Classic episode - Why is gravity so weird?

Why is gravity so much weaker than the other forces?

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Episode Transcript

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Speaker 5 (02:00):
I just think it's fascinating that it's such a fundamental
force in the universe, right, Like it's basically the thing
that builds galaxies and keeps planets moving right and gives
structure to the entire cosmos.

Speaker 1 (02:15):
That's right. On the largest scale, it's actually the most
important force. It's the reason why things look the way
they do. It's the reason why our planet is round.
It's the reason why we're on the planet.

Speaker 5 (02:27):
It's pretty important, and yet we don't know a lot
about it, right, Like, there's some really deep and strange
mysteries about it.

Speaker 1 (02:35):
On one hand, we have a theory which works really
really well. On the other hand, we have questions about
it which seems really really basic.

Speaker 5 (02:42):
And not only that, it's very different than all the
other forces of nature.

Speaker 1 (02:46):
That's right, one of these things is not like the
other ones.

Speaker 5 (03:08):
Hi am morhee.

Speaker 1 (03:09):
I'm a cartoonist and I'm Daniel. I'm a particle physicist.

Speaker 5 (03:12):
And this is our podcast Daniel and Jorge explain the universe.

Speaker 1 (03:16):
In which a cartoonist and a physicists try to figure
out how to make the universe understandable to anybody.

Speaker 5 (03:22):
Yeah, and today on the podcast we are examining a
very heavy topic, gravity and specifically why is gravity so.

Speaker 1 (03:37):
Weak and strange. Gravity, as we said earlier, is something
which controls the structure of the universe. I mean, the
reason the Solar System looks the way it does is
because of gravity. The reason the Earth is round is
because of gravity. The reason we have galaxies is because
of gravity.

Speaker 5 (03:54):
The reason we weigh so much is because of gravity. Right,
it's not my.

Speaker 1 (03:58):
Belt, No, that's because of late night cake eating.

Speaker 5 (04:03):
But it's such a fundamental force of nature, right, Like
it's present in our everyday life. We spend a lot
of time thinking about gravity, right, how not to fall down,
how not to drop things, how to go up buildings,
how to go down buildings.

Speaker 1 (04:18):
Right, that's right. It seems like one of the most
important forces. I mean, if you ask people, you know,
to name a force or what kind of forces the
experience in their life, gravity is the one that's present
in their lives.

Speaker 6 (04:28):
Right.

Speaker 1 (04:28):
You're climbing upstairs, you're fighting gravity, you trip, you fall down,
you're feeling gravity. You look around you. The shape of
things is controlled by gravity. And that's why it's particularly
strange that gravity is the weakest force of all the
forces we've discovered. It's by far the weakest.

Speaker 5 (04:45):
Yeah, it's really strange to hear you say that, Like,
how can gravity be weak? Like, you know, like it's
keeping the whole Earth together, it's making the entire planet
swing around, go in a circle, basically. Right. Without gravity,
we would just shoot off into space.

Speaker 1 (05:00):
That's right. It's a really strange situation. And there's other
things about gravity we don't understand as well. It's really strange.
It doesn't play well with the other forces. It's very,
very weak. It's a total mystery to science, except that
we have a theory which works beautifully right. We can
calculate exactly how mercury orbits the sun. We can send
things in outer space and know with to millimeter precision

(05:20):
exactly where they're going to land. We have a working
theory that we can use, right, but we don't understand
it on a conceptual level. We have these basic, deep
questions about what gravity is and how the universe works
because of it.

Speaker 5 (05:32):
So it's a weird question, and maybe one of the
people hadn't thought about before. So Daniel went out as
usual and asked people on the street, why do you
think gravity is so weak?

Speaker 1 (05:42):
Here's what a random selection of folks who were willing
to talk to me on a Tuesday morning had to
say about gravity.

Speaker 6 (05:47):
I don't know.

Speaker 1 (05:48):
I should don't know about that, all right. I thought
it was a pretty strong force. I don't know, but yeah, because.

Speaker 5 (05:57):
It depends on the distance and it's long range one.
So that's why we feel it very weak most of
the time. Cool, No, Okay, I have no I'm sorry,
it's not very fruitful.

Speaker 3 (06:08):
Hmmm, I have no idea, but I'd be interested in
finding out why.

Speaker 5 (06:14):
All right, that was that was pretty good. Most people
weren't surprised when you said gravity's weak.

Speaker 1 (06:19):
I don't know. I feel like if all the questions
I've asked people, this is the one that flumms them
the most. You know, people were like, what, I have
no idea, or they had crazy ideas why gravity must
be weak. I feel like usually we get one person
who knows what the answer is or has a good
clue about what's going on. This time, I feel like
almost everybody was pretty clueless. I mean, one person said

(06:40):
I always thought gravity was pretty strong, right, which kind
of sums up the situation, right. Gravity's omnipresent in our lives.
It dominates our experience, and yet it's so weak compared
to the other really powerful forces we've discovered.

Speaker 5 (06:53):
Well, some people a couple of answers were that it
had to do with distance, like gravity gets really weak
with distance.

Speaker 1 (07:00):
That's right, And the problem there is that all the
forces get weak with distance, like electromagnetism also falls as
a distance grows. Right, So all of these forces follow
this one over r squared rule or are as your
distance from the thing that's giving.

Speaker 5 (07:15):
You the force, right, maybe maybe right?

Speaker 1 (07:18):
Maybe yeah, mostly we think, And so that can't be
the answer, right, because all the other forces have that
same feature.

Speaker 5 (07:24):
So when you say it's the weak is it's not
that it changes over distances differently than the other forces.

Speaker 1 (07:29):
That's right. So maybe we should talk about what the
forces are and compare them to each other so folks
can get an understanding of how crazy weak gravity is.

Speaker 5 (07:38):
Right. So, Daniel, what are the forces of nature besides
a bad movie with Ben Affleck than Center Bullet.

Speaker 1 (07:45):
Well, I think comedy. Comedy is definitely a force of nature.
You know, it solves big problems around the world. Now,
the fundamental forces are electromagnetism, right, that's the one that
controls electricity and magnetism obviously, and his responsible for the
cool things like light and lightning and all that cool stuff.
And then there's the weak nuclear force, which is a

(08:08):
force which is responsible for radioactive decay of a nuclei, right,
And the cool thing about electricity and magnetism and the
weak nuclear force. Is that we actually have shown that
there are two sides of the same coin. As a
particle physicist, we refer to them as one force. We
call it the electro week. So sort of magnetism lost
out there in the name merger, right, it should be

(08:29):
electromagnetic week. But nobody voted to keep magnetism in the
sort of the name of the partners in a law firm.

Speaker 5 (08:35):
Nobody lobbied for weak electro.

Speaker 1 (08:38):
Or magneto weak force. Yeah, yeah, again, we are suffering
the fate of some anonymous committee of scientists that get
to name these things. Right, Who are these people?

Speaker 5 (08:49):
Probably some grad student, right or some you know, like
this is really weird, we'll call it this.

Speaker 1 (08:55):
Yeah. So we have electricity and magnetism, which is a
single force. We have the weak nuclear force, which is
really should be combined with electricity magnetism. And then there's
the strong nuclear force. And this is the one that
holds the nucleus together. You know, the nucleus is of
just a bunch of positively charged protons and neutral neutrons. Right,
it says only positively charged particles in the nucleus. So

(09:15):
you might think, what it even holds the nucleus together. Right,
you have all this positively charged stuff should be repelling themselves. Well,
it's the strong nuclear force, and it does so by
exchanging these crazy little particles we call gluons, and that
holds the nucleus together, and it's pretty strong. It's even
stronger than electromagnetism.

Speaker 5 (09:32):
Well, let's take a step back. So in the universe
there's stuff.

Speaker 1 (09:36):
There's like, yes, firm that there is stuff in the universe. Yes,
without reservation, there is stuff.

Speaker 5 (09:43):
I'm glad we saw that question. But I mean it's
like there's stuff that has substance to it, that has
mass to it, or you know that it sort of exists.
And then there's also besides that, how these things interact
with each other, like how they affect each other.

Speaker 1 (09:57):
That's right. There's the matter and then there's the forces. Right,
the forces affect how they interact with each other.

Speaker 5 (10:02):
And that's pretty much the universe. That's like, it's matter
and forces.

Speaker 1 (10:07):
Yeah, one way to look at the universe is that
it's particles, right, or you would say matter and their forces.
In modern particle physics, we think about one level deeper,
which is we think of quantum fields and quantum fields
are responsible both for matter and for forces. So we
can talk about that maybe in another podcast. What is
a quantum field? And how can I get one? You know,
for lease or rent? What can they do for me?

(10:29):
But yeah, I think it's fair still to think about
the universe in terms of particles and forces.

Speaker 5 (10:34):
On that note, let's take a quick break.

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Speaker 5 (15:02):
There are only four kinds of forces.

Speaker 1 (15:04):
Yeah, there are four kinds of forces. So electromagnetism, weak
nuclear force, strong nuclear force, and then of course gravity. Right,
that's the fourth force that we've discovered.

Speaker 5 (15:14):
Okay.

Speaker 1 (15:14):
The fascinating thing is that different particles feel different forces, right, Like,
some particles feel this set of forces. Some particles feel
those set of force for example, right, particles with electric
charge feel electromagnetism. Right. The electron, for example, is negatively charged,
the proton is positively charged. You bring them close together,
they're gonna pull on each other. They're gonna stuck each

(15:36):
other together, right, because they have opposite charges. We all
know that, but you bring a neutral particle nearby, it
just totally ignores it, right, It doesn't feel it at all. Right, Right,
It's like it's like somebody's walking through a crowd of
people shouting, but they have headphones on so they can't
hear anything. They're totally oblivious to it.

Speaker 5 (15:53):
It's kind of like how we talked about in a
previous podcast. They're almost like languages or like social media platforms.
Like some people are on Twitter, some people are on Facebook,
but some people are not on this. And so if somebody,
if you're not on Twitter and somebody sends you a tweet,
you're not going to get it. And so it's just
different ways that particles interact.

Speaker 1 (16:10):
That's right. Gravity is the Google plus social media, right
because nobody uses the trends. It's ancient but powerless. Yeah,
And so different particles feel different forces. And for example,
an electron, while it feels electromagnetism because it has a
negative charge, it doesn't feel the strong force at all.

(16:31):
It will pass right by a bunch of particles that
are really tugging on each other with a strong force
and not be affected at all. Whereas quarks. Quarks feel
all the forces. They feel a strong force, which is
how they get pulled together in the nucleus. Remember, protons
and neutrons are made of quarks. Quarks feel electromagnetism because
they have electric charge, they feel the weak force. They
also feel gravity, of course, because they have masks. So

(16:53):
quarks get their fingers in everything.

Speaker 5 (16:56):
They get the feels for everything, They feel everything erect.

Speaker 1 (17:00):
They got the strong feels. Of course, they're really deeply
emotional part of that. And on the other side of
the spectrum, you've got things like neutrinos and trinos don't
have electric charge, so they ignore all electricity and magnetism. Right,
they don't interact with light. They're invisible. They pass right
through anything that They ignore electromagnetic bonds, so they pass

(17:21):
through most materials. They don't feel the strong force. The
only way they interact is with the weak force. And
the weak force is pretty weak, which is why neutrinos
can mostly just pass through matter unaffected.

Speaker 5 (17:36):
So we have four fundamental forces, right, and gravity is
one of these forces. And so when you say that
gravity is weak, you actually mean it's weak compared to
these other three forces.

Speaker 1 (17:46):
That's right. And so the ranking is the strong force
is the strongest, right, so that one is actually well named. Congratulations,
you know anonymous group of scientists. Yeah, we should be
called the as of twenty eighteen, currently known to be
the strongest force force. Right after that comes electromagnetism, and
you know, we know that force's pretty powerful. You stick

(18:07):
your finger in the socket, you're gonna feel the wrath
of electromagnetism. Right, It's not an unfamiliar feeling.

Speaker 5 (18:12):
Right, try to stick your finger in anything, you feel it, right,
because it's electromagnetism is the force that keeps you from
basically passing through the table or passing through your car.

Speaker 1 (18:23):
Right, that's right, because electromagnetism is the basis of chemical bonds, right,
and chemical bonds are really the thing that form the
structure of your body. Right. You think of your body
is like a bunch of particles, but it's held together
by all these forces. It's like a chain link fence
binding together these little particles that prevents you from passing
through something else. Yeah, So we got the strong force,
and then electromagnetism and then actually the weak nuclear force. Right,

(18:47):
this is the force that like powers neutrinos and radioactive decay.
It's much weaker than electromagnetism and much weaker than the
strong force.

Speaker 5 (18:56):
Even weaker than the weak is gravity.

Speaker 1 (18:58):
That's right. If you make a list like strong force, electromagnetism,
in the weak force, then you should leave like one
hundred blank pages, and then you get to gravity. Because
when we compare these forces, we put things like an
equal distance apart, and we compare the strength of the forces.
Gravity is ten to the thirty six times weaker than
the weak force. That's ten with thirty six zeros in

(19:21):
front of it.

Speaker 5 (19:22):
But isn't that sort of a matter of units or scale?
Do you know what I mean? Like, it's much weaker,
but only if you compare apples to apples, right, or
just oranges.

Speaker 1 (19:33):
That's right, But put two protons next to each other, right,
h Two protons have a certain amount of mass and
a certain amount of electric charge, and the force of
their charges is going to be much much stronger than
the force from their masses.

Speaker 5 (19:44):
Oh I see.

Speaker 1 (19:45):
So yeah, if everything was much much more massive, then
there would be stronger gravity. But you can compare these
things apples to apples by comparing them at you know
the same distance and the same basic unit of interaction.

Speaker 5 (19:55):
Right, But what if you take an apple put it
next to another apple?

Speaker 1 (19:59):
Well, I think you can do that experiment. Nothing's going
to happen because gravity is so weak. Right. You don't
see two apples like pulling themselves together on the counter, right,
And though built in apple collider, you know the apples
are not drawn to each other. Gravity is a super
weak force, and you can see this yourself. Right, you
can do an experiment where you counter the entire gravitational
force of an enormous celestial body like the Earth. Right,

(20:22):
take a small kitchen magnet and use it to hold
up a nail, and think about what's happening there, right,
You have the nail is being pulled down by every
single rock in the Earth. It's pulling with all of
its gravity. But a tiny little kitchen magnet totally overcomes that.

Speaker 5 (20:38):
It can lift a nail even though it's pulling, it's
being pulled down by the whole entire planet Earth.

Speaker 1 (20:44):
Right exactly. Now, imagine a magnet the size of the Earth, right,
I mean that would be that would be extraordinarily powerful.
And so you have basically like a gravitational blob the
size of the Earth still pretty ineffective compared to electromagnetism.

Speaker 5 (20:58):
Mmmm, so it's weak if you sort of compare it
by object, Like you said, if you take a proton
and put an extra proton, the force are going to
feel from electromagnetism is so much bigger than the force
of gravity. They're going to feel towards each other the
same with like two electrons or two quarks and things.

(21:19):
So in the scale of like the particles that we know, it's.

Speaker 1 (21:22):
A really weak force, that's right, exactly, And yet and
yet it seems to dominate, right. That's a bit of
a puzzle, Like, on one hand, it's super duper weak,
and we're telling you that it hardly counts for anything.
On the other hand, it's responsible for the structure of
the Solar System, man for the galaxy, and it's the
reason the universe looks the way it is, right, right,
And so that can be confusing to people, Like how

(21:42):
do you reconcile those two things in your head?

Speaker 5 (21:44):
Yeah, Like, why doesn't the Earth feel an electromagnetic force
with the Sun, which it would be so much bigger
than the force of gravity.

Speaker 1 (21:52):
Yeah, Well, it would be pretty shocking, And that's actually
the reason is gravity is different from the other forces
and that it can't be canceled out. Right, if there
was some huge electrostatic difference between the Sun and the Earth,
like a bunch of positive charges there and a bunch
of negative charges here, it would create such an enormous
force that it would be very quickly balanced. Like that's

(22:13):
what lightning is. Right. When there's a charge differential between
clouds and the grounds, it doesn't take that much before
those charges want to rearrange themselves to a lower energy configuration.
They rush down to the ground, or they'd rush up
to the clouds, or they jump the cloud cloud to
balance themselves out. Because you have two kinds of charges,
you have positive and you have negative, so you can

(22:33):
find an arrangement where basically everybody's happy. It's an equilibrium, right,
But that's not true for gravity.

Speaker 5 (22:39):
Okay, I get it. So for example, if the Earth
was every particle on Earth had a positive electromagnetic charge,
and every particle in the Sun had a negative electromagnetic charge,
there would be a humongous pull from electromagnetism, pulling the
Earth into the Sun.

Speaker 1 (22:56):
Yeah, we'd be toased pretty quick Yeah.

Speaker 5 (23:00):
Yeah, would be huge. Even the opposite. If we were
all positive and the Sun was all positive, we would
get shot out of the Solar system very quickly.

Speaker 1 (23:08):
That's right. And that's why you know, early days of
the Solar system being formed, you have these gases and
the gas and dust coalescing and very rapidly things neutralize, right,
because anything that feels an electrostatic force to something else
is going to find the opposite charge and they're going
to coalesce and they're going to make something neutral. Right.
That's why most of the things around you are neutral, right,

(23:29):
Most of the elements are neutral, because any deviation from
neutral results in a powerful force to neutralize it.

Speaker 5 (23:36):
So, thankfully the Earth is made out of both like
equal amounts of positive and negative particles, right, that's right.
Thankfully we're sort of balanced electromagnetically, and so even if
the Sun was all positive, we would look like neutral,
like a neutral ball to the Sun.

Speaker 1 (23:53):
Yeah, that's right. Where on large scales the Earth is neutral, right,
I mean, there might be some residual positive or negative
charge depending on the solar wind, et cetera. But basically
the Earth is neutral, and so the largest force of
the Earth feels is the gravity from the sun, even
though gravity is super duper weak, right, it doesn't take
a lot to counteract gravity. But it's the only player
left because everybody else is sort of pair it up

(24:15):
and danced off for the night, and gravity's just there left,
hold in the bag. And gravity can't be balanced, right.
You feel gravity if you have any mass. Right, there's
only positive masses, no such thing as a negative mass
to give anti gravity.

Speaker 5 (24:29):
Wow, well, let's keep going, but first let's take a
quick break. Okay, So that's how gravity is so much
weaker than the other forces. So how's it different than

(24:53):
the other three forces of nature?

Speaker 1 (24:55):
There's like no end to waste. The gravity is weird,
you know, there's no end to like the puzzles of
gravity is fascinating.

Speaker 5 (25:01):
Bottomless pit.

Speaker 1 (25:03):
That's right, it's a black hole of questions. And one
of my favorites is just that we have no way
to sort of fit gravity in with the way the
universe works according to everything else. You know, we talked
earlier about how we have particles and we have forces
or quantum fields equivalently, and that's a really successful way
to describe the universe. You know, we have the Large

(25:24):
Hadron Collider to explore these things really high energies. And
we've understood all sorts of things using this theory, but
that theory is used as quantum mechanics. So the way
we describe interactions, you know, the way we talk about
two electrons repelling each other, or the way lightning is
formed or anything, involves passing quantum particles back and forth.

(25:45):
And that's just not true for gravity.

Speaker 5 (25:47):
What does that mean? Passing particles back and forth? Like
when like if I have two magnets and they're attracted
to each other, they're not. They're not It's not like
an invisible telekinesis pulling on each other. They're actually swapping particles,
and I can see that is that kind of what
do you mean?

Speaker 1 (26:02):
That's exactly what I mean. That the way two things
interact via some force is by exchanging particles. And so
for example, electromagnetism, right, is the force behind a magnet.
And the way electromagnetism works, we think at a sort
of microscopic particle level, is that there's a particle that
transmits that force, that sends sort of the information back

(26:22):
and forth between two things that are feeling it and
in the case of electromagnetism, that particle is the photon. Right,
the particle is also a packet of light. So each
of the quantum forces that we talked about before, electromagnetism,
the weak force and the strong force, each of them
have a particle we associate with it. And that's not
just like some name tag we put on and say, hey,

(26:44):
you get this one, you get this one. We think
that that's the particle that's responsible for making the force work.
So when two electrons come near each other, how do
they repel each other? How does that actually happen? Well,
we think that they send photons out right, the electric
field of a moving electron, right, and accelerating electron generates photons,
and those photons interact with the other electrons, and so

(27:08):
basically the passing messages back and forth using these quantum particles.

Speaker 5 (27:12):
So gravity is weird because we don't know that there
is a quantum particle being exchanged when two things get
attracted gravitationally.

Speaker 1 (27:21):
That's right, So we have this great framework. We say, oh,
maybe all forces are quantum mechanical fields interacting with each other. Right,
Let's apply that to the electromagnetic field. Yeah, it works.
Let's apply that to the weak force. Yeah it works.
Let's apply to the strong force. Ooh, cool, it works.
Maybe this is something deep about the way the universe works.
Let's apply it to gravity. Uh. Oh, it doesn't work right,

(27:43):
So what does that mean? What does it mean when
I say it doesn't work? Well? For a theory to work,
it has to provide predictions for experiments. You have to
be able to say, okay, theory, what would happen in
this configuration if I shot a proton and another particle.
Predict what would happen, and then you can often do
the experiments and compare it right. Well, when you do
that for gravity, you try to form a quantum theory

(28:05):
of gravity, it doesn't work. You get nonsense answers. You
get answers like infinity right, or things disappear, or it
just it doesn't mathematically function Like, there's no way to
build a theory of gravity that we've discovered so far
that works, that actually explains the way these things happen.
There are a few candidates out there there pretty far

(28:26):
from being a functional theory of quantum gravity, things like
loop quantm gravity or string theory, but the basic problem
is that quantum mechanics and general relativity, which is our
best theory of gravity, do not play well together and
we have no functioning quantum theory of gravity.

Speaker 5 (28:44):
So does that mean that we don't have the right
theory or is that gravity is just not quantum in nature?

Speaker 1 (28:49):
That's exactly the question we don't know the answer to.
Right In one hundred years from now, somebody will know
the answer to that, I hope, and they'll look back
and they'll wonder, you know, why did those guys see
the clues? But we don't know. It could be that
there is a quantum theory gravity, we're just not smart
enough to think it up yet, right, Like the right
person hasn't been born yet to put the math together,
or maybe it requires a different kind of math that

(29:10):
we're using. Right, there's some assumption we're making that's a mistake.

Speaker 5 (29:13):
Or maybe just giving it a wrong name, like maybe
it should be gravit tunis or gravitinos gravitas. That's taken exactly.

Speaker 1 (29:26):
That's definitely the problem. That's step number one, when we
made a mistake in step number one, when we could
define the particle. The other option, of course, is that
maybe gravity is not a quantum force the way the
other forces are. Right. The other forces we call them
quantum forces because they're well described by quantum mechanics. But
gravity is kind of different. I mean, the current theory
we have a gravity general relativity. It doesn't like to

(29:48):
describe gravity as a force, right, describes gravity instead as
a bending of space. It says that when you have
mass somewhere in space, space no longer becomes straight, becomes bent. Right,
things move in curves and circles.

Speaker 5 (30:02):
And it's not like an actual just a mathematical nuance
or a mathematical perspective. What really confirms is it is
the idea that gravity can affect things that don't have mass. Right,
That's how we know it's more than just a force
between things that have mass. It actually like affects space
for things that don't have mass.

Speaker 1 (30:21):
Right, that's exactly right. So if you shoot a photon
through space that has mass nearby, the photon will not
move in what we consider to be a straight line, right,
It'll find a path through this bent space that involves
basically curving. And this is what Einstein predicted with his theory,
and they saw it, you know, and you can see
in space. It's called gravitational lensing. You can see photons

(30:42):
get bent by heavy objects, and it's because, as you say,
the heavy objects are bending space itself.

Speaker 5 (30:48):
Right, It's not like gravity is pulling the photon because
the photon doesn't have any mass.

Speaker 1 (30:53):
Right, that's right, the photon doesn't have any mass.

Speaker 5 (30:55):
Yeah, So that's how it's different. Like gravity seems to
affect things that don't have sort of its fundamental property,
you know, like electrominetic forces can affect something that does
not have an electric charge.

Speaker 1 (31:08):
That's true.

Speaker 5 (31:09):
Gravity can affect thing everything else, right.

Speaker 1 (31:11):
Yeah, that's a pretty deep insight there, Not that for
a cartoonist, not at all. Yeah, that's a fascinating way
to think about it. I think that's totally correct. Yeah.
And so if gravity is instead of being a force,
if it's a way we change the shape of space itself,
then maybe that's why we don't have a quantum theory
of it. Right. And that's amazing and it's fantastic and

(31:33):
it's exciting. And another reason why we have a hard
time bringing these two things together is that quantum mechanics,
the theory we've developed only works so far in flat space.
That is if there's really heavy stuff nearby, we don't
know how to do those quantum calculations. We can basically
only do quantum mechanics in places where there isn't really
strong gravity.

Speaker 5 (31:54):
So wait, it's a quantum physics doesn't work in reality basically?
Is that what you're saying? Like, it doesn't work in
the space that we actually live in.

Speaker 1 (32:04):
Well, it works basically everywhere except for close to black holes.
M Right. You need basically a black hole have enough
gravity to break down quantum mechanics because it's when when
space gets really distorted that you start to see the
effects of gravity on space, and then it becomes comparable
to the strength of other stuff, and that's when that's
when quantum mechanics breaks down. Yeah, quantum quantum field theory

(32:27):
works basically what we call flat space, whereas gravity bends space.

Speaker 5 (32:31):
Wow, so earlier when we categorize gravity as part of
these four fundamental forces, maybe that's just the wrong approach.
Maybe you know, do you know what I mean? Like,
maybe we shouldn't be categorizing these four things as one
category of quote forces.

Speaker 1 (32:51):
That's right. It could be could be that there is
no quantum theory of gravity as a fundamental force because
it isn't one. Yeah, and it's just a feature of space, right, Absolutely,
it's one possible explanation. But then we still need a
way to make quantum mechanics work in bent space, right,
And we still need to understand how to make our
theory of general relativity play well with quantum mechanics, because

(33:12):
we think quantum mechanics describes the universe, right, and general
relativity is not a quantized theory. It's it's continuous, right.
It treats space and everything as if it's infinitely divisible, right,
it's not a quantum theory at all, in fact that
it came about before quantum mechanics was even invented. And
so while the basic tenets of it how it distorted
space are probably correct, i mean, been verified to zillion

(33:34):
degrees of accuracy, it doesn't feel like it can be
a fundamental description of nature because it's not quantum mechanical.

Speaker 5 (33:41):
So, like we want to call it a force because
it seems to move things like all the other forces,
but it's maybe it's not a force. Maybe it's just
kind of like some other weird property of space.

Speaker 1 (33:52):
Yeah, exactly. You know, maybe we've been trying to put
a round peg into a square hole all these years.

Speaker 5 (33:59):
A gravity peg in a quantum hole.

Speaker 1 (34:01):
That's right, that's right. And there are other ways that
people are trying to solve this problem. Like one way
is thinking that maybe gravity is a fundamental force, but
it just works a little bit differently from the other forces.
For example, people think about how the universe might have
additional spatial dimensions, you know, like instead of just being
able to move in three directions, maybe there's like four
or five six dimensions that you can move in. And

(34:23):
folks who are interested in that should listen to our
podcast on extra dimensions.

Speaker 6 (34:27):
No.

Speaker 5 (34:27):
Yeah, we did a whole episode on extra dimensions, but
we didn't sort of get into this particular topic. So
tell us how extra dimensions might explain why gravity is
so weak.

Speaker 1 (34:37):
Yeah. The idea is that maybe gravity isn't so weak.
Maybe gravity is just as strong as all the other forces.
But if there's a whole other set of dimensions out
there that's ways directions that think can move, it might
be that gravity is the only thing that feels those dimensions, right.
It might be that those dimensions are invisible to electromagnetism

(34:57):
and to the weak force into the strong force, but
to gravity, and what that means is that gravity might
be basically leaking out into those other dimensions. You know,
we talked about how the farther away you get from something,
the weaker the forces. So like Mercury feels the force
of the Sun's gravity much more strongly than Pluto does. Right,
irrelevanti of whether or not you call it a planet,

(35:18):
it doesn't feel gravity very strongly. And that's because it's
further from the Sun, right. I mean that goes like
one over are squared or are is the distance it's
one of our squared because we have three dimensions. If
we had six dimensions, it would be one over R five, right,
which falls much more rapidly. So if there are additional
dimensions out there, okay, and only gravity feels them, then

(35:40):
that might be the reason why gravitational force falls so quickly.
Maybe gravity's actually just as strong as everything else when
you get really really close, But then these extra dimensions exist,
and most of gravity leaks out into those other dimensions.

Speaker 5 (35:53):
Oh, sort of like between you and me, there's not
just the three dimensions between you and me Ei, there
are other secret hidden spaces kind of between you and me.
Are these other dimensions.

Speaker 1 (36:06):
Exactly other ways for gravity to spread out, all right.

Speaker 5 (36:09):
And so gravity would be like just as strong as
all the other forces. But it's just flessing its muscles
in these other spaces that we can't see or feel exactly.

Speaker 1 (36:18):
It's like, you know, if somebody's at the center of
a crowd and they let go a really stinky far right,
the people next to them they smell it strongly, and
the people further away they smell it much more weakly,
and people outside don't smell it at all.

Speaker 5 (36:29):
All right, now imagine the farts really suddenly. But let's
let's let's go with it.

Speaker 1 (36:34):
Hey, I'm trying to make this successible. You know, this
is something everybody canna.

Speaker 5 (36:37):
Appreciate trying to make way, I get it cut it.

Speaker 1 (36:42):
But if there was somewhere else for that far to go,
you know, if it could move not just sideways, but
also could float up right, so you had a really
tall room in the far floated up, then people wouldn't
feel it as much because most of the far would
dissipate into the upper corners of the room. And so
gravity might be the same way. It might be that
you know, for the first millimeters, so the first centimeters,

(37:02):
so gravity gets very weak, very quickly. It falls off
really rapidly, and that then you know, at normal distances
like a meter or ten meters or whatever, you don't
feel those other dimensions anymore because the other dimensions only
activate it really really short distances. This is the theory
people came up with, and we don't know if it's real.
You know, we tested it so far. It seems like
gravity works the same way for galactic scales and for

(37:26):
earth scales, and for microscopic scales. It seems to always
fall off at the same rate as a function of distance.
So nobody's ever seen any evidence of these extra dimensions.
But it's a fascinating theory and it's you know, it's
one that would give kind of a natural explanation for
why gravity would fall off so quickly and why gravity
is so weak. It wouldn't explain all these other things.

Speaker 5 (37:45):
But in fact, people sort of try to use gravity
to see if there are other dimensions, right.

Speaker 1 (37:49):
Yeah, that's right. It would be a really cool clue,
right if And that's a fascinating way that science has done.
You know, you try to look at everything around you
and see if you can fit it all into one framework.
Can I use this one set of ideas to describe
everything right onto one part of concepts? Yep, that's right
in my fart theory of the universe. The best possible

(38:16):
way I think to unravel this is to actually go
visit a black hole. Because quantum mechanics and general relativity
tell you very different things about what's happening inside a
black hole. Right, as we said before, general relativity tells
you it's an infinite testimal dot of almost infinite density.
Quantum mechanics says, you know, the universe is quantized first
of all, so you can't have infinite testimal dots. And

(38:38):
also this sort of a minimum size to stuff, right,
and you can't have all that stuff compressed in such
a tiny little area. And so if you could see
inside a black hole, you would learn a lot about gravity.

Speaker 5 (38:48):
So what would be the plan. You would go into
a black hole, you would observe and discover how the
universe works, and then and then you'd be stuck there.

Speaker 1 (38:56):
That's right. They would have to send you a Nobel
prize into the black hole after just assume you'd figured
it out and cause the l prize into space into
the black hole. Anybod who's listening, please do not go
into a black hole. Please please do not go into
a black hole. But you know, we don't need to
visit black holes. We could try to create them here
on Earth.

Speaker 5 (39:15):
That sounds like a great idea.

Speaker 1 (39:17):
Yeah, doesn't that sound like a great idea. I mean,
I'm excited make it. Yeah, let's create a black hole
and study it. Right, if gravity gets really really powerful
when you get to really short distances because of this
extra dimension theory, then it might be that if you
shoot two protons together really really hard and they get
really really close to each other, that you can create
a super duper mini extra cute, little fuzzy black hole. Right,

(39:40):
I'm trying to make it sound like a cozy thing, not.

Speaker 5 (39:42):
A yeah, you're trying to sell it, right.

Speaker 1 (39:49):
And so before we turned on the Large Hadron Collide
about ten years ago, people thought maybe by smashing these
protons together, we could actually create black holes and we
could study them. We can reveal the deep secrets of gravity. Right, hmmm.

Speaker 5 (40:03):
So then the idea would be to try to make
them at the Large Hadron Collider and just can of
see what happens mm hm, like, does it tell us
something about gravity or quantum physics at the same time.

Speaker 1 (40:13):
Yeah, exactly. By seeing how often they're made and how
strong they are and what they turned into when they decay,
we could understand something about the way black holes work,
and that would have been really powerful. But unfortunately or fortunately,
depending on how feel above black holes. We haven't made
any black holes at the Large Hadron Collider that we've discovered.

Speaker 5 (40:32):
But maybe isn't it true that maybe you've made them
but they evaporate.

Speaker 1 (40:35):
Yes, these black holes would be very short lived. But
you know, everything we make at the Large Hadron Collider
is really short lived. These things last for like ten
to the negative thirty seconds or ten to the negative
twenty three seconds. We're pretty good at seeing short lived
stuff because it usually blows up into other things, and
a black hole would have a really unusual signature in
our detectors. It would be pretty clear to see if
we had made them.

Speaker 5 (40:55):
Okay, but short of going into the black hole or
detecting farts in dimensions, we may not know in the
near future what what makes gravity so different?

Speaker 1 (41:06):
That's right, it's going to take some work. I mean
the other direction, is theoretical, is to build up a
theory of quantum gravity sort of from the bottom up.

Speaker 5 (41:13):
Like start from the beauty of math and physics and
then try to build it up to our level exactly.

Speaker 1 (41:20):
And that's that's a wonderful way to do, is to say, like,
maybe the universe works in this way, this most basic
fundamental nature, and build it up from there and see
if you can describe the universe that we see around us.

Speaker 5 (41:31):
Wow, all right, well that's pretty shocking to think gravity
is such a place, such a big role in our lives,
and yet it's it's like the weakling in the universe, right,
It's like, imagine, imagine if if gravity was stronger, life
would be a lot more chaotic, right and crazy?

Speaker 1 (41:49):
Yeah, exactly. We would be closer to the Sun and
everything would feel more intense. It's fascinating to me that
gravity has been a mystery to physics for hundreds of years.
I mean, it was the focus of Isaac Newton's you know,
like hundreds of years ago people working on gravity. And
still today, even though we've made so much progress in
terms of gravity, we still have so much, so many
basic questions about it that we don't know the answers

(42:11):
to not even the really beginning of how to answer them.
To me, that's fascinating. Gravity is such a rich source
of mystery for physics and for everybody.

Speaker 5 (42:19):
Wow, all right, cool, I think it's maybe time to
push down this question. Thanks for joining us.

Speaker 1 (42:33):
If you still have a question after listening to all
these explanations, please drop us a line. We'd love to
hear from you. You can find us at Facebook, Twitter,
and Instagram at Daniel and Jorge that's one word, or
email us at Feedback at Danielandorge dot com. When you

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