made of
We know that it's about three-quarters Dark energy
We know it's about a quarter dark matter, and it's only a smidgen every day stuff like us
I'm a so this is very very exciting. We're basically done
We just have to figure out with Dark energy and Dark matter is and we'll be done
Right so I told you guys the timeline this was in 2000, right?
Thank God. He was totally wrong about it. I'm just being an easy problem because otherwise I wouldn't have things to work on right?
So I so work on this question of what is the dark matter and I have to say in the 17 years since Rocky gave
That talk we've made basically made zero truly significant progress
I'm figuring out what these two things are, and so I don't think that that makes us failures as physicists
I think that that just means physics is hard and the time scale is long and that this is one of the reasons why for
Example our governments need to have faith and just simply invest in us doing the work
because it's not going to happen on the time scale as an election or
Whatever your priority is might be right um
So I also want to make a comment about how we called
I'm the stuffed like us like everyday matter or normal matter
So if you look at the pie chart quite evidently we are not normal, right
I mean, we're women and non-binary people and trans people in physics. So we're not normal anyway some sense right I'm
But really the everyday stuff in the universe is dark matter and maybe dark energy. We still weren't even really native dark
Energy is the right description um and Voids actually space is mostly empty
So what's normal is emptiness was abnormal is that we came to be?
People talk a lot about dark matter. I saw a claim by a theoretical physicist whose name
I won't mention that um Dark matter was like foreboding and scary to people, so I've never actually
Experienced anyone who wasn't physicists make this claim to me about dark matter being foreboding and scary
But let me like clear the air in case there's anyone in the room feeling
frightened
So what is the case for Dark matter?
One of the reasons that I like working on Dark Matter by the way is that it was discovered by a woman, Vera Rubin
Who really should have won the Nobel prize, and I have like zero basis for this comment
But I have often felt that the nobel committee was waiting for her to die and they succeeded she died in December
On Christmas day in fact.
so the basic idea behind
Dark matter is that apparently we need more mass than we can see so again paying attention to our freshman physics class if
you think about the physics of rotation you remember that there is a relation between
How fast something is rotating and how much mass there is in it, right?
So you can actually?
Astronomy is very much like detective work if how do you map everyday physics on to stuff you see that's really far away
um and so
Vera went and looked at how fast stars were rotating in the galaxies and how much mass you would expect?
to be in their stars based on their rotation and
compared it to how much mass you would expect to be in their stars based on how much light they were emitting and
discovered that there was a Mismatch and
So she was not the one who came up with the dark matter paradigm
But she was really the first person to come up with compelling evidence for its existence
Of course there are two ways of looking at this piece of data
So either we are measuring the mass wrong
Or we need to modify gravity because we're filtering our data through the wrong
theory this is one of the reasons that it's actually very important to have a strong dynamic between observers and theorists and
Because this is a conversation that we continuous we have and I modified gravity is actually quite an active research program at perimeter
but I would say the majority of people in the community think of dark matter
As is the primary candidate and really when we say dark matter? We just mean but it's something that produces new lights and
Often you will hear people say that it's only interaction of Via gravity so I want to be clear
actually it's only significant interaction is via gravity we hope very very much that it has mild
interactions with other what we keep calling everyday particles because that's how we do dark Matter Detection experiments and
These are experiments that Canadian and American teams are involved in so this is something that I'm you know as a continent
we have invested in
so in the meantime
Over the years theorists have had a few ideas
About what dark matter might be?
So what you're looking at is the venn diagram to end all venn diagrams. This is the best venn diagram
You're ever going to see in your life, and I will fight anybody who argues with me about that.
And I have to say I can't even take credit for it. I really wish I had come up with this idea
This is why I'm Tim Tate. He's a phenomenologist at the university of California
so these are different theories of Dark matter, so you
know an
Experimentalist annoying problem of not being able to find a particular phenomenon
is like every theorist dream opportunity because it means that they can come up with every wild model that they can think of and
Publish about it and go run and tell people that their right and the observers don't have any evidence to tell them that they're wrong
So they get to just walk around telling people that they're right.
I'm not that kind of theorist, but there are a lot lots of those out there
but I just want to highlight a few things so you'll see
MSSM here, which is the minimally supersymmetric model?
So those words might not be familiar to you
But I'm sure many of you have heard that the large Hadron collider has been looking for supersymmetry
So we don't often make that connection, but Supersymmetric particles are potential Dark Matter candidates
you'll also see
theorists love the higgs you can make the higgs do anything
so people try and make the higgs be the inflaton
People at various points try to make the higgs be dark matter
when they realize that the higgs couldn't be dark matter they just modified the higgs to the little higgs to
Create a higgs that should be the dark matter. This is basically how doing theoretical physics work, so if you like kind of like, I'm
you know
Fixing broken things with calculus then theoretical physics is the job for you.
You'll also see something called sterile neutrinos here these are not the neutrinos that we've seen because neutrinos are not massive enough to be dark
Matter so what do you do when the particle doesn't do what you want you just make another one like right? so I
Have spent a lot of the last two years of my career living in this corner in the quantum chromodynamics
Accion Corner
and
Rather than tell you guys anything in detail about the acción otherwise other than it is your favorite dark matter candidate officially
Nobody tell me anything different until this conference is over and even then maybe keep it to yourself.
But so we have all of these models of dark matter
What do we do right like how do we tell the difference?
How do we start to make these distinctions?
So one of the things that were the years we thought about is what are the different types of phenomenology?
so a
Phenomenology that we're very well aware of in the laboratory
And I think that I'm people here at the IQC and in surrounding.
laboratories think about a lot is
To ask the question is is bose-einstein condensates. It's a one question you can ask is what if dark matter forms bose-einstein condensates?
does this produce an
unusual
Observational Phenomenology that we can then go out and look for with our hubble telescope with the James webb space telescope
that's going to be launched next year
So, what is a bose-einstein condensate?
so these are atoms or subatomic particles that are cooled to a critical temperature and that critical temperature is going to be determined by the
density of the Particles and also the potential that it's in and
Basically what you get is an unlimited number of Bosons
Sharing the same ground zero mode state so they start to act like one super particle one Super atom together
And so you can imagine already
that this might produce unusual
observational Impact that other particles will not have
So I just want to kind of give another kind of intuition
For whatever is Einstein condensate is so you think when when things were basically room temperature the particles are like billiard balls
and they're just bouncing off of each other and
Then as you get to lower temperatures you have to start thinking of them as a little bit quantum mechanics
So they're like little de Broglie wavelength right, so you just your little waves floating around
And then as you hit the critical temperature for Bose-Einstein condensate these wavelets start to add together coherently
Into one single wave so you can think of it in some sense as a coherent wave and if you can get to absolute zero
Then you can get a perfect Bose-Einstein condensate
So another way of putting this is that what we've been thinking about is quantum blobs and space
so we're the axion comes in the axion is a particle
And why it's your favorite dark matter particle everyone raise your hand. It's your favorite, right?
Yes, okay.
the axion actually solves another problem in the Standard model of physics
That's an outstanding problem. It's known as the strong CP problem
I won't get into it except I will say that it comes out of a mechanism
I'm developed by Roberto Pecchi and Helen Quinn. It's one of the very few things in theoretical physics named after a woman
She was actively involved in its production
So Pierce Zichivi and and a member of his group proposed in 2009 that the axion
Must form a bose-einstein condensate in the early universe
and basically the community has been trying to figure out whether pierre is right or not ever since and so this is something that I've
Been working on for a while and one of the questions that has come up
So when we talk about a bose-einstein condensate in the lab?
We're thinking like lab scale things that you can put on like an optics table that are fairly small, right?
But they're talking about something that might be galaxies size
So these are tens of kiloparsecs in scale and so you can think of a giant quantum blob
Might be surrounding us a completely invisible to the human eye giant quantum blob
So that's the kind of thing that we start to think about in the dark matter community um, so I'll just mention
Because you know it's not really a physics talk unless the physicist has plugged their own paper.
One of the questions that we were very much first interested in is whether dark matter.
axions form a bose-einstein condensate and then what the scale is and so actually
Sort of one of the big tensions in the community right now is that we think they scale is small like
Asteroid size or as my friend Anna Watts has been calling our little blobs "axtroids"
and so I gave the archive number here. This was a
Editors selection and physical review D a few years ago. It's a paper. I wrote it with I'm my postdoc advisor
Alan Guth and with Mark Hertzberg who's now at tufts
So I just want to wrap up by making a couple of comments
It's easy to get the physics talk and make it seem like doing physics is really all about
Making things up with calculus which is kind of what I said right? But there's actually a human story behind every physicist
trajectory and everybody's life
so these are some of the things that I have worked on and these are the
Institutions that I have gone through while I was working on them
So I'm sure you guys will notice that I've mentioned perimeter institute a bunch of times
I was a phd student here at the University of Waterloo.
and in addition to
Having kind of this trajectory. I wanted to get engaged some images of what I was up to you
And how I looked during the time that I was doing these things
So I picked the picture
from every stage of my academic career so starting with Freshman Chanda
so this was me at Harvard college as a freshman in my dorm room
with my very first camera that had a flash
this is me at the National Society of Black physicists meeting
after a long day of organizing sessions. when I was a graduate student at Santa Cruz
This is me just a few months after I arrived in Waterloo
And I think that this photo was taken as I was heading out with I'm what we used to call the glue mouse
To a gay club, so for me being part of the gay community at Waterloo was a really important thing.
This is me at the National Society of black physicists in 2011 I was coaching the conference that year and also
Organizing sessions, so I was a postdoc at NASA at this point
This was taken at my house
warming party in Cambridge when my husband, and I bought our home and when I was a postdoc at mit
And this is me giving a philosophy talk at the university of London just a couple of months ago
I'm so I also know you work in philosophy
And so I just kind of wanted to throw it there are various things that I did along the way I
didn't just do calculations and
So I mentioned NSBP. I was involved in queer organizing for the American astronomical society
I was vice president of the graduate student association here as well as at Santa Cruz
I recently won a 100,000 dollar Grant to study intersections of knowledge production and marginalization
from a philosophical perspective
And I really want to highlight one of the things that I had to develop during this time period Was an internal
Confidence that these were all important contributions to physics
Because I certainly wasn't going to be professionally rewarded for them
I get invited to come and speak at wonderful conferences like this one, but it's also the case that behind closed doors hiring committees
Or telling me you shouldn't be doing these things right. It's an interesting Mismatch between public and private
priorities and the Physics community
so the last thing that I want to mention about this is that one of the things that I did along the way I was
Perimeter's First Black North American graduate
I'm I was also possibly Waterloo physics as first Black North American Phd and
and unfortunately Canadian institutions are terrible about tracking this important Data and
Celebrating barrier Breakers, so I in fact don't even know and it was something that nobody ever discussed with me or said congratulations
Or that's an important moment for North Americans
So I just really want to highlight these are the things that we do along the way
Even if people don't tell us that we are doing them
Thank you
