Can you be motionless in space?

Everything is moving and spinning -- is it possible to be totally still in the Universe?

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Episode Transcript

Speaker 1 (00:08):
Hey, we're hey. When did you get up today? How
do you know I got up? I could be recording
this from my bed right now. Thanks for that mental image.
Now I kind of regret asking. And even if I'm
in bed, I'm technically still moving. Really is your bed
on wheels or something, or you have like a flying bed?
That would be exciting, But no, I'm on Earth and
the Earth is spinning right in space and it's also

(00:29):
flying around the Sun. So I'm still moving right? Did
that count? I mean, does your fitbit give you steps forth? Well?
I don't really believe in fitbits. I believe in that bits.
I have one to make one for cartoonists. Hi am

(00:58):
rhand Ma cartoonists and the creator PhD Comics. I'm Daniel.
I'm a particle physicist and a professor. You see Irvine
and it feels like I'm always in motion. Oh yeah,
like your mental gears are always turning or one of
those people that have worked on a treadmill all the time. No,
I definitely do not work on a treadmill. I work
on a chair and I lean way back with a crazy,

(01:19):
ridiculous posture that would make like any ergonomic specialist cringe.
And that's what you mean by motion, that's your workout,
leaning back for a nap. No, I mean that's sort
of always scrambling from one thing to the other, working
on this. Oops, that's late running over here. It feels
like being an adult in today's modern world is always
scrambling from one thing to another. You know what you mean.

(01:39):
But you do know you have a choice there, Daniel,
I could retire early, Yeah, you can. You cannot do
so many things that who would I even be? Man?
Who would I even be? Welcome to existential questions with
Daniel and Jorge, No, but seriously, welcome to a podcast
Daniel and Hojorge Explain the Universe, a production of I
Heart Radio in which we do delve into the deepest

(01:59):
of exist to questions why does the universe exist? How
does it all work? What is our place in it?
How long will it last? How will it end? And
whose fault will it be when it finally goes poof?
In which we dig deep into the very smallest, tiniest
little bits of that universe, asked the basic questions about
how everything works, and explain all of the answers as

(02:20):
far as we know them to you. Yeah, because It
is a confusing and vast universe, and it's a pretty
restless universe. It seems to be always in motion. There's
always something going on in the university because you know,
it's so big, and there's always I don't know, and
exploding stars somewhere. There's planet spinning everywhere, asteroids flying through
the sky. It does seem to be sort of in

(02:41):
slow motion violence. You know, you look out into the
night sky and you just sort of glance at it,
and it seems static. It's not like the stars are
whizzing around in front of your eyes. But you know,
you pay attention, you see the night sky slide by,
and the longer you watch, the more you notice that,
like crazy stuff is happening out there, that the explosions
that take millions of years but are still very dramatic.

(03:04):
So everything up there is actually in motion. We just
sort of live in a tiny little burst of time
where things seem to be stationary. Yeah, and there's not
just a lot of action going on out there. There's
a lot of action inside of us. And in the
smallest of particles, everything is always you know, vibrating or
spinning or quantum spitting or disappearing and appearing at the
same time. Yeah, you're right. Quantum mechanics says that everything

(03:26):
is in motion and has to be in motion, that
nothing can actually come to rest, that nothing in the
end can really have no energy. So the very nature
of our existence seems to be in motion. Yeah, and
it does seem like nowadays live involves a lot of
moving around. You know, it seems like things are spinning
and moving and changing faster than we can you know,

(03:46):
get ahold of it. And so you know, the idea
of resting or being motionless, or you know, just stopping
and not doing anything is it's kind of weird, right,
maybe to a lot of people. Yeah, maybe that. I
think a lot of people did more of that in
this life last year than they're used to. Went to
fewer places, canceled traveling, didn't go to the office as much.
So a lot of people were sort of stuck in

(04:07):
a smaller orbit than they usually are by the pandemic.
But still everybody is still moving. Yeah, it's been kind
of a tough year for everybody, but it's still fun
to kind of think about the universe and all the
things that are going on inside of it, and we
especially like to ask interesting questions in this podcast about
you know, what's theoretically possible and what is theoretically impossible

(04:30):
or what is theoretically nonsensical. That's right, and we're not
the only ones wondering about those kinds of questions. All
of our listeners are out there thinking about the nature
of the universe and what's possible and what their experience
is like in it. And a lot of people right
in with a particular question when they notice that everything
in the universe seems to be moving. Everything is sliding
or spinning or orbiting or zooming through space. And I

(04:53):
think this inspires people to ask this particular question about
whether motionlessness is possible. Yeah, so to be on the podcast,
we'll be tackling the question can you be motionless in space? Now? Daniel,
do you think people are you know, being aspirational with

(05:14):
this question, like how can I be motionless in space?
Or are they asking you think the theoretical question is
is it possible to be not moving at all in
this universe? I don't think anybody is asking a practical question.
I don't think they're trying to develop one of those
like extreme isolation pods where you can float out in
space and have nothing touch you or anything like that.

(05:34):
I think people are pushing the envelopes because they want
to know what's possible. So in that sense, I guess
it's a theoretical question. Just like in our Extreme Universe
podcast episodes, sometimes you learn something about the nature of
space by looking at the extreme situation, asking what's the
fastest you can go or what's the slowest you can go,
what's the hottest something can be, what's the coldest something

(05:55):
can be. So since everything seems to be moving, I
think people are wondering is it even post the all
theoretically for something to be totally at rest? What would
that mean, what would it require? What does it reveal
about the nature of the universe? Right? Yeah, Still I
mean to think that a physicist might ask a practical question.
Sorry about that, but it is a pretty interesting theoretical question,

(06:16):
like can you be not moving? I guess, And do
you think that's more about staying still or a feeling
that you're not moving? Do you know what I mean? Like,
do you think people are asking about is there a
point in the universe that's technically not moving relative to
everything else? Or do you think it means just like,
how can I not have an emotion relative to anything else? Yeah,

(06:36):
I think there's a lot of interesting stuff to unpack
there about like the very nature of what it means
to be in motion, that we're going to have to
dig into, because I think something about this question reveals
that people are thinking about speed in a way that
comes naturally to them on the surface of the Earth,
where it makes sense to talk about what my speed is.
But when you go out into space, things change. Things
are different the same way that like up and down

(06:58):
have a meaning on the surface of the Earth but
don't really make sense anymore out in space. I think
we're going to learn that the whole concept of velocity
is a little bit different than what a lot of
people had in mind. And so this is a great question,
not because the answer is simple and reveals the truth
about the universe, but because the nature of the question
makes you rethink the whole nature of motion. Yeah, and

(07:19):
then you have to ask the follow up question, which
is can you be emotionless in space? After learning the
answer to the first question, I think we know the
answer that it's called the movie gravity. Oh, movie criticism
and physics all in one podcast. Seriously, nobody seems to
have any emotions in the movie. They're all just like stoic,
just trying to not die. I think in space? Can

(07:42):
you be alive in space? That's the question they were asking,
not just standing still because you're dead. But yeah, this
is a pretty interesting question, and so, as usually, we
were wondering how many people out there have thought about
this question and whether or not they have an answer
that they might have thought of. Daniel went out there
into the internet to ask the question, Shan, can you
be motionless in space? That's right, I go out into

(08:04):
the web and beat the bushes for people who are
interested in answering these questions for us. If you are
out there on the internet and have not participated, please
we want to hear your voice, especially if you're from
a location we haven't heard anybody from before. We would
love to hear your voice on the podcast, So please
write to us two questions at Daniel and Jorge dot com.
So think about it for a second. Do you think

(08:25):
it's possible to be motionless in space? Here's what people
had to say. Well, I can be motionless if I
don't move a muscle, So nothing on me would move,
that would qualify as motionless, I guess, But relative to
something else, I would probably never be motionless because everything
else is moving. The Sun is moving around the center

(08:46):
of the galaxy, and the planets around the Sun, everything
else is moving. Even space itself is expanding. So even
if I'm in a point in space and the space
around me is expanding, then the things around me would
be moving along with it as well. So can you
be motionless in space? Yes, if I don't move a muscle. No,

(09:08):
relative to anything else, I don't think you can be
motionless in space. If two bodies are passing by each
other and neither is accelerating, both bodies, from their perspective
would feel that they were standing still and the other
one was moving. It doesn't seem like it, since your
motion would be relative to whatever it was around you.

(09:31):
So even if you're standing still on Earth, the Earth
is spinning and moving around the Sun, And if you're
standing still next to the Sun, it's spinning around the
galaxy and the galaxy is moving. Um, but maybe it's
possible to just stick still with respect to the the
fabric of space. Well, if I'm not moving at all, yes,

(09:56):
But motionless like not moving from the we really regard
into something like the moon, Earth's sun, galaxy, the galaxy
cluster Lannique, and so on. Probably I would be moving.

(10:17):
Motion is relative, measured relatively to other things. So I
guess you could technically you would always be motionless and
always be moving in all different directions at the same time.
With space expanding, I don't know if that becomes a
factor too, but probably does. I don't think that you
can be motionless in space. I think that there's a
reason why Einstein thought up the theory of relativity, because

(10:41):
there is no super position that we can use to
compare positions in space against. You've only really got what
you have, which is your own frame of reference, and
then you compare that to something else. And because everybody
else has a different reference, there is no set central
position where something is not moving. If I somehow ended

(11:06):
up in space and I wasn't moving for some reason, um,
according to which one Newton's first law, UM, an object
that is not moving, we'll stay stationary. UM. So I
suppose if somehow, I don't know, if the Earth vanished

(11:26):
and I was left suspended in space, UM, and I
wasn't moving, then I would be motionless in space, all right.
A lot of people there doesn't think to think it's
possible to be motionless. Yeah, yeah, exactly, It's it's fascinating.
I think people are just naturally reathless or they have

(11:50):
one of those restless leg syndromes. Yeah, there are those
people who are always tapping on something or got like
a fidget spinner or something. Yeah, I know what my
kids would say. I would say, no, it's impossible right now,
what I would say about my children even if they
were in space, and the kids would say, like, and
why would you want to? That seems really boring, right,
just lying there doing nothing. Yeah, So it's an interesting question.

(12:12):
I guess the question sort of boils down to, like
it's not about standing still, but it's more about moving, right,
like your whole body moving somewhere, right, because technically we
are always vibrating, right, like if we have a temperature,
your our molecules are moving. This is more about, you know,
whether we're as a whole dane still or translating or
moving or going from one place to another, right. Yeah,

(12:33):
I think we should sort of like approximate you as
a little dot or a point particle and ignore all
the motion inside you, and then ask the question, can
point particle, you can spherical? You be motionless with respect
to everything? Is that even possible? Right? Like cartoon Jorge,
So this should be easy because I'm good at ignoring
all the emotions inside of me. Right, that was a

(12:56):
little dark. No, I'm just kidding, but yeah, it's about
whether or not we're moving in relative or moving in
space as a whole. Yeah, exactly. And one of the
most important things to understand is that there is no
absolute motion. All motion is relative. It's always defined relative
to something else. You Know. People writing often and ask
questions about like special relativity, and usually their questions start

(13:18):
with something like if I was in a spaceship and
I was going really really fast, and they don't say
what they're going really really fast relative to? You know,
they have this sense that like there's something that happens
when you get up to high speeds. But the thing
that's missing there is like who are you speeding by?
Where are you going fast relative to? There is no

(13:39):
sense in which you have speed other than that it's
measured relative to other things or people, right, Because I
guess motion is a quantity that is that can't exists
on its own, right, Yeah, exactly. If you are, for example,
in an empty universe, right it's just you floating in
space and there's nothing else in the universe, then you

(14:00):
or speed doesn't make any sense. You have no velocity.
You can't have velocity because velocity is just motion relative
to something else. You know. I guess this might be
confusing to people because I wonder, like, you know, I
think a lot of us maybe imagine that, you know,
the universe maybe has an extent, like a limit, like
a wall at some point. Maybe it's a big sphere,

(14:20):
maybe it's a big blob, maybe it's a donut. But
it has sort of like a shape of it. So
couldn't I measure my speed or my motion relative to
that shape? No, because the universe is actually symmetric. Like
if you do some experiment over here and then you
do the same experiment over there, you always get the
same answer. There's no point in space that's different than

(14:40):
another point in space, Like space has no texture. There's
no like way to tell where you are in space.
I mean, it might be that the universe is finite
and has some like weird edge to it, but we
haven't observed that, and the current cosmological models usually assume
that the universe is infinite and that every point in
it behaves the same way, Like the laws of physics

(15:02):
are the same no matter where you are, and so
you can't do an experiment determine where you are. So
it's not like you can feel space moving by or
measure yourself your location relative to some like absolute point
in space. There is no absolute point, and so there
is also no absolute velocity. Well, there's no absolute point
that we know of, right, But could there be one

(15:23):
if like the universe does have a shape or like
a wall or limit in some scenarios, yes, in most scenarios, no, Like,
even if the universe is not infinite, right, it might
not have an edge. Like imagine the universe is closed
and finite the way it like wraps around itself. That
doesn't mean that there's any special point. It can be

(15:44):
finite and still have like no special location to it.
Imagine you're like on the surface of a sphere, right,
then every point on that sphere is really the same,
even though the service is not infinite, right, Yeah, I guess,
like if the universe was like at the pag max screen.
Then there's technically no real place in the pac Man's
screen because it just loops around forever. But I guess

(16:05):
I'm just trying to get to the possibly that maybe
it does have an edge, in which case there would
be something like an absolute position. Right. If the universe
did have some sort of like strange wall as an
edge to it, or some like deformity in its geometry,
then yes, that would break this cosmological principle that every
location is the same, and then you could measure your
velocity relative to that there would be a special location

(16:27):
in space. But still your velocity would only have meaning
a relative to something. And you can define your velocity
to be relative to like that weird edge of space
or the Sun or the moon, or there's dust particle,
but the definition of your velocity still only has meaning
relative to something, right, Yeah, because I guess you know
motion or velocity, it's like the change in a quantity,

(16:50):
which is distance. So you can have distance if you
don't measure relative to something else, right, yeah, exactly, And
this is actually really closely connected to like all sorts
of interesting deep physics of the universe. You know the
fact that space seems to be the same everywhere. That
if you do your experiment here and then you transport
it ten light years over there and do it again,
that you get the same answer. That's connected to an

(17:13):
important law of physics, which is conservation of momentum. And
we're gonna do a whole fun podcast episode about this
deep theory of physics called Nuther's theorem that tells you
that anytime you have a symmetry like that, something where
the universe doesn't care where you are, you get some
conserved quantity, something which doesn't change as you do your experiments.
So in this case, the connection is the fact that

(17:33):
you can move from one place in space to another
and not have your experiment change. Is why we have
conservation of momentum, which is sort of mind blowing to me.
But yeah, exactly, velocity is defined relative to other things
in space, not relative to space itself, right, And I
think it extends not just to like your precision in
the universe, right, Like you can do an experiment here

(17:55):
or there and it should be worked out the same,
but it also it comes up in doing the experiment
at different velocities. Right. I can do my experiments going
at a hundred moss per hour relative to the Earth,
or I can do it at a hundred thousand miles
per hour. I should get the same results if I'm
going at a constant speed, right, Yeah, exactly. If you're
in a box, you can't measure your velocity relative to
stuff outside the box if you can't see that stuff

(18:16):
at all. So if you do an experiment, it shouldn't
be sensitive to your velocity relative to that stuff. So
the classic scenario is like you set up some experiment.
I don't know what it is. It's got you know,
like balls swinging and hitting each other or whatever, and
then you gently accelerate up to some higher speed, right,
And the key there is gently accelerates so you don't
like destroy everything. Now your speed is high relative to

(18:38):
like the surface of the Earth or the planet you're
on or whatever. You do the same experiment, you should
get exactly the same result. And that's not just some
like weird esoteric thing that means that you can't measure
your velocity. Is no experiment you could do that would
give a different answer if your velocity relative to that
planet is zero or a thousand meters per second, And
that means you can't build a device to measure that velocity. Right,

(19:02):
And again this applies to just to double check, this
applies to like constant velocity. Right. If I'm accelerating, then
that's a whole different ball game, exactly. Acceleration is totally different,
which is also really interesting. Acceleration is something you can measure.
There is absolute acceleration. If you're in a box, you
can measure your acceleration. Right. You can do a simple
experiment toss a ball up in the air and it

(19:22):
will move differently if you're under acceleration then if you're not.
And also you'll feel it. If you're in a box
and it's accelerating, it will feel just like gravity. Right.
Acceleration feels just like gravity, which was the whole inside
which led to general relativity and that whole revolution and
understanding space and time. But position and velocity only makes
sense relative to other things, right. And I think what

(19:45):
you're saying, basically just to kind of drive this home,
is that like, if you're inside of a box out
in space, it's sort of impossible to know how fast
that box you're in is moving relative to other things. Right.
If it's moving at a constant speed, or not. It's
impossible to tell that, you know, boxes floating out in

(20:06):
space or it's like moving super fast across the galaxy. Yeah, exactly,
as long as you can't look outside the box. Like
if you have a window, you can look outside and
you can see things moving by and measure it. But
if all you can do is measure things inside the box,
then yeah, you can't measure your velocity relative to anything
outside the box. There's no way to tell, right, And
so I think what you're getting at is that basically

(20:26):
just the word motionless doesn't really have any meaning, right
because you might think you're motionless now inside your box,
but really you could be moving really fast or not
at all, or moving in any kind of crazy direction
outside of that box. So really the word motionless doesn't
mean anything from a physics math point of view. Yeah,
it's either totally meaningless or it's just totally arbitrary. Like

(20:47):
you can pick a definition of a reference frame and say,
I'm going to say that the Earth is at the
center of my reference frame. Now my velocity has meaning.
I'm talking about velocity relative to the Earth. But you
could also pick anything else. You could pick the sun,
you could pick that grain of dust. You could pick
a distant comment. Your answer depends on your choice, and
your choice is totally arbitrary, and no choice is better

(21:08):
than any other. So you can either say velocity is meaningless, right,
or you can say it only has meaning when you
make an arbitrary choice of what you're measuring it relative to. Right.
So basically, when you try to answer the question can
you be motionless in space, you're saying that's kind of
a nonsensical question, or like an impossible question to ask
in terms of the math and in the physics, because

(21:29):
there's no way to tell if you are motionless, because
it depends on what you measure your motion relative to
and it could be anything. It could be anything, and
even if you pick something, it would be totally different
according to somebody else. Yeah, exactly, Like in some sense
the answer is trivial, like, yes, you can be motionless
in space if you measure your motion relative to yourself.
So by definition, your velocity is zero relative to yourself. Boom,

(21:52):
your motionless in space. So that's what I meant when
I said, like, this question is interesting because this whole
question of velocity, I think people have an intuitive sense
of like motion is something that you can measure, but
you can't actually measure it in a pure sense. You
can only measure relative to other things, and so it
becomes kind of arbitrary and unfortunately meaningless. All right, well,
I think that's a little counterintuitive because our daily experience

(22:14):
is that we are moving on Earth, and the Earth
is moving around the Sun, and then the Sun is
moving around the galaxy. So let's dig a little bit
deeper into these types of motions and then let's try
to answer whether or not it is actually possible to
get around that loophole. But first let's take a quick break.

(22:42):
All right, we're trying to answer the question can you
be motionless in space? And the answer is um, yes
and no, or or ask a better question? Is the
answer it's yes according to our legal department, as long
as you define a reference brain right, because idea is
that you know, I can always say emotionless relative to

(23:02):
whatever box I'm in, but you know who knows what
this box is moving relative to? Yeah, And that's sort
of like the abstract theoretical answer, and it's unsatisfying because
there are some reasonable choices you can make, right in theory,
what reference frame you pick to measure your motion is
totally arbitrary and and there's no one preferred over others.

(23:23):
But there are things around us that it makes sense
to define your motion relative to. Right, you know, we
have the Earth, we have the Sun, we have the galaxy,
and it's fascinating how we are moving relative to those things. Yeah,
and it's not a little bit of motion. We're going
pretty fast right here on Earth. So what like, let's
maybe take it one step at a time. What if

(23:43):
I define our emotion as relative to the Earth or
the center of the Earth, how fast are we moving? Yeah? Right,
relative to the Earth or the center of the Earth.
Those are two different things. If you say, what's my
motion relative to this patch of earth underneath my feet, Well,
if you're just standing on it, then it's obviously zero.
But if you say, what's my motion relative to the
very center of the Earth, then you have to measure

(24:04):
the spinning of the Earth, right, Because the Earth is
not just a ball of rock moving through space. It's
also spinning, spinning pretty quickly like it's a big rock,
and it spins once every twenty four hours, so that's
pretty high speed. You know, at the equator, for example,
the surface of the Earth is moving at six kilometers

(24:24):
per hour relative to the center of the Earth, And
of course that depends on your latitude, because at the
north pole it's not moving at all, and at the
south pole is not moving at all, and at the
equator it has that maximum speed. Right, Although I wonder
if you're committing the same error that we were pointing
out earlier, because you just said the Earth is spinning
really fast, But don't you have to say what it's
spinning fast relative to? Yeah, exactly, like, couldn't the whole universe,

(24:48):
like strange coincidence, be spinning kind of at the same
rate the Earth is, in which case we're not really spinning. Yes,
And here we're talking about spinning relative to the center
of the Earth. Right, when you talk about spin, you
have to pick an axis around which you're spinning. And
so you're right that there's no like preferred access there.
And that's actually a really interesting question I want to

(25:09):
get into in a future episode. But whether or not
the whole universe is spinning, or whether the Earth is spinning,
it's a deep question called mocks principle that we should
dig into. But you're right, you need to pick a
reference frame there. So here we've picked the center of
the Earth, or more specifically, if we're talking about spinning,
an access that goes from the north to the south
pole right, So we're spinning really fast relative to that access,

(25:31):
and maybe a common question might be like, why don't
we feel that motion? Like you know, if I sit
in a Merry Go round or one of those state
fair rights that spin your round, I definitely feel that,
But we don't feel this crazy spinning of the earth
right now. Yeah, it's really interesting. And if you dig
back into history, as science was sort of like figuring
out that the Earth was spinning, that it was moving

(25:54):
in this way, people realize this and they're like, well,
that's ridiculous, Like if the Earth was spinning that fast,
you would definitely feel it, wouldn't we And so it
was counted to people's impressions like when don't we fly
off into space? Right? And the answer is yes, we
would fly off into space if the Earth was spinning faster,
you know, like if you speed up a Merry Go
round and you can't hold on anymore, then you fly

(26:15):
off the Merry go round. Well, what's happening here on
Earth is that we are spinning, like gravity is holding
us down to the surface of the Earth, and gravity
is more powerful than that's tripetal force. And also the
Earth's spin is very very smooth and doesn't change. Like
the Earth was spinning up and slowing down all the time,
then you would definitely notice that. But because it's very

(26:36):
nearly constant, it just sort of gets like subtracted out
from the gravity that you feel. Like you feel gravity, right,
it's holding you to the Earth. You notice it. If
the Earth wasn't spinning, there would be more effective gravity,
Like gravity would feel stronger if the Earth wasn't spinning.
So you are feeling the spinning of the Earth as
a sort of like slight lessening of the gravity you feel,
but it doesn't change very much you don't notice, right,

(26:58):
which you just made me think that like if the
Earth wasn't spinning, we would all weigh a little bit more, yeah,
like we would feel gravity, we would be heavier. Yes,
and you do weigh more at the north pole than
you do at the equator, but only by a very
small amount. And that's why you don't typically notice these things.
And that's why the whole sense that the Earth is
spinning underneath us feels weird because it's not something you

(27:19):
can intuitively grasp, right. But I think, you know, I
think you sort of hit on it when you said
that the Earth is spinning really smoothly, like like that's
I think that's one reason why we don't feel this
crazy spinning. But I think maybe the other part of
it is that it's it's not kind of like a
perfect motion system, right, Like we still do technically feel

(27:40):
things like koreolitis acceloration, right, and and things that would
happen if you were kind of in a merry go
around trying to get to the center or trying to
move around and merry go around. We technically still feel
those weird forces that they're just kind of small relative
to the size of the Earth. Absolutely, you can do
experiments to prove that the Earth is spinning because a
rotating reference frame is not inertial reference frame for you

(28:01):
special relativity wonks out there, and so you can definitely
detect that what happens when you have a reference frame
that's accelerating and when you're spinning that's acceleration because you
need a force towards the center of the spinning What
happens when your reference frame is spinning is that you
get some apparent force. It feels like there's some force
doing something, even though it's just duty your spinning. And

(28:22):
here on Earth that's the Coriolis force. And so, for example,
if you drop a rock from the top of a
very tall tower, you can measure how far it moves
sort of sideways in a way that it wouldn't if
the Earth wasn't spinning. You know, it moves like a
couple of centimeters when it falls like a hundred and
fifty meters. So it's a small and subtle effect, but
you definitely can measure it, and it would be more
dramatic if the Earth sped up. Interesting, So, like if

(28:44):
you went up to the top of the tall tower
and you drop the rock, it wouldn't fall straight down.
It would sort of curve in this weird way because
the Earth is spinning. Yeah, exactly. Like imagine you're back
on that Merry Go Round and you want to throw
a ball to your friend who's in a different spot
on the Merry go Round. You can't act you just
throw it in a straight line towards your friend, because
by the time the ball gets there, your friend will

(29:05):
have like rotated away. So if you want to throw
the ball so that it gets to your friend, you
gotta throw it like a little bit to the left,
because if you throw a ball straight while you're spinning
on a merry go round in your view, the ball
doesn't move straight, it'll like curve to the right. So
you've gotta account for all these things when you're throwing
the ball. And so because the earth is spinning, the
same effect happens when you like drop a rock from

(29:25):
the top of a tower, or if you've ever been
to one of those cool science museums where they have
one of those really tall pendulum, it's called the foe
called pendulum, but you have to say with the French
accent it's called a pendulum. Focal is an experiment done
in the eighteen fifties originally that proved that the Earth
was spinning because you can feel this effect on this pendulum, right.
The pendulum is like a heavy weight on a very

(29:47):
long string, and so it's sensitive to small pushes in
various directions. You set the pendulum going back and forth,
and then it eventually just starts spinning on its own.
And that spinning of course, is coming from the Coriola's force.
It's coming from the in of the Earth. Right. So
I think all these things kind of add up to
that conclusion that we might feel like we're motionless here

(30:07):
on Earth, and that even though motionless doesn't mean anything,
we still sort of feel motionless. But really there are
these strange forces going on, right because the Earth is
spinning and the reference frames are accelerating right, m exactly.
And if the Earth was not spinning, if there was
no like acceleration, because remember, spin is acceleration, then there
be no way to measure the Earth's velocity relative to

(30:28):
other stuff. So we can measure the Earth's spin only
because it is acceleration. It's not just constant velocity. That's
a bit counterintuitive because it feels like it's constant because
it's a constant rate of spin. But constant spin requires
acceleration because requires a force to move you towards the
center of the spin. All right, well, what about relative
to the Sun. That's a pretty stable and almost stationary

(30:52):
big thing. Can we can we be motionless relative to
the Sun. Yeah, that's actually a really interesting question. And
you know, the Earth, of course is moving pretty fast
relative to the Sun, and we should be glad that
we are, because it's the reason that we don't just
like plunge headfirst into the Sun. Right. People think about like,
if you're near a black hole, would you just get
automatically sucked up, when the answer is no, if you

(31:15):
can get into orbit around the black hole, And the
same thing is true for orbiting around any gravitational object.
Like the reason the Earth doesn't fall into the Sun
is because we have high speed relative to the Sun.
You know, this is the kind of stuff people are
talking about with these like New Shepherd and Virgin galactic
launches into space. You know, people are saying that's really
super cool and awesome, but you know, all they did

(31:36):
was sort of like go up into space. The much
more difficult thing is to get up into space and
then get into orbit because that requires a super fast
velocity relative to the Earth. So the Earth is moving
relative to the Sun at like thirty kilometers per second,
and we should be glad that it is, because otherwise
we would fall headfirst into that huge burning ball of plasma.

(31:57):
You mean, those commercial flights that just kind of dip
into space. They don't like, staying in space is a
lot harder. Yeah, staying in space is a lot harder
than dipping your toes and then coming back to Earth.
Like they were just up in space for a few
minutes and they just came right back. But you know,
what NASA has done, and even SpaceX is done, is
much more difficult because you need a much higher velocity
to stay in space. Right, Staying in space basically means

(32:20):
falling towards the Earth and missing it, sort of like
in the Hitchhiker's Guide to the Galaxy. And to do that,
you need to be moving fast enough that when you
fall towards the Earth, it's sort of not there anymore,
just like the motion on the Merry Go Round. Yeah
you like overshoot it? Yeah, exactly, overshoot it. And so
that's what the Earth is doing around the Sun. We're
moving at thirty kilometers per second, which is pretty fast,

(32:40):
but that's the velocity we need because the Sun's gravity
is so strong. That's the velocity we need to overshoot
it every time we fall in towards it. Wow, Well,
what about relative to the galaxy? Um? Can we how
fast is the Sun moving relative to the galaxy? The
Sun is really zipping around right here, we're talking about
gravitational system. And at the core of the galaxy is

(33:02):
an enormous mass of stuff. Right. We are sort of
like out in the suburbs, where there's like one star
every few cubic light years, But in the center of
the galaxy, things are much dense or much crazier, right,
and they're hot, throbbing urban center. There's an enormous black
hole with millions and millions of stars worth of mass
and then just lots of stars, and so there's an

(33:24):
extraordinarily strong gravitational force on the Sun from the center
of the galaxy, and so the Sun is orbiting the
center of the galaxy. But to avoid falling into that
black hole, it has to move really fast. It moves
at eight hundred thousand kilometers per hour relative to the
center of the galaxy. Wow, that's crazy. Like if you
plant the flag in the middle of the galaxy, that's

(33:45):
how fast we're moving relative to that. Yeah, relative to
that black hole, we are moving at eight hundred thousand
kilometers per hour. It's pretty impressive. But you know, the
galaxy is so big that it still takes like two
hundred million years for the Sun to go around the
center of the galaxy, Like a galactic year is two
million earth years. Wow, that's a long time to wait

(34:07):
for your birthday every time. But I think the point
is that, you know, you might think that you're motionless here,
but actually you're moving relative to the Sun of the Earth.
And actually you might think that the Earth is not moving,
but then it's moving relative to the Sun, and the
Sun is moving relative to the galaxy by a lot um.
But then I guess the question is is the galaxy

(34:27):
moving relative to anything else? Right? I think this sort
of goes back to the heart of the original question,
which is like can you be motionless in space? Can
you like get away from all of this stuff? Or
like the other question is like the galaxy itself can
it just be hanging out in space? So this is
a really interesting question. But again you have to measure
the motion of the galaxy relative to other stuff. And

(34:48):
so now what's the other stuff when you can look
at other nearby galaxies and measure like our velocity relative
to Andromeda or relative to other galaxies that are nearby,
but that's just sort of seems arbitrary. Is just you know,
a random galaxy nearby? What you can do, though, which
I think is pretty cool, is you can find the
motion of our galaxy relative to like all of the

(35:09):
stuff in the universe, like the average of all of
the things in the universe. Interesting I mean in terms
of mass or energy or just like to think that
it has some sort of like aggregate that's not moving exactly.
We talked earlier about how you can't measure your velocity
relative to space itself, right, but you can measure your
velocity relative to stuff. And even though there's no preferred

(35:31):
location in space, there is stuff in space, right, you
can ask, like, is there a velocity where you're not
moving relative to like all of the average stuff. And
so the way cosmologists do this is they look at
the cosmic microwave background radiation. This is the radiation that's
left over from the very very early universe, that plasma
that was hot and glowing. Around three eighty thousand years

(35:53):
after the beginning of the universe, the universe became transparent,
and that light has been bouncing around ever since. In
so that light sort of tells us about where the
stuff was in the very early universe, and we can
measure our velocity relative to this radiation which is sort
of like measuring your velocity relative to the stuff in
the early universe. So while you can't measure your velocity

(36:15):
relative to like empty space, space is not empty. It's
filled with stuff, and you can actually find a preferred
reference frame in which the cosmic microwave background radiation or
the plasma that generated it is at rest. WHOA, I
feel like you just kind of pulled a fast one
on me, Like at first, you can convince me at
first that there's no way to have an absolutely velocity,

(36:36):
But now and you're sort of telling me that there
is kind of a way to do it if you
depending on how you define what the universe is right exactly,
imagine an empty universe. You can't have any velocity in
that empty universe. Now put ten galaxies in that universe.
You can say, well, I could have a velocity relative
to one galaxy or another one, or I could just say,

(36:56):
what's my velocity relative to all the stuff, Like find
the ridge motion of all the stuff in the universe,
and you could say that's my velocity, and it's a
reasonable definition. It's sort of arbitrary, but it's also sort
of not arbitrary because like there's only one way to
choose the average velocity of all the stuff in the universe, right,
because that is the universe, right, Like, who cares? So

(37:17):
that space is slippery and undefinable, and you can't, you know,
measure a relative to it. What matters is this stuff
in it? Maybe? I guess that you know, it depends
philosophically if you think space is fundamental or mass is
fundamental or whatever. I mean. You could also define a
frame in which those ten galaxies, your whole universe in
this example, is moving right at a billion miles per

(37:37):
hour to the left. You know, you could define that
reference frame also the universe theoretical physics says their equivalent,
But yeah, I think it makes sense to define a
reference frame relative to all the stuff in the universe.
And the crazy thing is we can kind of do that.
And we can do that by looking at the cosmic
microwave background radiation and asking are we moving through that
radiation at some speed in some direction? All right, well,

(37:58):
let's get into how we can actually to hell that
velocity relative to the background radiation, and maybe there are
other ways to be motionless in the universe. But first
let's take another quick break all right, So it is

(38:22):
sort of possible to define motion relative to all the
stuff in the universe, not to space, but to all
the stuff in the universe. You're saying you can do
that through the cosmic microwave background radiation. Now that's the
like the leftover light from the Big Bang. Are you
saying that we can tell which way we're moving relative
to that kind of glow? We can, absolutely, because like

(38:44):
everything else, we can measure our velocity relative to the
stuff that emitted it by using red shifts and blue shifts.
Like if a star is moving away from us, then
the light that it sends us is red shifted. It's
wavelength is lengthen it's stretched out because that's is moving
away from us. And if it starts moving towards us,
then its wavelength is shrunk. It's like squeezed down. It's

(39:06):
blue shifted. And when we measure the cosmic bacrowave background radiation,
we notice a very very strong effect that one side
of the sky is red shifted and the other side
of the sky is blue shifted. So that very clearly
gives you a measurement for like our motion through the
cosmic microwave background radiation. M M. Interesting. It's sort of
like if you stick your head out this side of
a moving car. You know, one side of your head

(39:28):
would feel the air hitting one side of your face
harder than it would on the other side, and then
that's how you know that you're moving in a particular
direction relative to the air you're moving in. Yeah, exactly.
It's like if you said, well, let's fill the whole
universe with air, then all of a sudden, there is
any reference frame that makes sense, like your air speed
through this universe, right, and it kind of is sort

(39:49):
of filled with air. I mean, it's not actually air molecules,
of course, but it's radiation from the early universe, and
we can measure our speed relative to it, like the
speed of the cosmic microwave back under radiation wind m m.
So like if we look in one direction, this micro
background radiation looks a little bluer, and then we looked
on the other side, it looks a little redder, and

(40:10):
that doesn't change I guess, right, it's it's sort of
relative to what frame of motion. I guess you can
measure relative to our galaxy, right, Yeah, our galaxy is
moving through this now Earth of course, is moving around
the Sun, which is moving around the center of the galaxy,
so you have to subtract that out. But we measure
this as the motion of our galaxy through the c MB,

(40:31):
and it's pretty cool. And it's also not that small,
like we're kind of clipping along through the c NB
at a pretty healthy rate. Yeah, it's like millions of
kilometers per hour. Yeah, exactly two point one million kilometers
per hour through the c MB. And for those of
you who are enthusiasts about the c MP, you might
know that we talk a lot about the details of
the scene, being like the wiggles in it, how it's

(40:52):
a little hotter here and a little colder there, and
that corresponds to fascinating information about the nature of the
early universe. That's after we sup tracked out this big
red shift and blue shift effect. We sort of like
neutralize that so we can just look at the relative
variations here, we're talking about a velocity relative to the CNB.
We subtract that out and then we look for these

(41:12):
wiggles to extract all sorts of cool physics juice about
the universe, and it has a lot of items c
I imagine for Cosmos. It's probably toxic. You know, everything
out there in space will kill you. I'll give you
a good sumber. You just made me think that. You know,
the CMB comes from the Big Bang, which is the
beginning of the universe. Right, So if there was a

(41:34):
relative velocity between the CNB, which represents the stuff in
the universe, and actual space, then it would have to
come from the Big Bang, right, Like it would mean
that the Big Bang was sort of moving relative to
space when it happened. But that's arbitrary, right. The motion
of the CNB relative to space depends on defining a
reference frame for space, which doesn't exist. So you can

(41:58):
imagine the CNB as stay scenary in space, or you
can imagine the CNB and the Big Bang is like
moving through space at a zillion miles per hour. They're
totally equivalent, and you can't tell the difference because you
can't define a reference frame for space. Right. But it's
kind of weird to think that the Big Bang happened
at a zillion miles per hour. Yeah, it is weird,
and it is more natural to define a reference frame

(42:18):
for like the stuff. And it's also kind of cool
because it feels like a choice was made. Right. It
feels like, well, the stuff is here and it's not
over there, and it's not moving at this speed. But
really it's all relative, right. It feels unnatural to imagine
the stuff moving in a million miles per hour. It
feels more natural to say, let's choose a reference frame
with the stuff is zero. But that's sort of our intuition.

(42:40):
It's not like physically meaningful. But so I guess then,
you know, if we are moving relative to the CNB,
do you know which way we're going, Like, are we
moving up? Like relative to California? Are we moving up
down that? Right? Relative to the universe? Like can you
compute that? We can compute that, and there is a vector.
It doesn't make sense to talk about it relative to
California because California is directed through the CMB changes all

(43:02):
the time, because you know, the Earth is spinning and
the Earth is moving around the Sun, and yeah, it's
always moving. But at any given time you could compete like, oh,
right now we are technically moving through the stuff in
the universe in this direction. Yeah, yeah, you can do
that calculation. In fact, maybe we should make a website
for that. That would be pretty fun for people to
see where we're moving through the universe and half past
we're going at any particular time. Yeah, Now, is it

(43:23):
possible then to be sort of motionless relative to the CNB,
Like are there spots in the universe or could we
you know, as we're moving and spinning and moving through
the galaxy and the Solar System, could we at some
for an instant be not moving relative to the CMB. Yeah,
that is totally possible. And astronomers and astrophysicists called this
peculiar velocity because you know, like on average all the

(43:45):
stuff is stationary relative to the CNB, but you know,
nothing is stationary. Everything is like switching around and moving
relative to each other, like our galaxy and the next
galaxy over Andromeda are moving towards each other, for example.
But it is possible we just don't have and to
be stationary relative to the CNB. But you could like
get in a spaceship fly out between galaxies, measure your

(44:07):
velocity relative to the CNB and like perfectly adjusted so
that you're not moving. So it is sort of technically
possible to be motionless relative to the the stuff in
the universe, Yes, but not to space. But to the
stuff that the in the in the universe. You could
you know, fly out there and go too point one
million kilometers per hour in the right direction, and you
might achieve velocity that makes you still relative to the

(44:31):
entire universe. Yeah, exactly, you would have no average velocity
relative to all the stuff in the universe. You know,
that wouldn't change like special relativity effects because those things
are still relative to other observers and stuff like that.
But yeah, you could be motionless relative to the stuff
in the universe. That's pretty cool to think that there

(44:52):
is it is possible to achieve that, And I wonder
if we sort of sometimes sort of achieve it, right
like as we're spinning around the Earth and as the
Earth is spinning around the Sun, or do you think
that because the galaxy is moving so fast that there's
no way we can sort of cancel out that motion. Yeah,
our motion relative to the CMB as the galaxy is
much greater than even the Sun's motion through the galaxy. Right, Like,

(45:15):
the galaxy is moving at two point one million kilometers
per hour through the CMB. The Sun is moving in
eight hundred thousand kilometers per hour. So even if the
Sun was moving in just the right direction, Like opposing
the galaxy's motion to the CMB, it would still only
reduce it down to like, you know, one point three
million kilometers per hour, or it can make it even

(45:36):
faster up to like, you know, almost three million kilometers
per hour. But we don't ever actually achieve zero velocity
relative to the c MB. Interesting, but it is possible,
which I think is pretty cool. But there is one
last sort of confounding factor, which is the fact that
space is expanding. Now, how does that affect this possibility
of being motionless relative to the universe. Yeah, it confuses everything,

(45:58):
you know, because we're not just talking about objects being
static in space. Right. Space is expanding, which means new
space is being made between things. Right, so you have
a bunch of different things happening at once. You have
like the universe expanding, so that even if nothing was
moving relative to any of the other stuff, still distances
between things would be growing because space is being created

(46:20):
between us and other galaxies, which is like whole mind
bending concept of its own right. But then we're also
interested in that motion, like are we moving relative to
Andromeda whereas our galaxy going So cosmologists separate this out
and the two pieces as they are. Right, there's the
expansion of the whole universe, which is like happens that
in the same level, the same way everywhere between us

(46:42):
and other galaxies, between me and you, between the Earth
and the Sun, all this stuff. And then there's this
sort of local motion, like we call this peculiar velocity
relative to that expansion, and so astronomers define these things
called co moving coordinates, where we basically subtract out the
expansion of the universe and say, let's just isolate the
peculiar velocity, the stuff that's like only due to like

(47:04):
local gravity. I guess I'm not sure probably what that means.
Does that mean that it is not possible to find
that spot where you're not moving relative to the universe
because the universe is also expanding, so things will be
sort of moving relative to you even if you find
that spot. No, I think it still makes sense. I mean,
find that spot where you're not moving relative to the CMB. Now,
everything is expanding away from you, but that's true wherever

(47:27):
you are, so that doesn't change your average velocity relative
to the CMB because things are moving away from you.
Always in every direction, so the average velocity still would
be zero. It does mean that everything is moving away
from you always, and so nothing is really ever at rest.
But you can still have average velocity of zero relative

(47:47):
to all the stuff in the universe, even though that
stuff is expanding. Like imagine you're standing on the surface
of a sphere and you find a spot where you're
not moving relative to like all the average stuff in
the universe. Now that spheres exp banding, so everything is
getting bigger, but you're sort of still at the center
of all those velocities, right. I see, like the universe
could be getting bigger, but you'd still be still relative

(48:10):
to all of it. Yes, even though it's growing. Yes,
as long as you're defining your reference for him to
be like the average motion of all the stuff in
the universe, right, and as long as the universe is
not finite, because if it is finite, then you kind
of have to find the center of mass, or you
have to kind of find the sweet spot center in
order for really to be motionless. All right, Well, there

(48:30):
is another interesting scenario, which is this idea that you
can move through time or not move through time. I'm
not sure, so Daniel, How does time fit into this
idea of being motionless in space? Yeah, I think a
lot of people think about our motion through space when
they read time chapel novels, because sometimes you have, like
your protagonists creates a time travel device and they go

(48:51):
back in time, and then the astute reader things, hold
on a second. If you're going back in time, aren't
you going to miss the Earth? Like the Earth is
moving around the Sun. If you go back in time
of month, you should be in deep space, right? Don't
you need to move through time and space in order
to catch up with the Earth. So a lot of
readers write into me with this quibble about the science
fiction novels they read, right, because like a million years ago,

(49:14):
the Earth was not in the same spot at all, right,
because the galaxy is technically moving a couple of million
miles per hour. Yeah, sort of. And it's a fair
point because things are in motion, and so you need
to move sort of through time and through space. But again,
it sort of depends on your reference frame. If your
reference frame is like the center of the Earth, then
you know, none of that motion is really relevant and

(49:34):
it doesn't affect like how time works or how space works.
If your reference frame is the center of the galaxy,
then it does kind of matter. And so it sort
of depends on like when you're programming your time machine,
what coordinates does it take? You know, is it taking
its coordinates relative to this center of the galaxy, in
which case you better be careful about how you type
them in, or is it taking its coordinates relative to

(49:56):
the Earth for example, Right, But the problem is that
the Earth is accelerating, and the UH and the galaxies
and the Solar System is accelerating, So it would probably
be really really complicated, right to sort of keep that
same reference frame exactly, And so if you're going to
move through time, you need to also be moving through
space to make sure you land in the right spot.
Some good advice for when we when I build that

(50:18):
time machine, or at least good advice for science fiction
authors when you write time travel into your novel, at
least make sure to include this so that our listeners
don't get annoyed. Right, right, you know, you have to
add the caveat that it's a space time machine, not
just a time machine, exactly, exactly, every working time travel
machine is actually a space time travel machine. There you
go h G. Wells got it totally wrong. We should

(50:40):
have been its titles. Too bad. We can't have him
on the podcast. If we had a time machine, we
could have him on the podcast. Yeah, but he would
be in a totally different prison. You're right, we'd be
interviewing him from two million miles away. All right, Well,
I think that answers the question pretty well. Can you
be motionless in space? The answer is no, but you
could be most and list relative to the stuff in

(51:02):
the universe, which is pretty much the universe, right, Like
you could You could technically be motionless relative to the
stuff in the universe, just not relative to space. WHOA,
you just demoted space to not be like an important
part of the nature of the universe. That's kind of
a big deal. I think I demoted relative to the
question in the podcast episode, but no disrespect to space.

(51:22):
I like space. I like my space. But yeah, we
hope you enjoyed Dad. Thanks for joining us, See you
next time. Thanks for listening, and remember that Daniel and
Jorge explained. The Universe is a production of I Heart

(51:43):
Radio or more podcast For my heart Radio, visit the
I Heart Radio app, Apple Podcasts, or wherever you listen
to your favorite shows,