What is the Big Rip?

Daniel and Jorge talk about what would happen if dark energy increased and tore the Universe apart.

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Episode Transcript

Speaker 1 (00:08):
Hey, okay, I'm confused about something in the Star Wars universe. Well,
I've seen those movies, which means I have a PhD
in them. That's how they give out PhDs, right yeah,
at Star Wars University. I think that's the only requirement
sw go wookies. So my confusion is the Star Wars
universe has humans in it, right, like people. Ah, well

(00:29):
that's never clear. You know, they look like humans, but
technically they're all aliens right there e t s extrat rest. Well,
they're definitely biological humans. But they also have like super
advanced technology, right like far future stuff. Yeah. Yeah, they
have war drives and spaceships and light sabers. But it
also says that it takes place a long, long time ago,

(00:52):
So like, is it the past or is it the
future with fancy technology? Yeah? Yeah, I know. That's the
beauty of Georgia. Lucas is opening line a long time
ago in a galaxy far far away. This is something
that happened a long time ago, that's happening right now,
or it's going to happen in the future. Maybe in
the future I'll finally understand it. You just need to
rewatch the movies a few times. Maybe it's time I

(01:14):
get a second PhD hi am or handmade cartoonists and
the co author frequently asked questions about the Universe. Hi,

(01:35):
I'm Daniel. I'm a particle physicist and a professor at
UC Irvine, and I'm not prepared to defend the physics
of Star Wars. There is physics in Star Wars. That's
the problem. There isn't that much, so we can't defend
it well. I think from the beginning they say it's
a fantasy. They never claim it's science. I think that's
how George Lucas conceived it. He always thought of it

(01:56):
as a fantasy. It's like fantasy plus Westerns in space.
Anything is better in space, right except breathing? I guess
I don't know. It's dessert better in space necessarily. If
it's ice cream, sure that's gonna stay less and cold,
isn't it. I've had astronaut ice cream. It doesn't compare.
Welcome to our podcast, Daniel and Jorge Explain the Universe,
a production of I Heart Radio, in which we think

(02:17):
that the mysteries out in space are actually quite delicious.
We take a deep sip of all of the questions
we have about the nature of the universe, the way
things work, the way things are, the way they come
together to make this universe that we can somehow amazingly
inexplicably analyze and understand with our tiny little brains. We

(02:37):
can cast our simple mathematical stories over them and try
to get some understanding for why things happen and how
things happen. That's right, It's an amazing universe. And we
like to use the Force here in this podcast to
understand things like forces in the universe and particles and
stars and galaxies and black holes, because one day we
might be able to get really up close to these

(02:59):
kinds of we use the force. Really, are you using
the Jedi mind trick on me right now? I'm using
the electromagnetic force that we're transmitting on That's true, we
are using forces, But I thought there was a big
difference between forces and the force. I mean, in the
Star Wars universe, they have the normal forces, right, they
also have the force. Mm. Well, we've always talked in
this podcast how there might be one unifying force to

(03:22):
the universe, right, so maybe there is the force. Do
we also discuss miny Chlorians, where it's a far too
controversial even for us. See that's an attempt to describe
the force in terms of a scientific explanation. Maybe that's
why it wasn't so popular that you mean the Star
Wars movies weren't popular the prequels. Man, Yes, there's a

(03:42):
lot of controversy there. Yeah, they only made three kajillion dollars. Yeah,
but it is an awesome universe, full of galaxies that
are far far away and lots of events that happened
a long long time ago. Because the universe has been
around for a pretty long time and hopefully it will
be around for quite a while longer. Maybe, But because
is that it is a physical universe. It is at
the mercy of forces. We think that forces in this

(04:05):
universe control the shape of everything we experience, from the
reason that you don't fall through your chair to the
reason you are held on the Earth and the Earth
orbits around the Sun. The very structure of the galaxy
and the large scale structure of the universe are determined
by forces. Wait wait, wait, are you saying gravity is
a force? Gravity is a fictitious force. Yes, absolutely, it's

(04:27):
a Star Wars force. It's the Star Wars of forces.
I always wonder how they can stand up in those
spaceships when they're out in space fiction. That's how they
can do it. But in our universe, forces do determine
the large scale structure of everything if you include gravity
on that list, and they control how the universe in
the past has turned into universe we see today, and
also they will determine the universe's future. That's right, because

(04:50):
as still an ever lasting as the universe may seem,
it's actually changing. It has been changing, and it will
keep on changing. Used to be super super diverse, small
or at least super super dense, and now it's much bigger,
and it might keep changing in the future. Yeah, it
can be difficult to sort of think on the time
scale of the universe. You're used to looking up in

(05:12):
the night sky and seeing it always be the same.
The stars are not disappearing, they're not changing, they're not dancing.
But we have learned in many situations that the universe,
or even just the Earth changes on time scales that
are well beyond what humans are used to thinking about.
Millions of years ago, the Earth looked quite different. Billions
of years ago, the Earth didn't even exist, and so

(05:32):
the universe itself is rapidly changing, and we don't know
if we are a significant fraction of the way through
the history of the universe, or if this is just
the first brief flash of a universe that will last
for trillions or quadrillions or quintillions of years. Are you
asking if the universe has peaked already? Exactly is it
time to buy or sell shares in the universe? Well,

(05:55):
I think by shares of the universe, you just won't
be alive, probably by time someone catches in the universe.
Who exactly can you sell your shares the universe too?
I suppose is there a market out there in the
multiverse stock market? Maybe you just enjoy the dividends. Life
is pretty good, right, life is pretty good. In fact,
I enjoy the universe. But I wonder how long this
situation will last. How long will we be able to

(06:18):
sit on a nice cozy rock toasting our toes by
the fire of a distant sun. Is this something which
will last for billions or trillions of years in our universe?
Or is it a brief moment of respite on this
resort we call Earth. Yeah, because the universe has been
changing and it will keep on changing, probably, and so
we can ask what does the future hold? Can we
predict what's going to happen to the universe and we

(06:40):
measure it, and how do we know that's what it's
gonna do? Are we better able to predict the future
of the universe than we are able to predict the
future of the stock market, for example? And so to
be on the podcast, we'll be asking the question what
is the Big Rip? As this related to anyone's pants, Daniel,

(07:02):
It's what happens if you eat too much astronaut ice
cream or you sit down to watch the Star Wars
movies one too many times. No, it's a fun speculative
idea about the potential future of the universe because we're
still developing our understanding of how the universe works and
what all the forces at play are, and there are
enormous gaps remaining in that understanding. There's a large set

(07:23):
of possible futures for the universe, and the Big Rip
is one of the craziest ones. Yeah. I think we've
talked a little bit in this podcast about the end
of the universe, right. We had Katie Mack here talked
about her book The end of everything, and she kind
of walked us through a couple of the possible scenarios
for the universe. Yeah, that was a lot of fun
and it's a great book folks should check out if
you're interested in cosmology and reading about depressing ways we

(07:46):
can all die. And we also talked in great depth
on the podcast about some of the forces that are
at play there and what we understand about them and
what we don't understand about how they are still shaping
our universe today. Now this is called the Big Rip.
Now our physicist gonna change the name a little bit
later on though, the bigger rip or the even larger,

(08:07):
the even bigger rip. I'm looking forward to the super
rip because then the rs blend together. The cosmic rip
would in the cosmic rip be a better name for it, yeah,
or the cosmic rift. But we do have a lot
of ideas about how the universe might evolve and what
might happen to it trillions of years into the future
or maybe billions of years into the future, and this
is one of those ideas, and it's pretty interesting. It's
one of maybe what like three or four possible things

(08:29):
that might happen to the universe. I think it's actually
an infinite spectrum of possible outcomes to the universe. So yeah,
this is one of those, right right, that's right. They
could be a big rip, a bigger rip, small rip,
a medium sized rip, a pocket size rip, and then
of course there's all the ideas we just can't anticipate
because we are just so clueless about how the universe works.
We've only understood recently pretty basic stuff about things that

(08:50):
are controlling the evolution of the universe, so we should
definitely avoid being too confident but even categorizing the amount
of our understanding. All right, So today we're going to
focus on one possible thing that might happen to the universe.
And so, as usual, we were wondering how many people
have thought about the big Rip or what it could be.
So thanks very much to everybody who answers these questions
for the podcast, and if you would like to parts

(09:11):
to pay for future episodes, please don't be shy. It's easy,
it's fun, it doesn't hurt at all, Just right to me.
Two questions at Daniel and Jorge dot com. So think
about it for a second. What do you think the
big rip is? Here's what people had to say. I
think the big Rip is one of the possible ways
the universe might end UM where something at the subatomic level,

(09:31):
basically the whole universe on rabbles on itself. And I
want to say it has something to do with anti matter.
Maybe this was disgust UM two, like a meeting UM
took place where a lot of known physicists We're talking
about how the universe might end and theories, and reportedly

(09:56):
UM at this meeting, bon Laborritos were or so I
think somehow it's linked to this meeting. So the Big
Rip is a scenario for the end of the universe
where basically space time expands so quickly that every particle,
every subparticle gets ripped apart from each other and basically

(10:17):
can never meet another because the distance between any one
and another it's expanding fast from the speed of light,
so it's not very fun. The big rip is when
the universe just rips itself apart because it doesn't have
enough mass for the gravity to crunch back in on itself.
The group is a theory that posits that at the
auto is the end of the universe UM, there would

(10:37):
be almost like an inflation that causes everything in the
universe to move further apart, but um at a rapid
rot almost like an explosion. I think, all right, some
pretty definitive answers here. It's when everything ripped apart. Yeah,
in that sense, you might say it's a well named

(10:57):
physics theory. Yeah, yeah, I'll get it to them. Oh well,
let's find out what it is first though, and see
if it's related to a banana barrito and ripping into
a banana bridle. I'm not sure where that comment was going.
It was like a burrito made out of banana peals?
Is that the reference? Yeah, I don't know. That's a
slippery slope there. To mess with a burrito wrappings. I
don't know if you're supposed to eat a banana barrito

(11:19):
or smoke it. That's actually not a bad idea to
put plantains inside of a burrito. I think you got
something here. Listener, Well, let's get into a Daniel step
us through what is the big rip? So the big
rip is sort of like a super accelerated version of
what we already think is happening to our universe. Current
accepted idea of the cosmology of the universe. Is that

(11:41):
the universe is expanding, and that that expansion is accelerating,
meaning things are getting further and further apart. New spaces
being created all the time, everywhere in the universe, and
that's happening faster and faster every year. So even our
current universe is sort of already tearing itself apart. An
expansion is happening, and it's happening faster and faster every year.

(12:02):
The Big Rip is like a super charged version of
that that's going to accelerate the acceleration of that expansion,
so that everything gets pulled apart to the tiniest bits
at the end of time. Right, that's something we only
learned about recently, right, maybe in the last hundred years,
that the universe is actually expanding, it's not sitting still. Yeah,
we learned about a hundred years ago that the universe

(12:23):
is not just like a bunch of stars floating in space.
Back before Edwin Hubble, in the beginning of the last century,
people thought the universe was just like one galaxy. There's
just a bunch of stars out there floating in space,
and it was the way it was and always had been,
and the most natural theory for the universe was that
it always had been that way, and it always would
be that way. It was just sort of like static

(12:43):
and constant. But then Hubble saw other galaxies super duper
far away. He identified smudges in the telescopes, not as
nebula in our galaxy, but actual separate galaxies far away,
and he was able to measure the velocity of those
galaxies to see they were all moving away from us.
So surprise, the prize the universe is actually expanding. Mm hmm,

(13:04):
super interesting. How did he measure that the galaxy super
moving away? You can measure the redshift of the light
from those galaxies, so it looks a little redder than
the life from our galaxy, Then you know it's moving
away from me. If it looked a little bluer, it
would mean that it was moving towards us. Things that
emit light and have a relative velocity, the frequency of
that light changes. It's a basic Doppler shift kind of effect,

(13:26):
and things that are moving away from us, the light
gets stretched out to make it redder. And Hubble was
also able to measure the distance to these things, so
he was able to show the things that are further
away are moving away from us faster than things that
are closer. Now that this makes sense with our sort
of like theories about the universe and the makeup of
it and what it could do, Like, what did Einstein

(13:47):
think of this? Now, this was really confusing to folks
like Einstein at the time. You know, before Einstein, we
had an idea of gravity as a force. Mass pulls
on other mass, stuffed tugs together gently. Right. Einstein in
up with this idea that actually gravity is not a force,
it's a curvature of the universe, that space itself is
bent by mass and energy, and that's why things tend

(14:09):
or sort of rolled together. The problem Einstein faced, even
before Hubble's realization, was that this predicted that the universe
would collapse, that all the mass and the energy and
the universe would sort of pull itself together and shrink
the universe. At the time, they thought the universe was static, right,
They thought that it was just sort of hanging out there.
So Einstein needed to invent something to balance the mass

(14:30):
pulling everything together. So he added a fudge factor to
his theory, something we now call the cosmological constant, which
we've given outwards pressure to balance all of the mass
coming in. So Einstein had this idea of a universe
sort of balanced on a knife edge, this outward pressure
providing exactly what you need to balance the inward pull
of all the mass. And then Hubble literally blew that

(14:52):
all up, right, because I guess if you imagine a
bunch of stuff just floating out there in space as
far as we knew back then, they should just all
come together because of ay, right, Like, if you put
two rocks out there in space, away from a lot
of other stuff, is that there two rucks are going
to attract each other and come together, right, And so
if you have a bunch of stars or a bunch
of planets out there in space, and the universe as

(15:12):
we saw it, it should have all sort of crunched
together by now, right. If things are just hanging out there,
they have no relative velocity to start with. You put
two rocks anywhere in the universe, they will tug on
each other, and you give them enough time, they will
come together. So Einstein was sort of like puzzled, like,
why does my theory predict that the universe should collapse
right into one giant black hole effectively? So he added

(15:33):
a fudge factor, could in the universe be sort of
like our Solar system, Like our Solar system is out
out there in space, but it's not collapsing, right, Things
are moving around in orbits. Yeah, there is something that's
keeping the Solar system from collapsing rapidly, which is angular momentum.
So the Earth, as you say, is in orbit around
the Sun, just doesn't immediately collapse into the Sun. That orbit, though,
will decay. You know, eventually the Earth will lose some

(15:56):
of that velocity because it's bumping into stuff and it's
really eating away energy and gravitational waves. So if you're
talking about like the really deep future, then in Einstein's picture,
eventually everything would collapse into a black hole. M But
why did Einstein feel like you needed to add a
fudge factor to make the universe static? Could in the
universe be on its way to crunching down into a

(16:17):
black hole? It could have been, and we didn't have
great measurements, but the sort of prevailing view of the
universe was that it was static. We didn't see anything moving,
We didn't have great measurements. That which just sort of
like the universe we thought we lived in. It looked static.
It looks static, and so Hubble, you use this really
cool observation by another astronomer, Henrietta Levitt, who discovered a
certain kind of star called sephids. These are a particular

(16:39):
kind of starring You can use a trick to tell
how far away they are just by looking at the
light from them. We have a whole episode about Ubble's discoveries.
But Hubble was the first one to really be able
to tell how far away things were, and so he
could measure these velocities and he could tell that there
was this trend that things further away we're moving away
from us faster and faster. So that was the first
clue that actually the universe is expanding. Yeah, that mustn't

(17:01):
blown people's minds. How do you think that was received,
that people believe Hubble at first, or were they like, no,
you're crazy. I think the results were pretty solid because
they were based on these sephids, which were pretty hard
to dispute. And you can verify sephids using other distance
metrics like parallax. For things that are close enough up,
you can actually tell how far away something is based
on how it wiggles in the sky as we go

(17:22):
around the Sun. So there were a bunch of sefords
that people could verify exactly how they work using other methods,
and so it was kind of hard to dispute. But
it did lead to a big puzzle. Right. People were like,
hold on a second, we don't really understand what's going on.
So then Einstein actually had bandoned the cosmological constant. He's like, well,
scratch that. If the universe is expanding, we don't need
the cosmological constant to resist the expansion. Things are just

(17:44):
already zooming away from each other faster than gravity could
otherwise pull them together. So the Einstein's fudge factor was
actually holding back the universe in a way in his view,
just by virtue of Einstein's equations, you're saying the universe
would expand. What you're saying, No, you're saying the opposite. Right.
Einstein's new view was like, all right, maybe mass is
pulling the universe together, but it was already expanding. The

(18:07):
sort of two different aspects to think about there. One
is the rate of the expansion and the other sort
of the acceleration. Mass tends to like slow down the
rate of the expansion. But Einstein figured it's already expanding
and expanding so fast that the mass doesn't have time
to slow it down. It's sort of like hitting the
brakes on a car that's already going super duper fast.

(18:27):
So then he decided you didn't need that fudge factor. Yeah,
he figured, look, the expansion is positive, maybe the acceleration
is negative. Maybe mass is pulling everything forward, but we
don't need the fudge factor the cosmological constant to explain
why the universe is expanding anymore. Or he said, we
don't need the fudge factor to explain why the universe
hasn't crunched down. Yes, exactly, that's more accurate, thank you,

(18:48):
because it's already like growing out of control, So you
don't need to explain why it's not crunching that because
it's on steroids the universe exactly. He invented the cosmological
constant to explain why we had a static universe, and
then we discovered, oh, the universe isn't static, it's expanding.
So he sort of tossed it in the bin and
apologized for it. Did it really well? Famously, he said
that he thought it was one of his biggest scientific blunders. Yeah,

(19:10):
that guy, I couldn't get anything right. I'd like to
see humility in our great geniuses, you know. All right, well,
let's talk about what could be causing this expansion and
whether or not it's going to stay the same or
maybe ripped the universe apart. But first, let's take a
quick break. Alright, we're talking about the big rip, and

(19:41):
so Daniel let it rip. So for a long time
we knew that the universe was expanding, that we didn't
really understand what had caused it to expand, and we
thought maybe that mass in the universe was going to
slow down that expansion, but we didn't understand like, is
there enough mass in the universe to slow that expansion
down eventually to zero and maybe bring it back to
a big crunch, or is there not enough mass in

(20:03):
the universe to slow down that expansion? Like a rock
that you throw from the moon that will just go
out forever, right, there's not enough mass on the moon
to pull that rock back. Maybe the universe was like
that and we just continue to drift further and further
apart if there wasn't enough mass in the universe. So
people wanted to know the answer to that question. They
wanted to know. Willie universe keep drifting apart forever, gradually
slower and slower, or will eventually it slowed down and

(20:25):
come back into a big crunch That was sort of
the big question around the mid nineties, right, Or is
there a big plot twist in the middle there that
will totally change what we thought we've been watching on
the show. So spoiler alert for those of you who've
been saving papers from the mid nineties and having gotten
to read them yet. People developed a new way to
measure distances to even further objects, to things much much

(20:48):
further away, using type one a supernova special kind of
explosion of stars that tends to happen in the same
way every time, so we know how bright it should be.
So we can tell just by looking at the curve
of those stars how far away they are. Then by
looking at the red shift of them, we can also
tell how fast things are moving away. And this let
us look even further back in time to see the

(21:11):
deeper history of the expansion of the universe, and we
hoped it could help us decide between these two options.
Is the universe going to eventually slow down into a
big crunch or is it going to keep drifting apart forever,
gradually slowing down but never stopping. Couldn't they guess at
the time. I mean, if we had an idea of
the expansion of the universe, wouldn't at the time you
just be able to, you know, figure out if you

(21:32):
had enough mass to bring everything back together. Yeah, But
the data we're not sufficient to distinguish those two things.
It's like, if you're tracking an asteroid in space, you
can give a much better prediction of its future if
you have more data points, if you can look further
back in time to understand its trajectory, you can nail
down its future. In the same way, we didn't have
enough data points to distinguish between these two scenarios until
we look much further back in time and give us

(21:53):
like a longer lever arm to understand the evolving history
of the universe. But I guess if all we had
is mass out there in the universe, then even if
the universe was expanding pretty fast, wouldn't it all eventually
come back down? Would in gravity eventually win? Gravity doesn't
always win over velocity. Like if you're on the surface
of the Moon and you throw a baseball fast enough,

(22:15):
it will leave it. We'll have enough kinetic energy to
overcome the potential energy of gravity, and it can't escape.
But if there's only the Moon and that rock in
the entire universe, wouldn't that rock eventually come back. No,
it's possible for it to escape the gravitational attraction of
the Moon. If you give it enough velocity, it will
lose some of that velocity because the gravitational pull of

(22:35):
the Moon. But as it gets further and further away,
that gravitational pull gets weaker and weaker, and so it
starts to lose velocity slower and slower, but it never
goes to zero. So eventually will feel it slow down,
wouldn't it. No, it's possible to have escape velocity, right,
That's what escape velocity is, having enough kinetic energy to
overcome the potential energy of the gravity of an object. Well,
you can escape gravi it until you maybe fall into

(22:57):
another potential gravity. Well, but it was just you in
the moon, Eventually you would come back to the Moon,
wouldn't you. If it's just you and the Moon and
you have enough velocity, you can escape it. Think about
it this way. Two particles moving in opposite directions in
the universe don't necessarily have to fall back together if
they have enough velocity, there's a threshold there where, if
they're moving fast enough, they overcome their gravitational attraction, even

(23:19):
given infinite time, even given infinite time. Yeah, that's the
definition of escape velocity. I mean, I can escape the
velocity of the Earth, but eventually I'll come back to
the Solar system. Right. One way to understand how you
can actually escape the gravity of an object is to
think about the reverse process of falling into the object.
So think of all starting like at rest, zero velocity,

(23:41):
super duper far away, basically infinity away. Now you're right
that the Moon will tug on it, and eventually it'll
fall onto the Moon, and it will hit the Moon
with a certain speed, not an infinite speed. That speed
represents basically the energy difference between being on the Moon
and being infinitely far away. So now instead, if you

(24:01):
throw the ball away from the Moon with that same speed,
than what happens, Well, it reverses the process and it
loses all that velocity as it moves away, but it
has just enough to get infinitely far away before it
comes to a stop. So what that means is that
it takes a finite amount of velocity to get infinitely
far from the Moon's surface, and the same thing is

(24:22):
true for any surface is just a different velocity. So
now what happens if you throw the ball from the
Moon's surface a little bit faster than the escape velocity,
then it basically gets to infinity and still has some
speed left over, so it's not falling back even after
infinite time. All right. So then we expanded our view
of the universe and we measured the expansion of things

(24:43):
that were really far away. And what do we find.
We found, as we look deeper into the history of
the universe that we can make more confident predictions of
the future. And what we found was really shocking. We
found that the expansion of the universe wasn't decreasing slowly
or quickly. It wasn't decreasing at all. In fact, it
was increasing. That is that more sometimes the expansion seemed
to be happening faster and faster. That means that the

(25:04):
expansion of the universe was accelerating rather than slowing down.
So Einstein's picture of the universe expanding and somehow mass
slowing that down was wrong. There was another piece. There
was something else that actually was pushing out on everything
in the universe, making it move away from each other
faster and faster every year. Interesting, So the universe wasn't
just expanding, it was expanding faster and faster. What if

(25:27):
that was alarming, or if it was just interesting, or
how interesting would have been to find out that the
universe was actually collapsing. I remember when this discovery happened.
I was starting grad school. It was a huge shock.
Everybody was stunned. Nobody expected this result. It was a
massive revelation. It's the kind of thing you always dream
about in science, seeing something out there which surprises everybody,

(25:48):
which completely changes the way you think about the universe,
Like those are the best moments in science. So we
were all shocked, but we also knew that it was
a far future thing, like it was not going to
change our lives tomorrow or next year, or even in
a billion years. We're talking about the very very deep
future of the universe, not prediction for whether or not
you shoually have a picnic tomorrow. Right, And so we

(26:09):
learned I guess that the universe wasn't just expanding in
like a coasting kind of way. It was actually like
somebody was hitting the accelerator pedal on it, which means
there must be some kind of force or energy making
this happen right exactly, And immediately people went back to
Einstein's great blunder. Remember, Einstein added his cosmological constant, his
little bit of energy to the universe to balance the

(26:31):
mass that he thought was going to collapse the universe.
And then he got rid of it when he discovered
the universe wasn't static. And then people revived it there like, well,
we kind of need something to push out on the universe.
This cosmological constant. You stick it into Einstein's equations, and
it does just that. Creates this negative pressure pushes out
on everything. It expands space as time goes on. So

(26:53):
people plug this into Einstein's equations just to describe what
they saw was happening out there in the universe. That
expansion was accelerating, as you said, instead of slowing down.
So he was a genius, right, He didn't have to
be a falsely modest history justified his genius nous exactly.
His equations were so powerful in general they can even
describe discoveries made after his death. Yeah, so they called

(27:16):
this mysterious or energy making the universe expand faster and faster.
They give it a name dark energy. Yeah, and dark
energy is really just our observation that the acceleration of
the universe is expanding. We can describe it using Einstein's equations.
If we plug a number in and we can measure
that number and figure out what number we have to
put into Einstein's equations. That doesn't mean we understand why

(27:38):
that number is there or what this mechanism is dark energy.
It's not like dark energy is a theory, a piece
of physics that we understand we can make predictions for.
It's really just sort of like a descriptive framework for
something we don't yet understand. Right. And the name comes
from to words dark and energy. And it's dark because
you can't see it, right, It's not like the universe
is glowing from this energy g and it's energy because

(28:01):
it's doing work, right. Yeah, you definitely can't see dark energy.
That's always nothing called it dark because it was mysterious,
something we had been missing, something we couldn't yet explain.
It was like a gap in our understanding. But yeah,
it is also technically invisible. You can't look at a
piece of space and see whether or not there's dark
energy in it. What do you think they named the
dark energy just for the it's mysterious sounding name, not

(28:23):
because it's invisible to the visible light. I think so,
for example, they are also theories of like dark gravity
gravity that we hadn't accounted for yet. I think in general,
dark is applied to like mysterious things in physics that
doesn't seem very scientific then it. I'm not going to
defend the name of dark energy. Well, it just so
happens that it's also invisible, right, which is which makes it,

(28:44):
either by coincidence or on purpose, a an app name
for it, I suppose. I mean, to me, dark would
describe something that's not invisible but black, like charcoal is dark.
It's not invisible the invisible man, it's not dark, right,
you can't see through him. So a more accurate name
would be like visible energy or invisible matter. To me,
dark is not a very visually descriptive name for it. Well,

(29:06):
darkened as in it's not glowing. Yeah, that's true. It's
definitely not glowing, and it's an energy because it's doing work.
I guess, But where is this energy coming from? I guess, Well,
that's the big question. We don't know where this energy
is coming from. Einstein's equations tell you what the sort
of shape of spaces and how it transforms, but as input,
they require you to describe the universe, to say how

(29:27):
much mass is there, how much radiation is there, and
also how much potential energy is there. So Newton said
gravity is only between massive objects. Einstein's generalization is to
say no, gravity comes not just from objects with mass,
but all forms of energy, including potential energy and potential
energy actually has the opposite effect gravitationally as mass does.

(29:48):
So things with potential energy form a negative pressure. They
can expand the universe, they can push things apart. So
in order to describe the expansion of the universe, you
have to have some fields with potential energy that fill
the universe, that give you enough energy to accelerate the
expansion of the universe super dramatically. So you're saying that
maybe the universe just by itself in a vacuum and nothingness,

(30:09):
just space itself, has this potential energy, right, which is
making things expand. But why is it called potential, Like,
what's its potential, like it has the potential to do work.
Or what potential energy is the energy of configuration, right,
like a book on a shelf has gravitational potential energy
rather than kinetic energy, and waves can also have potential energy.

(30:30):
If you have a guitar string, for example, and you
pull it out but you don't yet release it, then
the tension in that string is giving it a lot
of potential energy. When you release it, the string that
vibrates it turns into kinetic energy, but that energy is
slashing back and forth between potential and kinetic as the
string vibrates. And quantum fields are the same way. The
fields that we think fills space can either oscillate with

(30:53):
kinetic energy and those are particles, or they can have
potential energy because of their configuration. For example, the Higgs
view we think has energy stored inside of it even
when it's not wiggling, sort of like stuck on this shelf,
it has a bunch of energy stored inside of it
just because of its configuration M and so we think
that's what dark energy is. It's some kind of potential

(31:14):
energy that the universe has, or that space has. We
know that space has some potential energy because of these
quantum fields. We think the quantum fields are real, We
think they have potential energy. We think all of space
really does have some potential energy. We also observe that
the universe is expanding, as if there is some potential
energy causing this gravitational repulsion. We try to bring these

(31:35):
two ideas together and say, is our estimate of the
amount of potential energy we already know exists in space
enough to describe this repulsion we see in the universe,
this expansion of the universe. People do that calculation, but
those two numbers do not agree. In fact, they disagree
by more than ten to the one hundred. So we
don't have an understanding of where the potential energy comes

(31:56):
from to create the expansion that we see in space.
We know the space has some potential energy in it,
it doesn't seem to have the right amount of potential
energy to cause the expansion we see out there in
the universe. You mean from a quantum field, we can
measure how much potential energy there has to be in
order to create this expansion, and then we can calculate
how much potential energy we think there is from the

(32:16):
quantum fields and those two numbers disagree by ten to
the one hundred. Well, at least you can't explain it
with the quantum fields that you know about, right exactly?
Could there be another quantum field or something or something
you're not seeing we're thinking about. Absolutely, there can be.
There has to be. There has to be some other explanation.
The point is just that we observe some expansion. We
think it might be due to some potential energy, but

(32:37):
we really do not have any understanding of the mechanism
for that potential energy to exist in the universe. All right, Well,
let's then assume there is some sort of potential energy
hidden in the universe, and there's quite a lot of it, right,
because it's making the universe expand faster and faster. But
it's just it's it's one of those things that only
you can only tell from over the whole universe, right,

(33:00):
can't tell, like looking at your hand in front of you,
that there is dark energy between you and your hand,
although there is dark energy between you and your hand,
that's right. Something people are often confused about is why
this expansion seems to be happening only between galaxies or
clusters of galaxies and not between you and your friend
or you and your lunch. And the answer is that
it is happening everywhere. All of space is expanding. The

(33:22):
distance between us and the Moon, and the distance between
us and the Sun. All of space is expanding simultaneously
at the same rate, all the time. It's actually a
very very small amount of expansion over many millions of
light years. Every second space grows by like a seventy kilometers.
It's a tiny, tiny level of expansion over short distances.
And over short distances like between me and my chair

(33:45):
or between the Earth and the Sun, other forces are
more powerful. So, for example, the Sun is powerful enough
to hold the Earth in its orbit even if space
is very gently expanding between it. But over very long distances,
like between galaxies, gravity gets very very weak, and dark
energy gets very very powerful, and so over those bigger distances,
dark energy winds. So in our current understanding of the universe,

(34:07):
dark energy is only effective at pushing apart things that
are very very far away from each other, like galaxies,
not things that are closer together like you and your lunch. Well,
it's more noticeable for things that are really far apart,
like galaxies, but it is sort of affecting our orbit
with the Sun, right Like, it's making it just a
little bit harder for the Sun to keep the Earth
in its orbit, and in a way, it's sort of

(34:27):
helping the Earth from collapsing into the Sun a little bit. Yeah,
it definitely plays a role, almost negligible, but yeah, not quite.
Universe would be a little bit different if that didn't happen.
All right, Well, I think the assumption so far is
that this dark energy is constant, that it's sort of
like there as a feature of the universe, and it's
always been there and maybe always will be there. But

(34:47):
the question is what if it's not. What if dark
energy changes? What if it decides that it wants to
join the dark side? And so let's get into what
might happen. But far ast, let's take another quick break.

(35:10):
All right, we're talking about the Big rip now, Daniel.
Is that what happens when the mind Cloreans decide to
go on strike and the whole universe falls apart. No,
that's when Disney by Star Wars and puts out a
bunch of low quality stuff. It's called the Big rip Off.
Not a fan huh of the new stuff? Why did
you just join the Star Trek camp while you're added.
I'm in both camps. I love Star Wars and Star Trek.

(35:32):
You just like stars do? I do like Stars Intact
anything with stars and sip almost anything. Yeah, but have
you seen and or Daniel? I have seen it? Yeah,
all right, I'm guessing your silence means that I'm not
a fan either. I like to say positive or silent
on the podcast. All right, Well, we're talking about the
Big Rip, which is a possible thing that might happen

(35:53):
to the universe, and it's related to a dark energy
which is making the universe expand faster and faster now.
But the universe hasn't always been expanding at the same
rate in its history, right, Yeah, the history of the
expansion the universe is quite complicated. We have some very
rapid expansion early on that we call inflation. Is sort
of like the last stages of the Big Bang, when

(36:14):
things expanded like by a factor tended the thirty intended
the minus thirty seconds. And then for a while the
universe was matter and radiation dominated. So the expansion was
still happening, but it was decelerating. It was slowing down
a bit. But dark energy was quietly building, and around
five billion years ago dark energy became the dominant component

(36:36):
of the universe and that's when the acceleration really took off.
And so the last five billion years, the expansion has
been accelerating. Now, when you say the dark energy kind
of agreed, did it actually grow or is it just
that the universe got bigger. What's the difference between those two, Well,
like for the same size universe, if the universe had
been the same size, what are you saying that dark
energy got stronger in the meantime or did it just

(36:59):
get more powerful because the universe is at bigger and
dark energy gets bigger the bigger spaces. Now, the current
theory is that dark energy is constant, that in a
certain amount of space you have a certain amount of
potential energy and that doesn't change. So dark energy, we think,
is a constant strength through time. But we do think
that the universe is expanding and is making new space

(37:19):
and therefore making more dark energy. Most of the stuff
in the universe dilutes as space gets bigger, Like you
have a certain amount of mass in the universe and
then things expand then the mass gets less dense. Dark
energy doesn't get less dense as the universe expands, because
it's an aspect of space itself. It's like inherent in space,
and so as the universe expands, dark energy doesn't shrink,

(37:42):
and so proportionately it grows to be a larger fraction
of the energy budget of the universe. So when you
say that the universe like it inflated really rapidly, then
it slowed down, then it picked back up again, that's
still consistent with a constant dark energy. But is that
only because you're assigning the accelerat a shan to slow
down to other things that you also don't know what

(38:03):
they are. Well, we think we know if the rest
of the universe is right. We think there's normal matter,
there's some radiation. We think there's a lot of dark matter.
We don't know exactly what dark matter is made out of,
but we have a pretty good sense of how much
of it there is and where it was and how
it controlled the large scale structure of the universe. But
in order to describe the expansion history that we see,
you need to plug in a certain amount of energy

(38:24):
per unit of space, and then it actually describes the
history quite nicely. But we still don't know what costs
in the initial inflation, right, the big bank. That could
have been also dark energy, but instead you're assigning it
to something else, right, I see, Yes, And there's still
a lot of confusion about what happened early on. The
current theory is that inflation may have been due to
some other field with a lot of potential energy, like

(38:44):
the inflaton field, because that expansion was quite different from
the expansion we're seeing now, different and just the rate
or different in the nature of it. Definitely different in
the rate, possibly also different in the nature. It could
have been a different field providing potential energy to create
at that expansion. We just don't know, huge question. Or
or it could have been dark energy to right, Or

(39:05):
it could have been dark energy that was changing. And
in fact, it's not quite accurate to say that the
picture of dark energy it's constant, describes the universe very well,
because there's some controversy there. We measure the dark energy
in the universe in late times using supernovas and also
in early times using its effect on the cosmic microwave
background radiation, we actually get different numbers by a little bit,

(39:25):
and that's been a persistent tension. It's called the Hubble
Tension whole podcast episode about that. That inspires people to
come up with other ideas, something called early dark energy,
to like add a little bit more dark energy early
on in the universe. So the very very beginning of
the universe, big question marks about how much expansion there
was and what caused it. After that, it's more steady
and it's well described by universe with almost constant dark energy.

(39:49):
But I say it's it's sort of a theory, right,
there's still the possibility that maybe dark energy will increase again,
or maybe this mysterious you know Inflanton or other quant
and field with potential energy might kick back in exactly
because we don't have a good theoretical description, so we
can't really make predictions. We're just observing things. It's like

(40:09):
if you're watching the weather and you're noticing some trends, like, hey,
in southern California, it seems to be the same temperature
every single day, because I mean, I could predict confidently
it's always going to be the same temperature only if
I actually understood what caused them, Like why is it
the same temperature every day? If I had some understanding
of the underlying mechanism that I could make some prediction. Otherwise,
I'm just observing and extrapolating ignorantly. And that's basically what

(40:31):
we're doing now. We don't understand the mechanism underlying it
at all. We just see these trends and we make
simplifying assumptions. I feel like you just described my job
on this podcast anyway, to extrapolate ignorantly for money, and
listeners shouldn't take this as a criticism, right, This is
the first step. This is very, very fresh science. We
only discovered this was happening a couple of decades ago.

(40:52):
And the first thing you do is observe and characterize
and look for patterns, and then you try to build
up some theory that describe And people are hard at
work and exactly that, trying to understand what's causing this
and what its future might be, because, as you say,
we don't know what's causing it. We don't know if
it's going to change in the future. Right, And so
I think we've talked about in the podcast before how
there are three possibilities. So the dark energy, or at

(41:16):
least whatever is powering or whatever power is, the expansion
of the universe could do one of their things. It
can go away, you can stay the same, or it
can get even stronger. Right, And so if it goes away,
then what happens to the universe? It crunches down. If
it goes away, then the universe is now matter and
radiation dominated, and those things tend to pull things back together.

(41:36):
And so then it's back to the question of like,
is there enough matter to slow things down and pull
them back together into a big crunch, or is there
enough velocity already in that expansion so that things skeet
away from each other, slowing down but never actually coming
back together. If you just like turned off the dark energy,
we don't know we can make that calculation. I can't
make that calculation today on the podcast, but maybe somebody

(41:58):
out there knows. But nobody's ever done it. It's sort
of a particular scenario where you had dark energy in
the universe or fourteen billion years and then suddenly turn
it off. I don't know if anybody's actually done that calculation.
All right, Well, that yours may may not crushed together.
What happens if dark energy stays the same, It's if
it stays constant that the way it is now. Then
the expansion of the universe continues, and it continues to accelerate,

(42:20):
which means that space between things grows faster and faster,
and over very large distances. That expansion is faster than
the speed of light, which means that things are disappearing
past the edge of our cosmic horizon. There are galaxies
out there who are shooting photons at us, and those
photons will never arrive because the space between us and
that galaxy is increasing faster than light is making progress

(42:44):
through that space. So, in that scenario where dark energy
stays constant, the observable fraction of the universe gets smaller
and smaller as time goes on, things start to disappear.
We don't think in that scenaria of the galaxy will
there at the party will always have enough gravity to
hold itself together, and the Earth will still orbit around
the Sun, but our galaxy will become more and more
isolated relative to other galaxies. Right. We talked about how

(43:07):
in this scenario, the nights guy gets dark and darker, right,
because all the stars, or at least all the galaxies
out there, will move out of our view, but will
add the stars move out of out our view the
ones in our galaxy. Isn't the opposite going to happen? Now?
The galaxy is probably strong enough, has enough gravity to
hold itself together if dark energy stays constant, so the
other galaxies will disappear, and future astronomers will look up

(43:31):
at the night sky and only see stars in our galaxy,
and they will think our galaxy is the whole universe
because they won't be able to see anything else. WHOA,
but how about future future future astronomers. Isn't there enough
stuff in our galaxy that it will eventually crunch down
into a black hole eventually? Yes, it will crunch down
into a black hole. Gravity will eventually win. Things are

(43:53):
swirling around and avoiding the inevitable. But you know, things
bump into each other and lose angular momentum, and they
radiate energy through gravitational waves. So the very very far
future is that the supermassive black hole eats our galaxy.
So the very deep future of the universe, if dark
energy is constant, is a bunch of black holes isolated
from each other. Yeah, too far away to even see

(44:14):
each other, right or affect each other, Yeah, exactly, Each
one will be past the other's cosmic horizons. Wow, not
a bright future for the universe. You don't want to
buy shares in that universe. Unless shares are for flashlights,
then yeah, those are going to become very, very valuable
in the future. So then there's a last scenario, which
is that maybe dark energy will somehow kick back in

(44:36):
or whatever made the initial inflation of the universe happen,
that might come back and which will make the universe
expand even faster than it is now. Yeah, there's this
fun idea that dark energy will convert into something called
phantom energy. This is energy which will grow even more
rapidly than just the expansion of space, so that as
space expands, the fraction of energy in each chunk of

(44:57):
space also goes up, which means that the acceleration increases
faster and faster. Wait, the idea is that dark energy
somehow evolved like a pokemon like it levels up. You
just need to buy more and more packs. That's all
that has to happen for this scenario to unfold. Nobody
is that the idea that it's like the same energy,
but somehow it gets kicked up the level or something.

(45:19):
The theoretical underpinnings of phantom energy are pretty fuzzy. They
require a bunch of really weird fields that have strange
things like negative kinetic energy. It's possible for them to
exist in the universe and sort of wake up only
in late times. This is the theories that people have developed,
and they would accelerate the expansion of the universe in

(45:39):
even more surprising ways because they have very strange kinetic
and potential energy. But the end result, I guess is
that it levels up to something called phantom energy, because
that just sounds more mysterious. I guess it's actually named
after the movie The Phantom Menace. Guy wrote this paper
called The Phantom Menace the Future of the Universe, So
he was a fan. He was defan, he writes in

(46:01):
the paper quote, a phantom is something which is apparent
to the site or other senses, but has no corporeal existence,
an appropriate description for a form of energy necessarily described
by unorthodox physics. So he's sort of putting in the
like ghostly category. But did he reference the movie? Oh absolutely,
it was very much a reference to the movie The
Phantom Menace that was mentioned in the academic paper The

(46:24):
Phantom Menace is part of the title of the paper. Yes,
the Phantom energy totally named after the movie The Phantom Menace,
or maybe he just named the title after the movie.
Doesn't mean that Phantom energy was based on the movie,
does it, Well, the science of Phantom energy is not
based on the movie. But yeah, he named it phantom
energy because he was inspired by the use of the
word phantom from The Phantom Menace. I guess you could

(46:45):
say he was a fan. I don't know if his
name was Tom, he should have changed it, But I
guess the point is that maybe this energy is going
to increase, level up, get stronger, which is going to
make the universe expand faster and faster and faster and
faster and faster, which might rip the universe apart. Right exactly,
Dark energy by itself will already rip galaxies apart, but

(47:07):
phantom energy will get more powerful, and so eventually it
will overcome even the gravity of our galaxy, holding the
galaxy itself apart, and as time goes on, it will
increase in power, eventually pulling our Solar system apart, and
then shredding the Earth and in the deep deep future
even pulling all atomic bonds apart. WHOA, So you're saying,

(47:29):
like like space itself will become like inhospitable almost in
a way. Space will be expanding so much, even at
the molecular sub atomic level, then not even quarks will
be able to hang onto each other. Not even quarks
will be able to pull each other apart. All bonds
eventually will be weaker than the phantom energy, which will
overcome everything. It's this which will overcome everything. So like

(47:53):
two quarks will be hanging out to each other, but
then space will rip it apart, and then they'll never
see each other again ever, right, Yeah, the final end
of the universe is sort of similar to what we
described with dark energy, where you had black holes separated
by essentially infinitely expanding space, so they can't communicate as
no interaction except the phantom energy. Version of that is
that particles are now separated by infinitely expanding space, so

(48:16):
they can't interact with each other. They can't even tell
that there are other particles in the universe. WHOA. So
then like every single particle in the known existence in
the universe will be by itself with no way to
communicate with any other particle unless I guess the space
makes a new particle next to it or something. Right, Well,
that's the really complicated thing about corks, right, is that

(48:38):
corks do not like to be by themselves. We think
that as you pull quarks apart, there's so much energy
in the strong force that it pops new corks out
of the vacuum. So nobody actually knows what's going to
happen to quirks. It might be that as phantom energy
pulls them apart, it creates this exponential cascade of particles
being produced, filling space with all sorts of quirks. So

(48:59):
we don't know who who's gonna win in the end.
They're the strong force or phantom energy. You mean, like
as the universe rips apart, it's also gonna make new quarks.
So what you're saying, like opening a bag of popcorns,
you rip it open, all these corks pop out. That's
what happens when we make pairs of quarks with the
large Hadron collider that have a large velocity relative to
each other. They created back to back. They're zooming away

(49:20):
from each other near the speed of light, and they
create this enormous shower of new corks. Between them out
of the energy contained in the strong force bonds between them.
And so we think the same thing might happen to
all quarks in the universe when phantom energy tries to
pull them apart from their partners. M hmm, but I
guess it will be sort of. I mean, things will
happen in order, like we won't be around to see that, right, Like,

(49:43):
first the galaxy is gonna, you know, rip the stars
within the gas. They're going to rip apart, but maybe
it's not strong enough to rip apart solar systems, but
eventually it's going to rip apart solar systems. And then
eventually it's going to rip apart stars and planets. So
the final big rip, according to some calculation, is going
to be in about twenty billion years. Wait what we
have a time estimate here? We have a time based

(50:06):
on estimates of the amount of phantom energy that might
be in the universe. This is total speculation, just like
pick some numbers and see how it plays out. But
it's fun to think about, like if dark energy starts
to accelerate, now, is that what you mean at a
certain value, like a random value, or what would value
like at a random value. Yeah, there's a whole spectrum
of possible different levels of phantom energy that might exist

(50:28):
in the universe, and they just would like pick a
number and they put it in and they can make
specific predictions. Though these are not like weather reports. You
shouldn't base your life around these. It's just like illustrative,
like to think about how fast things would happen. But
with enough phantom energy happening tomorrow, the universe could be
rip apart the day after tomorrow. Right, So the twenty
two billion years is just based on a number. It's

(50:49):
just based on a number, but it's a plausible number
when it's not completely inconsistent with what we see today
in the universe. Oh, meaning like if our measurements are
a little bit off and that we're rang in the sands,
then maybe the universe is expanding faster and faster and
dark energy is not constant. Than this is how much
time we have, Like this is the worst case scenario
based on our the fuzziness of our measurement. Yeah, and

(51:12):
the good news is that we have twenty billion years
until the final big rip. And the double good news
is that we think that the Earth will survive until
about thirty minutes before the end. Oh, that's good, So
we'll be around except for the last thirty minutes of it.
And between thirty minutes and the end is when the
Earth will get ripped apart and then eventually atoms, so

(51:33):
we'll miss the last fireworks, but we'll still be here
for most of it. Well, assuming the Earth is still here, right,
this is the Earth supposed to be swallowed up by
the Sun in like eight billion years. Yeah, the Sun
only has a few more billion years. But assuming that
we know, we move the Earth to some other Sun,
or we rehab the Sun or something like that, or
we maybe change the Earth's orbit and we end up

(51:53):
orbiting a white dwarf for billions of years. That could
happen if we managed to do that sort of solar
system engineering. Then the timeline is we have twenty billion
years until phantom energy pulls the universe apart. If phantom
energy even is a real thing, right, it might even
be like the descendants of Luke Skywalker who are watching
this happen may or may not be human. As we
discussed Earth, they certainly look human, well so do I, Daniel.

(52:18):
I do have my doubts about that, and you know,
the current evidence suggests that dark energy seems mostly constant.
We don't see it ticking up. That we do have
some questions about what's going on in the early universe.
There are a few measurements that disagree with that, like
studies of distant quasars that might suggest some slight increase
in the energy density of dark energy in recent times.

(52:40):
But for the most part, mainstream cosmologists think that dark
energy is constant. That's the simplest explanation. Though again, we
don't understand the mechanism for it, so we can't confidently
make hard predictions. Right, we don't know what it is.
And in fact, I feel like we're sort of defining
it to be constant, and so we're measuring it to
be constant. But actually the history says that it maybe
wasn't constant. That's actually true, and as we make observations,

(53:02):
we add bells and whistles to our models to accommodate
what we see, and then we try to explain it
and describe it. Wow to me. In the far future, though,
somebody will make a movie that says, a long time ago,
n galaxy, far far away, you figured out the phantom
energy and two guys talked about it on a podcast.
Not a very exciting movie. But you know that's as

(53:24):
you say, as you seem to think that's the trend
for these Disney Plus shows. No comment, We're just doing
it in with less special effects. All right, Well, I
guess stay tuned for two two billion years and then
we'll find out if that's true or not exactly. And
as time goes on, we'll learn more and more about

(53:45):
the universe, and we will refine our models and hopefully
be able to anticipate it long before it happens, or
just hang on as long as we can. All right, Well,
we hope you enjoyed that. Thanks for joining us, See
you next time. Yea. Thanks for listening, and remember that

(54:06):
Daniel and Jorge Explain the Universe is a production of
I Heart Radio. For more podcast from my Heart Radio,
visit the i heart Radio app, Apple Podcasts, or wherever
you listen to your favorite shows.