November 28, 2023 • 45 mins
Daniel and Jorge venture to the edge of human knowledge about black holes, gravity and magnetic fields.
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Speaker 1 (00:08):
Hey, Daniel, do you ever get tired of answering questions
from listeners?
Speaker 2 (00:12):
Not so far, But you know, ask me again in
another five years.
Speaker 1 (00:15):
Oh, what's going to happen in five years?
Speaker 2 (00:18):
I might have a different answer.
Speaker 1 (00:20):
Some places you get the same questions over and over.
Speaker 2 (00:22):
You know, there are a lot of common themes in
these questions, that's true.
Speaker 1 (00:25):
And do you have like pre prepared answers ready to go?
Speaker 2 (00:28):
You can't really do that because every question's a little
bit different. And for me, the fun part is figuring
out like what somebody misunderstood to lead to their confusion
and helping them unravel that.
Speaker 1 (00:41):
So you kind of just like program an AI to
answer questions for you, kind of like they do now
with like customer service lines.
Speaker 2 (00:47):
You could definitely program an AI to answer questions, but
it would generate nonsense.
Speaker 1 (00:51):
Sometimes, isn't the answer nonsense? In physics, especially quantum mechanics, the.
Speaker 2 (00:57):
Most amazing thing about the universe is that it doesn't
see aim to be nonsense. It seems to actually make sense.
Speaker 1 (01:03):
So far, Maybe I'll ask you again in five years.
Speaker 2 (01:06):
Maybe in five years you'll have replaced me with an AI.
Speaker 1 (01:09):
Maybe in five years will all be replaced by AIS
and only AIS will be listening to this, but maybe
not I.
Speaker 2 (01:15):
I Hi.
Speaker 1 (01:31):
I'm Jorge, a me cartoonists and the author of Oliver's
Great Big Universe him.
Speaker 2 (01:36):
You know, I'm a professor of physics and I do
experiments at CERN, and I don't think that I'm an AI.
Speaker 1 (01:42):
But you could be. Are you saying.
Speaker 2 (01:46):
We never know philosophically where our consciousness comes from. We
could all actually be AIS.
Speaker 1 (01:51):
Yeah, we could. I guess there's several possibilities, right, Like
we could be in a simulation or something and we
could all be AIS. Or you know, if the people
were really Jesus, all right, then technically we are kind
of artificial intelligence because we were made by another intelligence.
Speaker 2 (02:05):
Yeah, it certainly could be. Or we could all just
be cylons, you know, thinking we're humans, programmed to think
we are humans, but silicon underneath. Yeah.
Speaker 1 (02:15):
On a TV show that sadly got canceled.
Speaker 2 (02:19):
That was a great show.
Speaker 1 (02:20):
But anyways, welcome to our podcast, Daniel and Jorge Explain
the Universe, a production of iHeartRadio.
Speaker 2 (02:24):
In which we use our consciousness simulated or not, artificial
or not, to try to understand the nature of the universe.
Whether it's real or not, and whether our subjective experience
is organic or not. We think it's worthwhile to try
to understand what's out there, to try to make it
all work in our minds, to ask questions and seek answers,
(02:45):
and that's what this podcast is all about.
Speaker 1 (02:47):
Yeah, sometimes I feel like by intelligence is simulated, Like
I'm just pretending to be intelligent.
Speaker 2 (02:52):
What's the difference between being intelligent and effectively pretending?
Speaker 1 (02:56):
Oh? Good point, that's an intelligent answer. And I don't
mean that in a fix. I mean that in an
unartificial sense.
Speaker 2 (03:04):
Sometimes I feel like the most important function I serve
for my students is asking them dumb questions about their research.
And often I see it spark good ideas. They're like,
well that doesn't make any sense, but it gives me
a good idea about something I could do.
Speaker 1 (03:18):
So you're incentivized to ask dumb questions.
Speaker 2 (03:21):
I just simulate knowing what I'm doing, and somehow the
people around me get stuff done.
Speaker 1 (03:26):
Sounds like you could program an AI to ask dumb
questions and then you don't have to do anything.
Speaker 2 (03:31):
Yeah, exactly. I think often I could be replaced by
a cardboard cutout of myself. Just having students explain what
they're doing to me helps them understand what they're doing wrong.
Speaker 1 (03:39):
Yeah, and it has pre program answers like or questions like, huh,
that's really interesting. Have you checked the error bars?
Speaker 2 (03:47):
Are you sure about those assumptions?
Speaker 1 (03:49):
That's it. Just have it on loop. People come in,
they press a button, You're in a Caribbean island doing nothing.
Speaker 2 (03:54):
Yeah. Or they just pull a string behind me, or
I'm just like a stuffed Teddy bear.
Speaker 1 (03:58):
Yeah, there you go.
Speaker 2 (04:00):
Maybe we should actually make merch stuffed versions of us.
They pull the back of you and you go hmm,
and they pull the back of me and it goes chuckle.
Speaker 1 (04:07):
Yeah. Perfect, And then someone could just repidate the entire
podcast without us.
Speaker 2 (04:11):
There just stings. You could build a robot to pull
the strings and we'd be done.
Speaker 1 (04:18):
Yeah. Oh man, but I guess you need someone to
press the record book.
Speaker 2 (04:23):
I have students who can do that.
Speaker 1 (04:25):
Perfect. But yeah, it is a pretty interesting and amazing universe.
Whether it's simulated or not, or whether we are simulated
or not, and whether we are artificial or not. We
have questions about what's going on in this universe, about
how it all works.
Speaker 2 (04:37):
Scientists have questions and are busy doing experiments to try
to get answers. But we're not the only ones with questions.
Everybody out there asks questions about the nature of the
universe since the first people have looked up in the
night sky and wondered what all those twinkling lights were.
Being curious is just part of being human and looking
for answers is doing science, whether or not you're getting
(04:58):
paid for it.
Speaker 1 (04:58):
Yeah, it's not just a job of sign this to
ask questions about geners. It's your job. It's everybody's job
to look at the cosmos and wonder why it's all
there and how it all works.
Speaker 2 (05:06):
One of our goals on this podcast is to find
answers for you, but also to stimulate your questions, to
get you to think about the things you don't understand,
to hear what we're saying and then try to click
it together in your mind and when it doesn't quite fit.
We love if you reached out to us to ask
us your questions about the universe. We'll always answer them
to questions at Danielandjorge dot com.
Speaker 1 (05:29):
Yeah, everybody has questions, the kids, adults, and everyone in between,
and sometimes we'd like to answer those questions here on
the podcast.
Speaker 2 (05:35):
We absolutely do, so feel free to write to us
and ask us your questions. Sometimes I'll get a question
that I think, hmm, I bet other people want to
know the answer that, and so we'll answer it here
on the podcast.
Speaker 1 (05:45):
Do you sometimes think, oh, nobody else wants to know
the answer to that? Do you have the opposite feeling?
Speaker 2 (05:50):
I do sometimes get personal questions about people's life path
and stuff like that, and so yeah, that's individualized answers
that don't need to be on the podcast.
Speaker 1 (05:59):
Do you get a quot question that it's like so
complicated you don't think anyone else would be interested.
Speaker 2 (06:05):
I get a lot of people sending me their personal
theories of the universe, and I'm not sure anybody else
really wants to read those hundreds of pages written by
retired engineers.
Speaker 1 (06:14):
But what if they're right? Oh? I see, But then
it becomes your theory, and then you want everyone to
read about it.
Speaker 2 (06:22):
No. I read those theories and give them critiques, and
if there was something to it, then yeah, you'd hear
about it well.
Speaker 1 (06:27):
As Daniel say, we'd like to answer questions here on
the podcast, and so on. Today's episode will be tackling
listener questions number forty five, Gravity and black holes. That's
the theme of the questions today, gravity and black holes.
Speaker 2 (06:44):
Yeah, black holes and gravity seem to be on people's
minds the week that these questions came in.
Speaker 1 (06:50):
Yeah, and so we have some great questions here about
famous physics experiments, the event horizons of black holes, and
what happens since the Big Bang. Pretty deep questions, deep
in time and space. So we'll just jump right in.
Our first question comes from Sean from Canada.
Speaker 3 (07:06):
Hey, Daniel and Jorge, this is Sean calling from Canada.
I have a question about the observer effect. What would
happen if the observer was on the inside of the
event horizon of a black hole and the experiment being
observed was on the outside of the event horizon of
a black hole? Would it know that it's being observed?
(07:27):
Would the waves collapse and all that stuff?
Speaker 2 (07:31):
Yeah, let me know.
Speaker 1 (07:32):
Thanks, interesting question. I guess the gist of it is
that what happens if you're inside of a black hole
can't tell what's going on outside of the black hole.
Speaker 2 (07:40):
Yeah, there's a lot of really interesting stuff going on
in this question. It's about black holes, it's about quantum mechanics,
it's about all that kind of stuff. Of course, inside
a black hole, you can see things that are happening
outside a black hole, right. A black hole is where
information cannot escape from, but new information can always arrive,
Like photons can fall in do black holes, and if
(08:00):
you were inside a black hole, those photons could still
reach you. So from within a black hole, you can
observe things happening in the outside of the universe. But
I love this question because it touches on this complicated
quantum mechanical issue of observing things changing them right. Often
in quantum mechanics we say that observation changes an experiment,
And he's wondering, if you're doing that observation while you're
(08:23):
inside a black hole, can you change an experiment that's
outside a black hole.
Speaker 1 (08:28):
Because I guess in quantum mechanics, once you observe something
it like, it changes the wave function of it right exactly.
Speaker 2 (08:35):
And this is something in quantum mechanics that's not very
well understood. So often when you push the boundaries and
come up with crazy thought experiments, the answer is we
don't know or we have no idea because actually our
theory quantum mechanics doesn't make any sense, so it's probably
important to like sum up what is the observer effect
in quantum mechanics what we're talking about here.
Speaker 1 (08:55):
But I guess maybe I have many more basic questions
about the setup here. So like the observer, you are
inside the black hole, and this is I guess, assuming
you survive going into the black hole.
Speaker 2 (09:04):
Right, yeah, I assume. I assume you survive. If you're
observing the experiment.
Speaker 1 (09:07):
Like you have a camera and you take it inside
of the black hole and you somehow survive, you would
still be getting information from outside the black hole, but
you wouldn't, I guess. See, like the whole universe, like
I think we've talked about this before, the whole universe
would look like one pinpoint to you.
Speaker 2 (09:21):
That's right, All light that arrives on the black hole
would arrive to you and just one point. So like
the entire event horizon would be collapsed to a single
point in your vision. The rest every other direction from
your perspective would be towards the singularity. Because remember that
black holes are curvatures of space time, and so changing
(09:42):
the way space is organized inside the black hole.
Speaker 1 (09:45):
Okay, So now the scenario is that there's maybe like
an electron just outside the black hole, and it's about
to veer to the right or to the left depending
on some magnetic field right because it has some quantum
uncertainty about that. And then the question is could you
see that, Like, could the photon from that electron reach you?
Would it reach you?
Speaker 2 (10:02):
So a photon from that electron definitely could reach you.
If the electron gives off a photon that can fall
in the black hole, and then it can reach you
inside the black hole absolutely.
Speaker 1 (10:12):
What about like time, doesn't time slow down at the
surface of a black hole, or doesn't it stand still?
Speaker 2 (10:17):
So time does get slowed down by gravity. Places that
have strong curvature feel time going more slowly. So for example,
if you're near a black hole and you're looking at
the rest of the universe, your time is going more slowly.
You see the rest of the universe going more quickly.
Or if you're watching somebody fall into a black hole,
you see their time slow down. So from the outside
you can't actually see somebody fall into a black hole.
(10:39):
You're right, if time slows down so much as they
approach the event horizon, that it's not until, like time
equals infinity, that they actually fall in from your perspective.
But if you're the person falling into the event horizon,
then you just fall past the event horizon. You don't
notice these effects.
Speaker 1 (10:55):
The electron would just fly right in from your perspective
inside the.
Speaker 2 (10:58):
Black hole, inside the black hole exactly, but.
Speaker 1 (11:00):
Really outside of the black hole, it wouldn't happen for infinity.
Speaker 2 (11:03):
From the point of view of a distant observer watching
you fall in, it wouldn't happen until time egals infinity,
or until something else falls in the black hole and
grows it so that it encompasses you. That's the reason
that like real black holes in the universe can actually grow,
that they don't have to wait until time equals infinity
for things to fall in, because there's a whole series
of things falling in. Each one grows the event horizon
(11:25):
for the previous one.
Speaker 1 (11:26):
Okay, so you can get information from inside the black hole,
and I guess you're not really watching the electron. You're
just watching whether it veers to the rider to the left, right,
something to texts the electron going right or left or something.
Speaker 2 (11:37):
Yeah, I think the setupiece interested in is like an
electron is in a superposition of two possible states, like
does it go left or right? And somehow you maybe
use a photon to detect left versus right, and that
photon falls into the black hole. And he's wondering if
observing that photon inside the black hole collapses the way
functioning the experiment outside the black.
Speaker 1 (11:57):
Hole right, because I guess since you're inside the black hole,
there's like no way for the electron to know whether
you saw it or not exactly.
Speaker 2 (12:06):
That's where this cool quantum mechanics black hole paradox comes in,
because if you take away the black hole, we had
the sort of classic observer effect that the electron can
still be fifty percent chance left, fifty percent chance right
until its wave function is collapsed. When does the wave
function collapse? Well, nobody really knows the answer to that,
but one ridiculous but standard description or quantum mechanics says
(12:28):
that the electron's wave function is collapsed when is observed
by a classical object like a person or a big
detector or something. So the photon can bounce off of
the electron without collapsing its wave function because it's still
a quantum object. But then when that photon carrying that
information hits a screen or a detector or an eyeball
or something like that, a classical object, it collapses the
(12:50):
whole wave function. And that's when the electron decided, okay
I went left or okay I went right.
Speaker 1 (12:55):
But does it collapse only for the observer or for
the entire universe? If if you observe it, but I
don't know what you observe, is it still a quantum
object to me?
Speaker 2 (13:04):
Oh? Great question? And the answer to that depends on
your quantum mechanics philosophy. So in standard quantum mechanics Copenhagen interpretation,
it collapses for everybody, and it collapses instantly across space
and time. Those two objects are entangled. The photon and
the electron are quantum mechanically entangled, meaning that they share
a fate. They're connected to each other. If the electron
(13:25):
goes left, then the photon looks a certain way, and
if electron goes right, the photon looks another way. So
in your standard interpretation, as soon as you observe the photon,
that collapses the electron for everybody. But in other interpretations,
to quantum mechanics like Carlo Ravelli's relational quantum mechanics. Then
it only collapses for the person doing the observation. One
person can collapse it for themselves, somebody else could have
(13:47):
it be uncollapsed, and a third person can collapse it
in another way. So there's different theories of quantum mechanics
in the standard one that people typically think about and
we complain about a lot because it doesn't make much sense.
It's collapsed for everybody.
Speaker 1 (14:00):
It also sort of depends on the idea of short
Anger's box, right, doesn't it? Like if I wrap a
box or on you the observer and the electron, like,
it's still a quantum object to me, no matter whose
interpretation I think about, does it the cat is both
alive and dad and you saw it and not saw
it at the same time.
Speaker 2 (14:15):
Yeah, that is the paradox rate by Schrodinger's box, that
things can be unobserved but still be classical. So in
the standard Copenhagen interpretation we say classical objects collapse the
wave function and quantum objects do not. The problem with
the standard quantum mechanics is that there's no definition of
what's a classical and what's a quantum object, so it's
sort of a useless distinction. But in the standard interpretation
(14:37):
then you would still become collapse the wave function because
you'd be a classical object and your observation collapses it.
Even if I don't know what you've seen before. You're
not a quantum object, so you can't be in a superposition.
Speaker 1 (14:48):
Okay, so that this is an extra twist to it. Now,
let's say that you're the observer and you're inside of
a black hole and you saw the electron go right
or left. I think Sean is asking, how does that
affect things that the wavefund collapse for the electron or
is it still unknown for the rest of the universe.
Speaker 2 (15:03):
This is a really great and very very difficult question,
and before we answer it, I want to compare it
to a similar complicated question, which is just about entangled
objects that are really far apart right. A similar question
you might ask, is, well, well, if the photon is
really far away from the electron when it's observed, how
does the electron know to collapse? If the photon flies
(15:25):
for a thousand light years before it gets observed, how
does the electron then collapse instantly across time? These questions
are related because they have to do with apparently sending
impossible information. And this is a classic question in quantum
mechanics theory, right, And this is the paradox posed by
Einstein decades and decades ago when he can plain the
quantum mechanics makes no sense because it requires things to
(15:48):
violate special relativity to collapse instantly across time. Things outside
of each other's light cones somehow, causing each other to change.
Speaker 1 (15:56):
So, in the case of it entangled quantum paricles, the
answer that but it does travel faster than light in
a way, right, Like, once you collapse one half of
it a few light years away, it sort of instantly
changes what you have in front of you exactly.
Speaker 2 (16:10):
And there's a really crucial subtlety here. You're totally right
that the collapse happens instantaneously across space and time. So
quantum mechanics is what we call non local. And that's
because the wave function is broad. It doesn't just exist
in one place. Don't think of it like one particle
doing something to the other particle. It's one big quantum state,
and you collapse it anywhere. It collapses everywhere simultaneously. That
(16:32):
does happen instantaneously across space and time. But and this
is the crucial nuance, it doesn't send any information. So
collapsing the wave function with a photon really really far
apart doesn't send information to the electron. You can't use
it to like send signals faster than the speed of light.
Though a lot of people imagine that quantum mechanics entanglement
can do that, you can't actually send information. Just collapses
(16:55):
the whole wave function simultaneously. It's not a mechanism for
information transmission.
Speaker 1 (17:00):
I see. I think what you're saying is that, like
there's no rule to how big a quantum system can
be or how far apart its parts can be. So
like even a half, if I have one half here
and another half, you know, millions of lighters a way,
it's just still one quantum system. There's no rule in
quantum mechanics that says, oh, no, you're too far apart.
Now you're two separate quantum systems. You're actually like still
the same system exactly.
Speaker 2 (17:20):
And quantum mechanics explicitly is non local. Stuff can happen
coordinated across space and time. It doesn't have to be
like this thing bumps into that thing which is right
next to it. Very weird property of quantum mechanics that
we really don't fully understand.
Speaker 1 (17:35):
Okay, and so now the question is, what if half
of my system is inside of a black hole? Is
it still one system?
Speaker 2 (17:41):
Great question, and the answer depends on your theory of
quantum gravity, because now this is a question that involves
quantum mechanics. We're talking about quantum particles and wave functions,
and it involves event horizons, so gravitational effects. And the
truth is we don't know how to marry those two things.
So I'm sorry, Sean, you're asking a question we don't
really know the answer to because we don't have a
(18:03):
theory of quantum gravity.
Speaker 1 (18:05):
Meaning like we don't know how like if you distorted
gravity a lot, like in a black hole, you don't
know how it affects this idea of like a quantum
system being the two halves even though they're far apart exactly.
We just don't know it might affect it or it
might not affect it exactly.
Speaker 2 (18:19):
We don't know if gravity collapses wave functions or not,
or if gravity is fundamentally quantum mechanical and allows things
to be in superpositions even as they cross event horizons.
We don't have the answer to that, but I can
speculate an analogy to the other scenario where you have
two quantum particles really far apart, basically outside of each
other's light cones, which is sort of like being outside
(18:41):
of each other's event horizons. There's still the wave function
does collapse, but no information is transmitted. So I suspect
that what happens here is that if you observe the
photon inside the black hole, it does collapse the wave
function of the electron outside the black hole, but without
transmitting any information and so not breaking that rule of
(19:01):
black holes.
Speaker 1 (19:02):
WHOA Does that mean you could now communicate from inside
of a black hole to the outside of a black hole.
Speaker 2 (19:08):
No. In the same way that you can't use quantum
entangled particle collapse to send information, you also can't send
information from inside and event horizon using the collapse of
a quantum object across that event horizon. That's the analogy.
Speaker 1 (19:23):
So I wonder for like, practically speaking, you didn't really
collapse it because you're inside of a black hole and
nobody will ever know what you saw, So pretty much
in the rest of the universe. The half that's outside
is still quantum unknown.
Speaker 2 (19:36):
Yeah, that's very insightful because the reason you can't send
information across quantum particles faster than light is that you
can't know whether it's collapsed. Like if I have a
quantum particle and you have a quantum particle and they're entangled,
I can measure mine, which would collapse yours if you
haven't already measured it, But you can't tell if I've
collapsed at All you can do is measure your particle
and get like spin up or spin down, or left
(19:57):
or right. You can never tell that I've collapsed it.
That information doesn't get transmitted. And so in the same way,
if somebody observes that photon inside the event horizon, somebody
else looking at the electron can't tell whether the electrons
wave function has been collapsed or not.
Speaker 1 (20:11):
Okay, So then the answer for Sean is that we
have no idea. That's just a comment answer we give
you on the podcast, because nobody knows how gravity or
extreme gravity like black holes effects quantum mechanics and quantum
systems and wave collapse. But our best guess here on
the podcast is that it probably does collapse it, but
maybe it doesn't matter, so it doesn't really collapse it.
Speaker 2 (20:33):
Yeah, that's a great summary.
Speaker 1 (20:35):
Well, let's get to our other questions here today about
black holes and about the big Dang and magnetic fields.
So let's get to those, but first let's take a
quick break. Right. We're taking listener questions here today and
(20:59):
at least trying to answer them. Although sometimes the answer
is we don't nobody knows.
Speaker 2 (21:03):
Sometimes the answer is, great question, I wish I knew
the answer.
Speaker 1 (21:07):
Yeah, if you have the answer, write it to us
in one hundred page summary and then Daniel will read
it and let you know.
Speaker 2 (21:13):
That's right. Really, the answer some of these questions requires
us to develop theories of quantum gravity, and to figure
out how to develop those theories, we want to look
inside black holes, which is impossible, so we're a little
bit stuck sometimes.
Speaker 1 (21:25):
Well, you can look inside of a black hole, just
can't tell anyone what you saw.
Speaker 2 (21:30):
Yeah, that's right. That physicist who fell into a black
hole knows the answers, just can't get any awards for it.
Speaker 1 (21:36):
Yeah, that physicists solved everything. Let's throw a Nobel Prize
medal inside the black hole for them that million dollars
also or million coroner. I'm sure they can find a
good use for it in there. All right. So our
second question comes from Ryan, who lives in northern Virginia.
Speaker 4 (21:54):
Hello, Daniel and Hore. My name is Ryan and I
live in northern Virginia. I have a question for you
today about black holes, more specifically about their magnetic fields.
If the Earth's magnetic field comes from its liquid outer core,
where does a black holes magnetic field come from? Considering
there's no liquid core in the black hole and nothing
is supposed to be able to escape the event horizon,
(22:16):
I'm left to guess that the accretion disk is the
big driver of the magnetic field. But that's just a guess.
Thanks for considering my question, Love the show.
Speaker 1 (22:24):
Awesome great question, Ryan. You know I don't know the
answer here, and I'm gonna guess maybe the answer is again,
we don't know because it deals with black holes.
Speaker 2 (22:33):
No, this one I think we do know the answer to. Actually, well,
I know physics knows something, all right.
Speaker 1 (22:40):
Well, let's see. Ryan's question is where does a black
hole's magnetic field come from? Because I guess black holes
have a magnetic field. Do we know that for sure.
Speaker 2 (22:49):
Well, we do measure very strong magnetic fields near black holes.
Speaker 1 (22:53):
How do we measure them?
Speaker 2 (22:54):
How do we measure them? Great question? Well, we can
see the effect, right. Sometimes black holes have enormous jets
of stuff that shoot up and down on their north
and south poles, and we think that comes from the
magnetic field, like funneling particles up and down, sort of
the same way that the Earth's magnetic field causes northern lights.
Charged particles coming towards the earth magnetic field get funneled
(23:15):
up towards the north and south poles. Particles falling into
a black hole sometimes will miss because the magnetic field
will deflect them up and down, and you get these enormous,
like thousands of light years long jets of stuff shooting
out of black holes. We think from the magnetic fields.
Speaker 1 (23:29):
Well, I guess, first of all, we think those are
black holes and that those jets are coming from black holes.
Don't Like, we haven't actually seen the inside of what's
inside of those jets.
Speaker 2 (23:38):
We've study those jets in some great detail, and we
have really pretty good models that predict those jets. Recently,
we imaged a couple of black holes and saw ripples
in the accretion disk around them, and so we're able
to like really pin down the details of the magnetic
field near the black hole. I mean, we'd love to
send a probe near the black hole and measure those directly,
but there's a lot of indirect ways to measure those
(23:59):
magnetic fields, just by seeing the impact to have on
charge particles near the black hole.
Speaker 1 (24:05):
And I guess the other question is, how do he
knows those magnetic fields are coming from the black hole
enough from the stuff around the black hole.
Speaker 2 (24:10):
Yeah, that's a great question, and we don't know the
answer to that. We're sure that the stuff around the
black hole can make a magnetic field. Those are charged particles.
They're moving in a circle, so you have a current
moving in a circle that always generates a magnetic field.
The second part is thinking about whether a black hole
on its own could have a magnetic field even without
the accretion disc, even without the stuff swirling around it.
(24:32):
Whether just the black hole itself can have a magnetic
field is a really interesting question.
Speaker 1 (24:37):
Do we know the answer? Does a black hole on
its own have an inherent magnetic field?
Speaker 2 (24:42):
So we can answer that question theoretically, We've never seen
a black hole all by itself, without an accretion disk
and measured it. But according to general relativity, black holes
can have magnetic fields. And that's because black holes can
do two crucial things. One they can have an electric
charge and two they can can spin. And essentially anything
with an electric charge that spins has a magnetic field.
Speaker 1 (25:05):
But you're saying it's all theoretical though.
Speaker 2 (25:07):
It's theoretical because we've never observed a black hole without
any stuff around it and measured its magnetic field. That
would be an awesome test.
Speaker 1 (25:14):
Of this theory, I see. So basically we don't know.
Speaker 2 (25:21):
Yeah, that's true of lots of things. I suppose. We're
not sure about it, but we do have a pretty
good idea. And lots of our models of spinning black
holes and black holes with charge have been tested indirectly.
We've never done this exact test.
Speaker 1 (25:34):
Okay, So you're saying theoretically black holes do have magnetic
fields because they somehow preserve it, right even though you
when you throw charge particles in it with spin in
it and magnetic fields, presumably that doesn't get destroyed by.
Speaker 2 (25:48):
The black hole exactly. And Ryan is asking about, like
where that magnetic field might come from. Because you can't
see anything beyond the event horizon, So you can't have
like swirling matter within the event horizon and causing this
magnetic field. Why not, Because the details of anything like
that happening within the event horizon is shielded by the
event horizon. You can only know a few things about
(26:10):
what's happening inside the event horizon. You can know the
total mass, you can know the electric charge, and you
can know the spin.
Speaker 1 (26:17):
Meaning even if there are a bunch of electron spinning
inside of a black hole, the magnetic field they would
generate couldn't leak out of the black hole. Is that
what you're saying, Because the space would just be pointing inwards.
Speaker 2 (26:29):
A lot of the details of what's happening to those
electrons you wouldn't be sensitive to, Like if one electron
zigs up or zigs down, you couldn't sense that from
the outside. You can, however, sense that there are a
bunch of electrons, and you can sense that they're spinning overall,
because you can measure the total spin of the black
hole and the total electric charge of the black hole.
(26:49):
Like when electron falls into a black hole, just before
it falls in, it has an electric field, and when
it falls in, that electric field is now frozen on
the outside of the black hole. Whatever happened to the
electron after it falls in can no longer change that
electric field. It's sort of frozen there. So you can
tell that something has fallen in and that it had charge,
but the details what happens afterwards you're shielded from.
Speaker 1 (27:12):
So then are you saying, like, to get the magnetic
field of a black hole, you just multiply its charged
by its spin somehow, and that gives you like what
you would feel as a magnetic field outside of the
black hole. But those are like overall numbers, not related
to anything in detail inside of it.
Speaker 2 (27:28):
Exactly in the same way that an electron has a
little magnetic field. Right where does the magnetic field an
electron come from. It doesn't have a magnetic charge, It
has an electric charge, and it has quantum spin. Those
two things combined to give the electron a tiny little
magnetic direction, a magnetic dipole. And you can't tell what's
going on inside the electron. We think maybe it's a
(27:49):
fundamental particle. We have no idea. We can't see inside,
and it doesn't matter. We know it has an overall
charge and an overall spin, and so the overall charge
and spin of a black hole similarly gives it a
magnetic moment. It's a magnetic dipole.
Speaker 1 (28:03):
I wonder if, like Ryan's question was more like, you know,
how can a black hole have a magnetic field if
nothing can escape it? You know what I mean? Like,
if the electromagnetic field it has is due to the
stuff inside of the black hole, how can its magnetism
escape the black hole?
Speaker 2 (28:18):
Yeah, that's a great question. We have a whole episode
on how black holes can have magnetic fields and electric
fields and digs into the details of this question. Very briefly, though,
The answer is that the overall charge is essentially spread
out on the event horizon. So something falls into a
black hole, you're not getting information from within the event horizon.
(28:38):
You're just getting information from the event horizon. So think
about the event horizon itself as now having that charge
and having that spin. There might be crazy stuff going
on inside, weird quantum effects or singularities orringularities or whatever.
You can't tell, but you can tell that something charged
fell in, and you can tell without getting any information
about what's going on. Inside the event horizon.
Speaker 1 (29:01):
It sort of sounds like you're saying that the black
hole's magnetic field comes from its surface, Like it's the
surface of the black hole. That's basically you know, phasing
out to the rest of the universe, and you know,
emanating an electric charge and an electric field, and that's
why we can see it.
Speaker 2 (29:16):
Yeah, that's a good way to think about it. The
event horizon, or the surface of it equivalently, has three
properties mass, spin, and charge, and we can measure those
and those have an effect on the rest of the
universe right the same way, like the mass of the
black hole, even though it's contained within the event horizon,
still curves space outside the event horizon and can affect
the trajectories of stuff. Think of that as a property
(29:37):
of the event horizon. It doesn't matter what's going on
inside behind the screen of the event horizon, if things
are swirling around or not. All you know is the
overall mass, the overall charge, and the overall spin, and
that can create a magnetic field.
Speaker 1 (29:50):
But again, time slows down almost to a standstill near
the event horizon. How does the magnetic field ever get out?
Don't have to wait to infinity to feel that magnetic.
Speaker 2 (30:00):
Yes, so time near the black hole is really really
slowed down, not slowed down totally to infinity. So black
holes can radiate information for example, like if a black
hole gets accelerated by another black hole, it can radiate
a gravitational wave, or if it has charge, it will
also radiate photons. Again, these are coming from the surface
of the black hole, not from within it, so we're
(30:22):
not breaking the rules of black holes, but they can
radiate that information. And you're right that things near black
holes are slowed down, and so it does take longer.
And like those gravitational waves are slowed down by the
time dilation of the gravitational field. So without that effect,
those gravitational waves would look much crazier and the photons
would be much higher frequency. But they're stretched out and
(30:44):
red shifted by that time dilation, not all the way
to infinity, because the curvature isn't infinity outside the black hole.
Speaker 1 (30:50):
All right, Well, it sounds like the answer for Ryan
is that a black hole's magnetic field comes from its surface.
It's event horizon basically, or at least we can practically
think of it as coming from the surface and the
event horizon and that's why we're able to see it
and experience it. We think, we think we don't know
for sure because it's a black hole.
Speaker 2 (31:10):
We don't know for sure anything. We don't even know
if we exist or if this is a simulation. And
also remember that most of the encnic fields we've measured
probably do mostly come from the accretion disk of stuff
around them. But that's where he says we don't know
for sure.
Speaker 1 (31:24):
All right, Well, let's get to our last question of
the day, which is about the expanding universe and gravity
and the Big Bang. But first let's take another quick break.
(31:46):
All right, we're answering listener questions here, our favorite kind
of episode where we take your questions that you send
in and we try to answer them, usually with answers
that are not we don't know.
Speaker 2 (31:58):
We do our best.
Speaker 1 (32:00):
Sometimes nobody knows which is an answer technically it is.
Speaker 2 (32:03):
And I wonder if that's like really satisfying because it
means for the listener like, Ooh, I'm at the forefront
of human knowledge or really disappointing because like the rest
of humanity is still left unsatisfied.
Speaker 1 (32:15):
Yeah, I guess it is pretty exciting, right to be
to like come up against the boundary of human knowledge, right, yeah, exactly,
Like when I ask you a question and you don't
know the answer, I'm like, Wow, I am at the
boundary of Daniel's knowledge of the universe.
Speaker 2 (32:28):
Now, the boundary of Daniel's knowledge not the same as
the boundary knowledge. Let's not make that.
Speaker 1 (32:34):
Mistake, or at least the boundary of the research you've
been able to do for the last hour before the podcast.
Speaker 2 (32:41):
Exactly, I am at the boundary of human knowledge in
one time is a little corner of the vast sphere
of human knowledge.
Speaker 1 (32:49):
Well, we're all here with you, and so our last
question of the day comes from Argent phor Daniel.
Speaker 5 (32:54):
I have a question. Just got me thinking while I
was on the shore. We've come to understand that gravity
is bending of space time, and that's objects which would
normally travel in a straight line tend to take a
curve path around the body, which is distorting space time.
We also know that space itself is expanding in the
(33:16):
universe for the last ever since Big Bang happened. Do
we think the effects of gravity have changed over the
last couple billion years or do we expect it to
be different later now that we know that space itself
is expanding or stretching or thinning out, whatever you may
call it. Will that effect the way gravity acts and
(33:38):
behaves or has it changed over the years?
Speaker 2 (33:41):
What do you reckon?
Speaker 1 (33:42):
Awesome question? What do we reckon? Daniel? Do we know
the answer? In this case?
Speaker 2 (33:47):
I reckon that Urgent probably takes really long showers to
have such deep thoughts about the whole.
Speaker 1 (33:51):
History of the universe, which is awesome. Thank you Argent
for such a great question.
Speaker 2 (33:56):
So, as usual, we have some ideas about how this works,
but there's lots that we still don't understand, especially about
the expanding and the accelerating expansion of the universe.
Speaker 1 (34:07):
Okay, let me see if I understand Argent's question. He's
in the shower and he's wondering, you know, the universe
since the Big Bang has, first of all, it expanded
really fast. Space itself expanded really fast, and space today
is still expanding, and there's more and more space growing
and being created. The universe is expanding due to something
called dark energy. And I think his question is like,
(34:27):
is gravity affected by this expansion of space? Like do
we know if gravity itself has been the same and
for the last fourteen billion years or is there an
indication that maybe as a universe expands it could be
changing the effects of gravity like this gravity space dependent.
What do you reckon, Daniel, I.
Speaker 2 (34:46):
Think there's a crucial piece of the history of the
universe that you sort of yaddiyauted over there, because you're right,
the things did expand very quickly in the beginning, but
then then expansion actually decelerated because the stuff in the
universe slowed down the expansion. And then later on, like
six billion years ago, it started picking up again and
it started to accelerate the expansion. So this is funny,
(35:07):
sort of like zigzag in the history of the universe.
It wasn't always just accelerating expansion. It was always expansion,
but there was a period when that expansion was decelerating.
I emphasized that not just because it's a cool zigzag,
but to underline something which I think is in crucial
to answering Argin's question, which is that's part of gravity.
Gravity is not just things pulling themselves together, it's also
(35:28):
space expanding. That is general relativity, our framework that we
have and what Argent describes as like things moving through
bent space time that allows for the universe to expand.
That's sort of part of what gravity is.
Speaker 1 (35:40):
Well, what do you mean, like it's in the equations
of our theories of gravity for the universe to expand
due to dark energy.
Speaker 2 (35:48):
It's part of general relativity that the universe can expand
under certain conditions. So the broad answer to Argent's question is,
we think the rules of the universe, the rules of
gravity and space time and general relativity have not changed
changed over the last fourteen billion years, and we can
describe all of these weird epics of the universe using
one consistent framework, and that's sort of amazing. So the
(36:08):
rules haven't changed, even though the conditions do change from
year to year and things get further apart and whatever.
So there are specific conditions under which general relativity predicts
the universe will expand and that that expansion will accelerate.
If you have a bunch of energy inherent in space
stored in a field that has high potential energy, then
general relativity says space will expand and that expansion will accelerate.
(36:32):
So we see that happening in the universe. We look
back at the history of the universe, we see it's
expanding we see that expansion is accelerating, and so we say, oh,
there must be some energy stored in a field somewhere
with a lot of potential energy that's causing this. We
don't know what that is. We don't know what that
field is, We have no explanation for it. But general
relativity can accommodate that well.
Speaker 1 (36:51):
I think what you're saying is that physicists have a
set of equations that explain the universe, and that set
of equations has gravity in it, and it also as
expansion of the universe in it. So it's like they're
all actually kind of connected already into theories of physics.
Speaker 2 (37:05):
Yes, exactly.
Speaker 1 (37:06):
So it's not like one of them we don't know
if one of them is doing something the other one
doesn't know.
Speaker 2 (37:10):
That's right. And when people say gravity colloquially, they mean
like stuff attracting and things falling towards planets and whatever.
When physicists say gravity, they mean the whole shebang, They
mean the whole theory of space, time and all of
its consequences. Because moving from like a Newtonian view of
gravity as a force to an Einsteinian view of gravity
as motion of stuff through space time has all of
(37:31):
these consequences, not just oh, light is also bent by gravity,
but also the universe can expand and it could also collapse.
All of these things are consequences of this geometric view
of the universe we have from general relativity, and we
think that those rules have not changed. That the same
rules applied in the very very beginning and in the
middle point when things were decelerating, and now when things
(37:52):
are accelerating. So in the broadest sense, the rules of
gravity general relativity have not changed over the course of
the universe.
Speaker 1 (38:00):
I see, like the rules by which you mean the equations,
But I wonder if Argin means, like, you know, imagine
there's a term in your equations for gravity. I wonder
if he could mean that, you know, has that term
the equation change as the universe grew? Like could it
that be something the equations don't take into account, or
it could it be something we haven't noticed.
Speaker 2 (38:17):
Or or what. Yeah, there's a couple of ways in
which that could be true. First of all, we assume
that dark energy or whatever this is, this potential field
that's causing the accelerating expansion in the universe. We assume
that that's constant everywhere in space and everywhere in time,
and mostly that works. I mean, it said that we
can explain the whole history of the universe, and that's
mostly true, but there are some discrepancies, like we measure
(38:38):
it early in the universe, we measure it late in
the universe, and those two numbers don't quite agree. You
can read more about that. It's called the Hubble tension. Essentially,
that's predicting the rate of expansion, and different measurements don't
quite agree. So that's quite interesting. So it might be
that the dark energy is changing over time, and again
that wouldn't mean a change in the rules, but it
would mean some change in the conditions, which is affecting
(38:58):
like your experience of the Union. And also, maybe more importantly,
the second sense is that the density of stuff in
the universe is definitely decreasing. Like things used to be
really hot and dense and now they're very cold and
very far apart, and so there's definitely like less sense
of gravity in the universe. Because the mass density of
stuff in the universe is going down, space goes up,
(39:19):
the amount of mass doesn't change, so the density decreases,
things get further and further apart. You're feeling less gravity
from distant galaxies than you were before because they're now
further away from you, and that's going to keep going.
Speaker 1 (39:31):
Mm So I guess technically you would be feeling more
the gravity of Earth right as the universe gets more
empty and empty, right, Like, I'm way more in the
future regardless of what I what I do.
Speaker 2 (39:45):
If you're relying on distant gravities to lift you up
off the surface of the Earth and make you feel light,
then I have bad news for you.
Speaker 1 (39:51):
Yes, as my diet plan forget as epic.
Speaker 2 (40:00):
Yeah, exactly, I suggest hitting the gym instead of relying
on distant galaxies. But I'm not a health expert. Don't
take advice from me.
Speaker 1 (40:07):
Well, I wonder if Argine's question then maybe more simply
is like, you know, if I have a black hole
the same mass and I see it bend light around it,
is it going to bend light the same way now
in the future, in the past when the universe was
maybe more scrunched together, or is that light can we
bend differently depending on what the universe is doing, Like,
especially like let's say we're going through a period where
(40:30):
space is expanding faster and faster, or where we're hitting
you know, in that zig zag, where we're hitting a
point of maximum expansion, that light is going to bend
a little bit differently right than it would in a
period of not so fast expansion.
Speaker 2 (40:41):
All right, So now you've pushed this into a corner
of general relativity that we don't understand very well.
Speaker 1 (40:46):
So the answer is we don't know, We don't know.
Speaker 2 (40:48):
And also fascinatingly because we don't even understand our own theory,
like general relativity has no problem with having black holes
in an expanding universe, but we don't know how to
do that. Calculation like Einstein's equation are nasty and they're
very very difficult to solve. We can only solve them
in very specialized, simplified settings, like you have a black
hole in an otherwise empty universe that we can solve,
(41:11):
or you have a universe that's expanding, but the matter
in it is totally uniform, like dust sprinkled everywhere. We
don't know how to solve the equations for a black
hole in an expanding universe or a universe with like
chunky stuff in it. So we have all these approximations
and so the specific question you just asked, like what
happens to a black hole in an expanding universe? We
don't know how to do that calculation, but we think
(41:35):
that the rules are not changing, right, and so for
a black hole, gravity is basically the same as it
was a billion years ago and five billion years ago,
Like the nature of space itself is not changing. It
doesn't thin out, you know, as the universe expands, and
that expansion accelerats, you just get more space, and that
space behaves, we think, according to the same rules, and
so Bend's light the same way as it always did.
Speaker 1 (41:57):
All right, Well, then the answer origin seems to be
that you don't think that the rules of the universe
are changing, meaning like what the physicists would consider to
be gravity, which is the whole set of equations. You
don't think that's changing. But maybe the effects of a
black hole might be changing, except you don't know how
to calculate it.
Speaker 2 (42:12):
That's right. And there was even this fast on any
paper a few months ago about how like black holes
might be driving the expansion of the universe, right, that
black holes might actually be like weird clusters of dark energy.
So just to highlight like how little we understand the
expansion of the universe, and how tricky it is to
do these kind of calculations in any sort of realistic setting.
Speaker 1 (42:33):
Yeah, or in the shower.
Speaker 2 (42:36):
The shower is probably the best place to do these calculations.
Speaker 1 (42:39):
Yeah. Well, if it wasn't for gravity, you couldn't take
a shower. You definitely any gravity to shower.
Speaker 2 (42:44):
Oh my gosh, wow, thank you gravity. We should be
saying every time we have a shower. Yeah.
Speaker 1 (42:48):
If not for gravity, we'd all be a little bit stinkier,
or we'd all have to take baths in zero gravity,
which I think is dangerous, isn't it, Like you would
you would very quickly drown because the water would just sing.
Speaker 2 (43:00):
Golf you maybe, But again, don't take health advice from
this podcast. That is outside our area of expertise.
Speaker 1 (43:07):
Yeah, don't take health advice from a cartoonist, a physicist.
Speaker 2 (43:12):
Stay on your diet whatever it was before this podcast.
Speaker 1 (43:15):
That's right. Listen to a real doctor, not the academic kind, exactly.
Speaker 2 (43:21):
You know what the best thing about.
Speaker 1 (43:22):
Getting your PhD is, there's the best thing.
Speaker 2 (43:25):
Every meeting is now a doctor's appointment.
Speaker 1 (43:28):
There you go. I'm sure everyone loves doctor's appointments. Does
that mean that this podcast is a doctor's appointment for
the thousands of people who listen to.
Speaker 2 (43:37):
Us, I guess so. Yeah, oh man, keep your pants on, everyone, Yeah,
keep your pants.
Speaker 1 (43:42):
How I'm not gonna grab anything or ask you to cough.
Speaker 2 (43:46):
No, the only things we're probing are the nature of
the universe. The only black holes we're investigating are the
theoretical kind. That's right.
Speaker 1 (43:54):
That's right, only only physical dark matter that we're interested in.
All right, Well, that answers Arjie's question and everybody's question again,
and another interesting journey to the edge of human knowledge
and the realization of how much we know and still
have yet to know about the universe, which is kind
of exciting.
Speaker 2 (44:13):
That's right. So keep asking questions. You'll be surprised how
quickly you can get.
Speaker 1 (44:18):
To the edge of human knowledge or the edge of
a black hole.
Speaker 2 (44:21):
Apparently, or the edge of this doctor's appointment, or.
Speaker 1 (44:23):
The edge of this podcast. So we hope you enjoyed that.
Thanks for joining us, See you next time.
Speaker 2 (44:35):
For more science and curiosity. Come find us on social media,
where we answer questions and post videos. We're on Twitter, disport, Instant,
and now TikTok and remember that. Daniel and Jorge Explain
the Universe is a production of iHeartRadio. For more podcasts
from iHeartRadio, visit the iHeartRadio Apple Apple Podcasts, or wherever
you listen to your favorite shows.
Speaker 3 (45:00):
Th
Hey, Daniel, do you ever get tired of answering questions
from listeners?
Speaker 2 (00:12):
Not so far, But you know, ask me again in
another five years.
Speaker 1 (00:15):
Oh, what's going to happen in five years?
Speaker 2 (00:18):
I might have a different answer.
Speaker 1 (00:20):
Some places you get the same questions over and over.
Speaker 2 (00:22):
You know, there are a lot of common themes in
these questions, that's true.
Speaker 1 (00:25):
And do you have like pre prepared answers ready to go?
Speaker 2 (00:28):
You can't really do that because every question's a little
bit different. And for me, the fun part is figuring
out like what somebody misunderstood to lead to their confusion
and helping them unravel that.
Speaker 1 (00:41):
So you kind of just like program an AI to
answer questions for you, kind of like they do now
with like customer service lines.
Speaker 2 (00:47):
You could definitely program an AI to answer questions, but
it would generate nonsense.
Speaker 1 (00:51):
Sometimes, isn't the answer nonsense? In physics, especially quantum mechanics, the.
Speaker 2 (00:57):
Most amazing thing about the universe is that it doesn't
see aim to be nonsense. It seems to actually make sense.
Speaker 1 (01:03):
So far, Maybe I'll ask you again in five years.
Speaker 2 (01:06):
Maybe in five years you'll have replaced me with an AI.
Speaker 1 (01:09):
Maybe in five years will all be replaced by AIS
and only AIS will be listening to this, but maybe
not I.
Speaker 2 (01:15):
I Hi.
Speaker 1 (01:31):
I'm Jorge, a me cartoonists and the author of Oliver's
Great Big Universe him.
Speaker 2 (01:36):
You know, I'm a professor of physics and I do
experiments at CERN, and I don't think that I'm an AI.
Speaker 1 (01:42):
But you could be. Are you saying.
Speaker 2 (01:46):
We never know philosophically where our consciousness comes from. We
could all actually be AIS.
Speaker 1 (01:51):
Yeah, we could. I guess there's several possibilities, right, Like
we could be in a simulation or something and we
could all be AIS. Or you know, if the people
were really Jesus, all right, then technically we are kind
of artificial intelligence because we were made by another intelligence.
Speaker 2 (02:05):
Yeah, it certainly could be. Or we could all just
be cylons, you know, thinking we're humans, programmed to think
we are humans, but silicon underneath. Yeah.
Speaker 1 (02:15):
On a TV show that sadly got canceled.
Speaker 2 (02:19):
That was a great show.
Speaker 1 (02:20):
But anyways, welcome to our podcast, Daniel and Jorge Explain
the Universe, a production of iHeartRadio.
Speaker 2 (02:24):
In which we use our consciousness simulated or not, artificial
or not, to try to understand the nature of the universe.
Whether it's real or not, and whether our subjective experience
is organic or not. We think it's worthwhile to try
to understand what's out there, to try to make it
all work in our minds, to ask questions and seek answers,
(02:45):
and that's what this podcast is all about.
Speaker 1 (02:47):
Yeah, sometimes I feel like by intelligence is simulated, Like
I'm just pretending to be intelligent.
Speaker 2 (02:52):
What's the difference between being intelligent and effectively pretending?
Speaker 1 (02:56):
Oh? Good point, that's an intelligent answer. And I don't
mean that in a fix. I mean that in an
unartificial sense.
Speaker 2 (03:04):
Sometimes I feel like the most important function I serve
for my students is asking them dumb questions about their research.
And often I see it spark good ideas. They're like,
well that doesn't make any sense, but it gives me
a good idea about something I could do.
Speaker 1 (03:18):
So you're incentivized to ask dumb questions.
Speaker 2 (03:21):
I just simulate knowing what I'm doing, and somehow the
people around me get stuff done.
Speaker 1 (03:26):
Sounds like you could program an AI to ask dumb
questions and then you don't have to do anything.
Speaker 2 (03:31):
Yeah, exactly. I think often I could be replaced by
a cardboard cutout of myself. Just having students explain what
they're doing to me helps them understand what they're doing wrong.
Speaker 1 (03:39):
Yeah, and it has pre program answers like or questions like, huh,
that's really interesting. Have you checked the error bars?
Speaker 2 (03:47):
Are you sure about those assumptions?
Speaker 1 (03:49):
That's it. Just have it on loop. People come in,
they press a button, You're in a Caribbean island doing nothing.
Speaker 2 (03:54):
Yeah. Or they just pull a string behind me, or
I'm just like a stuffed Teddy bear.
Speaker 1 (03:58):
Yeah, there you go.
Speaker 2 (04:00):
Maybe we should actually make merch stuffed versions of us.
They pull the back of you and you go hmm,
and they pull the back of me and it goes chuckle.
Speaker 1 (04:07):
Yeah. Perfect, And then someone could just repidate the entire
podcast without us.
Speaker 2 (04:11):
There just stings. You could build a robot to pull
the strings and we'd be done.
Speaker 1 (04:18):
Yeah. Oh man, but I guess you need someone to
press the record book.
Speaker 2 (04:23):
I have students who can do that.
Speaker 1 (04:25):
Perfect. But yeah, it is a pretty interesting and amazing universe.
Whether it's simulated or not, or whether we are simulated
or not, and whether we are artificial or not. We
have questions about what's going on in this universe, about
how it all works.
Speaker 2 (04:37):
Scientists have questions and are busy doing experiments to try
to get answers. But we're not the only ones with questions.
Everybody out there asks questions about the nature of the
universe since the first people have looked up in the
night sky and wondered what all those twinkling lights were.
Being curious is just part of being human and looking
for answers is doing science, whether or not you're getting
(04:58):
paid for it.
Speaker 1 (04:58):
Yeah, it's not just a job of sign this to
ask questions about geners. It's your job. It's everybody's job
to look at the cosmos and wonder why it's all
there and how it all works.
Speaker 2 (05:06):
One of our goals on this podcast is to find
answers for you, but also to stimulate your questions, to
get you to think about the things you don't understand,
to hear what we're saying and then try to click
it together in your mind and when it doesn't quite fit.
We love if you reached out to us to ask
us your questions about the universe. We'll always answer them
to questions at Danielandjorge dot com.
Speaker 1 (05:29):
Yeah, everybody has questions, the kids, adults, and everyone in between,
and sometimes we'd like to answer those questions here on
the podcast.
Speaker 2 (05:35):
We absolutely do, so feel free to write to us
and ask us your questions. Sometimes I'll get a question
that I think, hmm, I bet other people want to
know the answer that, and so we'll answer it here
on the podcast.
Speaker 1 (05:45):
Do you sometimes think, oh, nobody else wants to know
the answer to that? Do you have the opposite feeling?
Speaker 2 (05:50):
I do sometimes get personal questions about people's life path
and stuff like that, and so yeah, that's individualized answers
that don't need to be on the podcast.
Speaker 1 (05:59):
Do you get a quot question that it's like so
complicated you don't think anyone else would be interested.
Speaker 2 (06:05):
I get a lot of people sending me their personal
theories of the universe, and I'm not sure anybody else
really wants to read those hundreds of pages written by
retired engineers.
Speaker 1 (06:14):
But what if they're right? Oh? I see, But then
it becomes your theory, and then you want everyone to
read about it.
Speaker 2 (06:22):
No. I read those theories and give them critiques, and
if there was something to it, then yeah, you'd hear
about it well.
Speaker 1 (06:27):
As Daniel say, we'd like to answer questions here on
the podcast, and so on. Today's episode will be tackling
listener questions number forty five, Gravity and black holes. That's
the theme of the questions today, gravity and black holes.
Speaker 2 (06:44):
Yeah, black holes and gravity seem to be on people's
minds the week that these questions came in.
Speaker 1 (06:50):
Yeah, and so we have some great questions here about
famous physics experiments, the event horizons of black holes, and
what happens since the Big Bang. Pretty deep questions, deep
in time and space. So we'll just jump right in.
Our first question comes from Sean from Canada.
Speaker 3 (07:06):
Hey, Daniel and Jorge, this is Sean calling from Canada.
I have a question about the observer effect. What would
happen if the observer was on the inside of the
event horizon of a black hole and the experiment being
observed was on the outside of the event horizon of
a black hole? Would it know that it's being observed?
(07:27):
Would the waves collapse and all that stuff?
Speaker 2 (07:31):
Yeah, let me know.
Speaker 1 (07:32):
Thanks, interesting question. I guess the gist of it is
that what happens if you're inside of a black hole
can't tell what's going on outside of the black hole.
Speaker 2 (07:40):
Yeah, there's a lot of really interesting stuff going on
in this question. It's about black holes, it's about quantum mechanics,
it's about all that kind of stuff. Of course, inside
a black hole, you can see things that are happening
outside a black hole, right. A black hole is where
information cannot escape from, but new information can always arrive,
Like photons can fall in do black holes, and if
(08:00):
you were inside a black hole, those photons could still
reach you. So from within a black hole, you can
observe things happening in the outside of the universe. But
I love this question because it touches on this complicated
quantum mechanical issue of observing things changing them right. Often
in quantum mechanics we say that observation changes an experiment,
And he's wondering, if you're doing that observation while you're
(08:23):
inside a black hole, can you change an experiment that's
outside a black hole.
Speaker 1 (08:28):
Because I guess in quantum mechanics, once you observe something
it like, it changes the wave function of it right exactly.
Speaker 2 (08:35):
And this is something in quantum mechanics that's not very
well understood. So often when you push the boundaries and
come up with crazy thought experiments, the answer is we
don't know or we have no idea because actually our
theory quantum mechanics doesn't make any sense, so it's probably
important to like sum up what is the observer effect
in quantum mechanics what we're talking about here.
Speaker 1 (08:55):
But I guess maybe I have many more basic questions
about the setup here. So like the observer, you are
inside the black hole, and this is I guess, assuming
you survive going into the black hole.
Speaker 2 (09:04):
Right, yeah, I assume. I assume you survive. If you're
observing the experiment.
Speaker 1 (09:07):
Like you have a camera and you take it inside
of the black hole and you somehow survive, you would
still be getting information from outside the black hole, but
you wouldn't, I guess. See, like the whole universe, like
I think we've talked about this before, the whole universe
would look like one pinpoint to you.
Speaker 2 (09:21):
That's right, All light that arrives on the black hole
would arrive to you and just one point. So like
the entire event horizon would be collapsed to a single
point in your vision. The rest every other direction from
your perspective would be towards the singularity. Because remember that
black holes are curvatures of space time, and so changing
(09:42):
the way space is organized inside the black hole.
Speaker 1 (09:45):
Okay, So now the scenario is that there's maybe like
an electron just outside the black hole, and it's about
to veer to the right or to the left depending
on some magnetic field right because it has some quantum
uncertainty about that. And then the question is could you
see that, Like, could the photon from that electron reach you?
Would it reach you?
Speaker 2 (10:02):
So a photon from that electron definitely could reach you.
If the electron gives off a photon that can fall
in the black hole, and then it can reach you
inside the black hole absolutely.
Speaker 1 (10:12):
What about like time, doesn't time slow down at the
surface of a black hole, or doesn't it stand still?
Speaker 2 (10:17):
So time does get slowed down by gravity. Places that
have strong curvature feel time going more slowly. So for example,
if you're near a black hole and you're looking at
the rest of the universe, your time is going more slowly.
You see the rest of the universe going more quickly.
Or if you're watching somebody fall into a black hole,
you see their time slow down. So from the outside
you can't actually see somebody fall into a black hole.
(10:39):
You're right, if time slows down so much as they
approach the event horizon, that it's not until, like time
equals infinity, that they actually fall in from your perspective.
But if you're the person falling into the event horizon,
then you just fall past the event horizon. You don't
notice these effects.
Speaker 1 (10:55):
The electron would just fly right in from your perspective
inside the.
Speaker 2 (10:58):
Black hole, inside the black hole exactly, but.
Speaker 1 (11:00):
Really outside of the black hole, it wouldn't happen for infinity.
Speaker 2 (11:03):
From the point of view of a distant observer watching
you fall in, it wouldn't happen until time egals infinity,
or until something else falls in the black hole and
grows it so that it encompasses you. That's the reason
that like real black holes in the universe can actually grow,
that they don't have to wait until time equals infinity
for things to fall in, because there's a whole series
of things falling in. Each one grows the event horizon
(11:25):
for the previous one.
Speaker 1 (11:26):
Okay, so you can get information from inside the black hole,
and I guess you're not really watching the electron. You're
just watching whether it veers to the rider to the left, right,
something to texts the electron going right or left or something.
Speaker 2 (11:37):
Yeah, I think the setupiece interested in is like an
electron is in a superposition of two possible states, like
does it go left or right? And somehow you maybe
use a photon to detect left versus right, and that
photon falls into the black hole. And he's wondering if
observing that photon inside the black hole collapses the way
functioning the experiment outside the black.
Speaker 1 (11:57):
Hole right, because I guess since you're inside the black hole,
there's like no way for the electron to know whether
you saw it or not exactly.
Speaker 2 (12:06):
That's where this cool quantum mechanics black hole paradox comes in,
because if you take away the black hole, we had
the sort of classic observer effect that the electron can
still be fifty percent chance left, fifty percent chance right
until its wave function is collapsed. When does the wave
function collapse? Well, nobody really knows the answer to that,
but one ridiculous but standard description or quantum mechanics says
(12:28):
that the electron's wave function is collapsed when is observed
by a classical object like a person or a big
detector or something. So the photon can bounce off of
the electron without collapsing its wave function because it's still
a quantum object. But then when that photon carrying that
information hits a screen or a detector or an eyeball
or something like that, a classical object, it collapses the
(12:50):
whole wave function. And that's when the electron decided, okay
I went left or okay I went right.
Speaker 1 (12:55):
But does it collapse only for the observer or for
the entire universe? If if you observe it, but I
don't know what you observe, is it still a quantum
object to me?
Speaker 2 (13:04):
Oh? Great question? And the answer to that depends on
your quantum mechanics philosophy. So in standard quantum mechanics Copenhagen interpretation,
it collapses for everybody, and it collapses instantly across space
and time. Those two objects are entangled. The photon and
the electron are quantum mechanically entangled, meaning that they share
a fate. They're connected to each other. If the electron
(13:25):
goes left, then the photon looks a certain way, and
if electron goes right, the photon looks another way. So
in your standard interpretation, as soon as you observe the photon,
that collapses the electron for everybody. But in other interpretations,
to quantum mechanics like Carlo Ravelli's relational quantum mechanics. Then
it only collapses for the person doing the observation. One
person can collapse it for themselves, somebody else could have
(13:47):
it be uncollapsed, and a third person can collapse it
in another way. So there's different theories of quantum mechanics
in the standard one that people typically think about and
we complain about a lot because it doesn't make much sense.
It's collapsed for everybody.
Speaker 1 (14:00):
It also sort of depends on the idea of short
Anger's box, right, doesn't it? Like if I wrap a
box or on you the observer and the electron, like,
it's still a quantum object to me, no matter whose
interpretation I think about, does it the cat is both
alive and dad and you saw it and not saw
it at the same time.
Speaker 2 (14:15):
Yeah, that is the paradox rate by Schrodinger's box, that
things can be unobserved but still be classical. So in
the standard Copenhagen interpretation we say classical objects collapse the
wave function and quantum objects do not. The problem with
the standard quantum mechanics is that there's no definition of
what's a classical and what's a quantum object, so it's
sort of a useless distinction. But in the standard interpretation
(14:37):
then you would still become collapse the wave function because
you'd be a classical object and your observation collapses it.
Even if I don't know what you've seen before. You're
not a quantum object, so you can't be in a superposition.
Speaker 1 (14:48):
Okay, so that this is an extra twist to it. Now,
let's say that you're the observer and you're inside of
a black hole and you saw the electron go right
or left. I think Sean is asking, how does that
affect things that the wavefund collapse for the electron or
is it still unknown for the rest of the universe.
Speaker 2 (15:03):
This is a really great and very very difficult question,
and before we answer it, I want to compare it
to a similar complicated question, which is just about entangled
objects that are really far apart right. A similar question
you might ask, is, well, well, if the photon is
really far away from the electron when it's observed, how
does the electron know to collapse? If the photon flies
(15:25):
for a thousand light years before it gets observed, how
does the electron then collapse instantly across time? These questions
are related because they have to do with apparently sending
impossible information. And this is a classic question in quantum
mechanics theory, right, And this is the paradox posed by
Einstein decades and decades ago when he can plain the
quantum mechanics makes no sense because it requires things to
(15:48):
violate special relativity to collapse instantly across time. Things outside
of each other's light cones somehow, causing each other to change.
Speaker 1 (15:56):
So, in the case of it entangled quantum paricles, the
answer that but it does travel faster than light in
a way, right, Like, once you collapse one half of
it a few light years away, it sort of instantly
changes what you have in front of you exactly.
Speaker 2 (16:10):
And there's a really crucial subtlety here. You're totally right
that the collapse happens instantaneously across space and time. So
quantum mechanics is what we call non local. And that's
because the wave function is broad. It doesn't just exist
in one place. Don't think of it like one particle
doing something to the other particle. It's one big quantum state,
and you collapse it anywhere. It collapses everywhere simultaneously. That
(16:32):
does happen instantaneously across space and time. But and this
is the crucial nuance, it doesn't send any information. So
collapsing the wave function with a photon really really far
apart doesn't send information to the electron. You can't use
it to like send signals faster than the speed of light.
Though a lot of people imagine that quantum mechanics entanglement
can do that, you can't actually send information. Just collapses
(16:55):
the whole wave function simultaneously. It's not a mechanism for
information transmission.
Speaker 1 (17:00):
I see. I think what you're saying is that, like
there's no rule to how big a quantum system can
be or how far apart its parts can be. So
like even a half, if I have one half here
and another half, you know, millions of lighters a way,
it's just still one quantum system. There's no rule in
quantum mechanics that says, oh, no, you're too far apart.
Now you're two separate quantum systems. You're actually like still
the same system exactly.
Speaker 2 (17:20):
And quantum mechanics explicitly is non local. Stuff can happen
coordinated across space and time. It doesn't have to be
like this thing bumps into that thing which is right
next to it. Very weird property of quantum mechanics that
we really don't fully understand.
Speaker 1 (17:35):
Okay, and so now the question is, what if half
of my system is inside of a black hole? Is
it still one system?
Speaker 2 (17:41):
Great question, and the answer depends on your theory of
quantum gravity, because now this is a question that involves
quantum mechanics. We're talking about quantum particles and wave functions,
and it involves event horizons, so gravitational effects. And the
truth is we don't know how to marry those two things.
So I'm sorry, Sean, you're asking a question we don't
really know the answer to because we don't have a
(18:03):
theory of quantum gravity.
Speaker 1 (18:05):
Meaning like we don't know how like if you distorted
gravity a lot, like in a black hole, you don't
know how it affects this idea of like a quantum
system being the two halves even though they're far apart exactly.
We just don't know it might affect it or it
might not affect it exactly.
Speaker 2 (18:19):
We don't know if gravity collapses wave functions or not,
or if gravity is fundamentally quantum mechanical and allows things
to be in superpositions even as they cross event horizons.
We don't have the answer to that, but I can
speculate an analogy to the other scenario where you have
two quantum particles really far apart, basically outside of each
other's light cones, which is sort of like being outside
(18:41):
of each other's event horizons. There's still the wave function
does collapse, but no information is transmitted. So I suspect
that what happens here is that if you observe the
photon inside the black hole, it does collapse the wave
function of the electron outside the black hole, but without
transmitting any information and so not breaking that rule of
(19:01):
black holes.
Speaker 1 (19:02):
WHOA Does that mean you could now communicate from inside
of a black hole to the outside of a black hole.
Speaker 2 (19:08):
No. In the same way that you can't use quantum
entangled particle collapse to send information, you also can't send
information from inside and event horizon using the collapse of
a quantum object across that event horizon. That's the analogy.
Speaker 1 (19:23):
So I wonder for like, practically speaking, you didn't really
collapse it because you're inside of a black hole and
nobody will ever know what you saw, So pretty much
in the rest of the universe. The half that's outside
is still quantum unknown.
Speaker 2 (19:36):
Yeah, that's very insightful because the reason you can't send
information across quantum particles faster than light is that you
can't know whether it's collapsed. Like if I have a
quantum particle and you have a quantum particle and they're entangled,
I can measure mine, which would collapse yours if you
haven't already measured it, But you can't tell if I've
collapsed at All you can do is measure your particle
and get like spin up or spin down, or left
(19:57):
or right. You can never tell that I've collapsed it.
That information doesn't get transmitted. And so in the same way,
if somebody observes that photon inside the event horizon, somebody
else looking at the electron can't tell whether the electrons
wave function has been collapsed or not.
Speaker 1 (20:11):
Okay, So then the answer for Sean is that we
have no idea. That's just a comment answer we give
you on the podcast, because nobody knows how gravity or
extreme gravity like black holes effects quantum mechanics and quantum
systems and wave collapse. But our best guess here on
the podcast is that it probably does collapse it, but
maybe it doesn't matter, so it doesn't really collapse it.
Speaker 2 (20:33):
Yeah, that's a great summary.
Speaker 1 (20:35):
Well, let's get to our other questions here today about
black holes and about the big Dang and magnetic fields.
So let's get to those, but first let's take a
quick break. Right. We're taking listener questions here today and
(20:59):
at least trying to answer them. Although sometimes the answer
is we don't nobody knows.
Speaker 2 (21:03):
Sometimes the answer is, great question, I wish I knew
the answer.
Speaker 1 (21:07):
Yeah, if you have the answer, write it to us
in one hundred page summary and then Daniel will read
it and let you know.
Speaker 2 (21:13):
That's right. Really, the answer some of these questions requires
us to develop theories of quantum gravity, and to figure
out how to develop those theories, we want to look
inside black holes, which is impossible, so we're a little
bit stuck sometimes.
Speaker 1 (21:25):
Well, you can look inside of a black hole, just
can't tell anyone what you saw.
Speaker 2 (21:30):
Yeah, that's right. That physicist who fell into a black
hole knows the answers, just can't get any awards for it.
Speaker 1 (21:36):
Yeah, that physicists solved everything. Let's throw a Nobel Prize
medal inside the black hole for them that million dollars
also or million coroner. I'm sure they can find a
good use for it in there. All right. So our
second question comes from Ryan, who lives in northern Virginia.
Speaker 4 (21:54):
Hello, Daniel and Hore. My name is Ryan and I
live in northern Virginia. I have a question for you
today about black holes, more specifically about their magnetic fields.
If the Earth's magnetic field comes from its liquid outer core,
where does a black holes magnetic field come from? Considering
there's no liquid core in the black hole and nothing
is supposed to be able to escape the event horizon,
(22:16):
I'm left to guess that the accretion disk is the
big driver of the magnetic field. But that's just a guess.
Thanks for considering my question, Love the show.
Speaker 1 (22:24):
Awesome great question, Ryan. You know I don't know the
answer here, and I'm gonna guess maybe the answer is again,
we don't know because it deals with black holes.
Speaker 2 (22:33):
No, this one I think we do know the answer to. Actually, well,
I know physics knows something, all right.
Speaker 1 (22:40):
Well, let's see. Ryan's question is where does a black
hole's magnetic field come from? Because I guess black holes
have a magnetic field. Do we know that for sure.
Speaker 2 (22:49):
Well, we do measure very strong magnetic fields near black holes.
Speaker 1 (22:53):
How do we measure them?
Speaker 2 (22:54):
How do we measure them? Great question? Well, we can
see the effect, right. Sometimes black holes have enormous jets
of stuff that shoot up and down on their north
and south poles, and we think that comes from the
magnetic field, like funneling particles up and down, sort of
the same way that the Earth's magnetic field causes northern lights.
Charged particles coming towards the earth magnetic field get funneled
(23:15):
up towards the north and south poles. Particles falling into
a black hole sometimes will miss because the magnetic field
will deflect them up and down, and you get these enormous,
like thousands of light years long jets of stuff shooting
out of black holes. We think from the magnetic fields.
Speaker 1 (23:29):
Well, I guess, first of all, we think those are
black holes and that those jets are coming from black holes.
Don't Like, we haven't actually seen the inside of what's
inside of those jets.
Speaker 2 (23:38):
We've study those jets in some great detail, and we
have really pretty good models that predict those jets. Recently,
we imaged a couple of black holes and saw ripples
in the accretion disk around them, and so we're able
to like really pin down the details of the magnetic
field near the black hole. I mean, we'd love to
send a probe near the black hole and measure those directly,
but there's a lot of indirect ways to measure those
(23:59):
magnetic fields, just by seeing the impact to have on
charge particles near the black hole.
Speaker 1 (24:05):
And I guess the other question is, how do he
knows those magnetic fields are coming from the black hole
enough from the stuff around the black hole.
Speaker 2 (24:10):
Yeah, that's a great question, and we don't know the
answer to that. We're sure that the stuff around the
black hole can make a magnetic field. Those are charged particles.
They're moving in a circle, so you have a current
moving in a circle that always generates a magnetic field.
The second part is thinking about whether a black hole
on its own could have a magnetic field even without
the accretion disc, even without the stuff swirling around it.
(24:32):
Whether just the black hole itself can have a magnetic
field is a really interesting question.
Speaker 1 (24:37):
Do we know the answer? Does a black hole on
its own have an inherent magnetic field?
Speaker 2 (24:42):
So we can answer that question theoretically, We've never seen
a black hole all by itself, without an accretion disk
and measured it. But according to general relativity, black holes
can have magnetic fields. And that's because black holes can
do two crucial things. One they can have an electric
charge and two they can can spin. And essentially anything
with an electric charge that spins has a magnetic field.
Speaker 1 (25:05):
But you're saying it's all theoretical though.
Speaker 2 (25:07):
It's theoretical because we've never observed a black hole without
any stuff around it and measured its magnetic field. That
would be an awesome test.
Speaker 1 (25:14):
Of this theory, I see. So basically we don't know.
Speaker 2 (25:21):
Yeah, that's true of lots of things. I suppose. We're
not sure about it, but we do have a pretty
good idea. And lots of our models of spinning black
holes and black holes with charge have been tested indirectly.
We've never done this exact test.
Speaker 1 (25:34):
Okay, So you're saying theoretically black holes do have magnetic
fields because they somehow preserve it, right even though you
when you throw charge particles in it with spin in
it and magnetic fields, presumably that doesn't get destroyed by.
Speaker 2 (25:48):
The black hole exactly. And Ryan is asking about, like
where that magnetic field might come from. Because you can't
see anything beyond the event horizon, So you can't have
like swirling matter within the event horizon and causing this
magnetic field. Why not, Because the details of anything like
that happening within the event horizon is shielded by the
event horizon. You can only know a few things about
(26:10):
what's happening inside the event horizon. You can know the
total mass, you can know the electric charge, and you
can know the spin.
Speaker 1 (26:17):
Meaning even if there are a bunch of electron spinning
inside of a black hole, the magnetic field they would
generate couldn't leak out of the black hole. Is that
what you're saying, Because the space would just be pointing inwards.
Speaker 2 (26:29):
A lot of the details of what's happening to those
electrons you wouldn't be sensitive to, Like if one electron
zigs up or zigs down, you couldn't sense that from
the outside. You can, however, sense that there are a
bunch of electrons, and you can sense that they're spinning overall,
because you can measure the total spin of the black
hole and the total electric charge of the black hole.
(26:49):
Like when electron falls into a black hole, just before
it falls in, it has an electric field, and when
it falls in, that electric field is now frozen on
the outside of the black hole. Whatever happened to the
electron after it falls in can no longer change that
electric field. It's sort of frozen there. So you can
tell that something has fallen in and that it had charge,
but the details what happens afterwards you're shielded from.
Speaker 1 (27:12):
So then are you saying, like, to get the magnetic
field of a black hole, you just multiply its charged
by its spin somehow, and that gives you like what
you would feel as a magnetic field outside of the
black hole. But those are like overall numbers, not related
to anything in detail inside of it.
Speaker 2 (27:28):
Exactly in the same way that an electron has a
little magnetic field. Right where does the magnetic field an
electron come from. It doesn't have a magnetic charge, It
has an electric charge, and it has quantum spin. Those
two things combined to give the electron a tiny little
magnetic direction, a magnetic dipole. And you can't tell what's
going on inside the electron. We think maybe it's a
(27:49):
fundamental particle. We have no idea. We can't see inside,
and it doesn't matter. We know it has an overall
charge and an overall spin, and so the overall charge
and spin of a black hole similarly gives it a
magnetic moment. It's a magnetic dipole.
Speaker 1 (28:03):
I wonder if, like Ryan's question was more like, you know,
how can a black hole have a magnetic field if
nothing can escape it? You know what I mean? Like,
if the electromagnetic field it has is due to the
stuff inside of the black hole, how can its magnetism
escape the black hole?
Speaker 2 (28:18):
Yeah, that's a great question. We have a whole episode
on how black holes can have magnetic fields and electric
fields and digs into the details of this question. Very briefly, though,
The answer is that the overall charge is essentially spread
out on the event horizon. So something falls into a
black hole, you're not getting information from within the event horizon.
(28:38):
You're just getting information from the event horizon. So think
about the event horizon itself as now having that charge
and having that spin. There might be crazy stuff going
on inside, weird quantum effects or singularities orringularities or whatever.
You can't tell, but you can tell that something charged
fell in, and you can tell without getting any information
about what's going on. Inside the event horizon.
Speaker 1 (29:01):
It sort of sounds like you're saying that the black
hole's magnetic field comes from its surface, Like it's the
surface of the black hole. That's basically you know, phasing
out to the rest of the universe, and you know,
emanating an electric charge and an electric field, and that's
why we can see it.
Speaker 2 (29:16):
Yeah, that's a good way to think about it. The
event horizon, or the surface of it equivalently, has three
properties mass, spin, and charge, and we can measure those
and those have an effect on the rest of the
universe right the same way, like the mass of the
black hole, even though it's contained within the event horizon,
still curves space outside the event horizon and can affect
the trajectories of stuff. Think of that as a property
(29:37):
of the event horizon. It doesn't matter what's going on
inside behind the screen of the event horizon, if things
are swirling around or not. All you know is the
overall mass, the overall charge, and the overall spin, and
that can create a magnetic field.
Speaker 1 (29:50):
But again, time slows down almost to a standstill near
the event horizon. How does the magnetic field ever get out?
Don't have to wait to infinity to feel that magnetic.
Speaker 2 (30:00):
Yes, so time near the black hole is really really
slowed down, not slowed down totally to infinity. So black
holes can radiate information for example, like if a black
hole gets accelerated by another black hole, it can radiate
a gravitational wave, or if it has charge, it will
also radiate photons. Again, these are coming from the surface
of the black hole, not from within it, so we're
(30:22):
not breaking the rules of black holes, but they can
radiate that information. And you're right that things near black
holes are slowed down, and so it does take longer.
And like those gravitational waves are slowed down by the
time dilation of the gravitational field. So without that effect,
those gravitational waves would look much crazier and the photons
would be much higher frequency. But they're stretched out and
(30:44):
red shifted by that time dilation, not all the way
to infinity, because the curvature isn't infinity outside the black hole.
Speaker 1 (30:50):
All right, Well, it sounds like the answer for Ryan
is that a black hole's magnetic field comes from its surface.
It's event horizon basically, or at least we can practically
think of it as coming from the surface and the
event horizon and that's why we're able to see it
and experience it. We think, we think we don't know
for sure because it's a black hole.
Speaker 2 (31:10):
We don't know for sure anything. We don't even know
if we exist or if this is a simulation. And
also remember that most of the encnic fields we've measured
probably do mostly come from the accretion disk of stuff
around them. But that's where he says we don't know
for sure.
Speaker 1 (31:24):
All right, Well, let's get to our last question of
the day, which is about the expanding universe and gravity
and the Big Bang. But first let's take another quick break.
(31:46):
All right, we're answering listener questions here, our favorite kind
of episode where we take your questions that you send
in and we try to answer them, usually with answers
that are not we don't know.
Speaker 2 (31:58):
We do our best.
Speaker 1 (32:00):
Sometimes nobody knows which is an answer technically it is.
Speaker 2 (32:03):
And I wonder if that's like really satisfying because it
means for the listener like, Ooh, I'm at the forefront
of human knowledge or really disappointing because like the rest
of humanity is still left unsatisfied.
Speaker 1 (32:15):
Yeah, I guess it is pretty exciting, right to be
to like come up against the boundary of human knowledge, right, yeah, exactly,
Like when I ask you a question and you don't
know the answer, I'm like, Wow, I am at the
boundary of Daniel's knowledge of the universe.
Speaker 2 (32:28):
Now, the boundary of Daniel's knowledge not the same as
the boundary knowledge. Let's not make that.
Speaker 1 (32:34):
Mistake, or at least the boundary of the research you've
been able to do for the last hour before the podcast.
Speaker 2 (32:41):
Exactly, I am at the boundary of human knowledge in
one time is a little corner of the vast sphere
of human knowledge.
Speaker 1 (32:49):
Well, we're all here with you, and so our last
question of the day comes from Argent phor Daniel.
Speaker 5 (32:54):
I have a question. Just got me thinking while I
was on the shore. We've come to understand that gravity
is bending of space time, and that's objects which would
normally travel in a straight line tend to take a
curve path around the body, which is distorting space time.
We also know that space itself is expanding in the
(33:16):
universe for the last ever since Big Bang happened. Do
we think the effects of gravity have changed over the
last couple billion years or do we expect it to
be different later now that we know that space itself
is expanding or stretching or thinning out, whatever you may
call it. Will that effect the way gravity acts and
(33:38):
behaves or has it changed over the years?
Speaker 2 (33:41):
What do you reckon?
Speaker 1 (33:42):
Awesome question? What do we reckon? Daniel? Do we know
the answer? In this case?
Speaker 2 (33:47):
I reckon that Urgent probably takes really long showers to
have such deep thoughts about the whole.
Speaker 1 (33:51):
History of the universe, which is awesome. Thank you Argent
for such a great question.
Speaker 2 (33:56):
So, as usual, we have some ideas about how this works,
but there's lots that we still don't understand, especially about
the expanding and the accelerating expansion of the universe.
Speaker 1 (34:07):
Okay, let me see if I understand Argent's question. He's
in the shower and he's wondering, you know, the universe
since the Big Bang has, first of all, it expanded
really fast. Space itself expanded really fast, and space today
is still expanding, and there's more and more space growing
and being created. The universe is expanding due to something
called dark energy. And I think his question is like,
(34:27):
is gravity affected by this expansion of space? Like do
we know if gravity itself has been the same and
for the last fourteen billion years or is there an
indication that maybe as a universe expands it could be
changing the effects of gravity like this gravity space dependent.
What do you reckon, Daniel, I.
Speaker 2 (34:46):
Think there's a crucial piece of the history of the
universe that you sort of yaddiyauted over there, because you're right,
the things did expand very quickly in the beginning, but
then then expansion actually decelerated because the stuff in the
universe slowed down the expansion. And then later on, like
six billion years ago, it started picking up again and
it started to accelerate the expansion. So this is funny,
(35:07):
sort of like zigzag in the history of the universe.
It wasn't always just accelerating expansion. It was always expansion,
but there was a period when that expansion was decelerating.
I emphasized that not just because it's a cool zigzag,
but to underline something which I think is in crucial
to answering Argin's question, which is that's part of gravity.
Gravity is not just things pulling themselves together, it's also
(35:28):
space expanding. That is general relativity, our framework that we
have and what Argent describes as like things moving through
bent space time that allows for the universe to expand.
That's sort of part of what gravity is.
Speaker 1 (35:40):
Well, what do you mean, like it's in the equations
of our theories of gravity for the universe to expand
due to dark energy.
Speaker 2 (35:48):
It's part of general relativity that the universe can expand
under certain conditions. So the broad answer to Argent's question is,
we think the rules of the universe, the rules of
gravity and space time and general relativity have not changed
changed over the last fourteen billion years, and we can
describe all of these weird epics of the universe using
one consistent framework, and that's sort of amazing. So the
(36:08):
rules haven't changed, even though the conditions do change from
year to year and things get further apart and whatever.
So there are specific conditions under which general relativity predicts
the universe will expand and that that expansion will accelerate.
If you have a bunch of energy inherent in space
stored in a field that has high potential energy, then
general relativity says space will expand and that expansion will accelerate.
(36:32):
So we see that happening in the universe. We look
back at the history of the universe, we see it's
expanding we see that expansion is accelerating, and so we say, oh,
there must be some energy stored in a field somewhere
with a lot of potential energy that's causing this. We
don't know what that is. We don't know what that
field is, We have no explanation for it. But general
relativity can accommodate that well.
Speaker 1 (36:51):
I think what you're saying is that physicists have a
set of equations that explain the universe, and that set
of equations has gravity in it, and it also as
expansion of the universe in it. So it's like they're
all actually kind of connected already into theories of physics.
Speaker 2 (37:05):
Yes, exactly.
Speaker 1 (37:06):
So it's not like one of them we don't know
if one of them is doing something the other one
doesn't know.
Speaker 2 (37:10):
That's right. And when people say gravity colloquially, they mean
like stuff attracting and things falling towards planets and whatever.
When physicists say gravity, they mean the whole shebang, They
mean the whole theory of space, time and all of
its consequences. Because moving from like a Newtonian view of
gravity as a force to an Einsteinian view of gravity
as motion of stuff through space time has all of
(37:31):
these consequences, not just oh, light is also bent by gravity,
but also the universe can expand and it could also collapse.
All of these things are consequences of this geometric view
of the universe we have from general relativity, and we
think that those rules have not changed. That the same
rules applied in the very very beginning and in the
middle point when things were decelerating, and now when things
(37:52):
are accelerating. So in the broadest sense, the rules of
gravity general relativity have not changed over the course of
the universe.
Speaker 1 (38:00):
I see, like the rules by which you mean the equations,
But I wonder if Argin means, like, you know, imagine
there's a term in your equations for gravity. I wonder
if he could mean that, you know, has that term
the equation change as the universe grew? Like could it
that be something the equations don't take into account, or
it could it be something we haven't noticed.
Speaker 2 (38:17):
Or or what. Yeah, there's a couple of ways in
which that could be true. First of all, we assume
that dark energy or whatever this is, this potential field
that's causing the accelerating expansion in the universe. We assume
that that's constant everywhere in space and everywhere in time,
and mostly that works. I mean, it said that we
can explain the whole history of the universe, and that's
mostly true, but there are some discrepancies, like we measure
(38:38):
it early in the universe, we measure it late in
the universe, and those two numbers don't quite agree. You
can read more about that. It's called the Hubble tension. Essentially,
that's predicting the rate of expansion, and different measurements don't
quite agree. So that's quite interesting. So it might be
that the dark energy is changing over time, and again
that wouldn't mean a change in the rules, but it
would mean some change in the conditions, which is affecting
(38:58):
like your experience of the Union. And also, maybe more importantly,
the second sense is that the density of stuff in
the universe is definitely decreasing. Like things used to be
really hot and dense and now they're very cold and
very far apart, and so there's definitely like less sense
of gravity in the universe. Because the mass density of
stuff in the universe is going down, space goes up,
(39:19):
the amount of mass doesn't change, so the density decreases,
things get further and further apart. You're feeling less gravity
from distant galaxies than you were before because they're now
further away from you, and that's going to keep going.
Speaker 1 (39:31):
Mm So I guess technically you would be feeling more
the gravity of Earth right as the universe gets more
empty and empty, right, Like, I'm way more in the
future regardless of what I what I do.
Speaker 2 (39:45):
If you're relying on distant gravities to lift you up
off the surface of the Earth and make you feel light,
then I have bad news for you.
Speaker 1 (39:51):
Yes, as my diet plan forget as epic.
Speaker 2 (40:00):
Yeah, exactly, I suggest hitting the gym instead of relying
on distant galaxies. But I'm not a health expert. Don't
take advice from me.
Speaker 1 (40:07):
Well, I wonder if Argine's question then maybe more simply
is like, you know, if I have a black hole
the same mass and I see it bend light around it,
is it going to bend light the same way now
in the future, in the past when the universe was
maybe more scrunched together, or is that light can we
bend differently depending on what the universe is doing, Like,
especially like let's say we're going through a period where
(40:30):
space is expanding faster and faster, or where we're hitting
you know, in that zig zag, where we're hitting a
point of maximum expansion, that light is going to bend
a little bit differently right than it would in a
period of not so fast expansion.
Speaker 2 (40:41):
All right, So now you've pushed this into a corner
of general relativity that we don't understand very well.
Speaker 1 (40:46):
So the answer is we don't know, We don't know.
Speaker 2 (40:48):
And also fascinatingly because we don't even understand our own theory,
like general relativity has no problem with having black holes
in an expanding universe, but we don't know how to
do that. Calculation like Einstein's equation are nasty and they're
very very difficult to solve. We can only solve them
in very specialized, simplified settings, like you have a black
hole in an otherwise empty universe that we can solve,
(41:11):
or you have a universe that's expanding, but the matter
in it is totally uniform, like dust sprinkled everywhere. We
don't know how to solve the equations for a black
hole in an expanding universe or a universe with like
chunky stuff in it. So we have all these approximations
and so the specific question you just asked, like what
happens to a black hole in an expanding universe? We
don't know how to do that calculation, but we think
(41:35):
that the rules are not changing, right, and so for
a black hole, gravity is basically the same as it
was a billion years ago and five billion years ago,
Like the nature of space itself is not changing. It
doesn't thin out, you know, as the universe expands, and
that expansion accelerats, you just get more space, and that
space behaves, we think, according to the same rules, and
so Bend's light the same way as it always did.
Speaker 1 (41:57):
All right, Well, then the answer origin seems to be
that you don't think that the rules of the universe
are changing, meaning like what the physicists would consider to
be gravity, which is the whole set of equations. You
don't think that's changing. But maybe the effects of a
black hole might be changing, except you don't know how
to calculate it.
Speaker 2 (42:12):
That's right. And there was even this fast on any
paper a few months ago about how like black holes
might be driving the expansion of the universe, right, that
black holes might actually be like weird clusters of dark energy.
So just to highlight like how little we understand the
expansion of the universe, and how tricky it is to
do these kind of calculations in any sort of realistic setting.
Speaker 1 (42:33):
Yeah, or in the shower.
Speaker 2 (42:36):
The shower is probably the best place to do these calculations.
Speaker 1 (42:39):
Yeah. Well, if it wasn't for gravity, you couldn't take
a shower. You definitely any gravity to shower.
Speaker 2 (42:44):
Oh my gosh, wow, thank you gravity. We should be
saying every time we have a shower. Yeah.
Speaker 1 (42:48):
If not for gravity, we'd all be a little bit stinkier,
or we'd all have to take baths in zero gravity,
which I think is dangerous, isn't it, Like you would
you would very quickly drown because the water would just sing.
Speaker 2 (43:00):
Golf you maybe, But again, don't take health advice from
this podcast. That is outside our area of expertise.
Speaker 1 (43:07):
Yeah, don't take health advice from a cartoonist, a physicist.
Speaker 2 (43:12):
Stay on your diet whatever it was before this podcast.
Speaker 1 (43:15):
That's right. Listen to a real doctor, not the academic kind, exactly.
Speaker 2 (43:21):
You know what the best thing about.
Speaker 1 (43:22):
Getting your PhD is, there's the best thing.
Speaker 2 (43:25):
Every meeting is now a doctor's appointment.
Speaker 1 (43:28):
There you go. I'm sure everyone loves doctor's appointments. Does
that mean that this podcast is a doctor's appointment for
the thousands of people who listen to.
Speaker 2 (43:37):
Us, I guess so. Yeah, oh man, keep your pants on, everyone, Yeah,
keep your pants.
Speaker 1 (43:42):
How I'm not gonna grab anything or ask you to cough.
Speaker 2 (43:46):
No, the only things we're probing are the nature of
the universe. The only black holes we're investigating are the
theoretical kind. That's right.
Speaker 1 (43:54):
That's right, only only physical dark matter that we're interested in.
All right, Well, that answers Arjie's question and everybody's question again,
and another interesting journey to the edge of human knowledge
and the realization of how much we know and still
have yet to know about the universe, which is kind
of exciting.
Speaker 2 (44:13):
That's right. So keep asking questions. You'll be surprised how
quickly you can get.
Speaker 1 (44:18):
To the edge of human knowledge or the edge of
a black hole.
Speaker 2 (44:21):
Apparently, or the edge of this doctor's appointment, or.
Speaker 1 (44:23):
The edge of this podcast. So we hope you enjoyed that.
Thanks for joining us, See you next time.
Speaker 2 (44:35):
For more science and curiosity. Come find us on social media,
where we answer questions and post videos. We're on Twitter, disport, Instant,
and now TikTok and remember that. Daniel and Jorge Explain
the Universe is a production of iHeartRadio. For more podcasts
from iHeartRadio, visit the iHeartRadio Apple Apple Podcasts, or wherever
you listen to your favorite shows.
Speaker 3 (45:00):
Th
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