July 25, 2024 • 52 mins
Daniel and Katie use their p-branes to explore a theory of everything build on vibrating membranes.
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Speaker 1 (00:07):
Hey, Daniel, have you guys figured out what's inside a
black hole? Yet?
Speaker 2 (00:12):
Unfortunately not? Still pretty confused.
Speaker 1 (00:14):
Okay, it sounds like you guys need to go back
to the drawing board get some new ideas.
Speaker 2 (00:20):
I know, but like from where the smartest people on
the planet have been stuck in this question for literally decades.
Speaker 1 (00:26):
See that is where you are going wrong. You are
looking to the smart people. If you need wacky, crazy ideas,
you need to ask the wacky crazy people like me.
Speaker 2 (00:39):
You're saying we should go to the insane asylum and
ask people what they think is inside a black hole.
Speaker 1 (00:43):
I think that they could come up with some good ideas.
They might be insane enough in the membrane to figure
it out.
Speaker 2 (00:51):
Insane in the brain. Hi, I'm Daniel. I'm a particle
physicist and a professor at UC Irvine. And if you
(01:12):
didn't get my Cypress Hill reference, you're officially young.
Speaker 1 (01:16):
I am Katie. I am not a physicist. I like animals, though,
and I like the universe. And I got that reference.
Speaker 2 (01:26):
Because you're insane in the membrane.
Speaker 1 (01:28):
Exactly, just the membrane, though the rest of me is perfectly.
Speaker 2 (01:32):
Sane and welcome to the podcast Daniel and Jorge Explain
the Universe, in which we do our best to bring
this insane universe into your brain. We try to make
it all make sense, from the tiniest little quantum particles
to the hugest swirling accretion disks surrounding super massive black holes.
(01:52):
We have this hunch that maybe the universe is understandable,
that it's a big mathematical puzzle that we can of
eventually figure it out if we put all of our
brains and membranes together. And our goal on this podcast
is to explain all of it to you.
Speaker 1 (02:08):
Now, that's another song, super Massive black Hole. I think
muse soundtrack to that really sort of indie movie called Twilight.
Speaker 2 (02:19):
Are you sure that wasn't part of the hip hop
wars in the nineties, super Massive black Hole?
Speaker 1 (02:24):
I couldn't say. In the nineties, I was not cool
enough to know.
Speaker 2 (02:29):
Well, you know, maybe there are some secrets in music
that can help us crack the mysteries of the universe,
because you know, some people say the universe is musical
and there's a connection between music and mathematics, right, So
maybe we have been looking in the wrong places.
Speaker 1 (02:44):
Yeah, Like I've heard this in terms of string theory,
where strings aren't you know, they're not like violin strings,
But it's something about some like either vibration or pattern. Honestly,
I do not understand it, but you know, well, I
think that is interesting that there is the idea that
(03:04):
a lot of the mysteries of the universe could be
about certain frequencies or patterns, which is also what is
the major components of music.
Speaker 2 (03:16):
Exactly, Although if you listen to Terrence Howard on Joe Rogan,
it's all frequencies.
Speaker 1 (03:20):
Man, is all frequencies?
Speaker 2 (03:22):
Man?
Speaker 1 (03:22):
Why am I not on Joe Rogan? See, I just
can say that too.
Speaker 2 (03:27):
I can because you believe that one times one equals one,
and Terrence Howard proves that it equals to And that's
why you're just not mathematically qualified to be.
Speaker 1 (03:38):
I just can't think outside of the box enough to
not do mauth good exactly.
Speaker 2 (03:43):
But we are fascinated by the mysteries of the universe.
We do think that there are mathematical solutions to them.
Maybe they are encoded in the sonatas of Mozart. Maybe
the engineers are right that it's all vibrations all the
way down. But we hope that there is an explanation.
And one of the biggest things and we need an
explanation for is how to think about the universe on
the smallest scales. What happens when things get really, really
(04:07):
dense and really really tiny. One of the biggest puzzles
in modern physics is how to put together the two
pillars of our understanding of the universe, relativity and quantum mechanics.
We've been banging our heads against this for almost one
hundred years, basically since we've had relativity and quantum mechanics
and realize that they are fundamentally incompatible at the smallest scale.
(04:30):
And we've been trying to figure this out. And today
on the podcast, we'll be exploring yet another attempt to
unify relativity and quantum mechanics. So on the podcast today
we'll be answering the question what is membrane theory?
Speaker 1 (04:49):
Okay, as a biology nerd, I'm pretty sure I can
answer this. A membrane is a semi permeable barrier, So
I solved it. Congratulations to me.
Speaker 2 (05:04):
What about the audio barrier between us and the listeners
the ideas from our brains and that their brains have
we permeated a membrane.
Speaker 1 (05:12):
I yes, why not. I don't know enough about audio
engineering to say no or philosophy, so I'm gonna say yes.
We're like salt ions through the airwaves, permeating the membrane,
so hopefully you can reach homeostasis.
Speaker 2 (05:32):
So I'm not surprised that when you heard this phrase
you thought of cellular membranes divisions between solutions. You want
to keep osmosis from, like moving all these bits of
salt over here, or using fats to keep that over there.
But it's not just in biology that we have membranes.
It turns out that they are fundamental concept in theories
(05:52):
of quantum gravity. But before we dig into that, I
was curious what everybody else out there thought when they
heard membrane theory. As usual, I asked our cadre of
volunteers to speculate on the question without the opportunity to
use Google. So, if you would like to join this
group of volunteers in the future, please don't be shy.
Write me to questions at Danielandjorge dot com. We all
(06:15):
want to hear what you have to say. In the meantime,
check out these answers from listeners. What do you think
membrane theory is here's what people had to say. That's
the first time I'm hearing golfit.
Speaker 3 (06:27):
But if I had to guess membranes, the function of
the membranes are to pass on stuff in one direction
and other stuff not in the other direction. So maybe
we're talking about it's a mechanism about particle coexistence through
a wall of things something like that.
Speaker 4 (06:45):
Just to guess, what comes to mind for me on
that one is that it's something that you use to
separate things, like in a fuel cell car, you know,
you separate components and you make energy. Maybe it's like
a desalination thing where you take salt.
Speaker 2 (06:57):
Out of water.
Speaker 4 (06:58):
So maybe there's some membrane here in the universe that's doing.
Speaker 2 (07:01):
That in space.
Speaker 5 (07:03):
I'm guessing membrane theory has to do with the outside
of a cell. Maybe how the membrane, you know, protects
the core of the cell and how it stays intact.
Speaker 2 (07:16):
I think it has to do with string theory. There
are strings that vibrate in there one dimension, and I
think a membrane is a something similar that can have
more than one dimension.
Speaker 1 (07:26):
See, I'm I'm definitely with the theory that everything is
a cell. If you look at the universe, it's just
a giant body for some kind of huge animal. You know,
it makes sense, right, you're saying the universe is alive. Yeah,
it's a big maybe a giant cat. I don't know.
(07:47):
Have you ever looked at like a black cat? Right,
It's it kind of has that sort of quantum mechanics
and general relativity paradox. Right, it's like a fluid, it's
a solid. It's sweet and loving, and then it bites you.
So yeah, I think the universe could be a giant cat.
And when you get down to the tiniest components there cells,
(08:09):
and yeah, it's been solved.
Speaker 2 (08:11):
You're welcome and we're done, Thank you very much. Physics
is over. Katie wins all of the Nobel prices. Heay, Well,
we're definitely hearing from listeners the connection to biology, which
makes a lot of sense, and the idea of having
two dimensional surfaces or even connections to string theory. So
there's a lot of good stuff in here that we're
(08:31):
going to dig into and explain in this episode. But
a plus to all the listeners.
Speaker 1 (08:37):
I mean, I would assume that, yes, it's probably not
like a cellular membrane. But if we're talking about a membrane,
I would guess it is some kind of barrier through
which certain physics transactions can occur. But that would be
my guess.
Speaker 2 (08:56):
Is this whole podcast a physics transaction? We are taking
your time and exchanging it for knowledge, is like a
physics transaction.
Speaker 1 (09:03):
You know what? That's pretty good. I think I'm wondering
about the exchange rate, though, because that's that's the real issue.
Speaker 2 (09:10):
Yeah, I think we're too high on the jokes permit
it and too low and the physics permitted so far.
Let's try to flip that right now.
Speaker 1 (09:16):
All right, well, okay, let me have it. Like, what's
going on with this membrane theory?
Speaker 2 (09:21):
So membrane theory is an attempt to crack the puzzle
of quantum gravity. So let's start with that. What is
the puzzle of quantum gravity? Why do we want to
crack it? What is the issue? Why are all the
smart people on the planet thinking they need to go
into the insane this islum if they can't figure this out?
The basic issue is we have two ways to describe
the universe. There's general relativity, which tells us about space
(09:42):
and time and energy, and the expansion of the universe
describes a lot of the big stuff. It tells us
how gravity works and how the universe is expanding, and
how far away galaxies are getting red shifted and all
that good stuff. And then we have quantum mechanics, which
describes the really small stuff, the little part of goals
light and all this kind of quantum fields and sort
(10:03):
of our understanding of microscopic matter. And the issue is
that we don't know how to make these two things
play well together.
Speaker 1 (10:11):
They don't play nice because I've actually, i think I've
been on the show a couple times when we talked
about this conundrum, and so it seems like, you know,
when you have these mathematical theories that describe each of them,
it works within it. So the general relativity math works
within general relativity. It seems really nice and neat and good.
(10:32):
Same thing for quantum mechanics. But then when you try
to cross the beams the math beams, suddenly it doesn't work.
Like if you're trying to use general relativity math to
describe what you know is observed in experiments happening on
sort of the quantum level, or vice versa. It no
longer works. Is that more or less?
Speaker 2 (10:53):
Yeah? I love crossing the math beams. That's awesome. I
want a t shirt that says I'm crossing the math beams.
But yeah, that's basic the idea. And remember that what
we're doing in physics is trying to build a mental
model that describes the universe easy. Those mental models are
always imperfect. They're always incomplete, they're always simplifications. Even if
(11:14):
you're talking about like the flight of a baseball, right,
how does a baseball fly across the field? Well, I'm
going to use a parabola in Newton's equations, but I
can't do the calculation very easily. I have had to
include air resistance, so I decide I'm not including that
because it's probably not important, and really, to answer my
question of whether the guy's going to catch it, air
resistance doesn't matter. I'm not going to include effects of
(11:34):
humidity and the siazillion things I could include in my
model to make it a very accurate description of the
universe that I don't need to to answer my question.
And so the models that we build to answer questions
about the universe are always incomplete, they are always approximations,
but they're still very very useful. And that's the issue
with quantum mechanics and general relativity is that they are
(11:54):
two different approximate descriptions of the universe that make different approximations,
different foundations assumptions that go into building those models that
are incompatible, and they let us describe different parts of
the universe, as you say, very very well. So if
I want to talk about how two electrons scatter off
of each other, I can use quantum mechanics and talk
about how they interact and the virtual particles they exchange
(12:16):
or the fields that ripple between them, and it all
works out amazingly well. And that can ignore what general
relativity would do in that situation because it's irrelevant. It's
like the wind resistance or the humidity on the baseball.
It doesn't affect the calculations, so I can ignore it.
Or if I want to say, hey, how do galaxies
form and how do they swirl around each other? I
can use general relativity to answer those questions, and that
(12:38):
can ignore the quantum effects because who cares what one
electron does in Andromeda doesn't affect whether our galaxy is
going to crash into that galaxy, general relativity dominates. The
amazing thing is that in every situation in our universe
you can use either quantum mechanics to explain it or
general relativity and ignore the other one. A perfect divorced
(13:00):
couple that have separated their lives and never have to interact.
You know, there are no argument at McDonald's about who's
taking the kid. Yeah, they're co parenting the universe. And
so you might think, all right, great, what's the problem,
right co parents can live in harmony without ever talking
to each other. Well, there's two problems. One is that's
really unsatisfying, right, Like, we want one explanation for the universe.
(13:24):
We don't want two different explanations. We don't want a
Russiaman universe where both parents tell very very different stories
about what's going on. Right.
Speaker 1 (13:34):
I get that.
Speaker 2 (13:36):
We think that there is one story about the universe.
There's something that's happening, and that there are rules that
are being followed, and we want to know what they are.
We want our best approximation of them. So it's deeply
unsatisfying to have two different, incompatible theories of the universe.
And also, there are moments in the universe a very
few places. In times when you can't ignore one ar
(13:58):
or the other, you need things like the heart of
a black hole a singularity. In general, relativity is incompatible
with quantum mechanics, which says you've got to have some
fuzziness or the Big Bang or the very early universe
when things were really, really hot and dense. You need
the rules of quantum mechanics to describe those particles. But
you can't ignore gravity because things are so hot and
(14:20):
so dense. So we desperately want to find a way
to bring these two together. But as you say, the
math beings don't cross, right.
Speaker 1 (14:27):
I mean, it's like, as physicists you now kind of
have to play as a couple's therapist, where you have
these two theories that are essentially speaking different languages and
they cannot come to an agreement, and they can be
perfectly functional on their own, but then when they come together,
they are unable to communicate. And the Yeah, I mean,
(14:50):
it seems like resolving that difference between the two theories,
like resolving why they don't work with each other, would
actually reveal some big things that we just fundamentally have
not understood yet about the universe.
Speaker 5 (15:06):
M M.
Speaker 2 (15:06):
You know, I've heard anecdotally about couples that don't actually
speak the same language, you know, where they have like
literally now yet they've fallen in love. That's actually true,
they have some other love language.
Speaker 1 (15:18):
Hi language interpretive there.
Speaker 2 (15:21):
Love at first sight, right, doesn't love it first word?
Speaker 1 (15:24):
Yeah.
Speaker 2 (15:24):
Anyway, you're right that quantum mechanics in general relativity don't
get along, and one of the reasons is that they
are built on very different assumptions. Like general relativity says
the universe is smooth, it's continuous, it's precise, there's an
infinite number of locations. It says that you can divide
space an infinite number of times, like relativity agrees with
Zeno's paradox, right that between you and a candy store,
(15:47):
there's always a distance that you can cut in half.
Space from the point of view of general relativity is
something that's smooth and continuous and you always have a
very specific location, whereas quantum mechanics says not. Nothing is
actually smooth and continuous. There are not infinite number of
locations between any two points. Things are discrete and chunky.
A beam of light is actually made up of little
(16:08):
pieces of light, little packets of light. Everything in the
universe is discrete, and it's also imprecise. None of these
little packets have a precise location that have probabilities. So
you see the foundations of these two theories are very
very different. They start from two very different places, and
so weaving them together has a lot of challenges. People
(16:29):
have been trying to make theories of quantum gravity to say, hey,
let's take gravity and try to describe it in the
language of quantum mechanics. For example, think of it like
a quantum field that are exchanging virtual particles. They even
have a name for these particles, it would be the graviton.
But when you sit down and try to do those calculations,
gravity is different from the other quantum forces because it
(16:50):
couples to itself. Everything that has energy has gravity, and
so if you emit a graviton, it also feels gravity,
and it emits gravitons, which emit more gravitons. You can
infinite number of gravitons, and then you start to get
nonsense answers. So as you say, the math beams don't cross.
Speaker 1 (17:06):
So in terms of gravitons, is that something that has
ever been able to be studying the same way that
you can study protons or is it just sort of
a byproduct of this seems like this could be a
thing based on the math that we have theorized about.
Speaker 2 (17:23):
Yeah, gravitons are purely theoretical, and they're not even coherently theoretical.
Theories that have gravitons in them just don't work their
problems with them, and so it's not just that we
haven't seen them. We don't even understand how they would
work if they did exist. And there also would be
really really hard to spot, Like if you're thinking about
gravitational waves from rotating black holes, for example, those are
(17:46):
not gravitons. Those are ripples in space and time. They
are like a beam of light. Gravitons would be like
taking that beam of light and breaking it up into photons.
So you take that gravitational wave and now break it
up into tiny little gravitons. But even gravitational waves are
really hard to see. Gravitons would be much much tinier,
well beyond our capability. But also mathematically they just don't work.
(18:09):
If you try to do calculations with gravitons, you get
weird answers like what's the probability that this electron is
going to go left? Oh, one hundred and forty percent?
What that doesn't make any sense, right, And so that's
telling you that fundamentally there is a problem with the
mathematics that you need to go deeper and start from
something else, change one of your assumptions in order to
make a working theory of quantum gravity.
Speaker 1 (18:31):
I mean this kind of reminds me in biology of
how like the history of biology and medicine, where we
would start to understand things like we would start to
understand how certain medications work, or you know, understand things like,
you know, a man and a woman make a baby
and the like, there seems to be these germinal cells responsible.
(18:52):
But then we didn't have the ability to get tiny
enough inside the human body where we couldn't see like proteins,
we couldn't see, you know, maybe we at some point
could see cells, but we couldn't see DNA. So there
were so many strange and interesting theories that kept circling
around trying to get closer and closer to the truth.
(19:14):
Like there were really funny ones like imagining that there's
just like a tiny person inside of a sperm cell
and then that grew into a baby. But essentially it's
like we were able to make scientific observations, but without
the ability to get small enough in terms of like
we didn't have electron microscopes, we didn't have the technology
or understanding to study DNA, these theories could not kind
(19:38):
of you know, interweave until we got to that point.
And that kind of seems like where, you know, sort
of like what's happening with the universe. Like we're able to,
you know, make all of these really interesting scientific observations
and they're not necessarily wrong, but there is some fundamental
aspect that it's not necessarily that it's too small to see,
(20:00):
but it's something that we can't see yet or something
that is really hard to observe that might help tie
these things together exactly.
Speaker 2 (20:09):
And because it's a question mark, it's deeply unsatisfying to
not have figured it out. We suspect that when we
do figure it out, it'll be something new, something fascinating,
something that tells us about the basic nature of the universe.
Because it's telling us that Gr's description of the universe
is wrong. Space is not just some bendable manifold and
(20:29):
the quantum mechanics description of the universe is wrong in
some important way. That's what I love about physics, because
it's not just I have a model in my head
that is predicting the universe. You can then look at
that model and ask questions about it that are philosophical
and like, huh, why does the universe work this way?
Or you can look at it and say, oh, that's
why time flows forwards and there's only one dimension of
(20:50):
it in three dimensions of space. If you have that
fundamental theory of the universe, we hope that those kind
of answers can come from it deep insights about the
very nature of reality. And for people who think like, oh,
that's so weird and abstract, I mean, that's like the
context of our whole lives, you know, our entire existence.
Understanding the basic nature of reality of space and time
(21:12):
and matter and energy like that is the stage of
our life, the context of our existence. The stakes could
literally not be higher.
Speaker 1 (21:19):
I mean it's interesting because I'm really curious about things
like animal and human behavior, understanding them and understanding things
like perception and you know, but those kinds of questions
I don't see as too fundamentally different from the questions
that physicists are answering, because in a way, you know,
our perception of things are sort of like behaviors and stuff.
(21:41):
That is how we're able to perceive the universe. And
so these kinds of questions of understanding. Of course, the
methodologies are very different, and what we find are going
to be very different with these two questions, but it's
that's still that kind of desire to understand what are
we and where are we? How do we function, and
how do we function in relation to our environment? And
(22:04):
you know, of course the universe being the largest environment
that we can think of in which we are. But
you know what, we should probably take a quick break
while I really ponder an egg and the membrane of
an egg and try to think about whether this is
something that could describe the universe. All right, so we
(22:39):
are back. I've been staring at this egg for five minutes.
Daniels can attest to that, and you know, I think
maybe the universe could be an egg with yellow stuff
on the inside. What do you think?
Speaker 2 (22:53):
I love your egg theory of the universe. I want
to see the math behind it before I really commit to.
Speaker 1 (22:58):
It one plus one equals too or wait, one time
is one equals too? I accidentally did I'm so bad
at math. I was trying to make a joke where
I did it bath and I did it correctly.
Speaker 2 (23:11):
Oops. Oops, oops.
Speaker 1 (23:13):
So, Daniel, I really want to get deeper into these
ideas because we've talked about how these things don't seem
to add up, and these attempts to make things to
add up have in some sense, I don't want to
say failed, but they haven't reached the finish line yet.
So like gravitons don't make sense yet, are there is
there anything promising where we are seeing some revelations that
(23:37):
may help us get closer to why there is this
fundamental miscommunication between general relativity and quantum mechanics.
Speaker 2 (23:46):
So there definitely has been some progress. Nobody's totally figured
it out, but some of the smartest folks on the
planet have some ideas. And before we get into membrane theory,
you need to take a step back and understand where
it came from, which is from string theory.
Speaker 1 (24:01):
Okay, I'm excited because I remember I remember watching I
Think like a PBS nova thing and they tried to
explain string theory, and it just confused me more than
I think, you know, like if you just said, like,
imagine what string theory is, I'd probably be less confused
at that point until after watching this documentary. I'm not
(24:22):
I don't want to be mean to PBS, but I
don't think they really explained it very well because it
was like they're like these vibrating strings like on a violin,
and it's like, I don't know that that makes a
lot of sense, and I'm confused. You mean, there's tiny
violins everywhere. What's going on? Are the world's smallest violins
making up the universe? So I do want to understand better.
Speaker 2 (24:44):
All right, let's see if we can do better than
Brian Green on PBS. The idea is to avoid some
of the mathematical problems that come when you try to
cross the beam. Those infinities. A lot of those infinities
come from the basic assumption that things are points, that
particles are time need dots because those have infinities in them.
There's infinite densities and the zero volume, et cetera. So
(25:06):
instead of having points, string theory says, what if everything
is a line, so a point is like zero dimensions, right,
it doesn't go in any way. But a string is
one dimension. It's like, well, let's have it have some extent,
and having it have a length means it's not infinitely
dense anymore. There's like a fundamental length to it, and
that avoids some of the infinities in the calculations. Is
(25:27):
like a minimum size to stuff, and that's the length
of a string. And so these strings would be the
fundamental bits of the universe. Essentially the universe is strings.
But these strings can do things. They can wiggle, right,
just like strings in our world, like a violin string.
Speaker 1 (25:42):
Can or or a guitar string if you prefer that.
Speaker 2 (25:48):
But we can't see those wiggles directly. And so what
we see is something really zoomed out, like the string wiggles.
This way, it looks like an electron. When you zoom
way out with string wiggles that way, it looks like
a muon the string. Another way it looks like a quark.
So the idea is not that the electrons and the
quarks are made of tinier particles the way that like
the atom is made of smaller particles, but that you
(26:10):
get something fundamentally different. Right, we need something fundamentally different
to solve this puzzle of quantum gravity. We need a
new idea, and so we say that these particles are
instead made of vibrating strings, and they just look like
different particles because we're too zoomed out to see the details.
Speaker 1 (26:26):
I guess for me, the question is like, I understand
the difference between a point and a line in terms
of dimensionality, but in terms of like a line of what?
Like That's where I get caught up, because I, you know,
usually it's so hard to think about the fundamental like
unit of something because maybe this is just biology brain,
(26:51):
but everything has a smaller thing in it, right, Like
You've got a mouse and the mouse has tissues, and
the tissues have cells. Cells have proteins, and the proteins
have molecules, and the molecules have atoms, and the atoms
have quarks, et cetera, et cetera. I might have skipped
a few steps, but you get the idea, which is
that I'm always thinking, like, what, what do you mean
(27:11):
like a string of what? A line of what?
Speaker 5 (27:14):
So?
Speaker 1 (27:14):
How has that resolved? Like what is? Because I'm assuming
it is not like a literal strand of you know,
like in biology, like a strand of protein. Like if
you're like, there's a string of something, I'm thinking like, oh,
is it proteins? Like you know, is it lipids? What's
it made out of? So in in physics, like what
is this line?
Speaker 2 (27:32):
Yeah, it's a great question, and I understand what you're saying.
You're imagining string in your mind. And you know, if
you're thinking about like a line of frosting on a cake,
you're thinking that squeezed out of some tube and the
line of frosting is made out of that frosting, and
therefore the frosting is the basic universe stuff, not the
line of it. And so you're wondering, like, well, what's
that string made out of? What is string stuff? And
(27:53):
the answer is we don't know. And you're right that
the pattern is that stuff has made a smaller stuff,
which has made a smaller stuff, which is made of
smaller stuff. And so far we've never seen anything that
is just itself that is not made of something.
Speaker 1 (28:06):
That's the truth, You're absolutely right.
Speaker 2 (28:09):
But we have this hunch, We have this hunch that
maybe it is that maybe there's a bottom to the
explanations of the universe. We don't know, And there are
philosophers out there who argue that it could be infinitely regressive, right,
that you just could keep going forever and ever and ever,
and there is no foundational firmament to the universe. Everything
is made of something smaller.
Speaker 1 (28:29):
I hate it either way, Daniel, like either explanation. It
feels uncomfortable somehow, right, Like if the explanation is like
there is the smallest unit and it's a line that wiggles,
I'm like really. And then if you're like no, but
then the line that wiggles, can you can infinitely get
smaller and smaller and smaller, And then still that It's like, really,
(28:49):
it's so hard, And I feel like maybe the reason
it's so difficult is that our human brains are geared
towards a certain type of understanding of things based on
what our evolutionary needs are in terms of something has
a start point and endpoint, or something is made out
of something else and time goes from point A to
(29:10):
point B. When someone who is not a physicist is
trying to think about these things, I think about stuff
that is probably not very relevant to it, Like when
I think of I don't know, you keep talking about
wiggly lines, and I just think about al dente spaghetti
and that's not what it is and it can't be.
But it's so hard to think of. Okay, there's a
(29:33):
basic unit that can't get any smaller, but it's not
made out of anything, and that, you know, it just
kind of breaks my brain. I cannot conceive of that.
Speaker 2 (29:44):
Well, let me put it in another way, which is
maybe easier to sit with in your brain, which is,
we don't know whether strings, if they exist, are the
fundamental basis of the universe, or if they're made of
something smaller. You can put it that way, right, And
we can put it that way because we actually don't
have to know. This is one of the beautiful things
about physics is that we can do calculations at various scales,
(30:05):
ignoring the internal details, not having to know them. Like
when we did that calculation of the baseball flying across
the field, we didn't have to keep track of all
the electrons and even the air resistance on all those
details to mostly get the right answer. You can do
physics at lots of different scales. So even if the
universe infinitely is made of smaller stuff, or if there
is some fundamental chunk to it, we can still do
(30:27):
physics about it without even knowing the answer. So thanks
to the universe for being understandable at lots of levels
even before we figured out quantum gravity. You can imagine
another scenario where in order to do any calculation you
had to understand all the little bits inside of it.
You had to figure out the fundamentals of quantum gravity
before you could make chicken soup. Right, But fortunately in
(30:48):
our universe you can throw baseballs and make chicken soup
and play violins without understanding all the details, so we
can make progress. We can say, well, maybe electrons are
made of strings without knowing whether those strings are also
made of something else, and still have some insight into
this layer of the universe, without knowing if there are
more layers beyond it.
Speaker 1 (31:07):
So we've got possible strings that we don't know exactly
if they exist. But it's a line that can wiggle
in the way in which it wiggles forms some kind
of different thing, which I can kind of accept at
this point. Is that sort of it? In terms of
string theories, it seems like there would probably be a
(31:27):
lot more complexity involved.
Speaker 2 (31:30):
Yeah, there is more complexity. The mathematics of those strings
is very cool. At first, when people were working it out,
they were only able to use strings to describe some
kinds of particles, particles that we call bosons, which are
photons and the W and the Z and the higgs
and the gluons. These are all the bosons, the force
carrying particles. So the original string theory could only describe bosons.
(31:53):
And then people worked on it and found new ways
for those strings to wiggle, so they could also describe fermions,
and that's called super string theory. Super as a reference
to this other idea, supersymmetry, which connects fermions and bosons.
Check out our whole episode about that. But so then
people developed super string theory, and then there was this
sort of revolution in the nineteen eighties when people got
(32:14):
really excited about it. They call it the first super
string revolution. And that's when people realize, Wow, this string
theory is not just a cool mathematical model. It can
describe all the kinds of particles in our universe. And
also it seems like a very promising theory of quantum gravity.
They were able to avoid some of the infinities of
earlier attempts the problems with gravitons by describing things in
(32:34):
terms of strings. So it was a very exciting time.
A lot of people worked on it, and the problem
was that they had lots of different ideas. So there's
not like one string theory or one way to do
string theory. People figured out a bunch of different kinds
of string theories, like you can have strings that are
always open, like they're just lines, or strings that are
closed which means they're loops, or you can have a
(32:55):
theory with strings sometimes are open and sometimes are closed,
or different kinds of ways to solve super gravity. And
so at the end of the eighties there was sort
of a confusion because there were like five different types
of string theory that were all seemed very very different
and all kind of worked, and people weren't sure sort
of where to go from there.
Speaker 1 (33:13):
Right. I mean, that seems kind of tricky because it's
almost like you're sort of filling in the gaps, right
with these different theories, and you can it seems like
they were able to come up with different sort of
math or different theories that did fill that gap in
different ways, and so I don't know how you would
pick which one works if they all sort of can
(33:36):
on average kind of like fix that gap.
Speaker 2 (33:39):
And that's very unsatisfying, right, because we think the universe
is following a set of laws. We think there is
one set of laws, and so then if you find
like two explanations for the universe that both work, you're like, well,
which one is really happening?
Speaker 1 (33:52):
Right?
Speaker 2 (33:53):
You know, is a deep philosophical question.
Speaker 1 (33:55):
Could there actually be something where on this level there
could be multiple sets of rules that all work at
the same time.
Speaker 2 (34:03):
Yeah, philosophers think it's possible that there are multiple explanations
for the universe, multiple theories that predict the universe and
describe it and explain what's happening, but have fundamentally different
stories about sort of what's going on behind the curtain.
We don't know if that's possible, but there's a group
of philosophers who think it might be. And boy, I
hope they're wrong because that would be very frustrating. In
(34:26):
the stupid strink community also was hoping they were wrong.
And we're trying to figure out this puzzle, and one
way to try to figure it out is to see
are there connections between these different theories. Can we show
that actually these theories are really the same thing dressed
up in different clothing, Like are we really just telling
the same story using different words or using different symbols.
(34:47):
It harkens back to like the nineteen twenties when people
were developing quantum mechanics, for example, and you had Schroeninger
he had his wave equation of quantum mechanics, and you
had Heisenberg, he had his matrix formulation of quantum mechanics,
and those two guys did not like each other. In fact,
they hated each other, and they also disliked each other's ideas,
like Heisenberg really didn't like Schrodinger's wave equation. You thought
(35:10):
it made quantum mechanics like too visual, it gave you
a mental image when in stage you just focus on
the math of the matrices. And everybody else hated Heisenberg's
matrices because nobody could understand what they meant. And then
a few decades later John von Neumann showed actually they're
the same. They make the same calculations. You can convert
one into the other, and so they're just like two
(35:32):
different ways to write the same thing, the way that
like algebra and geometry are fundamentally the same. You want
to solve a system of equations like two lines, you
can either draw them on a piece of paper and
see when they cross, or you can do a bunch
of algebra and solve for it. In the end, those
feel like two different kinds of math, but they really
are revealing the same thing or the same relationship between concepts.
(35:53):
So people were wondering, can we do that first dring theory?
Can we show that these different string theories They're called
type one, type two A, type two B, so.
Speaker 1 (36:03):
Thirty two sounds like a disease.
Speaker 2 (36:05):
And E eight x E eight. These are crazy names,
I know, terrible, terrible names. Will be deeply offended.
Speaker 1 (36:12):
I have type one string theory.
Speaker 2 (36:17):
I'm so sorry, kame. There's a group for that. So
people were wondering, is it possible these actually are different
mathematical expressions for the same phenomena. And it was a
hard problem. But there are smart people out there, and
this guy, Ed Witten, maybe one of the smartest dudes ever.
He's at the Institute for Advanced Studies near Princeton, and
(36:39):
he was playing with these strings. Remember, the strings don't
just exist in our three dimensions of space, the math
works best if space has nine dimensions. So these strings
are one dimensional lines through nine dimensional space, our three dimensions,
and then six more dimensions that we can't sense or
perceive or really experience in any way, but the strings
(37:00):
need them in order to make their math wiggle correctly.
Speaker 1 (37:03):
Hmm, yeah, no, I mean I think this is it's
always a wild time trying to think about other dimensions,
because we could probably explain other dimensions with math, but
to try to conceptualize them, I don't know if that's
even possible with our brains, given that our brains are
three dimensional brains and function in a sort of three
(37:25):
dimensional way. So without your neurons being able to span
into the other six dimensions, that seems difficult.
Speaker 2 (37:34):
It is very difficult. You're right, We intuitively think in
three dimensions. It's very hard to think in additional dimensions.
It's even hard to think in fewer dimensions. Like if
you try to imagine a two D sheet or one
D line, you're imagining it in three D space. You
put that sheet into three D space, or that line
in three D space. Or if I tell you imagine
(37:55):
a zero dimensional dot, you think of a point and
you sketch it out into some three D space, because
that's the natural playground of our mind. So if you
can't go down the dimension, there's no hope angling up
a dimension. It's really very difficult.
Speaker 1 (38:08):
I almost passed out once trying to think about like nothing,
like going you know, sort of the zero dimension thing,
trying to think about nothing. And I felt very weird
to try to think about that for too long. It
felt like my brain was kind of leaving my body.
Maybe I was just sleepy. I don't know. But yeah.
There's also that book Flat Landers, where it tries to,
(38:29):
in an artistic way, represent how difficult it is to
bridge the gap between a two D existence and a
three D existence. But you know, fundamentally, even that book
is describing it as a visual experience where having vision
requires three dimensions. It seems so yeah, and.
Speaker 2 (38:48):
So making progress on this requires super smart dudes to
do superstring theory. And so Edwinten was thinking about these
nine dimensional strings, and so those theories are ten dimensional
because it's nine facial dimensions and one time dimension. He
was thinking about these nine dimensional strings, and he was
inspired by this leap from zero dimensional points to one
dimensional lines. Strings and he was wondering, should we take
(39:11):
it a step further. Instead of thinking about these things
as one D strings in nine dimensional spaces, maybe they're
actually two dimensional objects membranes, right, sheets in higher dimensional space.
And so these would be like two D sheets in
ten dimensional space, which looks like one dimensional objects strings
(39:34):
if you only look at them in nine dimensions. So
the idea is he invents this extra dimension, this eleventh
dimension or a tenth dimension of space, and extends the
strings into that space to make them into membranes.
Speaker 1 (39:48):
So more like a sheets theory.
Speaker 2 (39:50):
Yeah, exactly, from strings to.
Speaker 1 (39:52):
Sheets sponsored by sheets the convenience store and gas station.
Speaker 2 (39:58):
So the exciting thing is that Witten thought that if
you worked with membranes instead of strings, you could explain
all these different string theories. That these five string theories
were actually just five different ways to look at the
same sheet. So you roll it up this way, it
looks like one. You roll it up another way it
looks like another. You look at it from this perspective,
(40:20):
it looks like a different string theory. But these five
string theories that people were playing with and confused about
were actually just like extreme examples of one membrane theory,
and this this famous talkie gives at University of Southern
California in ninety five where he points this out and
he makes this connection, and he has this diagram on
the slide which is just like all five theories and
(40:42):
it just like draws lines between them.
Speaker 1 (40:44):
Is it like a corkboard was the eldest shoveled?
Speaker 2 (40:48):
It's exactly like that. Yeah, it's not very compelling as
a diagram, and even his explanation is somewhat lacking. You know,
he doesn't have all the math. He has sort of
like this leap of intuition. He has some hints that
these things do connect to each other. It's like a
new direction forward. And it's sort of like the way
Fineman worked. You know, Fineman developed QED and he didn't
work out all the math came later when like Schwinger
(41:11):
worked through all the details to prove that Fineman's leaps
of intuition were correct. Witness sort of similar. He's like
sees these connections in his brain. He knows that it
can work, even if he hasn't like actually sat down
and worked through it all. And so this one talk
in ninety five inspired what they called the Second super
string Revolution and led to like hundreds and hundreds of
papers of people working on membranes. The interesting thing is
(41:35):
that Witten himself wasn't actually sure that membranes who were
going to work. He was like, hmm, it might be membranes,
it might not be memoranes. I'm not sure. He knew
that these things were connected, but he didn't want to
actually call his theory membrane theory, so he just called
it M theory, and he wrote in his paper quote,
we will non committally call it the M theory, leaving
(41:56):
to the future the revelation of M to membranes, Like
people really worked through the math and showed that these
things were two D objects or actually ten D objects,
then we could call it membrane theory. But until then,
let's just keep it M theory in case it turns
out to be like mouse theory or mama theory or
something else.
Speaker 1 (42:15):
Yeah. No, I mean I like that your hedge in
your bets. I also like this guy kind of sounds
like there's this I forgot his name, but I think
he is like a quote unquote neurosurgeon who kept claiming
that he could do like head transplants, and his demonstration
was a bunch of dried spaghetti and a banana to
(42:37):
show how you could basically like connect all of the
arteries and spinal cord and everything. I think maybe the
banana was supposed to be the spinal cord. Anyways, it
was like a spaghetti banana demonstration, which did not inspire confidence. So,
of course, I think with the physics, when you go
(42:58):
out on a branch in terms of physics, it's maybe
less risky than trusting someone who says they can do
a head transplant.
Speaker 2 (43:06):
Yeah, so I think Edwinten. I wouldn't trust him to
do a head transplant. But I'm glad that he's around
and he's helping us figure out the mysteries of quantum gravity.
And it's really cool that he was able to show
that these theories are related to each other. You know,
there are these funny dualities they find where they show
that this theory is mathematically equivalent to that theory. You know,
(43:27):
like this theory if you make it really strong, looks
like that theory if you make it really weak. It's
fascinating to show that the theories, even though they have
again very different of mathematical foundations. They really are exploring
the same concepts because the symbolism, the notation we use
is really just a way to describe the abstract ideas.
And so even if you use different notations and different symbols,
(43:49):
if you can show that the ideas are equivalent, then
you really have made a connection between them. And it's
a relief also to think, like, well, maybe there is
a connection, because then we don't have to pick one
of the theory. We don't have to have a reason
to choose one. We can just say, oh, they're all
just special cases of one unifying idea. And in the end,
that's what physics is trying to do, is come up
with some unifying, simplifying explanation for everything we see out
(44:13):
there in the universe.
Speaker 1 (44:14):
I mean, I find it really appealing not having to
make a decision between like really hard choices. That sounds great.
Sign me up for physics. Let's take a really quick break,
and then when we get back, let's talk more about
membrane theory and how it could tie everything up in
a nice little bow. All right, So I was a
(44:47):
little bit glib about tying everything up in a nice
little bow. I know that is the desire of physics,
and yet it seems pretty tricky to do that.
Speaker 2 (44:58):
It is pretty tricky, but along the way, we can
entertain ourselves by amusing notation and making up really weird
phrases and names for things. So physics, as everybody knows,
is very good at using inappropriate and confusing words to
describe things. And so physicists have taken this phrase membrane
and tried to generalize it to any dimensional surface. So, like,
(45:21):
you know, a membrane is like a two D surface.
You can imagine like a sheet or like a cell wall.
It's two dimensions, right, And so physicists don't call that
a membrane. They call that a two brain, okay, so
that they can call a string a one brain, or
like the point a zero brain. You're a zero brain, yeah, exactly. Well,
(45:45):
even worse is the general phrase for it. If you
have a surface in P dimensions, you call it a
P brain.
Speaker 1 (45:52):
That's what I call my dog all the time. I'm like,
look at you, old pepe brain.
Speaker 2 (45:56):
Yeah, well you didn't realize you're actually giving it a
vast You're connecting it to the fundamental theory of the universe.
Maybe cookie can reveal something true about reality.
Speaker 1 (46:06):
I look into her eyes, I see these deep pools
of knowledge. But then it turns out she just had
to burn.
Speaker 2 (46:14):
Cookie, had too many cookies.
Speaker 1 (46:15):
It sounds like, yeah, exactly. So now I'm confused because
I kind of got the idea of the membrane being like,
it's not a point, it's not a line. It's like
a plane, but not necessarily a flat plane, one that
could be sort of wrapped around different dimensions. So I
(46:37):
kind of get that. Now we're sort of this terminology
of zero brain being a point, one brain being a string,
two brain being a two D surface. What is the
point of having brain in there? Like as a term?
Like what and I don't mean this like in a
mean way, just like what purpose is that serving in
(46:58):
terms of helping with the research or the explanation.
Speaker 2 (47:02):
Yeah, it's a good question. Maybe physicists just like saying
brain because it doesn't sound smart, sounds like they're talking
about their brains. But physicists like to think about different
versions of ideas, not to be limited by our experience
of the universe, you know, where we have one dimensional
objects and two dimensional objects and three dimensional objects. They'd
like to generalize it and to be opened to other
(47:23):
dimensions and other scales, and so for example, Edwinton's first
idea was maybe the way to do this is to
use two dimensional sheets, which is fascinating to think, like, Okay,
the universe isn't made of points of stuff or even
lines of stuff, but maybe like sheets of stuff. It
would be pretty weird if the universe was made of
(47:44):
two dimensional things the fundamental nature of it, the basic
building block where sheets, that would be weird. But recently
people have been making some progress in an alternative version
of m theory in which the brains are five dimensionals,
so they use five brains, meaning that like you still
work in a theory where there are ten spatial dimensions
(48:04):
in one time dimension, but the fundamental building blocks of
the universe are not sheets. There five dimensional objects, which
is pretty hard to think about and impossible to visualize
with our three brains.
Speaker 1 (48:16):
Yeah, that's an interesting thing because usually the intuitive direction
of units right of stuff or like building blocks of
stuff is like you go from simple to more complex, right,
so like you'd start out with you know, zero dimensions
than one dimensions than two dimensions and three dimensions than
(48:37):
four dimensions, et cetera. Right, and then like as you
get to the smaller building blocks, the kind of intuitive
way is like the smaller the building block, the fewer
the dimensions. Right. But I think it is really interesting
the idea that the smallest building block could be something
that is actually operates among you know, more dimensions than say,
(48:59):
we did as human consciousness. Is because that seems, I
don't know, for some reason, that makes more sense to
me than like the smallest unit being like a point,
even though I cannot there is no way I can
even begin to conceive of five dimensions without sounding like
(49:20):
I'm high on Joe Rogan, I.
Speaker 2 (49:25):
Think you're right though, and I think the lesson there
is the universe is filled with surprises. You know. We
set up this question with we have a puzzle about
the fundamental nature of reality. Is a quantum mechanical? Is
it general relativistic? Is this something new and weird and different?
And we don't have an answer yet, But this line
of investigation building strings into membranes into p brains is
(49:48):
suggesting that we've been thinking about it wrong in terms
of tiny little objects that actually at the foundation of
the universe, the basic level of reality, the intellectual firmament
that we can finally reach built out of complex objects,
objects with five dimensions to them, or even two dimensions.
And that's the kind of revelation we're looking for, you know,
(50:08):
that's exactly the hope that the math points us to
structures that tell us something about what's actually happening out
there in reality. And in a way, that's a surprise,
because I don't expect our intuition to correctly guess how
the universe works. I expect it to be a surprise.
It would be quite disappointing if the universe was a
certain way and we were like, oh, yeah, that makes sense. Instead,
(50:29):
I want that moment where we're like, oh, wow, the
universe actually works in this weird way, how could that
possibly be? And then it requires like a reworking off
your mental model to incorporate that, But that brings you
more in aligned with the way the universe actually works.
And that's kind of the whole goal of science, right,
is to align our brains with the workings of the universe,
(50:49):
not just our silly, clueless, primitive guesses about how the
universe might work.
Speaker 1 (50:55):
So if it was up to me, I would just
hazard a guess that the universe is man, little worms, man,
just tile worms.
Speaker 2 (51:04):
I see. So that's your worm brain theory of the universe.
Speaker 1 (51:06):
My brain theory.
Speaker 2 (51:09):
You and RFKU.
Speaker 1 (51:10):
Yeah, I should run for president and me and my
worms know how.
Speaker 2 (51:15):
To run this chuntry Vice President Terrence Howard, all right, well,
thanks for coming along on this crazy mental journey down
into the fundamental nature of the universe to think about
weird quantum objects, also obeying the rules of gravity and
revealing that the universe is made out of building blocks
that we do not yet understand, but they might require
(51:38):
one brain's two brains or p dimensional pea brains.
Speaker 1 (51:42):
Thank you for helping me understand that the universe is
not made out of tiny violence. That really helps.
Speaker 2 (51:49):
It's only possible because your brain is not a banana.
All right, Thanks very much everybody, and tune in next
time for more science and curiosity. Come find us on
social media where we answer questions and post videos. We're
on Twitter, Discorg, Instant, and now TikTok. Thanks for listening,
(52:12):
and remember that Daniel and Jorge Explain the Universe is
a production of iHeartRadio. For more podcasts from iHeartRadio, visit
the iHeartRadio, app, Apple podcasts, or wherever you listen to
your favorite shows.
Hey, Daniel, have you guys figured out what's inside a
black hole? Yet?
Speaker 2 (00:12):
Unfortunately not? Still pretty confused.
Speaker 1 (00:14):
Okay, it sounds like you guys need to go back
to the drawing board get some new ideas.
Speaker 2 (00:20):
I know, but like from where the smartest people on
the planet have been stuck in this question for literally decades.
Speaker 1 (00:26):
See that is where you are going wrong. You are
looking to the smart people. If you need wacky, crazy ideas,
you need to ask the wacky crazy people like me.
Speaker 2 (00:39):
You're saying we should go to the insane asylum and
ask people what they think is inside a black hole.
Speaker 1 (00:43):
I think that they could come up with some good ideas.
They might be insane enough in the membrane to figure
it out.
Speaker 2 (00:51):
Insane in the brain. Hi, I'm Daniel. I'm a particle
physicist and a professor at UC Irvine. And if you
(01:12):
didn't get my Cypress Hill reference, you're officially young.
Speaker 1 (01:16):
I am Katie. I am not a physicist. I like animals, though,
and I like the universe. And I got that reference.
Speaker 2 (01:26):
Because you're insane in the membrane.
Speaker 1 (01:28):
Exactly, just the membrane, though the rest of me is perfectly.
Speaker 2 (01:32):
Sane and welcome to the podcast Daniel and Jorge Explain
the Universe, in which we do our best to bring
this insane universe into your brain. We try to make
it all make sense, from the tiniest little quantum particles
to the hugest swirling accretion disks surrounding super massive black holes.
(01:52):
We have this hunch that maybe the universe is understandable,
that it's a big mathematical puzzle that we can of
eventually figure it out if we put all of our
brains and membranes together. And our goal on this podcast
is to explain all of it to you.
Speaker 1 (02:08):
Now, that's another song, super Massive black Hole. I think
muse soundtrack to that really sort of indie movie called Twilight.
Speaker 2 (02:19):
Are you sure that wasn't part of the hip hop
wars in the nineties, super Massive black Hole?
Speaker 1 (02:24):
I couldn't say. In the nineties, I was not cool
enough to know.
Speaker 2 (02:29):
Well, you know, maybe there are some secrets in music
that can help us crack the mysteries of the universe,
because you know, some people say the universe is musical
and there's a connection between music and mathematics, right, So
maybe we have been looking in the wrong places.
Speaker 1 (02:44):
Yeah, Like I've heard this in terms of string theory,
where strings aren't you know, they're not like violin strings,
But it's something about some like either vibration or pattern. Honestly,
I do not understand it, but you know, well, I
think that is interesting that there is the idea that
(03:04):
a lot of the mysteries of the universe could be
about certain frequencies or patterns, which is also what is
the major components of music.
Speaker 2 (03:16):
Exactly, Although if you listen to Terrence Howard on Joe Rogan,
it's all frequencies.
Speaker 1 (03:20):
Man, is all frequencies?
Speaker 2 (03:22):
Man?
Speaker 1 (03:22):
Why am I not on Joe Rogan? See, I just
can say that too.
Speaker 2 (03:27):
I can because you believe that one times one equals one,
and Terrence Howard proves that it equals to And that's
why you're just not mathematically qualified to be.
Speaker 1 (03:38):
I just can't think outside of the box enough to
not do mauth good exactly.
Speaker 2 (03:43):
But we are fascinated by the mysteries of the universe.
We do think that there are mathematical solutions to them.
Maybe they are encoded in the sonatas of Mozart. Maybe
the engineers are right that it's all vibrations all the
way down. But we hope that there is an explanation.
And one of the biggest things and we need an
explanation for is how to think about the universe on
the smallest scales. What happens when things get really, really
(04:07):
dense and really really tiny. One of the biggest puzzles
in modern physics is how to put together the two
pillars of our understanding of the universe, relativity and quantum mechanics.
We've been banging our heads against this for almost one
hundred years, basically since we've had relativity and quantum mechanics
and realize that they are fundamentally incompatible at the smallest scale.
(04:30):
And we've been trying to figure this out. And today
on the podcast, we'll be exploring yet another attempt to
unify relativity and quantum mechanics. So on the podcast today
we'll be answering the question what is membrane theory?
Speaker 1 (04:49):
Okay, as a biology nerd, I'm pretty sure I can
answer this. A membrane is a semi permeable barrier, So
I solved it. Congratulations to me.
Speaker 2 (05:04):
What about the audio barrier between us and the listeners
the ideas from our brains and that their brains have
we permeated a membrane.
Speaker 1 (05:12):
I yes, why not. I don't know enough about audio
engineering to say no or philosophy, so I'm gonna say yes.
We're like salt ions through the airwaves, permeating the membrane,
so hopefully you can reach homeostasis.
Speaker 2 (05:32):
So I'm not surprised that when you heard this phrase
you thought of cellular membranes divisions between solutions. You want
to keep osmosis from, like moving all these bits of
salt over here, or using fats to keep that over there.
But it's not just in biology that we have membranes.
It turns out that they are fundamental concept in theories
(05:52):
of quantum gravity. But before we dig into that, I
was curious what everybody else out there thought when they
heard membrane theory. As usual, I asked our cadre of
volunteers to speculate on the question without the opportunity to
use Google. So, if you would like to join this
group of volunteers in the future, please don't be shy.
Write me to questions at Danielandjorge dot com. We all
(06:15):
want to hear what you have to say. In the meantime,
check out these answers from listeners. What do you think
membrane theory is here's what people had to say. That's
the first time I'm hearing golfit.
Speaker 3 (06:27):
But if I had to guess membranes, the function of
the membranes are to pass on stuff in one direction
and other stuff not in the other direction. So maybe
we're talking about it's a mechanism about particle coexistence through
a wall of things something like that.
Speaker 4 (06:45):
Just to guess, what comes to mind for me on
that one is that it's something that you use to
separate things, like in a fuel cell car, you know,
you separate components and you make energy. Maybe it's like
a desalination thing where you take salt.
Speaker 2 (06:57):
Out of water.
Speaker 4 (06:58):
So maybe there's some membrane here in the universe that's doing.
Speaker 2 (07:01):
That in space.
Speaker 5 (07:03):
I'm guessing membrane theory has to do with the outside
of a cell. Maybe how the membrane, you know, protects
the core of the cell and how it stays intact.
Speaker 2 (07:16):
I think it has to do with string theory. There
are strings that vibrate in there one dimension, and I
think a membrane is a something similar that can have
more than one dimension.
Speaker 1 (07:26):
See, I'm I'm definitely with the theory that everything is
a cell. If you look at the universe, it's just
a giant body for some kind of huge animal. You know,
it makes sense, right, you're saying the universe is alive. Yeah,
it's a big maybe a giant cat. I don't know.
(07:47):
Have you ever looked at like a black cat? Right,
It's it kind of has that sort of quantum mechanics
and general relativity paradox. Right, it's like a fluid, it's
a solid. It's sweet and loving, and then it bites you.
So yeah, I think the universe could be a giant cat.
And when you get down to the tiniest components there cells,
(08:09):
and yeah, it's been solved.
Speaker 2 (08:11):
You're welcome and we're done, Thank you very much. Physics
is over. Katie wins all of the Nobel prices. Heay, Well,
we're definitely hearing from listeners the connection to biology, which
makes a lot of sense, and the idea of having
two dimensional surfaces or even connections to string theory. So
there's a lot of good stuff in here that we're
(08:31):
going to dig into and explain in this episode. But
a plus to all the listeners.
Speaker 1 (08:37):
I mean, I would assume that, yes, it's probably not
like a cellular membrane. But if we're talking about a membrane,
I would guess it is some kind of barrier through
which certain physics transactions can occur. But that would be
my guess.
Speaker 2 (08:56):
Is this whole podcast a physics transaction? We are taking
your time and exchanging it for knowledge, is like a
physics transaction.
Speaker 1 (09:03):
You know what? That's pretty good. I think I'm wondering
about the exchange rate, though, because that's that's the real issue.
Speaker 2 (09:10):
Yeah, I think we're too high on the jokes permit
it and too low and the physics permitted so far.
Let's try to flip that right now.
Speaker 1 (09:16):
All right, well, okay, let me have it. Like, what's
going on with this membrane theory?
Speaker 2 (09:21):
So membrane theory is an attempt to crack the puzzle
of quantum gravity. So let's start with that. What is
the puzzle of quantum gravity? Why do we want to
crack it? What is the issue? Why are all the
smart people on the planet thinking they need to go
into the insane this islum if they can't figure this out?
The basic issue is we have two ways to describe
the universe. There's general relativity, which tells us about space
(09:42):
and time and energy, and the expansion of the universe
describes a lot of the big stuff. It tells us
how gravity works and how the universe is expanding, and
how far away galaxies are getting red shifted and all
that good stuff. And then we have quantum mechanics, which
describes the really small stuff, the little part of goals
light and all this kind of quantum fields and sort
(10:03):
of our understanding of microscopic matter. And the issue is
that we don't know how to make these two things
play well together.
Speaker 1 (10:11):
They don't play nice because I've actually, i think I've
been on the show a couple times when we talked
about this conundrum, and so it seems like, you know,
when you have these mathematical theories that describe each of them,
it works within it. So the general relativity math works
within general relativity. It seems really nice and neat and good.
(10:32):
Same thing for quantum mechanics. But then when you try
to cross the beams the math beams, suddenly it doesn't work.
Like if you're trying to use general relativity math to
describe what you know is observed in experiments happening on
sort of the quantum level, or vice versa. It no
longer works. Is that more or less?
Speaker 2 (10:53):
Yeah? I love crossing the math beams. That's awesome. I
want a t shirt that says I'm crossing the math beams.
But yeah, that's basic the idea. And remember that what
we're doing in physics is trying to build a mental
model that describes the universe easy. Those mental models are
always imperfect. They're always incomplete, they're always simplifications. Even if
(11:14):
you're talking about like the flight of a baseball, right,
how does a baseball fly across the field? Well, I'm
going to use a parabola in Newton's equations, but I
can't do the calculation very easily. I have had to
include air resistance, so I decide I'm not including that
because it's probably not important, and really, to answer my
question of whether the guy's going to catch it, air
resistance doesn't matter. I'm not going to include effects of
(11:34):
humidity and the siazillion things I could include in my
model to make it a very accurate description of the
universe that I don't need to to answer my question.
And so the models that we build to answer questions
about the universe are always incomplete, they are always approximations,
but they're still very very useful. And that's the issue
with quantum mechanics and general relativity is that they are
(11:54):
two different approximate descriptions of the universe that make different approximations,
different foundations assumptions that go into building those models that
are incompatible, and they let us describe different parts of
the universe, as you say, very very well. So if
I want to talk about how two electrons scatter off
of each other, I can use quantum mechanics and talk
about how they interact and the virtual particles they exchange
(12:16):
or the fields that ripple between them, and it all
works out amazingly well. And that can ignore what general
relativity would do in that situation because it's irrelevant. It's
like the wind resistance or the humidity on the baseball.
It doesn't affect the calculations, so I can ignore it.
Or if I want to say, hey, how do galaxies
form and how do they swirl around each other? I
can use general relativity to answer those questions, and that
(12:38):
can ignore the quantum effects because who cares what one
electron does in Andromeda doesn't affect whether our galaxy is
going to crash into that galaxy, general relativity dominates. The
amazing thing is that in every situation in our universe
you can use either quantum mechanics to explain it or
general relativity and ignore the other one. A perfect divorced
(13:00):
couple that have separated their lives and never have to interact.
You know, there are no argument at McDonald's about who's
taking the kid. Yeah, they're co parenting the universe. And
so you might think, all right, great, what's the problem,
right co parents can live in harmony without ever talking
to each other. Well, there's two problems. One is that's
really unsatisfying, right, Like, we want one explanation for the universe.
(13:24):
We don't want two different explanations. We don't want a
Russiaman universe where both parents tell very very different stories
about what's going on. Right.
Speaker 1 (13:34):
I get that.
Speaker 2 (13:36):
We think that there is one story about the universe.
There's something that's happening, and that there are rules that
are being followed, and we want to know what they are.
We want our best approximation of them. So it's deeply
unsatisfying to have two different, incompatible theories of the universe.
And also, there are moments in the universe a very
few places. In times when you can't ignore one ar
(13:58):
or the other, you need things like the heart of
a black hole a singularity. In general, relativity is incompatible
with quantum mechanics, which says you've got to have some
fuzziness or the Big Bang or the very early universe
when things were really, really hot and dense. You need
the rules of quantum mechanics to describe those particles. But
you can't ignore gravity because things are so hot and
(14:20):
so dense. So we desperately want to find a way
to bring these two together. But as you say, the
math beings don't cross, right.
Speaker 1 (14:27):
I mean, it's like, as physicists you now kind of
have to play as a couple's therapist, where you have
these two theories that are essentially speaking different languages and
they cannot come to an agreement, and they can be
perfectly functional on their own, but then when they come together,
they are unable to communicate. And the Yeah, I mean,
(14:50):
it seems like resolving that difference between the two theories,
like resolving why they don't work with each other, would
actually reveal some big things that we just fundamentally have
not understood yet about the universe.
Speaker 5 (15:06):
M M.
Speaker 2 (15:06):
You know, I've heard anecdotally about couples that don't actually
speak the same language, you know, where they have like
literally now yet they've fallen in love. That's actually true,
they have some other love language.
Speaker 1 (15:18):
Hi language interpretive there.
Speaker 2 (15:21):
Love at first sight, right, doesn't love it first word?
Speaker 1 (15:24):
Yeah.
Speaker 2 (15:24):
Anyway, you're right that quantum mechanics in general relativity don't
get along, and one of the reasons is that they
are built on very different assumptions. Like general relativity says
the universe is smooth, it's continuous, it's precise, there's an
infinite number of locations. It says that you can divide
space an infinite number of times, like relativity agrees with
Zeno's paradox, right that between you and a candy store,
(15:47):
there's always a distance that you can cut in half.
Space from the point of view of general relativity is
something that's smooth and continuous and you always have a
very specific location, whereas quantum mechanics says not. Nothing is
actually smooth and continuous. There are not infinite number of
locations between any two points. Things are discrete and chunky.
A beam of light is actually made up of little
(16:08):
pieces of light, little packets of light. Everything in the
universe is discrete, and it's also imprecise. None of these
little packets have a precise location that have probabilities. So
you see the foundations of these two theories are very
very different. They start from two very different places, and
so weaving them together has a lot of challenges. People
(16:29):
have been trying to make theories of quantum gravity to say, hey,
let's take gravity and try to describe it in the
language of quantum mechanics. For example, think of it like
a quantum field that are exchanging virtual particles. They even
have a name for these particles, it would be the graviton.
But when you sit down and try to do those calculations,
gravity is different from the other quantum forces because it
(16:50):
couples to itself. Everything that has energy has gravity, and
so if you emit a graviton, it also feels gravity,
and it emits gravitons, which emit more gravitons. You can
infinite number of gravitons, and then you start to get
nonsense answers. So as you say, the math beams don't cross.
Speaker 1 (17:06):
So in terms of gravitons, is that something that has
ever been able to be studying the same way that
you can study protons or is it just sort of
a byproduct of this seems like this could be a
thing based on the math that we have theorized about.
Speaker 2 (17:23):
Yeah, gravitons are purely theoretical, and they're not even coherently theoretical.
Theories that have gravitons in them just don't work their
problems with them, and so it's not just that we
haven't seen them. We don't even understand how they would
work if they did exist. And there also would be
really really hard to spot, Like if you're thinking about
gravitational waves from rotating black holes, for example, those are
(17:46):
not gravitons. Those are ripples in space and time. They
are like a beam of light. Gravitons would be like
taking that beam of light and breaking it up into photons.
So you take that gravitational wave and now break it
up into tiny little gravitons. But even gravitational waves are
really hard to see. Gravitons would be much much tinier,
well beyond our capability. But also mathematically they just don't work.
(18:09):
If you try to do calculations with gravitons, you get
weird answers like what's the probability that this electron is
going to go left? Oh, one hundred and forty percent?
What that doesn't make any sense, right, And so that's
telling you that fundamentally there is a problem with the
mathematics that you need to go deeper and start from
something else, change one of your assumptions in order to
make a working theory of quantum gravity.
Speaker 1 (18:31):
I mean this kind of reminds me in biology of
how like the history of biology and medicine, where we
would start to understand things like we would start to
understand how certain medications work, or you know, understand things like,
you know, a man and a woman make a baby
and the like, there seems to be these germinal cells responsible.
(18:52):
But then we didn't have the ability to get tiny
enough inside the human body where we couldn't see like proteins,
we couldn't see, you know, maybe we at some point
could see cells, but we couldn't see DNA. So there
were so many strange and interesting theories that kept circling
around trying to get closer and closer to the truth.
(19:14):
Like there were really funny ones like imagining that there's
just like a tiny person inside of a sperm cell
and then that grew into a baby. But essentially it's
like we were able to make scientific observations, but without
the ability to get small enough in terms of like
we didn't have electron microscopes, we didn't have the technology
or understanding to study DNA, these theories could not kind
(19:38):
of you know, interweave until we got to that point.
And that kind of seems like where, you know, sort
of like what's happening with the universe. Like we're able to,
you know, make all of these really interesting scientific observations
and they're not necessarily wrong, but there is some fundamental
aspect that it's not necessarily that it's too small to see,
(20:00):
but it's something that we can't see yet or something
that is really hard to observe that might help tie
these things together exactly.
Speaker 2 (20:09):
And because it's a question mark, it's deeply unsatisfying to
not have figured it out. We suspect that when we
do figure it out, it'll be something new, something fascinating,
something that tells us about the basic nature of the universe.
Because it's telling us that Gr's description of the universe
is wrong. Space is not just some bendable manifold and
(20:29):
the quantum mechanics description of the universe is wrong in
some important way. That's what I love about physics, because
it's not just I have a model in my head
that is predicting the universe. You can then look at
that model and ask questions about it that are philosophical
and like, huh, why does the universe work this way?
Or you can look at it and say, oh, that's
why time flows forwards and there's only one dimension of
(20:50):
it in three dimensions of space. If you have that
fundamental theory of the universe, we hope that those kind
of answers can come from it deep insights about the
very nature of reality. And for people who think like, oh,
that's so weird and abstract, I mean, that's like the
context of our whole lives, you know, our entire existence.
Understanding the basic nature of reality of space and time
(21:12):
and matter and energy like that is the stage of
our life, the context of our existence. The stakes could
literally not be higher.
Speaker 1 (21:19):
I mean it's interesting because I'm really curious about things
like animal and human behavior, understanding them and understanding things
like perception and you know, but those kinds of questions
I don't see as too fundamentally different from the questions
that physicists are answering, because in a way, you know,
our perception of things are sort of like behaviors and stuff.
(21:41):
That is how we're able to perceive the universe. And
so these kinds of questions of understanding. Of course, the
methodologies are very different, and what we find are going
to be very different with these two questions, but it's
that's still that kind of desire to understand what are
we and where are we? How do we function, and
how do we function in relation to our environment? And
(22:04):
you know, of course the universe being the largest environment
that we can think of in which we are. But
you know what, we should probably take a quick break
while I really ponder an egg and the membrane of
an egg and try to think about whether this is
something that could describe the universe. All right, so we
(22:39):
are back. I've been staring at this egg for five minutes.
Daniels can attest to that, and you know, I think
maybe the universe could be an egg with yellow stuff
on the inside. What do you think?
Speaker 2 (22:53):
I love your egg theory of the universe. I want
to see the math behind it before I really commit to.
Speaker 1 (22:58):
It one plus one equals too or wait, one time
is one equals too? I accidentally did I'm so bad
at math. I was trying to make a joke where
I did it bath and I did it correctly.
Speaker 2 (23:11):
Oops. Oops, oops.
Speaker 1 (23:13):
So, Daniel, I really want to get deeper into these
ideas because we've talked about how these things don't seem
to add up, and these attempts to make things to
add up have in some sense, I don't want to
say failed, but they haven't reached the finish line yet.
So like gravitons don't make sense yet, are there is
there anything promising where we are seeing some revelations that
(23:37):
may help us get closer to why there is this
fundamental miscommunication between general relativity and quantum mechanics.
Speaker 2 (23:46):
So there definitely has been some progress. Nobody's totally figured
it out, but some of the smartest folks on the
planet have some ideas. And before we get into membrane theory,
you need to take a step back and understand where
it came from, which is from string theory.
Speaker 1 (24:01):
Okay, I'm excited because I remember I remember watching I
Think like a PBS nova thing and they tried to
explain string theory, and it just confused me more than
I think, you know, like if you just said, like,
imagine what string theory is, I'd probably be less confused
at that point until after watching this documentary. I'm not
(24:22):
I don't want to be mean to PBS, but I
don't think they really explained it very well because it
was like they're like these vibrating strings like on a violin,
and it's like, I don't know that that makes a
lot of sense, and I'm confused. You mean, there's tiny
violins everywhere. What's going on? Are the world's smallest violins
making up the universe? So I do want to understand better.
Speaker 2 (24:44):
All right, let's see if we can do better than
Brian Green on PBS. The idea is to avoid some
of the mathematical problems that come when you try to
cross the beam. Those infinities. A lot of those infinities
come from the basic assumption that things are points, that
particles are time need dots because those have infinities in them.
There's infinite densities and the zero volume, et cetera. So
(25:06):
instead of having points, string theory says, what if everything
is a line, so a point is like zero dimensions, right,
it doesn't go in any way. But a string is
one dimension. It's like, well, let's have it have some extent,
and having it have a length means it's not infinitely
dense anymore. There's like a fundamental length to it, and
that avoids some of the infinities in the calculations. Is
(25:27):
like a minimum size to stuff, and that's the length
of a string. And so these strings would be the
fundamental bits of the universe. Essentially the universe is strings.
But these strings can do things. They can wiggle, right,
just like strings in our world, like a violin string.
Speaker 1 (25:42):
Can or or a guitar string if you prefer that.
Speaker 2 (25:48):
But we can't see those wiggles directly. And so what
we see is something really zoomed out, like the string wiggles.
This way, it looks like an electron. When you zoom
way out with string wiggles that way, it looks like
a muon the string. Another way it looks like a quark.
So the idea is not that the electrons and the
quarks are made of tinier particles the way that like
the atom is made of smaller particles, but that you
(26:10):
get something fundamentally different. Right, we need something fundamentally different
to solve this puzzle of quantum gravity. We need a
new idea, and so we say that these particles are
instead made of vibrating strings, and they just look like
different particles because we're too zoomed out to see the details.
Speaker 1 (26:26):
I guess for me, the question is like, I understand
the difference between a point and a line in terms
of dimensionality, but in terms of like a line of what?
Like That's where I get caught up, because I, you know,
usually it's so hard to think about the fundamental like
unit of something because maybe this is just biology brain,
(26:51):
but everything has a smaller thing in it, right, Like
You've got a mouse and the mouse has tissues, and
the tissues have cells. Cells have proteins, and the proteins
have molecules, and the molecules have atoms, and the atoms
have quarks, et cetera, et cetera. I might have skipped
a few steps, but you get the idea, which is
that I'm always thinking, like, what, what do you mean
(27:11):
like a string of what? A line of what?
Speaker 5 (27:14):
So?
Speaker 1 (27:14):
How has that resolved? Like what is? Because I'm assuming
it is not like a literal strand of you know,
like in biology, like a strand of protein. Like if
you're like, there's a string of something, I'm thinking like, oh,
is it proteins? Like you know, is it lipids? What's
it made out of? So in in physics, like what
is this line?
Speaker 2 (27:32):
Yeah, it's a great question, and I understand what you're saying.
You're imagining string in your mind. And you know, if
you're thinking about like a line of frosting on a cake,
you're thinking that squeezed out of some tube and the
line of frosting is made out of that frosting, and
therefore the frosting is the basic universe stuff, not the
line of it. And so you're wondering, like, well, what's
that string made out of? What is string stuff? And
(27:53):
the answer is we don't know. And you're right that
the pattern is that stuff has made a smaller stuff,
which has made a smaller stuff, which is made of
smaller stuff. And so far we've never seen anything that
is just itself that is not made of something.
Speaker 1 (28:06):
That's the truth, You're absolutely right.
Speaker 2 (28:09):
But we have this hunch, We have this hunch that
maybe it is that maybe there's a bottom to the
explanations of the universe. We don't know, And there are
philosophers out there who argue that it could be infinitely regressive, right,
that you just could keep going forever and ever and ever,
and there is no foundational firmament to the universe. Everything
is made of something smaller.
Speaker 1 (28:29):
I hate it either way, Daniel, like either explanation. It
feels uncomfortable somehow, right, Like if the explanation is like
there is the smallest unit and it's a line that wiggles,
I'm like really. And then if you're like no, but
then the line that wiggles, can you can infinitely get
smaller and smaller and smaller, And then still that It's like, really,
(28:49):
it's so hard, And I feel like maybe the reason
it's so difficult is that our human brains are geared
towards a certain type of understanding of things based on
what our evolutionary needs are in terms of something has
a start point and endpoint, or something is made out
of something else and time goes from point A to
(29:10):
point B. When someone who is not a physicist is
trying to think about these things, I think about stuff
that is probably not very relevant to it, Like when
I think of I don't know, you keep talking about
wiggly lines, and I just think about al dente spaghetti
and that's not what it is and it can't be.
But it's so hard to think of. Okay, there's a
(29:33):
basic unit that can't get any smaller, but it's not
made out of anything, and that, you know, it just
kind of breaks my brain. I cannot conceive of that.
Speaker 2 (29:44):
Well, let me put it in another way, which is
maybe easier to sit with in your brain, which is,
we don't know whether strings, if they exist, are the
fundamental basis of the universe, or if they're made of
something smaller. You can put it that way, right, And
we can put it that way because we actually don't
have to know. This is one of the beautiful things
about physics is that we can do calculations at various scales,
(30:05):
ignoring the internal details, not having to know them. Like
when we did that calculation of the baseball flying across
the field, we didn't have to keep track of all
the electrons and even the air resistance on all those
details to mostly get the right answer. You can do
physics at lots of different scales. So even if the
universe infinitely is made of smaller stuff, or if there
is some fundamental chunk to it, we can still do
(30:27):
physics about it without even knowing the answer. So thanks
to the universe for being understandable at lots of levels
even before we figured out quantum gravity. You can imagine
another scenario where in order to do any calculation you
had to understand all the little bits inside of it.
You had to figure out the fundamentals of quantum gravity
before you could make chicken soup. Right, But fortunately in
(30:48):
our universe you can throw baseballs and make chicken soup
and play violins without understanding all the details, so we
can make progress. We can say, well, maybe electrons are
made of strings without knowing whether those strings are also
made of something else, and still have some insight into
this layer of the universe, without knowing if there are
more layers beyond it.
Speaker 1 (31:07):
So we've got possible strings that we don't know exactly
if they exist. But it's a line that can wiggle
in the way in which it wiggles forms some kind
of different thing, which I can kind of accept at
this point. Is that sort of it? In terms of
string theories, it seems like there would probably be a
(31:27):
lot more complexity involved.
Speaker 2 (31:30):
Yeah, there is more complexity. The mathematics of those strings
is very cool. At first, when people were working it out,
they were only able to use strings to describe some
kinds of particles, particles that we call bosons, which are
photons and the W and the Z and the higgs
and the gluons. These are all the bosons, the force
carrying particles. So the original string theory could only describe bosons.
(31:53):
And then people worked on it and found new ways
for those strings to wiggle, so they could also describe fermions,
and that's called super string theory. Super as a reference
to this other idea, supersymmetry, which connects fermions and bosons.
Check out our whole episode about that. But so then
people developed super string theory, and then there was this
sort of revolution in the nineteen eighties when people got
(32:14):
really excited about it. They call it the first super
string revolution. And that's when people realize, Wow, this string
theory is not just a cool mathematical model. It can
describe all the kinds of particles in our universe. And
also it seems like a very promising theory of quantum gravity.
They were able to avoid some of the infinities of
earlier attempts the problems with gravitons by describing things in
(32:34):
terms of strings. So it was a very exciting time.
A lot of people worked on it, and the problem
was that they had lots of different ideas. So there's
not like one string theory or one way to do
string theory. People figured out a bunch of different kinds
of string theories, like you can have strings that are
always open, like they're just lines, or strings that are
closed which means they're loops, or you can have a
(32:55):
theory with strings sometimes are open and sometimes are closed,
or different kinds of ways to solve super gravity. And
so at the end of the eighties there was sort
of a confusion because there were like five different types
of string theory that were all seemed very very different
and all kind of worked, and people weren't sure sort
of where to go from there.
Speaker 1 (33:13):
Right. I mean, that seems kind of tricky because it's
almost like you're sort of filling in the gaps, right
with these different theories, and you can it seems like
they were able to come up with different sort of
math or different theories that did fill that gap in
different ways, and so I don't know how you would
pick which one works if they all sort of can
(33:36):
on average kind of like fix that gap.
Speaker 2 (33:39):
And that's very unsatisfying, right, because we think the universe
is following a set of laws. We think there is
one set of laws, and so then if you find
like two explanations for the universe that both work, you're like, well,
which one is really happening?
Speaker 1 (33:52):
Right?
Speaker 2 (33:53):
You know, is a deep philosophical question.
Speaker 1 (33:55):
Could there actually be something where on this level there
could be multiple sets of rules that all work at
the same time.
Speaker 2 (34:03):
Yeah, philosophers think it's possible that there are multiple explanations
for the universe, multiple theories that predict the universe and
describe it and explain what's happening, but have fundamentally different
stories about sort of what's going on behind the curtain.
We don't know if that's possible, but there's a group
of philosophers who think it might be. And boy, I
hope they're wrong because that would be very frustrating. In
(34:26):
the stupid strink community also was hoping they were wrong.
And we're trying to figure out this puzzle, and one
way to try to figure it out is to see
are there connections between these different theories. Can we show
that actually these theories are really the same thing dressed
up in different clothing, Like are we really just telling
the same story using different words or using different symbols.
(34:47):
It harkens back to like the nineteen twenties when people
were developing quantum mechanics, for example, and you had Schroeninger
he had his wave equation of quantum mechanics, and you
had Heisenberg, he had his matrix formulation of quantum mechanics,
and those two guys did not like each other. In fact,
they hated each other, and they also disliked each other's ideas,
like Heisenberg really didn't like Schrodinger's wave equation. You thought
(35:10):
it made quantum mechanics like too visual, it gave you
a mental image when in stage you just focus on
the math of the matrices. And everybody else hated Heisenberg's
matrices because nobody could understand what they meant. And then
a few decades later John von Neumann showed actually they're
the same. They make the same calculations. You can convert
one into the other, and so they're just like two
(35:32):
different ways to write the same thing, the way that
like algebra and geometry are fundamentally the same. You want
to solve a system of equations like two lines, you
can either draw them on a piece of paper and
see when they cross, or you can do a bunch
of algebra and solve for it. In the end, those
feel like two different kinds of math, but they really
are revealing the same thing or the same relationship between concepts.
(35:53):
So people were wondering, can we do that first dring theory?
Can we show that these different string theories They're called
type one, type two A, type two B, so.
Speaker 1 (36:03):
Thirty two sounds like a disease.
Speaker 2 (36:05):
And E eight x E eight. These are crazy names,
I know, terrible, terrible names. Will be deeply offended.
Speaker 1 (36:12):
I have type one string theory.
Speaker 2 (36:17):
I'm so sorry, kame. There's a group for that. So
people were wondering, is it possible these actually are different
mathematical expressions for the same phenomena. And it was a
hard problem. But there are smart people out there, and
this guy, Ed Witten, maybe one of the smartest dudes ever.
He's at the Institute for Advanced Studies near Princeton, and
(36:39):
he was playing with these strings. Remember, the strings don't
just exist in our three dimensions of space, the math
works best if space has nine dimensions. So these strings
are one dimensional lines through nine dimensional space, our three dimensions,
and then six more dimensions that we can't sense or
perceive or really experience in any way, but the strings
(37:00):
need them in order to make their math wiggle correctly.
Speaker 1 (37:03):
Hmm, yeah, no, I mean I think this is it's
always a wild time trying to think about other dimensions,
because we could probably explain other dimensions with math, but
to try to conceptualize them, I don't know if that's
even possible with our brains, given that our brains are
three dimensional brains and function in a sort of three
(37:25):
dimensional way. So without your neurons being able to span
into the other six dimensions, that seems difficult.
Speaker 2 (37:34):
It is very difficult. You're right, We intuitively think in
three dimensions. It's very hard to think in additional dimensions.
It's even hard to think in fewer dimensions. Like if
you try to imagine a two D sheet or one
D line, you're imagining it in three D space. You
put that sheet into three D space, or that line
in three D space. Or if I tell you imagine
(37:55):
a zero dimensional dot, you think of a point and
you sketch it out into some three D space, because
that's the natural playground of our mind. So if you
can't go down the dimension, there's no hope angling up
a dimension. It's really very difficult.
Speaker 1 (38:08):
I almost passed out once trying to think about like nothing,
like going you know, sort of the zero dimension thing,
trying to think about nothing. And I felt very weird
to try to think about that for too long. It
felt like my brain was kind of leaving my body.
Maybe I was just sleepy. I don't know. But yeah.
There's also that book Flat Landers, where it tries to,
(38:29):
in an artistic way, represent how difficult it is to
bridge the gap between a two D existence and a
three D existence. But you know, fundamentally, even that book
is describing it as a visual experience where having vision
requires three dimensions. It seems so yeah, and.
Speaker 2 (38:48):
So making progress on this requires super smart dudes to
do superstring theory. And so Edwinten was thinking about these
nine dimensional strings, and so those theories are ten dimensional
because it's nine facial dimensions and one time dimension. He
was thinking about these nine dimensional strings, and he was
inspired by this leap from zero dimensional points to one
dimensional lines. Strings and he was wondering, should we take
(39:11):
it a step further. Instead of thinking about these things
as one D strings in nine dimensional spaces, maybe they're
actually two dimensional objects membranes, right, sheets in higher dimensional space.
And so these would be like two D sheets in
ten dimensional space, which looks like one dimensional objects strings
(39:34):
if you only look at them in nine dimensions. So
the idea is he invents this extra dimension, this eleventh
dimension or a tenth dimension of space, and extends the
strings into that space to make them into membranes.
Speaker 1 (39:48):
So more like a sheets theory.
Speaker 2 (39:50):
Yeah, exactly, from strings to.
Speaker 1 (39:52):
Sheets sponsored by sheets the convenience store and gas station.
Speaker 2 (39:58):
So the exciting thing is that Witten thought that if
you worked with membranes instead of strings, you could explain
all these different string theories. That these five string theories
were actually just five different ways to look at the
same sheet. So you roll it up this way, it
looks like one. You roll it up another way it
looks like another. You look at it from this perspective,
(40:20):
it looks like a different string theory. But these five
string theories that people were playing with and confused about
were actually just like extreme examples of one membrane theory,
and this this famous talkie gives at University of Southern
California in ninety five where he points this out and
he makes this connection, and he has this diagram on
the slide which is just like all five theories and
(40:42):
it just like draws lines between them.
Speaker 1 (40:44):
Is it like a corkboard was the eldest shoveled?
Speaker 2 (40:48):
It's exactly like that. Yeah, it's not very compelling as
a diagram, and even his explanation is somewhat lacking. You know,
he doesn't have all the math. He has sort of
like this leap of intuition. He has some hints that
these things do connect to each other. It's like a
new direction forward. And it's sort of like the way
Fineman worked. You know, Fineman developed QED and he didn't
work out all the math came later when like Schwinger
(41:11):
worked through all the details to prove that Fineman's leaps
of intuition were correct. Witness sort of similar. He's like
sees these connections in his brain. He knows that it
can work, even if he hasn't like actually sat down
and worked through it all. And so this one talk
in ninety five inspired what they called the Second super
string Revolution and led to like hundreds and hundreds of
papers of people working on membranes. The interesting thing is
(41:35):
that Witten himself wasn't actually sure that membranes who were
going to work. He was like, hmm, it might be membranes,
it might not be memoranes. I'm not sure. He knew
that these things were connected, but he didn't want to
actually call his theory membrane theory, so he just called
it M theory, and he wrote in his paper quote,
we will non committally call it the M theory, leaving
(41:56):
to the future the revelation of M to membranes, Like
people really worked through the math and showed that these
things were two D objects or actually ten D objects,
then we could call it membrane theory. But until then,
let's just keep it M theory in case it turns
out to be like mouse theory or mama theory or
something else.
Speaker 1 (42:15):
Yeah. No, I mean I like that your hedge in
your bets. I also like this guy kind of sounds
like there's this I forgot his name, but I think
he is like a quote unquote neurosurgeon who kept claiming
that he could do like head transplants, and his demonstration
was a bunch of dried spaghetti and a banana to
(42:37):
show how you could basically like connect all of the
arteries and spinal cord and everything. I think maybe the
banana was supposed to be the spinal cord. Anyways, it
was like a spaghetti banana demonstration, which did not inspire confidence. So,
of course, I think with the physics, when you go
(42:58):
out on a branch in terms of physics, it's maybe
less risky than trusting someone who says they can do
a head transplant.
Speaker 2 (43:06):
Yeah, so I think Edwinten. I wouldn't trust him to
do a head transplant. But I'm glad that he's around
and he's helping us figure out the mysteries of quantum gravity.
And it's really cool that he was able to show
that these theories are related to each other. You know,
there are these funny dualities they find where they show
that this theory is mathematically equivalent to that theory. You know,
(43:27):
like this theory if you make it really strong, looks
like that theory if you make it really weak. It's
fascinating to show that the theories, even though they have
again very different of mathematical foundations. They really are exploring
the same concepts because the symbolism, the notation we use
is really just a way to describe the abstract ideas.
And so even if you use different notations and different symbols,
(43:49):
if you can show that the ideas are equivalent, then
you really have made a connection between them. And it's
a relief also to think, like, well, maybe there is
a connection, because then we don't have to pick one
of the theory. We don't have to have a reason
to choose one. We can just say, oh, they're all
just special cases of one unifying idea. And in the end,
that's what physics is trying to do, is come up
with some unifying, simplifying explanation for everything we see out
(44:13):
there in the universe.
Speaker 1 (44:14):
I mean, I find it really appealing not having to
make a decision between like really hard choices. That sounds great.
Sign me up for physics. Let's take a really quick break,
and then when we get back, let's talk more about
membrane theory and how it could tie everything up in
a nice little bow. All right, So I was a
(44:47):
little bit glib about tying everything up in a nice
little bow. I know that is the desire of physics,
and yet it seems pretty tricky to do that.
Speaker 2 (44:58):
It is pretty tricky, but along the way, we can
entertain ourselves by amusing notation and making up really weird
phrases and names for things. So physics, as everybody knows,
is very good at using inappropriate and confusing words to
describe things. And so physicists have taken this phrase membrane
and tried to generalize it to any dimensional surface. So, like,
(45:21):
you know, a membrane is like a two D surface.
You can imagine like a sheet or like a cell wall.
It's two dimensions, right, And so physicists don't call that
a membrane. They call that a two brain, okay, so
that they can call a string a one brain, or
like the point a zero brain. You're a zero brain, yeah, exactly. Well,
(45:45):
even worse is the general phrase for it. If you
have a surface in P dimensions, you call it a
P brain.
Speaker 1 (45:52):
That's what I call my dog all the time. I'm like,
look at you, old pepe brain.
Speaker 2 (45:56):
Yeah, well you didn't realize you're actually giving it a
vast You're connecting it to the fundamental theory of the universe.
Maybe cookie can reveal something true about reality.
Speaker 1 (46:06):
I look into her eyes, I see these deep pools
of knowledge. But then it turns out she just had
to burn.
Speaker 2 (46:14):
Cookie, had too many cookies.
Speaker 1 (46:15):
It sounds like, yeah, exactly. So now I'm confused because
I kind of got the idea of the membrane being like,
it's not a point, it's not a line. It's like
a plane, but not necessarily a flat plane, one that
could be sort of wrapped around different dimensions. So I
(46:37):
kind of get that. Now we're sort of this terminology
of zero brain being a point, one brain being a string,
two brain being a two D surface. What is the
point of having brain in there? Like as a term?
Like what and I don't mean this like in a
mean way, just like what purpose is that serving in
(46:58):
terms of helping with the research or the explanation.
Speaker 2 (47:02):
Yeah, it's a good question. Maybe physicists just like saying
brain because it doesn't sound smart, sounds like they're talking
about their brains. But physicists like to think about different
versions of ideas, not to be limited by our experience
of the universe, you know, where we have one dimensional
objects and two dimensional objects and three dimensional objects. They'd
like to generalize it and to be opened to other
(47:23):
dimensions and other scales, and so for example, Edwinton's first
idea was maybe the way to do this is to
use two dimensional sheets, which is fascinating to think, like, Okay,
the universe isn't made of points of stuff or even
lines of stuff, but maybe like sheets of stuff. It
would be pretty weird if the universe was made of
(47:44):
two dimensional things the fundamental nature of it, the basic
building block where sheets, that would be weird. But recently
people have been making some progress in an alternative version
of m theory in which the brains are five dimensionals,
so they use five brains, meaning that like you still
work in a theory where there are ten spatial dimensions
(48:04):
in one time dimension, but the fundamental building blocks of
the universe are not sheets. There five dimensional objects, which
is pretty hard to think about and impossible to visualize
with our three brains.
Speaker 1 (48:16):
Yeah, that's an interesting thing because usually the intuitive direction
of units right of stuff or like building blocks of
stuff is like you go from simple to more complex, right,
so like you'd start out with you know, zero dimensions
than one dimensions than two dimensions and three dimensions than
(48:37):
four dimensions, et cetera. Right, and then like as you
get to the smaller building blocks, the kind of intuitive
way is like the smaller the building block, the fewer
the dimensions. Right. But I think it is really interesting
the idea that the smallest building block could be something
that is actually operates among you know, more dimensions than say,
(48:59):
we did as human consciousness. Is because that seems, I
don't know, for some reason, that makes more sense to
me than like the smallest unit being like a point,
even though I cannot there is no way I can
even begin to conceive of five dimensions without sounding like
(49:20):
I'm high on Joe Rogan, I.
Speaker 2 (49:25):
Think you're right though, and I think the lesson there
is the universe is filled with surprises. You know. We
set up this question with we have a puzzle about
the fundamental nature of reality. Is a quantum mechanical? Is
it general relativistic? Is this something new and weird and different?
And we don't have an answer yet, But this line
of investigation building strings into membranes into p brains is
(49:48):
suggesting that we've been thinking about it wrong in terms
of tiny little objects that actually at the foundation of
the universe, the basic level of reality, the intellectual firmament
that we can finally reach built out of complex objects,
objects with five dimensions to them, or even two dimensions.
And that's the kind of revelation we're looking for, you know,
(50:08):
that's exactly the hope that the math points us to
structures that tell us something about what's actually happening out
there in reality. And in a way, that's a surprise,
because I don't expect our intuition to correctly guess how
the universe works. I expect it to be a surprise.
It would be quite disappointing if the universe was a
certain way and we were like, oh, yeah, that makes sense. Instead,
(50:29):
I want that moment where we're like, oh, wow, the
universe actually works in this weird way, how could that
possibly be? And then it requires like a reworking off
your mental model to incorporate that, But that brings you
more in aligned with the way the universe actually works.
And that's kind of the whole goal of science, right,
is to align our brains with the workings of the universe,
(50:49):
not just our silly, clueless, primitive guesses about how the
universe might work.
Speaker 1 (50:55):
So if it was up to me, I would just
hazard a guess that the universe is man, little worms, man,
just tile worms.
Speaker 2 (51:04):
I see. So that's your worm brain theory of the universe.
Speaker 1 (51:06):
My brain theory.
Speaker 2 (51:09):
You and RFKU.
Speaker 1 (51:10):
Yeah, I should run for president and me and my
worms know how.
Speaker 2 (51:15):
To run this chuntry Vice President Terrence Howard, all right, well,
thanks for coming along on this crazy mental journey down
into the fundamental nature of the universe to think about
weird quantum objects, also obeying the rules of gravity and
revealing that the universe is made out of building blocks
that we do not yet understand, but they might require
(51:38):
one brain's two brains or p dimensional pea brains.
Speaker 1 (51:42):
Thank you for helping me understand that the universe is
not made out of tiny violence. That really helps.
Speaker 2 (51:49):
It's only possible because your brain is not a banana.
All right, Thanks very much everybody, and tune in next
time for more science and curiosity. Come find us on
social media where we answer questions and post videos. We're
on Twitter, Discorg, Instant, and now TikTok. Thanks for listening,
(52:12):
and remember that Daniel and Jorge Explain the Universe is
a production of iHeartRadio. For more podcasts from iHeartRadio, visit
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your favorite shows.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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