December 31, 2024 • 23 mins
Daniel and Katie answer a question about building super duper long structures in space
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Speaker 1 (00:07):
So, Daniel, you do a lot of cooking. What is
the biggest kitchen implement that you have?
Speaker 2 (00:15):
Do We measure kitchen implements by size. Now is the
biggest one? The most important?
Speaker 1 (00:21):
It is to me, I got one giant ladle and
that is the most important. What is let's talk about
sheer volume? What takes up the most space for you?
Speaker 2 (00:31):
Well, actually, we went out and bought a huge soup pot.
Last time, we made soup for about one hundred people.
Speaker 1 (00:37):
One hundred people for dinner. That's a lot.
Speaker 2 (00:41):
Yeah. Well, you know, we were out celebrating solstice and
you got to go a little crazy on the solstice.
So we had one hundred people over for sit down
dinner and we made a lot of soup.
Speaker 1 (00:50):
I would rather burn my kitchen down in a ritualistic
bonfire than do one hundred sets of dishes after that.
Speaker 2 (01:00):
That sounds like a great way to celebrate the solstice. Actually,
kitchen bonfire.
Speaker 1 (01:04):
Kitchen effigy. There we go, No more washing dishes.
Speaker 2 (01:07):
Hooray, it's the solstice magic. Hi. I'm Daniel. I'm a
(01:28):
particle physicist and a professor a uc irvine and I'm
not into astrology, but I do love the Solstice.
Speaker 1 (01:34):
I am Katie Golden. I host podcast on animal behavior
called Creature Feature, and I am super duper into Solstice
magics such as logs in the house and putting stones
up such that they make interesting shapes and the light
(01:59):
hits them in just such a way.
Speaker 2 (02:02):
M I see you're building Katie hinge.
Speaker 1 (02:04):
Katie hinge. You know, Okay for the summer Solstice one,
I actually did talk about Britta Boyne, but I also
want to talk about how there's a wood hinge as
well as the stone hinge. And the word hinge it
actually comes from the idea of a thing hanging like
a hinge hanging. So stone hinge is like hanging rocks,
(02:28):
and wood hinge is another ancient people's way of creating
basically a annual sun dial, and that was made out
of wooden timber.
Speaker 2 (02:41):
I just always thought they were trying to hinge their bets.
I was thinking about starting a hinge.
Speaker 1 (02:46):
Fund, you know, Oh my god, Well we do need
to teach Daniel about the difference between a hinge and
a hedge.
Speaker 2 (02:56):
Well could you have a hedge hinge?
Speaker 1 (02:57):
Uh? You know what, It's never been done as far
as I know in gardening science, but that never doesn't
mean never.
Speaker 2 (03:05):
Well, okay, how about a biology one that a hedgehog
hinge hedgehog hinge.
Speaker 1 (03:09):
Well, you know, maybe there's a hedgehog hinge for hedgehogs
looking for love.
Speaker 2 (03:14):
All right, we'll hedge our bets until we get there.
But anyway, welcome to the podcast Daniel and Jorge Explain
the Universe, a production of iHeartRadio in which we do
not hedge our bets. We go all in on trying
to understand how the universe works and explain it all
to you. We tackle the biggest questions, from the very
nature of the universe to the smallest questions about quantum
particles and the fundamental nature of space and time and
(03:38):
everything in between, including how to get your hedgehogs out
of your hinge.
Speaker 1 (03:42):
So there is a question I always get about hedgehogs,
and it is how do they reproduce? And my answer
is very carefully, that's a.
Speaker 2 (03:54):
Very pointed answer, Katie. And people have questions about the universe.
They about hedgehogs, They want about quantum particles, they wonder
about quantum hedgehogs, they wonder about hinges and what ancient
people saw in them. They wonder what the solstice means,
and they wonder what's going on between us and distant stars.
And that's all part of doing physics. You don't have
(04:14):
to be a professional academic to be a physicist. You
just have to wonder about the nature of the universe
and then share that curiosity with everybody else, and we
hope you share it with us. If you have a
question about how the universe works, and you can find
an answer on Google or chat, GPT or your friendly
neighborhood physicists, please write to me to questions at Daniel
(04:34):
and Jorge dot com. We will answer it. Everybody gets
an answer in their inbox, and sometimes we take an
answer and put it right here on the podcast, also
because we've been missing you and we wanted to hear
from you again.
Speaker 1 (04:47):
So ninety nine percent of a part of cul physicists
job is asking the right questions and one percent is
you know, math or whatever.
Speaker 2 (04:58):
And this is also got to be rooting there for NAT.
Speaker 1 (05:00):
Napping is crucial, right right, And like a little bit
of grant writing.
Speaker 2 (05:05):
Occasionally, and so on today's episode, we'll be answering listener questions.
Winter Solstice Edition, Happy holidays and New Year and Solstice.
To everybody out there who celebrates whatever it is you celebrate. Today,
we're going to be celebrating my answering a really fun
(05:27):
question from a listener, A question he thought of while
he was in his backyard shed, maybe building his own hinge.
Here's the question from Alex.
Speaker 3 (05:37):
Hi, guys, I was working in my backhout on my shed,
and I was using a metal crowbar to help out
one day when I just realized holding it how strong
it was. So my question that came to me was,
what is actually the longest physical possible crowbar made of
metal that could exist in space? Is it possible that
(06:06):
you could build one? One could exist that's long enough
to stretch between stars, especially if you didn't have to
worry about adding to its length with unlimited supplies, and
if it was nowhere near any other gravitational objects. What
would the ramifications be of having it like a crowbar
where one end was light hours away from the other
(06:26):
or even light years away from the other. It seems
a bit weird to travel light speed and not get
from one end to the other on one particular object.
Speaker 1 (06:36):
Thank you, So you know I have a similar question
but once I just saw a crow bar on the ground,
I think there were some people working on something like
a manhole or something sort of nearby. But also I
wondered if the world operates by video game rules, which is,
if you find a crowbar, is that yours? Now? Do
(06:57):
you pick it up and put it in your inventory?
Or is that still stealing?
Speaker 2 (07:01):
I don't know. Maybe the world operates by checkof rules.
If you find a crowbar in act one, then you're
gonna have about to break into something with it in
Act three.
Speaker 1 (07:09):
I mean that is just video game rules.
Speaker 2 (07:11):
Also exactly exactly. I used to play like King's Quest
back in the day, and every time you found like
a weird magic rap mushroom, you put it in your
back pocket because you knew you were going to need
it to solve some puzzle later on.
Speaker 1 (07:24):
Get ye bucket. You're gonna need that bucket for the
dragon at the end of the.
Speaker 2 (07:28):
Game, exactly, and you can't go back, So get the
bucket now. And Alex is wondering about like the practical
limits of how big we could build something like, could
you build a crowbar that's long enough that you can
use it to like poke people on other planets. That
that's pretty crazy, thought, Alex.
Speaker 1 (07:45):
It's interesting, right, because sure you could have like a
large object, but the bigger it gets. Like, there's a
lot of questions here, right, we need to know about
a what are crowbars made out of? Steel? Iron? Steal?
And so it's like, I guess a lot of it
is basically the strength, like the steal, you know, the
(08:09):
the what steals made out of? How that would work?
But also you know how even if it's made out
of any material, right, Like let's say crobar made out
of whatever material, the strongest, hardest material you could get, Like,
is there a limit to the size of physical objects
in the universe before some wacky starts happening?
Speaker 2 (08:31):
Yeah, this is really fun And there's a really important
lesson here about how we do physics anyway, because an
important sort of often implicit step that we don't talk
about when we do physics is building a simplified model
of the universe. Like you want to answer a physics question,
you know, like a piano is falling from a window.
(08:52):
Is you going to squish that little doggie?
Speaker 1 (08:54):
No?
Speaker 2 (08:55):
Oh no, I hope the answer is no. But to
answer that physics question, what you have to do is
simplify at first. Because you don't care about a lot
of the details. You don't care about the color of
the piano, you can probably ignore the crosswinds. You build
a simplified model that just contains the information necessary to.
Speaker 1 (09:10):
Answer the question, like the breed of the dog for example.
Speaker 2 (09:14):
Yeah we don't care, I mean we care, but it
doesn't change the answer. And so the trick there is
to make a model that's simple enough that you can
actually answer it because you've included all the details of
all the quantum particles and be intractable, but is sophisticated
enough that it still provides a realistic answer. That's the
sweet spot for doing physics. And the interesting thing is
that that's a different model in every scenario. You can
(09:36):
ignore the winds in this case, but if you're solving
a different problem like what's going to happen to this
leaf and a tornado, you can't ignore the winds. So
every time you solve a physics problem, you need to
ask yourself, am I including the right assumptions or the
assumptions I'm making going to ruin it? And so I
run into this all the time with these very long
space rods.
Speaker 1 (09:56):
Aly.
Speaker 2 (09:56):
It turns out Alex is not the only person to
think about really long rods up a lot, because people
have this idea that a rod is sort of like
infinitely rigid. Like if I'm across the room from you
and have a dowel like a wooden stick, if I
push it, then you're gonna feel me pushing it. You're
holding the other end, you're gonna feel it. And people
imagine that sort of happens instantaneously, that if I push
(10:17):
on the stick on one side, you feel it instantly.
And that's mostly true, and for basically every problem you're
going to solve here on Earth, that's basically the case,
because the information travels very, very fast. But then people wonder,
all right, what if I take a rod and I
build it so it's like four light years long, and
I stretch it from here to Alpha Centauri and some
alien is holding the other side. Can I tap on
(10:39):
my side and use that to communicate faster than the
speed of light. That's a very common question I get,
And the answer is obviously no. You can't break special
relativity with a dowel that's four light years long.
Speaker 1 (10:52):
Even dowels have their limits.
Speaker 2 (10:54):
I guess yeah, And the reason is that you've broken
the assumptions. Down here on Earth, it works to assume
whom Yeah, The information travels instantly. That when you push
one side of the dowel, the other side moves instantly.
But that doesn't work anymore when the dowel's really really long,
because the time it takes now matters, because a dowel,
even here on Earth, doesn't transmit information instantly. What happens
(11:16):
when you push on one side of the dowel is
that you don't immediately move the other side. You push
on one side and it moves the layer of molecules
that are next to the edge, which you meant the
next layer, which moved the next layer, which moved the
next layer. Because a dowel is not infinitely rigid, it's
like a very stiff version of a tube of water
or like a string. You're pushing on it and there's
(11:36):
a wave of information that travels down the dowel. So
here on Earth, you push on one side of the dowel,
the other side moves very shortly afterwards, but not instantly.
It takes time for that information and move down the dowel. Now,
when your Dowel is four light years long. That time
is no longer something you can ignore. It plays a
big part in how long it takes for the information
(11:57):
to get there. And if you ignore that, then you
violating special relativity. And it seems like you could send
information to the stars faster than the speed of light,
which of course you can't.
Speaker 1 (12:06):
This is actually the same problem from a biological perspective
of having like a giant brain, right, could you have
an enormous brain that could like communicate instantly, right, like
some galaxy sized brain. And the problem is that the
way our brains work in the same way that you
talked about, how like the molecules have to push on
(12:29):
the other molecules, like our brain is all physics based.
Our whole bodies are basically a big Rubok Goldberg machine
of molecules bonking into other molecules, which creates things like thought.
And so if you have a say, a giant enough brain,
the time it would take to like have a single
thought would be incredibly slow. So the bigger the brain,
(12:53):
the more galaxy size the brain, actually the slower it
would take to have a.
Speaker 2 (12:58):
Thought, Yeah, exactly. And so if you're ignoring that when
you're just thinking about a small brain. You can no
longer ignore that in a large brain. So the lesson is,
when you're doing physics, you have to always think about
what are the assumptions we're making and are those assumptions
still valid for this scenario. In the case of the
like five light year long rod, if you assume instantaneous
(13:18):
motion from one side to the other, then you're assuming
special relativity is broken. So you can't then go and say, oh, look,
this rod breaks special relativity. Well, you assume to is
broken and that's why you broke it. And so there's
a lot of unpacking of those assumptions in these questions.
But Alex's question is a little bit different. He's not
trying to communicate with aliens. He's just trying to build
a really long rod, and he's wondering, like how big
(13:39):
could you make it? Anyway? And I think that's exactly
what he's digging into, Like what would break down? What
assumptions we make about building long rods would break down
if we try to make one that's like a light
year long, Which is a really.
Speaker 1 (13:51):
Cool question, yeah, because I mean there's a lot of
things that we could say, like on Earth, right, Like,
we could try to build a really long crow bar
and at a certain point it could collapse under its
own weight. But if something's in space, we'd have to
figure out what kinds of forces or how gravity would
be acting on something in a way that's different from Earth, right, Like, yes,
(14:15):
you can. You know, it's like have you ever you
know whiteboard pins? Like you create a big old lightsaber
out of whiteboard pins and at a certain point there's
too many and it collapses. But that's all using Earth physics.
So you could make a much longer whiteboard pin lightsaber
out in space because gravity is not impacting it in
(14:39):
the same way that it is on Earth. But then
once you get big enough, right with this pin dowel
or iron crowbar or whatever it is, something's happening. And
this is where I would like you to talk.
Speaker 2 (14:52):
Yeah, exactly. So let's take this question out into deep space.
And the first thing the wonder is like, well, what's
the biggest thing that we'd built in space so far?
And that's the International Space Station. It's not that impressively long,
it's about thirty six meters long, but you know, it's
not very far out in space, and they're not trying
to build something super duper long. I think the longest
(15:13):
thing that's ever actually been in space, it's more like
a kilometer. They build a space tether, which is like
a really long wire that you dangle from a spaceship
to try to like generate electrical current or to learn
to steer using mechnetic fields. So, like a kilometer long's
the biggest thing that we've ever put into space. But
again that's also just the near Earth orbit. So let's
(15:34):
go deeper out into space and try to build something
that's really long and think about the forces involved. Like
when you build a rod at a steel or even
a dowel out of wood or whatever, how are you
actually building that thing. Usually we ignore it and just say, oh,
it's some smooth, continuous substance. But if you zoom in,
the reason it takes time to propagate information along it
(15:56):
is the same thing that's holding it together, which is
the forces between those molecules. All of these objects in
the end are like a mesh of modules. Yet you
have these little bits of matter tied together by forces
to build something larger, and it's those forces that transmit
the information also limit how big something can get right
and so out into deep space. What is the thing
(16:16):
that's limiting us. Well, those forces can work. They can
tie something together basically infinitely, there's no limitation there. You
can just keep adding layers and layers and layers to
your rod. The thing that's going to keep you from
building that rod light years long or infinitely long in
the end, are going to be the gravitational effects, residual
as they are, and the nature of space and time itself.
(16:38):
But let's first talk about the gravitational effects. So one
effect are tidal forces. So you say, well, let's be
out between the stars. AX is actually talking about something
which stretches between the stars. You have like one end
at one star and the other end at another star.
And if you have something that's like five light years long,
you can't have it that far away from stars because
it's going to be big enough. There's always going to
(16:59):
be some nearby. And remember that gravity does more than
just pull on things. It can actually pull things apart.
These are called tidal forces. And for example, if you're
near a black hole, then your head can have a
different gravitational tug on it than your feet, and that
can effectively tear you apart. Like, if the black hole
is pulling on your feet harder than it's pulling on
(17:19):
your head because your feet are a little bit closer,
then it's going to pull you apart because its gravity
is really really strong. But if you're really really long,
then you don't need strong gravity to have tidal forces.
Because if one end of this rod is closer to
the star then the other end, and the rod is
really really long, that's going to be a very large
difference in the gravitational force from one end of the
(17:41):
rod to the other, and that star is going to
tear it apart. Even if the star doesn't have really
powerful gravity like black holes, the sheer length of the
rod makes the tidle forces very significant.
Speaker 1 (17:51):
I see. So you can't span a doll from one
start to the other because of the same title forces
that spaghetifies you in a black hole. But what if
you took away the stars? Right? Like, could you get
a like infinity rod if you took away stars and
(18:14):
just had it existing on its own in space without
hitting anything?
Speaker 2 (18:19):
Yeah? Right, so's get rid of the other gravity, and
you still have the issue of the gravity of the
rod itself. Right, You can't build an infinitely massive rod,
because eventually that thing is going to have its own
self gravity. It's going to collapse into a black hole. Like,
you can't just make a blob of metal and keep
adding blobs of metal to it and make it as
big as you want, because it's going to start collapsing.
(18:41):
This already happens for things like planets, like the Earth
is about the largest rocky planet you can make. You
can add more rock to it, but that's going to
mean more gravity, and it's just going to compress the
Earth further. So as you add more mass to the Earth,
it doesn't get any bigger, it just gets denser. And
eventually you keep adding mass, you're going to end up
up with a black hole. And so there is a
(19:02):
limit to how large and how massive you can make
something before it collapses into a black hole. So something
self gravity will also limit how large you can make
an object out of practical stuff like steel or wood.
Speaker 1 (19:15):
Okay, so what about a really thin rod? Now stay
with me. What if you have a rod that is
like one atom per unit, right, it is like one
atom thick, and then you just stack a bunch of
atoms into this very long rod. Would that still be
(19:35):
something that would at a certain point start to collapse
in on itself because of gravity, Or am I already
breaking some laws of physics by trying to create a
one atom diameter rod.
Speaker 2 (19:50):
Now you could probably make a carbon nanofiber eventually that's
like one atom thick and super duper long. I don't
think it's a technical problem there. But what you're going to
run into is a problem with a nature space and time.
And if you can get rid of gravity the nearby
stars and effectively get rid of the self gravity by
making this thing really really lightweight, you're going to run
into dark energy. So in short distances, like the size
(20:13):
of our Solar system of the size of our galaxy,
the dominant force is gravity. It holds things together, it
shapes things, it determines the nature of our universe. But
over very large distances, gravity gets weaker. Right, the further
you are away from something, the weaker it's gravity is.
And at those distances something else takes over, which is
dark energy, meaning the expansion of the universe itself. Remember
(20:35):
that everywhere in the universe is expanding. Take any arbitrary
chunk of space as time goes on, That space is
getting larger. It's making new space. So between the Earth
and the Sun, for example, new space is being made,
but the gravity of the Earth and the Sun overpowers it.
Between our galaxy and the neighboring galaxy, new space is
being made, but again the gravity overpowers it. But eventually,
(20:58):
between clusters of galaxy, dark energy becomes more powerful because
you have more of these cubes of space and each
one is expanding, so that adds up and gravity gets
very very weak. So take Alex's super duper long, infinitely
thin rod. Eventually it's going to be so long that
dark energy is going to tear it apart. It's going
(21:18):
to be creating new space between those atoms faster than
those atoms can recover and bind themselves together. So you
can get spaghettified by space and time.
Speaker 1 (21:28):
All right, So we cannot make an infinity rod. Unfortunately,
do we know, like how big something can get before
the expansion of the universe starts to break it apart.
Speaker 2 (21:42):
It's gonna be really really big. And remember that nearby
galaxies are millions of light years away, and dark energy
only really dominates between clusters of galaxies, So we're talking
hundreds of millions of light years. So if you can
overcome the gravity of nearby stars and overcome tidal forces
completely and overcome collapsing due to self gravity, then you
(22:05):
could still build something that's like hundreds of millions of
light years long. So that's pretty good, you know what.
Speaker 1 (22:11):
That sounds great. I'm gonna write a grant for U
to get started building on the biggest spaghetti that one could.
Speaker 2 (22:20):
Make, exact spaghetti simo.
Speaker 1 (22:24):
Yeah, I bet Italy's government would fun.
Speaker 2 (22:26):
That's gonna write, yes, in honor of the winter solstice.
I think that's a great idea. All right, Well, thank
you very much Alex for thinking big and wondering about
how far we can push our concepts of distance and
structure and space and time. Really fun way to explore
all of those different factors, and really appreciate everybody out
(22:47):
there who's thinking about the universe and wondering about it,
and who's brave enough to write into their favorite Internet
physicists to look for some answers. If you'd like to
see my email in your inbox, write to me two
questions at Daniel and Jorge dot com. I'd sure love
to hear from you. Thanks very much, Katie for pushing
the boundaries of space and time and humor today.
Speaker 1 (23:06):
And thank you for signing on to my petition for
Universe's longest spaghetti.
Speaker 2 (23:13):
Funded funded funded. All right, Thanks everyone for listening, and
tune in next time for more science and curiosity. Come
find us on social media where we answer questions and
post videos. We're on Twitter, This, Org, Instant and now TikTok.
Thanks for listening, and remember that Daniel and Jorge Explain
(23:35):
the Universe is a production of iHeartRadio. For more podcasts
from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever
you listen to your favorite shows.
So, Daniel, you do a lot of cooking. What is
the biggest kitchen implement that you have?
Speaker 2 (00:15):
Do We measure kitchen implements by size. Now is the
biggest one? The most important?
Speaker 1 (00:21):
It is to me, I got one giant ladle and
that is the most important. What is let's talk about
sheer volume? What takes up the most space for you?
Speaker 2 (00:31):
Well, actually, we went out and bought a huge soup pot.
Last time, we made soup for about one hundred people.
Speaker 1 (00:37):
One hundred people for dinner. That's a lot.
Speaker 2 (00:41):
Yeah. Well, you know, we were out celebrating solstice and
you got to go a little crazy on the solstice.
So we had one hundred people over for sit down
dinner and we made a lot of soup.
Speaker 1 (00:50):
I would rather burn my kitchen down in a ritualistic
bonfire than do one hundred sets of dishes after that.
Speaker 2 (01:00):
That sounds like a great way to celebrate the solstice. Actually,
kitchen bonfire.
Speaker 1 (01:04):
Kitchen effigy. There we go, No more washing dishes.
Speaker 2 (01:07):
Hooray, it's the solstice magic. Hi. I'm Daniel. I'm a
(01:28):
particle physicist and a professor a uc irvine and I'm
not into astrology, but I do love the Solstice.
Speaker 1 (01:34):
I am Katie Golden. I host podcast on animal behavior
called Creature Feature, and I am super duper into Solstice
magics such as logs in the house and putting stones
up such that they make interesting shapes and the light
(01:59):
hits them in just such a way.
Speaker 2 (02:02):
M I see you're building Katie hinge.
Speaker 1 (02:04):
Katie hinge. You know, Okay for the summer Solstice one,
I actually did talk about Britta Boyne, but I also
want to talk about how there's a wood hinge as
well as the stone hinge. And the word hinge it
actually comes from the idea of a thing hanging like
a hinge hanging. So stone hinge is like hanging rocks,
(02:28):
and wood hinge is another ancient people's way of creating
basically a annual sun dial, and that was made out
of wooden timber.
Speaker 2 (02:41):
I just always thought they were trying to hinge their bets.
I was thinking about starting a hinge.
Speaker 1 (02:46):
Fund, you know, Oh my god, Well we do need
to teach Daniel about the difference between a hinge and
a hedge.
Speaker 2 (02:56):
Well could you have a hedge hinge?
Speaker 1 (02:57):
Uh? You know what, It's never been done as far
as I know in gardening science, but that never doesn't
mean never.
Speaker 2 (03:05):
Well, okay, how about a biology one that a hedgehog
hinge hedgehog hinge.
Speaker 1 (03:09):
Well, you know, maybe there's a hedgehog hinge for hedgehogs
looking for love.
Speaker 2 (03:14):
All right, we'll hedge our bets until we get there.
But anyway, welcome to the podcast Daniel and Jorge Explain
the Universe, a production of iHeartRadio in which we do
not hedge our bets. We go all in on trying
to understand how the universe works and explain it all
to you. We tackle the biggest questions, from the very
nature of the universe to the smallest questions about quantum
particles and the fundamental nature of space and time and
(03:38):
everything in between, including how to get your hedgehogs out
of your hinge.
Speaker 1 (03:42):
So there is a question I always get about hedgehogs,
and it is how do they reproduce? And my answer
is very carefully, that's a.
Speaker 2 (03:54):
Very pointed answer, Katie. And people have questions about the universe.
They about hedgehogs, They want about quantum particles, they wonder
about quantum hedgehogs, they wonder about hinges and what ancient
people saw in them. They wonder what the solstice means,
and they wonder what's going on between us and distant stars.
And that's all part of doing physics. You don't have
(04:14):
to be a professional academic to be a physicist. You
just have to wonder about the nature of the universe
and then share that curiosity with everybody else, and we
hope you share it with us. If you have a
question about how the universe works, and you can find
an answer on Google or chat, GPT or your friendly
neighborhood physicists, please write to me to questions at Daniel
(04:34):
and Jorge dot com. We will answer it. Everybody gets
an answer in their inbox, and sometimes we take an
answer and put it right here on the podcast, also
because we've been missing you and we wanted to hear
from you again.
Speaker 1 (04:47):
So ninety nine percent of a part of cul physicists
job is asking the right questions and one percent is
you know, math or whatever.
Speaker 2 (04:58):
And this is also got to be rooting there for NAT.
Speaker 1 (05:00):
Napping is crucial, right right, And like a little bit
of grant writing.
Speaker 2 (05:05):
Occasionally, and so on today's episode, we'll be answering listener questions.
Winter Solstice Edition, Happy holidays and New Year and Solstice.
To everybody out there who celebrates whatever it is you celebrate. Today,
we're going to be celebrating my answering a really fun
(05:27):
question from a listener, A question he thought of while
he was in his backyard shed, maybe building his own hinge.
Here's the question from Alex.
Speaker 3 (05:37):
Hi, guys, I was working in my backhout on my shed,
and I was using a metal crowbar to help out
one day when I just realized holding it how strong
it was. So my question that came to me was,
what is actually the longest physical possible crowbar made of
metal that could exist in space? Is it possible that
(06:06):
you could build one? One could exist that's long enough
to stretch between stars, especially if you didn't have to
worry about adding to its length with unlimited supplies, and
if it was nowhere near any other gravitational objects. What
would the ramifications be of having it like a crowbar
where one end was light hours away from the other
(06:26):
or even light years away from the other. It seems
a bit weird to travel light speed and not get
from one end to the other on one particular object.
Speaker 1 (06:36):
Thank you, So you know I have a similar question
but once I just saw a crow bar on the ground,
I think there were some people working on something like
a manhole or something sort of nearby. But also I
wondered if the world operates by video game rules, which is,
if you find a crowbar, is that yours? Now? Do
(06:57):
you pick it up and put it in your inventory?
Or is that still stealing?
Speaker 2 (07:01):
I don't know. Maybe the world operates by checkof rules.
If you find a crowbar in act one, then you're
gonna have about to break into something with it in
Act three.
Speaker 1 (07:09):
I mean that is just video game rules.
Speaker 2 (07:11):
Also exactly exactly. I used to play like King's Quest
back in the day, and every time you found like
a weird magic rap mushroom, you put it in your
back pocket because you knew you were going to need
it to solve some puzzle later on.
Speaker 1 (07:24):
Get ye bucket. You're gonna need that bucket for the
dragon at the end of the.
Speaker 2 (07:28):
Game, exactly, and you can't go back, So get the
bucket now. And Alex is wondering about like the practical
limits of how big we could build something like, could
you build a crowbar that's long enough that you can
use it to like poke people on other planets. That
that's pretty crazy, thought, Alex.
Speaker 1 (07:45):
It's interesting, right, because sure you could have like a
large object, but the bigger it gets. Like, there's a
lot of questions here, right, we need to know about
a what are crowbars made out of? Steel? Iron? Steal?
And so it's like, I guess a lot of it
is basically the strength, like the steal, you know, the
(08:09):
the what steals made out of? How that would work?
But also you know how even if it's made out
of any material, right, Like let's say crobar made out
of whatever material, the strongest, hardest material you could get, Like,
is there a limit to the size of physical objects
in the universe before some wacky starts happening?
Speaker 2 (08:31):
Yeah, this is really fun And there's a really important
lesson here about how we do physics anyway, because an
important sort of often implicit step that we don't talk
about when we do physics is building a simplified model
of the universe. Like you want to answer a physics question,
you know, like a piano is falling from a window.
(08:52):
Is you going to squish that little doggie?
Speaker 1 (08:54):
No?
Speaker 2 (08:55):
Oh no, I hope the answer is no. But to
answer that physics question, what you have to do is
simplify at first. Because you don't care about a lot
of the details. You don't care about the color of
the piano, you can probably ignore the crosswinds. You build
a simplified model that just contains the information necessary to.
Speaker 1 (09:10):
Answer the question, like the breed of the dog for example.
Speaker 2 (09:14):
Yeah we don't care, I mean we care, but it
doesn't change the answer. And so the trick there is
to make a model that's simple enough that you can
actually answer it because you've included all the details of
all the quantum particles and be intractable, but is sophisticated
enough that it still provides a realistic answer. That's the
sweet spot for doing physics. And the interesting thing is
that that's a different model in every scenario. You can
(09:36):
ignore the winds in this case, but if you're solving
a different problem like what's going to happen to this
leaf and a tornado, you can't ignore the winds. So
every time you solve a physics problem, you need to
ask yourself, am I including the right assumptions or the
assumptions I'm making going to ruin it? And so I
run into this all the time with these very long
space rods.
Speaker 1 (09:56):
Aly.
Speaker 2 (09:56):
It turns out Alex is not the only person to
think about really long rods up a lot, because people
have this idea that a rod is sort of like
infinitely rigid. Like if I'm across the room from you
and have a dowel like a wooden stick, if I
push it, then you're gonna feel me pushing it. You're
holding the other end, you're gonna feel it. And people
imagine that sort of happens instantaneously, that if I push
(10:17):
on the stick on one side, you feel it instantly.
And that's mostly true, and for basically every problem you're
going to solve here on Earth, that's basically the case,
because the information travels very, very fast. But then people wonder,
all right, what if I take a rod and I
build it so it's like four light years long, and
I stretch it from here to Alpha Centauri and some
alien is holding the other side. Can I tap on
(10:39):
my side and use that to communicate faster than the
speed of light. That's a very common question I get,
And the answer is obviously no. You can't break special
relativity with a dowel that's four light years long.
Speaker 1 (10:52):
Even dowels have their limits.
Speaker 2 (10:54):
I guess yeah, And the reason is that you've broken
the assumptions. Down here on Earth, it works to assume
whom Yeah, The information travels instantly. That when you push
one side of the dowel, the other side moves instantly.
But that doesn't work anymore when the dowel's really really long,
because the time it takes now matters, because a dowel,
even here on Earth, doesn't transmit information instantly. What happens
(11:16):
when you push on one side of the dowel is
that you don't immediately move the other side. You push
on one side and it moves the layer of molecules
that are next to the edge, which you meant the
next layer, which moved the next layer, which moved the
next layer. Because a dowel is not infinitely rigid, it's
like a very stiff version of a tube of water
or like a string. You're pushing on it and there's
(11:36):
a wave of information that travels down the dowel. So
here on Earth, you push on one side of the dowel,
the other side moves very shortly afterwards, but not instantly.
It takes time for that information and move down the dowel. Now,
when your Dowel is four light years long. That time
is no longer something you can ignore. It plays a
big part in how long it takes for the information
(11:57):
to get there. And if you ignore that, then you
violating special relativity. And it seems like you could send
information to the stars faster than the speed of light,
which of course you can't.
Speaker 1 (12:06):
This is actually the same problem from a biological perspective
of having like a giant brain, right, could you have
an enormous brain that could like communicate instantly, right, like
some galaxy sized brain. And the problem is that the
way our brains work in the same way that you
talked about, how like the molecules have to push on
(12:29):
the other molecules, like our brain is all physics based.
Our whole bodies are basically a big Rubok Goldberg machine
of molecules bonking into other molecules, which creates things like thought.
And so if you have a say, a giant enough brain,
the time it would take to like have a single
thought would be incredibly slow. So the bigger the brain,
(12:53):
the more galaxy size the brain, actually the slower it
would take to have a.
Speaker 2 (12:58):
Thought, Yeah, exactly. And so if you're ignoring that when
you're just thinking about a small brain. You can no
longer ignore that in a large brain. So the lesson is,
when you're doing physics, you have to always think about
what are the assumptions we're making and are those assumptions
still valid for this scenario. In the case of the
like five light year long rod, if you assume instantaneous
(13:18):
motion from one side to the other, then you're assuming
special relativity is broken. So you can't then go and say, oh, look,
this rod breaks special relativity. Well, you assume to is
broken and that's why you broke it. And so there's
a lot of unpacking of those assumptions in these questions.
But Alex's question is a little bit different. He's not
trying to communicate with aliens. He's just trying to build
a really long rod, and he's wondering, like how big
(13:39):
could you make it? Anyway? And I think that's exactly
what he's digging into, Like what would break down? What
assumptions we make about building long rods would break down
if we try to make one that's like a light
year long, Which is a really.
Speaker 1 (13:51):
Cool question, yeah, because I mean there's a lot of
things that we could say, like on Earth, right, Like,
we could try to build a really long crow bar
and at a certain point it could collapse under its
own weight. But if something's in space, we'd have to
figure out what kinds of forces or how gravity would
be acting on something in a way that's different from Earth, right, Like, yes,
(14:15):
you can. You know, it's like have you ever you
know whiteboard pins? Like you create a big old lightsaber
out of whiteboard pins and at a certain point there's
too many and it collapses. But that's all using Earth physics.
So you could make a much longer whiteboard pin lightsaber
out in space because gravity is not impacting it in
(14:39):
the same way that it is on Earth. But then
once you get big enough, right with this pin dowel
or iron crowbar or whatever it is, something's happening. And
this is where I would like you to talk.
Speaker 2 (14:52):
Yeah, exactly. So let's take this question out into deep space.
And the first thing the wonder is like, well, what's
the biggest thing that we'd built in space so far?
And that's the International Space Station. It's not that impressively long,
it's about thirty six meters long, but you know, it's
not very far out in space, and they're not trying
to build something super duper long. I think the longest
(15:13):
thing that's ever actually been in space, it's more like
a kilometer. They build a space tether, which is like
a really long wire that you dangle from a spaceship
to try to like generate electrical current or to learn
to steer using mechnetic fields. So, like a kilometer long's
the biggest thing that we've ever put into space. But
again that's also just the near Earth orbit. So let's
(15:34):
go deeper out into space and try to build something
that's really long and think about the forces involved. Like
when you build a rod at a steel or even
a dowel out of wood or whatever, how are you
actually building that thing. Usually we ignore it and just say, oh,
it's some smooth, continuous substance. But if you zoom in,
the reason it takes time to propagate information along it
(15:56):
is the same thing that's holding it together, which is
the forces between those molecules. All of these objects in
the end are like a mesh of modules. Yet you
have these little bits of matter tied together by forces
to build something larger, and it's those forces that transmit
the information also limit how big something can get right
and so out into deep space. What is the thing
(16:16):
that's limiting us. Well, those forces can work. They can
tie something together basically infinitely, there's no limitation there. You
can just keep adding layers and layers and layers to
your rod. The thing that's going to keep you from
building that rod light years long or infinitely long in
the end, are going to be the gravitational effects, residual
as they are, and the nature of space and time itself.
(16:38):
But let's first talk about the gravitational effects. So one
effect are tidal forces. So you say, well, let's be
out between the stars. AX is actually talking about something
which stretches between the stars. You have like one end
at one star and the other end at another star.
And if you have something that's like five light years long,
you can't have it that far away from stars because
it's going to be big enough. There's always going to
(16:59):
be some nearby. And remember that gravity does more than
just pull on things. It can actually pull things apart.
These are called tidal forces. And for example, if you're
near a black hole, then your head can have a
different gravitational tug on it than your feet, and that
can effectively tear you apart. Like, if the black hole
is pulling on your feet harder than it's pulling on
(17:19):
your head because your feet are a little bit closer,
then it's going to pull you apart because its gravity
is really really strong. But if you're really really long,
then you don't need strong gravity to have tidal forces.
Because if one end of this rod is closer to
the star then the other end, and the rod is
really really long, that's going to be a very large
difference in the gravitational force from one end of the
(17:41):
rod to the other, and that star is going to
tear it apart. Even if the star doesn't have really
powerful gravity like black holes, the sheer length of the
rod makes the tidle forces very significant.
Speaker 1 (17:51):
I see. So you can't span a doll from one
start to the other because of the same title forces
that spaghetifies you in a black hole. But what if
you took away the stars? Right? Like, could you get
a like infinity rod if you took away stars and
(18:14):
just had it existing on its own in space without
hitting anything?
Speaker 2 (18:19):
Yeah? Right, so's get rid of the other gravity, and
you still have the issue of the gravity of the
rod itself. Right, You can't build an infinitely massive rod,
because eventually that thing is going to have its own
self gravity. It's going to collapse into a black hole. Like,
you can't just make a blob of metal and keep
adding blobs of metal to it and make it as
big as you want, because it's going to start collapsing.
(18:41):
This already happens for things like planets, like the Earth
is about the largest rocky planet you can make. You
can add more rock to it, but that's going to
mean more gravity, and it's just going to compress the
Earth further. So as you add more mass to the Earth,
it doesn't get any bigger, it just gets denser. And
eventually you keep adding mass, you're going to end up
up with a black hole. And so there is a
(19:02):
limit to how large and how massive you can make
something before it collapses into a black hole. So something
self gravity will also limit how large you can make
an object out of practical stuff like steel or wood.
Speaker 1 (19:15):
Okay, so what about a really thin rod? Now stay
with me. What if you have a rod that is
like one atom per unit, right, it is like one
atom thick, and then you just stack a bunch of
atoms into this very long rod. Would that still be
(19:35):
something that would at a certain point start to collapse
in on itself because of gravity, Or am I already
breaking some laws of physics by trying to create a
one atom diameter rod.
Speaker 2 (19:50):
Now you could probably make a carbon nanofiber eventually that's
like one atom thick and super duper long. I don't
think it's a technical problem there. But what you're going to
run into is a problem with a nature space and time.
And if you can get rid of gravity the nearby
stars and effectively get rid of the self gravity by
making this thing really really lightweight, you're going to run
into dark energy. So in short distances, like the size
(20:13):
of our Solar system of the size of our galaxy,
the dominant force is gravity. It holds things together, it
shapes things, it determines the nature of our universe. But
over very large distances, gravity gets weaker. Right, the further
you are away from something, the weaker it's gravity is.
And at those distances something else takes over, which is
dark energy, meaning the expansion of the universe itself. Remember
(20:35):
that everywhere in the universe is expanding. Take any arbitrary
chunk of space as time goes on, That space is
getting larger. It's making new space. So between the Earth
and the Sun, for example, new space is being made,
but the gravity of the Earth and the Sun overpowers it.
Between our galaxy and the neighboring galaxy, new space is
being made, but again the gravity overpowers it. But eventually,
(20:58):
between clusters of galaxy, dark energy becomes more powerful because
you have more of these cubes of space and each
one is expanding, so that adds up and gravity gets
very very weak. So take Alex's super duper long, infinitely
thin rod. Eventually it's going to be so long that
dark energy is going to tear it apart. It's going
(21:18):
to be creating new space between those atoms faster than
those atoms can recover and bind themselves together. So you
can get spaghettified by space and time.
Speaker 1 (21:28):
All right, So we cannot make an infinity rod. Unfortunately,
do we know, like how big something can get before
the expansion of the universe starts to break it apart.
Speaker 2 (21:42):
It's gonna be really really big. And remember that nearby
galaxies are millions of light years away, and dark energy
only really dominates between clusters of galaxies, So we're talking
hundreds of millions of light years. So if you can
overcome the gravity of nearby stars and overcome tidal forces
completely and overcome collapsing due to self gravity, then you
(22:05):
could still build something that's like hundreds of millions of
light years long. So that's pretty good, you know what.
Speaker 1 (22:11):
That sounds great. I'm gonna write a grant for U
to get started building on the biggest spaghetti that one could.
Speaker 2 (22:20):
Make, exact spaghetti simo.
Speaker 1 (22:24):
Yeah, I bet Italy's government would fun.
Speaker 2 (22:26):
That's gonna write, yes, in honor of the winter solstice.
I think that's a great idea. All right, Well, thank
you very much Alex for thinking big and wondering about
how far we can push our concepts of distance and
structure and space and time. Really fun way to explore
all of those different factors, and really appreciate everybody out
(22:47):
there who's thinking about the universe and wondering about it,
and who's brave enough to write into their favorite Internet
physicists to look for some answers. If you'd like to
see my email in your inbox, write to me two
questions at Daniel and Jorge dot com. I'd sure love
to hear from you. Thanks very much, Katie for pushing
the boundaries of space and time and humor today.
Speaker 1 (23:06):
And thank you for signing on to my petition for
Universe's longest spaghetti.
Speaker 2 (23:13):
Funded funded funded. All right, Thanks everyone for listening, and
tune in next time for more science and curiosity. Come
find us on social media where we answer questions and
post videos. We're on Twitter, This, Org, Instant and now TikTok.
Thanks for listening, and remember that Daniel and Jorge Explain
(23:35):
the Universe is a production of iHeartRadio. For more podcasts
from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever
you listen to your favorite shows.
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