November 26, 2024 • 48 mins
Daniel and Kelly answer questons about dark energy, slime molds and Hawking radiation!
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Speaker 1 (00:06):
Every discovery, every moment of insight, every aha or eureka
with the ideas click together in someone's mind to reveal
a deep truth about the universe. All of those begin
the same way with a question. In fact, all of
science starts with questions. The reason we know things about
clouds and beetles and black holes is because someone out
(00:28):
there had a question that kept them up at night,
so they were willing to stay up late looking at
the stars or counting beetles until they figured it out.
Science is just people asking questions they couldn't let go.
But it's not just professional scientists who ask questions and
move us forward. It's everyone. It's you, and we think
your questions also deserve answers, or at least replies that
(00:51):
make sense and help you grapple with what we do
and don't know about the topic. So if you have
a question about science or whatever, please write to us
to questions at Daniel and Kelly dot org. We'd love
to hear from you, and sometimes we'll answer those questions
right here on the pod. And so on today's episode,
we're going to be answering questions submitted by listeners and
(01:13):
more than that, and I'll admit to being a little
bit nervous about this part. We're going to go back
to those listeners with our answers and follow up to
see if our explanations scratch their itch or not. Today
Daniel and Kelly are getting graded by the listeners. So
today on Daniel and Kelly's Extraordinary Universe, we'll be answering
questions from listeners, Volume one.
Speaker 2 (01:50):
Hello, I'm Kelly Wienersmith, and I am so excited that
we're having our first listener Questions episode today.
Speaker 1 (01:57):
Hi, I'm Daniel. I'm a particle physicist, and I love
answering questions from the internet about physics, about philosophy, even
about dating.
Speaker 2 (02:06):
Really, you've answered questions on the show about dating.
Speaker 1 (02:10):
People send me all sorts of questions, you know. They
send me their treatise on the nature of the Universe,
They send me questions about career advice, how to get
into physics, and yes, sometimes people ask me questions about
their dating life, and hey, I don't claim any particular
expertise there, but I'll share my thoughts.
Speaker 2 (02:27):
Sure. Yeah, no, I'll share my thoughts on anything. So
I was actually going to ask you, what is the
weirdest or most surprising, like no negative connotation needed, but
weirdest or most surprising question you've ever been asked related
to your career as a physicist.
Speaker 1 (02:42):
Oh wow, that is such a good question. Now mentally,
cycling through the thousands of questions I've gotten over the years,
I think one of the most challenging questions to answer
are ones about people's personal experiences. People writing sometimes about
like their UFO experiences or their paranormal experiences, and they
want my physics knowledge and like, what else could have
(03:03):
explained it? And that's a delicate line to walk, because
you don't want to suggest that what they experienced is
not what they think they experienced, but you also want
to help them disentangle it and think about what else
might have explained it. That's maybe like the most oddball
and challenging kind of question to answer. I also sometimes
get really touching stories, like a woman who went through
(03:24):
her father's old belongings. He was, of course, a retired engineer,
and she found in there a treatise on the nature
of the universe, and she sent it to me and
she's like, look, I don't know if this is anything,
but if it is something, I feel terrible not sharing
it with the world. Can you tell me if this
is worthwhile or not?
Speaker 2 (03:41):
Aw, that's so cute. I know, was it worthwhile or
was it fun to read? But maybe not earth changing?
Speaker 1 (03:48):
There was nothing really earth chattering in there, but I
think she was happy to know that at least somebody
had looked at it.
Speaker 2 (03:54):
What's so cool that you were able to provide that?
Speaker 1 (03:55):
And how about you? Do you get weird questions from
the internet about parasites? People send you pictures of bits
of their body and be like, Kelly, what is this?
Do I need to go to the er?
Speaker 2 (04:04):
I do get photos of feces from time to time,
and it's worth noting that I cannot identify parasitic infections
from a picture of a bell movement their microscopic and
I can't. Also, I'm not a medical professional.
Speaker 1 (04:16):
So everybody out there who was about to email Kelly
a picture of their poop not worth your time.
Speaker 2 (04:21):
Please don't. I think the hardest question for me to answer, though,
was I was doing an interview for our book soon ish,
and I think the person doing the interview hadn't really
read the book, and so his question was, so, tell
me about the robots? The robots, and there was like
a different robot in every single chapter, and so I
didn't have any idea what he was talking about. This
(04:44):
is when I learned the trick that when you do
an interview, if someone asks you a question that you
don't really know what they're trying to get at, you
just decide what is the most interesting thing I feel
like talking about right now? And so I just picked
like my favorite robot and went off on that tangent.
It was, that's a learning experience.
Speaker 1 (05:01):
Sounds like you're ready to run for higher office.
Speaker 3 (05:03):
Now.
Speaker 1 (05:03):
I'm going to dodge your question to talk about the
thing I want to talk about instead.
Speaker 2 (05:08):
I don't think i'd make a good politician, all right.
Speaker 1 (05:11):
Well, you know I would vote for you to represent Virginia,
but not California. I don't think you can really appreciate
everything that California has to offer.
Speaker 2 (05:18):
I lived in California for a while. Is it that
you don't like Virginia and that's why you would vote
for me for Virginia. You want to harm Virginia in somewhere?
Speaker 1 (05:24):
Well, no, no, no, Virginia is for lovers. It's fantastic.
I just don't feel like you appreciate California. I mean,
you did leave, right, and so clearly you don't understand
that it's objectively the best place in the world to live.
Speaker 2 (05:35):
You know, I have not regretted leaving, sorry to say so.
I guess you're right. I shouldn't be representing California. And
maybe I'm going to regret that a decade from now
when I run for governor of California, if I've moved back.
But for now, I think we're just going to go
with no politics for Kelly.
Speaker 1 (05:50):
That sounds good because I'm gonna have to hold off
on endorsing you until I hear you change your opinion California.
All right, But let's not talk about Kelly's your future
plans to take over the world slash Solar system slash universe.
Let's get to questions from listeners, because today on Daniel
and Kelly's Extraordinary Universe, we are answering questions from you.
We think your questions are important. We want you to
(06:12):
understand the universe. We want you to get that satisfying
moment where everything clicks in your mind, and so we
encourage you to write to us with your questions to
questions at Danielankelly dot org. We will write back to you.
You'll hear what we do and don't know about whatever
it is you're interested in.
Speaker 2 (06:29):
We can't we do hear from you.
Speaker 1 (06:31):
Our first question today is from a really fun guy
named Barima who lives in Germany. He has a question
about gravity. Here is Barima's question.
Speaker 3 (06:40):
Hello, my name is Brima, living in Germany from England.
I'm a big fan of the podcast and I love
what you guys are about, Sir. Gravity becomes so strong
that it tarts space time, and I was thinking dark
energy basically does the same, but in reverse because it's
expanding the universe. Both of these phenomena bend or expand
fabric of space time. So my question is could dark
(07:04):
energy be anti gravity? Thank you for your time and
I hope you guys have a great day.
Speaker 2 (07:08):
Thank you so much for the question, Barima. Well, you know, Daniel,
that sounds like a question.
Speaker 4 (07:13):
For you.
Speaker 1 (07:15):
Gravity, space time and dark energy. Ooh, this is my
jam for sure.
Speaker 2 (07:20):
We've recently recorded episodes on what is time and what
is space which might provide some important context. But how
do we answer this question more directly?
Speaker 1 (07:29):
This is a great question because it gives us an
opportunity to connect a lot of ideas. You hear a
lot about space time as a fabric, black holes, having
extreme gravity, dark energy pulling space apart. How does it
all work? How do you think about that altogether? My
interpretation of Brima's question is that he's thinking about black
holes and he's heard that black holes tear space time,
(07:49):
so he's thinking about that as like pulling space itself apart.
And he's also heard that the universe is expanding in
an accelerating way, which feels like it's ripping space apart,
and so he's wondering, like, are those the same thing
or are they the opposite? Because black holes attract and
dark energy is pulling space apart, how does it all work?
(08:10):
And is dark energy actually the opposite form of gravity?
So we're going to give Burrimo a way to think
about dark energy in terms of gravity in general relativity
and link all these ideas together. But we should probably
start with black holes and space time and think about
what it means to tear space time.
Speaker 2 (08:27):
Apart, and does this have anything to do We had
a conversation about a map and how you can like
make the cities closer or farther apart. Is that the
right way to start thinking about this problem, or now
that we're talking about black holes, we're in a totally
different universe.
Speaker 1 (08:40):
No, that's exactly the right way to start thinking about this.
Let's get a mental picture of what space is or
space time is, and what it means to tear space
time or what happens when gravity gets really really strong.
So let's start with a model of space. What is
space space? We don't know what it is fundamentally, but
we know that we can measure the distance between two points.
You have like a ruler. You can measure how many
(09:02):
ticks are between two points, and you can do that
between La and Virginia, or you can do that between
Canada and Mexico, or between Seattle and Miami or whatever.
You can measure distances between points. So we know that
we can measure these distances. We don't understand what is
the underlying fabric and what is it doing and how
does it work, But we can measure these distances, and
we notice that if you put a mass in space,
(09:23):
like a star or a planet or whatever, those distances
get kind of wonky like things get closer together, things
get further apart. This is what we mean when we
say space is curved. It's not like it's curving in
some external dimension with a whole crazy rubber sheet analogy.
It just means that it's changing the intrinsic distances between stuff.
The curvature of space is not external and some other dimension.
(09:46):
It's internal. It's intrinsic. It's just a relative change of distances.
And so when we say space is curve, we just
mean you're tweaking all of those distances.
Speaker 2 (09:55):
I think if I were listening to the podcast, this
is where I would pause it and just stare at
the wall for five minutes and be like, how do
I make sense of this? It's all kind of complicated,
but yeah, I'm following.
Speaker 1 (10:06):
Yeah, And you call up this mental picture of a map.
So imagine you had a map the United States and
you laid it flat on a table and you measure
the distances between these cities. Those distances have to follow
some rules because the map is flat. If you measure
all those distances like from LA to Seattle, and Seattle
to New York and New York to Miami and Miami
back to LA, that's kind of a square, right, you
(10:28):
measure all those distances, and those distances have to follow
some rules because the map is flat on the table. Like,
from those distances, I can tell you how far it
is from LA to New York. It's constrained by those
other measurements. But what if I told you I'm just
going to go in and make LA and New York
closer together, I'm just squeezing them together. Well, then the
map can no longer be flat because I have to
(10:49):
like bunch up the material between LA and New York.
And that's what curving space does. It changes the relative
distances between these points, so they no longer add up
in the same way they would if they were on
flat space. That's what curved space is, just changes those
relative distances. And the crazy thing is that you can
do that. You can develop a model of space that
(11:09):
incorporates all these weird changes of distances. And that's what
we call curved space, all right.
Speaker 2 (11:15):
So it's never tearing. There's never a spot where it
like breaks and then there's nothing in between. It just
kind of gets like curvy, like a roller coaster.
Speaker 1 (11:23):
At some point exactly, you can't really tear space time.
That's like a dramatic visual people use, but it's not
a helpful way to think about it. And remember, we
don't know what space is. We have this beautiful mathematical
description from Einstein that lets us think about this concept
of curvature in terms of these changing relative distances, but
that's just our model. It's useful for describing space. Doesn't
(11:43):
always tell us what space actually is, but it does
predict crazy stuff like if you have a huge amount
of mass, the curvature gets really really strong, and you
get things like black holes, places where space is so
curved that light can no longer escape because not only
does it change the relation so distances, it changes like
the directions, and inside a black hole, space is now
(12:04):
one directional. Every direction inside a black hole is just
towards the center. It's not that light can't escape because
the force of gravity is so strong. It's because every
direction is towards the center. Now there are no other
directions inside a black hole. So a black hole is
so massive it like rearranges the relationships between points in space.
Speaker 2 (12:25):
Okay, so the order of the direction there is that
the black hole starts pulling on space. It's not that
like space gets bent for some other reason, and that
causes a black hole.
Speaker 1 (12:33):
Yeah, that's right. The presence of mass causes the bending
of space, and that's what the black hole is. Yeah, exactly. Okay,
So that's the way to think about like gravity and
black holes and bending of space time. But Burma is
asking us to connect that to the expansion of the
universe and how the universe we've noticed in the last
twenty years or so is not just getting bigger, it's
(12:54):
getting bigger faster and faster as time goes on. And
this is the mystery we call dark energy. We don't
understand the source of that expansion or why it's accelerating.
Speaker 2 (13:04):
Okay, so we know that it's accelerating, and we're using
dark energy as the explanation, and is that the extent
of what we know about dark energy is that it
is the magical way that this all works out.
Speaker 1 (13:15):
Essentially, dark energy is shorthand for saying, we see the
universe is accelerating its expansion, we don't understand why. Please
somebody figure it out, and we don't have a working explanation.
We have sort of like a sketch on the back
of a napkin idea that might work out, But currently
the calculations are not connecting, and they're off by like
(13:36):
ten with one hundred zeros. But the sketch of the
explanation actually comes from general relativity. General relativity, of course,
is Einstein's generalization of Newton's gravity. Newton says, masses attract
each other because there's a force. Einstein says, no, Actually
it's more complicated. Space time curves and it gives mostly
the same behavior. But there's a little bit more to
Einstein's general relativity than just mass bend space time. Einstein's
(14:00):
relativity also lets other things happen. So, for example, Einstein says, yes,
if you have mass in space time, then space curves
and things get closer together. But also if you fill
the universe with potential energy, not mass energy, but some
weird kind of potential energy, then it causes the opposite effect.
It causes things to move apart. It's like a negative pressure.
(14:23):
This is the fascinating thing is that Newton's gravity is
just attractive. You can only pull stuff together. Einstein's gravity
is a generalization of that and allows in some weird
situations for things to get pushed apart by general relativity.
Speaker 2 (14:36):
Okay, so we've got gravity and dark energy. Gravity pulls in,
dark energy pushes out. How do we determine who wins where?
Speaker 1 (14:44):
Yes, all right, great question. But first I want to
be technical about what we mean by gravity, because when
some people hear gravity, they think the pulling together part.
Other people hear gravity they think general relativity, which can
include dark energy. So in some sense, gravity could be
the attractive part and the dark energy part, or some
people could just think about gravity as the attractive part.
(15:05):
So let's just call gravity the attractive part, and when
we're talking about the whole shebang, we'll call it that
general relativity. So you're asking about, like when is the
attractive part of gravity, things tugging on each other when?
And when does dark energy the universe pulling itself apart? When?
And that depends on distance. So the attractive part of
the parts is like Newton, that gets strong when things
(15:25):
are closer together, Like the closer you are to a star,
the more it's gravity is going to pull on you,
the more space time is bent in a way that's
going to move you closer, and as you get further away,
that fades. So like we don't feel much gravity from
Jupiter because it's kind of far away. We don't feel
much gravity from other stars because they're even further away,
et cetera, et cetera. So gravity gets weaker with distance.
(15:47):
Dark energy has the opposite relationship. Dark energy is like
every chunk of space is getting bigger. So if you
just have one little chunk of space, it's getting bigger
by a tiny amount. But if you have lots of
chunks of space huge day distances, then that adds up,
and so over big distances, dark energy becomes very very powerful.
So like between our galaxy and other galaxies, there's a
(16:10):
lot of space. If all that space is expanding by
a little bit, all those little bits add up to
a huge expansion. So dark energy gets more powerful at
greater distances. So, for example, between our cluster of galaxies
and the neighboring cluster of galaxies, dark energy is winning.
There's not enough gravity to hold those together, and they're
getting pulled apart by dark energy. All that space is
(16:32):
expanding faster, and gravity can hold stuff together. But in
our Solar system, though, there is dark energy here and
it is expanding the space between our planet and the Sun.
Gravity is more powerful because it's a fairly small distance
so gravity wins, so shorter distances, like smaller than a
galactic supercluster, gravity wins big distances, bigger than a galactic supercluster,
(16:55):
dark energy wins.
Speaker 2 (16:57):
Okay, so that makes sense to me. And so you
said that that dark energy is a form of kinetic.
Speaker 1 (17:04):
Energy potential energy.
Speaker 2 (17:05):
Actually, wow, they're the same thing.
Speaker 1 (17:07):
They're so one hundred percent not the same time.
Speaker 2 (17:10):
Smart. Okay, it's a form of potential energy. And so
does that make dark energy like negative potential energy? Our
gravity and dark energy just opposites of one another.
Speaker 1 (17:22):
Yeah, great question. So number one, we don't know where
the potential energy comes from. That's the big mystery. Like
to have enough potential energy to explain the accelerating expansion
we see, you'd need a lot more energy than we
can account for. If you add of all the potential
energy we know about in the universe from the Higgs
field and all the other fields and all that stuff,
you get a number. That number we calculate doesn't match
(17:43):
the accelerating expansion we see in the universe, and it's
not even close. The two numbers are off by ten
to the one hundred and twenty. So general relativity has
a mechanism to create this negative pressure requires positive potential energy.
We can't explain source of that potential energy we don't know,
So that's the remaining mystery, Like there is no potential
(18:05):
energy we know about that is capable of doing this,
which might mean there's some other field out there we
don't understand. But it requires positive potential energy to create
this negative pressure, this pulling things apart. So to bring
this sort of back to Bhima's question, he's asking, like,
could dark energy be anti gravity? And the answer is
kind of yes, Like dark energy is a component of
(18:27):
general relativity that allows for pulling things apart, sort of
opposite to the attractive part of gravity. So if you
consider gravity to just be the attractive part of general relativity,
and then yeah, dark energy is sort of the opposite
of that. It's still a component of general relativity, but
it has the opposite effect that creates negative pressure.
Speaker 2 (18:46):
Okay, well, thank you for that great question, Burima.
Speaker 1 (18:49):
And so now I'm curious whether we answered Bhurima's question,
whether we scratched his itch, or whether we totally misunderstood,
or whether we just confused him further with our crazy
description of LA and my so I reached out to
Burima and I sent him our conversation to hear what
he had to say. Here's Burma's reaction. Okay, thank you
very much Burima for joining us here on the podcast
(19:11):
and for sending in such a wonderful and fun question.
So tell me what did you think of our answer
and did we answer your question? Did we create more
questions in your mind? I'm dying to hear your thoughts.
Speaker 5 (19:22):
Yeah, So thank you for answering the question. It's great
to be here. I think you guys pretty much answered
the question bang on. It did blow my mind, if
I'm being one hundred percent honest, because at first I
was like, Okay, where is this going, and then at
the end sort of just landed it very nicely. It
did raise another question that I have. You mentioned the
(19:43):
dark energy sort of being caused by potential energy, and
my follow up question was does that have anything to
do with then zero point energy?
Speaker 1 (19:54):
Yeah, so the two things are definitely connected. Zero point
energy is a description of basically minimum energy that a
quantum field can have. Quantum fields are like oscillating in space.
There's zigging and zagging, they're whizzing back and forth. There's
energy there of their motion, the changing of their values.
That's kinetic energy, and they can also have potential energy
if they're in some weird configuration. Zero point energy just
(20:16):
says that the total energy, the combination of kinetic and
potential and any other kind of energy, can never go
to zero because quantum fields can never be totally flat
like a classical field. An electrical field can be just zero.
You can have like no electric field because you have
no electric charges. It can be totally zero. But if
it's a quantum field, it's always buzzing and frothing a
tiny little bit. There's a minimum energy there. But the
(20:39):
potential energy we think is causing dark energy comes from
a field we don't know. We don't know what field
is out there doing it. There's only one field we
know about that has a lot of potential energy. That's
the Higgs field. We know that it fills space with
this weird potential energy that gives all particles mass. But
when we sit down and try to calculate is the
potential energy from the Higgs field enough to explain dark
(21:00):
energy and the acceleration, we find that it's not like
they're different by ten with one hundred zeros. So, yeah,
we're not even close to understanding the source of dark energy. Yeah,
we're not even close to being close.
Speaker 5 (21:15):
Yeah, okay, yeah, well thank you, yeah.
Speaker 1 (21:19):
Yeah, well, thanks very much for sending your question and
for doing this follow up. Lots of fun to chat
with you.
Speaker 5 (21:24):
Yeah, thank you very much. It's been a pleasure and
I learned something.
Speaker 1 (21:29):
And that's our entire goal. All Right, Thanks everyone, And
if you have a question about the nature of the universe,
or if you'd heard something you haven't quite understood, please
send it to us. We'd love to answer your question.
Speaker 2 (21:40):
All right, Well that was our first question. Now we're
going to move on to a question in Kelly's wheelhouse,
which we'll get to after the break. All right, we're
(22:05):
back from the break and we're going to tackle our
first biology oriented listener question. So Charlie Davidson had this
question for us.
Speaker 6 (22:14):
Hi, Daniel and Kelly, I've got a question for your
new podcast about slime mold computation. How is it possible
for a bunch of single celled organisms to perform programmable
computational tasks for people? It just seems wild to me,
so I'd love to hear more about it and find
out how on Earth that works. Thanks very much, by.
Speaker 2 (22:35):
Bye, oh Man, Charlie. In my family, we call this
the ten thousand dollars question because that's how much money
we lost thinking about this problem. So here is the story,
all right. So slime molds are single celled organisms that
are thought to be really great at solving mases. This
(22:56):
has become like a fact that's entered the you know,
general consciousness. You say something about slime molds and they'll
be like, oh, they're really great at solving mazes, and
they've become famous for like solving straight up mazes. They've
also become famous for being able to recreate transportation systems.
So if you put a bunch of different cities on
a map, and you put a piece of oat on
(23:17):
the different cities, the slime mold will start growing on
that oat. I believe it's actually eating the bacteria and
the fungus on that oat, and then it will spread
out and it will find the other oats, and if
it's working the way we want it to work, it
will then contract and only have the shortest paths between
those things. And so perhaps you've seen videos that like
(23:40):
where the slime molds have created this map that is
almost exactly the same as like the map of the
transportation system matches up almost perfectly with what the slime
mold did. It's really impressive.
Speaker 1 (23:49):
This is really appealing. I understand why people are into
this because it suggests like there's another way to do calculations,
or this is like a biological computer, or maybe even
some like awareness. Right. I feel like we were so
hungry to discover we're not alone in the universe that
we're looking for like aliens here on Earth, even in
slime molds.
Speaker 2 (24:06):
Yeah right, well, I mean if slime olds can be
that smart, what else have we missed? Right? That's incredible. Yeah,
and did you see the dark matter example?
Speaker 1 (24:13):
Mm hmmm I did. Yet they used slime molds to
understand the filaments of dark matter between galaxies, which was
pretty cool.
Speaker 2 (24:21):
I think that they used a computational model based on
the behavior of slime molds. Yeah, since it's like a
three D things that would be a little bit harder
to do.
Speaker 1 (24:29):
No, I don't think they had like cosmic slime molds
between actual galaxies. That would be awesome.
Speaker 2 (24:33):
Wow, that would be made me scary but interesting. So
my husband and I got really excited about these slime molds.
We're like, you know, this seems like such an easy
thing that you should be able to recreate at home.
And so many science experiments are you know that we
remembered that we did at school when we were kids.
We're like, not super exciting. They didn't necessarily stay with you.
(24:53):
So we got really excited about making slime mold mazes
that you could sell pretty cheaply to class so that
they could recreate these experiments.
Speaker 1 (25:02):
I'm getting an ironic foreshadowing vibe here that you're setting
us up for a big disappointment. Is this going to
be another Kelly throws cold water on things?
Speaker 2 (25:09):
I mean, that's what I do, right, How else could
this have.
Speaker 1 (25:12):
Gone into your skills? Kelly?
Speaker 2 (25:15):
You know, yeah, I didn't think this was going to
be my niche, but it is, so here we go,
all right. So Zach was excited about this first. I
was busy with something else at the time. So we
were living in Alabama and he was like in our
humid garage trying to use legos to build mazes, and
then he was pouring auger in there, and augur, is
this thing that like when it's hot it's sort of
like viscous and fluidy, but when it cools, it cools
(25:36):
to like kind of smooshy surface that something can grow on.
So he was trying to like make mazes in our
garage out of this stuff. And then he went to
Carolina Biological website and he bought slime mold. Specifically, he
bought fisarm polycephalus, which is the main like yellow species
that people usually see when they're thinking of these mazes.
Speaker 1 (25:54):
But tell us briefly, what is a slime mold exactly?
Is it a mold? Is it slime? Is it totally
badly named?
Speaker 2 (26:00):
It's not really a slime. It's not really a mold.
It's its own thing. It has a complicated life cycle.
But when it's at the part of its life cycle
where it is solving these mazes, it's a single cell
with a bunch of nuclei in it. Wow, which is
kind of amazing. I think we should actually have a
whole episode on why organisms would ever have multiple nuclei
(26:21):
in the same cell, Like what problems does that solve?
Because my brain like more than one nucleus. That just
doesn't make sense. So he was trying to do it
that wasn't working, and so then we moved to Virginia
and he was like, okay, you know what, I'm going
to like outsource to experts. So he hired an engineer
and he was like, all right, engineer, I want you
to make me a really nice maze because the augur
kept like seeping through my legos. It just wasn't working
(26:43):
the way I wanted it. To make me a really
nice maze with a really nice cover. And the engineer
is like, okay, great, I'll do that, but it's going
to cost ten thousand dollars to make an injection molded maze.
And Zach was like, oh, that's a little steep, but
I really think kids would enjoy this, and we're going
to do it. So he pays and he does it. Yeah,
I know, And so he ran it by me and
(27:04):
I was like, I don't know that that's a great decision,
but okay, let's try it.
Speaker 1 (27:08):
This is what happens when you have one family with
two nuclei right yere, different nuclei i making different decisions,
like you know, this slime mold is spending ten k
over here, and that nuclei is objecting to it. You know,
it's like a model of a family.
Speaker 2 (27:19):
That's totally true. I should have known this problem was coming.
So he gets this maze, and you know, we've had
a lot of conversations about like, oh, it's so funny
that Carolina Biological sells slime mold, but they don't sell
these mazes. I wonder why they don't sell these mazes.
And so we get the mazes and then Zach's like, okay,
so now I'm taking this project to the biologist. So
I got a bunch of augur, I got a bunch
of slime molds. I'm like using my sterile technique, and
(27:41):
I'm trying to run these mazes. And it's my job
to write the protocol and the direction so the classrooms
can do this. And so I start doing it and
it's not working. The slimepuwter is not solving the maze
the way it's supposed to.
Speaker 1 (27:55):
So what is it supposed to do? Exactly, Like you
put it in the beginning and you put an ode
at the end. It's supposed to find the shortest path
through the maze exactly, and how could it possibly do that?
Like it's supposed to explore every direction and then eventually
figure out which of the paths is found is the shortest,
and then slowly coalesce onto that. Is that the best
case scenario.
Speaker 2 (28:14):
So that's what we thought was supposed to be happening.
And so I contacted an expert who works in this field,
and I was like, it's not working for me? Why
is it not working for me?
Speaker 1 (28:23):
Meaning what were you seeing? Like it just didn't find
the end or found the wrong path, or it just didn't.
Speaker 2 (28:27):
Go anywhere, or it was not finding the shortest path.
I see something like twenty to thirty percent of the
time it would end up at the right path, which
was essentially like random chance. And I contacted a person
who was doing even simpler experiments in their class. But
it was like a peatrit dish and then an oat
in the middle is a starting point and an oat
on one side, and so it should have been very
(28:49):
simple to just like it expands and then it was
supposed to just sort of contract to just be this
short straight line distance. And they were like, oh, yeah,
that experiment never worked, but apparently at always, well maybe
your students are doing something wrong. So I reached out
to this expert and he's like, well, first of all,
the way that it solves it is it's following a
chemical trail, and so the chemical trail needs to be
(29:11):
incredibly easy to detect. So instead of oatmeal, you could
try something that's like creates more chemicals and makes a
more clear path. And I was like, well that's not
how I had been taught that this works. And I
was like, okay, well, what percent of the time, if
I'm doing it right, should I expect it to solve
the maze? Because, like I'm thinking, the answer should be
close to one hundred percent. Based on what people are
(29:32):
saying on Twitter.
Speaker 1 (29:34):
Always are reliable resource. Twitter is basically one big documentary, Right,
you can rely on it?
Speaker 6 (29:39):
Yeah?
Speaker 2 (29:39):
Right. We spent ten k based on Twitter advice. It
was a great choice.
Speaker 1 (29:42):
I cig Twitter in my science papers all the time.
Speaker 2 (29:44):
Oh wow, No, of course it's a good thing. You've
got tenure.
Speaker 1 (29:50):
Anyway, So you're told that these things don't actually solve
the problem. They just follow a trail, which is very
different from like considering all the past to figure out
which is shortest and then coalescing on that one. That's
like they just walked through to the solution.
Speaker 2 (30:02):
Sometimes I'll smell a hot dog, and I'll just walk
towards the source of the hot dog, and it's like,
not that different. That's not impressive that I can do that.
Speaker 1 (30:09):
Can you actually resist hot dogs? Like if you walk
after hot dog, everybody knows you're kryptonite. Now wow, it's
just like.
Speaker 2 (30:18):
I actually can't. I worked at the zoo once and
we switched from all beef hot dogs to all meat
hot dogs. Ooh, and wondering what that downgrade meant put
me off hot dogs because I started thinking about it
too hard. But anyway, well, let's not droll on hot dogs.
So I ask, Okay, if I find the perfect, very
smelly thing that the slime mold can like queue in on,
(30:39):
that's gonna work better than my oats, what percent of
the time should I expect this to work? And they
said thirty or forty percent. That's not great, no, And
that's when I realized. I went back through all the
papers and I was like, oh my gosh, it says
for the slime molds that solved the maize, but they
don't include the number of times the maze wasn't solved,
(31:00):
And so I think a lot of times what's happening
is like these scenarios are set up, and the one
time out of one hundred that the slime mold gets
it close, they're like, WHOA, that's incredible and that's what
makes the news. And maybe I'm missing something, but it
seems to me that, like, maybe under absolutely perfect conditions,
when you replicate things a bunch of times, slime molds
come up with the right answer. But as far as
(31:20):
I can tell, mostly they're following a chemical gradient. Probably
chemical gradients aren't that strong in nature, like as strong
as you're able to make it in these enclosed mazes.
So I am personally not super impressed with slime old
computational abilities. And maybe that's just me being bitter that
we weren't able to make these kits to give to
classrooms and we like tanked all this time and money
(31:41):
on the project. But that is my take on slime
mold computational ability.
Speaker 1 (31:46):
It sounds to me like somebody's got a room full
of monkeys and one of them types of Shakespeare, and
they're like, look, monkeys can tap Shakespeare. Let's make a
meme about it. I mean, is it better than that,
is actually a little bit better than random? Or is
it completely exaggerated.
Speaker 2 (31:58):
I think it is probably a little better than random.
Some of the problems that they're being asked to solve
are really complicated. But I do think it's mostly following
a chemical gradient, which is less interesting than doing computations
about the shortest way to get to a thing or whatever.
But I just feel like the whole answer has been
kind of over sold. And if somebody thinks that I'm
wrong and I've missed something, I would love to hear that,
(32:19):
because actually, we just found out that we have to
make a decision about whether or not we're going to
throw out that injection mold thing.
Speaker 1 (32:25):
You still have it.
Speaker 2 (32:26):
It's in a warehouse somewhere, and they're like, you can
either pay two hundred dollars to get rid of it,
or we can ship it to you on a palette.
And I'm like, I'm a palette. Where am I going
to keep this thing? Let us know if you know
the answer. But like, slime molds are still awesome, those
paths that they're creating that is a single cell with
multiple nuclei. There's also slime molds called dog vomit slime mold,
(32:48):
which you often find in your mulch on moist, warm
summer days and it does kind of look like dog
vomit and it's one of my favorite full of go septica.
And so slime molds are fascinating and we had the
miscategorized for a while. We kind of couldn't figure out
what they were. But I'm not totally convinced that they
are amazing problem solvers.
Speaker 1 (33:09):
Sorry, And are they always single cells? I mean we're
talking about an extended thing, right, It's like this single
cell can be like a meter across. That kind of
blows my mind.
Speaker 2 (33:18):
They have different stages in their life cycle. I think
at other stages they might not be single celled. Not
an expert on these, but at the stage that everybody's
seeing for the maze solving stage, they are a single
solve with a bunch of nuclei.
Speaker 1 (33:34):
And are there other examples of things out there in
nature that can do something similar and that are also
over sold or is there anything out there that actually
can solve this kind of problem in an impressive way
or is biology all just a dank meme.
Speaker 2 (33:49):
I'm reaching real far back here. I watched this really
interesting lecture from a woman who studied crows. So this
isn't like maze solving, but they're super clever. Like if
there was another crow in the room, they would bury
their treat and then when the crow turned around, they
would take the treat out and they'd bury it somewhere else.
So they knew like that bird was watching me and
(34:10):
I want to trick it, and that's not watching now,
So now it's time for me to move where I
hid my cash. Clever, there are very smart organisms. I
think this is just an exciting thing that escaped that
has maybe since been oversold.
Speaker 1 (34:22):
It sounds like the puzzle you really sold was why
Carolina Biological doesn't carry meses in their catalog.
Speaker 2 (34:29):
Exactly that is the puzzle we solved. And so now
we need to find out does Charlie Davidson like answers
that are kind of a bummer? And did I mistakenly
assume that he wanted to talk about slime wolds but
he had another single celled organism in mind. Let's hear
from Charlie and find out.
Speaker 6 (34:48):
Thank you for answering the question, guys, that's exactly what
I wanted to have answered. The computational bitites of slime
molds are no longer impressive to me either, but never mind,
can't win them all. I was hoping it would be
something far more amazing, but it's the way it is,
I guess. Thank you so much, sake. I do believe
we have dog vomit slime mold. In the UK, we
(35:09):
call it, which is brew If it's the same thing.
I'm not sure which name I prefer, but either or
ice codes. Thanks very much, look forward to future podcasts.
Speaker 1 (35:19):
All right, enough about single cell organisms, hot dogs and
slime molds. When we come back, we're going to tackle
another question about space and time and black holes. All right,
(35:45):
we're back, and we are answering questions from the audience.
Questions from people like you. If there's something about the
universe it's never clicked in your mind, or if you've
heard us talk about something that didn't quite make sense
to you, please write to us. We want to follow up.
We want those ideas to connect in your head so
that you feel like you understand as well. We will
answer any questions you send to us to questions at
(36:06):
danieland Kelly dot org, even dating questions. Though we don't
claim any expertise.
Speaker 2 (36:12):
Oh I'm an expert. I did a lot of dating.
But I don't know if anyone wants my advice.
Speaker 1 (36:18):
Well, if they know Zach, that they can evaluate whether
they think that went well for you or not.
Speaker 2 (36:23):
Yeah, it's up in the air.
Speaker 1 (36:26):
TBD. All right. In the meantime, here's a question we
got from Derek in New Hampshire, who's thinking about black
holes and Hawking radiation.
Speaker 4 (36:36):
I was wondering, can a black hole be so massive
that not even Hawkins radiation can escape from its gravitational pull?
Look forward to you and your answer.
Speaker 1 (36:47):
Thanks.
Speaker 2 (36:47):
All right, So this is a great question. We did
a little bit of an intro into black holes as
part of the very first question. Maybe the right place
to start is what is Hawking radiation?
Speaker 1 (36:59):
Yeah? Great, So Derek's basically asking about the glow that
we think black holes might make. We talked in the
earlier question about what black holes are. They are regions
of space time that are so bent, so deformed, that
space is now only pointing inwards. So you shine a
flashlight inside a black hole, it's only going to go
(37:19):
towards the center. There's no path out from behind the
event horizon. And that's a description of a black hole
that comes from general relativity it's Einstein's theory that says
space gets bent and the space tells matter how to
move and all this kind of stuff. But we know
that general relativity can't be the final story of the
universe because it's not compatible with the other story we
have about the universe, which is quantum mechanics. And in particular,
(37:41):
Einstein's theory of black holes predicts that they're totally black,
that if you look at a black hole, there's no glow.
It's not emitting anything, No light comes off of the
black hole. But if you do try to account a
little bit for quantum mechanical effects, and this is what
Hawking did, it predicts something different. It predicts that black
holes aren't not actually totally black, that they glow very
(38:02):
faintly with this radiation he called, of course, Hawking radiation.
Speaker 2 (38:07):
He named it after himself. Isn't someone supposed to do
that for you?
Speaker 1 (38:12):
He actually worked it out with a student of his.
But yeah, it's called Hawking radiation and not Hawking Beckenstein radiation.
Speaker 2 (38:18):
The next wasp by discover is gonna be Wienersmith's wasp
do it of course.
Speaker 1 (38:23):
Okay, this is really a very impressive bit of physics.
It's like an end run around a bigger problem. The
biggest problem in modern physics right now is like, how
do we reconcile quantum mechanics, which tells us that like
stuff doesn't have a specific location, it can be here
or it can be there. And general relativity, which tells
us like space gets bent based on where stuff is,
(38:44):
and general relativity can't handle if stuff doesn't have a
specific location, Like if the particles may be here and
maybe there is, space may be bent here and maybe
bent there or partially bent here, partially bent there. Nobody
knows how to bring these two things together, which is
what you have to do if you want, I want
a theory of general relativity that's consistent with quantum mechanics.
Nobody knows how to do that. Big question, lots of
(39:06):
Nobel prize is waiting. But what Hacking did was like
an end run around that. He's like, can't figure out
the big problem, but maybe I can sort of chip
away at it a little bit. So he found a
little trick that let him think about what happened to
quantum fields near an event horizon, and his trick let
him make this prediction that black hole should glow a
little bit.
Speaker 2 (39:26):
Can you remind me what an event horizon is?
Speaker 1 (39:29):
Right? Thank you? An event horizon is what we think
of is like the edge of the black hole. Inside
the event horizon, everything is trapped forever. Outside the event horizon,
you're still free. So you can approach a black hole,
be near the event horizon, and then escape and go
back to your planet and live a happy life. If
you cross the event horizon, you're in the black hole forever.
I think there's also a lot of confusion out there
(39:49):
about hawking radiation and what it means and how to
think about it, because I've said that we don't understand
how particles are affected by really strong gravity, And the
typical story you hear is that hawking radiation comes from
particles being created near the event horizon, like particle antiparticle
pairs popping out of the vacuum and one falls into
(40:11):
the event horizon and the other doesn't. And so to
do that calculation, it feels like you'd need to understand
how gravity works for particles. Well, the thing is, that's
not how hawking radiation works. That's the well worn pop
side cartoon version of it, but it doesn't actually make
any sense. I mean, virtual particles can't be treated like
(40:31):
real particles. They're not real particles. You shouldn't think of
the vacuum as like filled with actual particles that can
fall into black holes. And we don't know how to
do those calculations for gravity of particles. Instead, what Hawking
did was take a very different approach. He just said,
what happens to quantum fields if there's a discontinuity in space,
(40:51):
if there's an event horizon, how do I solve the
mathematics of a quantum field near an event horizon? And
what he found was the only way to make the
math work for quantum field near an event horizon was
to have an outgoing wave of radiation, and that's what
he interpreted as Hawking radiation. He doesn't have a microscopic
particle picture of Hawking radiation. What's happening to individual particles?
(41:14):
We don't know how to do that, but we do
know that quantum mechanics says, if there's an event horizon
in space, then your quantum fields have to radiate. And
the really cool thing about this is that you don't
need a complete solution to quantum gravity to attack it.
In this way. This is really Hawking's brilliance of finding
a sort of an end run around having to have
the whole picture and still getting this one result from
(41:36):
this mathematical trick. And there's another beautiful angle to this
to make it a little bit more satisfying. Even though
you can't think about the individual particles and how they're
affected by gravity, you can think about hawking radiation like thermodynamically.
The way Hawking thought about it and his student Bekenstein
was that black holes eat information, black holes eat entropy. Right,
(41:58):
all the disorder in the universe into a black hole.
Is it decreasing? Is it violating the second law of thermodynamics.
They showed that on one hand, you can think about
it mathematically quantum fields radiating energy near an event horizon,
But you can also think about it thermodynamically, meaning that
black holes, if they have information, if they have entropy,
they should have temperature. And if they have temperature, then
(42:20):
they glow like everything else in the universe that has temperature.
I glow, you glow, the sun glows. Things glow based
on their temperatures. Hotter things glow with higher frequency, colder
things glow with lower frequency. More infrared hot things glow
in like the X ray and the ultraviolet. So it
turns out you can model black holes as if they
(42:41):
are black body radiators, things that glow just based on
their temperature. Of course, they're extraordinarily cold, tiny, tiny temperatures.
And the weird thing is that as a black hole
gets bigger, it gets more massive, it actually gets colder
and it glows more dimly. So smaller black holes glow
more brightly and evaporate more quickly, and larger black holes
(43:04):
glow more dimly because they're colder. So that's another fun
way that you can think about hawking radiation that helps
you sort of get a mental picture of it.
Speaker 2 (43:12):
Okay, and then one more follow up question. So when
we've talked in the past, we've said that quantum mechanics
and general relativity they don't make the same predictions, But
usually that doesn't matter because any question that you have
usually just requires you to think in one of those terms.
That's right, Why with black holes, is it important to
(43:32):
understand both of them?
Speaker 1 (43:34):
Yeah, great question. Usually you can ignore general relativity when
you're doing quantum mechanics because particles have almost no mass
and so they hardly bend space, their gravity is basically irrelevant.
Usually you could ignore quantum mechanics when you're doing general
relativity because you're dealing with big masses like planets, and
for planets, the quantum mechanical effects a'll average out to zero,
so usually you could ignore one or the other. When
(43:56):
you're dealing with black holes, you're dealing with very short
distances or very very strong gravity. So now you want
to know the answer to like what happens to a
particle near the edge of an event horizon. You have
like very very strong gravity enough to pull on a particle,
and you want to know what's going to happen to
my electron? Is going to go this way? Or is
it going to go that way? Or if it splits
into other particles, what happens to it. Now you want
(44:17):
to answer questions about the gravity of particles, you need
to be able to include the effects of gravity and
to be able to describe that particle as a quantum
mechanical object, So you need both. Usually you don't care
about the gravity on individual electron, but if you want
to understand things like Hawking radiation, what happens to a
particle near the event horizon? You need the answers to those.
Speaker 2 (44:37):
Okay, so let's suggest black holes. If we could understand them,
that might be the way that we merge our understanding
of those two things.
Speaker 1 (44:43):
Oh. Absolutely, if we could see inside an event horizon,
we would know the answer to how to unify quantum
mechanics and gravity, because we would see is there a
singularity like general relativity predicts and quant mechanics says it's impossible,
or is there something else weird and fuzzy? But of
course we can't so we know the answer. It's there,
but it's frustratingly hiding behind the veil of the black hole.
(45:04):
The Derek's question was basically, could you make a black
hole so massive that even its hawking radiation can't escape?
So here you have a black hole and its emitting radiation.
Could it suck at that back in? Could the hawking
radiation get trapped by the black hole? The answer is,
we don't really know, because what you're asking requires us
to be able to think about the gravity on particles
(45:26):
near a black hole, and we just don't know how
to do that right because we don't know how to
think about gravity for things where we don't have a
way to describe their location exactly where they are through
space and time. General relativity is basically a classical theory.
It assumes that everything has a location and momentum, and
that can be well defined and you can do those calculations.
So short answer is, Derek, we don't know. The best
(45:47):
answer though is probably not. Hawking's calculations suggest that black
holes glow outside of the event horizon. Basically, what he
did in his calculation is figure out what happens to
a quantum field near an event horizon, and his solution
suggests there has to be outgoing radiation, and that radiation
is past the event horizon. So even if the gravity
is very very strong, it's past the event horizon, which
(46:09):
means technically it can still escape. That's the definition of
the event horizon. So if it couldn't escape, it would
be within the event horizon. But hawking radiation is always
emitted past the event horizon, so probably it's.
Speaker 2 (46:22):
Free, all right. So Derek, we want to know if
that explanation was satisfying. So we've reached out to Derek,
and here's what he said.
Speaker 1 (46:31):
You did.
Speaker 7 (46:31):
You an excellent job at it, answering the question as
best as you could I ever want to have a
big fear of missing out? And I can only hope
that technology will allow us to have the answers for
these types of questions.
Speaker 1 (46:44):
Thank you.
Speaker 2 (46:44):
Okay, so that's it for today. Thank you so much
to Barima and Charlie and Derek for sending in their questions.
We hope to get more questions. Actually, we already have
a stack ready for our listener questions number two, So
if you send your questions, be patient. We are going
to get to all of them, and we really appreciate
your questions. Can't wait to hear from you. Send us
(47:05):
emails at questions at Danielankelly dot org.
Speaker 1 (47:09):
Because it's not just our curiosity that drives sigence forward,
it's yours. It's the reason we're doing it. It's collective
curiosity of humanity is why we have science. So thanks
everyone for pushing knowledge forward.
Speaker 2 (47:28):
Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We
would love to hear from you, We really would.
Speaker 1 (47:34):
We want to know what questions you have about this
Extraordinary Universe.
Speaker 2 (47:39):
We want to know your thoughts on recent shows, suggestions
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Speaker 1 (47:46):
We really mean it. We answer every message. Email us
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Speaker 1 (48:02):
Don't be shy, write to us h
Every discovery, every moment of insight, every aha or eureka
with the ideas click together in someone's mind to reveal
a deep truth about the universe. All of those begin
the same way with a question. In fact, all of
science starts with questions. The reason we know things about
clouds and beetles and black holes is because someone out
(00:28):
there had a question that kept them up at night,
so they were willing to stay up late looking at
the stars or counting beetles until they figured it out.
Science is just people asking questions they couldn't let go.
But it's not just professional scientists who ask questions and
move us forward. It's everyone. It's you, and we think
your questions also deserve answers, or at least replies that
(00:51):
make sense and help you grapple with what we do
and don't know about the topic. So if you have
a question about science or whatever, please write to us
to questions at Daniel and Kelly dot org. We'd love
to hear from you, and sometimes we'll answer those questions
right here on the pod. And so on today's episode,
we're going to be answering questions submitted by listeners and
(01:13):
more than that, and I'll admit to being a little
bit nervous about this part. We're going to go back
to those listeners with our answers and follow up to
see if our explanations scratch their itch or not. Today
Daniel and Kelly are getting graded by the listeners. So
today on Daniel and Kelly's Extraordinary Universe, we'll be answering
questions from listeners, Volume one.
Speaker 2 (01:50):
Hello, I'm Kelly Wienersmith, and I am so excited that
we're having our first listener Questions episode today.
Speaker 1 (01:57):
Hi, I'm Daniel. I'm a particle physicist, and I love
answering questions from the internet about physics, about philosophy, even
about dating.
Speaker 2 (02:06):
Really, you've answered questions on the show about dating.
Speaker 1 (02:10):
People send me all sorts of questions, you know. They
send me their treatise on the nature of the Universe,
They send me questions about career advice, how to get
into physics, and yes, sometimes people ask me questions about
their dating life, and hey, I don't claim any particular
expertise there, but I'll share my thoughts.
Speaker 2 (02:27):
Sure. Yeah, no, I'll share my thoughts on anything. So
I was actually going to ask you, what is the
weirdest or most surprising, like no negative connotation needed, but
weirdest or most surprising question you've ever been asked related
to your career as a physicist.
Speaker 1 (02:42):
Oh wow, that is such a good question. Now mentally,
cycling through the thousands of questions I've gotten over the years,
I think one of the most challenging questions to answer
are ones about people's personal experiences. People writing sometimes about
like their UFO experiences or their paranormal experiences, and they
want my physics knowledge and like, what else could have
(03:03):
explained it? And that's a delicate line to walk, because
you don't want to suggest that what they experienced is
not what they think they experienced, but you also want
to help them disentangle it and think about what else
might have explained it. That's maybe like the most oddball
and challenging kind of question to answer. I also sometimes
get really touching stories, like a woman who went through
(03:24):
her father's old belongings. He was, of course, a retired engineer,
and she found in there a treatise on the nature
of the universe, and she sent it to me and
she's like, look, I don't know if this is anything,
but if it is something, I feel terrible not sharing
it with the world. Can you tell me if this
is worthwhile or not?
Speaker 2 (03:41):
Aw, that's so cute. I know, was it worthwhile or
was it fun to read? But maybe not earth changing?
Speaker 1 (03:48):
There was nothing really earth chattering in there, but I
think she was happy to know that at least somebody
had looked at it.
Speaker 2 (03:54):
What's so cool that you were able to provide that?
Speaker 1 (03:55):
And how about you? Do you get weird questions from
the internet about parasites? People send you pictures of bits
of their body and be like, Kelly, what is this?
Do I need to go to the er?
Speaker 2 (04:04):
I do get photos of feces from time to time,
and it's worth noting that I cannot identify parasitic infections
from a picture of a bell movement their microscopic and
I can't. Also, I'm not a medical professional.
Speaker 1 (04:16):
So everybody out there who was about to email Kelly
a picture of their poop not worth your time.
Speaker 2 (04:21):
Please don't. I think the hardest question for me to answer, though,
was I was doing an interview for our book soon ish,
and I think the person doing the interview hadn't really
read the book, and so his question was, so, tell
me about the robots? The robots, and there was like
a different robot in every single chapter, and so I
didn't have any idea what he was talking about. This
(04:44):
is when I learned the trick that when you do
an interview, if someone asks you a question that you
don't really know what they're trying to get at, you
just decide what is the most interesting thing I feel
like talking about right now? And so I just picked
like my favorite robot and went off on that tangent.
It was, that's a learning experience.
Speaker 1 (05:01):
Sounds like you're ready to run for higher office.
Speaker 3 (05:03):
Now.
Speaker 1 (05:03):
I'm going to dodge your question to talk about the
thing I want to talk about instead.
Speaker 2 (05:08):
I don't think i'd make a good politician, all right.
Speaker 1 (05:11):
Well, you know I would vote for you to represent Virginia,
but not California. I don't think you can really appreciate
everything that California has to offer.
Speaker 2 (05:18):
I lived in California for a while. Is it that
you don't like Virginia and that's why you would vote
for me for Virginia. You want to harm Virginia in somewhere?
Speaker 1 (05:24):
Well, no, no, no, Virginia is for lovers. It's fantastic.
I just don't feel like you appreciate California. I mean,
you did leave, right, and so clearly you don't understand
that it's objectively the best place in the world to live.
Speaker 2 (05:35):
You know, I have not regretted leaving, sorry to say so.
I guess you're right. I shouldn't be representing California. And
maybe I'm going to regret that a decade from now
when I run for governor of California, if I've moved back.
But for now, I think we're just going to go
with no politics for Kelly.
Speaker 1 (05:50):
That sounds good because I'm gonna have to hold off
on endorsing you until I hear you change your opinion California.
All right, But let's not talk about Kelly's your future
plans to take over the world slash Solar system slash universe.
Let's get to questions from listeners, because today on Daniel
and Kelly's Extraordinary Universe, we are answering questions from you.
We think your questions are important. We want you to
(06:12):
understand the universe. We want you to get that satisfying
moment where everything clicks in your mind, and so we
encourage you to write to us with your questions to
questions at Danielankelly dot org. We will write back to you.
You'll hear what we do and don't know about whatever
it is you're interested in.
Speaker 2 (06:29):
We can't we do hear from you.
Speaker 1 (06:31):
Our first question today is from a really fun guy
named Barima who lives in Germany. He has a question
about gravity. Here is Barima's question.
Speaker 3 (06:40):
Hello, my name is Brima, living in Germany from England.
I'm a big fan of the podcast and I love
what you guys are about, Sir. Gravity becomes so strong
that it tarts space time, and I was thinking dark
energy basically does the same, but in reverse because it's
expanding the universe. Both of these phenomena bend or expand
fabric of space time. So my question is could dark
(07:04):
energy be anti gravity? Thank you for your time and
I hope you guys have a great day.
Speaker 2 (07:08):
Thank you so much for the question, Barima. Well, you know, Daniel,
that sounds like a question.
Speaker 4 (07:13):
For you.
Speaker 1 (07:15):
Gravity, space time and dark energy. Ooh, this is my
jam for sure.
Speaker 2 (07:20):
We've recently recorded episodes on what is time and what
is space which might provide some important context. But how
do we answer this question more directly?
Speaker 1 (07:29):
This is a great question because it gives us an
opportunity to connect a lot of ideas. You hear a
lot about space time as a fabric, black holes, having
extreme gravity, dark energy pulling space apart. How does it
all work? How do you think about that altogether? My
interpretation of Brima's question is that he's thinking about black
holes and he's heard that black holes tear space time,
(07:49):
so he's thinking about that as like pulling space itself apart.
And he's also heard that the universe is expanding in
an accelerating way, which feels like it's ripping space apart,
and so he's wondering, like, are those the same thing
or are they the opposite? Because black holes attract and
dark energy is pulling space apart, how does it all work?
(08:10):
And is dark energy actually the opposite form of gravity?
So we're going to give Burrimo a way to think
about dark energy in terms of gravity in general relativity
and link all these ideas together. But we should probably
start with black holes and space time and think about
what it means to tear space time.
Speaker 2 (08:27):
Apart, and does this have anything to do We had
a conversation about a map and how you can like
make the cities closer or farther apart. Is that the
right way to start thinking about this problem, or now
that we're talking about black holes, we're in a totally
different universe.
Speaker 1 (08:40):
No, that's exactly the right way to start thinking about this.
Let's get a mental picture of what space is or
space time is, and what it means to tear space
time or what happens when gravity gets really really strong.
So let's start with a model of space. What is
space space? We don't know what it is fundamentally, but
we know that we can measure the distance between two points.
You have like a ruler. You can measure how many
(09:02):
ticks are between two points, and you can do that
between La and Virginia, or you can do that between
Canada and Mexico, or between Seattle and Miami or whatever.
You can measure distances between points. So we know that
we can measure these distances. We don't understand what is
the underlying fabric and what is it doing and how
does it work, But we can measure these distances, and
we notice that if you put a mass in space,
(09:23):
like a star or a planet or whatever, those distances
get kind of wonky like things get closer together, things
get further apart. This is what we mean when we
say space is curved. It's not like it's curving in
some external dimension with a whole crazy rubber sheet analogy.
It just means that it's changing the intrinsic distances between stuff.
The curvature of space is not external and some other dimension.
(09:46):
It's internal. It's intrinsic. It's just a relative change of distances.
And so when we say space is curve, we just
mean you're tweaking all of those distances.
Speaker 2 (09:55):
I think if I were listening to the podcast, this
is where I would pause it and just stare at
the wall for five minutes and be like, how do
I make sense of this? It's all kind of complicated,
but yeah, I'm following.
Speaker 1 (10:06):
Yeah, And you call up this mental picture of a map.
So imagine you had a map the United States and
you laid it flat on a table and you measure
the distances between these cities. Those distances have to follow
some rules because the map is flat. If you measure
all those distances like from LA to Seattle, and Seattle
to New York and New York to Miami and Miami
back to LA, that's kind of a square, right, you
(10:28):
measure all those distances, and those distances have to follow
some rules because the map is flat on the table. Like,
from those distances, I can tell you how far it
is from LA to New York. It's constrained by those
other measurements. But what if I told you I'm just
going to go in and make LA and New York
closer together, I'm just squeezing them together. Well, then the
map can no longer be flat because I have to
(10:49):
like bunch up the material between LA and New York.
And that's what curving space does. It changes the relative
distances between these points, so they no longer add up
in the same way they would if they were on
flat space. That's what curved space is, just changes those
relative distances. And the crazy thing is that you can
do that. You can develop a model of space that
(11:09):
incorporates all these weird changes of distances. And that's what
we call curved space, all right.
Speaker 2 (11:15):
So it's never tearing. There's never a spot where it
like breaks and then there's nothing in between. It just
kind of gets like curvy, like a roller coaster.
Speaker 1 (11:23):
At some point exactly, you can't really tear space time.
That's like a dramatic visual people use, but it's not
a helpful way to think about it. And remember, we
don't know what space is. We have this beautiful mathematical
description from Einstein that lets us think about this concept
of curvature in terms of these changing relative distances, but
that's just our model. It's useful for describing space. Doesn't
(11:43):
always tell us what space actually is, but it does
predict crazy stuff like if you have a huge amount
of mass, the curvature gets really really strong, and you
get things like black holes, places where space is so
curved that light can no longer escape because not only
does it change the relation so distances, it changes like
the directions, and inside a black hole, space is now
(12:04):
one directional. Every direction inside a black hole is just
towards the center. It's not that light can't escape because
the force of gravity is so strong. It's because every
direction is towards the center. Now there are no other
directions inside a black hole. So a black hole is
so massive it like rearranges the relationships between points in space.
Speaker 2 (12:25):
Okay, so the order of the direction there is that
the black hole starts pulling on space. It's not that
like space gets bent for some other reason, and that
causes a black hole.
Speaker 1 (12:33):
Yeah, that's right. The presence of mass causes the bending
of space, and that's what the black hole is. Yeah, exactly. Okay,
So that's the way to think about like gravity and
black holes and bending of space time. But Burma is
asking us to connect that to the expansion of the
universe and how the universe we've noticed in the last
twenty years or so is not just getting bigger, it's
(12:54):
getting bigger faster and faster as time goes on. And
this is the mystery we call dark energy. We don't
understand the source of that expansion or why it's accelerating.
Speaker 2 (13:04):
Okay, so we know that it's accelerating, and we're using
dark energy as the explanation, and is that the extent
of what we know about dark energy is that it
is the magical way that this all works out.
Speaker 1 (13:15):
Essentially, dark energy is shorthand for saying, we see the
universe is accelerating its expansion, we don't understand why. Please
somebody figure it out, and we don't have a working explanation.
We have sort of like a sketch on the back
of a napkin idea that might work out, But currently
the calculations are not connecting, and they're off by like
(13:36):
ten with one hundred zeros. But the sketch of the
explanation actually comes from general relativity. General relativity, of course,
is Einstein's generalization of Newton's gravity. Newton says, masses attract
each other because there's a force. Einstein says, no, Actually
it's more complicated. Space time curves and it gives mostly
the same behavior. But there's a little bit more to
Einstein's general relativity than just mass bend space time. Einstein's
(14:00):
relativity also lets other things happen. So, for example, Einstein says, yes,
if you have mass in space time, then space curves
and things get closer together. But also if you fill
the universe with potential energy, not mass energy, but some
weird kind of potential energy, then it causes the opposite effect.
It causes things to move apart. It's like a negative pressure.
(14:23):
This is the fascinating thing is that Newton's gravity is
just attractive. You can only pull stuff together. Einstein's gravity
is a generalization of that and allows in some weird
situations for things to get pushed apart by general relativity.
Speaker 2 (14:36):
Okay, so we've got gravity and dark energy. Gravity pulls in,
dark energy pushes out. How do we determine who wins where?
Speaker 1 (14:44):
Yes, all right, great question. But first I want to
be technical about what we mean by gravity, because when
some people hear gravity, they think the pulling together part.
Other people hear gravity they think general relativity, which can
include dark energy. So in some sense, gravity could be
the attractive part and the dark energy part, or some
people could just think about gravity as the attractive part.
(15:05):
So let's just call gravity the attractive part, and when
we're talking about the whole shebang, we'll call it that
general relativity. So you're asking about, like when is the
attractive part of gravity, things tugging on each other when?
And when does dark energy the universe pulling itself apart? When?
And that depends on distance. So the attractive part of
the parts is like Newton, that gets strong when things
(15:25):
are closer together, Like the closer you are to a star,
the more it's gravity is going to pull on you,
the more space time is bent in a way that's
going to move you closer, and as you get further away,
that fades. So like we don't feel much gravity from
Jupiter because it's kind of far away. We don't feel
much gravity from other stars because they're even further away,
et cetera, et cetera. So gravity gets weaker with distance.
(15:47):
Dark energy has the opposite relationship. Dark energy is like
every chunk of space is getting bigger. So if you
just have one little chunk of space, it's getting bigger
by a tiny amount. But if you have lots of
chunks of space huge day distances, then that adds up,
and so over big distances, dark energy becomes very very powerful.
So like between our galaxy and other galaxies, there's a
(16:10):
lot of space. If all that space is expanding by
a little bit, all those little bits add up to
a huge expansion. So dark energy gets more powerful at
greater distances. So, for example, between our cluster of galaxies
and the neighboring cluster of galaxies, dark energy is winning.
There's not enough gravity to hold those together, and they're
getting pulled apart by dark energy. All that space is
(16:32):
expanding faster, and gravity can hold stuff together. But in
our Solar system, though, there is dark energy here and
it is expanding the space between our planet and the Sun.
Gravity is more powerful because it's a fairly small distance
so gravity wins, so shorter distances, like smaller than a
galactic supercluster, gravity wins big distances, bigger than a galactic supercluster,
(16:55):
dark energy wins.
Speaker 2 (16:57):
Okay, so that makes sense to me. And so you
said that that dark energy is a form of kinetic.
Speaker 1 (17:04):
Energy potential energy.
Speaker 2 (17:05):
Actually, wow, they're the same thing.
Speaker 1 (17:07):
They're so one hundred percent not the same time.
Speaker 2 (17:10):
Smart. Okay, it's a form of potential energy. And so
does that make dark energy like negative potential energy? Our
gravity and dark energy just opposites of one another.
Speaker 1 (17:22):
Yeah, great question. So number one, we don't know where
the potential energy comes from. That's the big mystery. Like
to have enough potential energy to explain the accelerating expansion
we see, you'd need a lot more energy than we
can account for. If you add of all the potential
energy we know about in the universe from the Higgs
field and all the other fields and all that stuff,
you get a number. That number we calculate doesn't match
(17:43):
the accelerating expansion we see in the universe, and it's
not even close. The two numbers are off by ten
to the one hundred and twenty. So general relativity has
a mechanism to create this negative pressure requires positive potential energy.
We can't explain source of that potential energy we don't know,
So that's the remaining mystery, Like there is no potential
(18:05):
energy we know about that is capable of doing this,
which might mean there's some other field out there we
don't understand. But it requires positive potential energy to create
this negative pressure, this pulling things apart. So to bring
this sort of back to Bhima's question, he's asking, like,
could dark energy be anti gravity? And the answer is
kind of yes, Like dark energy is a component of
(18:27):
general relativity that allows for pulling things apart, sort of
opposite to the attractive part of gravity. So if you
consider gravity to just be the attractive part of general relativity,
and then yeah, dark energy is sort of the opposite
of that. It's still a component of general relativity, but
it has the opposite effect that creates negative pressure.
Speaker 2 (18:46):
Okay, well, thank you for that great question, Burima.
Speaker 1 (18:49):
And so now I'm curious whether we answered Bhurima's question,
whether we scratched his itch, or whether we totally misunderstood,
or whether we just confused him further with our crazy
description of LA and my so I reached out to
Burima and I sent him our conversation to hear what
he had to say. Here's Burma's reaction. Okay, thank you
very much Burima for joining us here on the podcast
(19:11):
and for sending in such a wonderful and fun question.
So tell me what did you think of our answer
and did we answer your question? Did we create more
questions in your mind? I'm dying to hear your thoughts.
Speaker 5 (19:22):
Yeah, So thank you for answering the question. It's great
to be here. I think you guys pretty much answered
the question bang on. It did blow my mind, if
I'm being one hundred percent honest, because at first I
was like, Okay, where is this going, and then at
the end sort of just landed it very nicely. It
did raise another question that I have. You mentioned the
(19:43):
dark energy sort of being caused by potential energy, and
my follow up question was does that have anything to
do with then zero point energy?
Speaker 1 (19:54):
Yeah, so the two things are definitely connected. Zero point
energy is a description of basically minimum energy that a
quantum field can have. Quantum fields are like oscillating in space.
There's zigging and zagging, they're whizzing back and forth. There's
energy there of their motion, the changing of their values.
That's kinetic energy, and they can also have potential energy
if they're in some weird configuration. Zero point energy just
(20:16):
says that the total energy, the combination of kinetic and
potential and any other kind of energy, can never go
to zero because quantum fields can never be totally flat
like a classical field. An electrical field can be just zero.
You can have like no electric field because you have
no electric charges. It can be totally zero. But if
it's a quantum field, it's always buzzing and frothing a
tiny little bit. There's a minimum energy there. But the
(20:39):
potential energy we think is causing dark energy comes from
a field we don't know. We don't know what field
is out there doing it. There's only one field we
know about that has a lot of potential energy. That's
the Higgs field. We know that it fills space with
this weird potential energy that gives all particles mass. But
when we sit down and try to calculate is the
potential energy from the Higgs field enough to explain dark
(21:00):
energy and the acceleration, we find that it's not like
they're different by ten with one hundred zeros. So, yeah,
we're not even close to understanding the source of dark energy. Yeah,
we're not even close to being close.
Speaker 5 (21:15):
Yeah, okay, yeah, well thank you, yeah.
Speaker 1 (21:19):
Yeah, well, thanks very much for sending your question and
for doing this follow up. Lots of fun to chat
with you.
Speaker 5 (21:24):
Yeah, thank you very much. It's been a pleasure and
I learned something.
Speaker 1 (21:29):
And that's our entire goal. All Right, Thanks everyone, And
if you have a question about the nature of the universe,
or if you'd heard something you haven't quite understood, please
send it to us. We'd love to answer your question.
Speaker 2 (21:40):
All right, Well that was our first question. Now we're
going to move on to a question in Kelly's wheelhouse,
which we'll get to after the break. All right, we're
(22:05):
back from the break and we're going to tackle our
first biology oriented listener question. So Charlie Davidson had this
question for us.
Speaker 6 (22:14):
Hi, Daniel and Kelly, I've got a question for your
new podcast about slime mold computation. How is it possible
for a bunch of single celled organisms to perform programmable
computational tasks for people? It just seems wild to me,
so I'd love to hear more about it and find
out how on Earth that works. Thanks very much, by.
Speaker 2 (22:35):
Bye, oh Man, Charlie. In my family, we call this
the ten thousand dollars question because that's how much money
we lost thinking about this problem. So here is the story,
all right. So slime molds are single celled organisms that
are thought to be really great at solving mases. This
(22:56):
has become like a fact that's entered the you know,
general consciousness. You say something about slime molds and they'll
be like, oh, they're really great at solving mazes, and
they've become famous for like solving straight up mazes. They've
also become famous for being able to recreate transportation systems.
So if you put a bunch of different cities on
a map, and you put a piece of oat on
(23:17):
the different cities, the slime mold will start growing on
that oat. I believe it's actually eating the bacteria and
the fungus on that oat, and then it will spread
out and it will find the other oats, and if
it's working the way we want it to work, it
will then contract and only have the shortest paths between
those things. And so perhaps you've seen videos that like
(23:40):
where the slime molds have created this map that is
almost exactly the same as like the map of the
transportation system matches up almost perfectly with what the slime
mold did. It's really impressive.
Speaker 1 (23:49):
This is really appealing. I understand why people are into
this because it suggests like there's another way to do calculations,
or this is like a biological computer, or maybe even
some like awareness. Right. I feel like we were so
hungry to discover we're not alone in the universe that
we're looking for like aliens here on Earth, even in
slime molds.
Speaker 2 (24:06):
Yeah right, well, I mean if slime olds can be
that smart, what else have we missed? Right? That's incredible. Yeah,
and did you see the dark matter example?
Speaker 1 (24:13):
Mm hmmm I did. Yet they used slime molds to
understand the filaments of dark matter between galaxies, which was
pretty cool.
Speaker 2 (24:21):
I think that they used a computational model based on
the behavior of slime molds. Yeah, since it's like a
three D things that would be a little bit harder
to do.
Speaker 1 (24:29):
No, I don't think they had like cosmic slime molds
between actual galaxies. That would be awesome.
Speaker 2 (24:33):
Wow, that would be made me scary but interesting. So
my husband and I got really excited about these slime molds.
We're like, you know, this seems like such an easy
thing that you should be able to recreate at home.
And so many science experiments are you know that we
remembered that we did at school when we were kids.
We're like, not super exciting. They didn't necessarily stay with you.
(24:53):
So we got really excited about making slime mold mazes
that you could sell pretty cheaply to class so that
they could recreate these experiments.
Speaker 1 (25:02):
I'm getting an ironic foreshadowing vibe here that you're setting
us up for a big disappointment. Is this going to
be another Kelly throws cold water on things?
Speaker 2 (25:09):
I mean, that's what I do, right, How else could
this have.
Speaker 1 (25:12):
Gone into your skills? Kelly?
Speaker 2 (25:15):
You know, yeah, I didn't think this was going to
be my niche, but it is, so here we go,
all right. So Zach was excited about this first. I
was busy with something else at the time. So we
were living in Alabama and he was like in our
humid garage trying to use legos to build mazes, and
then he was pouring auger in there, and augur, is
this thing that like when it's hot it's sort of
like viscous and fluidy, but when it cools, it cools
(25:36):
to like kind of smooshy surface that something can grow on.
So he was trying to like make mazes in our
garage out of this stuff. And then he went to
Carolina Biological website and he bought slime mold. Specifically, he
bought fisarm polycephalus, which is the main like yellow species
that people usually see when they're thinking of these mazes.
Speaker 1 (25:54):
But tell us briefly, what is a slime mold exactly?
Is it a mold? Is it slime? Is it totally
badly named?
Speaker 2 (26:00):
It's not really a slime. It's not really a mold.
It's its own thing. It has a complicated life cycle.
But when it's at the part of its life cycle
where it is solving these mazes, it's a single cell
with a bunch of nuclei in it. Wow, which is
kind of amazing. I think we should actually have a
whole episode on why organisms would ever have multiple nuclei
(26:21):
in the same cell, Like what problems does that solve?
Because my brain like more than one nucleus. That just
doesn't make sense. So he was trying to do it
that wasn't working, and so then we moved to Virginia
and he was like, okay, you know what, I'm going
to like outsource to experts. So he hired an engineer
and he was like, all right, engineer, I want you
to make me a really nice maze because the augur
kept like seeping through my legos. It just wasn't working
(26:43):
the way I wanted it. To make me a really
nice maze with a really nice cover. And the engineer
is like, okay, great, I'll do that, but it's going
to cost ten thousand dollars to make an injection molded maze.
And Zach was like, oh, that's a little steep, but
I really think kids would enjoy this, and we're going
to do it. So he pays and he does it. Yeah,
I know, And so he ran it by me and
(27:04):
I was like, I don't know that that's a great decision,
but okay, let's try it.
Speaker 1 (27:08):
This is what happens when you have one family with
two nuclei right yere, different nuclei i making different decisions,
like you know, this slime mold is spending ten k
over here, and that nuclei is objecting to it. You know,
it's like a model of a family.
Speaker 2 (27:19):
That's totally true. I should have known this problem was coming.
So he gets this maze, and you know, we've had
a lot of conversations about like, oh, it's so funny
that Carolina Biological sells slime mold, but they don't sell
these mazes. I wonder why they don't sell these mazes.
And so we get the mazes and then Zach's like, okay,
so now I'm taking this project to the biologist. So
I got a bunch of augur, I got a bunch
of slime molds. I'm like using my sterile technique, and
(27:41):
I'm trying to run these mazes. And it's my job
to write the protocol and the direction so the classrooms
can do this. And so I start doing it and
it's not working. The slimepuwter is not solving the maze
the way it's supposed to.
Speaker 1 (27:55):
So what is it supposed to do? Exactly, Like you
put it in the beginning and you put an ode
at the end. It's supposed to find the shortest path
through the maze exactly, and how could it possibly do that?
Like it's supposed to explore every direction and then eventually
figure out which of the paths is found is the shortest,
and then slowly coalesce onto that. Is that the best
case scenario.
Speaker 2 (28:14):
So that's what we thought was supposed to be happening.
And so I contacted an expert who works in this field,
and I was like, it's not working for me? Why
is it not working for me?
Speaker 1 (28:23):
Meaning what were you seeing? Like it just didn't find
the end or found the wrong path, or it just didn't.
Speaker 2 (28:27):
Go anywhere, or it was not finding the shortest path.
I see something like twenty to thirty percent of the
time it would end up at the right path, which
was essentially like random chance. And I contacted a person
who was doing even simpler experiments in their class. But
it was like a peatrit dish and then an oat
in the middle is a starting point and an oat
on one side, and so it should have been very
(28:49):
simple to just like it expands and then it was
supposed to just sort of contract to just be this
short straight line distance. And they were like, oh, yeah,
that experiment never worked, but apparently at always, well maybe
your students are doing something wrong. So I reached out
to this expert and he's like, well, first of all,
the way that it solves it is it's following a
chemical trail, and so the chemical trail needs to be
(29:11):
incredibly easy to detect. So instead of oatmeal, you could
try something that's like creates more chemicals and makes a
more clear path. And I was like, well that's not
how I had been taught that this works. And I
was like, okay, well, what percent of the time, if
I'm doing it right, should I expect it to solve
the maze? Because, like I'm thinking, the answer should be
close to one hundred percent. Based on what people are
(29:32):
saying on Twitter.
Speaker 1 (29:34):
Always are reliable resource. Twitter is basically one big documentary, Right,
you can rely on it?
Speaker 6 (29:39):
Yeah?
Speaker 2 (29:39):
Right. We spent ten k based on Twitter advice. It
was a great choice.
Speaker 1 (29:42):
I cig Twitter in my science papers all the time.
Speaker 2 (29:44):
Oh wow, No, of course it's a good thing. You've
got tenure.
Speaker 1 (29:50):
Anyway, So you're told that these things don't actually solve
the problem. They just follow a trail, which is very
different from like considering all the past to figure out
which is shortest and then coalescing on that one. That's
like they just walked through to the solution.
Speaker 2 (30:02):
Sometimes I'll smell a hot dog, and I'll just walk
towards the source of the hot dog, and it's like,
not that different. That's not impressive that I can do that.
Speaker 1 (30:09):
Can you actually resist hot dogs? Like if you walk
after hot dog, everybody knows you're kryptonite. Now wow, it's
just like.
Speaker 2 (30:18):
I actually can't. I worked at the zoo once and
we switched from all beef hot dogs to all meat
hot dogs. Ooh, and wondering what that downgrade meant put
me off hot dogs because I started thinking about it
too hard. But anyway, well, let's not droll on hot dogs.
So I ask, Okay, if I find the perfect, very
smelly thing that the slime mold can like queue in on,
(30:39):
that's gonna work better than my oats, what percent of
the time should I expect this to work? And they
said thirty or forty percent. That's not great, no, And
that's when I realized. I went back through all the
papers and I was like, oh my gosh, it says
for the slime molds that solved the maize, but they
don't include the number of times the maze wasn't solved,
(31:00):
And so I think a lot of times what's happening
is like these scenarios are set up, and the one
time out of one hundred that the slime mold gets
it close, they're like, WHOA, that's incredible and that's what
makes the news. And maybe I'm missing something, but it
seems to me that, like, maybe under absolutely perfect conditions,
when you replicate things a bunch of times, slime molds
come up with the right answer. But as far as
(31:20):
I can tell, mostly they're following a chemical gradient. Probably
chemical gradients aren't that strong in nature, like as strong
as you're able to make it in these enclosed mazes.
So I am personally not super impressed with slime old
computational abilities. And maybe that's just me being bitter that
we weren't able to make these kits to give to
classrooms and we like tanked all this time and money
(31:41):
on the project. But that is my take on slime
mold computational ability.
Speaker 1 (31:46):
It sounds to me like somebody's got a room full
of monkeys and one of them types of Shakespeare, and
they're like, look, monkeys can tap Shakespeare. Let's make a
meme about it. I mean, is it better than that,
is actually a little bit better than random? Or is
it completely exaggerated.
Speaker 2 (31:58):
I think it is probably a little better than random.
Some of the problems that they're being asked to solve
are really complicated. But I do think it's mostly following
a chemical gradient, which is less interesting than doing computations
about the shortest way to get to a thing or whatever.
But I just feel like the whole answer has been
kind of over sold. And if somebody thinks that I'm
wrong and I've missed something, I would love to hear that,
(32:19):
because actually, we just found out that we have to
make a decision about whether or not we're going to
throw out that injection mold thing.
Speaker 1 (32:25):
You still have it.
Speaker 2 (32:26):
It's in a warehouse somewhere, and they're like, you can
either pay two hundred dollars to get rid of it,
or we can ship it to you on a palette.
And I'm like, I'm a palette. Where am I going
to keep this thing? Let us know if you know
the answer. But like, slime molds are still awesome, those
paths that they're creating that is a single cell with
multiple nuclei. There's also slime molds called dog vomit slime mold,
(32:48):
which you often find in your mulch on moist, warm
summer days and it does kind of look like dog
vomit and it's one of my favorite full of go septica.
And so slime molds are fascinating and we had the
miscategorized for a while. We kind of couldn't figure out
what they were. But I'm not totally convinced that they
are amazing problem solvers.
Speaker 1 (33:09):
Sorry, And are they always single cells? I mean we're
talking about an extended thing, right, It's like this single
cell can be like a meter across. That kind of
blows my mind.
Speaker 2 (33:18):
They have different stages in their life cycle. I think
at other stages they might not be single celled. Not
an expert on these, but at the stage that everybody's
seeing for the maze solving stage, they are a single
solve with a bunch of nuclei.
Speaker 1 (33:34):
And are there other examples of things out there in
nature that can do something similar and that are also
over sold or is there anything out there that actually
can solve this kind of problem in an impressive way
or is biology all just a dank meme.
Speaker 2 (33:49):
I'm reaching real far back here. I watched this really
interesting lecture from a woman who studied crows. So this
isn't like maze solving, but they're super clever. Like if
there was another crow in the room, they would bury
their treat and then when the crow turned around, they
would take the treat out and they'd bury it somewhere else.
So they knew like that bird was watching me and
(34:10):
I want to trick it, and that's not watching now,
So now it's time for me to move where I
hid my cash. Clever, there are very smart organisms. I
think this is just an exciting thing that escaped that
has maybe since been oversold.
Speaker 1 (34:22):
It sounds like the puzzle you really sold was why
Carolina Biological doesn't carry meses in their catalog.
Speaker 2 (34:29):
Exactly that is the puzzle we solved. And so now
we need to find out does Charlie Davidson like answers
that are kind of a bummer? And did I mistakenly
assume that he wanted to talk about slime wolds but
he had another single celled organism in mind. Let's hear
from Charlie and find out.
Speaker 6 (34:48):
Thank you for answering the question, guys, that's exactly what
I wanted to have answered. The computational bitites of slime
molds are no longer impressive to me either, but never mind,
can't win them all. I was hoping it would be
something far more amazing, but it's the way it is,
I guess. Thank you so much, sake. I do believe
we have dog vomit slime mold. In the UK, we
(35:09):
call it, which is brew If it's the same thing.
I'm not sure which name I prefer, but either or
ice codes. Thanks very much, look forward to future podcasts.
Speaker 1 (35:19):
All right, enough about single cell organisms, hot dogs and
slime molds. When we come back, we're going to tackle
another question about space and time and black holes. All right,
(35:45):
we're back, and we are answering questions from the audience.
Questions from people like you. If there's something about the
universe it's never clicked in your mind, or if you've
heard us talk about something that didn't quite make sense
to you, please write to us. We want to follow up.
We want those ideas to connect in your head so
that you feel like you understand as well. We will
answer any questions you send to us to questions at
(36:06):
danieland Kelly dot org, even dating questions. Though we don't
claim any expertise.
Speaker 2 (36:12):
Oh I'm an expert. I did a lot of dating.
But I don't know if anyone wants my advice.
Speaker 1 (36:18):
Well, if they know Zach, that they can evaluate whether
they think that went well for you or not.
Speaker 2 (36:23):
Yeah, it's up in the air.
Speaker 1 (36:26):
TBD. All right. In the meantime, here's a question we
got from Derek in New Hampshire, who's thinking about black
holes and Hawking radiation.
Speaker 4 (36:36):
I was wondering, can a black hole be so massive
that not even Hawkins radiation can escape from its gravitational pull?
Look forward to you and your answer.
Speaker 1 (36:47):
Thanks.
Speaker 2 (36:47):
All right, So this is a great question. We did
a little bit of an intro into black holes as
part of the very first question. Maybe the right place
to start is what is Hawking radiation?
Speaker 1 (36:59):
Yeah? Great, So Derek's basically asking about the glow that
we think black holes might make. We talked in the
earlier question about what black holes are. They are regions
of space time that are so bent, so deformed, that
space is now only pointing inwards. So you shine a
flashlight inside a black hole, it's only going to go
(37:19):
towards the center. There's no path out from behind the
event horizon. And that's a description of a black hole
that comes from general relativity it's Einstein's theory that says
space gets bent and the space tells matter how to
move and all this kind of stuff. But we know
that general relativity can't be the final story of the
universe because it's not compatible with the other story we
have about the universe, which is quantum mechanics. And in particular,
(37:41):
Einstein's theory of black holes predicts that they're totally black,
that if you look at a black hole, there's no glow.
It's not emitting anything, No light comes off of the
black hole. But if you do try to account a
little bit for quantum mechanical effects, and this is what
Hawking did, it predicts something different. It predicts that black
holes aren't not actually totally black, that they glow very
(38:02):
faintly with this radiation he called, of course, Hawking radiation.
Speaker 2 (38:07):
He named it after himself. Isn't someone supposed to do
that for you?
Speaker 1 (38:12):
He actually worked it out with a student of his.
But yeah, it's called Hawking radiation and not Hawking Beckenstein radiation.
Speaker 2 (38:18):
The next wasp by discover is gonna be Wienersmith's wasp
do it of course.
Speaker 1 (38:23):
Okay, this is really a very impressive bit of physics.
It's like an end run around a bigger problem. The
biggest problem in modern physics right now is like, how
do we reconcile quantum mechanics, which tells us that like
stuff doesn't have a specific location, it can be here
or it can be there. And general relativity, which tells
us like space gets bent based on where stuff is,
(38:44):
and general relativity can't handle if stuff doesn't have a
specific location, Like if the particles may be here and
maybe there is, space may be bent here and maybe
bent there or partially bent here, partially bent there. Nobody
knows how to bring these two things together, which is
what you have to do if you want, I want
a theory of general relativity that's consistent with quantum mechanics.
Nobody knows how to do that. Big question, lots of
(39:06):
Nobel prize is waiting. But what Hacking did was like
an end run around that. He's like, can't figure out
the big problem, but maybe I can sort of chip
away at it a little bit. So he found a
little trick that let him think about what happened to
quantum fields near an event horizon, and his trick let
him make this prediction that black hole should glow a
little bit.
Speaker 2 (39:26):
Can you remind me what an event horizon is?
Speaker 1 (39:29):
Right? Thank you? An event horizon is what we think
of is like the edge of the black hole. Inside
the event horizon, everything is trapped forever. Outside the event horizon,
you're still free. So you can approach a black hole,
be near the event horizon, and then escape and go
back to your planet and live a happy life. If
you cross the event horizon, you're in the black hole forever.
I think there's also a lot of confusion out there
(39:49):
about hawking radiation and what it means and how to
think about it, because I've said that we don't understand
how particles are affected by really strong gravity, And the
typical story you hear is that hawking radiation comes from
particles being created near the event horizon, like particle antiparticle
pairs popping out of the vacuum and one falls into
(40:11):
the event horizon and the other doesn't. And so to
do that calculation, it feels like you'd need to understand
how gravity works for particles. Well, the thing is, that's
not how hawking radiation works. That's the well worn pop
side cartoon version of it, but it doesn't actually make
any sense. I mean, virtual particles can't be treated like
(40:31):
real particles. They're not real particles. You shouldn't think of
the vacuum as like filled with actual particles that can
fall into black holes. And we don't know how to
do those calculations for gravity of particles. Instead, what Hawking
did was take a very different approach. He just said,
what happens to quantum fields if there's a discontinuity in space,
(40:51):
if there's an event horizon, how do I solve the
mathematics of a quantum field near an event horizon? And
what he found was the only way to make the
math work for quantum field near an event horizon was
to have an outgoing wave of radiation, and that's what
he interpreted as Hawking radiation. He doesn't have a microscopic
particle picture of Hawking radiation. What's happening to individual particles?
(41:14):
We don't know how to do that, but we do
know that quantum mechanics says, if there's an event horizon
in space, then your quantum fields have to radiate. And
the really cool thing about this is that you don't
need a complete solution to quantum gravity to attack it.
In this way. This is really Hawking's brilliance of finding
a sort of an end run around having to have
the whole picture and still getting this one result from
(41:36):
this mathematical trick. And there's another beautiful angle to this
to make it a little bit more satisfying. Even though
you can't think about the individual particles and how they're
affected by gravity, you can think about hawking radiation like thermodynamically.
The way Hawking thought about it and his student Bekenstein
was that black holes eat information, black holes eat entropy. Right,
(41:58):
all the disorder in the universe into a black hole.
Is it decreasing? Is it violating the second law of thermodynamics.
They showed that on one hand, you can think about
it mathematically quantum fields radiating energy near an event horizon,
But you can also think about it thermodynamically, meaning that
black holes, if they have information, if they have entropy,
they should have temperature. And if they have temperature, then
(42:20):
they glow like everything else in the universe that has temperature.
I glow, you glow, the sun glows. Things glow based
on their temperatures. Hotter things glow with higher frequency, colder
things glow with lower frequency. More infrared hot things glow
in like the X ray and the ultraviolet. So it
turns out you can model black holes as if they
(42:41):
are black body radiators, things that glow just based on
their temperature. Of course, they're extraordinarily cold, tiny, tiny temperatures.
And the weird thing is that as a black hole
gets bigger, it gets more massive, it actually gets colder
and it glows more dimly. So smaller black holes glow
more brightly and evaporate more quickly, and larger black holes
(43:04):
glow more dimly because they're colder. So that's another fun
way that you can think about hawking radiation that helps
you sort of get a mental picture of it.
Speaker 2 (43:12):
Okay, and then one more follow up question. So when
we've talked in the past, we've said that quantum mechanics
and general relativity they don't make the same predictions, But
usually that doesn't matter because any question that you have
usually just requires you to think in one of those terms.
That's right, Why with black holes, is it important to
(43:32):
understand both of them?
Speaker 1 (43:34):
Yeah, great question. Usually you can ignore general relativity when
you're doing quantum mechanics because particles have almost no mass
and so they hardly bend space, their gravity is basically irrelevant.
Usually you could ignore quantum mechanics when you're doing general
relativity because you're dealing with big masses like planets, and
for planets, the quantum mechanical effects a'll average out to zero,
so usually you could ignore one or the other. When
(43:56):
you're dealing with black holes, you're dealing with very short
distances or very very strong gravity. So now you want
to know the answer to like what happens to a
particle near the edge of an event horizon. You have
like very very strong gravity enough to pull on a particle,
and you want to know what's going to happen to
my electron? Is going to go this way? Or is
it going to go that way? Or if it splits
into other particles, what happens to it. Now you want
(44:17):
to answer questions about the gravity of particles, you need
to be able to include the effects of gravity and
to be able to describe that particle as a quantum
mechanical object, So you need both. Usually you don't care
about the gravity on individual electron, but if you want
to understand things like Hawking radiation, what happens to a
particle near the event horizon? You need the answers to those.
Speaker 2 (44:37):
Okay, so let's suggest black holes. If we could understand them,
that might be the way that we merge our understanding
of those two things.
Speaker 1 (44:43):
Oh. Absolutely, if we could see inside an event horizon,
we would know the answer to how to unify quantum
mechanics and gravity, because we would see is there a
singularity like general relativity predicts and quant mechanics says it's impossible,
or is there something else weird and fuzzy? But of
course we can't so we know the answer. It's there,
but it's frustratingly hiding behind the veil of the black hole.
(45:04):
The Derek's question was basically, could you make a black
hole so massive that even its hawking radiation can't escape?
So here you have a black hole and its emitting radiation.
Could it suck at that back in? Could the hawking
radiation get trapped by the black hole? The answer is,
we don't really know, because what you're asking requires us
to be able to think about the gravity on particles
(45:26):
near a black hole, and we just don't know how
to do that right because we don't know how to
think about gravity for things where we don't have a
way to describe their location exactly where they are through
space and time. General relativity is basically a classical theory.
It assumes that everything has a location and momentum, and
that can be well defined and you can do those calculations.
So short answer is, Derek, we don't know. The best
(45:47):
answer though is probably not. Hawking's calculations suggest that black
holes glow outside of the event horizon. Basically, what he
did in his calculation is figure out what happens to
a quantum field near an event horizon, and his solution
suggests there has to be outgoing radiation, and that radiation
is past the event horizon. So even if the gravity
is very very strong, it's past the event horizon, which
(46:09):
means technically it can still escape. That's the definition of
the event horizon. So if it couldn't escape, it would
be within the event horizon. But hawking radiation is always
emitted past the event horizon, so probably it's.
Speaker 2 (46:22):
Free, all right. So Derek, we want to know if
that explanation was satisfying. So we've reached out to Derek,
and here's what he said.
Speaker 1 (46:31):
You did.
Speaker 7 (46:31):
You an excellent job at it, answering the question as
best as you could I ever want to have a
big fear of missing out? And I can only hope
that technology will allow us to have the answers for
these types of questions.
Speaker 1 (46:44):
Thank you.
Speaker 2 (46:44):
Okay, so that's it for today. Thank you so much
to Barima and Charlie and Derek for sending in their questions.
We hope to get more questions. Actually, we already have
a stack ready for our listener questions number two, So
if you send your questions, be patient. We are going
to get to all of them, and we really appreciate
your questions. Can't wait to hear from you. Send us
(47:05):
emails at questions at Danielankelly dot org.
Speaker 1 (47:09):
Because it's not just our curiosity that drives sigence forward,
it's yours. It's the reason we're doing it. It's collective
curiosity of humanity is why we have science. So thanks
everyone for pushing knowledge forward.
Speaker 2 (47:28):
Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We
would love to hear from you, We really would.
Speaker 1 (47:34):
We want to know what questions you have about this
Extraordinary Universe.
Speaker 2 (47:39):
We want to know your thoughts on recent shows, suggestions
for future shows. If you contact us, we will get
back to you.
Speaker 1 (47:46):
We really mean it. We answer every message. Email us
at Questions at Danielankelly.
Speaker 2 (47:52):
Dot org, or you can find us on social media.
We have accounts on x, Instagram, Blue Sky and on
all of those platforms. You can find us at and
K Universe.
Speaker 1 (48:02):
Don't be shy, write to us h
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Kelly Weinersmith
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