February 18, 2021 • 40 mins
Daniel and Jorge explain Roger Penrose's Conformal Cyclic Cosmology and what it means about the origins of the Universe.
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Speaker 1 (00:08):
Hey, Jorgey, do you ever get the feeling that this
has all happened before? Well, this is our two and
fifty episode, so yeah, there's a sense of deja vu. Yeah,
but think a little bigger than that, like you know
about the whole universe? You mean, like, has there been
another universe before this one? Yeah? Or is our universe
the first one? I hope we're the first ones that
(00:31):
would be special. I don't know. I'd like us to
not be the first, so the universe has had a
chance to like iron out some of the kinks. You
don't want to be in season one of the universe, No,
it always takes a few seasons to figure it out.
You want to be this season finale or the series finale? Well,
you know, it's tricky because sequels are you know, hit
(00:51):
or miss? Hi am or Hey, I'm a cartoonist and
the creator of PhD comics. Hi, I'm Daniel. I'm a
(01:12):
particle physicist, and I'm the first generation physicist in my family.
Oh really, hopefully the last or maybe the last. How
are you kids feeling about the whole thing? Yeah? I
think I might be the physics finale in this family.
I am definitely a first generation cartoonists from Panama. Well,
there you go. You don't have to do what your
parents have done. Well, actually, my parents are pretty good
(01:33):
artists as well, even though they're also engineers. Awesome, but
welcome to our podcast Daniel and Jorge Explain the Universe,
a production of I Heart Radio in which we take
you on a tour of all the amazing questions about
our universe, how we will end, how it began, how
it works right here daying in the middle of it,
and on our tour of the universe, we stop and
talk about how it works, why it works, and what
(01:54):
we don't understand, hopefully leaving you with some understanding of
your own. Yeah, because there is a to understand in
this universe. It's big and complex and old and possibly infinite,
and it may not stop there with the universe, I mean, yeah, exactly.
We have questions about how far the universe goes on,
Does it wrap around on itself? Does it go on forever?
(02:15):
And we have questions about how long the universe will
continue and where it came from, was there a beginning
at all? Or does the universe extend back forever in time? Yeah,
because we think of the universe as everything there isn't,
ever has been, and ever will be. But there are
a lot of theories in physics that maybe does. It
is not the only universe, you know. There's ideas about
(02:36):
parallel universes and multi universe, and there's also ideas about
other universe that may come to be or that have
been before. That's right. If you are used to the
feeling that the universe has dwarfed us, that we are
finding ourselves to be a tiny cosmic spec on a vast, vast,
unimaginable huge scale, then get ready to blow your mind
(02:56):
at an even deeper level, because it turns out our
universe may not even be everything. It may only be
one of many universes. Yeah. This actually blows my daughter's
mind a lot. She's like, how can there be multiple universes?
Isn't the universe all that there is? And I think
she's again, you know, carrying on my tradition of complaining
about naming things in physics. There you go, she's a
(03:19):
second generation name complainer. Yeah, physics name complainer. I'm so proud.
But it's a good point because often we define the
universe to be like everything as we know it at
that moment, and then when we realize, oh, there's more,
we don't just redefine the universe to also include that,
we're like, oh, let's call that another universe, and so
it does get pretty awkward. Yeah, well, maybe universe is
(03:40):
more like everything we could potentially reach at the moment,
you know, like everything that exists with us. Yeah, well
that's sort of like the observable universe is like everything
that can influence us, everything that we can interact with
because it has had time to send us light. So
that's definitely one fair definition of the universe. But you
could also imagine, hey, this stuff going on out there
that's not like within a sphere centered around my head,
(04:03):
shouldn't you also include that in the universe. And then
you can imagine forwards and time and backwards and time,
and you know, it's nice to have a definition of
the universe that doesn't center a human because it doesn't
feel like we are sort of essentially important to the universe,
right Well, I like being the center of my universe,
and our our listeners are the center of our universe.
(04:23):
For sure, They're definitely important. Yeah, everyone special. There's this
question of where the universe came from and what's going
to happen to it? And I think more important is
that question about where the universe came from, Like how
can so much stuff just come out of nothing? Yeah?
And it's a really fun exploration because you look at
the way the universe is now you say, where did
(04:44):
this come from? And Okay, cool, we understand how the
solar system formed, Well where did that stuff that made
the Solar system come from? And it's this cycle of
stepping backwards and further and further into the depths of
time and wondering like how far can we go to
understand the origin of everything? And is there a final
answer or could you go forever? Right? Yeah, because we're
(05:04):
not used to this idea of something coming from nothing, right,
I mean, it would be weird if the universe suddenly
appeared out of nothingness. Yeah, well, it would be weird
if the universe wasn't weird. Right. Basically, everything we've learned
about the universe shocked and surprised us. So if we
found an answer and just went like, oh, yeah, that
kind of makes sense, that would be kind of surprising.
All right. So at some point the universe that have
(05:25):
came into existence was created in the Big Bang. But
I guess the big question is kind of what happened
before the Big Bang and where did the universe come from?
And so there are a lot of theories out there
about what could have happened or what happened, but none
of them are nailed down, right, That's right. There's still
a lot of speculation. We don't really know what happened
before the Big Bang, and we might not ever know,
(05:45):
and so there's a huge variety of theories out there
that explained what could have happened. Maybe there was nothing,
maybe there was a big crunch that proceeded the Big Bang.
But today I wanted to talk about one really specially
interesting theory. They gained popularity recently because it's proponent one
Nobel Prize last year. M. Yeah, this is a theory
that talks about the universe is a big cycle, right,
(06:06):
like maybe there were other universes before our universe. Yeah, exactly.
This theory sees the universe is big cycles, but not
the kind you're probably familiar with. You've probably heard of
the theory that the universe goes through a cycle of
bangs and then crunches and bangs and then crunches This
is a totally different idea that has a sickly cosmology
at its heart. All right, So today on the podcast,
(06:28):
we'll be asking the question, what is the conformal cyclic
cosmology theory? All right? This is not the usual big
bank to big crunch universe theory. You're saying. It's different.
It's different. It goes for the cycle approach. It says,
you know, let's sweep away this question of whether there
(06:50):
was the beginning by saying there was never beginning. There's
an infinite number of cycles. But it doesn't link up
big crunches to big bangs. It's a totally different idea,
a little bit more bonkers and super fascinating because it
suggests that you might be able to see an imprint
of the previous universe, somehow left on our universe. Well,
(07:12):
let's maybe catch up our listeners, because the idea they
might have heard about is that the universe, you know,
came out of a big bang, out of a really
small space. Then it was huge. It exploded basically in
the big bang, and then after you know, maybe trillions
of years, it collapses back down into a big crunch,
which then triggers another big bang. For another universe, kind
(07:33):
of like Season two or a sequel to the Universe,
and then that universe explodes and expands, and after trillions
of years it crunches back down again, and so on
and so on at infinitum. Right, and so that's the
basic idea that people usually talk about when they talk
about cycles of the universe. Yeah, exactly. So that's the
typical idea. But today we're going to explore a different one. Yeah. So,
(07:56):
as usual, Daniel went out there to ask people on
the internet if they heard of this new theory about
universe cycles. That's right, So thank you to everybody who
shared your speculation. And if you are willing to answer
random questions from me online for us to use on
the podcast, please write to us two questions at Daniel
and Jorge dot com. So think about it for a second.
(08:17):
Have you heard of any theories about the universe cycling
over and over again? Here's what people had to say. Okay,
you are clearly just taking birds together now, but I
will try to give you a guess. Anyway, cycled cosmos
could mean it is something about the form of all universe,
So instead of being infinite, it could be somehow bent
(08:41):
in itself, so you wouldn't never reach an edge but
just start over. Or it could be about its growth
and its development, like there could be a big crunch
at the end of the life cycle followed by another
big bang and so on. This makes me think of
the theory that I've heard that the universe keeps being
(09:01):
created over and over again, so it grows and grows
and grows and then becomes a black hole, and then
the black hole creates its own universe in a sort
of big bang like event. And so that's what makes
me think of And since the word conformal is in there,
I'm guessing maybe every universe is the same over and
over again. I think it has something to do with
(09:23):
the cycles that we see in the cosmos, like the
births and the deaths of stars and galaxies. I'm not sure,
but I think it might have to do with like
the universe cycling between a big bang and a big crunch.
All Right, it sounds like people have heard about this
general idea of crunches and bangs, bangs, bangs bang guy bangs. Yeah,
(09:50):
And one of the answers seems to be following in
your tradition of complaining about the name, you're just sticking
words together. It's fair both English professors and professors are
guilty of that. But yeah, so, I guess let's talk
about this idea of inflation in the early universe. I mean,
(10:11):
where did this idea that there could be a cycle
to the universe come from? And we thought of it first. Yeah,
the origins of it come from the realization in the
last few decades that the universe might have had some
sort of starting point. Remember, like a hundred or so
years ago, people looked at its stars and they didn't
see the stars moving by eye, and they figured, hey,
I guess the universe is just statics, just like a
(10:32):
bunch of stars hanging out in space. And it was
very natural for people to think that it could have
always been that way. It looks pretty old, after all,
and so why not imagine it lasted forever. But then
when Hubble discovered the universe was expanding, that sort of
changed the story. It suggested that the universe is changing
and couldn't always have looked the way it does. And
(10:52):
then when you extrapolate backwards in time and you think, well,
if it's expanding now, then it should have been contracting
as we go back in time. That takes you back
to something that feels sort of like a beginning, a
point when the universe is much much more dense, yeah,
much more raw, right, like the whole entire universe, every
star in galaxy you ever seen, was in a really
(11:13):
small space about fourteen billion years ago, and everything was
just like a state of plasma, right, like just raw energy.
That's right. When the universe was much younger, it was hotter,
and it was denser, and so things work differently, you know,
just like there are different phases of matter that you're
familiar with water, you can be ice or liquid or gas.
The universe itself sort of has phases, and when stuff
(11:36):
is much much denser, there are different rules of physics
that emerge, and so like the laws of physics, they
don't violate the ones we have now, but they sort
of operate under different regimes. Different laws emerge, and so
it was very different from the way we imagine it now,
and we have some direct evidence that that actually existed.
This isn't just a calculation in people's minds. We've seen
(11:57):
light from that early universe plasma or diving at Earth.
It's called the cosmic microwave background radiation and it's sort
of like the last glow from the Big Bang. Yeah,
so we can see light that kind of escaped that
plasma right before and basically evaporated, right, yeah, exactly, and
that plasma sort of faded out and cooled off and
turned into neutral atoms, and then we can see that
(12:19):
light because it's still banging around the universe. The universe
sort of became transparent at that moment. So that was
like a really exciting piece of evidence when people saw
the microwave background radiations is several decades ago, really confirming
that that thing actually happened, That the universe once was
a big hot plasma, and that's very different from the
way it is today. Right, Well, it was a hot
(12:39):
mass back then, and it seems like it's a hot
mass right now. We're constantly on the edge of catastrophe.
But there are a lot of things we don't understand,
like what happened before that Big Bang with that big
hot ball of plasma. Yeah, that hot ball plasma is
an exciting threshold reach. We're looking back fourteen billion years
into the history of the universe. But you know, we
want to probe, but we want to know where that
(13:01):
ball of plasma came from, what explains how that got
there and what made that? You know, we want to
keep stepping this ladder backwards in time to understand really
what was going on, and the way to do that
is to ask more questions, to say, like, do we
understand the way that ball of plasma look? Can we
explain it? Do we understand, for example, all of the
ripples in it? Because the light we see from that
(13:21):
ball of plasma is not all the same temperature. There's
some variations up and down in that light. Yeah, And
so our prevailing theory about what happened during those first
moments of the universe is called inflation, right, and that
sort of explains kind of what happened since the Big Bang,
but it doesn't quite explain what happened before. As we
go backwards in time from the cosmic microway background radiation,
(13:44):
we add this step where the universe expanded very dramatically
by a factor of ten to the thirty intend to
the minus thirty seconds, and then answers a lot of
the questions that we have about the wiggles and the
cosmic microwave background radiation. The temperature of the universe, and
we have a whole podcast episode about that you can
dig into. And so that's really cool. That's in a
huge advance, sort of like taking us yet further back.
(14:07):
But you know, we want to go to time equal zero, right.
Inflation takes us to time equals ten to the minus thirty,
but it doesn't explain how that got there, right. We
want to take the next step of that ladder backwards
in time. And that's the question that a lot of
these theories are probing, is trying to explain, like, how
did you get to inflation? What created the situation that
made this universe inflate in such an insane way? Yeah,
(14:30):
because we don't really know what causes that inflation, right,
I mean, it's something literally cost the universe to explode.
Something really made the universe explode and expand in this
crazy way, and we are just the beginning of understanding
what that might be. We're like putting together ridiculous sounding
theories to potentially explain how that might work. One of them,
for example, is that there was a field, a new
(14:53):
field that filled all the universe. You're familiar with, for example,
the electromagnetic field or gravitational fields, or the Higgs field.
Now imagine a new field, and it's called the inflaton field,
just to have a ridiculous name, and it's some new
kind of matter which expands super duper rapidly and for
some reason at some point decays into normal matter. And
(15:14):
that's one idea for like nucle eating our universe, that
the universe was filled with this in phloton field, which
at some point decayed into real matter, which then became
our universe. But of course that just you know, begs
more questions like well, where does the in photon field
come from? And what made that? And so you could
go on forever if you keep just sort of stacking
explanations on top of each other, which is why one
(15:36):
sort of attractive conceptual alternative is to try to sort
of loop it back to the end of the universe
and make your idea be a cycle which sort of
explains itself. All right, Well, let's get into this interesting
new theory, the conformal cyclic cosmology theory by Roger Penrose,
and let's talk about whether or not it could actually
let us see a little bit of the previous universe.
(15:59):
But let's take a quick break, all right, we're talking
about a small question, you know, where did the universe
come from? And has it always been here? And we
(16:20):
talked a little bit about the idea of inflation that
the universe somehow expanded really quickly at the beginning of time,
or the ti equals zero as we know it. But
the question is what happened before to equal zero? Time
equals zero in the universe? Was there a previous universe
or did the universe come out of nothing? And there's
this idea, Daniel, that maybe before our universe expanded, there
(16:41):
was another universe that maybe crunched together, and that's kind
of I think what a lot of people have heard about.
But you're saying that there's problems with this idea. Yeah, well,
one problem with that idea is that it starts from
a singularity. You know, you project backwards in time, our
universe gets more and more dense. Eventually it gets infinitely dense.
(17:02):
That's the singularity. You know. I think a lot of
people in their minds when they talk about the Big Bang,
they're imagining a very dense dot of matter in an empty,
infinite universe. But instead you should be imagining a universe
filled with stuff. But that stuff is of infinite density.
So the Big Bang, as we imagine, it's sort of
happened everywhere all at once. It's a question of density
(17:23):
rather than a question of location and matter exploding into
empty space. And the problem really is that singularity. The
singularity is not a physical thing. It's not something that
we can understand it. It reflects a breakdown in our theory.
General relativity tells us if you sort of follow its
laws naively, that things get denser and denser, and then
the curvature gets infinite as the density gets infinite. But
(17:46):
that's not something we can deal with. We can grapple with,
like general relativity fails when the curvature gets infinite. So
if you want to connect our universe to a previous
universe by saying it went through a singularity, then that's
kind of a problem because the singularity feels sort of
like nonsense. It feels like when the theory is failing,
when a theory needs a new idea. M hmmm, well,
(18:08):
it seems like maybe the real problem is that this
big bang and big crunch idea requires you to have
a big crunch, right, But we don't know if the
universe will actually come back together to create a big crunch.
That's right, You need some mechanism to reverse what we
see happening now. What we see happening now is that
the universe is expanding, and that expansion is accelerating. It's
(18:29):
happening faster and faster, So our universe certainly doesn't look
like it's heading for a big crunch. On the other hand,
we have no idea what's causing that expansion to accelerate.
There's some mechanism there that goes by the name of
dark energy, but we don't understand it, so we don't
know whether it will continue. Turned on about five billion
years ago, and it might turn off, it might turn around.
(18:51):
So we don't necessarily see a big crunch happening in
our universe. But we also can't really rule it out
because we just don't understand the basic mechanisms at play.
But you're right, if you want to have a big crunch,
something's got to do the crunching. Yeah, And we kind
of had this idea before we knew about the accelerating
expansion of the universe, Like before it made sense that
(19:11):
you know, the universe would kind of expand and then
gravity would win out at the end, and the universe
would contract and collapse back into a singularity perhaps and
then a none of the universe would come out of that.
But again, that requires you to have a big crunch.
And what happens if you can't really have a big crunch.
Does that mean that, you know, we can't have any
more universes, like we're the last one? Maybe? Yeah, Well
(19:34):
that's where Penrose's idea comes in. He has this concept
for allowing cycles even if the universe never crunches back.
That's sort of the heart of his idea, right, because well,
that would be the only thing that could work at
this point, right, because if we never have a big crunch,
like if a big crunch is not in our future
or any other universe that have was created like ours,
(19:56):
then this idea of a big crunch to a big
bang can't happen. Yeah, exactly. You can't go from crunch
to bang if you don't go to the crunch. So
there's two possibilities. It seems like either we're the only
in last verse because we're going to expand out into nothingness,
or maybe there's a clever new idea that let's just
come up with a new universe out of this infinite expansion. Yeah,
and that's Penrose's idea. He says, let's think about the
(20:20):
very very end of the universe and try to connect that,
try to loop that back to the beginning of the
universe without going through a big crunch. And what he
ends up doing is sort of like a weird mathematical trick,
which might be physical, but it sort of blows your mind.
It's pretty cool idea. So it is the idea that
it looped back to the beginning of our universe or
(20:40):
to the beginning of a different universe. The idea is
that it would begin a new universe. And here's the
basic concept. You think about the very very far future
of the universe. We're talking like ten to the one
hundred years. What's our prediction for how our universe will
look then, tend to the one hundred years, tend to
the one hundred. It's like a one with a hundred zeros.
(21:01):
It's a lot of years. It's like more than trillions,
it's like bazillions. I don't think we've even named those
scientific prefixes. You know, right, if the Universe is a
television series, we are like still in the opening credits
of episode one, right, because even a trillion years is
like one tend to the twelve. This is tend to
a hundred. Yeah, this is tend to the one hundred.
So it's just a ridiculous number. And you'll understand why
(21:24):
in a minute. Because he wants to get to the
point when the universe is smooth again. He wants to
wait for all the black holes to die. So the
current trajectory for our universe if nothing changes with dark energy,
is that everything is getting pulled apart. But you have
these local gravitational clumps like our galaxy and our solar system,
So those things will eventually collapse gravitationally, forming black holes,
(21:47):
and these black holes will get really really far apart
because of dark energy. Well, what happens to a black hole?
Do black holes live forever? We actually know that they don't.
Write Hawking radiation is a way that they can give
off little bits of energy really really massive black holes
and made a very very small amount of Hawking radiation.
So he's thinking in the deep, deep far future, when
(22:07):
you form all these black holes, they get separated by
dark energy, and then they leak their radiation back out
into the universe. You have to wait for them all
to die. So the end of our he calls them eon,
is when all of our black holes sort of just
turned into radiation. They basically evaporated into photons or or
what black holes evaporate into all kinds of things exactly.
(22:29):
They can evaporate into electrons or into other kinds of corks,
or into photons or whatever. So they've got to give
up all of their light. And then he's imagining this
universe is sort of smooth again, and he's trying to
make a connection between the end of our universe and
the start of the next universe. And the connection he
makes is like, well, our universe started out kind of
smooth before, like quantum fluctuations and everything and inflation blew
(22:52):
it up into actual interesting structure. So if the end
of the universe ends up sort of like smooth fields
of radiation, he's going to try to connect that to
the beginning of the next universe, which also starts smooth.
I feel like it's a little different because you know,
our universe that far into the future sounds kind of cold.
It might be smooth, and it might be you know,
(23:14):
kind of random and homogeneous, and there's electrons and quarks
flying around, but things are still pretty discreet, like things
are in the form of electrons or quarks. Right, it's
not like pure energy like we think of at the
beginning of our universe. Yeah, exactly. The density feels different.
And here's when the mathematical trip comes in. It turns
out that if our universe has only photons in it,
(23:36):
or more specifically, only massless particles in it, then you
can change the length scale of the universe without changing
any of the physics. You can say, what used to
be a light year is now a millimeter, and all
the physics will work the same. All the massless particles
will operate the same way they had before. They won't
notice what. Yeah, I thought particles had kind of like
(23:59):
a minimum distance to them. Well, these particles we don't
think of as having a size, right, We don't think
of the photon is having like a physical extent to it.
Just think of it. It's like a little blip in
the field. And these fields, at least the massless fields,
have this weird property that you can scale them by
a number and nothing will change. All the physics will
be the same. It's sort of like if we just
(24:21):
changed all the rulers and made everybody smaller. Nobody would
notice the difference, right, all of a sudden, we're all
much tinier than we were before. But we also changed
the rulers, so nobody can tell. If the laws of
physics are invariant to that kind of transformation, then you
wouldn't notice the difference. So he noticed this about the
universe very specifically that only has massless particles in it.
(24:43):
You can do this and not change anything. Doesn't work
if there are any particles that have mass. Right, But
it sounds like we skipped the step though, Like how
do we go from black holes evaporating into electrons and
cords to now everything just being photons? Yes, a very
good point. He did skip a step. But you know,
the way these theoretical laration's work is like, m that
seems like an unsolvable problem. He'll put it on the
(25:03):
shelf for now and get back to it. What what
do you mean? I mean because we talked about how
an electron well might never decay, right, Yeah, exactly, He's
got a problem with electrons. You know, like most particles
in the universe, top corks takes bosons will decay and
go down to lighter and lighter particles. And there's only
a very small number of particles in the universe that
(25:24):
are stable. And so the photon, for example, is stable.
You can have a photon, it can hang out forever,
it can fly across the universe. But also electrons are stable.
We don't know of any way for an electron to
turn into something lighter, right or quarks? Right aren't? Don't
quarks also last forever, like if they're in a proton. Yeah,
quarks can last forever. They can turn into other stuff.
But basically quarks can last forever. Protons, however, might decay, right,
(25:47):
We don't know. Protons we think last forever. We've never
seen one decay, but there are some theories in which
they can decay into lighter stuff. But you'd be stuck
with some massive particles. And so to go from a
universe that has like photons and a few electrons in
it to universe with just photons, he has to invent
some sort of new physics thing, and he calls it
the arab On field that turns all these massive particles
(26:09):
somehow now into photons. He calls it the wave my
hand fee field. It's very hand wavy. But you know,
Penrose is a big thinker. He's like trying to get
the big structure right. He's like, you know, can I
somehow work out this bigger problem, then I'll come back
in and patch up these other holes and see if
I can find something that fills them in m M.
(26:30):
So he's saying, let's say that eventually, maybe in a
long time, all matter particles decay into massless photons or
massless particles. Right, that's the that's the leap of faith here,
and then that creates a state that's basically pure energy, right,
in which case it's sort of scale less, like it's
a millimeter and of a light ear make no difference
(26:51):
between the two. Exactly, it's scale less, so you can
change your scale and nothing is different because things that
don't have mass. Our skill is yeah, exactly. A photon
sees the whole universe anyway, is shrunk and to a point, right,
it's moving at the speed of light, and so distance
doesn't really make any difference to the photons. The whole
universe is length contracted anyway, it doesn't matter ten light years,
one light year, one millimeter, like space itself. The idea
(27:14):
of distance doesn't make sense anymore, or at least if
you scale everything the same way, nothing changes. And so
he says, well, let's take this huge expanded universe and
then just sort of like redefine it to be a
very dense, smooth universe, and boom, you have the conditions
that were at the beginning of our universe. Right at
(27:34):
the beginning of our universe there was a state. We
don't understand it, but it's postulated that it was there,
and it was very very dense with energy, and it
was very smooth, and that that then, you know, expanded
to turn into our universe. The image of penrose Is
universe is like every universe is a further expansion on
the previous one. It's like this endless series of expansions.
We just redefine the terms. Wow, but then each new
(27:57):
universe is bigger than less, yes, by a lot exactly.
We just keep changing the scale. So the whole previous
universe would be contained within like a tiny dot of
our universe, and our entire universe would be contained within
a tiny dot of the next one, kind of like
a Russian doll, but at a ginormous scale, yes, and
going on forever backwards and forwards in time, backwards and
(28:20):
forwards in time exactly. And so he gets this sort
of like cyclic structure where the end of the universe
connects to the beginning of the universe. But it doesn't
have to have a crunch, right, doesn't need to explain
the crunch. He needs lots of other stuff he's got
to explain to me work, but he doesn't need the crunch.
And there's a big advantage there because the crunch destroys
all the information. Like, if there was a crunch, then
(28:43):
it went through a singularity and any information about that
previous universe is gone, it's destroyed. But if this series
of infinite expansions is remapping and then expansion, then you
could find traces of the previous universe in our universe. Right,
it's kind of like a more like a blooming universe
rather than a sickly universe. Yeah, exactly. It's pedals within
(29:05):
pedals within pedals, right, each one nested within the previous one,
like an infinite fractal or something. Yeah, it's like a
fractal universe theory. It's pretty cool, all right. Well, let's
get into whether or not this theory even makes sense
it may not, and talk about whether or not there
is evidence out there in the cosmic microwave background radiation
(29:26):
to support this theory. But first, let's take a quick break.
All right, we're talking about the infinite universe as a
(29:46):
Russian doll theory. This is Roger Penrose's conformal sickly cosmology
theory that says that the universe came from another universe
expanding infinitely out, and that after our universe expand ends
almost infinitely out, another universe will grow from that state
of pure energy you should measure like a trumpet with
its horn, and then another one coming out of its horn,
(30:08):
another one coming out of its horn, and it's just
like endless cycle of growth. So I'm curious, or what
would you have named this theory if you could come
up with it the trumpet theory? They had the Russian
ball theory. I don't know. I think cycles cycled though.
It is kind of a weird name though, because it's
not quite a cycle, right, It's more like a blooming
(30:28):
universe theory maybe, yeah, big bloom, there you go. It
doesn't run the same forwards and backwards, right, It doesn't
have that sort of time symmetry to it. It definitely
just keeps expanding as time goes forwards. So the thing
I like about the Big Crunch Big Bang idea is
that it does have some sort of time symmetry. You
can imagine running things backwards and time and it would
look sort of the same. All right, So let's talk
(30:49):
about whether this makes sense. This is something that the
physicists are actually considering. Like, I know, he won a
Nobel Prize, but he didn't win a Nobel price for
this theory. No, there are a lot of things named
after Penrose in physics Penrose diagrams, Penrose tilings, and he
recently won a Nobel Prize for thinking about black hole.
So definitely a smart guy. But a lot of these
(31:10):
really smart physicists get famous for a few ideas, and
those few ideas are like a small fraction of all
the ideas they toss out there and see which one sticks.
So often they come up with a lot of crazy,
bonkers ideas that you know, never really hang together. So
this is not one that's in the main stream of cosmology, Like,
this is not one that a lot of people are
working on. And Penrose proposed in about two thousand and
(31:32):
twelve in a paper in a book, and it got
a lot of attention for a while also because he
claimed he could actually see the evidence of a previous
universe m so meaning it sort of works mathematically like
if we can get the universe to this state of
pure energy without any massive particles, then the math does
kind of suggest that you could get another universe out
(31:53):
of that. Yeah, so that's what made it interesting. Yeah, mathematically,
there is an idea there that you can map the
end of our universe to the beginning of our universe
that have a very similar sort of structure to them.
So there is a cool idea there. But you know,
you gotta stick in something that makes the universe turned
into just photons, and that's not something we understand at all.
(32:14):
And then you also got to look for the evidence
of it. You know. The best theories are ones that
make predictions and say, if this is true, there would
be some sort of like indistinguishable mark in the universe.
That's what was so exciting. For example, about the cosmic
microwave background radiation. It was predicted people said, well, if
there was a big bang, then there should have been
this moment when the universe went from opaque plasma to
(32:37):
transparent neutral ions and we should be able to see it.
And so that's pretty awesome to actually go out and
find that fingerprint that you predicted. So then Penrose, you know,
he rose to this challenge and he made predictions for
what he said should be out there evidence of previous universes, right,
and so he looked in the cosmic microwave background radiation
and what did he see? Did he see evidence for
(32:58):
this blooming universe theory? The big bloom he actually did.
He claimed very significant evidence of previous universes in the
cosmic microwave background radiation. And the way he thought it
would look are these things called Hawking points. And Hawking
point is where there was a huge supermassive black hole
in the previous universe which then evaporated. But a left
(33:21):
sort of a mark is a place in that universe
where there's maybe more radiation density than others. It's like
a non smoothness in the previous universe because you had
so much radiation from this really massive black hole, and
then when you map it back to the beginning of
the universe, it sort of gets squeezed down. You squeeze
all that radiation together and it makes basically a little
hot spot in the next universe. So every supermassive black
(33:44):
hole should leave like a little hot spot in the
next universe, and that should be seen in the cosmic
microwave background radiation. You should get like a little bit
of a warm spot in that radiation, like a little
scar kind of from the previous universe. Yeah, like a
little scar. And so the cosmic microwave background radiation, you know,
it's data that's out there. It's public. Anybody can go
download it and look at it and analyze it. It's complicated,
(34:07):
you know, you've got to really be an expert to
understand what you're seeing. But when Penrose put out this theory,
he also put out a paper claiming six sigma discovery
of twenty Hawking points in the cosmic microwave background radiation.
That means that he was claiming to see something that
was not just like random fluctuations of noise. Six sigma
means that he's like ruled out the fact that this
(34:28):
could just happen by random chance. He was very convinced
he was actually seeing these Hawking points super massive black
holes from a previous universe. Alright, So the idea is that,
you know, in the previous universe there probably were a
lot of super massive black holes, or are you saying
there was just one. No, they were probably a lot
to you know, yeah, because everything would eventually crunch into
(34:48):
a black hole, and those black holes might crunch together,
and so you in the previous universe, if you run
time long enough, you get these super massive black holes.
And he's saying that even these kind of super massive
holes would survive this process that makes everything massless, or
some evidence of them would survive, and that would survive
also this reblooming of the universe. Yeah, exactly. Their radiation
(35:10):
would leave like a little warm spot when the universe
blooms to the next eon. And because they're so massive,
that would be enough radiation that it would sort of
leak through a little bit. Remember, that's maybe the fate
of every galaxy. Every galaxy has at its heart a
big black hole. And the reason that we haven't fallen
into that black hole is just because we have enough
sort of speed to zip around it the way the
(35:31):
Earth zips around the Sun. But eventually we can lose
that speed. We can radiate off energy or collide with
stars and the fate of basically everything is eventually to
fall into that black hole and make it even more massive.
So the whole Milty Way will eventually be a supermassive
black hole and then evaporate its energy through Hawking radiation
m M. And so in this theory, you don't need
perfect smoothness in the universe to retrigger a new universe.
(35:55):
You can have these kind of hot spots. You can
have these little hot spots which you need is the
universe is only filled with massless particles, and then you
can map it back down to a new universe. So
this is pretty exciting. People like wow. Penrose claims he
sees like an imprint of a previous universe. That's sort
of amazing, right, But but of course we don't think
(36:16):
we live in these universe Nobody takes this theory seriously.
And the reason is that other people went and looked
at the data. They downloaded it and they analyzed it.
And there are a lot of experts out there who
really know what they're doing, and they didn't see these things.
They don't see these circles that Penrose claims he sees
with six sigma confidence. Yeah, exactly. He claims he saw them,
and they analyze them and they didn't see them. And
(36:37):
then multiple other groups analyzed them and they also didn't
see them. What like, isn't the data there? How can
some people see something and others not. Well, it depends
on how you're analyzing the data. You know, there's a
lot of steps involved in the assumptions you're making and
how you're calculating these things. And for a while nobody
could reproduce pen Rose's team's results, and then people found
the mistake. Turns out he had run some sort of
(36:59):
special version of an analysis code that nobody else agreed
was really accurate, and he wasn't really comparing what everybody
understood to be the predictions for Hawking points to the
actual data. It sort of felt a little bit cooked up. Alright,
So then maybe what he saw wasn't there. But that
doesn't mean I guess that the theory is necessarily wrong, right,
(37:20):
It doesn't mean the theory is wrong. And in the
last decade or so he's come up with other predictions,
you know, he said, oh, well, if my theory is right,
then we should see some interesting pattern of gravitational waves
or various other predictions so he still believes in it,
he's still talking about it, he's still excited about it,
he still makes up ideas for how we could test it.
And you're right, it's not something we've ruled out. You know,
(37:42):
maybe that we don't see those hawking points, but maybe
we just haven't looked, or maybe they're too subtle, or
maybe there are other ways to test this theory. And
this is a challenge for a lot of these theories.
You know, many cosmologies don't predict things that we can test.
They're talking about things that happened a long time ago
a really tiny scales, and it's hard to them up
with an experiment to test these things. So kudos to
(38:03):
him for coming up in the new cosmology and a
way to test it. That's pretty awesome. Yeah, And it's
not like we have a lot of other ideas line around, right,
Like we have no idea what happened before the Big Bang.
There's no real theory, and the theory of a big
crunch may never happen or may never have happened, yeah,
and may not be testable. So it's definitely a time
when people should be creative and it should be out
(38:24):
there exploring and creating new ideas and thinking broadly about
what could explain the universe that we see. Right, it's
time to go big, think creatively. Yeah. And one of
my favorite quotes from Penrose about this theory is what
he says, and I quote, of course the theory is crazy,
but I strongly believe that we have to take it seriously.
He's like, it's a crazy theory, but it's also a
(38:46):
crazy universe. Exactly, it's a crazy universe. It's gonna need
a crazy explanation. And also we got to be creative.
You know, sometimes you come up with a bad idea,
but it stimulates other better ideas in other theorists, so
you shouldn't just you know, like only share your only
finished ideas. There's a marketplace is a conversation of ideas.
That's how we get to these answers, right, yeah, physics mart.
(39:07):
That's where you go and buy ideas off the shelf.
I think it was more like a salon, you know,
sipping tea and chatting about our ideas about the universe.
Al Right, Well that's Roger Penrose is conformal cyclic cosmology,
and it kind of gets you to think about where
the universe came from, and whether distance really means anything
(39:27):
at all, because apparently it doesn't. If you're a photon,
then it certainly doesn't. You're happy to rescale an entirely
enormous inflated universe down to a tiny, little dense universe.
To photon, a millimeter is the same as a light year, exactly.
It takes the same amount of time. So if you're
building a house for a photon, you know, don't worry
(39:47):
so much abou getting the measurements right. And if you
can save yourself a lot of a building equipment, make
it a millimeter pig. All right, Well, that gives us
all a lot to think about and to think about
our origins and we're we came from? And could there
have been other universes before hours? Like maybe are we
season two hundred and seventy sevens of the Universe series
(40:08):
when the writers finally figure out what's going to happen
to these characters when we jumped to Shark twenty universes ago.
All right, we hope you enjoyed that. Thanks for joining us,
see you next time. Thanks for listening, and remember that
(40:29):
Daniel and Jorge explained the universe is a production of
I heart Radio or more podcast from my heart Radio.
Visit the I heart Radio app, Apple Podcasts, or wherever
you listen to your favorite shows.
Hey, Jorgey, do you ever get the feeling that this
has all happened before? Well, this is our two and
fifty episode, so yeah, there's a sense of deja vu. Yeah,
but think a little bigger than that, like you know
about the whole universe? You mean, like, has there been
another universe before this one? Yeah? Or is our universe
the first one? I hope we're the first ones that
(00:31):
would be special. I don't know. I'd like us to
not be the first, so the universe has had a
chance to like iron out some of the kinks. You
don't want to be in season one of the universe, No,
it always takes a few seasons to figure it out.
You want to be this season finale or the series finale? Well,
you know, it's tricky because sequels are you know, hit
(00:51):
or miss? Hi am or Hey, I'm a cartoonist and
the creator of PhD comics. Hi, I'm Daniel. I'm a
(01:12):
particle physicist, and I'm the first generation physicist in my family.
Oh really, hopefully the last or maybe the last. How
are you kids feeling about the whole thing? Yeah? I
think I might be the physics finale in this family.
I am definitely a first generation cartoonists from Panama. Well,
there you go. You don't have to do what your
parents have done. Well, actually, my parents are pretty good
(01:33):
artists as well, even though they're also engineers. Awesome, but
welcome to our podcast Daniel and Jorge Explain the Universe,
a production of I Heart Radio in which we take
you on a tour of all the amazing questions about
our universe, how we will end, how it began, how
it works right here daying in the middle of it,
and on our tour of the universe, we stop and
talk about how it works, why it works, and what
(01:54):
we don't understand, hopefully leaving you with some understanding of
your own. Yeah, because there is a to understand in
this universe. It's big and complex and old and possibly infinite,
and it may not stop there with the universe, I mean, yeah, exactly.
We have questions about how far the universe goes on,
Does it wrap around on itself? Does it go on forever?
(02:15):
And we have questions about how long the universe will
continue and where it came from, was there a beginning
at all? Or does the universe extend back forever in time? Yeah,
because we think of the universe as everything there isn't,
ever has been, and ever will be. But there are
a lot of theories in physics that maybe does. It
is not the only universe, you know. There's ideas about
(02:36):
parallel universes and multi universe, and there's also ideas about
other universe that may come to be or that have
been before. That's right. If you are used to the
feeling that the universe has dwarfed us, that we are
finding ourselves to be a tiny cosmic spec on a vast, vast,
unimaginable huge scale, then get ready to blow your mind
(02:56):
at an even deeper level, because it turns out our
universe may not even be everything. It may only be
one of many universes. Yeah. This actually blows my daughter's
mind a lot. She's like, how can there be multiple universes?
Isn't the universe all that there is? And I think
she's again, you know, carrying on my tradition of complaining
about naming things in physics. There you go, she's a
(03:19):
second generation name complainer. Yeah, physics name complainer. I'm so proud.
But it's a good point because often we define the
universe to be like everything as we know it at
that moment, and then when we realize, oh, there's more,
we don't just redefine the universe to also include that,
we're like, oh, let's call that another universe, and so
it does get pretty awkward. Yeah, well, maybe universe is
(03:40):
more like everything we could potentially reach at the moment,
you know, like everything that exists with us. Yeah, well
that's sort of like the observable universe is like everything
that can influence us, everything that we can interact with
because it has had time to send us light. So
that's definitely one fair definition of the universe. But you
could also imagine, hey, this stuff going on out there
that's not like within a sphere centered around my head,
(04:03):
shouldn't you also include that in the universe. And then
you can imagine forwards and time and backwards and time,
and you know, it's nice to have a definition of
the universe that doesn't center a human because it doesn't
feel like we are sort of essentially important to the universe,
right Well, I like being the center of my universe,
and our our listeners are the center of our universe.
(04:23):
For sure, They're definitely important. Yeah, everyone special. There's this
question of where the universe came from and what's going
to happen to it? And I think more important is
that question about where the universe came from, Like how
can so much stuff just come out of nothing? Yeah?
And it's a really fun exploration because you look at
the way the universe is now you say, where did
(04:44):
this come from? And Okay, cool, we understand how the
solar system formed, Well where did that stuff that made
the Solar system come from? And it's this cycle of
stepping backwards and further and further into the depths of
time and wondering like how far can we go to
understand the origin of everything? And is there a final
answer or could you go forever? Right? Yeah, because we're
(05:04):
not used to this idea of something coming from nothing, right,
I mean, it would be weird if the universe suddenly
appeared out of nothingness. Yeah, well, it would be weird
if the universe wasn't weird. Right. Basically, everything we've learned
about the universe shocked and surprised us. So if we
found an answer and just went like, oh, yeah, that
kind of makes sense, that would be kind of surprising.
All right. So at some point the universe that have
(05:25):
came into existence was created in the Big Bang. But
I guess the big question is kind of what happened
before the Big Bang and where did the universe come from?
And so there are a lot of theories out there
about what could have happened or what happened, but none
of them are nailed down, right, That's right. There's still
a lot of speculation. We don't really know what happened
before the Big Bang, and we might not ever know,
(05:45):
and so there's a huge variety of theories out there
that explained what could have happened. Maybe there was nothing,
maybe there was a big crunch that proceeded the Big Bang.
But today I wanted to talk about one really specially
interesting theory. They gained popularity recently because it's proponent one
Nobel Prize last year. M. Yeah, this is a theory
that talks about the universe is a big cycle, right,
(06:06):
like maybe there were other universes before our universe. Yeah, exactly.
This theory sees the universe is big cycles, but not
the kind you're probably familiar with. You've probably heard of
the theory that the universe goes through a cycle of
bangs and then crunches and bangs and then crunches This
is a totally different idea that has a sickly cosmology
at its heart. All right, So today on the podcast,
(06:28):
we'll be asking the question, what is the conformal cyclic
cosmology theory? All right? This is not the usual big
bank to big crunch universe theory. You're saying. It's different.
It's different. It goes for the cycle approach. It says,
you know, let's sweep away this question of whether there
(06:50):
was the beginning by saying there was never beginning. There's
an infinite number of cycles. But it doesn't link up
big crunches to big bangs. It's a totally different idea,
a little bit more bonkers and super fascinating because it
suggests that you might be able to see an imprint
of the previous universe, somehow left on our universe. Well,
(07:12):
let's maybe catch up our listeners, because the idea they
might have heard about is that the universe, you know,
came out of a big bang, out of a really
small space. Then it was huge. It exploded basically in
the big bang, and then after you know, maybe trillions
of years, it collapses back down into a big crunch,
which then triggers another big bang. For another universe, kind
(07:33):
of like Season two or a sequel to the Universe,
and then that universe explodes and expands, and after trillions
of years it crunches back down again, and so on
and so on at infinitum. Right, and so that's the
basic idea that people usually talk about when they talk
about cycles of the universe. Yeah, exactly. So that's the
typical idea. But today we're going to explore a different one. Yeah. So,
(07:56):
as usual, Daniel went out there to ask people on
the internet if they heard of this new theory about
universe cycles. That's right, So thank you to everybody who
shared your speculation. And if you are willing to answer
random questions from me online for us to use on
the podcast, please write to us two questions at Daniel
and Jorge dot com. So think about it for a second.
(08:17):
Have you heard of any theories about the universe cycling
over and over again? Here's what people had to say. Okay,
you are clearly just taking birds together now, but I
will try to give you a guess. Anyway, cycled cosmos
could mean it is something about the form of all universe,
So instead of being infinite, it could be somehow bent
(08:41):
in itself, so you wouldn't never reach an edge but
just start over. Or it could be about its growth
and its development, like there could be a big crunch
at the end of the life cycle followed by another
big bang and so on. This makes me think of
the theory that I've heard that the universe keeps being
(09:01):
created over and over again, so it grows and grows
and grows and then becomes a black hole, and then
the black hole creates its own universe in a sort
of big bang like event. And so that's what makes
me think of And since the word conformal is in there,
I'm guessing maybe every universe is the same over and
over again. I think it has something to do with
(09:23):
the cycles that we see in the cosmos, like the
births and the deaths of stars and galaxies. I'm not sure,
but I think it might have to do with like
the universe cycling between a big bang and a big crunch.
All Right, it sounds like people have heard about this
general idea of crunches and bangs, bangs, bangs bang guy bangs. Yeah,
(09:50):
And one of the answers seems to be following in
your tradition of complaining about the name, you're just sticking
words together. It's fair both English professors and professors are
guilty of that. But yeah, so, I guess let's talk
about this idea of inflation in the early universe. I mean,
(10:11):
where did this idea that there could be a cycle
to the universe come from? And we thought of it first. Yeah,
the origins of it come from the realization in the
last few decades that the universe might have had some
sort of starting point. Remember, like a hundred or so
years ago, people looked at its stars and they didn't
see the stars moving by eye, and they figured, hey,
I guess the universe is just statics, just like a
(10:32):
bunch of stars hanging out in space. And it was
very natural for people to think that it could have
always been that way. It looks pretty old, after all,
and so why not imagine it lasted forever. But then
when Hubble discovered the universe was expanding, that sort of
changed the story. It suggested that the universe is changing
and couldn't always have looked the way it does. And
(10:52):
then when you extrapolate backwards in time and you think, well,
if it's expanding now, then it should have been contracting
as we go back in time. That takes you back
to something that feels sort of like a beginning, a
point when the universe is much much more dense, yeah,
much more raw, right, like the whole entire universe, every
star in galaxy you ever seen, was in a really
(11:13):
small space about fourteen billion years ago, and everything was
just like a state of plasma, right, like just raw energy.
That's right. When the universe was much younger, it was hotter,
and it was denser, and so things work differently, you know,
just like there are different phases of matter that you're
familiar with water, you can be ice or liquid or gas.
The universe itself sort of has phases, and when stuff
(11:36):
is much much denser, there are different rules of physics
that emerge, and so like the laws of physics, they
don't violate the ones we have now, but they sort
of operate under different regimes. Different laws emerge, and so
it was very different from the way we imagine it now,
and we have some direct evidence that that actually existed.
This isn't just a calculation in people's minds. We've seen
(11:57):
light from that early universe plasma or diving at Earth.
It's called the cosmic microwave background radiation and it's sort
of like the last glow from the Big Bang. Yeah,
so we can see light that kind of escaped that
plasma right before and basically evaporated, right, yeah, exactly, and
that plasma sort of faded out and cooled off and
turned into neutral atoms, and then we can see that
(12:19):
light because it's still banging around the universe. The universe
sort of became transparent at that moment. So that was
like a really exciting piece of evidence when people saw
the microwave background radiations is several decades ago, really confirming
that that thing actually happened, That the universe once was
a big hot plasma, and that's very different from the
way it is today. Right, Well, it was a hot
(12:39):
mass back then, and it seems like it's a hot
mass right now. We're constantly on the edge of catastrophe.
But there are a lot of things we don't understand,
like what happened before that Big Bang with that big
hot ball of plasma. Yeah, that hot ball plasma is
an exciting threshold reach. We're looking back fourteen billion years
into the history of the universe. But you know, we
want to probe, but we want to know where that
(13:01):
ball of plasma came from, what explains how that got
there and what made that? You know, we want to
keep stepping this ladder backwards in time to understand really
what was going on, and the way to do that
is to ask more questions, to say, like, do we
understand the way that ball of plasma look? Can we
explain it? Do we understand, for example, all of the
ripples in it? Because the light we see from that
(13:21):
ball of plasma is not all the same temperature. There's
some variations up and down in that light. Yeah, And
so our prevailing theory about what happened during those first
moments of the universe is called inflation, right, and that
sort of explains kind of what happened since the Big Bang,
but it doesn't quite explain what happened before. As we
go backwards in time from the cosmic microway background radiation,
(13:44):
we add this step where the universe expanded very dramatically
by a factor of ten to the thirty intend to
the minus thirty seconds, and then answers a lot of
the questions that we have about the wiggles and the
cosmic microwave background radiation. The temperature of the universe, and
we have a whole podcast episode about that you can
dig into. And so that's really cool. That's in a
huge advance, sort of like taking us yet further back.
(14:07):
But you know, we want to go to time equal zero, right.
Inflation takes us to time equals ten to the minus thirty,
but it doesn't explain how that got there, right. We
want to take the next step of that ladder backwards
in time. And that's the question that a lot of
these theories are probing, is trying to explain, like, how
did you get to inflation? What created the situation that
made this universe inflate in such an insane way? Yeah,
(14:30):
because we don't really know what causes that inflation, right,
I mean, it's something literally cost the universe to explode.
Something really made the universe explode and expand in this
crazy way, and we are just the beginning of understanding
what that might be. We're like putting together ridiculous sounding
theories to potentially explain how that might work. One of them,
for example, is that there was a field, a new
(14:53):
field that filled all the universe. You're familiar with, for example,
the electromagnetic field or gravitational fields, or the Higgs field.
Now imagine a new field, and it's called the inflaton field,
just to have a ridiculous name, and it's some new
kind of matter which expands super duper rapidly and for
some reason at some point decays into normal matter. And
(15:14):
that's one idea for like nucle eating our universe, that
the universe was filled with this in phloton field, which
at some point decayed into real matter, which then became
our universe. But of course that just you know, begs
more questions like well, where does the in photon field
come from? And what made that? And so you could
go on forever if you keep just sort of stacking
explanations on top of each other, which is why one
(15:36):
sort of attractive conceptual alternative is to try to sort
of loop it back to the end of the universe
and make your idea be a cycle which sort of
explains itself. All right, Well, let's get into this interesting
new theory, the conformal cyclic cosmology theory by Roger Penrose,
and let's talk about whether or not it could actually
let us see a little bit of the previous universe.
(15:59):
But let's take a quick break, all right, we're talking
about a small question, you know, where did the universe
come from? And has it always been here? And we
(16:20):
talked a little bit about the idea of inflation that
the universe somehow expanded really quickly at the beginning of time,
or the ti equals zero as we know it. But
the question is what happened before to equal zero? Time
equals zero in the universe? Was there a previous universe
or did the universe come out of nothing? And there's
this idea, Daniel, that maybe before our universe expanded, there
(16:41):
was another universe that maybe crunched together, and that's kind
of I think what a lot of people have heard about.
But you're saying that there's problems with this idea. Yeah, well,
one problem with that idea is that it starts from
a singularity. You know, you project backwards in time, our
universe gets more and more dense. Eventually it gets infinitely dense.
(17:02):
That's the singularity. You know. I think a lot of
people in their minds when they talk about the Big Bang,
they're imagining a very dense dot of matter in an empty,
infinite universe. But instead you should be imagining a universe
filled with stuff. But that stuff is of infinite density.
So the Big Bang, as we imagine, it's sort of
happened everywhere all at once. It's a question of density
(17:23):
rather than a question of location and matter exploding into
empty space. And the problem really is that singularity. The
singularity is not a physical thing. It's not something that
we can understand it. It reflects a breakdown in our theory.
General relativity tells us if you sort of follow its
laws naively, that things get denser and denser, and then
the curvature gets infinite as the density gets infinite. But
(17:46):
that's not something we can deal with. We can grapple with,
like general relativity fails when the curvature gets infinite. So
if you want to connect our universe to a previous
universe by saying it went through a singularity, then that's
kind of a problem because the singularity feels sort of
like nonsense. It feels like when the theory is failing,
when a theory needs a new idea. M hmmm, well,
(18:08):
it seems like maybe the real problem is that this
big bang and big crunch idea requires you to have
a big crunch, right, But we don't know if the
universe will actually come back together to create a big crunch.
That's right, You need some mechanism to reverse what we
see happening now. What we see happening now is that
the universe is expanding, and that expansion is accelerating. It's
(18:29):
happening faster and faster, So our universe certainly doesn't look
like it's heading for a big crunch. On the other hand,
we have no idea what's causing that expansion to accelerate.
There's some mechanism there that goes by the name of
dark energy, but we don't understand it, so we don't
know whether it will continue. Turned on about five billion
years ago, and it might turn off, it might turn around.
(18:51):
So we don't necessarily see a big crunch happening in
our universe. But we also can't really rule it out
because we just don't understand the basic mechanisms at play.
But you're right, if you want to have a big crunch,
something's got to do the crunching. Yeah, And we kind
of had this idea before we knew about the accelerating
expansion of the universe, Like before it made sense that
(19:11):
you know, the universe would kind of expand and then
gravity would win out at the end, and the universe
would contract and collapse back into a singularity perhaps and
then a none of the universe would come out of that.
But again, that requires you to have a big crunch.
And what happens if you can't really have a big crunch.
Does that mean that, you know, we can't have any
more universes, like we're the last one? Maybe? Yeah, Well
(19:34):
that's where Penrose's idea comes in. He has this concept
for allowing cycles even if the universe never crunches back.
That's sort of the heart of his idea, right, because well,
that would be the only thing that could work at
this point, right, because if we never have a big crunch,
like if a big crunch is not in our future
or any other universe that have was created like ours,
(19:56):
then this idea of a big crunch to a big
bang can't happen. Yeah, exactly. You can't go from crunch
to bang if you don't go to the crunch. So
there's two possibilities. It seems like either we're the only
in last verse because we're going to expand out into nothingness,
or maybe there's a clever new idea that let's just
come up with a new universe out of this infinite expansion. Yeah,
and that's Penrose's idea. He says, let's think about the
(20:20):
very very end of the universe and try to connect that,
try to loop that back to the beginning of the
universe without going through a big crunch. And what he
ends up doing is sort of like a weird mathematical trick,
which might be physical, but it sort of blows your mind.
It's pretty cool idea. So it is the idea that
it looped back to the beginning of our universe or
(20:40):
to the beginning of a different universe. The idea is
that it would begin a new universe. And here's the
basic concept. You think about the very very far future
of the universe. We're talking like ten to the one
hundred years. What's our prediction for how our universe will
look then, tend to the one hundred years, tend to
the one hundred. It's like a one with a hundred zeros.
(21:01):
It's a lot of years. It's like more than trillions,
it's like bazillions. I don't think we've even named those
scientific prefixes. You know, right, if the Universe is a
television series, we are like still in the opening credits
of episode one, right, because even a trillion years is
like one tend to the twelve. This is tend to
a hundred. Yeah, this is tend to the one hundred.
So it's just a ridiculous number. And you'll understand why
(21:24):
in a minute. Because he wants to get to the
point when the universe is smooth again. He wants to
wait for all the black holes to die. So the
current trajectory for our universe if nothing changes with dark energy,
is that everything is getting pulled apart. But you have
these local gravitational clumps like our galaxy and our solar system,
So those things will eventually collapse gravitationally, forming black holes,
(21:47):
and these black holes will get really really far apart
because of dark energy. Well, what happens to a black hole?
Do black holes live forever? We actually know that they don't.
Write Hawking radiation is a way that they can give
off little bits of energy really really massive black holes
and made a very very small amount of Hawking radiation.
So he's thinking in the deep, deep far future, when
(22:07):
you form all these black holes, they get separated by
dark energy, and then they leak their radiation back out
into the universe. You have to wait for them all
to die. So the end of our he calls them eon,
is when all of our black holes sort of just
turned into radiation. They basically evaporated into photons or or
what black holes evaporate into all kinds of things exactly.
(22:29):
They can evaporate into electrons or into other kinds of corks,
or into photons or whatever. So they've got to give
up all of their light. And then he's imagining this
universe is sort of smooth again, and he's trying to
make a connection between the end of our universe and
the start of the next universe. And the connection he
makes is like, well, our universe started out kind of
smooth before, like quantum fluctuations and everything and inflation blew
(22:52):
it up into actual interesting structure. So if the end
of the universe ends up sort of like smooth fields
of radiation, he's going to try to connect that to
the beginning of the next universe, which also starts smooth.
I feel like it's a little different because you know,
our universe that far into the future sounds kind of cold.
It might be smooth, and it might be you know,
(23:14):
kind of random and homogeneous, and there's electrons and quarks
flying around, but things are still pretty discreet, like things
are in the form of electrons or quarks. Right, it's
not like pure energy like we think of at the
beginning of our universe. Yeah, exactly. The density feels different.
And here's when the mathematical trip comes in. It turns
out that if our universe has only photons in it,
(23:36):
or more specifically, only massless particles in it, then you
can change the length scale of the universe without changing
any of the physics. You can say, what used to
be a light year is now a millimeter, and all
the physics will work the same. All the massless particles
will operate the same way they had before. They won't
notice what. Yeah, I thought particles had kind of like
(23:59):
a minimum distance to them. Well, these particles we don't
think of as having a size, right, We don't think
of the photon is having like a physical extent to it.
Just think of it. It's like a little blip in
the field. And these fields, at least the massless fields,
have this weird property that you can scale them by
a number and nothing will change. All the physics will
be the same. It's sort of like if we just
(24:21):
changed all the rulers and made everybody smaller. Nobody would
notice the difference, right, all of a sudden, we're all
much tinier than we were before. But we also changed
the rulers, so nobody can tell. If the laws of
physics are invariant to that kind of transformation, then you
wouldn't notice the difference. So he noticed this about the
universe very specifically that only has massless particles in it.
(24:43):
You can do this and not change anything. Doesn't work
if there are any particles that have mass. Right, But
it sounds like we skipped the step though, Like how
do we go from black holes evaporating into electrons and
cords to now everything just being photons? Yes, a very
good point. He did skip a step. But you know,
the way these theoretical laration's work is like, m that
seems like an unsolvable problem. He'll put it on the
(25:03):
shelf for now and get back to it. What what
do you mean? I mean because we talked about how
an electron well might never decay, right, Yeah, exactly, He's
got a problem with electrons. You know, like most particles
in the universe, top corks takes bosons will decay and
go down to lighter and lighter particles. And there's only
a very small number of particles in the universe that
(25:24):
are stable. And so the photon, for example, is stable.
You can have a photon, it can hang out forever,
it can fly across the universe. But also electrons are stable.
We don't know of any way for an electron to
turn into something lighter, right or quarks? Right aren't? Don't
quarks also last forever, like if they're in a proton. Yeah,
quarks can last forever. They can turn into other stuff.
But basically quarks can last forever. Protons, however, might decay, right,
(25:47):
We don't know. Protons we think last forever. We've never
seen one decay, but there are some theories in which
they can decay into lighter stuff. But you'd be stuck
with some massive particles. And so to go from a
universe that has like photons and a few electrons in
it to universe with just photons, he has to invent
some sort of new physics thing, and he calls it
the arab On field that turns all these massive particles
(26:09):
somehow now into photons. He calls it the wave my
hand fee field. It's very hand wavy. But you know,
Penrose is a big thinker. He's like trying to get
the big structure right. He's like, you know, can I
somehow work out this bigger problem, then I'll come back
in and patch up these other holes and see if
I can find something that fills them in m M.
(26:30):
So he's saying, let's say that eventually, maybe in a
long time, all matter particles decay into massless photons or
massless particles. Right, that's the that's the leap of faith here,
and then that creates a state that's basically pure energy, right,
in which case it's sort of scale less, like it's
a millimeter and of a light ear make no difference
(26:51):
between the two. Exactly, it's scale less, so you can
change your scale and nothing is different because things that
don't have mass. Our skill is yeah, exactly. A photon
sees the whole universe anyway, is shrunk and to a point, right,
it's moving at the speed of light, and so distance
doesn't really make any difference to the photons. The whole
universe is length contracted anyway, it doesn't matter ten light years,
one light year, one millimeter, like space itself. The idea
(27:14):
of distance doesn't make sense anymore, or at least if
you scale everything the same way, nothing changes. And so
he says, well, let's take this huge expanded universe and
then just sort of like redefine it to be a
very dense, smooth universe, and boom, you have the conditions
that were at the beginning of our universe. Right at
(27:34):
the beginning of our universe there was a state. We
don't understand it, but it's postulated that it was there,
and it was very very dense with energy, and it
was very smooth, and that that then, you know, expanded
to turn into our universe. The image of penrose Is
universe is like every universe is a further expansion on
the previous one. It's like this endless series of expansions.
We just redefine the terms. Wow, but then each new
(27:57):
universe is bigger than less, yes, by a lot exactly.
We just keep changing the scale. So the whole previous
universe would be contained within like a tiny dot of
our universe, and our entire universe would be contained within
a tiny dot of the next one, kind of like
a Russian doll, but at a ginormous scale, yes, and
going on forever backwards and forwards in time, backwards and
(28:20):
forwards in time exactly. And so he gets this sort
of like cyclic structure where the end of the universe
connects to the beginning of the universe. But it doesn't
have to have a crunch, right, doesn't need to explain
the crunch. He needs lots of other stuff he's got
to explain to me work, but he doesn't need the crunch.
And there's a big advantage there because the crunch destroys
all the information. Like, if there was a crunch, then
(28:43):
it went through a singularity and any information about that
previous universe is gone, it's destroyed. But if this series
of infinite expansions is remapping and then expansion, then you
could find traces of the previous universe in our universe. Right,
it's kind of like a more like a blooming universe
rather than a sickly universe. Yeah, exactly. It's pedals within
(29:05):
pedals within pedals, right, each one nested within the previous one,
like an infinite fractal or something. Yeah, it's like a
fractal universe theory. It's pretty cool, all right. Well, let's
get into whether or not this theory even makes sense
it may not, and talk about whether or not there
is evidence out there in the cosmic microwave background radiation
(29:26):
to support this theory. But first, let's take a quick break.
All right, we're talking about the infinite universe as a
(29:46):
Russian doll theory. This is Roger Penrose's conformal sickly cosmology
theory that says that the universe came from another universe
expanding infinitely out, and that after our universe expand ends
almost infinitely out, another universe will grow from that state
of pure energy you should measure like a trumpet with
its horn, and then another one coming out of its horn,
(30:08):
another one coming out of its horn, and it's just
like endless cycle of growth. So I'm curious, or what
would you have named this theory if you could come
up with it the trumpet theory? They had the Russian
ball theory. I don't know. I think cycles cycled though.
It is kind of a weird name though, because it's
not quite a cycle, right, It's more like a blooming
(30:28):
universe theory maybe, yeah, big bloom, there you go. It
doesn't run the same forwards and backwards, right, It doesn't
have that sort of time symmetry to it. It definitely
just keeps expanding as time goes forwards. So the thing
I like about the Big Crunch Big Bang idea is
that it does have some sort of time symmetry. You
can imagine running things backwards and time and it would
look sort of the same. All right, So let's talk
(30:49):
about whether this makes sense. This is something that the
physicists are actually considering. Like, I know, he won a
Nobel Prize, but he didn't win a Nobel price for
this theory. No, there are a lot of things named
after Penrose in physics Penrose diagrams, Penrose tilings, and he
recently won a Nobel Prize for thinking about black hole.
So definitely a smart guy. But a lot of these
(31:10):
really smart physicists get famous for a few ideas, and
those few ideas are like a small fraction of all
the ideas they toss out there and see which one sticks.
So often they come up with a lot of crazy,
bonkers ideas that you know, never really hang together. So
this is not one that's in the main stream of cosmology, Like,
this is not one that a lot of people are
working on. And Penrose proposed in about two thousand and
(31:32):
twelve in a paper in a book, and it got
a lot of attention for a while also because he
claimed he could actually see the evidence of a previous
universe m so meaning it sort of works mathematically like
if we can get the universe to this state of
pure energy without any massive particles, then the math does
kind of suggest that you could get another universe out
(31:53):
of that. Yeah, so that's what made it interesting. Yeah, mathematically,
there is an idea there that you can map the
end of our universe to the beginning of our universe
that have a very similar sort of structure to them.
So there is a cool idea there. But you know,
you gotta stick in something that makes the universe turned
into just photons, and that's not something we understand at all.
(32:14):
And then you also got to look for the evidence
of it. You know. The best theories are ones that
make predictions and say, if this is true, there would
be some sort of like indistinguishable mark in the universe.
That's what was so exciting. For example, about the cosmic
microwave background radiation. It was predicted people said, well, if
there was a big bang, then there should have been
this moment when the universe went from opaque plasma to
(32:37):
transparent neutral ions and we should be able to see it.
And so that's pretty awesome to actually go out and
find that fingerprint that you predicted. So then Penrose, you know,
he rose to this challenge and he made predictions for
what he said should be out there evidence of previous universes, right,
and so he looked in the cosmic microwave background radiation
and what did he see? Did he see evidence for
(32:58):
this blooming universe theory? The big bloom he actually did.
He claimed very significant evidence of previous universes in the
cosmic microwave background radiation. And the way he thought it
would look are these things called Hawking points. And Hawking
point is where there was a huge supermassive black hole
in the previous universe which then evaporated. But a left
(33:21):
sort of a mark is a place in that universe
where there's maybe more radiation density than others. It's like
a non smoothness in the previous universe because you had
so much radiation from this really massive black hole, and
then when you map it back to the beginning of
the universe, it sort of gets squeezed down. You squeeze
all that radiation together and it makes basically a little
hot spot in the next universe. So every supermassive black
(33:44):
hole should leave like a little hot spot in the
next universe, and that should be seen in the cosmic
microwave background radiation. You should get like a little bit
of a warm spot in that radiation, like a little
scar kind of from the previous universe. Yeah, like a
little scar. And so the cosmic microwave background radiation, you know,
it's data that's out there. It's public. Anybody can go
download it and look at it and analyze it. It's complicated,
(34:07):
you know, you've got to really be an expert to
understand what you're seeing. But when Penrose put out this theory,
he also put out a paper claiming six sigma discovery
of twenty Hawking points in the cosmic microwave background radiation.
That means that he was claiming to see something that
was not just like random fluctuations of noise. Six sigma
means that he's like ruled out the fact that this
(34:28):
could just happen by random chance. He was very convinced
he was actually seeing these Hawking points super massive black
holes from a previous universe. Alright, So the idea is that,
you know, in the previous universe there probably were a
lot of super massive black holes, or are you saying
there was just one. No, they were probably a lot
to you know, yeah, because everything would eventually crunch into
(34:48):
a black hole, and those black holes might crunch together,
and so you in the previous universe, if you run
time long enough, you get these super massive black holes.
And he's saying that even these kind of super massive
holes would survive this process that makes everything massless, or
some evidence of them would survive, and that would survive
also this reblooming of the universe. Yeah, exactly. Their radiation
(35:10):
would leave like a little warm spot when the universe
blooms to the next eon. And because they're so massive,
that would be enough radiation that it would sort of
leak through a little bit. Remember, that's maybe the fate
of every galaxy. Every galaxy has at its heart a
big black hole. And the reason that we haven't fallen
into that black hole is just because we have enough
sort of speed to zip around it the way the
(35:31):
Earth zips around the Sun. But eventually we can lose
that speed. We can radiate off energy or collide with
stars and the fate of basically everything is eventually to
fall into that black hole and make it even more massive.
So the whole Milty Way will eventually be a supermassive
black hole and then evaporate its energy through Hawking radiation
m M. And so in this theory, you don't need
perfect smoothness in the universe to retrigger a new universe.
(35:55):
You can have these kind of hot spots. You can
have these little hot spots which you need is the
universe is only filled with massless particles, and then you
can map it back down to a new universe. So
this is pretty exciting. People like wow. Penrose claims he
sees like an imprint of a previous universe. That's sort
of amazing, right, But but of course we don't think
(36:16):
we live in these universe Nobody takes this theory seriously.
And the reason is that other people went and looked
at the data. They downloaded it and they analyzed it.
And there are a lot of experts out there who
really know what they're doing, and they didn't see these things.
They don't see these circles that Penrose claims he sees
with six sigma confidence. Yeah, exactly. He claims he saw them,
and they analyze them and they didn't see them. And
(36:37):
then multiple other groups analyzed them and they also didn't
see them. What like, isn't the data there? How can
some people see something and others not. Well, it depends
on how you're analyzing the data. You know, there's a
lot of steps involved in the assumptions you're making and
how you're calculating these things. And for a while nobody
could reproduce pen Rose's team's results, and then people found
the mistake. Turns out he had run some sort of
(36:59):
special version of an analysis code that nobody else agreed
was really accurate, and he wasn't really comparing what everybody
understood to be the predictions for Hawking points to the
actual data. It sort of felt a little bit cooked up. Alright,
So then maybe what he saw wasn't there. But that
doesn't mean I guess that the theory is necessarily wrong, right,
(37:20):
It doesn't mean the theory is wrong. And in the
last decade or so he's come up with other predictions,
you know, he said, oh, well, if my theory is right,
then we should see some interesting pattern of gravitational waves
or various other predictions so he still believes in it,
he's still talking about it, he's still excited about it,
he still makes up ideas for how we could test it.
And you're right, it's not something we've ruled out. You know,
(37:42):
maybe that we don't see those hawking points, but maybe
we just haven't looked, or maybe they're too subtle, or
maybe there are other ways to test this theory. And
this is a challenge for a lot of these theories.
You know, many cosmologies don't predict things that we can test.
They're talking about things that happened a long time ago
a really tiny scales, and it's hard to them up
with an experiment to test these things. So kudos to
(38:03):
him for coming up in the new cosmology and a
way to test it. That's pretty awesome. Yeah, And it's
not like we have a lot of other ideas line around, right,
Like we have no idea what happened before the Big Bang.
There's no real theory, and the theory of a big
crunch may never happen or may never have happened, yeah,
and may not be testable. So it's definitely a time
when people should be creative and it should be out
(38:24):
there exploring and creating new ideas and thinking broadly about
what could explain the universe that we see. Right, it's
time to go big, think creatively. Yeah. And one of
my favorite quotes from Penrose about this theory is what
he says, and I quote, of course the theory is crazy,
but I strongly believe that we have to take it seriously.
He's like, it's a crazy theory, but it's also a
(38:46):
crazy universe. Exactly, it's a crazy universe. It's gonna need
a crazy explanation. And also we got to be creative.
You know, sometimes you come up with a bad idea,
but it stimulates other better ideas in other theorists, so
you shouldn't just you know, like only share your only
finished ideas. There's a marketplace is a conversation of ideas.
That's how we get to these answers, right, yeah, physics mart.
(39:07):
That's where you go and buy ideas off the shelf.
I think it was more like a salon, you know,
sipping tea and chatting about our ideas about the universe.
Al Right, Well that's Roger Penrose is conformal cyclic cosmology,
and it kind of gets you to think about where
the universe came from, and whether distance really means anything
(39:27):
at all, because apparently it doesn't. If you're a photon,
then it certainly doesn't. You're happy to rescale an entirely
enormous inflated universe down to a tiny, little dense universe.
To photon, a millimeter is the same as a light year, exactly.
It takes the same amount of time. So if you're
building a house for a photon, you know, don't worry
(39:47):
so much abou getting the measurements right. And if you
can save yourself a lot of a building equipment, make
it a millimeter pig. All right, Well, that gives us
all a lot to think about and to think about
our origins and we're we came from? And could there
have been other universes before hours? Like maybe are we
season two hundred and seventy sevens of the Universe series
(40:08):
when the writers finally figure out what's going to happen
to these characters when we jumped to Shark twenty universes ago.
All right, we hope you enjoyed that. Thanks for joining us,
see you next time. Thanks for listening, and remember that
(40:29):
Daniel and Jorge explained the universe is a production of
I heart Radio or more podcast from my heart Radio.
Visit the I heart Radio app, Apple Podcasts, or wherever
you listen to your favorite shows.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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