January 10, 2023 • 47 mins
Daniel talks with Dr. Katie Robertson about whether there even is a single unified theory of physics for us to discover.
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Speaker 1 (00:08):
The long arc of physics bends towards what exactly. Over
the centuries, we have developed theories to explain the universe,
and then seeing them overturned replaced by something new. Einstein's
gravity replaces Newton, quantum mechanics up ends a deterministic universe.
It feels like progress, but is it. We imagine that
(00:28):
there is a single, beautiful, simpol set of laws that
control how the universe works, and that with each new
idea we are getting closer to the deep truth. But
what if there is no single deep truth? Then what
is it that we are learning anyway? I'm Daniel, I'm
(01:01):
a particle physicist and a professor at UC Irvine, and
I'm spending my life chasing the truth of the universe.
And Welcome to the podcast Daniel and Jorge Explain the Universe,
a production of I Heart Radio in which we don't
shy away from trying to discover the truth of the universe,
as blindingly bright as it may be. We bring you
as close as possible to our current understanding of what's
(01:24):
out there in the universe, from particles two galaxies, what
we do and do not understand. My friend and co
host Jorge is on a break, so I've invited a
guest to chat with us today about this journey to
understand the universe. I personally see our cosmos as if
it was a giant detective novel. We gather clues and
try to figure out what is going on. What story
(01:46):
out there explains everything that we see. As we collect
more information, we can rule out ideas that we had initially.
Sometimes we get a clue that provides a huge plot twist.
What the universe is fundamentally random? What gravity isn't the
force after all? Mind blown? Those are my favorite moments
in science because they make me feel like we are
(02:08):
taking steps towards the truth, like we're on a road
towards figuring out what the story of the universe is.
Because any good detective novel has to be just one
simple requirement. It absolutely positively, without any deviation, has to
follow its own rules. No cheating, no magic, no sudden
(02:31):
changing of the rules to reveal the murderer. If the
reader is going to have a fair chance that puzzling
out the answer, then the clues have to make sense.
They have to be real hints about the actual underlying story.
There has to be a coherent story, one that's self consistent,
and we expect that to be true about the universe
as well. Most of us who are not philosophers or
(02:53):
super skeptics, think that the universe is real, that it's
out there, that it's following some set of laws, and
that by paying attention we could figure out what those
laws are. We feel like we're chipping away at it
from different angles chemistry, biology, physics, but in the end
we're all working towards revealing a single, larger truth. We're
(03:14):
each turning on our own lampposts and shining light on
what's under them, with the idea that more light means
a better view and that eventually we will be able
to see the whole picture. But how do we know
that's true. Is it possible that there isn't a single
coherent story of the universe, that laws in different contexts
(03:35):
and different situations could be incompatible with each other, That
each field of science might be its own separate patch,
not part of a larger quills. So today on the podcast,
we'll be asking the question, could a grand unified theory
of physics be impossible? To help me tackle this grand
(03:59):
as dopequest? I've invited a philosopher of physics who spends
all of her days thinking about this particular question. So
it's my pleasure to welcome to the podcast, Dr Katie Robertson.
Katie has degrees in physics and philosophy, including a PhD
in philosophy from Cambridge. She's now a fellow at the
University of Birmingham, where she thinks about how the microscopic
(04:20):
laws of physics weave themselves together to form the world
we experience, from thermodynamics to the arrow of time and
black holes. Katie, Welcome to the podcast, and thank you
very much for joining us. Thank you so much for
having me. So let's get started by getting to know
you and your interests a little bit. Obviously, black holes
and the deep mysteries of physics are fascinating, but I'm
sure there were many directions open to you, from experimental
(04:42):
physics to theoretical all the way to philosophy. What made
you choose this path? Why do philosophy rather than theoretical
physics or experimental physics? Um well, I think I was
always interested in the conceptual questions in physics. Ravans are
getting really confused in high school physics and asking my
teacher like of what isn't then electron Who's like, well,
that's kind of a philosophical question. And so then having
(05:06):
studied physics and philosophy together, it was kind of like
the philosophy of physics, which was the thing that really
kind of grabbed me. And I was really bad at experiments.
I managed in my first year labs to get the
gravitational constant to be a thousand, So I think that
was never going to be an avenue for me. Unfortunately,
what's for the orders of magnitude between friends? Anyways? So
(05:29):
do you take that's a philosophical question to be an
encouragement or like a discouragement from the physicist? That might
seem like, you know, that's not really territory we want
you to be asking, But it sounds like you took
it as like, yeah, go dig deeper into that. I
guess the sociological thing, isn't it whether you think it's
a good question or not. I mean, I guess in
some ways it's not an encouraging thing. Like if you
(05:50):
think something is purely philosophical, you might think that means
that it's out of the reach of empirical support, and
that's normally seen as a bad thing, right. The key
feature of sciences that we can do experiments and get
evidence in that way. But I think there's kind of
like a continuum between the two, between physics and philosophy,
and often in the history of physics, lots of physicists
have had certain like philosophical convictions that have led them
(06:14):
to their results. So I think it's quite interesting seeing
how the two kind of mixed together, So, you know,
I I find it quite interesting. But yeah, so some
might find it discouraging to find out it's it's a
philosophical question. I think that a lot of the questions
we do in physics are philosophical, and a lot of
physicists have strong philosophical positions, which is usually I don't
do philosophy, which is actually, of course a strong philosophical position, right, Yeah,
(06:39):
I mean something like Ironstein, right, with his worries about
quantum mechanics, were really driven by like philosophical views of
what the world should be like. So yeah, I guess
it's one of those things. You know, you've got philosophical views,
it's just whether you've explicitly stated them and come to
terms with them. Or whether they're kind of hiding buried
in new somewhere. So, then, of all the questions in
(07:00):
physics and philosophy, what's the one that keeps you up
at night? I'm often describing science to our listeners is
like just a bunch of people who are curious about
the world. Everybody's chosen their one question to devote their
life too. So what's the question you would ask like
the oracle or super advanced aliens if you had the opportunity.
So one question that I have the maybe it's like
(07:23):
one of those sort of questions that doesn't have a
clear empirical answer that maybe the aliens wouldn't be any
better off with. But one question I find really interesting
is this question about what the relationship is between like
what our theories tell us the world is like and
what the world is like. So is it going to
be that our um theories, you know, miss out some
stuff or are we like using you know, often we
(07:44):
have like kind of extra mathematical structure more than what
we need in our theories. And sometimes we can know that,
we can know there's extra kind of descriptive fluff fur um,
and sometimes we don't. So I yeah, I guess I'm
interested in, like, you know, how what we should read
off from our theories? You know, which bit should we
take to be true and really about the world, which
bits are kind of just kind of extra stuff that
(08:08):
doesn't really correspond to one of them? Wonderful? Well. I
love how philosophy lets us ask like profound questions about
things that seem ordinary, right, like is our science teaching
us anything at all? Or whatever? And one question that
I really struggle with is like, why can I watch
a ball fly through the air and describe it using
fairly simple equations? You know, why is it possible for
(08:31):
me to do that? And the naive answer and maybe
the listener out there is thinking, well, because the universe
follows laws, and we can deduce those laws, no big deal.
But I think as a particle physicist that probably those laws,
if they exist, they operate at the microscopic level right
on particles or strings or whatever the basic bits are.
So if I'm watching those basic bits themselves, I can
use those laws to describe them. But I'm not right.
(08:51):
I'm massively zoomed out. If I'm watching a baseball, it
has like ten to the twenty nine particles in it. Why,
if I'm looking at ten to the twenty nine basic bits,
do I see anything that makes sense? Why isn't it
all just fuzz and chaos? I mean, I don't have
a simple rule that predicts the role of a die
or the movement of the stock market because it's so
sensitive to those turned details. Why isn't it always like that?
(09:12):
Why when you zoom out in the world, does any
sort of simplicity seem to emerge? Can you help us
get a grasp on that kind of question? Yeah, I
mean there's been a lot of different responses that people
have given, So, I mean there's a kind of defeatist response, right,
which is, well, it's very complicated, but we've got to
do what we can to make sense of it. And
so even though it appears that things are simple, that's
(09:35):
just how we have to approach it, you know, in
the same way you might think, well, the reason that
we have to I don't know, use Newtonian mechanics or
do biology and chemistry is just because we're really bad
at solving the rod in an equation for complicated systems,
and that's why we have these kind of other theories.
So that's the kind of like defeatist option, which is
(09:56):
that we're just not good enough at solving the really
tough things. If we could, maybe we would use those
instead to understandable going across the room. So is that
saying that the universe really is complicated and that we're
just making like a weak approximation of it by describing
it simply. It's sort of like it's part of the
fact that we're you know, in the same way that
if a child doesn't know very much language, then they're
(10:18):
going to describe the world in a kind of much
less colorful way perhaps than an adult would describe the world.
And so that makes it seem like the reason we
see any simplicity is like, well, we're just a bit simple,
so we have to be able to see things that way,
which I find a bit well, it's defeatus. But also
I think it would be kind of amazing, right if
we were just not very good at describing the world,
(10:38):
and the ways in which we did describe the world
was so successful, right, Like, it seems like it's not
just um, sometimes people have this distinction between the way
the world really is versus like what's our perspective on it? So,
you know, we see the flowers in the garden in
a really different way from how bees see flowers, because
our eyes are sensitive different parts of the electromanity spectrum.
(11:00):
So you might think, well, maybe some of the simplicity
is a bit like the kind of color of the flowers.
It's just like how we see things rather than how
they really are. But I don't really like that way
of thinking about it, because I think we're getting something
really right. You know. It's not just that we're using
simple laws because we're simple people. Is that there is
this kind of macroscopic simplicity out of this kind of microscopic,
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kind of incredibly complicated stuff going on. Nonetheless, this kind
of higher or emergent level, you get this kind of simplicity, right,
Like to use your analogy of a child, maybe a
child doesn't use flowery language, but when they say me
want candy, you understand right, it works. It's successful. And
when I'm taking an approximation of something, because they can
to the full calculation and taking the first second third
(11:43):
order of perturbation theory, I mostly get the answer right
and I can ignore the other details. And if the
universe was just chaos and fuzz then that wouldn't work right,
and it doesn't. For example, when I try to predict
the stock market, trust me, I've tried. You know, it
doesn't work. So I feel like the defeatist answer seems
to totally fail at explaining why simplicity emergence. And also
(12:04):
do the defeatists call themselves the defeatists? I guess maybe
the more correct way of labeling them it might might
be somebody who would say something like, there's just a
kind of methodological autonomy. Like the reason we have this
methodology where there's all these different scientific disciplines that's focused
on different things. They have their own conferences, but in
(12:24):
large they just talk to each other rather than you know,
sometimes talk between each other. But you know that the
reason we have science kind of like hived into these
different kind of institutions is just because that's how we
go about doing it. So you can think about as
being the kind of methodological autonomy. It's like, perhaps the
answer isn't just that it's you know, it's simpler to
use Newtonian physics for calculating what's going to happen with
(12:46):
the ball across the park. It's not just that. Is
also that that's the kind of right laws to be
using at that level. So that would be a kind
of different way of thinking about it, where it's not
just that we're not very good at solving the Stronian
equation for complicated systems, it's it's actually these other laws
and equations are kind of more suited. In the same
way that if I ask you what the weather is
(13:08):
going to be tomorrow because I want to go to
the park, the kind of right grain of answer is like,
you know, it'll be sunny, it'll be raining. It won't
be like to give me a kind of complete survey
of what the weather across the whole world's gonna be like.
So one alternative answer to just saying well, we've got
to do things that way in the kind of defeatist
or kind of methodological approach, would be to say, well, actually,
(13:30):
there's kind of different laws are appropriate for different things
in the same way different tools are appropriate for different
tasks or something like that. But does that reject like reductionism,
Does that say that those laws ethicals are made for example,
doesn't arise somehow from like the too ing and throwing
of the basic bits that they emerge at their own level,
or you suggesting that they do emerge, that they're just
(13:52):
are naturally these different scales which the universe coalesces into simplicity. Right.
So I think reductionism is very for debate because lots
of people mean different things by it, right, Like some
people mean by it again a kind of methodology, like, hey,
you want to understand something, look at its component parts.
That's the best way to go about doing it. If
I want to understand this thing, I want to understand
(14:13):
all of its parts, and that's how I'll understand it.
That's what a particle physicists would do, for example. And
you know that also goes across other sciences. For instance,
you know, if you want to understand disease, some people think,
really the crucial thing to understand is the kind of
genetic factors that lead to that disease. Other people might think, oh,
perhaps there's a kind of the environment plays a large role.
So there's kind of this kind of theme of understanding
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things in terms of their parts kind of goes across
all the different sciences. I think that's one form of reductionism.
Another form of productionism would be to kind of be
a kind of more meaty claim about the way the
world is, so to say, really, all that exists is
the very fundamental particles, whatever they turn out to be
in the end, they're going to be all that there
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really is. Everything else is just the kind of different
way of talking about those things, a very complicated different way.
But I think that the kind of probably the most
useful way of talking about reductionism is to talk about
how we understand, like how one theory is related to another.
So the kind of obvious example of this is, you know,
Newtonian mechanics was very successful. Ultimately we think that it's
(15:16):
not quite right, and if things are either very heavy
or very moving, very fast or very small, then it
doesn't work. But we can show how in certain limits,
if your football is being kicked by human rather than
a kind of incredibly strong alien, then it's going to
be traveling at speeds when Newtonian mechanics is so really good.
So we can understand how those theories are related to
(15:37):
each other. In particular, we can understand how to construct
one theory out of another, you know, in a particular
limits you get back your one theory from another. And
I think that relationship is really useful for seeing which
scales you think different theories will work out, because if
you can show that you're going to get back Newtonian
mechanics in the low velocity limits, then that kind of
explains why Neuchinian mechanics was really good there. And I
(15:59):
think that's a way of being that as a kind
of one pattern emerging out of another more fundamental pattern
in a certain regime. So I think reduction is really
helpful for understanding how the different kind of theories and
laws that we have all fit together. You asked whether
that's compatible with thinking there are laws at different levels,
(16:19):
So some people have said no, if you've got kind
of emergent laws, emergence, you know, it's one of those words,
it's like so controversial what you mean by it. But
for some people, emergence just means the failure of reduction.
So for those people that story about getting theories back
in different limits or whatever, that's going to be a
case of reduction. And if there's reduction, then there's no emergence.
(16:40):
So there aren't these kind of there's a kind of
no meaty sense in which there's these kind of new
things at higher levels. Really it's all just the fundamental things,
and you can show why you thought there were other things.
You can show why you thought there were Newtonian forces,
but really there isn't. That was just a kind of
old way of speaking. I kind of prefer the view
where you think different laws is emerging and they're all
(17:02):
kind of on a part with each other in the
sense of like some laws are more fundamental than other laws,
but none of them are like kind of second grade citizens.
You know, they're like you get the laws of Newtonian
mechanics emerging house of relativistic laws, but that you know,
that's just the right laws have in that domain when
things are going nice and slow. Then that's kind of
(17:24):
the way to the kind of laws to use. I
like your organization of the topics there in terms of complexity,
like the idea that maybe Einstein's view of gravity is
more complete, but it's too complicated. Like if I wanted
to solve the question of like what is the Earth's
orbit going to be, and you gave me Einstein's gravity,
I'll be like, well, I'll be here for a while,
(17:45):
Whereas Newtonian mechanics is going to give me the answer
straight away, and it's also going to give me a
story that I can tell that I understand. And maybe
this is also the argument you're making that some of
these laws are just more useful in their explanation. Like
if I want to tell you what happened to the
ball this afternoon, and then I give you a description
of all ten of the twenty nine particles and what
(18:06):
each of them did, doesn't really answer your question. But
if I say, oh, it flew in a parabola and
landed feet from home base or whatever, that's sort of
the story the explanation that we're looking for. So does
that mean that it sort of depends on the question
we're asking, that there are no more fundamental rules. They're
just sort of like laws that answer the questions we're asking.
(18:26):
So I guess the worry with that is that if
it just depends on what question we're asking, you might
then think, well, that just depends on what you care about,
and so it's really just tied into your interests, and
then that kind of starts to look like it's dragging
us in the defeatist direction, where it is all connected
to what we understand about the world rather than how
(18:46):
the world really is. So I think that helpful way
to go is to think of what sense is Newtonian
mechanics better for describing the trajectory of the ball? And
I think that the kind of right answer for that is, well,
when somebody asks you a question, you need to give
them the right amount of details. It's not just that
(19:06):
that's more useful, like that's the better explanation. And so
that would then mean the kind of structures and laws
associated to the kind of less fundamental theory are doing
the kind of best explanation. And normally people think if
something's giving you the best explanation, that's the thing we
should take to be true. So this is sometimes called
(19:27):
inference to the best explanation. What's the reason why the
apple fell to the ground? Is it because the fairies
pushed it? Or is it because Newtonian mechanics, or is
it because I look the wrong way? You know, you
can think of all the different possible explanations, and the
kind of best explanation is the one that we normally
take to be true. So if you can kind of
give a reason why these non fundamental theories, you know,
(19:48):
we think they're less complete, they're missing some of the
details about the world, but nonetheless we think that they're
perhaps giving the best explanations. Then we can still be
committed to all of this kind of emergent structure, and
we don't have to relegate it to just kind of
useful stories that we tell. We can really say that
it's getting at what the world's like. We're lucky that
there's some simplicity, and that's kind of useful for us,
(20:09):
we want to say, and that's really this interesting fact
about the world. This is kind of deep thing that
despite all this kind of fundamental complexity, there's some kind
of relative simplicity at the kind of less fundamental or
macroscopic level. Okay, I can't wait to dive deeper into
that topic, but first we have to take a quick break. Okay,
(20:39):
we're back and we're talking with philosopher Katie Robertson about
whether the universe makes sense, whether there is a single
theory of physics out there. And it certainly seems convenient
that there are sometimes simple stories that you can tell,
and I certainly get the argument that, like, sometimes those
simple stories really are the answer. You don't necessarily want
(21:01):
the totally microscopic picture in every sense. But the thing
that still puzzles me is why that's possible, And the
thing I can't get over is the fact that sometimes
it's not. You know, sometimes we look at systems and
they are complex, and our approximations fail, and we can't
find a simple story to describe the path of hurricanes
or the fluctuations of the stock market. So it can
just be that we're looking at the universe and we're
(21:22):
asking these questions, we're always able to find some simple
story because we are not. So it makes me wonder
why they emerge in some cases and not in others,
and specifically why they seem to emerge at various scales, right,
Like you say, we organize ourselves into physics and biology
and chemistry conferences. Is that because of some human interest
in the way the universe works at these levels? Or
(21:44):
is because the universe itself, you know, reveals itself and
simple stories only at some scales and not at some
other scales. If aliens are doing science on some other planet,
are they also doing physics and biology and chemistry and
having separate conferences the way they don't talk to each
other or do they have like a different ladder of
science is completely because of their own history. Is there
any way to grapple with those questions to try to
(22:06):
get the sense for why science seems to be simple
at some skills and not at others. I mean, it's
a really interesting question, right. The philosopher jerryford Or, I think,
said something. I'm want to fudge the quote a bit,
but it's something like, I expect to find out the
answer to why we have something other than physics. Why
isn't it just that we only have to do physics
and we don't have all these kind of different scales
(22:27):
and levels of which we talk about the world. He
said something like, I expect to find out the answer
to that question the day after I find out why
there's something rather than nothing, you know. He kind of said,
this is a bit of a million dollar question. To
my mind, I think there's going to be lots of
different answers to that, rather than one answer that fits
the relations between all different scales. So I think, as
is often the case in understanding how different scientific theories
(22:49):
are related to each other, the devil's going to be
in the details. So I think, in the case of
thinking about how we get kind of directed processes like
a cup of coffee cooling down or glass smashing the floor.
You know, these processes that we think of as being
directed in time, how we get that kind of macroscopic
pattern out of the microscopic pattern in so, how we
(23:09):
get that from the microdynamics, and how we get to
statistical mechanics. That's one area where I think we can
see how that happens, how we get that emergence. So
what we have in that case is that we have
a description that's really kind of detailed at the lower level. Right,
there's ten of the twenty three molecules and a gas.
That's a very complicated description. We can instead of talking
(23:29):
about exactly where molecule five and fifty three is, we
can talk about some kind of average properties of the gas.
So we can talk about kind of what's sometimes called
a kind of coarse grain probability distribution. Instead of following
exactly where every single passicle is, we just say on average,
there's a kind of an even smearing of them across
the box, for instance. And this kind of course graining
(23:50):
type procedure is a bit like averaging. You know, you
throw away some of the details, and sometimes when we
do this we can kind of uncover new patterns. We
can see that oh, actually, there's kind of a rule
about how this kind of new variable that we've defined works.
And sometimes when we do that, when we kind of abstract,
sometimes you might think of it as being, you know,
you're kind of throwing away some details like abstracting to
(24:13):
a new variable. Sometimes then we find a new law
in terms of that variable. So in the case of
statistical mechanics, we can throw away information about the correlations,
the kind of three or more practical correlations. Gas molecules
are all bump into one another and getting correlated with
each other. You can throw away the kind of three
or more partical correlations in such a way that you
can find a kind of new dynamics at the higher level,
(24:36):
where you've kind of got this course grain dynamics, or
something like the Boltzmann equation, which tells you how quickly
gases relax the equilibrium. That is kind of an example
of these coarse grained error of usal dynamics. So in
that case you've got kind of like a detailed story
about how you've got this higher level emergent kind of
description and structure in those specific cases. But you know,
there's also other cases where you might use something a
(24:57):
bit like course graining to kind of throw away the
details that you're going to be able to follow. And
sometimes that's good and you can find an equation. Sometimes
you can't, Like there's those really bad ways to average
or course grain, and that you get nothing out of him, right,
Like it's there's this nice quote by this I think
he's a historian of physics Van camp And who says
it's kind of the art of the physicists to find
the right variables rather than a kind of science of
(25:19):
like exactly how should we treat choose to course grain.
There's the kind of a lot of bad choices you
can make, but in some cases you can find a
kind of close form dynamics. And that's the case where
we think we found like a new pattern. But you
make it sound like a discovery, like you're stumbling over something.
You're like, ah, look, the universe is doing this thing right,
like we're coming into it. We don't necessarily understand why
(25:39):
it's possible to go from statistical mechanics description of all
those tiny little particles to like you know, thermodynamics of
gases and all this kind of stuff. And you use
the word abstraction, which I find really interesting because it
tells me that we're like summing up a lot of details,
were saying, forget all the details of what's in here,
I'm just going to call this thing a ball and
treat it like a point, right, where like dracting away
(26:00):
a lot of the details. And how do we know
that that kind of abstraction isn't sort of arbitrary or cultural? Right?
Is that us imposing our view on the world, like, oh,
this is interesting, that's not interesting, I want to tell
a story about this, Or is it the universe coalescing
around something like Again, I wonder whether that's us forcing
our sort of mental structure on the universe because we
(26:22):
can't possibly process all the details, or if it's really
that we're discovering this in the universe. How could we
possibly know the difference between those two scenarios without, of course,
talking to aliens about their science. How phony we can
meet those aliens. So people used to think that it
really was due to like our not being able to
kind of keep ahold of all of the details that
(26:42):
we use the kind of course graining procedure in statistical mechanics.
So people thought that the way we chose the kind
of averaging technique was according to what we could measure.
You know, we can't precisely know exactly where each molecule
is in the in the box of gas. Then they
use that as a kind of motivation for why you
could then course grain and throw away some of the
details because we couldn't measure it. But I actually think
(27:03):
that's a really bad explanation of why we cause grain,
because it's not like, as we've got better at measuring things,
we use different course graining schemes in statistical mechanics, right,
So it's not really linked to what we can see
in inverted commerce because if it were, then as what
we see can change, we would change kind of averaging
(27:23):
or course graining technique. So I think that for that reason,
it's more like the kind of discovering new patterns way
of thinking about it rather than it being kind of
connected to us, because if it was connected to us
and we change, would expect to see a change connected
to that. So yeah, in the in the staff Met case,
they really did think that. You know, there's some amazing
quotes about the time asymmetry that comes out of it.
I think somebody described it. I think Pritage and Stayer
(27:45):
subscribed it as allusory kind of resulted kind of entropic
asymmetry that you get. Somebody else says it's kind of
just anthropocentric, you know, it's a feature of us. But
I think that once we understand that these techniques that
we have of abstracting and throwing away details, they're not
necessar seratly connected to what we know about the world
in any kind of detailed way. It might be that
we're kind of attending to certain features of the world
(28:08):
rather than other bits. You know, we're not focusing on
all the kind of what's this particle doing over here,
and what's this one doing over here? And I'm going
to keep a track of what every single particle and
the gas is doing. I'm just gonna be interested in
a bit more of a zoomed out way. But that
zooming out isn't I think connected to kind of our
perspective on the world. This is interesting sort of second
class nature to things that emerge that we talked about
(28:30):
all the time in particle physics. So I never really
thought of it as like, you know, derogatory. But you know,
there's recent ideas about how space itself and maybe even
time are not fundamental to the universe they emerge, meaning
that you could have a universe without space before the
quantum bits of woven themselves together into reality, or you
could have a universe without time. And it's sort of
(28:51):
like demotes those things and says they're not essential, they're
not fundamental, And it seems to me like you're making
the argument that they shouldn't be a demotion, that there's
just you know, there's a set of these ideas and
different ones are applicable in different places, in different contexts,
but we shouldn't think of the most fundamental is necessarily
the most primary or the most true. Is that fair?
(29:12):
And yeah, I think so. There's a kind of tendency
sometimes in philosophy to really only focus on the fundamental.
I mean, I guess Um Anderson and his famous more
is more as different paper right, was kind of pointing
to a similar tendency within physics. He were saying, Look,
it's really important to look at these other areas of physics,
not just fundamental physics. And yeah, I think it's right
to think of these non fundamental things as not kind
(29:36):
of second class in that way, not just because you know,
condensed matter physicists want funding to um but because they're
also telling it's true things about the world. And it's
kind of an interesting conundrum I think connected to the
one that you mentioned at the outset about you know
why is why is it all not just kind of
buzzing confusion? Why do we get the simplicity? I think
an interesting question is, you know, even if we were
(29:58):
to understand the very kind of fundamental nature of the world,
that'd still be so much we didn't know, right, Like
we wouldn't understand stereotype threat in psychology or something, you know,
Like it's not like just knowing about the fundamental is
enough to give for you the kind of knowledge of
all these other levels. So I think, yeah, understanding these
levels is really important as well. Yeah, I think you're right.
And obviously, even if we had like string theory or
(30:21):
the most fundamental theory, it wouldn't tell us, you know,
how do you raise your children, or how do you
make chicken soup? You know, or even where is the
ball going to fly when somebody hits it with a bat.
And I think maybe the primacy comes because some people,
not everybody, are interested in the most fundamental questions. They
want to know what is the most fundamental picture of
the universe, even if that is not relevant to our
everyday lives and too important questions like how can we
(30:43):
build a faster computer? You know, etcetera, etcetera. Something that
confuses me about these non fundamental theories, these effective theories,
you know, the ones that work so well fluid dynamics
and galaxy in formation, is that they feel sometimes inconsistent,
you know, like, for example, the basic equation of fluid dynamics,
because the Naviti Stokes equation makes this assumption that the
fluids you're describing is continuous, that it's explicitly not made
(31:07):
of tiny little bits like like of saying, but of
course we know that they are right. So shouldn't theories
like fit together more smoothly? I mean, I love how
Newtonian theory is an extreme case of Einsteinian theory, but
that seems like is that maybe an exception because in
other cases, you know, the assumptions you have to make
at different levels are incompatible. It gives me a sense
(31:28):
of science is more like you know, a disjoint patchwork
than really like a smooth idea that you're like shining
a lamp post on at different scales. Yeah, that's a
really interesting question because you know, one way to get
around the fact that the navious equation says that everything
is continuous is to say, well, instead of it's saying
this false thing, we're just gonna say that it shouldn't
(31:50):
say anything about that. You know, we should just reinterpret
it as like not committing either way. And so you
can kind of think of a kind of selective approach
to your theories, you know, like some bits of the
we shouldn't take too seriously. And that's often what people
have thought about old theories, right, which is they got
some bits right and they've got some bits wrong. And
one way that sometimes people like to think about the worlds,
which comes back to this question of how our theories
(32:10):
relate to the world, is that not everything they say
is correct. So some people want to say that the
really important thing that's kind of continuous between the different
scales and continuous across and theory change is the kind
of mathematical structure, the kind of extra details about what
the kind of furniture of the world is, like whether
fluids are continuous or not. That's the kind of thing
(32:32):
where historically they've got it a bit wrong, but normally
the mathematical equations are at least approximately the right thing.
So this is sometimes called like structural realism, And the
idea is that instead of kind of taking your scientific
theory at its word, you should really only be committed
to the kind of mathematical structure of the theory. But
doesn't the math come out of these assumptions that you
(32:52):
start from these assumptions and then you can build the
math on top of them and like the axiomatic foundations
of the theory, right, how can you have the math
without foundations? Well, this is a kind of a tricky
question for the structural realists, right, they want to say
the laws, we're getting those right, But what the kind
of objects in that those laws are we're not quite
social about. I mean, quantum mechanics is are kind of
(33:13):
clear case for this, right, Like we're really confident about
the strouding your equation exactly what quanstant particles are? Like,
you know you're gonna end up whether a big disagreement
when you have a group of this discussing it. So
the idea is that it's kind of like epistemic security.
You know, you don't want to put your neck over
the parapet too much. You've got to just commit to
the bits of your theory that you think are really
(33:34):
kind of secure and good. And maybe these are these
assumptions about, for instance, fluids being continuous are kind of
the kind of ladder or scaffolding that helps you get
to your theory. But you can kind of kick away
afterwards and say, the thing I'm really confident about and
I think is getting at the nature of the world
is the kind of equations and the math. But everything
(33:55):
else I'm going to just not commit too much. Too well.
I can't be too critical of that kind of strategy,
since as a particle physicist, I couldn't even really tell you, like,
what is a particle? After all? Right, And you're right,
we certainly do a lot of particle physics, and we
collide them and we describe them, and we have excellent
descriptions of them without even really knowing what it is
we're talking about. So I definitely have very little ground
(34:16):
to stand on there. Okay, I have a lot more
questions for you, Katie, but first we have to pause
for another quick break. All right, we're back and we're
talking to Dr Katie Robertson, a philosopher of physics, about
(34:40):
whether it's possible to understand everything in the universe with
a single theory. I want to take us in another direction,
which is sort of further down this skeptical road. You know,
if each science is helping us understand a part of
the world, and if we say, you know, each one
has our own area of validity, is it possible that
we can eventually stitch them together to get a whole
list day understanding of the underlying truth. The idea being
(35:03):
like the more lamp posts you turn on, the more
ground truth you're revealing. And I'm reading this book by
Nancy Cartwright who has this school of thought. Her book
is called The Dappled World, and she seems to be
arguing that there might not be unity to science, that
there isn't a whole truth underneath it, that we're revealing,
that each piece could actually be separate and not link
(35:23):
up into a coherent picture. Frankly, as a somebody who's
born and bred as a particle physicist, I struggle to
comprehend this argument. What is the argument here? Can you
walk us through how to get to that sort of
state of mind? So I guess you can think of
there's being kind of two issues. The first is we
seem to go about doing science in this very kind
(35:44):
of institutional each in this kind of patchworkboy, right, the
kind of I think she describes it as like, you know,
some of the edges line up neatly, others are kind
of afraid and they don't quite connect. You know, some
disciplines really do kind of fit together with each other
in a nice way, and other ones that's a bit
more complicated. But we seem to get away with doing
things like that. So there's kind of one question which
is like, how can we do that if really everything
(36:09):
is made up of whatever the most fundamental stuff is
why did we get away with ignoring those details? Which
is kind of the question that we started with um.
And then the question on the kind of other side
is if you think that all these patches don't line up,
they're not unified, then how come we sometimes have processes
like kind of you can think of like a causal
(36:30):
process is leaping across patches. And when we have, for instance,
m R I scans for the detection of disease, for instance,
that seems like a case where we can't say or
biology is just about something like totally different from physics,
Because if that were the case, why would physics be
so useful in understanding things in biology? So I kind
of see the patchwork view as giving you an easy
(36:51):
answer to the first problem. Why is that all these
different things at different levels, Well, there's just different things
going on at different levels. There isn't this kind of
unified picture. So it kind of gives you an easy
answer to that question. But then you have a hard answer,
which is, well, if these patches are kind of insulated
from each other in this different way, why is it
(37:13):
that there's these kind of it looks like kind of
causal processes going between them, or kind of threads running
through different sciences. So I think that's part of the motivation.
But another key part of Cartwright's picture is that she
has a I think it was the book before the
daff Wled World, a book with the title how the
Laws of Physics Lie clickbaid, clickbaid. It's from the eighties,
(37:36):
but definitely you know the original philosophy physics clickbait where
she argues that you know, our laws are so abstract
and they apply in such tightly controlled situations and the
lab that we're used to kind of screening off the
kind of noise from the environment, but really kind of
out in the wild. The laws is kind of a
lawless land, you know, the laws that we're used to having,
(37:59):
we have no have good reason for thinking that they
would carry across, which is a view I find hard
to stomach. And like you, I like the idea of
there being kind of the different things happening at different scales,
but I still like thinking that it's kind of all
connected in there's these kind of links between them. Things
emerge out of other things, And I'm they're fan of
(38:19):
the more emergentist type view than the patch Bork view,
but that's that's the motivation. I think. Well, I'm sort
of shocked that you describe the picture of there are
just different rules for different situations. It's sort of like
the easy answer, because that like rocks me to the core.
I have a hard time understanding, like with then what
is the universe right? Like how does it decide when
to use one set of laws and another set of laws?
(38:41):
In carent writes books, she has this quote which when
I've read this, I'd like dropped the book. I couldn't
believe it. She says laws of nature are limited in
their range and regions that seem to overlap. There may
be no rules at all for composing the separate effects,
and some situations may not be subject to law at all.
It happens happens by hap, which is like, is the
(39:03):
universe whimsical? Is it just like making stuff up as
it goes along? I mean, that's certainly not my experience
of the universe and the experience of experimental physics for
hundreds of years. Is this sort of like a an
exercise and skepticism by Cartwright? Like, how do we really
know that the laws that we isolate in the laboratory
also apply out on the wind blown streets? Or do
(39:25):
you think is really a coherent philosophical position and one
that's revealing our blinders? Are you know, the assumptions we've
been making about the universe because of the way our
minds work. It's an interesting question because I think that
I kind of have the same gut feeling as you
in that when you think about describing a bigger and
bigger system, there's no point where you're told, no, don't
(39:46):
take the tensive product of those two systems together. The
shortening equation, it will stop working. So it doesn't seem
to really go with what our experience of doing physics
is like. But Cartwright is very sensitive, I think, to
the kind of details of the practice of physics in
a way that sometimes philosophers have just assumed, well, there'll
be a theory that applies to everything, and they've sort
(40:07):
of just taken it as this kind of brute fact
about the way the world is. And I guess I
see her as sort of like poking at that assumption
and saying, well, how well justified is that? I think that, Yeah,
my my hunch is that I think that we can
say that it's a world just assumption and that it
hasn't not worked so far. But equally, I guess I
(40:29):
think her emphasis on just how tightly controlled certain experimental
contexts are and being careful about kind of exporting that
to other cases, I think it is an important thing,
And I think at the beginning of her book she
has this kind of way of casting what she's doing
is a slightly different approach. So she says there's kind
(40:50):
of two enterprises that science is involved in representing the
way the world is, and then intervening on the world,
and obviously others answers, like medical sciences obviously really interested
in the intervening parts in medicine. Sometimes we know exactly
what to do to help something, we don't necessarily know
the mechanisms behind it that mean that that works, but
(41:11):
we know how to intervene on the world sometimes at least.
And she kind of puts herself in the camp of saying,
I'm not as interested in the project of representing the world.
I'm more interested in the project of intervening on the world.
But she worries that the by not thinking about how
we want to intervene on the world, the fact that
that's what she's interested in. She has these kind of
(41:33):
lovely pictures where she shows like that maybe you remember
them from the beginning of the book, where it's like
kind of like the messy house and then the tidy house,
and she kind of says, we need to understand that
the world is kind of messier than we think that
it sometimes is, because then when we want to intervene
on the world, we're going to be more successful in
doing so because we've got a kind of better idea
of what things are like. And so I think that's
(41:54):
part of her motivation. But I think at the end
of the day, I still come down on there. I
think that it is much more connected. I don't think
there's these kind of lawless lands between the patterns of laws.
So yeah, I think I'm with you on that one. Well.
One of her examples that I found really interesting was
thinking about how to apply physics in the real world. Right,
(42:15):
And so you take a coin, for example, and it drops,
and you can say, well, coin is mostly described by
F equals I may, it's mostly just dominated by gravity.
Is fairly simple situation, And I guess this is the
kind of thing she would say, is essentially screened off
from the other details. But if instead of dropping a coin,
you drop like a bank note and it's a windy day,
then could you possibly ever describe the motion of that
(42:36):
bank note using ff equals I may it's like this
bit of wind, in that bit of wind, and the
other bit of wind, and in that situation, like you know,
one might ask, is it just too complicated and it's
a lot of different sums, or is it really not
described by any physics at all? And I guess her
point is you can't ever really tell, right, you know,
in the absence of a model that yields accurate predictions,
(42:57):
we have no grounds for thinking that any particular law applies.
Is another quote from her book, And I guess I
find that useful as like a warning, like keep in mind,
you don't really know how to solve most of the
situations in the world outside of your well controlled experiments.
But you know, we also have this history and physics
of success. You know, we build the transistors in the laboratory,
(43:18):
and then they fly airplanes that mostly don't crash right
out in the complicated world. And in the history of
physics we see this like unification, where electricity and magnetism
come together, we add the weak force. Maybe in the
future we'll be able to combine that with the strong
force and gravity. It seems to me like argument of
history at least is against her. Is that the view
(43:38):
mostly in mainstream philosophy, or is there a camp of
people who are continuing this work. So there are a
camp of people that are continuing in the kind of
car right line of thinking. I think you're completely right
to kind of characterize it as a kind of kind
of epistemic humility warning, you know, like you don't have
a warrant to say that it's definitely gonna work. So
I think that's a really important part of the project
(44:00):
xt And but then on the other hands, you kind
of a tone in the other direction, which is, well,
we've we've not yet found a situation where that doesn't
you know, for for objects of the size of a banknote,
just summing up all the forces on it doesn't work
as a way of predicting what happens. Okay, maybe we
won't ever be able to do it in the case
of the banknotes. It's just too complicate it. But I
(44:20):
guess that's that's the kind of warrant that we have,
kind of holding onto the idea that maybe we can't
predict it, but it is like predictable in principle. Maybe
aliens with their supercomputers have totally solved that problem, all right.
So then my last question for you is, aside from
meeting aliens with super advanced answers to questions in physics
and philosophy, what do you think are prospects from making
(44:41):
progress on these questions. I mean, we can't ever really
understand how a banknote flutters in the wind. Are we
going to be able to figure out if there is
a grand, unified theory out there for us to work towards,
or if the universe is really just a patchwork. How
do we understand these things? Our philosopher is gonna be
arguing about this for a thousand years, or we actually
to figure this out. I guess we don't. I don't know, really,
(45:02):
because I think that it comes back to like whether
we think that even if it's going to be a patchwork,
even if you know, sometimes people say it's kind of
turtles all the way down. You know, we could just
keep smashing particles together and finding new particles forever and ever.
You know, you make that sound like a bad thing,
That sounds like job security for me. In that case,
(45:23):
then we would expect kind of you know, that there
isn't a fundamental level. That would be a bit like
saying perhaps I'm tempted to think that even if we
that could be the case, or it could be a patchwork,
we still the best methodology that we would have is
to keep looking for kind of more fundamental theories and
I think working out how everything kind of patches together,
(45:45):
you know, is it going to be that we always
have a kind of effective theory that works within a
certain domain, and then a more fundamental theory underlying that.
Um it would be really interest I mean, there's, particularly
for the case of things like black holes as fast
anating questions of how things will turn out. So I'm
tempted to think whilst at the moment I placed my
bets on it not being a patchwork in the sense
(46:07):
of there's lawless kind of lands between the patches, will
be interesting to find out. Well. I like the way
you describe the arc of science there were like discovering.
We're letting the universe tell us its story, and I
just hope that we're not too biased by the way
we're listening to the story, to the story we want
to hear that we are able to absorb, you know,
the shocking truth of the universe, because it sometimes takes us,
(46:30):
you know, decades or centuries to really come to grips
with what the experiments are telling us. It's it's hard
to deviate sometimes from sort of like the historical path
of science. And you know, I'm metor I can pronounce
that phrase epistemical humility. We should try to maintain that
as much as possible, but also make progress on the
science at the same time. Well, thanks very much for
joining us today on the podcast and for talking about
(46:52):
these really important but also very abstract questions about the
way we do science. Thanks for having me, Thanks everyone
for listening. Tune in next time. Yeah, thanks for listening,
and remember that Daniel and Jorge Explain the Universe is
a production of I Heart Radio. For more podcast from
(47:14):
my heart Radio, visit the i heart Radio app, Apple Podcasts,
or wherever you listen to your favorite shows. Yea
The long arc of physics bends towards what exactly. Over
the centuries, we have developed theories to explain the universe,
and then seeing them overturned replaced by something new. Einstein's
gravity replaces Newton, quantum mechanics up ends a deterministic universe.
It feels like progress, but is it. We imagine that
(00:28):
there is a single, beautiful, simpol set of laws that
control how the universe works, and that with each new
idea we are getting closer to the deep truth. But
what if there is no single deep truth? Then what
is it that we are learning anyway? I'm Daniel, I'm
(01:01):
a particle physicist and a professor at UC Irvine, and
I'm spending my life chasing the truth of the universe.
And Welcome to the podcast Daniel and Jorge Explain the Universe,
a production of I Heart Radio in which we don't
shy away from trying to discover the truth of the universe,
as blindingly bright as it may be. We bring you
as close as possible to our current understanding of what's
(01:24):
out there in the universe, from particles two galaxies, what
we do and do not understand. My friend and co
host Jorge is on a break, so I've invited a
guest to chat with us today about this journey to
understand the universe. I personally see our cosmos as if
it was a giant detective novel. We gather clues and
try to figure out what is going on. What story
(01:46):
out there explains everything that we see. As we collect
more information, we can rule out ideas that we had initially.
Sometimes we get a clue that provides a huge plot twist.
What the universe is fundamentally random? What gravity isn't the
force after all? Mind blown? Those are my favorite moments
in science because they make me feel like we are
(02:08):
taking steps towards the truth, like we're on a road
towards figuring out what the story of the universe is.
Because any good detective novel has to be just one
simple requirement. It absolutely positively, without any deviation, has to
follow its own rules. No cheating, no magic, no sudden
(02:31):
changing of the rules to reveal the murderer. If the
reader is going to have a fair chance that puzzling
out the answer, then the clues have to make sense.
They have to be real hints about the actual underlying story.
There has to be a coherent story, one that's self consistent,
and we expect that to be true about the universe
as well. Most of us who are not philosophers or
(02:53):
super skeptics, think that the universe is real, that it's
out there, that it's following some set of laws, and
that by paying attention we could figure out what those
laws are. We feel like we're chipping away at it
from different angles chemistry, biology, physics, but in the end
we're all working towards revealing a single, larger truth. We're
(03:14):
each turning on our own lampposts and shining light on
what's under them, with the idea that more light means
a better view and that eventually we will be able
to see the whole picture. But how do we know
that's true. Is it possible that there isn't a single
coherent story of the universe, that laws in different contexts
(03:35):
and different situations could be incompatible with each other, That
each field of science might be its own separate patch,
not part of a larger quills. So today on the podcast,
we'll be asking the question, could a grand unified theory
of physics be impossible? To help me tackle this grand
(03:59):
as dopequest? I've invited a philosopher of physics who spends
all of her days thinking about this particular question. So
it's my pleasure to welcome to the podcast, Dr Katie Robertson.
Katie has degrees in physics and philosophy, including a PhD
in philosophy from Cambridge. She's now a fellow at the
University of Birmingham, where she thinks about how the microscopic
(04:20):
laws of physics weave themselves together to form the world
we experience, from thermodynamics to the arrow of time and
black holes. Katie, Welcome to the podcast, and thank you
very much for joining us. Thank you so much for
having me. So let's get started by getting to know
you and your interests a little bit. Obviously, black holes
and the deep mysteries of physics are fascinating, but I'm
sure there were many directions open to you, from experimental
(04:42):
physics to theoretical all the way to philosophy. What made
you choose this path? Why do philosophy rather than theoretical
physics or experimental physics? Um well, I think I was
always interested in the conceptual questions in physics. Ravans are
getting really confused in high school physics and asking my
teacher like of what isn't then electron Who's like, well,
that's kind of a philosophical question. And so then having
(05:06):
studied physics and philosophy together, it was kind of like
the philosophy of physics, which was the thing that really
kind of grabbed me. And I was really bad at experiments.
I managed in my first year labs to get the
gravitational constant to be a thousand, So I think that
was never going to be an avenue for me. Unfortunately,
what's for the orders of magnitude between friends? Anyways? So
(05:29):
do you take that's a philosophical question to be an
encouragement or like a discouragement from the physicist? That might
seem like, you know, that's not really territory we want
you to be asking, But it sounds like you took
it as like, yeah, go dig deeper into that. I
guess the sociological thing, isn't it whether you think it's
a good question or not. I mean, I guess in
some ways it's not an encouraging thing. Like if you
(05:50):
think something is purely philosophical, you might think that means
that it's out of the reach of empirical support, and
that's normally seen as a bad thing, right. The key
feature of sciences that we can do experiments and get
evidence in that way. But I think there's kind of
like a continuum between the two, between physics and philosophy,
and often in the history of physics, lots of physicists
have had certain like philosophical convictions that have led them
(06:14):
to their results. So I think it's quite interesting seeing
how the two kind of mixed together, So, you know,
I I find it quite interesting. But yeah, so some
might find it discouraging to find out it's it's a
philosophical question. I think that a lot of the questions
we do in physics are philosophical, and a lot of
physicists have strong philosophical positions, which is usually I don't
do philosophy, which is actually, of course a strong philosophical position, right, Yeah,
(06:39):
I mean something like Ironstein, right, with his worries about
quantum mechanics, were really driven by like philosophical views of
what the world should be like. So yeah, I guess
it's one of those things. You know, you've got philosophical views,
it's just whether you've explicitly stated them and come to
terms with them. Or whether they're kind of hiding buried
in new somewhere. So, then, of all the questions in
(07:00):
physics and philosophy, what's the one that keeps you up
at night? I'm often describing science to our listeners is
like just a bunch of people who are curious about
the world. Everybody's chosen their one question to devote their
life too. So what's the question you would ask like
the oracle or super advanced aliens if you had the opportunity.
So one question that I have the maybe it's like
(07:23):
one of those sort of questions that doesn't have a
clear empirical answer that maybe the aliens wouldn't be any
better off with. But one question I find really interesting
is this question about what the relationship is between like
what our theories tell us the world is like and
what the world is like. So is it going to
be that our um theories, you know, miss out some
stuff or are we like using you know, often we
(07:44):
have like kind of extra mathematical structure more than what
we need in our theories. And sometimes we can know that,
we can know there's extra kind of descriptive fluff fur um,
and sometimes we don't. So I yeah, I guess I'm
interested in, like, you know, how what we should read
off from our theories? You know, which bit should we
take to be true and really about the world, which
bits are kind of just kind of extra stuff that
(08:08):
doesn't really correspond to one of them? Wonderful? Well. I
love how philosophy lets us ask like profound questions about
things that seem ordinary, right, like is our science teaching
us anything at all? Or whatever? And one question that
I really struggle with is like, why can I watch
a ball fly through the air and describe it using
fairly simple equations? You know, why is it possible for
(08:31):
me to do that? And the naive answer and maybe
the listener out there is thinking, well, because the universe
follows laws, and we can deduce those laws, no big deal.
But I think as a particle physicist that probably those laws,
if they exist, they operate at the microscopic level right
on particles or strings or whatever the basic bits are.
So if I'm watching those basic bits themselves, I can
use those laws to describe them. But I'm not right.
(08:51):
I'm massively zoomed out. If I'm watching a baseball, it
has like ten to the twenty nine particles in it. Why,
if I'm looking at ten to the twenty nine basic bits,
do I see anything that makes sense? Why isn't it
all just fuzz and chaos? I mean, I don't have
a simple rule that predicts the role of a die
or the movement of the stock market because it's so
sensitive to those turned details. Why isn't it always like that?
(09:12):
Why when you zoom out in the world, does any
sort of simplicity seem to emerge? Can you help us
get a grasp on that kind of question? Yeah, I
mean there's been a lot of different responses that people
have given, So, I mean there's a kind of defeatist response, right,
which is, well, it's very complicated, but we've got to
do what we can to make sense of it. And
so even though it appears that things are simple, that's
(09:35):
just how we have to approach it, you know, in
the same way you might think, well, the reason that
we have to I don't know, use Newtonian mechanics or
do biology and chemistry is just because we're really bad
at solving the rod in an equation for complicated systems,
and that's why we have these kind of other theories.
So that's the kind of like defeatist option, which is
(09:56):
that we're just not good enough at solving the really
tough things. If we could, maybe we would use those
instead to understandable going across the room. So is that
saying that the universe really is complicated and that we're
just making like a weak approximation of it by describing
it simply. It's sort of like it's part of the
fact that we're you know, in the same way that
if a child doesn't know very much language, then they're
(10:18):
going to describe the world in a kind of much
less colorful way perhaps than an adult would describe the world.
And so that makes it seem like the reason we
see any simplicity is like, well, we're just a bit simple,
so we have to be able to see things that way,
which I find a bit well, it's defeatus. But also
I think it would be kind of amazing, right if
we were just not very good at describing the world,
(10:38):
and the ways in which we did describe the world
was so successful, right, Like, it seems like it's not
just um, sometimes people have this distinction between the way
the world really is versus like what's our perspective on it? So,
you know, we see the flowers in the garden in
a really different way from how bees see flowers, because
our eyes are sensitive different parts of the electromanity spectrum.
(11:00):
So you might think, well, maybe some of the simplicity
is a bit like the kind of color of the flowers.
It's just like how we see things rather than how
they really are. But I don't really like that way
of thinking about it, because I think we're getting something
really right. You know. It's not just that we're using
simple laws because we're simple people. Is that there is
this kind of macroscopic simplicity out of this kind of microscopic,
(11:22):
kind of incredibly complicated stuff going on. Nonetheless, this kind
of higher or emergent level, you get this kind of simplicity, right,
Like to use your analogy of a child, maybe a
child doesn't use flowery language, but when they say me
want candy, you understand right, it works. It's successful. And
when I'm taking an approximation of something, because they can
to the full calculation and taking the first second third
(11:43):
order of perturbation theory, I mostly get the answer right
and I can ignore the other details. And if the
universe was just chaos and fuzz then that wouldn't work right,
and it doesn't. For example, when I try to predict
the stock market, trust me, I've tried. You know, it
doesn't work. So I feel like the defeatist answer seems
to totally fail at explaining why simplicity emergence. And also
(12:04):
do the defeatists call themselves the defeatists? I guess maybe
the more correct way of labeling them it might might
be somebody who would say something like, there's just a
kind of methodological autonomy. Like the reason we have this
methodology where there's all these different scientific disciplines that's focused
on different things. They have their own conferences, but in
(12:24):
large they just talk to each other rather than you know,
sometimes talk between each other. But you know that the
reason we have science kind of like hived into these
different kind of institutions is just because that's how we
go about doing it. So you can think about as
being the kind of methodological autonomy. It's like, perhaps the
answer isn't just that it's you know, it's simpler to
use Newtonian physics for calculating what's going to happen with
(12:46):
the ball across the park. It's not just that. Is
also that that's the kind of right laws to be
using at that level. So that would be a kind
of different way of thinking about it, where it's not
just that we're not very good at solving the Stronian
equation for complicated systems, it's it's actually these other laws
and equations are kind of more suited. In the same
way that if I ask you what the weather is
(13:08):
going to be tomorrow because I want to go to
the park, the kind of right grain of answer is like,
you know, it'll be sunny, it'll be raining. It won't
be like to give me a kind of complete survey
of what the weather across the whole world's gonna be like.
So one alternative answer to just saying well, we've got
to do things that way in the kind of defeatist
or kind of methodological approach, would be to say, well, actually,
(13:30):
there's kind of different laws are appropriate for different things
in the same way different tools are appropriate for different
tasks or something like that. But does that reject like reductionism,
Does that say that those laws ethicals are made for example,
doesn't arise somehow from like the too ing and throwing
of the basic bits that they emerge at their own level,
or you suggesting that they do emerge, that they're just
(13:52):
are naturally these different scales which the universe coalesces into simplicity. Right.
So I think reductionism is very for debate because lots
of people mean different things by it, right, Like some
people mean by it again a kind of methodology, like, hey,
you want to understand something, look at its component parts.
That's the best way to go about doing it. If
I want to understand this thing, I want to understand
(14:13):
all of its parts, and that's how I'll understand it.
That's what a particle physicists would do, for example. And
you know that also goes across other sciences. For instance,
you know, if you want to understand disease, some people think,
really the crucial thing to understand is the kind of
genetic factors that lead to that disease. Other people might think, oh,
perhaps there's a kind of the environment plays a large role.
So there's kind of this kind of theme of understanding
(14:35):
things in terms of their parts kind of goes across
all the different sciences. I think that's one form of reductionism.
Another form of productionism would be to kind of be
a kind of more meaty claim about the way the
world is, so to say, really, all that exists is
the very fundamental particles, whatever they turn out to be
in the end, they're going to be all that there
(14:55):
really is. Everything else is just the kind of different
way of talking about those things, a very complicated different way.
But I think that the kind of probably the most
useful way of talking about reductionism is to talk about
how we understand, like how one theory is related to another.
So the kind of obvious example of this is, you know,
Newtonian mechanics was very successful. Ultimately we think that it's
(15:16):
not quite right, and if things are either very heavy
or very moving, very fast or very small, then it
doesn't work. But we can show how in certain limits,
if your football is being kicked by human rather than
a kind of incredibly strong alien, then it's going to
be traveling at speeds when Newtonian mechanics is so really good.
So we can understand how those theories are related to
(15:37):
each other. In particular, we can understand how to construct
one theory out of another, you know, in a particular
limits you get back your one theory from another. And
I think that relationship is really useful for seeing which
scales you think different theories will work out, because if
you can show that you're going to get back Newtonian
mechanics in the low velocity limits, then that kind of
explains why Neuchinian mechanics was really good there. And I
(15:59):
think that's a way of being that as a kind
of one pattern emerging out of another more fundamental pattern
in a certain regime. So I think reduction is really
helpful for understanding how the different kind of theories and
laws that we have all fit together. You asked whether
that's compatible with thinking there are laws at different levels,
(16:19):
So some people have said no, if you've got kind
of emergent laws, emergence, you know, it's one of those words,
it's like so controversial what you mean by it. But
for some people, emergence just means the failure of reduction.
So for those people that story about getting theories back
in different limits or whatever, that's going to be a
case of reduction. And if there's reduction, then there's no emergence.
(16:40):
So there aren't these kind of there's a kind of
no meaty sense in which there's these kind of new
things at higher levels. Really it's all just the fundamental things,
and you can show why you thought there were other things.
You can show why you thought there were Newtonian forces,
but really there isn't. That was just a kind of
old way of speaking. I kind of prefer the view
where you think different laws is emerging and they're all
(17:02):
kind of on a part with each other in the
sense of like some laws are more fundamental than other laws,
but none of them are like kind of second grade citizens.
You know, they're like you get the laws of Newtonian
mechanics emerging house of relativistic laws, but that you know,
that's just the right laws have in that domain when
things are going nice and slow. Then that's kind of
(17:24):
the way to the kind of laws to use. I
like your organization of the topics there in terms of complexity,
like the idea that maybe Einstein's view of gravity is
more complete, but it's too complicated. Like if I wanted
to solve the question of like what is the Earth's
orbit going to be, and you gave me Einstein's gravity,
I'll be like, well, I'll be here for a while,
(17:45):
Whereas Newtonian mechanics is going to give me the answer
straight away, and it's also going to give me a
story that I can tell that I understand. And maybe
this is also the argument you're making that some of
these laws are just more useful in their explanation. Like
if I want to tell you what happened to the
ball this afternoon, and then I give you a description
of all ten of the twenty nine particles and what
(18:06):
each of them did, doesn't really answer your question. But
if I say, oh, it flew in a parabola and
landed feet from home base or whatever, that's sort of
the story the explanation that we're looking for. So does
that mean that it sort of depends on the question
we're asking, that there are no more fundamental rules. They're
just sort of like laws that answer the questions we're asking.
(18:26):
So I guess the worry with that is that if
it just depends on what question we're asking, you might
then think, well, that just depends on what you care about,
and so it's really just tied into your interests, and
then that kind of starts to look like it's dragging
us in the defeatist direction, where it is all connected
to what we understand about the world rather than how
(18:46):
the world really is. So I think that helpful way
to go is to think of what sense is Newtonian
mechanics better for describing the trajectory of the ball? And
I think that the kind of right answer for that is, well,
when somebody asks you a question, you need to give
them the right amount of details. It's not just that
(19:06):
that's more useful, like that's the better explanation. And so
that would then mean the kind of structures and laws
associated to the kind of less fundamental theory are doing
the kind of best explanation. And normally people think if
something's giving you the best explanation, that's the thing we
should take to be true. So this is sometimes called
(19:27):
inference to the best explanation. What's the reason why the
apple fell to the ground? Is it because the fairies
pushed it? Or is it because Newtonian mechanics, or is
it because I look the wrong way? You know, you
can think of all the different possible explanations, and the
kind of best explanation is the one that we normally
take to be true. So if you can kind of
give a reason why these non fundamental theories, you know,
(19:48):
we think they're less complete, they're missing some of the
details about the world, but nonetheless we think that they're
perhaps giving the best explanations. Then we can still be
committed to all of this kind of emergent structure, and
we don't have to relegate it to just kind of
useful stories that we tell. We can really say that
it's getting at what the world's like. We're lucky that
there's some simplicity, and that's kind of useful for us,
(20:09):
we want to say, and that's really this interesting fact
about the world. This is kind of deep thing that
despite all this kind of fundamental complexity, there's some kind
of relative simplicity at the kind of less fundamental or
macroscopic level. Okay, I can't wait to dive deeper into
that topic, but first we have to take a quick break. Okay,
(20:39):
we're back and we're talking with philosopher Katie Robertson about
whether the universe makes sense, whether there is a single
theory of physics out there. And it certainly seems convenient
that there are sometimes simple stories that you can tell,
and I certainly get the argument that, like, sometimes those
simple stories really are the answer. You don't necessarily want
(21:01):
the totally microscopic picture in every sense. But the thing
that still puzzles me is why that's possible, And the
thing I can't get over is the fact that sometimes
it's not. You know, sometimes we look at systems and
they are complex, and our approximations fail, and we can't
find a simple story to describe the path of hurricanes
or the fluctuations of the stock market. So it can
just be that we're looking at the universe and we're
(21:22):
asking these questions, we're always able to find some simple
story because we are not. So it makes me wonder
why they emerge in some cases and not in others,
and specifically why they seem to emerge at various scales, right,
Like you say, we organize ourselves into physics and biology
and chemistry conferences. Is that because of some human interest
in the way the universe works at these levels? Or
(21:44):
is because the universe itself, you know, reveals itself and
simple stories only at some scales and not at some
other scales. If aliens are doing science on some other planet,
are they also doing physics and biology and chemistry and
having separate conferences the way they don't talk to each
other or do they have like a different ladder of
science is completely because of their own history. Is there
any way to grapple with those questions to try to
(22:06):
get the sense for why science seems to be simple
at some skills and not at others. I mean, it's
a really interesting question, right. The philosopher jerryford Or, I think,
said something. I'm want to fudge the quote a bit,
but it's something like, I expect to find out the
answer to why we have something other than physics. Why
isn't it just that we only have to do physics
and we don't have all these kind of different scales
(22:27):
and levels of which we talk about the world. He
said something like, I expect to find out the answer
to that question the day after I find out why
there's something rather than nothing, you know. He kind of said,
this is a bit of a million dollar question. To
my mind, I think there's going to be lots of
different answers to that, rather than one answer that fits
the relations between all different scales. So I think, as
is often the case in understanding how different scientific theories
(22:49):
are related to each other, the devil's going to be
in the details. So I think, in the case of
thinking about how we get kind of directed processes like
a cup of coffee cooling down or glass smashing the floor.
You know, these processes that we think of as being
directed in time, how we get that kind of macroscopic
pattern out of the microscopic pattern in so, how we
(23:09):
get that from the microdynamics, and how we get to
statistical mechanics. That's one area where I think we can
see how that happens, how we get that emergence. So
what we have in that case is that we have
a description that's really kind of detailed at the lower level. Right,
there's ten of the twenty three molecules and a gas.
That's a very complicated description. We can instead of talking
(23:29):
about exactly where molecule five and fifty three is, we
can talk about some kind of average properties of the gas.
So we can talk about kind of what's sometimes called
a kind of coarse grain probability distribution. Instead of following
exactly where every single passicle is, we just say on average,
there's a kind of an even smearing of them across
the box, for instance. And this kind of course graining
(23:50):
type procedure is a bit like averaging. You know, you
throw away some of the details, and sometimes when we
do this we can kind of uncover new patterns. We
can see that oh, actually, there's kind of a rule
about how this kind of new variable that we've defined works.
And sometimes when we do that, when we kind of abstract,
sometimes you might think of it as being, you know,
you're kind of throwing away some details like abstracting to
(24:13):
a new variable. Sometimes then we find a new law
in terms of that variable. So in the case of
statistical mechanics, we can throw away information about the correlations,
the kind of three or more practical correlations. Gas molecules
are all bump into one another and getting correlated with
each other. You can throw away the kind of three
or more partical correlations in such a way that you
can find a kind of new dynamics at the higher level,
(24:36):
where you've kind of got this course grain dynamics, or
something like the Boltzmann equation, which tells you how quickly
gases relax the equilibrium. That is kind of an example
of these coarse grained error of usal dynamics. So in
that case you've got kind of like a detailed story
about how you've got this higher level emergent kind of
description and structure in those specific cases. But you know,
there's also other cases where you might use something a
(24:57):
bit like course graining to kind of throw away the
details that you're going to be able to follow. And
sometimes that's good and you can find an equation. Sometimes
you can't, Like there's those really bad ways to average
or course grain, and that you get nothing out of him, right,
Like it's there's this nice quote by this I think
he's a historian of physics Van camp And who says
it's kind of the art of the physicists to find
the right variables rather than a kind of science of
(25:19):
like exactly how should we treat choose to course grain.
There's the kind of a lot of bad choices you
can make, but in some cases you can find a
kind of close form dynamics. And that's the case where
we think we found like a new pattern. But you
make it sound like a discovery, like you're stumbling over something.
You're like, ah, look, the universe is doing this thing right,
like we're coming into it. We don't necessarily understand why
(25:39):
it's possible to go from statistical mechanics description of all
those tiny little particles to like you know, thermodynamics of
gases and all this kind of stuff. And you use
the word abstraction, which I find really interesting because it
tells me that we're like summing up a lot of details,
were saying, forget all the details of what's in here,
I'm just going to call this thing a ball and
treat it like a point, right, where like dracting away
(26:00):
a lot of the details. And how do we know
that that kind of abstraction isn't sort of arbitrary or cultural? Right?
Is that us imposing our view on the world, like, oh,
this is interesting, that's not interesting, I want to tell
a story about this, Or is it the universe coalescing
around something like Again, I wonder whether that's us forcing
our sort of mental structure on the universe because we
(26:22):
can't possibly process all the details, or if it's really
that we're discovering this in the universe. How could we
possibly know the difference between those two scenarios without, of course,
talking to aliens about their science. How phony we can
meet those aliens. So people used to think that it
really was due to like our not being able to
kind of keep ahold of all of the details that
(26:42):
we use the kind of course graining procedure in statistical mechanics.
So people thought that the way we chose the kind
of averaging technique was according to what we could measure.
You know, we can't precisely know exactly where each molecule
is in the in the box of gas. Then they
use that as a kind of motivation for why you
could then course grain and throw away some of the
details because we couldn't measure it. But I actually think
(27:03):
that's a really bad explanation of why we cause grain,
because it's not like, as we've got better at measuring things,
we use different course graining schemes in statistical mechanics, right,
So it's not really linked to what we can see
in inverted commerce because if it were, then as what
we see can change, we would change kind of averaging
(27:23):
or course graining technique. So I think that for that reason,
it's more like the kind of discovering new patterns way
of thinking about it rather than it being kind of
connected to us, because if it was connected to us
and we change, would expect to see a change connected
to that. So yeah, in the in the staff Met case,
they really did think that. You know, there's some amazing
quotes about the time asymmetry that comes out of it.
I think somebody described it. I think Pritage and Stayer
(27:45):
subscribed it as allusory kind of resulted kind of entropic
asymmetry that you get. Somebody else says it's kind of
just anthropocentric, you know, it's a feature of us. But
I think that once we understand that these techniques that
we have of abstracting and throwing away details, they're not
necessar seratly connected to what we know about the world
in any kind of detailed way. It might be that
we're kind of attending to certain features of the world
(28:08):
rather than other bits. You know, we're not focusing on
all the kind of what's this particle doing over here,
and what's this one doing over here? And I'm going
to keep a track of what every single particle and
the gas is doing. I'm just gonna be interested in
a bit more of a zoomed out way. But that
zooming out isn't I think connected to kind of our
perspective on the world. This is interesting sort of second
class nature to things that emerge that we talked about
(28:30):
all the time in particle physics. So I never really
thought of it as like, you know, derogatory. But you know,
there's recent ideas about how space itself and maybe even
time are not fundamental to the universe they emerge, meaning
that you could have a universe without space before the
quantum bits of woven themselves together into reality, or you
could have a universe without time. And it's sort of
(28:51):
like demotes those things and says they're not essential, they're
not fundamental, And it seems to me like you're making
the argument that they shouldn't be a demotion, that there's
just you know, there's a set of these ideas and
different ones are applicable in different places, in different contexts,
but we shouldn't think of the most fundamental is necessarily
the most primary or the most true. Is that fair?
(29:12):
And yeah, I think so. There's a kind of tendency
sometimes in philosophy to really only focus on the fundamental.
I mean, I guess Um Anderson and his famous more
is more as different paper right, was kind of pointing
to a similar tendency within physics. He were saying, Look,
it's really important to look at these other areas of physics,
not just fundamental physics. And yeah, I think it's right
to think of these non fundamental things as not kind
(29:36):
of second class in that way, not just because you know,
condensed matter physicists want funding to um but because they're
also telling it's true things about the world. And it's
kind of an interesting conundrum I think connected to the
one that you mentioned at the outset about you know
why is why is it all not just kind of
buzzing confusion? Why do we get the simplicity? I think
an interesting question is, you know, even if we were
(29:58):
to understand the very kind of fundamental nature of the world,
that'd still be so much we didn't know, right, Like
we wouldn't understand stereotype threat in psychology or something, you know,
Like it's not like just knowing about the fundamental is
enough to give for you the kind of knowledge of
all these other levels. So I think, yeah, understanding these
levels is really important as well. Yeah, I think you're right.
And obviously, even if we had like string theory or
(30:21):
the most fundamental theory, it wouldn't tell us, you know,
how do you raise your children, or how do you
make chicken soup? You know, or even where is the
ball going to fly when somebody hits it with a bat.
And I think maybe the primacy comes because some people,
not everybody, are interested in the most fundamental questions. They
want to know what is the most fundamental picture of
the universe, even if that is not relevant to our
everyday lives and too important questions like how can we
(30:43):
build a faster computer? You know, etcetera, etcetera. Something that
confuses me about these non fundamental theories, these effective theories,
you know, the ones that work so well fluid dynamics
and galaxy in formation, is that they feel sometimes inconsistent,
you know, like, for example, the basic equation of fluid dynamics,
because the Naviti Stokes equation makes this assumption that the
fluids you're describing is continuous, that it's explicitly not made
(31:07):
of tiny little bits like like of saying, but of
course we know that they are right. So shouldn't theories
like fit together more smoothly? I mean, I love how
Newtonian theory is an extreme case of Einsteinian theory, but
that seems like is that maybe an exception because in
other cases, you know, the assumptions you have to make
at different levels are incompatible. It gives me a sense
(31:28):
of science is more like you know, a disjoint patchwork
than really like a smooth idea that you're like shining
a lamp post on at different scales. Yeah, that's a
really interesting question because you know, one way to get
around the fact that the navious equation says that everything
is continuous is to say, well, instead of it's saying
this false thing, we're just gonna say that it shouldn't
(31:50):
say anything about that. You know, we should just reinterpret
it as like not committing either way. And so you
can kind of think of a kind of selective approach
to your theories, you know, like some bits of the
we shouldn't take too seriously. And that's often what people
have thought about old theories, right, which is they got
some bits right and they've got some bits wrong. And
one way that sometimes people like to think about the worlds,
which comes back to this question of how our theories
(32:10):
relate to the world, is that not everything they say
is correct. So some people want to say that the
really important thing that's kind of continuous between the different
scales and continuous across and theory change is the kind
of mathematical structure, the kind of extra details about what
the kind of furniture of the world is, like whether
fluids are continuous or not. That's the kind of thing
(32:32):
where historically they've got it a bit wrong, but normally
the mathematical equations are at least approximately the right thing.
So this is sometimes called like structural realism, And the
idea is that instead of kind of taking your scientific
theory at its word, you should really only be committed
to the kind of mathematical structure of the theory. But
doesn't the math come out of these assumptions that you
(32:52):
start from these assumptions and then you can build the
math on top of them and like the axiomatic foundations
of the theory, right, how can you have the math
without foundations? Well, this is a kind of a tricky
question for the structural realists, right, they want to say
the laws, we're getting those right, But what the kind
of objects in that those laws are we're not quite
social about. I mean, quantum mechanics is are kind of
(33:13):
clear case for this, right, Like we're really confident about
the strouding your equation exactly what quanstant particles are? Like,
you know you're gonna end up whether a big disagreement
when you have a group of this discussing it. So
the idea is that it's kind of like epistemic security.
You know, you don't want to put your neck over
the parapet too much. You've got to just commit to
the bits of your theory that you think are really
(33:34):
kind of secure and good. And maybe these are these
assumptions about, for instance, fluids being continuous are kind of
the kind of ladder or scaffolding that helps you get
to your theory. But you can kind of kick away
afterwards and say, the thing I'm really confident about and
I think is getting at the nature of the world
is the kind of equations and the math. But everything
(33:55):
else I'm going to just not commit too much. Too well.
I can't be too critical of that kind of strategy,
since as a particle physicist, I couldn't even really tell you, like,
what is a particle? After all? Right, And you're right,
we certainly do a lot of particle physics, and we
collide them and we describe them, and we have excellent
descriptions of them without even really knowing what it is
we're talking about. So I definitely have very little ground
(34:16):
to stand on there. Okay, I have a lot more
questions for you, Katie, but first we have to pause
for another quick break. All right, we're back and we're
talking to Dr Katie Robertson, a philosopher of physics, about
(34:40):
whether it's possible to understand everything in the universe with
a single theory. I want to take us in another direction,
which is sort of further down this skeptical road. You know,
if each science is helping us understand a part of
the world, and if we say, you know, each one
has our own area of validity, is it possible that
we can eventually stitch them together to get a whole
list day understanding of the underlying truth. The idea being
(35:03):
like the more lamp posts you turn on, the more
ground truth you're revealing. And I'm reading this book by
Nancy Cartwright who has this school of thought. Her book
is called The Dappled World, and she seems to be
arguing that there might not be unity to science, that
there isn't a whole truth underneath it, that we're revealing,
that each piece could actually be separate and not link
(35:23):
up into a coherent picture. Frankly, as a somebody who's
born and bred as a particle physicist, I struggle to
comprehend this argument. What is the argument here? Can you
walk us through how to get to that sort of
state of mind? So I guess you can think of
there's being kind of two issues. The first is we
seem to go about doing science in this very kind
(35:44):
of institutional each in this kind of patchworkboy, right, the
kind of I think she describes it as like, you know,
some of the edges line up neatly, others are kind
of afraid and they don't quite connect. You know, some
disciplines really do kind of fit together with each other
in a nice way, and other ones that's a bit
more complicated. But we seem to get away with doing
things like that. So there's kind of one question which
is like, how can we do that if really everything
(36:09):
is made up of whatever the most fundamental stuff is
why did we get away with ignoring those details? Which
is kind of the question that we started with um.
And then the question on the kind of other side
is if you think that all these patches don't line up,
they're not unified, then how come we sometimes have processes
like kind of you can think of like a causal
(36:30):
process is leaping across patches. And when we have, for instance,
m R I scans for the detection of disease, for instance,
that seems like a case where we can't say or
biology is just about something like totally different from physics,
Because if that were the case, why would physics be
so useful in understanding things in biology? So I kind
of see the patchwork view as giving you an easy
(36:51):
answer to the first problem. Why is that all these
different things at different levels, Well, there's just different things
going on at different levels. There isn't this kind of
unified picture. So it kind of gives you an easy
answer to that question. But then you have a hard answer,
which is, well, if these patches are kind of insulated
from each other in this different way, why is it
(37:13):
that there's these kind of it looks like kind of
causal processes going between them, or kind of threads running
through different sciences. So I think that's part of the motivation.
But another key part of Cartwright's picture is that she
has a I think it was the book before the
daff Wled World, a book with the title how the
Laws of Physics Lie clickbaid, clickbaid. It's from the eighties,
(37:36):
but definitely you know the original philosophy physics clickbait where
she argues that you know, our laws are so abstract
and they apply in such tightly controlled situations and the
lab that we're used to kind of screening off the
kind of noise from the environment, but really kind of
out in the wild. The laws is kind of a
lawless land, you know, the laws that we're used to having,
(37:59):
we have no have good reason for thinking that they
would carry across, which is a view I find hard
to stomach. And like you, I like the idea of
there being kind of the different things happening at different scales,
but I still like thinking that it's kind of all
connected in there's these kind of links between them. Things
emerge out of other things, And I'm they're fan of
(38:19):
the more emergentist type view than the patch Bork view,
but that's that's the motivation. I think. Well, I'm sort
of shocked that you describe the picture of there are
just different rules for different situations. It's sort of like
the easy answer, because that like rocks me to the core.
I have a hard time understanding, like with then what
is the universe right? Like how does it decide when
to use one set of laws and another set of laws?
(38:41):
In carent writes books, she has this quote which when
I've read this, I'd like dropped the book. I couldn't
believe it. She says laws of nature are limited in
their range and regions that seem to overlap. There may
be no rules at all for composing the separate effects,
and some situations may not be subject to law at all.
It happens happens by hap, which is like, is the
(39:03):
universe whimsical? Is it just like making stuff up as
it goes along? I mean, that's certainly not my experience
of the universe and the experience of experimental physics for
hundreds of years. Is this sort of like a an
exercise and skepticism by Cartwright? Like, how do we really
know that the laws that we isolate in the laboratory
also apply out on the wind blown streets? Or do
(39:25):
you think is really a coherent philosophical position and one
that's revealing our blinders? Are you know, the assumptions we've
been making about the universe because of the way our
minds work. It's an interesting question because I think that
I kind of have the same gut feeling as you
in that when you think about describing a bigger and
bigger system, there's no point where you're told, no, don't
(39:46):
take the tensive product of those two systems together. The
shortening equation, it will stop working. So it doesn't seem
to really go with what our experience of doing physics
is like. But Cartwright is very sensitive, I think, to
the kind of details of the practice of physics in
a way that sometimes philosophers have just assumed, well, there'll
be a theory that applies to everything, and they've sort
(40:07):
of just taken it as this kind of brute fact
about the way the world is. And I guess I
see her as sort of like poking at that assumption
and saying, well, how well justified is that? I think that, Yeah,
my my hunch is that I think that we can
say that it's a world just assumption and that it
hasn't not worked so far. But equally, I guess I
(40:29):
think her emphasis on just how tightly controlled certain experimental
contexts are and being careful about kind of exporting that
to other cases, I think it is an important thing,
And I think at the beginning of her book she
has this kind of way of casting what she's doing
is a slightly different approach. So she says there's kind
(40:50):
of two enterprises that science is involved in representing the
way the world is, and then intervening on the world,
and obviously others answers, like medical sciences obviously really interested
in the intervening parts in medicine. Sometimes we know exactly
what to do to help something, we don't necessarily know
the mechanisms behind it that mean that that works, but
(41:11):
we know how to intervene on the world sometimes at least.
And she kind of puts herself in the camp of saying,
I'm not as interested in the project of representing the world.
I'm more interested in the project of intervening on the world.
But she worries that the by not thinking about how
we want to intervene on the world, the fact that
that's what she's interested in. She has these kind of
(41:33):
lovely pictures where she shows like that maybe you remember
them from the beginning of the book, where it's like
kind of like the messy house and then the tidy house,
and she kind of says, we need to understand that
the world is kind of messier than we think that
it sometimes is, because then when we want to intervene
on the world, we're going to be more successful in
doing so because we've got a kind of better idea
of what things are like. And so I think that's
(41:54):
part of her motivation. But I think at the end
of the day, I still come down on there. I
think that it is much more connected. I don't think
there's these kind of lawless lands between the patterns of laws.
So yeah, I think I'm with you on that one. Well.
One of her examples that I found really interesting was
thinking about how to apply physics in the real world. Right,
(42:15):
And so you take a coin, for example, and it drops,
and you can say, well, coin is mostly described by
F equals I may, it's mostly just dominated by gravity.
Is fairly simple situation, And I guess this is the
kind of thing she would say, is essentially screened off
from the other details. But if instead of dropping a coin,
you drop like a bank note and it's a windy day,
then could you possibly ever describe the motion of that
(42:36):
bank note using ff equals I may it's like this
bit of wind, in that bit of wind, and the
other bit of wind, and in that situation, like you know,
one might ask, is it just too complicated and it's
a lot of different sums, or is it really not
described by any physics at all? And I guess her
point is you can't ever really tell, right, you know,
in the absence of a model that yields accurate predictions,
(42:57):
we have no grounds for thinking that any particular law applies.
Is another quote from her book, And I guess I
find that useful as like a warning, like keep in mind,
you don't really know how to solve most of the
situations in the world outside of your well controlled experiments.
But you know, we also have this history and physics
of success. You know, we build the transistors in the laboratory,
(43:18):
and then they fly airplanes that mostly don't crash right
out in the complicated world. And in the history of
physics we see this like unification, where electricity and magnetism
come together, we add the weak force. Maybe in the
future we'll be able to combine that with the strong
force and gravity. It seems to me like argument of
history at least is against her. Is that the view
(43:38):
mostly in mainstream philosophy, or is there a camp of
people who are continuing this work. So there are a
camp of people that are continuing in the kind of
car right line of thinking. I think you're completely right
to kind of characterize it as a kind of kind
of epistemic humility warning, you know, like you don't have
a warrant to say that it's definitely gonna work. So
I think that's a really important part of the project
(44:00):
xt And but then on the other hands, you kind
of a tone in the other direction, which is, well,
we've we've not yet found a situation where that doesn't
you know, for for objects of the size of a banknote,
just summing up all the forces on it doesn't work
as a way of predicting what happens. Okay, maybe we
won't ever be able to do it in the case
of the banknotes. It's just too complicate it. But I
(44:20):
guess that's that's the kind of warrant that we have,
kind of holding onto the idea that maybe we can't
predict it, but it is like predictable in principle. Maybe
aliens with their supercomputers have totally solved that problem, all right.
So then my last question for you is, aside from
meeting aliens with super advanced answers to questions in physics
and philosophy, what do you think are prospects from making
(44:41):
progress on these questions. I mean, we can't ever really
understand how a banknote flutters in the wind. Are we
going to be able to figure out if there is
a grand, unified theory out there for us to work towards,
or if the universe is really just a patchwork. How
do we understand these things? Our philosopher is gonna be
arguing about this for a thousand years, or we actually
to figure this out. I guess we don't. I don't know, really,
(45:02):
because I think that it comes back to like whether
we think that even if it's going to be a patchwork,
even if you know, sometimes people say it's kind of
turtles all the way down. You know, we could just
keep smashing particles together and finding new particles forever and ever.
You know, you make that sound like a bad thing,
That sounds like job security for me. In that case,
(45:23):
then we would expect kind of you know, that there
isn't a fundamental level. That would be a bit like
saying perhaps I'm tempted to think that even if we
that could be the case, or it could be a patchwork,
we still the best methodology that we would have is
to keep looking for kind of more fundamental theories and
I think working out how everything kind of patches together,
(45:45):
you know, is it going to be that we always
have a kind of effective theory that works within a
certain domain, and then a more fundamental theory underlying that.
Um it would be really interest I mean, there's, particularly
for the case of things like black holes as fast
anating questions of how things will turn out. So I'm
tempted to think whilst at the moment I placed my
bets on it not being a patchwork in the sense
(46:07):
of there's lawless kind of lands between the patches, will
be interesting to find out. Well. I like the way
you describe the arc of science there were like discovering.
We're letting the universe tell us its story, and I
just hope that we're not too biased by the way
we're listening to the story, to the story we want
to hear that we are able to absorb, you know,
the shocking truth of the universe, because it sometimes takes us,
(46:30):
you know, decades or centuries to really come to grips
with what the experiments are telling us. It's it's hard
to deviate sometimes from sort of like the historical path
of science. And you know, I'm metor I can pronounce
that phrase epistemical humility. We should try to maintain that
as much as possible, but also make progress on the
science at the same time. Well, thanks very much for
joining us today on the podcast and for talking about
(46:52):
these really important but also very abstract questions about the
way we do science. Thanks for having me, Thanks everyone
for listening. Tune in next time. Yeah, thanks for listening,
and remember that Daniel and Jorge Explain the Universe is
a production of I Heart Radio. For more podcast from
(47:14):
my heart Radio, visit the i heart Radio app, Apple Podcasts,
or wherever you listen to your favorite shows. Yea
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