What are cosmic strings?

Learn about cosmic strings with Daniel and Jorge.

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Episode Transcript

Speaker 1 (00:08):
Hey, Daniel, I have a question for you about how
physics works. All right, shoot, yeah, what happens when it
doesn't work? Like what happens when you're wrong? That really
depends depends on what how wrong you are. No, it
depends on whether you're an experimentalist or a theorist. It

(00:29):
makes a difference. Oh yeah. For an experimentalist, if you
are wrong one time, it's like a career death. It's
like getting caught from murder. You know, once is enough
to send you away forever. You murdered science. If you
if your results are wrong, you murdered your credibility. But
not for a theorist. Like if a theorist is wrong,

(00:49):
there's no consequence. No, almost every single paper written by
a theorist is wrong, and in fact, if they are
right even one time, they win. The Nobel problem does
sound like better? Odds, Daniel, Why did you even become
an experimentalist? I asked myself that question every day. I

(01:23):
am Jorge make cartoonists and the creator of PhD comics. Hi,
I'm Daniel. I'm a particle of physicist, and though I've
never been wrong in a scientific paper, I have zero
Nobel prizes, No wait, that's not actually true. I do
have a tiny slice of a Nobel Prize. Well, you
could be wrong about having a Nobel Prize, like you could.
I could write a paper about having a Nobel Prize

(01:44):
and they'll be wrong and then get a Nobel Prize
for it in literature maybe. But anyways, welcome to our
podcast Daniel and Jorge Explain the Universe Even the Wrong Parts,
a production of I Heart Radio, in which we take
a trip around the universe, giving you a tour of
everything that's amazing, everything that's exciting, everything that's real, and

(02:04):
everything that's theoretical. Not just what's out there in the universe,
but what's inside the minds of scientists, what they're hoping
to discover out there in our universe. That's right, We
take you on a trip across the cosmos, not just
to see what's there, but what might be there. What's
physicists think might be the next big idea that could

(02:25):
revolutionize how we understand the universe. And we have a
special group of people whose job it is just to
come up with crazy ideas that might describe our universe.
You have a group of people just to be wrong.
Is that kind of how it works. They only have
to be right occasionally. But yeah, basically, just throw ideas
out there. It's like the brain, the brain trust. Yeah,

(02:48):
it's like a brainstorming, you know, like maybe the universe
works this way. Go check. Oh no, I guess not.
Maybe the universe works that way. Go check. Oh no,
I guess not. Keep coming up with ideas, folks, Yeah,
because the universe is pretty crazy out there. You know,
there are a lot of things that we didn't expect,
and so as crazy as an idea might seem right now,

(03:09):
it could be right. Yep. Absurdity is no obstacle to reality.
I mean, you can't take a theory of physics and
say that's too crazy, because some of these crazy ideas
turned out to be real, you know, quantum mechanics and relativity.
There have been moments in history when we had to
accept things that were very difficult to swallow, and that

(03:30):
means we need to keep our minds wide open to
future crazy ideas. Yeah, you could be absurd and be
right at the same time. That's the situation of the universe.
That's your review of the Universe on its Amazon web page.
Absurd but right, absurved but true. Five stars. Yeah, that's
kind of like this podcast a Cartoonists and physicism physics

(03:53):
for an hour, And I wonder what that's like sometimes
for a theorist, because I'm not a theorist. You know,
you spend your life coming up with ideas maybe there's
this particle, maybe the universe works that way, and and
predicting them and suggesting ways to check but almost never correct. Right.
Most theorists who write papers, most of their theories don't
even get checked because we can't check all of them,
and when they do, mostly they just get ruled out. Yeah.

(04:16):
I guess there are a lot of theorists out there
and they can't all be right right, and they can't
all be checked. So how does how do these ideas
come through to get checked? Yeah? Well, if you're a theorist,
you have some crazy new idea, you say, I think
the universe works this way, and then you have to
make a prediction. You have to say, well, if somebody
did such and such experiment, they could verify my theory.

(04:39):
Like Einstein had his theory relativity, and he predicted something
would happen when light bent around the sun or when
light bent around the moon during an eclipse, so it
make a very specific prediction. Then the key is you
have to find an experimentalist someone to do that experiment
and check your prediction. If you can't convince anybody that
your prediction is worth checking, it just doesn't get checked.

(05:01):
Is there like an app for physicists to match experimentalists
with theories, you know, like a dating app physics or
or checker. Yeah, I'm not sure. Um, you know it's
sort of arbitrary. You know, experimentals will read a paper
and say, oh, that's really cool, I want to check that.
Or me as an experimentals, I'll go to conferences and

(05:22):
talk to theorists and hear about the new ideas and
try to think about what's most interesting to test. Because
you can't test everything, you have to make your choices. Yeah,
I guess you swipe left or right depending on whether
you think it could be right or what are you
based on? Like is it is it? Are you tempted
by like, oh that would be a big fish to catch,
or are you tempted by like is this an easy

(05:44):
fish that I could verify? Well, that's a great question.
I'm a bit unusual in particle physics. Most people choose
theories that they think sound sort of aesthetically beautiful, like
supersymmetry and gravity and all these things. They have like
a deep fear redical reason to motivate that theory, like
why we think it exists? Um. For me, I'm more

(06:05):
interested in stuff that's uh going to be a surprise,
Like I'd like to look for something that isn't predicted,
So I try to do experiments that nobody's predicted, because
then if you see something new, a new particle, then
you get to be the first person to describe it,
and it sort of comes out as a pleasant surprise
for the community. So it is like a dating app.
You swipe left or right if it's like, oh this

(06:26):
is beautiful, I like it, or on this floats my boat,
I'm gonna swipe it. All right, You're right, I give up.
Physics is just like a dating app. It's basically the
same thing. Well a lot of it. Amazing and incredible
discoveries have been made this way. For example, the Higgs
boson was really just a theory out of the blue,
and it was a theory for a long time until

(06:46):
people decided to try to test it. That's right, and
people spend decades trying to test this theory, and finally
we build a collider or powerful enough that we could
create the Higgs boson and prove that it existed. And
so this theory is to fifty years or Elier had
predicted the existence of this particle, was proved right and
got his Nobel prize. Yeah, that was like a like
a twenty billion dollars swipe there, you know, that was

(07:08):
a big swipe that that was good dollars. Yeah, but
you know, he wasn't the only one to predict it.
And there was a lot of controversy when we discovered
the Higgs boson. Who was going to get the prize
for it? Should it just be Higgs, should also be
this guy Englert who was around and wrote a lot
of very similar papers but didn't get his name on
the particle. And then there was a whole other group

(07:30):
of people that wrote very similar papers, but we didn't
get any part of the prize. That's right, And so
today we'll be talking about a prediction from a theorist
that maybe should have gotten the Higgs Nobel Prize but didn't.
And he made his second prediction about the universe that
we're going to be talking about today. That's right. And
this comes from a question from a listener. Somebody wrote

(07:51):
it and said, hey, could you explain this to us?
I just don't get it. Yeah, So this is a
question that Peter from Poland sent us via email, and
so to be on the pro and we'll be asking
the question what is a cosmic string? I don't want
to string people along. Let's just let's just get down

(08:12):
to it. Daniel. Yeah, well I was thinking, you know,
silly string versus string theory, and there's a lot of
different combinations there, but a lot of strings in physics. Yeah,
it's a great question. Thank you Peter from Poland for
writing in, and anybody out there, if there's something in
physics you've heard about but haven't really understood any of

(08:32):
the explanations, send to us. We're going to try to
break it down. And this is a tantalizing subject because
we're not just talking about strings. We're talking about cosmic strings.
So they sound like a very big deal, and they
are kind of a big deal. They're not small strings
like maybe some people might be imagining it. That's right.
This is not you know, star studied strings in your

(08:53):
drawer or anything like that. These are things that could
span the entire observable universe. And so we were wondering
how people had heard of these two words put together
costmaking strings out there, and how many people maybe even
had an idea but what it could be. So, as usual,
Daniel went out there and as people in the street,

(09:13):
if they've heard what a cosmic string is, so before
you hear these answers, think to yourself for a moment,
do you know what a cosmic string is? What would
you say if I asked you on the street. Here's
what people had to say. It sounds like a Marvel
movie before me? Is that similar to string theory? The
loops that way upon it's like a fifth dimension potentially?

(09:34):
Do you know all this stuff? I don't know any
of this. I don't know any it's something, um, I
don't have no idea. Cosmic strings something that uh, and
then I think that's what space string. QUITE have no idea.
If you laugh, is it sound funny? It just sounds

(09:56):
like like science fiction. I heard of cosmic bowling. You're
not cosmic cosmic bowling? What's that? That's when they shut
down the lights for Friday night bowling, strings that you know,
unite like different potential space and time like you Yeah,
like space and time like a pass I guess in

(10:16):
a way when it's stringing together, str together, I have
no idea something to deal with. I don't know um energy, energy,
and I don't have no idea how okay, but so
very much obviously cosmic, yes, but strings those starts together now,
all right, Not a lot of familiarity, although I do

(10:39):
like the answer the person who said it sounds like
a Marvel movie to me, which it totally does. You know,
infinity stones, cosmic strings, quantum realm. You're you guys are
all watching the same movies. You could put cosmic in
front of anything. It would sounds like a Marvel movie.
Cosmic quantum, cosmic bowling. I like that answer. I was like, yeah,

(11:00):
that does sound like a good idea. I'd like to
go to cosmic bowling, cosmic breakfast, cosmic fast. All right. So,
not a lot of people seem to know what it was,
although it definitely sounded science and science fiction. A lot
of people said, oh, it sounds like science fiction, or
it sounds like something that might be related to string

(11:21):
theory or physics or energy. It definitely has a science
feel to it. Yeah, and it might have just been
the way my hair looked that day. Maybe it looked
more like a crazy physicist, or maybe it just does
sound like a sort of a physics thing. So people
are definitely guessing that. I'm trying to imagine how you
can look more like a physicist, Daniel, It's kind of hard.
It's kind of hard to imagine. I don't know. I
guess I could put on a lab coat. I mean

(11:42):
I don't usually with a lab code when I'm walking around.
You put on a marble costume and boom, I need
an m c U lab coade so I can do
both things at once. Oh, that would be that's a
good idea. Actually print um something fun on a lap code.
M that sounds like merch. Get on that people, next
product for the Daniel and Jorge explain the universe store.

(12:04):
But all right, so let's get into it. Daniel, what
what are they? What is a cosmic string? And I
I am totally with the people on the street. I've
never heard of this concept before this morning. Well there's
a good reason, because cosmic strings are a pretty crazy idea.
They're pretty far out there, but they're really fun and
conceptually sort of mind blowing, which is why I think

(12:25):
the theory stuck around for a while. People get swiping
it because it sounded fun. Yeah, everybody wants this theory
to be true. And so what is a cosmic string?
A cosmic string is a line in space where the
space itself is a little bit different from the way
spaces for us, from me and you and most of
the space in the universe. It's like a little bit

(12:46):
of leftover from the Big Bang where it never quite
cooled and relaxed the way the space for us has.
It's like a pocket, like a pocket or a bubble,
or like a stretch dog bubble. Is that kind of
what mean? No, it's a really long, thin line, like
it's maybe a phemptometer wide, so like super duper tiny,
like the width of a proton. But then it can

(13:06):
be super long, like it could be as long as
the observable universe, like nine billion light years. It's kind
of like a crack in space itself. Yeah, and you
have to think about what space is and remember that
space used to be really different. Right back when the
universe was created. Everything was hot and dense and there's

(13:27):
a lot of energy everywhere. And remember that space is
not emptiness. Space has all this stuff in It has
these quantum fields. And when you put energy into space,
what you're doing is you're making those fields wiggle. And
so back in the very early universe, those fields were
going crazy because it was so much energy everywhere. So
everything was wiggling really fast, and everything had a lot

(13:47):
of energy. In our book, we talked about how space
is kind of like a goo. It's like, it's not emptiness.
It's more like it's like something that you're swimming in almost,
and it can wiggle and bed and push you in
different directions. Right, that's right. Gravity does really weird things
to space. It can stretch it, it can bend it, it
it can ripple it. But for now, let's just think

(14:08):
about like one unit of space, Like what's in that
box of space? And in that box of space are
quantum fields. Now, the universe started out really hot and
dense and really energetic, and those fields had a lot
of energy in them. But the space that we're familiar
with that operates in the way that we expect, like
has electrons in it and and atoms and stuff that

(14:28):
only came about after the universe relaxed a little bit.
We talked about on the Higgs Boson episode that there's
one of these quantum fields, the Higgs one, that when
it relaxed, when the universe cooled down, that this field
didn't go all the way down to zero, sort of
got stuck on a shelf. Right, Like the field that
the universe is made out of are not necessarily static,

(14:51):
like they can be kind of buzzing with energy. That's right.
Every time you have a particle that's a ripple in
the field, which means you've injected energy into it. Now,
most of the few can go down to zero like
you've got no electrons in your box of space. That
fuel is at zero. But the Higgs boson never gets
down to zero. Got stuck on this shelf. And so
how does that explain these pockets or these cracks in space?

(15:13):
So what happens when the universe is expanding, is it
it's cooling, right, All this energy is getting spread out
into more and more space. It's like you're stretching out
the fields, right, Like you're stretching them out basically, and
so they calmed down. Yeah, you have the same amount
of energy in more space, and so it gets deluded.
So everything's like cooling and relaxing and sort of like

(15:33):
you know, you you toss your blanket over your bed
and it sort of settles down and settles over your bed, right,
like a cosmic nap is like a cosmic blanket. Yeah,
and it settles down. But the Higgs field got stuck. Right.
But here's the thing. The Higgs field has lots of
different ways to get stuck on that shelf. Is that

(15:54):
shelf is not just like one little balcony. It's like
a long round balcony, and the universe can get stuck
in different spots on that shelf. And so as the
universe is cooling, if this chunk of space over here
got stuck on a different spot then that chunk of space,
then there's this sort of boundary between them, this place
between them that doesn't quite work because it's sort of

(16:16):
trapped between space that got that cooled in two different ways.
It's kind of like how you know, water or air
has different states like solid liquid and gas, and you know,
as you cool something down, you can form these little
pockets of liquid or gas or what's either one solid

(16:37):
water crystal. Yeah, it's like when you, like when you
stick water into the freezer and it cools down and
forms ice. It doesn't form like this perfect solid of ice.
It forms like it has bowls and cracks and wiggles
and it is that kind of what you're saying, is
happened happened? Or how is happening to space right now?
Exactly like that, if you cool water down, then you

(16:57):
get a crystal. But it doesn't, as you say, turn
into a crystal all at once. There's these sites that
begin because they're the coldest, little dots, and the crystals
start to form there, and then they form out from
those little spots where they have nucleated. And then what
happens when two crystals meet, You have this boundary, right,
and you don't have a perfect crystal. You have a
defect in the crystal. That's why, like some diamonds are

(17:19):
perfect and some diamonds are not because there's a defect
there where in the crystal where one half of it
is cooled in a different time than the other half,
so they're not all lined up perfectly. The same thing
happened to space, maybe, like there are imperfections in space,
there are imperfections in their defects or cracks in space.
Where on one side the Higgs field, it's at the

(17:40):
same level, right, it's just pointed in a different direction,
because the Higgs field has sort of two we call
them degrees of freedom, the level let it relaxed that
and also where on that shelf it got stuck. So
if this chunk of space is stuck on a different
spot in the shelf, then that chunk of space, it's
sort of like your ice cooling at different ways. In
different ways, the stoles are oriented in different directions, and

(18:02):
so at the boundary you get this thing that doesn't
quite make sense. So I always thought the universe was
pretty pretty good, but I guess it's not a triple
A diamond quality space. I mean, I love our universe.
I would not trade it in for anything. I think
it's perfect just the way it is. But it might
have these cracks in it, right, And we don't know.
We have never seen one of these things, but it

(18:22):
might have these cracks in it. That's the idea. That's
the concept of a cosmic string, cosmic flaws in space itself.
And so along that line, it's like the universe never
got to cool because it doesn't know like should I
cool in this way or should I cool in the
other way. It's sort of like trapped between them, and
so it still has that energy density from the initial
universe when everything was really hot and dense. And so

(18:45):
these cosmic strings, even though they're really really thin, they're
like a femtometer wide. They're incredibly massive, and they could
be holding energy like the cracks or the flaws in
the universe could be storing some sort of energy or
tension into them. Absolutely incredible amounts of energy. Like two
centimeters of a cosmic string weighs as much as Mount Everest.

(19:07):
A kilometer of cosmic string weighs more than the Earth.
And so we're talking about these things. They could be
like ninety billion light years long. It's an enormous amount
of energy. What you just totally correct my mind here, Daniel,
cosmically cosmically dude. But all right, so let's get into
it and why is physicists think these crazy cracks might

(19:30):
exist and whether or not they're real. But first let's
take a quick break. Okay, so you're saying that as
the universe was cooling or assets cooling right now, you

(19:51):
might have these areas these lines, these huge lines in
space that are sort of like cracks, like where space
is kind of freezing into different crystals like structures or
different modes, and so you have these kind of edges
to the wrinkles in space itself due to the Higgs
field precisely, and we are in the crystal part, right,

(20:14):
we're in the part of space that cooled, and these
chunks of space that all cool sort of together. That's
like could be as wise nine billion night years like
the observable universe. So it's not like you have a
little pocket of space, assize your hand and the next
pocket is different, the next pocket is different. If there
are these pockets and they're vast, they're incredibly enormous, but
then at their edges there can be these cracks. And

(20:36):
you're saying, these edges, these boundaries look like strings, and
so why don't they look like walls or like you know,
planes out in space. Why is it shape like a
long like you're super thin but really long string. Yeah,
that's a great question. That's because the Higgs boson. The
field for the Higgs has a lot of different ways
you can relax, Like there's one level at which you

(20:59):
can relax one and energy level, but on that energy
level can sort of point in a lot of different directions.
And so the way to get a boundary is like
if you had two different energy levels and and the
boundary like a would be like a plane between them.
But um, because there's only one energy level, everywhere in
space has that energy level, but they just point in
different directions. And so what you get is this defect

(21:21):
that's like a string. And then as you go around
the string, the Higgs field is pointing in different directions,
and so it points in a different direction every point
around the string. And then the only place where you
can't get sort of like smoothness is along this one
infinitesimally thin line where space doesn't know where to point
because every point everything around it is pointing in a

(21:42):
different direction. So it's like I can't relax. I don't
know which way should I go. It's kind of like
me in this podcast, We're going in every direction. What
happens if I touch one of these strings? Like what
if I'm touch one of these things and I run
into like, you know, like a spiderweb, you know, I'm
walking down the street and just run into one. Well,

(22:03):
I would recommend wearing oven myths first of all, because
there's a lot of energy there. Oh, that's right, they
trap energy. It's like a so I guess it's more
like a wrinkle in space. Right, It's not so much
like a crack, but it's more like, you know, like
you're tucking in or you're bending a lot of space
along the line of it. Yeah, a wrinkle is a
good way to do it. I think a cosmic wrinkle

(22:24):
um would have been a good way to sell this
thing that could be the sequel to the Plaguind novels
A Wrinkle in Space Time. Turns out there was physics
behind that novel. You would notice one almost immediately if
you saw one, because there's so much mass that they
bend the space around them the way everything does. Everything
with mass bend space, and it would cause a huge

(22:45):
gravitational lens. So it would really distort the way light
moved around it. Wow, like a black hole. Be like
a black string. Yeah, it would be a lot like
a black hole, except it would be really really thin
and very very long. Okay, there would be probably crazy
stuff happening around it, right, like a you know, it
wouldn't just sort of sit there in space that there
would be you know, some kind of you know, cosmic

(23:07):
storm kind of swirling around it. Would there be uh
in the m c U version of this movie, then yell.
The visual effects would be dramatic all around it. Is
that what you're thinking? Yeah, yeah, what what does the
gauntlet that holds the cosmic strings look like? No, it's
actually fascinating because, unlike a black hole, which has enormous
gravitational pull and so has a huge amount of stuff

(23:28):
around it, like a maelstrom that's like giving off light
because of all the gravitational energy and the and the
title forces, cosmic strings don't actually provide a strong gravitational pull,
like they distort space, but they don't necessarily create gravity themselves.
It's a really weird consequence. It depends on the shape
of the string, if they're a loop or if they're straight.

(23:51):
It's actually quite complicated. Didn't you say that it has
more mass than the Earth? Yes, or like, you know,
it's just really massive, but it's a mass but no gravity.
It has mass, it distores space, so it can become
a gravitational lens, but it doesn't necessarily attract you because
of the configuration of it. It depends precisely on the
shape of it. Remember, general relativity tells us that gravity

(24:14):
is much more complicated than just things that have mass
pull on each other. It depends a lot on the
shape of that stuff. That's why if you have the
right configuration of stuff, you can even get repulsion like
dark energy. And so these cosmic strings are a really
weird little object. And and it depends exactly on the
configuration of it whether you get pulled into it or repelled,
or whether it basically ignores you. So when you say

(24:35):
it's massive, it's it's really more like the equals mc square,
Like it just has a lot of energy to it. Yeah,
it has a huge amount of energy, a lot of
energy density in a really small spot. All right, Well,
it sounds kind of dangerous and that maybe you don't
want to run into one of these strings out there
in space unless you want to win a Nobel prize,
unless you want to die trying, I guess. But why

(24:57):
why do phacests think they might exist? Is this thing
that you're pretty sure of or it's a crazy idea?
What would what would make someone think of these strings
as possibly being out there? Well, it comes from this
guy named Tom Kibble, and Kibble was one of the
folks who was around when the whole idea of the
Higgs boson was being invented, This question of like how

(25:19):
do particles get mass? And do we need to invent
a new quantum field that fills space that gives particles mass?
And you know, anytime theorists come up with some new idea,
then they like to play with it and they say, oh, okay,
now we have a new toy, this Higgs field. What
else does it mean? You know, how can we what
consequences would it have? And so he was thinking about

(25:39):
the early universe and how the Higgs field would be
cooling as the universe expanded, and then he hit on
this idea. He thought, wait a second, what if it
doesn't cool evenly? Would you get these cracks? And I
guess that was just really fun to think about. He
also he didn't get included in the Nobil Prize because
he sort of came in a time he'd bit too
late on those papers. So maybe he was going for
a backup Nobel Prize strategy. I wonder if his name help,

(26:02):
you know, maybe the committee was like, we can't give
it no prize to someone named Kimble. You know, there's
a whole group of people. There's like three folks out
there who were writing papers right at the same time
as Higgs and Englert, and they just got totally snubbed
by the Nobel Prize committee. Wow, it's just about when
they submitted the paper or when when they came up

(26:24):
with the idea. There's a lot of controversy because it's
you know, some journals that the date on the paper
reflects when you submitted it, and in other journals it
reflects when it was finally accepted after review. And so
there's a lot of controversy about who came up with
the idea first. And you can only give the prize
to three people. And the three people who everybody mostly

(26:45):
agrees came up with the idea first Higgs, Englert, and Brown.
They were they won the prize except for Brown who
had died already, so it was just split to the
Higgs and England. And then in the second tier they
were like three people and so they were like, well,
it either it gives two or we give it to five.
We can't give it to five, so I guess we'll
just snub that whole second tier. Wow, is there a

(27:06):
runner up Nobel Prize honorary. Yeah, it's sort of like
fake gold, you know, just like hollow plastic. It's not
nearly as cool. Okay, so that's the theory. The theory
is that asked the universe is cooling, You got these
kind of flaws and how the Higgs field was cooling down,
and so you form these crazy strings. But they're not

(27:28):
related to string theory, right. That might be confusing because
they're both strings, but there are totally different scales. That's right,
they're not related to string theory at all. String theory
deals with like the fundamental nature of the universe on
the smallest scale, like ten to the minus thirty five meters,
is everything actually made out of these tiny vibrating strings.
The thing they have in common is the sort of

(27:49):
analogy we use in our minds where we put them that, like,
you know, this thing is really long and thin, so
let's call it a string. So fundamental strings that are
really tiny we think might be these one dimensional objects.
So they're really long and thin, not that long actually, um,
but they're much longer than they are thin and cosmic strings.
Are you know, light years long and a femptometer thin.

(28:11):
So the only thing they really have in common is
that name. But there's there were other reasons to think
that cosmic strings might have existed, all right, So then,
so what was the motivation for these Like I know
they were playing around with the theory of the Higgs field,
but what makes this a particularly fun theory, like you said,
or interesting theory to look for. Well, you're right, it's

(28:32):
a fun idea and it's fun to play with, but
there's a lot of things that get theories excited and
fun to play with. I mean, they're fun strings. That's
what they do. They just go in their office and
play with strings. Um No, The thing that made this
idea sort of stick in people's minds was that they
thought it might solve a problem that we had, which
is that we didn't understand like why we had galaxies.

(28:53):
We didn't understand why the universe had structure at all.
We talked about this on the podcast before, like the
universe started totally smooth. How do you get any clumping?
How do you get things started so that gravity can
take over and give you stars and planets and rabbits
and hamsters? Right, Like where did that initial texture of
the universe come from, or the initial clumping of stuff? Exactly?

(29:16):
We could have been in a universe where everything was
just spread out and bland and boring and gray. Right,
that's right. And somebody was thinking about cosmic strings early on,
and they calculated like, well, how many cosmic strings would
there have been? And then they calculated like, well, how
many galaxies are there? And those two numbers were pretty similar,
so that they thought, wait a second, me, me, cosmic strings, galaxies.

(29:38):
Maybe the reason we have structures because of cosmic strings.
Maybe these cracks in space, these imperfections, are the reason
that stuff started to clump together and form structure and
planets and hamsters and ice cream and bananas. So maybe
cosmic strings explained the universe. It would have tied everything
up pretty neatly with a string, exactly. It would have
been quite the cosmic solution. That's why people got excited

(30:00):
about it, because you have this new toy which is
connected to this fun new theoretical idea of higgs boson,
and maybe it solves the problem you have. All right, Well,
it sounds really tantalizing, and I'm definitely seeing the fun
of it. And I definitely feel like I'm being strung
along here to some interesting conclusion. So let's get into
whether or not they are real and how we might

(30:22):
actually see these cosmic strings out in space. But first
let's take another quick break. Okay, Daniel, So our cosmic

(30:42):
strings real, and how will we know? Are we Are
we going to see them out in space? Are we
gonna be looking out into space one day and see, like,
wait a minute, what is that little crack we check
our glasses and our telescopes. It's not a crack in
the lens. It's an actual crack in space, in the
universe itself. That would be pretty awesome. I mean, what

(31:02):
a thing to discover, What a moment that would be,
to see a crack in space itself. Unfortunately, no human
has had that experience yet. As far as we know,
there are no cosmic strings out there. Like how you said,
no humans. I don't want to rag on alien science,
you know, I'm hoping those guys have made some advances
well past what we have done, so that when they
come visit, they share with us all those secrets. No

(31:23):
human that we know of, no human that we know of,
and no human would make this discovery, and I think
keep it to themselves because it would be of really
cosmic significance. And remember we also we can't say they
don't exist. We can just say we haven't seen them,
so we don't know that they exist. Okay, so we
haven't seen one yet, but it's a theoretical prediction that

(31:44):
it sounds fun and that might explain some of the
structure in the universe. So are people looking for these
cosmic cracks or are we just hoping that one day
we maybe see them, Like, are active search for these cracks?
I'm just waiting for alien you accords to come pulling
one and drop it on the Earth. That's what that's

(32:04):
what they used to steer the the cosmic unichorus. They
used cosmic strings. No, that will be the opening scene
in the Marvel movie about cosmic strings. Um. But people
were thinking that maybe this affected the shape of the universe,
and they had all these predictions like if these cracks
in space were the things that caused sort of the
large scale structure, the reason we have galaxies, then they

(32:25):
had predictions for how the universe should have sort of
been rippling in its first moments. And remember that we
have seen the early universe. We can look back in
time and see what the universe looked like when it
was very young. Called this the cosmic microwave background radiations
leftover glow from the Big Bang. But didn't these strings
form way after the Big Bang when everything was cooling down?

(32:47):
Or or was it that it? Did they start wrinkling
right after the Big Bang? Right after the Big Bang? Yeah,
it's when as space was expanding. That's when sort of
things were cooling and the ice crystals of space were forming,
and and the cosmic microwave background happened like hundreds of
thousands of years later. And now we've seen that. So
these cosmic strings, the idea was invented before we had

(33:08):
precise measurement of this cosmic microwave background light, and it
made very specific predictions for what that light should look like.
And then we saw that light from the early universe
and it didn't look right. It doesn't look the way
you would expect it to if cosmic strings were real, Really,
you would see this in the cosmic microwave background, Like
aren't these I mean, aren't these cracks you're saying they're

(33:30):
one phantometer? Then how would you even see them? In
the cosmic background. If they're there and they did affect
the sort of structure of the universe, you would start
to see that structure beginning to form in the very
early universe. I mean they've had three hundred thousand years
or so to start to get things starting to wiggle,
and we do see structure in the early universe. I
mean early universe is very smooth because it was early

(33:52):
on and things were just getting started. But we look
at that light and we see like hot spots and
cold spots. We can analyze those rates of hot spots
and cold spots and say what theory would give us
sort of that level of fluctuation, that level of structure
at that time, and cosmic strings just predicts sort of
a different distribution of hot spots and cold spots than
we see. Really, even if them, what if there aren't

(34:14):
as many strings as you thought there might be, you
know what I mean, like maybe there's just just far
and few in between for you to see them. Know,
the pattern is just wrong. It's not like about the number,
it's about the distribution, how far apart they are and
sort of how they affect the shape of space. Instead,
it's totally consistent with just quantum fluctuations in the early
universe then getting blown up by inflation. So there were

(34:37):
sort of two competing theories, like this random fluctuation plus
inflation or cosmic strings. And now the data really look
a lot like random fluctuations plus inflation and not like
cosmic strings. I guess that's good, right, because if it
turned out that the the universe as a baby had
a lot of wrinkles in it, that would be kind
of strange and disturbing, wouldn't Who wants to see a wrinkly,

(35:02):
old looking baby. Man, if the universe is listening to
this podcast, you're in trouble. I'm already in troubled in
But you know, if cosmic strings do exist, they don't
have to have formed the structure. This is like, if
they caused the structure, here's what that structure should look like.
But they could still exist. It could be that they're
still out there. They're just not responsible for the structure

(35:24):
of the universe as we know it. Oh, I see,
we know that there. They maybe didn't have a hand
in structuring the universe, but they could still be out there.
They're just sort of like under the radar more than
you thought they would be. That's right, and so we
have other ways to look for cosmic strings that people
are actively doing right now. What are some of the
ways that we can search for these cosmic strings. Well,

(35:46):
cosmic strings have a lot of energy density, and so
they do this gravitational lensing thing. They bend space, and
so if you have a really bright source of light
behind a cosmic string and you're standing in front of it,
then you see like sort of a doubling of an
image because the light we get bent around the string.
Like if I had a flashlight and there's a cosmic
string between us, and I turned on my flashlight, you'd

(36:06):
see two bulbs, right, But wouldn't aren't these strings really thin?
You know, I'm trying to think about how much distortion
a little string, and Megan, it would be kind of tiny,
right would it would be really hard to see, Like
a small imperfection in such a huge canvas would be
really thin, but it'd be really really massive. Right. Say
we took them Mount Everest and squeezed it down to

(36:29):
a tiny string, right then it could have a significant impact,
all right, So and we would we would maybe see
not not as a lens but like a kind of
like a lens in the form of a string, kind
of like we would see doubles all along the string itself, precisely.
And so what we've done is we looked out in
the space and we look for this kind of effect.

(36:50):
And we see gravitational lensing all the time in space.
Usually it's black holes or blobs of dark matter, this
kind of stuff. But as you say, a cosmic string
would look a little different. And people have seen like
pairs of galaxies in the sky near each other that
looked really really similar, and they thought, oh, wait, maybe
that's a cosmic string, but then they look closer when
they discovered nope, it's just two similar galaxies. It's not

(37:11):
a reflection. It was just Bob's hair that fill in
the lens of our telescope. Yeah, And so these days
there's another way to look for cosmic strings that people
think is the most promising. What's that? And that also
has to do with their gravitational effects, because these cosmic strings,
we don't think they're just floating there. We think that
they are so much energy, they're like whipping and ripping

(37:32):
and crackling. No way, what Yeah, like you know, lightning
bolts um coming from fingertips in a marble movie. Right, yeah, Oh,
they're active, these strings, These boundaries can move, yeah, because
I guess the the field is shifting around it, and

(37:53):
so the boundaries is like fluid. Yeah. And also the
strings can get twisted and if they cross over each other,
they can break, and then you get ends, and those
ends can like whip around like crazy. It's it's pretty nuts.
Can they form loops and knots? They can form loops absolutely. Yeah.
Can you make a cosmic knot? I cannot make a

(38:14):
cosmic knot, but the universe might be capable. If you
get one of these crazy strings in a in a
strange shape, then its movement can get generated a lot
of gravitational waves. And we now have gravitational wave detectors
like Ligo that saw when two black holes aid each other,
or when two neutron stars collided. They create these ripples

(38:35):
in space itself, and we can see that now. Wow,
it's like a picturing like a snake trashing in a
puddle of water, Like it's moving and it's generating ripples
that we might be able to see precisely, but we
don't know how fast they move, and so they could
be like zipping around really fast, generating enormous signals of
gravitational waves that we could detect. Or it could be

(38:57):
like a cosmic time scale thing where they're like decades
long signals. These ripples, you have to like take data
for a hundred years before you see the up and
the down, So we don't quite know what to look for.
They could be not whipping around, but maybe just whipping
around precisely, precisely, And so people are using gravitational wave

(39:20):
detectors here on Earth. Do you have these long hauls
filled with vacuum and lasers to measure space really precisely
to see if these little ripples, And then people also
trying to use the entire galaxy as a gravitational wave detector. Yeah,
why not? Well, I mean, I got other things to
use the galaxy war but if it's there, if it's there,
might as well use it to find cosmic blacks whole strings?

(39:44):
Why not? Yeah? And I love this idea because, um,
it just sort of takes what's already out there and
tries to use it to do science. Like you could
never build a galaxy size physics experiment, but hey, just
take the galaxy and turn it into an experiment. I
love this idea. And so what's the idea here that
the string might as it's moving around, kind of affect
the things around it. The idea is just to build

(40:06):
a bigger detector, Like the larger your gravitational wave detector
is the smaller wiggle you can see. It's easier to
see in a larger detector because it's uh, it's just more.
You have more sensitivity too, because it's over more space.
And so the idea is to build one the size
of the galaxy. You know, you can't build your own detector,
but there are things out there that you can use

(40:27):
as a detector. And the thing that we can use
are these stars called pulsars. These are stars that are
emitting light in a regular pattern like when they were
first discover They you see these these regular beaps from space.
And so if the space between us and some of
these pulsars gets wrinkled and a little bit or ripples happen,
then it changes how the pulsing of these pulsars. And

(40:49):
so the idea is to use all of these sort
of measure the smoothness of space. Oh, I see, but
that's only if these strings are moving fast enough for
us to sort of noticed them or notice the difference. Yeah.
If if they take a hundred years to send a signal,
then our grand students are going to be really old
before they get their PAGs. You don't sound that surprised, Daniel,

(41:14):
like it's a big deal. You're like, I might take
a five years or hundred years. I can't. Hey, it's research.
I can't predict, right, That's what I always tell my students.
You never know. You're the first person to ever do this.
So you told them that you could be wrong. I
tell him, We've never published a paper knowingly wrong yet,
so don't be the first. So many caveats in that statement, Daniels,

(41:35):
So many caveats. I had that vetted by my legal department.
All right, So I guess that answers a question. What
is a cosmic string. It's a It's like an imperfection
in this in the fabric of the universe itself. It's
like a wrinkle caused by the stretching of it and
the weird cooling of the hicks Field. I can't believe

(41:56):
I just said that in one sentence. Yeah, and you
know these quad and fields are not just an idea,
they're real. They're out there. And as the universe cooled
from the like hot nasty quantum fields, too cold crystallized
quantum fields that we have today, then how that cooling
happened could have affected the way the universe is formed.
And it's cool to think that what we might do
with this knowledge, right, Like, if we know that space

(42:20):
can wrinkle and crack like this, who knows what we
could do with space? Possibly? Can we faul space? Can
we make space origami? The one thing we can never
do is get the Nobel Prize for Tom Kimble. Oh
did he pass away? He passed away? So he missed
the Nobel Prize for the Higgs boson. And if he

(42:41):
was right about cosmic strings, he missed that one also, Right,
But you can still get in on the party by
maybe being the president of the food discovers it? Right,
that's right, and maybe time people will get another kind
mentioned in the Nobel Prize acceptance speech, which is almost
like a run rough prize. Right. Well, I guess the
idea is that maybe someone listening to this out there

(43:02):
might be the person who discovers it. Might be you
might be me. Might be someone listening to this who
discovers these wrinkles in reality that's right, or something even crazier.
The next time you hear a theorist talk about some
totally bonkers notion about the way the universe or space
might work, then remember there are crazier ideas out there

(43:23):
that are actually real. That's right. They could still be crazy,
but they might also be right. You never know, m
that's the wrinkle on your reason. Thank you very much,
Peter for that question. I love email questions from listeners,
so please, if there's something you'd like to hear us discuss,
send it to us two questions at Daniel and Jorge
dot com. You hope you enjoyed that. Thanks for listening.

(43:45):
See you next time. Before you still have a question
after listening to all these explanations, please drop us a line.
We'd love to hear from you. You can find us
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(44:08):
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