October 31, 2019 • 51 mins
A conversation with astrophysicist Dan Hooper about his new book, At the Edge of Time
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Speaker 1 (00:08):
One of the deepest goals of physics is to help
us understand our context. Are we humans at the center
of everything or are we in an irrelevant little corner
of the universe? Was the universe created with us in it?
Or did it exist for an unimaginable eons before we arrived.
(00:28):
The answers to each of these questions helps us know
our place or lack of it, in the universe. It
helps us know how to live our lives. But nothing
touches these issues more deeply than understanding the very birth
of the universe. What, if anything, can we ever hope
to reveal about those first few moments of creation? Hi,
(01:08):
I'm Daniel Whitson. I'm a particle physicist and a professor
you see Irvine, and I am the co host of
today's podcast, Daniel and Jorge Explain the Universe, brought to
you by I Heart Radio listeners. The podcast now that
we love to examine big questions, deep questions, questions about
things really far away, questions about things under our feet,
(01:30):
questions about how things around us work. But we're also
interested in the really deep questions, not just questions of space,
but also questions of time and so while Jorge is
still away and not available today. I'm very pleased to
have on the podcast today a friend of mine, a collaborator,
a colleague, and a upcoming author of a book I
(01:50):
think all of you would be excited about. His name
is Dan Hooper. He is a theoretical astrophysicist at FIRMY
National Accelerator Laboratory and ACT. He is the head of
the theoretical astrophysics group there, and he has a new
book coming out about the beginning of the universe. It's
called At the Edge of Time and it's going to
be available in November five from Princeton University Press. Now,
(02:13):
I've had the opportunity to take a look and at
advanced copy of this book, and I think it's awesome.
It talks about a lot of the really amazing questions
we like to dig into on the podcast. So without
further Ado, let me introduce to you my friend and colleague,
Dan Hooper. Thanks. I'm really excited to be here. Yeah. Well,
thanks for coming on the podcast and talking to us
about all the amazing and incredible things that we like
(02:35):
to think about. And apparently you like to write about
one thing we like to do in this podcast is
talk about things that are on the cutting edge of science,
things that scientists themselves are thinking about, but then trying
to break it down in a way that makes sense
to people. People can actually come away feeling like they
understand what we're talking about, not just repeating various jargon. Thanks.
(02:56):
I really enjoy trying to think of ways to a
some of the scientific ideas that I explore my research
for people who aren't scientists, whether that be my non
scientist friends or uh my family members. Uh. I really
like stretching that part of my brain that uh one
uses and communicating these exciting and very different ideas. And
(03:20):
I think your book does a great job of this.
I really conveying not just what we know, but also
what we don't know, where the edge of knowledge is
and and it is something else. It shows us that
science is personal. I think one of the great things
about your book is that it reflects who you are.
Doesn't just show science for being some monolith of knowledge
or something some sort of objective intellectual pursuit, but it
(03:44):
shows us that science really is of the people, by
the people, and for the people, because in the end,
science is just humans answering human questions. For other humans.
Science is always just a work in progress. Um, the
questions we're asking today, we'll probably not be the questions
that we find answers to ultimately. And when it comes
(04:04):
to the sort of stuff that I work on, I
would be shocked and maybe a little disappointed if it
turns out that the ideas we have about how things
are going to play out turn out to be right.
I really like the mystery that that's involved. And uh,
the surprise when we find out something we weren't expecting,
I only hope. So I love scientific surprises. But tell me,
(04:25):
what was your motivation for writing a popular science book
about this rather than just sort of continuing in the
conversation at the level of academia. Why bring this question
to the people. Long before I ever became a scientist,
I loved popular physics books. I used to read any
number of books by folks like Paul Davies, MITCHA. Kaku,
Kip Thorne, and this st just blew my mind learning
(04:48):
about quantum mechanics and learning about UH relativity, cosmology and
kind of the philosophical implications of all of it. Um. So,
when I became a science entist, I decided it would
be fun to kind of stretch my brain and uh
and try to try my hand at popular science writing myself.
(05:09):
This isn't the first time I've ever been in a
popular science book, but I haven't written popular science in
a long time. And uh, it's exciting, new challenge. I
love new challenges, and uh, this was no exception wonderful.
So as a theoretical astrophysicist and a cosmologist, you're dealing
with questions about like the origin of the universe and
the beginning of space and time, the very creation of
(05:30):
our cosmos. When you travel around, say you're on an
airplane and some random person asks you what do you do?
Do you have an easy time explaining to them what
you do and why it's interesting, or do you get
a sort of a lot of glazed looks. The reactions
I get are kind of all over the map. Occasionally
you get lucky and you start that conversation and the
person is excited, and uh, you know, maybe they think
(05:54):
that's the perfect person to sit next to for the
course of the flight. Um, they always wanted to know
about cosmology and finally have an opportunity to to ask
somebody all the questions they build up over time. And
sometimes you sit next to somebody who, just for whatever reason,
they just don't have the you know, the kind of
intellectual curiosity for this sort of subject that you or
(06:16):
I might have and uh and in sometimes you get
the people who confuse cosmologists with cosmetologists, and that's pretty awkward. Um,
so yeah, you can. You can have just about any
kind of experience on a plane. When you tell them,
UM about my line of work. Are you willing to
give advice on lipstick colors or not? I mean, I'd
be willing to give you my advice and just about anything,
(06:38):
but I don't think you should take it. For one thing,
I'm I'm color blind, so i'd probably be pretty bad
at that job. All right, Well, I think that these
kind of topics are totally accessible because I think everybody
wants to know the origins where we came from, because
it tells us something about why we're here and what
it means. Um And I posted a question on Twitter
(06:59):
this week, and I say, hey, I get to ask
a leading cosmologist questions about the beginning of the universe.
What should I ask? And boy, our listeners really showed up.
We've got a long list of questions, and we're going
to listen to some of those questions and answer some
of those questions. But I was just impressed at how
much of a vein it touched in people. It doesn't
surprise me. I'm excited about this stuff. I guess our listeners,
(07:19):
of course, are also excited about this stuff. But I
think it goes to something else about cosmology and early
universe physics, is that it really borders with philosophy. You know,
some of the questions we ask are hard physics questions,
like when was dark matter made? Do we have a
model for the production of these nuclei? But the answers
to those questions have broad reaching implications for philosophy, for
(07:41):
the nature of our existence, the meaning of the context
of it. Throughout history, human beings of all times and
all cultures have looked up at their night sky and
wondered about the universe and how it came to be
the way that it is. In that respect, we're just
like all of those people, but in one important way
we're really different. For the first time in human history,
(08:03):
when we look up at the night sky, we more
or less know what it is we're looking at. We
understand these things, and that's a truly new development. Um.
I think it's just amazing that we can take pictures
of things in the sky and when we see a star,
we know how nuclear fusion works in its core. And
when we see planets, we understand how they formed and
(08:25):
why they behave the way they do and what they're
made of. When we look at the expansion of the
universe and we look at the Big Bang, we understand
how our universe evolved from its first second up to
the current era, like over thirteen billion years. I I
think that's absolutely, you know, flabbergasing, just amazing that that
(08:45):
we've been able to make this incredible human accomplishment. It's
the kind of thing that if you went back a
few hundred years and drop that knowledge on leading minds
of the day, their minds would be blown right, It'd
be hard for them to really even understand what you're
talking about. And now we know those things, and that
gives me enthusiasm that today's questions will one day be answered.
The humans will know the answer to the questions we
(09:06):
are struggling with today. Makes me want to jump in
a time machine and fast forward. In the long run,
I'm definitely a scientific optimist. I think only a fool
bets against the progress of science and the very long run.
We might not solve every question tomorrow, but as long
as human beings managed to exist and not destroy themselves,
(09:26):
I don't think there are any answerable questions that we
won't eventually answer. Wonderful Well, I noticed in your book
that while your topics touch on these important matters that
connect to philosophy, unlike some other noted cosmologists, you sort
of stayed in your lane and talked mostly about the
physics um and so I want to take the opportunity
(09:47):
to push you a little bit on this podcast. When
we have an expert come in, we like to play
a game we call ask the wrong Expert. So I'm
gonna ask you some questions about philosophy, and this gives
you an opportunity to, you know, pun tificate ignorantly, and
we don't expect you to be an expert. First question
is about whether the universe actually exists. So do you
(10:08):
think the universe, the physical universe a exists sort of
outside of our human experience, like it would be there
even if we weren't here to experience it. B only
exists as a mathematical model in our minds. C is
an unanswerable question. We can never know or D you're
already regretting coming onto our podcast, I definitely come down
(10:30):
on C for this one. Um. All we can really
do is organize our consciousness experiences, including our observations of
the world. UM, try to make sense of them. Try
to come up with order organizing principles or theories, if
you will, that explain as much about our observations as
we can, and then use those theories to make predictions
(10:54):
about what will happen in our conscious experience going forward.
It could be that those theories we construct in that
way map very precisely or or closely onto something real,
a real world that those theories describe, or maybe not.
We don't really have any way of finding out. But
it doesn't really matter, because science works even if the
(11:18):
world it describes is not a real thing. UM. I
have a supercomputer in my pocket in the form of
a cell phone, and that thing works because of the
scientific method. And um, you know, modern medicine and transistors
and any number of other amazing modern technologies work because
(11:41):
of the scientific method, even if the world that it
underpins uh is very different from that described in our theories. Well,
that's amazing, Um. I agree with you. We might not
be able to answer it, but to me it matters
deeply whether what we're doing is just sort of playing
in our minds or answering real questions about the univers
And that's one of the reasons why I'm very much
(12:02):
looking forward to the day when we meet alien physicists
and perhaps get a chance to understand how a different
kind of consciousness might probe the universe, and and maybe
draw some sort of triangulation there about what's really happening.
But in the end, I agree with you, we probably
can't ever know. But that leads me to my second
question about the working of the human brain. Do you
(12:24):
think that the human brain is either a deterministic like
a big complicated mechanical watch in which we have no
free will, be deterministic, but yet there's somehow still room
in there for free will see nondeterministic because of quantum
mechanics like Penrose things, or d nondeterministic because of sort
of sort of magic, supernatural extra extra physical force. I
(12:48):
think this is a really good question, but I don't
think any of my my answer really falls into any
of these four categories or A, B, C, or D.
So I'm going to kind of give you my my
own e if you will answer. So. I think the
laws of nature are not deterministic. Quantum mechanics doesn't appear
to be deterministic. It might be in some sort of
everready in many world sense, But as far as any
(13:12):
experiment I would conduct, I can only probabilistically work out
what's going to happen in that experiment. So, for all
intents and purposes, UH, the laws of physics are not deterministic,
And since the human brain is a machine that follows
the laws of physics in our world, it also is
not deterministic. But as far as free will is concerned,
(13:34):
I don't think that matters. What I mean by that
is just because something in my brain is random and
not predictable doesn't mean I'm free to make any choices.
If I walked around flipping a coin to decide whether
I'm gonna do thing A or thing B next, that
doesn't give me any freedom. It just means I'm not predictable. So,
(13:56):
at least in any morally culpable sense, I don't believe
there's any reason to think there's free will and unit
that's a very sophisticated answer. I think I agree with
you on all points, and we're actually gonna dig into
that in depth in a future episode of this podcast.
So thanks for playing along with our silly game. But
the reason we brought you onto the podcast is to
talk about what you are an expert in, and that's
(14:18):
the early universe and the very beginning of time. And
so I want to dig into the details and pick
your brain about how our universe began. But first let's
take a quick break. Okay, we're back and we're talking
(14:41):
with Dan Hooper. He's a theoretical physicist at Firmy National
Accelerated Laboratory and the author of the upcoming book At
the Edge of Time, which explores the very beginning of
the universe. And Dan, first question for you to have
about what you actually know about is about how the
universe began. I would I would love if you would
sort of walk us through the very beginning of the universe.
(15:03):
And I'll give you two options here. Either walk us
through forwards from the moments of creation or backwards from
what we actually know into what we don't know. But
I'd love a sort of tour of the very first
moments of the universe. So even if you hadn't given
me the option, I definitely would have suggested going from
the present backwards because that's just a lot easier way
(15:24):
to describe it. So let me do it that way.
When we look at it out at our universe today,
we see that space is expanding. And what I mean
by that is all the objects in space, at least
the objects that are far away, like galaxies, for example,
they're all moving away from us, and the farther away
something is from us, the faster it's moving away from us.
This is because any two points in space, the amount
(15:48):
of space between them is growing as time goes on.
This is something we call Hubble's law. So because space
is expanding, that means that in the past our universe
uh was more compact, more dense, and as a consequence,
it was hotter, and in the future it will be
less dense and even cooler than it is today. So
(16:10):
if you run those equations backwards, you'll eventually point a
time reach a point in time where the universe was
very hot. Um So thirteen point eight billion years ago,
only a few hundred thousand years after the Big Bang,
you reach a point where the entire universe was filled
with uh some light and electrons and protons and things
(16:30):
that were all at a temperature of about three thousand degrees.
So three thousand degrees is an important point in in
the history of the universe because at three thousand degrees
you find that atoms begin to melt. This is what
I mean by that. So if I take some ordinary
atoms and I dump it in some thorough baths somewhere
(16:51):
that has a temperature more than three thousand degrees, well,
if I do that, those atoms, all the electrons that
are bound up on those atoms are gonna break off.
They're gonna basically those atoms are going to fall apart
into their protons and nuclei and electrons. So that means
that before this this key point three eighty thousand years
after the Big Bang, the universe was full of electrons
(17:15):
and protons and nuclei, but no neutral atoms. And then
after this point, basically all those things glued together into
into electrically neutral atoms. Before that transition, the universe was opaque,
meaning light couldn't couldn't move through space. Because of all
these charged particles in it. But after this point, the
(17:35):
universe became transparent to light. And that means that at
this transition, um awful lot of light was dumped into
the universe, and that light exists everywhere today. It's moving
in all directions and in all places, and in fact,
in this very room, or any any room, every cubic
centimeter of space has over four hundred photons that were
(17:56):
produced in this transition. We call that the causing mic
wave background. And over the last fifty years or so,
becausemologists have been studying this been greater and greater detail.
A lot of what we know about our universe's history
comes directly from observing that light that was released when
the first atoms are formed only a few hundred thousand
years after the Big Bang. All right, but let me
(18:18):
ask you a question there to clarify. So you're saying,
we look out of the universe, we see things are expanding,
and if we want to run the clock backwards, we say, well,
therefore things must have been denser before, because things are
getting less dense now. And so the universe now is transparent.
Light can fly through it. It seems, you know, we
can look out in the night sky and see billions
of light years away because you run the clock backwards
(18:40):
until everything sort of scrunches back together, and you talk
about this plasma that fills all of space, and I
think a lot of our listeners probably imagine that the
Big Bang is sort of the creation from one point,
that everything in the universe came from one spot. And
so if you talk about running the clock backwards from
the current universe getting to something that fills all of space,
(19:02):
and I think I wonder if our listeners have a
clear mental picture of what that means, Like, are you
saying that the cosmic microwave background was created by a
plasma that literally filled the entire universe or was the
stuff in the universe sort of smaller and more localized
back then. Probably the single biggest misconception about the Big
Bang it was is that it was some event that
took place at some place, some explosion that all the
(19:24):
stuff came out of. But that's kind of misses the point.
So when I say the cosmic microwave background fills all
of space today, I mean all of space everywhere, and
when it was formed, it was formed at a point
in time where the entire universe, all of space was
filled with this three thousand degree plasma that slowly or
(19:46):
solely transformed into a three thousand degree gas of electrically
neutral particles. And if you go back farther, it's not
that the Big Bang happened somewhere, is that the entire
universe was in this hot and dense state. The Big
Bang wasn't something it happened in one place. It was
a state that the universe started out in. So I
wonder if people would find it more natural to talk
(20:07):
about space being more dense or the stuff in space
being more dense, rather than actually being smaller, because it
sounds like you're talking about sort of stretching out the
space between the stuff, not actually shrinking it down into
a dot. But it's pretty hard to get your mind
around an infinite universe filled with an infinite amount of
stuff and having it still squished down into an infinite universe. Well,
(20:29):
there are a couple of different ways you can think
about it. Um One way you can think about it
is to imagine that the universe might not go on
in all directions forever. It might not be infinite, and
we don't know it. It's possible that that's true. Maybe
the universe, if you go far enough in one direction,
wraps around on itself. Uh. And and this would be
a much farther away than we can see at the
(20:51):
present time. But maybe if you went far enough, you'd
find you'd come out back where you started. Um. I
like using the analogy of the old arcade game from
My My Youth of Asteroids. If you fly the UH
spaceship off the side of the screen Asteroids, you come
out on the opposite side of the screen. Maybe our
universe works this way too. And if that's the case,
then essentially the screen that you're playing on in the
(21:14):
to take my analogy further, has been expanding. And that
means that the total volume of the screen or area
of the screen and the two dimensional example was smaller
in the past, but still the screen occupied all of
the space that existed at the time. So if you
if that helps you to think about it better, that's
one way you can imagine expanding space, uh, without imagining,
(21:39):
for example, space growing into something or or the Big
Bang happening somewhere as opposed to everywhere at the same time. Yeah,
and I think that it's just hard for us to
grasp the concept of infinity. Like, if you take a ruler,
there's an infinite number of places on that ruler between
you know, one inch and two inch, because you know,
there's an infinite number of real numbers. If you shrunk
that ruler, there would still be an a number of places, right.
(22:01):
The infinity doesn't get less infinite just because you shrunk it,
which is sort of counterintuitive. Okay, So let's go back
even farther in time now. So instead of talking about
the universe as it was a few hundred thousand years
after the Big Bang, let's go back to the first
seconds or minutes after the Big Bang. In this state,
the universe was at a billion degrees everywhere throughout all
(22:23):
of space, and at a billion degrees um, things start
to resemble what you would find today inside the core
of very massive stars, and that means that nuclear reactions
can efficiently go on so throughout the entire universe. During
these first seconds and minutes, the entire universe functioned like
(22:44):
a giant nuclear fusion reactor. Protons and neutrons, which up
until this point have been free, we're being combined to
form things like deuterium and helium and lithium and brillium
and releasing energy in the pro sys and uh, we
can use our theories to calculate how much of all
(23:04):
this should have been formed, how much helium, hydrogen, deuterium, lithium,
and brillium. And when we go out and measure how
much of these things there are in the universe, it
turns out that it gives the right answer. So that
gives us a lot of confidence that we understand how
our universe has expanded and evolved from about the first
(23:25):
second after the Big Bang up to the present. All right,
but that's sort of in more indirect evidence than the
stuff we know about later, Like when we talk about
this cosmic microwave background radiation, that's sort of a smoking
gun that that plasma existed because we're seeing it, whereas
the indirect evidence is just sort of like the expansion
of the universe. Now we're talking about things that happened
(23:46):
before that that we can't directly see because the universe
was was opaque. You're talking about developing models that predict
what we would see today if that were true, and
then we find that stuff that's confirmation, But is do
we find more direct evidence would be possible to see
more crisply into into that sort of initial plasma, those
(24:07):
those hot fusion seconds, and and and prove more directly
that that really happened. Well, first of all, I think
the evidence that the universe played out in the way
that the big Bang theory predicts from the first few
seconds onward is pretty strong. It would be quite a
coincidence if the ratios of all those light nuclear elements
matched what we observed just by you know, just your coincidence.
(24:30):
So I think probably a pretty good reason to think
that that's how things played out. That being said, there
are ways that we one day could hope to more
directly measure this era of cosmic history. Um, it's a
little bit science fiction any because it's it's very hard
to do, But someday I think we will directly measure
the neutrinos that were released from our universe about a
(24:52):
second after the Big Bang, so kind of like the
light was released into the universe a few hundred thousand
years after the Big Bang, those neutrinos started to be
able to travel uh safely through the universe without interacting
too much at about a second after the Big Bang.
In other words, the universe became transparent to neutrinos very
shortly after the Big Bang. Now, these neutrinos are very
(25:12):
hard to detect, and uh, there are some ideas about
how one might go about doing it, but I think,
you know, some decades from now, it's very possible that
will be measuring these neutrinos and studying them, studying those
neutrinos in the same sort of way we currently study
the photons that were released much later. Wonderful. That's a
great point, um. I think the cosmic microwave background radiation
(25:34):
is fascinating because it's light we directly see from the
early universe, and of course it's limited because before that
time the universe was opaque. The light that was created
before that was reabsorbed. But as you point out, neutrinos
operate differently, and the universe is transparent to neutrinos today,
and it was transparent earlier. Right that cosmic microwave background
(25:54):
or sorry, that initial plasma in the first hundred thousand
years or fifty thousand years or first few minut it
to the universe. The universe was still transparent to neutrinos. Then,
that's what you're saying, And so we can see those
initial neutrinos. That's right. I mean it will won't be easy.
The same reason that the universe was transparent to neutrinos
so early makes those neutrinos really hard to detect. But
(26:15):
we do imagine one day we'll be able to conduct
a sort of measurements that would actually be able to
detect these neutrinos and learn what that our universe was
like only a second after the Big Bang, much more
directly than we currently can. And it's just another reason
why we should keep sort of opening new eyes to
the universe, looking at the universe through electromagnetic radiation, through neutrinos,
(26:37):
through gravitational waves, because they give us power to look
further and further back on the universe and see different
kinds of stuff. But we haven't seen that yet, right,
that's right. We can't do the sort of direct observations
of the first second or fraction of a second yet.
There's no reason to think that in the distant future, uh,
cosmologists won't be able to do precisely that. Well, this
(26:59):
is a per fixed spot to take a break. We'll
be right back, all right, So take us further back.
We were with a few minutes after the Big Bang,
So going back even further into the first seconds or
(27:22):
first fractions of a second after the Big Bang, we
don't really have any direct way to create images or
even to see the stuff that emerged from this period
of universe's history. So instead what we have to do
is we have to rely on experiments that we can
do in the laboratory where we try to recreate the
conditions of the very early universe and just to understand
(27:45):
where the laws of physics were at that very very
early time. So the main experiments I'm talking about are
what we call particle accelerators, which you you know very
well of course, Daniel um So right now, the world's
most powerful particle accelerator is the Large Hadron Collider. The
Large Hatron Collider is a seventeen mile underground circular tunnel,
(28:06):
and around that tunnel, powerful magnets accelerate protons to nearly
a speed of light um. I think the number is
ninety nine nine nine of the speed of light, awfully
close to the maximum and speed limit of the universe.
We then take those protons and collide them head on
inside of big detectors, and the goal here is to
(28:27):
put as much energy at one place at one time um,
and through Einstein's equals mc squared, we convert that energy
into mass, so we can create exotic forms of matter
that don't exist very accessively or readily in our universe today.
We discovered the Higgs boson this way, but there are
a bunch of different kinds of quarks and leptons and
(28:48):
things called gauge bosons, and all of these things we
can study in these particle accelerators, and all of these
things we think we're plentiful and abundant throughout the universe
is early fraction of a second. I see. So we
developed models that we think describe what happened, and then
we can go test those models by creating similar situations
in the laboratory. Yeah, that's exactly right. So if we
(29:09):
don't know what the laws of physics were under these conditions,
what how the universe works under these really really high
temperatures or energies, we can't really put forth a educated
guess about how the early universe might have played out.
If we can study those laws of physics in these
particles accelerators, we can at least intelligently speculate about what
(29:33):
the first say, trillionth of a second after the Big
Bang was likely. Uh like, right, So let's us test
our models, so lets us understand whether what we think
happened might have actually happened. But again, it's not as
direct as we'd like. It's another piece of the evidence
that constrains what could have happened. But of course, as humans,
(29:54):
we like visual proof, we like very direct evidence. Sometimes
I think about solving science questions is as the way
a a detective might be solving a murder mystery. In
the end, you'd love to have the body and a
lot of physical evidence, but sometimes all you have is
indirect constraints. You know when the person was by videos
somewhere else, and you have an alibi here and alibi there.
(30:15):
You can sort of piece the story together without the
direct evidence of the body of the smoking gun. You're
never sure, but you can do your best with what
you have. Sure, I of course agreed, but I think
it's important to not uh say that just because your
evidence is indirect, that it's necessarily weak. There are a
lot of things that science has done by accumulating indirect
(30:38):
evidence that has led to really strong conclusions. Conclusions we
have enormous confidence in um. Sometimes the right array of
indirect evidence can lead you very confident you understand the
problem you're looking at. Now. I'm very sensitive to that
as well, because everything we discovered in particle colliders we
(30:58):
have seen indirectly. We never observed these particles in our
hands or can play with them or touch them, where
we're looking at their indirect decays and then the observations
in the detectors. That's right. But just because we haven't
ever seen a Higgs boson doesn't mean we're in any
way not confident that it exists. We've measured it in
numerous number of indirect ways. We measured all these things
(31:21):
about it, and as a consequence, we're really sure that
the Higgs boson is a real thing that we're we're
observing and at the large Hattern collider, all right, And
so our knowledge of physics, let's is extrapolated back and
we can check our understanding of how that works. Using
particle colliders to create really hot, dense, energy rich environments.
How far back does that take us? How far back
(31:42):
do we think we might understand the universe? Well? The
protons that we're colliding together at the Large Hattern Collider. Um,
they're colliding with the kinds of energies that the particles
had about a trillionth of a second after the Big Bang.
So by studying these collisions at the Large Hattern collider,
we get a atty good picture for what the unit
(32:02):
early universe was very likely to be have been like
about a trillionth of a second after the Big Bang.
Before that, we don't really have a clue as to
what the laws of physics were, how the sequence of
events might have played out. And is that because we
don't have accelerators that are big enough, Like we built
an accelerator the size of the Solar system that could
collide particles that even higher energy. Would that let us
(32:24):
see further back in time? Yeah, that's right. If we
had a particle accelerator that accelerated particles to even higher
speeds and collided them with more energy than a large
hatter and clider does, we could push back even farther
and closer to the Big Bang if we'd understand the
laws of physics at earlier times and be able to
(32:44):
reasonably construct that early history of our our universe. So
what do we imagine? What do we think might have
happened before a trillionth of a second. We don't know
for sure, but we have at least some good reasons
to think that at some early point in our univers history,
space then just expand quickly and and steadily, but in
(33:05):
kind of a giant burst. This is what we call
cosmic inflation. So when we look at, for example, the
uniformity of our universe, it's basically got the same amount
of stuff everywhere. Or when we look at the geometrical
flatness of the universe, by which I mean that space
on large scales doesn't seem to be curved or warped.
(33:25):
But as the you know, follows the sorts of laws
of geometry that you learned in high school. Uh, these
things lead us to think that the universe probably underwent
this burst of inflationary growth at a very early time.
That being said, we can't really be sure that happened.
We have some, you know, provisional evidence that it probably did,
(33:46):
but we don't know much about this period or why
or how it took place. All right, And here is
a perfect opportunity to ask you a question from Twitter.
Here's a question from Twitter user myself, Bara, who says
how does physics actually test or prove inflation theory. What
kind of test would you propose to verify whether inflation
was reality or just a model we use that explains
(34:09):
the data we have. That's a great question. So let
me start, though by going back a little bit, so
in the nineties seventies, when the Big Bang theory was
kind of becoming, uh the established consensus view of our
universe's history at that point in time, there were a
couple of problems that emerged. One is is that the
(34:29):
universe really seems to be quite uniform, and it's very
hard to understand why, um, some piece of the universe
way over there, and some other piece of universe and
some opposite direction billions and billions and billions of light
years away, why they would be so much alike. It
really seemed like these parts of the universe had had
a chance to synchronize with each other, and we didn't
(34:50):
have any way of explaining that. Also, we didn't have
any way of understanding why the universe was so flat.
And I mentioned this before, but what I really mean
by that is if I take three points in space
and I draw a triangle between them, this is a
huge triangle billions of light years across. If I add
up the angles of that triangle, I always get about
eighty degrees. In other words, like the Euclidean geometry you
(35:13):
learned about in ninth or tenth grade, that seems to
apply to our universe and a larger scales, and that
doesn't have to be the case. Einstein showed us that
space can be curved positively or negatively, and we should
have kind of expected our universe to have been curved,
or at least people argued that. So to solve these puzzles,
people around ninety Alan Bouth and others proposed that the
(35:36):
early universe may have had this inflationary phase where it
grew really fast. When it grows, it flattens out space.
That's kind of a natural dynamical consequence of inflation, and
also it gives all of the points that we see
in space a chance to synchronize early on, explaining why
there's so much alike. Now, Okay, So if that were
(35:56):
the end of the story, I think it would be
unclear yer weather inflation would be a popular theory. It
would have been really hard to say that, uh, we're
really convinced that happened, it would would just not be
enough evidence. But inflation back in the eighties was shown
to make a couple of predictions. For one thing, it
said that when you get around one day to measuring
(36:18):
the details of the temperature patterns and the causic microwave background,
you're going to find that those temperature patterns are what
we call nearly scale invariant and adiabatic. Now those are
some complicated sounding words, but they predicted fairly specific kinds
of patterns in this light. And when we got around
to measuring that and the nineties, two thousands, and as
(36:38):
recently as as as the last few years of the
Pluck satellite, it turns out that those predictions panned out.
The way that the these temperature patterns actually appear in
the universe are consistent with what inflationary theory predicted. And
as a result, most cosmologists today think it's probably pretty
likely that inflation or something like it took place. We're
(37:01):
not sure, but we think it's pretty likely for the
most part. And so that's very important because sometimes you
cook up a scientific theory to sort of describe what
you've seen, you have a lot of freedom there to
sort of tweak the parameters and make sure it describes
what you've seen. But the real test, of course of
whether it's real is can it predict something it hasn't
seen yet, And so you're saying that inflation has sort
(37:21):
of passed that test. It says, if this was true,
you should expect to see these weird, particular fluctuations in
the energy from the early universe. And we have seen that.
That's right. If it weren't for these predictions and the
fact that they turned out to be correct, um, there
wouldn't be nearly as much confidence that our universe really
had an inflationary era and shortly after the Big Bang?
(37:42):
Do you think that's a widely held view in cosmology?
Would a random cosmologist I asked on the street agree
with you about that? Yeah, more or less. I mean,
there are a few cosmologists out there who are, you know,
argue against inflation as the best answer, and uh, and
they're they're they're constructing competing theories and things. But I
think if you did a of it, you'd find the
vast majority of cosmologists would agree with the statement that
(38:03):
our universe probably had an inflation area. All right, So
you've taken us back to the very very early moments
of the universe, where we have inflation, when the universe
expands by a ridiculous quantity in a in a ridiculously
short time. What about before that? What caused inflation? What
happened before inflation? Well, the real answer is, we just
(38:23):
don't know. We don't have any way to observe how
our universe was in this extremely early era of cosmic history,
and we don't have any experiments that we know how
to do, at least yet to tell us what the
laws of physics that dictated that era might have been.
We do know that if you go back far enough
in time, the theories we have that describe the laws
(38:45):
of physics and our universe must break down. We know
this because the general theory of relativity describes gravity and
space and time isn't compatible at extremely high energies with
the laws of quantum mechanics as we know them, So
one or both of those theories must break down um.
As it turns out, sometime in the first ten of
(39:06):
the minus forty three seconds after the Big Bang, we
simply have no clue uh what uh the universe might
have been like or even if we're asking the right
questions about it during that era that we call the
quantum gravity era. Well, that sounds like the way we
talk about the interior of black holes. We know that
general relativity is a strong theory, it's been tested in
(39:26):
lots of ways, but we suspect that inside a black
hole it might be wrong because it gives predictions that
disagree with quantum mechanics. Is it a similar way to
think about it. Yeah, it's a lot like that. In fact,
I would go as far as to say that it's
possible that when we do have a you know, real
theory of quantum gravity, questions like what's inside of a
black hole, those questions won't even make sense anymore. That
(39:49):
they will have a complete description of nature um, but
there won't be an interior of black holes. And and
maybe something equally surprising pertains to the quantum gravity era
of our universe. Who knows? Wonderful, Well, this is the
perfect time to ask you a question from a listener.
Here's an audio question from Anders from Norway. Hi. This
is Ander's moan from Oslo, Norway. I was wondering about time.
(40:11):
Did it behave differently when the universe was younger and denser.
That's a great question. So the first thing to appreciate
is that time is awfully weird even in the universe today. Um,
the sort of linear, you know, series of events that
that UH physics used to be based on, like in
the Newtonian worldview, was overturned by UH by Einstein more
(40:35):
than a century ago. And in general relativity time really
behaves pretty weird. So the length of time that passes
between two events will depend on, for example, what frame
of reference you're doing the measuring, and and things like this,
and the being in the presence of a strong gravitational
field can make time pass differently in things like this.
(40:56):
So time is very weird. But what I would say
with that being said is that the way that time
works in the universe today is not meaningfully different from
how it worked a thousand years or a year, or
a second after the Big Bang, or even a trillion
of a second. But if you go back even farther,
if you reach the point of the quantum gravity area era,
(41:17):
we know that time must have been very different than
anything we're currently imagining. We don't know what it was like,
but um, I think it's a safe bet that it
was very different from anything one might experience today. So
you're painting a pretty big question mark earlier than ten
of the mind seconds is and we don't know what's there.
We can't even really imagine it. But if you're a cosmologists,
(41:40):
you spend your life thinking about this stuff. You must
have a sort of a mental picture when you think
about what happened before inflation, when you think about the
moment of creation WATI equal zero, what do you have
in your mind? Well'm usually the kind of person who's
perfectly happy to speculate about things we don't know anything about.
But when it comes to that quantum gravity era era,
I'm not even you know, super comple doing it, and
(42:00):
just there's we have no foundation to really build upon um.
But that being said, you know, some people in the
worlds of string theory or loop quantum gravity do try
to construct ideas of what sort of things may have
existed at this time. Maybe the universe wasn't four dimensional
or with three dimensions was based on one time, but
(42:21):
it had more dimensions of space, and maybe space consisted
of you know, concluded things like you know, strings and
membranes and other sorts of exotic objects. Um, you know,
maybe the space itself was in a superposition of different
states of curvature and all this sort of stuff, and
you can put all these sorts of words of things.
I'm not sure that, uh, your listeners are going to
(42:44):
really be able to wrap their head around the stuff
I'm saying right now, But frankly, I'm not sure that
I'm able to either. So we're all in the same boat,
all right. But it was fascinated here anyway. Um, I
was wondering, what would you sort of hope for in
so in terms of future experiments that we're going to
get a grasp on what happened before ten of the
minus forty three? What future experiments would you like to
(43:07):
fund if you had infinite resources, what would you build
in order to give us a clue as to what
happened in the very first instance of the universe. Well,
in the more near term, we're going to measure the
cause of microave background in greater and greater detail. We're
gonna look for things like B mode polarization and non gaussianity.
These are the sorts of signatures that, if we were
(43:29):
to see them, would tell us something about the inflation
are epoch. So, for example, if we measure these what
we call demode polarization signals, you'd be able to know
roughly what the energy density of the universe was during inflation.
That allows us to like take the list of all
of our different inflationary theories and shrink it down into
a much more manageable number of possibilities. Um, it won't
(43:50):
tell us everything we want to know about inflation, but
it will give us a lot closer and it will
make us a lot more confident that you know, something
like inflation in fact took place in the more are
distant future a little bit more science fiction. E. I
imagine one day we're going to study the cause of
neutrino background, and we're not only going to detect it,
but we're gonna measure it with the kind of precision
(44:10):
that we've already measured the cosmic microwave background. So we
will learn as much about the universe as it was
a second after the Big Bang as we currently know
about the universe hundreds of thousands of years after the
Big Bang. This is something that will happen a long
long time from now. It's not something that I'm going
to see happen in my career, probably, But you know,
(44:31):
there's lots of reasons to think that the long term
future of cosmology is going to be a very exciting endeavor.
All these experiments that you envisioned, they all sound wonderful,
and I'd like to know the answers to them also,
But would any of them give us an insign to
what happened in those very first few moments before ten
to the minors forty three? Some of them will give
us a clue as to what happened in the later epics,
(44:52):
But will any of them pierce that veil and tell
us what happened in the quantum gravity era? Well, the
veil that separates us from the quantum gravity era is
a very thick veil. Indeed, Um, it's hard to imagine
how we're really going to figure out what that period
of our universe's history might have been like. I don't know.
Maybe one day strength theorists will UH make progress in
(45:13):
such a way that allows us to make testable predictions
that will give it this period of time. Um. But
I suspect that when or if we ever do UH
get some insights in this period of time, it will
be in the context of theories that we haven't even
thought about yet, or experiments that I can't even wrap
my heads around, like and it head around it. It
would be like asking a philosopher from a thousand years
(45:35):
ago to speculate about how twentieth century physics is going
to play out. Um, you know, there's no one could
have imagined relativity and quantum mechanics. Uh, you know, some
some distance in time ago like that. And Uh. Similarly,
I imagine that if you, you know, if we try
to imagine what physics three years from now will look like,
(45:58):
we would come up very very short and trying to
put our heads around anything like that or even imagining
what that might look like. I agree. I think if
you showed a philosopher from a thousand years ago a
children's book about astrophysics, they would not understand it. And
in a similar way, if you could somehow steal a
children's book about astrophysics from the year three thousand, you
(46:19):
and I would be baffled. We wouldn't be able to
get past the first page. I expect um, But those
concepts would be very natural to people, people thinking and
breathing and living and asking questions. Then something I really
liked about your book is that you said we are
in a time of reckoning, and it gives me the
sense that we expect physics to be revolutionized. We expect
that we might learn things about the universe that would
(46:41):
fundamentally change our ideas about them. I think this connects
back to the sort of philosophical implications of this kind
of research. And so to close out, I want to
ask you, what do you imagine the sort of deep
problems with physics might be reconciled in the next hundred
or two hundred years. I can't expect you to know
the answers, but at least what do you think there
are the questions we might get answers too? Well? Of
(47:02):
course I don't know for sure, no one does. But
when I look at the various puzzles and problems faced
by cosmologists today, it gives me reason to at least
suspect that the early universe played out very differently than
the textbooks currently describe. So here's what I have in mind. So, um,
(47:24):
when I if we if we just take the laws
of physics as we currently understand them and run them
through the early universe, those laws of physics say that
all of the matter and all of the antimatter should
have been destroyed. They should have destroyed each other in
the first fraction of a second um and that would
have left our universe without any atoms in it. And
yet our universe is full of atoms. I'm made of atoms,
(47:44):
You're made of atoms. Everything we know and directly experience
is made of atoms. So somehow things must have played
out differently than anything we currently understand in that first
fraction of a second after the Big Bang. Similarly, a
problem that I work on a lot is that of
dark matter. If you asked a bunch of people specialized
in the dark matter ten years ago, they would have
(48:05):
probably told you that it's likely that dark matter consists
of these things called whimps, weekly interacting massive particles. But
we've looked for whimps, and we we we know what
kind of experiments we needed to do to find whimps,
and we've done those experiments and we just haven't found anything. Um. Now,
it's possible that whimps will be discovered any day now,
and they're right around the corner. But I think at
(48:25):
a minimum, it's fair to say that it's surprising that
those whimps haven't shown up. So that could be that
the dark matter is just made of something different than
we had currently imagined, or it might mean that the
early universe played out differently. Our arguments for what whimps
should look like in what experiments we would have to
do to discover them, we're based on our understanding of
(48:48):
how things played out in the early universe when the
whimps were being created. If the early universe played out
differently than we had imagined, then the way that dark
matter would have been created and the kind of experiens
we'd have to do to find dark batter could be
very different. And then of course there's a problem of inflation. Uh,
somehow the universe got very flat and somehow the universe
(49:09):
got very uniform, and inflation is a good description of that.
But we don't know how how that played out. We
don't know how or why inflation happened the way it did.
Um I think it's fair to say that we have
more more questions than answers when it comes to the
inflationary era, and possibly related to inflation is the issue
(49:30):
of dark energy. We've learned in the last twenty years
at our universe isn't just expanding, it's expanding at an
accelerating rate, and that seems to suggest that empty space
has a certain amount of energy built into it, a
kind of vacuum energy. Um. Maybe this is similar to
the kind of energy that drove inflation shortly after the
Big Bang, and is happening now in a more gentle way.
(49:52):
We don't know, But all of these things, to my mind,
collectively point to some very weird and counterintuitive stuff that
I'd have played out in that first second or millions
or billions or trillion of a second after the Big Bang. Um,
that's where my money is on a new big revolutions
in physics. Well, I appreciate your scientific honesty that you're
(50:14):
willing to admit what we don't know, and also you're
a scientific optimism that one day scientists will unravel these
ideas and maybe on a podcast in a hundred years
they'll be chatting casually about answers to these questions. Thanks
very much for coming on our podcast today and talking
to us about these amazing questions about the nature of
the universe and its origins. And remember, everybody, Dan's book
(50:35):
is called At the Edge of Time. It comes out
on November five from Princeton University Press. I totally encourage
you to check it out if you're into origins of
the universe and cosmic questions. Thanks again, Dan for joining us,
and thank you listeners for tuning in. If you still
(50:58):
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 at Facebook, Twitter, and Instagram at
Daniel and Jorge That's one Word, or email us at
Feedback at Daniel and Jorge dot com. Thanks for listening,
and remember that Daniel and Jorge Explain the Universe is
a production of I Heart Radio. For more podcast from
(51:20):
my Heart Radio, visit the I Heart Radio app, Apple Podcasts,
or wherever you listen to your favorite shows. Yeah
One of the deepest goals of physics is to help
us understand our context. Are we humans at the center
of everything or are we in an irrelevant little corner
of the universe? Was the universe created with us in it?
Or did it exist for an unimaginable eons before we arrived.
(00:28):
The answers to each of these questions helps us know
our place or lack of it, in the universe. It
helps us know how to live our lives. But nothing
touches these issues more deeply than understanding the very birth
of the universe. What, if anything, can we ever hope
to reveal about those first few moments of creation? Hi,
(01:08):
I'm Daniel Whitson. I'm a particle physicist and a professor
you see Irvine, and I am the co host of
today's podcast, Daniel and Jorge Explain the Universe, brought to
you by I Heart Radio listeners. The podcast now that
we love to examine big questions, deep questions, questions about
things really far away, questions about things under our feet,
(01:30):
questions about how things around us work. But we're also
interested in the really deep questions, not just questions of space,
but also questions of time and so while Jorge is
still away and not available today. I'm very pleased to
have on the podcast today a friend of mine, a collaborator,
a colleague, and a upcoming author of a book I
(01:50):
think all of you would be excited about. His name
is Dan Hooper. He is a theoretical astrophysicist at FIRMY
National Accelerator Laboratory and ACT. He is the head of
the theoretical astrophysics group there, and he has a new
book coming out about the beginning of the universe. It's
called At the Edge of Time and it's going to
be available in November five from Princeton University Press. Now,
(02:13):
I've had the opportunity to take a look and at
advanced copy of this book, and I think it's awesome.
It talks about a lot of the really amazing questions
we like to dig into on the podcast. So without
further Ado, let me introduce to you my friend and colleague,
Dan Hooper. Thanks. I'm really excited to be here. Yeah. Well,
thanks for coming on the podcast and talking to us
about all the amazing and incredible things that we like
(02:35):
to think about. And apparently you like to write about
one thing we like to do in this podcast is
talk about things that are on the cutting edge of science,
things that scientists themselves are thinking about, but then trying
to break it down in a way that makes sense
to people. People can actually come away feeling like they
understand what we're talking about, not just repeating various jargon. Thanks.
(02:56):
I really enjoy trying to think of ways to a
some of the scientific ideas that I explore my research
for people who aren't scientists, whether that be my non
scientist friends or uh my family members. Uh. I really
like stretching that part of my brain that uh one
uses and communicating these exciting and very different ideas. And
(03:20):
I think your book does a great job of this.
I really conveying not just what we know, but also
what we don't know, where the edge of knowledge is
and and it is something else. It shows us that
science is personal. I think one of the great things
about your book is that it reflects who you are.
Doesn't just show science for being some monolith of knowledge
or something some sort of objective intellectual pursuit, but it
(03:44):
shows us that science really is of the people, by
the people, and for the people, because in the end,
science is just humans answering human questions. For other humans.
Science is always just a work in progress. Um, the
questions we're asking today, we'll probably not be the questions
that we find answers to ultimately. And when it comes
(04:04):
to the sort of stuff that I work on, I
would be shocked and maybe a little disappointed if it
turns out that the ideas we have about how things
are going to play out turn out to be right.
I really like the mystery that that's involved. And uh,
the surprise when we find out something we weren't expecting,
I only hope. So I love scientific surprises. But tell me,
(04:25):
what was your motivation for writing a popular science book
about this rather than just sort of continuing in the
conversation at the level of academia. Why bring this question
to the people. Long before I ever became a scientist,
I loved popular physics books. I used to read any
number of books by folks like Paul Davies, MITCHA. Kaku,
Kip Thorne, and this st just blew my mind learning
(04:48):
about quantum mechanics and learning about UH relativity, cosmology and
kind of the philosophical implications of all of it. Um. So,
when I became a science entist, I decided it would
be fun to kind of stretch my brain and uh
and try to try my hand at popular science writing myself.
(05:09):
This isn't the first time I've ever been in a
popular science book, but I haven't written popular science in
a long time. And uh, it's exciting, new challenge. I
love new challenges, and uh, this was no exception wonderful.
So as a theoretical astrophysicist and a cosmologist, you're dealing
with questions about like the origin of the universe and
the beginning of space and time, the very creation of
(05:30):
our cosmos. When you travel around, say you're on an
airplane and some random person asks you what do you do?
Do you have an easy time explaining to them what
you do and why it's interesting, or do you get
a sort of a lot of glazed looks. The reactions
I get are kind of all over the map. Occasionally
you get lucky and you start that conversation and the
person is excited, and uh, you know, maybe they think
(05:54):
that's the perfect person to sit next to for the
course of the flight. Um, they always wanted to know
about cosmology and finally have an opportunity to to ask
somebody all the questions they build up over time. And
sometimes you sit next to somebody who, just for whatever reason,
they just don't have the you know, the kind of
intellectual curiosity for this sort of subject that you or
(06:16):
I might have and uh and in sometimes you get
the people who confuse cosmologists with cosmetologists, and that's pretty awkward. Um,
so yeah, you can. You can have just about any
kind of experience on a plane. When you tell them,
UM about my line of work. Are you willing to
give advice on lipstick colors or not? I mean, I'd
be willing to give you my advice and just about anything,
(06:38):
but I don't think you should take it. For one thing,
I'm I'm color blind, so i'd probably be pretty bad
at that job. All right, Well, I think that these
kind of topics are totally accessible because I think everybody
wants to know the origins where we came from, because
it tells us something about why we're here and what
it means. Um And I posted a question on Twitter
(06:59):
this week, and I say, hey, I get to ask
a leading cosmologist questions about the beginning of the universe.
What should I ask? And boy, our listeners really showed up.
We've got a long list of questions, and we're going
to listen to some of those questions and answer some
of those questions. But I was just impressed at how
much of a vein it touched in people. It doesn't
surprise me. I'm excited about this stuff. I guess our listeners,
(07:19):
of course, are also excited about this stuff. But I
think it goes to something else about cosmology and early
universe physics, is that it really borders with philosophy. You know,
some of the questions we ask are hard physics questions,
like when was dark matter made? Do we have a
model for the production of these nuclei? But the answers
to those questions have broad reaching implications for philosophy, for
(07:41):
the nature of our existence, the meaning of the context
of it. Throughout history, human beings of all times and
all cultures have looked up at their night sky and
wondered about the universe and how it came to be
the way that it is. In that respect, we're just
like all of those people, but in one important way
we're really different. For the first time in human history,
(08:03):
when we look up at the night sky, we more
or less know what it is we're looking at. We
understand these things, and that's a truly new development. Um.
I think it's just amazing that we can take pictures
of things in the sky and when we see a star,
we know how nuclear fusion works in its core. And
when we see planets, we understand how they formed and
(08:25):
why they behave the way they do and what they're
made of. When we look at the expansion of the
universe and we look at the Big Bang, we understand
how our universe evolved from its first second up to
the current era, like over thirteen billion years. I I
think that's absolutely, you know, flabbergasing, just amazing that that
(08:45):
we've been able to make this incredible human accomplishment. It's
the kind of thing that if you went back a
few hundred years and drop that knowledge on leading minds
of the day, their minds would be blown right, It'd
be hard for them to really even understand what you're
talking about. And now we know those things, and that
gives me enthusiasm that today's questions will one day be answered.
The humans will know the answer to the questions we
(09:06):
are struggling with today. Makes me want to jump in
a time machine and fast forward. In the long run,
I'm definitely a scientific optimist. I think only a fool
bets against the progress of science and the very long run.
We might not solve every question tomorrow, but as long
as human beings managed to exist and not destroy themselves,
(09:26):
I don't think there are any answerable questions that we
won't eventually answer. Wonderful Well, I noticed in your book
that while your topics touch on these important matters that
connect to philosophy, unlike some other noted cosmologists, you sort
of stayed in your lane and talked mostly about the
physics um and so I want to take the opportunity
(09:47):
to push you a little bit on this podcast. When
we have an expert come in, we like to play
a game we call ask the wrong Expert. So I'm
gonna ask you some questions about philosophy, and this gives
you an opportunity to, you know, pun tificate ignorantly, and
we don't expect you to be an expert. First question
is about whether the universe actually exists. So do you
(10:08):
think the universe, the physical universe a exists sort of
outside of our human experience, like it would be there
even if we weren't here to experience it. B only
exists as a mathematical model in our minds. C is
an unanswerable question. We can never know or D you're
already regretting coming onto our podcast, I definitely come down
(10:30):
on C for this one. Um. All we can really
do is organize our consciousness experiences, including our observations of
the world. UM, try to make sense of them. Try
to come up with order organizing principles or theories, if
you will, that explain as much about our observations as
we can, and then use those theories to make predictions
(10:54):
about what will happen in our conscious experience going forward.
It could be that those theories we construct in that
way map very precisely or or closely onto something real,
a real world that those theories describe, or maybe not.
We don't really have any way of finding out. But
it doesn't really matter, because science works even if the
(11:18):
world it describes is not a real thing. UM. I
have a supercomputer in my pocket in the form of
a cell phone, and that thing works because of the
scientific method. And um, you know, modern medicine and transistors
and any number of other amazing modern technologies work because
(11:41):
of the scientific method, even if the world that it
underpins uh is very different from that described in our theories. Well,
that's amazing, Um. I agree with you. We might not
be able to answer it, but to me it matters
deeply whether what we're doing is just sort of playing
in our minds or answering real questions about the univers
And that's one of the reasons why I'm very much
(12:02):
looking forward to the day when we meet alien physicists
and perhaps get a chance to understand how a different
kind of consciousness might probe the universe, and and maybe
draw some sort of triangulation there about what's really happening.
But in the end, I agree with you, we probably
can't ever know. But that leads me to my second
question about the working of the human brain. Do you
(12:24):
think that the human brain is either a deterministic like
a big complicated mechanical watch in which we have no
free will, be deterministic, but yet there's somehow still room
in there for free will see nondeterministic because of quantum
mechanics like Penrose things, or d nondeterministic because of sort
of sort of magic, supernatural extra extra physical force. I
(12:48):
think this is a really good question, but I don't
think any of my my answer really falls into any
of these four categories or A, B, C, or D.
So I'm going to kind of give you my my
own e if you will answer. So. I think the
laws of nature are not deterministic. Quantum mechanics doesn't appear
to be deterministic. It might be in some sort of
everready in many world sense, But as far as any
(13:12):
experiment I would conduct, I can only probabilistically work out
what's going to happen in that experiment. So, for all
intents and purposes, UH, the laws of physics are not deterministic,
And since the human brain is a machine that follows
the laws of physics in our world, it also is
not deterministic. But as far as free will is concerned,
(13:34):
I don't think that matters. What I mean by that
is just because something in my brain is random and
not predictable doesn't mean I'm free to make any choices.
If I walked around flipping a coin to decide whether
I'm gonna do thing A or thing B next, that
doesn't give me any freedom. It just means I'm not predictable. So,
(13:56):
at least in any morally culpable sense, I don't believe
there's any reason to think there's free will and unit
that's a very sophisticated answer. I think I agree with
you on all points, and we're actually gonna dig into
that in depth in a future episode of this podcast.
So thanks for playing along with our silly game. But
the reason we brought you onto the podcast is to
talk about what you are an expert in, and that's
(14:18):
the early universe and the very beginning of time. And
so I want to dig into the details and pick
your brain about how our universe began. But first let's
take a quick break. Okay, we're back and we're talking
(14:41):
with Dan Hooper. He's a theoretical physicist at Firmy National
Accelerated Laboratory and the author of the upcoming book At
the Edge of Time, which explores the very beginning of
the universe. And Dan, first question for you to have
about what you actually know about is about how the
universe began. I would I would love if you would
sort of walk us through the very beginning of the universe.
(15:03):
And I'll give you two options here. Either walk us
through forwards from the moments of creation or backwards from
what we actually know into what we don't know. But
I'd love a sort of tour of the very first
moments of the universe. So even if you hadn't given
me the option, I definitely would have suggested going from
the present backwards because that's just a lot easier way
(15:24):
to describe it. So let me do it that way.
When we look at it out at our universe today,
we see that space is expanding. And what I mean
by that is all the objects in space, at least
the objects that are far away, like galaxies, for example,
they're all moving away from us, and the farther away
something is from us, the faster it's moving away from us.
This is because any two points in space, the amount
(15:48):
of space between them is growing as time goes on.
This is something we call Hubble's law. So because space
is expanding, that means that in the past our universe
uh was more compact, more dense, and as a consequence,
it was hotter, and in the future it will be
less dense and even cooler than it is today. So
(16:10):
if you run those equations backwards, you'll eventually point a
time reach a point in time where the universe was
very hot. Um So thirteen point eight billion years ago,
only a few hundred thousand years after the Big Bang,
you reach a point where the entire universe was filled
with uh some light and electrons and protons and things
(16:30):
that were all at a temperature of about three thousand degrees.
So three thousand degrees is an important point in in
the history of the universe because at three thousand degrees
you find that atoms begin to melt. This is what
I mean by that. So if I take some ordinary
atoms and I dump it in some thorough baths somewhere
(16:51):
that has a temperature more than three thousand degrees, well,
if I do that, those atoms, all the electrons that
are bound up on those atoms are gonna break off.
They're gonna basically those atoms are going to fall apart
into their protons and nuclei and electrons. So that means
that before this this key point three eighty thousand years
after the Big Bang, the universe was full of electrons
(17:15):
and protons and nuclei, but no neutral atoms. And then
after this point, basically all those things glued together into
into electrically neutral atoms. Before that transition, the universe was opaque,
meaning light couldn't couldn't move through space. Because of all
these charged particles in it. But after this point, the
(17:35):
universe became transparent to light. And that means that at
this transition, um awful lot of light was dumped into
the universe, and that light exists everywhere today. It's moving
in all directions and in all places, and in fact,
in this very room, or any any room, every cubic
centimeter of space has over four hundred photons that were
(17:56):
produced in this transition. We call that the causing mic
wave background. And over the last fifty years or so,
becausemologists have been studying this been greater and greater detail.
A lot of what we know about our universe's history
comes directly from observing that light that was released when
the first atoms are formed only a few hundred thousand
years after the Big Bang. All right, but let me
(18:18):
ask you a question there to clarify. So you're saying,
we look out of the universe, we see things are expanding,
and if we want to run the clock backwards, we say, well,
therefore things must have been denser before, because things are
getting less dense now. And so the universe now is transparent.
Light can fly through it. It seems, you know, we
can look out in the night sky and see billions
of light years away because you run the clock backwards
(18:40):
until everything sort of scrunches back together, and you talk
about this plasma that fills all of space, and I
think a lot of our listeners probably imagine that the
Big Bang is sort of the creation from one point,
that everything in the universe came from one spot. And
so if you talk about running the clock backwards from
the current universe getting to something that fills all of space,
(19:02):
and I think I wonder if our listeners have a
clear mental picture of what that means, Like, are you
saying that the cosmic microwave background was created by a
plasma that literally filled the entire universe or was the
stuff in the universe sort of smaller and more localized
back then. Probably the single biggest misconception about the Big
Bang it was is that it was some event that
took place at some place, some explosion that all the
(19:24):
stuff came out of. But that's kind of misses the point.
So when I say the cosmic microwave background fills all
of space today, I mean all of space everywhere, and
when it was formed, it was formed at a point
in time where the entire universe, all of space was
filled with this three thousand degree plasma that slowly or
(19:46):
solely transformed into a three thousand degree gas of electrically
neutral particles. And if you go back farther, it's not
that the Big Bang happened somewhere, is that the entire
universe was in this hot and dense state. The Big
Bang wasn't something it happened in one place. It was
a state that the universe started out in. So I
wonder if people would find it more natural to talk
(20:07):
about space being more dense or the stuff in space
being more dense, rather than actually being smaller, because it
sounds like you're talking about sort of stretching out the
space between the stuff, not actually shrinking it down into
a dot. But it's pretty hard to get your mind
around an infinite universe filled with an infinite amount of
stuff and having it still squished down into an infinite universe. Well,
(20:29):
there are a couple of different ways you can think
about it. Um One way you can think about it
is to imagine that the universe might not go on
in all directions forever. It might not be infinite, and
we don't know it. It's possible that that's true. Maybe
the universe, if you go far enough in one direction,
wraps around on itself. Uh. And and this would be
a much farther away than we can see at the
(20:51):
present time. But maybe if you went far enough, you'd
find you'd come out back where you started. Um. I
like using the analogy of the old arcade game from
My My Youth of Asteroids. If you fly the UH
spaceship off the side of the screen Asteroids, you come
out on the opposite side of the screen. Maybe our
universe works this way too. And if that's the case,
then essentially the screen that you're playing on in the
(21:14):
to take my analogy further, has been expanding. And that
means that the total volume of the screen or area
of the screen and the two dimensional example was smaller
in the past, but still the screen occupied all of
the space that existed at the time. So if you
if that helps you to think about it better, that's
one way you can imagine expanding space, uh, without imagining,
(21:39):
for example, space growing into something or or the Big
Bang happening somewhere as opposed to everywhere at the same time. Yeah,
and I think that it's just hard for us to
grasp the concept of infinity. Like, if you take a ruler,
there's an infinite number of places on that ruler between
you know, one inch and two inch, because you know,
there's an infinite number of real numbers. If you shrunk
that ruler, there would still be an a number of places, right.
(22:01):
The infinity doesn't get less infinite just because you shrunk it,
which is sort of counterintuitive. Okay, So let's go back
even farther in time now. So instead of talking about
the universe as it was a few hundred thousand years
after the Big Bang, let's go back to the first
seconds or minutes after the Big Bang. In this state,
the universe was at a billion degrees everywhere throughout all
(22:23):
of space, and at a billion degrees um, things start
to resemble what you would find today inside the core
of very massive stars, and that means that nuclear reactions
can efficiently go on so throughout the entire universe. During
these first seconds and minutes, the entire universe functioned like
(22:44):
a giant nuclear fusion reactor. Protons and neutrons, which up
until this point have been free, we're being combined to
form things like deuterium and helium and lithium and brillium
and releasing energy in the pro sys and uh, we
can use our theories to calculate how much of all
(23:04):
this should have been formed, how much helium, hydrogen, deuterium, lithium,
and brillium. And when we go out and measure how
much of these things there are in the universe, it
turns out that it gives the right answer. So that
gives us a lot of confidence that we understand how
our universe has expanded and evolved from about the first
(23:25):
second after the Big Bang up to the present. All right,
but that's sort of in more indirect evidence than the
stuff we know about later, Like when we talk about
this cosmic microwave background radiation, that's sort of a smoking
gun that that plasma existed because we're seeing it, whereas
the indirect evidence is just sort of like the expansion
of the universe. Now we're talking about things that happened
(23:46):
before that that we can't directly see because the universe
was was opaque. You're talking about developing models that predict
what we would see today if that were true, and
then we find that stuff that's confirmation, But is do
we find more direct evidence would be possible to see
more crisply into into that sort of initial plasma, those
(24:07):
those hot fusion seconds, and and and prove more directly
that that really happened. Well, first of all, I think
the evidence that the universe played out in the way
that the big Bang theory predicts from the first few
seconds onward is pretty strong. It would be quite a
coincidence if the ratios of all those light nuclear elements
matched what we observed just by you know, just your coincidence.
(24:30):
So I think probably a pretty good reason to think
that that's how things played out. That being said, there
are ways that we one day could hope to more
directly measure this era of cosmic history. Um, it's a
little bit science fiction any because it's it's very hard
to do, But someday I think we will directly measure
the neutrinos that were released from our universe about a
(24:52):
second after the Big Bang, so kind of like the
light was released into the universe a few hundred thousand
years after the Big Bang, those neutrinos started to be
able to travel uh safely through the universe without interacting
too much at about a second after the Big Bang.
In other words, the universe became transparent to neutrinos very
shortly after the Big Bang. Now, these neutrinos are very
(25:12):
hard to detect, and uh, there are some ideas about
how one might go about doing it, but I think,
you know, some decades from now, it's very possible that
will be measuring these neutrinos and studying them, studying those
neutrinos in the same sort of way we currently study
the photons that were released much later. Wonderful. That's a
great point, um. I think the cosmic microwave background radiation
(25:34):
is fascinating because it's light we directly see from the
early universe, and of course it's limited because before that
time the universe was opaque. The light that was created
before that was reabsorbed. But as you point out, neutrinos
operate differently, and the universe is transparent to neutrinos today,
and it was transparent earlier. Right that cosmic microwave background
(25:54):
or sorry, that initial plasma in the first hundred thousand
years or fifty thousand years or first few minut it
to the universe. The universe was still transparent to neutrinos. Then,
that's what you're saying, And so we can see those
initial neutrinos. That's right. I mean it will won't be easy.
The same reason that the universe was transparent to neutrinos
so early makes those neutrinos really hard to detect. But
(26:15):
we do imagine one day we'll be able to conduct
a sort of measurements that would actually be able to
detect these neutrinos and learn what that our universe was
like only a second after the Big Bang, much more
directly than we currently can. And it's just another reason
why we should keep sort of opening new eyes to
the universe, looking at the universe through electromagnetic radiation, through neutrinos,
(26:37):
through gravitational waves, because they give us power to look
further and further back on the universe and see different
kinds of stuff. But we haven't seen that yet, right,
that's right. We can't do the sort of direct observations
of the first second or fraction of a second yet.
There's no reason to think that in the distant future, uh,
cosmologists won't be able to do precisely that. Well, this
(26:59):
is a per fixed spot to take a break. We'll
be right back, all right, So take us further back.
We were with a few minutes after the Big Bang,
So going back even further into the first seconds or
(27:22):
first fractions of a second after the Big Bang, we
don't really have any direct way to create images or
even to see the stuff that emerged from this period
of universe's history. So instead what we have to do
is we have to rely on experiments that we can
do in the laboratory where we try to recreate the
conditions of the very early universe and just to understand
(27:45):
where the laws of physics were at that very very
early time. So the main experiments I'm talking about are
what we call particle accelerators, which you you know very
well of course, Daniel um So right now, the world's
most powerful particle accelerator is the Large Hadron Collider. The
Large Hatron Collider is a seventeen mile underground circular tunnel,
(28:06):
and around that tunnel, powerful magnets accelerate protons to nearly
a speed of light um. I think the number is
ninety nine nine nine of the speed of light, awfully
close to the maximum and speed limit of the universe.
We then take those protons and collide them head on
inside of big detectors, and the goal here is to
(28:27):
put as much energy at one place at one time um,
and through Einstein's equals mc squared, we convert that energy
into mass, so we can create exotic forms of matter
that don't exist very accessively or readily in our universe today.
We discovered the Higgs boson this way, but there are
a bunch of different kinds of quarks and leptons and
(28:48):
things called gauge bosons, and all of these things we
can study in these particle accelerators, and all of these
things we think we're plentiful and abundant throughout the universe
is early fraction of a second. I see. So we
developed models that we think describe what happened, and then
we can go test those models by creating similar situations
in the laboratory. Yeah, that's exactly right. So if we
(29:09):
don't know what the laws of physics were under these conditions,
what how the universe works under these really really high
temperatures or energies, we can't really put forth a educated
guess about how the early universe might have played out.
If we can study those laws of physics in these
particles accelerators, we can at least intelligently speculate about what
(29:33):
the first say, trillionth of a second after the Big
Bang was likely. Uh like, right, So let's us test
our models, so lets us understand whether what we think
happened might have actually happened. But again, it's not as
direct as we'd like. It's another piece of the evidence
that constrains what could have happened. But of course, as humans,
(29:54):
we like visual proof, we like very direct evidence. Sometimes
I think about solving science questions is as the way
a a detective might be solving a murder mystery. In
the end, you'd love to have the body and a
lot of physical evidence, but sometimes all you have is
indirect constraints. You know when the person was by videos
somewhere else, and you have an alibi here and alibi there.
(30:15):
You can sort of piece the story together without the
direct evidence of the body of the smoking gun. You're
never sure, but you can do your best with what
you have. Sure, I of course agreed, but I think
it's important to not uh say that just because your
evidence is indirect, that it's necessarily weak. There are a
lot of things that science has done by accumulating indirect
(30:38):
evidence that has led to really strong conclusions. Conclusions we
have enormous confidence in um. Sometimes the right array of
indirect evidence can lead you very confident you understand the
problem you're looking at. Now. I'm very sensitive to that
as well, because everything we discovered in particle colliders we
(30:58):
have seen indirectly. We never observed these particles in our
hands or can play with them or touch them, where
we're looking at their indirect decays and then the observations
in the detectors. That's right. But just because we haven't
ever seen a Higgs boson doesn't mean we're in any
way not confident that it exists. We've measured it in
numerous number of indirect ways. We measured all these things
(31:21):
about it, and as a consequence, we're really sure that
the Higgs boson is a real thing that we're we're
observing and at the large Hattern collider, all right, And
so our knowledge of physics, let's is extrapolated back and
we can check our understanding of how that works. Using
particle colliders to create really hot, dense, energy rich environments.
How far back does that take us? How far back
(31:42):
do we think we might understand the universe? Well? The
protons that we're colliding together at the Large Hattern Collider. Um,
they're colliding with the kinds of energies that the particles
had about a trillionth of a second after the Big Bang.
So by studying these collisions at the Large Hattern collider,
we get a atty good picture for what the unit
(32:02):
early universe was very likely to be have been like
about a trillionth of a second after the Big Bang.
Before that, we don't really have a clue as to
what the laws of physics were, how the sequence of
events might have played out. And is that because we
don't have accelerators that are big enough, Like we built
an accelerator the size of the Solar system that could
collide particles that even higher energy. Would that let us
(32:24):
see further back in time? Yeah, that's right. If we
had a particle accelerator that accelerated particles to even higher
speeds and collided them with more energy than a large
hatter and clider does, we could push back even farther
and closer to the Big Bang if we'd understand the
laws of physics at earlier times and be able to
(32:44):
reasonably construct that early history of our our universe. So
what do we imagine? What do we think might have
happened before a trillionth of a second. We don't know
for sure, but we have at least some good reasons
to think that at some early point in our univers history,
space then just expand quickly and and steadily, but in
(33:05):
kind of a giant burst. This is what we call
cosmic inflation. So when we look at, for example, the
uniformity of our universe, it's basically got the same amount
of stuff everywhere. Or when we look at the geometrical
flatness of the universe, by which I mean that space
on large scales doesn't seem to be curved or warped.
(33:25):
But as the you know, follows the sorts of laws
of geometry that you learned in high school. Uh, these
things lead us to think that the universe probably underwent
this burst of inflationary growth at a very early time.
That being said, we can't really be sure that happened.
We have some, you know, provisional evidence that it probably did,
(33:46):
but we don't know much about this period or why
or how it took place. All right, And here is
a perfect opportunity to ask you a question from Twitter.
Here's a question from Twitter user myself, Bara, who says
how does physics actually test or prove inflation theory. What
kind of test would you propose to verify whether inflation
was reality or just a model we use that explains
(34:09):
the data we have. That's a great question. So let
me start, though by going back a little bit, so
in the nineties seventies, when the Big Bang theory was
kind of becoming, uh the established consensus view of our
universe's history at that point in time, there were a
couple of problems that emerged. One is is that the
(34:29):
universe really seems to be quite uniform, and it's very
hard to understand why, um, some piece of the universe
way over there, and some other piece of universe and
some opposite direction billions and billions and billions of light
years away, why they would be so much alike. It
really seemed like these parts of the universe had had
a chance to synchronize with each other, and we didn't
(34:50):
have any way of explaining that. Also, we didn't have
any way of understanding why the universe was so flat.
And I mentioned this before, but what I really mean
by that is if I take three points in space
and I draw a triangle between them, this is a
huge triangle billions of light years across. If I add
up the angles of that triangle, I always get about
eighty degrees. In other words, like the Euclidean geometry you
(35:13):
learned about in ninth or tenth grade, that seems to
apply to our universe and a larger scales, and that
doesn't have to be the case. Einstein showed us that
space can be curved positively or negatively, and we should
have kind of expected our universe to have been curved,
or at least people argued that. So to solve these puzzles,
people around ninety Alan Bouth and others proposed that the
(35:36):
early universe may have had this inflationary phase where it
grew really fast. When it grows, it flattens out space.
That's kind of a natural dynamical consequence of inflation, and
also it gives all of the points that we see
in space a chance to synchronize early on, explaining why
there's so much alike. Now, Okay, So if that were
(35:56):
the end of the story, I think it would be
unclear yer weather inflation would be a popular theory. It
would have been really hard to say that, uh, we're
really convinced that happened, it would would just not be
enough evidence. But inflation back in the eighties was shown
to make a couple of predictions. For one thing, it
said that when you get around one day to measuring
(36:18):
the details of the temperature patterns and the causic microwave background,
you're going to find that those temperature patterns are what
we call nearly scale invariant and adiabatic. Now those are
some complicated sounding words, but they predicted fairly specific kinds
of patterns in this light. And when we got around
to measuring that and the nineties, two thousands, and as
(36:38):
recently as as as the last few years of the
Pluck satellite, it turns out that those predictions panned out.
The way that the these temperature patterns actually appear in
the universe are consistent with what inflationary theory predicted. And
as a result, most cosmologists today think it's probably pretty
likely that inflation or something like it took place. We're
(37:01):
not sure, but we think it's pretty likely for the
most part. And so that's very important because sometimes you
cook up a scientific theory to sort of describe what
you've seen, you have a lot of freedom there to
sort of tweak the parameters and make sure it describes
what you've seen. But the real test, of course of
whether it's real is can it predict something it hasn't
seen yet, And so you're saying that inflation has sort
(37:21):
of passed that test. It says, if this was true,
you should expect to see these weird, particular fluctuations in
the energy from the early universe. And we have seen that.
That's right. If it weren't for these predictions and the
fact that they turned out to be correct, um, there
wouldn't be nearly as much confidence that our universe really
had an inflationary era and shortly after the Big Bang?
(37:42):
Do you think that's a widely held view in cosmology?
Would a random cosmologist I asked on the street agree
with you about that? Yeah, more or less. I mean,
there are a few cosmologists out there who are, you know,
argue against inflation as the best answer, and uh, and
they're they're they're constructing competing theories and things. But I
think if you did a of it, you'd find the
vast majority of cosmologists would agree with the statement that
(38:03):
our universe probably had an inflation area. All right, So
you've taken us back to the very very early moments
of the universe, where we have inflation, when the universe
expands by a ridiculous quantity in a in a ridiculously
short time. What about before that? What caused inflation? What
happened before inflation? Well, the real answer is, we just
(38:23):
don't know. We don't have any way to observe how
our universe was in this extremely early era of cosmic history,
and we don't have any experiments that we know how
to do, at least yet to tell us what the
laws of physics that dictated that era might have been.
We do know that if you go back far enough
in time, the theories we have that describe the laws
(38:45):
of physics and our universe must break down. We know
this because the general theory of relativity describes gravity and
space and time isn't compatible at extremely high energies with
the laws of quantum mechanics as we know them, So
one or both of those theories must break down um.
As it turns out, sometime in the first ten of
(39:06):
the minus forty three seconds after the Big Bang, we
simply have no clue uh what uh the universe might
have been like or even if we're asking the right
questions about it during that era that we call the
quantum gravity era. Well, that sounds like the way we
talk about the interior of black holes. We know that
general relativity is a strong theory, it's been tested in
(39:26):
lots of ways, but we suspect that inside a black
hole it might be wrong because it gives predictions that
disagree with quantum mechanics. Is it a similar way to
think about it. Yeah, it's a lot like that. In fact,
I would go as far as to say that it's
possible that when we do have a you know, real
theory of quantum gravity, questions like what's inside of a
black hole, those questions won't even make sense anymore. That
(39:49):
they will have a complete description of nature um, but
there won't be an interior of black holes. And and
maybe something equally surprising pertains to the quantum gravity era
of our universe. Who knows? Wonderful, Well, this is the
perfect time to ask you a question from a listener.
Here's an audio question from Anders from Norway. Hi. This
is Ander's moan from Oslo, Norway. I was wondering about time.
(40:11):
Did it behave differently when the universe was younger and denser.
That's a great question. So the first thing to appreciate
is that time is awfully weird even in the universe today. Um,
the sort of linear, you know, series of events that
that UH physics used to be based on, like in
the Newtonian worldview, was overturned by UH by Einstein more
(40:35):
than a century ago. And in general relativity time really
behaves pretty weird. So the length of time that passes
between two events will depend on, for example, what frame
of reference you're doing the measuring, and and things like this,
and the being in the presence of a strong gravitational
field can make time pass differently in things like this.
(40:56):
So time is very weird. But what I would say
with that being said is that the way that time
works in the universe today is not meaningfully different from
how it worked a thousand years or a year, or
a second after the Big Bang, or even a trillion
of a second. But if you go back even farther,
if you reach the point of the quantum gravity area era,
(41:17):
we know that time must have been very different than
anything we're currently imagining. We don't know what it was like,
but um, I think it's a safe bet that it
was very different from anything one might experience today. So
you're painting a pretty big question mark earlier than ten
of the mind seconds is and we don't know what's there.
We can't even really imagine it. But if you're a cosmologists,
(41:40):
you spend your life thinking about this stuff. You must
have a sort of a mental picture when you think
about what happened before inflation, when you think about the
moment of creation WATI equal zero, what do you have
in your mind? Well'm usually the kind of person who's
perfectly happy to speculate about things we don't know anything about.
But when it comes to that quantum gravity era era,
I'm not even you know, super comple doing it, and
(42:00):
just there's we have no foundation to really build upon um.
But that being said, you know, some people in the
worlds of string theory or loop quantum gravity do try
to construct ideas of what sort of things may have
existed at this time. Maybe the universe wasn't four dimensional
or with three dimensions was based on one time, but
(42:21):
it had more dimensions of space, and maybe space consisted
of you know, concluded things like you know, strings and
membranes and other sorts of exotic objects. Um, you know,
maybe the space itself was in a superposition of different
states of curvature and all this sort of stuff, and
you can put all these sorts of words of things.
I'm not sure that, uh, your listeners are going to
(42:44):
really be able to wrap their head around the stuff
I'm saying right now, But frankly, I'm not sure that
I'm able to either. So we're all in the same boat,
all right. But it was fascinated here anyway. Um, I
was wondering, what would you sort of hope for in
so in terms of future experiments that we're going to
get a grasp on what happened before ten of the
minus forty three? What future experiments would you like to
(43:07):
fund if you had infinite resources, what would you build
in order to give us a clue as to what
happened in the very first instance of the universe. Well,
in the more near term, we're going to measure the
cause of microave background in greater and greater detail. We're
gonna look for things like B mode polarization and non gaussianity.
These are the sorts of signatures that, if we were
(43:29):
to see them, would tell us something about the inflation
are epoch. So, for example, if we measure these what
we call demode polarization signals, you'd be able to know
roughly what the energy density of the universe was during inflation.
That allows us to like take the list of all
of our different inflationary theories and shrink it down into
a much more manageable number of possibilities. Um, it won't
(43:50):
tell us everything we want to know about inflation, but
it will give us a lot closer and it will
make us a lot more confident that you know, something
like inflation in fact took place in the more are
distant future a little bit more science fiction. E. I
imagine one day we're going to study the cause of
neutrino background, and we're not only going to detect it,
but we're gonna measure it with the kind of precision
(44:10):
that we've already measured the cosmic microwave background. So we
will learn as much about the universe as it was
a second after the Big Bang as we currently know
about the universe hundreds of thousands of years after the
Big Bang. This is something that will happen a long
long time from now. It's not something that I'm going
to see happen in my career, probably, But you know,
(44:31):
there's lots of reasons to think that the long term
future of cosmology is going to be a very exciting endeavor.
All these experiments that you envisioned, they all sound wonderful,
and I'd like to know the answers to them also,
But would any of them give us an insign to
what happened in those very first few moments before ten
to the minors forty three? Some of them will give
us a clue as to what happened in the later epics,
(44:52):
But will any of them pierce that veil and tell
us what happened in the quantum gravity era? Well, the
veil that separates us from the quantum gravity era is
a very thick veil. Indeed, Um, it's hard to imagine
how we're really going to figure out what that period
of our universe's history might have been like. I don't know.
Maybe one day strength theorists will UH make progress in
(45:13):
such a way that allows us to make testable predictions
that will give it this period of time. Um. But
I suspect that when or if we ever do UH
get some insights in this period of time, it will
be in the context of theories that we haven't even
thought about yet, or experiments that I can't even wrap
my heads around, like and it head around it. It
would be like asking a philosopher from a thousand years
(45:35):
ago to speculate about how twentieth century physics is going
to play out. Um, you know, there's no one could
have imagined relativity and quantum mechanics. Uh, you know, some
some distance in time ago like that. And Uh. Similarly,
I imagine that if you, you know, if we try
to imagine what physics three years from now will look like,
(45:58):
we would come up very very short and trying to
put our heads around anything like that or even imagining
what that might look like. I agree. I think if
you showed a philosopher from a thousand years ago a
children's book about astrophysics, they would not understand it. And
in a similar way, if you could somehow steal a
children's book about astrophysics from the year three thousand, you
(46:19):
and I would be baffled. We wouldn't be able to
get past the first page. I expect um, But those
concepts would be very natural to people, people thinking and
breathing and living and asking questions. Then something I really
liked about your book is that you said we are
in a time of reckoning, and it gives me the
sense that we expect physics to be revolutionized. We expect
that we might learn things about the universe that would
(46:41):
fundamentally change our ideas about them. I think this connects
back to the sort of philosophical implications of this kind
of research. And so to close out, I want to
ask you, what do you imagine the sort of deep
problems with physics might be reconciled in the next hundred
or two hundred years. I can't expect you to know
the answers, but at least what do you think there
are the questions we might get answers too? Well? Of
(47:02):
course I don't know for sure, no one does. But
when I look at the various puzzles and problems faced
by cosmologists today, it gives me reason to at least
suspect that the early universe played out very differently than
the textbooks currently describe. So here's what I have in mind. So, um,
(47:24):
when I if we if we just take the laws
of physics as we currently understand them and run them
through the early universe, those laws of physics say that
all of the matter and all of the antimatter should
have been destroyed. They should have destroyed each other in
the first fraction of a second um and that would
have left our universe without any atoms in it. And
yet our universe is full of atoms. I'm made of atoms,
(47:44):
You're made of atoms. Everything we know and directly experience
is made of atoms. So somehow things must have played
out differently than anything we currently understand in that first
fraction of a second after the Big Bang. Similarly, a
problem that I work on a lot is that of
dark matter. If you asked a bunch of people specialized
in the dark matter ten years ago, they would have
(48:05):
probably told you that it's likely that dark matter consists
of these things called whimps, weekly interacting massive particles. But
we've looked for whimps, and we we we know what
kind of experiments we needed to do to find whimps,
and we've done those experiments and we just haven't found anything. Um. Now,
it's possible that whimps will be discovered any day now,
and they're right around the corner. But I think at
(48:25):
a minimum, it's fair to say that it's surprising that
those whimps haven't shown up. So that could be that
the dark matter is just made of something different than
we had currently imagined, or it might mean that the
early universe played out differently. Our arguments for what whimps
should look like in what experiments we would have to
do to discover them, we're based on our understanding of
(48:48):
how things played out in the early universe when the
whimps were being created. If the early universe played out
differently than we had imagined, then the way that dark
matter would have been created and the kind of experiens
we'd have to do to find dark batter could be
very different. And then of course there's a problem of inflation. Uh,
somehow the universe got very flat and somehow the universe
(49:09):
got very uniform, and inflation is a good description of that.
But we don't know how how that played out. We
don't know how or why inflation happened the way it did.
Um I think it's fair to say that we have
more more questions than answers when it comes to the
inflationary era, and possibly related to inflation is the issue
(49:30):
of dark energy. We've learned in the last twenty years
at our universe isn't just expanding, it's expanding at an
accelerating rate, and that seems to suggest that empty space
has a certain amount of energy built into it, a
kind of vacuum energy. Um. Maybe this is similar to
the kind of energy that drove inflation shortly after the
Big Bang, and is happening now in a more gentle way.
(49:52):
We don't know, But all of these things, to my mind,
collectively point to some very weird and counterintuitive stuff that
I'd have played out in that first second or millions
or billions or trillion of a second after the Big Bang. Um,
that's where my money is on a new big revolutions
in physics. Well, I appreciate your scientific honesty that you're
(50:14):
willing to admit what we don't know, and also you're
a scientific optimism that one day scientists will unravel these
ideas and maybe on a podcast in a hundred years
they'll be chatting casually about answers to these questions. Thanks
very much for coming on our podcast today and talking
to us about these amazing questions about the nature of
the universe and its origins. And remember, everybody, Dan's book
(50:35):
is called At the Edge of Time. It comes out
on November five from Princeton University Press. I totally encourage
you to check it out if you're into origins of
the universe and cosmic questions. Thanks again, Dan for joining us,
and thank you listeners for tuning in. If you still
(50:58):
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 at Facebook, Twitter, and Instagram at
Daniel and Jorge That's one Word, or email us at
Feedback at Daniel and Jorge dot com. Thanks for listening,
and remember that Daniel and Jorge Explain the Universe is
a production of I Heart Radio. For more podcast from
(51:20):
my Heart Radio, visit the I Heart Radio app, Apple Podcasts,
or wherever you listen to your favorite shows. Yeah
Hosts And Creators
Daniel Whiteson
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