Could black holes be making the Universe expand faster?

Daniel and Jorge discuss a brand new result that suggests that black holes might be driving the unexplained expansion of the Universe

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Episode Transcript

Speaker 1 (00:08):
Hey, Daniel, have you been keeping up with the science
news headlines? Oh? What does that mean? What do you mean? Oh,
I'm guessing there was some new clickbait article about how
scientists mate bananas go faster than light or something crazy.
They have you eat them faster than light. But that's
not news. Well they are kind of slippery. But are

(00:29):
you saying that we shouldn't trust science headlines? You think
it's fake news? Well, you know, sometimes the headlines don't
reflect within the article, and sometimes the news article doesn't
reflect the actual research that's been done, and sometimes the
research itself it's questionable. We Oh, you're saying even peer
reviewed papers can be wrong. What can we trust? Then

(00:50):
you can trust podcasters, I guess I hope all podcasters,
even the ones that make tales of sasquatch. All right,
you can trust us, Just trust us, well you us,
I mean, I'm a cartoonist. Padn't trust me with physics verification?
Then you got to listen to the podcast Learn Physics
so you can figure it out for yourself. Trust yourself. Oh,

(01:13):
I see this is now a self improvement podcast. Hi.
Am Jorheme, a cartoonists and the creator of PhD comics. Hi,

(01:35):
I'm Daniel. I'm a particle physicist and a professor you
see Irvine, and I do believe that learning physics is
a form of self improvement. Well, it depends on what
kind of physics, doesn't it. How about the physics of
eating fatty foods? And Yeah, the more you understand it,
the better you are informed, and the more educated choices
you can make. Yeah, but educated choices in this stally
meaning it's the right. I know potato chips aren't good

(01:58):
for you, but I still eat him. And you'd rather
eat them and not know that they're not good for you? Huh? Yeah,
maybe maybe that might help my self improvement. It might
help yourself enlargement. Yeah, my happiness. Oh wait, did you
mean something else to each of their own chip? But anyways,
Welcome to our podcast, Daniel and Jorge Explain the Universe,

(02:19):
a production of iHeartRadio in which we try to help
you on your journey of self improvement by teaching you
everything we do and do not know about the universe.
We also help you on your journey of mental self
enlargement as we try to grow your brain in your
mind and fit more understanding of the universe into it.
Because the universe is big and filled with mysteries and

(02:41):
all sorts of things that we have and have not
figured out, things that future physicists, maybe one of you
out there will figure out one day. Yeah, because it
is an amazing universe, one that is always expanding, it seems,
with all kinds of interesting knowledge and interesting phenomena to study,
to wonder about, to ask questions about, and also to
crime into your brain. And it seems like every single

(03:03):
day we're learning something that science has figured out. They've
done a new study on banana slugs, or they've done
a new study on bananas. There's a huge population and
scientists out there doing studies, learning things about the universe
and putting them out there in papers. Well, that's kind
of what you would expect, right, I mean, scientists aren't
working all the time and they should becoming up Whitney results, right,
Otherwise what are they doing exactly? And it's a wonderful,

(03:26):
delicious fountain of knowledge that science is creating. And that
knowledge is not just for other scientists, it's for everybody.
We all want to know. What are the answers to
the deep mysteries of the universe? How fast is it expanding?
What's inside black holes? How did our solar system get
to be the way that it is. So it's not
just other physics professors who read the writings of physics professors.

(03:48):
It's everybody out there who wants to know the answers
to these big questions. Yeah, sometimes what scientists discover gets
into the news media and out there into the general population.
But I feel like it's it's kind of a filter though,
Like only the juicy headlines make it out there into
the big newspapers. It is a bit of a mystery
to me what gets covered. I mean, I read a

(04:09):
lot of physics papers, and then sometimes I'll read a
popular article about one, and I'll think, like, why did
this one get chosen to make a big deal about
It's not really that big a deal, but you know,
you can take some little aspect of it and make
it sound like it's a really big deal, because most
people out there don't understand a bigger picture of the field.
Is this really a big step forward or is it
a tiny little increment? And we're just hearing about the

(04:31):
overall motivation for this entire line of research. So it's
hard when you're not an expert to really understand what
was a breakthrough and what wasn't. Well, I don't think
it's a big mystery. There's probably a science reporter out
there that needs to also work to write something on
a deadline. Probably, Yeah, I guess you got to pick
something to trumpet about. That's the job. The really good articles, though,

(04:53):
do put things in context. They talk to experts, or
they are written by experts, so the reader can really
get a sense of is this a huge, huge leap
forward or is this just promising potential breakthroughs or what's
really going on? Well, it seems like there's a interesting
science headlines every other week, But I guess sometimes people
need a little bit of help figuring out which ones
are a big deal and which ones are maybe a

(05:15):
little bit, you know, over enthusiastically reported on by the reporter.
If you just believe all the headlines that you read,
you would think that every couple of weeks there's a
result that's going to change fundamentally the way science works.
That like, science is going to pivot on this result
that that we'll look back on history and say, wow,
there was a time before and after we knew this
one fact in reality, though, a lot of times you'll

(05:38):
read about something which sounds like a big deal, and
then you'll never hear about it again, which tells you like,
maybe it wasn't really that big a deal. So it's
hard to sift through and figure out like which ones
historically are actually going to seem like pivot moments in
history and which ones are just going to have sort
of filled the news cycle for that week. But I
feel like that's kind of maybe one of the exciting

(05:58):
things about science. You know, this idea that establish ideas
can be overturned at any moment, and you know, everyone's
working on a big idea of their own, you know,
because we haven't figured things out, and so everyone has
a different angle on it, and any focus that anyone
makes could potentially, in reality, overturn what we know. Right,
You're absolutely right, And it's tempting to look back on
history and say, oh, there was an obvious line, a

(06:21):
step from A to B to C to D, and
that's how we got to where we are. But when
you're in the moment, you don't know which direction is
going to bear fruit and which one isn't. The true
history of science is sort of like a big branching
tree where lots of those branches were later abandoned or
died off, and when you're at the tip of the
latest branch, you don't necessarily know which direction to go.

(06:41):
So that's why people are exploring in lots of different
directions and exclaiming excitedly when they figure out something cool.
That might mean that this is the future path of
all of science. But maybe it's not. Maybe it just
dies off after the next branch. You're right, we never
do know in the moment. Yeah, you don't want to
be that reporter who finds out about something amazing Indensis man,

(07:02):
this was an okay result. Yeah, that's true. But it
also means that you do need to read all these
articles with a grain of salt, and sometimes a spoonful
of salt. It seems like, for example, a recent headline
that's made the rounds that everyone seems to be very
excited about, you've got a lot of questions about it. Yes,
there was an article last week that lots of people

(07:23):
read and thought, oh my gosh, this seems like a
really big deal. I wonder if it's true, And they
sent it to me, so I got dozens of emails
from listeners and tweets from people asking me, is this
for real? What do you think? It seems like it
would be more efficient if all reporters just ask you
every time they write a science article, and then you

(07:43):
could just, you know, impart your judgment. Well you know
that happened. Sometimes they do reach out to me to
ask me for comment, and reporters out there email me.
I actually write back. I'd be happy to comment on
research articles. I don't know do they want, Maybe they
don't want. Maybe they don't if you're trying to get
readers to read their headlines and click through. And now

(08:04):
for a splash of cold water. Daniel Whites, Well, the
article that came out, it does sound pretty interesting. That
has to do with black holes and the expansion of
the universe. So today on the podcast, we'll be asking
the question, good black holes be making the universe expand faster?
Black holes and dark energy too great taste? That tastes

(08:28):
great together? Do they? Man? I feel like it's like
black holes versus dark energy. It's like Emperor Popatine fighting
Darth the It sounds to me like the last round
of the Battle of the Bands. Yeah, there you go.
We can just sit back with some popcorn and watch
what happens. I think black holes and dark energy they've

(08:49):
gotta be like metal bands or sort of like goth
rock or something. Yeah, I'm sure there are grows up
there with those names. But this is an interesting question
because at first hearing it kind of sounds kind of intuitive, right,
like black holes suck stuff in, they make things more compact,
and ye, how can they be making the universe expand faster? Exactly?
So it's got all the elements of a huge scientific

(09:10):
revolution and big splash in the news. Right, it's counterintuitive,
and it solves more than one mystery, like what's going
on with black holes and what's going on with dark energy?
Oh my gosh, maybe one explains the other. So it's
very tantalizing. Yeah, it's always exciting when there's like a
crossover event, right, like Marvel and DC, like Superman and

(09:31):
Spiderman working together or against each other making the universe faster.
It's like combining two tasty sandwiches. You know, peanut butter
sandwich is good, a ruben is good. Would a Ruben
with peanut butter be even better? Well, until you do
the experiment, you can't know for sure, right, Daniel, you're
going to do that experiment? You know, if I was
a lunch eating kind of person, I might, but I'll

(09:52):
have to leave it to you. I'll pass. I don't.
I don't think I need to know that the result
listeners let us know. But it's interesting. So this paper
came out last week right as of this recording. It did,
and it's set the physics world of buzz all sorts
of cosmologists and experts in black holes and in dark energy.

(10:12):
We're arguing about whether this paper made any sense and
what it meant and whether we could believe it. Oh right,
because there are experts in both areas and this one
try to put them together. Did they ask for a
permission or you don't need to ask for permission to
write a paper. You can just write it and send
it out there and see if people will read it.
Why can it They need permission to publish a paper,

(10:33):
thoughn't you? It requires the whole committee to approve your paper.
To be approved, you definitely need reviewers and all that
kind of stuff. But you can just write a paper
and put it on the archive and you know people
will read it. These days, journal review is sort of
a secondary process. People read papers well before they're ever
reviewed by journals. Wait wait, wait, wait what you can
just post things on the internet without permission. Yeah, this

(10:54):
is a site called archive dot org where all physicists
post their papers before they go to the journals, because
the journals take forever to review stuff, and you want
people to read your results basically as soon as they're ready.
So these days most of the actual science happens on
what we call preprints, where people post their papers before
they go to the journals. Wow, that sounds like having
a policy debate over Twitter comments. You wait until you

(11:20):
checked it out first, or maybe that is sort of
a now part of the process of experts checking it out,
you put it out to the whole community. Yeah, there's
actually a vigorous debate about whether we even need journals
anymore now that we have the Internet. Journals aren't necessary
for actually publishing and distributing papers. You just have them online,
so they're really just there to provide peer review. But
you know, there's a lot of question about whether peer

(11:42):
review actually adds anything to papers, or if it just
delays them and burdens a bunch of people with extra work.
I guess that feels a little risky. I mean that's
sort of like calling Twitter comments peer review or like
the like bunds, like, oh, this paper got two thousand likes,
it must be true. Well, I never read and believe
a paper just as it's been peer reviewed. I'm going
to read it myself and see if it makes sense anyway.

(12:04):
All right, Well, fortunately people out there have us, or
at least they have you, to go through papers like
this one to see if it makes sense, and they,
I guess they have me to ask you about it.
That's my role exactly. And so this paper was a
lot of fun to read and to talk to my
colleagues about. And I also went out there to gather
opinions from random people I ran into on the UC

(12:24):
Irvine campus. Yeah, because as usual, we're wondering how many
people out there I had heard about this paper or
had an opinion about whether black holes can make the
universe grow faster. Usually people had to say that's not
my area of expertise. My understanding was like they're an
energy sync though, like the energy goes like it's like
the one place where matter could possibly no one like

(12:47):
actually be destroyed. So I'm not sure how to answer
that question, but my guests would be the negative or
it would do the opposite. But again I'm not I
guess that would be an astrophysicist would be their expertise.
I don't know. I don't really know much about black holes,
and so I'm assuming maybe I wouldn't think so, because
like black holes are meant to like go inwards right

(13:11):
like almost like a funnel, and it's they seem to
be pulling things in, So I would almost expect the opposite,
where it would like help fast forward the I don't
know when everything condenses. That's my opinion, at least. I'm
not a physics I don't know. So I was actually
just reading this paper last week. I think it's a

(13:32):
really interesting result, you know. I think the media has
maybe blown it a little bit out of proportion and
portrayed it in a way that I don't think it's
one hundred percent accurate. However, I do think there is
always interesting. I think what they're doing in the paper,
looking at sort of black holes as a different type
of energy source to drive the expansion, is a really

(13:52):
cool idea. So yes, I think it's possible, but maybe
not in the way that's been portrayed by the media. Wow. Okay,
I don't know, but since the universe is expanding and
black holes are part of it, I'm gonna go with yes. No,
I don't think black holes is gonna mat of his
expand because they sucked things towards them with some gravity,
so they wouldn't be pushing things away and expand. They

(14:14):
would if anything decreases as the universe. I didn't read
science or would probably referred to, so I'm not really sure.
In my black hole compressed as a matter, So I
I'm not sure how it would expand any universe. Oh.
I don't really know much about black holes, so I
don't really know it sounds plausible to you at all? Yeah,
I mean, I guess all right. Most people had not
heard of the article, although I was surprised that one

(14:36):
person had just read that paper. Were you like what
or did you ask your office mate or one of
your grad students. I didn't have a whole lot of time,
so I was wandering around the physics portion of the campus,
and I'm pretty sure I did hit an astrophysics grad
student who had actually read the paper. Oh, I see
this is a little bit loaded of a sample. My
favorite response was a person who suggests that I go

(14:58):
and ask a physicist for an answer. That sounds like
a very sensible thing to do. Why didn't you just
ask a physicist, Daniel, Yeah, good question exactly. Maybe I should.
I should go get a PhD in physics and I
should go figure this out myself. You should be like
a professor or something, and then you can answerr questions

(15:18):
for a living. Yeah. I think that person misunderstood what
I was trying to do with my question. I think
she thought I was wandering around campus looking for somebody
to explain this paper to me. Oh, I see, I see. Well,
I guess there aren't that many people walking around asking
physics questions. Did you think maybe you were like somebody
lost on campus. Yeah, you know, it's famously hard to
tell physicists apart from homeless people, and so I think

(15:40):
maybe she would just being polite and patronizing me. Well,
it's an interesting paper, and so let's dig into it.
What does the paper say? So, in a nutshell, the
paper says that black holes out there in the universe
are the source of dark energy, that they are the
reason that the universe's expansion is accelerating. That the expansion

(16:01):
of the universe is getting faster and faster every year.
That's the basic idea of the paper. That sounds pretty cool.
All Right, we're done. I'm off to have a peanut
butter ribbon sandwich. Yeah, I'm kind of hungry. I prefer
almond butter. All right, good to know. We might have
to do a side experiment on that. But let's maybe

(16:22):
break it down for people, and let's start with just
the idea that the universe is expanding. Some people might
not know that the universe is getting bigger and bigger,
and it's getting bigger at a faster and faster rate. Yeah.
This phenomenon goes by the name of dark energy, which
is a very mysterious sounding name for something we don't
really understand very well. But we do know some things,

(16:43):
Like we look out there into the universe and we
watch galaxies. We measure their velocity relative to us by
looking at how the light from them is red shifted,
because things that are moving away from us faster will
have the wavelengths of their light stretched out longer and longer.
We call that red shifting. And we look out into
the universe, and as we look out further and further,
we're looking further back in time because it takes time

(17:06):
to get here. So we can see how fast things
are moving away from us now the close up stuff,
and how fast things were moving away from us earlier.
So we can see sort of how much this is
changing our things moving away from us faster and faster
every year, or is it slowing down? And about twenty
years ago we went out and did this measurement using
very precise techniques involving supernovas and exactly how they blow

(17:27):
up and all that stuff, and we found something very surprising.
We discovered that the universe is expanding, and that expansion
is speeding up, meaning that every year galaxies out there
are moving away from us faster and faster. And so
that's what we call dark energy. We don't know what's
doing it, we don't understand the mechanism for it, but
we see that this is happening, and we want to

(17:49):
understand it. Yeah, and you call it dark energy because
it's kind of like an energy, right, Like it requires
work and energy to make the universe bigger, because you're
sort of creating more and more space. That's right, and
we are making more space between galaxies actually everywhere in
the universe. We think that space itself is expanding. So
if you have your picture in your mind of the

(18:10):
universe's expansion is sort of like a bomb with a
tiny little dot at the center that blows up and
everything flies through space, you should try instead to think
about it as like a universe already filled with stuff,
which then expands, creating new space between everything in the
universe all over the place. So it's sort of like
this stretching of space or this expansion of space itself.

(18:31):
And you're right, that makes more energy because we think
that every chunk of space comes with energy, and that
energy then drives the expansion, which makes more space, which
drives the expansion even more. And so that's why it's accelerating,
sort of like taken off. And then it's called dark
because there's no visible evidence of it in a way,
right like this, like everything's glowing or something, or there's

(18:54):
some kind of explosion that you can see. It's like
an invisible force that's growing the universe. It is invisible.
But I think probably it's called dark because it's mysterious,
because we don't understand it. It's like unexplained. It's an
area we have yet to illuminate. So I think it's
sort of like mentally dark more than physically dark, though
also invisible. You know. We call it dark energy, which

(19:17):
suggests that it's like a thing we understand is something
in physics. It's happening, but really we don't understand where
this comes from. It's something we see happening in the
universe and we can describe in some ways using our theories,
but we don't know really where it comes from at all. Yeah,
it's a big mystery, maybe even the biggest mystery in
the universe, right is it's a mystery that kind of

(19:37):
permeates the entire universe, and the universe is pretty big.
It definitely dominates the universe. Like, if you add up
how much energy it takes to make this happen, it's
like seventy percent of the energy in the universe. So
you take a cubic light year of space, for example,
and you say how much energy is stored in like
all the gas and the stars and the planets. That's
like five percent of the energy in that cube. Another

(20:00):
twenty five ish percent is dark batter that also has
energy in it and the rest of its seventy percent
of the energy budget of the universe. Is this weird stuff,
dark energy that's causing the universe to expand faster and
faster every year. But again we don't really know why
it's happening or where it comes from. We can describe
it in our theories, like we have general relativity that

(20:22):
tells us how the universe works and how space works
and how it can expand, and there is an option
in general relativity to make this kind of thing happen. Yeah,
you have some theories that it maybe is like a
property of space itself, like space itself is potential energy
and it can't help itself but to get bigger. That's right.
And remember that while general relativity is a theory of gravity,

(20:43):
and we tend to usually think of gravity is like
something that attracts stuff. Are you're attracted to the Earth,
the Earth is attracted to the Sun, And we think
of general relativities like explaining that kind of stuff, that
gravity is purely attractive. General relativity is more complex than that.
It's not just like how much mass and energy is
there in a certain place. It also depends on the
distribution of that mass and energy, and also on the

(21:04):
kind of energy. So example, if you have a lot
of potential energy in a part of space, it can
generate a negative pressure, it can cause the expansion of
that space. So Einstein's equations of all these different kind
of knobs that can make space do different kinds of things.
So if you say, well, space might have a lot
of potential energy into it, you add this thing we
call the cosmological constant, where all of space just has

(21:27):
this potential energy in it that can actually cause this
kind of expansion. Then of course you can ask like, well,
why would it have this cosmological constant? Where is this
potential energy coming from? And that's sort of where we are.
That would be sort of a very deep question about
the very nature of space, right. That's right, as you
say space we think has energy in it, Like we

(21:47):
know that space has quantum fields inside of it. Right,
There's a field for the electron on, a field for
the Higgs boson, and a field for the photon. It
has all these fields in it, and those fields have
some potential energy. We know that because they're quantum fields
can't relax all the way down to zero energy, and
so for a while, people thought, oh, maybe that's it.
Maybe all the fields that are out there in space
they have this potential energy, and that potential energy was

(22:10):
causing the expansion of the universe. So people sat down
to try to calculate it and say, well, how much
potential energy is there in all of those fields, and
how much potential energy would you need to explain this
expansion of the universe to provide the potential energy that
will allow general relativity to drive the universe expanding this way.
So you sit down and calculate those two numbers, and

(22:30):
you hope they agree, because that would mean that it's
an explanation. But instead they disagree, and they disagree not
by a little bit, but by a number like ten
to the hundred and twenty. So like, we really just
don't understand this at all. Yeah, it's a big mystery.
And so the universe is expanding faster and faster and
we don't know why. And then now this paper is
kind of saying that maybe black holes are the source

(22:53):
of that expansion, and so let's get into what exactly
black holes are and how they might be fueling dark energy.
But first let's take a quick break, all right, we

(23:15):
are playing MythBusters today kind of news headlines with papers
that have been published. There's been a paper recently that
has a pretty juicy headline that says that or that
asks the question whether black holes can be making the
universe expand faster? Now, Daniel, is this a paper that
just dropped on the internet or is this a paper
that has already been peer reviewed. This is a paper

(23:36):
that has been peer reviewed. These guys did not drop
it on the Internet before they sent it to reviewers,
so they kept a little bit tight to their chest.
I think also they linked it with a bunch of
publicity and stuff. So sometimes people don't put their papers
up in the Internet before they get peer reviewed. And
I think that's actually more common in astronomy than it is,
like in particle physics. Interesting, why do you think that is?

(23:59):
Astronomers know how to play the press game a little
better than particle physicists, or particle physicists just like to
post them to the Internet. Well, particle physicists are the
ones who invented this whole idea of putting things on
the Internet. I mean, we invented the Worldwide Web. We
have these big international collaborations and Also, I think for
particle physics, by the time you have a paper ready,
usually it's been reviewed by like five thousand of your

(24:20):
other colleagues whose names are also on the paper, and
so the peer review process feels a little bit more
like a rubber stamp in particle physics than in other fields.
All right, Well, this paper that came out recently says
that black holes could be what's making the universe expand
faster and faster. And so we talked about what dark
energy is, what the expansion of the universe is. Now
let's talk a little bit about black holes, Like how

(24:40):
do you explain what a black hole is? And what
don't we know about them? Right? And so the takeaway
from dark energy is the universe is expanding, it's expanding
faster and faster. We don't know why that's happening because
we can't explain where this potential energy is coming from,
this sort of vacuum energy of the universe. All right,
So that's a huge mystery, as you said, right, big

(25:00):
not understood thing in the universe. Now, one of the
other really fascinatings, big misunderstood things in the universe r
of course black holes that we've talked about on the
podcast lots of times, because they're so fascinating and amazing
and might contain within them like secrets of the nature
of space and time and all sorts of crazy stuff
because they are very extreme situations. They are a spot

(25:22):
in space that is so dense with energy and matter
that space is curved so intensely that nothing can escape
past this event horizon. That even photons which travel at
the speed of light are trapped inside because space is
curved essentially so that it's one dimensional. Every direction forward
once you're inside a black hole leads towards the center

(25:43):
of the black hole, and in general relativity, it says
that this force is so powerful that everything inside the
black hole eventually collapses to the very very center, forming
a singularity, a dot of infinite density because there's a
lot of mass with zero volume. Yeah, chatted about this
a lot. It's interesting that for black holes it's all

(26:03):
about the density of mass, right of matter, because gravity
gets stronger the closer you get to it, and so
if you put a lot of mass in a small spot,
that means you can get really close to it, and
so at some point that gravity gets so crazy, so
big that it actually creates a hole in space. You're
exactly right. It's all about the density. Like the same
mass that could create a black hole if you squeezed

(26:25):
it down, could also not create a black hole. If
it was more spread out, like the mass of our
sun could create a black hole, if something squeezed it down,
or if the Sun stopped exploding, which is what's preventing
it from collapsing into something more dense. So it's not
just about the amount of mass, it's about the density.
And that means that you can have black holes of

(26:45):
all sorts of masses. You can have black holes like
the mass of our sun. You can have black holes
like ten times the mass of the sun, a billion
times the mass of the sun. Black holes coming in
a huge variety of sizes and masses. And that's one
of the big puzzles about black holes. Yeah, well, it's
maybe even stepping back a little bit. We don't actually
know if black holes are real, real, like we talked

(27:06):
about them like they are, but actually they are Kenneth theoretical,
and we have pictures of them, but we're not quite
sure what's in the picture. Right, that's exactly right. We
have a model from general relativity that predicts that this
would happen, and it says, if you get matter dense enough,
then you should create this event horizon and have a
singularity on the inside. And for a long time that
was just theoretical, and people thought, that's weird. I bet

(27:29):
something prevents that from happening. That seems too strange. But
then we saw these things out in the universe, and specifically,
what we saw were very dark portions of space that
had a lot of curvature to them, very strong gravity.
For example, we saw stars whizzing by very close and
getting turned around by strong gravity, but we didn't see
anything at that location. So we crossed off a bunch

(27:50):
of candidates. Oh maybe it's a neutron star. Nope, Oh
maybe it's this, maybe it's that, maybe it's the other thing,
And eventually the only thing left was a general relativity
black hole. That's the only sort of explanation we had
for this kind of phenomena. But it's not a direct observation, right,
it's not like we've seen the event horizon literally or
we verify that it really is a black hole. We

(28:11):
just sort of like observe things closer and closer and
closer to the black hole that haven't yet fallen in
that tell us it must be something very dense and
very dark, right, something super dense, super dark that doesn't shine.
But it could be just a dark hole, not just
a black hole, for example, could just be a lot
of mass compacted really tightly, but not necessarily a singularity,

(28:32):
which is what the name originally was given in General
relativity exactly. Early on, it was sort of the only
candidate to explain these kind of things, and that's one
reason why people started believing they exist. But recently there's
been sort of a flourishing of other ideas, other possibilities
that might explain the same observations, Other things that would
look just like these black holes but would not be

(28:53):
black holes. We talked about a few of them on
the podcast, things like dark stars. These are stars that
are collapsing due to gravity, but they're collapsing super duper
slowly because the gravity slows down time, so it's not
actually a singularity. It's just sort of like a collapsing
star frozen in time, which eventually will bounce back and
maybe turn into like a white hole. Or we've talked

(29:14):
about fuzzballs which are these weird phenomena from string theory
and all sorts of other various ideas, And the thing
that all these ideas have in common is that they
are quantum mechanical. One of the big problems with the
idea of a black hole from general relativity is the
singularity is the idea of having all this mass in
a tiny little dot that breaks quantum mechanics. Quantum mechanics

(29:36):
says you can't do that. It violates the uncertainty principle
and all sorts of basic principles of quantum mechanics. And
general relativity is not compatible with quantum mechanics, which is
one reason why See inside a black hole would be
so awesome, because because they see finally a battle between
general relativity and quantum mechanics and see who won. So
we think almost certainly general relativity is wrong and needs
to be modified by some theory of quantum gravity that

(29:59):
tells us what else is going on inside a black hole.
Maybe it's basically like a general relativity black hole, but
with a quantum blob of a singularity instead of an
actual dot. Maybe it's something totally different, like a fuzzball
or a dark star or something even weirder. Yeah, it
could be some kind of strange crossover event in their
like Captain America versus Batman exactly. And it's also important

(30:20):
to understand that the black holes that we've sort of
figured out how to calculate, these predictions we've made for
like you should see a black hole under these conditions,
those only really describe very simplified situations. Nobody actually has
been able to calculate a black hole like the ones
that we see out there, that the ones we suspect
exist in our universe. The kind of black holes we

(30:42):
can calculate are the ones where you have like a
dot of mass and otherwise empty universe. We know how
to do that calculation in Einstein's theory. The Einstein's theory
is very very messy, it's very complicated. It's almost impossible
to do anything realistic like in Einstein's theory. You can't
even do two dots of mass. We can't even of
the Earth going around the Sun. In Einstein's theory, even

(31:03):
basic stuff like that is too hard. And so, for example,
what we haven't done in Einstein's theory is figure out
how a black hole can survive in an expanding universe
like we always do our calculations in a flat universe
where space isn't expanding, so nobody even really knows, like
what happens to a black hole when the universe is expanding,
especially if that black hole is spinning. So it's not

(31:26):
like we, even in general relativity, have a great description
of what we've seen out there in the universe. You
mean at least the general relativity version of them, right,
But there could be other versions of a black hole,
or like a dark hole or a black divid maybe
that do I explain what's out there. We're not quite
sure what that is right exactly, And we also don't

(31:46):
know how they get so big sometimes exactly. That's one
of the other really deep mysteries about black holes, especially
the kind of black holes talked about in this paper.
These are the black holes at the centers of galaxies.
You can have a black hole just from a star
at the end of its life, it goes to Brenova
and collapses and you get a black hole. It's like
five or ten times the mass of our sun. That's
cool we see in those when we think we understand them.

(32:06):
But also there tend to be black holes at the
hearts of galaxies, Like at the center of our galaxy
there's a very big black hole with lots and lots
of mass, And at the center of many galaxies there
are black holes with millions or billions of times the
mass of our Sun. And we see these even very
far back in the early universe. If you look at
light that's been traveling for a very very long time

(32:27):
from very distant galaxies, you can see galaxies in the
first billion years of the universe that already have black
holes at their centers that are like a billion times
the mass of the Sun. And this is a big mystery.
Nobody understands how those black holes got so big so fast. Well,
it's kind of an amazing thing that we can tell
that there are black holes in these galaxies so far away. Yeah,

(32:48):
that's exactly right. It's fascinating, and we can tell them
often because they are quasars. Quasars are black holes that
have very strong magnetic fields that are spinning really really fast,
and so they emit these jets of light that are
super duper bright, so we can see them from very
very far away, so they're not always like super direct
observations of the black holes it's not like we've imaged

(33:08):
them the way we've imaged a couple of black holes
using the event horizon telescope. Again, black holes are almost
always indirect, but we're pretty confident that there's something very
dark and very massive and very dense at the hearts
of these galaxies. And we don't understand how you make
a gravitational object whatever it is, that massive, Like there
just isn't enough time for it to eat enough gas
and dust and stars to get that big that fast.

(33:32):
So there's all sorts of theories about how those black
holes might have gotten so big so fast it was
super mass. Now we have two big mysteries, two big
things out there in space. One is the expansion of
the universe. It's getting bigger and bigger, faster and faster.
We don't know that that's dark energy. And then there's
black holes, which we know some about but we're not

(33:53):
quite sure on the details or what's actually going on
inside of them. And now this new paper says and
maybe these two things are related, like maybe black holes
are the reason the universe is expanding. So what does
this paper actually say. Yeah, it's super fun and fascinating. Actually,
the couple of papers. The first paper makes a really
interesting just sort of observation about the masses of black holes. Wait,

(34:15):
it's several papers. Yeah, they wrote a couple of papers.
The first paper is like details of about the black
hole masses, and the second paper is this crazy theoretical
interpretation about it. Like they dropped the movie and the
sequel of the exactly. Yeah, two seasons of your favorite
show all the same time. The Netflix model of physics
or the event I guess, the Avengers endgame model. There

(34:37):
you go, film both movies at the same time. We
often do this. We work on several papers all at
once and then publish them all at the same time
because they're all sort of connected to each other. Or
you want to be the first person to write an
interpretation of your crazy new observation, so you write your
interpretation paper at the same time as you write your
observation paper, and you publish them separately. All right, So
this paper is talking about the masses of these black holes.

(34:59):
They went out and they measured the masses of a
bunch of black holes. Over time, they looked at closer
by galaxies that are newer, and they look deep into
the ancient past at very old galaxies, and they were
interested in how fast black holes are getting bigger. Like,
you have a galaxy and it's spinning, it's got a
black hole at its center. Black hole is going to
be eating gas and dust and stars, and the galaxies

(35:21):
also grow. Galaxies grow by gobling up gas from the
intergalactic medium and also by merging with each other. So
essentially what they did is they compared these two things.
They said, well, how fast are black holes growing and
how fast are galaxies growing? And what they noticed is
that the galaxies are not growing as fast as the
black holes are growing. So one question is like, well,

(35:42):
how did black holes get big in the early universe.
The other question is how do they keep getting bigger
all the time. So this is a really interesting result
because they're showing that black holes are growing unexplainedly quickly.
I see. Okay, So this first paper that's sort of
like a survey, right, Like they just looked at into
space and they looked at the younger galaxies and older

(36:02):
galaxies that have black holes in them, super massive black holes,
and they compared the young galaxies with the older galaxies,
and they said, between the two, in general, our galaxies
getting bigger and at what rate? And for those black holes?
Are those black holes getting bigger and at what rate?
And you're saying that the first paper just says black
holes seem to be getting bigger faster than galaxies are

(36:23):
getting bigger. Yeah, black holes are getting bigger, like eat
to twenty times faster than the galaxies they are in.
They are growing much more quickly than the rest of
their neighborhoods. But wouldn't that be explained by the idea
that the black holes are basically eating the galaxies because
like galaxies don't have a lot of things around them,
so they can't really grow that fast. But black holes

(36:45):
have a galaxy around them, and so maybe it could
just be that the black holes are eating up their
own galaxies and getting bigger. That way, we actually do
expect galaxies to grow. Remember that something like forty to
fifty percent of all the protons in the universe are
not eating galaxies yet they're between galaxies. There are these
filaments of gas between the galaxies that are still flowing
into the galaxies. Right now, every galaxy sits at the

(37:07):
bottom of a gravitational well created by its dark matter,
and there are these like rivers of gas flowing into
galaxies making them bigger, and then also galaxies merge, and
so galaxies we do expect them to grow, and you're right,
black holes we also expect them to grow. And you
can do studies of these things, and you can predict
how fast galaxies and black holes should grow, and it
should be about the same rate. You know, there's some

(37:29):
limit to how fast a black holes should be able
to grow because as it gets more powerful, it's acretion
disk gets very intense the stuff that's swirling around it,
and it is very hot and agitated and hasn't yet
fallen back into the black hole, and it generates a
lot of radiation which actually pushes away gas. So black
holes can't just grow like infinitely quickly, and galaxies should
be able to grow about the same rate. But what

(37:51):
we see is a big discrepancy that we don't understand.
So black holes are growing much faster than their galaxies,
which is not what our models predict. M Okay, that's
a mystery. That's a weird thing. So that's the first
paper and the second paper says, well, you know, black
holes are growing faster than we think, but it's actually
connected to something else. They notice that black holes are

(38:14):
growing at the same rate as the universe itself. That
the expansion of the universe we talked about, this unexplained
accelerated expansion matches very nicely the rate at which black
holes are gaining mass. So these two unexplained things seem
to be happening about the same pace. Like let's say

(38:34):
the universe is expanding how fast, like a thousand percent
per year or something like that. The expansion rand of
universe is a little bit more tricky to measure. It's
in terms of like kilometers per parsee per second, so
it's a little bit complicated. But you know, in a
cartoon version, it's like if the volume of the universe
doubles soared the mass of these black holes. So as
the universe gets bigger, black holes get bigger at the

(38:55):
same rate, which could just be a huge coincidence perhaps,
But these maybe these authors are saying that it's not
a coincidence exactly. These authors are saying it's not a coincidence,
and they have a theory which predicts this, which explains
the connection between the black holes mask getting bigger unexplainedly,
and the universe getting bigger unexplainedly. They want to explain

(39:18):
both of these things at the same time. All right, well,
I'm hooked. I want to know what this theory is,
and so let's dig into it. And also let's see
what our critic Daniel has to say about this theory.
But first, let's take another quick break or I we're

(39:44):
talking about the expansion of the universe, and a new
paper or a new set of papers it says that
maybe black holes are the ones that are somehow connected
to this expansion of the universe. So we talked about
how the universe seems to be expanding at a high rate.
That also seems to Madge how fast black holes out
there in the middle of galaxies are expanding, which could

(40:04):
be a coincidence. But these authors are saying that it's not,
and they have a theory that links the two of them. So, Daniel,
what's the theory. So the theory is pretty crazy but
also a lot of fun. The idea is that black
holes are not black holes as we imagined in general relativity.
They're not point masses at the centers of these event horizons. Instead,

(40:25):
there's something very very different that inside the event horizon
is not a point mass, but instead it's a ball
of vacuum energy. So what does vacuum energy? What does
that mean? Remember, vacuum energy is the thing we thought
might explain the expansion of the universe. We know in
general relativity, if the universe if empty space, what we

(40:47):
call the vacuum space, particles in it that has some
kind of energy, and that energy can drive the expansion
of the universe. In this theory, instead of having that
energy everywhere in the universe, you have like localized blobs
of that energy. It can form black holes that regions
of very very high vacuum energy and form something that
looks like a black hole. What okay, okay, let's maybe

(41:10):
take a step back here. Are they saying that when
you make a black hole, you're creating a bubble of
vacuum energy, or are you saying that when you have
a lot of vacuum energy that is what you call
a black hole. It's the second we're saying that the
things we're calling black holes are actually bubbles of vacuum energy.
They're not compressed masses. Here, we're talking about the things

(41:31):
that the centers of galaxies, stellar black holes from collapsed stars,
probably black holes that's not what these guys are talking about.
They're talking about the huge blobs of the centers of galaxies.
They're suggesting they're not black holes like we imagined. Instead,
that are these weird blobs of vacuum energy that somehow
mysteriously form, or that are that started somehow, or that
the universe started with. What are they saying, are these bubbles?

(41:53):
How can they have the gravity of black holes if
they have negative energy? So they don't explain what this
vacuum energy is or where it comes from. That's just
sort of left a big question mark. But there is
a history of people developing these kinds of ideas. I mean,
go back to what we were talking about earlier, people
trying to understand how you could have a spinning black

(42:15):
hole in an expanding universe. Nobody's solved those equations in
Einstein's theory. Nobody really knows if it's even possible in
Einstein's theory. So that leads people to explore other kind
of things, like instead of having a singularity the heart
of it, what if you put like a little expanding
universe inside the black hole, right, it might help you
match the expanding universe outside the black hole. So they

(42:37):
put this sort of like expanding vacuum energy inside the
black hole, and what they see is an incredible distortion
of space. There's no singularity, there's no event horizon, but
there is an intense curvature of space, which would look
a lot like a black hole, in the same way
that like a fuzzball doesn't actually have an event horizon,
but it's still really curves space, and so it looks

(42:59):
a lot like a black hole, or the way a
dark star is not technically an event horizon because eventually
everything comes out of it. These things don't have event horizons.
They were invented in the sixties original by some Souviet physicists,
and people have been playing around with them. They're just
like another weird prediction of something that would look black
hole em but you would still get sucked into it

(43:20):
because I thought a vacuum energy, you know, had like
negative gravity or something like that. That's a cosmological connection
we'll get to in a minute. They think this vacuum
energy might be driving the expansion of the universe globally
but locally. Weirdly, it also looks like a black hole,
like if you're near by it then it bends space
intensely because instead of having vacuum energy everywhere, you have

(43:42):
it localized. It's only this one spot at the heart
of the galaxy, So that discrepancy having it there but
not over here creates curvature in the region between it
and that looks a lot like a black hole. It
looks like a black hole. But wouldn't it be like
reverse gravity, Like wouldn't it push things away like in
the pulling ball analogy in the rubber sheet. Wouldn't something

(44:03):
like this be like lifting up the rubber sheet, like
pinching it and pulling it up? Or am I getting
vacuum energy confused with negative energy? This is not negative energy, right?
Vacuum energy is just potential energy, not negative energy. And
Einstein's equations are not very intuitive, right, Like, it's not
very intuitive to understand why in some cases potential energy
causes expansion of space. Here, this vacuum energy seems to

(44:26):
be doing two things. It creates this almost kind of
like event horizon locally and also drives the expansion of
the universe globally. Whether this makes any sense at all
is a topic of intense debate among cosmologists. I talked
to a bunch of them over this last week. Half
of them were like, this is nonsense. The other half
was like, well, maybe under certain conditions that might happen.

(44:47):
But this is definitely a very, very fringe theory that
a lot of cosmologists don't accept. Even just this part
of it, This idea of a Gravis star something with
vacuum energy inside it, which looks like a black hole
from the outside. A lot of people don't believe that's
even possible. Well, what's their excuse for it, Like, how
do they explain it? Why is there so much vacuum

(45:08):
energy concentrated in one spot? What keeps it together? They
don't have an explanation in this paper. What they do
is they say, look, there's an apparent connection between the
mass of the black holes and the expansion of the universe.
And if you accept this theory that there are vacuum
energy interior or objects at the hearts of these galaxies
that would explain it, it doesn't argue for that theory.
It doesn't justify that theory, doesn't explain where this vacuum

(45:31):
energy comes from or what it is at all. It
just says that there is a theory that allows you
to connect these two observations. It feels kind of like
a made up theory, a little bit like it feels
like the issues came up with a theory just to
say that they have a theory. It's a little bit
at hoc, right, It's not something that's been thoroughly worked out. Again, remember,
nobody knows how to solve Einstein's equations under all these

(45:51):
weird conditions expanding universes, spinning stuff, vacuum interiors, or singularities.
Nobody knows what the solutions are like, so nobody can
even really say if this is consistent or inconsistent with
general relativity. Some of the cosmologists I talk to you said,
there's no way this is consistent with gr Other people thought, hey,
maybe it might be. There are people working on these

(46:12):
kinds of solutions. But the really interesting part of the
paper is that they argue that having this vacuum energy
inside the black holes somehow contributes to the expansion of
the universe as a whole. I mean, we're used to
thinking black holes like acting locally, they suck stuff in nearby.
This is suggesting that because they have vacuum energy in them,
instead of like dense mass. They're also contributing to the

(46:34):
cosmological equation of state, the thing that affects the entire
expansion or contraction of the universe. And that's even harder
for most cosmologists I talk to to swallow. Yeah, because
it's not like these black holes are everywhere and spread
evenly across the universe. They're just at the very center
of some galaxies, and those galaxies are pretty far apart

(46:54):
from each other. Right, If they are the source of
expansion in the universe, wouldn't you then see like hot
spots of exp in some places, and in places where
there are in delities or black holes, you would see
no expansion. Yeah, that's exactly right, and that would be
very very weird and also not explained in this paper.
They don't even really talk about this aspect of it,
and it would be something very very strange in physics.

(47:16):
We have in physics this sort of like hierarchy of scales,
where really tiny stuff doesn't usually affect really really big stuff,
like things that happen inside the Sun don't affect the
galaxy as a whole, or things that you do don't
usually affect the motion of the entire Earth. Where the
sort of hierarchy of scales, really really high energy stuff
at very very small distances doesn't usually affect low energy

(47:39):
stuff over larger distances, and this would break that. This
would say the things that are happening like inside black
holes can affect the universe as a whole. That's very
very weird. It's weird, not just because black holes are
weird and dark energy is weird. It would require like
a very different sort of paradigm of physics. It would
tell something very very new is going going on, something

(48:00):
hard to swallow. Yeah, like, yeah, these sources of vacuum
energy and somehow their effect is evenly spread out to
the universe somehow. That's kind of what you're saying, right,
That would be weird. That would be very strange. And
that doesn't mean it's not happening. We should be ready
for strange stuff. History of physics is filled with times
when people are like, well, the only way to explain

(48:21):
this would be this totally crazy idea that can't possibly
be true, And then it turns out it is true.
It just it requires us to accept something new. This
could be one of those moments, right, or maybe not.
So It's not always easy to tell, but there's a
lot of skepticism. One reason is that this is like
an explanation for what's happening. It's not at all a
conclusive explanation. It's not the unique explanation. It might be

(48:45):
that you could explain black holes growing at the same
rate of the universe in some other way. Instead of
black holes driving the expansion of the universe, maybe there
is something else that's driving both. Right, So it feels
sort of like this describes it, but it doesn't clinch
it necessarily. We're not sure that this is what's happening
just because it describes it. Science has to be predictive,

(49:07):
not just descriptive. It could just be a coincidence, is
what you're saying. It could be a coincidence, or could
just be that we have the causality backwards. Instead of
black holes driving the expansion of the universe, something else
could be driving both of them, so they could be connected.
It just might not be this theory of vacuum interior
black holes driving somehow magically the expansion of the universe. Well,

(49:27):
that would be a juicy headline too. Couldn't the expansion
of the universe be making black holes bigger. I mean
that's the idea, right, Like, maybe the universe is expanding
for some reason, for because of dark energy, and somehow
that a fact causes black holes to get bigger too. Yeah, exactly,
And if you understood where this vacuum energy came from,
maybe that would be the source of it. And this paper, again,

(49:48):
it doesn't address that. Either doesn't say where this vacum
energy is coming from or what it's made out of.
Is it made out of quantum fields like we suspect,
or is it something totally different. We just don't know.
But this paper got peer reviewed, and if you had
been one of the peer reviewers, what would you have
set If I had been one of the peer reviewers,
I would have asked for a lot more details about
this theory and some comments about these obvious questions, you know,

(50:10):
like how is it possible for localized objects to contribute
globally to the expansion of the universe, and also how
is it possible for black holes whose mass is a
tiny fraction of the mass of the universe? Right, black
holes are a little fraction of the five percent of
the universe that's our kind of stuff. Dark energy is
seventy percent how is it possible for this tiny mass

(50:32):
fraction to drive this huge energy in the universe. So
I want to ask those questions, and I imagine that
the authors of this paper are getting those questions from
their colleagues, and I'm looking forward to hearing some answers
and some follow up papers. Well, it sort of sounds like,
you know, they discovered something that is significant and is
interesting and it is noteworthy. Right, they discovered that black

(50:52):
holes are increasing at a rate that's higher than the
galaxies around them, and they're also increasing at a rate
that seems to match the expansion of the universe. Like,
that's an interesting result. The right that it hadn't been
published before that is definitely a very interesting result. So
that's probably, you know, publish worthy. It's just that the
ideas are putting forth to maybe explain this are a
little bit on the fringe side, and that's probably also

(51:13):
why they put it out in two different papers. The
first one, he's here the black holes we found. The
second one is here's our crazy idea to explain it.
And so the second one is definitely a bit more speculative.
There are also questions being raised about the first paper,
you know, people are looking at this paper and saying, well,
you've looked at a bunch of black holes snapshots in time.
You never watched an individual black hole grow at the

(51:35):
rate of the universe. We can't possibly do that. You
have to observe it for billions of years. Instead, you
look at different black holes through history, and you try
to tell a story about how, in general black holes
are growing. There are some assumptions there that you're making, right,
that black holes in different regions of the universe who
are growing at the same rates, etc. And so people
are also asking questions about that paper. But I think
that one's probably pretty solid. It's really this connection between

(51:57):
black holes and the dark energies theoretical interpretation that's a
lot more speculative and a lot of fun also, right,
And I want to be too negative about it. I
love new ideas, I love breakthroughs, I love speculation. But
you know, we got to put it in context and
think about all the question marks that come with it. Right.
But that's kind of the norm in physics, right, Like,
if you have a wild idea, you're allowed to publish

(52:19):
a paper with a wild idea, right, Like, as long
it has some sort of basis in reality, or at
least some indication some hints that are based in reality,
which this one did. You're sort of allowed in physics, right,
the polish crazy ideas. Sure, And it's also totally reasonable
to start off with a half formed idea to say, look,
here's something crazy and fascinating. We don't have all the

(52:40):
details worked out, but maybe it's something in this direction.
And somebody else will read the paper and be like, huh,
here's an obvious hole that needs to be filled. I
wonder if And then I'll have an idea and they'll
explain it. And so it's totally fine to not have
solved everything in one paper, right, to say, maybe this
direction works, and here's some indications that it might be
a fruitful path. Let's keep going this way, and then

(53:01):
everybody jumps on it. I need to proves them wrong
or supports it. We'll see. Yeah, like the Higgs boson.
I mean, Peter Higgs got the Nobel Prijec because he
polished the crazy idea without a lot of paces in
an actual experiments. Right, He's like, hey, maybe there's a
field called the Higgs field and the Higgs boson, and
and that was an explanation, right, It was an explanation

(53:21):
and not the only explanation exactly. And one nice thing
about this paper is that they suggest some ways to
check these results. As a bunch of details that people
can do studying the causer of microwave background and how
stars are whizzing around, they make a bunch of predictions
if this theory is right, things we might be able
to test. And so there's a lot of really fun
work we can do in the next few years to
see if indeed black holes aren't driving the expansion of

(53:44):
the universe or not. Do you think I can get
my theory polish through peer review about Superman and Spider
Man causing the growth of black hole? I think you
have to choose very carefully the journal you're going to
send that to, Yeah, the Journal of or hit cham
on Twitter. There you go. Or I'll put it on
archive at archive dot org. There you go, Archive dot

(54:07):
org ya, And then I can be a polished physics theorist.
Join the club. All right, Well, lots to think about here,
I guess again. The main lesson is stay tuned. I mean,
people have crazy ideas about things, and they observe the
universe and they find interesting coincidences and that may or
may not be coincidences. And that's how science moves forward,
is noticing these weird things and putting out their potentially

(54:29):
crazy ideas that sometimes turn out to be true, and
we can't always tell them the moment, which paper is
going to be something that resonates through history and is
read by generations to come, and which is just going
to be another in an exciting press release that nobody
ever talked about Again. All right, well, we hope you
enjoyed that. Thanks for joining us, see you next time.

(54:55):
Thanks for listening, and remember that Daniel and Jorge explain
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